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<br /> Mr. M. ScottMansholt—CEMC
<br /> Fourth Quarter Groundwater Monitoring and Sampling Report and
<br /> 2005 Annual Summary December 22,2005
<br /> Vernalis Pump Station, Vernalis, California Page 4 of 7
<br /> groundwater samples analyzed. However, TPHd and PAHs were detected in all the grab
<br /> groundwater samples analyzed.
<br /> 2005 Investigation.7 In May 2005, SAIC advanced six soil borings (SB-22 through SB-36) and
<br /> three well borings (MW-5 through MW-7) at the site. The soil and well borings were advanced
<br /> to various depths between 40 and 71.5 feet bgs. Based on the soil chemical analytical results, it
<br /> appeared the affected soil north-northwest, north-northeast, south-southwest, and south-southeast
<br /> of the former boiler house and pump house has been laterally delineated. Based on the grab
<br /> groundwater chemical analytical results, it appeared that affected groundwater is delineated west-
<br /> northwest of the former pump house and boiler house. However, groundwater north-northeast
<br /> and southeast of the former pump house and boiler house appeared to be affected by dissolved-
<br /> petroleum constituents.
<br /> Arcos Property
<br /> 2003 Site Investigations.' In October of 2003, Geomatrix conducted a preliminary soil and
<br /> groundwater investigation at the Arcos property,which was part of the Former Vernalis Pump
<br /> Station,but was not under environmental investigation prior to 2003. The preliminary site
<br /> investigation included review of public records, historical maps, aerial photographs, the
<br /> geophysical survey, evaluation of current property conditions, and subsurface investigation.
<br /> Between October 20 and 28, 2003, Gregg Drilling,under the supervision of Geomatrix, advanced
<br /> 12 soil borings, ASB-1 through ASB-12, on and around the Arcos property. TPHc were detected
<br /> in borings ASB-1, ASB-2, and ASB-4 at a maximum concentration of 17,000 mg/kg. TPHc were
<br /> not detected in any other borings. Low concentrations of BTEX and PAHs were sporadically
<br /> detected in several soil samples. Geomatrix collected grab groundwater samples from soil
<br /> borings ASB-1, ASB-5 through ASB-8, ASB-10, ASB-11, and ASB-12. TPHd were detected in
<br /> grab groundwater samples collected from borings ASB-1, ASB-5, ASB-6, ASB-7, and ASB-11,
<br /> at a maximum concentration of 2,900 pg/L.
<br /> PETROLEUM DISTRIBUTION IN GROUNDWATER
<br /> Based on the previous soil and groundwater investigations, petroleum-affected soil and
<br /> groundwater have been delineated vertically to a maximum depth of approximately 80 feet bgs.
<br /> The RWQCB approved the delineation results in their letter dated March 19, 2004. Based on the
<br /> 2005 site investigation, it appears that affected soil north-northwest, north-northeast, south-
<br /> southwest, and south-southeast of the former boiler house and pump house is laterally delineated,
<br /> and that affected groundwater is delineated west-northwest of the former pump house and boiler
<br /> house. Groundwater monitoring wells were installed during the May 2005 investigation.
<br /> Monitoring and sampling activities have occurred twice since the wells were installed. A sheen
<br /> of SPO was observed well MW-1. Dissolved-phase crude oil is indicated by TPHd analyses.
<br /> TPHd has been detected in one well, MW-7, at concentrations of 240 and 620 pg/L. No TPHg or
<br /> BTEX have been detected in the groundwater from the site wells. Low levels of PAHs have been
<br /> detected in groundwater from MW-2,MW-3, MW-6, and MW-7.
<br /> 7. SAIL,June 2005,Soil and Groundwater Evaluation,Draft Analytical Results from May 2005 Investigation,
<br /> Vemalis Pump Station,Vemalis California.
<br /> 8. Geomatrix Consultants, Inc.,January 2004,Report of Soil and Groundwater Investigations,Former Roberts
<br /> Property, Vemalis,California.
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