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Design Report
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Lyman Creek Reservoir Improvements Project It
Bozeman, IVIT -7
PREPARED BY: James Nickelson, P.E.
DATE: July 1, 2010
INTRODUCTION
The under drain of the Lyman Creek Reservoir collects water that seeps from the
reservoir and discharges water into a drainage way. The purpose of this project is to
provide a dechlorination system that will allow the system to comply with MPDES Permit
MT0031631. The permit requires that a dechlorination system be in place by January 1,
2011.
PERMIT REQUIREMENTS
The permit requires that chlorine removal equipment be installed. Permit limits for Total
Residual Chlorine are 0.00165 mg/I on an average monthly basis and 0.1 mg/I on a
daily maximum basis. Sampling results with results of less than 0.1 mg/I are considered
to be in compliance with the permit.
DESIGN CRITERIA
Design criteria has been developed as follows:
Maximum Flow Rate 200,000 gpd (139 gpm)
Typical Influent Chlorine Level less than 2 mg/I
Sodium Sulfite Tablet Storage 6 months
Chlorine removal see permit requirements
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NA0417\055\D0CS\Reports\Task Memo Dechlor.doc
July 1,2010
Lyman Creek Restoration Improvements Morrison-Maierle Inc.
PROPOSEDIMPROVEMENTS
The proposed improvements include a sodium sulfite tablet feeder, expansion of a
building to provide for tablet storage and site grading and drainage work to allow for
improved access to the site.
A Norweco Bio-Dynamic Series 4000 tablet feeder has been selected as the treatment
system. The tablet feeder is a passive treatment system. As water flows through the
feeder, the sodium sulfite tablets convert the chlorine. The feeder has multiple feed
tubes and adjustable weirs to allow for a range of discharges and chlorine
concentrations. It is anticipated that only one feeder tube will be required due to the low
residual chlorine concentration. The weir will need to be adjusted on occasion to
optimize the treatment. Since the flow and residual chlorine concentration due not vary
significantly the adjustments will be minimized. The capacity of the feeder is 200,000
gpd. The city's intent is to limit the maximum flow rate for the discharge to this rate and
will take steps to lower the flow rate if it begins to approach this limit. Current discharge
rate is approximately 60 gpm (86,000 gpd) and the city is beginning the process to seal
some of the leaks within the reservoir.
The tablet feeder will be installed in line with the existing drain line. The feeder will be
provided with a metal hatch for access purposes. A trail will be constructed from the
tablet storage building to the feeder.
The existing inlet building will be expanded to allow for storage of pails of sodium sulfite
tablets. Due to vehicular access concerns during the winter months, the city intends to
store enough sodium sulfite in the storage building to allow for 6 months of use. Based
on a flow rate of 100 gpm and a chlorine residual of 2 mg/I approximately 2,200 pounds
of 35% sodium sulfite tablets will be needed. The tablets normally come in 45 pound
pails. It will require 50 pails to meet the 6 month requirement. The building expansion
is sized adequately to allow for this to be stored.
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NA0417\055\DOCS\Reports\Task Memo Dechlor.doc
July 1,2010