Groundwater-tracing field tests in a basalt aquifer in central O'abu. 3. A large open-tank experiment to determine the feasibility of using the helium tracer.
REPORT DOCUMENTATION FORM WATER RESOURCES RESEARCH CENTER
University of Hawaii at Manoa I SERIES
Special Report 06.01:90
NUMBER
3TITLE
Injected helium: A new hydrological tracer
2COWRR flELD-GROUP 4REPORT DATE 5NO . OF PAGES 6NO . OF TABLES
June 1990
ix +94 19
7NO. OF
1 flGURES
38
9GRANT AGENCY
Sushil K. Gupta L. Stephen Lau Philip S. Moravcik Aly EI-Kadi
National Science Foundation
IOCONTRACT NUMBER
11 DESCRIPTORS:
CES-8818175 helium, tracer, injection, groundwater, basalt, aquifer, soil water, sands open water
IDENTIFIERS:
12ABSTRACT (PURPOSE, METHOD. RESULTS. CONCLUSIONS)
Five types ofexperiments were conducted to investigate dissolved helium gas as an injected water tracer, both in the subsurface water and open water: instrument development, sand column, soil columns, groundwater in basalt aquifer, and open water in tank and flume. Thirty-four Board of Water Supply pumping wells were sampled and 7 USGS wells were utilized. Much subsurface water data were simulated by transport models. The project developed a helium-detection system which consists of a thin quartz-glass membrane and a diode-ion pump. The system responded linearly to helium diffusion through the membrane over a range of six orders of magnitude. The test results demonstrated that helium is an ideal water tracer for groundwater in the saturated zone because of the attributes of helium: conservative nature, easy to use, low cost, absence in nearly all natural water, safety to the environment and humans. For the unsaturated-zone tests, exchange of helium with air entrained in the porous media reduced the usefulness of helium. In the open-water tests, helium behaved like fluorescein in a relatively tranquil submerged environment for hours but was gradually lost through air-water interface, thus limiting the usefulness of helium to short-duration studies or in a submerged environment. .....
2540 Dole Street • Honolulu, Hawaii 96822· U.S.A. • (808) 948-7847
AlTIHORS:
Dr. Sushil K. Gupta Scientist'SE' Physical Research Laboratory Navrangpura, Ahmedabad 380009 India Tel.: 02721462129 Dr. L. Stephen Lau Researcher Water Resources Research Center and Professor Department of Civil Engineering University of Hawaii at Manoa 2540 Dole Street Honolulu, Hawaii 96822 Tel.: 808/956-3096 FAX: 808/956-5044 Mr. Philip S. Moravcik Graduate Research Assistant Water Resources Research Center University of Hawaii at Manoa Tel.: 808/543-8249 (Hazard Evaluation and Emergency Response Program) Dr. Aly EI-Kadi Associate Researcher Water Resources Research Center and Associate Professor Department of Geology and Geophysics University of Hawaii at Manoa 2525 Correa Road Honolulu, Hawaii 96822 Tel.: 808/956-6331
INJECTED HELIUM: A New Hydrological Tracer
Sushil K. Gupta L. Stephen Lau Philip S. Moravcik AlyEI-Kadi
Special Report 06.01:90
June 1990
PREPARED FOR
National Science Foundation Project Completion Report for ''Injected Helium: A New Hydrological Tracer" Project No.: CES-8818175 Project Period: 1 March 1989-30 November 1990 Principal Investigator: L. Stephen Lau Co-Investigators: Sushil K.Gupta Hans-Jurgen Krock
WATER RESOURCES RESEARCH CENTER
University of Hawaii at Manoa Honolulu, Hawaii 96822
vii
CONTENTS ABSTRACT............................................................
v
INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Nature, Scope, and Objective of Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Related Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
DE'fECTION SYSTEM
5
Quartz Diaphragms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
Diode-Ion Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
Instrument Calibration .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
Procedure for Determining Net Helium Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Collection and Storage of Water Samples .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
DESCRIPTION OF THE EXPERIMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
Sand-Column Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
Short Soil-Column Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
Groundwater Experiments
23
Open-Tank Experiment
......................................
26
Small-Flume Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
RESULTS AND DISCUSSION..............................................
29
Sand-Column Laboratory Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
Short Soil-Column Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
Groundwater
Experi~ents
Open-Tank Experiment
34 '
'-. . . . . . . . . . . . . . . . . .
39
Small-Flume Laboratory Experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
MODELING OF SAND-COLUMN AND GROUNDWATER EXPERIMENTS . . . . . . . . . .
44
Sand-Column Experiment
45
Groundwater Experiments
45
Conclusions
54
.................................................
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
56
Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
Recommendations
57
ACKNOWLEDGMENTS..................................................
59
REFERENCES CI'fED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
viii APPENDICES
63
Rgures 1. Rate of Penneation of Gases Through Solids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2. Schematic Diagram of Helium Water Analyzer. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
3. Stages of Making the Thin (Micron Range) Quartz-Glass Diaphragms Used in the Helium Water Analyzer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
4. (a) Mechanism by Which Diode Pump Removes Noble Gases (Cross-Section of Single Cells) (b) Multicell Assembly of Diode-Ion Pump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 9
5. Pumping Speed vs. Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
6. Current vs. Pressure for Diode-Ion Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
7. Instrument Calibration Curve Using Three-Minute of Five Different Helium Solutions
13
8. Schematic Diagram ofInstrument Test Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
9. Instrument of Perfonnance During Alternating Flow of Helium Solution and Blank Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
10. Instrument Calibration Curve Using 1 Minute Flow of Helium Solution. . . . . . . . . . .
17
11. Residual Helium in Solution Stored in Soda Glass Bottles with Rubber Stoppers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
12. Residual Helium in Solution Stored in Soda Glass Bottles with Rubber Stoppers, Experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
13. Residual Helium in Solution Stored in Soda Glass Bottles with Rubber Stoppers, Experiment 3 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
14. Points Sampled for Background Helium on O'abu ... . . . . . . . . . . . . . . . . . . . . . . .
24
15. Plan of Waipahu Well Field, with Well Locations. . . . . . .
.. . . .. . . . . . . . . .. . .
25
16. Diagram of Open Tank.
..................
28
17. Laboratory Plume-Tracing Experiment Using Helium. . . . . . . . . . . . . . . . . . . . . . . .
29
18. Breakthrough and Evolution Curves, Sand-Column Experiment 1, Comparing NaCI and Helium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
19. Breakthrough and Evolution Curves, Sand-Column Experiment 2, Comparing NaCI and Helium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
20. Breakthrough and Evolution Curves, Sand-Column Experiment 3, Comparing NaCI and Helium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
21. Breakthrough and Evolution Curves, Sand-Column Experiment 4, Alternating Flow of Tracer and Blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
22. Breakthrough and Evolution Curves, Soil-Column Experiment I, Comparing NaCI and Helium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
23. Breakthrough and Evolution Curves, Soil-Column Experiment 2 Comparing NaCI and Helium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
24. Breakthrough Curves of Three Experiments at Waipahu Wells Using USGS Well "A" as Injection Well and BWS Well 4 as an Observation Well. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
. .. . . . . ..
ix 25. BreakthroughCurves, for BWS Wells 1 and 2, at Waipahu Groundwater-Tracing Experiment 4 26. Change in Helium Concentration in Well "F" After Cessation of Injection, Groundwater-Tracing Experiment 4. . . . . . . . . . . . . . . . . . . . . . . . . . . .
38 38
27. fluorescence and Helium Signal at Position 1, Plume-Injection Experiment, Look Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28. fluorescence and Helium Signal at Position 2, Plume-Injection Experiment, Look Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
29. fluorescence and Helium Signal at Position 3, Plume-Injection Experiment, Look Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
30. Residual Helium in an Undisturbed Open Tank at Look Laboratory. . . . . . . . . . . . .
43
31. Simulated and Measured Results for Sand-Column Experiment 2 ......... 32. Comparison Between Analytical and Numerical Results for Sand-Column Experiment 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
40
46
33. Fence Diagram of the Subsurface Basalts Under the Eight Observation Wells. . . . . . . 34. Simplified Geologic Cross-Section of a Portion of the Valley Wall, Waikele Valley, Waipahu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47 48
35. Diagrammatic Sketch of a Basalt Chip that has Well-Development Diktytaxitic Texture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
36. Simulated and Measured Results for Groundwater Experiment 2 . . . . . . . . . . . . . . . .
51
37. Simulated and Measured Results for Groundwater Experiment 3 . . . . . . . . . . . . . . . .
51
38. Simulated and Measured Results for Groundwater Experiment 4 . . . . . . . . . . . . . . . .
52
Table 1. Parameters Used for the Simulation of Groundwater Experiments 2 Through 4 . . . . .
53
INTRODUCTION With increasing emphasis on maintenance and protection of the hydrologic environment, it becomes important to be able to predict the path that a given mass of water will follow and the degree of dilution and dispersion that this water will undergo. For example, it may be important to know the path, extent, and dilution of a mass of wastewater injected into a groundwater body, an ocean, or a lake. Similarly, when abstracting water, it may be important to know the origin of the water being pumped and the spatial extent of the effect of this abstraction. Tracers, both environmental and injected, are often used to obtain this information. Conventional tracers, largely composed of various types of salts and dyes, are not conservative and are subject to sinking due to density differences. Large quantities of these tracers are often required due to high detection limits. Radioactive substances, also commonly employed as hydrological tracers, are detectable at very low concentrations; however, their use requires special training, sophisticated detection equipment, and elaborate safety measures due to the hazardous nature of radioactive isotopes. A need therefore exists for an inert, conservative, and convenient tracer. Hydrologic information so obtained may be applied to a wide variety of problems involving the movement of water, including underground injection control, subsurface infiltration of wastewater, groundwater tracing, and validation of groundwater-flow models. Tracer data also have many applications in the study of open-water bodies, such as in tracing effluent plumes discharged into the suboceanic environment. In this report the applicability of dissolved helium as a tracer of water movement in a variety of hydrologic environments is examined. This discussion is based on research conducted at the Water Resources Research Center (WRRC) of the University of Hawaii at Manoa.
......
Helium, first discovered by spectroscopic examination of the sun during an eclipse in 1868 was not found on Earth until 1895. It is now known to occlude in minerals and to accumulate with other gases in pockets in the Earth's crust (having been released from the planet's interior), and in the atmosphere. Helium atoms have a simple atomic structure-a nucleus with two accompanying electrons in a closed shell-that makes them nonreactive. Helium atoms do not bond and are monoatomic molecules (unlike hydrogen atoms, for example, which are generally found in pairs and are diatomic molecules) and are extremely small (atomic diameter, 1.95 au). Helium has a number of other characteristics that make it useful as a tracer of water movement, including the following: - low background atmospheric concentration (5.3 ppm vol) - low molecular diffusion constant in water (approx. 5 x 10-5 cm2/s)
2 - moderate solubility in water (approx. 1%) - wide availability at low price ($7/m 3) - nontoxic nature. These unique properties and helium's potential as a groundwater tracer were recognized by Carter et al. (1959), but helium has not been used as an injected tracer of water movement because of the lack of a reasonably convenient method of measurement. Measurement in water has been performed mainly by mass spectrometry, a procedure not readily performed in the field. Friedman and Denton (1975) of the U.S. Geological Survey (USGS) and Seitz and Holland (1986) of the U.S. Bureau of Mines developed portable helium "sniffers" for field use based on the mass-spectrometric method. These instruments were used originally for estimation of helium content in soil gas and subsequently in a variety of other applications ranging from prospecting for radioactive ore deposits (Reimer et al. 1979) to earthquake prediction (Reimer 1984). This type of instrument was never used in attempts to trace water movement. The helium sniffer is based on a modification of a commercially available helium leak detector and is very sensitive (measuring ppb levels). The sniffer is primarily designed for air and gas samples, but helium dissolved in water can also be measured by equilibrating a volume of air with a low but known helium concentration with the water sample and then measuring the change in helium concentration in the air. For the types of applications we have in mind, the degree of sensitivity provided by the mass-spectrometric method is unnecessary because the atmospheric concentration of about 5.3 ppm is expected to provide a more or less uniform background in hydrological investigations. The small size of the helium atom means that helium will permeate through materials that have lattice structures with holes larger than the diameter of a helium atom (Fig. 1). Specifically, helium permeates through quartz glass at a rate as much as 1,000 times faster than hydrogen molecules; the next largest to the helium (Norton 1952; Altemose 1961). Upon the helium detection system employed in these experiments is based upon this fact. Levina et al. (1975) first made use of the high permeability of helium through quartz glass to develop an instrument that can detect helium dissolved in water at the ppm level. This instrument has been used in the Soviet Union for studies related to structural mapping of the Earth's crust, mineral prospecting (Eremeev et al. 1972; Dikum et al. 1975), and earthquake prediction (Barsukov et al. 1984). Following the work of Levina et al. (1975), Gupta (1983) developed, using a commercially available ion pump, an instillment for the detection of helium dissolved in water. The possibility of utilizing this instillment for water movement studies was realized and a project proposal was made in 1987 to 1988 to explore this possibility. WRRC conducted studies to demonstrate the utility of helium gas as a tracer of water movement. The research project was supported jointly by the National Science Foundation and WRRC.
3 -4
~
Helium-quartz glass Helium-Pyrex glass H2 -quartz glass Helium-soda lime glass
-6
w
~
!;(
----- ------
a:
z
0
-8
~ w ~
a: a..
w -10 0
---
~
8 ...J
-12 TEMPERATURE °C 1200
600
400
200
100
+25
0
-23
-14 2
0.5
3
4
1000 TEMPERATURE oK SOURCE: Adapted from Norton 1952. NOTE: Units for permeation constant K 1 are cm 3 of gas (STP)/s1cm 2 arealmm thickness/1 atm partial pressure difference.
Figure 1. Rate of permeation of gases through solids One~expects about
8.1 x 10-6 mg Hell water in all samples in equilibrium with atmospheric
air at sea level. The solubility in seawater is somewhat less than in fresh water (Weiss 1971; Smith and Kennedy 1983). Most groundwater has a helium concentration close to the expected back.ground value, making helium useful as a tracer (Davis et al. 1985). However, in regions of helium release from deep-seated cracks and. fissures in the lithosphere, shallow groundwatei" is known to have as much as 10 ml helium/l water, that is, as much as five to six orders of magnitude greater than ambient atmospheric concentration (Dikum 1975). This concentration is close to the maximum solubility (approx. 8 ml helium/l water at 1 atm of helium). This gives a maximum dynamic range of more than five orders of magnitude in routine tracing experiments with the proposed method.
Nature, Scope, and Objective of Research NATURE. A new hydrological tracer method based on the injection of helium gas or gas solution and subsequent monitoring for this dissolved helium both in space and time, in flow in porous media and open water, has been investigated.
4
SCOPE. The research problem involved the design and fabrication of a helium water analyzer that utilizes the high permeability of helium through quartz-glass membranes. Complete instrumentation and a standardized procedure for investigating the applicability of helium as a tracer of water movement were developed for several different experiments, including: 1. Sand-column and soil-column laboratory experiments comparing the behavior of helium to that of common table salt, sodium chloride (NaCl), as a tracer.
2. Groundwater-tracing field tests in a basalt aquifer in central O'abu. 3. A large open-tank experiment to determine the feasibility of using the helium tracer method in open-water bodies, comparing its perfonnance with that of fluorescein dye.
4. A small flume experiment to determine the feasibility of continuously monitoring a stream of flowing water with the analyzer.
OBJECTIVE. The objective of the research was to exploit the unique properties of helium gas and to develop a simple method of hydrological tracing using injected helium.
Related Research Probably the first study employing helium as an injected tracer of groundwater movement was conducted by Carter et al. (1959). In spite of the very obvious advantages of helium over other substances-namely salts, dyes, and radioisotopes-the method could not be further developed because of the lack of a convenient method of measurement. The mass-spectrometric method necessitated the shipment of water samples from the field test site to a specialized laboratory for later measurements. The possibility of the loss of helium in handling and storing of water samples added to the complexity of field operations. Previous studies have indicated thatJnjected helium will work as a nearly conservative tracer in hydrological environments. In support of this, the following points from the literature
are cited: 1. Soil air in regions of radioactive mineral accumulations is known to contain significantly higher concentrations of helium, with the greatest helium anomaly not directly above the ore body, but displaced in the direction of groundwater movement (Reimer et al. 1979). 2. Ocean water at a depth of 2 to 3 Ian in both the Pacific and Atlantic oceans in regions of crustal spreading exhibit supersaturation of helium by 11 %, resulting from release of mantle helium at spreading centers, as indicated by high 3He to 4He ratios (Craig et al. 1975; Lupton 1976; and Lupton et al. 1977).
5 3. Helium concentration of groundwater in regions of hot spots as well as deep-seated fissures and fractures is as much as six orders higher than background values, again displaced in the direction of groundwater movement (Datta et al. 1980). 4. The use of helium as a mineral prospecting tool and in earthquake prediction (see Journal ofGeophysical Research volume 92 [B12] special section on helium studies in geology) depends on some of the gas aforementioned unique properties.
DETECTION SYSTEM The instrument used in these experiments directly detects helium dissolved in water. Water passes over one side of a very thin quartz-glass membrane. Helium in the water permeates through the membrane into a high vacuum environment (approx. 10-9 torr*) on the other side. This minute increase in the pressure in the evacuated chamber causes an increase in the pumping rate and the ion current in a diode-ion pump. The increase in ion current is proportional to the rate of helium permeation through the quartz-glass membrane, which in turn is proportional to the concentration of helium dissolved in water (or any other fluid) on the nonvacuum side of the membrane. This detection idea is not new. Eremeev et al. (1972) used this method for routine monitoring of helium concentration (at ppm levels) from spring water in their research on structural mapping, ore deposit forecasting, and earthquake prediction in the USSR. d:
The detection instruments used in our experiments consisted of commercially available diode-ion pumps, electronic meters, and the quartz-glass diaphragms themselves (Fig. 2). The instrument is portable and reasonably durable. The first unit was developed by Gupta (1983) for use as a tool for mineral prospecting in India and was transported several thousand kilometers by Jeep over rough roads without damage.
The Quartz Diaphragms The quartz-glass diaphragms were made by an expert glassblower (Fig. 3) at the Scripps Institution of Oceanography, University of California, in La Jolla, California. The method of blowing these diaphragms was outlined by Gupta (1983). The diaphragms were blown as thinly as possible to maximize helium permeation while maintaining the structural strength necessary to withstand a pressure differential of one atmosphere, and the flow of water on the concave side. The Pyrex glass housings of the diaphragms were blown at the University of Hawaii at Manoa.
*1 torr = 1 mmHg = In60 atm =133.3 pascals.
6
Quartz-Glass Diaphragm Helium Atom ..-t--i Graded Seal Protective Pyrex-Glass Housing To Drain ~
To Meter ==::::::;;~
Figure 2. Schematic diagram of helium water analyzer (quartz diaphragm, Pyrex housing, and diode-ion pump)
Gas permeation across a membrane is described by the permeation equation (Norton 1952) q = K) At (p) ; P 2)
where q KI A
t PI P2 d
(I)
= volume of gas permeation (cm3/s) = permeation velocity constant (cm3 gas at STP*/cm2 area/mrn thickness/atm gas pressure difference) = area of the membrane exposed (cm2) = time (s) = gas pressure on high side (atm) = gas pressure on low side (atm) = thickness of the membrane (mrn) .
*Standard temperature and pressure =273°K and 760 mm Hg.
7
9mml
) A. Quartz glass is heated and end sealed
j
-~-~----'-~-_::) B. Quartz glass is blown out in a bubble
j c
C. Bubble is heated and suction applied to the tubing drawing thin glass membrane inside SOURCE:
Adapted from Gupta 1983.
Figure 3. Stages of making the thin (micron range) quartz-glass diaphragms used in the helium water analyzer
It is evident that the thinner the membrane and the larger its area, the higher will be the rate of helium permeation across it. The sensitivity of the dissolved helium detection unit is dependent on these factors. Temperature also has an effect on the permeation of helium through quartz glass. The equation which describes this relationship is (Norton 1952): K.
= A exp
(j§)
(2)
where A
= =
R
= the gas constant (8.3 x 107 erglg mole/oK)
T
= the absolute temperature (OK)
Q
= heat of activation of the process per gram atom.
KI
permeation velocity constant as above constant
From this equation, it is evident that the plot of In Kl against Iff gives a straight line whose slope defines Q (Fig. 1).
8
The Diode Ion Pumps The ion pumps employed were manufactured by the Varian Company. Three different pumps were used, one with a capacity of 0.16 Us (model no. 913-0040), one with a capacity of 2 Us (model no. 913-0045), and one with a capacity of 8 Us (model no. 911-5005). An ion pump is a device used to remove gases from a system in order to create ultrahigh vacuum environments. The generic name of this device is sputter-ion pump or ion-getter pump because some of the gas molecules undergo ionization and cause sputtering of the gettering agent. The gettering agent chemically reacts with the active gases to form stable compounds that are deposited on the internal walls of the pump. The getter is usually a titanium cathode which is sputtered away by the gas ions formed under the influence of high voltage in the range of 3 to 7 kV DC. Gas molecules enter a field of high-speed electrons, where some are subjected to collisions. When a collision occurs, a molecule may lose one or more of its electrons, thereby becoming a positively charged ion. Under the influence of a strong electric field, these ions are accelerated into the titanium cathode. The force of this collision is sufficient to cause very small particles, usually atoms, to be physically removed from the electrode and "sputtered" onto the adjacent walls of the pump. This particulate titanium is extremely reactive and will chemically unite with such active gases as oxygen, nitrogen, carbon monoxide, and carbon dioxide. The resulting compounds accumulate on surfaces of the pump walls. The noble gases-helium, neon, argon, krypton, and xenon-are nonreactive and are pumped by "ion burial," the plastering over of inert gas atoms by the sputtered gas atoms. Helium is also pumped by diffusion into titanium. By these mechanisms, the diode-ion pump is capable of removing gas molecules and creating very high vacuum environments.
In its simplest form, an ion pump consists of a central anode unit in the form of a small section of metal tubing, open at each end (Fig. 4). A plate of electrically grounded titanium metal is placed opposite each open end. This forms the cathode. The function of the anode cell structure is to contain a cloud of high energy electrons, which are constrained by the magnetic field provided by the permanent magnets outside the electrodes. The field causes the electrons to move in spiral paths. This increases the likelihood of the electrons striking gas molecules, thereby creating positive ions. These ions are accelerated by the positive anode voltage and made to smash into the titanium cathode plates. It should be noted that to be pumped, a gas molecule need not be ionized; only a relatively few are. Most are pumped by chemically uniting with the sputtered titanium or by ion burial. The function of the ions is to maintain a fresh supply of gettering material. Before attaching the quartz diaphragm unit to an ion pump, helium permeation across the diaphragm was measured using a helium leak detector (also manufactured by the Varian
9 Titanium Cathode Plates
Magnet
Control Unit
Titanium Atoms
\ Entrapment of Buried Helium Atoms
a. Stanaara Ion pump SOURCE:
Multicell Anodes
b. Standard diode pump
Adapted from Varian Vacuum Division 1979.
Figure 4. (a) Mechanism by which diode pump removes noble gases (cross section of single cells); (b) multicell assembly of diode-ion pump
.,
CompaIl;¥). Only those diaphragms that had leak rates of more than 10-6 std.cm3/s were used. The highest leak rate obtained from any diaphragm was 4 x 10-6 std.m3/s (this diaphragm, broke after approximately one month of nearly continuous use). Pump speed varied with pressure and different gases (Fig. 5). For helium, pumping speed was less than 30% of that for air. Current drawn by an ion pump was proportional to the rate of ion production due to electron collision which in turn was proportional to gas pressure inside the pump. Figure 6 is a plot of current versus pressure supplied by the manufacturer (Varian Vacuum Division). The single pump-control unit employed (Varian model no. 921-0015) supplied, regulated, and monitored the power that was applied to the ion pumps. For an equivalent full-scale meter deflection in any current range, a negative (with respect to the chassis) 1oo-millivolt signal provides full-scale deflection for a recorder through two banana jacks at the back of the control unit. No recorder, however, was employed in these studies. A digital meter (Fluke model no. 87) was employed to provide a digital readout of the ion current (converted to millivolts across a 20m resistor). The pumps were attached to the quartz diaphragms under high vacuum, and the integrity of the connections was tested using a helium leak detector. The pump/diaphragm units were baked
10
Cl
w w
125
a. en 100 Cl
w
~ a:
75
LL
50
0
I-
zw
c.:> a: w
a.
25 0 10.10
10'S
10-9
10-7
10.5
10-6
10-4
PUMP PRESSURE (torr) NOTE: Units of speed are Vs.
Figure 5. Pumping speed versus pressure
10-4
'E'
- - ---- -
10.5
g
,,-
800·Gauss magnet 1250·Gauss magnet 2Vspump 8Vspump
/ / / / /
w a: 10-6 ::>
/ /
en en w
/ / /
a: a. 10.7 a.
/ /
~
/
::>
/
a.
/
10-8
/
/ /
10.9 .01
.1
1
10
100
1,000
PUMP CURRENT (j.lA) SOURCE: Adapted from Varian Vacuum Division 1979.
Figure 6. Current versus pressure for diode-ion pumps
10,000
11
in a vacuum at approximately 350°C using laboratory heating tapes and were hermetically sealed.
Instrument Calibration It has already been noted that the ion current in the diode-ion pump is proportional to the pressure in the pump (Fig. 6). It has also been noted that the permeation of helium across the quartz membrane is proportional to the difference in partial pressures of helium between the two sides of the membrane (Eq. 1). Permeation of other atmospheric gases through the membrane can be neglected because of their large molecular size or low partial pressure in the Earth's atmosphere. Under normal conditions, the pressure on the vacuum side of the quartz glass varies between about 10-9 torr (corresponding to the volumetric proportion of helium in air, 5 ppm) to about 10-3 torr for pure helium at 1 atm. Thus, P2 in Eq.l is always negligible in comparison to PI, making the permeation rate of helium essentially proportional to the partial pressure of helium on the nonvacuum side. The solubility of helium in water depends upon the partial pressure of helium in solution. According to Henry's law: XA
PA
=K
(3a)
where
XA PA K
= = =
mole fraction of gas in liquid equilibrium partial pressure of gas in contact with liquid Henry's gas constant (1.09 x 1()8 torr at 20°C) .
To convert mole fraction to mg/l (G) G
=
1
~~A (~~) 1()6 PA
=
e-:
=
2.22 x lOS (K
K
(4.003) A) 18.016 1()6
~Ap A)
where G
= the concentration of dissolved helium in water (mg/l)
MA
=
Ms
= molecular weight of water.
molecular weight of helium
(3b)
12
Combining the three proportionalities-the pump pressure and the pump current, the partial pressure of helium on the nonvacuum side and the penneation rate of helium across the quartz membrane, and Henry's law-it is evident that the change in ion current of the pump is expected to be proportional to the concentration of dissolved helium in the water flowing over the membrane. Figure 7 shows the observed relationship between the helium signal recorded on a digital meter and the helium concentrations in the gas standards used to prepare five standard helium solutions. These solutions were prepared by bubbling each of the certified helium/nitrogen mixtures through a diffuser into a few liters of water at room temperature for at least 15 minutes. The observed helium signal is the change in the potential drop (in units of 10-2 m V) across a 20 KQ resistor due to the change in the ion current that results when a
sample containing dissolved helium passes over the quartz membrane. The relationship is, as predicted, linear. Figure 7 is the calibration curve for the detector assembly incorporating an 8 Us diode pump (App. Table A.I). All helium concentrations measured by the instrument are referred to in tenns of the helium concentration in the air/gas in equilibrium with water at room temperature and ambient pressure. The equation of the least square fit line in Figure 7 is 10g(H) = 1.4382 + 1.0007 10g(S)
(4)
where H = helium concentration in the gas (ppmv) in equilibrium with helium solution (gas equilibration units) S = helium scale reading (10- 2 mY) . The preceding equation simplifies to H =27.43SI.OOO7 ... 27.43S .
(5)
As the exponent is essentially equal to unity, the equation is linear between H and S. For S
=1, H =27.43 ppmv the minimum detection limit. In absolute mgll units, this corresponds to a minimum detection limit of 4.2 x 10-5 mgll water. To convert H, the helium concentration in ppm, in gas equilibration units estimated using the calibration curve (Fig. 7), to milligrams of helium per liter of water one employs Eq. 3 after multiplying the helium ppm value by 760 x 10-6 to obtain the partial pressure P of helium in torr. The conversion equation simplifies to Eq. 6 G
= 2.22 x
lOs x 760 x H x 10- 6 (K - H x 760 X 10.6 )
(6)
13
E
Q. Q.
7 Log H = 1.4382 + 1.007 Log S R2 = 0.999
~
:::E C/)
::J
w
250
200
J:
en
150
100 0
10
20
30
40
50
60
70
80
90
100
110
TIME (min)
NOTE: Helium solution concentration
=7,500 ppm air equivalent.
Figure 9. Instrument of performance during alternating flow of helium solution and blank water
change in the instruments, therefore, may be affected by the flow rate of water across the membrane. The water flow rate may also affect the rate of signal change because the helium that permeates the membrane originates from a very thin (possibly only a few molecules thick) layer of water in contact with the quartz glass. The rate of replacement of this layer influence the rate of signal change. In order to ascertain the effect of water flow rate on signal change, a number of tests were performed comparing the I-minute signal to the 3-minute signal for flow rates .... -
between 60 and 150 mUmin. Flow rate in the tested range was found to have no significant effect on the ratio of I-minute signal to 3-minute signal (App. Table A.3). This ratio, however, was affected weakly by the concentration of helium in the sample. A standard operating flow rate of 100 ± 5 ml/min, therefore, was chosen on the basis of a compromise between the desirability of rapid purging of the system and avoiding undue stress on the quartz-glass membrane. The standard operating procedures of maintaining a sample flow rate of 100 ± 5 mUmin for 3 minutes and a similar flow rate/duration for blank water between samples was adopted for all the experiments, with the exception of the open-tank experiments, for which it was felt that the withdrawal of the required 300 ml of sample would disrupt the flow regime in the tanks to an unacceptable degree.
16
In all cases, the net helium signal (S) was taken to be the difference between the 3 minute
reading (SA) and the average of (1) the meter reading before the sample was introduced into the analyzer (B I) and (2) after 3 minutes of blank flow beyond the 3-minute sample reading (B2); that is: (7)
It was observed that B2::; Bl but always> O.98Bl. It is important to note that one could also use 1- or 2-minute readings to estimate the helium concentration in any sample. This may be useful when available sample volume is for some reason limited. To do this, one must prepare a calibration curve using 1- or 2-minute readings. Figure lOis the I-minute reading calibration curve obtained for our instrument using the same standard helium/nitrogen mixtures that were employed in making the 3-minute curve (Fig. 7). The relationship between S (net helium scale reading) and H (the net helium concentration in the solution, ppm in gas equilibration units) is, as with the 3-minute curve, linear. The equation describing the line is: log(H)
= 1.5398 + 1.0034 log(S)
(Sa)
or H
= 34.663SI.OO34 "" 34.66S
(8b)
which gives a minimum helium detection limit of 35 ppm (gas equilibration units). It is evident that the sensitivity of the instrument is diminished by taking shorter readings and that there is more scatter of the data points at lower helium concentrations (Fig. 10).
Collection and Storage of Water samples The helium analyzer can be used to continuously monitor helium content in a stream of water. It is often necessary, however, to collect discrete samples on site for later analysis, as when there are several sources being sampled simultaneously and only one analyzer is available. Furthermore, it may be desirable to collect duplicate samples, one for immediate measurement in the field and the other for confirmation later under more controlled conditions. It was found that temperature variations such as occur outdoors over the course of a day affected the instrument's performance possibly by altering the permeability of the quartz membrane itself. We recall that quartz glass permeability varies directly with temperature, according to Eq. 2, and/or through temperature's effect on the instrument's electronic components. Samples taken at different times from several sources may have different temperatures. To compare such samples, it may be desirable to store them at the same ambient temperature for a day or two to
17
E 0.
7
.e,
Log H = 1.5398 + 1.0034 Log 5 R2 = 0.998
X
~ rJ)
6
< (!) Z
z
0
5
~
a:
~ zw
4
()
z
0
()
3
~
:::>
::J
w 2 :i :I:
(!)
0
..J
1 0
2
3
4
5
LOG 5, HELIUM SCALE READING
NOTE: Numbers in parentheses refer to the number of data points. Figure 10. Instrument calibration curve using 1-minute flow of helium solution
allow their temperatures to equalize. Field measurements, however, are useful for monitoring the progress of the experiment in real time. Helium permeates readily through many materials, therefore it is important to choose carefully the containers in which to store water samples intended for analysis. The optimal material for such containers is a special type of copper tubing in which samples are sealed by crimping either end. This tubing has extremely low helium permeability and is often used in scientific experiments but its high cost and inconvenience preclude its use in most hydrological investigations where large numbers of samples from a great many points over a long period are required. Thick-walled soda lime glass bottles stoppered with conventional laboratory black rubber stoppers are an acceptable alternative sampling vessel, provided the storage time is not excessively long. Permeation of helium through such bottles at room temperature is < 3.8
X
10- 12 cm3 STP/cm 2 arealmm thickness/atm partial pressure difference. This rate is 99% helium) with water in a commercial carbonation unit. This method produces a supersaturated helium solution due to the extra-atmospheric pressure in the carbonator. The initial concentration of this solution was 43% higher than what would be obtained using pure helium at 1 atmosphere (the partial pressure of helium in the initial solution was 1 086 torr). The bottles were stored in an air-conditioned laboratory, and over the next 54 days, 4 to 6 bottles were opened periodically and analyzed for helium content. Figure 11 illustrates the loss of helium from the first set of 24 bottles (the data are presented in App. Table A.4). It can be seen that the initial loss of helium is rapid and that this rate gradually decreases as the helium concentration in the bottles approaches equilibrium with the ambient atmosphere. Assuming that the rate of helium loss is proportional to the helium concentration, an equation analogous to radioactive decay can be written as: He = Heo x e-A.t
(9)
where He = residual helium concentration Heo = initial concentration at time t = 0 . Therefore, the half-life of the helium in the bottles is given by the following equation: _ 0.693 T0.5- A. .
(10)
The first 3 points in the data set for this experiment best fit a curve with TO.5 = 25.21 days, which gives an average helium loss of2.5% for the first day and 7.9% for the first three days. The final 3 points in the data set best fit a curve which gives To.5= 119.74 days. In the second set of 24 bottles, the helium solution was produced by bubbling 10.84% (balance N2) helium gas through a diffuser into the water, thereby producing a lower concentration solution. These bottles were stored under the same conditions as the first set. Periodically, 4 to 6 bottles were opened and analyzed for helium content. Figure 12 illustrates the loss of helium from these bottles during the storage period. The best fit line through the data gives a To.5 = 46.74 days, indicating an average loss of helium of 1.5% for the first day and a loss of 4.4% for the first three days of storage. The data can be found in Appendix Table A.5.
19 11.0....----------------------------,
_ 10.8 c;; c:
Cl
i;i)
E .2 10.6
=
Ln S 10.657 - (5.7886· 10·~. t R2 = 0.930
Q)
:I:
c;;
::J
~ CI> 10.4
fS en
5
Ln S =10.860 - (2.7493.10.2). t R2= 0.800
10.2
10.0
_
L_.._.J..-_~_...L...
o
10
_1__....J...._
20
__L..:lIlo...____L.._
__L_
30
___L_
40
_ _ J_ _L _ . . _ _ l
50
60
t, STORAGE TIME (days) NOTE: Initial solution supersaturated with helium. Rate of loss was more rapid during the first 11
days, by which time the partial pressure of helium was reduced to 1 atm.
Figure 11. Residual helium in solution stored in soda glass bottles with rubber stoppers 8.5.------------------------_----, Ln S =8.3178 - (1.4830.10. 2). t R2 =0.921
8.3
-c;; c:
Cl
i;i)
8.1
E .2 Q)
;S
en
7.9
5 7.7 T112= 46.74 days
7.5 '-----'-----'----.........-_--'-_ _---'-_ _ o 10 20 30
___L_ __ _ J I . -_
__l
40
STORAGE TIME (days) NOTE: 10.84% helium gas used at ambient temperature and pressure.
Figure 12. Residual helium in solution stored in soda glass bottles with rubber stoppers, experiment 2
20
In the third experiment, 24 bottles were filled with sample water from a production well during an injection test in the basalt aquifer in Waipahu. As in the first two experiments, these samples were stored and bottles were periodically opened and their residual helium content measured. The observed data (App. Table A.6) best fit a line that gives a TO.5 = 69.86 days (Fig. 13). The results of these bottled sample storage experiments indicate that the loss of helium from well-stoppered soda lime bottles is very small « 3% ) if the storage period is < 24 hours. For longer storage periods, a better container would be required.
DESCRIPTION OF THE EXPERIMENTS To investigate the applicability of helium as a hydrological tracer, a number of experiments were performed. These included experiments in tracing water in porous media and in openwater bodies. The following sections describe these experiments.
Sand-Column Experimems This set of experiments employed a Plexiglass column (height, 183.5 cm; diameter, 8.7 cm). The column was filled with a water-saturated uniform quartz sand (ASTM designation C-190). Helium- and NaCl- (common salt) tagged water was introduced into the column. Samples were continuously taken from the column outlet port and measured using the helium water analyzer instrument and with a conductivity bridge (Yellow Springs Instrument Co. model 31A). In sand-column experiment I, a salt solution equilibrated with 99% helium gas at room temperature was used. This solution was allowed to enter the column with approximately 3 cm '.
of head for a period of 56.5 minutes, and then flow of untagged water was resumed. The initial electrical conductivity (EC) of the tagged solution was 7 x 103 J.lmhos/cm versus 7 x 1()2 J.lmhos/cm for the untagged water passing through the column. The tracer solution passed
through the column at an average rate of 110 mlImin. The data of the tracer breakthrough and elution are in Appendix Table A.7 . In sand-column experiment 2 a salt solution with a reduced helium concentration (approximately one-third of the concentration of the solution used in experiment 1) was employed. This solution entered the column with approximately the same amount of head, for a period of 58 minutes, and then flow of untagged water was resumed. The initial EC of the second tracer solution was again 7 x 103 J,lmhos/cm, as compared with 7 x 102 J.1mhoslcm for the untagged water passing through the column. The tracer solution passed through the column
NOTE: Helium solution was a field sample collected during an injected helium tracer test.
Figure 13. Residual helium in solution stored in soda lime glass bottles with rubber stoppers, experiment 3
at an average rate of 103 ml/min. The data of the tracer breakthrough and elution are in Appe~dix
Table A.S. In sand-column experiment 3 a solution with a helium concentration of 500 ppm (gas ,0
equilibration units) was used. The solution entered the column with approximately the same amount of head for a period of 3S minutes, and then flow of untagged water was resumed. The initial EC of the tracer solution was5.4-x 1()3 JlIllbos/cm, as compared with 5 JlIllbos/cm for the ....
untagged distilled water passing through the column. Distilled water was used- in the initial saturation of the column and as the blank water during the experiment. The tracer solution passed through the column at an average rate of 738 mlImin. The data of the tracer breakthrough and elution are in Appendix Table A.9. In experiments 2 and 3, greater care was taken to ensure complete saturation of the sand column, as it was believed that incomplete saturation had affected the results of the first experiment. Different concentrations of helium solution were employed in these experiments to determine what effect, if any, relative concentration would have on the transport of the helium through the column. Sand-column experiment 4 involved repeated alternation between heliumlNaCI-tagged solution and blank water. The tracer solution had a helium concentration of 330 ppm (gas equilibration units) and EC of 4.4 x 103 J.Lmho/cm. The distilled blank water had an EC of
22 7 Jlmho/cm. Distilled water was used in the initial saturation of the column and as the blank water during the experiment. The duration of these alternating pulses was increased as the experiment progressed. This experiment was performed to determine if repeated loading and elution of the column would affect the performance of the gaseous tracer, perhaps through a slight detention of helium in the column, which might result in protracted elution time. The data of the tracer breakthrough are in Appendix Table A.l O. It should be noted that the helium analyzer had not been calibrated for experiments 2 and 3 because the standard gas mixtures had not been received. The glass diaphragm used in these experiments subsequently broke before the instrument could be calibrated. Absolute concentration therefore is not known in these experiments. As the calibration curve for the helium water analyzer shown in Figure 7 is linear, correct C/Co values were obtained using the net signal.
Short-Soil Column Experiments Further experiments were performed utilizing a small column of soil of the Wahiawa series to determine if any delaying processes would affect the performance of helium as a tracer in a medium rich in organic material and clay. A steel column 15 cm long and 10.2 cm in diameter was used. During the column-packing process, a considerable quantity of fine material was lost, yet the soil maintained its fine, claylike character. Once again helium was used in conjunction with NaCl. Despite the fact that this column was much shorter than the column used in previous experiments, water flowed slowly through the soil because of its relatively low hydraulic conductivity. A greater amount of head therefore, was, employed in these experiments in order to obtain_ samples from the outflow in a reasonable amount of time. The outflow from the column passed directly through the analyzer for ~se experiments, and readings were taken every minute.
In short soil-column experiment 1, a solution with a helium concentration of 750 ppm (gas equilibration units) was used. This solution was allowed to enter the column with approximately 60 to 80 cm of head for 30 minutes, and then flow of untagged water was resumed. The initial EC of this solution was 1.8 x 103 Jlmhos/cm, as compared with 6.6 x 102 Jlmhos/cm for the untagged water passing through the column. The tracer solution passed
through the column at an average rate of 65 mVmin. The data of the tracer breakthrough are in Appendix Table A.II. In short soil-column experiment 2, the column was repacked and a tracer solution with a helium concentration of 8400 ppm (gas equilibration units) was used. This solution entered the column with approximately the same amount of head, for 29 minutes, and then flow of untagged water was resumed. The initial EC of this tracer solution was 7 x I ()3 J.1mhos/cm, as
23 compared with 7 x
102
JlInhos/cm for the untagged water passing through the column. The
tracer solution passed through the column at an average rate of 60 mlImin. The data of the tracer breakthrough are in Appendix Table A.12.
Groundwater Experiments Having determined that helium functioned essentially as an ideal tracer in the laboratory columns, we decided to try some experiments in groundwater tracing in the field. To determine background groundwater helium level, samples were taken from 34 Honolulu Board of Water Supply (BWS) production wells and tunnels around O'ahu. As expected, no detectable helium signal was found in any of these samples. Helium concentration in all of the samples was below 28 ppm (gas equilibration units) (Fig. 7). Figure 14 shows the locations of the wells and tunnels sampled. It was concluded that natural background helium in O'ahu groundwater was negligible and therefore would not interfere with our groundwater tracing experiments. This suggests that helium may be preferable over conventional salt for use as a groundwater tracer in many areas. Four groundwater tracing experiments were performed at a site near Waipahu, O'ahu utilizing four BWS production wells and two observation wells drilled by the USGS in 1988 for use in some earlier tracer experiments. Our experiments consisted of introducing helium, both in the form of a saturated solution of water and as a gas, into injection wells and monitoring the helium.:signal at nearby production wells, when in operation, each pumping continuously at a rate of 1 750 gpm (6.624 m 3/min). Figure 15 shows where these experiments were performed. Commercial grade helium (99% or better) was used for all the groundwater tracing . experiments. Collecting samples was performed by inserting a tube from the well taps to the . bottom of the collection bottles and filling the bottles, to overflowing to exclude any water which had equilibrated with the air in the bottles. To remove air from the bottles, a piece of nylon fishing line was first placed in the bottles and then withdrawn as the stoppers were pushed in. The fishing line provided a passage for excess water, and any trapped air bubbles, to escape. The stoppers were then taped over with masking tape to prevent their accidental dislodging and were stored upside down until analyzed.
GROUNDWATER EXPERIMENT 1. The first of our four groundwater tests involved injecting a slug of 170 liters of helium-saturated water into USGS injection well "A,"located 26.21 m from BWS production well 4. The injection was performed by siphoning the injectate down a
1.25-cm diameter PVC tube to approximately 24.4 m below the water surface. This depth was chosen because Honolulu BWS and USGS indicated that this was where the most productive area of the aquifer (personal communication Cliff Voss, USGS). Injection took approximately
24
LOCATION 1 2 3 4 5 6
7 8 9 10
32
•
11 12 13 14 15
2
•
9
16
BWSI.D. NO. 2153-11 211>1-12 3405~2 4101~7
3553-00 2112-31 2302-
:i 0.0010
w :::c
0.0005 -
10
20
30
40
50
TIME SINCE START OF INJECTION (Days) NOTE: USGS well"F" used for injection of helium tracer.
Figure 25. Breakthrough curves for BWS wells 1 and 2, at Waipahu groundwater-tracing experiment 4
,
-1 , . . . . - - - - - - - - - - - - - - - - - - - - - - - ,
• 1st measurement • 2nd measurement
-2
~
-3
c:
....J
-4 Ln (C/C o ) =-1.4287 - 0.37882 • t R2 = 0.953 -5
~_l_---.JL.__--L
o
_
__l._---L_......L_
246
_L_....L.._~l>._....J
8
10
t. TIME SINCE CESSATION OF INJECTION (Days)
Figure 26. Change in helium concentration in well -F" after cessation of injection. groundwater-tracing experiment 4
39 water flowing through the aquifer, it is felt that dilution of the water in well "F" was responsible for the higher observed rate of signal decrease relative to the open tank.
Open-Tank Experiment To reiterate, this experiment involved injecting a plume of helium- and fluorescein-tagged water at one end of a long open tank. Helium and fluorescein concentrations were subsequently monitored over time at seven points in three positions along the length of the tank. The results of these measurements are plotted in Figures 27 through 29. Each of the curves appearing in these figures represents a set of measurements made at a particular position at a different sampling time. The locations of the seven sampling points across the width of the tank are shown along the x axis. It is interesting to note that for the first 250 minutes or so after the start of injection, the dis-
tribution of helium and fluorescein was virtually identical. After approximately 300 minutes, the tracers had mixed thoroughly with the contents of the tank, and all samples showed similar levels of each tracer. After this time, fluorescence in all samples stayed the same, while helium signal gradually declined. This decrease in helium signal is due to the diffusion of the gas in the water of the tank into the ambient atmosphere. Figure 30 illustrates the rate of loss of helium from the air-water interface over the 8 days following the injection of the tracer plume. The figure indicates that if we assume a first-order reaction for the loss of helium from the tank, the half-life (time required for the loss of 50% of dissolved helium from any initial value) was 3.17 days. This suggests that during the initial 300 minutes of injection, the loss of helium from the air-water interface was less than 5%. The Look Laboratory experiment demonstrated that helium behaved as a nearly ideal tracer of water movement in open-water bodies, provided that the plume being traced did not come into contact with the surface. At the air-water interface, helium was lost. The rate of loss under undisturbed conditions, such as existed during the course of our experiment, was slow enough to permit comparison with fluorescein dye. It was concluded that a plume-tracing study using injected helium can be conducted in open-water bodies provided that the duration of the test is not excessively long or that the plume being traced is not expected to be at the surface for a long time.
Small-Aume Laboratory Experiment This experiment consisted of injecting a small plume of tracer solution (approximately 150 ml/min) into a small flume with water flowing through at a rate of approximately 52.5 l/min. Sampling was conducted by siphoning directly from the flume into the helium
2
10-
i
--;:;:;;;;;;~~::------------
I
FLUORESCENCE
10.
3
f:!£c.&a 3
k 5 ..
- - - -
I
HELIUM
at! 'I' §!l'.i~'~.~~~=~;;;;;~: =: • t: =. 5)
1O-21~~
- is ;;.--.
_.C....._
l.
10. 3
................ ______._
_ ••••• _ •••••
_.::':.....=-.=.:=:8-.....,.,..,.,....
-.:.-..:.~.:...::-
- -
-
_.....
.•. _._._.
.. ---
g ....... 10- 4
10. 4
r-
I
10.5 ·60
.............
~~~..:.--:~.+-;~-.-.
T =3058
-
T=19
- a -
_
T=61
--.- T =7222
-
T=227
- - T=10048
..-
T= 2839
-48
-36
--••. T = 1557
-
T=12009
_
_.+-
T = 12174
-24
-12
0
12
24
36
10.5 I -60
I
DISTANCE FROM CENTER (in.)
I
-48
I
I
I
-36
I
-24
I
I
-12
I
I
0
I!
12
DISTANCE FROM CENTER (in.)
NOTE: T - minutes. NOTE: Transverse sampling positions are shown as distance from center; each curve represents a different sampling time.
Figure 27. Fluorescence and helium signal at position 1, plume-injection experiment, Look laboratory
I
24
I
36
o
10.3
t'~_----1_-.•. -. •. --..--=lF=-... ~ • •
Ii
Ii
•
10.3
I
10'4
I
10.5
g 10'4 ~
10,5 I -60
I
-
1=34
-
1=1457
-
1=2852
I
!
!
I
I
I ! !
-48
-36
-24
-12
I
I
!
I
!
I
I
I
J
I
I
I
J
!
I
I
!
,
,
,
I
,
I
0
12
24
36
-60
-48
DISTANCE FROM CENTER (in.)
-36
-24
-12
0
12
DISTANCE FROM CENTER (in.)
NOTE: Transverse sampling positions are shown as distance from center; each curve represents a different sampling time.
Figure 28. Fluorescence and helium signal at position 2, plume-injection experiment, Look laboratory
24
36
42
10- 2
FLUORESCENCE
10- 3
---=-~
-----
0
~
(,)
10.4
f-
T =49 T =242
-
T = 1447
··4·-
T =3135
- .. -
T =3147
--..-. T =2865
--
10.5
•
•
•
•
•
T = 7202 T =7192 I
-60
~
-48
I
I
I
I
I
I
-36
-24
-12
0
12
24
36
10.2
HELIUM
10.3 ....- - - - _.....
--- --. -- -. -. ---.------.--- - --.•. _.•.
o
§
*',...........
...... "
:a-;~
........... _-----::..-.:.=
10. 5 '----'--..I..-...........--'----'--....L-.---"-~_L.......__l..._.L___'_ _ -60 -48 -36 -24 -12 0 12
_'____'__....L...___..J
24
36
DISTANCE FROM CENTER (in.) NOTE: Transverse sampling positions are shown as distance from center; each curve represents a different sampling time.
Figure 29. Fluorescence and helium signal at position 3, plume-injection experiment, Look laboratory
43
Or------------------------, DISTANCE FROM LONGITUDINAL AXIS (in.)
+
+
-60 -36
x
0
•
+12
o -24
•
+24
o
6
Ci c
:.c
-12
a +36
-1
~ Q)
a:
Q)
ro ()
C/)
E .2
Qi ~
enc
-2
...J
=
Ln S -0.34295 - 0.21844 • t R2 = 0.971 -3
L-._...L-_...L-_......L..._.......J.._-..J_ _..L....-_...L-_...L-_......L..._---l
o
2
4
6
8
10
TIME SINCE START OF INJECTION (Days)
Figure 30. Residual helium in an undisturbed open tank at Look Laboratory
water analyzer while the sampling tube was moved to different locations around the tank. Measurement was made at one depth only during this experiment, at the level of the injection point. At each location, sampling was of 3-minute duration.
.......,.
Figure 17 illustrates the average signal measured over a 3-minute period and the range of variation at each location. The average values represent the overall degree of mixing and dilution of the plume. The range (signal fluctuation) indicated the variability of mixing at each Doint. The smaller the range the more complete mixing. The contour plots in Figure 17 illustrate that closer to the point of injection, the average helium signal strength and the range was higher indicating that little dilution and mixing had taken place in this part of the flume. As the sampling port left the injection point, the average signal and the range both decreased, demonstrating that the tracer had undergone considerable mixing along the length of the flume. It was noted that there were small areas of high helium concentration near the inflow, probably
the result of back-eddying because the inflow port, a 5-cm diameter orifice 10 cm off the bottom of the flume, did not provide an even flow along the tank's cross section. Small stagnant areas of water may have collected in the corners adjacent to this orifice. The results of
44 the small-flume experiment demonstrate that the helium water analyzer can be conveniently used for continuous monitoring.
MODELING OF SAND-COLUMN AND GROUNDWATER EXPERIMENTS The objective of the modeling exercise in this section is threefold: (1) to examine the validity of the solute transport model in describing the dispersion of dissolved helium gas, (2) to estimate the dispersive characteristics of the Hawaiian basalt aquifer, and (3) to provide a set of recommendations for future experimental studies. The first two objectives are very much constrained by availability of limited infonnation about the aquifer site. The model chosen for simulating the groundwater experiments is the USGS twodimensional solute transport model known as MOC, which was developed by Konikow and Bredehoeft (1978). The model utilizes the method of characteristics and the finite-difference technique in solving the solute transport problem. The code is widely used for the analysis of field problems (e.g., Bouvett 1983; Chapelle 1986; and Sophocleous 1984). The model was applied in Hawai'i by Or and Lau (1987) for the analysis of the transport of DBCP (dibromochloropropane) in the basal lens in and down-gradient from the Mililani area of Central O'ahu. More recently, it was used in assessing the potential for groundwater contamination due to the proposed urban development in the Pearl Harbor area (Oki et a1. 1990). Here, the model is applied to situations dominated by radially convergent and divergent flow around wells. For such situations, as indicated by EI-Kadi (1988), care must be taken in applying the model, especially in mesh design, to avoid inaccuracies. EI-Kadi tested the code for a recharge/recovery SIngle well, a recharge/recovery doublet, and a plume capture by one and two wells. Results for all cases included fluctuations in well concentrations and a relatively large mass balance error. Apart from the doublet case, it was concluded that such errors can be acceptable for practical purposes. In the current modeling effort, much care was taken to minimize such inaccuracies. The groundwater experiments included a pulse-type boundary condition, that is, injection is perfonned over a finite period of time. MOC is not equipped to simulate a time-dependent boundary condition for solute transport. This was resolved by running the code for a source with specified concentration (Co) for the injection time, To. The model was then run a second time by using the resulting concentrations as the initial condition considering the source to be shut off.
45
Sand-Column Experiment The results of one of the sand-column experiments are used here to test the two-phase calculation scheme, as described earlier. Arbitrarily chosen was experiment 2 (see pp. 20-22, 29-32). Such results are suitable for initial testing due to two facts:
(1) the controlled
experiment for a homogeneous coarse sand is relatively easier to simulate, and (2) an analytical solution is available for this case. The problem is treated as a one-dimensional flow and transport problem under a constant steady state head gradient. The known information include the following: Column length = 183 cm (6.02 ft) Column diameter =8.7 cm (0.285 ft) Discharge = 103 m1/min (5.745 x 10- 5 ft 3/s) Hydraulic head differential
=30 cm (1.0 ft)
The domain is discretized to a 20 by 3 mesh of dimensions 0.334 ft by 0.285 ft for each element. No-flow boundaries are set along the sides of the column and specified-head boundary along the two ends of the column. From the available information, the specific discharge is 3.252 x 10-4 m/s (0.001 ftls). From Darcy's law, a value of hydraulic conductivity of 0.002 m/s (0.007 ftls) is estimated. Assuming a porosity of 0.42, the seepage velocity is 7.743 x 10-4 m/s (0.003 ftls). A slightly higher value of discharge (107.3 ml/min) provided the best results. The values of longitudinal ,. and transverse dispersivity that gave the best results are 0.6 cm (0.02 ft) and zero, respectively. Results of the simulation are compared to the experimental results of helium in Figure 31. Reasonable match between experimental results can be seen. The discrepancies are due to the inaccuracies in the experimental results as explained earlier, that is, due to the formation of the ',bubbles released from the tap water used to the saturated the column (see pp. 29-32). To gain confidence in the numerical results, the analytical solution of Ogata and Banks (1961) was used to verify the numerical results. Figure 32 shows a good match between the analytical and numerical results. For the pulse problem, it may be concluded that MOC performs satisfactorily.
Groundwater Experiments The test site is located near Waipahu, O'ahu, Hawai'i. The geology of the site is illustrated in Figures 32 and 34 (Multhap et al. 1990). The site is characterized by pahoehoe,'a 'a, and clinker, the principal extrusive rock forms. Detailed descriptions of the geologic and hydrogeologic features of these rocks is found in Mink and Lau (1980). Provided is a summary of these features.
46 1.2 - - - Simulation ~ Experiment
1.0
0.8
0.6 0
u ........ u
0.4
0.2
A
0.0
-0.2 50
0
100
150
200
Time (min)
Figure 31. Simulated and measured results for sand-column experiment 2. The discrepancies are due to the inaccuracies in the experimental results explained in Results and Discussion of Experiments, herein.
1.2 Simulation: t • Simulation: t - - - Analytical 6
1.0
0.8
< >
To To
II
ll/ 0.6 0
u ........ u
0.4
0.2
J
0.0
-0.2 0
50
100
150
200
Time (min)
Figure 32. Comparison between analytical and numerical results for sand-column experiment 2. Good match between results can be seen, indicating that the numerical code performs satisfactorily for the pulse problem with pulse duration of To (equals 58 minutes).
--------------------IOrtef".-
----I. 1M -
•• F'gYre...............
......
....
.......,. '.'~. ,"-:'
.~.
:.
'.
............
'"
..
t
io
EXP\.ANATlON
......,.,
_ _ _ _ "'0""" .urlac. ~_
_ _ _ _ flow
..-.sa"
t.,,...r !,. ,. .,..,,. ..::t L.'.... ec."
(tt)
SOURCE: Multhaup at al. 1990.
Figure 33. Fence diagram 01 the subSurtace basaKs under the eighl observalion wells
48
EI.v.tlon (1 •• U
200
l
ground surface 20-30~
T
......... '
_ ... :.
.. ~:..:..~~_
,-J;~"'_
:'~-"
.,
.: .. :.~. '.
...... :.;.:,..- __
a clinker
aa
2'
__ • ;
..:..:::,...:....'"' .:.;.., -
v •• 'el ••
"';-;".
eO
dense ae flow Inter/or
, -
150
- ...
~
'"
,__ ",,-
_
-.o'. -:- __ -:.
__ eo
_,. '7':"'-:-' '
1-2"10 v •• lel ••
r.r.- ollvln. and plagloela ••
••
20-30~ v •• lel •• ollvln....nd plagloelaa.phyrlc ....--:~~_--18-lool lIow unll
62' "'-J:.......----.;,..:..:..~::J.:::p a hoe ho e flo w unit a (dlklyla.ltle t •• tur.)
100
v•• lel••
flow boundarle. (r.dd.n.d horIzon.)
50
f
... ....
..".
" .. " -' " .. .. .. . '':'-'-,":,-..;..:..:~ ...:.;_.;:.~ .::
..
""
1
L ....• ...... :. -
1-'"10 vulel••
r.r. ollvln.
denae aa t JIterlor o w z aa clinker
aa
-...
sa rollte Ie er
••- - - . - • .-.'.:"....- ... ':''t-
1 3+'
. .. .. .. ..... ....... .... .. ...... .::.:.. .. i·":-·:':':::·~~~.
~
•
....t.:.
- . - . - - ...
~
aa
-:'~-:.~
._."1"':--:,.-:--
":" " .•_'"';
.. .a. -::. ,:........_ ••••.,. '"'"'-' ...~ •.: -=-' :.:.
. 1_-
+ J...--------?---?-----1----Walkele Stream
_
~------
ore .. C'lay
...
!.e.d. !.!!.!........
COMmon ollvln.
SOURCE: Multhaup 9t al. 1990.
Figure 34. Simplified geologic cross-section of a portion of the valley wall, Waikele Valley, Waipahu
49 Pahoehoe refers to the lava flows having smooth, hummocky, glassy surfaces surrounding highly vesicular interiors (Fig. 35). A single pahoehoe unit may consist of many individual toes, pods, and other ovoidal shapes. Although highly porous, its intergranular-type permeability is low. En masse, however, permeability may be high due to the existence of structural features. Such structural features include the opening between units, the presence of lava tubes, and cooling joints normal to the flow surface. Lava tubes are not as common as the other two factors. The 'a'a-clinker association consists of a dense, massive discontinuous phase, the 'a'a core, bounded by spiny, fragmented lava breccia called "clinker." Vesicles in 'a'a are relatively few, large, and of irregular shape. As in pahoehoe, practically all permeability of the 'a'aclinker association results from structural features. The openings in clinker beds are probably the most effective of the common permeability elements of the extrusive rocks. Pahoehoe and the 'a 'a-clinker association cannot be treated as separate rock masses with respect to hydrological characteristics. Pahoehoe is more common near zones of eruption and 'a'a toward the downslope margins of the shields. The ratio of the rock masses depends on the location. One example is leeward O'ahu, Hawai'i where, at a distance of 8.05 km (5 miles) from the Koolau rift zone, about 75% of the rock consists of 'a'a, of which the clinker comprises up to 45% (Wentworth and Macdonald 1953). The hydraulic conductivity of extrusive rocks ranges between 300 to 1 500 m/day (1,000 to 5,000 ft/day). The successive layering of lava flows suggests the the horizontal component of hydraulic conductivity is greater than the vertical component. Due to such structural features as cracks, joints, and bridging, the vertical component can be significant. The effective porosity is often assumed as 10%. There is much uncertainty about the dispersivity values for Hawai'i rocks. Available values are not of much help as recent studies indicate the scale dependence of dispersivity. The classic convection-dispersion equation fails in dealing with this dependence. A longitudinal dispersivity value of 76 m was suggested by Souza and Voss (1987) and was later adopted by Oki et al. (1990). The latter study showed insensitivity to the value of dispersivity, apparently due to the fact that the transport was mainly convective. The modeling effort covered groundwater experiments 2, 3, and 4. Numerous runs were performed to obtain the best fit possible. The difficulties in modeling are caused mainly by the absence of complete geologic and hydrologic information about the system under consideration. Details of modeling are as follows.
MODELING. Details of experiments 2 through 4 are described in pages 23-27. Data used in the simulations are given in Appendix Table A.l. In the table, Nx and Ny are the number of increments in x and y direction, respectively, d x and dy are the size of the mesh in x and y direction, respectively, To is the injection time, DL is the longitudinal dispersivity, atlal is the
50
olivine phenocry.t.
plegloelue mlerophenoery.t.
ve.lele
Icale
~=!;=~oi2 In 6o~:::;:=! ' 1 ;::;=0;:;=1 ' 2 ' 3 '.4 6 mm
Sample 18 drawn approximately 10 tlme8 actual 81ze. SOURCE: Multhaup at al. 1990.
Figure 35. Diagrammatic sketch of a basalt chip that has well-development diktytaxitic texture. The sample is from a pahoehoe flow, 9 ft below mean sea level in well A.
ratio of transverse to longitudinal dispersivity, n is porosity, and B is the effective aquifer thickness. A specified head boundary was chosen for all sides. Because a steady-state situation was assumed, transmissivity and storage coefficient do not contribute to the solution for solute transport. Velocity depends only on well fluxes, porosity, and aquifer thickness (see the analytical solution for a system of wells in an infinitely large aquifer, lavandel et al. 1984). Transmissivity controls only the drawdown in the aquifer. A few runs were performed with different values of transmissivity; very close results were obtained. Comparison between the numerical and experimental results is shown in Figures 36 through 38 for experiments 2, 3, and 4, respectively. Reasonable match can be seen for experiments 2 and 3. Poor agreement between the experimental and numerical results can be seen for experiment 4. The percent mass error was acceptable, in general, with a maximum absolute value of 10% at small simulation times and much lower at larger times. Some fluctuations were noticed in the values of well concentrations; yet the behavior of results is generally acceptable. In addition to the nature of the flow field dominated by radial flow, Konikow and Bredehoeft (1978) pointed out, these inaccuracies are related to the manner in which concentrations are computed at sink nodes and to the method of estimating the mass of solute removed from the aquifer at sink nodes during each time step. DISCUSSION. The parameters a], at/a], and B in Tablel were the main fitting parameters. Numerous runs were performed. Actually the need for a two-step modeling procedure, due to
51 Dispersivity - 11 ft
0.006
,-----~-----r----..;----_,.----~---__,
A
Experiment
- - - Simulation
0.004
0.002
0.000 .......:;....::.._ _--'0.0
'-
__'
~
~
1000.0
500.0
__J
1500.0
Time (min)
Figure 36. Simulated and measured results for groundwater experiment 2. Results represent relative concentration in well 4. (See Fig. 24; reasonable match can be seen)
0.0015
...----~------,...----~---____.----~---__,
A
Experiment
- - - Simulation A
.......
0.0010
o
~ u 0.0005
A
0.0000
U
0.0
A
'--_ _----'L...-_ _----'_-.:::=:::L==:===..... 500.0
1000.0
--.J 1500.0
Time (min)
Figure 37. Simulated and measured results for groundwater experiment 3. Results represent relative concentration in well 4. (See Fig. 24; reasonable match can be seen)
52 0.0015
r-----.---~---~--~---~--....,____--~--__,
• • Experiment - - - Simulation
0.0010
o
u
"u 0.0005
0.0000 L..---":::...-=-_ _----L 0.0
10.0
- ' - -_ _--I...._ _~ ' _ __ ___l.__ ____'"_ __ _ J
20.0
30.0
40.0
Time (days)
Figure 38. Simulated and measured results for groundwater experiment 4. (See Fig. 25) The poor match seen is attributed to difficulties in modeling the correct flow field due to the absence of complete information about the system.
the pulse-type boundary condition, complicated the effort further. An iterative procedure was adopted because the output from the first phase (a continuous source, for time less or equal to To) constitutes the input to the second phase (no source, for time greater than To). The values of the fitting parameters shown in Table 1 gave the best fit. An additional complication was the discrepancy regarding the experimental and simulated relative-peak concentration of helium in "
the pumped well water. As can be seen in Figures 36 to 38, the peaks are 0.52% and 0.11 % of the initial concentration, for experiments 2 and 3, respectively. For experiment 4, the peak relative concentration for wells 1 and 2 are, respectively, 0.12% and 0.06% of the initial concentration. Numerical simulations showed much higher peak concentrations for experiments 2 and 3 than were measured experimentally. On the other hand, for experiment 4, the numerical relative peaks were lower than the measured values. The initial relative concentrations in the domain for each experiment were scaled by a factor (SF) which was estimated by trial and error. The values for SF are 0.15 for experiments 2 and 3, and 7.0 for experiment 4. The scaling process indicates that for experiments 2 and 3, the well system does not capture all the injected helium, while additional helium was captured by the wells for experiment 4. Another difficulty was the need to consider the effective thickness of aquifer as a simulation variable with a value that depends on the experiment itself. Note that for
53 TABLE I. PARAMETERS USED FOR THE SIMULAnON OF GROUNDWATER EXPERIMENTS 2 THROUGH 4 Nx
Ny
dx
dy
To
al
adal
n
B
SF
(-)
(- )
(ft)
(ft)
(hr)
(ft)
(-)
(-)
(ft)
(-)
2
16
14
\5
14
3.6
\\
0.1
0.\
100
0.\5
3
16
\4
15
14
0.5
28
0.1
0.1
50
0.\5
4
\8
14
40
40
38.16
250
0.1
0.1
300
Experiment
7
experiments 2 and 3 the helium was bubbled into the water column at a point 24.4 m (74 ft), while that for experiment 4 was at a point 48.77 m (160 ft) below land surface. Due to the stratified nature of the system, only a portion of the formation, namely, the most conductance ones, were expected to contribute to the solute transport. The first conclusion that comes quickly to mind is that the flow field is not simulated correctly. The need to consider the relatively large effective thickness, especially for experiments 2 and 4, indicates that the helium solution is moving at a much slower velocity than expected. The small concentration peaks for experiments 2 and 3 indicates that helium is lost somewhere in the aquifer system. A study of other well systems in the area indicates that none were active within a radius of more than 2,000 ft (Chester Lao, BWS, personal communication). Actually, the wells east and south of the pumping site (about 3,000 ft away), ,.". if considered, can cause even faster velocity field and decrease the simulated arrival times. For
experiments 2 and 3, no helium was detected in wells 2 and 3, located only 160 and 145 ft, respectively, from the injection well. Thus, it is not likely that helium could have been extracted by wells that are more than 3,000 ft away. The well system to the north of the site is about 7,000 ft away and is not likely to affect the flow field. in the area under consideration. The well field to the west of the site is about 1,500 ft and was not operational at the time of the experiments (Chester Lao, BWS, personal communication). Even if it was operational, it could not adversely affect the simulation results of experiment 4. The possibility of a regional flow causing the discrepancy was also examined. The flow is likely to occur from north to south direction. This can cause even worse simulation results for experiment 4. Simulations that considered regional flow in different directions were tried without much success. At this stage, an explanation for the results is merely speculative, due to the absence of a more complete set of information about the system. The use of a two-dimensional model to describe a three-dimensional flow situation is certainly a possible culprit. Another possibility is the treatment of a preferential flow system (due to the existence of structural features) as a uniform porous medium. It is likely due to structural features, such as cracks, joints, and
54
bridging, that the vertical component of rock permeability is significant. The effective thickness of the aquifer was found to increase with To, the injection period (Table 1), an indication of the importance of the velocity component in the vertical direction. If the flow field was modeled incorrectly, the same value of that thickness was likely to be needed for experiments 2 and 3, for which the only difference is the value of To. Note also that dispersivity values are related to both To and the travel distance. The dependence on travel distance (compare experiments 2 or 3 and experiment 4) supports recent studies (e.g., Gelhar 1986). The dependence on To (compare experiments 2 and 3), although dispersivities are in the same order of magnitude, can be another proof of the importance of the vertical flow component. The simulation of experiment 4 was far off the experimental results due to two factors. First, scale of the experiment is relatively large, causing more variability. Second is due to an injection episode about five days earlier (see pp. 23-26). The injection lasted about three hours and the wells were monitored for 2.5 days and then the experiment was abandoned. The results simulated are those for an injection performed three days later. The impact of the abandoned experiment was ignored. The need to scale the numerical results up indicates that there exists helium solute in the aquifer before the experiment starts, due for sure to the abandoned experiment, but possibly also due to the injection performed for experiments 2 and 3. Note that the experimental results in Figure 38 show a background concentration, that is, concentration higher than zero at early times. The figure shows also a shorter arrival time for the peak in well 2 than well I (12.5 days for well 2 versus 15 days for well 1), although well 1 is closer to the injection well. (Note also that well 2 is closer than well I to the site of experiments 2 and 3.) The numerical results show faster arrival peak for well I and zero concentrations at time equal zero, as should be expected and consistent with modeling assumptions. Although it is not very well defined in Figure 38, a double-peak breakthrough can be inferred, especially for well 2. « .....
Can this behavior be attributed to structural features at the site? If experiment 2 and 3 were continued for longer period, could another peak be detected? Additional research is certainly needed to search for answers to these questions.
Conclusions We started this section by stating the objective of the modeling exercise. Three objectives were stated. The first was to examine the validity of the solute transport model in describing the dispersion of the helium gas. A controlled laboratory column experiment was easily simulated. Simulating field studies was more difficult due to these factors: 1. The dispersion phenomenon is three-dimensional, as many studies previously indicate; the news that this conclusion has been demonstrated in the case of the Hawaiian aquifers that consist of consolidated layered formations, each with considerable
55 different characteristics. In addition, structural features were not considered. Hence the two-dimensional flow and transport model that treats the flow domain as a single layer of homogeneous porous media is not suitable for the current situation. The twodimensional confined model requires the use of an "effective" aquifer thickness. As the injection time increases it is likely that more of the aquifer is involved in the transport process. 2. The role of preferential flow and heterogeneities was not addressed. 3. Detailed information about the system is not available; for example, information about advancement of the helium plume in the aquifer can help in characterizing dispersivity values and its scale-dependence. Also, uncertainty regarding the initial concentration in the injection wells exists due to the absence of direct measurements. Information about the regional flow is not available. A three-dimensional flow field that accounts for layering as well as spatial distribution of wells, we believe, is necessary for better and meaningful results. Although every effort was taken to examine the possibility of regional flow and of interference of other well fields, more information is certainly needed. Of course the use of a three-dimensional flow and transport model that considers variability and preferential flow is unrealistic at this stage due to the absence of the necessary data. The second objective was to estimate the dispersive characteristics of the groundwater aquifer.:Again, the dispersive characteristics of the sand experiment was easily estimated. Due to the difficulties described, although fitting theoretical results to the experimental data is possible, some of the parameters are found to be merely fitting parameters. The study supports the contention that dispersivity is scale-, and possible, time-dependent. The third objective was to provide a set of recommendations for future experimental "
studies. Actually the experimental work was designed to demonstrate the use of the helium as tracer in groundwater assessment and to determine the accuracy of field measurements of concentrations. Hence the experiments were not intended for model validation. For future studies, the following reconunendation are made regarding the experimental work: 1. Use additional monitoring wells to describe the time evolvement of the threedimensional plume. A multilevel measurement of concentration should be performed (Mackay et a1. 1986). The resulting information can be used in characterizing the dispersivity values and relating them to spatial variability of hydraulic conductivity (Sudicky 1986). 2. Measure the initial concentrations in the injection wells. 3. Define the flow field accurately.
56
In conclusion, although the modeling exercise was not a complete success, we feel that it has shown interesting features of the study site. Further experimental and theoretical studies are strongly recommended. The guidelines presented above can help in designing future field studies.
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS Summary and Conclusions Developed was a simple, portable, instrumentation that makes use of the preferential permeation of helium through quartz glass to measure the concentration of helium dissolved in water. A user's guide to the prototype water helium analyzer developed by this project is provided in Appendix C. The calibration experiments that were conducted have shown that the instrument response was linear over the entire useful range of five to six orders of magnitude (Fig. 7). We have shown that samples of water containing dissolved helium could be conveniently collected and stored for a short duration in soda lime glass bottles (e.g., beer bottles) with rubber stoppers. The loss of helium from such bottles during 24-hr storage was 2 to 3% (Figs. 11 to 13). Laboratory-sand and soil-column experiments were performed. These demonstrated that helium behaved as an ideal tracer during saturated flow through porous media (Figs. 19, 20, 21, and 23). Unsaturated flow could not be effectively traced with helium because of the exchange of gases between the air and the tracer solution (Figs. 18 and 20). Measurement of helium concentration in 34 groundwater sources on the island of O'ahu indicated that background helium levels on that island were below the detection limit of the ......,-
instrument (28 ppmv gas equilibration units). Thus, there was no background helium present to confuse the results of tracing tests which utilized this method (Fig. 14). Field groundwater tracing experiments (Figs. 24 to 26) conducted in a basalt aquifer in central O'ahu, indicated that the use of helium to trace groundwater movement was practical and convenient. Aquifer parameter estimation has been made. An examination of the data suggests that the helium used in the tracing experiments behaved like the salt tracers (NaBr) used in a series of experiments performed in the same wells under similar conditions by the USGS,
in 1988-89 (pp. 23-26) (Voss and Souza, personal communication, 1989).
The results of laboratory open-tank plume-tracing experiments (Figs. 27 to 30) indicated that the helium water analyzer could be used both for the analysis of discrete samples and for continuous on-line stream monitoring. The behavior of helium was found to be virtually identical to that of fluorescein dye during these experiments (Figs. 27 to 29). In the open-water
57
bodies, it was noted that initially dispersion and mixing of the tracers rapidly reduced the concentration of the tracer plume, but no significant loss of helium to the atmosphere occurred during this phase. Loss of helium from a water body can occur only at the air-water interface. Helium, therefore, can serve as a useful tracer in studies of the movement of water in the subsurface environment. In an experiment conducted in a large open tank (surface area approximately 88 m2) three days were required for the loss of 50% of the initial helium concentration (Fig. 30). The results of the studies described demonstrate that helium dissolved in water is an easyto-use, conservative tracer of water movement under saturated conditions (in the case of groundwater studies) or in the underwater environment (in the case of open-water body studies). The helium water analyzer has been found to be an efficient, inexpensive device for measuring helium dissolved in water.
Recommendations INSTRUMENTATION. There are a number of improvements which could be made to increase instrument efficiency. At present, the instrument requires about 6 minutes per measurement. This can be reduced by measuring the rate of signal change over a fixed time interval, and using this rate as a predictor of the ultimate signallconcentration. To do this, water sample flowing over the membrane would have to be regulated more closely. r.':
The prototype unit used consisted of three separate parts: diode-ion pump/diaphragm assembly, the control unit, and the digital meter. It would be more convenient to use the instrument if it were of a single composite unit. In studies lasting for long periods, it would be convenient to have a recording device attached to the control unit of the analyzer. This could easily be achieved for the,control units are already equipped with jacks designed specifically for this purpose. HYDROLOGICAL FIELD STUDIES. A variety of field hydrological studies still need to be performed to increase confidence in the helium tracing method, to explore the applicability of the method, and to determine its limitations. Among others, the following possibilities could be explored: 1. We have seen that the presence of air bubbles in sand/soil-columns retarded the movement of helium tracer, with respect to water movement under unsaturated conditions. Using another conservative tracer (such as salt) along with helium, it should be possible to inverse the process and estimate the degree of saturation of a porous medium. 2. It was not possible to monitor the concentration of helium in the injection wells during our groundwater-tracing experiments at Waipahu, O'ahu because there was no second
58 instrument to measure the high concentrations expected in the injection weBs. It was assumed, therefore, helium concentrations in the injection weBs were equal to what would be obtained by equilibration with water under ambient temperature and pressure conditions. Although this assumption has been verified in the laboratory, it should also be verified in the field, particularly in places of active flow through the aquifer. Furthermore, as the injection depth increases one expects a higher concentration of helium due to higher pressure at the point of injection. This needs to be studied under controlled conditions. 3. We have assumed that the rate of helium injection by bubbling helium into the wells was equal to the filtration velocity of the water through the well. This assumption should be verified. Further, it is necessary to do a double tracer test, for example, helium and a conservative tracer like salt (chlorides and bromides) not subject to loss to air, to determine if the filtration velocity can be estimated by measuring the decreasing helium concentration in the well water. 4. We performed groundwater-tracing experiments only in a basalt aquifer. It is necessary to do further experiments in other types of aquifers. 5. A better type of sampling bottle could be developed. The rubber stoppers used to seal the bottles have a high permeability to helium and could possibly be replaced with a better substitute. 6. A planned experiment involving the tracing of an effluent plume in the ocean could not be performed for reasons beyond our control. Helium seems particularly weB suited to such studies because it has a relatively low detection limit and real time on-line measurements can be made. These are definite advantages in the ocean, where dilution is rapid and large. 7. The helium tracer method appears to be well suited for studies of stream reaeration. At present such hydrocarbon gases as propane are employed in these studies. Measurement of samples is done by gas chromatography, and samples require special handling and preparation. Furthermore, the use of these explosive gases poses a hazard. Hydrocarbon gases can be lost, as they are not entirely conservative and may react with organic matter present in the stream. The helium-water method provides several advantages over propane and other hydrocarbon gases in this application, for example, the analysis can be done inexpensively in the field. The use of the helium method is in no way dangerous, and no special handling or preparation of samples is needed.
59
ACKNOWLEDGMENTS During the course of our investigations, help and support were received from numerous individuals. The project has benefited by their constructive criticism and practical ideas. We would specifically like to record our appreciation of the painstaking effort put in by William Cooper, the glassblower in the chemistry department at the University of Hawaii at Manoa. We would also like to thank D. Lal of the Scripps Institution of Oceanography, University of California at La Jolla, for his help in getting the quartz-glass diaphragms blown in the Institution's glass shop. We gratefully acknowledge the help of Andy Rivera of Andy's Vending in Honolulu, who very kindly provided the carbonation unit used in some experiments. Chester Lao and Alwin Morisako of the Honolulu Board of Water Supply, who not only help us in the collection of groundwater samples from many locations on O'ahu but also coordinated the pumping schedule of the wells at Waipahu to facilitate our experimentation. It is a pleasure to extend our thanks to them. We are also pleased to acknowledge the permission, help, and information received from Charles Ewart and Clifford Voss of U.S. Geological Survey in connection with groundwater-tracing experiments at Waipahu. Roland Kanno of the J.K.K. Look Laboratory provided a helping a hand and company during plume-tracing experiments. Thanks are extended to R.K. Varma, Director of Physical Research Laboratory, Ahmedabad, India, for granting Sushil Gupta a leave of absence to work on this project.
REFERENCES CITED Altemose, V.O. 1961. Helium diffusion through glass. J. Appl. Phy. 32:130-,9'-1316. Barsukov, V.L.; Varshal, G.M.; and Zamokina, N.S. 1984. PAGEOPH 122:143-155. Bear, J. 1979. Hydraulics of Groundwater. McGraw-Hill International Book Co., p. 272. Bouvette, T.C. 1983. The characterization of hazardous waste site with analytical and numerical models. M.S. thesis, Rice University, Houston, Texas. Carter, R.C.; Kaufman, W.J.; Orlob, G.T.; and Todd, D.K. 1959. Helium as a groundwater tracer. J. Geophys. Res. 64:2433-2439. Chapelle, F.H. 1986. A solute transport simulation of brackish water intrusion near Baltimore, Maryland. Ground Water 24(6):741-751. Craig, H.; Clarke, W.B.; and Beg, M.A. 1975. Excess 3He in deep water on the East Pacific Rise. Earth Planet. Sci. Lett. 26: 125-132.
60 Datta, P.S.; Gupta, S.; layasurya, A; Nijampunkar, V.N.; Sharma, P.; and Plusnin, M.L 1980. A survey of He in groundwater in parts of Sabarmati basin in Gujarat State and in 1aisalmer district, Rajasthan. Hydrolof. Sci. Bull. 26: 183-193. Davis, S.N.; Campbell, D.l.; Bently, N.W.; and Flynn, T.J. 1985. Groundwater Tracers. National Water Well Association, Worthington, Ohio, pp. 122-124. Dikum, AV.; Korobeynik, V.M.; and Yanitskiy, LN. 1975. Some indications of existence of transcrustal gas flow. Geochem. Int. 12(6):73-78. EI-Kadi, A.I. 1988. Applying the USGS mass-transport model (MOC) to remedial actions by recovery wells. Ground Water 26(3):281-288. Eremeev, A.M.; Sokalov, V.A.; Solovov, A.P.; and Yanitskiyu, LN. 1972. Application of helium surveying to structural mapping and ore deposit forecasting. Geochem. Exploration, 1972 M.l. Jones ed. Institution of Mining and Metallurgy, London, U.K. Friedman, 1. and Denton, E.H. 1975. "A portable helium sniffer." U.S. Geological Survey Open File Report 75-532. Gaspar, E. 1987. Modern Trends in Tracer Hydrology. Volume 2, CRC Press Inc., Boca Raton, Florida. Gelhar, L.W. 1986. Stochastic subsurface hydrology from theory to application. Water Resour. Res. 22(9): 135S-145S. Gupta, S.K. 1983. Design of an ion pump based analyzer for geological investigations. Curro Sci. 52:469-471. Javandel, 1.; Doughty, c.; and Tsang, C.F. 1984. Groundwater transport: Handbook of mathematical models. American Geophysical Union, Washington, D.C. Water Resources Monograph 10, 228 p. Konikow, L.F., and Bredehoeft, J.D. 1978. Computer model of two-dimensional solute transport and dispersion in ground water. U.S. Geological Survey, Techniques of WaterResources Investigation. Bk. 7, Ch. C2. . Levina, L.Ye, V.V. Pimenov, V.Ye. Stadnik, et al. 1975. Ekspress-informans. VIEMS, Sr. X, issue 1 (text in Russian). Lupton, J.E., 1976. The He distribution in deep water over Mid-Atlantic Ridge. Earth Planet. Sci. Lett. 32:371-376. ___, Weiss, R.F.; and Craig, H. 1977. Mantle helium in Red Sea Brines. Nature 266:244246. Mackay, D.M.; Freyberg, D.L.; Roberts, P.V.; and Cherry, l.A 1986. A natural gradient on solute transport in a sand aquifer, I. Approach and overview of plume movement. Water Resour. Res. 22(13):2017-2029. Mink, l.F., and Lau, L.S. 1980. Hawaiian groundwater geology and hydrology, and early mathematical models. Technical Memorandum Rep. No. 62, Water Resources Research Center, University of Hawaii at Manoa, Honolulu.
61 Multhaup, R.A. 1990. "Vesicle distributions and their use as volcanological tools in understanding Hawaiian lava flows." M.S. thesis, University of Hawaii at Manoa. 100 p. _ _ . 1990-1991. Vesicle distributions and their use as volcanological tools in understanding Hawaiian lava flows. U.S. Geological Survey, Reston, VA. 100 p. _ _ _; Voss, c.I.; and Souza, W.R. 1990. Subsurface mapping of basalts based on petrographic characterization of cuttings from borehole drilling on Oahu, Hawaii, WaterResources Investigation Report WRIR 89-4181, U.S. Geological Survey, Water Resources Division, Reston, Virginia. Norton, F.J. 1952. Diffusion of gases through solids. General Electric Review 55(5):28-29. Ogata, A., and Banks, RB. 1961. A solution of the differential equation of longitudinal dispersion in porous media. USGS Professional Paper411-A, pp. AI-A7. Oki, D.S.; Miyahira, RN.; Green, R.E.; Giambelluca, T.W.; Lau, L.S.; Mink, J.F.; Schneider, R.C.; and Little, D.N. 1990. Assessment of the potential for groundwater contamination due to proposed urban development in the vicinity of the U.S. Navy Waiawa Shaft, Pearl Harbor, Hawaii, Spec. Rep. 03.02.90, Water Resources Research Center, University of Hawaii at Manoa, Honolulu. Or, S., and Lau, L.S. 1987. Modeling of trace organics (DBCP) transport in Pearl Harbor aquifer, O'ahu, Hawai'i: Method of characteristics, phase II. Tech. Rep. No. 175. Water Resources Research Center, University of Hawaii at Manoa, Honolulu. (in press) -Reimer, G.M.; Denton, E.H.; Friedman, I.; and Otton, J.K. 1979. Recent developments in uranium exploration using U.S. Geological Survey's mobile helium detector. J. Geochem. Expl. 11: 1-12. ____. 1984. Prediction of central California earthquakes from soil-gas helium. PAGEOPH 1222:369-375. Seitz, c.A. and P.W. Holland. 1986. An improved analyzer for a determination of helium 4 in parts-per-billion range. Report RI09010, 7 p. U.S. Bureau of Mines, Amarillo, Texas. Smith, S.P. and Kennedy, B.M. 1983. The solubility of mobile gases in wat~r and NaCl brine. Geochimica Cosmochimica Acta 47:503-515. Sophocleous, M.A. 1984. Groundwater flow parameter estimation and quality modeling of the equus beds aquifer in Kansas, U.S.A. J. Hydro. 69: 197-222. Souza, W.R, and Voss, c.1. 1987. Analysis of an anisotropic coastal aquifer system using variable-density flow and solute transport simulation. J. Hydro. 92: 17-41. Sudicky, E.A. 1986. A natural gradient on solute transport in a sand aquifer: Spatial variability of hydraulic conductivity and its role in the dispersion process. Water Resources Res. 22( 13):2069-2082. Varian Vacuum Products, Palo Alto Vacuum Division. 1979. Instruction: Vac Ion pump control unit and 8, 20, 30, and 60 I Vac Ion pumps. Manual 87-400-256A. 68 p. Weiss, R.F. 1971. Solubility of helium and neon in sea water. J. Chem. Eng. Data 167:235241.
62 Wentworth, C.K., and Macdonald, G.A. 1953. Structure and form of basaltic rocks in Hawaii. Bull. 994, U.S. Geological Survey, Washington, D.C.
63
APPENDIX CONTENTS B. AVAILABLE DATA OF WELLS USED IN GROUNDW ATER EXPERIMENTS . . . . .
88
Well 1 (Original Code 24I-lB). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
Well 2 (Original Code 241-1 A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
Well 3 (Original Code New Well No.1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
90
Well 4 (Original Code New Well No.2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
90
C. A USER'S GUIDE TO THE PROTOTYPE WATER HELIUM ANALyZER.........
91
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
Operating Instructions
92
Switch-Off Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
94
Instructions for Dismantling and Packing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
94
Tables A,I. Helium Analyzer Calibration Test Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
A.2. Performance of Water Helium Analyzer During Alternating Flow of Helium Solution and Blank Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
A.3. Performance of Water Helium Analyzer at Different Sample Flow Rates. . . . . . . . .
67
AA. Residual Helium in Stored Bottles, Experiment 1, Supersaturated Helium Solution Equilibrated at He Partial Pressure of 1086 torr. . . . . . . . . . . . . .
70
A.5. Residual Helium in Stored Samples, Experiment 2, 10.84% Helium Gas Used to Make Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
71
A.6. Residual Helium in Stored Bottles, Experiment 3; Sample Obtained from BWS Production Well During the Course of an Injection Experiment (Low Concentration as Would Typically be Encountered During a Field Experiment) '. . . . . . . . . . . . . . . . . . . . . . . . . . .
72
A. 7. Breakthrough and Elution of NaCI and Helium Tracers 1l1rough a Column 183.5 cm Long, 8.7 cm in Diameter, Filled with Clean, Quartz Sand-Column (Experiment 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
A.8. Breakthrough and Elution of NaCI and Helium Tracers 1l1rough a Saturated Sand Column (Experiment 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
74
A.9. Breakthrough and Elution of NaCI and Helium Tracers 1l1rough a Saturated Sand Column (Experiment 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
A.tO. Breakthrough and Elution of NaCI and Helium Tracers 1l1rough a Saturated Sand Column (Experiment 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
A.II. Breakthrough and Elution of Helium and NaCI Tracers in Short Soil Column (Experiment 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .
77
A.12. Breakthrough and Elution of Helium and NaCI Tracers in Short Soil Column (Experiment 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
78
A.I3. Results of Field and Laboratory Measurements of Samples from Waipahu Wells During Groundwater Tracer Experiments 1,2, and 3 . . . . . . . . . . . .
79
' ....,.
64 A.14. Helium Tracer Breakthrough and Elution Data, Experiment 4, Samples From BWS Waipahu Production Wells I and 2
81
A.15. Helium Concentration in Samples Taken from Water Table in USGS Observation Well "F" at Waipahu after Cessation of Helium Injection for Groundwater Tracing Experiment 4 . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
A.16. Spatial and Temporal Variation of Helium Concentration Expressed as CICo after Injection of HeliumlFluorescein Tracer Plume in an Open Tank at Look Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
A. 17. Spatial and Temporal Variation of Fluorescence Expressed as CICo after Injection of HeliumlFluorescein Tracer Plume in an
Open Tank at Look Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
A.18. Sand-Column Experiments, Computation of Porosity and Longitudinal Dispersity of Sated Uniform Quartz Sand (ASTM Disgination C-190) . . . . . . . . . . .
87
990000 990000 990000 990000 990000 990000 990000 990000 990000 990000 990000 990000
35,100 34,195 36,004 34,049 33,657 34,440 35,802 34,595 37,010 37,927 36,968 39,727
34,345 34,101 35,827 33,939 33,602 34,337 35,763 34,498 36,901 37,882 36,877 39,520
........ ........ ........
........ ........
........ ........
........ ........
........ ........ ........ ........ ........ ........ ........
........ ........ ........ ........ ........ . ....... ........
108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400 108400
3,851 3,953 4,046 4,076 4,128 4,133 4,139 4,138 4,241 4,094 4,072 4,060 4,046 4,068 4,030 4,057 4,138 4,162 4,183 4,206
3,698 3,869 3,977 4,063 4,092 4,107 4,112 4,111 3,933 4,019 4,032 3,999 4,027 4,005
2,934 3,129 3,234 3,270 3,306 3,331 3,318 3,227 3,229 3,238 3,229 3,222 3,214 3,199
3,092 3,234 3,285 3,352 3,353 3,362 3,348 3,776 3,844 3,852 3,844 3,848 3,820 3,829
........ ........
........ ........ ........ ........
........
........
........
........ ........ ........ ........
11 000 11000
362 350
316 341
;265 . 283
275 267
........
........ ........
........
........
........
000 000 000 000 000 000 000 000 000 000 000 000 000
362 361 359 363 369 342 355 357 352 365 342 363 .....
348 341 355 345 352 359 324 346 352 356 355 362 362
274 281 292 264 281 284 279 287 271 285
..... ..... .....
278 282 285 287 285 268 279 283 282 286 292 283 287
965.73 965.73 965.73 965.73 965.73 965.73 965.73 965.73 965.73 965.73
40 39 39 40 40 38 39 38 40 40
38 38 39 40 40
28 29 28 30 27
36 36 37 37 37
95.63 95.63 95.63 95.63 95.63 95.63 95.63 95.63 95.63 95.63 95.63
3 3 4 4 3 3 4 4 4 3 3
3 4 4 3 3 4
4 3 3 3 3 2
2 3 2 2 3
11 11 11 11 11 11 11 11 11 11 11 11 11
Narn: See Figures 7 and 10. *The belium concentrations refer to the amount of belium in tbe gas used to prepare tbe tracer solution.
66 APPENDIX TABLE A.2. PERFORMANCE OF WATER HELIUM ANALYZER DURING ALTERNATING FLOW OF HELIUM SOUITION AND BLANK WATER TIME (min)
FIRST RUN 0 1 2 3 4 5 6 7 8 9 10
HElJUM SOLUTION R.DW Fract. Plateau Signal Net Signal
BLANK SOLUllON R.DW Net Signal Fracl. Residual Signal
0 108 174 198 211 219 225 231 236 242 247 250 254 258 262 267 269 269
0.000 0.401 0.647 0.736 0.784 0.814 0.836 0.859 0.877 0.900 0.918 0.929 0.944 0.959 0.974 0.993 1.000 1.000
238 88 55 42 34 28
1.000 0.370 0.231 0.176 0.143 0.118
20 17 14 11 9
0.084 0.071 0.059 0.046 0.038
5 2 0 0
0.021 0.008 0.000 0.000
SECOND RUN 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
0 128 169 185 196 204 211 216 220 223 227 231 234 237 241 244 245 245
0.000 0.522 0.690 0.755 0.800 0.833 0.861 0.882 0.898 0.910 0.927 0.943 0.955 0.967 0.984 0.996 1.000 1.000
235 91 55 42 34 28 23 19 17 13 11 9 7 5 4 3 2 0
1.000 0.387 0.234 0.179 0.145 0.119 0.098 0.081 0.072 0.055 0.047 0.038 0.030 0.021 0.017 0.013 0.009 0.000
TIllRDRUN 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
0 129 165 182 195 202 207 214 221 226 230 233 235 238 240 242 243 245
0.000 0.527 0.673 0.743 0.796 0.824 0.845 0.873 0.902 0.922 0.939 0.951 0.959 0.971 0.980 0.988 0.992 1.000
236 94 57 43 35 30 25 21 18 15 13 11 8 6 4 3 1 0
11
12 13 14 15 16 17
NOTE: See Figure 9.
.~
1.000 0.398 0.242 0.182 0.148 0.127 0.106 0.089 0.076 0.064 0.055 0.047 0.034 0.025 0.017 0.013 0.004 0.000
67 APPENDIX TABLE A.3. PERFORMANCE OF WATER HELIUM ANALYZER AT DIFFERENT SAMPLE FLOW RATES Flow Across Membrane
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution Solution Solution Solution Solution
Helium Signal (SI) 1 minute
Helium Signal (S3) 3 minute
Flow rate across membrane = 64.7 29,300 32,630 32,550 33,490 33,140 34,150 33,310 33,930 33,300 33,860 33,410 33,870 33,250 33,850 33,200 33,880 33,370 33,970 33,410 34,000
ml/min 36,660 35,070 36,940 36,220 36,940 36,570 37,400 36,980 37,370 37,060 37,400 37,140 37,520 37,230 37,600 37,340 37,820 37,550 37,910 37,650
=0.88 =0.92
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution Solution
Flow rate across membrane = 95.3 33,830 34,170 34,320 34,760 34,640 34,990 34,890 .~ 35,120 34,830 35,320 35,030 35,360 35,190 35.530
ml/min 38.940 37,430 38,700 38,230 38,990 38,600 39,030 38,770 39,370 39,130 39,530 39,240 39,810 39,530
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution
Flow rate across membrane = 137.0 mVmin 50,840 43,420 48,110 43,560 49,070 43,720 48,160 43.510 48,260 43,060 47,750 42,710 44,710 40,550 47,630 42,160
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
0.80 0.93 0.88 0.92 0.90 0.93 0.89 0.92 0.89 0.91 0.89 0.91 0.89 0.91 0.88 0.91 0.88 0.90 0.88 0.90
0.87 0.91 0.89 0.91 0.89 0.91 0.89 0.91 0.88 0.90 0.89 0.90 0.88 0.90 = 0.88
=0.91
0.85 0.91 0.89 0.90 0.89 0.89 0.91 0.89
=0.88 =0.90
68 APPENDIX TABLE A.3.-Continued Flow Across Membrane
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution
Helium Signal (SI) I minute
Helium Signal (S3) 3 minute
Flow rate across membrane = 66.0 mllmin 4,620 3,880 4,440 3,930 3,990 4,580 4,010 4,540 4,620 3,980 4,030 4,570 4,650 4,020 4,620 4,060 4,660 4,060 4,630 4,060 4,640 4,070 4,020 4,600
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution
Flow rate across membrane = 102.2 mllmin 4,860 4,020 4,020 4,510 4,630 3,950 4,550 4,030 4,000 4,570 4,720 4,160 4,750 4,130 4,140 4,720 4,130 4,800 4,780 4,190
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution
Flow rate across membrane = 102.2 mllmin 4,850 4,090 4,560 4,030 4,160 4,730 4,080 4,660 4,140 4,740 4,140 4,730 4,190 4,750 4,720 4,110 4,180 4,780 4,750 4,130 4,780 4,190 4,770 4,160
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
0.84 0.89 0.87 0.88 0.86 0.88 0.86 0.88 0.87 0.88 0.88 0.87 =0.86 = 0.88
0.83 0.89 0.85 0.89 0.88 0.88 0.87 0.88 0.86 0.88 = 0.86 = 0.88
0.84 0.88 0.88 0.88 0.87 0.88 0.88 0.87 0.87 0.87 0.88 0.87 =0.87 =0.87
69 APPENDIX TABLE A.3.-Continued Flow Across Membrane
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution
Helium Signal (SI) I minute
Helium Signal (S3) 3 minute
Test 4, 02/26/90 Flow rate across membrane = 150.0 mllmin 1,340 1,637 1,426 1,143 1,514 1,163 1,460 1,158 1,160 1,491 1,184 1,494 1,502 1,164 1,487 1,168 1,159 1,498 1,490 1,173 1,[69 1,501 1,181 1,491
Average ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing)
Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank Helium Blank
Solution Solution Solution Solution Solution Solution
Ratio SJlS3
0.82 0.80 0.77 0.79 0.78 0.79 0.77 0.79 0.77 0.79 0.78 0.79 =0.78 =0.79
Flow rate across membrane = 69.5 ml/min 1,564 1,096 1,110 1,422 1,109 1,491 1,124 1,457 1,477 1,104 1,463 1,125 1,471 1,101 1,129 1,470 1,449 1,087 1,446 1,119 1,433 1,062 1,104 1,432
0.70 0.78 0.74 0.77 0.75 0.77 0.75 0.77 0.75 0.77 0.74 0.77 = 0.74 =0.77
A verage ratio of 1- to 3-minute signal (helium solution flowing) Average ratio of 1- to 3-minute signal (blank flowing) "".
70 APPENDIX TABLE A.4. RESIDUAL HELIUM IN STORED BOTILES. EXPERIMENT 1. SUPERSATIJRATED HELIUM soumON EQUll...IBRATED AT He PARTIAL PRESSURE OF 1086 TORR Storage Time (days)
o o o 6 6 6 6
6 11 11 11 11
11 11
22 22 22 22 22 22 54 54 54 54 NOTE: See Figure 11.
S, Helium Scale Reading
54 172 46687 51 991 44015 47895 45 100 46205 44725 42561 37285 34903 39063 37726 36541 37842 37 176 37041 36520 38285 37662 31 055 32771 30868 29740
In (S)
10.90 10.75 10.86 10.69 10.78 10.72 10.74 10.71 10.66 10.53 10.46 10.57 10.54 10.51 10.54 10.52 10.52 10.51 10.55 10.54 10.34 10.40 10.34 10.30
71 APPENDIX TABLE A.5. RESIDUAL HELIUM IN STORED SAMPLES, EXPERIMENT 2, 10.84% HELIUM GAS USED TO MAKE SOLUTION
Storage Time
S, Heliwn
(days)
Scale Reading
0.00 0.00 0.00 0.00 0.00 0.00 9.00 9.00 9.00 9.00 9.00 19.20 19.20 19.20 26.20 26.20 26.20 26.20 30.86 30.86 30.86 30.86 NOTE: See Figure 12.
4344 4211 4 125 4067 4 142 4012 3448 3656 3 396 3 330 3632 3 187 3279 3246 2513 2584 2650 2690 2505 2642 2841 2817
In (5)
8.38 8.35 8.32 8.31 8.33 8.30 8.15 8.20 8.13 8.11 8.20 8.07 8.10 8.09 7.83 7.86 7.88 7.90 7.83 7.88 7.95 7.94
72 APPENDIX TABLE A.6. RESIDUAL HELIUM IN STORED BOTILES, EXPERIMENT 3; SAMPLE OBTAINED FROM BWS PRODUCfION WELL DURING THE COURSE OF AN INJECTION EXPERIMENT (LOW CONCENTRATION AS WOULD TYPICALLY BE ENCOUNfERED DURING A FIELD EXPERIMENl)
Storage Time
S, Helium
(days)
Scale Reading
0.00 0.00
45 45 41 46 43 46 40 39 42 40 40 36 40 41 39 40 39 41 34 36 37 37 36 38
2.68 2.68 3.75 3.75 7.01 7.01 9.00 9.00 12.00 12.00 14.11 14.11 14.11 16.57 16.57 16.57 18.87 18.87 18.87 21.06 21.06 21.06 NOTE: NOTE:
In (S) 3.81 3.81 3.71 3.83 3.76 3.83 3.69 3.66 3.74 3.69 3.69 3.58 3.69 3.71 3.66 3.68 3.66 3.70 3.52 3.57 3.60 3.62 3.57 3.63
Helium solution obtained from Waipahu production well 1 during fourth injection test (sample 1/66). See Figure 13.
73 APPENDIX TABLE A.7.
Minutes Since Start 0.0 3.6 6.7 8.5 10.7 15.0 19.3 23.5 20.6 24.8 28.3 30.3 32.7 33.8 36.1 38.6 41.2 42.8 45.5 46.6 49.4 50.7 51.8 53.1 55.6 56.5 57.0 58.9 62.0 64.4 65.3 68.0 71.1
72.3 74.3 76.2 78.0 80.2 NOTE: NOTE: NOTE:
HeCIC o
BREAKlliROUGH AND ELUTION OF NaCl AND HELIUM TRACERS THROUGH A COLUMN 183.5 CM LONG, 8.7 CM IN DIAMETER, FILLED WIlli CLEAN QUARTZ SAND-COLUMN, EXPERIMENT 1 EC CICo
tagged water flow starts 0.00 0.06 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.69 0.00 0.98 0.00 0.98 1.02 0.00 1.02 0.98 blank water flow starts 0.01 1.05 1.00 1.00 0.03 1.00 0.06 1.00 1.00 1.00 0.11 1.00
Minutes Since Start 82.2 84.7 85.7 87.3 89.2 91.3 92.7 94.5 96.0 97.5 98.9 101.1 102.1 103.8 105.3 107.0 107.9 110.0 113.5 116.0 121.8 125.1 132.8 136.2 145.3 150.0 155.0 162.7 164.7 172.4 175.5
Tagged water with 99% helium at ambient temperature and pressure. Flow rate through column about 110 ml/min. See Figure 18.
He CICo
ECCIC o
1.02 1.02 0.19 1.02 1.02 0.25 0.95 0.61 0.36 0.23 0.11 0.40 0.02 0.00 0.00 0.00 0.49 0.00 0.00 0.69 0.76 0.00 0.86 0.00 0.97 0.00 1.00 0.00 0.97 0.00 0.86
74 APPENDIX TABLE A.8. BREAKTHROUGH AND ELUTION OF NaCI AND HELIUM TRACERS TIlROUGH A SATURATED SAND-COLUMN. EXPERIMENT 2 Minutes Since Start
0.0 2.7 3.9 8.2 9.5 10.7 13.0 14.0 15.0 17.0 18.3 19.5 20.9 22.3 24.2 24.7 25.9 27.3 28.3 30.1 32.3 32.9 34.3 35.7 36.8 38.3 39.4 42.0 43.1 45.7 46.7 48.3 50.3 51.9 53.0 54.7 55.4 57.4 58.3 58.7 61.6 63.1 NOTE: See Figure 19.
HeC/C o
EC C/Co
tagged water flow starts
0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.07 0.30 0.45 0.72 0.59 0.91 0.70 0.97 0.71 1.00 0.91 1.00 0.94 blank water flow starts 1.00 1.00 0.96
Minutes Since Start
64.3 66.0 67.5 69.4 70.5 72.3 73.6 75.9 77.0 79.3 82.5 83.7 85.0 86.5 87.7 93.9 95.0 96.6 97.8 99.3 100.3 102.0 103.0 104.8 106.2 108.0 109.0 110.7 111.8 113.5 115.2 116.8 119.0 120.2 122.3 123.8 131.3 154.6 156.8 202.0 204.0
He C/Co
ECC/Co
1.00 0.96 1.00 0.98 1.00 1.00 1.00 0.98 1.00 1.02 1.00 1.03 1.00 1.01 1.00 1.01 1.00 0.94 0.95 0.73 0.55 0.32 0.18 0.16 0.02 0.09 0.00 0.08 -0.01 0.06 -0.01 0.05 -0.01 0.04 -0.01 0.04 0.03 0.01 -0.01 0.01 0.03
75 APPENDIX TABLE A.9. BREAKTHROUGH AND ELlJTION OF NaCl AND HELIUM TRACERS THROUGH A SATURATED SAND-COLUMN, EXPERIMENT 3 Minutes Since Start
HeC/C o
EC C/Co
0.0 5.0 10.2
tagged water flow starts 0.00 0.00
0.04 0.02
14.8 19.4 24.2
0.00 0.00 0.00
0.03 0.04 0.05
28.7 33;5
0.00 0.00
0.06 0.07
38.5 44.1
blank water flow starts
49.0 53.8
0.00 0.00 0.00
58.6 63.4 68.3 73.5 79.0 84.5
0.44 0.94 1.00
89.6 94.2 102.3
0.88 1.13 0.81
108.8 113.2 118.1 124:0 128.8 133.9 138.8 144.5 152.6 158.5 163.8 168.5 174.0
0.19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
NOTE: See Figure 20.
1.00 1.00 1.00
0.10 0.09 0.04 0.24 0.72 0.87 0.98 1.00 1.00 1.00 1.00 0.78 0.11 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
76 APPENDIX TABLE A.lO. Minutes Since Start 0.0 3.0 6.5 10.3 13.0 14.7 17.2 20.2 21.9 24.3 27.5 30.3 33.0 36.9 39.0 40.7 43.5 45.1 47.2 48.6 50.8 53.0 54.3 55.0 56.2 58.7 60.0 63.1 63.5 64.4 66.7 68.2 70.0 70.7 72.8 74.5 77.0 82.2 84.6 87.0 88.2 91.7 93.0 95.2 97.0 98.5 100.7 101.6 102.2 103.3 106.0 107.2 109.8 NOTE: See Figure 21.
He CICo
BREAKTHROUGH MTI ELUTION OF NaCI AND HELIUM TRACERS THROUGH A SATURATED SAND-COLUMN, EXPERIMENT 4 EC CICo
tagged water flow starts 0.00 0.00 0.00 0.00 0.00 0.00 blank water flow starts 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 tagged water flow starts 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 blank water flow starts 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.18 0.57 0.66 0.92 tagged water flow starts 0.87 1.00 0.96 0.97 0.98 0.89 0.78 0.35 blank water flow starts ',. 0.29 0.07 0.15 0.44 0.90 0.91 0.92 1.00 0.62 0.67 0.33 0.39 0.09 0.04 tagged water flow starts 0.21 0.02 0.22 0.31 0.72
Minutes Since Start Ill. 7 115.0 116.4 118.8 120.1 121. 7 123.3 124.7 126.8 127.5 128.0 129.8 131.5 134.8 136.5 137.9 139.4 140.6 142.0 143.5 145.8 147.3 148.5 150.3 151.6 153.6 154.8 157.1 158.6 161. 7 163.3 164.8 166.2 168.2 169.2 172.0 173.2 174.6 176.0 177.5 178.7 180.8 184.5 186.7 188.3 190.5 192.1 193.0 196.1 197.0 200.2 201.1
He CICo
EC CICo
0.78 0.98 0.93 1.00 0.98 0.89 0.68 0.44 0.21 blank water flow starts 0.27 0.07 0.19 0.03 0.02 0.01 0.15 0.01 0.01 0.12 0.01 0.09 0.00 0.01 0.08 0.03 0.18 0.34 0.58 0.69 0.89 0.93 0.90 0.98 0.98 0.98 0.90 1.00 1.00 0.94 1.00 1.00 0.78 0.60 0.44 0.21 0.07 0.29 0.05 0.23 0.02 0.19 0.00
77 APPENDIX TABLE A.ll. BREAKTIlROUGH AND ELUTION OF HELIUM AND NaCl TRACERS IN SHORT SOIL-COLUMN, EXPERIMENf 1 Minutes Since Start
0 1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 30 31 32 33 34 35 NOTE: See Figme 22.
HeC/Co
ECClCo
tagged water flow starts 0.08 0.00 0.08 0.00 0.00 0.00 0.00 0.08 0.08 0.08 0.01 0.08 0.04 0.08 0.11 0.08 0.21 0.08 0.17 0.38 0.25 0.50 0.61 0.42 0.50 0.70 0.75 0.58 0.58 0.80 0.80 0.67 0.67 0.80 0.86 0.75 0.75 0.86 0.86 0.75 0.83 0.89 0.89 0.83 0.89 0.83 0.89 0.83 0.83 0.89 0.89 0.83 0.92 0.89 0.89 0.92 blank water flow starts 0.92 0.89 0.91 0.92 0.91 0.92 0.91 0.92 0.91 0.92 0.92 0.91
Minutes Since Start
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69 70 90 91
HeClCo
ECC/Co
0.91 0.90 0.86 0.86 0.75 0.63 0.47 0.35 0.23 0.18 0.13 0.11 0.08 0.06 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 ·0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01
0.92 1.00 1.00 1.00 0.92 0.92 0.75 0.67 0.67 0.58 0.50 0.42 0.33 0.33 0.33 0.25 0.25 0.25 0.25 0.25 0.17 0.25 0.25 0.17 0.17 0.17 0.25 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17
0.01
78 APPENDIX TABLE A.l2. BREAKTIlROUGH AND ELUTION OF HELIUM AND NaCI TRACERS IN SHORT SOIL-COLUMN, EXPERIMENT 2 Minutes Since Start
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 29 30 31 32 NOTE: See Figure 23.
HeC/Co
ECClCo
tagged water flow starts
0.02 0.02 0.01 0.02 0.01 0.02 0.02 0.01 0.02 0.00 0.02 0.00 0.02 0.00 0.00 0.03 0.08 0.06 0.14 0.09 0.24 0.16 0.29 0.36 0.41 0.48 0.54 0.61 0.71 0.65 0.760.74 0.81 0.81 0.81 0.86 0.81 0.90 0.93 0.81 0.88 0.95 0.88 0.97 0.99 0.90 1.01 0.90 1.01 0.90 1.01 0.90 1.02 0.90 1.01 0.90 blank waterflow starts 1.01 0.92 1.01 0.92 1.00 0.92 1.00 0.92
Minutes Since Start
HeC/Co
ECC/Co
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
0.99' 0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.91 0.90 0.87 0.84 0.79 0.73 0.65 0.56 0.46 0.38 0.31 0.23 0.18 0.14 0.11 0.08 0.06 0.05 0.03 0.02 0.01 0.00 0.02 0.02 0.01
0.92 0.92 0.92 0.92 0.92 0.92 0.92 0.90 0.89 0.86 0.85 0.78 0.68 0.59 0.46 0.35 0.30 0.20 0.15 0.11 0.09 0.07 0.06 0.05 0.04 0.04 0.03 0.03 0.03 0.03 0.02 0.02 0.02
79 APPENDIX TABLE A.l3. RESULTS OF FIELD AND LABORATORY MEASUREMENTS OF
SAMPLES FROM WAIPAHU WELLS DURING GROUNDWATERTRACING EXPERIMENTS 1, 2, AND 3 MIN. SINCE START EXPERIMENT 1 OF INJECTION Field Laboratory
o
injection starts
1 2 3 4 6
7 15 23 30 31 33 34 50 51 52 65 73 76 80 84 95 98 100 108 115 128 130 133 144 145 153 158 161 168 186 190 193 200 216 218 219 224 233
EXPERIMENT 2 Field Laboratory
injection starts 2.00E-05 1.80E-05
1.00E-05
1.80E-05
l.OOE-05
1.80E-05
EXPERIMENT 3 Field Laboratory
injection starts
injection stops 7.00E-05
4.00E-05
4.00E-05 1.20E-05 injection stops
l.OOE-05 1.00E-05 1.00E-05 1.00E-05
1.00E-04
4.00E-05
8.00E-05
4.00E-05
9.00E-05
6.00E-05
2.00E-04
1.60E-04
6.90E-04
'5.30E-04
I.08E-03
7.70E-04
9.50E-04
8.90E-04
l.01E-03
8.00E-04
1.80E-05 1.80E-05
1.00E-05 l.00E-05 l.80E-05
1.00E-05
l.00E-05
1.00E-05
l.00E-05
7.00E-05
1.00E-05 1.80E-05
1.60E-04
l.80E-04
5.40E-04
3.90E-04
9.40E-04
6.60E-04
1.24E-03
9.30E-04
l.72E-03
9.90E-04
1.00E-05 1.80E-05
6.00E-05
3.00E-05
8.00E-05 4.00E-05
4.00E-05
2.00E-05
4.00E-05 3.00E-05
.............. 2.65E-03
5.00E-05
7.00E-05
2.27E-03
4.00E-05 injection stops
4.00E-05
l.80E-05 4.14E-03
2.00E-05
3.00E-05
3.37E-03
80 APPENDIX TABLE A.13.-Continued MIN. SINCE START OF INJECllON 250 262 273 280 285 292 307 310 314 322 340 343 362 371 373 385 401 433 463 493 523 553 583 613 643 675 701 731 793 853 913 1060 1123 1156 1668 1187 1221 10000 NOTE:
NOTE:
EXPERIMENT 1
EXPERIMENT 2
EXPERIMENT 3
Field
Laboratory
Field
Laboratory
Field
Laboratory
3.00E-05
5.00E-05
5.18E-03
4.69E-03
............
............
............
............
............
............
8.60E-04
6.70E-04
2.00E-05
1.80E-05
............
............
............
............ ............
............
5.60E-03
5.12E-03
............
............ ............
............ ............
............ ............
............ ............
7.00E-04
6.00E-04
1.80E-05
............
............
............
............
6.44E-03
5.28E-03
............ ............ ............
............
............ ............
5.l0E-04
4.80E-04
............
5.l8E-03
............
............ ............
2.00E-05 2.00E-05
............ ............
............ ............
1.00E-05 1.00E-05
1.80E-05
............ ............
l.00E-05
5.81E-03
............
............
............
............
5.60E-04
4.40E-04
1.00E-05 1.00E-05
1.00E-05
............
............
............
............
............ ............
............ ............
............
4.20E-04
3.60E-04
4.91E-03
............
............
3.80E-04 3.20E-04 2.70E-04 2.90E-04 2.30E-04 2.30E-04
3.50E-04 3.20E-04 2.60E-04 2.40E-04 2.40E-04 2.20E-04 2.30E-04 1.90E-04 l.80E-04 l.80E-04 1.80E-04 l.60E-04 1.40E-04 1.40E-04 1.40E-04 l.20E-04 l.20E-04
9.90E-04 5.40E·04
Injection well was USGS observation wen "A". Monitoring well was BWS production well 4. Experiment 1 injectate was 170 1 of belium saturated water. Experiment 2 and 3 injection performed by bubbling 99% belium gas in wen. BWS wells 2. 3. and 4 pumping at 6.624 m'Jmin eacb during test. Co assumed to be belium saturation value at ambient temperature and pressure. See Figure 24.
............
............ ............ l.OOE·04 1.OOE-04 4.00E-OS
81 APPENDIX TABLE A.14. HELIUM TRACER BREAKTHROUGH AND ELUTION DATA, EXPERIMENT 4 SAMPLES FROM BWS WAIPAHU PRODUCTION WELLS 1 AND 2 SAMPLE* NO.
Days Since Injection Start
Weill Sample 1
0.00 1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 20 21 22 23 24 25 26 28
0.05 0.25 0.41 0.55 0.59 0.63 0.67 0.72 0.76 0.80 0.84 0.88 0.92 0.97 1.01 1.05 1.09 1.22 1.26 1.30 1.34 1.38 1.42 1.47 1.55
1.73 1.77 1.81 1.85 2.13 2.50 3.01 3.17 3.53 4.29 4.51 5.00
WeIl2 Sample 1
Well 2 Sample 2
helium injection started 1.19E-04 1.40E-04 1.9SE-04 1.67E-04 1.67E-04 1.74E-04 1.67E-04 1.12E-04 9.77E-05 1.19E-04 9.07E-05 1.05E-04 1.40E-04 1.12E-04 9.77E-05 1.40E-04 ............ 1.54E-04 2.02E-04 1.74E-04 1.88E-04 1.74E-04 1.95E-04 2.02E-04 2.5IE-04
1.19E-04 1.40E-04 1.19E-04 1.40E-04 1.19E-04 1.12E-04 1.40E-04 1.19E-04 1.19E-04 1.19E-04 1.33E-04 1.33E-04 1.40E-04 1.40E-04 1.33E-04 1.33E-04 1.60E-04 1.47E-04 1.47E-04 1.47E-04 1.60E-04 1.67E-04 1.47E-04 1.54E-04 1.54E-04
9.07E-05 1.0SE-04 1.19E-04 1.0SE-04 1.19E-04 1. 12E-04 9.77E-05 9.77E-05 9.07E-05 1.19E-04 6.28E-05 ............ ............ 5.58E-05 5.58E-05 5.58E-05
............ 9.07E-05 9.07E-05 1.0SE-04 1.12E-04 1.12E-04 9.77E-05 1.19E-04 1.40E-04
8.37E-05 8.37E-05 9.07E-05 9.77E-05 7.68E-05 9.77E-05 8.37E-05 9.07E-05 3.49E-05 8.37E-05 9.07E-05 9.77E-05 9.77E-05 8.37E-05 8.37E-05 9.77E-05 7.68E-05 7.68E-05 9.07E-05 9.07E-05 9.77E-05 9.07E-05 8.37E-05 '" 9.07E-05 9.77E-05
helium injection stopped
1.59 31 32 33 34 36 38 39 41 42 44 45 46
Hf11UM (CQ}) Weill Sample 2
1.40E-04 1.88E-04 1.74E-04 1.74E-04 1.95E-04 I.60E-04 2.58E-04 2.6SE-04 2.79E-04 3.35E-04 3.35E-04 3.42E-04
1.60E-04 1.60E-04 1.47E-04 1.60E-04 1.74E-04 1.74E-04 1.88E-04 2.09E-04 2.51E-04 3.35E-04 3.63E-04 3.28E-04
............
............
9.07E-05 1.05E-04 1.12E-04 1.05E-04 1.40E-04 1.l2E-04 1.47E-04 1.60E-04 2.02E-04 2.09E-04 2.44E-04
8.37E-05 7.68E-05 9.77E-05 1.l2E-04 9.77E-OS 1.40E-04 1.40E-04 1.47E-04 2.02E-04 2.09E-04 2.6SE-04
82 APPENDIX TABLE A.14.-Continued SAMPLE* NO. 48 49 50 51 53 54 55 57 58 59 61 62
64 65 66 67 68 69 70 71 72
73 74 75
HFJ.lUM(0C0)
Days Since Injection Start
Well 1 Sample 1
Well 1 Sample 2
Well 2 Sample 1
Well 2 Sample 2
5.51 5.99 6.51 7.02 7.52 8.52 9.11 10.22 11.29 12.16 13.21 14.15 14.99 17.48 19.05 21.50 22.27 26.01 28.13 30.26 33.26 35.28 37.97 40.14
3.98E-Q4 4.40E-04 4.95E-04 6. 14E-Q4
4. 19E-04 4.26E-04 5.37E-04 6.00E-04 6.42E-04 8.09E-04 8.86E-04 8.58E-04 1.03E-03 1.09E-03 1.20E-03 1.10E-03 1.20E-03 1.22E-03 1.26E-03 1.28E-03 1.20E-03 1.17E-03 1.12E-03 9.49E-04 8.93E-04 8.44E-04 7.61E-04 7.47E-04
2.51E-Q4 3.07E-Q4 2.86E-Q4 3.77E-04 4. 12E-04 4.40E-04 5.02E-04 4.81E-04 5.86E-04 6.07E-04 5.86E-04 5.30E-04 ............ 5.30E-04 5.51E-Q4
2.79E-04 2.79E-04 3.07E-04 3.91E-04 4. 12E-04 4.47E-04
6.21E-04 8.37E-04 9.21E-04 8.58E-04 1.05E-03 1.12E-03 1.05E-03 1.26E-03 1. 16E-03 1.21E-03 1.26E-03 1.28E-03 1.23E-03 1.17E-03 1.06E-03 9.49E-04 9.21E-04 7.88E-04 7.47E-Q4 7.26E-Q4
5.65E-04 4.74E-04 4.47E-Q4 3.91E-04 4. 19E-Q4 3.35E-04 3. 14E-Q4
............ 2.58E-04
Injection well was USGS observation well "F". Monitoring wells were BWS production wells 1 and 2. Injection performed by bubbling 99% helium gas in well. BWS wells 1 and 2 pumping at 6.624 m3 each during test. Co assumed to be helium saturation value at ambient temperature and pressure. N01E: See Figure 25. *BWS Waipahu production wells 1 and 2. N01E:
5.23E-04 4.95E-04 5.86E-04 6. 14E-04 5.51E-04 4.95E-04 ............ 4.74E-04 5.51E-04 ............ 4.74E-04 4.47E-04 4. 19E-04 3.35E-04 3.63E-04 3.07E-04 2.93E-04 2.58E-04
83 APPENDIX TABLE A.15. HELruM CONCENTRATION IN SAMPLES TAKEN FROM WAlER TABLE IN USGS OBSERVATION WELL "F' ATWAIPAI«J AFIER CESSATION OF HELlliM INJECTION FOR GROUNDWA1ER TRACING EXPERIMENT 4 Time Since Stop of In In Serial Sample 1 Sample 2 (Sample 1) Injection (Sample 2) No. 1
0.56
0.28
0.27
-1.26
-1.32
2
1.43
0.10
0.10
-2.26
-2.31
3
3.71
0.06
0.06
-2.87
-2.85
4
5.44
0.03
0.03
-3.51
-3.54
5
7.54
0.01
0.02
-4.33
-4.20
NOTE: See Figure 26.
APPENDIX TABLE A.16. SPATIAL AND TEMPORAL VARIATION OF HELIUM CONCENTRATION EXPRESSED AS ClCo AFTER INJECTION OF HELIUMIFLUORESCEIN TRACER PLUME IN AN OPEN TANK AT LOOK LABORATORY DAYSSlNCE INJEcnON START
DISTANCE IN INCHES OF SAMPliNG TIJBE FROM WNGmJDINAL AXIS OF TANK
-60
-36
-24
-12
0
12
24
36
63 85
72
158 113
204 123
325 126
72 48
71
72
51
....
43
60
44
34
35 45 42 49 41 43 30
59 43 45 51
320 126 77 52 19 45
324 115 75 51 43 43
193 114 73 51 42 41
48
56
50
46
44 44
46
40
40
40
40
41 28
40 28
40 28
40 28
26 26
26
1:7 26
25 1:7
25
28
26 13
28
28
28
14 13 15 14
13 12 16 14
13 13 15 14
12 14 11
13
15 12
14 15 12 12
POSmONl
0.01 0.16 1.08 1.97 1.98 1.99 2.06 2.11 2.12 2.18 2.19 5.02 5.01 5.00 4.99 6.97 6.98 , 7.05 7.06 7.08 7.(JJ
7.23 8.34 8.41 8.44 8.45 8.53
77
55 43 36 73 50 49
194 77 47 38 35 56
44
44
42 46
44
41 42
41
40
28
28
29
28
24
24 26
26
15 . 15 16 15 15 14 14 11 11 11 11 12
41 44 28 27 25 27
13
13
12
13 15 15
17
14 13 15 11 12 11
11 12
13
15 11 12 11 11 11
14 13 17 15 12 15 11 12 11 10 11
28
13 16 15 13
15 11 12 11 10 12
49
11 11
11 11 11
10
11
11
45
27
11
12 11
0 ,J
START
-60
-36
-24
-12
0
12
24
113 71 43
294 71 38
264 73 43
210 70
220 74
239
60
44
178 76 19
43
204 61 42
57
42 70 34 41
174 83 45
184 70 43
169 73 41
40
40
40
44
40 40
40
41
40
40
26 24
26 24
27 25
68 68 35 41 43 28 26
179 80 59
44
57 77 35 42
28 26
28
28 27
POSmON2
0.02 1.01 1.98
68
POSmON3
0.17 1.00 1.99 2.18 2.19 4.99 5.00
77
36
=
NOTE: Co of injectate 6S 410 helium signal reading. NOTE: See Figures XI to 30.
,I
41 26 28
27
APPENDIX TABLE A.17. SPATIAL AND TEMPORAL VARIATION OF FLUORESCENCE EXPRESSED AS C/Co AFI'ER INJECIlON OF HELlUMlFLUORESCEIN TRACER PLUME IN AN OPEN TANK AT LOOK LABORATORY DAYS SINCE INJECTION START
DISTANCE IN INCHES OF SAMPLING 11mE FROM LONGITUDINAL AXIS OF TANK
-60
-36
77
74 73
-24
-12
0
12
24
36
75
76 73 74 76 74
.... 73 73 76 75
76 73 73 76 75 75 74 73 73
76 73 74 76 74 75 75 73 73
73 73 73 76
....
....
74
POSmONl
1.97 2.11 2.12 5.02 5.01 6.97 6.98 7.05 7.06 7J11 7.00 7.23 8.34 8.41 8.44
77 73 75 77 74 74 74
72
72 72
72
78 74 71 73 75 73
76 75 74 73 74 74
73
....
....
71
71
72
74 73 73
75 73 74
77
73 74 72 71
....
....
72 72 69
72 72 69
72 71
72 71
72 71
72 72
(f}
(f}
(f}
69
70
(f}
68
68
68 68
(f}
68
69 68
70 69 67
68
68
97 73 75
263 74 74
249 75 75
188 75 74
197 76 75
152 77 74
197 76 74
169
....
0 73 75 74
3 58 73 74 71
3 80 74 73
3 174 75 73 73 74 75 77
3 151 75 75 75 74
3 161 76 76 75
0 152 75 74 76 74
77
75 75
72 72
70 70
72 69
POSmONl
0.02 1.01 1.98
77
74
POSmON3
0.03 0.17 1.00 1.99 2.18 2.19 4.99 5.00
70 73 72
73 75 76 77
NOTE: Co of the tracer 101ntion NOTE: See Figures T1 to 30.
71 72
75 75
72
71 72
75 75
73 76
=68 624.5 fluorescence scale reading.
75
72
77
75
APPENDIX TABLE A.18. SAND-COLUMN EXPERIMENTS. COMPlITATION OF POROSITY AND LONGmJDINAL DISPERSITY OF SATED UNIFORM QUARTZ SAND (ASlM DESIGNATION C-I90) Expt. No.
Flow Rate (F) Through the Column (cm3/min)
1
110
2
3
4
NOTE:
TRACER DATA OF ECJHe During Loading! Elution (llE)
t(cleo = 1/2) (min)
Outflow Volume During to to t(cleo = 1/2) v = F.t(cleo = 112)
Porosity n=vN
at t( cleo = 1/2)
()xJ()t= F/(A.n)
()cJdt
()c/i) = ()c/()t «()tI()x)
IlL = 11[41tX «()cfc)xf]
EC
L E
39.0 38.5
4290 4235
0.39 0.39
0.1294 0.1667
4.74 4.77
0.0273 0.0350
0.58 0.35
EC
L E
40.4 42.3
4161 4450
0.38 0.41
0.1135 0.1481
4.56 4.25
0.0249 0.0349
0.70 0.36
He
L E
42.4 42.3
4367 4450
0.40 0.41
0.0703 0.1519
4.33 4.25
0.0162 0.0358
1.65 0.34
EC
L E
61.5 65.8
4490 4806
0.41 0.44
0.1000 0.1031
2.98 2.79
0.0335 0.0370
0.39 0.32
He
L E
60.0 65.8
4380 4806
0.40 0.44
0.1042 0.0954
3.06 2.79
0.0341 0.0342
0.37 0.37
EC
Fll'St L LastE
50.3 58.3
4476 5188
0.41 0.47
0.1091 0.1026
3.65 3.15
0.0299 0.0326
0.48 0.41
He
Fll'StL LastE
49.1 58.3
4370 5188
0.40 0.47
0.1500 0.0576
3.74 3.15
0.0401 0.0183
0.27 1.29
103
73
89
Length of the column (x) Internal diameter of the column (d) Volume of the column (V) Cross-sectional area of the column (A)
=
183.SOem,
= 8.70em = 10908.49 em' = S9.4Sem2•
88 APPENDIX B. AVAILABLE DATA OF WELLS USED IN GROUNDWATER EXPERIMENTS WELL 1 (ORIGINAL CODE 241-1 B) Location Owner
60 ft East of Well A Suburban Water System
Altitude
200ft
Drilled
May 19 to June 25, 1954 by Samson and Smock Ltd.
Diamerer
16 in. (ill)
Depth
355 ft
Casing
231 ft 2 in.
Heal
July 9, 1954, 18.19 ft; July 14, 1954, 18.29 ft
Chloride
July 9, 1954, 100 ppm (average for 6 samples taken during 6 br pumping test)
Use
Municipal Supply
Capacity
Tested by pumping for 6 hours, July 9, 1954
BenchMark Log
Rate (RPm)
Drawdown (ft)
400 700 900 1000 1100
0.8 1.5 1.9 2.2 2.4
Top of concrete base of pump (Mauka-Ewa Comer), 1-1/2 ft above ground; altitude 201.71 ft 0 19 34 35 41 43 49 56 75 79 87
90 107 112 130 133 138 142 153
-
-
-
..-
19 ft 34 35 41 43 49 56 75 79 87
90 107 112 130 133 138 142 153 155
Brownc1ay Boulders Red clay Boulders Clay Small boulders Hard boulders Hardrodc Medium hard aadced rock Hard rock Medium hard Rock Hard rock Medium hard rock Hardrodc Very hard rock Hardrodc Soft rock Medium hard rock Soft rock
155 164 167 173 177 180 185 193 201 209 224
226 281 286 289 301 328 333 335
-
.-
-
164 167 173 177 180 185 193 201 209 224 226 281 286 289 301 328 333 335 355
Medium hard rock Very hard rock Hard rock Medium bard rock Soft rock Medium hard rock Hard rock Medium bard rock Hard rock Medium bard rock Soft rock Medium bard rock Hard rock Medium bard rock Hard rock Medium hard rock Hard rock Soft rock Medium bard rock
89 WELL 2 (ORIGINAL CODE 241-1 A) Location
60 ft East of Well 2
Owner
Suburban Water System
Altitude
202ft
Drilled
May to June, 1954 by Samson and Smock Ltd.
Diameter
16 in. (ID)
Depth
350 ft
Casing
231 ft 2 in.
Heal
July, 1954, 17.5 ft
Use
Municipal Supply
Capacity
Tested by pumping for 6 hours, July 9, 1954
Bench Mark
Log
Rate(apm)
Drawdown (ft)
450 675 850 1000 1200
1.1 1.9 2.4 3.1 4.2
Top of concrete base of pump (Mauka-Ewa Comer), 1-1/2 ft above ground; altitude 201.71 ft 72 - 77 ft 77 82 82 91 91 92 92 100 100 102
102
113
113 115 143 149 150 156 160 166 169 174 176 186 191 214 249 273 276
115 143 149 150 156 160 166 169 174 176 186 191 214 249 255 273 276 303
303
306
306 311 327 329
311 327 329 355
255
Boulders, red clay Few boulders, clay Loose boulders with clay Boulders Hard rock Clay Soft rock with clay Medium hard rock Hard rock Hole dry; unable to get sample; formation not hard Hard rock Medium hard rock Hard rock Medium hard rock Clay with few boulders • Hard rock and clay Hard rock Medium hard rode, soft in places Medium hard rode Hard rock Medium hard rock Hard rock Medium'hard rock Hanlrock Medium bard rock Hanlrock Medium bard red rock Hard rock Soft rock Medium hard rock
90 WELL 3 (ORIGINAL CODE NEW WELL NO.1) Location Well Data from Rotary Table Elevation Depth Length of Casing
100 ft North of Well 2 210.9 ft 386 ft (-175 ft) 254 ft (-47 ft)
January 31, 1969,24.03 ft 16 in. (10) Tested by pumping for 6 bours, January 17, 1969 Rate (&pm) Drawdown (ft)
Heal Diameter Capacity
0.69 0.69 1.39 5.54 6.47 8.78
656 667 1053 1429 2459 2951 Driller's log not available
WELL 4 (ORIGINAL CODE NEW WELL NO.2)
Location
60 ft West of Well 3
Well Data from Rotary Table Elevation Elevation
210.9 ft 210.9 ft 386ft (-175 ft)
Depth Length of Casing
254 ft (-47 ft)
January 17, 1969,24.26 ft 16 in. (10) Tested by pumping for 6 bours, January 17, 1969 Rate (apm) Prawdown (ft)
Heal Diameter Capacity
808 1034 1542 2100 2542 3051
1.38 2.42 4.85 10.16 14.90 21.71
Driller's log not available. Well logs for A and F also not available. Elevations and depth to water table measured during the course of belium-tracing experiments on April 20, 1990
Well Code
Eleyalion (ft)
Head (ft)
A B C D E
204.19 240.53 194.11 216.73 202.30
19.80 16.18 19.98 20.13 19.85
91
APPENDIX C: A USER'S GUIDE TO THE PROTOTYPE WATER HELIUM ANALYZER
Inslallation The water helium analyzer illustrated in Figure 2 consists of the following: 1. A 2 Us (Varian model 913-00(5) or 8 Us (Varian model 911-5005) diode-ion pump and its magnet (Varian model 913-0112 for the 2 Us pump and model 911-0030 for the 8 Us pump) attached to the thin quartz glass membrane with its Pyrex housing. 2. A pump control unit (Varian model 921-(05). 3. A digital multimeter (Fluke model 87). 4. Polyinsulated cable with MS power unit connector and silicon rubber high voltage connector (Varian model 924-0121). 5. Insulated connecting cables with banana jacks on one end to connect the multimeter to theb~kofthepumpcontrmumt
The control unit will operate from a single phase 115 volt, 60 Hz power (or 230 V, 50 Hz) source. The ion pump is connected to the control umt high voltage outlet by the coaxial high voltage cable. The insulated center conductor furnishes the positive high voltage to the ion pump. The outer shield of the coaxial cable is internally attached to the connector housing. This is the negative electrical connection to the ion pump and is also the ground lead from the pump case. This arrangement requires a ground spring for contact between the connector housing and the base of the pump high voltage insulator. The other end of the high voltage cable is connected to the high voltage receptacle on the rear of the control unit with an MS- [(military specification MIL-C-5015) type connector]. To install the high voltage connector: 1. Place the ground spring in the recess on the pump's high-high voltage insulator. 2. Place the connector on the pump's high voltage insulator. Push the connector as far as it will go with a quarter-tum twist Be certain not to displace the ground spring. 3. Attach a braided ground lead from the control unit to the pump body. To install the digital multimeter: On the back of the control unit chassis there are two standard banana jacks, made primarily to accommodate a recorder. The connections accommodate a dual banana plug (general radio no. 279-MB). The black jack is grounded to the control unit chassis. The voltage on the red jack varies from 0 to -100 mV with respect to the grounded blackjack, -100 mV corresponding to full scale analog meter deflection for all current ranges. The maximum impedance into the banana jacks is 20 Kn.
92
Connect the com (common) terminal of the digital meter to the red banana jack and the VO terminal to the black banana jack. This prevents the appearance of a -ve sign in the digital meter display.
Operating Instruclions Important: We are not yet ready to switch on the high voltage. 1. Prepare the water inflow and drainage connections to the housing of the quartz membrane as shown in Figure 8. Use 1/4" diameter flexible tubing, a three-way valve on the inflow side, and a two-way valve on the drain to regulate flow rate. 2. Place a carboy full of blank water (tap water in most cases) at a level higher than the diaphragm assembly and/or the drain outlet, and put the inlet hose in it
3.
Using a hand-operated vacuum pump or your mouth on the outlet tube, start a siphon of the blank water through the diaphragm assembly. Exercise caution when doing this, as excessively fast flow over the membrane may result in damage.
4.
By adjusting the valve on the drain tube, regulate the flow rate of water through the instrument to the 100 ±5 mVmin.
5.
The siphon must also be established in the other hose leading from the three-way valve. This is the hose that the sample will eventually travel through on its way to the analyzer. Place the end of this hose in a reservoir of blank water and change the position of the three-way valve. The water may flow through the tube by itself. If not, then again apply suction to the drain hose. It may be necessary to do so to remove any air bubbles in the tube.
6.
After bubbles have been purged, allow the water to flow from the blank water carboy to '-_ the instrument.
7.
Flip the main power toggle switch on the control unit to the ON position.
8.
To monitor the control unit output voltage, turn the METER RANGE knob to the 5 kV range.
9.
To monitor the ion pump current, tum the METER RANGE knob to an appropriate current range (usually 50 J1A or 5 J1A). If the unit has not been in operation for a long time, the starting current may be quite high, and it may be necessary to use the 500 J1A range.
10. Allow the unit to stay on and note that the pump current should gradually decrease to as low as 0.5 to 1.0 J1A. Important: If the pump current does not decrease and the analog meter on the control unit shows approximately 3.5 kV in the 5 kV range, the pump is not operating. This can happen if the quartz diaphragm breaks or the high voltage connections are improperly made. Check the connections.
93 11. Start the Fluke 87 multimeter by turning the switch to the DC mV position while pressing the yellow button. If the yellow button is not kept pressed down, the meter will have a resolution of only 0.1 mY. The resolution will be ten times greater (0.01 mY) if the button is kept pressed while switching the meter on. This resolution is what we used in our experiments. 12. Once the ion current has stabilized at an acceptably low level (this may take 1 to 2 hours if the instrument has been non-inoperative for a long time), we are ready to make measurements. 13. Put the sample side tubing into the water to be analyzed ensuring that no air bubbles are introduced into the hose during transfer from one container to the other. This sample should be elevated to approximately the same level as the reservoir of blank water to maintain the appropriate flow rate. 14. Turn the three-way valve so that the blank water stops flowing to the instrument and the sample water starts flowing. Start timing. 15. Record the reading on the multimeter after 1 minute and after 3 minutes of sample flow. At 3 minutes, switch the three-way valve back so that the flow of blank water resumes. After this, record 1 minute and 3 minute readings on the multimeter. While the blank water is flowing put the sample tubing into your next sample (step 13). Mter 3 minutes of blank water flow change the position of the three-way valve to start reading the next sample. Take the readings as described earlier. Repeat steps 13-15 for each sample you '("
have. Tabulate your results as below: Sample J.D.
At Start
DIGITAL MElER READINGS After After x =SA - B 1 (For Sample) 1 Minute 3 Minutes x =SA· B2 (For Blank)
Net Helium Signal S =x + yl2
Test Sample Blank
Important note: H the helium content of the sample is high, the ion current will overshoot the analog meter on the control unit and the reading on the digital meter will be >100 mY. Place the MElER RANGE knob on a higher range. Allow the reading to stabilize. The one-minute reading therefore serves as an important guide to range selection, and helps you monitor the instrument's perfonnance through calculation of the 1- minutel3-minute ratio.
16. H conversion from helium scale reading to absolute heli!1m in gas equilibration units is required, use a previously obtained calibration curve as in Figures 7 or 10. Use eq. 6 to
94 convert helium concentration in gas equilibration units to mg Hell of water and multiply by a factor of 5.6 to convert to ml Hell water. In most hydrological experiments we need C/Co; therefore, absolute calibration may not be
necessary. A calibration experiment, however, is important to ensure that the system response is linear over the entire useful range.
Switch-Off Procedure 1. Allow blank water to flow over the quartz diaphragm for some time to purge out any residual helium from the last sample measurement. 2. Switch off the digital meter. 3. Tum the MElliR RANGE knob on the control unit to the 5 kV position. 4. Place the main power toggle in the off position.
Instructions for Dismantling and Packing 1. Allow 15 to 20 minutes after switch-off for capacitors in the control unit to discharge. 2. Remove HV connector from the pump. 3. Remove the ground connection from the ion pump. 4. Remove the HV connector cable from the back of the control unit chassis. 5. Remove water by blowing air on the housing of the detector. 6. Pack the detector assembly safely in the cardboard carrying box (with the provided packing).
