SEDIMENT FILTER BAG DEMONSTRATION A SUCCESS
Todd Giddings, Ph.D., P.G.
Sediment filter bags have been widely used on small bridge construction jobs where there is no space available to construct a sedimentation basin. Muddy, sediment-laden water is pumped from the bridge pier excavations and is discharged into a sediment filter bag where almost all of the suspended sediment is contained. The almost sediment-free water discharges through the walls of the bag and flows into the stream. This relatively new technique of sediment control seemed like it could be very useful in meeting the sediment control requirements for well construction, so I asked Frank Roberts & Sons, Inc. of Punxsutawney to send a small size filter bag to demonstrate at the Field Conference. All we had to do was slip the spout of the filter bag over the end of the diverter pipe to have instant sediment containment and control.
The small size filter bag was made of non-woven geotextile fabric that looked like heavy felt cloth, measured 6 ¼ feet wide by 15 feet long, and was rated for an initial water flow rate of 800 gallons per minute. I asked for help fastening the spout of the bag onto the diverter discharge pipe, and several people refused. “The filter bag will blow up and burst, injuring the spectators” they said. “This rig has 1050 cubic feet per minute of air, and the air flow will cause the bag to whip around and knock down spectators” another person said. I insisted the bag would work, and we fastened the spout onto the discharge pipe with a ratchet strap. All the skeptics stood way back, or crouched behind the rig, and the drilling began. What a surprise, as the bag slowly inflated and contained all the cuttings, and didn’t burst or flap around. Cloudy water seeped gently from the bag and flowed toward the nearby pond. The skeptics had forgotten that air permeability is always greater that water permeability, and this bag was rated for 800 gpm of initial water flow. As the bottom of the filter bag filled up with cuttings, the water seeped through the bag higher up on the sides.
We were drilling in shale, and the hammer drill bit created the usual
size chips, along with sand, silt, and clay size particles.
Some of the silt and clay was of natural origin from within the fractures
and bedding planes of the shale bedrock. Even the surges of water and the blasts of air when the rods
were changed didn’t affect the filter bag.
The water seeping from the filter bag was muddy in appearance, but
contained only clay size particles. If
you were located right on the bank of a small stream classified as high-quality
or extreme-value, then you would have to take additional steps before
discharging the muddy-looking water into the stream channel.
Remember, every receiving stream and discharge location has different discharge requirements, which is why you should discuss the location with the Conservation District first, before you begin drilling. The small size sediment filter bag costs less than $80, and double and quadruple sizes are available. The day after the demonstration, the Funks Drilling crew used a fork-lift to pick up the filter bag and carry it away. No, the bag didn’t split or burst when lifted, and the field grass beneath had so little fine sediment on it that a rainstorm would erase all signs the filter bag had ever been there. So another advantage of using a filter bag is when site cleanup has to be done to ‘house-lawn clean’ standards. Other erosion and sediment control measures are presented in the DEP two-page E&SC fact sheet titled Erosion and Sediment Control Best Management Practices For Water Well Drilling and Aquifer Testing. To read this Fact Sheet on this Web site or to print a copy of it, click here.
You can order a sediment filter bag from Frank Roberts & Sons, Inc. by calling 800-262-8955.
Here is an example of how well sediment filter bags work when you have to control sediment and muddy water right next to a trout stream.
This sediment filter bag is in use right next to Spring Creek (the creek is only 20 feet from the bag) in Centre County. This section of Spring Creek is known as "Fisherman's Paradise" and you must release all trout caught here. This stream is a high quality, cold-water fishery rated stream and hence sediment control here is very critical. This method of containing and treating the muddy water being pumped into this sediment filter bag was approved by the Fish and Boat Commission.