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i ` California RP-Tional ,Water Quality Control Boardp p Central Valley Region Peter M.Rooney Sacramento Main Office >3d J.Schnabel Secretary for Internet Address: h*://www.swreb,ca.gov/—rwgcb5lhome.htmi Char Environmental 3443 Roe'tier Road,Suite A,Sacramento,California 95827-3003 Protection Phone(916)'255-3000•FAX(915)255-3015 TO: Gordon L. Boggs I FROM: Mark R. List UST Program Manager Engineering Geologist DATE: 28 August 1998 ' SIGNATURE: a. _ SUBJECT: FILE REVIEW FOR CLOSURE CONCURRENCE, FULLER MOBILE HOME PARK, 365 E. LOUISE,LATHROP, SAN JOAQUIN COUNTY At the n ahe San o request f tJoaquin Co q - ,r 1 �q � only Environmental Health Division (SJCEHD), and the State Water Resources Control Board, Underground Storage Tank Cleanup Fund (SWRCB/UST-CUF), a file review was completed to determine if Board staff agree with the SJCEHD and SWRCB/UST-CUF determination of no further action required at;the above referenced site. This information was obtained C during my review of the Regional Board casefile, and the SJCEHD casefile for the Fuller Mobile Horne Park, and following a site visit and phone conversations with the consultant (WHF, Inc.). Background: } I' T On 7 September 1990, one 1,000-gallon leaded gasoline UST and one 500-gallon diesel UST were removed from the site. Although hydrocarbon odor and discoloration were evident during tank excavation activities, the excavation was backfilled with the soil generated during the tank removals. Twelve soil borings and seven groundwater monitoring wells have been installed on-site to delineate the vertical and lateral extent of soil and!�groundwater contamination. The extent of soil and groundwater contamination appears to be adequately defined with the borings and well network, based on analytical sampling results. The highest concentrations of TPHg and TPHd contamination are present in the soil near the former UST excavation at approximately 12;:5 feet figs. The contaminated zone appears to extend to'17.5 feet bgs, with no significant soil contamination below this interval. Groundwater below the site has historically been impacted with TPHg, TPHd,and BTEX. The most recent groundwater sampling data (collected 418198), indicate no detectable concentration of contamination in any well, above the laboratory reporting limit,with the exception;of one TPHd detection in MW-7 at a concentration of 60 The groundwater elevation during the 8 April 1998 sampling event was the highest historic water surface elevation recorded for the site. The high groundwater may account for some degree of dilution of the contaminants, however,lit is unlikely that;dilution alone would account for the significant reduction in contaminant concentrations since'the 6 March 1997 sampling event. 76 California Environmental Protection Agency Recycled Paper w i