SITE INFORMATION AND CORRESPONDENCE_1987-1992

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O STATE OF CALIFORNIA PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— —" CENTRAL VALLEY REGION 3443 ROUTIER ROAD, SUITE A It, 3 F SACRAMENTO, CA 95827-3098 ' ' PHONE: (916) 361-5600 FAX: (916) 361-5686 Fit eY k 1 � , 23 May 1991 Mr. Wilbur Smith MAY 24 1990 Lincoln Properties, Ltd. ENVIRONMENTAL HEALTH 374 Lincoln Street PER MIT/SERVICES Stockton, CA 95207 EARLY WARNING MONITORING WELL, LINCOLN VILLAGE CENTER, STOCKTON, SAN JOAQUIN COUNTY - CASE NO. 3002 We have reviewed your April 1991 Early Warning System Workplan (Workplan) , in which you propose to complete a monitoring well (MW) in the shallow ground water between the source of the halogenated volatile organic compounds (HVOCs) and the City of Stockton Supply Well No. 11. Your goal in placing the MW 300 feet upgradient from Well No. 11 is to detect the pollutants before they reach the drinking water supply well and to bound the plume in the shallow ground water. We agree that the ground water should be monitored to early detect the HVOCs. You should monitor the water-bearing zones to the depth necessary to protect Well No. 11. In a 22 May 1991 telephone discussion with Mr. Michael Tognolini of Kennedy/Jenks/Chilton Consultants (KJC) , he informed me that Well No. 11 is completed between about 270 and 320 feet deep. Therefore, the vertical extent of the HVOC pollution must be defined by means of MWs completed to at least 320 feet deep and in which no HVOCs have been detected. Most samples taken from MWs completed in either the shallow or intermediate water-bearing zones (Zones "A" and "B" , respectively) have contained detectable HVOC concentrations. In particular, while some shallow MWs have not contained detectable HVOCs, the MW (MW10) downgradient from the most highly polluted area in the direction of Well No. 11 contained substantial HVOCs. Therefore, the early detection well proposed for installation between MW10 and Well No. 11 may serve to define the plume in the shallow zone in the direction of Well No.11. However, the proposed MW will not adequately moniotr the deeper water-bearing zones. Also in our 22 May discussion, Mr. Tognolini informed me that the Phase III Investigation Workplan, which is in preparation, will propose three monitoring wells to be completed in Zone "B" along the northeast property line in the MW10 vicinity. Placing MWs in this vicinity may define the plume in this water-bearing zone and may also serve as early detection MWs. Similarly, the Phase III Workplan will propose additional MWs in the deeper water-bearing zone (Zone "C") downgradient from the HVOC source in the direction of Well No. 11 . To date, HVOCs have not been detected in samples taken from the single MW completed in the deeper zone.