11 Construction Site Erosion and Sediment Control
Recommended Reading
The Environmental Protection Agency (EPA) is tasked with enforcing the Clean Water Act which, among other things, regulates the discharge of pollutants from point sources. One example is sediment from construction sites. More information on this topic is available from the EPA’s Stormwater Discharge from Construction Activities web page (US EPA Office of Water 2022b). While other pollutants from construction sites can be discharged to surface water bodies, sediment is the primary concern. Turbidity is the primary measurement used to assess water quality in runoff from construction sites. The EPA’s web page on Turbidity Benchmark Monitoring (DeWatering) under the Construction General Permit provides an overview of measuring turbidity and monitoring water quality of runoff from construction sites (US EPA Office of Water 2022a).
Learning Objectives
By the end of the laboratory you will:
- Identify conservation practices used on active construction sites and disturbed areas
Materials
Materials required to complete this laboratory activity include the following:
- Camera or a smart phone with a camera
Safety
Construction sites are dangerous places. This scavenger hunt activity requires you to visit construction sites. Please do not enter construction sites without explicit permission from the construction site manager. You may observe and photograph the construction site from a safe distance that is open to the public, such as from a nearby road, sidewalk, or fenceline. Do not trespass on private property. Wear appropriate personal protective equipment as necessary. Please do not act in a conspicuous manner that may raise suspicion from construction workers or passersby.
You are encouraged to talk to the contractors on site, if they are willing. You will likely find that most construction workers, such as the family members of the author of this laboratory manual, are very friendly and more than happy to talk to you about construction and the practices they use on site.
Introduction
Construction sites often have large areas of disturbed soils with minimal ground cover. If storms occur before that soil is covered, significant amounts of soil can be eroded from the site and delivered to nearby streams and surface water bodies as sediment. Sediment from construction sites is considered a point-source pollutant, and can cause serious disturbances to streams, floodplains, and other downstream water bodies. As a result, sediment from construction sites is regulated in the US by the Environmental Protection Agency (EPA) for all sites that are at least 1 acre (0.41 hectares) in size, or that are part of a planned development that exceeds 1 acre in size. Sediment contributes to increased turbidity in water, which can be easily measured on site. As a result, the EPA (2022a) has developed turbidity benchmark monitoring requirements that set a maximum amount of turbidity that can be tolerated in nearby streams as a result of construction site activities.
Construction Site Conservation Practice Scavenger Hunt
There are many different conservation practices that can be deployed on construction sites to reduce soil erosion and sediment discharges to streams. A selection of these process are listed below. For this activity you will observe construction sites that are active or were recently active. You need to identify and photograph six different construction site conservation practices being used. Visits to multiple construction sites may be required to identify six practices in total. You may count duplicate conservation practices toward the six practices only if they were observed on separate construction sites. For example, if silt fences are installed on two separate construction sites you may submit photos of the silt fences from both construction sites and count them as two of the six conservation practices.
Construction Site Conservation Practices
- Seeding to grass
- Straw mulch
- Hydromulch
- Ground blanket
- Silt fence
- Special silt fence
- Temporary diversion
- Temporary slope drain
- Riser basins
- Temporary silt basin
- Temporary rock silt check
- Temporary rock sediment dam
- Rock pipe inlet sediment trap
- Rock inlet sediment trap
- Stilling basin
- Surface outlet (skimmer)
- Flashboard riser outlet
- Baffles
- Polyacrylamide (PAM)
Laboratory Report
This scavenger hunt does not conform to our traditional laboratory report format. Please use the following headings and sections in your report.
Name
Laboratory Number and Title
Date the Exercise was Conducted
Introduction
Provide a brief introduction describing why conservation practices are important for disturbed areas like construction sites.
Description of Construction Site(s)
Identify the location of the construction site and describe what is being constructed to the best of your knowledge. If you observe the construction site regularly, describe things you have noticed over time about the activities on site regarding conservation practices, soil disturbance, runoff, etc.
Construction Site Conservation Practices and Assessment
Name at least six conservation practices that you observed at the construction site(s) and provide a captioned picture that you took of each of these practices. Note that using images taken by others may constitute a copyright infringement and violates the student code of conduct.
Discussion
Provide your assessment of whether or not the conservation practice was installed correctly and if maintenance is needed for each of the six practices you documented from this scavenger hunt. Further, evaluate whether erosion and sediment are being adequately controlled at this site, and if additional conservation practices may be needed.
Summary
Summarize your observations and assessments.
References
US EPA Office of Water. 2022a, February 8. Turbidity Benchmark Monitoring (Dewatering) under the Construction General Permit. https://www.epa.gov/npdes/turbidity-benchmark-monitoring-dewatering-under-construction-general-permit.
US EPA Office of Water. 2022b, March 17. Stormwater Discharges from Construction Activities. https://www.epa.gov/npdes/stormwater-discharges-construction-activities.
