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Eum u G.5.u—J. <br /> MAnecv,Rama.Ez <br /> Water Boards et-arc.9AD--POPHMENTK PAOTC01,0'. <br /> Central Valley Regional Water Quality Control BoardE 1 C'T AIN <br /> APR 22' 2014 <br /> 21 April 2014 <br /> Ralph Lee White Peter Bui & Kimberly Hoang <br /> 2201 East Eighth Street 4004 Maddie Circle <br /> Stockton, CA 95206 Stockton, CA 95209 <br /> WORK PLAN AND DOCUMENTS REVIEW FOR RALPH'S SQUARE, 2211 SOUTH AIRPORT <br /> WAY, STOCKTON, SAN JOAQUIN COUNTY, RB CASE#390995 <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the Groundwater Report-First Quarter 2014 (Report) and the Soil Vapor <br /> Investigation Work Plan (Work Plan). The Report and the Work Plan were received as an email <br /> attachment on 15 April 2014 and electronically in GeoTracker on 10 April 2014, respectively <br /> from your consultant Advanced GeoEnvironmental, Inc. (AGE), <br /> The Report provides the 4 March 2014 groundwater monitoring results of MW-1 through <br /> MW-11. The data show methyl tert butyl ether(MTBE) concentrations have generally declined <br /> from one to three orders of magnitude since the last complete round of sampling in October <br /> 2008, with the exception MW-5, which increased from 17,000 micrograms per Liter(ug/L)to <br /> 28,000 ug/L. The data show the MTBE plume has migrated at least 50', and is undefined to the <br /> east. The MTBE plume is defined to the west by MW-1, to the north by MW-7 and MW-8,to the <br /> south by MW-9, to the southeast by MW-10, and vertically in the source area by MWA 1. <br /> The San Joaquin County Environmental Health Department (SJCEHD) approved a work plan <br /> for a groundwater investigation to define the downgradient extent of the plume in a letter dated <br /> 27 August 2009. In the Report, AGE proposed to complete the delayed investigation by <br /> installing one soil boring (B-5) 80'to the east of the Ralph's Square building, which is about <br /> 60' east of the USTs pit. B-5 would be located about 20' east of a residence on Phelps Street. <br /> AGE proposed to collect one grab groundwater sample from B-5. AGE recommended <br /> submitting a new sensitive receptor survey, stating a water supply well has been confirmed in <br /> City of Stockton Park to the northeast. <br /> In the Work Plan, AGE proposed installation of five (5) soil vapor wells completed to five (5) feet <br /> below ground surface (' bgs), one well in the underground storage tanks (USTs) pit and the <br /> remaining four wells between the USTs pit and the Ralph's Square building, to evaluate the <br /> threat from vapor intrusion. Two soil borings are proposed to be advanced to 10, bgs with soil <br /> samples collected at 5' bgs and 10' bgs, one in the USTs pit and the second 20'to the northeast <br /> near MW-2, to evaluate for a bio-attenuation zone. I concur with the tasks proposed in the Work <br /> Plan with the conditions stated below. <br /> KAnL E. LONCLCY SCO, P.E., CHAIR I PAMELA C. Cnrmoii P.E.,8CEE,cxECLITIVE orriccri <br /> 11020 Sun Center Drive#200.Rancho Cordova,CA 95670 1 www,waterboardB.ca.<Iov/centraWalley <br /> C1.1—LeD-eE. <br />