Blue Green Algae Task Force Identifies Domestic Sewage as a Contributor to Algal Blooms

by SC Contributors Jerry Smith and Jim Metzler

On August 1st the Blue Green Algae Task Force held their third meeting. This is the first of two articles analyzing that meeting. This article will summarize one of the meeting topics: domestic sewage. Next week’s article will summarize the second topic, innovative technologies, as well as our thoughts on what to expect from the Task Force.

Regulation of Septic Tanks and Sanitary Sewer Overflows

To make this lengthy document more consumable, key concepts are highlighted in bold text.

As part of the Task Force’s ongoing discussion of sources of nutrients that may impact the quality of freshwater ecosystems and cause harmful algal blooms, the August 1st meeting also featured an extended discussion of the disposal and treatment of domestic sewage, specifically onsite sewage treatment and disposal systems (a.k.a., septic systems) as well as a discussion of Sanitary Sewer Overflows (SSOs).

It is estimated that statewide there are 2.5 million septic systems and that approximately one-third of Florida’s population use septic systems to treat their domestic waste water. The primary regulatory authority for the installation, repair, operation and alterations of septic systems is the Florida Department of Health (FDOH). FDOH estimates that 40 percent of the state’s septic system are located in environmentally sensitive areas. Last year the FDOH conducted roughly 71,000 inspections of septic systems and responded to approximately 3,000 complaints about ineffective septic systems. The remainder of the state’s population is served by domestic waste water facilities permitted by the FDEP. There are approximately 2,000 domestic waste water facilities in the state. These waste water facilities are permitted to treat 2.7 billion gallons of water each day.

The FDOH made a presentation to the Task Force in which they stated that the majority of the septic systems in Florida are considered to be conventional systems. They consist of a hopefully watertight septic tank and a drain-field, or soil adsorption field. While the term treatment is associated with septic systems, unless an advanced treatment component is added to the conventional system, the nutrient reduction caused by these systems is limited by the site specific soil conditions present. As a rule of thumb, a 10 to 50 percent reduction in nitrogen can be expected through the drain-field.

The primary form of nitrogen leaving the drain-field is nitrate, which is a very mobile contaminant in groundwater. Dr. Roeder of the FDOH stated his belief that most septic systems work well. He also stated that requiring people to upgrade their septic system to modern standards when they are forced to repair them would not be very effective as only 1% of septic systems get repaired annually. For more information on how a septic system works, see here.

Dr Parsons wanted to know the impact of septic systems on key Florida waterbodies. He asked, for example, how much of the nitrogen that flows into Lake Okeechobee comes from septic systems. That answer was not immediately forthcoming, and Dr. Sullivan pointed out that the answer, when it does come, might not be meaningful. His reasoning was that even if the total amount of nitrogen was low, if the nitrogen was largely ammonia, that could still be a significant driver of algal blooms.

The Task Force noted that before they can make their recommendation on reducing nitrogen loading from septic systems, that more data is needed to better understand how much these systems ultimately contribute to algal blooms. Forthcoming Task Force recommendations may include expanded inspection and oversight of existing septic systems, converting conventional septic systems to advanced nitrogen reduction systems, or transition from septic systems to public sewer. The Task Force recognized that it is not practical and too expensive to collect data from the all the state’s septic systems, and a more focused study of vulnerable areas in the state is needed.

A sanitary sewer overflow (SSO) event is the release of untreated or partially treated wastewater from a municipality’s sanitary sewer system. The observed points of discharge of these overflows can be sewage backup into homes, places of business, through manholes, and into surface water bodies prior to it reaching the treatment plant. While these events may be limited in duration there are environmental concerns regarding the impact on rivers and lakes. Because the SSO is partially treated or untreated sewage there is the potential for these events to cause illness should people be exposed or come in contact with this water.

In its presentation to the Task Force, the FDEP summarized the SSO events that have occurred statewide over the past two years. The two primary causes of sanitary sewer overflows are excessive rainfall resulting in water getting into the sanitary sewer system, and the loss of electrical power. Over the two-year time period, approximately 300,000,000 gallons of partially or untreated water were discharged as a result of an SSO event. After each event, FDEP environmental specialists reviews the final data from the utility regarding their wastewater release. They use this data to assess the event and its overall impact to the environment and to determine whether additional actions should be taken.

During its discussion of the SSO, Task Force members noted that if rainfall could infiltrate the sanitary sewer pipes, is it highly likely that these pipes are leaking sewage at other times. While the Task Force is looking to assess the impact of nutrient loading from SSO events, they expressed their concern that there is an ongoing release of sewage, and hence nutrients, through leaking pipes that is not being accounted for.

The next meeting of the Task Force is expected to be in early September. Tentative topics for discussion is storm water regulation, and the health impacts of Microcysins. Agendas and presentation material from previous meetings and the August 1 meeting are posted on their website. There is a place on their website for public comments and questions. The Task Force is actively seeking public input. We strongly suggest that if you have any questions or comments, that you send them to the Task Force.

The source of the above graphic is: https://www.gbra.org/septic/index.html

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