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Microbial risk assessment is a structured approach to estimating
risks associated with environmental exposure to pathogens by using
available environmental data. In this report the researchers took
advantage of three sources of environmental data to estimate risk:
1) pathogen monitoring of raw sludge efficacy of treatment
processes, and pathogen monitoring of post-treatment biosolids.
This risk assessment approach is able to estimate risks even for
Class A biosolids where post-treatment monitoring data are all
below the detectable level. Using this approach this report
provides risk estimates for a number of different models to gain
insight into risks associated with different aspects of the
biosolids treatment and application process. This report provides
an approach to conducting risk assessments that takes advantage of
pathogen data from raw sludge and data on treatment process
efficacy as additional data sources to the post-treatment data. In
this context the raw sludge and treatment data are considered prior
information that can inform the risk estimate, and the post
treatment data is used to inform the likelihood. The risk
assessment framework present in this report provides a mechanism to
discuss biosolids management microbial risk using a common metric
for comparison of treatment methods, management alternatives, and
potentially to set risk-based standards for microbial contaminants
in biosolids.
Newport Bay (Orange County, California) is listed by the California
State Water Resources Control Board (SWRCB) as a water quality
limited receiving water body because of sporadic exceedances of the
fecal coliform water quality objectives for body contact
recreation. Consistent with federal and state requirements, a Total
Maximum Daily Load (TMDL) is being implemented in the watershed.
The fecal coliform TMDL in Newport Bay is a phased approach for
understanding and controlling the microbiological water quality in
the to ensure the reasonable protection of the Bay?s beneficial
uses. An important initial step within that TMDL was to assess the
impairment of the body contact recreation beneficial use (REC-1) of
Newport Bay receiving waters through characterizing the risk of
illness associated with REC-1 exposure. A health risk assessment
investigation was developed to characterize that risk. The health
risk assessment investigation involved the integration of a
population based model of disease transmission, a water quality
modeling component necessary for estimating pathogen dose as part
of the exposure assessment, and site-specific population use and
receiving water data collection. The Water Environment Research
Foundation funded the water quality modeling component of the
health risk assessment investigation, which is the focus of this
report. Also provided within this report is an overview of the
health risk assessment methodology, a summary of the major findings
from the risk assessment investigation, and a discussion of how the
health risk methodology may be applied to other watersheds where
impairment of the REC-1 beneficial use is in question. The major
findings of the health risk assessment investigation indicated that
(1) the risk of illness from REC-1 use in Newport Bay, estimated
using two separate methods was generally below levels considered
tolerable by US EPA, and (2) the reduction of controllable sources
of pollution would not appreciably reduce the existing risk. Based
on the collection of site-specific exposure data and the health
risk characterization, it was determined that evaluating the
impairment of the REC-1 beneficial use requires a more rigorous and
comprehensive health based approach than that prescribed by the
current regulations for recreational waters.
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