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**We're not sure what this question refers to, but the page [[Understanding and interpreting soils and soil boring reports for infiltration BMPs]] provides information on what information to collect with soil borings. The critical factor to consider in conducting borings when designing an infiltration BMP is to identify any restrictive layer in the soil profile. A SWPPP could utilize information from the manual in describing how BMP design and investigations will be conducted, or simply reference the manual. | **We're not sure what this question refers to, but the page [[Understanding and interpreting soils and soil boring reports for infiltration BMPs]] provides information on what information to collect with soil borings. The critical factor to consider in conducting borings when designing an infiltration BMP is to identify any restrictive layer in the soil profile. A SWPPP could utilize information from the manual in describing how BMP design and investigations will be conducted, or simply reference the manual. | ||
*What is the general thought of infiltration in areas that are in active karst features (less than 50 feet of soil cover) but it is not located in the DWSMA or Wellhead protection area? I have heard the term higher engineering review to determine if infiltration can be done in Karst areas but what does the higher enginnering review actually consist of? | *What is the general thought of infiltration in areas that are in active karst features (less than 50 feet of soil cover) but it is not located in the DWSMA or Wellhead protection area? I have heard the term higher engineering review to determine if infiltration can be done in Karst areas but what does the higher enginnering review actually consist of? | ||
− | **The Construction Stormwater Permit | + | **The 2013 Construction Stormwater Permit prohibited infiltration of stormwater runoff “within 1,000 feet up-gradient or 100 feet down-gradient of active karst features unless allowed by a local unit of government with a current MS4 permit”. The 2018 CSW permit no longer allows the option of infiltration under these conditions. The question implies that active karst has been identified at a site. Investigation methods in karst areas are discussed [https://stormwater.pca.state.mn.us/index.php?title=Karst#How_to_investigate_for_karst_on_a_site here]. Higher engineering review is not defined in the permit, nor is it clear what the intent of the higher review is. Presumably a higher engineering review would indicate that there is sufficient confining material between the bottom of the practice and the nearest underlying aquifer. This would be based on the presence of some confining layer of sufficient thickness to attenuate pollutants should the practice fail. This type of analysis should be conducted by a licensed geoscientist or engineer. Additional information may be found at [https://stormwater.pca.state.mn.us/index.php?title=Karst#General_stormwater_management_guidelines_for_karst_areas General stormwater management guidelines for karst areas] and at the [http://www.dnr.state.mn.us/waters/groundwater_section/mapping/sensitivity.html MNDNR's webpage on groundwater sensitivity]. |
*Does the manual address infiltration in D soils - as required by several watershed districts? | *Does the manual address infiltration in D soils - as required by several watershed districts? | ||
**The Construction Stormwater permit prohibits infiltration in areas of predominately Hydrologic Soil Group D (clay) soils unless allowed by a local unit of government with a current MS4 permit. Meeting the 1 inch volume requirement and the 48 hour drawdown requirement on D soils would require a very large infiltration practice. The manual provides [https://stormwater.pca.state.mn.us/index.php?title=Soils_with_low_infiltration_capacity#What_are_general_stormwater_management_guidelines_for_sites_with_low_infiltration_capacity_soils.3F management guidelines for sites with D soils]. | **The Construction Stormwater permit prohibits infiltration in areas of predominately Hydrologic Soil Group D (clay) soils unless allowed by a local unit of government with a current MS4 permit. Meeting the 1 inch volume requirement and the 48 hour drawdown requirement on D soils would require a very large infiltration practice. The manual provides [https://stormwater.pca.state.mn.us/index.php?title=Soils_with_low_infiltration_capacity#What_are_general_stormwater_management_guidelines_for_sites_with_low_infiltration_capacity_soils.3F management guidelines for sites with D soils]. | ||
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*We are in sandy soils with some basins infiltrating at 10+ inches/hr. Is there a reccomended maximum infiltration rate for pollutant removal? | *We are in sandy soils with some basins infiltrating at 10+ inches/hr. Is there a reccomended maximum infiltration rate for pollutant removal? | ||
**The Construction Stormwater permit prohibits infiltration in areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour or as allowed by a local unit of government with a current MS4 permit. The reason for this prohibition is the likelihood that pollutants will not be attenuated by the practice. We have looked for information in the literature to support this and for guidance on how to modify soils that have excessive infiltration rates, but we have been unable to find good information on the topic. Amending with compost and/or clay is a likely mechanism for reducing infiltration rates, but we cannot yet quantify these effects. | **The Construction Stormwater permit prohibits infiltration in areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour or as allowed by a local unit of government with a current MS4 permit. The reason for this prohibition is the likelihood that pollutants will not be attenuated by the practice. We have looked for information in the literature to support this and for guidance on how to modify soils that have excessive infiltration rates, but we have been unable to find good information on the topic. Amending with compost and/or clay is a likely mechanism for reducing infiltration rates, but we cannot yet quantify these effects. | ||
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+ | [[Category:Level 3 - General information, reference, tables, images, and archives/Reference/Training, webinars, and workshops]] |
Below are questions submitted during the December 15, 2016 webinar on Infiltration. Answers include links and if appropriate, links to additional information.
This page was last edited on 6 December 2022, at 14:28.