Debris Management Site Acreage and Volume Reduction

ScopeStorm debris goes first to a temporary site where it is stacked, sorted, ground, or burned, and the site's size and the time to work down the pile follow from the Corps of Engineers model. Debris stacked 10 ft high puts 4,840 square yards times 3 1/3 yards -- about 16,133 cubic yards -- on an acre, and only 60% of a site holds piles: the rest is haul roads, fire breaks, burn pits, sorting areas, and household hazardous waste collection, so the storage acreage is divided by 0.6. For a 659,100 cubic yard event that is about 40.9 acres of piles and 68.1 acres of site, against 65.9 acres by the guide's rule of thumb of 100 acres per million cubic yards, printed as a cross-check. A site turned over every 45 to 60 days serves more than its standing capacity, so the acreage divides by the number of times it fills during the recovery; two fills cut the land to about 34 acres. Reduction is the whole strategy: grinding leaves a quarter of the woody volume as mulch and burning leaves a twentieth as ash -- 197,730 cubic yards of woody debris becomes about 49,400 cubic yards of mulch or 9,900 of ash. At 125 cubic yards an hour per grinder, the middle of the guide's 100 to 150 for contaminated debris, four machines working 10 hour days need about 40 days. It does not select or permit a site, address air, water, and soil permits, ash testing, mulch pile fire risk, or restoration, and monitored grinder production governs over any rate. FEMA-325, the state environmental agency, and the applicant's debris management plan govern.

Formula or tablestorage acres = volume / (4,840 sq yd per acre x stack height / 3); gross acres = storage acres / land-use fraction (0.60 -> x 1.66 in the guide); cross-check = 100 acres per 1,000,000 cy; cycled acres = gross acres / fills over the recovery; ground volume = woody x 0.25, burned = woody x 0.05; machine-hours = woody / rate; days = machine-hours / (machines x hours per day).

Source and editionFEMA-325, Public Assistance Debris Management Guide (July 2007), Appendix B, USACE model Step 2 (10 ft stack, 60% land use, factor 1.66, site cycling every 45 to 60 days) and the reduction ratios, Chapter 8 (about 100 acres per million cubic yards), and the guide's warning that contaminated debris averages 100 to 150 cy/h through a grinder; FEMA 329 (2010) for 16,133 cy per acre at 10 ft.

Free accessFEMA-325 and FEMA 329 are free federal publications on fema.gov; the factors are public-domain USACE and FEMA figures.

What governsEstimate. AHJ and licensed professional govern.

API field namesdebris_volume_cy, woody_volume_cy, stack_height_ft, land_use_fraction, site_fill_count, reduction_method, processing_rate_cyh, machine_count, operating_hours_per_day, storage_acres, gross_site_acres

• Ten foot stack about 16,133 cubic yards per acre; the guide's rounded figure is 16,117FEMA-325 Appendix B; FEMA 329
• Sixty percent of the land holds piles the rest is roads, buffers, burn pits, sorting, and household hazardous wasteFEMA-325 Appendix B
• Grinder rate is the guide's contaminated-debris range default 125 cy/h, the middle of 100 to 150; monitored production governsFEMA-325