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BACKGROUND ' The site is located on west side of Milgeo Avenue at the inter section Wilma Road, adjacent to Highway 99 The property is zoned industrial and is presently utilized as a distribution warehouse Local land use in the immediate vicinity of the site is agricultural and industrial, residential areas are Iocated south of the site The site is fw-thei described as being located in the southeast quarter of Section 19, Township 2 South , Range 8 East, Mount Diablo Base and Meridian (Manteca Quadrangle, 7 5-Minute USGS Topographic Series, 1968, photo revised 1987) 1 SITE DESCRIPTION ' A former truck fueling system operated on the site for approximately 30 years Currently a pool construction company operates a materials staging wai ehouse on the site The site consists of two wood-frame warehouse building structui e and an asphalt-paved and rock covered vehicle storage ai ea Local land use in the immediate vicinity of the site is agricultural and industrial,residential al eas ' are Iocated south of the site ' UNDERGROUND STORAGE TANK REMOVAL It is our under standing that six USTs were i emoved fi om three separated excavations on the property lin April 1994 one waste oil UST, one diesel UST and four unleaded gasoline USTs Petroleum ie hydi ocarbons were detected in soil samples collected from beneath the USTs at the time of removal Soil excavated during the UST i emoval was used to backfill each excavation Clean soil was imported ' to "cap" each excavation PREVIOUS SUBSURFACE INVESTIGATION The following is a brief summary of site assessment activities tIn December 1995, AGE advanced five soil probe borings at the site Free hydrocarbon product was encountered in ground water samples collected from the site However, soil ' samples indicated that hydrocai bon-impacted soil was limited to the capillary fringe or lower vadose zone (Tables 1 and 2) Locations of the probe bonngs are illustrated on Figure 2 ' In June 1996, AGE installed four ground water monitoring wells • On 29 July 1999,a total of six soil probe borings (P6 through P 11)were advanced at the site ' and off the site north, east and northwest of the former UST location TPH-d was detected in all five of the grab ground water samples analyzed at concentrations from 430 dig/l to 1,100 µg/l TPH-g was detected in three soil samples analyzed at concentrations as great as 350 ' rrulligram per kilogram(mg/kg) in soil sample P 10-20' TPH-g was detected in soil from 15 feet and 25 feet bsg at concentrations of 160 mg/kg and 14 mg/kg, respectively TPH-g was . not detected in soil samples collected at a depth of 30 feet or 35 feet bsg TPH-d was ' detected in soil samples collected from a depths of 15, 20 and 25 feet bsg at concenti ations of 5,100 mg/kg, 13,000 mg/kg and 490 mg/kg, respectively TPH-d was not detected in soil