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--- infiltration_exemptions [2023/11/28 12:32] – 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, that can't be removed with conventional excavation equipment, 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 partial areas of 5+ feet of clay-textured soils (or with measured infiltration rate <0.6 in/hr), that can't be removed with conventional excavation equipment, 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;
+    * 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.
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 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.