Greening Martha : Highlights of MVC's wastewater management study
The Martha's Vineyard Commission (MVC) has released the Martha's Vineyard Wastewater Management Study, an evaluation of the issues confronting the Vineyard as a result of wastewater disposal.
Martha's Vineyard is faced with significant challenges in restoring and maintaining water quality in coastal ponds, where excessive nitrogen loading has resulted from on-site wastewater disposal and other causes. The study was carried out by consultants Wright-Pierce, and included a two-year data collection and evaluation process in cooperation with an oversight committee of town appointees. This study will help the towns and the MVC devise an informed plan to facilitate wastewater management improvements.
The study started with a broad assessment of wastewater management needs based on an up-to-date evaluation of assessors and water supplier data. Next, a number of wastewater management alternatives were evaluated, ranging from individual towns acting alone to various regional approaches. The effectiveness and cost of four technical approaches to wastewater treatment and disposal were evaluated, namely individual on-site systems, small cluster systems, satellite plants, and traditional municipal wastewater facilities. Then, many regulatory tools were identified and evaluated as to their effectiveness in addressing wastewater nitrogen impacts, given local needs and circumstances. Lastly, a review was conducted of existing regulations, bylaws and policies to ascertain their effectiveness and to recommend possible enhancements. The study looked at six case study areas, one in each town, to focus on the range of issues and possible solutions.
Here are some of the key findings.
Currently only about 11% of the 14,000 developed parcels on Martha's Vineyard are tied into wastewater treatment systems. The remainder dispose of their waste using Title 5 systems that, while protecting public health, do not remove the nutrients that wastewater contains. Foremost among these is nitrogen. It is the missing nutrient in coastal waters and when provided to excess, it causes growth of algae and microscopic plants that impact the ponds by shading out eelgrass and removing oxygen from the water column. This results in loss of habitat for fish and shellfish.
From a detailed study of water-meter records, the study concluded that residential water use varies from 140 to 210 gallons per house per day. This results in a daily wastewater flow of 2.7 million gallons of wastewater Island-wide. Of this total, 74% flows through wastewater disposal systems and, by way of the groundwater, enters our coastal waters.
Over 70% of the land area of the Vineyard is in the watershed of one of our 19 embayments that are sensitive to nitrogen. Of the total daily wastewater flow, about 2 million gallons per day are disposed in the watersheds of nitrogen-sensitive coastal waters carrying 160,000 pounds of nitrogen each year.
The study estimates that wastewater treatment needs to be increased from an average of 290,000 gallons per day (gpd) by another 670,000 gpd to address current nitrogen problems.
Expected growth is projected to increase the wastewater flow by an additional 1.5 million gallons per day, a 55% increase. About 60% of this will need to be collected and treated to remove nitrogen to preserve the quality of our coastal ponds. This means a further expansion of treatment by 900,000 gpd. Future growth is a critical aspect of treatment requirements because if a pond has a nitrogen problem today, then all future wastewater needs to be treated.
The cost of treatment will be very high, ranging from $30,000 to $60,000 for each property served by a municipal treatment system. The total construction cost just to deal with current needs may reach $200 million, in addition to annual operation and maintenance. This cost could double or more, in order to accommodate future growth. If wastewater treatment systems must be put in place to reduce coastal pond nitrogen loading, then the first focus should be on existing unsewered neighborhoods with small lots.
This study sets the basic framework for managing wastewater on Martha's Vineyard. Given the scope of the challenge and the large potential cost of treatment, considerable additional study will be needed to determine the most cost-effective solutions. Precise treatment requirements will be determined as the Massachusetts Estuaries Project studies are completed, refining our understanding of each pond's needs and allowing more precise cost analyses.
The report is available at mvtimes.com, in all town libraries, and from the Martha's Vineyard Commission's website (www.mvcommission.org). Simply type "wastewater management:" into the search box.
Mark London is executive director of the Martha's Vineyard Commission.