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1 INTRODUCTION This report presents the results of our recent environmental investiga#aon and groundwater sampling program at the Ranch Market, at 23569 Santa Fe Rd in Riverbank, California Tlie work described here in was conducted in accordance with our work plan dated June, 1998, which was reviewed and approved by the San Joaquin County Public Health Services, Environmental Health Division Work consisted of the drilling and sampling of four soil bonngs/monitonng wells to confirm the vertical and horizontal extent of soil and groundwater contamination at the subject site SITE HISTORY The site is located at the southeastern intersection of Santa Fe Road and Henry Road in Riverbank, California(Figure 1) Improvements consist of one single story brick building, with the remainder of the site covered with asphalt The site was previously operated as a commercial gasoline fuel station Currently the site is being used as a mini-market (Figure 2) On May 20, 1991, Semco removed the pumps and three underground storage tanks, two one thousand gallon tanks and one five hundred gallon tank The tanks and pumps were located in front of the building The analytical results from the laboratory indicated the presence of petroleum hydrocarbon in the soil at the bottom of the tank excavation On January 23, 1998 one soil boring (B-1) was dulled by Pierson drilling Analytical results from the laboratory indicated the presence of Petroleum Hydrocarbons in the soil and groundwater The surface of the area where the tanks were located was patched with four to six inches of asphalt concrete RECENT FIELD ACTIVITIES On November 24, 1998, four soil borings/monitoring wells (MW-1, MW-4) were drilled to • assist in determining the lateral and vertical extent of soil and groundwater contamination and to define the hydraulic gradient The wells depth of approximately 40 feet was drilled, using hollow stem auger equipment Undisturbed soil samples were collected at five foot intervals and transported in a cooled container to the Sherwood Laboratory in Hilmar Two inch ID Schedule 40 PVC casing were installed to the bottom of the well at 40 feet bgs Slotted casing, with 0 02 inch slots, was placed in the bottom 15 feet of the well, about 10 feet in the present water table and 5 feet above it Directly above the sand opposite the blank casing, we placed 3 feet of hydrated bentonite Above the bentonite to the surface we sealed the annulus with cement The wells were logged geologically and all important information is included in the well logs which are presented in Appendix A. After the traffic boxes had been installed and the casing cut to fit the boxes, we surveyed the elevation of the top of each casing in well MW-4 with a transit We arbitrarily assigned a datum of 100 feet to the top of each casing in well MW4 The wells were developed by bailing out approximately 3 well volumes of water By this time a notable clarification of the bailed water had occurred All bailed water for development or sampling was placed in drums and stored on site After well development was completed and the water level stabilized the depth of the water and the total depth of the well Then 3 well volumes of water were withdrawn from the well using a decontaminated steel bailer The physical parameters of temperature, conductivity and PH were measured The well sample sheets are enclosed in this report Once the parameters had stabilized and the wells had recovered, a water sample was obtained with a decontaminated bailer All samples were kept in a cooler on ice and forwarded to Sherwood Labs in Hilmar, CA The identity of the samples and depth of collection are presented in Appendix C.