Cooking Dirt

A six-foot chain link fence secures the area from animals and unauthorized personnel, and OIT/NRC also established a series of aquifer monitoring wells and implemented a comprehensive well testing program to ensure that the water table remains unaffected.

Depending on the size of the job, clients may bring contaminated soil to ASR or the company may go to them.

“We have the only mobile unit in the state, so if the job is large enough to make it financially feasible, we can take everything from our site, put it on trucks, and drive it to a client’s location,” says Shippen, giving the example of a large Superfund clean-up site with thousands of tons of contaminated soil. “There are a lot of mitigating factors involved, including the time of year and also if the job would require us to be on-site for a couple months or more.”

“We’ve mobilized before, though it’s not something that we’ve really marketed,” adds Anchorage Sand & Gravel Vice President and General Manager Ryan Zins. “It’s based upon demand, and like any construction company, we look at our backlog and crew availability; we don’t [mobilize] to take care of a heating oil spill in someone’s backyard.”

Remediating Damage

The most efficient way to treat petroleum-contaminated soil is to heat it. At OIT/NRC, soil is put into a high-temperature thermal oxidizer that is 50 feet long with an 8-foot diameter drum. Temperatures are kept between 900 and 1,500 degrees Fahrenheit in the primary chamber and between 1,700 and 2,100 degrees Fahrenheit in the secondary chamber to burn off the gas.

“Unfortunately, landfarming like they do in the Lower 48 won’t work up here,” Sanford explains. “While New Mexico and California can let materials bake away in the desert, that’s not going to work with Tanana silts. In Alaska, the season is also a real player in what we can do.”

According to Sanford, the oxidizer remediates any level of hydrocarbon contamination while providing clean-up levels with air quality nearly five times cleaner than ADEC regulations. “Alaska Source Testing comes in once a year to test to make sure we are meeting all regulations,” he adds.

In April, OIT/NRC became the first facility permitted to burn PFAs (per- and polyfluoroalkyl substances), which are used in industrial and residential applications and are found in a wide range of consumer products such as carpet treatments, non-stick cookware, water-resistant fabrics, food packaging materials, and personal care products.

“PFAs are also found in the fire retardants used all over the country,” says Sanford, who added that the company received its first such materials from Eielson Air Force Base in May and expects to receive similar contaminants from Fairbanks International Airport and the City of Fairbanks, among other clients.

Depending on the material, it can take anywhere from a few days to process contaminated soil to much longer. “In perfect conditions, you could treat 1,000 tons of soil in a few days,” says Shippen of ASR’s system, which pre-treats the soil at about 600 degrees and destroys the volatized vapors at approximately 1,600 degrees in a thermal oxidizer. “But if it’s really wet, it can take a lot longer because you have to heat the water before you can volatize the contaminants.”

“Gravel runs better than sand, sand runs better than silt—and clay is the worst,” says Sanford. “Organics may also slow running time. The deciding factor on price is the moisture content and contamination level—the higher those are, the longer residence time in the kiln and the more it costs.”

Moisture content definitely makes a difference—wash bay soil, which results from places like truck shops and fire stations washing their vehicles—can cost three times as much because there is so much water in the soil.

“We can run three tons an hour if it’s wet, or eighteen tons an hour if it’s perfect material,” says Sanford.

Depending on the time of year, there can also be a backlog, delaying how long it takes for a load of soil to be fully recycled. “Soil that comes in today will be processed six weeks from now because of what’s in front of it,” says Sanford. “Sometimes it takes a week or two depending on backlog.”

Once it’s fired up, the OIT/NRC plant runs 24/7 for six to eight weeks, then shuts down for two days for maintenance. The season runs from May 1 to October 30. “We are limited by what we can do in winter because the material is frozen, which makes it very difficult to deal with,” says Sanford, adding that most maintenance is performed during colder months.

“While we can run year-round, it is definitely more labor-intensive in the winter months, so we tend to stockpile material during that time of year and start burning it again in spring,” adds Zins.

The Finished Product

After the soil has been remediated, it needs to be tested before getting the all clear. “We have a third party test our piles every week, and the information is shared with the state,” says Sanford. “Once it is certified as clean, you can do almost anything you want with it, short of using it in wetlands.”

The company uses gravel to make sewer rock and adds clean peat to make topsoil or garden soil. “We sometimes get rocks the size of Volkswagens that we crush to make D1; anything three inches and up, we screen it, wash it, and sell it,” says Sanford of the recycled material.

The company prides itself in taking a leadership role in protecting the environment, and even uses recycled fuel in the burning process. “We use about 2,000 gallons a day, and we purchase fuel from NRC made of used oil combined with virgin diesel in an 80/20 mix,” says Sanford. “We’re reusing a waste product to burn the contaminants out.”

ASR also uses a third-party impartial consultant to test its finished product, and once given the go-ahead, sells or provides it free-of-charge to the construction industry as well as other buyers. “At that point, it has met Alaska’s most stringent criteria, so it is available for basically unrestricted use,” says Shippen. “The soils we generate are 95 percent compactable fill, which can be used in a variety of situations including for topsoil or for road projects.”

“By offering a way to treat contaminated soils in-state, we’re lowering our carbon footprint because we don’t have to ship it out,” says Zins. “We’re creating a clean, recycled product that can be used in berms, building projects, for soil stabilization on hillsides, and more.”