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It is widely assumed that small-scale hydroelectric power is environmentally benign. However, even small dams can exacerbate water quality problems, particularly in the Assabet, where slow-moving water promotes eutrophication (excessive weed growth). The dams also block free movement of fish and other riverine wildlife. Using the latest scientific information available, and the results of long-term monitoring, OARS presses for critical assessment of the true impacts of small-scale hydro. Our Dams and Sediment page describes the science behind the impacts. The forthcoming Sediment and Dam Removal study by the Army Corps of Engineers looks at the impact of dams on water quality and some of the benefits of dam removal. Our River Restoration and Dams page describes OARS' community-wide discussions about the pros and cons of dam removal. The Low Impact Hydropower Institute shows how hydropower plants can be evaluated to deterinine and minimize environmental impact.

Maynard: OARS has successfully advocated for maintaining adequate flow in the river in Maynard, where a diversion of river water to Clock Tower Place (CTP) until recently compounded the water quality problems of the river. The Ben Smith Dam was built in 1847 to create a large impoundment to power the local woolen mill. A 1600-foot long canal diverted water from the impoundment, ending at a gatehouse and two mill ponds at the mill buildings, now CTP. This system is still in place, with water flowing under the CTP buildings and discharging back to the Assabet off Walnut Street.

Alerted by an OARS member, and working with federal and state fish, wildlife and environmental agencies, OARS presented monitoring records and scientific data to support a requirement for maintaining a flow in the river of at least 39 cubic feet per second (cfs). See OARS' comment letter on the FERC review on the Comment Letters and Appeals page. Maintaining a minimum flow in the river during low flow periods, as part of a natural flow regime, protects fish habitat, water quality, and recreational and permitted commercial uses by downstream businesses.

An authorization by the Federal Energy Regulatory Commission (FERC) to generate hydroelectricity was surrendered by the owners of CTP in 2002. This surrender was accepted by FERC in 2004, subject to the flow management and monitoring conditions advocated by OARS and others. Flow monitoring gages in the river and canal have been installed and can be viewed at www.bensmithdam.com.

Following the surrender, Wellesley/Rosewood/Maynard Mills, L.P., the CTP owners, decided to re-evaluate the production of hydropower at the mill. In 2007 Wellesley/Rosewood received a $500,000 grant from the Massachusetts Renewable Energy Trust to study, design and construct a hydropower system. Operating such a system will require a new authorization by FERC. FERC's review process provides for public review and comment.

Acton: Acton Hydro owns the Powdermill Dam (next to Rte. 62) with its small hydroelectric facility. The Powdermill impoundment was drawn down in 2004 to allow for dam repair and refilled in 2013/14. The repairs included restoring structural integrity to the dam, completing modifications to the spillway to pass more flow, and installing a slot for a fish ladder when and if fish passage becomes necessary. Currently fish passage is not required because there are no migrating fish reaching that location. The plant's electricity output will be in direct proportion to the flow of the river and will typically shut down during low-flow summer and fall months. The electricity is expected to be available to Concord Light Plant customers as "green" power.