SITE INFORMATION AND CORRESPONDENCE_FILE 1

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i i DEPTH TO GROUNDWATER: According to San Joaquin County Flood District maps, groundwater was as high as 47 ' bgl in the ,Spring of 1986 . Monitoring activi- ties since April, 1992 have recorded an average water table depth of about 72' bgl ; levels have '.fluctuated an average of 4 . 62' . PRIOR USE OF UST' S: Two, 5, 000 gallon UST' s which had been used for storing diesel , fuel were removed from the property in March, 1987 . There are no j records available concerning amounts of fuel used during the time the tanks were in use. Refer )to prior reports for more details . SUMMARY OF PRIOR WORK: i March, 1987 - two, 5, 000 gallon diesel UST' s removed from site by Thorpe Oil Co. Soil samples taken from beneath the tank revealed the presence of benzene, xylene, TVPH, & TEPH. Disposition of removed spoil not known. March, 1988 - Thorpe Oil Co. reexcavated the site, and soil samples were taken at 28' & 29' below grade. Laboratory results revealed the presence of xylene & TVPH in both samples. The excavation was filled with clean material . i September, 1991 - Correspondence, WJH to EHD, retained by Marci ' s Diesel Service. April 3 . 6 , & 7 1992 - Three. ( 3) monitoring wells placed on site to depths of 84' , 86' , & 89' bgl . Casing size on MW-1 was 4" OD, MW-2 & MW-3 was 2" OD. ' Details of work included in report titled "GROUNDWATER INVESTIGATION REPORT" dated May, 1992 . The locations of those wells are shown on PLATE III . April 16, 1992 - Initial groundwater measuring and sampling of the three wells revealed that', BTEX, TPH-G,; & TPH-D were below detection limits . Hydraulic gradient to the west. May 15 , 1992 - Three wells sampled again, all ND. Hydraulic grdient still to west. Sept. 15 , 1992 - Only MW-1 sampled; small ,amount of TPH-D. Dec. 30 , 1992 - Only MW-1 sampled; all ND. March 17 . 1993 - MW-1 only sampled; all ND. i June 18 , 1993 - Only MW-1 sampled; detected benzene, xylene, & TPH-D. 3