Example on calculating a Running Annual Average
The following example describes the calculation process for a running annual average. This example
shows an atrazine running annual average that is calculated for two TAPs.
TAP 01 South WTP (ug/l) TAP 02 West WTP (ug/l)
Monitoring Quarter Atrazine
Quarterly
Results
Running
Annual
Average*
Atrazine
Quarterly
Results
Running
Annual
Average*
Jan 1997 thru
March 1997 3 NC 1 NC
April 1997 thru
June 1997 10 NC 2 NC
July 1997 thru
Sept 1997 9 NC 4 NC
Oct 1997 thru
Nov 1997 4 NC 1 NC
Jan 1998 thru
March 1998 2 6.3 OVER MCL 2 2.3 Under MCL
April 1998 thru
June 1998 1 4 OVER MCL 1 2 Under MCL
July 1998 thru
Sept 1998 2 2.3 Under MCL 1 1.3 Under MCL
Oct 1998 thru
Dec 1998 2 1.8 Under MCL 1 1.3 Under MCL
NC = Running Annual Average was not calculated.
* The running annual average is calculated by adding the current quarter plus the three
previous quarters and then dividing by four.
In this example, TAP 01 had the highest results; thus, these values will be used in the “Water Quality
Data” table. For TAP 01, no individual quarterly results exceeded the MCL during 1998; however,
the running annual average exceeded the MCL for two quarters.
Therefore, your “Water Quality Data” table for atrazine would look like:
MCL MCLG Level
Found
Range Sample
Date
Violation Typical Source
Atrazine 3 0 2 1-2 YES* Runoff from herbicide
used on row crops
* In your footnote page, you must include the length of the violation, corrective action being
taken by the water supply, and the mandatory health effects language.
