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Specifications are provided for different levels of liners. Although specifications for clay liners are included with Levels 1 and 2, clay liners are generally not recommended.
 
Specifications are provided for different levels of liners. Although specifications for clay liners are included with Levels 1 and 2, clay liners are generally not recommended.
 
*Level 1 liner - for sites with high potential for groundwater contamination
 
*Level 1 liner - for sites with high potential for groundwater contamination
**HDPE liner criteria:
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**HDPE (high density polyethylene) liner criteria:
 
***Minimum thickness shall be 60 mils.
 
***Minimum thickness shall be 60 mils.
 
***Design according to the criteria in Table 3 of the [http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_026465.pdf NRCS 313, Waste Storage Facility technical standard].
 
***Design according to the criteria in Table 3 of the [http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_026465.pdf NRCS 313, Waste Storage Facility technical standard].

Revision as of 15:12, 2 December 2015

Liners are designed to limit infiltration of water from a stormwater Best Management Practice (BMP) into underlying and adjacent soil.

Conditions where liners are required

Under the Construction Stormwater General Permit:

  • The Permittee(s) must ensure filtration systems with less than three (3) feet of separation from seasonally saturated soils or from bedrock are constructed with an impermeable liner.
  • The SWPPP must identify additional or different measures necessary (e.g. impervious liner in pond bottom) to assure compliance with surface and groundwater standards in Minn. R. chs. 7050 and 7060 in karst areas and to ensure protection of drinking water supply management areas (see Minn. R. 4720.5100, subp. 13).

Although this second bullet does not specifically require a liner, a liner represents on method of complying with the permit requirement.

Certain sectors covered under an Industrial Stormwater Permit are required to have liners for ponds constructed after April 5, 2010.

Conditions where liners are recommended

Liners are recommended for the following conditions.

  • Circumstances where a permanent pool is needed but difficult to maintain due to site conditions. Examples include constructed wet detention ponds or constructed wetlands requiring a permanent pool and underlain by areas with Hydrologic Soil Group A soils, gravel, or fractured bedrock
  • Permeable pavement designs in compacted fill soils.
  • Areas where seepage from a BMP into the groundwater would otherwise occur but should be avoided due to risk of groundwater contamination. These include
  • Locations where recommended horizontal or vertical separation distances cannot be achieved
  • Use impermeable liner as needed to separate tree BMPs from road, parking lot, sidewalk or adjacent walls or building foundation

Liner specifications

Specifications are provided for different levels of liners. Although specifications for clay liners are included with Levels 1 and 2, clay liners are generally not recommended.

  • Level 1 liner - for sites with high potential for groundwater contamination
  • Level 2 liner - for sites with low groundwater pollution potential
  • Liners for facilities covered by an Industrial Stormwater Permit and where ponds are allowed with a constructed liner

Decision process for selecting liner level

The following table summarizes the process for selecting a liner.