For environmental engineers at the U.S. Army Corps of Engineers – Alaska District, vegetable crops and livestock are not landfarming. It is a method used to clean contaminated soil associated with an obsolete fuel storage tank in the Arctic.
Within the Corps’ Formerly Used Defense Sites Program, experts are challenged to find new and cost-effective means to cleanup defunct military infrastructure leftover from earlier generations. Alaska’s remoteness, arctic climate and logistics pose the biggest challenges to accomplishing these missions. Engineers must consider expensive mobilization costs and availability of local resources when deciding how the sites will be remediated.
“Alaska is an entirely different environment than the rest of the U.S.,” said Aaron Shewman, environmental engineer and innovative technology advocate for the Alaska District. “Our objective is to mobilize as few times as possible to get the work done and get a ‘cleanup complete’ designation from the Alaska Department of Environmental Conservation.”
Landfarming is a potential solution to meet the needs of the FUDS program across Alaska. The process includes removing contaminated soil from the source location, spreading it across an expansive area one to two feet thick, tilling consistently and then letting nature take control. If a balance of warm soil temperature, moisture, aerobic activity and constant monitoring is achieved, then conditions are ideal to increase microbial activity that will degrade the pollutant.
“What landfarming does is attempt to accelerate nature’s process that would take many years,” said Will Mangano, environmental engineer and technical lead on the FUDS Tank Site E project near Nome.
Four miles north of downtown Nome, a World War II-era fuel storage tank leftover from the Army Air Corps deteriorated over time and tainted the surrounding soil. The vessel could store about 1 million gallons of diesel fuel at one time. During the summer, the Corps removed the rusty steel container and its foundation, but was left with about 30,000 tons of petroleum-contaminated material to remediate.
Tank Site E is one example of a project that presents logistical difficulties that raises mobilization costs. With a population of about 4,000 and located more than 500 miles northwest of Anchorage, the city of Nome is only accessible by sea or air.
The Corps considered potential contractor proposed solutions that included burning the pollution out of the soil onsite, excavating and barging the dirt off site, and, finally, landfarming. The latter presented a cost savings of about $3 million, Mangano said.
“So many innovative technologies that are developed are electricity or power intensive and require a lot of maintenance and monitoring,” Shewman said. “Landfarming saves the government money. Excavating the soil, treating it and then possibly reusing it as fill is a money saver with less mobilization required.”
Spread over 12 acres, the Corps is landfarming the soil at the Nome site and is expected to meet the state’s cleanup requirements by 2019. If the conditions are not met, the contractor will remove the material off site, Mangano said.
However, there are significant challenges associated with the process. Contractors have to cover the soil with plastic liners to create a greenhouse effect to keep the area warm due to Nome’s cold climate. Therefore, spring and summer months are the most effective for the procedure because the ground and material are thawed.
“Nome will definitely provide the wind (aeration),” Mangano said. “The summers are going to be when we aggressively keep the heat, moisture and tilling up.”
Furthermore, the method’s efficiency is determined by the type of waste being eradicated. If contaminates degrade through evaporation or microbial activity more easily, then there is a greater chance for a successful operation. For example, gasoline degenerates faster than heavy tars, Mangano said.
“We are confident it will work (at Nome),” he said. “I think it will be a good opportunity for the contractor to demonstrate that landfarming is a viable option even for the middle range hydrocarbons like diesel that the Corps sees at FUDS sites.”
Indeed, landfarming is a flexible technology that can be customized as needed to the specifics of each case, Shewman said. Additives, such as fertilizers, help microbes do their job, Mangano added. Either way, the environmental cleanup method has the potential for positive results.
“Landfarming is not just a passive technology, you still need to engage it,” Mangano said. “We jumped on the idea to pull this material out of the ground and let natural ambient conditions take over.”