GROUNDWATER QUALITY OF PANDAVAPURA TOWN, MANDYA DISTRICT, KARNATAKA, INDIA

Quantity of water without quality has no significance in terms of usage and hence chemical quality of water has gained equal importance with quantity. Groundwater due to its movement in the water bearing formations contains chemical ions and hence never occurs in a pure form. The concentration of chemical ions in groundwater depends on the environment, and surface as well as subsurface rate of percolation.

the determination of various ionic constituents;

classification;

determination of water use based on the interrelation of constituents;

identification of geochemical patterns and

hydrogeochemical model developed by statistical methods like principal component analysis (PCA), cluster analysis (CA) and regression analysis (RA).

Utilizing the chemical parameters, hydrogeologists can successfully and effectively discuss the suitability of groundwater for domestic, irrigation or industries, its residence time within the water bearing formations, and its corrosive action on the pipelines used for its transport to different consumer points.

Pandavapura town extending over an area of 534 sq. km is situated towards the western part of Mandya district (Latitude 12o24'40" & 12o24'40" N and Longitude 76o30'0" & 76o47'40" E) [Map.1]. The rock formations here belong to the most ancient age and are classified into two groups - Dharwar Schist (as narrow linear on belts) and peninsular gneisses/granites. The town has semi-arid climate.

Average annual rainfall in Mandya district is 691.2mm. It is mostly confined to the period from April to November. The highest rainfall occurs in October. Thundershowers are experienced in the latter half of the hot season. There are on an average, 45 rainy days in the basin. During March-May there is a continuous rise in temperature. April is the hottest month with daily average maximum of 35oC and minimum of 21oC. Relative humidity is high during S-W Monsoon, moderate in the post S-W monsoon and driest during December-May with <50%. The wind condition is generally moderate, southwesterly or westerly from May-September and northeast in October. During March and April winds blow southwest or westerly in the mornings and northeasterly or easterly in the afternoon. From the IMD published data it has been interpolated that the AET, PET and WD in this basin are 80, 160 and 80cm respectively.

Twenty ground water samples were systematically collected and have been subjected to chemical analysis following the ISI (1964) methods (Map.2).

The ppm ionic concentration data has been fed to the HYCH programme (Balasubramanian et al., 1986) and a thematic map for direct consumer advice is prepared. The salient features are tabulated in Table 1 and the maps are prepared for detailed applications.

The samples were analyzed and processed for various parameters and the following thematic maps for direct consumer advice were generated.

Based on this premise, water quality could be split in to <500, 500 to 1000, >1000ppm. TDS <500ppm is ideal for any type water usage, 500 to 1000ppm could be used after simple purification processes where as >1000ppm will be difficult to use without costly treatment (Map.3). Higher TDS concentration is due to the stay of water in the subsurface and rock water interaction (Freeze and Cherry 1979).

Based on this parameter, groundwater is divided into two zones (Map.4) following the classification of Wilcox L.V. (1948). Ec is a measure of the degree of the mineralization of the water, which is dependent on rock water interaction, and thereby the residence time of the water in the rocks (Eaton, 1950). From Map.4, area of permissible water quality is minimum, followed by the area of doubtful water quality which is large downstream.

Richards (1954) defined Adsorption Ratio as [(Na/Ca)+(Mg/2)] where all the ionic concentrations are expressed in epm. This has a direct relation to the adsorption of Na by soil. From Table 1 as well as Map.5 it can be seen that almost 98% of the groundwater belongs to excellent quality for irrigation.

SAR	WATER CLASS	NO. OF SAMPLES
<10	Excellent	19
10-15	Good	1

Ryzner (1944) and Badrinath et al (1994) have used an index to evolve the corrosive tendency of groundwater pipes.

where all the ionic values are expressed in ppm. Water with a CR<1 could be transported by metallic pipes and for other waters with an index >1 metallic pipes should be replaced by non-corrosive PVC pipes. It can be noticed in Map. 6 that the upper reaches use metallic pipes for transport of water to consumer ends. Whereas at lower reaches, groundwater has an index >1 and is transported by PVC pipes.

Based on Handa (1964) water has been classified with reference to hardness. Both permanent and temporary hard water is present in the ground water samples. From Table 1, it could be visualized that 52% of the samples belong to temporary hard water and 48% belong to permanent hard water (Map.7).

This part of Handa's classification refers to the utility of groundwater for irrigation needs. Based on this, water quality could be split in to 3 varieties of salinity sodium hazard units. From C3S2 to C3S1 from Table 1 as well as Map.8 it could be seen that 70% of the water belongs to C3S1 type, followed by C2S1 type (25% of water). Water of this quality is suitable for highly permeable soils, otherwise the crops will be highly affected.

Based on this classification, the groundwater of the area is found to be dominated by fresh brackish followed by fresh oligohaline, brackish, medium alkaline and highly alkaline water (Map.9).

Using data for the Stuyfzand's groundwater facies, the area can be classified into area dominated by 40% CaHCo3 and 30% MgHCo3 (Map.10).

Based on this classification, the groundwater quality of the area has been dominated by static and disco-ordinate regimes, followed by dissolution and mixing (Map.11).

From Map.12, it is clear that majority of the water samples collected belong to (+)Na+Mg surplus indicating fresh water intrusion.

Water is of good quality if permeability index falls into class I, II, III of Doneen's diagram. Majority of water samples falls in class II indicating high permeability horizons.

Badarinath, S.D, Raman, V., Gadkari, S.K, Mahaisalkar, V.A and Deshpande, V.P., 1994. Evaluation of Carbonate stability Indices for Sabarmati river water, Ind, Water W.Assn, 16, pp.163-168.

Balasubramanian, A., Subramanian, S.N and Sastri, J.C.V., 1991. HYCH BASIC Complex Program for Hydro geological Studies, Groundwater management and Development in irrigation and other water sector, 7-8 March 1991, Trivandrum.

Eaton, E.M., 1950 Significance of carbonates in irrigation waters, Soil Sci., 69, pp.123-133.

Freeze, R.A., Cherry, J.A. 1979. Groundwater, Prentice Hall. Inc., New Jersey, 604. Handa, B.K., 1964. Modified classification procedure for rating Irrigation waters, Soil. Sci., 98.

I.S.I, 1964. Indian Standard methods of sampling and test (Physical and Chemical) for water used in industry 122pp.

Richards, L.A., 1954. Diagnosis and improvement of saline and Alkali soils. USDA handbook 60, 160pp.

Ryzner, J.W., 1944. A new index for determining amount of Calcium carbonate scale formed by water, J. Amer.W.W. Assn., 36, pp.472-486.

Wilcox, L.V., 1948. The quality of water for irrigation uses U.S. Dept. Agri. Bull. 962, Washington, d.c.40pp.

TABLE 1: CHEMICAL CONSTITUENCY OF GROUNDWATER IN PANDAVAPURA TOWN

SL NO	LOCATION NAMES	Ec	PH	Ca	Mg	Na+K	HC0₃	C0₃	Cl	N0₃	S0₄	TDS
1	Petrol bunk	1250	7.90	105	65	77	377	53	148	71	38	750
2	Govt. Hospital	980	7.30	64	38	49	301	7	81	21	33	480
3	Bovi colony	1000	8.85	36	39	52	191	24	98	31	8	430
4	Lakshmi theatre	990	8.56	51	17	20	137	19	48	31	4	226
5	Nagamangala road	2200	8.64	78	15	261	225	48	277	71	110	1070
6	Beer Setthalli	1000	8.85	136	82	146	328	82	350	40	25	1019
7	Bus stand	1200	7.20	77	28	63	95	2	87	35	210	730
8	B.D Office	1098	8.21	36	68	21	157	10	148	79	26	525
9	A.C.office	1700	7.40	73	69	114	294	14	168	35	156	800
10	Subramanian temple	2500	8.20	190	47	119	416	1	333	88	30	1076
11	Ganapathi temple	2200	8.30	177	43	106	403	1.0	300	76	37	1116
12	Ragavendra theater	800	8.40	59	32	40	294	29	39	26	4	395
13	Water tank	2300	7.92	85	21	253	179	48	353	50	6	1110
14	Vijaya college	980	7.30	35	24	20	203	12	11	7	18	260
15	Pump house	1150	7.30	64	17	23	220	1	28	42	11	410
16	Harohalli school	1200	7.90	26	30	67	232	8	50	40	17	505
17	Garadimane street	850	7.40	25	7	39	140	6	25	12	10	274
18	Marigudi temple	1155	8.02	50	59	24	240	8	109	40	26	625
19	Harohalli kere	2200	8.20	190	47	121	410	6	03	49	98	60
20	Pandavapura town	1000	7.70	180	43	119	320	8	8	210	100	30

1.) P.E.S College of Engineering,
Mandya-571401

2.) Hydrogeology Laboratory,
Department of Geology,
Manasagangotri,
Mysore-570006

MONTHS	SEASONS
December-February	Dry with clean bright weather
March-May	Hot
June-October	Southwest monsoon
November	Retreating/Post Monsoon

RANGE	NO. OF SAMPLES
750-2000	16
2000-3000	04
TOTAL	20

PH

Na+K