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Stantec
<br /> Site History and Previous Investigations
<br /> Stockton Charter Way Commingled Plume
<br /> February 15, 2011
<br /> In May 2001, SECOR contracted Gregg Drilling & Testing, Inc. (Gregg) to advance four soil
<br /> borings (SB-5 through SB-8) using CPT technology. A second borehole was advanced
<br /> adjacent to each soil boring, and groundwater samples were collected at discrete intervals
<br /> based upon the pore pressure observations. No soil samples were collected. TPHg,
<br /> CPT/membrane interface probe technology, and DP-1 and benzene, and MTBE were detected
<br /> in groundwater samples collected from these borings at concentrations up to 100,000, 6,900,
<br /> and 280 pg/L, respectively. These activities are summarized in the SECOR Site Assessment
<br /> Report and Work Plan for Further Assessment dated March 5, 2002.
<br /> In a March 4, 2004, Conceptual Site Model, Secor stated that five supply wells were located
<br /> between '/4 and '/2 mile of the site.
<br /> In July and August 2005, SECOR contracted Precision to advance 19 soil borings (CPT-1
<br /> through CPT-10; using DP-3 through DP-10; using direct push technology). No soil samples
<br /> were collected from CPT-1 through CPT-10. TPHg, total petroleum hydrocarbons as diesel
<br /> (TPHd), benzene, and MTBE were detected in soil samples collected during the direct push
<br /> activities at concentrations up to 1,700, 1,600, 3.4, and 0.68 mg/kg, respectively. TPHg, TPHd,
<br /> benzene, and MTBE were detected in groundwater samples collected from these borings at
<br /> concentrations up to 380,000, 210,000, 24,000, and 17,000 pg/L, respectively. These
<br /> activities are summarized in the Blasland, Bouck & Lee, Inc., an ARCADIS company of
<br /> Syracuse, New York Site Assessment Report dated December 18, 2006.
<br /> In January 2008, ARCADIS contracted Cascade Drilling Incorporated of Rancho Cordova,
<br /> California to install nine groundwater monitoring wells (four A zone: MW-4A through MW-7A,
<br /> one B zone: MW-7B, and four C zone: MW-4C through MW-7C). TPHg, TPHd, benzene, and
<br /> MTBE were detected in groundwater samples collected from these borings at concentrations up
<br /> to 380,000, 160,000, 24,000, and 34,000 fag/L, respectively. These activities are summarized in
<br /> the ARCADIS Groundwater Assessment Report dated August 2008.
<br /> A groundwater monitoring and sampling program has been in place at this property since March
<br /> 1995.
<br /> Remediation Activities
<br /> In September 1996, Touchstone Developments Environmental Management (Touchstone)
<br /> supervised the removal of two 10,000-gallon gasoline USTs, one 6,000-gallon gasoline UST,
<br /> one 1,000-gallon waste oil UST, associated dispenser islands and product lines, one dual-post
<br /> hydraulic hoist with tank, two semi-hydraulic hoists, and one sump from the property. The
<br /> 10,000-gallon USTs contained supreme unleaded and regular unleaded gasoline. The 6,000-
<br /> gallon UST contained unleaded plus gasoline. Over-excavation was performed in the former
<br /> UST complex, former product dispenser islands area, and the dual-post hydraulic hoist area.
<br /> The over-excavated areas were sampled and enlarged based upon the analytical sample
<br /> results. Approximately 52 soil samples (T1 through T6, TXS1 through TXS6, TXB1
<br /> through TXB3, UO, UOB, P1 through P7, PXS1 through PSX3, PXB1 through PXB7,
<br /> OX1 , OX2, OXS1 through OXS3, OXB1 through OXB4, RF, RF2, H1 through H4,
<br /> HT, HX, and SUMP) were collected during these activities. TPHg, benzene, MTBE,
<br /> and total oil and grease were detected in soil samples collected during the removal and
<br /> excavation activities at concentrations up to 3,000, 14, 28, 14,000 mg/kg, respectively. These
<br /> Appendix A- Site History and Previous Investigations.doc 4
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