Coarse wood chips are used to fill “biofilter bags” made from plastic netting, either nondegradable or biodegradable, depending upon customer preference. Finely ground materials are screened at least twice and marketed as horticultural compost, mulch or for animal bedding. “We get everything from stumps to leaves from franchised haulers in the region,” says Grabhorn. Woody materials are then put through three grinders, a Diamond Z, Morbark and Duratech.
Also located at Lakeside Reclamation is a comparative test site conducted by the Oregon Department of Environmental Quality (DEQ) and Metro Regional Government using compost to control erosion from storm water runoff on steep slopes. This test is part of a larger project Dave Kunz of DEQ and John Foseid of Metro are running to evaluate best management practices to control storm water runoff. The test area is on a portion of a closed landfill that is permitted for alternative cover. The landfill is covered with about five feet of native clay and uses a mix of cottonwood conifer trees, along with ground cover, to uptake moisture on and at the base of the steep slopes.
The site is steep with about a 4.5 to one slope, and extends to about 100 yards wide and 40 yards from the top to the bottom of the slope. The test employs four plots of land on the slope, each 15 feet wide and running the entire length of the slope (about 110 feet). The first plot has an application of three inches of compost with grass seed mix. The second has one inch of compost with the grass seed, and the third, one inch of compost without the seed mix. The fourth is a control plot with only the clay cover and some hand broadcast grass seed mix. Plots one through three also have three compost berms on them: one at the top, one in the middle and one at the bottom of the slope. The berms are about four feet wide at the base and two feet high at the top. The berms are designed to absorb storm water and reduce the velocity of runoff on these steep slopes.
The berms will be regularly inspected for a full year, during both the rainy and dry seasons, to determine the effectiveness of runoff control and vegetation growth. On the control plot, existing rills and water channels are evidence of concentrated runoff that gather momentum going down the steep slope. With increased rain, the rills may deepen. The effects of the compost and the berms (on the test plots) should be in stark contrast to the control plot (i.e. no rills, gullies or channels).
Additional analysis will compare the control plot, seeded without organic amendments, to the three test plots that have different layers of compost and seed mixes. This test will provide information on the benefits of compost to clay in establishing and maintaining permanent ground cover on a slope. In this case, the ground cover is being used for erosion control. The data can also help determine the cost effectiveness of compost use for erosion control and ground cover health.