Cape Cod’s Aquifer


Zoe Simmons

All of Cape Cod gets its water from what we call an aquifer. An aquifer is a body of water below the ground full of fresh water. Our aquifers were formed thousands of years ago when the earth was changing. Cape Cod was formed by glaciers. These glaciers covered this part of the world at the time. When they receded, they left behind rocks, clay and sand. Glaciers were responsible for much of what we love about Cape Cod. When you are out walking on the Cape and come across big boulders, those are called glacial erratics. Those boulders are left there from the glaciers! Glaciers created kettle ponds. The sand that was left here formed the dramatic and unique shape of Cape Cod. 

They also created perfect conditions for an underwater reservoir. The glaciers created layers that are perfect for holding water underground. Whenever it rains, these bodies of water keep getting replenished.

Laura Kelly is the founder of Protect Our Cape Cod Aquifer, and an established environmental activist. Kelly elaborates on the vital importance of the aquifer which, in some places on the Cape, is literally inches beneath our feet. Indeed, any water that we use in our houses to drink, to wash, to flush our toilets, to water our lawns comes directly from the aquifer. Once we use the fresh water, however, it can go back into the water cycle dirty or even toxic polluting the very aquifer we need to live. 

The water we use goes into a septic system. That goes out into what is called a leaching field. In the leaching field, the sewage water goes into the ground. It eventually ends up draining into the soil deep enough that it seeps into our aquifer. “Our drinking water is right below us,” says Kelly, and because of that, anything we treat our lawns with or that we put down our drains like soap or cleansers ends up in our aquifer.


It is also important not to waste clean water that comes directly from a good source. If you waste the water, then there will be less water to dilute the bad stuff that drains into the aquifer. 

Anything that we put on our lawns will sink down into the soil – and eventually into the aquifer. And eventually, back into our drinking water. 

When it rains, that water drains and washes anything that is in our soil closer to the aquifer. This means that everything in the sewage water and all the materials or chemicals on our lawns will get pushed down closer to the aquifer. If we have irrigation (a sprinkler system), that will speed up this process. 

People who live on ponds have an even greater effect on the aquifer. If they use chemicals on their lawns, those chemicals will seep directly into the pond and contaminate the pond water. This creates a bacteria reaction. The ponds become toxic and people swimming or dogs drinking in the ponds become exposed to dangerous toxins. Some dogs have even died from drinking contaminated water. 

If the ponds have bacteria in them, then why can’t we put chemicals in them? Well, we do, but some of these chemicals are worse than the bacteria itself. Some ponds on the Cape have been treated with what is called Alum. It is a byproduct of aluminum. 

We know that the aquifer is right below us, but how close is it to us? 

If you live in Brewster, Chatham, Harwich, Orleans, and Dennis, the aquifer is about 30 feet between you and the aquifer. 

If you live near Eastham, there is only 10-15 feet between you and the aquifer.

If you live near Hyannis, then there is 60 feet between you and the aquifer.

If you live in Provincetown there is only 2 feet between you and the aquifer. Although the aquifer is present in Provincetown, you can’t actually drink the water from it. The first reason is that the ground in P-town is pretty much at sea level so the aquifer water there is salty. The second reason is that below houses in P-town are sewer systems so the aquifer and the sewers are in the same spot. That’s why Provincetown gets its drinking water from Truro. 

“Where’s the moment that I call the tipping point? We’ll never know until it happens. The tipping point is when, for whatever reason, our drinkable water is not drinkable anymore. At that point, it’s too late,” Kelly warned. “Once this drinkable water is gone, (…) there’s no plan.”


So we know that the aquifer is right below us and we know how it got here. But how do we protect it? If we contaminate this aquifer enough, we won’t be able to drink from it anymore. Below are ways that you can help the aquifer. 


How to help keep the aquifer clean:

  • Use non toxic toothpaste 
  • Don’t use fertilizers or pesticides on your lawn
  • Plant naitive plants in your backyard
  • Properly dispose of chemicals such as paint or motor oil
  • Fix any faucets that drip
  • Try to take shorter showers
  • Only wash full loads of laundry 
  • And only wash your dishwasher when it is full too!
  • Water the plants during the coolest parts of the day 
  • Recycle
  • Use non-toxic household cleaners  
  • Learn more about our aquifer and get involved! 


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