Since 2006, Trihydro has been the prime consultant assisting the Eden Valley Solid Waste Disposal District (EVSWDD) with various solid waste management projects. Changes to their solid waste management system have been driven by Wyoming Department of Environmental Quality (WDEQ) concerns with existing groundwater monitoring data and limited remaining permitted disposal capacity at their unlined landfill. Additionally, the results of the integrated solid waste management (ISWM) plan prepared by Trihydro demonstrated that the continued operation of the landfill was not economically feasible.
Initial project activities included a groundwater investigation and expansion of the groundwater monitoring network for the unlined landfill, which was funded by Wyoming’s Municipal Solid Waste Landfill Monitoring Program. Once a final decision was made to close the landfill, Trihydro designed, permitted, and constructed a new transfer station, and is assisting the EVSWDD with the operations contract. Most recently, Trihydro designed, permitted, and oversaw the construction of a water balance cover system for the 20-acre unlined landfill footprint. The water balance cover project included the identification and characterization of a suitable borrow source, a vegetation survey, and extensive unsaturated flow modeling of various climatic conditions to demonstrate the performance of the water balance cover system. Modeling of climatic scenarios simulated performance during an average year, the year with the highest ratio of precipitation to potential evaporation, and the wettest 10-year period. The water balance cover system includes two field-scale pan lysimeters with instrumentation and data loggers that will be used to evaluate the performance of the final cover system over time. In conjunction with the closure permit application process, Trihydro facilitated negotiations with the WDEQ for a deferred closure schedule that accommodated a large amount of debris from a school construction and demolition project. The anticipated waste stream allowed the facility to accommodate the needs of the local community and reduce the amount of clean fill material required to reach final grades.
Various projects at the Eden Valley Landfill and Transfer Station were complicated by the fact that the existing landfill was located on federal land leased from the Bureau of Reclamation (BoR), which does not have a mechanism for disposing of property. Trihydro facilitated the process of transferring the existing landfill lease area to the EVSWDD and secured a materials management lease on adjacent BoR land to provide a low-cost borrow source for the approved water balance final cover system. Additionally, Trihydro successfully coordinated the requirements of the BoR, Bureau of Land Management (BLM), Environmental Protection Agency (EPA), Health and Human Services (HHS), and the General Services Administration (GSA) to convey an additional 45 acres of public land adjacent to the landfill as a buffer for the landfill and provide a location for the new transfer station.
Trihydro provided bid support services, contract administration, and construction quality assurance throughout the construction of the landfill closure. The Engineer’s Estimate for the closure was $877,392 and the 20-acre closure was constructed for $717,590. Currently, Trihydro performs environmental monitoring services for EVSWDD in the form of semi-annual groundwater sampling, quarterly methane monitoring, monthly lysimeter monitoring, and reporting.