Exeter, NH: Northern Utilities Former MGP Site, In-Situ Stabilization
Geo-Con completed a site remediation consisting of stabilizing approximately 0.5 acres of land within a residentially zoned area near the center of town in Exeter, New Hampshire. The site was the location of a former Manufactured Gas Plant (MGP) where the processes generated the release of coal-gasification related material including, but not limited to, volatile and semi-volatile organic compounds in the form of LNAPL and DNAPL. This particular site contained free product of benzene and naphthalene within 3 feet of the surface. Because of extremely close proximity to a retirement home, day care facility and dormitories for a boarding school, noise and odor were of the highest concern.
The client's on-site engineer handled public relations with the community and the state regulatory agencies directly. Town meetings were held local residents during the entire project to answer any questions and deal with any community concerns.
Geo-Con administered noise and odor control measures during the entire project. Noise reducing equipment or equipment modification from diesel to electric was incorporated wherever possible. Perimeter fencing with cloth material was also used to screen and divert sound upward. Odor control was established by ensuring constant application of odor reducing agents to the disturbed areas and soil material. The limits of the stabilized area involved an irregular shaped area encompassing approximately 11,000 sf on the northern portion of the property. Approximately 7,900 CY of impacted soil were stabilized in-situ utilizing a combination of jet grouting and Geo-Con's Shallow Soil Mixing (SSM) technologies. Jet grouting was used for perimeter stabilization (510 lf), while SSM was used for interior stabilization. Reagents used for stabilization included city water, Type I Portland cement, organophillic clay and sodium bentonite. Geo-Con personnel successfully executed the project with no incidents, while handling a confined work area, obstructions, and nearby community concerns.
This project has been cited by the State of New Hampshire as the correct methodology in dealing with this type of contamination.