Sheetflow Erosion and Sediment Control

June 30, 2020

Sand Bag Berm Around Catch Basin

Photo: David Jenkins

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).

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

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?

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

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.

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