|
1. INTRODUCTION
<br /> Former Exxon Retail Site (RS) 7-3942 is a vacant lot located at 4444 North Pershing Avenue,
<br /> Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and
<br /> Rosemarie Lane (Figure 1) Used oil and three grades of gasoline were stored in four
<br />' underground storage tanks, which were removed in July 1986
<br /> A Shell service station and a 7-11 food and gasoline service store are located on the southwest
<br />' and northwest corners, respectively, of the intersection of North Pershing Avenue and Rosemarie
<br /> Lane Previous laboratory analyses have consistently detected Total Petroleum Hydrocarbons as
<br />' gasoline (TPH-g), and benzene, toluene, ethylbenzene, and total xylenes (BTEX) in groundwater
<br /> samples collected from MW8 and MW9, which are located adjacent to the Shell site and the 7-11
<br /> site, upgradient and crossgradient of former Exxon RS 7-3 942
<br />' On 20 May 1998, groundwater was purged and sampled from 14 groundwater monitoring wells
<br /> (MW2—MW13, UV13-MW1, UVB-MW2), three groundwater recovery wells (RW1, RW2, and
<br />' RW4), two soil vapor extraction wells (V2, V3),two piezometers (P1, P2), and one injection
<br /> well (I W I) Vapor extraction well VI was not sampled on 20 May, because it did not contain a
<br /> measurable quantity of water Vapor extraction well V4 was not sampled on 20 May, because of
<br />' the presence of liquid-phase hydrocarbons (LPH) Figure I shows the locations of former site
<br /> facilities and the locations of all Exxon wells on and off the site, except MWI I The location of
<br /> MWI I is shown in Figure 2
<br />' 2. SUMMARY OF RESULTS
<br /> On 20 May 1998, 25 wells were monitored for the presence of LPH, using an optical interface
<br />' probe LPH was observed in well V4 with an apparent thickness of 0 07 feet The approximate
<br /> groundwater flow direction on 20 May was to the north-northeast, with a gradient of
<br /> approximately 0 003 to 0 02 (Figure 3), which is consistent with previous groundwater
<br />' monitoring data for the site Groundwater elevations on 20 May are presented in boldface type
<br /> in Table 1, along with previous data, and are shown in Figure 3 Field documents are included as
<br /> Appendix A
<br />' After the depths to water were measured, wells MW2—MW13, RW 1, RW2, RW4, V2, V3, Pl,
<br /> P2, IWI, UVB-MWI, and UVB-MW2 were purged by vacuum truck and sampled At least
<br /> 3 well casing volumes of purge water were removed from each well with the exception of three
<br /> wells Wells MW3, MWS, and MW6 dewatered after approximately I casing volume was
<br /> removed Each of these three wells was allowed to recover to at least 80 percent of its original
<br /> level prior to sampling After purging, groundwater samples were collected with factory-cleaned
<br /> disposable polyethylene bailers Groundwater samples were collected in 40-m1 VOA vials The
<br /> vials were labeled and stored in an ice-filled cooler and transported under chain of custody The
<br /> groundwater samples, a field-prepared rinse blank, and a laboratory-prepared trip blank were
<br /> submitted to Sequoia Analytical, where they were analyzed for TPH-g by California
<br /> EPA-modified EPA Method 8015 and for BTEX by EPA Method 8020 The samples were also
<br /> WM1 73942 Q598 TX I
<br />
|