HomeMy WebLinkAboutIV. COW Agenda Item Disinfection By-Products Rule Stage 2 Comliance
Mount Prospect Public Works Department
INTEROFFICE MEMORANDUM
TO:
FROM:
DATE:
SUBJ:
Background
VILLAGE MANAGER MICHAEL E. JANONIS
DEPUTY DIRECTOR OF PUBLIC WORKS
FEBRUARY 3,2010
DISINFECTION BY~PRODUCTS COMPLIANCE & HYDRAULIC
WATER MODEL REPORT
In fall 2007, staff requested funds to secure technical assistance with efforts to comply
with the requirements of the Disinfection By-Products Rule Stage 2 (DPBR/Stage 2).
DBPR/Stage 2 is a federal rule promulgated by the United States Environmental
Protection Agency (USEPA). It requires water purveyors to identify and, if necessary,
take steps to minimize the presence of disinfection by-products in drinking water.
Specifically, this rule requires water system owners to determine the concentrations of
trihalomethanes (TTHM) and haloacetic acids (HAAS) in their distribution systems. If
these concentrations exceed certain USEPA-mandated action levels, steps must then be
taken to reduce these concentrations.
Disinfection by-products (TTHMs and HAAS) occur in drinking water as a consequence
of the decomposition of chlorine (CI2). The USEPA has determined that trihalomethanes
and haloacetic acids are carcinogens and can contribute to the formation of certain
cancers if long-term exposures are significant.
The use of chlorine as a disinfection agent is ubiquitous in the United States. Chlorine is
commonly added to drinking water throughout the country to destroy bacteria and
prevent the spread of water-borne disease. Chlorine is added to Mount Prospect's
drinking water by the City of Chicago water purification plants. In addition, both the
Northwest Suburban Municipal Joint Action Water Agency (NWSMJAWA) and the Public
Works Department typically add additional chlorine to water during warm weather
months when chlorine residuals dissipate quickly.
Initially, the DBPR/Stage 2 rule required Mount Prospect to develop a disinfection by-
products water sampling plan. This plan had to be designed to collect water samples
from the portions of the distribution system where water age is the oldest and/or
conditions are most favorable for the formation of disinfection by-products. The
identification of sample site locations had to be based on scientific reason, such as a
hydraulic water model. Sites solely identified by anecdotal reasoning or institutional
knowledge about aged water areas were not acceptable to USEPA.
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February 3, 2010
Disinfection By Products Compliance and Hydraulic Water Model Report
Additionally, staff intended to utilize the required hydraulic water model to analyze the
overall performance of the water distribution system and identify potential improvements
that could increase operational efficiencies, improve capital project planning, enhance
emergency response planning, and alleviate historically observed deficiencies such as
localized water pressure extremes (low water pressure and high water pressure) and
insufficient fire flow.
It is significant to note that the request for proposals (RFP) prepared to solicit the
requisite technical services necessary for this project stipulated the creation of the
computerized hydraulic water model utilizing MWH Soft water modeling software. This
stipulation was based on staffs assessment that the MWH Soft product best suited the
needs of the Village. Specifically, staff determined that MWH Soft had the most intuitive
user interfaces and the best integration with the Village's existing geographic information
system (GIS) software. The MWH software, along with the hydraulic water model and all
scenario iterations, became the property of the Village at project conclusion. This
software and model can now be utilized by staff to analyze distribution system problems
and assess development impacts.
A complete listing of the scope of work included in this project is summarized below:
· Prepare and calibrate a hydraulic water model.
· Conduct model simulations including maximum day demands, maximum day
plus fire flows, maximum hour demand on maximum day, and minimum hour
demand on maximum day with storage tank replenishment.
· Conduct extended period simulation to identify areas with greatest potential for
developing disinfection by-products.
· Provide Disinfection By-Products Rule compliance assistance.
. Evaluation operation of existing water distribution system
. Conduct a water main break analysis
· Prepare an Insurance Services Office (ISO) review and report.
· Perform future needs analysis and compile recommendations for system
improvements.
The Village Board awarded a contract for the scope of work described above to Burns &
McDonnell engineering consultants of Downers Grove, Illinois. Burns & McDonnell
completed the project in spring 2009.
Results
Disinfection Bv-Products Compliance. Efforts to comply with USEPA's Disinfection By-
Products Rule included the development of a water system network model and the
identification of sampling sites where oldest water in the distribution system could be
analyzed. The model and sampling sites were approved by USEPA. Subsequent water
sampling from these sites revealed trihalomethane levels lower than 40 mg/Liter and
haloacetic acid levels lower than 30 mg/Liter. These results demonstrate that the Village
is in compliance with the Disinfection By-Product Rule. Moreover, no corrective action to
further reduce these levels is necessary at this time. More importantly, these results
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February 3, 2010
Disinfection By Products Compliance and Hydraulic Water Model Report
indicate that the Village has stable, consistent water that is not unduly conducive to the
formation of disinfection by-product carcinogens.
Hydraulic Water Model. Attached please find a 16-page summary report prepared by
Burns & McDonnell that highlights the findings generated by the hydraulic water model.
Of note, are a series of recommended phased water distribution system improvements
totaling $15.3 million. These improvements are intended to minimize deficiencies and
improve system operation as funds allow over an extended, multi-year timeline.
Conclusion
Staff is seeking the Village Board's direction with respect to utilizing the findings of the
hydraulic water model report as a general guidance document for long-term water
distribution system capital improvements. Appropriate staff, as well as a representative
from Burns & McDonnell, will be on hand at the February 9 Committee of the Whole
meeting to present these results and entertain discussion as warranted.
Sean P. Dorsey
Cc: Director of Public Works Glen Andler
Water/Sewer Superintendent Mall Overeem
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