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APPENDIX A Central Valley Regional Water Quality Control Board Letter dated August 7,2019 ��\ � � ` ��mil\\� —...—� •. •t as. � s µ 0.t _ -- is 17 i ..,...w. Chevron -2- 7 August 2019 Alden Park Tracy,San Joaquin County Water Boards ��w'"''mm �•�T�'�"' . Groundwater Monitoring Well MW-14—Concentrations of TPHd reported for -- `..--._. ----- ----------- groundwater samples collected during 17 of 19 monitoring events since August Central Valley Regional Water Quality Control Board 2003 were less than the laboratory reporting limits.During the two monitoring events in February 2017,a maximum TPHd concentration reported was 100 pg/L. 7 August 2019 • Arcadis proposes to abandon groundwater monitoring wells MW-11,MW12,and MW-14 in accordance with San Joaquin County Environmental Health Michael N.Oliphant Department requirements. Chevron Environmental Management Company 6001 Bollinger Canyon Road An absorbent sock will be redeployed within monitoring well MW-21 if petroleum P.O Box 6012 hydrocarbon sheen or separate-phase hydrocarbons(SPH)are detected during San Ramon,CA 94583 - the quarterly SPH monitoring and recovery activities,or the annual groundwater monitoring event.If a petroleum hydrocarbon sheen or SPH are not detected REVIEW—RESPONSE TO COMMENTS—2019 ANNUAL GROUNDWATER within monitoring well MW-21,then continued use of an absorbent sock or other MONITORING REPORT,ALDEN PARK,TRACY,SAN JOAQUIN COUNTY passive SPH recovery method Is not warranted.The collection and analysis of a groundwater sample from monitoring well MW-21 would provide confirmation that The Central Valley Regional Water Quality Control Board(Central Valley Water Board) the dissolved-phase petroleum hydrocarbon concentration is not indicative of staff(Staff)received the subject response to comments(Response)on 1 July 2019 for SPH. the Alden Park site(Site)in Tracy.The Response was prepared by Arcadia U.S.,Inc., (Arcedis),and submitted on behalf of Chevron Environmental Management Company Comment (Chevron).The Response was submitted to a letter from the Central Valley Water Board dated 14 May 2019,to justify the removal of groundwater monitoring wells • Staff concurs with the request to remove groundwater monitoring wells MW-1 i, MW-11,MW-12,and MW-14 from Monitoring and Reporting Program MRP R5-2006- MW-12,and MW-14 from the MRP.The MRP states in part:'....and before 0812(MRP),and to further explain the redeployment of an absorbent sock in well destruction of a groundwater monitoring or extraction well(s),the Discharger shall MW-21.This letter summarizes the Response and provides Staff comment and submit plans and specifications to the Central Valley Water Board for review and directives. approval by the Executive Officer'Staff request that Chevron submit a workplan that describes the plans and specifications for abandonment of Response Summary the three groundwater monitoring wells. • Groundwater Monitoring Well MWA 1—Concentrations of total petroleum . All materials and procedures used during the destruction of wells MW-11,MW- hydrocarbon as diesel(TPHd)reported for groundwater samples collected during 12,and MW-14 need to conform with the standards under Water Wells and 14 of 16 monitoring events since August 2005 were less than the laboratory Monitoring Wells in the Califomia Well Standards Bulletin 74-90(June 1991)and reporting limits.During January 2010,two monitoring events had reportable Bulletin 74-81(December 1981),adopted by the Department of Water concentrations,the maximum was 93 micrograms per liter(pg/L)in January Resources,and in accordance with a work plan approved by the Central Valley 2010. Water Board Staff.A report describing the well destruction activities needs • Groundwater Monitoring Well MW-12—Concentrations of TPHd reported for to be submitted. groundwater samples collected during 30 of 31 monitoring events since April . Staff concurs with the removal of polynuclear aromatic hydrocarbons from the 1996 were less than the laboratory reporting limits.During the one monitoring MRP as stated in the Staff letter dated 14 May 2019. event in February 2017,a concentration of 92 pg/L was reported. • If the absorbent sock in well MW-21 is removed due to lack of SPH,and if subsequent monitoring events show evidence of SPH In the well,then an absorbent sock should be redeployed. Wa E.LO.OLlY S.D.P E,uu.i r.,•—Pu The revised MRP will be issued as a separate document,and all groundwater ,wew.•i.w•e.um,ro ..,....u,w.m,.,.w,.,,.wmn monitoring activities,reporting,and sampling will need to be conducted In accordance with the revised MRP.