Concentrations and detection limit information: guide to reporting

This document explains how you report concentration data to the National Pollutant Release Inventory (NPRI). For complete reporting requirements, see the Guide for reporting to the NPRI.

Report average concentration and detection limit information related to the following:

Concentration and method detection limit units                                               

You must report the average annual concentration and method detection limit (MDL) in parts per million (ppm). Depending on how the concentration measurement was taken, you may need to convert the units from a percentage (%), mg/kg (for solids) or mg/L (for liquids) into ppm as follows:

Detection limit information

The MDL is the smallest concentration of the substance under analysis (that is, the analyte) that produces an instrumental response. The MDL must meet the analyte detection and identification criteria of the specified test method. Report the following:

A number of scenarios are possible after you take multiple measurements of the concentration of a substance in a given process stream:

When you report concentration data, you also need to indicate if the related quantity (release to water or disposal of tailings or waste rock) was estimated using half the MDL. In addition, you need to report if more than one MDL applies. In the case of multiple MDLs, you can provide additional information in the comment field. 

A flowchart showing how you report multiple measurements of the concentration of a substance in a given process stream. Text version below.

Using the method detection limit to report to the NPRI
Long description

This flowchart describes how you report on multiple measurements of the concentration of a substance in a given process stream.

The box at the top reads, “Multiple measurements of the concentration of a substance in a given process stream are taken.” Three arrows lead from that box.

The box on the left side reads, “All measurements are above the method detection limit (MDL). A vertical arrow from that box leads to a box that reads, “The measured concentration of the substance should be used.”

The middle box reads, “Some measurements are above the MDL and some are below the MDL.” A vertical arrow from that box leads to a box that reads, “A concentration equal to half of the MDL should be used for measurements below the MDL.”

The box on the right side reads, “All measurements are below the MDL.” A vertical arrow from that box leads to a box that reads, “Is there a reason to believe the substance is present?” A horizontal arrow labeled “YES” leads to a box that reads, “A concentration equal to half the MDL should be used for measurements below the MDL.” A vertical arrow labeled “NO” leads to a box that reads, “The concentration of the substance can be assumed to be zero.”

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