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Firestone Store#3573 400 North El Dorado Street, Stockton, California October 25, 1995 VES Quarterly Report and Request for Closure-4589 Page 9 of 14 ' 3 4 2 Mass Removed based on Analytical Results The San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) uses a simple molecular weight calculation to convert ppm analytical values to mass values when permitting air treatment facilities. That conversion calculation has been used here to estimate the mass of hydrocarbon removed during system operation based on analytical results generated over that operational period. The SJVUAPCD calculation states that X ppm VoCs x X tt 3 X 75 pounds X I pound-mole X 1440 mins p X pounds mins pound-mole 386 tt 15Y day— ' (lab results) (set air (molecular weight (molecular volume (time (VOC mass flow rate) of weathered gas; of ideal gas) conversion) treated) SJVUAPCD estimate) ' The two variable components in this equation are the ppm concentrations from the laboratory analyses and the time period of system operation at these concentrations. Using the TPH-G Concentration Graph, constant values have been established for these two variables by estimating an average TPH-G level for each seven- day operational period (each seven-day period is equal to the sampling frequency) Based on the constant ppm concentration determined for each seven-day period, the mass calculation was performed for each week of system operation, with the sum of those calculations being equal to the total mass of TPH-G removed An example calculation for the one week period from November 24 through November 30, 1994, is included In Appendix 7 7 As stated previously, the TPH-G off-vapor concentrations ranged from a p 9 maximum of 667 7-ppm at initial startup on November 4, 1994, to 28 7-ppm at final shutdown on May 8, 1995 Based on these results, and the SJVUAPCD calculation, an estimated 195-pounds of TPH-G compounds have been removed from soil at the site The difference between the mass removal estimate based on carbon use (280-lbs) and the estimate based on the conversion calculations (195-lbs? may be attributable to a number of factors One of those factors Is diminished adsorption capacity of the carbon due to elevated vapor moisture content and temperature It is reasonable to presume that the actual mass of TPH-G removed from the subsurface at this site is a value somewhere between the two estimates RYAN-M[7RPHY, 1NC70 RPORAIFW Deaver EnVboumenLd CA SbVC60n Ms011121gMent Los Angdes I