Iowa

Iowa Department of Natural Resources
Stormwater Program
Wallace State Office Building
502 E. 9th Street
Des Moines, IA 50319-0034

NPDES General Permit #1 for Stormwater Discharge Associated with Industrial Activity: effective 10/1/12 thru 10/1/17.

12. SAMPLE TYPE

TYPE For discharges from holding ponds or other impoundments with a retention period greater than 24 hours, (estimated by dividing the volume of the detention pond by the discharge rate) a minimum of one grab sample may be taken. For all other discharges, data shall be reported for both a grab sample and a composite sample. All samples shall be collected from a discharge resulting from a storm event that is greater than 0.1 inches in magnitude and that occurs at least 72 hours from the previously measurable (greater than 0.1 inch rainfall) storm event. The grab sample shall be taken during the first hour of the discharge. The composite sample shall either be flow-weighted or time- weighted. Composite samples may be taken with a continuous sampler or as a combination of a minimum of three sample aliquots taken in each hour of discharge for the entire discharge or for the first three hours of the discharge, with eachaliquot being separated by a minimum period of fifteen minutes. Only grab samples may be collected and analyzed for the determination of pH, temperature, cyanide, total phenols, residual chlorine, fecal coliform, fecal streptococcus, and oil and grease.

Magnitude: 0.1 inch or greater

Interval Between Storms: at least 72 hours

NPDES General Permit #3 for Stormwater Discharge Associated with Industrial Activity for Asphalt Plants, Concrete Batch Plants, Rock Crushing Plants, and Construction Sand and Gravel Facilities: effective 10/1/2012 thru 10/1/17

C. SAMPLE TYPE

A minimum of one grab sample shall be taken. All such samples shall be collected from the discharge resulting from a storm event that is greater than 0.1 inches in magnitude and that occurs at least 72 hours from the previously measurable (greater than 0.1 inch rainfall) storm event. The required 72-hour storm event interval is waived where the preceding measurable storm event did not result in a measurable discharge from the site. The required 72-hour storm event interval may also be waived where the permittee documents that less than a 72-hour interval is representative for local storm events during the season when sampling is being conducted. The grab sample shall be taken during the first 30 minutes of the discharge. If the collection of a grab sample during the first 30 minutes is impracticable, a grab sample can be taken during the first hour of discharge, and the discharger shall submit with the monitoring report a description of why a grab sample during the first 30 minutes was impracticable. If storm water discharges associated with industrial activity commingle with process or non- process water, then where practicable, permittees must attempt to sample the storm water discharge before it mixes with the non-storm water discharge.

Magnitude: 0.1 inch or greater

Interval Between Storms: at least 72 hours

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