Construction sites

Construction sites are a significant source of stormwater pollution if not properly managed. As land is cleared, graded, and reshaped, exposed soil can easily be carried by rain into nearby waterways, contributing to sedimentation, flooding, and pollution. To address this, Iowa follows regulations under the federal National Pollutant Discharge Elimination System (NPDES), administered by the Iowa Department of Natural Resources (IDNR).

ISWEP offers training and certification through its Iowa Certified Construction Site Pollution Prevention Inspector and Installer program. This training helps ensure that contractors and inspectors understand erosion and sediment control BMPs, permit requirements, and how to keep sites in compliance.

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NPDES and General Permit No. 2

In Iowa, stormwater discharges from construction sites are regulated under General Permit No. 2, part of the state’s delegated NPDES program. This permit covers most construction activity that disturbs one acre or more of land (or less if part of a larger common plan of development).

Permit coverage requires filing a Notice of Intent (NOI) with the IDNR and preparing a Stormwater Pollution Prevention Plan (SWPPP). The SWPPP outlines all erosion and sediment control practices, site management strategies, and inspection protocols. Routine site inspections are required to ensure the BMPs remain effective and to document any changes to site conditions.

A SWPPP is a living document that identifies potential pollutant sources and describes practices used to prevent stormwater contamination during construction. Key components include:

  • Description of the project and site conditions
  • Erosion, sediment, and velocity control practices
  • Sequence and timing of BMP installation and removal
  • Good housekeeping practices
  • Management of non-stormwater discharges
  • Post-construction stormwater management features
  • Waste disposal procedures
  • Site maps and inspection schedules

The SWPPP must be updated to reflect changes in site conditions or BMPs and signed by the site owner and all contractors involved in land-disturbing activities. These certification statements must be kept on file for at least three years after project completion. Inspections are conducted routinely to ensure compliance.

Downloadable SWPPP templates are available from ISWEP or via EPA. Templates for large site inspections and residential/commercial sites are also available.

General Permit No. 2 requires that construction projects minimize soil compaction and preserve topsoil on site unless infeasible. Topsoil supports plant growth, reduces runoff, and improves infiltration—making it a valuable resource for both stormwater management and post-construction stabilization.

A Topsoil Management Plan should be included in or referenced by the project’s SWPPP. Key elements include:

  • Assessment: Evaluate topsoil depth and quality before construction using visual sampling at multiple representative locations across the site.
  • Preservation: Identify areas to remain undisturbed and avoid stripping topsoil from them. Strip only where excavation or grading is planned.
  • Stockpiling: Store topsoil in stable, well-drained areas away from waterbodies. Stabilize piles within 14 days using seed and mulch, and install sediment controls around the base.
  • Replacement: Redistribute topsoil to at least the pre-construction average depth in all revegetated areas. Loosen compacted subsoil before placement and avoid over-compaction.
  • Verification: Confirm replacement depth through field checks at a minimum of five locations per site or one per acre, whichever is greater.
  • Soil Quality Restoration (optional): Improve soil function by incorporating compost and tilling compacted areas to enhance infiltration and reduce runoff.

Topsoil preservation improves compliance, supports healthy vegetation, and can reduce the size of downstream stormwater controls. Always consult local ordinances for any additional requirements.

Erosion control focuses on preventing soil from detaching in the first place—making it the first and most important line of defense against stormwater pollution. Effective erosion control limits the amount of sediment that needs to be captured later with more costly measures.

Common erosion control practices include:

  • Mulching
  • Temporary or permanent seeding
  • Sodding
  • Rolled Erosion Control Products (RECPs)
  • Vegetative filter strips
  • Surface roughening
  • Preserving existing vegetation

The selection of BMPs should be based on slope, soil type, flow concentration, and construction schedule. Weekly inspections are required to ensure all controls are in place and functioning properly.

Sediment controls are designed to capture and settle soil particles that have already become mobilized, while velocity controls help slow down stormwater to reduce erosion potential.

These practices are often considered the last line of defense before runoff reaches a storm drain or waterbody. Common BMPs include:

  • Inlet protection
  • Silt fences
  • Check dams
  • Filter socks and wattles
  • Sediment basins and traps
  • Riprap and rock chutes
  • Level spreaders
  • Flocculants (in some cases)

Effectiveness depends on proper sizing, placement, and regular maintenance – especially after rain events.

General Permit No. 2 also requires good housekeeping to manage materials, waste, and other site activities that could pollute stormwater. These practices reduce the risk of illicit discharges from fuel, chemicals, debris, concrete, and other construction byproducts.

Examples of good housekeeping BMPs include:

  • Stabilized staging areas
  • Proper storage and containment of chemicals
  • Onsite SWPPP and inspection logs
  • Designated debris and material stockpiles
  • Spill kits and spill response procedures
  • Vehicle and equipment washing in designated areas
  • Concrete washout bins
  • Proper handling of wet saw cutting and wastewater

Two of the most common violations are poorly managed concrete washouts (which can release high-pH water) and sediment trackout onto roadways due to missing or undersized construction entrances. Both are enforceable infractions under the permit.

The SUDAS Manual (Divisions 9 and 11) offers detailed specifications for these practices.

If your construction project involves work in or near a stream, wetland, lake, or floodplain, additional permits may be required. A Section 401/404 permit—jointly administered by the IDNR and U.S. Army Corps of Engineers—is needed for activities such as:

  • Streambank or shoreline modification
  • Excavation or dredging in water bodies
  • Dam construction or modification
  • Placement of fill or riprap
  • Floodplain development
  • Work on sovereign lands and waters

To begin the application process, submit the Joint Application Form: Protecting Iowa Waters to both agencies.