ANNUAL AVERAGE FLOW
The arithmetic average of all daily flow determinations taken within the preceding 12 consecutive calendar months. The annual average flow determination shall consist of daily flow volume determinations made by a totalizing meter, charted on a chart recorder and limited to major domestic wastewater discharge facilities with a 1 million gallons per day or greater permitted flow.

DAILY AVERAGE FLOW
The arithmetic average of all determinations of the daily discharge within a period of one calendar month. The daily average flow determination shall consist of determinations made on at least four separate days. If instantaneous measurements are used to determine the daily discharge, the determination shall be the arithmetic average of all instantaneous measurements taken during that month. Daily average flow determination for intermittent discharges shall consist of a minimum of three flow determinations on days of discharge.

DAILY MAXIMUM FLOW
The highest total flow for any 24-hour period in a calendar month.

INSTANTANEOUS FLOW
The measured flow during the minimum time required to interpret the flow measuring device.
2-HOUR PEAK FLOW Applies to domestic wastewater treatment plants: The maximum flow sustained for a two-hour period during the period of daily discharge. Multiple measurements of instantaneous maximum flow within a two hour period may be compared to the permitted 2-hour peak flow.

MAXIMUM 2-HOUR PEAK FLOW
Applies to domestic wastewater treatment plants: The highest 2-hour peak flow for any 24-hour period in a calendar month.

DAILY AVERAGE CONCENTRATION
The arithmetic average of all effluent samples, composite or grab as required by the permit, within a period of one calendar month, consisting of at least four separate representative measurements. When four samples are not available in a calendar month, the arithmetic average of the four most recent measurements or the arithmetic average
(weighted by flow) of all values taken during the month shall be used as the daily average concentration.

7-DAY AVERAGE CONCENTRATION
The arithmetic average of all effluent samples, composite or grab as required by the permit, within a period of one calendar week, Sunday through Saturday.

DAILY MAXIMUM CONCENTRATION
The maximum concentration measured on a single day, by composite sample unless otherwise specified in the permit, within a period of one calendar month.

FECAL COLIFORM BACTERIA CONCENTRATION
The number of colonies of fecal coliform bacteria per 100 milliliters of effluent. The fecal coliform bacteria daily average is a geometric mean of the values for the effluent samples collected in a calendar month. The geometric mean shall be determined by calculating the nth root of the product of all measurements made in a particular period of time.

For example in a month’s time, where n equals the number of measurements made; or, computed as the antilogarithm of the arithmetic average of the logarithms of each measurement made. For any measurement of fecal coliform bacteria equaling zero, a substituted value of one shall be made for input into either computation method.

COMPOSITE SAMPLE
For domestic wastewater, a sample made up of a minimum of three effluent portions collected in a continuous 24-hour period or during the period of daily discharge if less than 24 hours, and combined in volumes proportional to flow, and collected no closer than two hours apart. For industrial wastewater, a composite sample is a sample made up of a minimum of three effluent portions collected in a continuous 24-hour period or during the period of daily discharge if less than 24 hours, and combined in volumes proportional to flow, and collected no closer than one hour apart.

GRAB SAMPLE
An individual sample collected in less than 15 minutes at peak flows.