By Sean Sheldrake, Rob Pedersen, and Alan Humphrey
In our previous blog posts we’ve talked about how EPA diving scientists support cleanups in the nation’s waterways through collection of samples. In this post, we’ll talk about miniature wells called “piezometers” that we and other divers place underwater.
What is a piezometer and what is it doing at the bottom of the river?
A piezometer (see photo 1) is a miniature well that lets us sample shallow groundwater—essentially a metal tube with a filter on the bottom to allow water to flow in, but keeping most sediment out. They can be installed both on land and underwater.
But why on earth would someone underwater want to drill for more water?! We do it to study pollution.
Groundwater that is contaminated by an upland industrial site can discharge into rivers and sounds. By the time that contaminated groundwater mixes with the water column, the pollution is difficult to detect. Worse yet, concentrations are far higher in the seafloor or river bottom, potentially harming critical links at the beginning of the food chain. If levels of groundwater contamination aren’t measured accurately and in the correct place, a big piece of the pollution puzzle could be missed.
How do you collect a well sample at the bottom of an estuary? Here’s what it looks like when we work:
Tending the diver and groundwater sample tubing is a tough job!
A surface supplied diver (see photo 2) takes the metal piezometer from the boat to the bottom while spooling out tubes that connects it to the boat or dive platform.
Don’t get tangled! Once underwater (see photo 3), the diver must be very careful to keep all their lines from being tangled; the slightest misstep and the sample line running to the surface could be pulled out, requiring the process to be restarted.
(Also see our previous post: Underwater with EPA Divers.)
With the tubing placed, water is pumped through the tube to the surface and checked (see photo 4) on board against samples taken from upland wells to ensure the right kind of sample is being taken. We pump water for the sample for 30 minutes to an hour, depending on the rate at which water will flow through the sediments. Then it’s time to move to the next spot.
With the data we collect, cleanup managers can determine whether groundwater and sediments require a cleanup, and once it’s started, whether it’s protecting the water.
For more information on EPA’s groundwater collection techniques, underwater, see: Adaptation of Groundwater Evaluation and Sampling Tools for Underwater Deployment.
Read more about the latest in EPA scientific diving at facebook.com/EPADivers.
About the authors: Sean Sheldrake is part of the Seattle EPA Dive unit and is also a project manager working on the Portland Harbor cleanup in Oregon. Sean Sheldrake and Alan Humphrey both serve on the EPA diving safety board, responsible for setting EPA diving policy requirements. In addition, they both work to share contaminated water diving expertise with first responders and others. Rob Pedersen is an EPA diver with decades of experience in environmental sample collection, and has also served on the EPA safety board.