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• allowing oxidation to continue to degrade the hydrocarbons that <br /> are present <br /> ON SITE ANALYSIS <br /> During the two hour tests, a photoionizing detector (HNu PID <br /> w/10 2 ev bulb) and GasTech LEL/02 meter were 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 common used LEL for gasoline <br /> is 1 40 = 14 , 000 ppmv * mg/L/250 ppmv * 6 21X10-5* * flow rate <br /> (cfm) * 120 minutes = 1 04 lb at 5% LEL and 2 08 lbs at loo LEL <br /> The extraction well vacuum was measured with a murcury manometer <br /> and the surrounding wells were gauged with a water manometer <br /> FLOW RATES <br /> Flow rates are measured at the site by use of orifice plates A <br /> one inch orifice was placed directly on the casing of the monitor <br /> well , carefully avoiding any vacuum leaks An orifice plate <br /> restricts the flow of air across it This restriction causes a <br /> pressure drop across the orifice By measuring the resulting <br /> pressure change across the orifice it is possible to calculate <br /> the air flow rate The flow rate is calculated by the pressure <br /> drop (millimeters (mm) water) across a square edge orifice plate <br /> Ve = CK sqr (P) Q = AVe <br /> Where <br /> Ve= velocity 3n feet per minute (fpm) <br /> C = Orifice Coefficient = 0 65 (for orifice used) <br /> K = Constant = 794 6 mm water <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 sgr (P) <br /> CALCULATIONS <br /> To calculate the pounds (lb) per day the concentration is <br /> multiplied by the volume of air produced in one day <br /> *The lab reports the Concentrations (C) of the air sampling in <br /> ug/liter The first step is to convert this value to lbs/cf <br /> u <br /> /ruiunr7c� <br /> �+ �+ xvv�./ iug/ i x V VUVUV1g/ ug X U UUL211 /g 51lJ X <br /> 28 321/cf = 0 00000006211b/cf <br /> The volume of air produced in one day, equals the flow rate (Q) x <br /> the time of flow <br /> V = Q x T = cf/day = cf/mi.n, x 1440mzn/day <br />. The volume must be corrected to standard temperature and pressure <br /> (STP) <br /> 3 <br />