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0 points does not indicate that a complete exposure pathway exists, but it does signal that the primary control system is not adequately controlling LFG by itself. If this occurs, additional monitoring and contingency actions will be implemented over a period of time as outlined in Figure 2. The additional activities will likely take several months to complete if the on-going monitoring indicates the most aggressive response is needed (i.e., install vertical vent wells in the dump and potentially convert the City's area -wide LFG system to active venting). A design report for any modifications to the LFG system will be submitted to the MPCA for review and approval at least two months prior to installation and the design report will include an installation timeline. Boreholes for vertical vent well installation will be at least 36 -inches in diameter, installed with 6 -inch diameter perforated piping, and backfilled with non -calcerous rock with a minimum diameter of 1.5 inches. The months -long schedule will be required for the City to install vertical vent wells and conduct a publicly -bid project to complete the liner system in Block B (if not already completed as part of development at that block), trench in new subsurface header piping for the 18 -acre consolidated dump area, and install a central active venting system operations area with a blower, power, controls, etc. It is expected that the secondary control measure (individual building venting systems) will continue to address the concerns for LFG exposure while the City completes the area -wide contingency actions. 2. The monitoring by the development block owners of their individual building venting systems represents the last subsurface monitoring point for assessing the overall LFG exposure pathway. As shown on Figures 2 and 3, the presence of persistent elevated readings in the City's system will trigger an increased level of monitoring at nearby building systems. The initial presence of elevated LFG at the building venting systems signals a more immediate concern and so provisions will be made to increase monitoring and rapidly implement contingency actions at the buildings if appropriate (i.e., convert the building venting system to active). The development block owners have the ability to rapidly convert their systems to active as compared to conversion of the City's area -wide system. This is because the subsurface and vent portions of the buildings' venting systems will already be constructed to operate as either passive or active, and so they will only need to add a blower and its controls to the building where power will already be available. Therefore, the building venting system represents the fastest means to address worst case conditions involving a nearly complete LFG exposure pathway as identified by either the City or development block owners' monitoring (see Figures 2 and 3). P:\Mpls\23 MM\62\2362489\WorkFiles\Eastern RAP 2008\LFG CAP\Revised March 2009 CAP\LFG Contingency Action Plan Revised March 2009.doc