Montana Department of Environmental Quality
Water Protection Bureau
Water Quality Discharge Permit Section
1520 E 6th Avenue
PO Box 200901
Helena, MT 59620-0901


General Permit for Storm Water Discharges Associated with Industrial Activity, effective 10/1/06 thru 9/30/11

 4. Sample Type

For all discharges, sampling data shall be obtained by collecting a grab sample.  The grab sample shall be taken during the first thirty minutes of the discharge. If the collection of a grab sample during the first thirty minutes is impracticable, a sample can be taken during the first hour of the discharge, and the discharger shall submit attached to the Department Discharge Monitoring Report form a description of why a grab sample during the first thirty (30) minutes was impracticable.  A composite sample may be required by the Department on a site-by-site basis. If required, composite samples shall either be flow-weighted or time-weighted. Potential composite samples may be taken with a continuous sampler or as a combination of a minimum of three grab sample aliquots taken in each hour of discharge for the entire discharge or for the first three hours of the discharge, with each aliquot being separated by a minimum period of fifteen (15) minutes.


Magnitude: creates discharge

Interval Between Storms: n/a



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