Hydrogeochemistry and Groundwater Quality in the ... - Springer Link

JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.74, October 2009, pp.459-468

Hydrogeochemistry and Groundwater Quality in the Coastal Sandy Clay Aquifers of Alappuzha District, Kerala T. M. MANJUSREE, SABU JOSEPH and JOBIN THOMAS Department of Environmental Sciences, University of Kerala, Thiruvananthapuram - 695 581 Email: [email protected] Abstract: Groundwater qualities of coastal aquifers in the Chennam-Pallippuram Panchayath of Alappuzha district, Kerala have been extensively monitored in summer from January to May, 2007 to assess its suitability in relation to domestic and agricultural uses. The water samples (n=36) were analyzed for various physico-chemical attributes like temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), Na, K, Ca, Mg, alkalinity, hardness, silica, chloride, salinity, total dissolved solids (TDS) and sulphate (SO42-). Values of most of these parameters fall within permissible limits. Major ionic relationships indicate that weathering reactions have insignificant role in the hydrochemical processes of the shallow groundwater system. Hydrogeochemical processes controlling the water chemistry are precipitation rather than rock- water interaction. Various determinants such as Sodium Absorption Ratio (SAR), Percent Sodium (Na %), Residual Sodium Carbonate (RSC), and Kelley’s Ratio revealed that most of the samples are suitable for irrigation. Keywords: Hydrogeochemistry, Groundwater quality, Alappuzha, Kerala.

INTRODUCTION

Groundwater is one of the primary sources of water for human consumption, agriculture and industrial uses in Kerala. Determination of physical, chemical and bacteriological quality of water is essential for assessing its suitability for various purposes like drinking, domestic, agricultural and industrial uses. During the past decades, reports of groundwater contamination have increased public concern about groundwater quality (Yanggen and Born, 1990). Quality deterioration of groundwater is reported from certain parts of the state, especially from Alappuzha district and is a matter of great concern. A knowledge on hydrogeochemical processes that control its chemical composition leads to improved understanding of hydrochemical systems and this can contribute to effective management and utilization of the groundwater resource by clarifying relations among many hydrogeological parameters. In the present study, the physico-chemical quality of groundwater from the coastal aquifer in ChennamPallippuram panchayath has been assessed with reference to their suitability for drinking and agricultural purposes.

Latitudes. 9°43'00" and 9°50'00" N and Longitudes 76°21'00" and 76°25' 00" E. It is in the coastal land of Alappuzha district and on an average 8 km inland from the Arabian seashore (Fig.1). The southern, eastern and western sides of the study area are encircled by the Vembanad Lake, one of the Ramsar sites in Kerala. The major factors affecting the groundwater resources are extensive sand mining, population pressure, wetland filling, infiltration of pollutants from coir retting, cement factory, brick manufacturing and saline water intrusion from surrounding lakes. Geomorphology

The study area is the part of a wide and long sand bar. This sand body occurs in two geomorphic forms viz. sand dunes and interdune sheets. There are numerous small and large mounds or dunes of silica sand of various heights from 2 to 8 m, which make the topography rolling. The general elevation of the terrain is less than 5 m above MSL. The western side of the study areas is flanked by the Vayalar lake and the eastern side by Vembanad lake.

Study Area

The present study covers an area of 25.33 km2 in Chennam-Pallippuram panchayath and lies between

Hydrogeology

The general geology of the study area and its environs

0016-7622/2009-74-4-459/$ 1.00 © GEOL. SOC. INDIA

460

T. M. MANJUSREE AND OTHERS

Fig.1. Geological map of the study area.

show that the sand bodies are underlain by the arkosic sediments and laterites of Warkalli Formation, followed by mixed chemical and clastic sediments of the Quilon Formation (Fig.1). These sedimentary formations are underlain by the rocks belonging to the khondalites, charnockites, granite gneisses, pegmatites and dykes. Khondalites and charnockites have undergone extensive migmatisation (Soman, 2002). The geology and geomorphology of the study area control its groundwater resources. The litholog of a borehole located at Pallippuram (Lat. 09°44'48"N and Long. 76°21' 53"E) indicates that the unconsolidated Quaternary sediments comprising sands constitute the upper layer (thickness 9 m), underlain by clay (33 m), clayey sand (12 m), laterites (19 m), clay with limestone (6 m), clay with few sand (57 m), sandy clay (31 m) etc. However, towards the coastal side (western part), the Quaternary sedimentary sequence, consisting of alternate layers of sand and clay, has a total depth of 445 m at Arthungal (Lat. 09°39'32" N and Long. 76°17'59" E). The sedimentary sequence attained a maximum thickness of over 600 m in

the Ambalapuzha-Alappuzha regions. The sandy aquifer in the area acts as a reservoir of water. The availability of groundwater is controlled by thick sand and clay zones. In the study area, the major aquifer, composed of sand, is shallow and unconfined. Normal mode of extraction of groundwater is through bore wells, open wells, hand pipes etc. This panchayath has 50 public open wells, 13 hand pumps and a public water supply tank (capacity 65,000 litres), which use bore wells as source. The diameters of open wells range from 1.5 to 2 m, and well depth is limited to 8 m. The depth to water table is shallow and ranges from 3.5 to 4 m below ground level (bgl) during the pre-monsoon, 2 to 3 m bgl during the monsoon and 3 to 4 m bgl during the post-monsoon periods. Due to overexploitation of groundwater and extensive sand mining, water table shows lowering trend in some parts of the study area. Climate

Climatologically, the region experiences a humid tropical climate. The area receives copious rainfall from two distinct spells, the SW and NE monsoons with an average annual JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009

HYDROGEOCHEMISTRY AND GROUNDWATER QUALITY IN THE COASTAL SANDY CLAY AQUIFERS, KERALA

461

8.1; avg = 6.8) and majority of this fall in acidic category. The EC ranges from 61 (GW8) to 609 (GW4) µs/cm and two samples (GW2 and GW12) show relatively higher values during May, 2007. The seasonal average of TH is 110.31 mg/L and the quality of water varies from soft to hard. Concentration of Ca2+ and Mg2+ ranges from 6.79 (GW1 and GW5) to 79.89 mg/L (GW7) for Ca2+ and 1.48 (GW8) to 62.15 mg/L (GW9) for Mg2+ respectively. The lowest and the highest values of chloride are from GW1 (14.9 mg/L) and GW4 (312.02 mg/L) respectively, and the characteristics of the water samples varies from oligohaline to brackish. The concentration of bicarbonate varies from 46.96 to 244 mg/L. Alkalinity of most of the samples comes under permissible limit, but some locations (e.g., GW2) marked highest values during January (174 mg/L) and March (200 mg/L). This may be due to the nearby cement factory and leachates from the waste disposed from the factory. The concentration of Na+ and K+ showed wide variations from 0.1 (GW8) to 50 mg/L (GW12) for Na+ and 0.8 (GW1, GW6) to 21 mg/L (GW2) for K+ respectively. Very low quantity of SO4 2- (0.68—6.08 mg/L) was obtained during the study period. Comparatively less variation was registered in the case of Si (10.61 to 27.32 mg/L) in the water samples. The level of DO in groundwater ranges from 3.04 to 8.1 mg/L. It is an indicator of healthy state of water and value below 3 mg/L is hazardous to man (Radhakrishnan et al. 2007). TDS content falls between 98 (GW8) and 555 mg/L (GW4). Yet, almost all samples come under permissible limit

rainfall of 350 cm (Iyer, 1984). The average annual temperature is about 33°C. Materials and Methods

Water samples (n = 36) were collected from 12 open wells (GW1—GW12) spaced ~2.0 km apart, covering the Chennam-Pallippuram panchayath for three periods (January, March and May, 2007). Samples were analyzed in the laboratory for the physico-chemical attributes like pH, electrical conductivity (EC), total hardness (TH), Dissolved Oxygen (DO), total dissolved solids (TDS), dissolved silica and major ions (Ca2+, Mg2+, Na+, K+, Cl–, HCO 3 – and SO 42–). All parameters were analyzed by following standard methods (APHA, 1995). The pH and conductivity were measured by using Systronics micro pH meter model 361 and Deluxe conductivity meter model 601.Total Hardness(TH), Ca2+, Mg2+, Cl– and HCO3– were determined by titration. Na+ and K+ were measured by Flame photometry, SO 42– and dissolved silica by Spectrophotometric method at 420 and 410 nm respectively. DO was estimated by Winkler’s method. TDS were determined gravimetrically, and salinity was calculated from the chloride values (Saxena, 1998). RESULTS AND DISCUSSION

A summary of the physico-chemical analysis of the groundwater samples is presented in Table 1. The pH of most samples show a narrow range (5.97-

Table1. Descriptive statistics of groundwater samples during the study periods, January, March and May, 2007 Parameters Temp pH EC TH Ca2+ Mg2+ ClHCO3TA Na+ K+ SO42Si DO TDS Salinity

January 2007 Mean 22.7 6.47 155.58 126.33 20.69 25.16 27.72 187.75 97.33 9.83 4.71 1.33 18.98 5.23 181.33 50.66

SD 1.07 0.40 58.40 57.38 11.01 12.84 10.81 42.20 34.59 7.56 5.35 0.97 3.43 1.38 56.6 19.52

March 2007

Max

Min

Mean

24.0 7.46 274 200 43.74 53.49 49.64 212.28 174 25.5 21.0 4.28 26.57 8.15 296 89.6

21.0 5.97 67 50 6.76 8.09 14.970.76 58 2.9 0.8 0.68 13.47 3.04 141 26.92

26.7 6.86 158.83 100.42 29.45 19.67 52.42 95.97 85.33 4.05 4.08 1.24 22.42 4.79 186.17 94.64

SD 0.94 0.46 73.42 53.44 12.91 14.39 19.97 64.46 52.83 7.49 4.18 0.82 2.64 1.44 70.28 36.05

May 2007

Max

Min

Mean

28.0 8.0 296 200 60.97 62.15 105.37 244 200 25.6 15.9 3.53 27.32 8.03 324 192.03

25.0 6.3 66 25 18.92 1.94 35.46 46.36 38 0.1 1.4 0.76 19.34 3.03 98 64.04

7.07 181.0 104.17 39.60 19.76 89.57 123.42 101.17 12.04 4.47 1.76 16.40 4.43 265.75 161.65

SD 0.41 158.58 38.95 16.18 15.84 81.32 50.24 41.19 13.65 3.57 1.43 3.85 1.45 114.19 146.78

Max

Min

8.06 609 190 79.89 62.15 312.02 244 200 50 11.6 6.08 22.81 7.12 555 563.23

6.62 61 50 16.82 1.94 35.45 73.2 60 2.8 1.5 0.87 10.61 3.04 171 76.81

SD-Standard Deviation; All units are expressed in mg/L except pH, EC (µS/cm);TH-Total Hardness asCaCO3; TA-Total Alkalinity; TDS-Total Dissolved Solids JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009

462


as per WHO standards (500 mg/L). Salinity ranges from 26.92 to 563.23 mg/L, and based on this, all the samples are of good quality. Among the major cations, Mg2+ played a dominant role in January, but in the other two periods Ca2+ was dominant. So cations Ca2+ and Mg2+ showed a prominent role in the study area. The concentration of Na+ and K+ are relatively low when compared to other major cations. The abundance of other cations and anions are Ca2+>Mg2+>Na+>K+ and HCO3->Cl->SO42–. Among the major anions, HCO 3– is dominated and Cl- has only secondary importance. Sulphate ion is recorded as 1% in three periods. Major Ion Chemistry

Mg2+

Na+ + K+

The dissolved ions in groundwater are derived from various sources and compositional relations among them, can reveal the origin of solutes and the processes that generated the observed water compositions. The Na+: Cl– ratio has frequently been used to identify saline water intrusion (Sami, 1992) .Based on the Na+/Cl– molar ratio, Meybeck (1987) interpreted the source of Na+ in water as silicate weathering if the value is greater than 1.0. While

comparing the aforesaid chemical quotient, it is clear that all the values are less than 1.0 (except for GW12 in January) implying that the source of Na+ is not due to the silicate weathering in the study area. Further, the low ratio of (Na+ + K+) vs. TZ+ also suggests that the contributions from the silicate weathering are insignificant (Sarin et al. 1989). Again, there is no parallel enrichment of the ions, suggesting that the source of both the ions is not due to dissolution of chloride salts (Jalali, 1999). The lower Na+: Cl- ratio might be due to reaction with clay minerals exchanging Na+ for Ca2+ and Mg2+ ions (Mercado, 1985; Al-Khashman, 2007). The plot of (Na+ + K+) vs. Cl- (Fig.2a) shows that most of the values fall on and below the equiline and suggests that the alkali is not balanced by the chloride ions. The correlation between Ca 2+ and HCO 3– is not significant and indicates that the contribution of Ca2+ through calcite dissolution is not relevant. The interrelationship between HCO3– vs. Mg2+ and HCO3– vs Na+ (Figs.2b and c) shows that most of the data deviated from the expected 1:1 relation and this indicates the multiple sources of Mg2+ and Na+. The deviation from the 1:1 relation of Ca2+ vs. SO42–

HCO3–

Na+

Ca2+ + Mg2+

Cl–

HCO3–

HCO3– + SO42– +

+

–

Fig.2. Plot showing the interrelationship between (A) (Na + K ) vs. Cl , (B) (HCO3– + SO42–).

HCO3–

vs. Mg , (C) HCO3– vs Na+, (D) (Ca2+ + Mg2+) vs. 2+

JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009


indicates that dissolution of gypsum is not a major source of Ca2+. The poor correlation between Mg2+ and SO42(0.047) as well as between Na+ and SO42- (0.269) suggests that dissolution of Na+ and Mg2+ minerals is not the major source of sulphate in the groundwater. The deviation from the 1:1 equiline plot of (Ca2+ + Mg2+) vs. (HCO3- + SO42-) (Fig. 2d) suggests that dissolution reactions of calcite, dolomite and gypsum are not dominant in the system. Ion exchange tends to shift the points to the right of the equiline due to an excess of HCO3– + SO42(Cerling et al. 1989; Fisher and Mullican, 1997). If there was a large excess of Ca2+ + Mg2+ due to the reverse ion exchange process over HCO3– + SO42– , then the points would have plotted to the left side of the equiline. Mechanisms Controlling Groundwater Chemistry

Hydrochemical Facies

The Hydrochemical evolution of groundwater can be understood by plotting the major cations and anions in the Piper trilinear diagram (Piper, 1944). This diagram reveals similarities and differences among groundwater samples because those with similar qualities will tend to plot together as groups (Todd, 2001). This diagram is very useful in bringing out chemical relationships among groundwater in more definite terms (Walton, 1970). The geochemical evolution can be understood from the Piper plot, which has been divided into six sub categories viz. I (Ca-HCO3 type); II (Na-Cl type); III (Mixed Ca-Na-HCO3 type); IV (Mixed Ca-Mg-Cl type); V (Ca-Cl type) and VI (Na-HCO3 type). The diagram (Figs. 4a, b and c) revealed that the majority of samples during March (66%) and May (50%) fall in the category of Ca-Cl2 type. But during January, about 91% of

TDS (mg/L) TDS (mg/L)

TDS (mg/L)

Cl/Cl+HCO3

Na+K/Na+K+Ca

Na+K/Na+K+Ca

Na+K/Na+K+Ca

TDS (mg/L)

TDS (mg/L)

the Gibbs diagram (Figs.3a, b and c). About 14% of the samples suggest that chemical weathering of rock-forming minerals influences the groundwater quality, whereas, 86% of the remaining shows precipitation dominance.

TDS (mg/L)

Gibb’s diagrams that represent the ratios of Na+:(Na+ + Ca ) and Cl–:(Cl– + HCO3–) as a function of TDS are widely employed to understand the functional sources of dissolved chemical constituents, such as precipitation-dominance, rock-dominance and evaporation dominance (Gibbs, 1970). The chemical data of groundwater samples are plotted in 2+

Cl/Cl+HCO3

Cl/Cl+HCO3

Fig.3. Gibbs (1970) diagrams for the cations and anions of groundwater, (A) January, 2007; (B) March, 2007; (C) May, 2007. JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009

463

464


Fig.4. Hill piper diagrams for groundwater for the months (A) January, 2007; (B) March, 2007; (C) May, 2007.

samples come within Ca-HCO3 type. One sample in each of the three periods fall under Ca-Mg-Cl type. During the study period, alkaline earth metals like Ca2+ and Mg2+ exceed the alkalies, and Ca2+ plays a dominant role controlling the cation chemistry. In the case of anions, except in January, in the other two periods strong acid shows dominance over weak acid and HCO-3 and Cl- has influence almost equal to Ca2+, which indicates the salt water intrusion into the fresh water aquifer of the region. The changes in hydrogeochemical phases of groundwater in the study area can be interpreted from Johnson’s (1975) modified diagram. In this, the upper half represents waters having high Mg/CaCl2 and Ca/MgSO4 content (i.e. static basin). The lower half represents normal water found in a dynamic basin. It is seen that most of the samples are between the static and mixing regime. Mixing and dissolution by rain water plays a vital role in the change of groundwater faces from one to another. The comparison of the Trilinear plot of hydrochemical faces with Johnson’s (1975) diamond field reveals that most of the samples fall near the proximity of recent dolomitic water. Interrelationship Between Chemical Parameters

Correlation coefficient is used as a commonly used

measure to establish the relationship between two variables. It is simply a measure to exhibit how well one variable predicts the behaviour of the other. Based on groundwater chemistry, three sets of strong relationships (Table 2) exist between major cations and anions (Douglas and Leo, 1977). These are: 1. The highly competitive relationship between ions having same charge but a different valence number e.g. Ca2+ and Na+. 2. The affinity between ions having different charges but the same valence number e.g. Na+ and Cl–. 3. The non-competitive relationship between ions having the same charge and same valence number e.g. Ca2+ and Mg2+. The highly competitive relationship: SO42- with Cl (.58**) has significant correlation; Ca2+ with Na+ (.23); Mg2+ with Na+(.15); SO42- with HCO3- (.32); and Ca2+ with K+ (.35) have low positive correlation. The affinity ions relationship: Na+ with Cl- (.41*); Na+ with HCO3- (.46**); K+ with HCO3- (.51**) have significant positive correlation. Ca2+ with SO42- (.29); Mg2+ with SO42(.05) have low positive correlation. JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009


465

Table 2. Interrelationship between various physico-chemical parameters of groundwater during the study periods, January, March and May, 2007 Temp Temp pH EC TH Ca2+ Mg2+ ClHCO3TA Na+ K+ SO42Si DO TDS Salinity

1.00 0.49 * 0.12 -0.26 0.50* -0.32 0.51* -0.15 -0.15 -0.34 0.09 -0.08 0.55** 0.13 0.04 0.51*

pH 1.00 0.36* 0.14 0.63** -0.07 0.25 0.63** 0.63** 0.10 0.40* 0.33* 0.15 0.13 0.57** 0.25

EC

Ca2+

TH

1.00 0.44** 1.00 0.39* 0.13 0.19 0.69** 0.63** 0.13 0.51** 0.35* 0.51** 0.35* 0.65** 0.37* 0.14 0.13 0.59** 0.24 0.43** 0.27 -0.06 -0.19 0.79** 0.42* 0.63** 0.13

1.00 -0.16 0.35* 0.46** 0.46** 0.23 0.36* 0.29 0.12 -0.13 0.61** 0.35*

Mg2+

1.00 -0.02 0.13 0.13 0.15 -0.05 0.05 0.22 -0.25 0.19 -0.02

Cl-

HCO3-

TA

Na+

K+

SO42–

1.00 0.08 0.08 0.41* 0.06 0.58** 0.09 0.13 0.75** 1.00**

1.00 1.00** 0.46** 0.51** 0.32 0.32 -0.16 0.69** 0.08

1.00 0.46** 0.51** 0.32 0.31 -0.16 0.69** 0.08

1.00 0.16 0.27 0.22 -0.07 0.65** 0.41*

1.00 0.03 0.42* -0.13 0.38* 0.06

Si

1.00 0.23 1.00 0.14 -0.07 0.59** 0.28 0.59** 0.09

DO

1.00 -0.08 0.13

TDS

Salinity

1.00 0.75** 1.00

* Correlation is significant at the 0.05 level (2-tailed). ** Correlation is significant at the 0.01 level (2-tailed). EC - Electrical Conductivity; TH - Total Hardness; TA - Total Alkalinity; DO - Dissolved Oxygen; TDS - Total Dissolved Solids

The non-competitive relationship: Ca2+ with Mg2+ has negative correlation; HCO3- with Cl- (.08); Na+ with K+ (.16) have low positive correlation. Irrigation Water Quality

Groundwater is valuable only when its quality is suitable for a variety of purposes. Water for irrigation should satisfy the needs of soil and the crop as the liquid phase in soil water plant growth and crop production. EC and Na+ play a vital role in the suitability of water for irrigation. The high salt content in irrigation water causes an increase in soil solution osmotic pressure. The salts, besides affecting the growth of plants directly, also affect soil structure, permeability and aeration, which indirectly affect plant growth. The suitability of water for irrigation can be estimated by means of many determinants, though, Sodium Adsorption Ratio (SAR), Percent Sodium (Na%), Permeability Index (PI), and Residual Sodium Carbonate (RSC) usually rank high. Sodium Absorption Ratio (SAR)

Excess Na+ in water produces the undesirable effects of changing soil properties and reducing soil permeability (Kelley, 1946). Hence, for considering the suitability for irrigation, the assessment of Na+ concentration is essential. The degree to which irrigation water enters into cation exchange reactions in soil can be indicated by SAR. The Na+ replacing adsorbed Ca2+ and Mg2+ is a hazard as it causes damage to the soil structure, making it compact and impervious. SAR is defined: JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009

SAR =

Na + Ca 2+ + Mg 2+ 2

where the concentrations are reported in meq/L. Irrigation water classified based on SAR (Richards, 1954) has indicated that all the water samples collected for the three months belongs to the excellent category. US Salinity Laboratory (USSL) also suggested a diagram (Figs.5 a, b and c) for rating irrigation water, wherein SAR is plotted against specific conductance. Na+ and salinity hazard are the two important parameters, which can indicate suitability of water for irrigation purposes. From the figures, it has been found that about 83% of the samples fall within C1S1 category. Percent Sodium (Na %)

When the concentration of Na+ is high in irrigation water, Na+ tends to be absorbed by clay particles, displacing Mg2+ and Ca2+ ions. This exchange process of Na+ in water for Ca2+ and Mg2+ in soil reduces the permeability and eventually results in soil with poor internal drainage. Hence, air and water circulation is restricted during wet conditions and such soil are usually hard when dry (Collins and Jenkins, 1996; Salesh et al. 1999). The Na% is calculated using the formula given below: Na % =

(Ca

2+

( Na + + K + ) × 100 + Mg 2+ + Na + + K + )

where the concentrations are reported in meq/L. Based on

466


Fig.5. Rating of water samples in relation to salinity and sodium hazard, (A) January, 2007; (B) March, 2007; (C) May, 2007.

this, about 83% of the samples of January, 91% of March and 83% of May belongs to the excellent category and the rest are considered as good. Wilcox’s (1955) diagram is adopted for classification of irrigation, wherein the EC is plotted against Na%. Based on Wilcox classification all the samples belong to the excellent to good category. Residual Sodium Carbonate (RSC)

In water having high concentration of HCO3, - there is a tendency for Ca2+ and Mg2+ to precipitate as CO32-. The excess sum of CO32- and HCO3- in groundwater over the sum of Ca2+ and Mg 2+ also influences the suitability of the groundwater for irrigation which is evaluated based on Residual Sodium Carbonate.

(

−

RSC = HCO3 + CO3

2−

) − (Ca

2+

+ Mg 2 + )

where the concentrations are reported in meq/L. Lloyd and Heathcoat (1985) have classified irrigation water based on RSC as (1) suitable (2.5). The RSC values for all the sampling periods indicate that the groundwater have good quality for irrigation. Permeability Index (PI)

The Permeability index also indicates whether groundwater is suitable for irrigation. Doneen (1964) classified irrigation water based on the Permeability index: PI =

Na + + HCO3

(Ca

2+

−

+ Mg 2 + + Na +

) × 100

where the concentrations are reported in meq/L. Accordingly, water can be classified as Class I, II and III. Class I and II water are categorized as good for irrigation with 75% or more of maximum permeability. Class III water is unsuitable with 25% of maximum permeability. About 94% of the samples belong to Class I and Class II. But each of the samples during March (GW5) and May (GW9) belongs to Class III. Kelley’s Ratio (KR)

The level of Na+ measured against Ca2+ and Mg2+ is known as Kelley’s Ratio, based on which irrigation water can be rated (Kelley, 1946; Paliwal (1967). Concentration of Na+ in irrigation water is considered to be in excess, thereby making the water unsuitable, if Kelley’s ratio is >1. Hence only water with Kelley’s ratio < 1 is suitable for irrigation. 100% of the groundwater samples during the study periods record KR value 50 makes it unsuitable (Lloyd and Heathcoat, 1985). Excess amount of Mg2+ reduces yield of crop. About 50% samples of January and May are suitable, and 25% samples of March are unsuitable for irrigation. JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009


CONCLUSION

A detailed study of the groundwater quality of the coastal aquifers of Chennam-Pallippuram panchayath revealed the following: 1. Overall evaluation during the study period showed that the groundwater in the area is soft to hard, oligohaline to brackish and slightly acidic in nature. 2. The dominance of the cations and anions showed the following order: Ca 2+ >Mg 2+ >Na +>K + and HCO3->Cl->SO42-. 3. The Piper trilinear diagram revealed that the alkaline earth metals exceed alkalies and strong acids exceed weak acids for March and May periods (except January). Dissolution of carbonate minerals adds significant amount of Ca2+ and Mg2+ to the groundwater, similarly tendency for fixation of alkalies by clay minerals and participation of it in the formation of secondary minerals cause the lessening of the amount of alkalies. Further, CaHCO3 is the dominant hydrochemical facies in the study area because the water table is very shallow.

467

4. From the Gibb’s diagram, precipitation has been identified as the dominant factor in controlling the shallow groundwater hydrochemistry. 5. Based on the USSL diagram, about 83% of samples come under low salinity and sodium hazard. 6. The values of KR, SAR, Na% and RSC for all the periods are within permissible limit. 7. The Permeability Index and Magnesium ratio indicated that some of the samples during the study periods are unsuitable for irrigation. From the above analysis, it is concluded that the groundwater in Chennam-Pallippuram panchayath is suitable for domestic and agricultural purposes, but more care should be taken to avoid contamination and overexploitation of groundwater.

Acknowledgements: We would like to thank the unknown reviewer for the valuable suggestions to improve this paper. We also thank State Groundwater Department for providing the borehole data.

References AL KHASHMAN, O. (2007) Study of water quality of springs in Petra region, Jordan, A three-year follow-up. Water Resource Management, v.21(7), pp.1145-1163. APHA. (1995) Standard methods for the examination of water and waste water, 19th edition. American Public Health Association, Washington DC. CERLING, T.E., PEDERSON, B.L. and DAMM, K.L.V. (1989) Sodium Calcium ion exchanging in weathering of Shale, Implication of global weathering. Budget, v.17, pp.552-554. COLLINS, R. and JENKINS, A. (1996) The impact of agricultural landuse on stream chemistry in the middle Hills of Himalaya, Nepal. Jour. Hydrol., v.185(71), pp.86. DONEEN, L.D. (1964) Notes on water quality in Agriculture, Published as a water science and engineering paper, 4001, Department of water science and engineering, University of California. D OUGLAS , E.B. and L EO , W.N. (1977) Hydrogeochemical relationships using partial correlation coefficient. Water Resource Bull., v.13, pp.843-846. FISHER, R.S. and MULLICAN, W.F. (1997) Hydrochemical evolution of Sodium Sulfate and Sodium Chloride groundwater beneath the northern Chihuahnan desert, Trans - Peccos, Texas, USA. Jour. Hydrol., v.5, pp.4-16. G IBBS, R.J. (1970) Mechanisms controlling World’s Water Chemistry, Sci, pp.1089-1090. I YER, N.J. (1984) Report of investigation for silica sand in Chennam- Pallippuram village, Cherthala Taluk, Alappuzha JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009

district, Kerala, Govt. of Kerala, Department of Mining and Geology, 70p. JALALI, M.(1999)The potassium quantity intensity relationship and the effect of applied potassium on exchangeable and solution potassium in some Hamadan soils. Research Report, Bu-AliSina University. JOHNSON.(1975) Hydrochemistry in Groundwater exploration, Groundwater Symposium, Bulawano. KELLEY, W.P.(1946) Alkali Soil – Their Formation Properties and Reclamation. Reinold Publication, New York, pp.124-128. LLOYD, J.W. and HEATHCOAT, J.A. (1985) Natural inorganic hydrochemistry in relation to groundwater: an introduction, Oxford University Press, New York, pp.296. MEYBECK, M. (1987) Global Chemical weathering of surficial rocks estimated from river dissolved rock, American Jour. Sci, pp.401-428. MERCADO, A. (1985) The use of hydrochemical pattern in carbonate, sand and sandstone aquifers to identify intrusion and flushing of saline water, Groundwater, v.23, pp.335-344. PALIWAL, K.V. (1967) Effect of Gypsum application on the quality of irrigation water. The Madras Agri. Jour., v.59, pp. 646647. PIPER, A.M. (1944) A graphical procedure in the geochemical interpretation of water, America. Geophys. Union, Trans, pp.914-928. RADHAKRISHNAN, R., DHARMARAJ, K. and RENJITHAKUMARI, B.D. (2007) A Comparative Study on the Physicochemical and

468


Bacterial Analysis of Drinking, bore well and sewage water in the three different places of Sivakasi, Tamil Nadu. Jour. Environ.and Biol., v.28(1), pp.105-108. RICHARD, L.A. (1954) Diagnosis and improvement of saline and alkali soil, U.S. Department of Agriculture Handbook, No.60, pp.160. SALESH, A., AL-RUWAIH, F. and SHEHATA, M.(1999) Hydrogeochemical processes operating within the main aquifers of Kuwait. Jour. Arid Environ., v.42, pp.195-209. SAMI, K.(1992) Recharge mechanism and Geochemical process in semi-arid sedimentary basins, Eastern Cape, South Africa. Jour. Hydrol., pp.27-48. SARIN, M. M., KRISHNASWAMI, S., DILLI, K., SOMAYAJULU B.L.K. and MOORE, W.S. (1989) Major ion chemistry of GangaBhramhaputhra river basin: Weathering process and fluxes

to the Bay of Bangal. Geochim Cosmochim Acta, pp.9971009. SAXENA, M.M. (1998) Environmental Analysis, Water, Soil and Air. Agrobotanical Publication, Bikaner, pp.28-87. Soman, K. (2002) Geology of Kerala. Geological Society of India, Bangalore, pp.32 TODD, D.K. (2001) Groundwater Hydrology. John Wiley and Sons Publication, Canada, pp.280-281. WALTON, W.C. (1970) Groundwater Resources Evaluation. Mc Graw Hill Book Co., New York. WILCOX, L.V. (1955) Classification and use of irrigation water, U.S Department of Agriculture, Washington, 969p. YANGGEN, D.A. and BORN, S.M. (1990) Protecting Groundwater quality by managing local land use. Jour .Soil Water Conservation., v.45(2), pp.207-210.

(Received: 9 January 2009; Revised form accepted: 6 May 2009)

JOUR.GEOL.SOC.INDIA, VOL.74, OCT. 2009