|
' L INTRODUCTION
<br /> Former Exxon Retail Site (RS) 7-3942 is a vacant site located at 4444 North Pershing
<br /> Avenue, Stockton, California, on the southeast corner of the intersection of North Pershing
<br /> Avenue and Rosemarie Lane Three grades of gasoline and used oil were stored in four
<br /> underground storage tanks, which were removed in July 1986
<br /> Groundwater monitoring wells MW 1-MW7 were installed on site and MW 8-MW 10 were
<br /> installed off site between January 1987 and April 1988 RW1-RW3 were installed on site in
<br /> May 1990 From January through April 1991, EA installed IW1, Pl, P2, RW4, V1-V4,
<br /> I MW 11, MW 12, and two vapor monitoring cluster wells on and off the site Two air sparging
<br /> wells (SWI, SW2) and one off-site monitoring well (MW13) were installed in May 1993
<br /> Soils beneath the site consist of clayey and silty alluvial sediments to a depth of 10-15 feet
<br /> below ground surface Between 10-15 feet and 35-40 feet the soils consist of coarser
<br /> sediments-clayey sands, sands, and gravels that are intersected by discontinuous clayey
<br /> lenses ranging from a few feet to 25 feet in thickness The coarser sediments are underlain
<br /> by clays and silts to an unknown depth
<br />' A Shell service station and a 7-11 food and gasoline service store are located at the southwest
<br /> and northwest corners, respectively, of the intersection of North Pershing Avenue and
<br /> Rosemarie Lane Previous sampling has consistently found TPH-g and BTEX in MW8,
<br /> which is located adjacent to the Shell site, upgradient to former Exxon RS 7-3942
<br /> On 2 August 1994, groundwater from six monitoring wells (MW 1, MW8, MW9, MW 10,
<br />' MW 12, and MW13), three groundwater recovery wells (RW 1, RW2, and RW4), two
<br /> piezometers (PI and P2), one soil vapor extraction well (V2), and one infection well (IW1)
<br /> were purged and sampled Figure 1 shows the locations of all wells on and off the site
<br />' except MW 11 and the locations of former site facilities Figure 2 shows the vicinity of
<br /> former Exxon RS 7-3942 and locations of all wells off the site
<br />' 2. SUMMARY OF RESULTS
<br />' On 2 August, wells were monitored for the presence of liquid-phase hydrocarbons and water
<br /> levels in all wells on and off the site (with the exception of wells MW7, MW 11, SW 1,
<br /> and SW2) were measured with an optical interface probe Measurements and groundwater
<br />' elevations for 2 August are presented in boldface type in Table 1, along with previous data
<br /> The indicated direction of the groundwater gradient is to the north-northeast, at a magnitude
<br /> of 0 009 (Figure 3), which is consistent with previous data Groundwater elevations have
<br /> decreased approximately 0 5 feet since the previous quarter Field documents are included as
<br /> Appendix A
<br /> After the depths to water were measured, selected wells (MW 1, MW8-MW 10, MW 12,
<br /> MW13, RW1, RW2, RW4, P1-P2, rWl, and V2) were purged by vacuum truck and sampled
<br /> At least three well casing volumes of purge water were removed from each well before
<br />' 73942Q894 1 1
<br />
|