Workers operate a GeoProbe at the Grand Junction, Colorado, Disposal Site to extract multiple core samples through the cell cover.

Workers operate a GeoProbe at the Grand Junction, Colorado, Disposal Site to extract multiple core samples through the cell cover.

The U.S. Department of Energy (DOE) Office of Legacy Management (LM) is in the preliminary stages of a pilot study on the feasibility of converting select disposal cell covers from rock riprap to an alternative type of cover referred to as an evapotranspiration cover.

Unlike the rock covers, evapotranspiration covers feature vegetation. Because plants remove water from the soil, allowing vegetation to grow on a cell cover could potentially limit precipitation from leaking into the cell below, where contaminated materials are stored. This could, in turn, help prevent groundwater contamination.

“It’s wonderful to see nature in action and how these natural processes align with our mission,” said Bill Frazier, LM site manager. “The study is very important in showing us this alignment and how we can better manage our sites and keep our disposal cells protective into the future.”

At LM’s Grand Junction, Colorado, Disposal Site, Frazier and colleagues from LM’s Applied Studies and Technology group are testing the concept in a series of test plots. In March, the team mobilized a GeoProbe — a piece of machinery used to take core samples of soil from various depths — to extract multiple core samples through the cell cover and bedding material, down to the bottom of the radon barrier that limits radon gas from the contaminated materials from reaching the atmosphere. The data from these core samples will provide baseline measurements on current cell cover properties, before vegetation is established.

Once the team installs monitoring instruments into the cell, it will begin establishing vegetation in the test plots. After a lengthy monitoring period, ideally a decade or more, the team will once again extract core samples, this time to determine how the vegetation has impacted the cell — specifically, its ability to prevent groundwater contamination and limit radon release into the atmosphere.

“Some of the questions that we hope to answer are: If you establish plants on the cell, will this limit percolation of precipitation through the cover into the groundwater? And will the establishment of vegetation on the cover negatively impact the cover in any way?” said Aaron Tigar, a research assistant with the Legacy Management Strategic Partner contractor.

The researchers hope to glean information on how to best establish vegetation on a rock-armored cell, as well as how to most effectively monitor vegetation growth and water balance on the cell.