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F-12 REFERENCES APPENDIX G DiGiulio,C.Paul,R.Cody, R.Willey,S.Clifford,R.Mosley,A.Lee,K.Christensen and BAROMETRIC PRESSURE,RAINFALL,and SOIL DRAINAGE R.Costa,2006a. Comparison of Geoprobe PRT and AMS GVP Soil-Gas Sampling Systems with Dedicated Vapor Probes in Sandy Soils at the Raymark Superfund Site. Barometric Pressure Fluctuations EPA/600/R-06/111. National Risk Management Research Laboratory,Office of Research and Development,U.S.Environmental Protection Agency.Cincinnati,OR Soil Gas November. http://www.epa.gov/ada/pubs/report.html. Massmann and Farrier(1992)evaluated the significance of barometric pressure Hartman,B.2006.How to Collect Reliable Soil-Gas Data for Risk-Based Applications- fluctuations on the transport of atmospheric gas into the vadose zone. They examined Specifically Vapor Intrusion;Part 4-Updates on Soil-Gas Collection and Analytical situations in which barometric fluctuations will yield a significant affect on the vadose • Procedures,LUSTLine Bulletin 53,September 2006. zone. Model calculations showed that fresh air may migrate several meters into a highly permeable subsurface during large barometric pressure cycles and the depth of Smith, Roy-Keith,2003.Guide to Environmental Analytical Methods, 5'h Edition.Genium penetration increases as the thickness and permeability of the vadose zone increases. Publishing Corporation,2003. Massmann and Farrier(1992)thus suggested that the concentration of volatile contaminants may be lower when barometric pressures are high and that soil gas SW-846,1996; Test Methods for Evaluating Solid Waste,Physical/Chemical Methods, measurements will show the largest fluctuations during times of rapidly rising or falling S W-846:Methods 80006,8015,8021,82608,Various Revisions,U.S.Environmental barometric pressures. During these large barometric pressure changes,as indicated by Protection Agency,Washington,D.C., 1996.SW846 On-liner httv://www.epa.gov/sw- Figure 8 of their paper,soil gas at 1.5 meters(5 feet)may be diluted with atmospheric 846/sw846.htm air by 30 to 50 percent. US EPA, 1999:Compendium of Methods for the Determination of Toxic Organic Surface Flux Compounds in Ambient Air. Methods TO-13,TO 15,TO-17,Second Edition,U.S. Environmental Protection Agency, Research Triangle Park,NC,January 1999;EPA Clements and Wilkening(1974)demonstrated empirically that atmospheric pressure 600/625/R-961010b. changes of one to two percent associated with the passage of frontal systems will produce changes in the flux of radon from the subsurface by 2010 60 percent. The actual magnitude of the change in the radon flux depends upon the rate of change of the barometric pressure and its duration. The effect of pressure changes to VOC concentrations in soil gas is expected to be similar. Rainfall Events Surface flux Kienbusch and Ranum(1986)evaluated the affects of rainfall on the collection of flux • chamber measurements on open ground. In tests at a simulated landfill,water was added to dry soil cells to simulate rainfall. Trace precipitation(0.01 inches)had no effect on measured emission fluxes from the ground. Heavier rainfall(0.4 inches), however,did have an effect. The emission flux was decreased by 90 to 95 percent and the reduction in emissions lasted for over eight days. These results are consistent with other field observations(Radian Corporation,1984;Eklund, 1992). Soil Drainage Gardner et al.(1970)derived approximate solutions for unsaturated flow following 12/10/2009 _89- 12/10/2009 _90-