Recommendations for structural BMP use in settings with shallow soils and shallow depth to bedrock.
Link to this table
| BMP |
Shallow soil and shallow depth to bedrock considerations |
| Bioretention |
Should be constructed with an underdrain or liner if minimum separation distance of three (3) feet is not present between practice bottom and bedrock.1 |
| Media filter |
- Recommended practice in areas of shallow bedrock and soil
- Can be located in bedrock, but will be expensive due to blasting
|
| Vegetative filter |
- Recommended practice in areas of shallow bedrock and soil.
- Dry swales with engineered soil media will need an underdrain if minimum separation distance of three (3) feet is not present between bottom of practice and bedrock
|
| Infiltration trench or basin |
- Will be limited due to minimum separation requirement. Surface area to depth ratios of practices may need to be larger. Arch pipe and other perforated storage "vault" practices can help increase treatment volumes within limited spaces.
- If used, should have supporting geotechnical investigations and calculations
- Use with PSHs should be carefully considered. Pre-treatment should be extensive to limit risk of groundwater contamination if groundwater is close to the land surface.
- Local review authority should be consulted for approval
|
| Stormwater ponds |
- Will have depth limitation to consider, making surface areas larger for a given storage volume.
- Shallower depths may be undesirable from an aesthetic standpoint, particularly if wide fluctuations in water level are expected.
- Bedrock should act like a liner and help to maintain a permanent pool, unless fracture zone is present
|
| Constructed wetlands |
- Applied more easily than ponds, but will also require larger surface area to drainage area ratios.
- Bedrock should act like a liner and help to maintain a permanent pool, unless fracture zone is present
|
1A liner is required under the Construction Stormwater General Permit.
