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CeohN*a(Tedwirs Inc. Page 2 Valentine(Eldorado St.) Work Plan Addendum Project No. 723.2 January 13, 1999 Soil Sample Collection Due to the proximity to B-1, the boring will be free drilled to a depth of 50 feet bgs. Soil samples will then be collected continuously from 50 feet to total depth with a modified California split-spoon sampler. Samples will be collected for geological and laboratory evaluation. A boring log for B-1 is included as Figure 2 and a 3-dimensional cross section of the site is included as Figure 3. Soil Sample Analysis Based on field screening observations up to two soil samples from each borehole will be submitted to Sherwood Laboratories of Hilmar (State Certified Laboratory 91400) for analysis for benzene, toluene, ethylbenzene and xylene (BTEX) by EPA method 8020, gasoline range petroleum hydrocarbons (TPH-Gas) by EPA method 5030/8015(m) and Methyl Tertiary Butyl Ether (MTBE) by EPA method 8020. Two soil samples will be analyzed fot the fuel oxygenate suite (MTBE, D1PE, ETBE, TAME & TBA) by EPA method 8260. The detection limits for these compounds are listed below. A Chain of Custody will be completed for all samples collected and tracked to ensure sample integrity. Detection Limits: BTEX MTBE-8020 Ethers-8260 TBA-8260 TPH-G Soil (µg/Kg) 3.0 50 5 20 1,000 Monitoring Well Construction The monitoring wells will be constructed using 1.0 inch inside diameter PVC casing with flush threads. The screened intervals will be 5 feet in length. The exact depth interval will be determined by the geology in the field in consultation the supervising geologist and the county inspector. The screen intervals will target course grained units of the aquifer. Construction is proposed as follows: • casing will be 1.0-inch diameter schedule 40 PVC with flush threads • screened intervals will be 5 feet in length • #12 sand filter pack will surround and extend two feet above the 0.010" screened intervals • decontaminated surge block will be used to achieve a maximum density filter pack • annular space between the top of the filter pack from the deeper screened section and the bottom of the upper screened section will be sealed by use of Pel-Plug weighted, retarded hydration, bentonite pellets and allowed to hydrate one h fo our After discussion with Robert Vickery of V&W Drilling, the use of Pel-Plug is recommended rather then a grout because in his experience there have been too many problems with the grout getting into the screened sections. • two feet of this,,- el-Plug material will be added to the top of the filter pack of the upper-screeneds • surface seal will be achieved by pumping a neat cement grout (augmented with < 4% bentonite)via a tremie tube • the wells will be secured with a locking watertight cap encased in flush mounted traffic rated well boxes. The table below shows well construction. See Figure 4 for a schematic of monitoring well construction.