Erosion control and water-quality monitoring at a petroleum landfarm

To provide for the economical remediation of approximately 20,000 tonnes of petroleum-contaminated soil (PCS), the University of Idaho developed a 4-hectare landfarm in 1994-95. Strict erosion control was required for the landfarm, because no soils could be allowed to leave the site. An integrated erosion control plan was implemented, relying on organic mulch, a soil berm (seeded and protected by erosion control blankets), multiple silt fences, leafy cover crops, and a storm-water drainage/collection system. In addition, to keep the PCS layer aerated, deep sub-soil plowing was done across the site, which also served to maintain good infiltration characteristics and to inhibit runoff and erosion. All storm-water runoff, both surface water and shallow ground water, is collected with a gravel-filled trench drain and perforated pipe system at the downslope end of the landfarm. During the first quarter of 1996, the landfarm was subjected to two severe stormwater runoff events, one associated with the February flooding that impacted the entire Pacific Northwest and one associated with a 24-hr, 41-mm rainfall event in April. Both storm events provided rigorous tests of the erosion control practices, but neither caused any visible or measurable erosion from the petroleum landfarm.