What's in your bag?

Over the last few years I have become aware that most people feel that a sand bag is a sand bag, is a sand bag. But there is a difference, especially if we are talking about compliance with the NPDES permit and specifically using the right type of bag for the job.

Sand Bags, i.e. bags filled with "sand", have a specific, and limited application to either become part of a dam or to divert storm water around a working area (run-on control).

Gravel Bags, specifically bags filled with birds eye (5/16") gravel, are the bag of choice in most jurisdictions because they allow water to slow down as it passes through and therefor allows the sediment to drop out (settle) behind the bag. The advantage is that it reduces the amount storm water de-watering required, as it allows water passing out of the site to be sediment free.

Rock Bags, typically 3/4" Rock is specified and often required by jurisdictions with especially fine silts which might clog regular gravel bags and therefor become ineffective except as a dam.

So, why is the wrong bag in the wrong application on the job, it isn't cost, because the pricing is usually the same, or relatively close, no, the reason is a lack of understanding, either by the inspector, the contractor or both. Do the bag suppliers know the difference? They should, or you may as well use dirt bags...Oh, that's right, some people still do.