Source Zone Delineation Demonstration Report - Triad Resource ...

5.2.1.2 In Situ PermeabilityThe transient pressure distribution measured at a site during soil vapor extraction can be used to estimatethe soil permeability to vapor flow. The change in the subsurface pressure distribution with time P ? (r,t) isgiven by (Bear, 1979; Johnson et al., 1990): x' Q eP dx(1) k x4pm2r eμ μ 4kPatmtThe behavior of the integral is such that for (r 2 /4kP atm t) less than 0.001, its value is very close to theasymptotic limit, and for (r 2 /4kP atm t) less than 0.1, equation (1) can be approximated by:where 2 ' Qr eμP 0.5772 ln ln t k 4kPatm 4pm μ (2)P ’ = gauge pressure measured at distance r and time t (g/cm-s 2 );m = vent well screen interval (cm);r = radial distance from the vapor extraction well (cm);k = soil permeability to air flow (cm 2 ); = viscosity of air (1.8 x 10 -4 g/cm-s at 18 C); = air-filled soil void fraction;t = time (s);Q = volumetric vapor flow rate from the extraction well; andP atm = ambient atmospheric pressure (where 1 atm is equal to 1.013 x 10 6 g/cm-s 2 ).Equation (2) predicts that a semilog plot of the pressure (P ’ ) as a function of time will yield a straight linewith slope A and y-intercept B equal to:QA (3) k 4pm μ 2Qr eμB 0.5772 ln (4) k 4kPatm4pm μ March 2003 5-34 OU 12 Demonstration ReportFinal