1 For example, the information entered in the ATP worksheets for sample # B982305A ( Millbrae, CA) lists the date for the original sample density determination as 12 23 98. This is also the date entered for the inoculation of the test media and for the comparability study results. As discussed in this attachment, however, the Colitag   method takes 24 hours to complete and the reference methods each require a minimum of 48 hours. Hence, the dates entered in the worksheets cannot possibly reflect all of the actual dates for the corresponding steps in the evaluation of the Colitag   method. EPA's presumption for this method evaluation, as for previous method evaluations, is that the certified drinking water laboratory performing the comparability studies employed a reasonable hold time for all samples. Although the analysis described in this Attachment can confirm this for some samples only, the information available to EPA is insufficient to refute EPA's general presumption for any of the samples. Attachment 1 Description of CPI Comparability Study Log Sheet Hold Times for Colitag   Background/ Assumptions EPA's analysis of the Colitag   ATP Worksheets suggests that some data were likely entered onto the worksheet ( and were dated) days after the original data collection. 1 One explanation for such cases is that data may have been entered into laboratory notebooks on a real time basis and subsequently transferred to the worksheets, with the dates in the submitted worksheets reflecting the dates of transcription rather than those corresponding to the underlying lab procedures.

Laboratory record keeping practices such as this ( i. e., transferring data from laboratory notebooks to summary worksheets) are not uncommon.

Consistent with past practice under the ATP program, original lab notebooks were not requested by EPA, nor were they submitted to EPA. Since such notebooks were not submitted to EPA,

they are not part of the administrative record for the decision to approve Colitag   . Accordingly,

any information contained in such notebooks did not enter into EPA's decision. As a result, EPA does not have the necessary information available to calculate a precise " hold time" ( i. e., the time elapsed between the original [ pre chlorination] density determination and the post chlorination measurement, both of which are used to calculate log reduction). Nonetheless, the information in the record, coupled with an understanding of the timing and scope of the test procedures used in the comparability studies, does allow EPA to conservatively estimate hold times. 2 Colitag   test results [ total coliforms + E. Coli] ( 24 hr) Inoculation of test media ( presumed to take place immediately after the postchlorination measurement) Postchlorination measurement BGLB ( reference method) total coliform results ( 48 96 hr)

EC MUG ( reference method) E. Coli results ( 48 72 hr) The key information that EPA determined it could consistently and reliably use to evaluate hold time was the " Test Material/ Equipment Transfer Receipt" ( the " chain of custody" record documenting the date/ time when the sample was received in the Biovir laboratory) and the data sheets documenting " Results of ATP Comparability Study of Method for Total Coliform Bacteria/

Escherichia Coli" ( i. e., the " comparability study sheets").

One can be confident that the initial density determination occurred no earlier than the date that the sample was received in the laboratory. Moreover, when the sample arrived in the laboratory in the afternoon, one can reasonably predict that in most instances the initial density determination occurred no earlier than the following day, based on the complexity and duration of the test procedure. Accordingly, EPA believes it is reasonable to add 1 day to the laboratory receipt date to establish a reasonably conservative estimate of the pre chlorination measurement date when the sample arrived in the afternoon.

One can also estimate the post chlorination measurement date, based on an understanding of the comparability study timing, as outlined below:

Comparability Study Timeline Complete total coliform results should be available no later than 4 days after inoculation, since the 2 If EPA were to build in an assumption that any length of time elapsed in between the post chlorination measurements and inoculation of the test media, this would necessarily push back the estimated points at which the post chlorination measurements were taken and reduce the " hold time" between the initial density determination and the post chlorination measurements.

3 total coliform reference method requires 48 96 hours to complete. Similarly, complete E. Coli results should be available no later than 3 days after inoculation, since the E. Coli reference method requires 48 72 hours to complete. The Colitag   portion of the test results should be available one day after inoculation, since the Colitag   test requires 24 hours to complete for both total coliforms and E. coli. ( For the purposes of estimating hold time for these comparability study samples, EPA has made the conservative presumption that inoculation of the test media takes place immediately following the post chlorination measurement. 2 )

EPA surmises that the dates on the comparability study sheets reflect either the date that data were initially transferred ( no earlier than 24 hours after inoculation of the test media, when Colitag   results might be available) or the date when all data were transferred ( no earlier than 48 72 or 48 96 hours after inoculation of the test media, when results from the E. coli and total coliform reference methods, respectively, might be available). Accordingly, one may subtract 1 3 days from the date on the comparability study sheets for E. Coli results and 1 4 days from the date on the study sheets for total coliform results, as appropriate, to identify a range of conservatively estimated post chlorination measurement dates. As reflected in the estimates of sample specific hold times ( below), in those cases where the higher end of the range yielded an illogical estimated date ( i. e., suggestive of the post chlorination measurement preceding the prechlorination measurement) EPA has used a narrower range for the study duration adjustment ( reflecting a more conservative approach) to yield a reasonable estimated date.

A conservative hold time may be computed as the difference between the estimated prechlorination and post chlorination measurement dates. Applying this approach, EPA concluded that reasonable hold times could be established for the six samples described below. Applying the approach to the other four samples ( Shaumberg, IL 990052A, Mission, KS 990217A,

Jacksonville, FL 990025A and Salem, OR 990273A) did not allow EPA to establish a reasonable, 4 conservative hold time estimate. EPA hastens to add, however, that this information does not lead inexorably to the conclusion that the hold times were unreasonable and EPA continues to make the general assumption that each of the samples was held for a reasonable period of time.

In the alternative, EPA investigated what impact removal of the four samples mentioned above would have on the Agency's assessment of Colitag   . As is described in Attachment 2,

elimination of these four samples from the statistical analysis would not alter EPA's conclusion.

Sample Specific Hold time Estimates Millbrae, CA 982084A. This sample was received at 10: 35 on 11 10 98 as is indicated on the Biovir Laboratories Inc. Sample Transfer Receipt. Because this sample was received early in the day, EPA assumed that work began on this sample on 11 10 98. Thus, 11 10 98 was established as the estimated pre chlorination measurement date. The date on the study sheets for this sample was 11 11 98 ( for both the total coliform and E. coli results). In light of the above discussion,

and considering that post chlorination measurements cannot precede pre chlorination measurements, an adjustment of one day is reasonable, in which case the estimated postchlorination measurement date is 11 10 98. Therefore, the estimated hold time for this sample is < 24 hours.

Millbrae, CA 982305A. This sample was received at 14: 45 on 12 16 98 as is indicated on the Biovir Laboratories Inc. Sample Transfer Receipt. Because this sample arrived late in the day,

EPA assumed that work began on this sample on 12 17 98. Thus, 12 17 98 was established as the estimated pre chlorination measurement date. The date on the study sheets for this sample was 12 23 98 ( for both the total coliform and E. coli results). In light of the above discussion, an adjustment of 1 3 days is conservative, in which case the estimated post chlorination measurement date is between 12 20 98 and 12 22 98. Therefore, the estimated hold time for this sample is no more than 3 5 days.

Watertown, WI 990095A. This sample was received at 09: 00 on 2 2 99 as is indicated on the 5 Biovir Laboratories Inc. Sample Transfer Receipt. Because this sample arrived early in the day,

EPA assumed that work began on this sample on 2 2 99. Thus, 2 2 99 was established as the estimated pre chlorination measurement date. The dates on the total coliform study sheet for this sample was 2 7 99. In light of the above discussion an adjustment of 1 4 days is conservative, in which case the estimated post chlorination measurement date is between 2 3 99 and 2 6 99.

Therefore, the estimated hold time for this sample is no more than 1 4 days. ( Using the E. coli study sheet date of 2 6 99 and the conservative adjustment of 1 3 days for E. coli results yields an estimated hold time of no more than 1 3 days.)

Mission, KS, 990442A This sample was received at 13: 15 on 4 27 99 as is indicated on the Biovir Laboratories Inc. Sample Transfer Receipt. Because this sample arrived late in the day,

EPA assumed that work began on this sample on 4 28 99. Thus, 4 28 99 was established as the estimated pre chlorination measurement date. The date on the total coliform study sheet for this sample was 4 30 99 ( no date is available for the E. coli results). In light of the above discussion,

and considering that post chlorination measurements cannot precede pre chlorination measurements, an adjustment of 1 2 days is conservative, in which case the estimated postchlorination measurement date is between 4 28 99 and 4 29 99. Therefore, the estimated hold time for this sample is 1 day.

Liberty, MO, 990443A This sample was received at 13: 15 on 4 27 99 as is indicated on the Biovir Laboratories Inc. Sample Transfer Receipt. Because this sample arrived late in the day,

EPA assumed that work began on this sample on 4 28 99. Thus, 4 28 99 was established as the estimated pre chlorination measurement date. The date on the total coliform study sheet for this sample was 4 30 99 ( no date is available for the E. coli results). In light of the above discussion,

and considering that post chlorination measurements cannot precede pre chlorination measurements, an adjustment of 1 2 days is conservative, in which case the estimated postchlorination measurement date is between 4 28 99 and 4 29 99. Therefore, the estimated hold time for this sample is 1 day.

Ames, IA, 990438A. This sample was received at 10: 15 on 4 27 99 as is indicated on the Biovir 6 Laboratories Inc. Sample Transfer Receipt. Because this sample arrived early in the day, EPA assumed that work began on this sample on 4 27 99. Thus, 4 27 99 was established as the estimated pre chlorination measurement date. The date on the total coliform study sheet for this sample was 4 30 99 ( no date is available for the E. coli results). In light of the above discussion,

and considering that post chlorination measurements cannot precede pre chlorination measurements, an adjustment of 1 3 days is conservative, in which case the estimated postchlorination measurement date is between 4 27 99 and 4 29 99. Therefore, the estimated hold time for this sample is no more than 2 days.