INDUSTRIAL STORMWATER

DISCHARGE SAMPLING

If your industrial operations include stormwater runoff, then the National Pollutant Discharge Elimination System (NPDES) Permitting Program is one of your concerns. If you need to obtain a permit to discharge storm water, part of that permit application includes collecting and analyzing outflow samples, under fairly demanding meteorological conditions. The Skywatch Weather Center can help you satisfy these requirements.

Valid outflow runoff sampling requires:

• a grab sample taken during the first 30 minutes of discharge due to the storm event

• a flow-weighted composite sample taken during the entire event or during the first 3 hours of the event

• the storm event must produce greater than 0.10 inches of precipitation

• there must be at least 72 hours of dry weather since the last storm event

• the variance in duration of the event should not exceed 50% from the average or median storm event in the area*

• the variance in total rainfall of the event should not exceed 50% from the average or median storm event in the area*

The documentation of the storm event requires several items of information, some of which must be recorded on site, and some of which require access to meteorological information on a continuous basis for your area. These data include:

• date of the storm event

• duration of the storm

• total rainfall recorded during the storm event

• number of hours since the previous measurable storm event

• the maximum outfall flow rate during the storm event

• the season

• the form of the precipitation (rainfall or snowmelt)

Even if your company is capable of gathering and analyzing the samples, it can be a time-consuming job to track the weather in order to know when enough dry weather has occurred, when the rain is going to start, and to document the average or median storm event statistics for the area. There may be rain in your area, but you end up with a sampling crew sitting on their hands for several hours, waiting for it to start. Worse yet, the rain never hits your little corner of the world, you've wasted a whole shift, and you've got to crank up the troops to do it again at the next threat of rain.

The Skywatch Weather Center is ready to help you. Once you hire us, we track the weather for your location until we identify a storm event which will satisfy the sampling requirements. You get notified in enough time to set up for sampling, with details on the storm's onset and expected duration updated until you get the desired sample. We also provide documentation on the normal statistics for your area, based upon data from National Weather Service sites in the vicinity.

All of these features are available for a fixed rate, based solely on the number of valid samples and outflow locations you need to characterize. Whether we have to monitor the weather for a week or a month to get you that sample, it still only costs you that fixed fee. Discounts are available for:

• multiple sampling points at a facility,

• covering all corporate activity nationwide,

• quarterly sampling scheduled on a year to year basis.

For further information, and to discuss your specific situation, call our Sales Department at 1-888-818-7250.

*If feasible. Some sites have such light rainfall events that it might not be possible to get 0.10 inches of precipitation in a 3 hour period. In another location, the precipitation during a particular season may be so sporadic that the only episode during the season must be used, even though it doesn't meet the "should not exceed 50% from average or median rainfall" criteria.

For more information on the regulations, check out the EPA Headquarters website.

A comprehensive presentation of the standard is available at the EPA Region 6 website.

The Federal Register listing of the Phase 2 regulations is available at 64 Fed. Reg. 68722.

For more information contact our webmaster or call us at 1-800-SKYWATCH  1-800-759-9282

Copyright © 2007, Air Science Consultants, Inc.