SITE INFORMATION AND CORRESPONDENCE

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J GEOMATRJX station. According to the ESA(Geological Technics, 1995),the former TAOC pump station was owned by Vernalis Enviropur-West(1141 Highway 33)in 1995 and was used for bulk l storage of petroleum and oil products. 1.3 REGIONAL GEOLOGY AND HYDROGEOLOGY The site is located in Vernalis within the northwestern part of the San Joaquin Valley of California. The San Joaquin Valley is bounded to the west by the Coast Ranges and to the east by the Sierra Nevada. The surface topography of the Vernalis area slopes downward to the 1 northeast(from the Diablo Range to the San Joaquin River). The ground surface elevations of r-I the site range from approximately 105 to 110 feet above mean sea level (fmsl) (Figure 1). The J prominent feature in the vicinity of the site is the complex of streams, creeks, rivers, canals,and aqueducts. These water features include the underground Hetch Hetchy Aqueduct about 800 feet south of the site, the San Joaquin River about 3 miles east of the site,the Delta- Mendota Canal about 2 miles west of the site, and the California Aqueduct about 4 miles west of the site. Vernalis is located within the Alluvial Fans and Plains geomorphic unit(USGS, 1971). The geologic units in this area include unconsolidated deposits at shallow depths. Underlying the unconsolidated deposits are flood-basin deposits of a maximum thickness of 50 feet, including l stream-channel deposits of coarse sand and gravel. Alluvium of a maximum thickness of 200 feet underlies the flood-basin deposits. } An upper water-bearing zone has been identified in this area and primarily includes the alluvium and flood-basin deposits (USGS, 1971). According to the data presented in the USGS (197 1) report, the water level in the upper water-bearing zone in the vicinity of the Vernalis area was between 70 and 80 fmsl (or about 30 to 35 feet bgs), and the horizontal groundwater 1 flow direction was to the northeast. J 1.4 INVESTIGATION OBJECTIVES As described in Section 2.1, site investigations previously had been conducted at the Bellini property. Based on a review of the results of a site investigation completed in 2002 (Geomatrix, 2002a), the RWQCB requested additional data. The purpose of the recent Bellini property investigation was to assess the lateral and vertical extent of petroleum-impacted soil and groundwater both on and off site, including the vertical extent of affected soil and 1 groundwater at depths greater than 45 feet bgs in the area of the previous boring SB-14. The Bellini property investigation and results are presented in Section 2.0. _ I IAPROJECI150005011.00015011-03.dm 3