NEW! Approved Experimental Nitrogen Reducing Layered Soil Treatment Area Septic System


Guidance Document - Town of Charlestown Nitrogen Reducing Layered Soil Treatment Area (LSTA)


RIDEM Certificate of Approval Alternative / Experimental OWTS Technology Program - LSTA


Town of Charlestown Comprehensive Application for Alternative OWTS Technology: Nitrogen Reducing Layered Soil Treatment Area




The Town of Charlestown has long recognized for the need for lower cost, passive and effective nitrogen (N) reducing septic system technology. Nitrogen reducing systems are required for any septic system installation in Rhode Island's coastal zone watershed....and for good reason!

Nitrogen is a pollutant that, in densely developed areas like the coastal zone of Charlestown, primarily originates from septic systems. Our groundwater and surface waters in Charlestown are critically sensitive to this nitrogen. Charlestown relies ONLY on septic systems for wastewater disposal (which recycles our wastewater back into the groundwater) and ONLY relies on that local groundwater for drinking water. Nitrogen in drinking water is a contaminant. 

Further, nitrogen laden groundwater in the coastal zone moves into the nearby salt ponds and acts as fertilizer, creating algae blooms, low water clarity, oxygen deficiencies and bad smells. Our town relies on our coastal zone as our primary economic driver. Healthy coastal ponds and groundwater resources = healthy economy. 

Nitrogen reducing septic systems work well if properly managed. In fact, nearly all nitrogen reducing systems sampled in a recent study in Charlestown achieved a required 50% reduction of nitrogen from wastewater. However, these systems can be costly and complicated and if not monitored can discharge concentrations of nitrogen to the groundwater above the required limits even if they meet the 50% reduction requirement. A simpler and less costly solution has been a long term goal for the Town. 

The Town's Onsite Wastewater Management Office conducted extensive research, collaborated with the University of Rhode Island Laboratory of Soil Ecology and Microbiology (LSEM), the New England Onsite Wastewater Training Program and the Barnstable County Department of Health and Environment-Massachusetts Alternative Septic System Test Center  to identify a passive and cost effective concept that effectively reduces nitrogen from onsite wastewater. The Town termed this method of wastewater treatment the "Nitrogen Reducing Layered Soil Treatment Area" (LSTA) septic system. 

The concept is simple. LSTA discharges wastewater from a septic tank to a leach field constructed of sand over a sand and sawdust mixture. This unique layering of material promotes the necessary environments for wastewater treatment and nitrogen reduction without complicated components. 

Schematic of LSTA from above and in Cross Section

  Schematic of LSTA from above and in Cross Section


In 2020, the Town partnered with the University of Rhode Island Laboratory of Soil Ecology and Microbiology (LSEM) and prepared and submitted an application for Experimental OWTS technology approval to the Rhode Island Department of Environmental Management OWTS Division in September. On April 8, 2021, the Town successfully received a formal RIDEM Certification from the Alternative Experimental OWTS Technology Program certifying the technology as approved for experimental use here in Charlestown. 

Over the next two years, the Town and LSEM will conduct a series of piloting assessments of the technology in Charlestown. Systems will be installed and sampled and efficiency and performance will be calculated. Peer reviewed reporting will be conducted to publish findings and as data warrant an application for full approval will be submitted to the RIDEM.  


Recent press coverage of LSTA from EcoRI

The Possible Future of Septic Systems: A Simpler, Cheaper Nitrogen-Removing Design - April 03, 2021