|
Stantec �, �.
<br /> Site History and Previous Investigations
<br /> Chevron and ARCO Commingled Plume No. CP0034
<br /> October 26, 2011
<br /> Since discovery of the pipe leak in 1984, 21 groundwater monitoring wells (E-1 through E-12,_
<br /> BHD-1, BHD-2, PR-1, PR-2, and MW-1 through MW-5), 12 SVE wells (V-1 throug -12), and
<br /> nine AS wells (S-1 through S-9) have been installed.
<br /> In 1998, during the installation of a pay-quick machine, a contractor at the site broke a fiberglass
<br /> product line beneath the southern dispenser island. The broken line was repaired immediately
<br /> and approximately three cubic yards of soil were excavated from beneath the broken product
<br /> line. Soil samples collected after the excavation of the soil contained low levels of petroleum
<br /> hydrocarbons.
<br /> In 1999. one 10,000-aallon, fiberglass gasoline UST, product lines, vapor lines, and dispenser
<br /> islands were removed from the site. ma cracks that appeared to have been created during
<br /> excavation activities were observed in the tank. Soil samples collected from beneath the USTs
<br /> contained maximum GRO, benzene, and MTBE concentrations of 690 mg/kg, 0.692 mg/kg, and
<br /> 0.156 mg/kg, respectively. Soil samples collected beneath the product lines and dispenser
<br /> islands contained maximum GRO, benzene, and MTBE concentrations of 102 mg/kg, 0.298
<br /> mg/kg, and 124 mg/kg, respectively. Di-isopropyl ether, tert amyl-methyl ether, ethyl tert-butyl
<br /> ether, tert-butyl alcohol, and ethanol were reported as non-detect in all soil samples (SECOR,
<br /> 1999).
<br /> One 550-a Ihn, double-walled, fiberglass waste oil UST was removed from the site in 2002.
<br /> r The tank appeared to be in goo condition with no holes or cracks. One soil sample was
<br /> collected from the center of the tank pit at a depth of approximately 11 ft bgs. Hexavalent
<br /> chromium, chromium, nickel, zinc, and lead were reported at concentrations of 1.4 mg/kg, 35
<br /> mg/kg, 38 mg/kg, 49 mg/kg, and 12 mg/kg, respectively. All other constituents analyzed for were
<br /> reported as non-detect.
<br /> On June 12, 2007, SECOR staff oversaw WDC perform the destruction of MW-4 in accordance
<br /> with San Joaquin County Environmental Health Department (SJCEHD) requirements.
<br /> On December 3, 2007 SECOR (now Stantec) submitted a Work Plan for Well Abandonment for
<br /> groundwater monitoring wells E-7, E-8 and BHD-1 due to their location in roadways. Routine
<br /> sampling of these wells presented a significant hazard to the people conducting the field work.
<br /> In a letter dated January 2, 2008, the San Joaquin County Environmental Health Department
<br /> (SJCEHD) approved the destruction of the wells with the provision that wells BHD-1 and E-8 be
<br /> over drilled to depth, and all contents of the wells removed. Stantec requested that the wells be
<br /> pressure grouted to surface during a verbal conversation with SJCEHD in December 2008 to
<br /> avoid the hazards of over drilling in the street. The work, as requested, was approved by
<br /> SJCEHD via email correspondence dated March 27, 2009. Between November 9th and
<br /> November 11, 2009, Stantec supervised Cascade Drilling, LP (Cascade) as they destroyed
<br /> three groundwater monitoring wells (BHD-1, E-7 and E-8). Stantec supervised Ramsey
<br /> Engineering (Ramsey) as they re-paved the former locations of the wells.
<br /> During the summer of 2011, the municipal well on the northeast corner of Ben Holt and
<br /> Plymouth Road was decommissioned.
<br /> 94275 Site History and Previous Investigations.doc 3
<br />
|