FIGURE 1 Compostmethods evaluated: (a) static compostwindrows, (b) forcedaeration system, and (c) rotary drum.

Composting RoadkillResearch and Implementation by theVirginia Department of Transportation B R I D G E T D O N A L D S O N A N D D A V I D W I L S O N

More than 1.2 million deer–vehicle colli-sions occurred in the United States in2014. Removing and disposing of the deer

carcasses and those of the millions of other animalskilled in collisions with vehicles are essential ser-vices that transportation agencies provide.

According to a national survey in 2005, the 23responding states predominantly managed roadkillwith a combination of landfills and burial. Commonshortcomings cited included the long travel distancesto landfills, landfill restrictions, and a lack of viableburial areas (1).

Problem Each year, vehicles in Virginia hit more than 56,000deer. The Virginia Department of Transportation(DOT) spends more than $4 million to remove anddispose of the carcasses of deer and other wildlife.Road maintenance teams need roadkill managementstrategies that are viable, environmentally compliant,and cost-effective.

Composting roadkill is not common in theUnited States, although composting livestock car-casses is a frequent practice not only in the UnitedStates but worldwide. Under Virginia law, compost-ing benign roadkill is subject to the same siting, con-struction, and testing requirements that apply to thedisposal of sewage sludge and household waste. Theactions necessary to adhere to the broader compost-

ing regulations are beyond the typical budgets andduties of a state DOT maintenance staff; as a result,the regulations could limit the adoption of a com-posting program in many states.

SolutionIn 2009, the Virginia Transportation Research Coun-cil (VTRC) began a series of research projects to eval-uate the environmental implications of compostingroadkill and the utility of the practice as an option formanaging the carcasses in a way that protects theenvironment and passes regulatory review. VTRCevaluated three methods (Figure 1, below); the cri-teria and results are shown in Table 1 (page 48).

Compost WindrowsResearchers constructed windrows with deer car-casses placed side by side between layers of woodchips, a source of carbon. The absorbent, bulky qual-ity of the wood chips helped to maintain the propermoisture levels and oxygen flow for composting, andthe high carbon content balanced the high nitrogencontent of the animal carcasses.

Virginia’s solid-waste management regulationsaim to control the amount of leachate entering watersources from composting operations. Leachate is theproduct of precipitation that percolates through thecompost and contains extracted or dissolved com-post material. The VTRC researchers found that the

Donaldson is SeniorResearch Scientist,Virginia TransportationResearch Council,Charlottesville. Wilson isEnvironmental ProgramManager, VirginiaDepartment ofTransportation,Richmond.

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natural filtration through the soil reduced theleachate constituents to nominal concentrations (2).In addition, the windrows achieved high tempera-tures that quickly destroyed pathogens (Figure 2,below).

Compost Vessels Static compost windrows are economical and needlittle maintenance but require a large amount ofspace; if left unturned, the windrows produce maturecompost in 10 to 11 months. The researchers there-fore investigated rotary drum and forced-air systems,vessels that have smaller footprints and are designedto contain leachate; moreover, the compost maturesrelatively quickly.

Rotary drums operate with an electric motor thatautomatically rotates to aerate and mix the material.The drums also include an aeration system and wire-less sensors for the temperature.

The forced-air system has two or more adjoiningconcrete containers—depending on the roadkill vol-ume requirements for the area—and a three-walled,covered area for storage and curing. A mounted airpump forces air into the composting materialthrough tubes in the container floor.

VTRC evaluated rotary drums and a forced-airsystem with the criteria listed in Table 1. The com-post generated from both systems met all criteria,and with consistent management and oversight, thesystems performed well from an operational per-spective (3).

ApplicationThe VTRC research established that the compostingmethods evaluated are effective and do not contami-nate groundwater or surface water and do not spreadpathogens. Virginia DOT and the state’s Department ofEnvironmental Quality executed a joint memoran-48

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FIGURE 2 Illustrations of plot design, windrow construction, and placement offlasks containing pathogens: Windrow A, with leachate filtered through soil andcollected in a buried lysimeter; Windrow B, with leachate not filtered through soil;and Control Pile C, containing no deer and with leachate not filtered through soil.A temperature data logger was placed between the pathogen flasks in all threepiles.

Criterion Windrows Vessels: Rotary Drum and Forced Air System

Compost temperatures 150°F and higher; met EPA criteria forpathogen destruction

150°F and higher; met EPA criteria for pathogen destruction

Pathogensa Confirmed destruction Confirmed destruction

Leachate volume 2 percent of the precipitation that fell on thewindrow plots left the piles as leachate.b

Not applicable: leachate was contained.

Leachate contaminants Filtration through soil reduced contaminantsto nominal concentrations.

Not applicable: leachate was contained and recycled within the forcedair system.

Operational performance Not applicable: no operation required Performed well with oversight and management

Plant germination andgrowth

Not tested Plants grown with compost grew significantly larger by weight thanthose grown with soil.

Maturation time 11 to 12 months 2.5 to 4.5 months

Cost Nominal—wood chips are free for someDOTs.

Ranges from $43,000 to $139,000, depending on vessel capacity; theforced-air system is the most expensive option evaluated but is cost-effective with sufficient carcass volume.

TABLE 1 Evaluations of Compost Windrows and Vessels: Criteria and Research Findings

a E. coli, Salmonella, and ascarid ova (roundworm eggs).b Low volumes of leachate are partly the result of the high absorption capacity of wood chips.

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dum of understanding (MOU) for composting animalremains from roadway maintenance operations (4).

The MOU outlines operational requirements forcarcass composting—for example, the siting, con-struction, leachate capture, and compost testing. Byincreasing the prospects for Virginia DOT to imple-ment composting, the agreement promotes the reuseof material that otherwise would be placed in a land-fill.

VTRC recently completed guidelines for compost-ing, including detailed descriptions of materials, thesteps, and the time and the temperatures needed toachieve compost maturity. The guidelines also includebeneficial applications for the finished compost.

Virginia DOT currently has five compost vesselsthat serve 15 maintenance areas. The agency plans toincrease windrow composting throughout the stateand to locate several additional composting vesselsstrategically.

The compost method chosen for an area dependson the volume of roadkill and the availability ofspace. Forced-air composting is the most prevalentmethod in Virginia, because the technique can han-dle a large volume of roadkill within a relatively smallfootprint.

BenefitsResearch found that the compost methods that wereevaluated provide Virginia DOT with a much-neededand more efficient alternative to the current practicesfor managing roadkill. Composting provides a viableoption in maintenance areas that have long travel dis-tances to disposal facilities or that no longer havelandfills accepting animal remains. Composting alsooffers environmental benefits, potential savings, anda practical end product.

In contrast with disposal at a landfill, compostinganimal carcasses saves valuable landfill space anddecreases the volume of organic byproducts, whichare known sources of methane, a greenhouse gas.

VTRC researchers expect to find substantial costsavings from windrow composting, which requiresno investment for areas that have a free source ofwood chips. The initial investment for a compostvessel ranges from $43,000 to $139,000, butresearchers found that a vessel can pay for itself if itreplaces a lengthy drive to a landfill (5). Efforts toenhance the potential for greater savings from vesselcomposting are ongoing. Initiatives under wayinclude the following:

u Ensuring that the size of the vessel matchesthe area’s volume of carcasses,

u Pooling carcasses with other maintenanceareas, and

u Applying finished compost in road projects.

Applications include compost blankets—a layerof composted material spread on the soil—and com-post berms, which reduce erosion and stormwaterrunoff. Virginia DOT will use compost to establishvegetation for site restoration, aesthetics, or generallandscaping.

For more information, contact Bridget Donald-son, Senior Research Scientist, Virginia Transporta-tion Research Council, 434-293-1922; bridget.donaldson@vdot.virginia.gov.

AcknowledgmentsThe authors acknowledge Jimmy White, Audrey Moruza,Ed Wallingford, Robert Perry, and Ann Overton for theirwork on Virginia DOT’s roadkill composting program.

References1. Maryland State Highway Administration. Summary of

Responses to Maryland Survey on Animal Carcass Disposal.American Association of State Highway and TransportationOfficials, Washington, D.C., 2005. http://research.transportation.org/Pages/RACSurveyResultsOrganizedbyYear.aspx.

2. Donaldson, B. M., G. P. Smith, Y. J. Kweon, N. Sriran-ganathan, and D. L. Wilson. Composting Animal CarcassesRemoved from Roads: An Analysis of Pathogen Destructionand Leachate Constituents in Deer Mortality Static WindrowComposting. Publication VCTIR 12-R12. Virginia Centerfor Transportation Innovation and Research, Char-lottesville, 2012.

3. Donaldson, B. M., and J. W. White, Jr. Composting AnimalMortality Removed from Roads: A Pilot Study of Rotary Drumand Forced Aeration Compost Vessels. Publication VCTIR13-R8. Virginia Center for Transportation Innovation andResearch, Charlottesville, 2013.

4. Virginia Department of Environmental Quality and Vir-ginia Department of Transportation. Memorandum ofUnderstanding Between the Virginia Department of Environ-mental Quality and the Virginia Department of Transporta-tion: Composting Animal Road Mortality from VDOTMaintenance Roadway Operations. Virginia Department ofEnvironmental Quality, Richmond, 2015.

5. Moruza, A. K., and B. M. Donaldson. An Evaluation of theEconomics and Logistics of Animal Mortality Composting forthe Virginia Department of Transportation. PublicationVCTIR 15-R18. Virginia Center for Transportation Inno-vation and Research, Charlottesville, 2015.

EDITOR’S NOTE: Appreciation is expressed to G. P.Jayaprakash, Transportation Research Board, for hisefforts in developing this article.

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Suggestions for Research Pays Off topics are wel-come. Contact Stephen Maher, TransportationResearch Board, Keck 486, 500 Fifth Street, NW,Washington, DC 20001 (202-334-2955; smaher@nas.edu).

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