1. What is a Regional Stormwater Management System (RSMS)?
An RSMS is a facility designed, constructed, and maintained to manage stormwater for one to multiple parcels and may serve one or more projects within a defined drainage area (you can think of this like the service area of a mitigation bank). Its purpose is to prevent flooding, reduce pollution, and manage stormwater discharges for a larger area compared to a conventional system.
2. How does an RSMS differ from traditional stormwater management systems?
Unlike stormwater management systems that are integrated within a development project, an RSMS is permitted as a standalone stormwater management system to serve multiple projects in a defined area. It also provides a mechanism for accountable nutrient reduction across a HUC 12 or potentially larger watershed, enabling more efficient land use and potentially lower development costs through offsite compensatory treatment credits (aka Stormwater Nutrient Credits).
3. What are the main advantages of using an RSMS?
– Cost Efficiency: Offsite treatment infrastructure can reduce site development costs.
– Improved Water Quality: Centralized treatment in larger, professionally managed stormwater facilities achieve higher pollutant removal rates.
– Flexibility in Development: Developers may reduce on-site treatment requirements by utilizing offsite credits.
– Comprehensive Watershed Management: Better tracking and accountability of stormwater nutrient reduction at a watershed scale.
4. How are pollutant load reductions allocated in an RSMS?
RSMS facilities track pollutant removal in pounds or kilograms, ensuring allocations do not exceed their permitted treatment capacity. Records of these allocations must be maintained permanently by the RSMS permit holder and reported as specified in Sections 9.7.3 and 12.6(d) of the Applicant’s Handbook.
5. What permitting requirements apply to RSMS?
RSMS must be permitted under the Environmental Resource Permit (ERP) program. This includes demonstrating reasonable assurance of compliance with water quality standards, long-term operations and maintenance, and accurate tracking of nutrient load reductions.
6. How does an RSMS provide stormwater nutrient credits (SNCs)?
An RSMS can generate SNCs by documenting excess treatment capacity in an accounting ledger, much like a wetland mitigation bank. These credits can then transferred to other entities within the same service area (e.g. hydrologically connected or within the same watershed) to offset their pollutant loading requirements. Keep in mind that the user of an SNC must still meet the water quantity requirements of ERP (e.g. pre-post rate control) and must demonstrate that the discharge of less than fully treated stormwater does not adversely impact any downstream waters.
7. Who is responsible for maintaining an RSMS?
The permit holder of the RSMS is responsible for its operation, maintenance, and compliance with all applicable regulations. This includes maintaining accurate records of stormwater treatment allocations and ensuring that the system operates within its design capacity.
8. Does the user of SNCs have any ongoing responsibilities after the credits are transferred to their project from an RSMS?
No. Like a wetland mitigation credit, the purchaser bears no long-term responsibility for the continued operations and maintenance of the nutrient credit generating project. That obligation falls solely on the RSMS permit holder.