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. concentrations Selected samples are also analyzed by dual <br /> chromatograph comparison A Photovac 10550 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 as 1 401 = 14 , 000 ppmv * mg/L/250 ppmv * 6 21X10-5 * flow <br /> rate (cfm) * 120 minutes = 1 04 lb at 5o LEL and 2 08 lbs at 140 <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 = 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 /> Q = A X 0 65 X 794 6 X sqr (P) <br /> CALCULATIONS <br /> To calculate the pounds (lb) per day the concentration is <br /> multiplied by the volume of air produced an one day <br /> *The lab reports the Concentrations (C) of the air sampling in <br /> ug/later The first step as to convert this value to lbs/cf <br /> PAGE 4 R603 UPDATE-40 8/29/95 <br />