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Tlrscer Research Corporation <br /> 1 <br /> -Sampling Efficiency <br /> Soil gas/groundwater pumping is monitored by a vacuum gauge to ensure that <br /> an adequate flow of gas from the soil is maintained A reliable gas sample can be <br /> obtained if the sample vacuum gauge reading is at least 2 inches Hg'less than the <br /> maximum measured vacuum of the vacuum pump <br /> Analytical Quality Assurance Samples <br /> Quality assurance samples are performed at the listed, or greater, frequencies <br /> W in Table 3 The frequency depends on the number of samples analyzed and the length <br /> of time of the survey <br /> Table 3. Quality Assurance Samples <br /> Sample type Frequency <br /> Ambient Air Samples 3 per day or 1 per site <br /> Analytical Method Blanks 5% (1 per 20 samples or i a day) <br /> Continuing Calibration Check 20% (1 every 5 samples) <br /> _ Field System Blank 10% (1 every 10 samples or I a day) <br /> Reagent Blank 1 per set of working standards <br /> Replicate Samples 10% of samples collected f <br /> The ambient air samples are obtained on site by sampling the air immediately <br /> outside the mobile analytical van and directly injecting it into the GC. Analytical <br /> method blanks are taken to demonstrate that the analytical instrumentation is not <br /> —� contaminated These are performed by injecung tamer gas (nitrogen) into the GC <br /> with the sampling syringe Subsamplmg syringes are also checked in this fashion <br /> The infector port septa through which samples are mjected into the GC are <br /> replaced daily to prevent possible gas leaks from the chromatographic column All <br /> samphng and subsamphng syringes are decontaminated after use and are not used <br /> }� again until they have been decontaminated by washing in anionic detergent and <br /> baking at 900C. <br /> July 19,1994 Page 8 11402915 <br />