Answer: Title 5 septic systems are designed to protect public health by removing solids and bacteria from sewage. The design does not remove nitrogen and phosphorus, which are the nutrients that are causing poor water quality in our ponds and embayments.
Solids are collected in the septic tank and the remaining liquid flows into the leaching field which soaks into the ground, ultimately reaching groundwater. This liquid contains high concentrations of dissolved nitrogen and some phosphorus, among other things put down the drain.
The nitrogen and phosphorus-rich liquid percolates down through soil to the groundwater that flows into our ponds and embayments. On Cape Cod, septic systems are the major source of excess nutrients contributing to poor water quality, followed by fertilizers and stormwater runoff.
What is your town doing about its wastewater problem? See State of the Waters Action Plan to see what needs to be done.