deploy site-specific options such as quantitative microbial risk assessment (QMRA)
or natural source exclusion (NSE) that are becoming part of the regulatory framework [103–105].
6.1 Quantitative Microbial Risk Assessment
The goal of quantitative microbial risk assessment (QMRA) is to quantify the
relative risks to humans from exposure to recreational water impacted by different
sources of fecal contamination and to clarify which pathogens cause illnesses to
swimmers in water bodies that are impacted by specific sources of fecal contamination. To accomplish this, it will be necessary to determine the degree to which
risks of illness depends on or varies with the source(s) of contamination. The
context for regulators and the regulated community is to assess if the relative risk
differences are sufficient to warrant consideration for alternative (yet equivalent)
water quality standards. While QMRA has proven useful for increasing the understanding of apparent and relative human health risks from exposure to various
sources of fecal pollution, regulators currently do not have the information necessary to develop nationally applicable water quality criteria based on different
sources of fecal contamination. However, it may be possible to develop sitespecific criteria protective of recreational use that take into account the relative
risk of sources, provided the sources affecting a specific water body are well
understood both spatially and temporally.
6.2 Natural Source Exclusion
The goal of NSE is to implement alternative site-specific FIB objectives for water
quality, assuming that dischargers (1) control all anthropogenic sources of indicator
bacteria to a water body, (2) demonstrate that all anthropogenic sources of indicator
bacteria to a water body are controlled, and (3) demonstrate that the remaining
indicator bacteria densities do not indicate a health risk. When the sources can be
proven less risky to recreational users, a different (larger) criterion value for FIB
might be appropriate. Like QMRA, regulators do not yet have sufficient information to develop such new water quality criteria as each case will be geographically
specific. Any case-by-case consideration for NSE must be scientifically defensible,
well documented, and supported with data and information and provide for public
comment and access to information.
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281
or natural source exclusion (NSE) that are becoming part of the regulatory framework [103–105].
6.1 Quantitative Microbial Risk Assessment
The goal of quantitative microbial risk assessment (QMRA) is to quantify the
relative risks to humans from exposure to recreational water impacted by different
sources of fecal contamination and to clarify which pathogens cause illnesses to
swimmers in water bodies that are impacted by specific sources of fecal contamination. To accomplish this, it will be necessary to determine the degree to which
risks of illness depends on or varies with the source(s) of contamination. The
context for regulators and the regulated community is to assess if the relative risk
differences are sufficient to warrant consideration for alternative (yet equivalent)
water quality standards. While QMRA has proven useful for increasing the understanding of apparent and relative human health risks from exposure to various
sources of fecal pollution, regulators currently do not have the information necessary to develop nationally applicable water quality criteria based on different
sources of fecal contamination. However, it may be possible to develop sitespecific criteria protective of recreational use that take into account the relative
risk of sources, provided the sources affecting a specific water body are well
understood both spatially and temporally.
6.2 Natural Source Exclusion
The goal of NSE is to implement alternative site-specific FIB objectives for water
quality, assuming that dischargers (1) control all anthropogenic sources of indicator
bacteria to a water body, (2) demonstrate that all anthropogenic sources of indicator
bacteria to a water body are controlled, and (3) demonstrate that the remaining
indicator bacteria densities do not indicate a health risk. When the sources can be
proven less risky to recreational users, a different (larger) criterion value for FIB
might be appropriate. Like QMRA, regulators do not yet have sufficient information to develop such new water quality criteria as each case will be geographically
specific. Any case-by-case consideration for NSE must be scientifically defensible,
well documented, and supported with data and information and provide for public
comment and access to information.
Microbial Source Tracking: Advances in Research and a Guide to Application
281