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

ASPECT CONSULTING 14 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 2.4.4.2.1 Pre-RI Water Level and Tidal Study Data During the Phase 2 ESA (Aspect, 2013a), water level measurements were collected during February, July, and September 2012 from a variable number of Upland Area monitoring wells existing at the time. This included (elevations relative to NAVD88 vertical datum):  A low-tide set of groundwater level measurements was collected in the existing six monitoring wells on February 17, 2012, just before a low tide of elevation approximately -2 feet;  A low-tide set of groundwater level measurements was collected from 35 wells on July 3, 2012, shortly after a low tide of elevation approximately -5 feet, and a high-tide set of measurements was collected on July 6, 2012, shortly after a high tide of elevation of approximately 10 feet; and  A low-tide set of groundwater level measurements was collected from 49 wells on September 14, 2012, shortly after a low tide of elevation approximately -1 feet, and a high-tide set of measurements was collected on September 13, 2012, shortly before a high tide of elevation approximately 8 feet. Table B-1 in Appendix B presents the collective groundwater level data, along with monitoring well survey data, for the Upland Area monitoring wells. Groundwater in the fill is hydraulically connected to the East Waterway, and tidally induced water table fluctuations near the East Waterway range between about 2 and 7 feet depending on the location, based on data from the tidal study data conducted in 2012 as part of the independent Phase 2 ESA (Aspect, 2013a). The Upland Area tidal study was conducted over a period of large tidal fluctuations (maximum of approximately 15 feet) to evaluate effects of tidal fluctuations on nearshore groundwater levels, and thus flow directions, throughout the tidal cycle. The tidal study was conducted July 3 through 6, 2012, and involved the collection of continuous water level measurements throughout a 72-hour period at 12 upland monitoring wells (Figure 2-4): shoreline wells REC7-MW-1, REC7-MW-2, MW-6, UST70-MW2, REC7-MW-3, and REC7-MW-4, and inland wells NRP-MW-4, UST69-MW-1, AP-MW-1, REC5-MW-1, UST68-MW-1, and UST-68-MW-5. Tidal fluctuations in the East Waterway were also measured throughout the 72-hour period (station TM-1 depicted on Figure 2-9). Figure 2-8 depicts the tide and groundwater elevations over time collected during the 72-hour tidal study. During that 72-hour tidal study, wells located within about 100 feet of the shoreline showed clearly identifiable tidal response, with average tidal efficiencies4 ranging from 0.08 to 0.69, and tidal lag times 5 ranging from 0.6 to 2.5 hours (Table 2-2). The tidal efficiencies and lag times presented in Table 2-2 represent the arithmetic average of water level responses measured during one major falling tide, one major rising tide, one minor 4 “Tidal efficiency” is the ratio of the groundwater elevation change to corresponding tide elevation change. 5 “Tidal lag time” is the time difference between tide elevation peak and corresponding groundwater elevation peak.