UCMR3 300.1 Chlorate – Chlorine Dioxide Disinfectant

If your PWS uses chlorine dioxide as a disinfectant, UCMR3 chlorate samples collected from entry point locations must be sparged with inert gas to remove any potentially present residual chlorine dioxide prior to EDA preservation (see EPA Method 300.1, Sect. 8.4).

This requirement applies, even if your PWS demonstrates, through analysis of your water, that no chlorine dioxide is entering the distribution system. Samples collected from the distribution system maximum residence time location or from a consecutive PWS receiving water previously treated with chlorine dioxide do not need to be sparged UNLESS chlorine dioxide is used as a residual disinfectant or applied as booster disinfection.

To sparge a sample, you will need to have nitrogen or another inert gas available on-site.  If you do not, consider purchasing a small disposable helium tank (typically used for filling balloons).  Samplers will need to have training in the safe operation of a pressurized gas cylinder and regulator, and will need to have the glassware, gas cylinder, tubing, pipettes and other supplies on hand.

The procedure for sparging a sample prior to EDA preservation is as follows:

The sample should be collected in a clean, wide mouth flask (do not collect the sample directly into the sample bottle with the EDA preservative). A clean flask should be used for each sample. The sparging gas should be an inert gas such as a lecture bottle of nitrogen, helium or argon fitted with a regulator and connected to a disposable glass Pasteur pipette with PVC tubing. A clean Pasteur pipette should be used for each sample. The gas flow should be adjusted to produce a steady flow of bubbles. After 10-15 minutes of sparging, the chlorine dioxide residual should effectively have been removed from the sample. The sample can then be poured from the flask into the sample bottle containing the EDA preservative.