Office of Ground Water and Drinking Water January 20, 2012

MEMORANDUM

SUBJECT: Basis for Expedited Approval of EPA Method 1623.1

FROM: Carrie Miller Standards and Risk Management Division, Technical Support Center

TO: The Record

A U.S. Environmental Protection Agency (EPA) method 1623.1 was developed for monitoring Cryptosporidium oocysts under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2SWTR)

. This regulation establishes or extends treatment technique requirements in lieu of maximum
contaminant levels for Cryptosporidium . Public water systems must conduct an initial and a second
round of source water monitoring for each plant that treats a surface water or ground water under
direct surface water i nfluence. To implement t hese requirements, EPA must assess Cryptosporidium occurrence in raw surface waters used as source waters for drinking water treatment plants. EPA
Method 1623 .1 was developed to support this assessment. EPA has approved one method for Cryptosporidium thro ugh the notice

- and

- comment rulemaking process. This memo provides the requisite data to support approval of EPA met hod 1623.1 as an optional alternate method for meeting
the monitoring requirements of EPA

.

Method 1623.1 is for the detection of Cryptosporidium (CAS Registry number 137259

- 50

- 8) in water by concentration, immunomagnetic separation (IMS), and immunofluorescence assay microscopy. Cryptosporidium is further characterized using 4',6

- diamidino

- 2

- phenylindole staining and differential

in terference contrast (DIC) microscopy.

Method 1623.1 relies on fluorescent and DIC microscopy for detection ; thus, the perform ance char acteristics of method 1623.1 were compared to the characteristics of EPA Method 1623 which is
also a microscopy

- based met hod that is approved in the regulations at 40 CFR 141. 704(a) for Cryptosporidium analysis in source water

. The substantial change from Method 1623 is the addition of sodium hexametaphosphate for use with the Envirochek HV filter . Method 1623.1 also incor porates a rinse to remove excess debris during immunomagnetic separation of the oocysts and cysts.

The method performance data presented in this memo include s two EPA studies which showed improved accuracy and precision for detecting the concentration of Cryptosporidium oocysts in water when NaHMP was added: 1) a single la boratory side

- by

- side analysis that compared samples from nine public water system sources processed by 1623 , and by 1623.1

, and showed an average improvement of 18 percentage points (p = 0.0001); and 2) a multi

- laboratory side

- by

- side analysis that resulted in an

average Cryptosporidium recovery improvement with the NaHMP, compared to no addition, of 15 percentage points for the three source waters tested (p=0.0197).Figure 1 . Results of single laboratory side

- by

- side analysis. Cryptosporidium matrix spike recoveries from 9 sources comparing methods 1623 and 1623.1 (n=4). Error bars are ± one standard error of the

mean. Figure 2 . Results of side

- by

- side analysis in 4 laboratories. Cryptosporidium matrix spike recoveries from 3 sources comparing analyses with, and without, dispersant addition (n=12). Error bars are ±
one standard error of the mean.

An additional study successfully validated Method 1623.1 in fourteen laboratories and demonstrated a

mean Cryptosporidium recovery from source water of 61.2% with an average within laboratory RSD of
12.7%. A summary of the precision and recovery for Method 1623.1 was com pared to the previous validation study for Method 1623 (Table 1 ). The Cryptosporidium reagent water and source water mean percent recoveries are ≥20 percentage points higher than the previous validation study. The mean RSD
has decreased for Cryptosporidium in both matrices with Method 1623.1.

Table 1. Comparison of Study Results to Previous Validation

Cryptosporidium

Matrix Statistic Method 1623 Method 1623.1

Reagent Water Mean % Recovery 40 60

Mean RSD 24 16

Source Water Mean % Recovery 38 61

Mean RPD 36 13

These data from the 1623.1 validation were used to develop quality control criteria for laboratory performance. For each criterion, the distribution of recovery was estimated by using random effects ANOVA. The recovery limits were estimated as the 5 th percentile of the predictive distribution for each criterion. The lower limit acceptable for recovery of Cryptosporidium detected in reagent and sou rce water increased by 22 and 19 percentage points, respectively, over Method 1623 criteria. Laboratories performing Method 1623.1 should have better detection rates and follow more stringent quality control criteria than those laboratories following Method 1623.