Ground-water quality data in the north San Francisco Bay hydrologic provinces, California, 2004: Results from the California Ground-water Ambient Monitoring and Assessment (GAMA) program

Kulongoski, Justin T.; Belitz, Kenneth; Dawson, Barbara J.

Abstract:

Ground-water quality in the ~1,000 square-mile (mi2) North San Francisco Bay study unit was investigated from August to November, 2004, as part of the California Groundwater Ambient Monitoring and Assessment (GAMA) program.Samples were collected from 89 public-supply wells, 7 hydrothermal wells, and 1 hydrothermal spring in Napa, Sonoma and Marin Counties. Eighty-four of the public-supply wells sampled were selected to provide a spatially distributed, randomized monitoring network for statistical calculations. The study was designed to provide a spatially-unbiased assessment of raw ground-water quality within the study unit, as well as a statistically-consistent basis for comparing water quality in different study units. Ground-water samples were analyzed for major and minor ions, trace elements, nutrients, volatile organic compounds, pesticides and (or) pesticide degradates, waste-water indicators, dissolved methane, nitrogen, carbon dioxide and noble gases (in collaboration with Lawrence Livermore National Laboratory). Naturally occurring isotopes (tritium, carbon-14, oxygen-18, deuterium and helium-4) also were measured in these samples to help identify the source and age of the sampled ground water. Results show that no anthropogenic constituents were detected at concentrations higher than those levels set for regulatory purposes, and relatively few naturally-occurring constituents were detected at concentrations greater than regulatory levels. In this study, 21 of the 88 volatile organic compounds (VOCs) and gasoline additives and (or) oxygenates investigated were detected in ground-water samples, however, none were above established maximum contaminant levels (MCL). Thirty-two percent of the randomized wells sampled during the North San Francisco Bay GAMA study had at least a single detection of a VOC or gasoline additive and (or) oxygenate. The most frequently detected compounds were chloroform, found in 12 of 84 randomized wells sampled; carbon disulfide, found in 8 of 84 randomized wells sampled; and toluene, found in 4 of 84 randomized wells sampled. Trihalomethanes were the most frequently detected class of VOCs. Nine of the 122 pesticides and (or) pesticide degradates investigated were detected in ground-water samples, however, none were above established MCLs. Seventeen percent of the randomized wells sampled during the North San Francisco Bay (NSF) GAMA study had at least a single detection of pesticide and pesticide degradate. Herbicides were the most frequently detected class of pesticides. The most frequently detected compound was simazine, found in 8 of the 84 of the randomized wells. Chlordiamino-s-triazine and deisopropyl atrazine were both found in 2 of the 84 randomized wells sampled. Thirteen waste-water indicators were detected in ground-water samples in the NSF study unit. Twenty-two of the 84 randomized wells sampled for waste-water indicators had at least one detection. Isophorone was the most frequently detected in 6 out of 84 randomized wells. Bisphenol-A, caffeine, and indole each were detected in 3 out of 84 randomized wells. Major and minor ions and dissolved solids (DS) samples were collected at 33 public-supply wells; 3 samples had DS concentrations above the secondary maximum contaminant level (SMCL) of 500 mg/L. Ground-water samples from 32 public-supply wells were analyzed for trace elements. Arsenic concentrations above the MCL of 10 ?g/L were measured at 4 public-supply wells, Boron concentrations above the detection level for the purpose of reporting (DLR) of 100 ?g/L were measured at 19 wells. Iron concentrations above the SMCL of 300 ?g/L were measured at 7 wells, a lead concentration above the California notification level (NL) of 15 ?g/L at one well, and manganese concentrations were above the SMCL of 50 ?g/L at 17 wells. Vanadium concentrations above the detection level for the purpose of reporting (DLR) of 3 ?g/L were measured at 9 public-supply wells; and chromium(VI) co

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USGS Numbered Series

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76808

Citation Author:

Kulongoski, Justin T.; Belitz, Kenneth; Dawson, Barbara J.

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California Water Science Center

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ENGLISH

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110

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x, 100 p.

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Data Series

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Citation Series Number:

167

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Ground-water quality data in the north San Francisco Bay hydrologic provinces, California, 2004: Results from the California Ground-water Ambient Monitoring and Assessment (GAMA) program; 2006; DS; 167; Kulongoski, Justin T.; Belitz, Kenneth; Dawson, Barbara J.