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City of Stockton A68108.01B �•' February 6, 1997 Page A-3 at approximately 4°C. Upon arrival at the laboratory, the samples will be preserved for analysis as appropriate. Samples may be delivered to Twining's chemistry laboratory in Fresno, California. The Twining representative in charge of the field work transports or directs the transportation of the samples and custody forms to the laboratory, where the samples are transferred to the sample control department. A receiving clerk, or an authorized analyst, signs the custody forms, presents a duplicate copy to the Twining representative, and transfers the samples to a laboratory analyst. The laboratory manager retains possession of the custody s.- forms during analyses of the samples. The laboratory manager's responsibilities include monitoring the sample integrity within the -- laboratory. This involves assigning each sample a laboratory number and maintaining cross- reference between the sample's field and laboratory identifications. The analysts' responsibilities include maintaining accurate records of the samples analyzed along with the analytical data produced. This involves labelling chromatograms and maintaining the laboratory numbers on sub-samples taken from the submitted samples, labelling glassware used in the analyses, and properly labelling sample extract containers with each sample's laboratory number. Following analyses, the samples are transferred to a limited-access storage room. Chain-of- i custody forms, chromatograms, and other pertinent information are filed for future { reference. Splits of samples analyzed are kept for 30 days. Samples containing hazardous I concentrations will be returned to the client for disposal. A-4 Standard Operating Procedures for Laboratory Quality Assurance/Quality Control: These laboratory QA/QC procedures were developed to reduce outside interferences during analyses of samples. The laboratory director is responsible for creating and maintaining the program. General QA/QC procedures follow: ■ Analytical instruments are serviced on a regular basis to assure accurate calibration; ■ Organic-free water is monitored daily for quality; �. ■ Gas chromatographs are calibrated daily; ■ Method blanks are run to check whether the glassware and reagents are free {... of interference from chemicals that would invalidate the analyses; ■ Standards are prepared using the applicable reference materials;