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�.. r og S0 im PME, 1. INTRODUCTION As requested Ly Exxon Company, U.S.A.,EA installed one groundwater monitoring well,one groundwater recovery well,one injection well,four vapor extraction wells,two piezometers,and two permanent soil vapor monitoring cluster wells at former Exxon Retail Site(RS) 7-3942 in Stcckton, California, during the weeps of 14 and 21 January 1991 and 13 February 1991. To define the downgradient extent of the dissolved constituent plume a groundwater monitoring well was installed northeast of the site at the Crestwood Hospital parking lot on 17 April 1991. The wells were installed as the first step in completing a combined groundwater(GETS)and;oil vapor(VETS)extraction and treatment system,which will remediate petroleum hydrocarbons in the groundwater and soils beneath and downgradient of the site. Water extraction wells will pump impacted groundwater into the treatment system and will lower the water table to expose soils containing entrapped product; the product can then be more quickly and efficiently removed by vapor extraction wells. Other monitoring wells will be used simultaneously to enhance and monitor the system and accelerate remedial action. 1.1 SITE DESCRIPTION The site, located at 4444 Pershing Avenue in the northwest parr of Stockton,is near the north bank of the Calaveras River, about 2.5 miles from its confluence with the San Joaquin River (Figure 1). According to maps of the San Joaquin Connty Flood Control and Water Conserva- tion District(FCWCD), the prevailing groundwater gradient r.-;ar the site is to the northeast, forced in that direction by groundwater pumping within and north of the city. Presently,the site on the southeast corner of North Pershing Avenvie and Rosemarie Lane is an unimproved grassy lot from which all buildings and installations i,ave been removed. The areas to the northeast and southwest of the site are occupied by apartment buildings (Figures 2 and 3). Across Pershing Avenue and Rosemarie Lane,about 140-240 feet from the site boundaries, there i.' a Shell service station and a 7-Eleven store that retails gasoline. North of the site across Rosemarie Lane is the Chateau Convalescent Hospital and office buildings. The well inventory of the California Department of Water Resources in Sacramento indicates that there are four wells within one-half mile of t'ie site and 10 wells within one mile. Within one mile of the site in the downgradient direction,there are no wells pumping water either from a shallow perched zone or from a deeper water-bearing zone. Water supply wells in the area are typically more than 345 fc,;t deep and are screened at depths greater than 144 feet.