Septic System Impact
Carlisle’s Development Standards have long recognized the unique challenges
we face to accommodating multi-family housing that relies on septic systems.
Not only do we face common state-wide challenges, but
our geology and sub-surface conditions pose particular and unique risks as well.
Our Development Standards make this clear by stating:
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Carlisle geographically is an area of extensive wetlands, high water table, and extensive ledge.
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Carlisle has no town water back-up. Unlike a number of Massachusetts towns covered by Title 5, if a residence or business loses a well to pollution, there is no town water which can be brought in, or any town wells at all.
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Carlisle presently has no municipal sewerage (sic) to hook up to in cases of septic system failure.
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The Development Standards also state that “Current estimates indicate that the distance viruses and bacteria travel is much greater than previously estimated. In Carlisle, where groundwater travels some distance through bedrock crevices, pollution may not be adequately filtered in gravel or sand with Title 5 percolation rates used for design.”
Here is a link to Carlisle’s Development Standards, which start at page 69 in these rules and regulations:
https://www.carlislema.gov/DocumentCenter/View/285/Subdivision-Rules-and-
Regulations-PDF
How do the currently proposed MBTA plans address sewage disposal and how do these septic systems impact housing density in Carlisle?
The prior MBTA Communities subcommittee spent all their time developing a plan that claims to rely on conventional septic system technology to limit density.
But what would happen if a developer chose not to rely on conventional septic
technology and instead used a more advanced wastewater solution?
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There’s no way to know what would happen because at that point the Planning Board’s proposed zoning rules would be totally out of alignment with the wastewater technology being used.
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For example, a developer could implement nitrogen-screening septic technology under current Title 5 rules, which would allow them to exceed the Planning Board’s limits and place 50% more bedrooms on a parcel. Yet these nitrogen-screening systems, despite being allowed under state law, have caused problems here in Carlisle when they have been used, such as at Benfield Farms and recently at Woodward Village.
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A developer could build a wastewater treatment plant and with this technology, there would not be any limits on the number of bedrooms they could place on a parcel. Here is a graphic representation of how many housing units could be built using different types of septic technology.
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