California's Groundwater Ambient Monitoring and Assessment Program: Reflecting the Legacy and Contributions of Jacob Rubin

As a scientist, as a teacher, and as a leader, Jacob Rubin had a deep and lasting influence at the USGS. He was an analytical thinker who had a genuine respect for disciplines and approaches different than his own, including the importance of place-based research. From that perspective, Jake was an early and strong proponent of the USGS National Water Quality Assessment Program (NAWQA).

In California, the USGS is collaborating with the State Water Board to implement a comprehensive evaluation of California's ground-water quality. The overall effort is identified as the Groundwater Ambient Monitoring and Assessment Program (GAMA), and the USGS effort focuses on basins that provide water for public supply (Priority Basin Project). The design of the state-scale Priority Basin Project is based, to a large extent, on the national-scale NAWQA program.

The Priority Basin Project has been designed to balance the need for statewide consistency with the need for local relevancy. Within each basin, equal-area-grid sampling is used to provide a statistically robust assessment of ground-water quality at the basin-scale, and additional wells are sampled to address process-related issues. The samples are analyzed for an extensive suite of inorganic constituents, including age-dating, and for an extensive suite of organic constituents at very low concentrations (<1 ppb). The combination of age dating and low-level detections of organic constituents provides an opportunity to evaluate the connection of that part of the aquifer system used for public supply with potential sources of contamination. The Priority Basin Project also utilizes data collected for the purposes of regulatory compliance. Based on sampling to date, and depending on location, about 10% to 20% of the resource has concentrations of inorganic constituents above health-based benchmarks. In contrast, organic constituents are less frequently detected above benchmarks (generally less than 1%).