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Carbon dioxide (CO2) concentration is measured from the tedlar bag samples by connecting a Drager tube and pump to the inlet/outlet of the tedlar bag CO2 reading in percent is then obtained and recorded on the chrmoatogram produced from the GC- FID analysis FLOW RATES Flow rates are measured at the site using an orifice plate . A one inch orifice-sampling manifold is placed directly on the casing of the monitor well , carefully avoiding any vacuum leaks An orifice plate restricts the flow causing a pressure drop across the orifice By measuring the resulting pressure change across the orifice it is possible to calculate the air flow rate The flow rate is calculated by the pressure drop (millimeters (mm) mercury or water) across a square edge orifice plate Ve = CK sqr (P) Q = AVe Where Ve= velocity in feet per minute (fpm) C = Orifice Coefficient = 0 65 (for orifice used) K = Constant 794 6 for mm water or 2929 8 for mm mercury P = Pressure differential across the orifice Q = Flow rate in cubic feet per minute (CFM) A = Area orifice in square feet 1 " = 0 00545 ft2 Q = A X 0 65 X 794 6 X sqr (P) CALCULATIONS To calculate the pounds (lb) per day the concentration is multiplied by the volume of air produced in one day *The lab reports the Concentrations (C) of the air sampling in ug/liter The first step is to convert this value to lbs/cf (pounds per cubic foot) lug/l x 0 0000018/ug x 0 002205lb/g x 28 321/cf = 0 0000000621lb/cf The volume of air produced in one day, equals the flow rate (Q) x the time of flow V = Q x T = cf/day = cf/min x 1440 min/day The volume must be corrected to standard temperature and pressure (STP) P = Pressure = 14 7 lb/int @ STP V = Volume cf T = Temperature in degrees above absolute Zero = 491 58oR @ STP Using the Ideal Gas Law P1V1/T1 = P2V2/T2 Solving for V2 =P1V1T2/P2T1 PAGE 4 R603 UPDATE-43 3/25/96