Posted on August 23, 2021
A construction effort as massive as the Houston Ship Channel Expansion Improvement Project — designed to accommodate the wider and deeper ships now carrying goods back and forth between Asia and the U.S. — has many regulatory requirements that need to be met.
With 30 years of regulatory experience, U.S. Army Engineer Research and Development Center (ERDC) Environmental Laboratory Research Biologist Dr. Cheryl Montgomery had the expertise to meet one of them. Through research, she led her team to reach a consensus with the Texas Commission on Environmental Quality (TCEQ) that material dredged for the project would not pose a risk to human health and the environment.
Testing and evaluation was completed on dredged material from the entire 52-mile length of the channel, but the modeling stage for dredged material evaluated from the inland segment of the project required an innovative approach.
“The TCEQ gave us concurrence on the material going to upland placement areas in the landlocked area north of Morgan’s Point,” Montgomery said. “When we pick material up from the bottom of the ship channel and put it in an upland placement area, water drains off it. This water runs back into the ship channel, and we need to make sure the water would be safe — that’s where the modeling for the state of Texas was done.”
ERDC Environmental Laboratory’s Susan Bailey used a model called CD FATE, which is designed for “continuous discharge from dredging operations into open waters,” to predict what would happen after the discharge water returned to the environment.
Montgomery described how default values used for the first screening of calculations in the model were based on the assumption that everything in the discharge environment was pristine.
“The team found that when we used these parameters on this first round of calculations, we couldn’t answer the question of whether the discharge would be harmful,” she said. “We felt there was uncertainty in the model results because it was likely the default parameters didn’t match the site as well as they could.”
Montgomery said that in U.S. industrial urban areas like Houston, a regional chemical load is always present at the site; consequently, using the first round of calculations was appropriate only for the initial screening evaluation.
For the second round of calculations, the ERDC researchers considered regional background levels in and around the site, as well as local conditions, working with TCEQ to reach a consensus on using site-specific numbers for a risk evaluation. The calculations incorporated concentrations of what was already in the area, which were higher than the default values.
“The thing I love about this kind of work is that it’s a bit like sleuthing,” Montgomery said. “If you don’t pass the default parameters that the agencies set for you, you really have to pull apart the problem and think critically about which parameters are appropriate and which aren’t.
“Then you need a technically defensible reason why some aren’t appropriate, and you also need valid reasons for why you would propose something different,” she continued. “If it doesn’t make sense for my site, what would make more sense, what reflects the conditions at the site better — and that’s where experience and judgement come in.”
The CD FATE model uses a certain default toxicity number. The research team took a novel approach by working together with TCEQ to derive mutually agreed-upon toxicity numbers when the default values were sometimes not the most appropriate for the site.
ERDC Environmental Laboratory Deputy Director Dr. Brandon Lafferty said this was a precedent-setting example of doing site-specific work, and he was excited by the team’s accomplishments and what they mean for the U.S. Army Corps of Engineers and other stakeholders.
“We spend millions of dollars on dredging in these types of projects,” he said. “Before we move this material and place it somewhere, it’s vital for everyone that we ensure it’s safe to do so.”
“This project is one of the joys of being at this point in my career — instead of just defaulting to the way things have always been done, you take something apart and improve upon it, making it site-specific but remaining protective of human health and the environment,” Montgomery said.
