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01 ME $. i N ..rte 'a r.. '` � +.; - r. :S'. •^'` �+ "` 'f - o. � t;A INTRODUCTION During the weeks of January 18 and January 25, 1988, Brown and Caldwell (BC) conducted an investigation in the vicinity of ARCO Products Company (ARCO) station No. 2133, located at 2908 Benjamin Holt Drive in Stockton, California (Figure 1). Four groundwater monitoring wells were installed off site c, Benjamin Holt Drive and Plymouth Road, wring the investigation. Locations of the Four monitoring wells are shown on Figur= 2. The off-site wells were installed according to BC's recommendations and work plan included in BC's June 10, 1987, Site Assessment Report for the subject site. After installation, each well was surveyed by Meridian Consulting Engineers of Sacramento, for ground surface and top-of-casing elevations. is In March 1988, Armour Petroleum personnel repaired the hydropurge pump of the on- site recovery system. On March 22, 1988, BC personnel reactivated the product recovery system. On May 2, 1988, BC persongel completed the first round of quarterly sampling of six selected wells. ,r FIELD METHODS Four soil boreholes were drilled by P.C.-Exploration, Inc., (PC) with a truck-mouni,.d drilling rig equipped with 8-inch-inside-diameter and 12-inch-outside-diameter hollow-stem augers. PC then installed a monitoring well in each borehole. PC has a C-57 contractors license. Borehole Drilling " Each borehole was advanced to approximately 30 feet, or about 20 feet below the groundwater surface. Heaving sands entered each borehole through the bottom of the augers, therefore, the completed total depth of each borehole was approximately 28 feet. Soil samples for lithologic classification and potential Iaboratory analyses were collected at 5-foot intervals by using an 18-inch-long by 2--inch-diameter Modified California-type sampler with 6-inch-long brass tube finers. The drive sampler was driven ahead of the auger into undisturbed soil. Each borehole was logged from the samples taken at 5-foot intervals, using the Unified Soil Classification system. Borehole logs are presented in Appendix A. The ends of the tubes were covered with foil and a plastic cap taped to the. ` tube. .These samples were stored in a chilled ice chest from coilection through delivery to Eureka Laboratories, Inc. (Eureka), a state-certified analytical laboratory in Sacramento, Caiifornia. The soil samples were analyzed for benzene, ethylbenzene, toluene, and xylene (BETX) by U.S. Environmental Protection Agency (EPA) Method 3020, total Petroleum fuel hydrocarbons by EPA Method 8015, modified, and total lead by EPA Method 6010. Cuttings from each borehole were sealed in 55-gallon drums and temporarily stored on site pending results of the analytical tests.