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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 15 falling tide, and one minor rising tide during the three-day monitoring period. Wells located 200 feet or more from the shoreline did not show a significant tidal response. Well NRP-MW-4, located roughly 400 feet from the shoreline, exhibited small-scale cyclical water level fluctuations (Figure 2-8). However, the fluctuations do not appear to be in response to tides since there is no consistency in timing of groundwater level peaks compared to tide peaks (in fact, there are more groundwater level peaks than tidal peaks in the period of monitoring), and the groundwater level fluctuations are uniform in magnitude regardless of the magnitude of tidal fluctuation (e.g., between low tide and lower-low tide). Of the six shoreline wells monitored for the tidal study, the largest groundwater fluctuations (greatest tidal efficiencies) were observed in the southernmost wells REC7-MW-4 and REC7-MW-3 located adjacent to the slip (approximately 6.9 and 5.1 feet of fluctuation, respectively). Groundwater levels in both wells show a gradual draining as the tide recedes and a rapid rise as the tide rises above the respective water table elevations (Figure 2-8). To the north along the shoreline, maximum groundwater fluctuations of approximately 1.2, 1.1, and 1.9 feet were measured in shoreline wells UST70-MW-2, REC7-MW-2, and REC7-MW-1, respectively. Shoreline well MW-6, located within the footprint of the former Log Pond, showed little fluctuation (approximately 0.3 feet) and with no apparent tidal signature (Figure 2-8). Likewise, well REC6-MW-2, located within the Log Pond footprint north of MW-6 exhibited water level changes of less than 0.2 feet between low-tide and high-tide measurements made in both July and September 2012 (full water level data presented in Table B-1 of Appendix B). The lack of tidal response in shoreline wells MW-6 and REC6-MW-2 is consistent with the low permeability of the Log Pond fill. The tidal study data were analyzed using the method of Serfes (1991) to derive a 72-hour tidally averaged groundwater elevation for each monitoring location. The tidally averaged groundwater elevations, mapped on Figure 2-8, were then used to assess the net (tidally averaged) groundwater flow direction and hydraulic gradients. While nearshore groundwater flow directions reverse diurnally with the tide, the tidally averaged groundwater flow directions along the shoreline of the Upland Area are toward the west with the expected net discharge to the East Waterway (Figure 2-9). Since that study, numerous additional monitoring wells have been installed in the Upland Area and more robust groundwater elevation contour maps developed from the more recent data, as described below. 2.4.4.2.2 RI Water Level Data As part of the RI data collection, groundwater level measurements were collected from all accessible Upland Area monitoring wells during the middle of the tidal range during two different seasonal conditions: from 71 existing monitoring wells on November 26, 2013, and from 103 wells on May 8, 2014 (after installation of the 36 new wells for IA confirmation groundwater monitoring). A supplemental round of Site-wide water levels was also collected from 102 wells on February 8, 2016. In March 2017, during the wettest wet season on record, water level measurements were collected in 68 wells during a groundwater sampling event representing extreme wet season conditions. Figures 2-10,