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San Joaquin County EHD September 5, 2008 Page 7 of 10 states that 1 psig of injection pressure is necessary for every 2.3 feet of hydraulic head (US EPA, 1995). . Ground Zero proposes installing ASW1 approximately 15 feet below the water table which according to the US EPA would require a minimum injection pressure of 6.5 psig. The minimum injection pressure necessary to induce flow is given by: Pmin (psig) = 0.43 Hi, +Ppacking+Pformation The pressure at which fracturing of the aquifer can occur is given by: Pfracture (psig) = 0.73 D Where Hi, is the depth below water.table to the top of the injection well screened section (feet), Ppacking + Pformation is air entry pressures for the well annulus packing material and the formation (psig), and D is the depth below ground surface to the top of the air injection well screened interval. Ppacking + Pformation is generally negligible and for this model is assumed to be 0.2 psig, the average value for sand (Leeson, et..al., 2002). We can conclude that the minimum pressure required is 6.7 psig and closely fitting the EPA model projections. Aquifer fracturing is likely to occur at 5 1.1 psig. "At start-up it is not unusual for users to exceed Pmin by as much as 5 to 10 psig to initiate flow quickly. The injection pressure then generally declines to about Pmin as steady flow conditions are approached. Pressures in excess of Pfracture can cause fracturing of the formation ; however, as the pressure drops off rapidly away from aninjectionpoint, the extent of fracturing in most cases is expected to be limited to the area immediately surrounding the well"(Leeson, et. al., 2002). According to the calculations above, even if the-initial pressures exceed Pt„in by as much as 5 to 10 psig the estimated Pfracture will not be exceeded. "It is desirable to begin the test with an air injection flow rate of 20 ft3/min if possible. The air injection pressure at the on-set of flow should be recorded, as well as pressures every 5 to 10 minutes" (Leeson, et. al., 2002). Increased flow rates and injection pressures generally causes in. increase in the density of the air flow network, and can cause air to breakthrough soil layers under which it might normally be stratified at lower injection flow rates (<5 cfm). Low air flow rates generally yield less extensive and less effective air distributions (Johnson, P.C., et. al., 2002). Ground Zero proposes initiating the pilot test with an air injection flow rate of 20 cfm if possible without exceeding Pfracture. GAGROUNDWHARRYS AUTO\Reports\Workplans\wp sve pilot test.doc