Project Overview

NTH originally became involved with the City of Pontiac’s Collier Road Landfill in 1982, when the former unregulated fill area was closed and a new landfill, fully compliant with Michigan’s then current P.A. 641 design criteria, was constructed. The new landfill unit included a compacted clay liner and a separate leachate collection system built on top of the former fill area. To mitigate potential groundwater contamination from the former fill, a perimeter soil-bentonite slurry wall and an internal perimeter drain were installed to lower the leachate/ groundwater head within the fill.

The facility was operated as a licensed municipal solid waste disposal landfill for over 20 years and reached final permitted capacity in 2006. At that time, NTH oversaw and certified installation of the final landfill cap and passive methane venting system. Due to on-going groundwater quality and methane questions, primarily associated with legacy issues from the former unregulated fill area, a Consent Agreement was reached with the Michigan Department of Environmental Quality (MDEQ) to declare the landfill closed and enter post-closure maintenance status in 2015. The Consent Agreement also included provisions for the City to access financial assurance funding mechanisms to allow them to utilize the dollars to fund ongoing maintenance and compliance activities, a unique solution at the time for MDEQ.

Since that time, NTH Consultants Ltd. has provided monitoring and maintenance services to ensure compliance with regulatory requirements, including compliance with provisions of the Consent Agreement, and to protect public health and the environment working with limited resources to address on-going PA 451 requirements.

Project Scope

NTH provided investigation, design, and construction services for the City throughout the site closure and landfill development process. As part of our services, NTH has assisted the City to address the presence of PFAS compounds detected in the landfill leachate, which is permitted to be discharged to the GLWA/WRC sanitary sewer. NTH conducted testing and developed a Best Management Plan (BMP) that includes measures to monitor and reduce the PFAS mass that is discharged from the site.

In accordance with a request from the Michigan Department of Environment, Great Lakes, and Energy (EGLE), NTH conducted sampling and analysis to evaluate PFAS concentrations in groundwater adjacent to and downgradient of the landfill. The sampling was conducted using strict quality control procedures that are necessary to eliminate potential cross-contamination of the samples from ambient PFAS. The results indicated minimal PFAS detections, some of which apparently attributed to upgradient sources. Evaluation of the groundwater flow conditions by NTH indicated that continued operation of the landfill’s leachate control/extraction system will likely be effective in mitigating the landfill as a source of continued PFAS to the local groundwater regime. EGLE accepted our findings and has not required continued PFAS monitoring.

Our project team has provided post-closure monitoring and maintenance services for the Collier Road Landfill since 2006. In addition to implementing the routine groundwater, leachate, and methane monitoring programs, we have performed supplemental groundwater and methane investigations to address potential off-site migration issues. NTH designed and supervised installation of a supplemental leachate well extraction system to supplement the historic gravity drain as well as stormwater management concerns. We have also represented the City of Pontiac during interactions with the Michigan Department of Environment, Great Lakes, and Energy (EGLE) to address regulatory compliance requests and financial assurance inquiries, including adherence to the Consent Agreement provisions.

Specific services that NTH provides to the City of Pontiac for the Collier Road Landfill include:

  • Part 115 leachate, surface water, and groundwater monitoring and reporting
  • GLWA/WRC leachate discharge permitting and monitoring
  • Landfill cover inspection and maintenance
  • Part 115 methane monitoring and reporting
  • Groundwater monitoring well installation, abandonment, and maintenance
  • Gas monitoring probe installation and maintenance
  • Storm water inspection and sampling
  • Groundwater sampling and laboratory services coordination
  • Agency inspections and correspondence
  • Remote video camera condition surveys of landfill leachate collection and transmission piping
  • Design and oversight of storm sewer slip-lining to eliminate discharge of contaminated shallow groundwater from an adjacent property
  • Installation of new monitoring wells and abandonment of unused monitoring wells
  • Design and oversight of supplemental leachate extraction well system as part of response activities to mitigate potential off-site groundwater migration issues
  • Design and oversight of rehabilitation of concrete storm water channels on the landfill cap
  • Leachate sampling for analysis of per- and ploy-fluroalkyl substances (PFAS) and other emerging contaminants following EGLE protocol.
NTH’s Value Added:

NTH has provided a proactive approach to site maintenance issues by planning and implementing preventive measures before problems arise and keeping the site in compliance with its Post-Closure Plan and environmental regulations and provisions of the City’s Consent Agreement. NTH has successfully addressed the recent issue involving PFAS originating from the landfill through development of BMPs for leachate discharge and groundwater analysis to evaluate potential off-site migration.