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STATE OF CALIFORNIA-Environmental Prote Agency ' PETE WILSON,Govemor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 3443 Routier Road,Suite A ' Al-Tit -- Sacramento,CA 95827-3096 "_�`;r PHONE:(916)255-3000 FAX:(916)255-3015 8� 3 1 May 1996 Ms. Katie Hower Chevron Pipeline Company 4000 Executive Parkway, Suite 400 San Ramon, CA 94583 RESULTS OF SOIL AND GROUND WATER SAMPLING, CHEVRON PIPELINE LEAK, MOUNTAIN VIEW TOWNHOMES SITE, SAN JOAQUIN COUNTY I have reviewed the 11 April 1996 Soil and Ground Water Characterization Report prepared by EMCON for the Chevron Pipeline leak site at 415 Mount Diablo Avenue in Tracy. The report documents the results of the latest investigation which involved the installation and sampling of three ground water monitoring wells. Previous soil and ground water sampling investigations have shown that petroleum constituents still contaminate the subsurface soils at concentrations up to 29,000 mg/kg as measured by EPA Method 8015M for total petroleum hydrocarbons (TPH) as diesel. Polynuclear aromatic hydrocarbons (FNAs) also have been detected in soils in the same area. The contamination is generally found at or below the water table which is approximately 20 feet below the ground surface. Free product also has been observed near the water table. The recently installed monitoring wells show that the ground water flow direction is approximately N15E. Monitoring well MW-1 is completed approximately 20 feet away from the area of soil contamination in the direction N19W. MW-2 is approximately 65 feet away in the direction N55E, and MW-3 is approximately 50 feet away in the direction N10W. Based on the above data, all three ground water monitoring wells are at least 25 degrees away from being directly downgradient of the known contaminant source. Because of this it is unclear if the monitoring wells will accurately provide water representative of that which is flowing through the contaminated area. I have some concerns about the analytical results generated from the laboratory. First of all, because short-chain hydrocarbons and diesel were the dominant hydrocarbons detected in the original soil samples (geoprobe sample GP-6), the crude oil standard used for the most recent sampling is inappropriate. Using crude oil as the standard against particularly short-chain hydrocarbons will not produce accurate laboratory results. Second, even though the extraction sample preparation method was used, many of the chromatograms still show the existence of short-chain hydrocarbons which implies that much higher concentrations of these hydrocarbons are really present in the sample than what was reported. For the short-chain hydrocarbons, the purge and trap method would have been a more appropriate sample preparation technique to use rather than extraction. In fact, in the November 1995 Report of Geoprobe Soil and Ground Water Sampling Program, the laboratory data sheets show that soil samples were analyzed using the purge and trap method and compared to a diesel standard. In that analysis, GP-6 showed up to 29,000 mg/kg although these results were not included in the tables or text of the report.