The Southern Ocean Landfill (SOLF) is located on a 283 acre tract in Ocean County, New Jersey. The privately owned landfill is comprised of two distinct disposal areas, a 50 acre unlined landfill area and a 12 acre lined landfill. In an effort to achieve proper closure, Ocean County entered into a partnership agreement with the New Jersey Department of Environmental Protection (NJDEP) to assume responsibility for the closure work. The NJDEP provided a grant in the amount of $15 million to the Ocean County Board of Chosen Freeholders to fund the proper closure and long-term, post-closure operation, maintenance and monitoring of the 50 acre unlined landfill area.
The County retained Hatch Mott MacDonald (HMM) to complete permit application packages, prepare the engineering design and provide construction management services to close the 50 acre unlined landfill and, under a separate contract, to provide post-closure management services. The closure design included consolidation of waste areas within the landfill footprint and regrading to reduce steep sideslopes. The cap design consisted of a 12 in landfill gas collection and bedding layer overlain by a 40 mil thick synthetic geomembrane cap, an 18 in sand drainage layer (incorporating drainage piping in shallower topslope areas) and 6 in of vegetated topsoil. The gas management system consisted of a network of perforated collection pipes placed in the sand layer which passively vents gases to the atmosphere. On the surface of the landfill, three miles of drainage swales and downchutes were constructed to convey stormwater runoff to retention basins at the base of the landfill.
HMM’s construction management services on the project included shop drawing review, construction oversight, quality control on all cap elements, contractor invoice processing, design interpretations, punchlist and as-built documentation.
As part of its design, HMM developed an innovative stormwater management design that achieved a zero discharge under compounded 100 year and subsequent 10 year storm events. This design was a key factor in securing the approval of the New Jersey Pinelands Commission. HMM also resolved issues related to hydrogen sulfide gas odors associated with the 12 acre adjoining landfill by specifying and installing a gas flare. We currently provide operation and maintenance of the flare.
HMM also completed the design and construction management of a new leachate pumping station and force main for the lined landfill area. The new force main also conveyed condensate from the active gas management system to the leachate storage facility. The leachate storage facility consisted of an in-ground, exposed geomembrane lined lagoon. HMM designed and oversaw the installation of surface aerators on the lagoon. Leachate from the lagoon is trucked to the Ocean County Utilities Authority (OCUA) treatment plant. HMM prepared procurement documents for the five-year leachate hauling contract.
HMM has provided post-closure monitoring of the active gas venting system on the 12 acre lined landfill and groundwater quality monitoring data review. We performed a statistical analysis of groundwater quality trends for 14 years of data and determined the cap had a positive effect on groundwater quality. The data supported a proposal to reduce monitoring from quarterly to annual.
Other tasks in HMM’s scope of work included:
HMM incorporated sustainability into its landfill closure design: