Water Quality Management - River Dynamics and Integrated River Management - page 598

time required to complete a group of test procedures to identify many pathogens would greatly reduce
the usefulness of the test results. Thus, such a group of test procedures is not applicable to the frequent
routine sampling of water supplies and contact recreation (swimming, water skiing, kayaking, etc.) areas.
Instead public health officials have tried to identify organisms that are indicative of human fecal matter
and human pathogens. These indicator bacteria are monitored under the premise that if their concentrations
are appropriately low the concentrations of pathogens also will be low and human health will be protected.
An ideal indicator organism should be associated with sources of human pathogens, unable to grow in
aquatic environments, applicable to all types or water, and remain quantifiable after infectious levels of
pathogens have disappeared (Oregon DEQ, 1994). The indicator organism also must correlate with the
presence of human pathogens and the risk of disease.
In the U.S., in the early 1970s most states selected total coliforms or (primarily) fecal coliforms as the
appropriate indicator of pathogen contamination. The typical fecal coliform standard is ķ the log mean
of five or more samples taken over a 30-day period should not exceed 200 MPN or CFU/100 mL, and
ĸ no single sample should exceed 400 MPN or CFU/100 mL (where MPN is the most probable number,
and CFU is colony forming units). Total coliforms and fecal coliforms are present in high abundance in
the gastrointestinal tracts of most warm-blooded animals, and the detection of these organisms implies
the presence of fecal contamination. The number of coliform organisms in human feces is very great, the
daily per capita excretion varying from 125 to 400 billion (Clark et al., 1977, p. 261).
As a result of the Cabelli et al. (1982), Cabelli (1983), and DuFour (1984) epidemiological studies
(study of disease in populations), the USEPA (1986a) recommended E. coli and enterococci spp. for
monitoring the microbial quality of freshwaters. These epidemiological studies statistically correlated
indicator organism concentrations and incidence of illness in swimmers exposed to the water, formulating
a relationship between indicator organism concentrations and health effects. That is, regression results for
illness versus either E. coli or enterococci were used to develop criteria for geometric mean levels of
these indicators corresponding to the target acceptable illness rates. These studies were done from 1973
to 1982 on 6 ocean beaches and 5 fresh water beaches, four on Lake Erie in Ohio and one on Keystone
Lake in Tulsa, Oklahoma. Some of these beaches were investigated two or three times, resulting in
essentially 9 epidemiological trials (tests) for fresh water. Even though the criteria were determined from
beaches they have been readily applied in rivers. The Ambient Water Quality Criteria for Bacteria adopted
by USEPA (1986a) are as follows. For salt water, the log 10 mean of five or more samples taken over a
30-day period of enterococci levels should not exceed 35 MPN/100 mL and no single sample should
exceed 104 MPN/100 mL. For fresh water, the log 10 mean of five or more samples taken over a 30-day
period of Escherichia coli ( E. coli ) should not exceed 126 MPN/100 mL and no single sample should
exceed 235 MPN/100 mL. Jin et al. (2004) also found that enterococci appeared to be a more reliable
indicator than E. coli and fecal coliforms for brackish waters.
Despite the USEPA's publication of new standards in 1986 most states continue to use the conventional
fecal coliform standard to assess compliance with establish standards for recreational water. State agencies
have not switched to the new recommendations for the following reasons (Jin et al., 2004):
(1) There is no clear advantage in health risk assessment,
(2) Viral agents have different kinetics of inactivation,
(3) Parasitic disease organisms are not considered, and
(4) The fecal coliform group has been a fairly good indicator based on past experience.
Further, the regulated and scientific communities continue to question the validity of the 1986 Ambient
Water Quality Criteria for Bacteria as discussed in the following paragraphs.
The draft “USEPA Guidance Document” (USEPA, 2003a) stated that the 1986 bacteria standards based
on concentrations of enterococci and E. coli are scientifically more defensible than the old standards,