Dane County Stormwater Manual

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stormwater_maintenance [2022/07/29 15:22] – adminstormwater_maintenance [2025/01/15 09:57] (current) – megan_duffy
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 The cost, level of effort and expertise required to maintain stormwater practices varies, depending on the type, size and complexity of the practice. Routine maintenance, such as mowing and removing debris or trash, is needed multiple times each year and can easily be performed by most landowners. More significant maintenance, such as removing accumulated sediment is needed less frequently, but requires more skilled labor and special equipment. Inspection and repair of critical structural features, such as embankments and outlet structures, needs to be performed by a qualified professional that has experience in the construction, inspection, and repair of these features. The financial cost of maintaining stormwater practices should be understood at the time of permitting and planned for after construction is complete. The cost, level of effort and expertise required to maintain stormwater practices varies, depending on the type, size and complexity of the practice. Routine maintenance, such as mowing and removing debris or trash, is needed multiple times each year and can easily be performed by most landowners. More significant maintenance, such as removing accumulated sediment is needed less frequently, but requires more skilled labor and special equipment. Inspection and repair of critical structural features, such as embankments and outlet structures, needs to be performed by a qualified professional that has experience in the construction, inspection, and repair of these features. The financial cost of maintaining stormwater practices should be understood at the time of permitting and planned for after construction is complete.
  
 +For practice specific flyers, see the [[Stormwater Resources]] page. 
  
 =====Maintenance Agreement===== =====Maintenance Agreement=====
-A signed and notarized {{ :stormwater_maintenance_agreement.pdf |stormwater maintenance agreement}}, with $30 recording fee (made out to "Register of Deeds"), is required before a stormwater permit can be issued. The agreement binds maintenance to the current property owner and details specific maintenance tasks for practices located on the site.+A signed and notarized {{:stormwater_maintenance_agreement.pdf |Stormwater Maintenance Agreement}} ( {{ :maintenance_agreement.doc| }}), with $30 recording fee (made out to "Register of Deeds") must be provided before a stormwater permit can be issued. Once recorded, this document binds maintenance requirements to the property owner. The agreement must have an Exhibit A that provides the legal description of the property and details specific maintenance tasks for practices located on the site. {{ :wiki:images:maintenance_exhibit_b.pdf |Exhibit B}} shows a simplified site plan and clearly identifies the location of all stormwater practices. 
 + 
 +{{ :wiki:images:maintenance_map.png?600 |}}
  
 ====General Maintenance Requirements==== ====General Maintenance Requirements====
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   * Remove sediment from permanent pool once average depth is 3.5 feet or less. Protect liner from damage during sediment removal, if present.   * Remove sediment from permanent pool once average depth is 3.5 feet or less. Protect liner from damage during sediment removal, if present.
   * Excavation is prohibited below the original design depth unless approved by Dane County Water Resources Engineering Department.   * Excavation is prohibited below the original design depth unless approved by Dane County Water Resources Engineering Department.
-  * Repairs must restore the pond to the approved plan design.+  * Repairs must restore the practice to the approved plan design.
  
 ===Dry Pond=== ===Dry Pond===
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   * Inspect twice a year to ensure proper operation and check for any potential problems, such as: sediment accumulation, subsidence, erosion, damage to the emergency spillway, and woody vegetation.   * Inspect twice a year to ensure proper operation and check for any potential problems, such as: sediment accumulation, subsidence, erosion, damage to the emergency spillway, and woody vegetation.
   * Removed accumulated sediment from the pond as necessary. Sediment removal will be more frequent than in a wet pond due to the smaller storage volume.   * Removed accumulated sediment from the pond as necessary. Sediment removal will be more frequent than in a wet pond due to the smaller storage volume.
 +  * Repairs must restore the practice to the approved plan design.
  
 ===Infiltration Basin=== ===Infiltration Basin===
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   * Restoration includes removing the top 2 to 3 inches, chisel plowing, then adding topsoil and compost before seeding. If deep tilling is used, the basin shall be drained and the soils dried to a depth of 8 inches. If the basin was planted in turf grass and clogging again occurs after these restoration procedures have been used, the owner /operator shall replant with prairie style vegetation using the soil preparation method recommended by the native nursery in the area.    * Restoration includes removing the top 2 to 3 inches, chisel plowing, then adding topsoil and compost before seeding. If deep tilling is used, the basin shall be drained and the soils dried to a depth of 8 inches. If the basin was planted in turf grass and clogging again occurs after these restoration procedures have been used, the owner /operator shall replant with prairie style vegetation using the soil preparation method recommended by the native nursery in the area. 
   * During winter months, all draw down devices in the pond shall be opened to discourage infiltration of runoff water containing high levels of chlorides.   * During winter months, all draw down devices in the pond shall be opened to discourage infiltration of runoff water containing high levels of chlorides.
-  * Repairs must restore the pond to the approved plan design.+  * Repairs must restore the practice to the approved plan design.
  
 ===Bioretention Device=== ===Bioretention Device===
  
-  * Inspect quarterly to ensure proper function and check for any potential problems. If standing water is observed 24 hours after rainfall, the basin is clogged and must be restored according to the approved plan design.+  * Inspect quarterly to ensure proper function and check for any potential problems. If standing water is observed 24 hours after rainfall, the basin is failed and must be restored according to the approved plan design.
   * Maintain vegetation type specified in approved plan. Remove all other vegetation from device as needed.   * Maintain vegetation type specified in approved plan. Remove all other vegetation from device as needed.
   * Repair eroded areas as needed.   * Repair eroded areas as needed.
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   * Water plants as needed during first growing season and during dry periods after first growing season.   * Water plants as needed during first growing season and during dry periods after first growing season.
   * Treat diseased trees and shrubs as needed.   * Treat diseased trees and shrubs as needed.
-  * Do not be dump snow into device.+  * Do not dump snow into device.
   * Once a dense vegetation layer is formed, additional mulch does not need to be added.   * Once a dense vegetation layer is formed, additional mulch does not need to be added.
-  * Repairs must restore the pond to the approved plan design.+  * Repairs must restore the practice to the approved plan design.
  
 ===Permeable Pavement=== ===Permeable Pavement===
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     * Replenish the joint aggregate in accordance with industry recommendations.     * Replenish the joint aggregate in accordance with industry recommendations.
     * If necessary, remediate the system by extracting accumulated debris and aggregate from the joints using a vacuum and re-filling the joints with new aggregate.     * If necessary, remediate the system by extracting accumulated debris and aggregate from the joints using a vacuum and re-filling the joints with new aggregate.
-  * For permeable asphalt and concrete, repairs may be done with conventional impervious materials if the total impervious repair areas do not exceed 10% of the original permeable surface area and runoff from the repair areas will run on to adjacent permeable areas. The 10% threshold may only be exceeded if design calculations confirm that the system is still able to accept the full loading for which it was originally designed. +  * For permeable asphalt and concrete, repairs may be done with conventional impervious materials if the total impervious repair areas do not exceed 10% of the original permeable surface area. 
-  * The following activities shall be prohibited from occurring on the permeable pavement surface: temporary or permanent stockpiling of soil, snow or other material that can potentially cause or contribute to clogging; application of pavement seal-coating; application of sand for deicing.+  * The following activities shall be prohibited from occurring on the permeable pavement surface: 
 +    * Temporary or permanent stockpiling of soil, snow or other material that can potentially cause or contribute to clogging. 
 +    * Application of pavement seal-coating. 
 +    * Application of sand for deicing.
   * If the pavement surface infiltration rate is questionable at any time during the effective life of the pavement, the administering authority may require infiltration rate testing to verify that the surface infiltration rate is no lower than 10 in/hr. If the surface infiltration rate is lower than 10 in/hr, appropriate action shall be taken to restore the infiltration rate to an acceptable level based on the remaining effective life of the pavement.   * If the pavement surface infiltration rate is questionable at any time during the effective life of the pavement, the administering authority may require infiltration rate testing to verify that the surface infiltration rate is no lower than 10 in/hr. If the surface infiltration rate is lower than 10 in/hr, appropriate action shall be taken to restore the infiltration rate to an acceptable level based on the remaining effective life of the pavement.
   * If verification of in place pavement surface infiltration rates is necessary, conduct pavement surface infiltration rate testing per ASTM C1701, ASTM C1781, or other methods approved by the County.   * If verification of in place pavement surface infiltration rates is necessary, conduct pavement surface infiltration rate testing per ASTM C1701, ASTM C1781, or other methods approved by the County.
-  * Repairs must restore the component to the specifications of the approved plan.+  * Repairs must restore the practice to the approved plan design.
  
 ===Sorbent Inlet Filters=== ===Sorbent Inlet Filters===
  
-  * The Owner shall install and maintain a [insert oil control device called for per design], or equal, to mitigate sediment and/or oil and grease in stormwater runoff. +  * Maintain [insert oil control device called for per design], or equal, according to the manufacturer's guidelines. 
-  * Inlet filters shall be maintained per manufacturer guidelines. +  * Inspect inlet filters quarterly. Repair when the performance of a filter is compromised. 
-  * Inlet filters shall be inspected quarterly. Repair work needs to be done whenever the performance of a stormwater structure is compromised. +  * Replace inlet filters once a year and if the filter is damaged.
-  * Inlet filters shall be replaced once a year, or more frequently, if the filter is damaged. +
-  * Owner shall maintain records of inspections, cleaning and replacement of the device or components of the device.+
  
 ===Storm Sewer=== ===Storm Sewer===
  
-  * Visual inspection of components shall be performed and debris removed from inlets and storm sewer manholes. +  * Inspect storm sewer after rainfall and remove debris from inlets and outfalls 
-  * Repair inlet/outlet areas that are damaged or show signs or erosion. +  * Repair inlets and outfalls that are damaged or show signs of erosion. 
-  * Rip-rap shall be replaced as necessary. +  * Replace rip-rap as necessary. 
-  * Repairs must restore the component to the specifications of the approved plan.+  * Repairs must restore the system to the approved plan design.
  
-===Grassed Swale===+===Vegetated Swale===
  
-  * Inspect swales annually to detect and remedy nuisance conditions such as standing water or trash dumping. The swale shall be [specify design vegetation type]. Annual inspection should determine if vegetation is per plans (i.e., appropriate vegetation present, lack of weeds and woody growth), and if not, measures should be taken to establish appropriate vegetation.  +  * Inspect swales annually to detect and remedy nuisance conditions such as standing water or trash dumping. 
-  * Areas of swale showing signs of soil erosion should be repaired.  +  * Maintain vegetation type and height specified in approved plan. 
-  * Areas of swale with no vegetation shall be restored to good vegetated catch. +  * Repair areas of swale showing signs of erosion.  
-  * Limit off-street parking or other activities that may cause rutting or soil compaction in swales and repair as needed.  +  * Limit off-street parking or other activities that may cause rutting or soil compaction in swales. 
-  * Limit the use of pesticides and fertilizer if swale is used for water quality control.  +  * Limit the use of pesticides and fertilizer. 
-  * Maintain a height of [specify design height for vegetation] when mowing or cutting.  +  * Remove sediment when visible or if standing water exists for 24 hours after a rainfall/runoff event. After sediment removal, repair any damaged or eroded areas by filling with topsoil, reseeding and matting to reestablish vegetation.  
-  * Remove sediment when infiltration rates are impeded, sediment accumulation is visible, or if standing water exists for 48 hours after a rainfall/runoff event. Avoid compaction of the soil in the swale during the sediment removal process. After sediment removal, repair any damaged or eroded areas by filling with topsoil. [Remove compaction language, if swale does not provide infiltration]. Reseed as needed to reestablish vegetation.  +  * Repairs must restore the practice to the approved plan design.
-  * Repairs must restore the component to the specifications of the approved plan.+
  
 ===Infiltration Trench=== ===Infiltration Trench===
  
-  * Perform monthly physical inspections during the first year of operation, then annually.  +  * Inspect monthly during the first year of operation, then twice per year. The infiltration trench is considered failed if water is present in the observation well 72 hours after the last storm event and must be restored according to the approved plan design. 
-  * Accumulated material or debris on the surface of the infiltration trench shall be removed immediately when discovered.  +  * Remove accumulated material or debris on the surface of the trench and outlet regularly. 
-  * Snow shall not be placed in the effective infiltration area. It may be placed on the pretreatment area, if present. +  * Do not be dump snow into trench. 
-  * Any outlet structure, pipe or swale shall be cleaned of accumulated material or debris immediately when discovered, or at least twice each year.  +  * Repairs must restore the practice to the approved plan design.
-  * Water depth in the observation pipe shall be measured and recorded twice per year at 72 hours after a rainfall event of 0.5 inches or more during a 24-hour period. The infiltration trench will be considered failing if water is present 72 hours after the last storm event.  +
-  * Repairs must restore the component to the specifications of the approved plan.+
  
 ===Underground Infiltration Chamber=== ===Underground Infiltration Chamber===
  
-  * Perform monthly physical inspections during the first year of operation, then annually. +  * Inspect monthly during the first year of operation, then twice per year, in early spring and early fall. The infiltration chamber is considered failed if water is present 72 hours after the last storm event and must be restored according to the approved plan design. 
-  * Water depth in the chamber shall be measured and recorded twice per year 72 hours after a rainfall event of 0.5 inches or more during a 24-hour period. The infiltration trench will be considered failing if water is present 72 hours after the last storm event.  +  * Repairs must restore the practice to the approved plan design.
-  * Repairs must restore the component to the specifications of the approved plan.+
  
  
 ===Filtration Device=== ===Filtration Device===
  
-  * Proprietary filtration devices shall be installed and maintained in a manner consistent with laboratory testing and modeling assumptions used to predict effectiveness. This includes the following requirements: +  * Maintain [insert device name] according to the manufacturer's guidelines. 
-    * The device shall be installed in accordance with manufacturer recommendations. +  * Inspect filtration devices twice per year, in early spring and early fall.  Removal of sediment and debris shall be performed once 8 inches in depth or the volume exceeds 15% of the total storage volume. 
-    * the installed device shall be equipped with an internal or external bypass to divert flows in excess of the design treatment flow rate. + 
-  * Filtration devices shall be inspected semi-annually in early spring and early fall.  Cleaning of TSS and other debris shall be performed anytime the sediment in the unit reaches 8 inches in depth or the volume exceeds 15% of the total storage volume.+====Additional Forms==== 
 +{{ ::release_of_restriction.pdf |Release of Deed Restriction}}
  
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