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16a w- City of Stockton May 29, 1996 A681OZ07A 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 Soil Sample Handling: 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 detectorPTD . The ( ) procedure for performing head space analysis are describe in a subsequent paragraph (if pertinent to this investigation). Generally, soil samples selected for analyses typically represent those which the field screening indicated will be most likely to contain the contaminate of concern. In most instances the deepest two samples and/or and sample collected from just above groundwater are selected for analyses. Samples intended for chemical analyses are sealed with Teflon tape and plastic end caps, labeled, placed on ice, and delivered to a laboratory, along with chain-of-custody documentation. A-2 Standard Operating Procedures for Equipment Decontamination: Proper decontamination procedures reduce the potential for: cross-contamination among sample locations; and introduction of contamination from outside sources. Before, during, and following sampling operations, sampling equipment is thoroughly cleaned using a high pressure hot water (steam) washer or washed in a low-phosphate soap and water solution, and rinsed in clean water before each use. The type of soap used will depend upon project requirements. Well casing, screen, end caps, and centralizers will also be cleaned using the steam washer. Steam cleaning condensate will be containerized for to later disposal. Generally, disposal will be the client's responsibility. A-3 Standard Operating Procedures for Sample Handling and Chain-of-Custody: t`. Records are developed for samples which include: sampling date, sample type, location,job number, name of sampling personnel, and method of preservation. Each sample container is labelled immediately following collection. Chain-of-custody protocol, as described in United States Environmental Protection Agency, 1986, Test Methods for Evaluating Solid Waste, SW-846, Third Edition, is followed. Samples will be maintained at approximately 4°C. Upon arrival at the laboratory, the samples will be preserved for analysis as i.. appropriate.