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WDODARR &CURRAN 2008). Previous studies have indicated that TDS concentrations may be higher in the vicinity of Well 21 than in Wells 6 through 10. In September 2014,TDS concentrations in Well 9 and Well 10 ranged from 270 mg/L to 310 mg/L(UNICO Engineering, 2015), which is below the secondary MCL.11 During the same sampling event, concentrations of TDS within Well 21 ranged from 630 mg/L to 660 mg/L, which is above the recommended secondary MCL but well below the upper limit of 1,000 mg/L and suitable for drinking water and irrigation.12 2.3.2.1.3 Industrial Contamination Groundwater contamination has been identified at several locations in the City due to industrial processes. Contamination plumes are associated with pollution from Sharpe Army Depot and Occidental Chemical Corporation (OCC), now owned by J.R. Simplot Company (Simplot).13 Contamination of groundwater at the Sharpe Army Depot consists primarily of trichloroethene, tetrachloroethene, and cis-1,2-dichloroethene. The plume is located at depths of approximately 50 to 150 ft bgs. Due to concerns of potential contamination from the plume,the City abandoned Well 5 and constructed Well 10 as a replacement well. Three groundwater extraction and treatment systems are located at Sharpe Army Depot and are used to treat existing groundwater contamination (RBF, 2009). The OCC plume, in the upper aquifer, consists primarily of the pesticides 1,2-dibromo-3-chloropropane (DBCP) and ethylene dibromide (EDB), and the chemical solvent sulfolane. The OCC has been conducting investigation and remediation activities at the site since 1979, and a groundwater remedial system has been in place since 1982. The current groundwater remedial system extracts groundwater from up to 18 extraction wells and treats the groundwater using granular activated carbon.Treated water is then re-injected into the confined aquifer beneath the Corcoran Clay, which is located between 230 ft bgs and 300 ft bgs. Sulfolane has not been detected in any of the City's wells; however, it has been detected in Simplot's water supply well within 1,000 feet from the City's well field. In July 2018, OCC subsidiary Glenn Springs Holdings, Inc. (GSH) and the City met to discuss the migration of sulfolane to Simplot's supply wells and towards the City's Wells 9 and 10. To prevent further migration of sulfolane towards the City's well field, the City shut down all of its wells in January 2019 and OCC expanded its groundwater extraction system.The City plans to restart Wells 6,7,8,and 10 in late 2020,with pumping monitored to limit plume migration. 2.3.2.1.4 Unregulated and Emerging Contaminants Perfluorooctanesulfonic acid (PFOS)and Perfluorooctanoic acid (PFOA)are organic chemicals synthesized for water and lipid resistance and are used in a wide variety of consumer products as well as fire-retarding foam and various industrial processes.These chemicals tend to accumulate in groundwater,frequently associated with source locations such as a factory or airfield.There are currently no maximum contaminant levels(MCLs)for PFOS or PFOA; however, the SWRCB announced in February 2020 that it is establishing RLs of 10 parts per trillion (ppt)for PFOA and 40 ppt for PFOS (SWRCB, 2020).14 Under a new California law (Assembly Bill 756), if a water system receives a SWRCB These values are generally confirmed by the City's Consumer Confidence Reports for 2014 and 2015,where TDS concentrations in groundwater ranged from 280 mg/L to 387 mg/L.Since Well 21 was inactive during this period,these values are representative of water quality within Wells 6 through 10. 12 Samples were collected in two private wells in the vicinity of Well 21.Concentrations of TDS in these wells ranged from 500 mg/L to 570 mg/L. 13 The OCC site is currently owned by J.R.Simplot Company,which operates two supply wells for on-site potable and production uses.OCC retains remediation responsibilities through its subsidiary Glenn Springs Holdings,Inc. 14 This action follows the SWRCB's August 2019 reduction of the NLs for the two contaminants from 14 to 5.1 ppt for PFOA and from 13 to 6.5 ppt for PFOS.A notification level is a health-based concentration of a contaminant in drinking water that warrants notification and further monitoring and assessment. Califia(0011533.00) 29 Woodard&Curran, Inc. River Islands Phase 2 Development Water Supply Assessment September 2020