Executive Summary

The Cape Cod Commission began the Cape Cod Coastal Embayment Project in 1993 based on concerns about the impacts of development on coastal water quality. The Project, which was partially funded by a Department of Environmental Protection (DEP) grant using Section 319 funds from the Clean Water Act, focusses on identifying the nitrogen sensitivity of nine embayment systems, the nitrogen loads these systems are currently receiving and will receive once all land within their watersheds are developed, and potential nitrogen management strategies for embayments or subembayments receiving too much nitrogen now or in the future. During the course of the project, project staff reviewed water quality assessment techniques, nitrogen loading limits, and regulatory protection strategies. The Commission is currently using findings from this project in regulatory deliberations and as guidance for further refinements of assessments techniques.

The nitrogen loading analyses completed for this project found that existing nitrogen loading exceeded at least one of the nitrogen loading limits for all 9 of the project embayments: Round Cove, Allens, Saquatucket and Wychmere Harbors in Harwich, Popponesset Bay in Barnstable and Mashpee, the Three Bay System in Barnstable, West Falmouth Harbor, the Upper Bass River System in Yarmouth, Dennis, and Brewster, and the Nauset Marsh Estuary System in Orleans and Eastham. If subembayments are considered, 23 of 37 coastal waters have existing nitrogen loads exceeding at least one nitrogen loading limit. Buildout within subwatersheds increases this ratio to 24 of 37.

Project findings found that determining nitrogen loading within a coastal watershed can be as complex or as simple as desired. On-going discussions among Commission and numerous scientists, including two large meetings hosted by the Commission in January 1995 and February 1998, have identified the differences between data gathering and modeling approaches, as well as areas for further investigation. Attendees at these meetings included representatives from DEP, Buzzards Bay Project (BBP), Woods Hole Oceanographic Institute (WHOI), UMASS-Dartmouth/Center for Marine Science and Technology (UMASS/CMST), US Geological Survey, Waquoit Bay National Estuarine Research Reserve (WBNERR), Boston University Marine Program/Marine Biological Laboratory (BUMP/MBL), Barnstable County Department of Health and the Environment, University of Connecticut, and University of Rhode Island. Preliminary analyses and discussion at these meetings suggest that loading approximations using various methods, including criteria from DEP, CCC, and BBP models, result in acceptable ranges, but recent research claims of extensive denitrification in the Cape Cod aquifer require further assessment.

Project staff suggest that the use of the modified TB91-001 method obtains the necessary information for development water quality models, examination of wastewater treatment options, and requires relatively little data input, especially with the use of existing Geographic Information System (GIS) coverages. Development of GIS parcel coverage information is necessary for subsequent wastewater facilities planning assessments for areas that are identified as having excessive nitrogen loads.

Flushing studies of coastal embayments are also a key for developing water quality protection options. Comparing nitrogen loads to local residence time calculations can produce estimates of average expected nitrogen concentrations and reasonable assessment of general ecosystem conditions. Water quality data can later be incorporated into appropriate flushing study models to accurately predict nitrogen concentrations throughout a coastal embayment and refine the assessment of ecosystem conditions and potential management options.

Critical attention needs to be focussed on the development of appropriate nitrogen loading limits. The assessment of nitrogen loads to and water movements within an embayment are adequate at this point for regulatory and planning decisions, but definition of the appropriate nitrogen limit requires additional attention. Through the work of BBP, UMASS-D/CMST, WHOI, BUMP/MBL, the Coalition for Buzzards Bay, WBNERR, and numerous citizen groups, additional water quality information has been developed for a number of Cape Cod embayments. The Commission suggests that this data should be reviewed, and considered with the available nitrogen loading information, to provide more refined nitrogen loading standards for coastal embayments. Additional review of this data also should be able to help refine the predictive ability of nitrogen loading and coastal flushing models. In parallel, the state should similarly look to develop eutrophication standards for coastal waters with an eye toward inclusion of this information in the Massachusetts 305(b) reports that are submitted to EPA.

Even given some of the uncertainty surrounding the recommended nitrogen limits, discussions and analysis of nitrogen loading management options should be initiated and/or continued in watersheds to embayments where limits are exceeded. In the subembayments where existing loading exceeds even the highest loading standard considered, the process of evaluating options should be accelerated, including:

1. identifying areas of high density development for potential sewering,
2. identifying potential parcels for neighborhood or larger wastewater treatment facilities, and
3. clarification of potential costs and institutional arrangements for septic system management and/or sewer districts.

In addition, discussions should also focus on ways to limit impacts from future development within these watersheds, since additional development will further stress these ecosystems. Subwatersheds to the following embayments are in this category: Mashpee River in Popponesset Bay, Prince Cove Proper and Prince Cove Arm in the Three Bay System, Oyster Pond in West Falmouth Harbor, Dinahs Pond and Mill Pond in Upper Bass River, and Allens Harbor (arm).

Town Boards of Health currently have the authority under Title 5 to assist in the protection of coastal embayments by designating embayments as nitrogen sensitive. The materials gathered under this grant provide sufficient information for impacted embayments to be designated as nitrogen sensitive embayments. Communities should recognize that a Title 5 nitrogen sensitive designation will require all septic systems within the respective watersheds to be 440 gpd/acre or less (310 CMR 15.214). This limit will provide some level of protection, but will be insufficient for adequate protection of certain, more sensitive, embayments.

Although the Commission has the ability to assist the towns in adopting coastal water quality protection strategies through the review of Local Comprehensive Plans (LCPs), new construction within the fairly limited undeveloped areas of the Cape will occur prior to formal adoption of regulations to implement the LCPs. In addition, since many coastal systems are already overloaded by existing development within their watersheds, improved wastewater treatment will have to involve the retrofitting of existing septic systems or sewering. Since the Commission will be reviewing only a small percentage of redevelopment of parcels and hardly any single family residences upgrading septic systems, towns will have to provide the bulk of implementation of coastal water quality protection plans.

With the limitations of Title 5 to address coastal water quality and the longer time frame inherent in LCP implementation in mind, staff recommend that towns immediately begin consideration of BOH regulations requiring denitrifying septic systems for all new and replacement septic systems within the delineated watersheds, unless a flushing study and nitrogen loading assessment indicate that this is not necessary or it is anticipated that aggregated nitrogen removal treatment (large or small community sewering) can be provided within five years.

In addition, since many water quality problems are masked by the slow flow of groundwater and lack of observation until they are manifested in a significant way (e.g., a fish kill or algal bloom), project staff suggest that a coordinated citizens coastal water quality monitoring network be developed for Cape Cod. Significant efforts in Falmouth and along Buzzards Bay can be used as templates for this network and the existing expertise at the Commission, WBNERR, BBP, UMASS-Dartmouth, Cape Cod National Seashore, WHOI, BUMP/MBL, the Coalition for Buzzards Bay and others can be tapped to bring it to fruition. Data gathered by this network could be used to refine management strategies, help inform the public of the water quality problems, and help involve more of the public in the protection of coastal water quality.