3815_PGSF WMVD Pkg 2_Vol 4-2_03.03.2026_BXWA_Certified

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 105 encountered at depths ranging from 37 to 52 feet bgs in all borings, except the easternmost boring location (LP-B-06), where it was encountered at 29 feet bgs. In all borings except LP-B-06 and LP-MW-04, a layer of sawdust was observed on top of native soil, at thicknesses ranging generally from 2 to 10 feet. The sawdust contained petroleum-like odors and sheen, which is interpreted to be attributable to lube oil used in historical operations of the Clark-Nickerson Mill. Deep monitoring wells (LP-MW-03, LP-MW-05, LP-MW-06, and LP-MW-07; Figure 6-C1) were installed with screens installed across the sawdust layer to evaluate potential impacts to groundwater from detected TPH in sawdust, as discussed further below. The fill soil that overlies the sawdust or is present overlying native soil in areas where sawdust was not observed, consists predominantly of silty sand and sandy silt with debris (concrete, brick, asphalt, wire, woody debris) and shell fragments. The Log Pond fill soil is siltier than the dredge fill soil that is present across most of the rest of the Upland Area. One IA area is located within the Log Pond Area (Figure 6-C1). Test trenches, excavated in the location of a geophysical anomaly detected in the southcentral portion of the former log pond, identified the buried concrete foundation and footings of the former chip conveyor. A petroleum sheen was observed on shallow seepage in one of the exploratory trenches, and soil samples collected from the trenches contained TPH-G, TPH-D+O, total cPAHs, and mercury above the PCLs. During the second IA, the Log Pond Chip Conveyor area was excavated to remove concentrations of TPH and total cPAHs in soil, as well as mercury, that exceeded the PCLs on the east side of the concrete foundation. The IA removed approximately 403 tons of contaminated soil from the Log Pond Chip Conveyor Area (Aspect, 2021). For current conditions, the constituents detected in one or more samples of the Log Pond Area media at concentrations exceeding their respective PCLs are as follows:  TPH-D+O and total xylenes in soil  Total cPAHs in soil and groundwater  Naphthalene, 2-methylnaphthalene, acenaphthene, and dibenzofuran in soil  Arsenic, copper, lead, mercury, and nickel in soil and groundwater  Zinc in soil  PCP in groundwater  Total PCBs in soil  Vinyl chloride in groundwater Constituents that were not detected at concentrations greater than the PCLs in soil or groundwater samples from Log Pond Area include TPH-G, BTEX, VOCs, dioxins/furans, and the SVOCs and metals not specifically included in the previous list. The sample locations for constituents detected at concentrations exceeding the PCLs in the Log Pond Area of Unit C are presented on Figures 6-C2 through 6-C11. The data for