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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 2 <br />Following this second phase of expansion, the treatment capacity of the combined systems was <br />increased to 1,350 gpm. <br />Groundwater treatment and injection of treated groundwater are regulated in accordance with Regional <br />Water Quality Control Board (RWQCB) Waste Discharge Requirement (WDR) Order R5-2021-0011, <br />issued March 4, 2021. Under the WDR a maximum of 1,350 gpm can be injected into the aquifer below <br />the Corcoran Clay and 1,250 gpm to the aquifer above the Corcoran Clay. <br />The GETS and MBBR are currently limited to a total flow of approximately 600 gallons per minute due to <br />treated water injection capacity constraints. This volume is below the permitted treatment and injection <br />capacity limit, and is in part due to decreased capacity due to injection well failure and declining injection <br />capacities in operational injection wells. Therefore, additional injection capacity is required to increase the <br />overall injection capacity. <br />2.3 Injection Network and Capacity <br />Extracted groundwater is conveyed to the treatment system, treated, and injected into four onsite injection <br />wells that are screened below the regionally extensive Corcoran Clay (deep zone injection wells; IW-1, <br />IW-2, IW-3R, and IW-4 as shown on Figure 2); and two shallow wells screened above the Brown Clay <br />(shallow zone injection wells; INJ-13 and EW-07). The deep zone injection wells inject treated water at <br />depths of ranging between 300 to 696 feet bgs. <br />Changes in the injection well network with time are summarized below: <br /> Between September 27, 2013 and July 2015, INJ-13 (formerly EW-03) was brought on-line to <br />inject water in the permeable zone above the Corcoran Clay. However, by 2015, the injection <br />rate declined to 20 gpm, at which stage the well was taken off-line, the injection at this location <br />suspended. In 2020, the injection well INJ-13 was brought back online to conduct a limited <br />injection test to evaluate the injection well performance. The work was conducted in accordance <br />with the February 25, 2020, Shallow Piezometer Installation and Injection Test Work Plan <br />(Arcadis 2020a). Based on the results, the injection test was extended for an additional four <br />weeks into the third quarter of 2020, as approved by the RWQCB. Injection of treated water into <br />INJ-13 on a regular basis was re-implemented in February 2021. <br /> In 2014, INJ-14 was installed with the screen positioned above the Corcoran Clay, but was never <br />brought online. This well was destroyed in February 2018 prior to offsite development in <br />accordance with the Well Destruction Work Plan Addendum dated December 21, 2017 (Arcadis <br />2017). <br /> On May 23, 2019, injection well IW-3 was installed below the Corcoran Clay in conjunction with <br />treatment system expansion and was brought online in third quarter 2019. However, this well <br />was shut down after approximately one month of operation due to a failure of the cement surface <br />seal. This well was destroyed on February 14, 2020 in accordance with the IW-3 Well <br />Destruction Work Plan Addendum dated December 6, 2019. <br /> In November 2019, IW-3R was installed below the Corcoran Clay as a replacement for IW-3. <br />Injection well IW-3R was brought online on March 4, 2020.