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least 90 percent of the analyses requested. t Section 2.0 Equipment and Sampling Quality Control Procedures Field Quality Control Checks Field QC checks are used to assess the representativeness of the sampling activity. They are designed to determine what effects activities such as sample collection, bottling, shipping and storage have on sample integrity and to ensure that samples available for analysis in the laboratory are representative of actual conditions at the site. Field QC checks include trip blanks, equipment blanks, ambient conditions blanks, bottle blanks, and field duplicates. Trip Blanks Volatile organic chemical samples may be subject to loss of sample integrity by the diffusion of volatile chemicals into or from the sample under the Teflon-lined silicone rubber septum of the sample vial. In order to monitor for this type of contamination during water sample shipment and handling, trip blanks, prepared by the analytical laboratory, are prepared by filling two 40-m1 glass sample vials with analyte-free water. These blanks accompany the samples at all times, in the field as well as the laboratory. All trip blanks are analyzed, and in the event concentrations above the reporting limit appear, the data from the associated samples should be qualified if the concentrations in the samples are less than five times that in the trip blanks for VOC's which are not common laboratory contaminants. For compounds which are common laboratory contaminants, re.-ults should be qualified if the concentrations in the samples are less than ten times the concentration in the blank (EPA, 1988). Equipment Blanks Equipment rinsate blanks will be collected periodically to ensure the sampling procedure or equipment is not responsible for introducing contaminants into the samples. These samples will be collected by filling a decontaminated sampling bailer or other decontaminated sampling equipment with analyte-free water and pouring it into the sample bottles. When analytes are detected in the equipment blanks, the associated data should be qualified if concentrations in the samples are greater than the reporting limit but less than five times that in any blanks for compounds which are not common laboratory contaminants and ten times that in blanks for compounds which are common laboratory contaminants (EPA 1988). Ambient Condition Blank An ambient conditions blank (field blank) is collected as specified by the client, or as `rl , determined by field personnel. Examples of situations where field blank samples are recommended would be sites where fuel is being unloaded during sampling, stock-