Rising Groundwater Threatens Coastal Wells And Septic Systems
On Feb. 10, Alissa Cox, a Ph.D. candidate at URI’s Laboratory of Soil Ecology and Microbiology, made a presentation to the Charlestown Town Council to explain her research and data which shows ever rising water tables and a reduction in the separation of septic systems and ground water in the town’s coastal areas.
Ms. Cox used the depth to groundwater (seasonal high water table) reported on historic septic system permit applications and then compared the current depth to groundwater for the same systems. She had depth to groundwater data from over 400 systems going back to the 1960’s. The current groundwater depth was measured using ground penetrating radar. She also has a small number of groundwater monitoring wells to directly measure the changing groundwater levels.
The results show that on average, groundwater is rising about one half-inch per year.
The distance between septic systems and the groundwater is needed so that wastewater can be treated and digested by soil microorganisms before it reaches the groundwater. Without the minimum separation, wastewater doesn’t get the necessary treatment, and during storms when water levels are raised even higher, the wastewater may receive no treatment at all. Untreated septic waste can then reach the coastal ponds causing environmental problems such as algal blooms, or enter drinking water wells and cause human health issues.
The rate of sea level rise is important to rising groundwater levels, but it is not the main driver of rising levels locally. Increasing precipitation, also associated with climate change, is the largest source of increased water going into the ground, along with septic systems that are putting more water into the ground than is being drawn out by water wells. In the coastal area, there are many homes with large cisterns underneath houses that are filled by tanker trucks with water from outside the local watershed. This imported water makes the problem worse.
Cox advised that if the Town went to piped drinking water rather than individual wells, the rising groundwater would become even worse leading to even more septic system failures.
Matt Dowling, Charlestown’s Wastewater Manager, said the town is studying the relationship between groundwater quality and septic-system density. He is also a co-author with Ms. Cox on related publications and they are looking for solutions.
One solution is to work with DEM to alter the way they measure depth to groundwater in the sandy soils in the coastal region. DEM could improve their methods for seasonal high water table determination by using long-term site data rather than a single measurement or soil profile description; look at a local long-term well network and tie site measurement to trends in our area; and consider increasing separation distance requirements for new systems.
You can see the slides used in Ms. Cox’s presentation.
Banner image is a slide from Ms. Cox’s presentation.
February 20, 2020 @ 3:35 pm
This article, while well articulated is slightly misleading from the presentation given. Ms. Cox did have the DEM records from 486 systems but was only able to capture direct measurements from a much smaller data set, 10 systems, 2 of which were in SK. Of those 10, 2 were fine all the time, 5 were fine unless there was a major storm event (very few times in her data) and 3 that were bad all the time. Additionally, as to the infiltration to the pond, Ms Cox’s direct quote “There is some water that moves to the salt pond and ocean but how much and how fast that’s not very well understood, ground water’s very complicated.” I think what is clear here is that far more data is necessary to understand exactly what the extent of the problem is. She suggested having fixed test wells throughout the area that can be monitored regularly to get a sense of where the tables really are. This situation is certainly something that needs to be studied and if need be corrected but without a complete picture, i.e. more data, it will be hard to make well informed decisions as well as well crafted regulations and ordinances. I look forward to additional information coming from this.
February 20, 2020 @ 1:21 pm
Septic Systems of Maine offers the De-Nyte, passive, in-ground de-nitrification septic systems, which are effective and less costly than property-value and quality of life damaging above-ground systems,
plaguing the area today…
These systems are approved in Maine and New Hampshire, at more reasonable cost, etc.
February 20, 2020 @ 7:12 pm
Is there someone that does these locally, or is it not approved in RI?
February 20, 2020 @ 10:14 am
Cox’s assertion about piping in water that will lead to septic failure needs to be substantiated. Is this statement verifiable scientifically? If not this statement will contribute to a political narrative based on misinformation leading to bad decisions. This assertion seems to support mandating de-nite systems for all homes south of route 1 and other sensitive areas near bodies of water in other parts of Charlestown. Roy E. Jacobsen