Wide Range of LM Expertise Tapped for Rifle Disposal Cell Pore Water Extraction Project

When the U.S. Department of Energy (DOE) Office of Legacy Management (LM) recently faced an operational challenge at the Rifle Disposal Site in Colorado, it took subject matter experts across a wide array of disciplines to tackle it.

The 71-acre disposal cell was constructed in 1996 to contain uranium mill components and mill tailings from two former uranium and vanadium processing sites, known as Old Rifle and New Rifle, located near the city of Rifle, Colorado. The disposal cell is a Uranium Mill Tailings Radiation Control Act (UMTRCA) Title I disposal cell, and is located 6 miles north of the City of Rifle in Estes Gulch.

Beginning in 2001, water began accumulating inside the disposal cell and had to be pumped into a nearby lined evaporation pond. As the system aged, the environmental remedy was unable to keep up with the rapidly rising water levels, threatening the system’s structural stability. As a result, in 2024, LM prioritized developing and executing a new network of strategically placed, solar-powered extraction wells and evaporation ponds to address the issue.

“Once we realized that our existing infrastructure was not keeping up with the rising water levels, the first approach was to look at modifying operational parameters to maximize pumping rate,” said UMTRCA Team Lead Paul Kerl. “We redeveloped existing wells and we freeze-proofed existing infrastructure to maximize run time and pump year-round, but unfortunately that still wasn’t enough. Seeing the water levels rising further, we assessed the risks associated with saturating the side slope of the disposal cell and realized a full court press was needed to implement a priority project to mitigate the risks in very short order. Only a multi-disciplinary, rapid response, cross functional team could develop and implement a project to quickly address these risks. Fortunately, the Office of Legacy Management has such a team,” said Kerl.

After briefing the situation, the site team rapidly gathered all the support needed to prepare for successful project execution and risk mitigation. The team coordinated communication and support across the organization, including from leadership, finance, regulatory, planning, design and construction teams, IT, communications, asset management, environmental compliance, project management, radiation safety, surveying, contracting and subcontracts, safety, and data management. All stakeholders treated this project with high priority, acknowledging the risks, and executing the project as the organization’s top priority.

“This was an all-in effort,” Kerl said, “and the dedication and professionalism of the joint LM-LMS team paid dividends and drove success.”

A variety of challenges had to be addressed before work on the site began, such as environmental compliance issues related to radiological waste removal, water rights, and required project permitting. The environmental compliance team assessed the potential effects of the project on the land, the air, wildlife, water, and plants.
LM completed an extensive review of the disposal cell construction and water accumulation to determine how many new extraction wells were needed and the best placement of the wells for maximum efficiency. To avoid hitting buried mill materials during drilling, hydrogeologists depended on a geophysical survey, finding the best location to place the new wells.

“To simulate how the water levels within the cell would change because of pumping, we developed a numerical groundwater flow model. Historically, what we knew about the cell came from three locations: the two standpipes with 30 years of water level records, plus one that’s dry. That didn’t give us a lot of information to calibrate a single groundwater flow model,” said LMSP Senior Hydrogeologist Pete Schillig. 

“To account for the uncertainty, we developed an ensemble approach and calibrated 223 numerical groundwater flow models. With that ensemble, we selected a design strategy that worked for all the models in the ensemble,” Schillig said.

After LM completed the planning phase, work began at the site in June 2024. Despite a compressed schedule, the team managed parallel tasks and subcontractors seamlessly.

The project team set up drilling on top of the disposal cell. To avoid disturbing the existing riprap cover layer, workers made a temporary road surface using interlocking, heavy-duty construction mats. After building a path, LM brought in a drill rig and on-site equipment. LM used “super sacks” to store drill cuttings, including tailings material, away from the construction area. Once filled, each sack was brought to a radiation control area and cordoned off with radiological hazard signs. During drilling, the makeshift paths were moved and repositioned to accommodate each drilling area. These mats provided safe, stable surfaces for the workers.

Throughout drilling operations, LMSP used a LIDAR, or light detection and ranging, system to scan the disposal cell and address the concern of maintaining disposal cell integrity during drilling.

“LIDAR sends a single beam of light to a point or points on the ground to the front slope of the cell. When it does that, the light bounces back to the instrument and the instrument knows its location and orientation,” said LMSP Surveyor Services Lead Jeff Schaaf. 

Using the LIDAR system, LM confirmed that no movement of the cell occurred while equipment and staff performed work.

Once all preparations were complete, drilling began. The goal was to drill 10 additional extraction wells, totaling 12 wells actively drawing water from the cell. An additional four monitoring wells were drilled to measure water levels in the cell. While the main drilling work progressed, other workers constructed the modular evaporative ponds.

The introduction of new wells and more infrastructure meant that additional power was needed to operate the system. Once drilling was completed on the disposal cell, the new solar power systems and System Operation and Analysis at Remote Sites (SOARS), were put in place to provide the power. The SOARS system allows LM to operate and monitor the new water extraction system remotely.

After the components for the SOARS systems were complete and the pipeline from the wells was attached to the modular evaporative ponds, extraction rates of pore water – the water that infiltrates the small spaces between grains of soil and sand – were tested. The first test demonstrated a steady 2.5 gallons per minute. Once the first well began producing water from the cell, the remaining wells were brought online.

The additional water removal meant more evaporative capacity was needed too.

“The site was originally built with one small evaporative pond, but we needed to install two additional one-acre modular evaporation ponds to support the volume of pore water to be extracted from the cell,” said LM Site Manager Mary Young.

Construction and engineering teams worked together to secure a plan for the two modular evaporative ponds. Procurement streamlined acquiring the equipment and continued to play a key role in resolving supply issues as they arose.

With the maintenance efforts for the disposal cell complete, it was time to restore the surrounding land to its condition before work began. Workers first scored the soil to help native plants take root. After that, native plant seeds were planted to revegetate the area and stabilize the disturbed soil.

Work on the site is now complete and the wells are working as expected, extracting pore water necessary to maintain cell integrity. Site monitoring using data collected and transmitted by the SOARS stations and adherence to the long-term surveillance plan will continue to protect human health and the environment.

“This project required personnel with expertise in many areas,” Young said. “We completed this complex project with a comprehensive approach that has allowed us to maintain the integrity of the disposal cell.” 

Kerl agreed, saying the joint effort and the outcome of the project was a success by all measures.

“I am extremely proud of the team’s dedication, professionalism, long hours, and esprit de corps exemplified during the execution of this important priority project,” Kerl said. “I congratulate you all on a job well done.”