Jesse -

The drainage areas were usually 1-2 acres for those basins, wi th some fluctuations as grading

p rogressed.

There are a number of reason s that the turbidity was not as well c ontrolled on that site as has been the case for subsequent projects. Firs t, we had just co mpleted a series of tests under controlled conditions using the PAM logs and found great success, so we cont inued working with them for the most part. As we learned over time, they are not as "robust" as the more successf ul powder on wattle system we now

p romote. They tend to harden and become insol uble when exposed to sun and drying conditions, and often they get coated in sediment and debris.

Second, as we also now know, without good cooperation fr om the contractors, there is little hope in achieving good turbidity control. In that situation, with miles of construction underway, this was quite evident in the behavior of differ ent contractors we encountered on di fferent sections. Sometimes they would bend over backwards to make adjustments in th e plans to accommodate our systems, but mostly they ignored or even thwarted our efforts (not intentionally - they we re just doing what they had always done or had to do to build the road). On this site , as with most we've been on, contractor cooperation was voluntary and usually deadlines and progres s were more important than our project.

And finally, since this site was about 3 hours away, it was not unusual for major "insults" to anything we set up to occur prior to storm events without our knowin g , reducin g or eliminatin g an y effects of our Re: question on I-485 project Rich McLaughlin

to: Jesse Pritts 06/16/2011 01:32 PM Cc: 'Melanie McCaleb', Scott King, "Jamie_Sta nsell@Ncsu. Edu" Hide Details From: Rich McLaughlin <sscram@ncsu.edu>

To: Jesse Pritts/DC/USEPA/US@EPA

Cc: 'Melanie McCaleb' <melanie.mccaleb@g mail.com>, Scott King <seking3@ncsu.edu>, "Jamie_Stansell@Ncsu. Edu" <jamie_stansell@ncsu.edu>

Please respond to rich_mclaughlin@ncsu.edu

History: This message has been replied to and forwarded. Page 1 of 3

9/12/2011 file://C:\Documents and Settin g s\ jp ritts\Local Settin g s\Tem p \notes87944B\~web0900.htmsystems. One of our most successful basins had great results while everything we installed remained intact, but as the grading operation took out parts of it (ditches, forebay, eventually even the skimmer outlet) the performance declined.

As a result of our experience on that and many other si tes, one of the key elements we emphasize in our training is maintaining control over the drainage system , because it is where most turbidity control will occur using PTS. This means that somebody has to have authority to quickly repa ir or replace areas that are impacted. If a utility line excavation cuts thr ough a diversion ditch, that runoff needs to be directed into another treatment ditch. If a road cut divert s water from a treatment ditch, treatment has to be installed in the road or storm drain system. These are not difficult or particularly expensive to use, but it is a different way of thinking as you can no longer assume that as long as the runoff hits a silt fence or sediment basin, you are in compli ance. Unless you are collecting al l the water and using an active treatment system, which might be preferable to some develope rs or in some circumstances.

Overall, the more control we have over the drainage system the better our results. The mountain road

p roject was a good example because all the drainage was captured in a single ditch, so the PTS functioned almost pe rfectly throughout the monitoring period. Perhaps we could install and monitor PTS on the next EPA building project to show how well it works!

I hope this helps. Let me k now if you need more details.

Rich

On 6/15/11 4:47 PM, Pritts.Jesse@epamail.epa.gov wrote:

Hi RichI have a couple of follow-up questions on this site and the data you collected. First, do you know generally what the drainage area of the
basins were? I don't need the exact number for each of the six basins using PAM, but a general sense would be helpful. Second, in general the performance of the basins w/ PAM in terms of effluent turbidity was much lower (meaning higher turbidity in the treated discharge) than the other sites you've looked at. Can you offer any insights into the reasons why performance was generally not as good as the other sites evaluated? Is it just that this site was larger, with more intensive earthwork and/or more intense or larger storms, or was there some differences in the technologies employed at this site that gave poorer performance? Or, would you characterize the performance of the basins w/ PAM as being good, and is the higher effluent turbidity just a reflection of the capabilities of the technology? Any perspective you can offer would be helpful.

ThanksJesse

Jesse W. Pritts, P.E. U. S. Environmental Protection Agency
Office of Water 1200 Pennsylvania Ave. NW (4303T) Washington, DC 20460
tel 202-566-1038
fax 202-566-1053 Page 2 of 3

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-- Richard A. McLaughlin, Ph.D. Professor/Extension Specialist Soil Science Department North Carolina State University
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