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We would like to offer the following suggestions for changes to 12 VAC5-462 Swimming Pool Regulations Governing the Posting of Water Quality Test Results. Added text is underlined, deleted text is in crosshatch font.
12VAC5-462-290. Water quality standards- chlorine.
For minimum chlorine residuals, we would like to offer the following three options for discussion:
Option 1
1. Pools.
|
Free Residual Disinfectant |
Minimum |
Maximum |
|
Chlorine |
1.0 ppm (for pools with no cyanuric acid) 2.0 ppm (for pools with cyanuric acid) |
4 |
The 1.0 ppm minimum without CYA and the 2.0 ppm minimum in the presence of CYA in Option 1 are from the current 2018 edition of the Model Aquatic Health Code (MAHC). Justification of these values may be found in the Annex to the MAHC.
For more detailed information on cyanuric acid, please see option 3 below.
The maximum chlorine residual of 4 ppm is based on the maximum allowed by EPA.
Option 2
1. Pools.
|
Free Residual Disinfectant |
Minimum |
Maximum |
|
Chlorine |
1.0 ppm (for pools with no cyanuric acid) See table below for pools with cyanuric acid |
4 |
Minimum chlorine residual for pools with cyanuric acid
|
Minimum chlorine residual, ppm |
Range CYA, ppm |
|
2 |
1 to 30 |
|
3 |
31 to 60 |
|
4 |
61 to 90 |
Option 2 was taken from the Model Aquatic Health Code change request which received the majority of votes during the latest revision cycle (CR 5.7.3.1.1.2.2-0001). Since the 2021 MAHC has not yet been published, it is not known whether CDC will accept the CMAHC vote.
Option 3
1. Pools.
|
Free Residual Disinfectant |
Minimum |
Maximum |
|
Chlorine |
1.0 ppm (for pools with no cyanuric acid) Cyanuric acid concentration divided by 15 (for pools with cyanuric acid) |
4 |
The Council for the Model Aquatic Health Code (CMAHC) has a committee for investigating the effects of cyanuric acid on disinfection. The CMAHC Chlorine Stabilizers Ad Hoc Committee has published a paper (Falk 2019) that has the following conclusions:
Although we cannot directly measure HOCl concentrations with pool test kits, the HOCl concentration can be estimated using a ratio of free chlorine measured by DPD (DPD-FC) and CYA. As shown in the following table, the HOCl concentration is constant with constant CYA: DPD-FC ratio:
|
CYA, ppm |
DPD-FC, ppm |
HOCl, ppm |
|
20 |
1 |
0.02 |
|
40 |
2 |
0.02 |
|
60 |
3 |
0.02 |
|
80 |
4 |
0.02 |
The committee recommends setting a maximum CYA:DPD-FC ratio as a way to ensure a minimum HOCl concentration.
The following table shows the HOCl concentrations for various CYA:DPD-FC ratios at pH 7.5:
|
CYA, ppm |
DPD-FC, ppm |
HOCl, ppm |
|
0 |
1 |
0.49 |
|
15 |
1 |
0.026 |
|
20 |
1 |
0.020 |
|
30 |
1 |
0.013 |
|
45 |
1 |
0.0086 |
The MAHC currently has a minimum 2 ppm DPD-FC when CYA is used, and a 90 ppm CYA maximum. This is essentially a 90:2, or 45:1 ratio, which results in a minimum HOCl concentration of 0.0086 ppm.
The debate has been about which ratio (or HOCl concentration) to choose. Of course there is no perfect method for drawing a line in the sand for an issue that the industry has been debating for decades. However, we believe that the strongest argument amongst the various proposals is the comparison to monochloramine.
Monochloramine was chosen as a standard because it is commonly used in drinking water treatment where contact times through water distribution systems can be very long, but it is not considered a sufficient disinfectant for pool water treatment where bather-to-bather disease transmission can occur very quickly. Monochloramine has the added advantage that there is a wealth of data for it and EPA has published standard CT values (CT = concentration x time needed to achieve inactivation) for its use in drinking water. The EPA values for Giardia were used in the comparison because this organism is relevant to recreational water and has a larger CT value than typical bacteria. Following is a table from EPA comparing the Giardia CT values for free chlorine and monochloramine.
Table from EPA LT1ESWTR Disinfection Profiling and Benchmarking, 2003 EPA 816-R-03-004
|
Pathogen |
CT Free Chlorine, ppm min |
CT Chloramine, ppm min |
|
Giardia |
45 |
750 |
The supplemental material of the Falk 2019 publication shows that a limiting CYA/FC ratio of 15:1 would ensure that the inactivation time for Giardia in a stabilized pool is at least equivalent to 1 ppm monochloramine.
When setting a CYA limit, it is important to consider both the benefits and drawbacks of using it. In 1974 Canelli studied the stabilizing effect of CYA on chlorine residuals. His data shows that the largest effects from CYA are seen at low concentrations. The data also show that a 15:1 ratio is sufficient for stabilizing chlorine residuals.
Drawing a line in the sand for setting a CYA limit in pools is difficult because it is difficult to determine how much is enough to stabilize chlorine residuals, and how much is too much for sacrificing chlorine efficacy. Chlorine stabilization data will vary with sunlight intensity and water chemistry. Likewise, chlorine kill rates will vary depending on many factors, including organism type and water chemistry.
We would like to propose that the limit should be set so that the killing power of chlorine with CYA will not be less than that of combined chlorine (e.g. monochloramine) for Giardia. In aquatic venues, the killing power of monochloramine is generally not considered sufficiently effective for pathogens like Giardia, so we should ensure that the efficacy of chlorine is not compromised by the use of CYA to the point where chlorine is less effective than monochloramine.
12VAC5-462-290. Water quality standards- cyanuric acid.
1. Pools.
|
Free Residual Disinfectant |
Minimum |
Maximum |
|
Cyanuric acid |
0 ppm |
30 ppm |
2. Spas.
|
Free Residual Disinfectant |
Minimum |
Maximum |
|
Cyanuric acid |
0 ppm |
0 ppm |
The cyanuric acid limit is based on the arguments above for Option 3. In order to maintain chlorine efficacy so that chlorine is at least effective as 1 ppm monochloramine, if the minimum chlorine residual is 2 ppm, then the maximum cyanuric acid would be 30 ppm.
The prohibition of cyanuric acid in spas is based on the current MAHC.
Thank you for your consideration of these proposed changes. Please let us know if you have any questions or require any further information.
Best regards,
Ellen Meyer
Sigura
1200 Lower River Rd NW
Charleston, TN 37310
References
Canelli, E.D., Chemical, bacterillogical, and toxicological properties of cyanuric acid and chlorinated isocyanurates as applied to swimming pool disinfection, a review, AJPH February 1974, 64(2) 155-162, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1775396/ .
Centers for Disease Control and Prevention (CDC), Model Aquatic Health Code, 2018, https://www.cdc.gov/mahc/editions/current.html .
EPA Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) Disinfection Profiling and Benchmarking Technical Guidance Manual, 2003 EPA 816-R-03-004, https://www.epa.gov/dwreginfo/long-term-1-enhanced-surface-water-treatment-rule-documents .
Falk, R.A., Blatchley, E. R., Kuechler, T. C., Meyer, E. M., Pickens, S.R., Suppes, L. M., Assessing the Impact of Cyanuric Acid on Bather’s Risk of Gastrointestinal Illness at Swimming Pools, Water 2019, 11(6), 1314; doi:10.3390/w11061314, https://www.mdpi.com/2073-4441/11/6/1314