Sheetflow Construction Erosion and Sediment Control

October 6, 2019

Construction Entrance Fail

This is a 30 + acre site with one access point, this one. If this was my project, I would have specified a tire wash with an asphalt exit to the street. The tire wash would have been long enough for two tire rotations, have high pressure, low volume nozzles located such that all tire surfaces were sprayed. This system would also have an on-board, treatment polymer injection system to keep the tire wash water relatively clean. I would have specified that the water be tested for turbidity daily, measured at 50 NTUs or less. Since the water is classified as “process water”, I would have required it to be tested for metals and other contaminants, then hauled to an appropriate disposal facility.
Photo: David Jenkins

October 4, 2019

Broken Waterline

Broken 16 inch waterline. Fortunately, all of the muddy water was contained in a 72″ storm pipe with a valve. Water was then pumped to a Chitosan-enhanced Sand Filtration (CESF) system for treatment to 5 NTUs for discharge to a creek. Knowing this project was going to be constructed over several winter seasons, we specified the CESF system in the contract.
Photo: David Jenkins

March 8, 2019

Curb Inlet Protection

According to the Minnesota Stormwater Manual:

“Inlet protection devices intercept and/or filter sediment before it can be transported from a site into the storm drain system and discharged into a lake, river, stream, wetland, or other waterbody.

These devices also keep sediment from filling or clogging storm drain pipes, ditches, and downgradient sediment traps or ponds.

Inlet protection may also include placement of a barrier to create a bypass of an inlet transferring flow downstream to a sediment trap, basin, or other inlet discharging to a non-critical area.”

Nothing wrong with sediment control BMPs, as they are necessary tools in an effective erosion and sediment control system.  However, these do not “filter” sediment. 

When properly installed, these allow for ponding of water which allows larger sediment to settle out, keeping it out of the storm system.  This is a good thing, but doesn’t necessarily prevent water quality non-compliance.   

I do like this statement in the manual : “Caution: To the extent feasible, erosion prevention practices such as stabilization are preferred to sediment control practices.”

In my world, where we have to meet a turbidity effluent limit of 25 NTUs, stabilization and stormwater management are the primary methods used to meet strict turbidity limits.  

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