Isotopic characterization of onsite wastewater treatment (septic) system effluent

Background Information:

• Onsite wastewater treatment, or septic, systems are a potentially large source of nitrogen to ground and surface waters, contributing to eutrophication of surface waters and public health concerns associated with toxic algal blooms and nitrate contamination of drinking water supplies.

• Mixing models use the natural abundance of nitrogen isotopes to identify contributions of various nitrogen sources to recipient waters, given that the isotope signature of each source is known.

• Isotope signatures are known to change during conversions between various forms of nitrogen.  Existing data on the 15N of nitrogen leaving septic systems does not consider the potential variation among a large number of systems or between types of onsite treatment systems. 

Project Objectives:

• Characterize the nitrogen isotope ratio of inorganic nitrogen in the effluent of several onsite wastewater treatment systems.

• Assess the variation in effluent nitrogen isotope signatures associated with the differing levels of treatment occurring in conventional and advanced onsite wastewater treatment systems.