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Membrane Filtration Regulations and Determination of Log Removal Value 143
successfully demonstrates to the state that its membrane filtration system can achieve part of the
required Cryptosporidium treatment credit, as listed in the right-hand column (i.e., under “Type of
Existing Filtration – Alternative Filtration Technologies”) of Table 4.1. However, the utility opts
not to use its membrane filtration system for the purposes of LT2ESWTR compliance. In this case,
the utility would be required to use other toolbox options to obtain all of the Cryptosporidium
treatment credit required under the rule.
Under the LT2ESTWR, the regulatory basis for a membrane filtration process to receive
treatment credit for Cryptosporidium is the demonstration of removal efficiency through
challenge testing and the demonstration of membrane system integrity through routine direct
integrity testing and continuous indirect integrity monitoring. These criteria form the basis for
the potential for membrane filtration systems to be awarded up to a maximum of 5.5 log
Cryptosporidium removal credit for complying with the requirements of the previously promulgated
surface water treatment rules in combination with any additional Cryptosporidium
treatment credit that may be required under the LT2ESWTR.
With respect to the challenge testing requirements of the rule, the two most likely options
available to utilities with existing membrane filtration systems are to grandfather data
generated during the pilot testing conducted as part of the permitting process (if applicable)
or to use data from challenge testing conducted by the membrane manufacturer in its effort to
qualify its product(s) for Cryptosporidium removal credit under LT2ESWTR (since challenge
testing is required on a product-specific and not a site-specific basis).
Existing membrane facilities will also have to meet the direct integrity testing and
continuous indirect integrity monitoring requirements of the LT2ESWTR to qualify for
treatment credit under the rule. This may necessitate that some facilities implement new
integrity verification practices, since state requirements vary widely, and some may not
require direct integrity testing at all (5, 18, 19). However, this is not anticipated to be
problematic for many existing facilities, since most membrane filtration systems applied to
surface water are equipped with the ability to conduct some form of direct integrity testing. In
addition, although states may not have explicit indirect integrity monitoring requirements,
turbidity monitoring (the default method of continuous indirect integrity monitoring under
the LT2ESWTR) is nonetheless required for compliance with the various existing surface
water treatment rules. In some cases, utilities may need to purchase additional equipment to
comply with the integrity verification requirements of the rule.
Another consideration for existing membrane facilities required to meet the LT2ESWTR
criteria is replacement membrane modules. When replacement modules are installed, it is
necessary to verify that the specific modules used meet the quality control release value of the
nondestructive performance test as a means of indirectly verifying removal efficiency.
The regulatory framework developed for membrane filtration under the LT2ESWTR
addresses many of the specific capabilities and requirements of the technology and thus
may introduce new concepts that might not be included in a given state’s current regulatory
approach for membrane processes, particularly if the state currently considers membrane
filtration as an AFT, as described in the US EPA Guidance Manual for Compliance With the
Filtration and Disinfection Requirements for Public Water Systems Using Surface Water
Sources (4). Although states may choose to adopt aspects of the LT2ESWTR framework for