m |
|||
Line 5: | Line 5: | ||
==Iron in iron enhanced sand filters== | ==Iron in iron enhanced sand filters== | ||
*No amendment added to attenuate P; DP removal = 0% | *No amendment added to attenuate P; DP removal = 0% | ||
+ | |||
+ | Two tiers for crediting dissolved phosphorus exist and conditions needed to meet the criteria are described. | ||
*Tier 1: Amendment added and meets the following; DP removal = 40% | *Tier 1: Amendment added and meets the following; DP removal = 40% | ||
**Iron enhanced system, and | **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 | **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 | + | **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 (see [[Assessing the performance of iron enhanced sand filter]]), and |
− | **Annually or as needed remove vegetation and accumulated sediment (as needed, typically | + | **Annually or as needed remove vegetation and accumulated sediment (as needed, typically after a storm greater than 1 in of precipitation), and |
**Rake surface with a steel-tipped rake to break up oxidized iron clumps or crust that may form, 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 | + | **System designed to allow drying (e.g. exposed to sunlight and access to air through drain tile) |
− | + | **<span title="Level Spreaders are measures that reduce the erosive energy of concentrated flows by distributing runoff as sheet flow to stabilized vegetative surfaces."> '''[https://files.nc.gov/ncdeq/Water%20Quality/Surface%20Water%20Protection/SPU/SPU%20-%20BMP%20Manual%20Documents/BMPMan-Ch08-20100309-DWQ-SPU.pdf Level spreader]'''</span>, modified pond inlets, or other method or design for spreading water across the system, and | |
− | |||
− | |||
− | ** | ||
− | |||
− | |||
− | |||
− | |||
**Enhanced pretreatment designed to remove organic material (see [https://igeowater.com/mpca/#/intro Pretreatment Practice Selection Tool] to identify practices effective at removing debris and solids), and | **Enhanced pretreatment designed to remove organic material (see [https://igeowater.com/mpca/#/intro 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 | **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. | **Inspection and maintenance agreement established that identifies the entity responsible for inspection and maintenance. | ||
+ | *Tier 2: Determined from water quality monitoring. See [[Assessing the performance of iron enhanced sand filter]]. | ||
==Iron in iron enhanced wet pond benches== | ==Iron in iron enhanced wet pond benches== |
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.
Two tiers for crediting dissolved phosphorus exist and conditions needed to meet the criteria are described.
An iron-enhanced sand filtration bench in a wet pond is essentially a wet extended detention pond with a permanent pool and a flood pool. The dissolved phosphorus credit for this practice is 40% if the following design features are implemented.
The outlet structure of the pond is designed such that the water in the flood pool during and after a storm event is held above the elevation of the iron-enhanced sand filter bench, thereby allowing water to filter through the bench. The basic design elements of an iron-enhanced sand filter basin include: