GILFORD — At 2:30 p.m. on Aug. 7, 11 years after coal tar was discovered on four house lots on Liberty Hill Road, the last of 2,662 truckloads of contaminated soil — enough to cover more than 30 football fields to a depth of six inches — was hauled from the site.

John Shore, spokesman for Liberty Utilities, described the last truck as "a huge milestone for the company, the neighbors, the town and the state that heralds the completion of one of the largest environmental projects ever undertaken in New Hampshire. He said that the site remains to be back-filled, graded and seeded, work expected to be finished by Sept. 23 when grass will begin to grow.

The quality of groundwater at the site will be monitored for many years and while the site will remain undeveloped it will be open to limited recreational uses.

Work at the 4.5-acre site began in the spring of 2014, spanned two constructions seasons and cost $13 million. Each day trucks left the site with 20 cubic yards of contaminated soil and returned with an equal load of clean fill, timing their trips not to coincide with the school bus schedule. Contaminated soil was taken 34 miles to Environmental Soil Management Inc.'s facility in Loudon, where the contamination was removed by treatment with extreme heat. Charter Environmental Inc. of Boston undertook the project, which was designed by GEI Consultants Inc. of Woburn, Mass.

Throughout the project, air quality, noise and vibrations at the site were closely monitored in order to minimize any adverse effects on nearby residents. "We really did our best to minimize the disruption," Shore said. "The low number of complaints reflects that effort." At the same time, he noted that crews recorded more than 25,000 working hours without an injury at the site.

In the 1950s the coal tar, a byproduct from a manufactured gas plant that exploded 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 overlooked until 2004, when in the course of litigation it came to the attention of KeySpan, the corporate successor to the original gas company. KeySpan was itself acquired by National Grid in 2007, which was acquired by Liberty Utilities in 2012.

KeySpan and its corporate successors proposed several less extensive and expensive plans for addressing the contamination while town officials steadfastly insisted that all the coal tar on the site be removed. Ultimately the New Hampshire Department of Environmental Services (DES) agreed and ordered Liberty Utilities to remove it.

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