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Cryptosporidium (part 2 of 2) Page 2 of 11 � • � r r� . . . . Portland, Tacoma and Seattle). ■ Treatment - The SFPUC is performing an evaluation of its filtration practices at the Harry Tracy and Sunol Water Treatment Plants to optimize particulate removal. Pilot studies at Hetch Hetchy evaluated optimization techniques for Cryptosporidium removal. Disinfection studies were pe►formed at the University of Arizona evaluating the influence of existing physical and treatment conditions in the SFPUC Hetch Hetchy water delivery and treatment system on Cryptosporidium. These included pH changes (SFPUC water is increased from 7 to 10), pressure drops (there are two major powerhouses on the Hetch Hetchy Aqueduct that may rupture the oocysts), and sequential addition of disinfectants. These studies indicated that Cryptosporidium inactivation is currently negligible, but that sequentially adding chlorine followed by chloramine is capable of providing modest inactivation of Cryptosporidium. SFPUC testing showed up to 1 log (or 90 percent) Cryptosporidium inactivation was possible. The required ozone dose for inactivating Cryptosporidium in Hetch Hetchy has been determined to require a much longer reaction time than is conventionally used for ozonation. The risks of stimulating growth of opportunistic bacteria in consumer plumbing remains a concern with this option. ■ Watershed Protection - In 1997, the SFPUC engaged in an intensive public process to modify grazing practices in the Alameda watersheds to limit microbial risks. A series of best management practices have now been adopted. San Francisco Source and Treated Waters The SFPUC has been intensively monitoring all three of its sources for Cryptosporidium and Giardia since January 1993. Giardia and Cryprosporidium have been detected in a few samples. For monitoring, two methods have been used at different times. From ]anuary 1993 through October 1994, proposed Standard Method 97116 (without differential interterences contrast microscopy) was used. Since November 1994, the ICR method has been used. Using proposed Method 9711B, Cryptosporidium levels detected ranged from less than 0.1 to 0.8 oocysts per 100 liters in Hetch Hetchy water. Cryptosporidium was typically detected in approximately 30 percent of the samples collected. With the ICR method, presumptive Cryptosporidium levels in Hetch Hetchy water ranged from 0.4 to 7 oocysts per 100 liters, approximately an order of magnitude greater than results obtained using proposed Method 9711B. Oocysts continued to be detected in about 30 percent of samples even though the median detection limit increased from 0.1 to 1 oocyst per 100 liters with the method change. The difference in results appears to be related to method changes rather than environmental changes (i.e., increased watershed contamination). See Appendix E for further discussion on method differences. Cryptosporidium oocysts were also detected in some samples from San Antonio, Calaveras, and San Andreas Reservoirs (all of which are filtered) and in some finished waters. Three points should be noted. First, detection of oocysts in the treated water does not provide information about viability. There is a high likelihood that oocysts http://sfwater.org/printContent.cfrn/C ID/445/ 10/19/2004