Onsite Sewage Research Projects

| Introduction | Ongoing Research Projects | Upcoming Research Projects | Past Research Projects | 

Introduction

The research program has many current and upcoming projects looking at how onsite sewage treatment and disposal systems impact public health and the environment.

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Ongoing Research Projects

The research program is currently working on the research projects listed below.

Data Analyses to Investigate the Fate and Transport of Pollutants from Onsite Sewage Treatment and Disposal Systems in Soil and Shallow Groundwater (2022 - Ongoing)

The location of Onsite Sewage Treatment and Disposal Systems (OSTDS) relative to receiving waters is an important factor that influences the impact of OSTDS on water quality. It is critical to understand the fate and transport of OSTDS pollutants in soil and shallow groundwater in order to establish minimum OSTDS setbacks to sensitive receptors. Through the years, the Onsite Sewage Program (OSP) has investigated OSTDS pollutant transport through a series of plume studies. The OSP is now working with researchers from the Florida Agricultural and Mechanical University to evaluate the results from these studies. The goals of this project are to: 1) compile, evaluate, and synthesize the results from these studies to quantify key characteristics of plumes formed by OSTDS discharge; 2) identify factors that may impact the size and geometry of the plumes: and 3) evaluate the impact of these environmental factors. Results from this project will identify data gaps and additional studies needed to better understand OSTDS pollutant transport in soil and shallow groundwater. The results will also provide a basis for recommending approaches for updating setbacks from OSTDS to sensitive receptors.  A list of plume studies conducted by the OSP can be found here.  

Performance Evaluation of Inground Nitrogen-Reducing Biofilter Systems (2021 - Ongoing)

To reduce nitrogen loading from OSTDS to Florida groundwater and springs, the Florida Department of Environmental Protection (DEP) developed 13 basin management action plans (BMAPs) for 24 impaired Outstanding Florida Springs (OFS) and adopted them by Secretarial Order in June 2018. The OSTDS remediation plans in these BMAPs require nitrogen-reducing OSTDS for new construction permits located on lots less than one acre in priority focus areas (environmentally sensitive areas within the BMAP areas). Through partnerships with county governments, DEP provides funding to encourage OSTDS owners to upgrade their existing conventional OSTDS to nitrogen-reducing systems. One of the nitrogen-reducing systems approved in Florida is the inground nitrogen-reducing biofilter (INRB). This system includes an unsaturated sandy media layer underneath the drainfield followed by a layer of woody material mixed with fine aggregate media. The unsaturated sandy media layer is designed to convert ammonia in the septic tank effluent to nitrate. The saturated wood chip-fine aggregate media layer is designed to convert nitrate into nitrogen gas, removing nitrogen from wastewater. As more and more INRBs are being installed in Florida, it is critical to evaluate the performance of these systems under real-world operating conditions in different parts of the state.

This project provides for inspecting and sampling INRB systems installed at residences on a quarterly basis for two years. Data collected from this project will be used to evaluate the nitrogen-reducing efficiency of INRBs as well as the treatment efficiencies for other OSTDS pollutants such as phosphorus and fecal coliform. Results will also be used to identify factors that may impact treatment efficiencies, provide insight on the lifespan of the denitrification media, and could provide a basis for possible future system refinement. This project is funded by a federal Environmental Protection Agency (EPA) multipurpose grant. A PowerPoint presentation that summarizes the sampling results from two systems installed in Leon County can be found here.    

Estimation of Failure or Non-Conformance Frequency of OSTDS (2019 - Ongoing)

One approach to evaluate OSTDS environmental impacts is to determine the frequency of OSTDS that are not functioning properly. Frequency of OSTDS “failure” is often determined by multiplying the frequency of repair permits by a number of years before the system “failure” is identified. The accuracy of this approach has never been tested. In addition, other OSTDS non-compliance issues that don’t meet the definition of system failure of the system may also cause significant environmental concerns. The goal of this study is to collect and evaluate data from several OSTDS inspection programs, identify the type of OSTDS rule non-compliance and evaluate the frequency of the non-compliance. The information from the study will provide water resource managers with basic information to evaluate impacts from OSTDS. Data being collected and preliminary data analyses so far can be found in a presentation given to the Research Review and Advisory Committee (RRAC) that provided guidance to the Onsite Sewage Program on research at the time when this project was initiated. 

Development of Funding Mechanisms for OSTDS Remediation and Upgrade (2018 – Ongoing)

Each year, more than 15,000 OSTDS owners apply for repair permits to fix their malfunctioning OSTDS. The actual number of failed OSTDS may be significantly larger than this number. One factor that causes the delay of repair of failed systems is the lack of proper funding assistance. This project investigated possible funding sources in Florida and, specifically, focused on the mechanism that other states use to manage and distribute Clean Water State Revolving Fund (CWSRF) loans to help fund repair, replacement, and upgrade of onsite wastewater systems. Department staff is preparing a report to summarize the findings from the investigation. Some results from the investigation can be found in a presentation given to the Research Review and Advisory Committee (RRAC) that provided guidance to the Onsite Sewage Program on research at the time when this project was initiated.

Upcoming Research Projects

Performance Monitoring on Advanced OSTDS in Florida

There are more than 2.6 million OSTDS currently being used in Florida. The vast majority of these OSTDS are conventional systems (generally, a septic tank and drainfield for wastewater treatment and dispersal). “Advanced” OSTDS are also used across the state. These “advanced” systems include aerobic treatment units (ATUs) that add air to improve the wastewater treatment process, and performance-based treatment systems (PBTS) that are designed by engineers to target specific performance levels for specific wastewater pollutants. These advanced systems are generally either required by state rule/law or are required by local ordinances to protect receiving waters. Some of these advanced systems can help address unfavorable site conditions such as small lot size, inadequate setbacks from receiving waters, and insufficient authorized wastewater discharge.

Both ATUs and PBTS require operating permits from the Department of Health local county health department. Currently, there are about 10,000 advanced OSTDS across the state that hold active operating permits. This number is increasing as more advanced systems are installed to meet state or local regulatory requirements. It is critical to understand the overall performance of these systems across the state to ensure that they meet the wastewater treatment levels they are designed for. The goal of this project is to randomly select a subset of ATUs and PBTS across the state, inspect the operating conditions and collect samples from these systems. Results will be used to evaluate the systems' treatment efficiency and identify operating and maintenance issues associated with these systems. Data collected from this project may also provide a basis to establish mechanisms to facilitate the approval and introduction of more advanced OSTDS products into the Florida market.