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Firestone Store 03573 400 North El Dorado Street, Stockton, California <br /> October 25, 1995 VES Quarterly Report and Request for Closure-4589 Page 9 of 14 <br /> 3.4.2 Mass Removed based on Analytical Results <br /> The San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) uses <br /> a simple molecular weight calculation to convert ppm analytical values to mass <br /> values when permitting air treatment facilities. That conversion calculation has <br /> been used here to estimate the mass of hydrocarbon removed during system <br /> operation based on analytical results generated over that operational period. <br /> The SJVUAPCD calculation states that: <br /> X ppm VOCs x X rt 3 x 7-9 pounds x 1 pound•mole x 1440 sans AS X pounds <br /> pound-mole 386 tt ay -"day`W <br /> (lab results) (set air (molecular weight Imoleculw volume (time (vOc mass <br /> flow rate) of weathered gas; of ideal pas) conversion) treated) <br /> SJVUAPCD estimate) <br /> The two variable components in this equation are the ppm concentrations from <br /> the laboratory analyses and the time period of system operation at these <br /> concentrations. <br /> Using the TPH-G Concentration Graph, constant values have been established <br /> for these two variables by estimating an average TPH-G level for each seven- <br /> day operational period (each seven-day period is equal to the sampling <br /> frequency). Based on the constant ppm concentration determined for each <br /> seven-day period, the mass calculation was performed for each week of system <br /> operation, with the sum of those calculations being equal to the total mass of <br /> TPH-G removed. An example calculation for the one week period from <br /> November 24 through November 30, 1994, is included in Appendix 7.7. <br /> As stated previously, the TPH-G off-vapor concentrations ranged from a <br /> maximum of 667.7-ppm at initial startup on November 4, 1994, to 28.7-ppm <br /> at final shutdown on May 8, 1995. Based on these results, and the SJVUAPCD <br /> calculation, an estimated 195-pounds of TPH-G compounds have been removed <br /> from soil at the site. <br /> The difference between the mass removal estimate based on carbon use (280-lbs) <br /> and the estimate based on the conversion calculations (195-lbs) may be <br /> attributable to a number of factors. One of those factors is diminished adsorption <br /> capacity of the carbon due to elevated vapor moisture content and temperature. <br /> It is reasonable to presume that the actual mass of TPH-G removed from the <br /> subsurface at this site is a value somewhere between the two estimates. <br /> i <br /> • <br /> RYANAEURPHY. WCOMORATIM ]Dearer <br /> )I�riremse�l CWfibmcd"I Lm Angek <br />