Making Development Decisions Without Understanding Negative Impacts Is Irresponsible

There has been a recent assertion by those promoting increased housing development that the allowed number of dwelling units on any lot north of Rt.1 in Charlestown could be doubled if conventional septic systems were replaced with nitrogen-reducing systems. 



Nitrogen-reducing septic systems remove at least half of the nitrogen, so the logic of this argument is that if you remove half the nitrogen from double the septage you will have the same impact with two houses that one house would have had. But this logic ignores both chemistry and biology.

An element is described as “limiting” where, if enough of the element is not present, certain chemical and biological processes will not occur. Nitrogen is the important (limiting) nutrient in water pollution in the coastal ponds in Charlestown where development is already well beyond carrying capacity, and where allowed development densities should not be increased even with nitrogen removal. However, the limiting nutrient in freshwater systems (mainly north of Rt.1) is phosphorus, not nitrogen, and no existing wastewater treatment system, whether nitrogen-reducing or not, removes phosphorus. 



Phosphorus is partially bound up by the soils beneath the wastewater treatment system, but doubling development will double the amount of phosphorus and increase the likelihood of causing pollution. Any phosphorus not bound up by drain field soils or other soils and vegetation surrounding the drain field migrates to the groundwater and to lakes and streams where it can stimulate biological activity beyond normal levels, a condition referred to as eutrophication. In addition to being smelly and unsightly, these blooms can often produce toxins that are harmful to humans, animals, and plants.

Toxic algae are currently blooming in Worden Pond in South Kingstown, and the RI Departments of Environmental Management and Health have issued a health advisory that people and pets should not even touch the water because it is so harmful to humans, pets, and aquatic life. Toxic algae blooms have also occurred occasionally in Charlestown at Watchaug and Pasquisset Ponds. 



Cyanobacteria. which are microorganisms capable of photosynthesis and which occur naturally in many freshwater ecosystems, are the culprit. But without the addition of phosphorus, they are not harmful. In the presence of even small amounts of phosphorus, an algal bloom can expand quickly, and cyanobacteria present in the bloom can produce highly potent toxins, known as cyanotoxins.

The source of excess phosphorus is usually a septic system. Examples of some local conditions that can increase the amount of phosphorus escaping drain fields are sandy and gravelly soils that allow rapid flow rates;  drain fields with thin soils, over shallow bedrock, or where water tables are high; drain fields close to lakes or streams; and wastewater from households that generate more wastewater than their septic systems were designed to handle.

We are already seeing the impact of excess phosphorus in our ponds. At a time when we should be looking for ways to reduce phosphorus loading, doubling the number of allowed dwelling units without fully understanding the long-term groundwater impacts is irresponsible.



Learn more: Reducing phosphorus runoff is necessary for cleaner lakes.

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You can learn more about the author, Ruth Platner, at her profile page.

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Banner image is a photograph of Watchaug Pond by Cliff Vanover.