Abstract
The State of California is heavily dependent on groundwater to meet municipal and agricultural needs for water, with some communities completely dependent on groundwater to meet these needs. With several consecutive years of drought over the past decade increasing the demand for quality groundwater in California, it is imperative to understand impacts to groundwater quality on a regional and local scale. The aim of this study was to assess the relationships among groundwater chemistry with soil and surface water chemistry. The study demonstrated that land use, surface water chemistry and surface water recharge interact and result in changes in groundwater chemistry in the central coast region of California. At the coast of Monterey Bay, saltwater intrusion was demonstrated to be affecting groundwater quality with ion chemistry in well water displaying similar character to seawater ionic composition. Similar ratios in Ca and Mg concentrations were observed between groundwater and surface water around Monterey Bay. In the vicinity of the San Ardo Oil Field, where land uses change from a mix of grazing/natural land and crop agriculture to primarily crop agriculture, as well as being the location where groundwater flow become constricted by natural subsurface structures, concentrations of Ca, Mg, K, SO4 and Cl show sharp increases while concentrations of Na in soil were demonstrated to be controlled by soil mineralogy and do not increase at this boundary. Understanding definite causes of localized patterns in groundwater chemistry within this study area is hindered by a lack of data on specific land use practices, soil samples at groundwater basins, and surface water samples in major water bodies. However, this study can be utilized to identify areas in the central coast region where specific land use practices are affecting the hydrologic cycle and where additional analyses would be useful.