Roads and Water Quality


by Bill Goosman, Colorado Department of Transportation

Roads can have substantial impacts on water quality and the functioning of natural waters. Controlling roadway-related pollution during the day-to-day operations of the Colorado Department of Transportation requires understanding a complex array of federal and state laws and orchestrating those directives through project planning, construction and ongoing maintenance.

Contaminants in Runoff Pollution
As rainwater and melting snow flow off roads, bridges, and parking lots, these surfaces are partially cleansed of dirt and dust, rubber worn from tires, metals ground from brake pads, and antifreeze, oil and other fluids dripped from engines. Depending on where the rain falls or the snow melts, this runoff pollution may be carried directly to streams and lakes.

Many road-related pollutants are associated with dirt and dust, i.e., sediment. Sediment arises from natural erosion or wind-blown dust, but human-caused surface disturbance contributes sediment in amounts several times that produced by natural processes. Another source of sediment is traction sand used during winter road maintenance. On Vail Pass, for instance, 18,000 tons of traction sand is applied over the course of a typical winter. Unless removed, this sand makes its way, sooner or later, to adjacent water bodies.

Sediment as pollution poses two problems. First, sediment alters both substrate and water column conditions. Larger particles settle out of the water in lakes and streams. In excess amounts, this buries aquatic plants and fish spawning areas, lowers substrate oxygen levels, traps emerging fry, and fills the pools and pockets between rocks and boulders on which young fish depend for protection. These conditions can particularly affect trout. The finest sediments remain suspended in the water column creating turbidity. This may prevent sunlight from reaching aquatic plants, cause water temperatures to increase, and suffocate fish and aquatic insects by adhering to gills. Second, other pollutants such as herbicides, fertilizers, and heavy metals (e.g., copper, lead, and zinc) adhere to sediment and are transported by wind and water. These pollutants degrade water quality and can harm aquatic life by interfering with photosynthesis, respiration, growth, and reproduction.

In terms of roadway maintenance, road “salts” – as solids or liquids – can be major pollutants. Snowmelt runoff containing dissolved salts can produce high sodium and chloride concentrations in ponds and lakes, upsetting natural water chemistry and causing problems for fish, amphibians, and the aquatic insects upon which they depend. These chemicals may also affect vegetation immediately adjacent to roadways. If fertilizers and herbicides are applied excessively or improperly, they can enter adjacent waterways and pose acute or chronic problems for aquatic life.

One last aspect of runoff affected by roads is water quantity. Impervious surfaces increase the amount of water that reaches water bodies and accelerates the speed at which it arrives. This is particularly true for – and detrimental to – streams. Although mountain and foothills streams have evolved to accommodate wide variations in seasonal flows, increases in the amount and timing of inflows may destabilize the balances achieved through natural processes. Stream systems may react to increased flows and flow velocities by straightening, deepening, or widening their channels. These processes may alter the character of a stream by, for instance, changing it from a single, deep, meandering channel to a braided stream with many small, shallow channels. This process may remove streamside vegetation and aquatic organisms, alter or degrade stream habitats for indigenous organisms, block migration routes, and remove important breeding areas.

Water quantity links back to water quality through the a phenomenon of “first flush.” During an extended dry spell, materials accumulate on and around roads, such as oil, tire wear, and accumulated traction sand. The first extensive rainfall or spring snowmelt tends to scrub the road of these accumulated materials, creating runoff with initially high levels of pollution.

These kinds of pollution are often hard to control because they arise in small amounts across the landscape in a manner that is difficult to pinpoint. As they coalesce in drainages, though, they may have significant cumulative impacts. There are, however, a variety of federal and state laws and regulations designed to address those impacts.

A word of caution as this discussion proceeds – water quality laws and regulations tend to be mind-numbingly complex. This article doesn’t even approach the status of primer on the subject and the discussion is by no means comprehensive of all water quality laws and regulations. However, the generalities presented remain true while still sparing the reader the gory details.

Water Quality Laws and Regulations
The most influential federal law affecting water quality is the Clean Water Act (CWA). The goal of the act is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.” CWA established the permitting structure for regulating discharges of pollutants into the waters of the United States, gave the U.S. Environmental Protection Agency (EPA) oversight authority, and created a process for setting and enforcing water quality standards for various contaminants in surface waters.

Water quality aspects of most CDOT projects are regulated under the National Pollutant Discharge Elimination System (NPDES) program in CWA Section 402. Under an agreement with the EPA, the NPDES program in Colorado is delegated to the Water Quality Control Division (WQCD) of the Colorado Department of Public Health and Environment. Controls within NPDES govern “municipal separate storm sewer systems,” known in the lexicon as MS4. In the main, this program oversees stormwater discharges into the nation’s waters from systems owned by states, cities, and other public entities. Because CDOT often connects to such stormwater systems, its activities are also subject to MS4 requirements. An MS4 permit is intended to limit the amount of stormwater discharges into storm sewers and to reduce the associated pollution in such flows. Beginning July 1, 2002, Phase II of the program applies to construction sites disturbing one or more acres of soil in areas with populations of 50,000 or more. There are some 45 such areas in Colorado. Prior to last July, such activities applied to a half-dozen areas in the state.

CWA Sections 404 and 401 also contain provisions to safeguard water quality. Section 404 governs dredge and fill operations in “waters of the United States” (including wetlands) by limiting or prohibiting the amount, location, and types of materials used in such activities. Section 401 requires that WQCD review of stormwater controls and water quality protection best management practices for activities permitted under Section 404.

Additional complexities arise when CDOT activities occur near “sensitive waters.” Most easily put, these regulations try to protect exceptionally high quality streams and they try to prevent the further degradation of streams with low water quality. The highest level of water quality protection applies to waters designated by WQCD as “outstanding.” These waters must be maintained and protected such that no discharges are allowed that would degrade existing water quality. At the other end of the spectrum are streams with impaired water quality, designated under CWA section 303(d). Generally speaking, standards are developed for various pollutants that affect water quality in each “303(d) stream” or stream segment. These standards are known as “total maximum daily load” (TMDL) and they are developed with an eye toward those aspects of the stream that limit its use as, for example, drinking water or for recreation. TMDLs limit the types and amounts of various pollutants that may be discharged.

Water Quality at CDOT
The myriad requirements in these federal and state water quality laws and regulations cut across all major activities at CDOT:

  • active construction sites, including land clearing and grading, excavation into hillsides (cut slopes), and areas where earth is deposited (fill slopes);
  • protection of sensitive habitats outside of designated work areas, such as wetlands, stream banks, and riparian areas;
  • ongoing maintenance operations, such winter sanding and summer application of herbicides and fertilizer; and
  • proper storage and handling of hazardous material or wastes, including careful containment of concrete truck washouts and concrete saw water.

CDOT has a correspondingly large array of policies and procedures to address the potential water quality impacts of these activities. In the main, dealing with road-related pollution starts with preventing soil and other materials from moving (i.e., erosion control) and, thereafter, follows with containment and treatment.

Controlling Road-Related Pollution
CDOT’s MS4 permit requires the department to operate various programs to protect surface waters from pollution associated with stormwater. Aspects of these programs include:

  • practices intended to control runoff during and after construction, and to properly maintain pollution control structures (e.g., cleaning sediment traps);
  • practices to control runoff from permanent road maintenance facilities;
  • street maintenance efforts to reduce the discharge of pollutants (e.g., road repair, snow removal and sanding activities, herbicides and fertilizers, maintenance of rights of way);
  • programs to detect and prevent the illicit discharge and improper disposal of materials; and
  • public education and outreach efforts on stormwater quality. The MS4 program also requires on-going training of maintenance employees.

One specific requirement of CDOT’s NPDES stormwater permit and a critical component for pollution control is the “stormwater management plan” (SWMP; pronounced “swamp”). All projects involving an earth disturbance at CDOT require a SWMP that identifies best management practices (BMPs) to be established and maintained on construction sites. These BMPs are designed to minimize the movement of sediment and other pollutants into surface waters. (More details later.)

The NPDES permit also regulates “dewatering” activities – situations in which water is pumped out of depressions or excavations such as those for bridge piers. Permit conditions restrict the amount of the sediment and other pollution in such water from reaching surface waters. Water must be collected and treated in specific ways to meet permit effluent requirements for water volume, total suspended solids, pH, and oil and grease. Periodic monitoring is required and the results must be reported to the state health department. Water Quality and Project Planning
In the early stages of the highway planning process, CDOT environmental personnel review the project in relation to water quality aspects. The size and complexity of the project and specific site conditions influence the degree of detail and coordination required. Considerations include: 1) the classification and designated beneficial uses of surface waters in the project corridor; 2) the presence of domestic and agricultural water sources; 3) existing stream fish habitat, including critical spawning and emergence times, and the existence of threatened or endangered species; 4) the presence of wetlands and important riparian habitats; 5) current and potential sources of pollutants; 6) existing and future stream structures required by the project; and 7) cumulative effects from construction in terms of sediment, nutrients, metals, etc. In sensitive watersheds, the planning process may also include discussions with the WQCD watershed coordinator, the Colorado Division of Wildlife, representatives of local watershed groups or groups such as Trout Unlimited, the Sierra Club, and adjacent landowners, both private and public.

With the preceding site conditions in mind, construction and hydraulic engineers and the SWMP designer coordinate on the specific aspects of the project that may impact water quality and quantity. The process starts with the overall drainage requirements of the project, including: 1) calculations of runoff, both pre- and post-construction; 2) the number and types of temporary and permanent stream crossings; and 3) the number, position, and size of culverts and roadside ditches. Discussions include the need for and placement of riprap or biological means to stabilize banks, methods to slow runoff, and the types and locations of temporary and permanent water quality features. Work proposed in and around dry drainages may also be similarly reviewed. Considerations are also given to existing soil types and vegetative cover and the anticipated extent and type of ground disturbance.

Stormwater Management Plans
The main objective of any SWMP is to prevent sediment from reaching adjacent waterways by using BMPs that:

  • specify project “phasing”— scheduling construction activities to limit the amount of soil disturbance;
  • revegetate or otherwise stabilize open ground and slopes, including seeding rates, methods, and species, mulching, and use of soil retention blanket;
  • detail the location of silt fence, erosion control logs, hay bales, and temporary fencing to cordon off sensitive areas;
  • use clean water diversion techniques to route water around exposed areas;
  • specify methods of material handling, on-site storage, spill prevention, and methods of waste disposal;
  • provide areas for washing vehicles before they leave the construction site, including designated areas for washouts for concrete trucks; and provide for grass swales, permanent sediment basins, and stormwater detention ponds to treat water that leaves the site.

An increasing amount of regulatory attention is being trained on the kinds of non-point source pollution discussed in this article. For further information on CDOT’s water quality programs and practices, please contact Gordon McEvoy, CDOT Water Quality Program Manager,             (303) 757-9343      .