The down side to using sandbags is that you can’t get a good seal and they leak. The idea behind this is that water ponds and some of the sediment settles out. With the leakage, little settling can occur. The catch basin insert will catch some of the sediment but since we are regulated on turbidity in Washington, neither BMP cuts turbidity low enough to meet the compliance standard. Our contract specifications require that discharges not exceed 25 Nephelometric Turbidity Units (NTUs).
The contractor had to connect a new storm system from up the hill into an existing catch basin in the foreground. After they completed the connection but before paving, they covered the pipe run with plastic and sand bags to protect from dirty water entering the catch basin. Work was completed during dry summer weather. Paving took place a couple of months later.
As of two days ago, there is new 30 mil PVC under the catch basin grate and turbid water is not draining into the catch basin. The contractor told their staff not to puncture the PVC. No word on whether they are thinking more proactively about this. The best measure is to keep the stockpile covered and the area cleaned up. We shall see what’s next.
The saga continues… the next inspection looked like the first inspection. 500 + NTU water draining into the catch basin. What happened?
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.
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.
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.
Then the sediment washing off of the uncovered stockpile drains into a catch basin which drains into a small salmon stream.
When inspecting a project, I always look closely at the storm drain system to verify whether any dirty water from the project will drain to an active system. In this example, the catch basin has been installed but the main line it is connected to is not active.
Powered by WordPress
