Available at: https://digitalcommons.calpoly.edu/theses/718
Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Misgana Kebede Muleta
Many small communities depend on groundwater sources for drinking water and they often use septic tanks for their sewer system needs. However, nitrates and other pollutants from septic systems can percolate to the aquifers and deteriorate quality of the groundwater, threatening the public health. This study has developed a groundwater model using Visual MODFLOW for an aquifer that is used as a water supply source for the cities of Beaumont and Cherry Valley, California. Septic systems are the suspected major source of nitrate contamination of the aquifer. The model has been developed to clarify the extent of interactions between nitrate pollutants, infiltration and percolation from a recently established series of artificial recharge ponds, groundwater recharge from natural sources, and pumping activities to meet local water uses. The primary objective of this study is to evaluate alternative hydraulic solutions that would limit the movement of the contaminants and minimize the risk of affecting the pumping wells. The study attempts to identify the best way to recharge the aquifer and influence movement of the nitrates so that polluted waters may have lower nitrate concentrations in the future, rather than allowed to encroach on critical production wells or led away from production wells to become a problem for future generations or neighboring areas. The data needed to build the model, including geological logs, precipitation, evapotranspiration, well locations, pumping schedules, water levels, and nitrate concentrations have been obtained from the Beaumont Cherry Valley Water District. The model has been calibrated to simulate the observed groundwater levels and the extent of pollution corresponding to the historical pumping rates, recharge rates and climate. The calibrated model has been used to evaluate alternative hydraulic solutions that would either localize the nitrate pollution thus limiting the impact on public welfare, or remove the nitrate pollution for potential treatment and remediation on the surface. The study results show that increased pumping of production wells or strategic placement of additional artificial recharge may reduce the concentrations of nitrate in the Beaumont Basin.