Passing Inspection

Construction and demolition (C&D) scrap materials make up a sizable portion of the solid waste generated each year. The U.S. Environmental Protection Agency (U.S. EPA) estimates that 136 million tons of C&D debris is produced annually in the United States.

 

Of this, material generated at new construction sites is estimated to be 11 million tons per year. Although this is a small portion of the overall C&D stream, it represents a significant amount of material that is often being landfilled.

 

The wood portion of this material has the potential for on-site beneficial reuse as mulch, for erosion control or as a substrate for heavy use areas.

 

 

A DIVERSE LUMBER YARD

 

Residential wood waste consists of many different products. Dimension lumber, such as 2 x 4s, is a good candidate for beneficial reuse because the only component is wood.

 

Treated lumber is often used for decks and other outdoor construction. The preservatives used in treated lumber often make it unsuitable for beneficial reuse.

 

Wild Setting 

 

Recyclers can, understandably, choose to see area residents who voice misgivings or opposition to their new business location as adversaries. One solid waste and recycling company in central Texas tried a new approach.

 

Preparing for its landfill/composting site in rural Austin, Texas, Disposal Systems Inc. (TDS) went to impressive lengths to prove its corporate neighborliness.

 

To ensure that any impact would be minimal, the company situated its disposal and composting areas on a massive 1,200-acre site. TDS dedicated 70 percent of that acreage to a buffer zone. How they chose to do so—incorporating into it a ranch, an entertainment pavilion, a skeet shooting range and a wild game preserve—is a testament to TDS’s approach to business and its public relations savvy.

 

Bob and Jim Gregory founded the company in 1977 and have taken it from its modest beginnings to one of the state’s largest waste collection, treatment and disposal companies. Today, TDS has four composting sites, employs more than 20 people and, through its composting operations, also successfully markets a full line of topsoil products.

 

In terms of processing, director of operations Jim Doersam says, "Any of the material that is not liquid in nature is first run through a Morbark Model 1300 tub grinder we have on site."

 

Having a landfill and running processing equipment, the Gregory brothers knew their company would be under intense scrutiny, so they went to great lengths to ensure that debris from the landfill and odor from the composting operation would not be a problem. They avoided surrounding the area with a chain link fence, which they felt would make the site appear prison-like, opting instead for a game fence, a barrier with smaller holes in it designed to keep predators away from the wild game.

 

With the fence in place, TDS made the next logical move: adding exotic game. The exotic game ranch has proven popular with everyone who visits the site, says Doersam. "The current park population is around 1,600 animals of 30 different species" from all over the world, including "bison, longhorn cattle, emu, impala, zebra, ostrich, wildebeest, gazelle, antelope and more." 

 

Residential construction contractors also use structural engineered wood products and finger-jointed studs that contain adhesives. Little published information is available on the potential environmental impacts of these materials. Consequently, there was a need to evaluate whether these materials are suitable for beneficial reuse.

 

The University of Georgia (UGA), in partnership with the Georgia Pollution Prevention Assistance Division, conducted a study to identify "red flags" that would preclude beneficial reuse of these products. This work was funded by the Georgia Pollution Prevention Assistance Division through the Solid Waste Trust Fund.

 

The UGA study used rainfall simulation on replicated small test plots to determine the effects of the ground engineered wood products on water quality as well as measuring any changes in soil chemistry.

 

The treatments compared were: a bare soil control, a 100 percent ground dimension lumber control, a ground mix of typical residential materials and a ground mix of 100 percent structural engineered wood products.

 

A nursery study was also conducted to evaluate the effects of mulches containing engineered wood products on common landscaping plants.

 

Before testing ground engineered wood products in the field, a toxicity characteristic leaching procedure (TCLP) was conducted to look for contaminants that could leach from the typical residential mix or from the 100 percent engineered wood products treatments. This test did not indicate there would be problems with the leachate.

 

THE RUNOFF EFFECTS

 

The field testing indicated few potential problems. The study looked for organic compounds associated with the adhesives in engineered wood products and finger-jointed studs in the runoff.

 

Large quantities of organic compounds, such as phenols, that would be associated with the adhesives from the engineered wood products were not found.

 

Organic materials such as wood, manures or composts leach naturally occurring organic compounds. When these compounds enter streams or ponds, these can reduce the oxygen content of the water. Low oxygen can harm fish or other aquatic life.

 

The study evaluated the potential for the ground wood wastes to impact oxygen demand by measuring biochemical oxygen demand in the runoff. There was no difference in biochemical oxygen demand between the dimension lumber control and the treatments containing engineered wood products, but initially all the mulch treatments had a higher average biochemical oxygen demand than the bare soil control.

 

After one year, the biochemical oxygen demand in the mulch treatments were not different from the bare soil control.

 

Nutrients such as nitrogen and phosphorus are another potential source of concern. High nutrient concentrations in streams and ponds can cause algae blooms and harm fish or other aquatic life.

 

Concentrations in the runoff were compared to those in minimally impacted streams, otherwise known as reference streams. The U.S. EPA uses reference streams to help states develop recommended criteria for water quality standards.

 

The average nutrient concentrations in runoff from the mulch treatments were highest during the initial rainfall simulation in 2002, when the mulches were fresh, and decreased after a year. The average total nitrogen in 2002 from the 100 percent engineered wood product treatment was above the U.S. EPA maximum for reference streams

(2.57 mg L^-1), but typical residential mix treatment was similar to that maximum.

 

After one year, average total nitrogen concentrations in runoff from 100 percent engineered wood products and typical residential mix treatments decreased to

0.92 mg L^-1. Total phosphorus concentrations in the runoff from the fresh mulch treatments in 2002 were below the 1 mg L^-1 level generally used for wastewater treatment plant discharges, but above the 25th percentile for reference streams of 0.03 mg L^-1.

 

After one year, the total phosphorus concentrations also decreased and were below the detection limit of 0.18 mg L^-1.

 

These results indicate a low potential for adverse impacts to surface water from a one-time application of the mulch. Although the 100 percent engineered wood products treatment initially had nitrogen concentrations above values desired for reference streams, this is a worst-case scenario. It is unlikely that wood waste mulch would consist of 100 percent engineered wood products, and the rainfall simulation was an extreme event.

 

Initial nitrogen concentrations in the typical residential mix, which is more likely to be representative of the scrap wood from residential construction, were much lower and nearer maximum values seen in reference streams in Georgia. Nutrient concentrations in runoff from ground wood wastes also have the potential to be reduced before reaching surface water as the runoff infiltrates into the soil or is filtered by passing through vegetated areas.

 

The mulch treatments resulted in few changes in soil chemistry. Available ammonium-nitrogen and phosphorus increased in the soil immediately below the 100 percent engineered wood products treatment, but these nutrients were retained in the soil immediately underneath the mulch.

 

The use of mulches made from engineered wood products had no effect on the growth of three commonly used landscaping plants. Root growth into the 100 percent engineered wood products mulch showed no growth-inhibiting toxic contaminants.

 

RECYCLING IMPACT

 

Structural engineered wood products comprise about 30 percent of the scrap wood from residential building projects. Because these products are used in all phases of construction, it is difficult for builders to segregate them from dimensional scrap lumber in order to process them separately.

 

Overall, the UGA study indicates mulches with a typical structural engineered wood product component should be safe for beneficial reuse or recycling on site.

 

The researchers hope to develop specific guidelines for beneficial reuse in conjunction with the Georgia Environmental Protection Division in the near future.