Treating wastewater properly is essential to both human and environmental health. The average house produces between 60-65,000 gallons of wastewater each year or about 170 gallons per day. In addition to the pollutants we regulate in wastewater – nitrogen and pathogens (viruses and bacteria) – it now includes an increasingly complex cocktail of pharmaceuticals, personal care products, and hazardous chemicals flushed into the system. Each residence annually releases about 13.5 pounds of nitrogen that enters the groundwater and the down-grade ponds, unless we act to reduce it or to intercept it before it arrives.
The Massachusetts Department of Energy and Environmental Affairs regulates wastewater treatment in the Commonwealth, setting standards for the installation and operation of facilities at all scales, focusing mainly on public health. Local Boards of Health may adopt more restrictive regulations.
Wastewater is the largest locally controlled source of nitrogen pollution to our groundwater and surface waters. Coastal salt ponds are more sensitive to nitrogen than people, so we need additional measures to limit nitrogen pollution beyond the requirements in place to ensure human health.
Wastewater leaving the septic tank contains about 35 parts per million of nitrogen. Natural nitrogen uptake and bacterial conversion to nitrogen gas lowers the septic system nitrogen by about 25% by the time it reaches a coastal pond.
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 1,200 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, though Title 5 is not focused on environmental water quality. 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 systems exceed 10,000 gpd, in areas where there are private wells or within the Zones of Contribution for public supply wells or in projects reviewed as Developments of Regional Impact by the MVC.
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 (see also section 10.4), 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.
Objective W2: Treat and dispose of wastewater in a manner that will support sustainable drinking water supplies and protect public health and surface water resources.
Managing wastewater to reduce nitrogen is one of the greatest challenges the Vineyard will have to face in the coming generation. It is essential to protect our drinking water. It is also the most important way to improve water quality in our coastal ponds, so we can restore eelgrass and maintain shellfish and finfish resources. This will involve major investments in infrastructure and management.
In drinking water quality protection areas, the target should be a nitrogen concentration of 5 parts per million or less. This requires about 1.5 acres per residence to achieve. For the watersheds of nitrogen impaired coastal ponds, the target for nitrogen reduction will be developed by the Massachusetts Estuaries Program, and will likely be much lower. It is likely that significant nitrogen reduction will be required in many watersheds.
The solutions will be costly and we need to identify creative ways to approach funding them, including impact fees, betterments, real estate tax add-on (a nitrogen tax), real estate tax abatement for private solutions, low interest/no interest loans, bonding, etc.
· Strategy W2-1: Prepare a summary Wastewater Management Plan. A first, general evaluation of current and potential wastewater management options is being carried out by the MVC Wastewater Management Committee in relation to the Island Plan. It should become the core of a more detailed plan to limit the impact of present-day and future wastewater disposal, which can be prepared after the Massachusetts Estuaries Project (see section11.4) has set nitrogen-loading limits for each coastal pond. The components needed include identifying the most likely ways to treat and manage wastewater, addressing water quality and eelgrass habitat restoration goals for each pond system, their associated levels of required nitrogen reduction, and the potential to achieve this through improving tidal circulation by dredging. The Plan will then identify various strategies that may be appropriate to protect water quality, based on factors such as housing density, water quality in the pond fed by the watershed and distance from wastewater treatment facilities. It will likely be necessary to prepare more detailed plans for areas that will be considered for sewage collection and treatment. The Plan should identify who will oversee the management program components and how it will be funded. A first step is an inventory and evaluation of existing septic systems to determine their position, type and condition. The Plan should include freshwater pond systems, which need to be protected from phosphorus loading, especially from wastewater disposal systems within 300 feet; this can be done with drip systems or disposal systems that utilize the soil uptake capacity.
Objective W3: Develop and implement nitrogen reduction on a watershed or Island wide basis.
Since the watersheds of most coastal ponds straddle town boundaries, we need to find ways to reduce nitrogen in a watershed-wide or an Island-wide way. This could involve agreements between Boards of Health to implement a common, Island-wide policy. We could create watershed districts, an Island regional Wastewater Management District, or utilize intermunicipal agreements, in order to lower nitrogen loads in the watersheds of specific, impaired ponds. If necessary, we could use the Martha's Vineyard Commission Act to allow Towns to implement regulations beyond current capability. (Other actions to address nitrogen reduction are described in the Coastal Ponds section.)
· Strategy W3-1: Expand sewers and centralized or package wastewater treatment in higher density areas. Identify higher density residential areas within each watershed – especially those within 10,000 feet of existing treatment facilities. These should allow the most cost-effective reduction in nitrogen-load reduction through wastewater treatment. (See figure x for a first approximation of these areas.) Inducements for tying in to a nitrogen reducing system could include an impact fee and rebate program, a real estate tax reduction, and a low interest loan program. The outfalls from future sewage treatment facilities should, whenever possible, be sited within those watersheds where the wastewater is generated or in a location that is more tolerant of the nitrogen loading that will result from disposal of the treated effluent. In some areas, it may be desirable to limit facility capacity to existing flows to minimize growth stimulus effects.
· Strategy W3-2: Facilitate the installation, monitoring, and operation of cluster and individual on-site systems with advanced nitrogen removal.Promote the use of cluster wastewater treatment systems over individual treatment where feasible, since they are more effective. A requirement for new systems to achieve a low nitrogen concentration at the parcel boundary is appropriate to protect drinking water and nearby surface waters. In watersheds with low housing density where wastewater collection and treatment is very costly, we need identify and use new individual systems approaches that are lower cost and that have minimal maintenance requirements such as urine-separating systems, composting toilets and effluent disposal in the root zone. Development of a regional denitrification program for inspection, sampling and maintenance programs would reduce homeowner costs and assure that systems operate as advertised. A computerized reporting system such as that used by Barnstable County (Carmody) is suggested. Such a system may be done as part of an intermunicipal agreement, as a County government program, or as part of a wastewater management district.
· Strategy W3-3: Set growth control regulations related to expansion of wastewater treatment. Improved wastewater treatment could allow additional development which would cancel out any improvements to the ponds. Therefore, regulations should be adopted in relation to the expansion of treatment, especially in nitrogen-sensitive watersheds. These regulations may include limits to increase in flow, increase in bedrooms or house footprint that sewering often induces. Other approaches include use of checker boarding or growth neutral regulations that limit development wastewater flow from new sewage service areas to pre-existing or otherwise permitted levels.
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