How do septic tanks pollute?

*this graphic was created using the 2018 Miami Dade County Septic Report. Learn more here.

Septic tanks were not made for South Florida

Even when functioning properly, septic systems are unsuitable for South Florida. This is because South Florida bedrock is composed of porous limestone, containing many small holes and spaces. We also lack a thick layer of soil - instead, much of our soil is sandy! The spaces in the rock beneath our feet and the sandy soil allow liquids to flow through the ground very easily. Normally, soils and bedrock would act as filters for septic waste -- much like how a coffee filter works! But, South Florida's geology means that wastewater from septic tanks is moving too quickly through the natural filters -- and that means more contamination is reaching our groundwater more quickly than it should.

How septic tanks pollute

Septic tanks can pollute both through groundwater and through stormwater runoff. The small spaces and holes in our geology do not properly filter septic waste before it reaches the groundwater. This means that - even when working properly - nutrient-rich septic waste can make its way through the groundwater system. Groundwater can move rapidly from septic tanks through the holey landscape beneath our feet and can quickly flow into nearby waterways. 

Septic tanks can also pollute through stormwater runoff. When septic tanks and drainfields become flooded from high water table levels, substantial rainfall, and/or high tides, they can overflow. When this happens, contaminated septic wastewater can runoff into nearby storm drains or even back up into the pipes on your property! Most storm drains in Miami-Dade County have no filtration and generally flow directly to canals, waterways, Biscayne Bay, and other coastal waters. This means, flooding in areas with septic tanks can result in serious pollution problems.

Scientific Summary