Phase 2 Landfill Closure, Hingham

Overview:

The Town of Hingham contracted with DCI staff to conduct a value engineering of the landfill’s pre-existing design and to negotiate design changes on their behalf with the Massachusetts Department of Environmental Protection (DEP) Southeast Regional Office.

About:

The Town of Hingham planned for the construction of its Phase 2 Landfill Closure (9.25-acres) for several years. After receiving preliminary cost estimates well in excess of the locally approved budget, the Town contracted with DCI staff to conduct a value engineering of the pre-existing design and to negotiate design changes on their behalf with the Massachusetts Department of Environmental Protection (DEP) Southeast Regional Office.

Following negotiation of the design changes with DEP, we developed detailed cost estimates, finalized the design and assisted the Town with permitting, public bidding and construction administration.

Approach

In May 2011, DCI staff submitted the revised Phase 2 Landfill Closure Design Plans and Specifications to DEP for approval. The submittal included revised technical specifications and drawings and revised Hydraulic Evaluation of Landfill Performance (HELP) modeling calculations. Large cost savings were realized in the revised cap detail and drainage and gas management systems.

Based on new investigations and findings, DCI staff designed a conventional textured liner capping system for the 6.25-acre sloped portions of the landfill, excluding the flatter compost area. A conventional smooth liner cap augmented by a 12-inch-thick reclaimed asphalt layer was approved over the flatter 1.5-acre compost area. The conventional cap design portions included soil gas vents and 6-inch-thick soil gas vent layer, the 40 mil impermeable High Density Polyethylene Liner (HDPE) material, a 12-inch-thick minimum sand drainage layer and an 8-inch-thick minimum vegetative layer.

The Town also investigated and designed a photovoltaic system to be placed over the 1.5 acre, non-compost area portion of the landfill that was closed using smooth flexible liner. DEP issued a “Technical Review Post-Closure Use Approval” for the Hingham Phase 2 Landfill Closure project in August 2011 and authorized the Town to proceed with Phase 2 landfill closure activities in accordance with their permit and all other applicable permits and approvals.

In the late summer and early fall 2011, DCI staff assisted the Town with public bidding of the project and made recommendations for awarding the project We then provided full-time construction resident engineering and construction administration services. During construction, DCI staff was responsible for overseeing Quality Assurance and Quality Control (QA/QC), including all geotechnical and HDPE liner testing. We observed construction activities for general conformance with the project plans and specifications, and took construction photographs on a daily basis for further documentation.