COMPLIANCE INFO_EW-5 INSTALL PERMIT PACKAGE 2/14/25

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Mr. Brenden Kenny Central Valley Regional Water Quality Control Board February 1, 2023 www.arcadis.com 3/6 include triple rise for sampling devices and pressure washing (or equivalent) of drilling equipment between drilling locations. Extraction well design will be aided by the lithologic conditions logged during drilling and the collection of soil samples from the adjacent piezometer locations. Soil samples will be collected from the intermediate saturated zone for sieve analysis from the potential extraction well screen interval and will be used for the extraction well slot size and filter pack design. After the extraction well has been designed and well materials sourced the extraction well will be installed. Soil cuttings, development water, and other investigation derived waste generated during the boring advancement and/or well completion activities will be stored at the site in properly labeled California Department of Transportation approved containers. Soil cuttings will be transferred and disposed of in the Landfill. Development water will be allowed to settle before being transferred to the leachate collection pond at the Landfill, with the remaining solids disposed of as solid waste. Monitoring Well and Piezometer Design The proposed groundwater monitoring wells and piezometers are located on Figure 1, with design presented in Table 1 and Attachment 3. The design of each piezometer and monitoring well will consist of a 2-inch schedule 40 polyvinyl chloride (PVC) pipe, with depth and screen interval comparable to the extraction well and lithology encountered. The piezometers and monitoring wells will be completed with 0.01-inch slot size screen, matching filter pack, anticipated as #2/12 silica sand, ensuring that a minimum of 3 feet of sand extends above the screen. Additional installation details are provided in the Work Plan (Arcadis 2019) and the Revised Work Plan Addendum (Arcadis 2022b). Extraction Well Design The proposed extraction wells are located on Figure 1, with the well design details presented in Table 1 and in Attachment 3. The design for each well will consist of a 6-inch schedule 80 PVC riser and stainless-steel wire wrap screen, with 20-30 feet length of screen, slot size to be determined by sieve sample analysis, and a 5-foot blank sump. The well screen will be positioned in the intermediate water bearing zone targeting the most permeable materials. The actual depth and well design will depend on the materials encountered at each location. Centralizers will be placed at the top and bottom of the screen and close to the surface. The screen interval will be backfilled with silica sand to match the respective screen slot size, ensuring that a minimum of 5 feet of sand extends above the screen. The wells will be periodically surged during placement of the filter pack to consolidate the sand. The extraction well annulus above the sand interval will be backfilled with a minimum of five feet of hydrated bentonite chips/pellets. Depth soundings will be utilized to evaluate the thickness and uniformity of the sand pack and bentonite seal, to assure that no bridging occurs. The remaining annulus will be filled to the ground with a neat Portland cement grout, pumped into place using positive displacement tremie techniques. The well screen dimension, material, and slot size may be subject to change based on geologic observations. The extraction wellheads will be completed as required to enable pump installation and conveyance line installation to the treatment system, including a concrete apron.