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Central Valley Regional Water Quality Control Board June 30, 2025 Page 2 carbon (GAC)vessels connected in series.Treated water is used for irrigation purposes by the Ripon Public Schools, and any treated water in excess of the irrigation demand is reinjected into the aquifer via two injection wells (IW-1 and IW-2; both screened in the A and C1 Zones) at the northern end of Ripon Public Schools property.The NATS extraction and injection well locations are shown on Figure 2. Currently the NATS is operating at an average flow rate of approximately 190 to 200 gallons per minute (gpm), which is below the system design flow rate of 300 gpm described in the North Area Groundwater Interim Remedial Action Plan (Haley&Aldrich, 2021).The lower flow rates are caused by the two injection wells having a lower capacity to discharge treated water than anticipated during the design process. Operational data from the NATS to date (flow and pressure at injection wells) is currently insufficient to determine whether the injection capacity limitations are related to biofouling/scaling of the injection well screens, localized lower permeability of the aquifer where the wells are installed, or both.To resolve this, piezometers are needed proximate to the existing injection wells to determine the hydraulic head in the aquifer during system operation.The installation of piezometers close to (e.g., within 5 to 10 feet of) injection wells IW-1 and IW-2 will allow for monitoring the effects of injection on the water level in the injection zone.This information will be used to assess the potential injection flow for each injection well and help to inform: (a) if additional injection wells are necessary to maintain capture; or(b) if using higher injection pressures in the existing extraction wells will allow for higher flow rates without causing negative impacts to the nearby aquifer. WALNUT AVENUE SYSTEM INTERMEDIATE AQUIFER MONITORING WELL The Walnut Avenue System is a groundwater extraction, treatment, and reinjection system that targets the Upper Aquifer(A Zone groundwater) and has been operating since September 2017. Groundwater in the vicinity of the Walnut Avenue System is extracted through two extraction wells: EU-5 and EU-6 (Figure 2). Extracted groundwater is treated by adsorption in two 10,000-pound GAC vessels in series located at 223 Walnut Avenue.Treated water is then conveyed to an injection manifold near the northern end of the former Site and is reinjected using three primary injection wells (IU-1, IU-2, and M- 2A),with a fourth well (EU-3) retained as a backup injection well.All four injection wells are screened in the A Zone. The current groundwater model simulations indicate some Intermediate Aquifer groundwater is captured by extraction well EU-6; however, modifications to the system may help extend the capture in the Intermediate Aquifer.As part of the evaluation,the RAP proposed installing an Intermediate Aquifer monitoring well to assess groundwater conditions northwest of the Walnut Avenue System in the vicinity of wells M-56A and M-57A(Figure 2). Piezometer and Monitoring Well Installation FIELD PREPARATION AND PERMITTING Prior to the start of field activities, Haley&Aldrich will review and update the current Site-specific Health and Safety Plan, obtain well installation permits from San Joaquin County Environmental Health Department, obtain encroachment permits from the City of Ripon for locations proposed in the right-of- way, coordinate access with the property owners (Ripon Public School and Ripon Christian School), and contract with a private utility location subcontractor and a drilling subcontractor. Haley&Aldrich will RICH