GILFORD — A decade after toxic coal tar was first discovered beneath house lots off Lower Liberty Hill Road, work to remove it is slated to begin next month.
Speaking to a public meeting last night Jim Ash of GEI Consultants, Inc., who has overseen the remediation of the site for a since the contamination was reported, said the project will proceed in two phases over the next two construction seasons. Altogether 93,000 cubic yards of soil, of which between 40,000 and 45,000 are expected to be contaminated and require treatment, will be excavated.
In the 1950s the coal tar, a by-product from a manufactured gas plant in Laconia, was dumped in a sand and gravel pit on the south side of lower Liberty Hill Road, which was subsequently reclaimed and divided into house lots. However, it was only discovered by KeySpan, the corporate successor to the original gas company which was itself acquired by National Grid in 2007, in the course of litigation in 2004. Of the four house lots — 69, 77, 83 and 87 — directly affected by the old dump, National Grid has acquired and demolished three in anticipation of excavating the site and dealing with the contaminated soils.
Ash estimated that 28,000 cubic yards would be removed and 27,000 cubic yards returned in 2,800 truckloads in the first phase and 12,000 cubic yards removed and 27,000 returned in 1,200 truckloads in the second phase. Altogether 2,000 truckloads of contaminated soil will be hauled from the site and an equal number carrying clean soil will return. A cubic yard of soil weighs approximately 1.33 tons.
Preparations will begin in March, weather permitting, Ash said. The site will be fenced and the vegetation cleared. A roadway and wash facility for the trucks will be built, together with a water treatment system. All groundwater removed from the soil before it is transported will be treated to standards set by the New Hampshire Department of Environmental Services and the United States Environmental Protection Agency. Air, noise and vibration monitoring systems will be erected. He expected these preparations would be complete within five to six weeks.
Ash noted that the thresholds for air pollution as well as noise and vibration levels at the perimeter of the site are "very conservative" and will be monitored around the clock. If the thresholds are breached, the contractor will be directed to change or suspend operations until specified levels are restored.
Throughout the course of the project Liberty Utilities will post a weekly update on its website — www.lowerlibertyhillsite.com. The company will also maintain a hotline — 603-216-3600 — and respond to questions and comments from the public within one business day.