Request for Proposal Des Moines Water Works 2022 Filter Rehabilitation Study The Des Moines Water Works is requesting proposals from qualified consulting engineering firms, licensed in the state of Iowa, to conduct an evaluation of the existing filtration plant at the Fleur Drive Water Treatment Plant. The general scope of services includes evaluation of the existing sixteen sand filters and the filtration process. The evaluation is to result in development of alternatives and formulation of recommendations that maintain or increase the current 75 million gallons per day maximum operating rate of the existing filtration plant. This is while also enhancing or maintaining present-day finished water quality that meets all federal and state standards. An assessment of modifications to filter operation and electrical and instrumentation systems for each of the alternatives developed is also included in the scope of services requested. Proposals must be postmarked or received by 2:00 p.m. on Monday, October 25, 2021. Proposals received after this time will not be considered. Refer to the contents of this Request for Proposal for additional information. For any questions please contact: Vern Rash, P.E., L.S. Des Moines Water Works 2201 George Flagg Parkway Des Moines, Iowa 50321-1190 515-283-8733 (phone) 515-283-2610 (FAX)
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The Des Moines Water Works is requesting proposals from qualified consulting engineering firms, licensed in the state of Iowa, to conduct an evaluation of the existing filtration plant at the Fleur Drive Water Treatment Plant. The general scope of services includes evaluation of the existing sixteen sand filters and the filtration process. The evaluation is to result in development of alternatives and formulation of recommendations that maintain or increase the current 75 million gallons per day maximum operating rate of the existing filtration plant. This is while also enhancing or maintaining present-day finished water quality that meets all federal and state standards. An assessment of modifications to filter operation and electrical and instrumentation systems for each of the alternatives developed is also included in the scope of services requested. Proposals must be postmarked or received by 2:00 p.m. on Monday, October 25, 2021. Proposals received after this time will not be considered. Refer to the contents of this Request for Proposal for additional information.
For any questions please contact:
Vern Rash, P.E., L.S. Des Moines Water Works 2201 George Flagg Parkway Des Moines, Iowa 50321-1190 515-283-8733 (phone) 515-283-2610 (FAX)
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I. GENERAL CONSIDERATIONS
A. Introduction
The Des Moines Water Works (“Water Works”) is requesting proposals from qualified
consulting engineering firms licensed in the state of Iowa, to conduct an evaluation of the
existing filtration plant at the Fleur Drive Water Treatment Plant as described in this Request
for Proposal (“RFP”).
Whenever the following terms are used in this RFP, the intent and meaning shall be
interpreted as follows:
• The “Project” shall mean the undertaking described in and governed by this RFP.
• The “Proposer” shall mean the engineering firm that has submitted a proposal in
response to this RFP.
• The “Consultant” shall mean the Proposer selected by the Water Works who
successfully executes a Professional Services Agreement with the Water Works for
completing the scope of work described in this RFP.
B. Project Background
The Water Works constructed a conventional lime softening plant in 1949 consisting of three
treatment basin and eight sand filters. In 1959, to increase treatment capacity, a third treatment
basin, a pre-sedimentation basin, and eight additional sand filters were built. A fourth
treatment basin was constructed in the mid-1970s.
The Fleur Drive Water Treatment Plant treats water from any combination of three raw water
sources of supply. These raw water sources are the infiltration gallery, Raccoon River and Des
Moines River. Pretreatment prior to application includes coagulation and pre-sedimentation
for initial turbidity removal and taste and odor control, lime softening and recarbonation.
Each of the filters has an area of 1,388 square feet and an original design capacity of six
million gallons per day (MGD) based on an average filtration rate of 3 gallons per minute per
square foot (gpm/ft2). This average filtration rate was a typical filtration rate for rapid sand
filtration in the 1970s and 1980s and results in a nominal design capacity of 96 MGD.
Observations of treatment plant operations in the early 1980s indicated actual filtration plant
capacity was significantly below the nominal design capacity. The cause for this reduction in
filtration plant capacity was identified as degradation of the filter media. This degradation of
the filter media was attributed to deficiencies in water stabilization and inefficient backwash
practices that relied on a water-only backwash system.
In 1986, Water Works conducted a filter study and evaluation to determine possible methods to
increase the capacity of the existing filter plant. The evaluation included a pilot scale
experimental study and an evaluation of the condition of the full-scale plant. A hydraulic
analysis of the filters and filter piping was also conducted as part of the 1986 study.
Recommendations resulting from this filter study and evaluation were summarized in the report
entitled, “Des Moines Water Works – Filter Study and Evaluation,” dated December 1986.
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The recommendations included in the following:
1. Convert operation of the filtration plant to variable declining rate control in lieu of the
original constant rate control.
2. Modify the water-only backwash system to include an air scour system and sequence
the backwash process to include a combination air and water backwash followed by a
full fluidized bed backwash as a rate of 16 gpm/ft2.
3. Investigate and select a method of preventing movement of the support gravel system
during the air scour portions of the backwash process.
4. Remove the non-functioning rate of flow controllers installed on the effluent piping
during the original filtration plant construction. Replace these flow controllers with
butterfly valves that can be adjusted to limit the initial clean filter flow rate to 5 gpm/ft2.
Total removal and replacement of the sand and support gravel from all sixteen filters was
undertaken in the late 1980s to address the degraded condition of the filter media and to
incorporate a supplemental air scour system as part of the filter backwash process. A
thorough inspection of the underdrain system was conducted after the existing filter media
was removed and prior to installation of the replacement media.
Figure 1, below, shows the underdrain system for the eight filters constructed in 1949. These
eight filters, Filters 1 through 8, use a traditional header/lateral underdrain system consisting
of 4-inch diameter cast-iron pipe spaced at nine inches on center. The 4-inch diameter cast-
iron laterals have 7/16-inch diameter holes, spaced at six inches, drilled in the bottom of the
pipe for collecting filtered water effluent and distributing filter backwash water.
Figure 1. Traditional 4-inch diameter header/ lateral underdrain system for Filters 1 through 8 that were
constructed in 1949. This photograph was taken immediately prior to installation of replacement filter media in
the late-1980s..
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Figure 2, below, shows the Wheeler underdrain systems that was used for the 1959 addition
to the filtration plant. Also seen in Figure 2 is the supplemental air scour system that was
installed in all sixteen filters prior to installation of the replacement filter media in the late
1980s.
Figure 2. Wheeler underdrain system for Filters 9 through 16 that were constructed in 1959. This photograph
was taken immediately prior to installation of replacement filter media in the late-1980s..
An important aspect of filter operation is maintaining the filter media in good condition.
Rapid sand filters are periodically “backwashed” to restore their capacity when effluent water
quality from the filter becomes unacceptable, or when the head loss through the filter reaches
a predetermined value. A single filter can typically operate from 35 to 40 hours before it
needs to be backwashed.
The Water Works currently operates the Fleur Drive Water Treatment Plant at a maximum
rate of approximately 75 million gallons of water per day (mgd) for summer/warm water
conditions.
C. Anticipated General Scope of Services
The selected firm will be expected to prepare their Professional Services Agreement to
include conducting a study to identify alternatives to increase filtration plant capacity and
enhance the quality of the filter effluent.
The general scope of services consists of:
1. Conducting an evaluation of the existing sixteen sand filters and the filtration process
at the Fleur Drive Water Treatment Plant.
2. Identifying deficiencies in the existing filtration process and equipment.
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3. Developing alternatives and formulating recommendations that:
a. Addresses the identified deficiencies in the filtration process and equipment.
b. Maintains or increases the current maximum operating rate of 75 mgd for the
filtration portion of the water treatment process.
c. Assesses the modifications that are needed to filter operation and to existing
electrical and instrumentation systems for each alternative.
d. Provides a finished water quality that meets all federal and state standards.
4. Preparing an inventory of:
a. Current regulatory requirements that may affect how implementation of the
recommended alternative is conducted.
b. Future regulations that could impact operational requirements for the recommended
alternative.
5. Identifying specific permits required for the recommended alternative and the
regulatory and permitting agencies involved.
Proposers are encouraged to visit the project site and discuss the project with Water Works
staff; however, the Water Works asks that appointments be made in advance for such visits.
D. Submittal of Proposal
Proposals must meet all of the requirements described in this RFP to be considered.
Six (6) copies of the proposal must be submitted in a sealed envelope plainly labeled with the
following information:
Des Moines Water Works
2022 Filter Rehabilitation Study
Name of the Proposer
Address of the Proposer
Hard copies of proposals can either be mailed or delivered to:
Des Moines Water Works
Attn: Vern Rash, P.E., L.S.
Engineering Department
2201 George Flagg Parkway
Des Moines, IA 50321-1190
In addition to the above, submit an electronic copy of the proposal in Adobe Acrobat