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+—' City of Stockton February 6, 1997 A68108.01B Page A-1 APPENDIX A THE TWINING LABORATORIES INC. STANDARD OPERATING PROCEDURES This appendix contains the standard operating procedures used by Twining in performing the investigation. Twining observes these procedures in order to obtain consistent, reliable +— data. A-1 Standard Operating Procedures for Drilling and Soil Sampling: Subsurface assessment and/or well construction permits are filed with the appropriate government agency before conducting field operations. Underground Service Alert is notified at least 48 hours prior to initiation of field activities. Field activities are performed under the �-' direction of a California registered geologist or certified professional engineer. Soil borings are drilled using an appropriate method. The method selected will depend upon project objectives and subsurface conditions. Typically soil boring are drilled using a Central Mine Equipment Company model 75 (CME-75) truck-mounted drill rig equipped with 6-5/8-inch outside diameter, continuous-flight, hollow-stem augers. Twining is a licensed drilling contractor under C-57 classification(Contractor's License No.506159). The soil borings are drilled under the direction of a Twining geologist. i Drilling and sampling equipment are thoroughly cleaned before, during and after each use. Cleaning procedures are described in a subsequent paragraph. i~ Soil samples are collected using a continuous-coring device, by driving a split-spoon sampler, or by grabbing samples from the drilling cutting returns. The sampler or coring device is lined with brass, stainless-steel, or acrylic tubes, in which samples may be retained for subsequent chemical analyses. To collect samples using the split-spoon sampler, the sampler is initially lowered to the bottom of the soil boring and driven 6 inches into undisturbed soil. It is then driven 12 inches deeper by repeatedly dropping a 140-pound weight from a height of 30 inches. The number of blows required to advance the sampler 12 inches is recorded on the boring logs as "blows per foot". This information is used in estimating soil density. fe- Soil samples are examined for the purpose of preparing lithologic logs Soils are logged consistent with the Unified Soil Classification System (USCS). The soil boring logs note soil �. types encountered at depth including consistency, soil moisture, particle size, color, and other distinguishing features. The soil samples are field screened for evidence of volatile organic chemicals (VOCs) and/or other contaminates. The field screening consist of; visual observation for straining or free fluids, unusual odor, and head space analysis using a photoionization detector (PID) {- or drager tube. The procedure for performing head space analysis are describe in a �.... subsequent paragraph (if pertinent to this investigation). r