The Analytical Side to Compliance with Drinking Water Regulations
Sep 24, 2012
Two new U.S. Federal regulations went into effect in 2009 that directly impact drinking water utilities that use chemical disinfection. Specifically, the Ground Water Rule and the EPA Method 334.0 are now in place with the purpose of improving the quality of drinking water. This paper summarizes the key elements of the new regulations and describes how they affect utilities’ daily operations, plus it will provide a comparison of available technologies for monitoring and calibration equipment as they relate to the regulations.
Ground Water Rule
- More than 3,300 people continuously monitor their disinfection concentration and maintain the minimum disinfectant residual concentration determined by the state.
- 3,300 people or fewer take daily grab samples or meet continuous monitoring requirements described above for those serving more than 3,300 people.
U.S. EPA Method 334.0
- Plant personnel must have a thorough knowledge of the equipment being utilized including its operation, maintenance and calibration.
- Plant personnel must document proof of this knowledge by a required initial demonstration of capability for use of both the grab sample measurement equipment as well as the on-line analyzer.
- Perform initial calibration of the grab sample method equipment throughout the range of use or perform a single calibration with a NIST traceable primary standard if the instrument is factory certified.
- Establish the frequency between needed calibration checks of the on-line analyzer with a rigorous initial testing procedure.
- If the on-line analyzer chlorine reading is not within +/- 0.1 mg/l or +/- 15% of the grab sample measurement, the following steps must be taken:
- Verify the calibration of the grab sample instrument using NIST traceable primary chlorine standards.
- Calibrate the on-line analyzer.
Finding the Right Solution
- Selecting the most appropriate on-line analyzer for your needs
- Selecting the most suitable grab sample measurement instrument for your needs
- Having access to step-by-step guides for the above instruments written specifically for the new regulations
Selecting the on-line analyzer
Amperometric analyzers provide continuous measurement, allowing for accurate dosing control.
DPD analyzers provide an analysis every three minutes, which is difficult to use for accurate dosing control.
|Life cycle costs||
Amperometric analyzers do not require reagents to operate, so there are no recurring costs.
DPD instruments require reagents for every analysis, usually performed every three minutes, and therefore have higher life cycle costs.
Amperometric analyzer sample waste stream does not require a sanitary sewer discharge.
DPD on-line analyzer sample waste is required to be discharged to a sanitary sewer.
|Accuracy||Both measurement technologies provide the required accuracy.|
|Variations in pH||
Amperometric analyzers have several simple options: use a membrane style sensor; a pH compensated bare electrode sensor; or a chemically buffered bare electrode sensor.
DPD analyzers do not require pH compensation because the sample is chemically buffered.
|High levels of iron and/or manganese||
Amperometric analyzers are not greatly affected by metals except when they are present at high concentrations.
DPD analyzers are prone to metal fouling and interferences.
|Calibration data storage||While this is not specifically instrument-dependent, the ability to store and recall previous calibration data is an easy and effective diagnostic tool.|
Selecting the grab-sample instrument
Amperometric titrators are by far more accurate than colorimetric instruments.
Hand-held instruments provide the accuracy required for meeting the EPA Method.
|Easy of use||
Amperometric titrators require specialized expertise and are more complex to use than colorimetric instruments.
Hand-held instruments that are certified by the manufacturer are easiest to use as they require a minimum of up-front calibration. If not certified by the manufacturer, they require extensive calibration at the plant prior to use.
|Life cycle costs||
Amperometric titrators are certainly more expensive than hand-held instruments for both capital and on-going costs.
|Primary standards for calibration||
Amperometric titrators do utilize stock solutions but require specialized expertise.
Hand-held instruments utilize prepared solutions that require dilution and mixing.
Beware; most primary standards have batch-to-batch concentration variations that require dilution calculations, use specialized glassware, and undergo extra washing and rinsing procedures, all of which take extra time.
For utilities that already employ titrators, such as the Series A790, they may be perfectly comfortable with those and there is no need to change. However, it may be advantageous to have a hand-held device to meet the added requirements of the Method.
Note: Colorimetric color wheels do not provide the accuracy required to meet the EPA Method and are therefore not permitted.
Access to step-by-step guides
- Procedure for the initial verification of the colorimeter or titrator
- Initial demonstration of capability for either a colorimeter or titrator
- Initial grab sample comparison testing required to put the on-line analyzer in use for compliance monitoring
- Establishing frequency of routine analyzer checks
- Routine comparison check for on-line chlorine analyzer
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