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**The manual does not discuss infiltration in areas of high road salt application. Areas of salt storage are discussed and may be considered [https://stormwater.pca.state.mn.us/index.php?title=Potential_stormwater_hotspots stormwater hotspots]. This is a topic that deserves some attention and it may be appropriate to designate transportation areas with high road salt application as stormwater hotspots. Specific guidance needs to be developed, however. | **The manual does not discuss infiltration in areas of high road salt application. Areas of salt storage are discussed and may be considered [https://stormwater.pca.state.mn.us/index.php?title=Potential_stormwater_hotspots stormwater hotspots]. This is a topic that deserves some attention and it may be appropriate to designate transportation areas with high road salt application as stormwater hotspots. Specific guidance needs to be developed, however. | ||
*What storm event needs to infiltrate within 48 hours when including the bounce in the drawdown depth? | *What storm event needs to infiltrate within 48 hours when including the bounce in the drawdown depth? | ||
− | **The Construction Stormwater permit requires that Permittee(s) must design the project so that the water quality volume of one (1) inch of runoff from the new impervious surfaces created by the project is retained on site (i.e. infiltration or other volume reduction practices) and not discharged to a surface water. This volume is considered to be captured instantaneously by the BMP and must be infiltrated within 48 hours. | + | **The Construction Stormwater permit requires that Permittee(s) must design the project so that the water quality volume of one (1) inch of runoff from the new impervious surfaces created by the project is retained on site (i.e. infiltration or other volume reduction practices) and not discharged to a surface water. This volume is considered to be captured instantaneously by the BMP and must be infiltrated within 48 hours. Note that all water delivered to the BMP must be removed from the BMP within the drawdown time, either through infiltration or through infiltration and outflow through an overflow pipe. |
*Was mentioned that mndot grade 2 compost was not recommended for filtration practices due to nutrient leaching. Are there alternative recommendations other than peat moss? | *Was mentioned that mndot grade 2 compost was not recommended for filtration practices due to nutrient leaching. Are there alternative recommendations other than peat moss? | ||
**The manual does not recommend that specific composts be used or not used. To reduce the likelihood of exporting phosphorus from BMPs that have an underdrain, the P content in the media must be less than 30 mg/kg per Mehlich III (or equivalent) test. This would equate to a media with about 5 percent organic matter with a P concentration of about 0.06 percent in the organic matter. We agree that the P content of different sources of organic matter will likely vary and that over time, less P is likely to leach from the media. We are hoping to eventually have more specific information about media and different sources of organic matter. | **The manual does not recommend that specific composts be used or not used. To reduce the likelihood of exporting phosphorus from BMPs that have an underdrain, the P content in the media must be less than 30 mg/kg per Mehlich III (or equivalent) test. This would equate to a media with about 5 percent organic matter with a P concentration of about 0.06 percent in the organic matter. We agree that the P content of different sources of organic matter will likely vary and that over time, less P is likely to leach from the media. We are hoping to eventually have more specific information about media and different sources of organic matter. | ||
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**Not sure what this question is asking. Infiltration basins, trenches, dry wells, and underground practices are [https://stormwater.pca.state.mn.us/index.php?title=Infiltration discussed together in the manual]. When there are differences between the practices they are pointed out. Examples include [https://stormwater.pca.state.mn.us/index.php?title=BMPs_for_stormwater_infiltration#Information_tables information tables]. | **Not sure what this question is asking. Infiltration basins, trenches, dry wells, and underground practices are [https://stormwater.pca.state.mn.us/index.php?title=Infiltration discussed together in the manual]. When there are differences between the practices they are pointed out. Examples include [https://stormwater.pca.state.mn.us/index.php?title=BMPs_for_stormwater_infiltration#Information_tables information tables]. | ||
*Many sites we work in have saturated soils within 3' of the existing ground and require mound septic systems. However, the soil borings show a C soil. How are we suppose to provide filtration when this in the case? | *Many sites we work in have saturated soils within 3' of the existing ground and require mound septic systems. However, the soil borings show a C soil. How are we suppose to provide filtration when this in the case? | ||
− | **Infiltration is prohibited in the Construction Stormwater permit | + | **Infiltration is prohibited in the Construction Stormwater permit if the seasonal high water table is within 3 feet of the bottom of the practice. See [https://stormwater.pca.state.mn.us/index.php?title=Glossary#S the definition of saturated soil]. An underdrain system is recommended in these situations. The permit requires filtration systems with less than three feet of separation to include in impermeable liner ([https://stormwater.pca.state.mn.us/index.php?title=III._STORMWATER_DISCHARGE_DESIGN_REQUIREMENTS#III.D._PERMANENT_STORMWATER_MANAGEMENT_SYSTEM Part III.D.1.h]). |
*Can you point out and discuss the underground systems/ | *Can you point out and discuss the underground systems/ | ||
**Infiltration basins, trenches, dry wells, and underground practices are [https://stormwater.pca.state.mn.us/index.php?title=Infiltration discussed together in the manual]. When there are differences between the practices they are pointed out. Examples include [https://stormwater.pca.state.mn.us/index.php?title=BMPs_for_stormwater_infiltration#Information_tables information tables]. | **Infiltration basins, trenches, dry wells, and underground practices are [https://stormwater.pca.state.mn.us/index.php?title=Infiltration discussed together in the manual]. When there are differences between the practices they are pointed out. Examples include [https://stormwater.pca.state.mn.us/index.php?title=BMPs_for_stormwater_infiltration#Information_tables information tables]. |
Below are questions submitted during the December 15, 2016 webinar on Infiltration. Answers include links and if appropriate, links to additional information.