Olsson Associates designed and implemented improvements for the Fort Hood Composting Facility through a contract with the U.S. Army Corps of Engineers-Tulsa District and Ayuda Management Corporation (Ayuda). The compost facility operations included processing as much as 2,000 cubic yards of petroleum-contaminated soils and absorbent materials per year and receiving as much as 500 cubic yards during any day. Facility owners would then reuse the remediated soils in a beneficial manner.
Fort Hood’s environmental staff indicated that their composting operations were inefficient and costly. Composting practices included placing contaminated soils and sorbents into “biopiles” and inoculating them with commercial microbial products. It was taking several months to years to process these compost and petroleum-contaminated soils, and the additives purchased to treat the materials was expensive.
In conjunction with providing updated and more effective equipment for compost operations, Olsson reviewed and re-engineered the composting process for the facility. This process included focusing on feedstock ratios that contained the petroleum-impacted soils mixed with wood chips used as bulking agents and an organic carbon substrate. To enhance the microbial populations, landscape trimmings and animal manures from the Fort’s equestrian stables were used to improve microbial populations and activity and also act as nutrient sources. The use of these materials eliminated the need for expensive microbial inoculants. In addition, Olsson provided calculation sheets and instructions for monitoring the decomposition process. Staff members could use the data to make adjustments as needed to facilitate more rapid processing of compost and contaminated soils.
Batch studies done on two materials—petroleum-contaminated soil and petroleum-contaminated absorbents—yielded excellent results. The petroleum-contaminated soil showed reductions of Total Petroleum Hydrocarbon (TPH) concentrations from more than 4,000 parts per million (ppm) to less than 180 ppm in less than three months. The petroleum-contaminated absorbent showed reductions of TPH concentrations from more than 8,000 ppm to less than 300 ppm in the same time period.
After five months, all gasoline and diesel range petroleum compounds were remediated from the materials. When completed, the “compost” was slated for beneficial use in soil erosion repair and cover materials.