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CONDOR EARTH <br />188 Frank West Circle, Suite 1 <br />Stockton, CA 95206 <br />209.234.0518 <br />Fax 209.234.0538 <br />w condorearth.com CONDOR <br />February 27, 2018 <br />Aimee Phiri, P.E. <br />Central Valley Regional Water Quality Control Board <br />11020 Sun Center Drive # 200 <br />Rancho Cordova, CA 95670 <br />SUBJECT: Review Comments for Revised Site Investigation Work Plan, Former Helena Chemical <br />Facility, 2245 West Charter Way, Stockton, San Joaquin County <br />Condor Job No. 6847A <br />Dear Ms. Phiri: <br />Condor Earth (Condor) reviewed the December 15, 2017 letter, wherein the Central Valley Regional Water <br />Quality Control Board (Central Valley Water Board) provided comments to the October 19, 2017 Work <br />Plan for Additional Site Investigation, Former Helena Chemical Facility, 2245 West Charter Way, <br />Stockton, California (Work Plan). Condor provides responses (underlined, below) to each of the Central <br />Valley Water Board's comments. <br />RESPONSE TO COMMENTS <br />Central Valley Water Board staff concur with the proposed number and locations of step-out borings <br />(B-42 through B-46) in the area where I ,2,3-TCP was previously detected at an elevated level (12 <br />micrograms per liter [ug/L] in a groundwater sample from boring B39/GW12). Staff also concur with <br />the analyses proposed for soil and groundwater samples that will be collected from these proposed <br />borings. <br />Response: Based upon the non-detect results of Atrazines analyses in each of the Site monitoring wells, <br />Condor proposes to remove Atrazines from the analyte list, although groundwater samples collected <br />from newly installed wells would be analyzed for Atrazines during the first sampling event. <br />Analytical data for a groundwater sample collected from monitoring well MW-3 in May 2016 <br />(following installation of the well) indicated the presence of 1,2,3-TCP at a concentration of 0.0057 <br />ug/L (and 0.0063 ug/L in a duplicate sample). Groundwater monitoring data for MW-3 has <br />indicated the presence of low levels of 1,2,3-TCP (approximately 0.0022 ug/L in June 2017 and <br />0.0038 ug/L in September 2017). Based on these data, it is possible that MW-3 is located on the edge <br />of a 1,2,3-TCP plume that may be present around B39/GW12. Therefore, Central Valley Water <br />Board staff recommend that step-out borings be advanced near MW-3 to collect soil and <br />groundwater samples for analysis of 1,2,3-TCP. Additionally, at least one boring should be <br />advanced in the area between B39/GW12 and MW-3 to verifi, whether or not a I,2,3-TCP plume <br />exists in this area. <br />Response: Condor proposes a step-out boring northeast of well MW-3 (between MW-3 and <br />B39/GW12), and a step-out boring south-southeast of well MW-3 in the assumed downgradient <br />direction and next to the former hazardous chemical storage area. It should be noted that although the <br />gradient was calculated to the northwest in May 2016 and June 2017, groundwater in most other