Pinellas County, FL Pool Study 1992 (1994)

[chem geek]

This thread presents my analysis of a study entitled, "A Comprehensive Study on The Microbicdal Properties of Stabilized and Unstabilized Chlorine and The Relationships of Other Chemical and Physical Variables in Public Swimming Pools; A Report on A Study Carried Out in Pinellas County, Florida, Summer/Fall, 1992". This link goes to a page at Oxy-Chem that contains the detailed study data. [EDIT] The links on the page were previously broken, but are now fixed. [END-EDIT]

The first thing that I did was to compile the source study data into a spreadsheet. This link is that spreadsheet put into HTML format so you can readily look at it. (If anyone wants the actual spreadsheets themselves, let me know and I'll post them or E-mail them to you). There were 486 pools in the study (the "N" column goes up to 494 because pools 14, 425, 434, 465, 466, 471, 473, 492 ended up not being measured or used). Originally they intended to monitor 500 pools, but 486 is what was ultimately used.

I then extracted out a subset of the columns of data and sorted by Free Chlorine and highlighted in red the bacteria and algae counts that were considered to be a problem (according to study criteria) and this may be found at this link. Finally, I calculated theoretical disinfecting chlorine (HOCl) concentrations and sorted by those and this may be found at this link.

The official position from a manufacturer I contacted was that they don't necessarily agree with my conclusions on the effects within pool water. They then talk about going through rigorous tests and studies before they are submitted to the EPA for federal registration. [EDIT] I am waiting for additional communication from them. [END-EDIT] So I'd like you to take a look at the same data and see if you can tell me what conclusions make sense.

I'm not concerned with bacteriological safety with high CYA in pools since it takes very, very little disinfecting chlorine to kill "easy-to-kill" bacteria. Hot tubs are another matter due to the bacteria that causes hot tub itch, Pseudomonas aeruginosa, and its much higher CT value (so it takes much higher chlorine concentrations to kill it). I think that the main problem with high CYA in pools is in terms of not preventing algae since higher chlorine levels seem to be needed to keep algae away, but this study makes absolutely no sense with regard to green algae (as you will see later).

(CONTINUED ON NEXT POST...)