40 CFR 141.534  How does my system use this data to calculate an inactivation ratio?
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§ 141.534 How does my system use this data to calculate an inactivation ratio?
Use the tables in § 141.74(b)(3)(v) to determine the appropriate CT99.9 value. Calculate the total inactivation ratio as follows, and multiply the value by 3.0 to determine log inactivation of Giardia lamblia:
If your system * * *  Your system must determine * * * 

(a) Uses only one point of disinfectant application  (1) One inactivation ratio (CTcalc/CT or 
(2) Successive CTcalc/CT 

(b) Uses more than one point of disinfectant application before the first customer  The (CTcalc/CT 
[67 FR 1839, Jan. 14, 2002, as amended at 69 FR 38856, June 29, 2004]