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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 19 Tidal study data from nearshore monitoring wells REC7-MW-1, REC7-MW-2, REC7-MW-3, REC7-MW-4, UST68-MW-5, and UST70-MW-2 (Figure 2-8) were determined to exhibit suitable tidal response to allow application of the Ferris (1963) methods. Because Upland Area groundwater’s highest beneficial use is discharge to the East Waterway, it is appropriate to focus the K estimates on the shoreline area. Table 2-2 presents the input data and the resulting K estimates for the six wells. The average (geometric mean) of the K estimates from the two methods represents a best-estimate K value for each well. The estimated K ranges from 5 x 10-4 centimeters per second (cm/sec) at REC7-MW-1 in Unit E to 3 x 10-2 cm/sec at UST70-MW-2 in Unit B 9 (Table 2-2). This K range, and a site-wide geometric mean K of 5 x 10-3 cm/sec from the six wells’ estimates, are considered reasonable for the sandy dredge fill comprising the bulk of the Upland Area fill unit. SLUG TESTING FOR LOG POND FILL AND SAWDUST UNIT Because tidal response was not observed in Log Pond shoreline wells, the tidal study method for estimating K specific to the Log Pond fill could not be conducted, as stated above. Therefore, slug tests were performed to estimate K for subsurface materials in the Log Pond area, in accordance with Aspect (2017b). Slug tests were conducted in wells LP-MW-2, LP-MW-4, and REC6-MW-2 screened in the Log Pond fill, and wells LP-MW-3, LP-MW-5, LP-MW-6, and LP-MW-7 screened across the deep sawdust layer. Except for well LP-MW-2, two or three tests (rising and falling head) were conducted in each well and the average K from the replicate tests were used to represent K for that location. Because of the very long water level recovery during testing of well LP-MW-2, only one test was conducted for that well. A geometric mean K was then calculated for the Log Pond fill and for the sawdust layer hydrostratigraphic units using the respective well estimates. Table 2-3 presents the slug test analysis parameters and results for the Log Pond wells. The geometric mean K for the Log Pond fill is 8 x 10-5 cm/sec, approximately 70 times lower than the Site-wide average K for the dredge fill outside of the Log Pond. The low K is consistent with the generally siltier fill material observed within the Log Pond. 2.4.4.2.4 Groundwater Velocity Estimates The K estimates can be used, with measured nearshore tidally averaged hydraulic gradient and estimated effective porosity, to estimate horizontal average linear (seepage) groundwater velocities for the nearshore portion of the Upland Area. A groundwater seepage velocity for the shoreline area is calculated using Darcy’s Law of the form: v = K * I / ne, where:  v = seepage velocity (feet/year);  K = hydraulic conductivity (feet/year); 9 For purposes of the RI/FS data analysis as described in Section 6.2, the Upland Area is divided into five Units A through E, from south to north (see Figure 2-3).