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-5 at a concentration of 3.8 ppb. No other petroleum <br /> Toluene was detected in MW <br /> hydrocarbons were detected in any of the samples analyzed. The analytical results of the <br /> groundwater samples are summarized in Table 2.The laboratory report and chain of custody <br /> are included in Appendix B. <br /> 5.0 CONCLUSIONS & RECOMMENDATIONS <br /> Low concentrationsop <br /> f petroleum hydrocarbons continue to be detected in samples from <br /> MW-1, MW-4 and MW-5, which are down or cross gradient of the former UST excavation. <br /> Where detected, hydrocarbon concentrations showed slight increases in each well since May <br /> 1994. However, only the concentration of benzene in MW-1 and MW-4 exceeds the <br /> Maximum Contaminant Level (MCL) for drinking water in the State of Califomia. <br /> Remediation of low concentrations of hydrocarbons in groundwater is often ineffective and <br /> impractical. It is unlikely that traditional methods (i.e. pump and treat, air sparging) would <br /> be successful in reducing hydrocarbon concentrations at the site. However, an "extended <br /> purge"or limited groundwater extraction of the affected wells may reduce remaining residual <br /> petroleum hydrocarbons in the groundwater. <br /> GeoAudit proposes to perform limited groundwater extraction of MW-1, MW-4 and MW-5 <br /> during the next quarterly monitoring event. Initially, approximately 300 to 500 gallons of <br /> water will be removed from MW-1. After completing the limited pumping of MW-1, <br /> approximately 100 gallons of water each will be removed from MW-4 and MW-5. After <br /> pumping, each well will be sampled. A Work Plan for limited groundwater extraction is <br /> included in Appendix C. <br /> 6.0 LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily <br /> exercised by environmental consultants practicing in this or similar localities. The findings <br /> were mainly based upon analytical results provided by an independent laboratory. <br /> Evaluations of the geologic conditions at the site have been made from a limited number <br /> of available data points (i.e. monitoring wells), and subsurface conditions may vary away <br /> from these data points. No other warranty, expressed or implied, is made as to the <br /> professional recommendations contained in this report. <br /> W.srsn Uh OMO-11-1.10 <br />