This silt fence looks pretty ugly and inspection shows it certainly needs maintenance; but does it? The silt fence made sense before we excavated several feet, now it doesn’t. There is a turbidity curtain in the river to the right and the contractor is careful to pull material back from the riverbank. I am going to let this go.
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This is the first project we have cut asphalt to allow construction stormwater to infiltrate. The area is paved, flat. The sweeper runs constantly but the water is still too turbid to go down the drain. The fill soil under the asphalt is sandy. If we just covered the catch basin with 30 Mil PVC, the area would just flood, then drain to another catch basin. Solution? Cut out a section of asphalt full depth to the sandy soil, fill with 3 to 5 inch rock. This way the water infiltrates but vehicles can drive over the hole. This is working really well so we will be doing this on future container dock upgrade projects.
Video: Kitsap SunThis was a 2 inch in 24 hour storm, or about a 2 year storm event, which should have been pretty easily contained if the pond had been designed as a temporary sediment pond for use during construction. Also, they should have had a construction stormwater treatment system set up to treat for turbidity. There really is no excuse for this. Poor planning.
I was just minding my own business last Friday, driving from Fred Meyer to the UPS store and passed this project. I told my wife I have to get a photo; she says okay since she knows me and my habit of stopping to take TESC photos.
I made a u -turn at the Wal Mart, drove back a block and stopped in the middle of the street to get this shot.
There is so much wrong here, where do I start? Clearly, dirt is tracked off of the project in the background, as you can see the sediment build up in the curb line. Someone told someone to put something in the swale to keep dirt out, then someone else installed this silt fence.
First off, silt fence needs to be trenched in and this just has a few rocks placed on the flap.
Second, they probably couldn’t trench this in anyway without tearing up the drainage swale.
Third, only two of the three curb cuts are backed by the silt fence.
Fourth, silt fence is a barrier, not a filter, and with the volume of water draining off the asphalt during a rain event, dirty water would just blow around and under the silt fence.
Conclusion, silt fence is never used in a water flow situation; it is only to contain eroded sediment from a sloped area. A better BMP here is a compost berm or something similar that would allow some water to pass but filter some sediment. Sand bags would work to keep everything out of the swale but then the dirty water would bypass to the next catch basin, which probably has a catch basin insert, which would collect sand and such but would not do anything for turbidity. So, what is the best BMP? Stop the !@#$ ing trackout in the first place!
We rarely use silt fence on smaller airfield projects because: the work areas are nearly flat, are surrounded by grass or pavement, the work takes a few months, usually in the summer or fall. Compost berms are frequently used to: contain water, divert water, prevent site runoff. A secondary benefit is filtration; there is some turbidity reduction. Lastly, when done,. we spread the compost out over the disturbed soil and hydroseed it, enhancing grass growth and eliminating the waste of land-filling silt fence.
Thousands of gallons of clean rainwater draining off the roof deck onto bare soil turning into thousands of gallons of water that’s too dirty to discharge without treatment. With pre-planning, a temporary collection system could have been developed and installed to contain, collect and convey the clean water to an existing drainage system. Without such a system, the dirty water had to be treated chemically to reduce the turbidity enough to discharge to the storm system.
My construction erosion inspection turned up a turbid discharge. A little bit of sediment track out each day builds up. The contractor was vacuum sweeping this area on a regular basis but the first rain shows how effective that was. I measured this discharge at 6000 nephelometric turbidity units (NTUs) using an old Hach 2100P turbidimeter. This meter only reads up to 1000 NTUs, so I had to dilute the sample 3 times to determine the actual reading.
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.
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.
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