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soil are TPHd, BTEX and MTBE. Soil has also been tested for TPHg, TBA, TAME, ETBE,
<br /> _ DIPE, EDB, 1,2-DCA, McOH and EtOH but no detectable concentrations of any of these
<br /> '} chemicals were reported in any soil samples. I-t is important to note that natural attenuation over
<br /> time has almost certainly resulted in reductions in petroleum hydrocarbon concentrations thus
<br /> rendering historic soil data, much of which was collected in the late 1990's, likely not
<br /> representative of current conditions.
<br /> Historical depth to groundwater beneath the site during the environmental monitoring period
<br /> (1997 to 2009)has been as shallow as 6.2 feet bgs and has averaged about 10 feet bgs. Based on
<br /> i this information, Stratus estimates that the vadose zone is generally only the first 5 feet bgs, the
<br /> fully saturated zone is about 10 feet and deeper, and that the intermediate interval between the
<br /> vadose and saturated zone (5 to 10 feet bgs) at the site represents the capillary fringe which can
<br /> be a `smear zone' (i.e. an area where petroleum hydrocarbons on or near the water table surface
<br /> would be shifted and redistributed as the groundwater surface fluctuates over time).
<br /> Given the fine-grained nature of soil within the uppermost 10 feet bgs at the site, it is unlikely
<br /> that contaminants would migrate in soil away from the source areas. In general, the lateral extent
<br /> of soil impact beneath the site is limited. Of the 106 total soil samples collected at the site and in
<br /> borings drilled at properties/areas surrounding the site, 5% of the samples were collected in the
<br /> vadose zone, 32% were collected in the smear/capillary fringe zone, and the remaining 63% were
<br /> collected beneath the water table. Of the 106 total soil samples, 75% of these soil samples
<br /> contain no concentrations of any petroleum hydrocarbons or fuel additives. Of the remaining
<br /> 25% that did contain detectable concentrations of one or more of the COCs (twenty-seven soil
<br /> ( 1 samples), two were collected in vadose soil (at depths of 4 feet bgs), six were collected in the
<br /> �✓ `smear'/capillary fringe zone (at depths of 6, 8, and 9 feet bgs) and the remaining nineteen were
<br /> collected beneath the water table in fully saturated conditions (at depths of 10.5, 15, 16, 18, 20,
<br /> 21, 22, 23, and 40 feet bgs).
<br /> Vadose and Smear/Capillary Fringe Zones: The six smear/capillary fringe and two vadose soil
<br /> samples that contained some impact were located near the former southern UST (132, SWNW,
<br /> GP-12), near the northern USTs (GP-4, GP-3) and downgradient to the northeast of the northern
<br /> USTs (GP-7, CPT-8). The maximum historic concentration of TPHd in the smear zone (1,000
<br /> mg/kg) was reported at a depth of 6 feet bgs at boring B-2 just outside the former southern UST
<br /> area. The maximum historic concentration of MTBE in the smear zone (0.064 mg/kg) was
<br /> reported at a depth of 9 feet bgs at boring GP-12 also located in the southern UST area. Based
<br /> on the distribution of samples and magnitude of impact to soil, the lateral extent of impact to soil
<br /> surrounding both former source areas (USTs) appears adequately characterized.
<br /> Saturated Zone: The twenty-one soil samples collected from beneath the water table that
<br /> contained some impact were located near the former southern UST (GP-9), near the northern
<br /> USTs (TK1E, TK2E, TK2W, GP-2; MWO-I x, MW-7, CPT-2, CPT-3) and downgradient to the
<br /> northeast of the northern USTs (GP-6, GP-7, GP-9, CPT-8, MW-8, and MW-9). The maximum
<br /> historic concentration of TPHd beneath the water table (660 mg/kg) was reported at a depth of
<br /> 10.5 feet beneath the northern former USTs. The maximum historic concentration of MTBE in
<br /> soil beneath the water table (0.46 mg/kg) was also reported at a depth of 10.5 feet bgs beneath
<br /> F ` the former northern USTs.
<br /> Page 13 STRATUS
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