The Crossroads Landfill has been in operation since 1976 to serve the waste disposal needs of Maine residents and businesses. Waste Management Disposal Services of Maine (WMDSM) acquired the facility in 1990. Through a series of Maine Department of Environmental Protection (MDEP) permits, WMDSM has expanded the facility to cover approximately one half of the 897-acre site. With the continuing demand for residential and commercial waste disposal services throughout New England, WMDSM chose to create additional disposal capacity at the site. They also want to reduce the potential long-term environmental liability associated with more than one million cubic yards of waste in unlined cells that came with the site purchase. WMDSM selected Geosyntec to provide engineering, permitting, and construction quality assurance services for the phase expansion of the facility.
Geosyntec's Scope of Services
The glaciomarine silts and clays up to 70 feet thick underlying the site make it well suited for a landfill from an environmental perspective. However, the site does pose geotechnical design challenges. The primary geotechnical issues are associated with sliding failures which can put the site's operational future in jeopardy. A slide failure had occurred at the site prior to Geosyntec's involvement. Geosyntec's approach to achieving both WMDSM objectives (capacity expansion and liability reduction) involved excavating over one million cubic yards of waste from the unlined area where a landslide had occurred. The excavated area was then used to construct a modern lined landfill for both excavated wastes and 4.5 million cubic yards of additional waste. Geosyntec designed a phased approach of excavating/moving some of the waste into a lined cell, lining the excavated area; excavating/moving more waste from an unlined area into the newly lined area; and repeating the sequence until the entire 45-acre area is lined. Doing so also allowed for the creation of the additional capacity concurrent with the excavation/construction process. Geosyntec performed a series of complex stability analyses to develop a safe method for excavating the unlined waste without causing stability failure of surrounding landfill units. We performed detailed consolidation testing and settlement analyses to optimize nearly 100,000 wick drains that promote clay strength gain upon filling the landfill with waste. The increase in foundational strength allowed substantially more waste to be placed in the landfill over a shorter period of time than would have otherwise been possible. Geosyntec's design also included over a mile of mechanically stabilized earth (MSE) perimeter berms around the newly lined area. The over-steepened exterior slope of these berms increased the disposal capacity of the newly lined area by several hundred thousand cubic yards. The Geosyntec design included installation of vibrating-wire piezometers and inclinometers under and around the newly lined area to monitor foundation pore-pressure and consolidation, thereby ensuring the ongoing safety of the facility for additional waste disposal configurations.
MDEP granted WMDSM an expansion permit in a risk-adverse regulatory climate in a community that, because of the previous failure, was skeptical of ongoing site operations. The project required a capital expenditure of approximately $50 million to address the waste relocation and create additional capacity that will serve New England disposal needs for years to come. WMDSM has not quantified the long-term reduction in environmental liability realized by excavating the old unlined waste; however, the project will continue to be a net gain, both financially and in terms of goodwill earned with the regulatory agency and the local community.