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Ms. Lori Duncan S E C O R u
<br /> May 27, 2005
<br /> Page 2
<br /> catalytic oxidizer. The SVE system has been deactivated due to high groundwater levels.
<br /> Prior to shutdown, the SVE system extracted approximately 70 pounds of gasoline from the
<br /> soil and groundwater beneath the site and the AS system was deactivated in May 2005.
<br /> The site is scheduled for demolition and UST removal in June 2005, with new USTs,
<br /> dispenser islands, and a station building to be constructed beginning in June 2005. In
<br /> preparation for site demolition, seven onsite groundwater monitoring wells (MW-1, MW-2,
<br /> MW-3, MW-4, MW-5, MW-7, and MW-9) and ten soil vapor extraction/air sparge wells
<br /> (VW-1, GM-1, GM-2, GM-3, GM-4, GM-5, GM-6, GM-7, GM-8 and GM-9) were destroyed
<br /> at the Chevron site in April and May 2005. The replacement of the monitoring wells
<br /> destroyed in May 2005 will occur following the completion of the station rebuild, as
<br /> proposed in SECOR's Work Plan for Well Destruction and UST Removal and the
<br /> addendum to this work plan, described below.
<br /> ARCO
<br /> At the ARCO site, four USTs and associated product lines and dispensers are present. A
<br /> release from a piping leak was discovered in 1984. A release of approximately 2,000
<br /> gallons of gasoline was reported in May 1989, and an unknown quantity of fuel was
<br /> released at the northern dispenser island in 1995. Since discovery of the piping leak in
<br /> 1984, 20 groundwater monitoring wells, 14 soil vapor extraction wells, and nine air sparge
<br /> wells have been installed. A groundwater extraction system was operated intermittently
<br /> from 1984 to 1996. In 1995, a SVE/AS system was installed at the site. The system has
<br /> since been deactivated due to high groundwater water levels, rendering operation
<br /> unfeasible. Currently nine groundwater monitoring wells are sampled quarterly, and
<br /> another 11 wells are sampled semi-annually.
<br /> Groundwater level and flow data suggest the shallow groundwater encountered at both
<br /> sites is a consistent regional water table that flows from south to north under both sites.
<br /> WORK PLAN FOR WELL DESTRUCTION AND UST REMOVAL ADDENDUM
<br /> In SECOR's original Work Plan for Well Destruction and UST Removal, Chevron
<br /> monitoring wells MW-1, MW-2, MW-3, MW-5, MW-7, and MW-9 were proposed to be �• L�'��
<br /> replaced by MW-1 R, MW-2R, MW-3R, MW-5R, MW-7R, and MW-9R, respectively (Figure
<br /> 2). The wells were originally proposed to be installed to 30 feet bgs with 15 feet of well
<br /> screen. Instead, SECOR proposes that wells MW-1 R, MW-2R and MW-3R first-be drilled
<br /> to 60 feet bgs to collect soil and grab groundwater samples for the ve ica a ineation
<br /> investigation. Soil and groundwater sample collection will be performed as described
<br /> below. Boreholes MW-1 R, MW-2R, and MW-3R will be tremie grouted from total depth to
<br /> approximately 20 feet bgs, or the top of the aquitard beneath the first water-bearing zone, if
<br /> encountered. Each well, including MW-5R, MW-7R, and MW-9R, will be installed to
<br /> approximately 20 feet bgs, or the bottom of the first water-bearing zone, with well screen
<br /> between approximately 5 and 20 feet bgs. Well construction details are provided in
<br /> Attachment 2.
<br /> WORK PLAN FOR SITE ASSESSMENT
<br /> In order to delineate the lateral and vertical extent of petroleum hydrocarbons in soil and
<br /> groundwater beneath the site, SECOR proposes the advancement of eight soil borings
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