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$ent By: RWOCB; 2553015; Apr-10 10:29AM Page 2/3 P i .. California Regional Water Quality Control Board v Central Valley Region Steven T. Butler,Chair 0 Winston H.Hicko: Gray Davis Secretary for - Sacramento Main Office Governor Environmental Inland Addtcss: hnp'//www.swrcb.mg0v/rwgcb5 Prosection 3443 Routim Road,Suitc A.S=a nto,Califmin 95827-3003 Phone(916)255.3000•FAX(916)255.3015 10 April 2000 Durhim Ali Jubari Nagi Saleh-Ali. Mohamed &Huda Gubary 667 O'Farrell Street#10 PO Box 1322 25 Poncetta Drive 9201 San Francisco, CA 94109 Riverbank, CA 95367 Daly City, CA 94015 REQUESTREVISED WORKPLAN TOASSESS GROUNDWATER CONTAMINATION, RANCHMARKET, 2356Y SOUTHSANTA FE ROAD,RIVERBANK, SAN JOAQUIN COUNTY We received your 31 March 2000 Workplan for Soil and Groundwater Assessment(Workplan) submitted by Secor international Incorporated (Secor). Secor proposes to drill one deep soil boring to 80 feet below ground surface (bgs), and four shallow soil borings to 40 feet, and install monitoring wells in each of the five soil boring locations. The deep monitoring well will be screened from 75 to 80 feet bgs, and the shallow monitoring wells from 20 to 40 feet bgs. Secor also proposes to complete video logging of domestic wells DW-1 and DW-2. Although the Workplan addresses most of the requirements in our 28 February 2000 letter, it does not provide a scope of work to define the lateral and vertical extent of on-site soil and groundwater contamination. Prior to installing additional wells, soil borings are required to identify the proper placement of monitoring wells. Vertical definition of soils utilizing a continuous coring method is needed near the former underground storage tanks (USTs),and next to domestic well DW-2. The proposed depth of the borings should be based on the total depth of DW-2 following the above video logging investigation. Additional borings can be completed by conventional push probe methods or other drilling methods utilizing a minimum five-foot sampling interval. Once vertical soil definition is completed, depth discrete water samples are needed to determine zones of groundwater contamination. As stated in the Workplan care must be taken to prevent cross-contamination of deeper water bearing units. These steps may include using a dual casing method or another drilling technology during the soil and groundwater investigation. The schedule of events as presented in the Workplan did not include the video logging investigation of domestic wells DW-1 and DW-2. The video logging should be completed prior to soil and groundwater investigation activities, and as soon as access agreements are completed with the necessary property owners. Following the video logging and the soil and groundwater investigations, and prior to monitoring well installation, a letter report must be submitted to this office for approval of proposed monitoring wells locations and screen zones. The locations of proposed monitoring wells (SBI to SB5)presented in the Workplan may be revised based on the soil and groundwater investigation and site conditions. Monitoring wells at SB2, SB3, and SB5 are appropriately placed as presented in the Workplan; whereas, SB4 should be placed east of its current location, and closer to the Ranch Market Store. SB 1 should be placed closer to DW-2, and may California Environmental Protection Agency