EZ DPD Questions and Answers
What chlorine testing is required by the US EPA?
The Surface Water Treatment Rule of 1989 requires that distribution systems using surface water as a source and serving more than 25 people disinfect the distribution system or meet maximum HPC levels. Disinfectant residual level must be ≥ 0.2 mg/L (ppm) or the HPC level must be below 500 cfu/mL. The disinfectant residual must be present in ≥ 95% of samples for 2 consecutive months.
Testing frequency requirements:
| POPULATION SERVED |
MINIMUM # SAMPLES/DAY |
| < 500 |
1 |
| 501 - 1000 |
2 |
| 1001 - 2500 |
3 |
| 2501 - 3300 |
4 |
| > 3300 |
continuous |
What is free chlorine?
Chlorine present as Cl2, HOCl and OCl- is free available chlorine. The active chlorine in the water for disinfection is also called free chlorine residual.
What is combined chlorine?
Chlorine that is bound to other elements or organic compounds but is still an effective disinfectant. Combined chlorine has been found to be more effective than free chlorine in controlling post-disinfection bacterial growth. Chloramines are an example of combined chlorine.
What are chloramines?
Chloramines are compounds formed by the reaction of chlorine and ammonia-nitrogen in water.
What is total chlorine?
Total chlorine is the combination of free chlorine and combined chlorine.
What is residual chlorine?
Residual chlorine is the chlorine that has not combined with organic matter.
What is the amount of DPD powder delivered by the EZ DPD dispenser?
The EZ DPD dispenser will deliver 0.04 - 0.09 grams of DPD powder each time the button is pressed.
What is the chlorine ppm detection range of the EZ DPD test?
The DPD test detection range is from 0.1 - 3.5 ppm.
What is the reference in Standard Methods for the Examination of Water and Wastewater, 20th Edition for IDEXX's EZ DPD?
Standard Methods for the Examination of Water and Wastewater, Section 4500-CI, G describes the DPD Colorimetric method for field testing chlorine.
Can I use EZ DPD for testing 25 mL samples?
Yes. Press the button three times for each 25 mL sample.
What should be done if the EZ DPD dispenser is plugged?
Remove the dispenser from the vial and clean it to dislodge anything clogging the dispenser. This can be done with a swab or other small device. The dispenser can also be cleaned with water. If you clean the dispenser with water, make sure that the dispenser is dry before putting the dispenser back on a vial of reagent.
What should be done if IDEXX DPD powder has clumped?
If the powder clumps, shake the vial to ensure free-flowing powder before dispensing.
What chlorine testing products will EZ DPD work with?
EZ DPD is capable of working with many products on the market, including: Hach™ Pocket Colorimeter™, Hach color wheel, Hach color cube, Lamotte™ colorimeter
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