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Californiaogional Water Quality CoWl Board
<br /> Central Valley Region }
<br /> �r l `
<br /> Karl E. Longley,ScD,P.E.,Chair '`k:;,, .:„:r'
<br /> Linda S. Adana Arnold
<br /> Secrelat),jor Sacramento Main Office
<br /> Enw,onnienral 11020 Sun Center Drive#200. Rancho Cordova;Califomia 956706114 D y warzenegger
<br /> Phone 916 ( ) ���� v D overnor
<br /> Praecrron ( )464-3291 •FAX 916 464-4645
<br /> hitp:/Av vw.waterboards.ca.gov/centralvallev
<br /> 1 March 2007
<br /> MAR 0 5 2007
<br /> ENVIRONMENT HEALTH
<br /> Mr. Darin Rouse Mr. Jay Allen PERMIT/SERVICES
<br /> Chevron Environmental Management Company Stone Brothers Management Company
<br /> 6001 Bollinger Canyon Road 1024 W. Robinhood Dr.
<br /> San Ramon, CA 94583 Stockton, CA 95207
<br /> REQUEST FOR MODIFICATIONS IN SAMPLING AND ANALYSES, REGIONAL WATER
<br /> QUALITY CONTROL BOARD - CENTRAL VALLEY REGION (WATERBOARD) CLEANUP
<br /> AND ABATEMENT ORDER (CAO) NO. 5-00-0707, FORMER UNOCAL STATION #5098 AT
<br /> 5606 PACIFIC AVENUE, AND FORMER MONTGOMERY WARDS AUTO SERVICE AT 5400
<br /> PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY
<br /> I reviewed the Request for Modifications in Sampling and Analyses (Report), received
<br /> 6 December 2006 from ENSR, consultant for Chevron Environmental Management (Chevron).
<br /> The Report includes copies of Regional Board staff directive letters dated 8 February 2002
<br /> and 14 April 2006, and provides ENSR's technical rationale for proposed changes to the
<br /> quarterly monitoring required under CAO No. 5-00-0707. CAO No. 5-00-0707 addresses
<br /> quarterly monitoring and states "...Starting 15 September 2000, return to quarterly sampling
<br /> and reporting for all existing wells (including RIM, added monitoring wells, and any
<br /> replacement well(s) for RIW. The added monitoring wells may include "sentry" wells placed
<br /> between RIW and any alternate groundwater source.", and also states that groundwater
<br /> analyses include "... TPHg, benzene, toluene, ethyl benzene, total xylenes, ethylene
<br /> dibromide, 1,2-dichloroethane, MtBE, TBA, DIPE, ETRE, TAME, ethanol, and methanol."
<br /> The Report includes an evaluation of the aquifer characteristics, co-mingled plumes
<br /> distribution, concentration trends, and the mass removed by soil and groundwater treatment;
<br /> and requests that analyses be limited to only include Total Petroleum Hydrocarbons as
<br /> gasoline (TPHg), Benzene, Toluene, Ethylbenzene, Xylenes (BTEX), and 1,2-Dichloroethane
<br /> (1,2-DCA). Tables 1 and 3 (Attached copies) from the Report list the Maximum Contaminant
<br /> Levels (MCLs), the San Francisco Bay Regional Water Quality Control Board Environmental
<br /> Screening Levels (ESLs) and the California State Action Levels (CSALs) as the lowest
<br /> applicable Waterboard Water Quality Goals (WQGs) for justification of analyses changes to
<br /> the groundwater monitoring. The Report requests changes from quarterly monitoring of all
<br /> wells to the frequency in the foll wing table.
<br /> Fre uenc Quarter) Semi-Annuall Annual) Discontinue
<br /> Wells MW-1, MW-2, MW- MW-9R, MW- " MW-5, MW-7, MW-10, MW- MW-14A, MW-
<br /> 3; MW-4, MW-6, 10A, MW-12, 13, MW-14, MW-17, MW-18, 15, MW-19S,
<br /> MW-8D, MW-1"1, MW-18D, MW- MW-19D, MW-22D, MW- MW-21S, MW-
<br /> MW-16, MW-25D 24S, MW-24D 23S, AS-26, MW-27 21D, MW-22S
<br /> 1- ENSR will evaluate 1,2-DCA concentrations annually for future recommendations.
<br /> 2- Sample first and third quarters.
<br /> 3- Sample third quarter
<br /> 4- Intermittent detections, only eight of which exceeded Water Quality Goals(WQGs)
<br /> California Environmental Protection Agency
<br /> aZd Recycled Paper
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