Evaluation of ground-water monitoring network, Santa Cruz County, California

The Santa Cruz County Flood Control and Water Conservation District seeks to improve the existing network of observation wells to monitor water levels and ground-water quality in the Pajaro Valley subarea and the Aptos-Soquel, San Lorenzo, and Santa Cruz Coastal subbasins in California. The proposed network , consisting of 92 wells, is designed to monitor changes in storage and quality of ground water resulting from climatic changes and management-induced stresses. In the proposed network , water levels in all wells would be measured semiannually, in April and September, and monthly in a few key wells. The water-level measurements would provide data that could be used to determine changes in ground-water storage. In addition to the currently monitored characteristics--temperature, specific conductance, pH, and chloride ion concentration--inclusion of annual sampling and analysis for major ions and nutrients is proposed. The network would also include sampling and analysis for trace elements once every 4 years. More frequent analyses are proposed in areas where water-quality problems are known to exist or where potential water-quality problems are recognized. Analyses for major ions, nutrients, and trace elements are included in the proposed network to provide baseline data for monitoring long-term changes in water quality and to detect any unexpected changes in quality. (USGS)