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Membrane Filtration Regulations and Determination of Log Removal Value 151
similar in quality to the modules subjected to challenge testing to demonstrate the ability of
the module of interest (which would not have been subject to challenge testing) to achieve
the same LRV. After a group of modules has been subject to challenge testing, the NDPT
is applied to those modules to determine an appropriate QCRV associated with the
removal efficiency observed during the test. Subsequently, all modules that are not subjected
to challenge testing must pass the same NDPT by exceeding the established QCRV
applicable to Cryptosporidium removal under the LT2ESWTR. Modules that do not
pass the NDPT at the QCRV would not be eligible for Cryptosporidium removal credit
under the rule and could not be used in any membrane filtration systems applied for this
purpose.
The LT2ESWTR does not specify a particular procedure for determining the QCRV
from the various modules that are subjected to challenge testing. Thus, the manufacturer or
independent testing organization may exercise its discretion in selecting an appropriate
methodology. The QCRV may be selected as the average result among the various modules
tested, the most conservative result (to establish the most stringent QA/QC standards), or
the least conservative result (to maximize the number of modules eligible for removal
credit under the LT2ESWTR). Alternatively, a methodology similar to that required by
the LT2ESWTR for determining the overall removal efficiency based on the number of
LRV observations could be applied to the various NDPT results to yield an appropriate
QCRV.
Note that the rule does not specify the manner in which the QCRV is determined from the
challenge test data; however, the methodology must be acceptable to each state in which
the product line is applied for the purpose of receiving Cryptosporidium removal credit under
the LT2ESWTR. It is recommended that each module subjected to challenge testing also
undergo subsequent nondestructive performance testing for the purpose of establishing a
QCRV. The manner in which the NDPT results are used to determine the QCRV should
reflect the manner in which modules are selected, as well as the range of LRVs observed
during the test. If modules are selected in a conservative manner and if the range of LRVs
observed during challenge testing is small, the average of the respective NDPT results from
the modules subjected to challenge testing might be selected to represent the QCRV.
However, if a statistical distribution of modules is selected for challenge testing or if the
range of LRVs observed during challenge testing is significant, a more conservative value is
recommended for the QCRV, such as the minimum of the NDPT results observed among the
tested modules.
Because it is common for manufacturers to conduct some type of NDPT on every module
as a routine component of its QA/QC program, the NDPT requirements of the LT2ESWTR
simply ensure that the QCRV used by the manufacturer is sufficient to justify the LRV for
Cryptosporidium demonstrated via challenge testing. Note that because different NDPTs
may be used by the various membrane module manufacturers, the rule does not specify a
particular type of NDPT. However, the NDPT used must be consistent with the resolution
requirements of the LT2ESWTR for a module to be eligible for Cryptosporidium removal
credit.