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Chapter 10
Roadside Management and Maintenance: Beyond Vegetation
10.16. Road Waste Management

DOT road maintenance activities generate large amounts of dirt, litter, or roadwaste debris from sweeping roadway surfaces, picking up litter, clearing vegetation, cleaning highway drainage systems, and clearing landslides from roadways. Roadwaste materials generally share the same contaminants of concern - bacteria, litter, sharps (glass, needles, etc.), chemicals from spills or illegal dumping, gasoline, oil, heavy metals.

In the past DOTs sometimes stockpiled or disposed much of this roadwaste at maintenance yards, back lots, or along highway right-of-way; however, these options are less viable with growing amounts of waste material, increasing highway traffic and pollution, less available land, and stricter environmental regulations. Managing DOT roadwaste using conventional methods calls for solid waste to go to landfills and liquid waste to sewage treatment plants. Just separating roadwaste into liquid and solid portions using conventional methodologies can be extremely difficult and expensive. Waste is often required to undergo expensive testing or sorting prior to disposal. Likewise disposal of all DOT solid waste in landfills can be impractical, inefficient and cost prohibitive. Landfills and sewerage hookups are not readily available for DOT roadwaste disposal in many areas.

Many roadwaste pollutants are easily detectable. Litter and trash in roadwaste piles can be detected visually. Many chemical pollutants can be detected as odd colors, stains, discoloration, or chemical smells. Other times pollutants can only be detected through chemical testing, or in the case of knowing oil or grease is present, it may still take laboratory testing to determine if levels are toxic. Heavy metals detection requires laboratory testing. Determining risk is key to knowing disposal options. If waste is full of trash, smells of oil and gasoline, it has a high toxic risk and reuse options are limited; hauling waste to a high-risk waste dump can be the quickest option. Trash may be able to be screened from medium risk waste and stored in an appropriate spot while toxic hydrocarbons (present from gasoline or oil contamination) break down. Later, such material may be appropriate for shoulder repair or patching holes under proper circumstances. Some roadwaste, such as landslide debris, has no (or low) toxic risk and can be used as clean fill. With clean waste, the main issue is finding an environmentally appropriate location for final placement where it will not erode or impact a wetland. [N]

ODOT undertook a Roadwaste Research Project in conjunction with the Oregon Department of Environmental Quality and various agencies concerned with highway operations to identify more efficient and effective ways to manage roadwaste materials. The first phase was a literature review, which identified current roadwaste issues and problems across the country and summarized the most effective methods yet developed to manage this special waste stream. Phase 1 findings were documented in the report "Roadwaste: Issues and Options" [N] . The second phase of the project pursued some of the more promising roadwaste management methods identified in Phase 1, with implementation and testing in the field. ODOT worked with local highway agencies in the Portland area to develop methods that would efficiently reuse or dispose of roadwaste generated from local urban roads. Field trials were conducted to collect data on pollutant levels associated with various roadwastes and disposal methods. Phase 2 findings were documented in ODOT Roadwaste Field Trials. [N] The Roadwaste Management Report summarized the findings of the research project and offered recommendations on how ODOT Districts can use this information to better manage roadwaste materials. The major findings of ODOT's Roadwaste Project can be summarized as follows:

  • Roadwaste covers a broad range of materials with a broad range of environmental risks. Roadwaste pollutant levels reflect highway traffic counts and surrounding land uses. Levels of pollutants and trash found in roadwaste will vary widely.
  • Some roadwaste is entirely free of contamination and can be managed as clean fill. Managing roadwaste efficiently and saving on disposal costs relies upon knowing when the waste is dirty, when it is clean, and when it is mildly contaminated. Roadwaste does not classify as a "hazardous waste" (except for the very rare spill or illegal dumping incident).
  • Knowing the characteristics and volumes of the waste a District collects helps in the selection of management methods that most efficiently address actual environmental risk.
  • Identifying and separating differing roadwastes allows more ready management while requiring less frequent analysis. District-level baseline waste characterizations help identify the most appropriate management methods to address actual risks.
  • Roadwaste must be properly managed to address environmental risk. Storing low risk roadwastes separate from more contaminated or trashy waste makes reuse easier and will help control management costs. Ready reuse is available for some materials; other materials require simple treatment. More contaminated materials may require a significant investment in treatment or ongoing tracking unless a conservative management option is selected; e.g., disposal in a permitted landfill. Complying with waste recommendations when nonhazardous wastes are mixed with hazardous wastes costs additional maintenance dollars.
  • Partnering with local agencies will save resources, and risks are minimal.
  • Efficient management of DOT roadwaste will require District level planning.

ODOT's Roadwaste Management Flowchart offers a planning process that can be used to manage the roadwastes that ODOT collects and environmental risks associated with them. Finally, it presents specific waste treatment and disposal options and discusses sorting, reuse, and recycling options. [N]

 

10.16.1 Stormwater System Residuals and "Vactor Waste:" Catch Basin, Sump and Line Cleanout
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On average, vactor waste is the most contaminated type of roadwaste with the highest environmental risk. "Vactor waste" is so named after a brand of eductor truck commonly used to vacuum out catch basins, sumps and storm sewer lines. Certain factors generally increase the risk of toxic contamination. Generally, the more silts or fine particles present, the higher the chance of contamination. Dead-end sumps will be more contaminated than catch basins, since catch basins let a lot of fine material pass through them. The higher the traffic count or average daily traffic (ADT), the higher the contamination levels. Wastes from more frequently cleaned sumps (or catch basins) can be expected to be cleaner.

Because vactor waste contains water, there is an increased risk for runoff and ground infiltration. Infiltration of contaminated water through porous gravel, sand, and fractured bedrock may threaten groundwater. Without contact of oxygen and sunlight, contaminants do not readily degrade. The fine particles in vactor waste are easily suspended in runoff and can dramatically impact stream health - both immediately and in the long term. Fines can carry high levels of contaminants and themselves pose threats, e.g., clogging fish gills and burying spawning beds. This wastewater requires special management and cannot be returned to the storm drain system or disposed on land without a water quality permit from the state environmental agency or EPA.

Basic environmental practices for dealing with vactor waste are outlined in Appendix B of ODOT's report:

  • Liquid fractions may not be disposed back into stormwater catch basins or collection systems that discharge to surface waters, wetlands, or the subsurface unless. Instead, these liquids should be disposed, after approval is obtained, to a sanitary sewer.
  • Sanitary sewers may require placement of vactor truck decant water only into high flow sewers or only after 24 hours to settle out the suspended solids.
  • Where sanitary sewers are not available, the DOT hazardous materials section may identify DOT-owned areas where public access is limited for field decanting of vactor solids or liquids under a state permit. Sites for land application of decant water should be free of runoff concerns and able to hold petroleum contaminants in the top layer of soil to insure the best chance for treatment, with controls preventing public access. Overuse should be avoided to prevent build up of contaminants.
  • Vactor solids tend to be more contaminated than liquids. Being harder to screen for trash and with less ready reuse options, vactor solids are a good candidate for disposal at a permitted landfill. An agreement to provide this material for use as landfill daily cover can substantially reduce disposal costs. All waste disposed at permitted landfills must be dry enough to pass the "paint filter test" and may face other requirements.
  • Some local agencies have invested in dewatering facilities and may be open to partnering.

Vac waste from bridge culvert cleanout normally produces rock and trash and very little fine material. Bridge scuppers will capture only well-washed rock and gravels. Since these wastes pose no real risk, they do not need to be tested. Free from trash, they are ready for immediate reuse. Clean, well-washed rock in the maintenance of other stormwater facilities can also be reused. Other vactor cleanout waste in the District might have unique characteristics and deserve separate management under its own category.

 

10.16.2 Road and Roadside Dirt and Debris
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Sweeper trucks remove dirt and debris from the highway system. Contaminant concentrations in sweepings are usually lower than those found in vactor waste, but even relatively clean sweepings can contain toxins and require careful management. The risks posed by these materials are similar to vactor wastes. Wastewater collected with wet road materials has many of the same concerns as vactor truck wastewater. Sweeper loads full of fallen leaves and other organic materials may be better managed by composting than by classic waste disposal.

The City of Portland separates street debris into heavy sand and light debris. Until 1988 sweeper debris was disposed of in general purpose landfills. By 1988 landfill space was diminishing and disposal rates jumped from $16.50 to $42.25 per ton. The rate is now $75 per ton. Sand, 20 percent of the volume but 80 percent of the weight of the debris, could be disposed of for free as cover materials. Separating sand from organic material saved the Bureau approximately $675,000 the first year. [N]

Basic environmental practices for dealing with sweeping dirt and debris are outlined in Appendix B of ODOT's report:

  • Screen regular sweepings, disposing trash and litter only at DEQ-permitted landfills.
  • Store materials such that rainfall will not cause any runoff. (Contaminated runoff could impact other areas on site, wetlands, or surface waters.) Store sweepings to minimize the potential for site impacts from roadwaste contaminants. Storage on an impermeable surface with leachate collection and/or protection from rainfall is preferable. Tarps may be used for cover, or berms or retention ponds may be used to contain runoff.
  • Winter road sand may be collected and reused once screened and sized. If sand washing is required to remove excess fines, minimize site impacts, collect the fine particles, and prevent runoff. (Pretreatment by settling or flocculation then permitted discharge to sanitary sewer is a sound practice).
  • Most roadwaste is very poor fill, tending to have poor compaction ratings, and reduces in volume substantially as organic matter decomposes.
  • Storage, processing and reuse of materials other than road sand and clean fill may require a state solid waste permit. Composting over 25 tons per year usually requires a site-specific permit.
  • Screened materials collected from areas known to have low impacts from roadwaste contaminants may be screened for trash and used as poor grade fill in DOT-owned and controlled areas. During storage and processing, fines should not be allowed to become airborne.
  • Sidecasting of minimally contaminated sweepings onto non-ditched shoulders can be appropriate if these roadsides are not adjacent to surface waters, wetlands, or stormwater management systems with discharge to surface waters, wetlands or the subsurface.

Winter Road Sand

Quick pick up of winter road sand on urban streets can reduce toxic pollutants and result in net direct cost savings. Many DOTs and local governments have road sweeping programs to reduce air and water pollution. Pollution reduction benefits have been quantified in a few cases. A 2002 WisDOT/FHWA/USGS study evaluated the effectiveness of an improved highway sweeping program using a high efficiency sweeper as a best management practice (BMP) for reducing pollutants in urban highway stormwater runoff, believed to be the most complete attempt to date to document the use of a high efficiency sweeper program on an urban freeway section. Based on data collected and analyzed during the study, it was calculated that a once per week freeway sweeping program using a high efficiency can be an effective stormwater runoff best management practice (BMP) for an urban freeway section. WisDOT subsequently developed guidelines for the purchase and use of high efficiency sweepers. [N]

Road sand quickly removed from roads after a thaw may be ready for reuse as is, or it may require a screening step to remove trash and/or to drop out the more contaminated and less useful fines. The recycled sand replaces new product that would otherwise have to be purchased, and recycling results in less waste to manage. Use of anti-icing and de-icing agents may reduce the need for road sand application.

Ditching Spoils and Sediment Pond Cleanout

Contaminant levels in ditching spoils will vary widely, depending on cleaning methods, water flow, traffic count, and surrounding land use. ODOT found that spoils collected from ditches draining high ADT roads in urban areas had contaminant levels as high as those found in vactor wastes, while ditchings from some rural areas tested completely clean. More rarely, rural ditch material had tested at high levels for heavy oils or other contaminants. ODOT manages rural ditchings from low-ADT roads as clean fill in most cases.

Roadway sediment ponds detain roadway runoff, dropping out contaminated fines. The spill containment attributes of sediment ponds may require testing for a broader range of constituents. Limited contaminant data on ODOT Interstate 84 sediment cleanout showed levels similar to catch basin and sump waste, in very similar material.

Landscape Cuttings: Greenwaste

DOTs can collect high volumes of organic matter during road projects or as a result of slides. In the fall, leaves can accumulate on roadways and in right-of-ways. Taken together, waste organic materials are termed "greenwaste." As buried organic matter can release toxic nitrates to groundwater, burial is not usually permitted. In addition, as vegetative matter decomposes it reduces significantly in volume, resulting in major settling issues on the ground surface - a problem shared to a lesser degree with sweepings and vactor wastes. Composting is the best alternative for clean greenwaste. Compost can be made on a district basis or hauled to a commercial composter if greenwaste volumes are low. See composting section.

Construction Site Soils and Slide Debris

Slide debris and construction site soils and slurries not impacted by road oils or heavy organic loads should be managed as clean fill. Greenwaste should be removed for composting. Care should be taken in storage and placement of these materials. In the Appendix is an example of generated waste from Oregon DOT.

 

10.16.3 Disposal and Re-use Options
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As transportation agencies, DOTs are required to accept long-term liability for the wastes it collects from highway maintenance. Only in cases such as a reported spill incident can the responsibility for waste management be placed on another party. Liability for environmental impacts from the wastes ODOT collects is unending; it is "cradle to grave." The challenge is to substantially limit risk and liability while not incurring undue cost. Reuse and disposal are the two major choices for managing roadwaste solids.

Re-use of Roadwaste

The key to reuse is viewing roadwaste as something of value rather than as something to discard - as a potential product rather than a waste, in which case stringent waste management regulations may not apply. Rather than paying tipping fees for disposal, the product is used to replace materials the DOT might otherwise need to purchase. Reuse also reduces the burden on expensive and difficult-to-site landfills. For a reuse option to work, it must protect human health and the environment while reducing total cost for managing the waste. Disposal of solid waste requires a permit. Only clean soil materials, weathered asphalt and concrete can be used as fill material without first obtaining a permit. Long-term storage, such as stockpiling, will be seen as disposal unless it can be shown to state and local environmental agencies that treatment or storage for eventual legitimate reuse is occurring. Routine screening for trash in loads may facilitate this.

Ready Reuse Options can include clean fill, winter road sand reuse, and managing gravel and rock. Besides screening for trash and keeping an eye out for impacts from spills and releases, no treatment or tracking of these clean materials is necessary. More specific reuse options may include: rock fall berms and noise barriers, use as soil amendment (freeway infields/median or agricultural use), poor grade utility trench fill, highway shoulder repair, and asphalt or cement or pre-fabricated concrete manufacture.

Untreated roadwaste has poor drainage characteristics and a poor compaction rating. Sweepings, vac wastes, etc. have a high organic component that will decompose, leading to settling, sinkholes and cracking. Thus untreated reuse of these materials is not recommended as construction site fill, or under roads or parking lots. High temperature thermal treatment, which burns off the organic materials along with the contaminants, can make fill options workable.

Berm or Noise Barrier Construction
Marginally contaminated roadwaste might be suitable for use as berm material. ODOT Region 1, District 2B, constructed a berm of roadwaste and landslide debris at the base of Rocky Butte in the City of Portland to prevent rock fall from reaching the I-205 freeway (Figure 13.1). Runoff from this area is contained and infiltrates into the ground through a level grassy area. There is no ready access for human contact. Sampling shows contaminant levels in the berm to be well below industrial cleanup thresholds. The berm and berm water runoff have been routinely sampled to assess contamination risks and to monitor the natural bio-degradation of petroleum contaminants.

Recommended practices:

  • Remove trash. Solid waste rules require that trash be removed prior to legitimate reuse.
  • Limit public access. Place barriers on ODOT-controlled property, so it is inaccessible to foot traffic.
  • Contain or treat stormwater runoff. Monitor for pollutants to insure they do not escape into runoff or into accessible areas of the property.
  • Limit contaminant levels to below state industrial cleanup thresholds.
  • Mixture with uncontaminated materials will reduce contaminant concentration. Roadwaste testing below the industrial cleanup standard might be mixed with clean fill or clean slide debris to reduce site contamination risks. Clean material can also be used to cap and contain material with low but significant contaminant concentrations. Any mixture of clean materials with contaminated materials, however, runs the risk of creating more contaminated materials.
  • Plant and/or mulch berms. Limit erosion and control dust.
  • Encourage biological treatment of contaminants with open air and plantings. You may also choose plants to enhance on-site phytoremediation.

The risk associated with using roadwaste for berms is low to moderate. With restricted public contact and controlled stormwater runoff, risk is dependent on contaminant concentration, site and soil characteristics, and future site use. Long-term tracking and monitoring of reuse sites is appropriate. DOT regional environmental representatives or a specialist from the state environmental agency can help assess proper placement and long term management of these berms.

Use as Soil Amendment
Use of roadwaste as soil amendment reduces costs substantially, and can even offset costs of purchasing new product. Risk can be effectively controlled by choice in placement. Most roadwaste has decent drainage characteristics, plentiful nutrients, and good water retention, with a good mix of particle sizes appropriate as an effective growing media. After the usual screening for trash, limited use of roadwaste as a soil amendment may be quite feasible if placement of contaminated material is carefully considered. Washington DOT (WSDOT) mixes vac waste with wood chips for an effective growing medium and uses it in freeway infields and medians. The wood, serving to improve the growing media, also fixes metals and petroleum compounds.

Recommended practices include the following:

  • To pursue reuse of roadwaste as a soil amendment, it is necessary to know the characteristics of the material. Placement of a product that would result in surface concentrations above industrial cleanup levels would prevent reuse.
  • When allowing reuse of untreated roadwaste on land out of DOT control, a contract with the landowner is recommended, limiting placement to cropland, with a significant setback from any water conveyance, state water, or wetland. A simple site review by qualified staff is recommended. Any material released should be at most only marginally contaminated, i.e. having a baseline waste characterization below industrial cleanup standards.
  • Place the product where risk of exposure is very low and risk of transport is minimized. With runoff issues controlled during placement and good vegetative cover, the problem becomes long-term tracking. Drying the vac sludge is not essential, as plantings do require moisture.
  • Track placement and conduct regular tests to track contaminants.
  • Take care to place the waste mixture over existing soil or clay, not over quickly draining sand or gravels.
  • Simple treatment by aeration has been observed to substantially reduce petroleum concentrations. The expected reduction of simple compounds prior to reuse will limit risk of transport. Heavier and harder-to-treat compounds are less mobile. To encourage further aeration and reduce chance for movement to the subsurface, placement should be limited to within two feet of ground surface. In addition, limit placement to areas with little or no chance of human exposure.
Poor Grade Utility Trench Fill
Massachusetts allows use of sweepings as poor grade utility fill. They term it "poor grade fill" because it has a poor compaction rating, quickly loses volume, has poor drainage characteristics for use as fill, and is marginally contaminated. Still, use as fill over utility lines is workable and can be protective. Mass Highway does note that the trench must be mounded up to allow for a substantial volume reduction in the fill material; otherwise, the utility line will start to look like a shallow ditch and will accumulate runoff. Mass Highway does not allow reuse of catch basin vac waste as fill, judging it to be too contaminated. Given the known problems with use of roadwaste under paved surfaces, placement is only recommended under open ground. What makes this option work well is that the material is not placed in concentration, so overall site impacts are not likely.

Limited reuse as poor grade utility fill away from ready human contact should not present significant risks.

  • The use should be limited to commercial or industrial properties and agency-controlled, limited access areas.
  • An uncontaminated soil trench cap can further limit potential exposure. Tracking placement of materials below industrial cleanup levels or on ODOT-controlled, limited access areas should not be necessary.
  • With a baseline contamination level established for vac waste, a DOT may be able to reuse waste as poor grade utility fill.
  • Be careful to not stockpile roadwaste for reuses that may never materialize; this reuse may be more appropriate for public works agencies with greater need for utility trench fill.
  • Screening for trash will likely be required prior to reuse.

Highway Shoulder Repair
As sweepings or vactor waste can substantially reduce in volume with time, use of these materials as highway shoulder fill can result in soft shoulder problems in the future. Furthermore, since most highway shoulders drop off into ditches, water quality issues may also limit reuse of sweepings and vactor waste in many locations. Potential for public access is another issue limiting use of more highly contaminated materials. It is important to limit material used for highway shoulder repair to relatively clean materials with good compaction ratings.

Asphalt, Cement or Pre-fabricated Concrete Manufacture
Asphalt and cement manufacturers can use fines or sand-sized feedstock from a variety of sources though materials with any significant organic matter content must be avoided. Asphalt plants need dry materials free of trash and they can use petroleum-contaminated soils. Cement manufacturers process their feedstock in a kiln, creating sand-sized particles for cement production. Cement kilns operate at extremely high temperatures; any organic matter present burns and as such adds fuel to the fire, which can create serious upset conditions if not anticipated. Cement kilns need to know the percent of organic matter present in their feedstock. Cement manufacturers often specify that vactor waste be free of oversized materials and debris, and tested for the eight TCLP metals to insure they are not accepting hazardous waste. Each manufacturer will impose its own conditions on acceptance.

Consistent supply of consistent material is key. Water content, trash content, organic matter content, particle size, and amounts are all important factors. As a supplier, the District/Region must be able to deliver product to meet the manufacturer's schedule. Collection schedules and capacity to safely store roadwaste materials that will go for reuse should be considered. Sweepings that have "cooked out" (i.e. composted) might make better asphalt feedstock, and might supply a more consistent organic matter percentage for cement production. Testing requirements might be waived after a District can show a consistent product.

Although it takes planning and effort to get roadwaste into a manufacturing process, it can pay off. Using more contaminated and problematic material (which poses higher disposal or management costs) as feedstock can yield substantial savings. The basic issue of consistency should be pursued in developing good partnership opportunities and long-term business arrangements. Transportation costs should be factored into any plans for use as feedstock, and hauling distance could limit the applicability of some business opportunities. Still, shipment to distant manufacturers could potentially be more cost effective than disposal. DOTs positions as large purchasers of asphalt and concrete can put them in a good negotiating position to have their roadwaste reused. Materials contracts might reasonably specify that a minimum percentage of acceptable roadwaste materials be used as feedstock in cement kilns.

The high temperatures in cement kilns destroy the PAHs and TPH fractions and virtually eliminate the risk otherwise inherent in the material. Heavy metals are bound into the cement and are unlikely to pose a concern at the concentrations present. Heavy metals do have the potential to be a concern in the disposal of cement mixer wash-out water; however, cement manufacturers currently use many other materials with higher metals concentrations as feedstock. PAHs do not pose a risk in asphalt, and asphalt uses petroleum as a binder in any case. Heavy metals content in waste asphalt should not prove to be a significant concern.

Treatment Options

Treatment is more cost-effective than disposal if the treatment costs (testing, hauling, managing, permits, treating, and tracking) are less than or equal to the disposal expenses plus the cost of buying the product new.

Composting
Composting can use a variety of materials as feedstock. Composting leaves and grass on a district level ("greenwaste") can bring savings over hauling the material to a commercial composter, especially if the compost can be used to replace purchased growing media. For efficient composting, some brush may require chipping, and thick, woody wastes may require tub grinding. Reuse of wood chips and making wood available for home use may also be workable. Washington DOT recycles their vactor sludge into a growing media by mixing it with wood chips.

Composting of non-greenwaste materials is also possible. The City of Portland has been composting greenwaste and sweepings for several years and has encountered good success. Removing trash and sharps (hypodermic needles and glass) is a problem encountered with composting sweepings. Cigarette butts are prevalent and particularly hard to screen out. Great Western Sweepings in Tualatin, Oregon, has worked out a dual screening system that ODOT found to work well.

Roadwaste does not need the turning that normal compost does, since it has a much lower oxygen demand. Treatment studies have also shown that petroleum compounds can bind with organic matter. Woody waste and compost can fix both metals and carcinogenic PAHs, preventing them from escaping into the surrounding environment.

Permits may be required for compost operations of a certain size (exceeding 25 tons of input per year in Oregon). ODOT has found there are benefits to obtaining a permit: DEQ can help solve site stormwater issues and provide you with technical assistance to ensure a good product. You will need to know how to avoid hot spot fires and also how to not end up with a stinking mess. The City of Portland study mentioned above may result in a better understanding of risks associated with composting. The use of composted material on lands outside of ODOT control is not recommended except for designated farm use (see Use as Soil Amendment). Although composting requires significant time and expense, the challenges are manageable and, in the right areas, the results will be well worth the effort.

Thermal Treatment
Thermal treatment is often used to destroy the gasoline and diesel petroleum fractions in soil collected from underground storage tank cleanups. Gas and diesel can be removed at relatively low temperatures. However, the gasoline and diesel fractions do not pose the most significant risk for management of common roadwastes. The low-temperature thermal desorption technology used by mobile soil burners does not destroy the major risks - carcinogenic PAHs and heavy metals. High-temperature thermal remediation (exceeding 650° F) appears to volatilize a significant portion of the CPAHs, substantially reducing the concentrations of the most significant contaminant. Volatilized contaminants not immediately destroyed are burned off at temperatures above 1,200° F in an afterburner.

The City of Portland takes their vac waste to TPST's high-temperature thermal desorption facility in North Portland. Prior to thermal desorption, the material is screened for trash. Water content needs to be 30 percent or less; this can be achieved by mixing with other batches. Treatment of CPAH-contaminated batches has shown that this technology can remove these compounds. Heated pile technology is expected to work as long as the material can effectively be stacked with the heating pipes.

High-temperature thermal treatment normally results in a sterile product, with all of the organic contaminants and vegetative matter destroyed. The compaction rating of the product is sufficient for use as construction fill. With no organic materials, there is nothing to degrade. The material is no longer suited for use as a growing medium though.

Testing for TCLP heavy metals may be required; facilities generally cannot accept roadwaste with a contaminant level so high that it qualifies as a hazardous waste. Minimal level of trash content may be allowable.

The City of Portland has netted $15 per ton cost savings over using Metro area landfills by using this approach. Little to no environmental risk is expected from reuse of roadwaste that has undergone high-temperature thermal treatment if adequate treatment standards are maintained.

Passive Bioremediation (Simple Aeration )
Bioremediation allows natural microorganisms to break down contaminants. Some micro-organisms can eat petroleum, using it for energy, and release carbon dioxide and water. Bioremediation cannot be used to "treat out" heavy metals, though metals may be rendered less mobile. "Passive bioremediation" means the microbes already present do their work, without steps taken to enhance their activity. In cleanup parlance, this is often termed "natural attenuation." Roadwaste piles left alone to naturally bio-remediate have had little or no detectable total petroleum hydrocarbons (TPH) in as little as six months.

Reducing diesel and heavy oil fractions does not eliminate the major risks associated with physical contact with roadwaste. The heavy metals and most of the CPAHs are still present. They are tightly bound into the material, however, and not readily transported to groundwater or surface water. In reducing TPH concentrations substantially, the most mobile and highest concentration contaminants are removed from the equation, making placement away from ready access much more workable. Uses for passive bioremediation include preparation for direct reuse (e.g. in noise barriers or rock fall berms), reduction of active decomposition and preparation for landfilling in a roadwaste landfill. Permits may be required by the state regulatory agency for passive bioremediation sites and technical assistance may be available. Care should be taken to make sure requirements address actual risks. Breakdown of organic matter releases organic acids, reducing pH. Lower pH environments can mobilize heavy metals. The same process can happen with composting roadwaste. Care should also be taken to minimize, control, monitor and/or treat stormwater runoff from all storage and treatment areas.

Active Bioremediation
Active bioremediation enhances the effects seen in passive bioremediation by adding nutrients to help feed the microbes, surfactants that release bound contaminants, and chemicals that help break down complex chemicals or that provide chemical sources of oxygen. Peroxides can break down complex carbon chains, in some cases making them more ready food for existing microbe populations, as well as introducing needed oxygen. Such techniques have mainly been used in treating petroleum-contaminated soils from underground storage tank cleanup sites. These lighter petroleum compounds are not a concern in roadwaste. The nutrients and microbe populations in roadwaste are usually quite capable of dealing with the normal petroleum fraction (see Passive Bioremediation, above). Thus, using a product designed to break down gas and diesel fractions as a roadwaste treatment technology can be a waste of time and money.

The microbes found in roadwaste are of hardy varieties. Some of the specialized microorganisms introduced to treat complex carbon compounds do not compete well with natural microbes. Special conditions may be required, including the presence of special nutrients or chemicals to enhance or kick-start biological activity; a certain temperature range perhaps found only during special times of the year; or a tight pH soil acidity range. Liming agents and other pH adjusters can be used to create an environment better suited to the microbes you are using. Nutrients may be needed.

Overall, active bioremediation is considered an expensive option practical for only a small percentage of roadwaste. Placement of treated materials depends on the success in reducing CPAH concentrations. Of course, heavy metals will not be removed. If heavy metals are present in high concentrations, they could limit potential reuse and may make landfilling a more practical option. Active bioremediation of roadwaste should focus on destruction of the CPAHs. Several samples should be run through a lab after treatment to establish that the treatment was successful.

Phytoremediation
Phytoremediation involves using plants to treat contaminants. Certain plant species have been identified that are good at removing or destroying certain types of contaminants. For the heavy metals in roadwaste, planting a variety of grass that is known for its high uptake of lead could result in a crop of grass high in lead content. The grass could either be disposed or, if high enough in lead content, be sent to a smelter to recover the lead. Lead values as high as one percent by weight have been observed in grass as rich as in some commercial ores.

While metals are a risk driver, carcinogenic PAHs are the main risk driver. Besides CPAHs in roadwaste, roadsides in high-traffic roadway corridors may increase in CPAHs over time due to the incomplete combustion of petroleum fuels. Mulberry bushes have been shown to break down CPAHs in the rhyzosphere (the biologically active root zone). Using plantings could be valuable both in treating roadwaste contaminants and as cover crops for roadwaste reuse sites. Using the right plants can also provide a defense against the build-up of CPAHs expected along high traffic corridors. Since roadway maintenance practices require planting cover crops, consider selecting cover crops that will reduce contaminant levels and act as a defense against future contamination.

Soil Washing
Soil washing removes contaminants from problem soils by rinsing; however, heavy hydrocarbons are adsorbed onto the surface of particles and will not readily dissolve into water. The goal is removal of the more highly contaminated fine particles from roadwaste, leaving the larger particle size fractions ready for reuse. (The wastewater would then need to be treated and the contaminated fines managed conservatively.) It may be possible to find a way to release all the contaminants into the rinsate, leaving clean dirt and contaminated water, which could be treated separately.

Removing fines creates a secondary problem: effectively managing the wastewater. Besides evaporating the water in large ponds, there is no simple technology to de-water the lighter suspended fines.

An aggressive surfactant may be able to break the bonds holding the contaminants to the roadwaste. However, these soaps or chemical agents themselves can be a problem. Lowering the pH of a roadwaste slurry could dissolve heavy metals into solution. Then the water could be chemically treated, flocculating out the metals. This would be an intensive process, however, and would not address the main risk driver (CPAHs). Thus acid release approaches do not appear workable. Removal of the liquid without entraining fines is difficult.

Field trials on this treatment method have not been conducted, so it is not known how applicable soil washing is for roadwaste management. Surfactant may be available that would release heavy petroleum compounds and metals into solution for removal and recovery and would not pose environmental harm in the resultant product. In theory soil washing could remove heavy metals and petroleum contaminants, leaving benign materials; however, there are too many variables to provide an overall evaluation of risk. The wastewater must be managed carefully, requiring a sealed system. Products resulting from any new treatment process would require laboratory tests to evaluate risk.

Disposal Options

Disposal in a permitted, municipal solid waste landfill is expected to virtually eliminate any future liability, a significant advantage. Most landfills cannot accept liquids or wetter sediments though. Costs for disposal at permitted landfills can vary widely.

Siting and obtaining a permit for a publicly-owned roadwaste landfill may be a better option if volumes are high and a good site is available. It is recommended that a roadwaste landfill be lined to prevent ready release of contaminants. Sharing costs and sharing liabilities with other government agencies is reasonable.

It is important to reconsider past practices. Disposal of roadwaste that does not classify as clean fill should not go to unlined construction and demolition (C&D) landfill. Many former sand or gravel pits operating as clean fill landfills are accepting roadwaste. The porous matrix of sand and gravel and the ready access to the water table at these sites makes them inappropriate for use as roadwaste landfills. Some sites have virtually injected contaminants into the subsurface by placing roadwaste in direct contact with the groundwater table. Problems in other states with old, unlined fills, are leading them to clear their roadwaste out of burial sites. Washington DOT is conducting site assessments and characterizing stockpiles of roadwaste, examining the potential for harm.

Permitted solid waste landfills are a sound, traditional waste management alternative and serve as a good option for small amounts of more highly contaminated wastes. Landfills are permitted to accept wastes within specified toxicity parameters and manage those risks well. Trash must be landfilled or recycled. Landfilling avoids costly laboratory tests and oversight. Tipping fees can be costly in some areas, though. Operating at high volumes, costs of disposal at permitted roadwaste landfills are likely to be much lower than regular solid waste tipping fees. Testing normal roadwaste prior to placement in a permitted solid waste landfill is not necessary and should be avoided if the District has a screening process in place to identify suspect loads.

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Table of Contents
 
Chapter 10
Roadside Management and Maintenance: Beyond Vegetation
10.1 Environmental Enhancement Practices and Partnership Efforts
10.2 Protection of Historic and Other Cultural Resources
10.3 Maintenance in Wetlands
10.4 Maintenance Near Waterbodies
10.5 Maintenance of Structures for Wildlife
10.6 Maintenance of Stormwater Facilities
10.7 Maintenance of Roadside Public Facilities
10.8 Management of Portable Sanitary/Septic Waste Systems
10.9 Maintenance of Shoulders and Roadway Appurtenances
10.10 Sweeping and Vacuuming of Roads, Decks, Water Quality Facilities, and Bridge Scuppers
10.11 Maintenance Stewardship Practices for Slopes, Drainage Ditches, Swales, and Diversions
10.12 Erosion and Sediment Control in Maintenance
10.13 Recycling in Roadside Maintenance Operations
10.14 Preserving Air Quality in Maintenance and Operations
10.15 Painting Operation Stormwater BMPs
10.16 Road Waste Management
10.17 Stockpiling, Spoil Disposal or Placement of Inert Fill
10.18 Maintenance of Soils
10.19 Emergency Actions
10.20 Field Review of Roadside Maintenance Operations
   
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