COMPLIANCE INFO_1991-1992 - Laserfiche WebLink

Home Browse Search

SF,NT BY:Commerce 12- 9-91 3:24AII ;# 6 4 Over the entire lifetime of a power plant project it probably doesn't exceed about two or three percent of the Total moisture in the landfill. Supporting computations are provided in the attached table . These are for several sites all of which are in California. The sites are designated according to eneral location. For example, 'INC V means the first- listed northern California site; SC 3 is the third- listed southern California site. Column 1 shows total gas energy recovery (billions of Btus) for the year 1989 through November 8 (total of 312 days) as the starting point. Assuming 1009 Btu$ per cubic foot of pure methane and using the typica plant inlet methane content for each fachi.ty, the inlet flow rates (millions of standard cubic feet per day) were calculated as shown in Column 2. The figures inparentheses in Column 2 are the typical inlet gas Btu contents per cubic foot , by plant. Column 3 shows the estimated amounts of waste in each landfill in millions of tons in place. These figures were obtained extramurally from landfill operators andgovernmental agencies during power plant project development. The assumed moisture content (column 4) is based upon Pacific Energy's experience with various landfills and knowledge of these specific ones. The percent moisture figures used are almost certainly correct within a factor of two. The third and fourth columns directly yield the fifth, which is millions of tons of water in lace. Water in the saturated as was computed from an assumed landfill gas temperature of 140F. At this temperature, the vapor pressure of water is about 150mm of mercury. At one atmosphere total pressure, this represents about 20% by volume. Thus Col 6' which is the extraction flow rate of water vapor in millions of standard cubic feet per day, is simply 20 percent of Column 2 Column 7 is the same as Column 6 except for the change of units to the more usual gallons per ' day. Finally, Columns T and b lead directly to Column 8, which is the percent of landfill water content removed per year through the process of gas extraction. The figures in Column 8 are almost certainly correct to within a factor of about four. Grouadu ter Cgatamination To date, there is no scientifically defensible study to show that returning condensate, or not returning it, has any bearing on groundwater contamination caused by a landfill. This is the carie, in part, because of the cellular structure and resulting horizontal stratification present in most landfills . The lifts of waste ordinarily constructed in a landfill are separated by soil laars. The soil layers tend to be limited in terms of hydraulic permeability, while the trash (especially if relatively fresh) tends to be fairly easyfor moisture to move through. It can be expected, therefore, tat as condensate percolates down into a landfill from a shallow point discharge, will tend to