Abstract
Publicly accessible soil and groundwater geochemistry databases were utilized to identify the distribution of major cations and anions in groundwater and cations in soil in the southern San Joaquin Valley (study area). The study area was divided into three geographic subareas based on proximity to the San Joaquin Valley axis and the presence or absence of the Corcoran Clay. These subareas were then further divided into intermediate and deeper groundwater intervals with the top of the Corcoran Clay or projected depth to the top of the Corcoran Clay as the boundary between the two intervals. Groundwater data from the United States Geological Survey (USGS) National Water Information System (NWIS) and California Department of Public Health (CDPH) databases were screened and used to present the spatial distribution of major ions in groundwater. Data from the USGS National Uranium Resource Evaluation (NURE) were used present the spatial distribution of major cations in soil. Concentration contour maps, Piper plots, box-whisker plots, and scatter plots indicate that groundwater chemistry varies across the study area and that the Corcoran Clay limits mixing of intermediate and deep groundwater where the Corcoran Clay is present. In general, cation distribution in intermediate groundwater is dominated by sodium (Na) with magnesium (Mg) and calcium (Ca) increasing in concentration in the southern and eastern parts of the study area. Intermediate groundwater is dominated by chloride (Cl-) across the western portion of the study area and sulfate (SO42-) across the eastern portion of the study area. The distribution of cations and anions in deep groundwater was similar to the intermediate groundwater with elevated concentrations of Na across the study area, elevated concentration of Cl- across the western portion of the study area, and elevated concentrations of SO42- across the eastern portion of the study area. Statistical analysis showed that Ca (negative correlation) and K (positive correlation) present the strongest correlations between intermediate groundwater chemistry and soil chemistry. Similarly, Ca (negative correlation) presented the strongest correlation between deep groundwater chemistry and soil chemistry; K showed a weak (positive) correlation between soil and deep groundwater chemistry. In addition, positive correlations were found between the molar ratio Mg:Na in soil and in both intermediate and deep groundwater..