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The label shows the date, time, sample ID# and analyses to be run <br /> and the sampler' s initials The tedlar bag samples are then <br /> Placed within a cooler, and are hand delivered to WEGE' s <br /> laboratory that same day <br /> The vapor sample is then inDected into an FID (Flame Ionizing <br /> Detector) chromatograph and the resulting chromatogram compared <br /> to standard chromatograms of known TFH (Total Fuel Hydrocarbons, <br /> gasoline) and BTEX (benzene, toluene, ethylbenzene, and xylenes) <br /> concentrations . Selected samples are also analyzed by dual <br /> chromatograph comparison A Photovac lOS50 photo-ionizing gas <br /> chromatograph is used to evaluate BTEX, TCE, PCE, and DCE <br /> Carbon dioxide (CO2) concentration is measured from the tedlar <br /> bag samples by connecting a Drager tube and pump to the <br /> inlet/outlet of the tedlar bag CO2 reading in percent is then <br /> obtained and recorded on the chrmoatogram produced from the GC- <br /> FID analysis <br /> ON SITE ANALYSIS <br /> During the two hour tests, a photoionizing detector (HNu PID <br /> w/10 2 ev bulb) and/or GasTech LEL/02 meter are used to perform <br /> • constant exhaust monitoring, see Field Notes - Appendix A. The <br /> LEL was used to insure that less than two pounds of hydrocarbons <br /> would be emitted during the test A commonly used LEL for <br /> gasoline is 1 40-. = 14 , 000 ppmv * mg/L/250 ppmv * 6 21X10-5 * flow <br /> rate (cfm) * 1.20 minutes = 1 04 lb at So LEL and 2 08 lbs at 10% <br /> LEL The extraction well vacuum and flow is measured with a <br /> mercury manometer and the surrounding wells were gauged with a <br /> water manometer <br /> FLOW RATES <br /> Flow rates are measured at the site using an orifice plate A one <br /> inch orifice-sampling manifold is placed directly on the casing <br /> of the monitor well, carefully avoiding any vacuum leaks An <br /> orifice plate restricts the flow causing a pressure drop across <br /> the orifice By measuring the resulting pressure change across <br /> the orifice it is possible to calculate the air flow rate The <br /> flow rate is calculated by the pressure drop (millimeters (mm) <br /> mercury or water) across a square edge orifice plate <br /> Ve = CK sgr (P) Q = AVe <br /> Where <br /> Ve= velocity in feet per minute (fpm) <br /> C = Orifice Coefficient = 0 65 (for orifice used) <br /> K = Constant w 794 6 for mm water or 2929 8 for mm <br /> mercury <br /> P = Pressure differential across the orifice <br /> Q = Flow rate in cubic feet per minute (CFM) <br /> A = Area orifice in square feet 1" = 0 00545 ft2 <br /> PAGE 4 R603 UPDATE-39 7/14/95 <br />