ARCHIVED REPORTS_XR0006232 - Laserfiche WebLink

Home Browse Search

16 1. INTRODUCTION Former Exxon Retail Site (RS) 7-3942 is a vacant site located at 4444 North Pershing Avenue, Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and Rosemarie Lane Three grades of gasoline and used oil were stored in four underground storage tanks, which were removed m July 1986 Groundwater monitoring wells MW i—MW 10 were installed on and off the site between January 1987 and April 1988 Groundwater extraction wells RW 1—RW3 were installed on the site in May 1990 From January through April 1991, EA installed infection well IW1, piezometers P1 and P2, extraction well RW4, soil vapor wells VI—V4, groundwater monitoring wells MW 11 and MW 12, and two vapor monitoring cluster wells on and off the site Two air sparging wells (SWI, SW2) and one offsite monitoring well (MW13) were installed in ' May 1993 The soil beneath the site consists of clay and silt to a depth of 10-15 feet below ground surface Between 10-15 feet and 35-40 feet the soil consists of clayey sand, sand, and gravel interbedded with discontinuous clay lenses ranging from a few feet to 25 feet in thickness These sediments are underlain by clay and silt to an unknown depth ' A Shell service station and a 7-11 food and gasoline service store are located at the southwest and northwest corners, respectively, of the intersection of North Pershing Avenue and Rosemarie Lane Previous laboratory analyses have consistently identified TPH-g and BTEX in groundwater samples collected from MW8, which is located adjacent to the Shell site, upgradient of former Exxon RS 7-3942 On 17 February 1995, groundwater from seven monitoring wells (MW I, MW4, MWS, MW9, MW 10, MW 12, and MW 13), four recovery wells (RW 1, RW2, RW3, and RW4), one 1 piezometer(P1), one soil vapor extraction well (V3), and one infection well (1W 1) was purged and sampled Figure 1 shows the locations of all wells on and off the site, except MW11, and the locations of former site facilities Figure 2 shows the vicinity of former Exxon RS 7-3942 ' and locations of all wells off the site 2. SUMMARY OF RESULTS ' On 17 February, wells were monitored for the presence of liquid-phase hydrocarbons and water levels in all wells on and off the site were measured with an optical interface probe The depth to water in all wells ranged from 25 00 feet to 3176 feet below ground surface The ' approximate groundwater flow direction on 17 February was to the north-northeast, with a gradient of approximately 0 008 (Figure 3), which is consistent with previous groundwater monitoring data for the site Groundwater table elevations have increased approximately 2 6 feet since the previous quarter Groundwater table elevation data for 17 February are presented in boldface type in Table 1, along with previous data Field documents are included as Appendix A WP61 73942Q295 2 1