Dust Control – Soil Stabilization – Erosion Control

An introduction to the EPA’s effluent limitations guidelines and source performance standards.

Check dams at a construction site are configured for use of chemical flocculant treatment.
Jesse Pritts, EPA

Although streams and rivers naturally carry sediment loads, discharges associated with construction activity can elevate these loads to levels above those in undisturbed watersheds. Discharges from land disturbance can increase the proportion of silt, clay, and colloidal particles in receiving streams because these fine-grained particles may not be managed effectively by conventional erosion and sediment controls that rely on simple settling.

In response to these issues, the U.S. Environmental Protection Agency (EPA) promulgated effluent limitations guidelines (ELGs) and new source performance standards for discharges from construction and development (C&D) sites on Dec. 1, 2009. ELGs are technology-based standards for control of wastewater and stormwater discharges from various categories of industry and are not risk-based, so different standards are not set for different receiving waterbodies. ELGs can be numeric standards (i.e., discharge limitations) and/or best management practices (BMPs) and process changes. Many of the C&D ELG requirements are already included in EPA and state construction general permits (CGP) and new requirements will be phased in over the next few years for sites to sample stormwater discharges and comply with a numeric effluent limitation of 280 nephelometric turbidity units (NTU). A sampling requirement will be triggered beginning Aug. 1, 2011, for sites disturbing 20 or more acres at once and beginning Feb. 2, 2014, for sites disturbing 10 acres or more at once.

ELG implementation
ELGs are incorporated into National Pollutant Discharge Elimination System (NPDES) permits and serve as the national technology “floor” for all dischargers for that category. Where the technology-based limitations are not sufficient to meet risk-based requirements, such as water quality standards, water quality-based effluent limitations apply. EPA and the states regulate stormwater runoff from construction sites greater than 1 acre primarily through construction general permits (CGPs). The C&D ELG requirements must be incorporated into general or individual permits whenever permits are re-issued during the next five years. (Note that EPA intends to issue a new CGP in June 2011.)

Many states have regulations addressing construction site stormwater runoff and most existing permits require that erosion and sediment controls be installed and maintained, but do not contain specific performance requirements. Design manuals contain detailed specifications. Some states (including California, Washington, Oregon, Vermont, and Georgia) have adopted numeric action levels/benchmarks for pollutants such as turbidity and require monitoring (see Table 1). California has an enforceable effluent limit of 500 NTUs that applies to some locations, referred to as “Risk Level 3” sites. Some watersheds (e.g., Lake Tahoe) and waterbodies require dischargers to meet numeric effluent limits for turbidity or other pollutants.

Prohibited discharges include wastewater from washout of concrete, unless managed by appropriate control. An improper construction entrance on a Southern California site allows soil to be tracked onto the street, over a curb into a gutter section.

Applicability to the industry
The C&D point source category covers firms classified by the Census Bureau into two North American Industry Classification System (NAICS) codes. Construction of Buildings (NAICS 236) includes residential, nonresidential, industrial, commercial, and institutional building construction.

Heavy and Civil Engineering Construction (NAICS 237) includes utility systems construction (water and sewer lines, oil and gas pipelines, power and communication lines); land subdivision; highway, street, and bridge construction; and other heavy and civil engineering construction. (Note that other types of entities not included in this list could also be regulated.) The rule may also apply to land-disturbing activities associated with certain mining activities as well as to activities at some landfills.

A single construction project may involve many firms from both subsectors. The number of firms involved and their financial and operational relationships may vary greatly from project to project. In typical construction projects, the firms identifying themselves as “operators” under a CGP are usually general building contractors or developers. While the projects often engage the services of specialty contractors, such as excavation companies, these specialty firms are typically subcontractors to the general building contractor and are not separately identified as operators in stormwater permits. Other classes of subcontractors, such as carpentry, painting, plumbing, and electrical services, typically do not apply for, nor receive, NPDES permits.

Details of the final rule
The non-numeric (narrative) effluent limitations represent a level of control that is technologically available and economically practicable, and represents the average of the best performance of construction sites in the C&D point source category. These requirements are well-established for construction activities in all parts of the country and are generally consistent with the requirements currently in place under the existing CGPs issued by EPA or the states. Many of these types of effluent limitations have been in place in NPDES permits for discharges associated with construction activity since at least the early 1990s. Even prior to the issuance of the 1990 NPDES Phase I stormwater regulations, existing state and local codes required implementation of erosion and sediment controls in numerous locations throughout the country. Many of these controls were first used beginning in the 1960s and 1970s and they represent traditional standard industry practices.

The EPA’s final rule requires that developers minimize the amount of soil exposed during construction activity and minimize the disturbance of steep slopes. Workers at this site in Northern Virginia are conducting mass grading, woody debris removal, and surface roughening of a slope as well as a previously graded and mulched section.

The C&D ELG takes this established approach to controlling stormwater discharges from construction sites and establishes minimum requirements for owners or operators of the site. In some cases the narrative requirements are more stringent than past requirements. For example, the soil stabilization requirements are more stringent than EPA’s 2008 CGP. Below are the details of the final rule:

Narrative requirements

* Control stormwater discharges to minimize erosion at outlets and downstream channel and streambank erosion.
* Minimize the amount of soil exposed during construction activity and minimize the disturbance of steep slopes.
* Provide and maintain buffers around surface waters and direct stormwater to vegetated areas, unless infeasible.
* Minimize soil compaction and, unless infeasible, preserve topsoil.

Soil stabilization and dewatering requirements

* Initiate stabilization of disturbed areas immediately whenever any clearing, grading, excavating, or other earth-disturbing activities have permanently ceased.
* Initiate stabilization immediately when earth-disturbing activities have temporarily ceased and will not resume for a period exceeding 14 calendar days.
* In arid, semiarid, and drought-stricken areas where vegetative stabilization is infeasible, alternative stabilization measures must be employed.
* Discharges from dewatering activities, including discharges from dewatering of trenches and excavations, are prohibited unless managed by appropriate controls.

Pollution prevention requirements

* Minimize the discharge of pollutants from equipment and vehicle washing, wheel wash water, and other wash waters.
* Wash waters must be treated in a sediment basin or alternative control that provides equivalent or better treatment prior to discharge.
* Minimize the exposure of building materials, building products, construction wastes, trash, landscape materials, fertilizers, pesticides, herbicides, detergents, sanitary waste, and other materials present on the site to precipitation and to stormwater.
* Minimize the discharge of pollutants from spills and leaks and implement chemical spill and leak prevention and response procedures.

A typical sediment trap is placed in the low spot of a small cleared and graded parcel in Northern Virginia. Storm drain inlet protection is used at a construction site in Northern Virginia to minimize the discharge of sediment and other pollutants.

Prohibited discharges include the following

* wastewater from washout of concrete, unless managed by an appropriate control;
* wastewater from washout and cleanout of stucco, paint, form release oils, curing compounds, and other construction materials;
* fuels, oils, or other pollutants used in vehicle and equipment operation and maintenance; and
* soaps or solvents used in vehicle and equipment washing.

Surface outlets

* When discharging from basins and impoundments, utilize outlet structures that withdraw water from the surface, unless infeasible.

Numeric effluent limitations and monitoring
EPA develops numeric effluent limitations based on a specific suite of technologies. For the C&D rule, the technology basis is polymer-aided settling. While permittees may use any technology to meet the 280 NTU limit, it is likely that construction sites in many areas of the country will need to utilize chemical flocculants, such as polyacrylamide (PAM), to meet the limitation. Since the monitoring requirements and turbidity limit only apply to sites that exceed the disturbed acreage thresholds, permittees may also utilize site-planning techniques, such as limiting the amount of land disturbed at any one time or phasing construction activities, as a way of complying with the rule. The following lists summarize need-to-know details of the limitations and monitoring requirements:

Technologies used for turbidity control include the following

* settling (sediment basins or channels with check dams);
* filtration, such as in-ground sand filters, geotextile bags, and practices located in channels (e.g., fiber check dams and geotextile products);
* polymer or flocculant addition, as necessary, particularly if fine silts and clays are present (common flocculants include PAM, chitosan, and alum);
* liquid polymer can be added in channels or inlets to sediment basins; and
* solid polymer can be land-applied or placed in channels (e.g., floc blocks, gel socks) or applied to check dams.

Turbidity limitation and monitoring

* 280 NTU Limitation is a Daily Maximum Value (i.e., not tied to background).
* Individual samples can be above 280 NTU as long as the average is below 280 NTU.
* The daily value at each discharge point is calculated by averaging all samples at that point.
* The limit is based on polymer-assisted settling, but permittees can use any technology.
* Zero discharge (such as infiltration, discharge to forested or vegetated buffers) can be used to avoid triggering monitoring requirements.
* Permittees can phase land-disturbing activities to stay below the disturbed acreage threshold.
* The limitation does not apply to interstate natural gas pipeline projects.
* The limitation does not apply on days when precipitation exceeds the local two-year, 24-hour storm event.

Sampling requirements

* Sampling is required at each discrete discharge point (basins, channels, pipes, et cetera).
* Sampling of sheetflow or diffuse runoff is not required as long as it does not become channelized prior to discharge.
* Sampling frequency is up to the permitting authority, but EPA recommends at least three grab samples per day at each discharge point (during normal working hours).
* For linear projects, the permitting authority can consider representative sampling instead of sampling at each discharge point.
* The permitting authority will specify data reporting requirements.
* EPA has not specified any analytical methods, but envisions that use of a properly calibrated field turbidity meter is adequate.

Samples show the difference between runoff from a site using traditional BMPs (right) and another site using advanced treatment (left).
Jesse Pritts, EPA

James H. Collins is the director of the environmental sciences group at Tetra Tech, Inc., Fairfax, Va. He can be reached via e-mail at james.collins@tetratech.com.