Part 1: Life on a (polluted) sandbar

Cape Cod is a beautiful and fragile place. When the glaciers retreated thousands of years ago, they left a sandy peninsula shaped like a bent arm off the coast of our continent that is reshaped each day by wind and water. Ocean breezes float from sand dunes and grasslands to the broom crowberries on the heath lands and through pitch pine forests. Nearly 900 freshwater ponds are deep enough to connect to the groundwater, which is the only source of drinking water for Cape Cod residents.

With a footprint just slightly larger than that of New York City, the Cape is small but popular. From 2019 to 2024, 20,000 people moved to Cape Cod. More than 232,000 residents live there year-round, and many seasonal residents are staying longer than in the past. Each year a whopping 5.5 million tourists visit.

All of those tourists and residents eat, and then they urinate and defecate into water-flushed toilets that drain, most commonly, into septic systems.Eighty-five percent of Cape Cod properties rely on septic systems, most of which release nitrogen and phosphorus into the sandy soil, which drains into groundwater and eventually to surface streams, ponds and coastal waters.

“We’re past the carrying capacity of the land,” says Bryan Horsley, project assistant at the Massachusetts Alternative Septic System Test Center (MASSTC) in Buzzards Bay. He joined MASSTC in 2021, researching and testing innovative septic systems, urine diverting and composting toilets, and other systems that are designed to remove nitrogen and phosphorus before it reaches groundwater.

Residential wastewater is roughly only 1% urine, but that urine contributes around 80% of the nitrogen and 55% of the phosphorus that’s disposed into the environment. When nitrogen travels to bays and estuaries, where under natural circumstances it would occur in limited quantities, the influx spurs overgrowth of algae, leading to outbreaks and harmful algal blooms (HABs) that can threaten public health and result in destruction of aquatic habitats and beach closures

Similarly, phosphorus has historically been scarce in Cape Cod’s freshwater ponds, thus keeping plant growth in check. When the phosphorus from septic systems and other sources reaches ponds, however, it fertilizes the algae, cyanobacteria and plants, causing harmful algal and cyanobacterial blooms and overgrowth. According to the Association to Preserve Cape Cod, in 2023, 90% of the coastal waters and 37% of the freshwater ponds that were assessed had unacceptable water quality.

“People excreting nutrients into water has resulted in widespread water pollution,” says Horsley. “In my previous job with the Association to Preserve Cape Cod, I helped start their program monitoring freshwater ponds, tracking cyanobacteria. I was blown away that literally every single pond I went to, I found it. The entire region is suffering, even areas where there’s not a lot of development. It’s basically affecting the whole groundwater aquifer.” Horsley is dedicated to ecological solutions for sanitation that will complete natural cycles and won’t increase our dependence on fossil fuels. That’s ecological sanitation—but how do we get there?

Regulations to the rescue?

In 1975, a new regulation was adopted, called Title 5, aimed at how septic systems could be improved in Massachusetts. Title 5 kept human health—rather than environmental concerns—front and center, and required the proper siting, construction, and maintenance of septic systems. That code has been updated numerous times to identify and protect natural resource areas of the Cape that are particularly sensitive to nitrogen pollution from septic tanks. Those areas cover about half of the Cape.

The nitrogen-sensitive areas of Cape Cod, shown in light and darker green, must comply with the updated environmental code Title 5 to reduce nitrogen pollution. Source: MASS DEP

Now, towns can require a homeowner in nitrogen-sensitive areas to replace their septic system with an innovative/alternative (I/A) nitrogen removing system within five years. Or, towns can try to reduce the pollution over 20 years using a variety of options under a watershed permit, including I/A septic system, sewers and other alternatives.

Why not sewer$?

Expanding sewer systems on Cape Cod, town by town, would cut nitrogen pollution by about 40 percent. But only six out of the 15 townships on the Cape have even partial sewer districts. Construction of more comprehensive sewers would take more than 30 years to complete and will likely cost communities around $100,000 per household to connect.

Household sewers must connect to wastewater treatment plants, which demand energy to pump, clean, and transport their treated wastewater and biosolids. These plants must be sited on available land and maintained for as long as they are in operation.

One town, Falmouth, in the southwestern corner of Cape Cod, began planning for a sewer project in 2010 and hoped to connect households by 2040. The estimated cost of the project is $33.5 million.

Only a fraction of the homes on Cape Cod are connected to sewers (black); 85% rely on septic systems (tan) and must comply with Title 5 code. Source: Association to Preserve Cape Cod.

Perhaps better septic systems?

A second solution to Cape Cod’s conundrum (mentioned previously above) might be installation of innovative/alternative (IA) septic systems. Some I/A septic systems remove nitrogen, others remove phosphorus, and some can remove both. The nitrogen-removing I/A systems rely on microbes that use a carbon source like wood chips to convert the ammonia and other nitrogen-containing compounds in waste water into nitrogen gas (which is environmentally harmless and already plentiful in our air).

Some of these I/A systems can be retrofitted to existing septic systems while others require a complete replacement of septic tank and leaching field. Installation of a residential sized I/A system is likely to cost between $30,000-$80,000 per household with $50,000 being considered average.

So where should the residents and municipalities on Cape Cod turn for answers? You might be surprised by the options described in Part 2.