FAX TRANSMISSION

To: FULL_SCALE UV PROJECT TEAM

From: Jim Malley

Date: July 10, 1997

Dear Associates:

My purpose for writing is to attempt to bring closure to the UV dosage issues that will be studied in our project. I promised to poll both the volunteer Technical Advisory Committee (TAC) and the AWWARF appointed Project Advisory Committee (PAC). The end result of that process was a consensus of those responding that the dose for S. Berwick should be set at 50 mW-sec/cm^2 based on the available scientific data and the dosages tested for Indianapolis be varied as 40, 60 and 80 mW-sec/cm^2.

I am proposing that we agree to these dosages and move forward with the equipment design, production and installation. Several members of the TAC and PAC from USEPA remain concerned with the need for testing a dosage of 140 mW-sec/cm^2 but all agreed that the costs likely put it beyond the scope of this research project.

On a scientific note, I should mention that several leading virologists (personal communications with Gerba, Sobsey and Margolin) are now suggesting an MPN type multiple dilution technique that combines PCR and cell culture for viral enumeration. This new technique which adds more statistical sensitivity to the viral assay results could radically change the literature values we have always accepted for the UV dose response of human viruses (one early, unsubstantiated study done here at UNH last week suggests that a dose of 80 mW-sec/cm^2 under ideal lab conditions maybe needed for 4-log rotavirus inactivation in some waters whereas our early work and that of others reported in the literature had placed it in the 20 to 40 mW-sec/cm^2 range. We have run a few studies with S. Berwick water on our previous AWWARF project which show that the proposed dose of 50 mW-sec/cm^2 will achieve a 4-log rotavirus inactivation even when using the new MPN RTPCR/cell culture approach.

Please let me know your thoughts so that we can move forward as efficiently as possible with this project.

Best Regards,

Jim

FAX TRANSMISSION

To: Jim Malley

From: Bill Cairns

Date: July 25, 1997

Subject: UV Dose Selection for the Groundwater Disinfection Demonstration Project

Jim,

Trojan has reviewed your fax of July 10th indicating the TAC and PAC consensus that for S. Berwick the UV dose should be 50 mW-s/cm^2 and for Indianapolis the dose should be 40, 60 and 80 mW-s/cm^2. We will follow the committees' recommendations and redesign the demonstration equipment to deliver these doses. I do not know whether TAC and PAC had access to our draft document sent to you on May 7th, but I hope that the committees' consensus was arrived at in light of the issues raised in the May 7th document. The comments below are also sharable. They reiterate a few of the issues, and raise a few issues deriving from your July 10th fax.

Trojan does not anticipate that use of a high UV dose will be either universally needed or practical. With that expectation in mind, Trojan will provide equipment to the Indianapolis project to allow testing of a lower UV dose (in the 20-30 mW-s/cm^2 range) in addition to the higher doses recommended by TAC and PAC.

1) Many of the groundwater-using installations being targeted for UV disinfection appear not to be using any disinfection at present, and a high disinfectant dose (with any disinfectant) would seem unnecessary for these sites. The benefits of encouraging communities to exercise care when selecting their potable water source should not be diluted by suggesting that a high disinfectant dose is a substitute for such care, or that because of the high dose, the standards used in selecting the source can therefore by relaxed. The multiple barrier approach (good source, good source protection, good treatment) to protecting potable water and public health should be encouraged. When financial resources are limited to communities and decisions must be made between expenditures for sourcing a water supply and expenditures for treating the water, there is more value to be derived from partitioning limited resources more towards selecting, monitoring and protecting a good source than towards applying a high disinfectant dose with the hope that the high disinfectant dose can overcome all unforseen consequences of relaxed water source selection and protection.

2) If good water sources do not need disinfection or only lower levels of disinfection, then poorer water sources would require higher levels of disinfection. Axiom 1: one dose does not fit all, and even an arbitrarily defined high dose may not be sufficient if water quality is not sustained at an appropriate level for that high dose. Axiom 2: sustaining good water quality will allow use of lower disinfectant doses. The key question is when is a disinfectant dose no longer adequately matched to the water quality being treated? Given the complex composition of source waters, a biological standard seems the most practical way to assess whether the disinfection process is adequate for the water quality being treated. There is more benefit to be gained in public health protection by encouraging awareness of, and designing for matching of disinfectant dose to water quality as assessed on the basis of achieving a biological standard, than to be gained by encouraging the concept of one disinfectant dose fits all scenarios. This importance of developing the habit of associating disinfectant dose with water quality may be less apparent in groundwater disinfection, but will be critical to achieving disinfection of surface water or blended ground-surface water to the same risk levels which can be achieved with good quality ground waters. If high disinfectant doses are specified for groundwaters, the doses for poorer quality surface waters would be unreasonably high and if the doses were reduced to practical levels, the result would be unequal risk to users of ground and surface water sources. There is a need to develop a uniform approach to disinfection.

3) The choice of a biological standard (organism, method and its target count) against which to monitor (or design) the performance of a disinfection system is not yet universally agreed upon, and care must be exercised in evaluating a disinfection technology on a given basis (e.g. cost to deliver a particular disinfectant dose) if that basis can not be used when making a cost-benefit comparison with other disinfection options. Although seeded organisms (bacteria and/or viruses) can be used to validate the delivery of the design dose, and for comparing the cost of different technologies each having to produce the same survival count (using the technology-specific dose for the seeded organism), the primary concern is whether the delivered dose is providing adequate pathogen reduction with the water quality or variation in water quality encountered in the water being treated. There is little interest in determining what high dose of disinfectant might be required to achieve several log reductions in counts of a seeded organism which can self-association at the high concentrations needed in the feed to monitor the reduction levels wanted. There is more interest in whether indigenous pathogens are associating with themselves or colloidal material at the much lower concentrations encountered in potable water sources, and whether the disinfectant dose is providing adequate control. Only a biological standard using indigenous indicators would appear to provide the necessary performance evaluation which is associated with the risk to public health risk from potable water.

4) Until the current biological standards have been correlated with the results of epidaemiological studies to benchmark the current risk level to public health, it is inappropriate to change to new standards (based on log reductions of a new indigenous indicator organism, on log reductions of a non-pathogen seeded organism, or even on new target counts for current indigenous indicators) without appropriate evaluation of the consequences of a change in the standard on the change in risk and cost-benefits relative to the current benchmark values. It is also inappropriate to establish standards which are different for different disinfectants without evaluating the implications for any changes in relative risk and cost-benefit which would result when changing from one disinfectant to a different disinfectant. It is consequently inappropriate to use dose as a surrogate for biological standards until validity has been established for the dose being able to preserve at least the current benchmark values of disinfection and risk and the water quality range over which the dose is applicable has been established. On the reasonable assumption that the quality of groundwater sources for potable water will have a lesser impact on disinfectant dose selection than will the water quality of treated surface waters, and on the assumption that the variation in groundwater quality will be less than the variation in purposes if such a dose has been validated to achieve the target disinfection level and can consistently do so over a definable range of water qualities found in different source waters. Validation of the design dose approach would require selection of a key indigenous indicator organism (e.g., rotavirus, coliforms, etc.) and identification of a target indicator level which is compatible with the target risk level sought. ALL disinfectants would then have to be dosed as necessary for each disinfectant to provide at least the same target level for that organism in a variety of waters having a specified water quality or better, PROVIDED THAT the same target level of indicator reflected the same risk level for different disinfectants (otherwise, different target levels would have to be developed for different disinfectants). Since pathogen levels (e.g., of rotavirus) could fluctuate widely in the pre-disinfected water and require large volumes for analysis, the presence of a more abundantly found organism suggesting contamination (e.g., coliforms, indigenous coliphage) may be more suitable, PROVIDED THAT target post-disinfection counts reflect appropriate target risk levels. In the absence of epidaemiological date relating the occurrence of specific pathogen indicators and/or fecal contamination indicators to public health risk, in the absence of water quality information identifying the statistical variation in such indicators, in the absence of an indication of what water quality parameter and its value is key to setting the limits of the design dose concept, and in the absence of agreement on indicator of choice, standardized assay methods, and target indicator level for acceptable risk, it is appropriate to compare current and new disinfection technologies on the performance benchmarks currently in use at specific sites, i.e., the level of indicator resulting from current disinfection practice where such practice exists, or the average level of indicator present in waters considered safe to use without disinfection). In most cases, benchmark values of disinfection process biological indicators will have to be determined by assays using much larger samples than currently used to determine the presence or absences of the indicator. The same kind of absolute pre- and post-disinfection microbial/viral counts for current and proposed indicators when undertaken in conjunction with epidaemiology studies would be needed to establish the impact on health risk of a change from one disinfection standard or indicator to another. Knowing the pre-disinfection level of any indicator and the post-disinfection level of that indicator following current disinfection practices, and knowing the dose-response curve for that indicator with different disinfectants allows one to determine the effective dose needed for any disinfectant to achieve the current benchmark disinfection levels. When the final indicator level and the dose to achieve that level has been validated as being adequate over several sites, then some confidence can be developed in stating that a dose-based design is possible, what that dose should be, and what the target level of indicator should be to produce potable water which is acceptable from a public health risk perspective. It still is required however that appropriate water quality parameters be defined to indicate when the water quality exceeds the limits below which a dose-based design is acceptable. A biological standard based design should always be considered an acceptable alternative to a dose-based design, and it is required that the target levels of disinfection, the indicator, method, etc. be defined and kept equivalent to those used in validating the dose-based design.

5) The published UV dose responses for the disinfectant-resistant rotavirus indicates a dose between 32 and 41 mW-s/cm^2 for a 4 log inactivation of rotavirus if the virus were present in the potable water at levels 4 logs higher than the level required for an acceptable level of risk (see the attached Table). The UNH studies suggested a similar low 50 mW-s/cm^2 for 4 log inactivation of rotavirus. However, even the highly polluted Seine River (surface water) in France would require less than a dose of 50 mW-s/cm^2 if all the virus particles were unassociated rotavirus particles (see the May 7 document). It is unlikely that groundwater would be so highly polluted as the Seine or as rich in particulates to which the viruses could adsorb (selection of source water should avoid such contamination); it is unlikely that all virus particles would be rotavirus (a 3 log reduction of rotavirus would require a dose between 24 and 31 mW-s/cm^2 and a 2 log reduction of rotavirus would require a dose between 16 and 21 mW-s/cm^2); and it is unlikely that all virus particles would remain throughout any process intended to improve water quality that was as poor as that found in the Seine River. Some of the older does-response data suffered from the absence of good intensity and hence dose measurement methods, or were complicated by microbial clumping phenomena visible in the data at viruses where association is less likely. With good quality groundwater sources (an assumed requirement if a design dose is to be a surrogate for biological standard-based design) the likelihood of having to use high disinfectant doses is remote.

6) Improvements in virus assay methods may allow detection of higher numbers of viral particles in the waters and the temptation is there to imply that larger numbers of virus particles must be inactivated using higher doses to achieve the same post-disinfection target level for acceptable risk; however, the human infectivity dose curves for the virus (required to determine the target disinfection level) and the disinfectant dose-response curve might also be adjusted to different levels with the better assay methodologies. There are many uncertainties associated with determining the dose which should be used for virus reduction during potable water disinfection. The number of viral particles required for infection is questioning how certain we are of this value when it is empirically determined during infectivity studies, and what the implications of higher viral doses for infectivity are when comparing the pre- and post-disinfection concentrations of viruses to determine the dose required to achieve this transformation. Equally uncertain is whether the improving viral assay methodologies are linear over a broad range of virus concentrations relative to older methods, whether improvements in recovery of both free and particle-associated viruses are incorporated into the new methodologies, and therefore whether the dose-response curves with different uncertainties, a first-principles approach to establishing the target level of indicator or pathogen may appear challenging; however, on a practical basis, if a given water supply has been demonstrated to be a safe water supply for the community from the public health perspective, then measurement by whatever technique of the pre- and post-disinfection virus levels, and the demonstration that any given disinfectant produces the same virus level when assayed using the same methodology would be adequate to compare the doses needed by different disinfectants to achieve comparable inactivation of the same virus. Improved methodologies might change our perception of the absolute values of virus particles present, but for comparative purposes, any reasonable technique may be adequate. This again points to the need to benchmark current performance levels (the comparative standard) with current disinfection practices prior to making changes in indicators, target indicator levels, or disinfectants used. Clearly too, the methodologies used must be noted for future reference against historic benchmarked values.

Bill