Understanding Construction Stormwater General Permit Regulations

Key Exclusions

Not all land disturbance requires this specific permit. Common exclusions include:

• Routine Maintenance: Activities intended to maintain the original line, grade, or purpose of a facility.
• Agriculture: Soil preparation for crops, such as disking or harrowing.
• Tribal Lands: Construction on tribal lands is regulated by federal permits rather than this state permit.
• Lake Tahoe: Projects within the Lake Tahoe Hydrologic Unit are governed by specific Lahontan Regional Water Board permits.
• Dredged Material: The discharge of dredged or fill material directly into waters of the state is regulated under CWA § 404 and § 401, not this General Permit.

Exam Tip: If a question asks whether a project disturbing 0.5 acres is covered, check if it is part of a "common plan of development." If it is, it likely requires coverage.

Pollution Control and Technology Standards

The permit mandates that dischargers use specific levels of technology to minimize the impact of their runoff. The goal is to reduce or eliminate pollutants through a tiered approach to technology:

1. Best Available Technology Economically Achievable (BAT): The most advanced technology that is economically feasible for the industry.
2. Best Conventional Pollutant Control Technology (BCT): Specifically targeted at controlling conventional pollutants.

Treatment Methods: Passive vs. Active

Depending on the site conditions and the nature of the sediment, dischargers may use different treatment strategies:

• Passive Treatment: This involves using natural or synthetic chemicals to induce coagulation and flocculation. This process helps fine particles clump together so they can settle more easily. Passive treatment does not rely on computerized, enclosed systems with pumps or real-time controls.
• Active Treatment Systems: For sites dealing with extremely fine particles (smaller than $0.02\text{ mm}$) that do not settle in conventional basins, active treatment systems may be required. These systems are more robust and can help sites meet strict numeric effluent limitations.

Monitoring, Limits, and Water Quality

To ensure compliance, the permit utilizes several quantitative metrics to track the quality of the water leaving the site.

Numeric Action Levels (NALs) and Effluent Limitations

The permit uses numeric action levels (such as for pH and turbidity) to provide operational data.

• Purpose of NALs: They act as an "early warning system." If a site exceeds an NAL, it indicates that the current Best Management Practices (BMPs) are underperforming.
• Corrective Action: Upon exceeding an NAL, the discharger is legally required to take corrective actions, such as maintaining, replacing, or installing new BMPs.
• Numeric Effluent Limitations: While NALs are operational, effluent limitations are stricter requirements often applied to sites using active treatment systems.

Water Quality Standards and TMDLs

Dischargers must also comply with receiving water limitations. This means that even if a site's discharge meets technology-based standards, it cannot cause the receiving waterbody to violate its established water quality standards.

In many cases, this is managed through Total Maximum Daily Loads (TMDL). A TMDL is the maximum amount of a specific pollutant that a waterbody can receive while still meeting water quality standards. The TMDL is calculated as:

$\text{TMDL} = \sum \text{Waste Load Allocations (Point Sources)} + \text{Load Allocations (Non-point Sources)} + \text{Background Loads}$

Special Protections: ASBS

In certain sensitive areas, such as Areas of Special Biological Significance (ASBS), the regulations are even more stringent. In these ocean areas, discharges are generally prohibited unless a specific exception is granted by the State Water Board. Dischargers in these areas may face intensive monitoring requirements, including biological surveys and bioaccumulation studies.

Post-Construction Requirements

For traditional (non-linear) construction projects, the responsibility does not end when the building is finished. Dischargers must implement permanent post-construction BMPs.

The primary goal of these permanent measures is to manage runoff rates so they match the pre-construction hydrology of the site. This "runoff reduction" approach helps protect the physical structure and biological integrity of the receiving aquatic ecosystems by preventing the sudden surges of water and sediment that typically follow urban development.

Summary of Discharger Responsibilities

The discharger (the entity responsible for the site) is ultimately responsible for all compliance. They must:

1. Designate a Legally Responsible Person to sign and certify all required documents.
2. Implement an iterative process of using and improving BMPs.
3. Ensure that all dewatering activities (pumping water from trenches or excavations) comply with pH and turbidity limits.
4. Maintain a Stormwater Pollution Prevention Plan (SWPPP) on-site.

Note on Dewatering: If you are dewatering a site, you must notify the Regional Water Board at least 24 hours in advance and ensure the discharge does not exceed numeric action levels for pH (6.5–8.5) or turbidity (250 NTU).