Location and Acreage:
Halifax/Hanson, MA | 528-Acres
Dominic Meringolo, Regional Leader and Senior Environmental Engineer
This pond, located in the towns of Halifax and Hanson, Massachusetts, is a significant ecological, historical, and recreational resource as well as an important supplementary water supply for the nearby City of Brockton. The 528-acre pond is bisected by Route 58, which splits the water body into two basins - east and west - directly connected only by a small culvert in the southern portion of the pond. Both basins are highly developed with residential homes and receive inputs from a suburban watershed of approximately 6 mi2.
Both basins have also been subject to algae blooms in the past several years; however, the western basin has undergone extensive algae blooms for the past 25 years. During the summers of 2010 through 2015 these blooms prompted the closure of the western basin to swimming and boating for much of the summer. Algae testing has been carried out both by the Massachusetts Department of Public Health (MA DPH) and Massachusetts Department of Environmental Protection (MA DEP) throughout the summer months. MA DPH also conducted analysis of water quality, including total phosphorus. These results show a definite association between concentration of total phosphorus and total cell count in the western basin throughout the summer.
Despite these water quality challenges, the western basin has been identified as an area of priority habitat by the Massachusetts Division of Fisheries and Wildlife (DF&W) Natural Heritage and Endangered Species Review Program (NHESP). The presence of the following three state-listed species of special concern has been confirmed as recently as June 2011: Tidewater Mucket (Leptodea ochracea), Eastern Pondmussel (Ligumia nasuta), and Umber Shadowdragon (Neurocordulia obsoleta).
Scope of Work:
Alum treatment to reduce in-pond phosphorus levels.
SOLitude was contracted to treat the pond using a specially designed spray barge. Operations were staged from the State owned boat ramp on Route 58. Extensive pre, during and post-treatment monitoring were conducted as part of this project to ensure stable pH levels were maintained through the treatment and to measure changes in phosphorus concentrations. The treatment was completed after 8 days.
The application was guided by on-board GPS equipment and the dose was split with one half the dose applied throughout the treatment area followed immediately by the second half dose. Given the presence of state listed mussel and dragonfly species, extensive monitoring conforming to State requirements was also conducted as part of this project.
Good results were observed following treatment and phosphorus levels were generally observed to be desirably below the target concentration of 20 ppb. Unfortunately, given the wet weather and sizeable remaining watershed loading, the pond did experience algal blooms and was still closed periodically during the summer. Based on monthly post-treatment sampling however, the alum treatment did meet the goal of significantly reducing the internal phosphorus load and conditions were greatly improved in the pond as a whole.
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