The Old Dixie MSW Landfill is the Authority’s active disposal site for the MSW that remains. The site is comprised of over 1,200 contiguous acres, with 90 acres permitted for municipal solid waste (MSW) with a total capacity of 11.4 million cubic yards. The initial load of waste was placed in July 1996, with an expected lifespan of 30 years. Today with approximately 60% of the permitted footprint constructed, the site’s remaining capacity is in excess of 34 years as a result of continually improving compaction rates, currently at 1,300 pounds per cubic yard. Extending the life of the landfill has also been achieved by diverting carpet waste, recirculating leachate, and using heavy equipment outfitted with localized GPS technology to achieve and monitor higher in-place densities than the original design parameters. The active landfill also includes an active landfill gas extraction system.
The Authority has sufficient acreage at the site to provide good borrow source material for the construction of soil liner as well as cover material for closures. However, because the soil does not meet the stringent requirements for permeability of a Subtitle-D bottom liner system (i.e. less than 1 × 10-7 cm/sec.), the Authority researched alternative liner systems that could 1) take advantage of onsite resources thus reducing material and transportation costs and 2) continue to meet the regulatory requirements of the Georgia Department of Natural Resources – Environmental Protection Division. With the assistance from the design engineer (Weston Solutions), the Authority was able to demonstrate that a 24-inch thick 1 × 10-5 cm/sec soil liner in combination with a geosynthetic clay liner was less permeable than the standard 1 × 10-7 cm/sec clay liner and thus receive approval as an alternative liner for the remaining 74 acres.
Another design enhancement involves the leachate drainage-protective cover layer above the synthetic geo-membrane. The prescriptive requirement is for the bottom 12 inches of drainage material to have permeability greater than 1 × 10-2 cm/sec and the top 12 inches to have permeability greater than 1 × 10-3 cm/sec. This design allows for free flow of leachate to collection trenches and sumps for subsequent removal while protecting the geo-membrane liner from sharp objects within the first lift of waste. The Authority quickly recognized that this element of construction for the Subtitle-D bottom liner system was the most expensive, due to it being required to have a minimal calcium requirement to prevent clogging. With northwest Georgia being underlain by limestone rock which is unacceptable, only river sand or crushed granite meet the low calcium content requirement. Both of these materials are located more than 60 miles from the site, adding significant transportation cost. Therefore, the Authority began searching for alternatives to the typical crushed granite aggregate (size 89) mined and processed from Georgia quarries located in and around the metro Atlanta area of Georgia. The Authority identified a combustion by-product of the power plant industry, washed bottom ash from the spent residual of coal combustion that has a density that is approximately 35% less than its granite counterpart and still has the required permeability characteristics and low calcium content. Due to the more angular nature of the coal ash (clinker), the Authority’s design engineer (Weston Solutions) completed an evaluation for puncture of the geo-membrane that concluded that a minor upgrade to the cushioning geo-textile was necessary to be able to use this material over the geo-membrane for the leachate drainage-protective cover layer. Once again, the Authority identified a suitable construction material alternative that was more cost effective based on the lower density and overall material cost, in part due to the material being located closer to the Dalton site. This time, the design alternative has the added benefit of being an industrial waste materials used for beneficial reuse.
Finally, the site utilizes leachate recirculation as its primary method to manage leachate generated by the facility. Leachate from the lined Sub-Title D landfill is either recirculated back into the waste or is pumped and hauled to Dalton Utilities and managed as industrial waste water. During 2008 approximately 66% of the leachate generated was recirculated and the remaining 34% was hauled to Dalton Utilities; therefore, saving significant time, money and resources.