Boil Water Advisories - Surface Water Treatment Rule - GWUDI
Boil Water Advisories - Surface Water Treatment Rule - GWUDI
CT=.2828 * ( pH^2.69 ) * ( Cl^.15 ) * (.933^(T-5)) * L
The applet below uses this formula to solve for any desired parameter.
If a well tests positive for e. coli bacteria, it is very likely that it will test positive for viruses as well. It seems reasonable, therefore, that the disinfection of a well that tests positive for coliform bacteria should be effective in inactivating viruses.
Just in case the Applet is not working - Here is a summary table with some inactivation and CT data as a function of pH, chlorine concentration, and log inactivations.
Water pH 6.0 at 0.5 C
| Chlorine Conc | 1.0 log | 2.0 log | 3.0 log |
| 0.4 mg/L | 46 (CT value) | 91 | 137 |
| 1.0 mg/L | 49 | 99 | 148 |
| 2.0 mg/L | 55 | 110 | 165 |
|
Chlorine Conc |
1.0 log |
2.0 log |
3.0 log |
|
0.4 mg/L |
65 (CT value) |
130 |
195 |
|
1.0 mg/L |
70 |
140 |
210 |
|
2.0 mg/L |
79 |
157 |
236 |
Water pH 8.0 at 0.5 C
|
Chlorine Conc |
1.0 log |
2.0 log |
3.0 log |
|
0.4 mg/L |
92 (CT value) |
185 |
277 |
|
1.0 mg/L |
101 |
203 |
304 |
|
2.0 mg/L |
115 |
231 |
346 |
The next question is how do know how much contact time you are providing?
Unfortunately, it is not as easy as dividing the storage volume by the flow rate. In order to count at all, there must be a separate inlet and outlet to the tank, widely separated. Even with this provided, the volume would then be discounted by one of the following baffling factors.
| Baffling Condition | Factor | Description |
|---|---|---|
| Unbaffled | 0.1 | No baffling, low length to width ratio. Also applies to agitated basins (e.g. flocculation tanks) |
| Poor | 0.3 | unbaffled inlet/outlet. No baffles inside basin. |
| Average | 0.5 | Baffled inlet or outlet. Some inter-basin baffles. |
| Superior | 0.7 | Baffled inlet and outlet, serpentine inter-basin baffles. |
| Excellent | 0.9 | As above. Very high length-to-width ratio. |
| Perfect (plug Flow) | 1.0 | Used for pipe flow |
Shock Well Disinfection Protocols
Water Quality Help Guides
Glossary of Water Terminology
Cryptosporidium Website
EPA
Interim Enhanced Surface Water Treatment Rule - EPA
Surface
Water Filtration Rule PADEP
Term 1 Enhanced Surface Water Treatment
Rule- PADEP
Drinking
Water Technologies for GUDI -PADEP
New
Drinking Water Regulations-PADEP
Note: (This formula was provided by Peter Martin, an associate Engineer with the Contra Costa Water District, and was published in the AWWA Journal AWWA 85:12:12 Dec 1993).The applet above uses this formula to solve for any desired parameter.
The applet may not be conservative for high pH, high chlorine residuals, and high temperatues.
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