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The boundary conditions for steady-state radial flow of LFG are: P=PW r=R,, P = PL r = RILFG The term RILFG is the radius of influence of a LFG collection well, and denotes the radial distance from the collection well where the pressure induced by the well is equal to the positive pressure PL within the landfill. Substituting the above boundary conditions for steady-state radial flow of LFG into the above steady-state radial pressure distribution equation results in a steady-state radial LFG pressure distribution equation: In(r R ) I'2(�) — Pw2 = \PiFG — 1'w) In( RI FG) Eauation 3 RW Where: Pr = Absolute pressure measured at a distance r from the collection well (g/cm-s2) PLFG = Absolute internal LFG pressure (Pa,m + PL) (9/cm-s2) Pte, = Absolute pressure applied to the collection well (g/cm-s2) RILFG = Radius of influence of the landfill gas collection well (cm) Rw = Radius of the gas collection well (cm) r = Distance from the collection well to pressure monitoring probe (cm) The Radius of Influence (RI) is one of the most important parameters to be considered in the design of a LFG collection system. Extraction wells should be placed so that the overlap of their radii of influence covers the entire landfill surface. The radius of influence (Rl,,,,) calculated using equation (1) represents the radial distance from the collection well where the induced pressure equals the atmospheric pressure. The radius of influence (RILFG) calculated by equation (3) represents the radial distance from the collection well where the pressure induced by the collection well equals the internal positive pressure of the landfill. The relationship of these two radii is shown in the following boundary flow conditions figure. As this figure illustrates, in a landfill, the atmospheric radius of influence also denotes the area surrounding the collection well where air intrusion is able to occur. It must be noted that both radii of influence (RI atmospheric and RILFG) are not constant parameters, but will vary depending on the amount of vacuum applied to the collection well and, in the case of RILFG , on the magnitude of the internal LFG pressure PL . It also must be noted that both radii of influence calculated by equations 1 and 3 represent averages over all the flow paths. These radii of influence should not be considered the maximum extent of any pressure gradient created by the collection well. 6 Installation Work Plan to Remediate Landfill Gas Migration J:\Allied\Forward\Workplan\Forward Evaluation - rev4.doc:9/15/2004 Ll