Discharge or leakage of wastewater and septic effluent

Wastewater and septic pollution in the Lagoon come from several sources: baseflow, direct wastewater discharges, and leaky or failed septic and wastewater infrastructure.

Baseflow is the portion of water in a stream or canal resulting from groundwater seepage into a channel slowly over time. It’s a problem for the Lagoon due to extensive, continuing use of septic rather than sewer systems in developed areas. Older septic systems and those near the Lagoon or close to high water tables are of particular concern.

Traditional septic systems can remove approximately 72% of total suspended solids (TSS), 34% of total nitrogen (TN) and 10% of total phosphorus (TP) when properly designed, maintained and installed. Advanced septic systems, although more expensive to install, are much more effective at removing TN. They have removal efficiencies of up to 90% per Florida Department of Health field testing.

Water Quality Issues

Wastewater quality issues arise in certain situations:

When septic systems pass their useful life expectancies at around 20 years
When they’re poorly designed or sited
When clusters of septic systems lie in densities exceeding the regional soils’ treatment capacity

In these cases, nutrients don’t filter through soils, and instead pass directly to groundwater and transport via baseflow to surface waters. This is particularly true in low elevation areas that are close to surface waters. In these locations, the drain field lies very close to the water table, usually resulting in insufficient effluent treatment.

Groundwater and surface water contamination follows when septic systems and wastewater pipes fail. The most serious problems involve nutrient and bacterial contamination.

When excessive nitrogen and phosphorus in partially treated wastewater discharge to sensitive coastal waters, this stimulates algal growth and affects dissolved oxygen levels. Bacterial and other potential pathogens can also be a concern.

Past hurricanes have highlighted the pitfalls of failing infrastructure and deferred maintenance, resulting in dilute but raw sewage discharge to the Lagoon. Septic systems close to the Lagoon or located where the water table is high may intersect the water table well before tank effluent permeates the soils. It achieves little, if any, treatment as a result.