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petroleum hydrocarbon constituents were also detected in the groundwater samples collected
<br />from the newly installed monitoring wells (MW -1 through MW -3). During the initial groundwater
<br />sampling event on September 26, 2011, concentrations of TPHg ranged from 760 to 12,000
<br />micrograms per liter (Fig/L), TPHd ranged from 64 to 1,400 ❑g/L, and benzene ranged from 4.3
<br />to 180 11g/L.
<br />Between September 26, 2011, and September 10, 2012, GHD (formerly W&K) conducted the first
<br />five quarterly monitoring events at the site. Beginning in the fourth quarter 2012, the property's
<br />new owner, Huntbrook, contracted RDM to perform future groundwater sampling, assessment,
<br />and remediation activities associated with the site.
<br />Between October 7 and December 3, 2013, RDM installed, surveyed, developed, and sampled
<br />monitoring wells MW -4, MW -6, MW -7, and MW -8. RDM also advanced one soil boring (RDM-1)
<br />inside the former station building, adjacent to the former fuel dispenser island; and attempted to
<br />advance a cone penetrometer (CPT) boring (CPT -1) to a depth of approximately 100 fbgs for
<br />vertical groundwater delineation, but refusal was encountered at approximately 70 fbgs due to a
<br />combination of geologic conditions and equipment limitations. The results of the investigation are
<br />summarized in RDM's Report Summarizing Installation of Monitoring Wells MW -4, MW -6, MW -7
<br />and MW -8, and Soil Boring RDM-1 and Fourth Quarter 2013 Groundwater Sampling, dated
<br />February 12, 2014.
<br />Between July 18 and 20, 2014, RDM supervised the installation of groundwater monitoring well
<br />MW -1B, soil vapor extraction wells SVE-1A/B and SVE-2A/B, and air sparge well AS -1. The
<br />purpose for deep monitoring well MW -1 B was to assess potential petroleum hydrocarbon impacts
<br />to the deeper groundwater -bearing zone (herein referred to as the "B" Zone) beneath the subject
<br />property. The purpose for the soil vapor extraction and air sparge wells was for performing remedial
<br />pilot testing. Results of the investigation are summarized in RDM's Report Summarizing Installation
<br />of Monitoring Well MW -1B, and Pilot Test Wells AS -1, SVE-1A/B and SVE-2A/B, dated August 15,
<br />2014.
<br />On July 24 and 25, 2014, RDM performed a 16 -hour (4 hours on each well) soil vapor extraction
<br />(SVE) test on SVE-1A/B and SVE-2A/B. RDM collected one air sample from each of the four wells
<br />for laboratory analysis. The TPHg concentrations in the vapor results ranged from 1,200 ppm in
<br />SVE-1A to 26,000 ppm in SVE-2B. Based on the average vapor concentration of 11,725 ppm
<br />from the four samples, RDM estimates that 242.63 pounds of vapor equivalent petroleum
<br />hydrocarbons (39 gallons of gasoline) were removed during the 16 -hour test. Considering the
<br />SVE test data, RDM's experience, soil lithology, and depth to water, RDM estimates there may
<br />be a residual of 10,000 to 20,000 pounds of vapor equivalent hydrocarbons (or 1,600 to 3,200
<br />gallons of gasoline) remaining in soil beneath the site. Results of the SVE pilot testing are
<br />summarized in RDM's Semiannual Groundwater Monitoring Report — Third Quarter 2014 &
<br />Remediation Pilot Testing Results Report, dated November 9, 2014.
<br />On August 25 through 29, 2014, RDM performed a 96 -hour air sparge test on AS -1. Utilizing a
<br />5 -hp compressor, an airline, and rotometer, RDM connected the air compressor to air sparge
<br />well AS -1. The compressor was setup inside the old station building to protect the equipment
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