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

ASPECT CONSULTING 20 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025  I = tidally averaged horizontal gradient (feet/foot); and  ne = effective porosity (dimensionless). A groundwater seepage velocity is calculated for fill unit within each Unit, and for the Log Pond fill and sawdust layer, using the average K value and hydraulic gradient for the Unit, as presented in Table 2-4. A Darcy velocity (also known as specific discharge), for use in volumetric flux calculations, is also calculated for each Unit by not including effective porosity in the equation. The average K values by Unit were derived as described above and are presented in Tables 2-2 and 2-3. An average hydraulic gradient along the shoreline of each Unit was calculated based on the tidally averaged (net) groundwater elevation contours presented on Figure 2-9. To calculate an average gradient for each Unit, the horizontal distance between the tidally averaged groundwater elevation contour located closest to the shoreline and the next groundwater elevation contour inland was calculated at 25-foot increments along the higher groundwater elevation contour. The gradient for each point was then calculated as the 1-foot elevation difference divided by the horizontal distance, and the average of the 25-foot point measurements within each Unit is applied as the average gradient for the Unit. The nearshore gradient within the Log Pond fill was calculated as the average of the tidally averaged groundwater elevations for wells REC6-MW-2 and MW-6 as depicted on Figure 2-9. The nearshore gradient for the Log Pond sawdust layer was calculated the difference between shoreline well LP-MW-7 groundwater elevation and the average tide elevation for a 2-day period in which the groundwater measurement was collected, averaged for the July and September 2017 groundwater measurements. Table 2-4 presents the tidally averaged hydraulic gradient for the fill unit in each Unit and for the Log Pond hydrostratigraphic units. Applying the Unit-specific average K and gradient estimates, and an assumed site-wide effective porosity of 0.2 based on literature values, the Upland Area groundwater seepage velocities in the fill unit outside of the Log Pond are estimated to range from 3 feet/year in Unit E to 100 feet/year in Unit B, with the variation due primarily to the K difference. The corresponding Darcy velocity estimates range from 1 cubic feet/square foot per year (ft3/ft2-year) in Unit E to 20 ft3/ft2-year in Unit B. Within the former Log Pond, the estimated groundwater seepage velocities in the lower-permeability Log Pond fill and sawdust unit are 0.8 and 5 feet/year (Darcy velocities of 0.2 and 0.9 ft3/ft2-year, respectively) (Table 2-4). 2.4.4.2.5 Estimates of Groundwater Flux to East Waterway The volumetric flux of groundwater (cubic feet per year [ft3/year]) from the fill aquifer to the East Waterway is also estimated for each Unit. To do so, the Unit-specific cross sectional area for flow perpendicular to the groundwater flow direction is estimated as the shoreline length multiplied by the aquifer thickness along the shoreline (thickness estimated as described above). The volumetric groundwater flux from each Unit is then calculated by multiplying the respective Darcy velocity by the shoreline cross sectional area. The estimated groundwater fluxes from the fill unit (excluding the Log Pond) to the East Waterway range from 10,000 ft3/year in Unit E to 420,000 ft3/year in Unit B. Within the Log Pond, the estimated groundwater fluxes from the Log Pond fill and sawdust unit are