There are four basic approaches to treating wastewater, which all meet state health protection requirements, but have very different levels of effectiveness when it comes to removing nitrogen.
Centralized wastewater treatment facilities fed by sewage collection systems are most suitable for higher density areas and can remove about 90% of the nitrogen.
Satellite treatment plants are most suitable for outlying, higher density areas, and remove up to 75% of the nitrogen.
Cluster treatment facilities, for groups of homes, typically offer treatment to remove about 50% of the nitrogen, but can have nitrogen removal equipment added which will remove 75%.
Individual on-site treatment systems, as regulated by Boards of Health under Title 5, remove about 40% of the nitrogen through biological treatment.
Currently, wastewater from about 1,800 properties is treated in one of the Island’s five wastewater treatment plants (Edgartown, Oak Bluffs, Tisbury, Airport, and Wampanoag Tribal Housing), while over 14,000 Vineyard properties (more than 90%) treat wastewater on site — in cesspools, in older septic systems, or in newer Title 5 septic systems.
Town Boards of Health enforce Title 5, the State Sanitary Code, to ensure wastewater disposal by septic systems protects human health, although Title 5 is not focused on the impact to surface waters. Protective measures include system design, location, distance to groundwater, and separation from down-gradient wells. The amount of potential nitrogen entering the groundwater from wastewater disposal is only regulated when
Centralized treatment is quite costly to build and maintain. When the cost is calculated over the lifetime of the system — including construction, operation and maintenance — the cost is $20,000 per residence if an existing sewer and a treatment plant with available capacity are nearby, and $75,000 to $100,000 per residence if a new treatment facility and sewers must be built. However, if nitrogen reduction is necessary, the cost of individual on-site treatment could be equally high for two reasons: the systems are not very effective so about three houses would need these systems to offset the nitrogen from each house that is over the nitrogen-loading limit for its location, and because these systems have high operating and maintenance costs. It is a real dilemma for the Vineyard that, for a large part of the Island, the density is so low that individual, on-site wastewater systems may be the only possible treatment.
Wastewater regulations often serve to limit number of buildings, or at least the number of bedrooms, that can take place in certain areas. A major concern with improving wastewater treatment is that this could then open up these areas to additional development. Therefore, we must carefully consider the need for wastewater treatment to be “growth neutral” and for zoning regulations to ensure that inappropriate development does not take place.
The MVC works with towns to evaluate the need to expand or upgrade their sewage treatment systems. When reviewing proposed Developments of Regional Impact, the Commission also carefully examines the proposal’s wastewater disposal, especially with respect to the amount of nitrogen being put into nitrogen-sensitive watersheds.