Monitoring Period Loads Report Help
The Water Pollutant Loading Tool calculates pollutant discharges by monitoring period and calendar year.
Monitoring Period Loads Report demonstrates how pollutant loads are calculated, based on reported discharge monitoring report (DMR) data and estimation methods, and allows users to see which discharge monitoring values were selected for the pollutant calculations. This report is available for each NPDES permit, calendar year, outfall (i.e., permitted feature), and parameter where loadings may be calculated.
The top of the report lists the facility's name in bold, the selected NPDES permit, and date range.
Charts
Monitoring Period-Level Load Chart
The monitoring period level loads by year, for a given parameter (parameter code) at a given outfall. Pop-ups for each value display the data are available in the table.
Table Columns
Monitoring Period
The end date of the monitoring period. Note that expanding the row will expose the equation for the loading calculation. This value is from ICIS-NPDES.
Discharge Information
Yes/no values for whether the discharge occurred, was reported, and was estimated. If the discharge occurred, but was not reported in ICIS-NPDES, the loading tool will "estimate" the load, e.g., extrapolate the annual loading to account for the monitoring period and avoid underestimation. These values are from ICIS-NPDES.
No Data Indicator
Displays the No Data Indicator (NODI) code and description, explaining the reason(s) why sampling results are not available on the DMR. Common reasons why the data may not be reported include no discharge during the period at an outfall or a sampling issue. These values are from ICIS-NPDES.
Below Detection Limit?
Yes or no value indicating whether the measurement is below the detection limit. This value is from ICIS-NPDES.
For pollutants measured at concentrations below the sample detection limit, the Loading Tool uses half the measured concentration value to calculate the monitoring period load. 1/2 of the sample detection limit is reflected in the Average Daily Value column when this occurs. For example, view the rows for 9/30/2020 and 10/31/2020 monitoring periods for this report showing calculations for phosphorus.
If the pollutant is measured below detection limits for all monitoring periods in a year, then the Loading Tool sets the annual pollutant load to zero. For example, iron measurements at an outfall during 2024.
Average Daily Value
The average daily value and units during the monitoring period.
This is the DMR value selected to be used for pollutant loading calculations. The Loading Tool selects one of (up to) five measurement for load calculation. The Water Pollution Search uses a "hybrid" method for non-detects. It sets non-detects equal to zero if the pollutant was not detected for all monitoring periods in the reporting year. If the pollutant was detected in at least one monitoring period, then the Loading Tool sets the non-detects equal to ½ the detection limit.
Refer to the Technical Users Background Document Section 3.2.1 for more details on the selection logic.
Measurement Type
The type of measurement (i.e., quantity or concentration). This value is derived in the Loading Tool based on the DMR Value Type.
DMR Value Type
The quantity or concentration value field associated with the DMR value. ICIS-NPDES contains five fields for storing DMR measurements. This value is from ICIS-NPDES.
Limit
The limit value and units for the pollutant discharge during the monitoring period, as specified in the NPDES permit by EPA or the authorized state agency. This value is from ICIS-NPDES.
Limit Set Designator
The alphanumeric code used to designate a particular grouping of parameters within a limit set, which defines the monitoring and reporting requirements for a group of limits. This value is from ICIS-NPDES.
Wastewater Flow (MGD)
The volume of wastewater, measured in millions of gallons per day (MGD) for the outfall and monitoring period. This value is from ICIS-NPDES.
Number of Days
The number of days in the monitoring period, which is derived in the Loading Tool.
Monitoring Period Load (lb/period)
The total calculated quantity of a pollutant discharged during a specific monitoring period, in pounds per period. This value is calculated in the Loading Tool.
Tip: Expand each row to view the equation used to calculate the load.
A yellow flag will display if the Loading Tool has calculated a Load Over Limit for the monitoring period, i.e. the average daily value exceeds the limit value. Hover over the yellow flag to see the load over limit value (pounds per monitoring period). For more detail including examples, see Load over Limit Calculations Option 1.
If the pollutant is measured below detection limit, the Loading Tool uses half the measured concentration value to calculate the load and the load over limit. In this case, if the measured concentration value exceeds the limit but half that value is below the limit, the calculated load over limit for the monitoring period will be zero. For example, if the reported concentration is non-detect at 5 mg/L and the limit is 3 mg/L, the Loading Tool will set the average daily value to 2.5 mg/L and the load over limit will be 0 pounds.
Annual Calculations
Annual Load from Monitoring Data (lb/yr)
The calculated amount of pollutant discharged, in pounds per year, from the sum of the monitoring period loads in the table.
Number of Months Requiring Estimation
The number of months that need estimation, in order to calculate an annual load.
If discharges are reported for every monitoring period in the calendar year, this value is 0.
Annual Load (lb/yr)
The calculated annual load, taking into account both monitoring period data and months requiring estimation. To avoid underestimating pollutant loads, the Loading Tool uses linear regression to account for monitoring periods without reported data. The "Annual Load from Monitoring Data" is multiplied by twelve and divided by twelve minus the number of months requiring estimation.
Refer to the Technical Users Background Document Section 3.2.4 for more information.