Upper/Middle Charles Total Maximum Daily Load (TMDL) Project

Stuart Cahill ©Boston Herald

Click here to read a March 6, 2010 blog from the Johnson Foundation about the TMDL and phosphorus in the Charles.

Charles River Watershed Association (CRWA) worked with the Massachusetts Department of Environmental Protection (MassDEP) and U.S. Environmental Protection Agency (US-EPA) to develop a nutrient Total Maximum Daily Load (TMDL) for the Upper/Middle Charles River. CRWA's project work was completed by October 2009 and revisions to the Final TMDL were by approved by US-EPA in June 2011.

A TMDL analyzes the pollution level that a river can receive and still meet appropriate water quality or aesthetic standards. TMDLs are created for all water bodies in the United States that fail to meet water quality or aesthetic standards due to one or more pollutants. TMDLs are also used to establish lower pollutant levels in permits governing wastewater treatment plants, new developments, and regulated industries.

Both measured streamflow and water quality data plus computer modeling are used to determine the amount of pollution that the river can sustain without violating these standards. The percent contribution from all pollution sources is also established. The Implementation Plan produced at the end of the TMDL process maps out the regulatory or voluntary process to reach the required level.

Background

Phosphorus is the primary nutrient of concern in the upper Charles River. Natural sources of phosphorus include soil and plant materials (like leaf litter) and small amounts of atmospheric deposition. Anthropogenic (human caused) sources of phosphorus include human waste from wastewater treatment plants and septic tanks; pet waste, manure, and fertilizers used on lawns, golf courses, or agricultural areas; and other sources such as motor vehicle exhaust, fuels, lubricants, detergents, and car wash products.

Stormwater runoff in the Charles contributes about two-thirds of the total annual phosphorus pollution load. This phosphorus may be natural, or caused by human activities, but much of it comes from impervious surfaces such as roads, parking lots, and buildings, especially in commercial, industrial, and high-density residential areas. These areas have the highest contributions of phosphorus because they are well connected to the river via the stormwater drainage systems. Natural areas such as forests and wetlands contribute relatively small amounts compared to developed areas.

Excessive phosphorus enters the upper Charles River, disturbing the river's natural nutrient balance and resulting in excessive algae and aquatic weed growth. In wet weather, stormwater runoff contributes most of the pollution while in dry weather, or drought-like conditions, the contaminants originate mostly from wastewater treatment plant outfalls. There are five active wastewater treatment plants in the upper watershed-three on the mainstem in Milford, Medway, and Medfield and two on the Stop River in Norfolk and Wrentham. About 40% of the land area in the Upper/Middle Charles River watershed is developed with large areas of impervious surfaces and lawns which are phosphorus sources that can be readily transported via stormwater to the river.

Goals & Objectives

The objective of this study was to develop a nutrient TMDL project to quantify nutrient loads impacting the Upper/Middle Charles River and develop a plan to reduce those loads to reasonable levels. Excessive nutrients create problems with algae and nuisance aquatic vegetation. This project seeks to identify, quantify, and reduce phosphorus levels to acceptable levels for the river and reduce associated algae and aquatic plant occurrence.

The original scope of this project was only for the Upper Charles but it was extended mid-project to include the Middle Charles. The Upper/Middle Charles TMDL covered 70 miles of the river from the source in Hopkinton to the Watertown Dam. The period of study was 2002 to 2005.

Project Highlights

The TMDL project measured streamflow and water quality concentrations to establish loads and impacts under existing conditions. Water quality models were then calibrated to these sampled conditions and used to determine the existing contribution to annual and seasonal loads. The water quality models were also used to help evaluate "what if" scenarios and identify the most appropriate cleanup approach. The TMDL Implementation Plan identified primary sources of contamination and most appropriate strategies for cleanup.

Flow monitoring was expanded from six existing mainstem sites to include nine additional tributary sites. These tributaries include Bogastow Brook, Chicken Brook, Fuller Brook, Hopping Brook, Mill River, Mine Brook, Stop River, Trout Brook, and Waban Brook.

Four rounds of water quality monitoring were performed in the Upper Charles on all major tributaries and selected mainstem locations. These water quality monitoring events sampled both wet- and dry-weather conditions. Impoundments were intensively surveyed because the worst water quality impacts are often manifested in slow-moving water. Nine impoundments were surveyed for bathymetry, sediment thickness, dissolved oxygen, sediment release rates, and extent of aquatic plant coverage.

The data collected as part of the Upper/Middle Charles TMDL were supplemented by water quality measurements made by the CRWA's IM3 project, MassDEP's Water Quality Assessments, Massachusetts Water Resources Authority's (MWRA's) CSO Receiving Water program, and US-EPA's Charles River Core Monitoring programs.

An HSPF water quality model was developed and calibrated using all available monitoring data. The calibrated HSPF model was used to evaluate different scenarios for controlling and managing nutrients. The draft Final Report evaluated various management strategies and developed the TMDL Implementation Plan to define concrete regulatory or voluntary strategies to lower phosphorus levels in the Upper/Middle Charles River.

A stakeholder meeting was held to present and discuss the draft Final TMDL report. MassDEP made revisions based on comments from stakeholders and from US-EPA and then prepared the Final TMDL report. US-EPA approved the Final TMDL after review.

Project Status (complete)

CRWA has completed all work required for this project and submitted four reports to MassDEP. The first two reports (2004, 2006) covered the extensive monitoring and data acquisition activities. The calibration report (April 2009) covered the development of an HSPF water quality model and its calibration to existing monitoring data. The draft Final TMDL (October 2009) reports on the modeling effort to evaluate the nutrient management scenarios required to develop the TMDL waste load allocations. This report also includes an Implementation Plan to define concrete regulatory or voluntary strategies to lower phosphorus levels in the Upper/Middle Charles River. The Final TMDL was by approved by US-EPA (June 2011).

The end result of the nutrient TMDL in the Upper/Middle Charles River will be better control of pollution from wastewater and stormwater sources and ultimately a cleaner, more useable river.

For more information, contact Mark Fabian. Click here for contact information.