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SHALLOW INJECTION WELL INSTALLATION WORK PLAN <br />arcadis.com <br />2022.02.15 OCC Lathrop_Shallow Injection Well Installation Work Plan_final 3 <br /> On December 12, 2021, injection well IW-4 was installed below the Corcoran Clay in accordance <br />with the Injection Well Installation Work Plan dated February 4, 2020 (Arcadis 2020b). This well <br />was brough online during the reporting period on February 9, 2021. <br /> Between September 2021 and October 2021, a significant decline in well performance was <br />observed at IW-2. By October 6, 2021, the well was no longer accepting flow from the treatment <br />systems, and therefore was taken offline. Assessment and rehabilitation activities consisting of <br />well development and a camera survey, confirmed that a significant well casing failure was <br />present at approximately 275 feet bgs and has rendered this well inoperable. This well will be <br />destroyed. <br /> Between October 29 and November 1, 2021, an initial injection test was conducted at former <br />extraction well EW-07 using a temporary high pressure rated hose connected to the GETS. The <br />initial results of the EW-07 injection test are promising and suggest that this well can operate as <br />an injection well with flows up to 200 gpm or more. The injection test was restarted on November <br />18, 2021 to evaluate long term flows of injection. During the longer-term injection test, no <br />surfacing of groundwater has been observed and only limited water level responses have been <br />observed in adjacent monitoring wells. The well is still operating to ensure that the injection rate <br />can be maintained before installing more permanent piping. A summary of injection test results <br />will be submitted in the first quarter of 2022. <br />Due to the well failure of injection well IW-2 and reduced injection capacity, the treatment systems can <br />operate at flows of approximately 600 gpm. Therefore, additional injection capacity is required to reach a <br />target of greater than 1,000 gpm. Under the WDR a maximum of 1,350 gpm can be injected into the <br />aquifer below the Corcoran Clay and 1,250 gpm to the aquifer above the Corcoran Clay. <br />3 WORK PLAN OBJECTIVE <br />Due to the recent GETS expansion, MBBR installation, and failure of injection well IW-2, additional <br />injection capacity is needed to operate each system at their respective targeted flow capacity. Therefore, <br />the objectives of this work plan is to propose the installation of two shallow injection wells in accordance <br />with the methods described in the below sections. <br />4 SHALLOW INJECTION WELL INSTALLATION <br />Arcadis proposes to install two shallow injection wells (IW-5 and IW-6, shown on Figure 2) in two phases. <br /> Phase 1: Advance two pilot borings from the ground surface to the top of the Brown Clay. The <br />total depth will be based on field observations and identification of suitable permeable zones for <br />fluid injection. Soil samples will be collected continuously from the surface to the total depth to <br />determine the permeable zones for screen placement and to provide sieve samples for filter pack <br />design. <br /> Phase 2: Following the filter pack/screen design and materials procurement, install a 10-inch <br />diameter stainless steel well with wire wrapped screen and PVC blank casing. <br />A summary of pre-field and proposed field activities are outlined in the below sections. A schematic of the <br />preliminary injection well construction is presented on Figure 3.