MPCA-approved mechanisms and values for removal of dissolved phosphorus from stormwater runoff
This page provides a summary of MPCA-approved mechanisms and values for removal of dissolved phosphorus from stormwater runoff. The discussion includes requirements for receiving the credit from the MPCA.
Information: Credits are subject to change based on available data
Iron in iron enhanced sand filters
- No amendment added to attenuate P; DP removal = 0%
- Tier 1: Amendment added and meets the following; DP removal = 40%
- Iron enhanced system, and
- Iron 5-8% by weight, high purity iron (90%+ elemental iron) with little or no toxic impurities (e.g., copper, cadmium, lead, etc.), and reactive with phosphate, and
- Inspect IESFs at least once annually, with more frequent inspections (monthly or quarterly) during the first 1-2 years if needed to ensure construction was successful, and
- Annually or as needed remove vegetation and accumulated sediment (as needed, typically once 5-10 years depending on contributing sediment and pretreatment), and
- Rake surface with a steel-tipped rake to break up oxidized iron clumps or crust that may form, and
- System designed to allow drying (e.g. exposed to sunlight, drawdown requirement)
- Tier 2: Amendment added and meets the following; DP removal =60%
- Iron enhanced system, and
- Iron 5-8% by weight, high purity iron (90%+ elemental iron) with little or no toxic impurities (e.g., copper, cadmium, lead, etc.), and reactive with phosphate, and
- Inspect IESFs at least once annually, with more frequent inspections (monthly or quarterly) during the first 1-2 years if needed to ensure construction was successful, and
- Annually or as needed remove vegetation and accumulated sediment (as needed, typically once 5-10 years depending on contributing sediment and pretreatment), and
- Rake surface with a steel-tipped rake to break up oxidized iron clumps or crust that may form, and
- System designed to allow drying (e.g. exposed to sunlight), and
- Level spreader, modified pond inlets, or other method or design for spreading water across the system, and
- Enhanced pretreatment designed to remove organic material (see Pretreatment Practice Selection Tool to identify practices effective at removing debris and solids), and
- Designed to be offline such that flows beyond the water quality volume flows are diverted around the system, and
- Inspection and maintenance agreement established that identifies the entity responsible for inspection and maintenance.