The Information Collection Rule Supplemental Surveys (ICRSS) were designed
to supplement the ICR with more reliable information on protozoa occurrence
. The surveys benefitted from measures that were not part of the ICR, notab
ly an improved protozoa detection method, an expanded quality control (QC)
program, and a centralized sample control center. Based on analyses of data
from the protozoa monitoring portion, the ICRSS have yielded measurable im
provements in the quality of protozoa occurrence data available to support
current rulemaking efforts. Compared with ICR results, ICRSS field sample d
ata are characterized by higher detection rates and fewer potential false-p
ositive results. Data from more than 400 source water QC samples analyzed d
uring the surveys indicated mean Cryptosporidium recoveries of 43 percent a
nd mean Giardia recoveries of 53 percent from field samples spiked with lab
oratory strains of these organisms. Results confirmed that the performance
of methods 1622 and 1623 during monitoring of 87 US source waters was consi
stent with their anticipated performance, demonstrated through interlaborat
ory validation studies conducted before surveys began.