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1✓ � Supplemental Preliminary Site Investigation for State Route 99/Hammer Lane Project No. H2O2 to Mark Thomas & Co., Inc. November 17, 1999 SUPPLEMENTAL PRELIMINARY SITE INVESTIGATION INTRODUCTION Project Location and Description The San Joaquin County Council of Governments (SJCOG), in cooperation with Caltrans, proposes the improvement of the existing Hammer Lane Interchange on State Route 99 in San Joaquin Couniy. Figure 1 shows the project site and vicinity. Figure i is a copy of a portion of the Thomas Bros. Maps, 1993. The proposed project is to include the improvement of the State Route 99/Hammer Lane Interchange and existing grade separated roadways located in the City of Stockton,San Joaquin County,California. The existing Hammer Lane Interchange is a local street interchange (modified Type L-6) with a two- lane overcrossing of a six-lane freeway. Modification of the interchange to a partial cloverleaf type (Type L-8) is proposed along with widening of the Hammer Lane Overcrossing. Aerial photography (1963) indicated that the project area was primarily in agricultural use prior to construction of State Route 99 and the Hammer Lane Overcrossing. Most of the area surrounding the site remains in agricultural use with the exception of several commercial structures near the existing interchange. Purpose and Scope of this Report Espana Geotechnical Consulting performed a limited Preliminary Site Investigation (PSI) for assessment of targeted properties within the limits of the proposed State Route 99 and Hammer Lane Interchange Improvement project in Stockton, California, dated February 26, 1999. Based on review of the PSI,officials at Caltrans District 10 requested that a supplemental investigation be performed to determine if petroleum hydrocarbons are present in the soil and ground water below the areas of the former underground storage tank locations at the abandoned gas station site (former Mobil Oil station) and the Auto Factory site (former Texaco station) shown on Figure 2 . Accordingly, we performed the following scope of work for the Supplemental PSI, which was reviewed and approved by Caltrans personnel: 1) A workplan was prepared and a site health and safety plan was submitted to the San Joaquin County Environmental Health Department(EHD). Necessary drilling permits were obtained from the EHD. 2) Drilled 3 borings (3 at each site, 6 total) within the former and/or suspected underground storage tank(UST) locations at two sites: 1)the Auto Factory (former Texaco) site, shown on Figure 3 and, 2) the abandoned gas station (former Mobil Oil) site, shown on Figure 4. At 1 `V ESPANA GEOTECHNICAL CONSULTING