Groundwater Vulnerability Assessment For Nitrate Pollution In The Salinas Valley Using A Modified Drastic Model

Groundwater is an integral piece of California's groundwater resources. One of the most common contaminants present in groundwater is nitrate. Nitrate contamination is often a result of agricultural land use activities on the ground surface. The study area for this analysis is the Salinas Valley Groundwater Basin, an agriculturally dominated basin in coastal California. The Salinas Valley Basin is both one of the most agriculturally productive areas of the state, as well as one of the most nitrate-contaminated basins in the state. The purpose of this research was to develop a groundwater vulnerability map for nitrate pollution in the Salinas Valley. A groundwater vulnerability assessment was carried out using a modified DRASTIC model. DRASTIC is a U.S. EPA rank-sum model for assessing groundwater vulnerability that incorporates depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone, and hydraulic conductivity. In order to modify the DRASTIC model to assess nitrate contamination specifically, a land use parameter was incorporated into the model. The results of this assessment found 2.9% of the Basin has very low vulnerability, 50.6% has low vulnerability, 42.9% has moderate vulnerability, and 3.6% has high vulnerability. The results of the groundwater vulnerability assessment could not be validated using measured nitrate concentrations in the Basin. Four possible reasons for the poor fit of this assessment have been identified: (1) the temporal variability of select DRASTIC parameters, (2) the inability of the land use parameter to accurately represent nitrate vulnerability, (3) the high spatial variable of nitrate contamination in the Basin, and (4) the static weights assigned to parameters by the DRASTIC model.

Groundwater is an important natural resource for numerous human activities, accounting for more than 50% of the total water used in the United States. Groundwater is vulnerable to contamination by several organic and inorganic pollutants such as nitrate, heavy metals, and pesticides. Assessment of groundwater vulnerability aids in the management and protection of limited groundwater resources. The focus of this thesis is to (1) statistically compare two groundwater vulnerability assessment models; modified DRASTIC (Acronym for Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone, and hydraulic Conductivity of aquifer) and ordinal logistic regression for NO3- contamination of shallow groundwater of the US, (2) analyze any discrepancies in the predictability of each of these models, and (3) discuss the advantage of each of the above-mentioned models with respect to performance, data requirement, and its ability to predict vulnerability. Analysis of NO3- concentration in groundwater allows for a reliable comparison of the two models. The results from the OLR model indicate a better correlation between the observed and average predicted probabilities. A very low R2 value was obtained between the modified DRASTIC and nitrate concentration, indicating poor prediction capabilities and need for high resolution data. Limitation with respect to requirement of more data with respect to prediction is seen in both the methods.

This volume offers detailed comparisons and validations of different methods of assessing groundwater vulnerability (DRASTIC, GOD, PI, RTt, AVI, SINTACS, COP). It contains new aspects of vulnerability assessment for the evaluation of coastal aquifer vulnerability and aquifer vulnerability to methane gas leakage from shale gas wells. The book also contains the results of studies on intrinsic and specific vulnerability assessment (migration of antibiotics and nitrate, groundwatersurface water interaction), with examples of the different national approaches to groundwater vulnerability mapping in Poland, Ireland, Italy and elsewhere. There are 15 chapters derived from two IAH conferences held in Ustron ́, Poland in 2015 and 2018. The book is valuable for those interested in groundwater vulnerability, in risk assessment, and in environmental issues. It is aimed at land use planners, water managers, the environmental industry, regional and local environmental protection councils and students studying hydrogeology and environmental sciences.

A Point Count System model, DRASTIC, was used to assess the groundwater pollution potential from nitrogen fertilizers in Ludhiana district of Punjab, India. Thematic maps of the seven parameters of the model i.e. depth to water table, recharge, aquifer media, soil, topography, impact of vadose zone and hydraulic conductivity were prepared in a geographic information system (GIS) environment to obtain nitrogen pollution potential indexes based on the consumption of nitrogenous fertilizers. The model was calibrated and validatedfor the region.Statistical analysis showed good agreement between model computed and observed values of Nitrate-N concentration. The model was used to predict the future scenario. As per model prediction, the area under critical value may reach up to 50730 ha by the year 2012. Machhiwara, Sidhwan bet and Ludhiana-2 blocks of the district will be severely affected.To prevent this grave situation, the areas having higher nitrate pollution potential index may be enforced with restricted fertilizer use and be made the focus of attention for preventing contamination of the underlying groundwater sources.

Since the need to protect ground water from pollution was recognized, researchers have made progress in understanding the vulnerability of ground water to contamination. Yet, there are substantial uncertainties in the vulnerability assessment methods now available. With a wealth of detailed information and practical advice, this volume will help decision-makers derive the most benefit from available assessment techniques. It offers: Three laws of ground water vulnerability. Six case studies of vulnerability assessment. Guidance for selecting vulnerability assessments and using the results. Reviews of the strengths and limitations of assessment methods. Information on available data bases, primarily at the federal level. This book will be indispensable to policymakers and resource managers, environmental professionals, researchers, faculty, and students involved in ground water issues, as well as investigators developing new assessment methods.