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I I I March 2006 4 053-2442 Second Addition (probes GP-32 and GP-34, Figure 2), one through the concrete floor of the First Addition (probe GP-33, Figure 2), and three off-site on the east side of Hamline Avenue (probes GP- 16 through GP-18, Figure 2). Two soil samples and 19 groundwater samples collected during the Supplemental Phase II ESA were submitted for VOC analysis and a subset of groundwater samples was also analyzed for GRO. I I I Laboratory analytical results indicated one soil sample, collected adjacent to a floor drain in the First Addition (probe GP-33, Figure 2) at a depth of two to four feet below grade, contained tetrachloroetehene at a concentration of 4.8 mg/kg. VOCs were below detectable concentrations in the other soil sample submitted for analysis. I I I I I I Detectable concentrations of one or more VOCs were measured in six of the 19 shallow groundwater samples collected from push probes. The highest tetrachloroethene concentration (820 /lg/l) was measured in a groundwater sample collected immediately east of the First Addition (probe GP-31, Figure 2). Tetrachloroethene was present in the water sample collected from an on-site push probe advanced approximately 25 feet west of the eastern property boundary (probe GP-20, Figure 2). VOCs were not measured at detectable concentrations in any groundwater samples collected from push probes advanced off-site, but. 2.0 PROPOSED SCOPE OF WORK Based on investigative work completed at the site to date, it appears VOCs measured in groundwater beneath the site originates near the First Addition. Work described herein focuses on further definition of the source of VOCs and further delineation of VOC-affected groundwater. Also included in this work plan is a description of work developed to assess potential affects on the local groundwater flow system as a result of a buried water line corridor along the east side of Hamline Avenue. Details regarding these plans are provided below. 2.1 Source Delineation I Measurable concentrations ofVOCs have been found in near surface soil samples collected above the water table at two locations; one just east of the First Addition (probe GP-4, Figure 2) and one from beneath the concrete slab underlying the First Addition (probe GP-33, Figure 2). In an effort to better delineate the source ofVOCs, we propose to advance up to approximately 20 push probes through the concrete slab underlying the First and Second Additions, and in the area just east of the First Addition, to obtain near surface soil samples for VOC analysis. Soil samples will be collected from a depth of one to two feet below grade/surface. The soil samples will be analyzed on-site in a mobile laboratory so that analytical results can be used to direct subsequent borings. Ten percent of soil samples collected from the suspected source area will be submitted to a fixed laboratory for confirmation analysis. Parameters and reporting limits for the mobile laboratory are listed in Table 2. I I The fITst push probe would be installed relatively near probe GP-33. If measurable concentrations of VOCs are found in the first soil sample, subsequent probes will be installed at a distance of 5 to 10 feet from the first probe to the extent possible, given structure and utility layout. Probe locations will systematically "step-out" in a grid pattern until measurable VOC concentrations are no longer found. The area targeted for source delineation is shown on Figure 2. Once the source area(s) is/are delineated, additional soil samples will be taken at various depth intervals to determine the vertical concentration gradient of VOCs in the unsaturated zone. Soil samples will not be collected from the saturated zone. I I I I