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HYDROCARBONS REMOVED FROM A VADOSE WELL SOP -25 Rev: JO'C POUNDS OF HYDROCARBON IN AN AIR STREAM INPUT DATA: 1) Air flow rate acfm (usually by Pitot tube) 2) Air pressure at the flow measuring device (in inches of H2O) (use {-) for vacuum) 3) Air temperature at the flow measuring device. 4) Hydrocarbon content of air (usually in mg/M3) for ppmv you need molecular weight. 5) Length of time (usually hours) over which flow rate occurred) From periodic measurements, a calculation of total pounds of hydrocarbons removed from a well or from a system are calculated. The input data listed above are measured at a point in time. To calculate quantities removed, some assumptions must be made about what was happening between measurements. The following assumptions will be used for the sake of consistency: ASSUMPTIONS: 1) Air flow for the period equals the average of the initial and final reading for the period. 2) Pressure and temperature for the entire period will be the final reading. 3) Hydrocarbon concentration for the period equals the average of the initial and final reading. 4) The hours of operation can be taken from an hour meter, an electric meter or will be assumed to be equal to the time between measurements. 5) If the unit is found down - try to determine how many hours it did operate and use the data taken for the previous period to make the calculations. Restart the unit and then take data to start the next period. SAMPLE DATA AND CALCULATIONS Date Time Temp Press HC conc Air flow Calc. deg F in H2O mg/M3 acfm Ib. rem. 1/6/95 11:00 70 -46 2000 120 1/7/95 13:00 55 -50 1350 90 1/8/95 10:00 80 -13 750 100 7.4 Calculate the pounds of hydrocarbon removed from the system during the basis period from 13:00 (1:00 pm) on the 7th to 10 am on the 8th. Pressure and temperature of the measurements (at the flow meter) must be corrected to the P and T used to report the HC concentration (which are P = 1 atm and T = 70 deg F). 1 atm = 14.7psia, 760 mm Hg, or 407 in H2O. Tam = 460 + T deg F Hours of operation = 21, T = 80, P = -13, HC = (1350+750)/2 = 1050 mg/M3' Flow = 95 (460+70) (407-13) 28.3 1050 1 21 x 60 x 95 x ----- — ---- x ----- x------ x ---- -- x------ = 7.4 lb (460+80) 407 1000 1000 454 hr min cu ft M3 g Ib Ib ----- x ---- x ----- x Tc., x Pcorr x ------ x ------ x ----- = ------ basis hr min cu ft M3 g basis 21 x 60 x 95 x 0.98 x 0.97 x 0.0283x 1.050 x1/454 = 7.41 b. cumulative lbs. (the running total) = the sum of all the previous periods. Note: If results are given in ppm, an assumption about the molecular weight of the hydrocarbon must be made to get Mg/M3. ppmv x molecular wt. /24.1 = mg/M3. (Use 102 for gasoline)