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Ask the Experts


What are estuaries?  

Estuaries are enclosed areas of the coastline where the fresh water from groundwater and streams is mixed with salt water from the surrounding oceans; essentially, where rivers meet the sea. Estuaries are critically important for sea grasses, scallops and soft shelled clams, and they serve as breeding grounds for offshore fish. These are also the primary recreational areas of Cape Cod.  

What is the state of Cape Cod’s bays, estuaries, and coastal waters?  

Shellfish bed closures in Cape Cod estuaries have greatly increased over the past several years and eelgrass has nearly disappeared from some estuaries within the past decade. The key contaminant causing degrading water quality in Cape Cod's coastal waters and estuaries is nitrogen. Nitrogen is present in human waste and it enters groundwater and surface water (lakes and ponds, rivers and streams) primarily through septic systems in most locations.  

What is a Comprehensive Wastewater Management Plan (CWMP)?  

CWMP refers to a Comprehensive Wastewater Management Plan. The purpose of a CWMP is to provide an environmentally and economically sound plan for wastewater treatment and disposal in communities for several years. CWMP planning evaluates a community’s existing wastewater treatment facility and collection system, addresses nitrogen loading impacts to the community’s coastal embayments, identifies water supply demand and supply constraints, and identifies and evaluates wastewater problems for all areas of the community. CWMP’s are subject to state and federal regulations, particularly those relating to watershed management directed by the Federal Clean Water Act.  

How does my septic system work?  

Septic systems use the soil to provide basic treatment of sanitary sewage generated by your household. Household sewage includes wastewater from toilets, sinks, showers, washing machines, garbage disposals and dishwashers. This sewage flows into your septic tank, which separates the wastewater from the solids (sludge and scum). The liquid waste then flows into the ground through the leaching facility or field—where it is discharged into the soil. While some contaminants are removed in this process, a typical septic system removes only limited amounts of nitrogen. The remaining nitrogen mixes easily with groundwater and eventually discharges into saltwater bays and estuaries.  

What is nitrogen loading?  

Nitrogen loading is an over-abundance of nitrogen in the estuaries, which causes algae to grow. This is called eutrophication. Excessive algae growth decreases the amount of light reaching the bottom, causing eelgrass to die from lack of sufficient sunlight. Algae can also contribute to low oxygen levels in the water. Muck builds up in the water, creates offensive odors and reduces depths. Oxygen depletion also places fish and shellfish at risk. On-site septic systems are the main source of nitrogen entering most of Cape Cod’s estuaries. Too much nitrogen in drinking water can cause a human health problem. Too much nitrogen in an estuary causes health problems for the entire ecosystem.  

Do Title 5 or Enhanced Septic Systems remove nitrogen?  

Septic systems - even newer Title 5 ones - don't remove enough nitrogen from wastewater. Nitrogen leaches into the groundwater and travels into ponds and estuaries. Excess nitrogen causes algae blooms, which remove oxygen from the water, and it affects water quality in saltwater bodies. Poor water quality can result in beach closings, shellfish bed closures and other, long-term impacts.