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Stormwater Fundamentals Series - ESC 101 – Expectations vs Realities
Ocean Protect
Overview
This video explains the fundamental principles of erosion and sediment control (ESC) on construction sites, highlighting the gap between expected best practices and on-the-ground realities. It emphasizes the importance of understanding soil types, site constraints, and the specific mechanisms of different ESC controls. The presentation details what constitutes a comprehensive ESC plan, the common pitfalls in their creation and implementation, and practical strategies for improvement, including focusing on erosion control, proper soil management, and realistic expectations for sediment capture.
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Chapters
- Erosion and sediment control (ESC) is crucial for preventing environmental harm to waterways, as sediment is a pollutant that impacts aquatic life and habitats.
- The general environmental duty requires individuals to take all reasonably practicable measures to prevent or minimize environmental harm.
- ESC plans should aim to minimize sediment leaving construction sites, whether as waterborne sediment or dust.
- Compliance with ESC can be demonstrated by adhering to best practice guidelines, such as the 'white book' (national) or specific state-level guidelines.
Understanding the legal and environmental reasons for ESC is essential for recognizing its importance and the consequences of non-compliance.
A sediment plume heading into a waterway after a rain event, causing environmental issues for aquatic animals by impacting their ability to breathe and their habitat.
- Erosion control focuses on minimizing exposed soil surfaces, using methods like geotextiles, rock, turf, or matting.
- Sediment control, exemplified by sediment fences, aims to capture sediment that has already detached from the soil.
- Both erosion and sediment control are critical and must be addressed in an ESC plan; focusing on only one is insufficient.
Recognizing the difference between erosion and sediment control helps in selecting and implementing the most effective strategies for site management.
Geotextile covering an embankment (erosion control) versus a sediment fence capturing sediment behind it (sediment control).
- An effective ESC plan requires a suitably qualified person, such as a CPESC or RSP-ESC, to develop it.
- Plans must be site-specific, considering factors like site complexity, soil types, topography, and proximity to sensitive receiving environments.
- Plans need to be flexible and adaptable to the dynamic nature of construction sites, which can change daily or weekly.
- Key elements include risk assessment, understanding soil behavior, managing topsoil, detailing erosion and sediment controls, and outlining discharge criteria.
A well-developed, site-specific ESC plan is the foundation for preventing environmental harm and ensuring regulatory compliance.
A large subdivision or infrastructure project might require a 10-20 page ESC plan, detailing various soil types, stages of work, and specific controls, unlike a single house block which might only need a few pages.
- In reality, ESC plans are often an afterthought, created quickly by less experienced staff with limited knowledge.
- Plans frequently focus too much on sediment control (like sediment fences) and neglect crucial erosion control measures.
- Common mistakes include not understanding site-specific risks, soil properties, or construction methodologies.
- There is often insufficient time and budget allocated for proper ESC plan preparation and on-site maintenance.
Understanding the common failures in ESC plan development and implementation is key to avoiding these pitfalls and improving site management.
A typical one-page ESC plan with just a drawing of a sediment fence, lacking detailed instructions or consideration for erosion control, is often insufficient.
- Different soil types (sand, silt, clay) behave differently regarding erosion and sediment settling.
- Sand settles quickly, while fine clay particles can take days to settle and are responsible for water turbidity.
- Sediment controls primarily work by retaining water long enough for natural settlement of coarser particles.
- Fine clay particles, due to their negative charge, resist aggregation and are difficult to remove without chemical treatment (coagulants/flocculants).
Knowledge of soil properties and how different ESC controls function is vital for selecting appropriate measures and having realistic expectations of their effectiveness.
Sediment fences are effective at capturing coarse sediment but do not significantly reduce turbidity caused by fine clay particles, as demonstrated by studies showing little improvement in downstream water clarity.
- Sediment fences are designed to pond water and capture coarse sediment, but they do not filter fine particles or reduce turbidity.
- Mulch berms offer some filtration but are primarily effective for coarse sediment capture.
- Sediment basins (Type D, C, B, A) are necessary for capturing fine sediments and reducing turbidity, especially Type A and B high-efficiency basins.
- Water quality objectives (e.g., 50 mg/L TSS) need careful consideration, as they may not always correlate with visually clear water, necessitating additional criteria (e.g., NTU limits).
Understanding the limitations of common controls like sediment fences and the capabilities of more advanced solutions like sediment basins ensures appropriate measures are chosen for specific site conditions and water quality goals.
A study showed sediment fences retained 67-91% of sediment by weight, but downstream turbidity often did not improve, highlighting their limitation with fine particles.
- Improve ESC by setting realistic expectations, understanding site-specific soil types, and protecting topsoil.
- Prioritize erosion control (ground cover) over solely relying on sediment control measures.
- Manage water on site by channeling dirty water to controls and diverting clean water around exposed areas.
- Stage work to allow for progressive rehabilitation and regular inspection and maintenance of controls.
Implementing these strategies can significantly enhance the effectiveness of ESC on construction sites, leading to better environmental outcomes and compliance.
Instead of just focusing on sediment fences, actively implementing ground cover and stabilizing exposed soil surfaces to minimize erosion in the first place.
Key takeaways
- Erosion and sediment control is a legal and environmental imperative, not just a best practice.
- Effective ESC requires a deep understanding of site-specific conditions, particularly soil types and topography.
- A comprehensive ESC plan must address both erosion control (preventing soil detachment) and sediment control (capturing detached soil).
- Common ESC measures like sediment fences have limitations, especially with fine clay particles and turbidity.
- Sediment basins, particularly high-efficiency types, are crucial for managing fine sediments and achieving better water quality outcomes.
- Realistic expectations, early planning, and continuous monitoring are essential for successful ESC implementation.
- Protecting and managing topsoil is vital for site rehabilitation and long-term environmental health.
- Focusing on erosion control measures like ground cover is more effective than solely relying on downstream sediment capture.
Key terms
Erosion ControlSediment ControlGeneral Environmental DutyBest Practice GuidelineSediment FenceSediment BasinDispersive SoilsTurbidityTotal Suspended Solids (TSS)CoagulantsFlocculants
Test your understanding
- What is the primary difference between erosion control and sediment control, and why are both necessary?
- Why is it important for an Erosion and Sediment Control (ESC) plan to be site-specific and adaptable?
- Explain the limitations of sediment fences in managing water quality, particularly concerning fine clay particles.
- How do soil types influence the selection and effectiveness of different erosion and sediment control measures?
- What are the key strategies for improving the practical implementation and effectiveness of ESC on construction sites?