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C-LEARWArER �i G R O U P, I IV C. JA P4 2 0 1995 1.0 INTRODUCFION ENVIRONMENTAL HEALTH This report was prepared by Clearwater Gro p,. Inc. (Clearwater)Aan11 a workplan for the completion of a Preliminary Site Assessment at the City of Ripon Corporation Yard, located at 1210 Vera Street in Ripon, California. 1.1 Site Description and Background The project site is located on the southerly outskirts of Ripon. The Stanislaus River meanders in a generally southwesterly direction just south of the site. (Figure 1). Based on a review of the region geology, sediments in the shallow subsurface of the yard likely consist of Quaternary river deposits (gravel, sand and minor clay). Depth to first water is estimated to be approximately 0-25 feet below ground surface based on the proximity of the site to the river. Groundwater flow beneath the site is estimated,to range in direction from west to south. Two 10,000 gallon underground storage tank (UST's) were removed in May 23, 1990. The site layout including former UST locations is presented in Figure 2. The yard is urkpaved. A review of available.tank 'removal documentation indicated that the tanks were used to store regular gasoline and diesel fuel. According to information provided by Neumiller & Bear lsee, a soil sample collected from beneath the usrs during removal contained total petroleum hydrocarbons .as diesel (TPHd) at a concentration of 9,800 pars per million. No information was available regarding analysis of the soil sample for gasoline constituents. The site currently has at least one above ground fuel to k. 2.0 'PROPOSED FIELD ACTIVITIES In order to evaluate the concentration/di tribution of hydrocarbons in the subsurface Clearwater recommends a preliminary site assessment be conducted. This assessment consists of drilling and installing three groundwater" monitoring .wells, surveying the .top of casing elevations, gituging, and sampling the wells. .A. Soil Borehole Drilling and Soil Sampling Clearwater recom-mends drilling three eight-' ch diameter soil borings, designated PMW-1,. PMW-2 and PMW-3 (Figure 2). The ' borings .will be drilled to approximately 10 feet below first encountered water. Clearwater anticipates drilling to 30 feet below grade, assuming first ground-water is encountered at approximately 20 feet below grade. The boring locations were selected to evaluate the lateral and vertical extent of hydrocarbons in the soil. A two-inch inside diameter split-spoon sampler, lined with brass tubes, will be used t collect soil samples at five-foot depth U-144 WT WORKPLAN 1 January 19, 1995