BMP Permits and Inspections
MSD issues permits
for post-construction BMPs
Construction permits for all permitted post-construction BMPs must be obtained before beginning construction. Application for all permits, except aboveground BMPs, shall be made by a master drainlayer. (Please note that an aboveground BMP's underdrain permit shall also be applied for by a master drainlayer.) The MSD construction inspector shall be notified at least 24-hours in advance of beginning BMP construction.
In addition to conventional construction items, construction inspectors typically determine whether the BMP construction materials in the field match shop drawing submittals, check BMP feature dimensions (for example, ponding depth), and determine whether BMPs are adequately protected from construction sediment.
Phasing of BMP construction with other site work is critical to BMP performance. Many post-construction BMPs act like filters and are very sensitive to construction sediment. Often, the BMP has to be completely reconstructed if construction sediment clogs the filter.
The performance of infiltration BMPs is also very sensitive to soil compaction and excavation technique; equipment that compacts or "seals" the soil subgrade can greatly reduce infiltration rates. When infiltration is required, equipment (like tracked excavators and buckets with teeth) that reduce compaction and loosen, till, or "rip" the soil subgrade is recommended.
In many cases where BMPs are constructed before construction activities are complete, MSD requires that BMPs be kept "off-line" until the drainage area to the BMP is stable. This means that stormwater flow should be diverted from the BMP until the final vegetative and/or hardscape cover is established. The determination of when the BMP can be brought on-line will be made by a MSD inspector.