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GAMA – Groundwater Ambient Monitoring & Assessment Program
Domestic Well Project
Domestic well water is for private use and consumption, typically by single family homeowners. Although its quality is not regulated by the State of California, private domestic well water is a concern. to local health and planning agencies, to State agencies in charge of maintaining water quality.
The GAMA Domestic Well Project samples domestic wells for commonly detected chemicals; at no cost to well owners who volunteer. Results are shared with the well owners and used by GAMA to evaluate the quality of groundwater used by private well owners. The Domestic Well Project has sampled five County Focus Areas in California as of 2009.
Current News
Results from the San Diego County Focus Area were released online in April 2009. Figures and tables are available below. See the Press Release.
Domestic Well Analytes
The GAMA Domestic Well Project tests for chemicals that are most commonly a concern in domestic well water:
- Bacteria (Total and Fecal Coliform)
- General Minerals (sodium, bicarbonate, calcium, others)
- General chemistry parameters (pH, TDS, others)
- Inorganics (lead, arsenic and other metals) and nutrients (nitrate, others)
- Organics (benzene, toluene, PCE, MTBE, and others)
Additional chemicals of concern occur in some areas of California. GAMA has previously sampled for:
- Radionuclides
- Perchlorate
- Pesticides
County Focus Areas
There have been five county focus areas sampled to date:
The focus areas are chosen based upon several parameters in close coordination with county agencies. The State Water Board incurs the cost of sampling and analyses.
County Focus Area Summary
The results from sampled domestic wells are compared to CDPH drinking water standards. Even though the State of California does not regulate domestic well water quality, it is informative for well owners to compare their results to these standards. Results from each focus area are summarized in the table below. The table shows the total number of wells with a chemical above a drinking water standard.
The results summarized in the table above are from wells sampled as part of a voluntary program. Therefore, the results may not reflect the spatial distribution of domestic wells or noted contaminants.
San Diego County Focus Area
In 2008 and 2009, approximately 137 domestic wells were sampled in San Diego County. Manganese was observed above the SMCL of 50 µg/L in 45 (33 percent) of the sampled wells. Radionuclides and pesticides were sampled in selected wells, in addition to the standard suite of analytes. Pesticides were not observed above the analytical detection limit in the San Diego study area. Thirty five percent of the 54 wells sampled for radionuclides exceeded the recommended levels of gross alpha activity.
- San Diego County Summary Table
- San Diego County Summary Report
Figures:
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| San Diego Sample Locations | San Diego Nitrate Results | San Diego Radionuclide Results |
Tulare County Focus Area
In 2006, 181 domestic wells were sampled in Tulare County. Forty one percent of the sampled domestic wells in Tulare County exceeded the drinking water standard for nitrate, and bacteria indicators were detected in 33 percent of the sampled wells. Concentrations of vanadium and VOCs were observed in more than 5 percent of the sampled wells.
- Tulare County Summary Report
- Tulare County Summary Table
Figures:
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| Tulare County Sample Location Figure | Tulare County Nitrate Results Figure | Tulare County Results with Coliform and/or Nitrate Figure |
Tehama County Focus Area
In 2005, 223 domestic wells were sampled in Tehama County. The majority of the wells sampled were in the vicinity of Red Bluff and Los Molinos. The main chemicals of concern were arsenic, iron, total coliform bacteria, arsenic, and iron. Twenty five percent of the wells (56 of 223) had positive total coliform detections. Fecal coliforms were detected in three wells. Fourteen percent of the wells had concentrations of both arsenic and iron above their associated CDPH MCLs or secondary MCLs.
- Draft Tehama County Summary Report (includes text, maps, summary tables, and figures, 13.58 MB)
- Tehama County Summary Table
Figures:
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| Tehama County Sampling Locations | Tehama County Nitrate Results | Tehama County Arsenic Results |
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| Tehama County Coliform Results | Tehama County Iron Results |
El Dorado County Focus Area
In 2003-2004, 398 domestic wells were sampled in El Dorado County. The main chemicals of concern were total coliform bacteria (104 of 398 wells), iron (above the SMCL in 76 of 398 wells), and manganese (above the SMCL in 91 of 398 wells).
- El Dorado County Summary Report
- El Dorado County Summary Table
Yuba County Focus Area
In 2002, 128 domestic wells were sampled in Yuba County. The main chemicals of concern were total coliform bacteria (28 of 128 wells), manganese (above the SMCL in 21 of 128 wells), aluminum (above the MCL in 18 of 128 wells), and iron (above the SMCL in 14 of 128 wells).
- Yuba County Summary Report
- Yuba County Summary Table