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o1) Sr 24 July 2000 AGE-NC Project No 99-0654 Page 2 of 6 2 2 UNDERGROUND STORAGE TANK REMOVAL On 21 October 1999, three USTs and associated piping and dispenser islands were removed from the site by Stockton Service Station Equipment Company (SSSEC) of Stockton, California The USTs were located in a common excavation near the northern portion of the property The axis of each tank was oriented roughly east-west Approximately 150 cubic yards of hydrocarbon-impacted soil were removed and stockpiled during excavation of the USTs 23 UST REMOVAL SOIL SAMPLE COLLECTION AND ANALYSIS Nine samples were collected beneath the USTs, six samples were collected beneath the dispenser area and two laboratory-composited soil samples were collected from the excavated stockpiled soil Methyl tertiary butyl ether (MTBE), tertiary butanol (TBA), tertiary-amyl methyl ether (TAME) were detected in each of the soil samples collected from the site Total petroleum hydrocarbons quantified as gasoline (TPH-g) were detected at concentrations up to 3,849 milligrams per kilogram . (mg/kg)beneath the western end of the center UST location Volatile aromatics (benzene, toluene, ethyl benzene and xylenes BTEX) were detected at concentrations up to 29,720 micrograms per kilogram (,ug/kg) from the same sample location A total of fifteen samples were collected beneath the USTs and dispenser area Two composite so]] samples were collected from the excavated soil All samples were collected by AGE personnel at the direction of PHS-EHD representatives 2 4 REGIONAL GEOLOGIC CONDITIONS The site is situated within the Great Valley Geomorphic Province of California, a large, elongate northwest tending, asymmetric structural trough The Great Valley Province has been filled with thick sequences of sediment ranging an age from Jurassic to Recent, creating a nearly flat lying alluvial plain, which extends from the Tehachapi Mountains in the south to the Klamath Mountains in the north The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origin The Great Valley Province has been subdivided into two major divisions identified as the Sacramento and San Joaquin Valleys The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the • principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basan (Basin 5-22) This basin is drained primarily by the San Joaquin Raver