Sheet Flow Construction Erosion Control

January 26, 2022

Measuring Turbidity

This is how you’re supposed to prepare and sample for turbidity. This is not how I have ever done it.

June 30, 2020

Sand Bag Berm Around Catch Basin

Photo: David Jenkins

You can’t get a good seal with a sand bag berm. Dirty water down the drain.

May 7, 2020

Turbidity 1-25-250 NTUs

Photo: David Jenkins

The sample on the left is just under 1 NTU, the middle is 25 NTUs, and the one on the right is 250 NTUs. In Washington state, the Construction Storm Water General NPDES Permit lists benchmarks that construction discharges must meet. These are: 0-25 NTUs everything is cool; 26 -249 NTUs not so good, upgrade your site best management practices (BMPs) and modify your SWPPP; 250 NTUs and above, call the Dept. of Ecology, upgrade BMPs, modify the SWPPP and monitor the water body that the project discharges to until you are in compliance.

April 17, 2020

Construction Inspection-Container Crane Rail Removal

Photo: David Jenkins

We are upgrading the dock to handle larger container ships so, the old cranes, and rails that they travel on must be removed. This is at the end of the “water-side” crane rail. This trench, or slot, is several hundred feet long. When it rains, it will fill with rainwater and overflow into the bay.

The trench is filled with dirt and concrete debris left over from the demolition and removal of the old rail, so the water will be turbid and have elevated pH. I told the contractor to block the end of the trench before it rains again, using cold patch asphalt or some other method of their choosing.

Because construction erosion and sediment control is about managing rainwater, I always look for ways water can discharge from a project. This is not something that would have been caught in the planning stage of the project.

April 7, 2020

Silt Fence Water Bars Fail

Photo: David Jenkins

Whenever I see something like this, it makes me think that the site owner/contractor either didn’t know what they were doing or bit off more project than they could chew, or both. These guys cleared, grubbed and graded something over 80 acres starting in late summer, failed to phase the work, failed to use soil cover practices, failed to listen to the experts and got nailed by the fall rains.

Erosion control is really about water control: reducing volume, preventing it from becoming turbid, and controlling where it goes. By the time the rains hit this project, there was too much water, it was too dirty, and there were too few options for controlling where it went.

In addition, they refused to set up a chitosan-enhanced sand filtration system to treat and discharge water; this left them no options and too much turbid water that had nowhere to go. As a result, they hammered a wetland, were fined heavily, and were shut down for months.

Silt fences are not meant to control water, convey water, filter water; they are designed to control eroded sediment. Ditches, berms (rock, gravel, triangular silt dikes, etc.) would have been better choices at this location. Not opening up so much area so late in the season would have been the best option. Their means and methods did not save them time or money.

April 1, 2020

Compost Berm

Photo: David Jenkins

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.

March 26, 2020

Roof Drains and Bare Soil

Photo: David Jenkins

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.

October 29, 2019

Open Catch Basin Open Again

Photo: David Jenkins

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

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?

Photo: David Jenkins

I inspected the open catch basin the next day to see if it was fixed, 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

Photo: David Jenkins

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.

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