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Recent research has shown that the concentrations of microbial
indicator organisms (e.g., fecal coliforms) in stormwater may be
quite high. However, studies have not clearly established
relationships between the concentrations of indicator organisms and
microbial pathogens in stormwater, or between stormwater indicator
organism concentrations and illness. Thus, it is difficult to
interpret indicator data collected by local public agencies in the
context of potential risk to human health. The primary objective of
this investigation was to generate guidance to enable more accurate
and defensible evaluations of stormwater microorganism data and the
associated risks to human health from exposure to microbial
pathogens in stormwater. The investigation consisted of three major
tasks: reviewing and summarizing relevant published literature,
conducting a web-based data questionnaire and developing a
science-directed data collection plan. Topics discussed include: 1)
waterborne pathogens that pose the greatest risk to human health,
2) concentrations of pathogens and indicator organisms observed in
stormwater, 3) defensible relations between indicator organisms and
pathogens of public health concern in stormwater, 4) the
environmental fate of pathogens and indicator organisms in
stormwater, 5) the use of microbial source tracking (MST)
techniques to identify sources of fecal contamination, and 6) the
effectiveness of stormwater microorganism control technologies and
associated costs. Additionally, recommended next steps needed to
enable defensible evaluations of stormwater microorganism data and
the associated risk to human health from exposure to stormwater are
presented. Next steps include the development of interim guidance
for management prioritization, pathogens enumeration method
development, and pilot and nation-wide data collection programs.
This investigation reviewed and evaluated methodologies used for
microbial risk assessment with respect to their applicability for
reclaimed water applications. The investigation was comprised of
five primary components: a comprehensive database of articles,
reports and books describing microbial risk assessment
methodologies was established and reviewed. Risk assessment
techniques and models were identified for estimating the public
health risk from exposure to microorganisms via reclaimed water
applications. Two models were identified for further evaluation: a
static (individual based) and a dynamic (population based). In the
third component, the two models were evaluated to differentiate
between the conditions under which models predict similar and
substantially different estimations of risk. Through numerical
simulation, exposure/pathogen combinations were identified when it
may be appropriate to use the less complex, static model. Case
study risk assessment scenarios demonstrated the model selection
process for three realistic, yet hypothetical reclaimed water
scenarios.The fourth component presents a constraint analysis for
existing reuse regulations. The constraint analysis is carried out
by documenting the existing reuse regulations. The constraint
analysis is carried out by documenting the existing regs in three
states for landscape irrigation and uses that comparison as a
starting point to identify how microbial risk assessment may be
useful within the context of existing and potential future water
reuse regulations. The investigation concludes by identifying
criteria for a computer interface that would allow regulatory
and/or municipal agencies/utilities to take advantage of the
analysis discussed in the report. This publication can also be
purchased and downloaded via Pay Per View on Water Intelligence
Online - click on the Pay Per View icon below
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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