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Andrew Richle 2 April 20, 2017 intersection of Church Street and West Tokay Street in June 2016. A treatment system was constructed on the adjacent Needham Elementary School property. This location is approximately 2400 feet down gradient of the source area. PCE at this location is encountered primarily in the intermediate depth zone between 75 and 125 feet. Extraction well EW-7 was constructed with a screen interval of 75 to 125 feet and a planned extraction rate of 50 gallons per minute. However, when tested during startup, EW-7 was found to yield less than 1 gallon per minute. Therefore EW-7 could not meet its design purpose of capturing and containing the PCE contamination in the mid-plume area. To determine a location for a new extraction well to replace EW-7, the City advanced one CPT boring (CPT-38) southeast of EW-7. After identifying sampling depths from the CPT logging, hydropunch-type groundwater samplers were advanced to collect groundwater samples at 85 and 114 feet below ground surface. The groundwater samples collected both contained PCE. PCE was detected at a concentration of 380 pg/L at 85 feet and 120 pg/L at 114 feet. For comparison, the groundwater sample collected from monitoring well G-25A, which is screened from 89 to 99 feet and is located just east of EW-7, contained 1,100 pg/L of PCE in November 2017. The City also conducted pump testing at G-25A in October 2016, and found that the 2- inch monitoring well could yield 8 gallons per minute. Based on the available information, the City is proposing to install a new 6-inch diameter extraction well screened to replace EW-7 approximately 20 feet north of G-25A. The new extraction well would be screened from 75 to 100 feet below ground surface and extract groundwater at 8 gallons per minute. The final depth, screen interval and extraction rate will be determined during construction and startup. Central Valley Water Board staff concurs with the proposed replacement extraction well. Please notify Central Valley Water Board staff at least one week prior to conducting the field activities. Please submit a report of well installation within 60 days of completing the field work. If you have any questions regarding this letter, please contact me at (916) 464-4665 or ncasebeer@waterboards.ca.gov . ORIGINAL SIGNED BY Nathan Casebeer, P.G. Engineering Geologist Private Sites Cleanup Unit cc: Varinder Oberoi, West Yost Associates, Pleasanton