The comprehensive geophysical method for detecting surface- groundwater interaction and contamination in India


1. INTRODUCTION

1.1GENERAL
Surface and Groundwater are usually interlinked with each other. There is significant variation in hydraulic connectivity of surface and groundwater whereas it is connect in all types of landscapes. Surface water refers to water occurring in lakes, rivers, streams, or other fresh water sources used for drinking water supplies.
Groundwater refers to any subsurface water that occurs beneath the water table in soil and other geologic forms (Rail, 2000). There are different set of contaminates in surface and groundwater, in surface water contain most bacteria and other micro-organism where as groundwater stores pesticide chemical and nirates. As surface and groundwater are usually interlinked with each other, contamination may shared between the two sources. Since ground water and surface water are essentially one resource, there is potential for the surface water quality to affect ground water and vice versa (Naiman et al.1995; Squillace et al. 1993). Interaction can take place in three ways:

A) Groundwater gaining the water from the stream water (Fig 1.1)
B) Groundwater losing the water to stream water (Fig 1.2)
C) Stream water gaining and losing the water to groundwater
 
Fig- 1.1 Groundwater gaining the water from the stream water (After Winter & others 1999)
 

Fig -1.2 Groundwater losing the water to stream water (After Winter & others 1999)
 
Understanding groundwater interaction with streams is essential for understanding contaminant transport. These interactions could affect the aquatic life and it may also deteriorates the quality of drinking water. Integration of groundwater and surface water can help to avoid problems that arise from managing one resource at the expense of the other particularly as solutions for better storm water management.

1.2 Surface and Groundwater Interaction
A detail understanding of hydrology of permeable aquifer is need for understanding of surface-groundwater interaction process and their spatial and temporal variation. An understanding of the mechanisms that control groundwater interaction with surface water is crucial for both the effective management of water resources and the conservation of its associated ecosystems. The quantification of groundwater-surface water interactions is vital to understanding contaminant movement and distribution, in addition to improving the management of water supplies (Wroblicky et al., 1998, Conant, 2004, Oxtobee et al., 2002). These interactions along streams and rivers can be quantified using point source monitoring equipment such as mini-piezometers, seepage meters and temperature surveys (Oxtobee et al., 2002). Exchange between groundwater-surface water regimes depends on many complex factors. Because these factors include bedrock topography, temporal climatic variations, sediment types, and hydrologic properties of the materials (Oxtobee et al., 2002, Cey et al., 1998)
 
1.3 Aquifer Filtration
The aquifer severs as a natural mechanical filter and also biochemically attenuates potential contamination present in surface water. Various processes take place during filtration such as physicochemical filtration, adsorption, reduction and biodegradation. The infiltration may be the direct result of an influent river under natural condition or it may be induce by purpose-built check dam to groundwater recharging facilities. The efficiency of this filtration process depends on site-specific factors such as characteristics of bed sediments, and retention time and surface water quality. Grain size and distribution of sediment are particularly important characteristics with respect to permeability and filtration efficiency.
 
1.4 OBJECTIVES
This study intends to enlighten the understanding the interaction between surface and groundwater, on Arani River, Tamil Nadu. A check dam is constructed on river Arani to create groundwater recharging facilities, for irrigation and to prevent water runoff in the sea. A few studies are currently been undertaken on various aspect of check dam. The main objectives of his study are to

•   Understand surface and groundwater interaction by geochemical indicators and
•   Study the effect of filtering biological load in the groundwater by the geological formation..
 
 

2. STUDY AREA
 
2.1 GENERAL
The present study was conducted to the north of Chennai in Periapalayam region. Periapalayam is town about 40 km north of Chennai, in Tiruvallur distr ict, Tamil Nadu state, India. The town is famous for the Sri Bhavani Amman Temple. This temple is located on the Arani River flowing through the town. The study area falls at the latitude of 13°18’N and its longitude position is 80°02’E. It comes under degree sheet number 66C published by survey of India of 1: 250,000 scale. In study area groundwater is extracted from Arani River basin is use for irrigation purpose as well as for drinking purpose. Araniyar area of the basin is 763 sq.km. Arani River is seasonal and carry substainal flow during monsoon only.
 
Fig 2.1 Location of study area
 
2.2 GEOLOGY
The study area consists of sand, clay and recent alluvium overlying on a thick pile of Gondwana shales, clays and sandstones rocks. The area mainly comprises of alluvial deposit which is interlayer of sand and clay patches. Subsurface Geology is as follow upper layer is sandy clay it is followed by conglomerate and then alluvial deposit and Gondwana group of rock as obtained from litho-log.
Fig 2.2 Geology of the study area
 

2.3 CLIMATE
The climate in the study area has tropical climate and dry one. For most of the year climate is hot and humid. The period between late May and Early June is the hottest part of the year. At this time the maximum temperature goes up to 38°C-42°C and the minimum temperature will be 18-20°C and January will be the coolest month. The average annual rainfall is around 1200mm/yr, 35% falling in the south west monsoon (June- Sep) and 60% during the northeast monsoon (Oct-Dec) (Elango et al 1933).
 
2.4 GEOMORPHOLOGY
Periyapalayam has the average elevation 50m. Fluvial and erosional landform are noticed in periyapalayam region. Fluvial feature like floodplain nearly a flat land adjacent to river and alluvial plain flat landform created by deposition of sediment over the years. Pediplain and upland is result of erosional process. Arani River passes through the region which meanders in the region. Topographically, the area has a very gentle easterly slope of with a few isolated hillocks and depressions.
 
Fig 2.3 Geomorphology of the study area
 
2.5 HYDROGEOLOGY
The present study is largely confined to the groundwater present in the alluvium deposits above the pre-quaternary. This formation largely consists of sands, sandy clays and with occasional clay lenses. The thickness of the aquifer zone is 50m. There is not much variation in its thickness from east to west since the level of bedrock and Pre-quaternary are generally at the same elevations except for small local variations. Groundwater occurs under unconfined conditions in this alluvium. In sedimentary formation the top recent alluvium comprising sand and sandy clay is followed by hard sandstone of Gondwana formation. It has been established that the shallow alluvial aquifers flanking the major stream courses have prolific yields whereas the Gondwana sediments form aquifers of poor to moderate potential with considerable variation in the quality of formation water
 
 
 
3. METHODOLOGY
 
3.1. FIELD STUDY
Toposheet of the Tiruvallur district of scale 1:250000 is used to demarcated the limit of the of the study area. And also Google Earth was made use of for identifying sample location. The sample location were chosen vicinity to check dam construct on Arani river in the study area. Both open well and bore well sample were collected.
 
3.2. SAMPLING
Samples were collect in the months from February to May. Total of fifteen sample were collected. The latitudes and longitudes of each location were determined by GPS. 500ml 0f water Sample were collected in clean and autoclave bottles, which are steam to sterilize bottles, so that all bacteria, viruses, fungi, and spores are inactivated in the bottles before sampling. The samples collected are closed tightly to avoid any atmospheric or air interactions. The samples labeled with the location name, latitude and longitude limits. The samples locations are shown in fig 3.1.
Fig 3.1 Water sample locations
 
Fig 3.2 Collection of water sample field photo
 
 
3.3 FIELD MEASUREMENTS (Physical)
In Situ Analysis
In Situ parameters such as pH, EC and TDS were measured with in the field. YSI multiparameter portable instrument was used to measure these parameters.
 
3.3.1 pH
The acidity or alkalinity of water is expressed by the activity of hydrogen ions (or pH) in a solution. pH can be defined as the negative logarithm (to the base 10) of hydrogen ion activity (g/l of water).The most commonly measured chemical attribute of water is its acidity or pH. Low pH levels can increase the solubility of certain heavy metals. A shift of pH in either direction from neutral may indicate the presence of a pollutant in the water. The pH of clean water depends on several factors, including the types of rock and vegetation. The pH was determined by a portable PH meter.
 
3.3.2. ELECTRICAL CONDUCTIVITY (EC)
Pure water is electrically non-conductive. But groundwater invariably contains dissolved solids and thus, is conductive. Its conductivity depends on the concentration of dissolved solids. The unit of measurement is µS/cm. The normal range of conductivity of groundwater is from 1 x 102 µS/cm to 5 x 105 µS/cm. Generally one mg/l of TDS gives rise to a conductivity of about 1.4 to 1.8 µS/cm, the average being 1.56. Thus, measuring the electrical conductivity gives a quick estimate of the ionic concentration present in a water sample. Since the EC is a property dependant on temperature as well, it is measured and reported at a standard 25°C.Thus, the electrical conductivity is the conductivity of one cubic centimeter of water at 25°C.The electrical conductivity of the ground water samples was measured by portable Ec meter.
 
3.4 LABORATORY ANALYSIS
The collection of samples and field measurements was followed by the lab analysis of the samples. The detailed methodology adopted is as follows:
 
3.4.1 Biochemical Analysis
Materials required:
Sample, Media components, Biochemical reagents ,Glass wares ,Petri plates , glass tube, L – Rods for spread plating, Inoculation loop, Gloves and face mask for safety requirements.
 
Experiment planned:
a) To identify the naturally present organism in the raw water
Media cultivation such as plating in (basal media to enrich the growth of the entire organism)

Colony morphology identification (select the each colony and plated in selective media to find out which organism)

Inoculating in selective media such as (Eosin Methylene blue agar, Thio citrate bile salt agar, Rappaport vassiliadis Salmonella agar, Staphylococcus selective agar , Salmonella Shigella agar, Macconkey agar) by this the genus can be identified
 
b) To find the organism is dominant in raw water
By serial dilution plating in basal media the amount of organism
Then plating in selective media to find which organism present as a dominant species in raw water.


Table 3.1 Selective media and their characteristics of the colony

Table 3.2 Serial dilution
 
After serial dilution was done 100µl was taken from each tube and plated separately in both (Selective media and non- selective media) incubated at 37˚C for 24 hours. Analytical procedure for bacterial were in accordance with specatification Cappuccino JG, Sherman .N ( 1987) microbiology laboratory manual.
Fig 3.3 Microbiological analysis lab photo
 
3.4.2 Geochemical Analysis
V olumetric analysis
Volumetric analysis is a general term for a method in quantitative chemical analysis in which the amount of a substance is determined by the measurement of the volume that the substance occupies. It is commonly used to determine the unknown concentration of a known reactant. Volumetric analysis is often referred to as titration, a laboratory technique in which one substance of known concentration and volume is used to react with another substance of unknown concentration. All the analysis where done following the standard procedure given in APHA 1995.
Table 3.3 Methodology adopted for analysis of ground water samples
 
3.5 Geophysical Survey
Resistivity geophysical surveys measure variations in the electrical resistivity of the ground, by applying small electric currents across arrays of ground electrodes. Unit electrode spacing is determined by parameters that include profile length, desired resolution and targeted depth penetration. A switching unit takes a series of constant separation readings along the length of the electrode array. The separation between sampled electrodes is then widened to increase the effective depth penetration and the procedure is repeated. Resistivity Imaging also known as resistivity tomography is an advanced development of the method. Enhanced data quality and resolution provide continuous two-dimensional resistivity models. Fifty or more electrodes are set-out in a regularly spaced array, connected to a computer-controlled resistivity meter via multicore cables. Advanced data processing using specialist inversion software removes distortions caused by the effects of electrode geometry, to produce a high resolution image of the variations in ground resistivity with depth. The model is contoured using a colour scale to produce a two-dimensional cross-sectional model of ground resistivity.
 
Fig 3.4 Resistivity survey field photo
 
Geophysical resistivity survey was carried out involving 1D and 2D Method. ABEM Terrameter was used for 1D survey and Multi electrode resistivity imaging system, WERT-60 was used for 2D ERT survey. The survey was carried at periyapalayam in study area across the Arani River.
 
3.5.1 Data acquisition and processing
Te resistivity survey was carried out in eleven locations acroos the study area. Out of which ERT was carried out in three locations and VES was carried out in eight locations. For 1D four electrodes were used to carry out the survey. And for 2D twenty nine electrode were used. IX 1D software has been used for analyzing the data for VES and RES 2D INV software was used for obtaining tomography data.
In this study the electrical resistivity method was used for delineating the subsurface geology, depth of aquifer and to infer what kind of aquifer exists below. Locations were selected based on the existing boreholes drilled within the study area.
 
Fig 3.5 VES Locations
 
 

4. RESULTS AND DISCUSSION


4.1 GENERAL
Total of fifteen samples were analyzed from surface and groundwater in periyapalayam for physico-chemical and microbial analysis to understand the surface and groundwater interaction. Physico-chemical and microbial analysis of surface and groundwater were interlinked. The geology of the area was also taken into consideration. Initially samples were collected from open well and tube well. After analyzing the sample twice, it is observed that the sample from open well showed an unexpected microbial load compared to tube well. Extensive field work was done and identified that open well is affected by anthropogenic activities. In order to avoid erratic values in the analysis, the open well data was omitted and hence preceded with tube well samples. Physical parameters such as pH, EC and Total hardness were measured along with chemical parameters such as Na, K ⁺, Ca²⁺, Mg²⁺, Cl⁻. Microbial load in both surface and groundwater were analyzed with certain organism such as E.coil, Clostridium, Salmonella & Shigella and Vibro Cholera. DGPS survey was done to know groundwater flow direction.
 
4.2 DGPS Survey
Differential Global Positioning System ( DGPS) survey was carried out to know the elevation of wells with respect to MSL. To know the depth and distribution of water table beneath the surface, water level of each well was measured using water level indicator. The surface elevation was subtracted to depth to water level at each well. Water level contour of 50ft contour interval were plotted (Fig 4.1).
Fig 4.1 Groundwater flow direction
 
4.3 Resistivity Results
The subsurface geology of the study area was confirmed with the aid of electrical resistivity survey. Both one dimensional and two dimensional surveys were carried out in the study area. The correlation of the two results explains the presence of four layers, which consist of top dry soil, fine sand, sandy clay and conglomerate. Cross section of 1D and Electrical Resistivity Tomography 2D is shown in (Fig 4.2 and Fig 4.3- 4.5)
 
Fig 4.2 Subsurface lithology obtained from 1D resistivity survey
 
Fig 5.3 ERT of VES 3


Sclumberger Location 2

 

Fig 5.4 ERT of VES 6

Schlumberger Location 3

Fig 5.4 ERT of VES 7
 
4.4 Conceptual Model
In cooperating the DGPS data and lithological knowledge based on resistivity survey, A conceptual model has been made to understand direction of the groundwater flow. The geology of the area is compared with old available litholog data.
 
Fig 4.6 Conceptual model of groundwater flow and subsurface geology in study area
 
4.5 Microbial Analysis
For microbial analysis two growth medium have been taken for this study. Growth medium is a gel designed to support the growth of microorganisms or cell. They are Nutrient media and Selective media.
 
4.5.1 Nutrient media
Nutrient media is an undefined medium, which contain all the elements that most bacteria need for growth. Distribution and statistical summary of microbial load based on nutrient media is shown in table 4.1 and 4.2. The variation of value along the west to east bank is show in Fig 4.7


Table 4.1 - Distribution of microbial load in surface and groundwater with the study area
 Fig 5.7 Microbial load in surface and groundwater in study area

Table 4.2 Statistical summary of microbial load of surface and groundwater in the study area 

From the above table 4.2 the organism present in surface water is substantially reduced in groundwater it indicated efficiency of geological medium to filter.
 
4.5.2 Selective media .
Selective media is used for the growth of only selected microorganism. For microbial analysis total eight selective media were used to identify the present of six different microorganisms in surface and groundwater. (See Table-4.1) Tube wells were analyzed only once with selective media. Distribution and statistical summary of microbial based on selective media is shown in table 4.3 and 4.4. The variation of various microorganism values along the west to east bank is show in Fig 4.8 and 4.9.
 

Table 4.3 Distribution of microbial load in surface and groundwater in the study area
 

Fig 5.8 E.coil and Clostridium distribution from west to east in study area
 
 
Fig 4.9 Salmonella & Shigella and Vibro Cholera distribution from west to east in study Area
 
Table 4.4 Statistical summary surface and groundwater microbial load in the study area

Staphylococcus and Streptococcus microorganism were absent in both Surface and Groundwater. Vibro Cholera is present only in surface water, and it is completely absent in groundwater (table 4.4)
 
4.6 Physico-chemical
pH of surface and groundwater were within the prescribed limit (6.5-8.5). And other physic-chemical parameter of both surface and groundwater within the limit of domestic use. But the value of groundwater sample exceed than that of surface water. This may be due to interaction of water and rock in the aquifer. Table: 4.1 shows both surface and groundwater physic-chemical parameter and there variation in both the source.
 
Table 4.5 Physico-chemical parameter of surface and groundwater within the study area
 

4. CONCLUSIONS
In order to investigate surface and groundwater interaction in Arani River Tamil Nadu, Surface and groundwater sample were collected and analyzed for microbial load and physico-chemical parameters.

The unconfined nature of the aquifer permit surface and groundwater interaction and contaminated have been transfer and it can be reflected from the quality of surface and groundwater. The result obtained from analyses of microbial load and physico-chemical shows surface and groundwater interaction and intermixing. Both surface and groundwater show high microbial pollution. It also infers efficiency of geological medium to filtrate the microbial load. However, to quantify the extent of microbial pollution and chemical composition of surface and groundwater and to understand the filtrating capacity of geological medium a detailed study need to be carried out.
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