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**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. | ||
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+ | ==Iron in iron enhanced wet pond benches== | ||
+ | An iron-enhanced sand filtration bench in a wet pond is essentially a [[Types of stormwater ponds#Extended wet detention basin|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. | ||
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+ | 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: | ||
+ | *iron-enhanced sand filter of desired width and length sited along the perimeter of the wet pond (iron-enhanced sands filters should be no less than 5 percent but no greater than 8 percent iron by weight to prevent clogging, see [[References for iron enhanced sand filter|Erickson et al., 2010, 2012]], and presentation by John Gulliver, September 2012). The 5 to 8 percent range is based upon iron filing material that is approximately 90 percent elemental iron with a size distribution approximately equal to that of C33 sand; | ||
+ | *outlet structure that controls the flood pool elevation and can receive the filter bed drain; | ||
+ | *subsurface drains at the filter bed bottom to drain the bed. The outlet of these subsurface drains should be exposed to the atmosphere and above the downstream high water level to allow the filter to fully drain; | ||
+ | *impervious barrier (typically [http://stormwater.pca.state.mn.us/index.php/Liners_for_stormwater_management geotextile liner], for example HDPE) between the pond and the trench to minimize seepage from the pond into the trench; | ||
+ | *filter draw down within 48 hours of storm completion to avoid filter fouling and to prepare the filter for next storm event; and | ||
+ | *the underdrain may consist of corrugated polyethylene pipe with slits not holes to prevent loss of sand and minimize clogging. If holes are used, the pipe should be covered with pea gravel. |
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.
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: