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--- infiltration_exemptions [2023/03/07 11:08] – admin
+++ infiltration_exemptions [2025/11/06 16:03] (current) – admin
@@ Line 15: / Line 15: @@
 Even on sites with clay soils, designing practices to increase stay-on is possible. Traditional infiltration practices that rely on ponding water, like bioretention, may need an underdrain and a shallower depth to meet drawdown requirements. Permeable pavement works best by infiltrating a distributed depth of water, which can work well on soils with lower infiltration rates. Other practices, such as green roofs or water re-use, do not depend on in-situ soils at all to keep runoff on the site.
-It is more difficult to meet the infiltration standard on sites with clay soils, so an alternative approach may be used, detailed below.
+It's more difficult to meet the infiltration standard on sites with clay soils, so an alternative approach may be used, detailed below.
-**Case 1** - Sites with 5+ feet of clay-textured soils (or with measured infiltration rate <0.6 in/hr) over entire site must meet the following requirements:
+  * If entire site has 5+ feet of clay-textured soils (or with measured infiltration rate <0.6 in/hr) that can't be removed with conventional excavation equipment, the requirements below may be used:
-  - Dedicate 2% of the site to infiltration practices that maximize infiltration and conform to applicable standards, e.g. maximum drawdown times, ;
+    * Dedicate 2% of the site to infiltration practices that maximize infiltration and conform to applicable standards, e.g. maximum drawdown times;
-  - Provide infiltration calculations and associated summary table.
+    * Provide infiltration calculations and associated summary table.
-**Case 2** – Sites with areas of 5+ feet of clay-textured soils (or with measured infiltration rate <0.6 in/hr) must meet the following requirements:
+  * If partial areas of site have 5+ feet of clay-textured soils (or with measured infiltration rate <0.6 in/hr) that can't be removed with conventional excavation equipment, the requirements below may be used:
-  - Provide a map delineating exempt and non-exempt areas;
+    * Provide a map delineating exempt and non-exempt areas;
-  - Infiltrate 90%  of the predevelopment volume from non-exempt areas;
+    * Infiltrate 90%  of the predevelopment volume from non-exempt areas;
-  - Dedicate 2% of the site to infiltration practices that maximize infiltration and conform to applicable standards, e.g. maximum drawdown times;
+    * Dedicate 2% of the site to infiltration practices that maximize infiltration and conform to applicable standards;
-  - Provide infiltration calculations and summary table for both non-exempt areas and full site.
+    * Provide infiltration calculations and summary table for both non-exempt areas and full site.
 It's recommended that designers wanting to request an exemption first discuss with staff for an official determination. Exemption requests must provide a preliminary site plan and soils testing  results in accordance with the [[https://dnr.wisconsin.gov/sites/default/files/topic/Stormwater/1002SiteEvalForInfiltr.pdf|DNR's Site Evaluation for Stormwater Infiltration]]. The evaluation will need to cover all of the site to be considered for exemption.
@@ Line 35: / Line 35: @@
 Presence of redoximorphic (redox) features may not reflect the current hydrologic conditions and are not definitive indicators of groundwater elevation. These features can occur in tight soils above the groundwater table and in recently drained soils, which may retain the presence of reduced features. It's important to remember that historically wet soils have been systematically drained for many years across Dane County. The soils investigation should indicate standing water, if encountered, which will provide the true groundwater elevation. For the most accurate reading, especially in tight soils, boreholes should be left open and measured after 24 hours.
-==== Bedrock ====
+===== Bedrock =====
 Sites with shallow bedrock should take an approach similar to those with shallow groundwater, detailed above. Bedrock infiltration rates are highly variable and will need to be determined by a geotechnical engineer and/or through discussion with WRE staff. Because bedrock may have a more direct path to groundwater, an additional 1 foot of sand (finer than coarse) below the engineered soil layer is necessary to meet separation requirements.
+===== Prohibitions =====
+Wisconsin Chapter 151 has [[https://docs.legis.wisconsin.gov/code/admin_code/nr/100/151/iii/124/3/a|infiltration prohibitions]] for certain land uses, but these are not exemptions. Sites with prohibited areas are still expected to meet the infiltration standard.