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Virginia Administrative Code (Last Updated: January 10, 2017) |
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Title 12. Health |
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Agency 5. Department of Health |
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Chapter 590. Waterworks Regulations |
Section 1280:12. APPENDIX L. DETERMINATION OF CT
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APPENDIX L. DETERMINATION OF CT.
Disinfection Criteria
A treatment system must provide a minimum 3-log (99.9%) reduction of Giardia cysts and a 4-log (99.99%) reduction of viruses, respectively. Table L-1 lists the log removal credits associated with four filtration processes and the inactivation levels that must be achieved by disinfection.
Determination of Compliance With Inactivation
To determine compliance with the inactivation requirements, a system must comply with the CT value(s) that is (are) based on disinfection conditions in the system during peak hourly flow. The "T" is the time in minutes it takes for the water during peak hourly flow to move between the point of disinfectant application and a point where "C", the residual concentration in mg/L, is measured before the water reaches the first customer. Contact time may be determined either by calculations, tracer studies, or an equivalent method as approved by the office. The contact time to be used for calculating CT is T10, which is defined as the detention time at which 90 percent of the water passing through a unit is retained within that unit (e.g. mixing basins, sedimentation basins, clearwells, storage reservoirs, etc.)
Systems with only one point of disinfectant application may determine the total inactivation on the basis of residual measurements at a single point prior to the first customer or at several points within the treatment train after the point of disinfectant application. In the latter instance, the residual profile is determined and the total inactivation is calculated as follows: (1) Determine the disinfectant residual, C, in mg/L at any number of points within the treatment train; (2) Determine the travel time, T, in minutes between the point of disinfectant application and the point where C is measured within the first section. For subsequent measurements of C, T is the time required for water to move from the previous residual-measurement point to the next; (3) Calculate CT corresponding to each residual measurement point (CTcalc); (4) Determine the log inactivation for each section; and (5) Sum the log inactivations for each section to determine the total log inactivation. Tables L-2 through L-7 give CT values required for 99.9 percent inactivation (3 logs) of Giardia cysts at various pHs and temperatures. Tables L-9 through L-15 give CT values required for Giardia cysts and viruses at various temperatures using free chlorine, chlorine dioxide, chloramines and ozone. The minimum expected temperature and the maximum expected pH should be used for the calculations. Generally, if the CT required for 3-logs inactivation of Giardia cycts is achieved, the CT required for 4-logs inactivation of viruses is also achieved.
Determination of Disinfectant Contact Time
The time within contact units (including mixing basins and storage reservoirs) that is to be used in calculations of CT should be the T10 value, as defined earlier. This value can be determined either by calculations that involve the theoretical hydraulic detention time (volume divided by flow rate) and factors that account for the degree of short-circuiting that might be expected through any given unit or by tracer studies.
When T10 values are calculated, the theoretical, hydraulic detention time in a particular unit is reduced by some fraction, the magnitude of which is dictated by the degree of short-circuiting that is possible within that unit. The significant design characteristics that determine the degree of short-circuiting include the length-to-width ratio, the degree of baffling within the basins, and the effect of inlet-baffling and outlet-weir configurations. The use of these factors to obtain a T10 value effectively reduces the magnitude of T for use in CT calculations so that achieving a required CT requires the application of more disinfectant (i.e. a higher concentration).
The purposes of baffling are to (1) maximize utilization of basin volume, (2) increase the plug-flow zone in the basin, and (3) minimize short-circuiting. Three general classifications of baffling conditions (poor, average, and superior) have been developed to categorize the results of tracer studies for use in T10 determinations. The T10/T ratios associated with each degree of baffling are summarized in Table L-8.
The three types of basin inlet baffling configurations are: a target-baffle pipe inlet, an overflow weir entrance, and a baffled, submerged orifice or port inlet. Typical intra-basin baffling structures include: diffuser (perforated) walls; launders; cross-, longitudinal-, or maze- baffling to cause either horizontal or vertical serpentine flow; and longitudinal divider walls, which prevent mixing by increasing the length-to-width ratio of the basins. Commonly used baffled outlet structures include free-discharging weirs, such as sharp-crested and V-notch, and submerged ports or weirs. Weirs that do not span the width of the basin, such as Cipolleti weirs, should not be used, as they may substantially increase weir overflow rates and the dead-space zone within the basin. Figures L-I through L-VI give examples of poor, average, and superior baffling conditions for rectangular and circular tanks.
Figure L-1 Poor Baffling Condition—Rectangular Contact Basin
Figure L-2 Poor Baffling Condition—Circular Contact Basin
Figure L-3 Average Baffling Condition—Rectangular Contact Basin
Figure L-4 Average Baffling Condition—Circular Contact Basin
Figure L-5 Superior Baffling Conditions—Rectangular Contact Basin
Figure L-6 Superior Baffling Conditions—Circular Contact Basin
The following is a sample problem based on the inactivation tables and T10 values calculated from information regarding the design features of the contact unit and the theoretical detention time. The disinfectant in this example is chlorine which is added just prior to the contact unit and the flow rate, pH, chlorine residual, and water temperature are assumed to be 1.5 MGD, 7.5, 1.0 mg/L, and 5 degrees C, respectively. The contact unit has a baffled inlet, intra-basin baffles, and a theoretical detention time of 90 minutes.
T10/T = 0.5 (see Table L-8)
T10 = 0.5 X 90 minutes = 45 minutes
CTcalc = 1.0 mg/L x 45 minutes = 45 mg-min/L
Note- Required inactivation is 0.5 logs since this particular disinfection process follows a conventional water treatment plant.
From Table L-3, 5°C
At pH = 7.5.C = 1.0 mg/L and CTcalc = 45 mg-min/L, interpolate the log inactivation.
CTcalc of 45 mg-min/L falls between CTs of 30 (0.5 log) and 60 (1.0 log)mg-min/L. The corresponding log inactivation would be as follows:
0.5 + [(45-30)/60-30) X (1.0-0.5)] = 0.75 logs
Therefore, the log inactivation requirement of 0.5 logs has been satisfied.
Although the detention time is proportional to flow, the relationship generally is not linear. Therefore, tracer studies may be used to establish detention times for the range of flow rates experienced within each disinfectant section.
Ideally, tracer tests should be conducted at a minimum of four flow rates that span the entire range of flows for the section being tested. The flow rates should be separated by approximately equal intervals to span the range of operation, with one near average flow, two greater than average, and one less than average. The flows should also be selected so that the highest is at least 91 percent of the highest flow rate expected to ever occur in that section. Four data points will ensure a good definition of the section s hydraulic profile.
Systems can perform just one tracer test for each disinfectant residual at a flow rate of not less that 91 percent of the highest flow rate experienced in that section. If only one tracer test is performed, the detention time determined by the test may be used to provide a conservative estimate in CT calculations for that section for all flow rates less than or equal to the flow rate during the tracer test. Since T10 is inversely proportional to flow rate, the T10 at a flow rate other than that occurring during the tracer study can be determined by multiplying the T10 determined from the tracer study by the ratio of the tracer-study flow rate to the desired flow rate. That is:
T10S = T10T x OT/OS
Where:
T10S = T10 at system flow rate
T10T= T10 at tracer flow rate
OT = tracer study flow rate
OS = system flow rate
When tracer studies are performed, several variables other than flow rate will affect the detention time, including varying water levels in tanks, seasonal fluctuations in flow, and differences in water temperature, which may cause thermal stratification. If these variables are significant, additional tracer studies to determine the appropriate T10 values may be warranted.
Two methods of tracer addition are commonly used in water treatment evaluations: the step-dose method and the slug-dose method. In general, tracer studies involve the application of a chemical to a system and tracking the effluent concentrations over time. The effluent concentration profile is evaluated to determine the detention time T10.
Step-dose tracer studies are frequently employed in drinking water applications because the necessary chemical feed equipment is available and the resulting profile of normalized concentrations versus time is used directly to determine the detention time (T10) required for calculating CT. The T10 value obtained from the studies is actually the time at which the effluent concentration of the tracer chemical is 10 percent of the added concentration.
The slug-dose method requires the addition of a large, initial dose of tracer to the incoming water. Samples are collected at the exit end of the unit for a period of time until the tracer passes through the unit. Disadvantages of this method include: (1) extremely concentrated solutions of chemicals are required; (2) intensive mixing is required to minimize potential density currents and to obtain uniform distribution; (3) the concentration and volume of the initial tracer dose must be calculated carefully to provide an adequate tracer profile; (4) the resulting profile of concentration versus time cannot be used directly to determine T10; and (5) a mass balance on the treatment section is required to determine whether the tracer was completely recovered. One advantage of this method is that it may be applied where chemical feed equipment is not available at the desired point of application or where the equipment that is available does not have adequate capacity.
Disinfection Profile and Benchmark
1. A disinfection profile is prepared by calculating the log inactivation for each disinfection segment of the treatment plant, from initial point of disinfectant addition to the entrance to the distribution system. The log inactivations for each segment are summed to yield the total plant log inactivation.
2. The procedure for computing the log inactivation is as follows:
a. Collect data daily (plants serving 10,000 or more people), or weekly on the same calendar day (plants serving less than 10,000 people), at each disinfectant residual sampling point during peak hourly flow, for:
(1) Water temperature (°C)
(2) Water pH (required for free chlorine calculation)
(3) Disinfectant residual concentration ("C," in mg/L)
b. Calculate contact time ("T," in minutes) for each disinfectant segment based on baffling factors or tracer studies.
c. Calculate CTactual for each disinfection segment under actual operating conditions.
d. Determine the CTrequired for 3-log Giardia inactivation (CT3-log Giardia) and/or 4-log virus (CT4-log virus) inactivation from the CT Tables.
e. Calculate the log inactivation for Giardia and/or viruses for each segment using:
(1) Log Inactivation of Giardia = 3.0 * CTactual /CT3-log Giardia
(2) Log inactivation of viruses = 4.0 * CTactual /CT4-log viruses
f. Sum the segment log inactivations to determine the plant log inactivation.
3. The disinfection profile is charted over the year and the benchmark is determined based on 12VAC5-590-500.
TABLE L-1 MAXIMUM LOG REMOVAL CREDITS ALLOWED FOR FILTRATION AND MINIMUM REQUIRED LEVELS OF INACTIVATION BY DISINFECTION
Minimum Required Disinfection
Type of Filtration
Maximum Log Removal Credits
(Log Inactivations)
Giardia
Viruses
Giardia
Viruses
Conventional
2.5
2.0
0.5
2.0
Direct
2.0
1.0
1.0
3.0
Slow Sand
2.0
2.0
1.0
2.0
Diatomaceous Earth
2.0
1.0
1.0
3.0
NOTE - The sum of the log removals for filtration plus disinfection must equal 3.0 for Giardia and 4.0 for viruses.
TABLE L-2
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINE AT 0.5 C OR LOWERCHLORINE CONCENTRATION
LOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
23
46
69
91
114
137
27
54
82
109
136
163
0.6
24
47
71
94
118
141
28
56
84
112
140
168
0.8
24
48
73
97
121
145
29
57
86
115
143
172
1.0
25
49
74
99
123
148
29
59
88
117
147
176
1.2
25
51
76
101
127
152
30
60
90
120
150
180
1.4
26
52
78
103
129
155
31
61
92
123
153
184
1.6
26
52
79
105
131
157
32
63
95
126
158
189
1.8
27
54
81
108
135
162
32
64
97
129
161
193
2.0
28
55
83
110
138
165
33
66
99
131
164
197
2.2
28
56
85
113
141
169
34
67
101
134
168
201
2.4
29
57
86
115
143
172
34
68
103
137
171
205
2.6
29
58
88
117
146
175
35
70
105
139
174
209
2.8
30
59
89
119
148
178
36
71
107
142
178
213
3.0
30
60
91
121
151
181
36
72
109
145
181
217
pH = 7.0
pH = 7.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
33
65
98
130
163
195
40
79
119
158
198
237
0.6
33
67
100
133
167
200
40
80
120
159
199
239
0.8
34
68
103
137
171
205
41
82
123
164
205
246
1.0
35
70
105
140
175
210
42
84
127
169
211
253
1.2
36
72
108
143
179
215
43
86
130
173
216
259
1.4
37
74
111
147
184
221
44
89
133
177
222
266
1.6
38
75
113
151
188
226
46
91
137
182
228
273
1.8
39
77
116
154
193
231
47
93
140
186
233
279
2.0
39
79
118
157
197
236
48
95
143
191
238
286
2.2
40
81
121
161
202
242
50
99
149
198
248
297
2.4
41
82
124
165
206
247
50
99
149
199
248
298
2.6
42
84
126
168
210
252
51
101
152
203
253
304
2.8
43
86
129
171
214
257
52
103
155
207
258
310
3.0
44
87
131
174
218
261
53
105
158
211
263
316
pH = 8.0
pH = 8.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
46
92
139
185
231
277
55
110
165
219
274
329
0.6
48
95
143
191
238
286
57
114
171
228
285
342
0.8
49
98
148
197
246
295
59
118
177
236
295
354
1.0
51
101
152
203
253
304
61
122
183
243
304
365
1.2
52
104
157
209
261
313
63
125
188
251
313
376
1.4
54
107
161
214
268
321
65
129
194
258
323
387
1.6
55
110
165
219
274
329
66
132
199
265
331
397
1.8
56
113
169
225
282
338
68
136
204
271
339
407
2.0
58
115
173
231
288
346
70
139
209
278
348
417
2.2
59
118
177
235
294
353
71
142
213
284
355
426
2.4
60
120
181
241
301
361
73
145
218
290
363
435
2.6
61
123
184
245
307
368
74
148
222
296
370
444
2.8
63
125
188
250
313
375
75
151
226
301
377
452
3.0
64
127
191
255
318
382
77
153
230
307
383
460
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
65
130
195
260
325
390
0.6
68
136
204
271
339
407
0.8
70
141
211
281
352
422
1.0
73
146
219
291
364
437
1.2
75
15
226
301
376
451
1.4
77
155
232
309
387
464
1.6
80
159
239
318
398
477
1.8
82
163
245
326
408
489
2.0
83
167
250
333
417
500
2.2
85
170
256
341
426
511
2.4
87
174
261
348
435
522
2.6
89
178
267
355
444
533
2.8
91
181
272
362
453
543
3.0
92
184
276
368
460
552
TABLE L-3
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINE AT 5 CCHLORINE CONCENTRATION
LOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
16
32
49
65
81
97
20
39
59
78
98
117
0.6
17
33
50
67
83
100
20
40
60
80
100
120
0.8
17
34
52
69
86
103
20
41
61
81
102
122
1.0
18
35
53
70
88
105
21
42
63
83
104
125
1.2
18
36
54
71
89
107
21
42
64
85
106
127
1.4
18
36
55
73
91
109
22
43
65
87
108
130
1.6
19
37
56
74
93
111
22
44
66
88
110
132
1.8
19
38
57
76
95
114
23
45
68
90
113
135
2.0
19
39
58
77
97
116
23
46
69
92
115
138
2.2
20
39
59
79
98
118
23
47
70
93
117
140
2.4
20
40
60
80
100
120
24
48
72
95
119
143
2.6
20
41
61
81
102
122
24
49
73
97
122
146
2.8
21
41
62
83
103
124
25
49
74
99
123
148
3.0
21
42
63
84
105
126
25
50
76
101
126
151
pH = 7.0
pH = 7.5
mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
23
46
70
93
116
139
28
55
83
111
138
166
0.6
24
48
72
95
119
143
29
57
86
114
143
171
0.8
24
49
73
97
122
146
29
58
88
117
146
175
1.0
25
50
75
99
124
149
30
60
90
119
149
179
1.2
25
51
76
101
127
152
31
61
92
122
153
183
1.4
26
52
78
103
129
155
31
62
94
125
156
187
1.6
26
53
79
105
132
158
32
64
96
128
160
192
1.8
27
54
81
108
135
162
33
65
98
131
163
196
2.0
28
55
83
110
138
165
33
67
100
133
167
200
2.2
28
56
85
113
141
169
34
68
102
136
170
204
2.4
29
57
86
115
143
172
35
70
105
139
174
209
2.6
29
58
88
117
146
175
36
71
107
142
178
213
2.8
30
59
89
119
148
178
36
72
109
145
181
217
3.0
30
61
91
121
152
182
37
74
111
147
184
221
pH = 8.0
pH = 8.5
mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
33
66
99
132
165
198
39
79
118
157
197
236
0.6
34
68
102
136
170
204
41
81
122
163
203
244
0.8
35
70
105
140
175
210
42
84
126
168
210
252
1.0
36
72
108
144
180
216
43
87
130
173
217
260
1.2
37
74
111
147
184
221
45
89
134
178
223
267
1.4
38
76
114
151
189
227
46
91
137
183
228
274
1.6
39
77
116
155
193
232
47
94
141
187
234
281
1.8
40
79
119
159
198
238
48
96
144
191
239
287
2.0
41
81
122
162
203
243
49
98
147
196
245
294
2.2
41
83
124
165
207
248
50
100
150
200
250
300
2.4
42
84
127
169
211
253
51
102
153
204
255
306
2.6
43
86
129
172
215
258
52
104
156
208
260
312
2.8
44
88
132
175
219
263
53
106
159
212
265
318
3.0
45
89
134
179
223
268
54
108
162
216
270
324
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
47
93
140
186
233
279
0.6
49
97
146
194
243
291
0.8
50
100
151
201
251
301
1.0
52
104
156
208
260
312
1.2
53
107
160
213
267
320
1.4
55
110
165
219
274
329
1.6
56
112
169
225
281
337
1.8
58
115
173
230
288
345
2.0
59
118
177
235
294
353
2.2
60
120
181
241
301
361
2.4
61
123
184
245
307
368
2.6
63
125
188
250
313
375
2.8
64
127
191
255
318
382
3.0
65
130
195
259
324
389
TABLE L-4
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINE AT 10 CCHLORINE
CONCENTRATIONLOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
12
24
37
49
61
73
15
29
44
59
73
88
0.6
13
25
38
50
63
75
15
30
45
60
75
90
0.8
13
26
39
52
65
78
15
31
46
61
77
92
1.0
13
26
40
53
66
79
16
31
47
63
78
94
1.2
13
27
40
53
67
80
16
32
48
63
79
95
1.4
14
27
41
55
68
82
16
33
49
65
82
98
1.6
14
28
42
55
69
83
17
33
50
66
83
99
1.8
14
29
43
57
72
86
17
34
51
67
84
101
2.0
15
29
44
58
73
87
17
35
52
69
87
104
2.2
15
30
45
59
74
89
18
35
53
70
88
105
2.4
15
30
45
60
75
90
18
36
54
71
89
107
2.6
15
31
46
61
77
92
18
37
55
73
92
110
2.8
16
31
47
62
78
93
19
37
56
74
93
110
3.0
16
32
48
63
79
95
19
38
57
75
94
113
pH = 7.0
pH = 7.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
17
35
52
69
87
104
21
42
63
83
104
125
0.6
18
36
54
71
89
107
21
43
64
85
107
128
0.8
18
37
55
73
92
110
22
44
66
87
109
131
1.0
19
37
56
75
93
112
22
45
67
89
112
134
1.2
19
38
57
76
95
114
23
46
69
91
114
137
1.4
19
39
58
77
97
116
23
47
70
93
117
140
1.6
20
40
60
79
99
119
24
48
72
96
120
144
1.8
20
41
61
81
102
122
25
49
74
98
123
147
2.0
21
41
62
83
103
124
25
50
75
100
125
150
2.2
21
42
64
85
106
127
26
51
77
102
128
153
2.4
22
43
65
86
108
129
26
52
79
105
131
157
2.6
22
44
66
87
109
131
27
53
80
107
133
160
2.8
22
45
67
89
112
134
27
54
82
109
136
163
3.0
23
46
69
91
114
137
28
55
83
111
138
166
pH = 8.0
pH = 8.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
25
50
75
99
124
149
30
59
89
118
148
177
0.6
26
51
77
102
128
153
31
61
92
122
153
183
0.8
26
53
79
105
132
158
32
63
95
126
158
189
1.0
27
54
81
108
135
162
33
65
98
130
163
195
1.2
28
55
83
111
138
166
33
67
100
133
167
200
1.4
28
57
85
113
142
170
34
69
103
137
172
206
1.6
29
58
87
116
145
174
35
70
106
141
176
211
1.8
30
60
90
119
149
179
36
72
108
143
179
215
2.0
30
61
91
121
152
182
37
74
111
147
184
221
2.2
31
62
93
124
155
186
38
75
113
150
188
225
2.4
32
63
95
127
158
190
38
77
115
153
192
230
2.6
32
65
97
129
162
194
39
78
117
156
195
234
2.8
33
66
99
131
164
197
40
80
120
159
199
239
3.0
34
67
101
134
168
201
41
81
122
162
203
243
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
35
70
105
139
174
209
0.6
36
73
109
145
182
218
0.8
38
75
113
151
188
226
1.0
39
78
117
156
195
234
1.2
40
80
120
160
200
240
1.4
41
82
124
165
206
247
1.6
42
84
127
169
211
253
1.8
43
86
130
173
216
259
2.0
44
88
133
177
221
265
2.2
45
90
136
181
226
271
2.4
46
92
138
184
230
276
2.6
47
94
141
187
234
281
2.8
48
96
144
191
239
287
3.0
49
97
146
195
243
292
TABLE L-5
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINE AT 15 CCHLORINE
CONCENTRATIONLOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6.0
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
8
16
25
33
41
49
10
20
30
39
49
59
0.6
8
17
25
33
42
50
10
20
30
40
50
60
0.8
9
17
26
35
43
52
10
20
31
41
51
61
1.0
9
18
27
35
44
53
11
21
32
42
53
63
1.2
9
18
27
36
45
54
11
21
32
43
53
64
1.4
9
18
28
37
46
55
11
22
33
43
54
65
1.6
9
19
28
37
47
56
11
22
33
44
55
66
1.8
10
19
29
38
48
57
11
23
34
45
57
68
2.0
10
19
29
39
48
58
12
23
35
46
58
69
2.2
10
20
30
39
49
59
12
23
35
47
58
70
2.4
10
20
30
40
50
60
12
24
36
48
60
72
2.6
10
20
31
41
51
61
12
24
37
49
61
73
2.8
10
21
31
41
52
62
12
25
37
49
62
74
3.0
11
21
32
42
53
63
13
25
38
51
63
76
pH = 7.0
pH = 7.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
12
23
35
47
58
70
14
28
42
55
69
83
0.6
12
24
36
48
60
72
14
29
43
57
72
86
0.8
12
24
37
49
61
73
15
29
44
59
73
88
1.0
13
25
38
50
63
75
15
30
45
60
75
90
1.2
13
25
38
51
63
76
15
31
46
61
77
92
1.4
13
26
39
52
65
78
16
31
47
63
78
94
1.6
13
26
40
53
66
79
16
32
48
64
80
96
1.8
14
27
41
54
68
81
16
33
49
65
82
98
2.0
14
28
42
55
69
83
17
33
50
67
83
100
2.2
14
28
43
57
71
85
17
34
51
68
85
102
2.4
14
29
43
57
72
86
18
35
53
70
88
105
2.6
15
29
44
59
73
88
18
36
54
71
89
107
2.8
15
30
45
59
74
89
18
36
55
73
91
109
3.0
15
30
46
61
76
91
19
37
56
74
93
111
pH = 8.0
pH = 8.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
17
33
50
66
83
99
20
39
59
79
98
118
0.6
17
34
51
68
85
102
20
41
61
81
102
122
0.8
18
35
53
70
88
105
21
42
63
84
105
126
1.0
18
36
54
72
90
108
22
43
65
87
108
130
1.2
19
37
56
74
93
111
22
45
67
89
112
134
1.4
19
38
57
76
95
114
23
46
69
91
114
137
1.6
19
39
58
77
97
116
24
47
71
94
118
141
1.8
20
40
60
79
99
119
24
48
72
96
120
144
2.0
20
41
61
81
102
122
25
49
74
98
123
147
2.2
21
41
62
83
103
124
25
50
75
100
125
150
2.4
21
42
64
85
106
127
26
51
77
102
128
153
2.6
22
43
65
86
108
129
26
52
78
104
130
156
2.8
22
44
66
88
110
132
27
53
80
106
133
159
3.0
22
45
67
89
112
134
27
54
81
108
135
162
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
23
47
70
93
117
140
0.6
24
49
73
97
122
146
0.8
25
50
76
101
126
151
1.0
26
52
78
104
130
156
1.2
27
53
80
107
133
160
1.4
28
55
83
110
138
165
1.6
28
56
85
113
141
169
1.8
29
58
87
115
144
173
2.0
30
59
89
118
148
177
2.2
30
60
91
121
151
181
2.4
31
61
92
123
153
184
2.6
31
63
94
125
157
188
2.8
32
64
96
127
159
191
3.0
33
65
98
130
163
195
TABLE L-6
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINE AT 20 CCHLORINE
CONCENTRATIONLOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6.0
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
6
12
18
24
30
36
7
15
22
29
37
44
0.6
6
13
19
25
32
38
8
15
23
30
38
45
0.8
7
13
20
26
33
39
8
15
23
31
38
45
1.0
7
13
20
26
33
39
8
16
24
31
39
47
1.2
7
13
20
27
33
40
8
16
24
32
40
48
1.4
7
14
21
27
34
41
8
16
25
33
41
49
1.6
7
14
21
28
35
42
8
17
25
33
42
50
1.8
7
14
22
29
36
43
9
17
26
34
43
51
2.0
7
15
22
29
37
44
9
17
26
35
43
52
2.2
7
15
22
29
37
44
9
18
27
35
44
53
2.4
8
15
23
30
38
45
9
18
27
36
45
54
2.6
8
15
23
31
38
46
9
18
28
37
46
55
2.8
8
16
24
31
39
47
9
19
28
37
47
56
3.0
8
16
24
31
39
47
10
19
29
38
48
57
pH = 7.0
pH = 7.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
9
17
26
35
43
52
10
21
31
41
52
62
0.6
9
18
27
36
45
54
11
21
32
43
53
64
0.8
9
18
28
37
46
55
11
22
33
44
55
66
1.0
9
19
28
37
47
56
11
22
34
45
56
67
1.2
10
19
29
38
48
57
12
23
35
46
58
69
1.4
10
19
29
39
48
58
12
23
35
47
58
70
1.6
10
20
30
39
49
59
12
24
36
48
60
72
1.8
10
20
31
41
51
61
12
25
37
49
62
74
2.0
10
21
31
41
52
62
13
25
38
50
63
75
2.2
11
21
32
42
53
63
13
26
39
51
64
77
2.4
11
22
33
43
54
65
13
26
39
52
65
78
2.6
11
22
33
44
55
66
13
27
40
53
67
80
2.8
11
22
34
45
56
67
14
27
41
54
68
81
3.0
11
23
34
45
57
68
14
28
42
55
69
83
pH = 8.0
pH = 8.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
12
25
37
49
62
74
15
30
45
59
74
89
0.6
13
26
39
51
64
77
15
31
46
61
77
92
0.8
13
26
40
53
66
79
16
32
48
63
79
95
1.0
14
27
41
54
68
81
16
33
49
65
82
98
1.2
14
28
42
55
69
83
17
33
50
67
83
100
1.4
14
28
43
57
71
85
17
34
52
69
86
103
1.6
15
29
44
58
73
87
18
35
53
70
88
105
1.8
15
30
45
59
74
89
18
36
54
72
90
108
2.0
15
30
46
61
76
91
18
37
55
73
92
110
2.2
16
31
47
62
78
93
19
38
57
75
94
113
2.4
16
32
48
63
79
95
19
38
58
77
96
115
2.6
16
32
49
65
81
97
20
39
59
78
98
117
2.8
17
33
50
66
83
99
20
40
60
79
99
119
3.0
17
34
51
67
84
101
20
41
61
81
102
122
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
18
35
53
70
88
105
0.6
18
36
55
73
91
109
0.8
19
38
57
75
94
113
1.0
20
39
59
78
98
117
1.2
20
40
60
80
100
120
1.4
21
41
62
82
103
123
1.6
21
42
63
84
105
126
1.8
22
43
65
86
108
129
2.0
22
44
66
88
110
132
2.2
23
45
68
90
113
135
2.4
23
46
69
92
115
138
2.6
24
47
71
94
118
141
2.8
24
48
72
95
119
143
3.0
24
49
73
97
122
146
TABLE L-7
CT VALUES FOR INACTIVATION OF GIARDIA CYSTS BY FREE CHLORINECHLORINE
CONCENTRATIONLOG INACTIVATIONS
LOG INACTIVATIONS
pH ≤ 6.0
pH = 6.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
4
8
12
16
20
24
5
10
15
19
24
29
0.6
4
8
13
17
21
25
5
10
15
20
25
30
0.8
4
9
13
17
22
26
5
10
16
21
26
31
1.0
4
9
13
17
22
26
5
10
16
21
26
31
1.2
5
9
14
18
23
27
5
11
16
21
27
32
1.4
5
9
14
18
23
27
6
11
17
22
28
33
1.6
5
9
14
19
23
28
6
11
17
22
28
33
1.8
5
10
15
19
24
29
6
11
17
23
28
34
2.0
5
10
15
19
24
29
6
12
18
23
29
35
2.2
5
10
15
20
25
30
6
12
18
23
29
35
2.4
5
10
15
20
25
30
6
12
18
24
30
36
2.6
5
10
16
21
26
31
6
12
19
25
31
37
2.8
5
10
16
21
26
31
6
12
19
25
31
37
3.0
5
11
16
21
27
32
6
13
19
25
32
38
pH = 7.0
pH = 7.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
6
12
18
23
29
35
7
14
21
28
35
42
0.6
6
12
18
24
30
36
7
14
22
29
36
43
0.8
6
12
19
25
31
37
7
15
22
29
37
44
1.0
6
12
19
25
31
37
8
15
23
30
38
45
1.2
6
13
19
25
32
38
8
15
23
31
38
46
1.4
7
13
20
26
33
39
8
16
24
31
39
47
1.6
7
13
20
27
33
40
8
16
24
32
40
48
1.8
7
14
21
27
34
41
8
16
25
33
41
49
2.0
7
14
21
27
34
41
8
17
25
33
42
50
2.2
7
14
21
28
35
42
9
17
26
34
43
51
2.4
7
14
22
29
36
43
9
17
26
35
43
52
2.6
7
15
22
29
37
44
9
18
27
35
44
53
2.8
8
15
23
30
38
45
9
18
27
36
45
54
3.0
8
15
23
31
38
46
9
18
28
37
46
55
pH = 8.0
pH = 8.5
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
8
17
25
33
42
50
10
20
30
39
49
59
0.6
9
17
26
34
43
51
10
20
31
41
51
61
0.8
9
18
27
35
44
53
11
21
32
42
53
63
1.0
9
18
27
36
45
54
11
22
33
43
54
65
1.2
9
18
28
37
46
55
11
22
34
45
56
67
1.4
10
19
29
38
48
57
12
23
35
46
58
69
1.6
10
19
29
39
48
58
12
23
35
47
58
70
1.8
10
20
30
40
50
60
12
24
36
48
60
72
2.0
10
20
31
41
51
61
12
25
37
49
62
74
2.2
10
21
31
41
52
62
13
25
38
50
63
75
2.4
11
21
32
42
53
63
13
26
39
51
64
77
2.6
11
22
33
43
54
65
13
26
39
52
65
78
2.8
11
22
33
44
55
66
13
27
40
53
67
80
3.0
11
22
34
45
56
67
14
27
41
54
68
81
pH = 9.0
(mg/L)
0.5
1.0
1.5
2.0
2.5
3.0
≤ 0.4
12
23
35
47
58
70
0.6
12
24
37
49
61
73
0.8
13
25
38
50
63
75
1.0
13
26
39
52
65
78
1.2
13
26
40
53
67
80
1.4
14
27
41
55
68
82
1.6
14
28
42
56
70
84
1.8
14
29
43
57
72
86
2.0
15
29
44
59
73
88
2.2
15
30
45
60
75
90
2.4
15
31
46
61
77
92
2.6
16
31
47
63
78
94
2.8
16
32
48
64
80
96
3.0
16
32
49
65
81
97
TABLE L-8
BAFFLING CLASSIFICATIONSBaffling Condition
T10/T
Baffling Description
Unbaffled (mixed flow)
0.1
None, agitated basin, very low length to width ratio, high inlet and outlet flow velocities
Poor
0.3
Single or multiple unbaffled inlets and outlets, no intrabasin baffles
Average
0.5
Baffled inlet or outlet with some intrabasin baffles
Superior
0.7
Perforated inlet baffle, serpentine or perforated intrabasin baffles, outlet weir or perforated launders
Excellent
0.9
Serpentine baffling throughout basin, very high length to width ratio
Perfect (plug flow)
1.0(1)
Very high length to width ratio (pipeline flow), perforated inlet, outlet, and intrabasin baffles
(1)At perfect plug flow conditions, T10 is equal to T.
Table L-9.
CT Values for Inactivation of Viruses by Free Chlorine, pH 6.0-9.0Inactivation (log)
Temperature (°C)
0.5
1
2
3
4
5
6
7
8
9
10
11
12
2
6.0
5.8
5.3
4.9
4.4
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
3
9.0
8.7
8.0
7.3
6.7
6.0
5.6
5.2
4.8
4.4
4.0
3.8
3.6
4
12.0
11.6
10.7
9.8
8.9
8.0
7.6
7.2
6.8
6.4
6.0
5.6
5.2
Inactivation (log)
Temperature (°C)
13
14
15
16
17
18
19
20
21
22
23
24
25
2
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
1.0
1.0
1.0
1.0
1.0
3
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
4
4.8
4.4
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-10.
CT Values for Inactivation of Giardia Cysts by Chlorine Dioxide, pH 6.0-9.0Inactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
0.5
10.0
8.6
7.2
5.7
4.3
4.2
4.2
4.1
4.1
4.0
3.8
3.7
3.5
1
21.0
17.9
14.9
11.8
8.7
8.5
8.3
8.1
7.9
7.7
7.4
7.1
6.9
1.5
32.0
27.3
22.5
17.8
13.0
12.8
12.6
12.4
12.2
12.0
11.6
11.2
10.8
2
42.0
35.8
29.5
23.3
17.0
16.6
16.2
15.8
15.4
15.0
14.6
14.2
13.8
2.5
52.0
44.5
37.0
29.5
22.0
21.4
20.8
20.2
19.6
19.0
18.4
17.8
17.2
3
63.0
53.8
44.5
35.3
26.0
25.4
24.8
24.2
23.6
23.0
22.2
21.4
20.6
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
0.5
3.4
3.2
3.1
2.9
2.8
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1
6.6
6.3
6.0
5.8
5.5
5.3
5.0
4.7
4.5
4.2
4.0
3.7
1.5
10.4
10.0
9.5
9.0
8.5
8.0
7.5
7.1
6.7
6.3
5.9
5.5
2
13.4
13.0
12.4
11.8
11.2
10.6
10.0
9.5
8.9
8.4
7.8
7.3
2.5
16.6
16.0
15.4
14.8
14.2
13.6
13.0
12.2
11.4
10.6
9.8
9.0
3
19.8
19.0
18.2
17.4
16.6
15.8
15.0
14.2
13.4
12.6
11.8
11.0
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-11.
CT Values for Inactivation of Viruses by Chlorine Dioxide, pH 6.0-9.0Inactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
2
8.4
7.7
7.0
6.3
5.6
5.3
5.0
4.8
4.5
4.2
3.9
3.6
3.4
3
25.6
23.5
21.4
19.2
17.1
16.2
15.4
14.5
13.7
12.8
12.0
11.1
10.3
4
50.1
45.9
41.8
37.6
33.4
31.7
30.1
28.4
26.8
25.1
23.4
21.7
20.1
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
2
3.1
2.8
2.7
2.5
2.4
2.2
2.1
2.0
1.8
1.7
1.5
1.4
3
9.4
8.6
8.2
7.7
7.3
6.8
6.4
6.0
5.6
5.1
4.7
4.3
4
18.4
16.7
15.9
15.0
14.2
13.3
12.5
11.7
10.9
10.0
9.2
8.4
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-12.
CT Values for Inactivation of Giardia Cysts by Chloramine, pH 6.0-9.0Inactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
0.5
635
568
500
433
365
354
343
332
321
310
298
286
274
1
1,270
1,136
1,003
869
735
711
687
663
639
615
592
569
546
1.5
1,900
1,700
1,500
1,300
1,100
1,066
1,032
998
964
930
894
858
822
2
2,535
2,269
2,003
1,736
1,470
1,422
1,374
1,326
1,278
1,230
1,184
1,138
1,092
2.5
3,170
2,835
2,500
2,165
1,830
1,772
1,714
1,656
1,598
1,540
1,482
1,424
1,366
3
3,800
3,400
3,000
2,600
2,200
2,130
2,060
1,990
1,920
1,850
1,780
1,710
1,640
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
0.5
262
250
237
224
211
198
185
173
161
149
137
125
1
523
500
474
448
422
396
370
346
322
298
274
250
1.5
786
750
710
670
630
590
550
515
480
445
410
375
2
1,046
1,000
947
894
841
788
735
688
641
594
547
500
2.5
1,308
1,250
1,183
1,116
1,049
982
915
857
799
741
683
625
3
1,570
1,500
1,420
1,340
1,260
1,180
1,100
1,030
960
890
820
750
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-13.
CT Values for Inactivation of Viruses by ChloramineInactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
2
1,243
1,147
1,050
954
857
814
771
729
686
643
600
557
514
3
2,063
1,903
1,743
1,583
1,423
1,352
1,281
1,209
1,138
1,067
996
925
854
4
2,883
2,659
2,436
2,212
1,988
1,889
1,789
1,690
1,590
1,491
1,392
1,292
1,193
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
2
471
428
407
385
364
342
321
300
278
257
235
214
3
783
712
676
641
605
570
534
498
463
427
392
356
4
1,093
994
944
895
845
796
746
696
646
597
547
497
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-14.
CT Values for Inactivation of Giardia Cysts by OzoneInactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
0.5
0.48
0.44
0.40
0.36
0.32
0.30
0.28
0.27
0.25
0.23
0.22
0.20
0.19
1.0
0.97
0.89
0.80
0.72
0.63
0.60
0.57
0.54
0.51
0.48
0.45
0.42
0.38
1.5
1.50
1.36
1.23
1.09
0.95
0.90
0.86
0.81
0.77
0.72
0.67
0.62
0.58
2.0
1.90
1.75
1.60
1.45
1.30
1.23
1.16
1.09
1.02
0.95
0.89
0.82
0.76
2.5
2.40
2.20
2.00
1.80
1.60
1.52
1.44
1.36
1.28
1.20
1.12
1.04
0.95
3.0
2.90
2.65
2.40
2.15
1.90
1.81
1.71
1.62
1.52
1.43
1.33
1.24
1.14
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
0.5
0.17
0.16
0.15
0.14
0.14
0.13
0.12
0.11
0.10
0.10
0.09
0.08
1.0
0.35
0.32
0.30
0.29
0.27
0.26
0.24
0.22
0.21
0.19
0.18
0.16
1.5
0.53
0.48
0.46
0.43
0.41
0.38
0.36
0.34
0.31
0.29
0.26
0.24
2.0
0.69
0.63
0.60
0.57
0.54
0.51
0.48
0.45
0.42
0.38
0.35
0.32
2.5
0.87
0.79
0.75
0.71
0.68
0.64
0.60
0.56
0.52
0.48
0.44
0.40
3.0
1.05
0.95
0.90
0.86
0.81
0.77
0.72
0.67
0.62
0.58
0.53
0.48
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments.
Table L-15.
CT Values for Inactivation of Viruses by OzoneInactivation (log)
Temperature (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
2
0.90
0.83
0.75
0.68
0.60
0.58
0.56
0.54
0.52
0.50
0.46
0.42
0.38
3
1.40
1.28
1.15
1.03
0.90
0.88
0.86
0.84
0.82
0.80
0.74
0.68
0.62
4
1.80
1.65
1.50
1.35
1.20
1.16
1.12
1.08
1.04
1.00
0.92
0.84
0.76
Inactivation (log)
Temperature (°C)
14
15
16
17
18
19
20
21
22
23
24
25
2
0.34
0.30
0.29
0.28
0.27
0.26
0.25
0.23
0.21
0.19
0.17
0.15
3
0.56
0.50
0.48
0.46
0.44
0.42
0.40
0.37
0.34
0.31
0.28
0.25
4
0.68
0.60
0.58
0.56
0.54
0.52
0.50
0.46
0.42
0.38
0.34
0.30
Source: AWWA, 1991. Modified by linear interpolation between 5°C increments
Historical Notes
Amended, Volume 21, Issue 13, eff. April 6, 2005.