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Workpl'�n For Additional Assessment and Feasi ty Study
<br /> Quik Stop Market No. 132
<br /> 3555 West Hammer Lane
<br /> Stockton, California
<br /> To further assess groundwater conditions beneath the site, ATC completed six soil borings (ATC-
<br /> 1 through ATC-6) on March 1, 1999. The purpose of that investigation was to further assess the
<br /> vertical and lateral downgradient extent of methyl tert-butyl ether (MTBE) concentrations in soil
<br /> and groundwater related to the site. TPH-G and BTEX were not detected in any of the soil
<br /> samples. Based on the results of the investigation, it appeared that MTBE has migrated a short
<br /> distance generally down-gradient of the site. The highest MTBE concentration detected in the
<br /> borings was 2,900 gg/L at a depth of 20 feet bgs. A depth discrete groundwater sample was
<br /> obtained in order to define the extent of petroleum hydrocarbons vertically. Based on the results,
<br /> it appeared that petroleum hydrocarbon impact is limited primarily to shallow groundwater(ATC,
<br /> April 1999).
<br /> In order to further define the lateral extent of MTBE concentrations in groundwater related to the
<br /> site, an additional groundwater monitoring well, MW-8 was installed off site. The SJCPHS-EHD
<br /> requested the work in a letter dated April'16, 1999. Monitoring Well MW-8 was screened in the
<br /> local lower aquifer (ATC, December 1999). All of the site wells were sampled in December
<br /> 1999; no concentrations of petroleum hydrocarbons were detected in monitoring well MW-8
<br /> (ATC, January 2000). ,
<br /> To further assess groundwater conditions beneath the site, ATC completed three soil borings
<br /> (SB-1, SB-2, and SB-3) on July 09, 2000. Groundwater samples were collected from the local
<br /> upper and lower aquifers. Four intersecting cross sections were constructed to illustrate the
<br /> vertical and lateral extent of MTBE concentrations in groundwater. Based on the results of the
<br /> investigation, ATC concluded that. TPH-G and MTBE have migrated only a short distance
<br /> generally down gradient on site, in the vicinity of boring SB-1, and off-site at low concentrations,
<br /> in the vicinity of soil borings SB-2 and SB-3. The lateral and vertical extent of petroleum
<br /> hydrocarbons and MTBE at the. site appears to be well defined in all directions, with the possible
<br /> exception of the area to the east-southeast of soil boring SB-3 (ATC, 2000).
<br /> References
<br /> ATC Associates Inc., October 1998, Revised Work Plan For.Additional Groundwater
<br /> Investigation, Quik Stop No. 132, 3555 West Hammer Lane, Stockton, California.
<br /> ATC Associates Inc.; April1999, Additional Groundwater Investigation, Quik Stop No. 132,
<br /> 3555 West Hammer Lane, Stockton, California.
<br /> ATC Associates Inc., December 1999, Additional Groundwater Investigation Letter Report, Quik
<br /> Stop No. 132, 3555 West Hammer Lane, Stockton, California.
<br /> ATC Associates Inc., October 2000, Additional Groundwater Investigation, Quik Stop No. 132,
<br /> 3555 West Hammer Lane, Stockton, California.
<br /> ATC Associates Inc., April 2001, Quarterly Groundwater Monitoring, First Quarter 2001, Quik
<br /> Stop No. 132, 3555 West Hammer Lane, Stockton, California.
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