Decision process for selecting liners

Design process for selecting the appropriate liner level.
Link to this table

Condition	Design level	Note
Filtration BMP with less than 3 feet of separation to seasonal saturated soil or bedrock	1	Required under the Construction Stormwater permit
BMP in confirmed potential stormwater hotspot with high or very high groundwater pollution potential or areas where infiltrating water will mobilize contaminants in soil or groundwater	1	Applies to all post-construction BMPs. See section on Potential stormwater hotspots for more information
Constructed ponds with less than 3 feet separation from seasonally high water table in a potential hotspot	1
Constructed wet ponds underlain by soils with an infiltration rate of 0.3 inches per hour or greater (HSG A or B soils)(see [1] or [2])	1	To maintain a permanent pool
Karst terrain with high or very high groundwater pollution potential1	1	See section on karst for more information
Prevent groundwater intrusion into a BMP requiring aerobic conditions, such as iron-enhanced media	1
Maintain permanent pool in constructed ponds or constructed wetlands in areas underlain by geologic material that is fractured or has a high infiltration rate	2
Separation distance from a BMP cannot be achieved	2
Separate tree BMP from road, parking lot, sidewalk or adjacent walls or building foundation	2	To prevent tree root intrusion. See link

¹ Groundwater pollution potential is determined based on hydrogeologic conditions, which are used to estimate the time of travel for water and conservative chemicals to pass through the soil and vadose zone and into groundwater.