prompting CWA amendments in 1987 that mandated compliance with regulations governing sediment, erosion, and stormwater runoff and discharges at and from construction sites (Faucette et al., 2009).

National Pollutant Discharge Elimination System

The National Pollutant Discharge Elimination System (NPDES) permit program was established to limit water pollution by regulating the point sources that discharge sediment-laden runoff into receiving waters (Campbell, 2022). Three goals of the NPDES permitting program for stormwater management associated with highway construction activities are to reduce erosion, minimize sedimentation, and minimize the discharge of pollutants (NMDOT, 2023). Enacted as part of the CWA, the NPDES dictates that discharging sediment into receiving waters is prohibited without a valid NPDES permit or waiver authorizing possible discharges. In the context of construction activities, the NPDES program regulates the quantity of sediment and other pollutants that can be discharged. Currently, 47 states and one U.S. territory are authorized to administer their own state NPDES programs, with oversight provided by the EPA. A state regulatory agency for environmental quality typically administers the NPDES for state DOTs to follow for highway construction.

Construction General Permit

The construction general permit (CGP), as part of the NPDES permit program, is typically administered by a state regulatory agency (except in Massachusetts, New Hampshire, New Mexico, and the District of Columbia, where the EPA issues the CGP). The CGP authorizes the discharge of allowable amounts of stormwater and non-stormwater associated with regulated construction activities into receiving waters. The CGP describes the construction activities covered under the permit, specifies activities eligible for waivers, and identifies activities requiring an authorized individual permit (EPA, 2022). Typically, every construction project that disturbs more than 1 acre of land requires a project-specific CGP.

The CGP provides regulations for properly discharging stormwater linked with construction site activities, thus ensuring compliance with permit requirements. Typically, these activities include the following:

• Discharging stormwater runoff from earthwork construction operations, concrete batch plants, asphalt batch plants, equipment staging areas, materials storage yards, and materials borrow areas
• Managing excavated materials disposal areas at, adjacent to, or near the permitted construction site that directly supports construction activities

New Mexico DOT adheres to EPA regulations, since it does not have a regulatory agency of its own to administer the CGP. It follows an NPDES CGP permitting process for highway construction (see Figure 1). The first step entails determining whether a project disturbs more than 1 acre of land. If so, the DOT requires a CGP for construction work. Coverage under the CGP is required by obtaining an individual NPDES CGP. The next step is determining whether the project encroaches on any threatened or endangered species or historic properties at the site. Upon this determination, New Mexico DOT prepares a project site-specific stormwater pollution prevention plan (SWPPP). The SWPPP is completed before submitting the notice of intent (NOI), which must be completed before the start of construction. After the SWPPP is prepared, the DOT and the contractor, at a minimum, must prepare and file an NOI with the EPA.

New Mexico DOT can delegate the responsibilities of individual parties in the SWPPP. Any actions or responsibilities delegated to the contractor or other third party are specifically addressed in the SWPPP. After the SWPPP has been prepared and an NOI has been submitted and accepted by the EPA, project construction may begin within 14 calendar days after acknowledgment of receipt of the completed NOIs.

During construction, the contractor installs and maintains control measures, which are inspected by New Mexico DOT personnel as outlined in the SWPPP. If site conditions, project design changes, or construction sequencing warrant revisions in the type, design, and scheduling of stormwater pollution control measures, the SWPPP must be revised, signed, and dated. The SWPPP is considered a living document and is updated as site conditions change during construction. Inspections of the site are conducted during construction. As necessary, changes to control measures must be made for any deficiencies found to ensure the SWPPP is followed and the project is in compliance with permit requirements.

Stormwater Pollution Prevention Plans

SWPPPs are comprehensive documents that manage and mitigate the potential impact of stormwater runoff from construction sites on water quality (Caltrans, 2016). All highway construction project sites are unique; therefore, the SWPPP is specifically prepared for each site. SWPPPs are required under the NPDES permitting program for construction activities when 1 or more acres of land are disturbed. SWPPPs are short-term solutions for only the construction phase of a project.

SWPPPs typically include the following components:

• Site map and assessment: Detailed information about the construction site, including the location, size, topography, soil types, potential problem areas, and proximity to receiving waters.
• Identification of potential pollutants: Assessment of potential pollutants generated by construction activities, such as sediment, chemicals, and debris.
• Stormwater management practices: Strategies and BMPs to prevent or minimize stormwater pollution, including erosion and sediment control (E&SC) measures, runoff management techniques, and pollution prevention practices.
• Monitoring and reporting procedures: Protocols for monitoring stormwater discharges, including sampling methods, frequency of monitoring, and reporting requirements to regulatory agencies.
• Employee training and education: Training programs for on-site personnel to ensure they understand their roles and responsibilities when implementing the SWPPP and preventing pollution.
• Emergency response plans: Procedures for responding to and managing emergencies such as spills, leaks, or extreme weather events that could impact water quality.
• Inspection and maintenance schedules: Regular inspection schedules and maintenance procedures for BMPs and E&SC measures to ensure they remain effective throughout the construction project.

According to Nevada DOT (NDOT, 2013), the construction site map is one of the most important elements of the SWPPP. The map includes site topography and drainage patterns along with the locations of the following components for stormwater management and E&SC:

• Erosion and sediment control BMPs used at the site
• Stabilized construction entrances and exits to prevent tracking sediment onto pavements

• Vehicle equipment maintenance, fueling, and cleaning areas
• Storage areas for construction materials, supplies, and waste
• Designated concrete washout areas
• Areas where stormwater runoff discharges outside the limits of the site into either the storm drain system or nearby waters
• Areas to be revegetated or stabilized with other methods

SWPPPs are crucial to ensuring compliance with NPDES permit requirements and protecting water quality during construction activities. SWPPPs are living documents that may be updated as the project progresses or as conditions change on the construction site.

Municipal Separate Storm Sewer System Permits

Municipal separate storm sewer systems (MS4s) are networks of conveyances, such as storm sewers, gutters, drains, and related infrastructure, that are owned by states, towns, villages, counties, and other public entities. These systems collect and discharge stormwater runoff within municipalities across a state into receiving waters (CDPHE, 2024). However, polluted stormwater runoff can be transported through these systems, discharging the untreated stormwater into receiving waters and causing issues with water quality. Therefore, to prevent pollutants and sediment from entering MS4s, transportation agencies are typically required to obtain NPDES permits and to develop a stormwater management program (SWMP) (EPA, 2024c).

The MS4 SWMP is a long-term strategy to implement a permanent solution for managing stormwater and water quality beyond construction. The SWMP outlines the stormwater management procedures to use in accordance with MS4 permit requirements in order to reduce the potential discharge of sediment and pollutants into receiving waters (National Association of Clean Water Agencies, 2018). The SWMP is not the same as the SWPPP: the SWMP is a long-term solution for managing stormwater discharges in general, while the SWPPP is a project site-specific plan for managing stormwater discharges and water quality during the construction phase of a project.

The MS4 permitting program includes six minimum control measures (MCMs). Each has a set of associated BMPs to help minimize discharges of pollutants and sediment in stormwater runoff. The following six MCMs guide the planning and implementation of the MS4 permitting program (Bustios and Stanhouse, 2024):

1. Public education and outreach on stormwater impacts
2. Public involvement and participation
3. Illicit discharge detection and elimination
4. Construction site stormwater runoff control
5. Post-construction stormwater management (PCSM)
6. Pollution prevention and good housekeeping

MS4 permits protect municipal stormwater systems from pollutants and sediment discharges. Unlike the CGP, the MS4 permit is not required specifically for construction activities outside of site stormwater management. Typically, state DOTs obtain coverage for construction activities through the CGP and develop a project site-specific SWPPP. In contrast, DOTs utilize the MS4 permit for their SWMP, which addresses pollutant and sediment discharges from any DOT property (including the right-of-way) and includes PCSM. In some cases, state DOTs are required to get MS4 and CGP permit coverage for a construction project, which means that DOTs must meet the MS4 and CGP permit requirements during construction. Colorado DOT (Colorado DOT, 2023) and Texas DOT (Texas DOT, 2018) require an MS4 permit and a CGP permit for construction projects that disturb 1 or more acres of land.

Erosion and Sediment Discharges

When total suspended solids or sediments occur in excessive quantities, the resulting degraded water quality can harm plants and animals and interfere with photosynthesis, respiration, growth, and reproduction. Sediment constitutes the primary environmental pollutant originating from construction sites, comprising approximately 10% of all sediment runoff into water bodies and aquatic environments (Belayutham et al., 2016).

Sedimentation emerges during land disruptions when conducting highway construction activities, facilitated by erosion and conveyed by rainfall and surface runoff. If suspended in water, sediments may become a major water pollutant. Sediment-loading causes the following impacts (FDOT, 2013):

• Construction areas with 10–20 times more soil particles lost compared to lands with vegetation
• Reservoirs, harbors, and canals clogged with silt
• Loss of recreational areas and wildlife habitats
• Reduction of the beneficial uses of water for humans
• Harm to plant, animal, and aquatic life

Sedimentation and pollution originating from highway construction activities have various impacts. Sediment contributes to the deterioration of water quality and disrupts the habitats of aquatic plants and species. Moreover, sediment deposition alters the hydrodynamic patterns and diminishes the visual appeal of fluvial landscapes (Reice and Carmin, 2000). Consequently, numerous federal and state legislative measures, regulations, and policies have been instituted to govern construction site pollution and safeguard water quality. Beginning in 2003, the EPA initiated the enforcement of BMPs and control measures at construction sites exceeding 1 acre to mitigate stormwater contamination from sediment and erosion (Faucette et al., 2009).

Texas DOT indicated that the effectiveness of BMPs in mitigating sediment-laden runoff and erosion hinges on proper installation and continuous maintenance (Barrett and Malina, 1995). Having adequate BMPs in place does not guarantee minimizing erosion and sediment-laden runoff unless implemented and upheld as intended. Texas DOT suggested that a viable approach to addressing this challenge involves implementing temporary and permanent water quality control measures at construction project sites if they are found to be discharging sediment into receiving waters.

Best Management Practices and Erosion and Sediment Control Measures

BMPs, also referred to as E&SC measures or control measures, are methods used to prevent or control construction stormwater runoff and discharge of sediment and pollutants into nearby receiving waters (EPA, 2024a). Table 1 lists BMPs and E&SC measures used for highway construction projects, collected from the EPA’s National Menu of BMPs for stormwater – construction (EPA, 2024a).

Hawaii DOT’s Construction Best Management Practices Field Manual outlines the practices and controls used for highway construction in Hawaii for the islands of Oahu and Maui. Hawaii DOT requires the use of construction stormwater controls that must be maintained due to the fragile nature of the Hawaiian ecosystem. The manual categorizes the BMPs across three areas: site management, erosion control, and sediment control. Table 2 outlines the BMPs across these categories at the Hawaii DOT (HDOT, 2021).

The South Carolina Department of Health and Environmental Control created a BMP handbook to help the South Carolina DOT evaluate numerous BMPs by detailing usage, installation,

Table 1. BMPs and E&SC measures for highway construction projects.

inspection, maintenance, and design specifications. The handbook also provides design aids to determine the efficiencies of various sediment control measures (SCDHEC, 2005). Table 3 outlines the erosion prevention, sediment control, runoff control, and conveyance measures used by the South Carolina DOT for construction activities.

California DOT (Caltrans) has a Construction Site BMP Manual (Caltrans, 2024) that guides project teams when selecting and implementing BMPs into highway construction projects. The manual provides a construction site BMP applicability flowchart (see Figure 2) that indicates whether the project triggers an SWPPP or a water pollution control plan and where to find information about BMPs for each of the steps in the flowchart. The manual also includes information about different permit requirements, SWPPP BMP requirements, minimum construction BMPs, and six categories of construction site BMPs.

The six categories of construction site BMPs at Caltrans are as follows (Caltrans, 2024):

1. Temporary soil stabilization
2. Temporary sediment control

Table 2. List of BMPs and E&SC measures used by Hawaii DOT for highway construction.

3. Wind erosion control
4. Tracking control
5. Non-stormwater management
6. Waste management and materials pollution control

Inspections

Adhering to permit requirements and following the SWPPP developed for a construction project requires regular inspections of BMPs and control measures at the highway construction site. Oklahoma DOT developed a Clean Water Inspection Form (see Appendix D) completed

Table 3. BMPs and control measures used by South Carolina DOT.

in the field and filed electronically. The fillable, PDF form requests information about the specific project, minimizations of erosion and sediment discharges, BMP maintenance, solid and hazardous waste, and documentation and SWPPP stabilization. The form also includes a section for signatures to hold project personnel accountable for adhering to permit requirements.

Nevada DOT provides guidelines for dividing construction sites into natural drainage areas and controlling erosion and sediment-laden runoff using BMPs. All construction BMPs are inspected weekly and within 24 hours of a half-inch rainfall event. All inspections are conducted by Nevada DOT qualified personnel or consultants who have attended stormwater management training and understand the general permit requirements from the Nevada Department of Environmental Protection. The inspector documents the inspection and observations and includes them with the SWPPP. The contractor is instructed to install and maintain all BMPs and control measures in good working order until project completion (NDOT, 2013).

The Utah Department of Environmental Quality (DEQ) is the regulatory agency that administers the general permit for stormwater discharges from construction activities for Utah DOT. The construction general stormwater permit includes requirements for qualified inspectors to perform inspections of BMPs and control measures for construction stormwater management. The DEQ defines a qualified person as knowledgeable in the principles and practices of E&SC measures and pollution prevention and possessing the skills to assess conditions at the construction site that could impact stormwater quality.

According to the Utah DEQ, qualified persons can be any of the following:

• Utah Registered Storm Water Inspector—State qualification
• Utah Department of Transportation Environmental Control Supervisor—State qualification
• Certified Professional in Erosion and Sediment Control—National qualification
• Certified Professional in Storm Water Quality—National qualification
• Certified Erosion, Sediment, and Storm Water Inspector—National qualification
• Certified Inspector of Sediment and Erosion Control—National qualification
• National Institute for Certification in Engineering Technologies, Erosion and Sediment Control, Level 3—National qualification

Utah DOT is required, at a minimum, to conduct site inspections of the BMPs and control measures installed and maintained by the contractor at least once every 7 calendar days or once every 14 calendar days and within 24 hours of the occurrence of a storm event of a half-inch or more, or the occurrence of runoff from snowmelt sufficient to cause a discharge. Utah DOT is required to maintain rain gauges properly at the construction site (Utah DEQ, 2020).