ICR SS Protozoan Data Site-by-Site: A Picture of <i>Cryptosporidium</i> and <i>Giardia</i> in U.S. Surface Water

The U.S. Environmental Protection Agency (USEPA) Information Collection Rule Supplemental Survey (ICR SS) required analysis of <i>Cryptosporidium</i> and <i>Giardia</i> in 10 L surface water samples twice a week for a year by USEPA Method 1623 at 80 representative U.S. public water systems (PWS). The resulting data are examined site-by-site in relation to objectives of the Federal drinking water regulation, The Long-Term (2) Enhanced Surface Water Treatment Rule (LT2), currently under formal 6-year review by the USEPA. The data describe <i>Cryptosporidium</i> and <i>Giardia</i> in watersheds nation-wide over a single annual cycle. Due to limited recovery efficiency measurement results are not fully quantified. In the required sample volumes of 10 L no <i>Cryptosporidium</i> were found in 86% of samples and no <i>Giardia</i> were found in 67% of samples. Yet, organisms were found in enough samples at 34 of 80 sites to detail a specrtum of occurrence and variability for both organisms. The data are shown to describe indivudual site risk essential for guidance of watershed and water treatment management by PWSs. The span of median occurrence for both organisms was about 2 orders of magnitude above the limit of detection (LD), ca. 0.05 raw no’s/L for <i>Cryptosporidium</i> and ca. 0.10 raw no’s/L for <i>Giardia</i>. Data analysis illustrates key features of <i>Cryptosporidium</i> and <i>Giardia</i> in surface water: presence is continuous not intermittent; zeros indicate presence below the LD; occurrence level and variations depend on watershed sources; risk depends on both magnitude and variability of concentration; accurate estimation of risk requires routine measurement of recovery efficiency and calculation of concentration. The data and analysis illustrate features of <i>Cryptosporidium</i> and <i>Giardia</i> occurrence in surface water relevant to their effective regulation for public health protection