ICR SS Protozoan Data Site-by-Site: A Picture of Cryptosporidium and Giardia in U.S. Surface Water Jerry E. Ongerth* Civil, Mining, & Environmental Engineering, University of Wollongong, Wollongong, New South Wales 2522, Australia * S Supporting Information ABSTRACT: The U.S. Environmental Protection Agency (USEPA) Information Collection Rule Supplemental Survey (ICR SS) required analysis of Cryptosporidium and Giardia 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 Cryptosporidium and Giardia 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 Cryptosporidium were found in 86% of samples and no Giardia 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 Cryptosporidium and ca. 0.10 raw no’s/L for Giardia. Data analysis illustrates key features of Cryptosporidium and Giardia 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 Cryptosporidium and Giardia occurrence in surface water relevant to their effective regulation for public health protection. 1. INTRODUCTION The waterborne protozoan pathogens Cryptosporidium and Giardia are the subject of Federal drinking water regulation in the U.S., the Long-term 2 Enhanced Surface Water Treatment Rule (LT2), 1 including formal Federal requirement for data collection, the Information Collection Rule (ICR). 2 Data on Cryptosporidium and Giardia occurrence in representative surface water sources used by public water systems (PWS’s) across the U.S. were produced in an addition to the Information Collection Rule called the Supplemental Survey (ICR SS). 2 Site-by-site analysis of this unique and extensive data set is used to raise timely issues relevant to drinking water regulation in the U.S. Significant work was done by the U.S. Environmental Protection Agency (USEPA) and contractors using data from the ICR and the ICR SS in developing and finalizing provisions of LT2. 1 However, in generalizing the negative-result-dominated data for the purpose of formulating monitoring requirements for LT2, implications of the data for each PWS and their individual sampling sites were not thoroughly explored. 3 The focus of the analysis in this paper is the ICR SS individual site data and their implications. In reviewing these data along with recently published analysis of the LT2 data some fundamental issues regarding the formulation of the Surface Water Treatment Rule are raised. The critical issue addressed by LT2 and to which the Cryptosporidium (and Giardia) monitoring of both the ICR SS and LT2 were directed is to identify the relative risk associated with these organisms to surface water-using PWS’s. 4 The rule includes risk management in four categories or “BINs” based on LT2 monitoring data, 3 imposing incremental Cryptosporidium control requirements for increasingly higher BINs. Recognizing the principle that risk is proportional to concentration, previous work on these organisms has established that the concentration of Cryptosporidium and Giardia is generally proportional to the extent and intensity of organism generating activity in the tributary watershed. 5,6 Hence, concentrations and risk should logically increase downstream with increasing watershed area and activities including domestic animal raising and human population. An overriding shortcoming of the ICR SS data is that recovery efficiencies were not measured nor applied to calculate concentrations from the raw numbers of organisms found. The concentrations of Cryptosporidium and Giardia in surface water in the U.S. are of particular importance in 2013. This is due to the LT2 requirement for a second round of Cryptosporidium monitoring by the same PWS’s beginning in 2016. 1 In addition the LT2 regulation is in the midst of a Received: June 24, 2013 Revised: August 13, 2013 Accepted: August 14, 2013 Published: August 14, 2013 Policy Analysis pubs.acs.org/est © 2013 American Chemical Society 10145 dx.doi.org/10.1021/es4027503 | Environ. Sci. Technol. 2013, 47, 10145-10154