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

ASPECT CONSULTING 16 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 2-11, 2-12, and 2-13 are water table elevation contour maps with inferred groundwater flow directions from the November 2013, May 2014, February 2016, and March 2017 and March 2017 measurements, respectively. Given the large number of wells measured, these data sets provide the most complete picture of water table elevations and thus interpreted groundwater flow directions for the fill aquifer system within the Upland Area. Apart from the Site-wide measurements, water level data were also collected in wells being sampled during quarterly groundwater monitoring events for the IA confirmation groundwater monitoring program (August and November 2014, February and November 2015, and May and August 2016) and in July and September 2017. Water levels were also measured in the five monitoring wells sampled at the end of September 2015. These data are presented in Table B-1 of Appendix B. However, data during the groundwater sampling events were collected over a few days and at variable tidal stages, so were not a Site-wide “snapshot” of water levels like the November 2013, May 2014, February 2016, and March 2017 data sets. Consistent with the prior data, the recent groundwater elevation contour maps indicate the expected general east-to-west groundwater flow directions across the Upland Area, with discharge to the East Waterway, but with localized flow direction variations. SEASONAL AND LONGER-TERM GROUNDWATER LEVEL CHANGES The groundwater levels across the Site show significant seasonality, with approximately 1- to 3-foot higher water levels in the wet season than occur in the dry season. Figure 2-14 depicts the measured change in water levels relative to a September 2012 baseline for five wells that are distributed throughout the inland portion of the Upland Area and having long-term monitoring records 6. Because some wells were decommissioned during mill demolition, data from proximate paired wells are combined to achieve the long-term record (e.g., wells MW-4 and BCT-MW-108). In addition to seasonal changes, the water table beneath the Upland Area has risen somewhat following completion of mill demolition in 2013. The water table rise is attributable to the Spring 2013 removal of approximately 32 acres of impervious surfaces that covered the mill property (impervious surface remains in the northern part of the property). Precipitation that prior to demolition ran off impervious surfaces as stormwater now infiltrates into the permeable surface of crushed material covering the 32 acres. The longer-term rise is more apparent in wet season (high) water levels, whereas dry season levels appear more consistent over time. Wet season water level data collected prior to demolition are only available for two inland wells7: February 2012 measurements from former wells MW-3 and MW-4 located in the former Bunker C Above Ground Storage Tank (AST) area immediately north of the warehouse (their data are the two dashed lines on Figure 2-14). 6 Shoreline wells are excluded from the analysis since their measurements were commonly collected at variable low tide levels (for sampling), which introduces bias when evaluating a long-term change for the Upland Area average condition. 7 And from four shoreline wells (MW-1, MW-2, MW-5, and MW-6; Table B-1 in Appendix B).