Confined and unconfined groundwater is found from 10 to 45 feet below ground surface (bgs) in fractured volcanic bedrock (Conejo Volcanics).
Targeted Environmental Media:
 Fractured Bedrock
The plume spans an area that is a third of a mile wide and one half mile long. Impacted groundwater is present to about 228 feet bgs and has traveled off-site approximately one quarter of a mile.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (480,000 µg/L)
- Chromium (39,000 µg/L)
- Other (Drilling and sampling wells. )
Comments:
The extent and nature of the impacted area was assessed by drilling and sampling 40 wells.
- Pump and Treat
- Soil Vapor Extraction
Comments:
Groundwater was extracted via 18 wells that withdrew water at rates of less than 0.5 to approximately 12 gallons per minute (gpm). Volatile organic compounds were treated through air stripping and the metals were treated by precipitation and micro-filtration.
The remedial objective was to clean up the groundwater to meet primary drinking water maximum contaminant levels (MCLs).
Though TCE concentrations within the plume have decreased significantly, the size of the TCE plume has not decreased. The size of the chromium plume has decreased by 93%. As of February 2007, the maximum levels of TCE and chromium were 2.7 ppm and 0.19 ppm respectively.
Over 16 years of experience at this site has shown that while metals can be efficiently removed from the area because of the solubility and mobility of chromium, the recalcitrant nature of TCE and likely historical presence of DNAPL has prevented its efficient removal.
References:
Bilodeau, Sally W. Chromium and TCE Clean Up of a Fractured Bedrock Aquifer in Southern California, Poster Abstract Session A4. Presented at the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 19-22, 2008.
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