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December 2, 1998 Page 2 of America and the service station was demolished in 1962 The USTs in the southern ' portion of the site were removed during demolition The site is currently an asphalt- paved parking lot owned by and servicing the Wells Fargo Bank located immediately to the south A limited subsurface investigation was conducted by L M Swift for Wells Fargo and is detailed in a Phase I Report, Addendum 1, dated March 29, 1994 The investigation _ ' included an underground electronic survey of the parking lot to determine if any abandoned USTs existed beneath the site, and exploratory borings to collect soil and groundwater samples The underground survey detected no large metal anomalies, and ' concluded that there were no USTs beneath the site However, hydrocarbon-impacted groundwater was detected in the northern portion of the site ' A Phase I Environmental Site Assessment, dated December 16„1994, was prepared by Enviros Inc for Unocal The site assessment concluded that twelve sites in the vicinity of the Unocal site had been identified as having impacted soil and groundwater ' However, none of these sites were identified in the immediate upgradient direction from the Unocal site Additionally, the report concluded that two former service stations were located across from and downgradient of the Unocal site, a former Shell Oil ' service station at the northwest corner of 1 l" Street and Central Avenue (from approximately 1949 to 1962), and a former service station(possibly Chevron) at the northeast corner of 11" and Central Avenue (from approximately 1913 to at least :962) �F In May 1995 nine exploratory soil borings were drilled and three groundwater monitoring wells (U-1 through U-3) were installed by PEG at the site Exploratory test pitting was performed and two abandoned UST's were encountered at the northern property boundary,beneath the 11' Street sidewalk A report documenting the soil and ' groundwater investigation was submitted to Unocal and San Joaquin County in December 1995 ' On September 6, 1996,Unocal submitted a corrective action plan to address hydrocarbon-impacted soils that might be encountered during removal of the USTs Two abandoned 550-gallon USTs were removed in November 1996 -A third UST was ' encountered during the removal activities and was properly abandoned in plac6 by grout infection One groundwater monitoring well (U-4) was installed in December 1996 in the location of the removed USTs to evaluate soil and groundwater quality ' Groundwater flow direction has consistently been to the north REGIONAL GEOLOGY The site is located in San Joaquin County, in the northern portion of the San Joaquin Valley San Joaquin Valley is a broad, alluvium filled basin bound to the east by the Sierra Nevada Mountain Range and to the west by the Coast Ranges The total thickness of the alluvial deposits in the valley is estimated to,be several thousand feet The alluvial sediments generally consist of poorly sorted fine sand and silt with less 910017 lA/SOLGWRPT doc r r