Ninigret Pond
Ninigret Pond - Looking North

Advanced / Denitrification Onsite Wastewater Treatment Systems

Advanced on-site wastewater treatment systems, including denitrification / Nitrogen (N) reducing septic systems are required in certain circumstances within the RIDEM delineated Salt Ponds Critical Resource Area in Charlestown. Our three Salt Ponds, Green Hill, Ninigret and Quonochontaug Ponds are all very sensitive to inputs of nutrients, especially Nitrogen.  Nutrients enter the ponds through groundwater and surface water and originate from many sources including septic systems, fertilizer, storm water runoff and animal waste. 

In Charlestown, the Salt Ponds Critical Resource Area consists of the drainage basin for all three of our Salt Ponds. This means that all surface water, groundwater and rain water that falls within this area drains toward the Salt Ponds. Click on the Charlestown Salt Ponds Critical Resource Area Map below to determine if your property lies within the Salt Ponds Drainage Basin. 

The Salt Ponds Critical Resource Area in Charlestown. Click on the image to access Charlestown's Web GIS. Once there, use the "Map Layer" tool bar in the upper right hand corner to select the "Salt Ponds Critical Resource Area" and use the controls to locate your property.

Nitrogen has recently been identified in drinking (well) water within some densely developed areas of the coastal zone at elevated levels. The EPA and the RI Dept. of Health indicate that drinking water levels of Nitrogen must not exceed 10 parts per million and has established the level of 5 parts per million as an "Action Level". In our densely developed coastal zones, groundwater concentrations of Nitrogen are commonly detected at and above the Action Level and in some wells exceed the threshold of 10 parts per million.  It has been determined that 80% of groundwater Nitrogen concentrations in the densely developed coastal zones originates from septic systems. 

Nitrogen reducing septic systems are required by RIDEM to reduce the Nitrogen concentrations in the discharged wastewater by 50% as compared to a conventional septic system and are must meet discharge concentrations of less than or equal to 19 parts per million. Currently N- Reducing septic systems account for 12% of all septic systems in Charlestown. 

Inspection and maintenance is required. Since these systems are complex, routine maintenance is required to ensure proper function and nutrient and bacteria reduction. According to Charlestown Town Ordinance and the RIDEM, all Advanced and Nitrogen reducing septic systems are required to be inspected/maintained by a vendor approved service provider at least annually. All maintenance records and inspection reports are required to be uploaded to the septic system database by your approved service provider.  System effluent sampling for laboratory analysis of  final wastewater discharge parameters may also be required.

Image courtesy of the New England Onsite Wastewater Training Center        

According to the RIDEM, denitrification on-site wastewater treatment systems are required within the Critical Resource Area for all new buildings being constructed and for all septic systems and cesspools being replaced.

An upgrade from a conventional septic system to a denitrification system may be required for:

1. Certain circumstances involving malfunctioning conventional septic systems. 

2.  Modifying certain physical parameters of your house (add a bedroom, add a level, change the footprint, conduct significant modifications to the structure). 

Please contact the Towns Wastewater Manager for additional information and guidance on this RIDEM State requirement. 

There are many types of denitrification septic systems that have been approved by RIDEM for use in the Critical Resource Area. A list of these approved systems can be found here. Also, the New England On-Site Wastewater Training Center provides a  summary of Advanced Treatment Systems here.

The chart below depicts the types of advanced treatment systems recently in use within Charlestown.