King County Environmental Purchasing Program

Shredded Wood-Waste and Landscape Mulch

• Introduction
• Usage History and Experience
• Bid and Contract Specifications
  • Hog Fuel
  • Bark and Wood Chips Specification (WSDOT)
  • Sample Specification: Animal Bedding/Temporary Road Surface/Mud Control
  • Landscape Mulch at the West Point Treatment Plant
  • Landscape Mulch at the King County Airport
• Product Experience
  • Temporary Road Base at the Cedar Hills Landfill
  • Landscape Mulch at the West Point Sewage Treatment Plant
  • Landscape Mulch at the King County Airport
• For More Information
• Vendor Information

Introduction

Wood-waste processors accept untreated, unpainted woody debris from construction and land-clearing operations, remove contaminants such as rocks and nails, and shred it into coarse "chips" that are sold as "Hog Fuel" (presumably named after the grinding machine, known as a "hog"), for use in mud-control and other applications. This material may be sold as "Coarse", "Medium", and "Fine" grades, each appropriate for different applications.

The "Coarse" grade material (particle size less than 5 inches) is used for temporary road surface, mud control in animal pastures, bedding for dairy cows and other animals, and for erosion control.

Horse-arena surface material, horticultural mulch, erosion control, and boiler-fuel applications typically require a "Medium" grade material (particle size less than 3.5 inches).

"Fine" grade material (particle size less than 2 inches) is used for horticultural mulch and soil amendment. Local landscapers report that the large particle size (relative to compost, peat and other relatively fine organic amendment materials) results in a mulch that allows water to percolate to the soil surface while retaining soil moisture. Used as a soil amendment, hog fuel results in a good soil structure when decomposition is complete, but the Nitrogen balance of the soil during decomposition must be carefully managed for optimum plant growth.

Processors are increasing their sources of woody material and are rapidly developing new materials and applications.

Usage History and Experience

Wood chips made from shredded land-clearing debris can be used as ground cover for erosion-control, horticultural mulch, and other applications. In the last year, the Solid Waste Division used it to stabilize temporary driving surfaces at the Cedar Hills landfill, especially during rainy seasons. In 2006, the Division purchased 85,000 cubic yards of shredded wood, or “hogfuel,” at a cost of nearly $60,000 and saved an estimated $85,000 by using this instead of virgin aggregate.

The winter of 2003 left 40,000 cubic yards of trees, limbs and stump debris from the wind and ice storms and floods that tore through the county. This expensive clean-up led the county Roads Division to invest in “HogZilla” – a hydraulic-coupling tub grinder that weighs more than 60,000 pounds – to chip away at this debris. The resulting wood chips were used for county construction projects, erosion control and landscaping. For more information, please see the press release, “County's monster HogZilla chomps away at debris”

Bid and Contract Specifications

King County specifies hog fuel for soil stabilization, road construction and erosion control at the Cedar Hills Landfill.

Coarse woody hog fuel

The hog fuel should be shredded bark or wood and shall be ground so that it meets the size, description and gradation analysis below.

In addition, the hog fuel shall contain a minimum of extraneous material. It shall contain no material that would be deleterious to equipment and shall not contain resin, tannin or other compounds in quantities detrimental to animals, plant life or water quality.

The bulk density shall be less than 22.2lbs per cubic foot on a bone dry basis.

Size description:  Up to 16” typical particle length.  1/8” to 4” typical cross section.

Gradation analysis:  By weight;

Hole size:  .............. 6”................. 4”.............. 2-1/2”........ 1-3/4”........ พ”.......... 3/8”

% passing:........... 99-100......... 75-95........... 60-80........ 45-65..... 28-38..... 10-30

The sample specifications below provide an indication of the characteristics that a user may wish to specify. Users should modify them to suit their particular needs.

Bark and Wood Chips Specification (WSDOT)

Washington State Department of Transportation (WSDOT) specification 9-14.4(3) for bark or wood chips is reproduced here from the 2006 Standard Specifications for Road, Bridge, and Municipal Construction, for reference. This specification is intended to help engineers to specify horticultural mulch for roadside landscape plantings.

9-14.4(3) - Bark or Wood Chips

Bark or wood chip mulch shall be derived from Douglas fir, pine, or hemlock species. It shall be ground so that a minimum of 95 percent of the material will pass through a 11⁄2-inch sieve and no more than 55 percent, by loose volume, will pass through a U.S. No. 4 sieve. The mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life.

Sample Specification: Animal Bedding/Temporary Road Surface/Mud Control

The sample specification below is offered only as a starting point for the development of a project specification (See discussion of "Medium" grade above)

 

Animal Bedding / Temporary Road Surface / Mud Control

Material shall be shredded bark or wood and shall be ground so that a minimum of 95 percent of the material will pass through a 5-inch sieve and no more than 45 percent will pass through a 3/4-inch sieve. The material shall contain a minimum of extraneous material. It shall contain no material that would be deleterious to equipment and shall not contain resin, tannin, or other compounds in quantities that would be detrimental to animals, plant-life or water quality.

Landscape Mulch at the West Point Treatment Plant

A demonstration of shredded wood-waste at the King County Jail in 1995, led to a collaboration between the vendor and the West-Point wastewater treatment facility of the Department of Natural Resources. They developed a specification for a horticultural mulch and used 4,000 yards of this material for that project, and saved over $6,000. The producer has opened a new market based on the product developed through that collaboration and is optimistic about future growth of this product.

Landscape Mulch at the King County Airport

Similar to the West Point project described above, the King County Department of Construction and Facilities Management used 600 cubic yards of this material, at a cost of nearly $5,000, for a holding area for nursery-stock at the King County Airport, mulch around the Administration Building, and other applications. The material is less expensive than bark and other mulches.

For More Information

King County Solid Waste Division
Cedar Hills Landfill Operations
Maple Valley, WA
(206)296-0497

 

 

Further information may be available through the following main menu selections:

King County Supply Contracts
Resources for Buyers
Standard Paragraphs for Contracts

Vendor Information

Rainier Wood Recyclers, (253)630-3565 Kent, WA

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