Change is bubbling up around Sawmill Pond in Davisville, but not much will be visible until spring of 2012.
The Town of North Kingstown has assembled $620,000 and hired environmental science and engineering firm Horsley Witten Group to oversee three projects designed to reduce the pollution and sediment that enters the nine-acre pond and then travels from the pond downstream into Narragansett Bay.
According to a 2005 report by Patty Gambarini of the Southern Rhode Island Conservation District, Sandhill Brook was dammed to create Sawmill Pond early in Colonial days and last used to power industry before the Civil War. Over the years its 65-foot-wide dam has been reduced to about one foot in height, and sediment has filled the impoundment to the point that it resembles a marsh more than a pond.
Yet surveys show its neighbors treasure the pond, and the currently closed Davisville Elementary School, which sits on the pond's western edge, has an outdoor classroom overlooking the water. The water's edge is parkland, and a footpath bisects the pond, connecting Sachem Road to the end of Lake Drive and the school.
Since the late 1970s, numerous studies have examined the pond, the 1.8-square-mile Sandhill Brook watershed that it belongs to, and the Hunt River that the brook eventually flows into. Scientists, professors and engineers have documented how erosion, leaking septic pools and stormwater degrade water quality and wildlife, including alewife fish that still try to scale the Sawmill Pond dam heading upstream to breed.
North Kingstown Planning Director Jon Reiner explains that most of the infrastructure built in the last century was designed to carry runoff away as quickly and directly as possible. As a result, an April 2010 watershed assessment by Horsley Witten reported that University of Rhode Island's studies of Sandhill Brook found "average bacterial levels exceeding those of other Hunt tributaries in 2007 through 2009 by a factor of five, all indicating impairment."
That 109-page assessment identified 29 potential "stormwater retrofit candidates." They range from bioretention areas such as rain gardens to new culverts to either rebuilding the Sawmill Pond dam or removing it entirely and clearing a channel for a reinvigorated stream.
Horsley Witten found that building all the retrofits would make the water much cleaner, but would cost between $2.7 million and $3.8 million, depending on whether the town preserves pond or turns it back into a stream.
For now, town planners are taking $410,000 remaining from a settlement received when the town sued the Navy for pollution on its former base at Quonset; $200,000 in a federal clean water grant awarded by the state Department of Environmental Management; and $10,000 from a community block grant to fund three projects from the top 10 recommendations that lie on town property:
- Constructing a bioretention area at Davisville Elementary School, with pervious pavers instead of impervious asphalt in part of the parking lot and dry swales to manage untreated stormwater runoff, designed to stop erosion and stabilize the pond slope.
- Stabilizing the slope where culverts funnel runoff from Lake Drive into the pond and repairing the outfall infrastructure with "stepped bioretention areas" that resemble a series of narrow terraces. The outfall pipe is broken and the area currently suffers from erosion and excessive leaf dumping.
- Creating a bioretention area on a Lake Drive lawn overlooking the water, with educational signage.
Rich Claytor, principal engineer at Horsley Witten, said Davisville residents attended two public meetings to review the 2010 watershed assessment, and he heard no objections to the firm's recommendations.
Reiner said that Horsley Witten will handle requesting proposals, evaluating bids and obtaining permits over the winter, with work expected to begin when the weather allows next spring.