Passive Soil Vapor Extraction - GSI Environmental Inc.

SRNL-STI-2009-00571Rev. 1basis. In areas within the contiguous United States, the diurnal atmospheric pressurefluctuations can range between 0.3 to 6 inches of water, with pressure highs observed inthe early morning and lows in the afternoon (ESTCP, 2006). Weather-front atmosphericpressure changes, on the other hand, typically last 3 to 5 days and can be of asignificantly higher magnitude than the diurnal fluctuations (Neeper, 2002). Typicaldiurnal changes in the barometric pressure are shown in Figure 2.3.aSurface PressureWell Pressure102010101000Pressure, mbarFlow, scfm80604020bMVE-8MHV-602/23/02 3/2/02 3/9/02 3/16/02 3/23/02 3/30/02 4/6/02Figure 2.3a: Typical Diurnal Changes in the Barometric and Subsurface Pressure at an SRS site,SC. b. Typical Daily Flow Rates Measured in Extraction Wells Undergoing Barometric Pumpingat an SRS Site, SC (adapted from Riha, 2005c).The pressure wave attenuation capacity of a site can also affect the duration of theequilibration period and is a function of the depth and vertical permeability of the vadosezone. Deep vadose zone contamination (Figure 2. 4), low permeability strata betweensurface and target zone, or presence of a surface seal (as utilized in BERT TMapplications) can extend the equilibration period resulting in longer exhalationresponses.8 Enhanced Attenuation TechnologiesPassive Soil Vapor Extraction