Data for Evaluating 1,2-Dibromo-3-Chloropropane (DBCP) Trends in California Groundwater

This data release documents dibromochloropropane (DBCP) data and environmental tracer data used to evaluate long-term trends and the history of DBCP in recharge in California groundwater. DBCP data from the California State Water Resources Control Board’s Division of Drinking Water (SWRCB-DDW), the USGS Groundwater Ambient Monitoring and Assessment Priority Basin Project (USGS GAMA-PBP), and from the USGS National Water Quality Network (USGS NWQN) were used to evaluate long-term DBCP trends (1980 - 2023) in wells and springs used for public, domestic, and irrigation supply, and for groundwater monitoring. Environmental tracers of tritium, noble gases, helium isotopes, and carbon-14 were used to compute the age of groundwater in wells in the San Joaquin Valley and Upper Santa Ana Watershed that were sampled as part of the USGS National Water Quality Network (1995-2013), USGS California Aquifer Susceptibility (2001-2002), and the USGS GAMA-PBP in 2004-2021. Dissolved gas models and concentrations of tracers used to date groundwater were computed by the USGS software program DGMETA (Jurgens and others, 2021). The age of groundwater was computed by calibration of age distribution models to the environmental tracers at each site using the USGS Software program TracerLPM (Jurgens and others, 2012). Details of the groundwater age modeling are described in the processing steps of the metadata file.

This data release contains seven tables formatted as tab-delimited text files. The first table contains site information and DBCP concentrations from public-supply wells using data from the SWRCB-DDW and USGS GAMA-PBP. The second table contains site information and DBCP concentrations for domestic, land use, and flow path studies sampled by the USGS GAMA-PBP and USGS NWQN. Table three contains detailed groundwater age model calibration results of sites used for determining the history of DBCP in recharge in the San Joaquin Valley and Upper Santa Ana Watershed. Table 4 contains dissolved noble gas model results, which are used to determine the concentration of the environmental tracer, tritiogenic helium-3 listed in table 5. Additionally, a data dictionary that contains a list of all field names and their descriptions is included in table 6 and a list of all abbreviations is provided in table 7.