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Scope/Content: Abstract: The purpose of this study is to provide planning assistance to the Massachusetts Department of Environmental Protection (DEP). DEP in conjunction with EPA and watershed stakeholders are investigating and implementing measures to improve water quality and the aquatic ecosystem of the Assabet River in order to meet its Class B water quality standard ("fishable and swimmable"). The study's role in this effort is to provide scientific and engineering information that will inform the decision making process. For most of its length, the Assabet River suffers from the effects of severe eutrophication due to nutrient loadings (particularly phosphorus) from wastewater treatment facilities (WWTFs), nonpoint sources, and sediments. Nuisance aquatic vegetation impairs designated uses including recreation, aesthetics, and fish and wildlife habitat. Due to excessive vegetation dissolved oxygen concentrations can vary a great deal over the course of a day particularly during the summer months, threatening the survival of fish and other aquatic organisms in the river. It is also aesthetically objectionable to many who live near the river and/or use the river for fishing and boating and other forms of recreation. Effects are most evident behind the numerous impoundments along the river where nutrients settle out. The DEP in 2004 prepared a "Total Maximum Daily Load for Phosphorus" (TMDL) for the river to address the eutrophication problem. The TMDL required implementation of measures to decrease phosphorus loading to the river and adopted an adaptive management approach in accordance with EPA approved procedures. The TMDL for the river can be viewed at http://www.state.ma.us/dep/brp/wm/tmdls.htm. Phase 1 of the TMDL required that the four aging WWTFs discharging to the Assabet River decrease the total phosphorus in their effluent to 0.1 mg/l (April to October) and 1.0 mg/l (November to March). The 0.1 mg/l requirement resulted in the need to add new phosphorus removal technology at the same time as doing significant facility upgrades. These upgrade are currently being implemented and paid for by the communities that own or use the WWTFs. Phase 2 of the TMDL required additional projects be implemented to continue to decrease total phosphorus loading to the river. The phosphorus TMDL indicated that to achieve water quality standards a 90 percent reduction in sediment phosphorus flux was needed in addition to decreasing the WWTFs effluent to 0.1 mg/l. Measures suggested to achieve the 90 percent sediment phosphorus flux reduction included dam removal and dredging. If these measures were ES-2 determined to be inadequate in achieving the desired reduction in phosphorus loading to the river then further decreases in discharges of phosphorus from the WWTFs would be required. Given the inherent difficulty in predicting the impact of sediment flux under the water quality conditions present at the time the TMDL was developed, it is reasonable from a scientific standpoint to monitor the effectiveness of the present wastewater treatment facility (WWTFs) upgrades before selecting the appropriate option(s) for making the necessary sediment flux reductions and verifying the model predictions. EPA and DEP have developed a detailed monitoring plan for the river to assess conditions following the implementation of phosphorus discharge reductions. The Corps "Planning Assistance to States" study provides information on dam removal and dredging to decrease sediment phosphorus flux and improve the aquatic habitat of the river. The Corps contracted with CDM to perform river analysis and modeling for the dam removal and dredging assessments. Dredging analysis results prepared by CDM showed dredging alone would at best achieve only short-term (~ two to four years) reductions in sediment-phosphorus release. This was because the continuing phosphorus discharge from the WWTFs and non-point sources replenish the phosphorus cycling from the sediment. Future monitoring of the effectiveness of the WWTFs upgr Scope/Content: Author affiliation: US Army Corps of Engineers
Ecology and river restoration Economics Engineering Fisheries and fish passage Sediment and channel dynamics Dams Dam retirement
Assabet River, MA Allen Street Dam Aluminum City Dam Ben Smith Dam Gleasondale Dam Hudson Dam Powdermill Dam