GroundRules
12VAC5-590-500: Disinfection criteria, determination of CT, disinfection profiles, and disinfection benchmarks for Giardia and virus inactivation
Where this section sits in the code
- Title 12. Health
- Agency 5. Department of Health
- Chapter 590. Waterworks Regulations
- Part II. Operation Regulations for Waterworks
- Article 3. Operation of Waterworks [Repealed]
A. A waterworks utilizing surface water sources or GUDI sources, in whole or in part, shall be disinfected in accordance with subsection C of this section and 12VAC5-590-1000.
B. The owner of a groundwater system subject to the requirements of 12VAC5-590-421 A 1 d shall provide primary disinfection treatment by means of one of the following:
1. A residual disinfectant concentration (C) and contact time (T) to achieve a 4-log removal or inactivation of viruses. CT shall be calculated in accordance with subsections C and D of this section, which contain information on calculation methods and contact tank baffling factors.
2. UV treatment to achieve a 4-log removal or inactivation of viruses. Log inactivation shall be determined in accordance with 12VAC5-590-401 E 7 c. A secondary disinfection residual in the distribution system may be required by the department.
C. Disinfection criteria.
1. An owner of a waterworks utilizing surface water sources, in whole or in part, or GUDI sources shall provide a minimum 3-log (99.9%) removal of Giardia cysts and a 4-log (99.99%) removal of viruses, respectively.
2. Additional inactivation levels that must be achieved by disinfection shall be in accordance with Table 500.1 for waterworks employing the filtration processes listed.
TABLE 500.1
Maximum Log Removal Credits for Various Filtration Technologies and the Resulting Minimum Required Logs of Inactivation by Disinfection
FILTRATION PROCESSa
MAXIMUM LOG REMOVAL CREDITS FOR FILTRATION
ADDITIONAL LOG INACTIVATION REQUIRED BY DISINFECTION
Giardia lamblia
Viruses
Giardia lamblia
Viruses
Conventional
2.5
2.0
0.5
2.0
Direct
2.0
1.0
1.0
3.0
Pre-engineered package
2.5
Zero
0.5
4.0
Diatomaceous Earth
2.0
1.0
1.0
3.0
Slow Sand
2.0
2.0
1.0
2.0
Membrane (MF or UF)
3.0
Zero
0.5
4.0
Bag or Cartridge
2.0
Zero
1.0
4.0
aRefer to Part III of this chapter for further description of the filtration processes.
D. A disinfection profile shall be developed in accordance with the procedures in subdivisions D 1, D 2, and D 3.
1. The owner shall monitor at least weekly for a period of 12 consecutive months to determine the total log inactivation for Giardia lamblia and viruses. If an owner monitors more frequently, then the monitoring frequency shall be evenly spaced. An owner of a waterworks that operates for fewer than 12 months per year shall monitor weekly during the period of operation.
2. The owner of a waterworks with a single point of disinfectant application before the entrance to the distribution system or with more than one point of disinfectant application shall conduct the monitoring in subdivisions D 2 a through D 2 e of this section.
a. For a waterworks using a disinfectant other than UV, the temperature of the disinfected water shall be measured at each residual disinfectant concentration sampling point during peak hourly flow or at an alternative location approved by the department.
b. For a waterworks using chlorine, the pH of the disinfected water shall be measured at each chlorine residual disinfectant concentration sampling point during peak hourly flow or at an alternative location approved by the department.
c. The residual disinfectant concentration (C) of the water before or at the first customer and before each additional point of disinfectant application shall be measured at peak hourly flow.
d. The disinfectant contact times (T) of the water before or at the first customer and before each additional point of disinfectant application shall be determined during peak hourly flow. The disinfectant contact time to be used for calculating CT is T10, which is the detention time at which 90% of the water passing through a unit is retained within that unit. T10 shall be determined either by calculations that involve the theoretical hydraulic detention time and baffling factors that account for the degree of short-circuiting that might be expected through any given unit or by tracer studies. The baffling factors listed in Table 500.15 shall be used in determining contact time if tracer studies are not performed.
e. Inactivation credits for ozone contactors will be based on only the chambers that have a measured ozone residual. A minimum of two dedicated online monitors per ozone contactor shall be installed at locations suited to the CT calculation method used. Ozone residual levels shall be monitored continuously and recorded. Methods for computing log inactivation of Giardia lamblia and virus shall be approved by the department. Tracer studies shall be required to verify T10 values before receiving inactivation credit.
3. Instead of conducting new monitoring under subdivision D 2 of this section, an owner may elect to meet the requirements of subdivision D 3 a or D 3 b of this section.
a. The owner who has at least one year of existing data that are substantially equivalent to data collected under the provisions of subdivision D 3 of this section shall use these data to develop disinfection profiles if the owner has neither made a significant change to the treatment practice nor changed sources since the data were collected. The owner may develop a disinfection profile using up to three years of existing data.
b. The owner may use a disinfection profile developed previously in accordance with the procedures in subdivisions D 1, D 2, and D 3 of this section, if the owner has neither made a change to the treatment practice nor changed sources since the profile was developed. An owner that has not developed a virus profile shall develop a virus disinfection profile using the same monitoring data on which the Giardia lamblia profile is based.
E. The owner shall calculate the total inactivation ratio for Giardia lamblia and viruses as specified in subdivisions E 1 through E 4 of this subsection based on CT99.9 (3-log) values using the appropriate values in Tables 500.2 through 500.14. Note that the 3-log values in the tables for Giardia lamblia also indicate that a 4-log virus inactivation can be achieved. pH and temperature values between the indicated values in Tables 500.2 through 500.14 shall be determined by linear interpolation, or the CT value at the lower temperature and at the higher pH shall be used. All parameters necessary to determine the total inactivation ratio shall be monitored during peak hourly flow.
1. The owner using only one point of disinfectant application shall determine the total inactivation ratio for the disinfection segment based on either of the following methods:
a. Determine one inactivation ratio (CTcalc/CT99.9) before or at the first customer during peak hourly flow.
b. Determine successive CTcalc/CT99.9 values, representing sequential inactivation ratios, between the point of disinfectant application and a point before or at the first customer during peak hourly flow. The owner shall calculate the total inactivation ratio by determining (CTcalc/CT99.9) for each sequence and then adding the (CTcalc/CT99.9) values together to determine total inactivation (∑ (CTcalc/CT99.9)).
2. The owner using more than one point of disinfectant application before the first customer shall determine the CT value of each disinfection segment immediately before the next point of disinfectant application, or for the final segment before or at the first customer, during peak hourly flow. The (CTcalc/CT99.9) value of each segment and (∑ (CTcalc/CT99.9)) shall be calculated using the method in subdivision E 1 a or E 1 b of this subsection.
3. The owner shall determine the total logs of inactivation of Giardia lamblia by multiplying the value calculated in subdivision E 1 a or E 1 b of this subsection by 3.0.
4. The owner shall determine the total logs of inactivation of viruses by multiplying the value calculated in subdivision E 1 a or E 1 b of this subsection by 4.0.
F. A disinfection benchmark shall be calculated following the procedures in subdivisions F 1, F 2, and F 3 of this subsection.
1. For each year of profiling data collected and calculated, an owner shall determine the lowest mean monthly level of both Giardia lamblia and virus inactivation. The owner shall determine the mean Giardia lamblia and virus inactivation for each calendar month for each year of profiling data by dividing the sum of daily or weekly Giardia lamblia and virus log inactivation by the number of values calculated for that month.
2. The disinfection benchmark is the lowest monthly mean value (for waterworks with one year of profiling data) or the mean of the lowest monthly mean values (for waterworks with more than one year of profiling data) of Giardia lamblia and virus log inactivation in each year of profiling data.
3. The owner of a waterworks using chloramines, ozone, or chlorine dioxide for primary disinfection shall calculate the disinfection benchmark for viruses from the data collected in the same manner used to calculate the Giardia lamblia disinfection benchmark.
G. The owner shall retain the disinfection profile in graphic form, as a spreadsheet or in some other format acceptable to the department for evaluation as part of sanitary surveys conducted by the department.
H. Before making a significant change to the waterworks disinfection practice, the owner shall review the disinfection benchmark and consult with the department.
1. Significant changes to disinfection practice are (i) changes to the point of disinfectant application, (ii) changes to the disinfectants used in the treatment plant, (iii) changes to the disinfection process, and (iv) any other modification identified by the department.
2. The owner shall submit the following information to the department as part of the consultation process: (i) a description of the proposed change; (ii) the disinfection profile and benchmarks established for Giardia lamblia and, if necessary, viruses; (iii) an analysis of how the proposed change will affect the current levels of disinfection; and (iv) any additional information to justify the change.
TABLE 500.2
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at Less than 0.5oC
FREE RESIDUAL
(mg/L)
pH
≤ 6.0 6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
137
163
195
237
277
329
390
0.6
141
168
200
239
286
342
407
0.8
145
172
205
246
295
354
422
1.0
148
176
210
253
304
365
437
1.2
152
180
215
259
313
376
451
1.4
155
184
221
266
321
387
464
1.6
157
189
226
273
329
397
477
1.8
162
193
231
279
338
407
489
2.0
165
197
236
286
346
417
500
2.2
169
201
242
297
353
426
511
2.4
172
205
247
298
361
435
522
2.6
175
209
252
304
368
444
533
2.8
178
213
257
310
375
452
543
3.0
181
217
261
316
382
460
552
TABLE 500.3
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at 5oC
FREE RESIDUAL
(mg/L)
pH
≤ 6.0
6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
97
117
139
166
198
236
279
0.6
100
120
143
171
204
244
291
0.8
103
122
146
175
210
252
301
1.0
105
125
149
179
216
260
312
1.2
107
127
152
183
221
267
320
1.4
109
130
155
187
227
274
329
1.6
111
132
158
192
232
281
337
1.8
114
135
162
196
238
287
345
2.0
116
138
165
200
243
294
353
2.2
118
140
169
204
248
300
361
2.4
120
143
172
209
253
306
368
2.6
122
146
175
213
258
312
375
2.8
124
148
178
217
263
318
382
3.0
126
151
182
221
268
324
389
TABLE 500.4
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at 10oC
FREE RESIDUAL
(mg/L)
pH
≤ 6.0
6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
73
88
104
125
149
177
209
0.6
75
90
107
128
153
183
218
0.8
78
92
110
131
158
189
226
1.0
79
94
112
134
162
195
234
1.2
80
95
114
137
166
200
240
1.4
82
98
116
140
170
206
247
1.6
83
99
119
144
174
211
253
1.8
86
101
122
147
179
215
259
2.0
87
104
124
150
182
221
265
2.2
89
105
127
153
186
225
271
2.4
90
107
129
157
190
230
276
2.6
92
110
131
160
194
234
281
2.8
93
111
134
163
197
239
287
3.0
95
113
137
166
201
243
292
TABLE 500.5
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at 15oC
FREE RESIDUAL
(mg/L)
pH
≤ 6.0
6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
49
59
70
83
99
118
140
0.6
50
60
72
86
102
122
146
0.8
52
61
73
88
105
126
151
1.0
53
63
75
90
108
130
156
1.2
54
64
76
92
111
134
160
1.4
55
65
78
94
114
137
165
1.6
56
66
79
96
116
141
169
1.8
57
68
81
98
119
144
173
2.0
58
69
83
100
122
147
177
2.2
59
70
85
102
124
150
181
2.4
60
72
86
105
127
153
184
2.6
61
73
88
107
129
156
188
2.8
62
74
89
109
132
159
191
3.0
63
76
91
111
134
162
195
TABLE 500.6
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at 20oC
FREE RESIDUAL
(mg/L)
pH
≤ 6.0
6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
36
44
52
62
74
89
105
0.6
38
45
54
64
77
92
109
0.8
39
46
55
66
79
95
113
1.0
39
47
56
67
81
98
117
1.2
40
48
57
69
83
100
120
1.4
41
49
58
70
85
103
123
1.6
42
50
59
72
87
105
126
1.8
43
51
61
74
89
108
129
2.0
44
52
62
75
91
110
132
2.2
44
53
63
77
93
113
135
2.4
45
54
65
78
95
115
138
2.6
46
55
66
80
97
117
141
2.8
47
56
67
81
99
119
143
3.0
47
57
68
83
101
122
146
TABLE 500.7
CT Values for 3-Log Inactivation of Giardia lamblia by Free Chlorine at 25oC and Higher
FREE RESIDUAL
(mg/L)
pH
≤ 6.0
6.5
7.0
7.5
8.0
8.5
≤ 9.0
≤ 0.4
24
29
35
42
50
59
70
0.6
25
30
36
43
51
61
73
0.8
26
31
37
44
53
63
75
1.0
26
31
37
45
54
65
78
1.2
27
32
38
46
55
67
80
1.4
27
33
39
47
57
69
82
1.6
28
33
40
48
58
70
84
1.8
29
34
41
49
60
72
86
2.0
29
35
41
50
61
74
88
2.2
30
35
42
51
62
75
90
2.4
30
36
43
52
63
77
92
2.6
31
37
44
53
65
78
94
2.8
31
37
45
54
66
80
96
3.0
32
38
46
55
67
81
97
TABLE 500.8
CT Values for Inactivation of Viruses by Free Chlorine, pH 6.0-9.0
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
0.5
1
2
3
4
5
6
7
8
2
6.0
5.8
5.3
4.9
4.4
4.0
3.8
3.6
3.4
3
9.0
8.7
8.0
7.3
6.7
6.0
5.6
5.2
4.8
4
12.0
11.6
10.7
9.8
8.9
8.0
7.6
7.2
6.8
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
9
10
11
12
13
14
15
16
17
2
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
3
4.4
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
4
6.4
6.0
5.6
5.2
4.8
4.4
4.0
3.8
3.6
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
18
19
20
21
22
23
24
25
2
1.4
1.2
1.0
1.0
1.0
1.0
1.0
1.0
3
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
4
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
TABLE 500.9
CT Values for Inactivation of Giardia lamblia by Chlorine Dioxide, pH 6.0-9.0
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
0.5
10.0
8.6
7.2
5.7
4.3
4.2
4.2
4.1
4.1
1
21.0
17.9
14.9
11.8
8.7
8.5
8.3
8.1
7.9
1.5
32.0
27.3
22.5
17.8
13.0
12.8
12.6
12.4
12.2
2
42.0
35.8
29.5
23.3
17.0
16.6
16.2
15.8
15.4
2.5
52.0
44.5
37.0
29.5
22.0
21.4
20.8
20.2
19.6
3
63.0
53.8
44.5
35.3
26.0
25.4
24.8
24.2
23.6
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
0.5
4.0
3.8
3.7
3.5
3.4
3.2
3.1
2.9
2.8
1
7.7
7.4
7.1
6.9
6.6
6.3
6.0
5.8
5.5
1.5
12.0
11.6
11.2
10.8
10.4
10.0
9.5
9.0
8.5
2
15.0
14.6
14.2
13.8
13.4
13.0
12.4
11.8
11.2
2.5
19.0
3.8
3.7
3.5
3.4
3.2
3.1
2.9
2.8
3
23.0
7.4
7.1
6.9
6.6
6.3
6.0
5.8
5.5
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
0.5
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1
5.3
5.0
4.7
4.5
4.2
4.0
3.7
1.5
8.0
7.5
7.1
6.7
6.3
5.9
5.5
2
10.6
10.0
9.5
8.9
8.4
7.8
7.3
2.5
2.6
2.5
12.2
11.4
10.6
9.8
9.0
3
5.3
5.0
14.2
13.4
12.6
11.8
11.0
TABLE 500.10
CT Values for Inactivation of Virus by Chlorine Dioxide, pH 6.0-9.0
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
2
8.4
7.7
7.0
6.3
5.6
5.3
5.0
4.8
4.5
3
25.6
23.5
21.4
19.2
17.1
16.2
15.4
14.5
13.7
4
50.1
45.9
41.8
37.6
33.4
31.7
30.1
28.4
26.8
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
2
4.2
3.9
3.6
3.4
3.1
2.8
2.7
2.5
2.4
3
12.8
12.0
11.1
10.3
9.4
8.6
8.2
7.7
7.3
4
25.1
23.4
21.7
20.1
18.4
16.7
15.9
15.0
14.2
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
2
2.2
2.1
2.0
1.8
1.7
1.5
1.4
3
6.8
6.4
6.0
5.6
5.1
4.7
4.3
4
13.3
12.5
11.7
10.9
10.0
9.2
8.4
TABLE 500.11
CT Values for Inactivation of Giardia lamblia by Chloramines, pH 6.0-9.0
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
0.5
635
568
500
433
365
354
343
332
321
1
1,270
1,136
1,003
869
735
711
687
663
639
1.5
1,900
1,700
1,500
1,300
1,100
1,066
1,032
998
964
2
2,535
2,269
2,003
1,736
1,470
1,422
1,374
1,326
1,278
2.5
3,170
2,835
2,500
2,165
1,830
1,772
1,714
1,656
1,598
3
3,800
3,400
3,000
2,600
2,200
2,130
2,060
1,990
1,920
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
0.5
310
298
286
274
262
250
237
224
211
1
615
592
569
546
523
500
474
448
422
1.5
930
894
858
822
786
750
710
670
630
2
1,230
1,184
1,138
1,092
1,046
1,000
947
894
841
2.5
1,540
1,482
1,424
1,366
1,308
1,250
1,183
1,116
1,049
3
1,850
1,780
1,710
1,640
1,570
1,500
1,420
1,340
1,260
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
0.5
198
185
173
161
149
137
125
1
396
370
346
322
298
274
250
1.5
590
550
515
480
445
410
375
2
788
735
688
641
594
547
500
2.5
982
915
857
799
741
683
625
3
1,180
1,100
1,030
960
890
820
750
TABLE 500.12
CT Values for Inactivation of Virus by Chloramines, pH 6.0-9.0
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
2
1,243
1,147
1,050
954
857
814
771
729
686
3
2,063
1,903
1,743
1,583
1,423
1,352
1,281
1,209
1,138
4
2,883
2,659
2,436
2,212
1,988
1,889
1,789
1,690
1,590
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
2
643
600
557
514
471
428
407
385
364
3
1,067
996
925
854
783
712
676
641
605
4
1,491
1392
1292
1193
1,093
994
944
895
845
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
2
342
321
300
278
257
235
214
3
570
534
498
463
427
392
356
4
796
746
696
646
597
547
497
TABLE 500.13
CT Values for Inactivation of Giardia lamblia by Ozone
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
0.5
0.48
0.44
0.40
0.36
0.32
0.30
0.28
0.27
0.25
1
0.97
0.89
0.80
0.72
0.63
0.60
0.57
0.54
0.51
1.5
1.50
1.36
1.23
1.09
0.95
0.90
0.86
0.81
0.77
2
1.90
1.75
1.60
1.45
1.30
1.23
1.16
1.09
1.02
2.5
2.40
2.20
2.00
1.80
1.60
1.52
1.44
1.36
1.28
3
2.90
2.65
2.40
2.15
1.90
1.81
1.71
1.62
1.52
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
0.5
0.23
0.22
0.20
0.19
0.17
0.16
0.15
0.14
0.14
1
0.48
0.45
0.42
0.38
0.35
0.32
0.30
0.29
0.27
1.5
0.72
0.67
0.62
0.58
0.53
0.48
0.46
0.43
0.41
2
0.95
0.89
0.82
0.76
0.69
0.63
0.60
0.57
0.54
2.5
1.20
1.12
1.04
0.95
0.87
0.79
0.75
0.71
0.68
3
1.43
1.33
1.24
1.14
1.05
0.95
0.90
0.86
0.81
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
0.5
0.13
0.12
0.11
0.10
0.10
0.09
0.08
1
0.26
0.24
0.22
0.21
0.19
0.18
0.16
1.5
0.38
0.36
0.34
0.31
0.29
0.26
0.24
2
0.51
0.48
0.45
0.42
0.38
0.35
0.32
2.5
0.64
0.60
0.56
0.52
0.48
0.44
0.40
3
0.13
0.12
0.11
0.10
0.10
0.09
0.08
TABLE 500.14
CT Values for Inactivation of Virus by Ozone
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
1
2
3
4
5
6
7
8
9
2
0.90
0.83
0.75
0.68
0.60
0.58
0.56
0.54
0.52
3
1.40
1.28
1.15
1.03
0.90
0.88
0.86
0.84
0.82
4
1.80
1.65
1.50
1.35
1.20
1.16
1.12
1.08
1.04
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
10
11
12
13
14
15
16
17
18
2
0.50
0.46
0.42
0.38
0.34
0.30
0.29
0.28
0.27
3
0.80
0.74
0.68
0.62
0.56
0.50
0.48
0.46
0.44
4
1.00
0.92
0.84
0.76
0.68
0.60
0.58
0.56
0.54
LOG INACTIVATION CREDIT
WATER TEMPERATURE (°C)
19
20
21
22
23
24
25
2
0.26
0.25
0.23
0.21
0.19
0.17
0.15
3
0.42
0.40
0.37
0.34
0.31
0.28
0.25
4
0.52
0.50
0.46
0.42
0.38
0.34
0.30
TABLE 500.15
Baffling Classifications
BAFFLING 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 intra-basin baffles
Average
0.5
Baffled inlet or outlet with some intra-basin baffles
Superior
0.7
Perforated inlet baffle, serpentine or perforated intra-basin baffles, outlet weir or perforated launders
Collected 2026-09-14T04:50:41Z. Source file · JSON