Sheetflow Construction Erosion and Sediment Control

October 29, 2019

Open Catch Basin Open Again

Filed under: Photo — Tags: , , , , , , — Sheetflow @ 4:55 am
Why, this was flooded yesterday, what happened? Photo: David Jenkins

The saga continues… the next inspection looked like the first inspection. 500 + NTU water draining into the catch basin. What happened?

30 mil PVC punctured to let water drain. Photo: David Jenkins

As suspected, someone didn’t like the flooding, so they punctured the 30 mil PVC. I am wondering why the contractor erosion control lead is not finding this.

October 28, 2019

Open Catch Basin Fixed?

Filed under: Photo — Tags: , , , , , , — Sheetflow @ 4:55 am
Catch Basin Blocked with 30 mil PVC Photo: David Jenkins

I inspected the open catch basin the next day, and this is what the contractor had done to keep turbid water out. I have nothing against doing this, but, since this does keep water out, flooding ensues. Flooding is okay if the catch basin is in a low spot and no one needs to work in the area.

I told the contractor that they might want to look at the storm system and see if there is a point where they can install a concrete plug temporarily and use the system for conveying the turbid water to their treatment system.

October 27, 2019

Open Catch Basin

Filed under: Photo — Tags: , , , , — Sheetflow @ 6:56 pm

I found this open catch basin during a construction erosion inspection. The turbidity of the water draining into it from the stockpile measured at over 600 NTUs. Note that there is an insert in the catch basin; these do nothing to reduce turbidity. I notified the contractor who should have found this in their daily inspections, which I pointed out to them.

October 21, 2019

“Means and Methods” vs. Best Management Practices

Demolition of landside crane rail on a shipping container terminal.

In my experience, managing contractor “means and methods” is more important than using the “right” best management practices. When turbidity is the standard for measuring water quality compliance, as in Washington state, site cleanliness is the key to prevention and compliance.

This contract requires that catch basin inserts be installed in all catch basins within the project boundaries. However, inserts are not at all effective in reducing turbidity in runoff. While removing the crane rail on this container terminal project, the contractor could clean up as the work progresses, place all material removed from the trench onto plastic for later removal, load into a Bobcat bucket, and pick up small debris with a shop vac. I can require these things in the contract that the contractor bids. It may cost extra; the extra cost may be worth it if it reduces my risk. If I tell the contractor after the contract is awarded, I will pay more.

I can also make suggestions during the work, pointing out that keeping things really clean will keep them in compliance with their NPDES permit. If framed in a way that shows benefit to the contractor, meaning reducing risk and cost, they will probably follow the suggestion.

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

September 17, 2019

Can’t Get Away From It

It doesn’t matter where I go, I always see some type of construction erosion issue. I went to visit relatives in Portland, Maine, flying in and out of Boston Logan International. In the terminal, waiting for my flight back home, I saw a construction project on the ramp; it had rained a few says before, hard. Obviously, the stockpile had not been covered before the storm and sediment washed off the pile into the drain.

I work at an airport that operates under strict turbidity effluent limits; here is how we do this kind of work:

(1) rarely do we allow stockpiles on the ramp because we rarely reuse the excavated material (it is either contaminated, unsuitable or doesn’t meet current FAA requirements); it is direct loaded into trucks and hauled off. When we do stockpile, we place dirt on plastic and cover it with plastic, using lots of sand bags to secure it from jet blast and wind.

(2) work areas are always isolated so there is no runoff from the site. Normally, we use four-inch extruded asphalt curbing along the base of the jersey barriers. Rolled hot mix asphalt (HMA) is used at the entrance point so water is contained but vehicles can access the site.  Water that builds up inside the curbing is pumped back into the excavation if clean, or a tank if contaminated.

I should have mentioned that we also have strict sediment trackout requirements: no visible sediment leaves the site at any time.  This is both because of the effluent limits and for safety reasons; dirt and debris that gets sucked up into a jet engine is damaging and possibly deadly.

Lastly, I am not casting aspersions on the folks at Logan; I don’t know their situation, permits, drainage system, or tolerance for risk.  Because of my situation, I have low risk tolerance for potential non-compliance with our permit and I notice when something would cause me grief at my airport.

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.  

January 14, 2019

Bonded Fiber Matrix BFM Needs to Cure Before it Rains

Bonded fiber matrix (BFM) needs to dry for 24 to 36 hours before it rains or else it can start to wash off.

February 25, 2011

Construction Stormwater General Permit

Construction Stormwater General Permit

Construction site operators are required to be covered by a Construction Stormwater General Permit if they are engaged in clearing, grading, and excavating activities that disturb one or more acres and discharge stormwater to surface waters of the state. Smaller sites may also require coverage if they are part of a larger common plan of development that will ultimately disturb one acre or more. Operators of regulated construction sites are required to:

  • Develop stormwater pollution prevention plans.
  • Implement sediment, erosion, and pollution prevention control measures.
  • Obtain coverage under this permit.

NEW! - 01/29/09 Ecology issues the Construction Stormwater General Permit December 1, 2010

WebDMRs and PARIS

Contact Us – Contact your Permit Administrator for permit assistance or your Regional Office for site specific questions.

Permit, Forms and Application – Permit, application, forms, and appeal information.

High Turbidity Reporting – Construction projects must report high stormwater turbidity results within 24 hours.  If you get a high result, call your Ecology regional office.

Resources and Guidance – DMRs, Stormwater monitoring,  manuals, 303(d) list information.

CESCL Training and Certification Programs

Historical Information – Pollution Control Hearing Board information, public comments.

Construction Stormwater General Permit.

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