A municipality in the Coastal Plain of eastern North Carolina contracted with Duncklee & Dunham to provide our professional input regarding the design and implementation of a remedial action plan (RAP) to remediate impacted soil and groundwater at a former Manufactured Gas Plant (MGP) site. At the request of the City, we provided the following services:

  • Identified deficiencies in the RAP, one of which was the lack of vertical delineation of soil contamination, which could have caused the proposed excavation of impacted soil to exceed the estimated depth provided in the RAP.
  • Recommended the designation of a structural/civil professional engineer to ensure the placement of sheet piles was sufficient enough to stabilize the banks of a creek to allow the safe remediation of soil in this area.
  • Recommended the utilization of an oxygen-releasing compound in the base of the excavations to enhance the groundwater-remediation process.
  • Provided a cost analysis of remediation subcontractor bids to confirm prices, rates, and totals were fair and accurate. Used this cost analysis, along with our experience and knowledge of competitive rates, to determine the subcontractor that would be the best choice for the City in order to better serve their interests.
  • Recommended the City retain their current environmental consultant to avoid changes to the work plan, avoid potential delays or a rebid of contractor services, and because of their historical knowledge of subsurface conditions and utilities.

Outcome:

  • The amount of soil excavated exceeded the original estimation, as we expected. The contractor that we recommended did not offer the lowest bid; however, they provided competitive removal, transportation and disposal rates which, in the end, made them the most cost-efficient contractor.
  • We developed and implemented a Post-Remedial Sampling and Analysis Plan that monitored the effectiveness of remedial activities in groundwater and residual sediments in the creek.
  • The oxygen-releasing compound applied to the base of excavations played a vital role in the remediation of soil and groundwater.
  • According to the regulator assigned to this project, we were the first in the state of North Carolina to implement NCDEQ’s Quick Cleanup Procedures for mildly contaminated sites to achieve a no-further action (NFA) determination from the NCDEQ. In addition to an evaluation of soil and groundwater conditions with respect to protection of groundwater and ecological risk, the use if these procedures involved the manipulation of NCDEQ’s risk-calculator tool to establish an acceptable health-based risk for residual soil left behind.
  • This site is the first MGP site to achieve no-further action status in the state of North Carolina that had significant groundwater contamination in the past.
  • The regulator assigned to the project also stated this site has been one of the swiftest remediation responses ever observed at a former MGP site.