CORRESPONDENCE_4/7/22 [REV] APPENDICES W/FIRE PERMIT

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Forward Resource Recovery Facility WDR Technical Report HDR Engineering, Inc. 6 October 2021 Stockton, CA 24-hour, 25-year storm NOAA, National Weather Service, Hydrometeorological Design Studies Center http://hdsc.nws.noaa.gov/hdsc/pfds/ 2.2 Geology The following geological data was obtained from the facility’s JTD, which is hereby incorporated by reference. The Forward Landfill is located in the Great Valley geomorphic province, which lies between the Sierra Nevada Range on the east and the Coast Range on the west. Regional geology includes the following types and origins of sediments, from oldest to youngest: Marine Sequence, Continental Sediment Sequence, and the Victor Formation. Exploratory borings and well installation programs performed at the site indicated that geologic materials beneath the site occur as lenticular units composed of clay, silt, and sand with minor amounts of gravel. Bedding ranges in thickness from a few inches to approximately 20 feet, which is consistent with deposition in a fluvial environment where the course of rivers or streams meanders and is subject to frequent flooding. The sediments observed in borings at the site appear to correspond with Pleistocene age Victor Formation and can be divided into the following three large groups: • Group A: Highly interbedded sand, sandy silt, clayey silt, silt, and clay. Most of the sediments have a highly oxidized appearance (orange-brown color). This group is located from the surface to approximately 28 to 40 feet below ground. • Group B: Interbedded sand, silty sand, silt, and clay. Sediments are less oxidized than Group A (gray-brown color). This group is located from approximately from approximately 28 to 40 feet deep (top) to 55 to 75 feet deep (bottom). • Group C: Fine- to medium-grained sand with some coarse-grained or gravelly layers. A few layers of silt and clay. Color is light brown to yellow brown. This group is located approximately 55 to 75 feet deep (top) to 110 feet (bottom). 2.3 Hydrogeology General As described in the facility’s JTD, incorporated here by reference, the surface soils near the site are primarily Clear Lake clay (CL) and Jacktone clay (ST), which are typical of Victor Formation sediments. The Clear Lake clay occurs primarily on the northern and southern portions of the site, while the Jacktone clay is more prevalent in the middle portion. Subsurface soils generally consist of interbedded layers of sand, silt, and lean clay. Hydraulic Conductivity Forward, Inc. performed a sampling and testing program to assess the permeability of the compost pad areas. The results of that study are included in the Compost Facility Stormwater Improvements Report from Lewis Engineering and in Appendix C of this report. Four samples collected in the southern half of the composting operations area had vertical hydraulic conductivities ranging from 4.9 x 10-6 to 1.5 x 10-7 cm/s. These results are compliant with the parameters of the General Compost Order WDR, which requires a hydraulic conductivity of 1.0 x 10- 5 cm/s or less on the compost pad.