Ground-water quality data in the San Fernando-San Gabriel study unit, 2005— Results from the California GAMA program

Status of groundwater quality in the San Fernando--San Gabriel study unit, 2005--California GAMA Priority Basin Project

“…For constituents with multiple types of benchmarks, this hierarchy may not result in selection of the benchmark with the lowest concentration. Additional information on the types of benchmarks and listings of the benchmarks for all constituents analyzed is provided by Land and Belitz (2008). For ease of discussion, relative-concentrations of constituents were classified into low, moderate, and high categories:…”

“…The primary data used for the grid-based calculations of aquifer-scale proportions of relative-concentrations were data from wells sampled by USGS for the GAMA Priority Basin Project (USGS-GAMA). Detailed descriptions of the methods used to identify wells for sampling are given in Land and Belitz (2008). Briefly, each study area was divided into 10-mi 2 (~25 km 2 ) equal-area grid cells, and in each cell, one well was randomly selected for sampling to represent the cell ( fig.…”

“…4) (Scott, 1990). In the San Fernando study area, to avoid cells with no wells, a 1.9-mi (3-km) buffer was drawn around each public-supply well, and these areas were aggregated into 10-mi 2 grid cells from which the wells were selected (Land and Belitz, 2008). Wells were selected to sample from the population of wells in statewide databases maintained by the CDPH and the USGS.…”

“…Samples from a subset of 24 wells were analyzed for major and minor ions, trace elements, nutrients, redox species, radiochemical constituents, carbon isotopes, N-nitrosodimethylamine (NDMA), perchlorate, and 1,2,3-trichloropropane (1,2,3-TCP). The collection, analysis, and quality-control data for the analytes listed in table 1 are described by Land and Belitz (2008). 1 Includes nine constituents classified as fumigants or fumigant synthesis byproducts.…”

“…An additional 42 organic constituents and 40 inorganic constituents were detected by USGS-GAMA, but were not selected for additional evaluation because either benchmarks were not established or detection was at low relative-concentrations (table 5). A complete list of the constituents investigated by USGS-GAMA in the FG study unit may be found in the FG Data Series Report (Land and Belitz, 2008). Table 2.…”