Summarizing the Data on a DMR

 

Definitions

SD's Surface Water Discharge permits require that the analysis results from a discharge be reported on a Discharge Monitoring Report (DMR) form. To understand how to properly report these results, we must first understand a couple of terms and how they relate to DMR reporting:

 

  • Seven-Day Average (or Weekly Average): The terms seven-day average and weekly average are usually used interchangeably. For the purpose of DMR reporting, a seven-day average is based on a calendar week that begins on Sunday and ends on Saturday. The seven-day averages for the month will be calculated for all weeks with a Saturday in the month. If the final week of the month does not include a Saturday, the seven-day average calculated for that week will be included on the next month's DMR. This will be explained in more detail below.

  • 30-Day Average (or Monthly Average): The terms 30-day average and monthly average are usually used interchangeably. For the purpose of DMR reporting, a 30-day average is based on a calendar month (even if there are 28, 29, or 31 days in the calendar month).

  • Daily Maximum: When you are required to report the Daily Maximum value on the DMR, use the highest daily value obtained during the reporting period (usually a calendar month).

  • Geometric Mean: The geometric mean is defined as, "the nth root of a product of n factors." Huh?! The most important things for you to understand about a geometric mean are:

     

    A geometric mean is NOT an average, and

      You must use a geometric mean instead of a 30-day average for total and fecal coliform values. 

 

The method to calculate a geometric mean will be explained below. 

 

The Daily Maximum, 7-Day Average, and 30-Day Average are the most common methods that most facilities have to report the data on their DMR. Many facilities are also required to report a Geometric Mean. 

Example

The best method for demonstrating how to calculate and report these values is by providing an example. 

The city of Townsville has a lagoon system for treating its wastewater and conducts periodic discharges from its facility. During a discharge, the city is required to sample three times the first week and once per week the following weeks until the discharge is terminated. The city is required to sample for Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), Ammonia, Fecal Coliform, pH, and Temperature. The city is also required to record and report its flow rate.

The city began discharging on the Monday May 28th, and completed its discharge on June 15th. Let's see how the city filled out its DMR: