5.8. SR 12-20-2004
Item 5.8.
1306\ Orono Parkway
Elk RIver, MN \\330
December 10, 2004
File No. 822560]-0030
Honorable Mayor and City Council
City of Elk River
13065 Orono Parkway
Elk River, MN 55330
RE: HEADWORK.5 IMPROVEMENT PROJECT
WASTEWATER TREATMENT PLANT (WWTP)
Dear Mayor and Councilmembers:
Attached is the Technical Memo prepared for the headworks pre-treatment improvements at the
WWTP. As the City Council will recall, this is the beginning of the WWTP where the sewage
influent is pumped from three major lift stations. Those three lift stations are located in East Elk
River, Trunk Highway 10 by the Chamber of Commerce building, and along Main Street at Evans
Avenue. They each collect sewage from various portions of the City and convey it to the WWTP.
The headworks portion of the WWTP was initially constructed in the 1975 upgrade. It has
occasionally, in the last 12 - 18 months, been overwhelmed by the amount of flow entering the
WWTP. Therefore, the City Council authorized this study to look at upgrading this portion of the
WWTP in early 2004. Completion of this study waited until adoption of the City's Comprehensive
Plan so that the study could look at an upgrade to the headworks portion of the WWTP which
would be appropriate long into the future.
The study basically recommends installation of new equipment that will provide capacity to this
portion of the WWTP for up to 3.5 million gallons per day and will fit in the existing building. The
one expansion to the building that is proposed is for the removal of grit. Currently, this is done in a
very labor intensive method by filling 20-gallon plastic buckets and handling them manually. The
recommendation for the upgrade is to use a conveyer system into a two-yard dumpster and have it
mechanically emptied to minimize the labor involved and to improve the safety aspects of this
operation. On page 15 of the report is an opinion of probable cost which estimates the construction
costs of the proposed improvements, including a contingency, at $1,132,000.
Phone: 763.635.1000
Fax: 763.63\.1090
www.cLelk-river.mn.us
At this point, it would be appropriate to consider the preparation of plans and specifications for the
headworks improvements. Attached is a resolution for the City Council's consideration which would
authorize work on the plans and specifications to begin. As indicated on page 15 of the Technical
Memo, the estimated engineering costs for the preparation of plans and specification is $148,000.
An anticipated schedule for the improvements would be to have plans and specifications completed
during the winter and early spring with bidding in the Spring of 2005 and substantial construction
completion during the 2005 construction season.
If you have any questions regarding the Technical Memo or other portions of this improvement, I
will be in attendance at your December 20, 2004 City Council meeting.
Sincerely,
Howard R. Green Company
Te~~
S:\PLANNING\Teny Maurer\CCmemos\12 20 04 WWTPHeadworks memo.doc
RESOLUTION 04-~
A RESOLUTION FOR THE CITY OF ELK RIVER
A RESOLUTION ORDERING THE
PREPARATION OF PLANS AND SPECIFICATIONS IN THE
MATTER OF THE WWTP HEADWORKS IMPROVEMENT OF 2004
WHEREAS the City Council has dilly consider the Technical Memo on the matter;
NOW, THEREFORE, BE IT RESOLVED by the City Council of the City of Elk River,
Minnesota:
1. Howard R. Green Company is hereby designated as Project Engineer for this improvement.
The Project Engineer is directed to prepare plans and specifications for the making of the
improvement and the solicitation of competitive bids.
Passed and adopted this 20th day of December, 2004.
Stephanie A. Klinzing, Mayor
ATTEST:
Joan M. Schmidt, City Clerk
S:IResolutions\2004 ResolutionsVJnapprovedlwwtp headworks.doc
TECHNICAL MEMO
To:
From:
Subject:
Date:
Distribution
Dawn Homer, Eric Evans ~
Pretreatment Improvements
November 17, 2004 r-Ic:MJard R. Green Company
INTRODUCTION
The headworks at the City of Elk River Wastewater Treatment Facility (WWTF) serves to
pretreat wastewater flowing into the plant with the primary objective of protecting
downstream pumps and equipment. Bar screens remove rags and large objects ITom
wastewater, which migbt otberwise be caught in downstream pumps. Grit removal systems
protect equipment ITom excessive abrasion. By removing grit at the head of the plant,
digester and aeration basin (future) grit accumulation is reduced. Additionally, the
Pretreatment Building contains flow measurement and influent sampling. The Minnesota
Pollution Control Association (MPCA) inspected the current plant headworks and
determined that the City needs to upgrade the pretreatment equipment, becallse the flow
capacity is inadequate and the existing manual bar screen is unacceptable.
Design of the proposed headworks improvements follows Ten State Standards (Great Lakes
- Upper Mississippi River - GLUMR). Selected standards of interest include:
Bar Screens:
. At design average flow conditions, approach velocities should be no less than
1.25 feet per second (FPS) and no greater than 3.0 FPS.
. Dual channels shall be provided and equipped with necessary gates to isolate flow
ITom any screening unit.
. The channel invert should be 3 to 6 inches below the invert of the incoming
sewer.
. Entrance channels should be designed to provide equal and uniform distribution
of flow to the screens.
. A convenient and adequate means for removing screenings shall be provided.
. Facilities must be provided for handling, storage, and disposal of screenings in a
manner acceptable to the regulatory agency.
. Floor design and drainage shall be provided to prevent slippery areas.
Grit Removal:
. A single manually or mechanically cleaned grit chamber with bypass is
acceptable for small wastewater treatment plants serving separate sanitary sewer
systems .
. Inlet turbulence shall be minimized in channel type units.
1
I
Bar Screens and Grit Removal
. Design peak hourly flow must be considered in evaluating unit processes,
pumping, piping, etc.
Some of the standards may not be amenable to the building layout and existing plant hydraulics.
If standards are not feasible, a variance may be requested by the City.
EXISTING PLANT
Wastewater Flow
Wastewater flows into the facility have steadily increased over the past ten years. The
flow rate over the last decade has risen to an average wet weather (A WW) flow of 1.1
miIlion gallons per day (MGD) and an average dry weather (ADW) flow of 1.0 MGD.
The 2002 population for the City of Elk River is reported as 18,000. According to the
City's land use plan, nearly 70% of the population is connected to the sanitary sewer.
Based on the average wet weather flow and the connected population, the average flow
per person is almost 90 gpdlcapita. A peak hourly wet weather (PHWW) flow of 1.8
MGD was recorded during a considerable rainstorm Based on the data, the PHWW to
A WW flow ratio is roughly 1.6. Raw wastewater enters the plant via force mains. The
lift stations leading to the plant provide some reservoir capacity, which helps to equalize
the flow and appears to reduce the peaking factor slightly.
Pretreatment Building
The existing Pretreatment Building is 34' -8" long by 29' -4" wide. The south half of the
building is 34' -8" long by 16' wide by 9'-4" high and houses one mechanical screen, one
manual screen, and flow measurement equipment. The north half of the building is 34'-
8" long by 11'-6" wide by 26' -0" high, has two levels, and houses the grit equipment.
Mechanical and electrical upgrades were performed on the existing Pretreatment Building
in 2000. The City replaced the building's roof and HVAC during the upgrades.
Existing Screening
The primary bar screen is a mechanical
climbing bar screen with 3/4-inch openings. A
manual screen provides redundancy to the
mechanical screen. Bypass piping, isolated by
slide gates, directs flow to a Sh011 channel
which contains a manual bar screen with I-inch
openings. The hydraulic capacity of the
mechanical screen is based on the 2'-0" wide x
3'-0" deep channel. If one channel is used
solely for redundancy and the screen is
unchanged, the channel capacity is
approximately 4.0 MGD. If both channels are used, the channel capacity is
approximately 8.0 MGD. The existing mechanical screen is 30 years old and needs to be
replaced. The photo on the top right shows the screening room looking west and shows
2
the mechanical screen on the left and the
manual screen on the right. The photo on the
bottom right shows the manual bar screen.
Debris collected !Tom both screens is manually
shoveled into 20-gallon garbage pails. The
mechanical screen collects approximately 13.5
gallons of debris per day. Plant staff gather the
garbage pails weekly and dispose of the waste
at the local landfill. Screenings collection and
disposal are a high maintenance process and a
safety hazard due to close contact with the waste.
Influent Sampler
Wastewater is sampled !Tom the channel immediately downstream of the bar screens.
Samples are drawn into sampler tubing and flow to a 1999 model sampler unit located in
the grit room. The existing sampler is equipped with remgeration to preserve samples.
Existing F10w Measurement
A 12-inch Parshall flume is used to measure the
incoming wastewater flow to the facility as
seen in the photo on the right. This flume has a
maximum capacity of 10.4 MGD based on the
assumption that downstream effects on the
wastewater would not cause the flume to
submerge. An ultrasonic level sensor measures
the water depth and sends the corresponding
signal to an influent recorder. The recorder
converts level to flow and sends the flow
information to a totalizer, which drives a
counter showing total flow.
A crack in the floor extends !Tom the flume in both directions. The Parshall Flume was
inspected visually, but no conclusive evidence of its condition was apparent. Measuring
tape is attached to the side of the flume to allow for a visual observation of the water
depth. The markings on the tape near the bottom were worn and not readable.
Existing Grit Facilities
Grit is removed !Tom the liquid stream by a grit
tank. An 18-inch pipe is available to bypass flow
during tank maintenance. The grit tank is 10'-0"
long by 6'-0" wide by 4'-0" deep with a sloped
bottom. The current grit tank is undersized. At
the current peak day flow of 1.8 MGD, the 1,160-
gallon grit tank has less than one minute detention
time. Ten States Standards recommends a
3
detention time of 3 to 5 minutes at design peak hourly flows. Assuming a 3-minute
detention time, the peak flow rate through the existing tank is 0.56 MGD, which is well
below the CUlTent peak day flow. Additionally, head10ss through the grit tank at higher
flow rates becomes problematic upstream. The grit tank is structurally sound and is in
working order, but at higher flow rates, it is expected to become less effective and to
cause hydraulic problems.
Grit is pumped ITom the grit tank sump using one of two 200 gallons per minute (GPM),
16-foot total dynamic head (TDH), 5 horsepower (hp), 1,725 revolutions per minute
(rpm), horizontal vortex type pumps. One grit pump is duty and one is standby. The grit
is dewatered through a grit classifier and hydro cyclone installed in 2002 and discharged
to disposal containers. The grit cyclone, in combination with the grit washing and
classification equipment, is capable of removing at least 95 percent of the 150-mesh grit
having a specific gravity of 2.65 or greater ITom the underflow of the grit tank. The
classifier and cyclone are sized to handle a grit flow of 200 GPM.
Grit is currently discharged into 20-gallon plastic garbage pails and collected in the grit
building for disposal. The grit equipment collects approximately 20 gallons of grit each
day. Plant staff gather the garbage pails weekly and dispose the grit at the hmdfil1. This
is a high maintenance process for plant staff and a safety hazard due to ITequent changing
of garbage pails.
FUTURE WASTEWATER FLOW
Operating data, population projections, and Ten State Standards provide a basis to project the
design flow for the year 2025 for the Elk River Headworks design concept. Operating data
show the 2003 A WW flow was 1.1 MGD with a PHWW flow rate of 1.8 MGD, thus giving a
peaking factor of 1.6. Howard R. Green Company evaluated the ultimate plant size based on
land available for expansion of various process units. The existing plant site has the capacity
to accommodate an average flow of 4.8 MGD limited by final clarifier capacity. Figure I
shows a site layout of the Elk River Wastewater Treatment Plant with tentative future
expansion and the current and expanded flow rates of various processes.
The City of Elk River population for the year 2025 is projected to be 35,000. Based on Ten
State Standards, the average per capita flow is 100 gallons per day, which gives a total
average flow of3.5 MGD for Elk River. Using a conservative peaking factor of2, peak flow
rate projects to 7.0 MGD for the year 2025.
General Improvements
As indicated by Ten State Standards, unit processes should be designed to handle
hydraulic peak flows. The proposed bar screens and grit units have been designed to
accommodate a peak flow of 7.0 MGD. Bar screen channels have been evaluated at a
flow of7.0 MGD to verify that the flow velocity and ITeeboard meet Ten State Standards.
The existing Parshall Flume is sized for a flow of 10.4 MGD and replacement has not
4
been considered. Manufactured vortex type grit units are available in a standard 7.0
MGD size, and that size has been assumed for design.
SCREENING IMPROVEMENTS
The objective of screening is to remove rags and coarse to fine solids from the influent
wastewater stream. Mechanically cleaned bar screens remove the larger solid materials from
municipal sewage and wastewater such as cloth, paper, kitchen refuse, pieces of wood, cork
and fiber. A bar screen is composed of vertical or inclined bars spaced at equal intervals
across a channel through which wastewater flows. Coarse solids are retained on the bars.
The use of bar screens tends to reduce labor costs, provide better flow conditions, and reduce
equipment wear downstream.
The existing manual and mechanical bar screen are proposed to be demolished. The primary
screen channel, bypass piping, manual screen channel, and concrete floor should also be
demolished. Two new channels and a new concrete floor are proposed for the west half of
the screening room (Figure 2). The existing channel, which contains the mechanical screen,
is too narrow for design flow capacity, and it is recommended that the channel be rebuilt. The
channel is proposed to be rebuilt between the west wall and the Parshall Flume. To
accommodate future peak flow, the channel should be widened to 2'-6". Velocity through
the channel, based on a channel configuration of 2' -6" wide by 3 ' -0" deep (with a flow depth
of 1'-2") and a flow of 3.5 MGD (A WW flow), would be 1.7 FPS. This meets Ten State
Standards requirement for a flow velocity greater than 1.25 FPS.
Currently, wastewater is piped into and out of the manual screen. A new channel must be
constructed to accommodate the redundant mechanical screen. The new channel would be
constructed parallel to the primary flow channel. It would have inlet and outlet channels that
connect to the primary channel. Slide gates would be provided to allow for isolation of the
channels.
Two identical, coarse mechanical bar screens, which accommodate flow rates of 7.0 MGD
each, are proposed at the inlet of the existing Pretreatment Building ahead of other
pretreatment processes. Raw wastewater would enter the channel and flow through one of
the two screens. The second screen would provide redundancy. In order to maintain gravity
flow through the plant, limiting the headloss through the screens is critical to screening
equipment selection.
The new bar screens would be cleaned with a climber rake mounted on the screen. The rake
would be set to run automatically in specified intervals (using a timer) or when water
upstream in the channel rises above a preset level. Disposal of screenings can be facilitated
several ways, which are described later.
Bar screens with clear openings of 3/4 inch are recommended. Bar screens with 1/4-inch
openings were evaluated, but headloss through the fmer screens was considered
unacceptable. Alternative models for mechanical screens are shown in Table 1 along with a
manufacturer cost comparison.
5
Manufacturer Model Flow, MGD Manufacturer Cost1,2
Mensch Crawler Vulcan 7.0 $175,000
USFiher/Envirex Series 1000 Rex 7.0 $70,000
ConClimber 206.08 Conclimber Screen 7.0 $100,000
.
Tablet. Bar Screen Alternatives
Cost does not Include InstallatIOn
2 Cost is for two bar screens
As stated previously, the Pretreatment Building had major improvements constructed in
2000. Howard R. Green Company recommends the City choose equipment that meets
clearance requirements of the existing building. The US FilterfEnvirex bar screens fit the
proposed channels and would require minor adjustments to equipment suspended ITom the
ceiling. The Conclimber bar screens fit in the building with adequate clearance if the
discharge height is low. The Mensch Crawler screens would require major modifications to
the Pretreatment Building due to inadequate climber clearance. All building adjustments
would be confirmed during final design.
Slide gates would be installed into the channels to direct flow into one bar screen or the
other, allowing for maintenance of the isolated bar screen while flow is diverted. A slide
gate is needed both upstream and downstream of each bar screen.
Grating wou1d be installed over existing and new flow channels. The grating provides a safe
surface for staff to walk across, but still allows easy access to the channels. The entire length
of the channel would be covered except at the bar screen and slide gates. Hinged grating
wou1d be provided to allow maintenance in areas where access is routinely required.
Additionally, guardrail is required around both mechanical bar screens and would be
installed for safety.
PARSHALL FLUME IMPROVEMENTS
The Parshall Flume has a flow capacity of 10.4 MGD, which exceeds the design peak flow of
7.0 MGD. Replacement ofthe flume is not necessary to meet the flow capacity, but minor
improvements should be made. The crack in the floor near the flume should be filled and
sealed. It is recommended that the Parshall Flume be fully inspected during renovations to
the Pretreatment Building. The flume may need to be replaced if its condition has
deteriorated significantly.
INFLUENT SAMPLER
The influent sampler is in acceptable condition and does not need replacement. Composite
samples are taken by the sampler based on flow-weighted sampling, which takes place at
preset intervals based on flume measurements. If the flume is replaced, the sampler needs to
be recalibrated.
6
GRIT REMOVAL
Grit removal follows screening and flow measurement. A vortex grit unit is recommended to
replace the existing basin.
The circular concrete grit tank design forces the flow in a vortex, depositing grit on the flat
bottom of the tank. Paddles operated by a smail drive unit sweep the flat bottom of the tank
and force grit towards the central grit hopper. The paddle action .also serves to fe-suspend
any organic material. The forced vortex design results in low head loss through the system,
even at peak flows. The grit tank would have piping to convey grit slurry through a grit
pump to the grit cyclone and associated grit classifier, which further dewaters and cleans the
grit prior to conveyance to a dumpster for final disposal.
Based on the evaluation, one 7.0-MGD grit unit is recommended to handle future plant
influent flow and side stream flow described later. An uncovered tank, located east of the
Pretreatment Building is proposed. Most vendor designs indicate a tank diameter of 10 feet.
The short detention time of the process makes it unlikely that significant odors would
develop, and so odor control is not included.
Alternatively, a dual grit tank system could be installed. Two, 4.0 MGD grit tanks would
provide adequate future PHWW flow capacity. Initially, one 4.0 MGD grit tank would be
installed north of the existing grit tank. An additional 4.0 MGD grit tank would need to be
installed at the site of the existing grit tank to meet future peak flows.
The grit tank would be located east of the building with the grit slurry pumps, described later,
located approximately 14'-0" below grade inside the Pretreatment Building. Cleanout
connections would be provided to assist with flushing the grit line. The grit slurry would be
periodically withdrawn and pumped to the grit classifier unit (equipped with a cyclone) to
further dewater grit. HRG intends to use the existing grit conveyor and classifier. Grit
suction and discharge lines would be kept short to minimize the potential for plugging.
Alternative models for the grit system are shown in Table 3.
Table 3.. Grit System Altemativ~
Manufacturer Model Flow, MGD
Jones and Attwood JetaGrit Trap 7.0
Smith & Loveless Pista Grit Chamber 7.0
USFilter/Envirex Vortex Grit System 7.0
XGT™ 300 Grit RemowlSystem 7.0
WesTech Vortex Grit Chamber 7.0
I Cost does not include concrete tank or equipment installation
Manufacturer Cose
$50,000
$62,000
$52,000
$40,000
$41,500
A channel would be built to flow out of the existing IS-inch grit tank bypass north into the
new grit tank. The wastewater flow would turn 270 degrees and then flow east away trom
7
the Pretreatment Building where it would discharge fi:om the channel into a 24-inch pipe
directed to the flow splitter structure.
PRIMARY CLARIFIER SPLITTER
Flow to the two primary clarifiers is currently split at the existing grit tank, which is planned
to be demolished. A new flow splitter must be constructed to facilitate flow between the two
existing primary clarifiers and two future primary clarifiers. Pipes extending towards the
future clarifiers would be plugged with a blind flange until they are needed. The primary
clarifier splitter structure is proposed to be located at the site of the now abandoned
rectangular primary clarifier. The splitter is to have a mixer installed that would aid in
coagulation of phosphorus removal chemicals. Demolition of the abandoned structure would
need to be completed prior to construction of the new splitter box.
CHEMICAL PHOSPHORUS REMOVAL
The MPCA has indicated that a phosphorus limit of 1.0 mgIL is anticipated. Elk River needs
to be able to meet effluent phosphorus limitations to renew the discharge permit. Chemical
phosphorus removal is reliable. Alum and ferric chloride are two chemicals that provide
phosphorus removal and improve sludge settling. Feed lines would be installed into the new
primary clarifier splitter and the secondary clarifier splitter for flexibility in controlling
phosphorus and sludge settleability. A chemical building is proposed to the south of the
splitter (Figure 1). Two 5,100-gallon tanks, housed within the chemical building, would
provide storage for a two-week supply of alum or ferric chloride at future design conditions.
Feed pumps, tubing, spill containment, and vent lines would be installed for chemical feeding
and safety.
PUMPS
Grit Pumps
The two existing grit pumps have been in service since 1975, and are due to be replaced.
Existing pumps are flooded suction pumps located in the lower level of the northeast side
of the Pretreatment Building. GTit pumps are sized to prevent settling of solids and
clogging in the sludge line fi:om the grit chamber to the cyclone. Replacement with
pumps sized to match the existing pumps is satisfactory. Both a duty pump and standby
pump, each with a flow capacity of 200 GPM at 16 feet TDH, are recommended.
Identical pumps are available for replacement !Tom Wemco. Gorman Rupp T -4 pumps,
which have a flow capacity of 250 GPM, are another replacement option. Two type CT
Series 6100 Morris pumps with a flow capacity of 200 GPM are an additional alternative.
The isolation and check valves on each pump would also be replaced.
Sump Pump
The sump pump currently in the northeast comer of the Pretreatment Building would be
replaced as needed. The 4-inch drainpipe, which is routed to drain into the end of the
Parshall Flume, does not need to be changed.
8
PRETREATMENTPIPE REROUTING
Several pipes are routed to the existing grit basin and will need to be rerouted to the proposed
tame Construction sequencing will be analyzed further during final design.
Grit Waste Pipe
A 6-inch sludge pipe ITom the grit tank draws grit ITom the tank to the grit pumps. This
6-inch pipe needs to be rer=ted to the new grit tank. The sludge line would be routed
and reduced as needed to match up with the grit tank as specified by the manufacturer.
Grit Classifier Overflow Pipe I Floor Drain
Overflow ITom the grit cyclone and grit washer flows through a 6-inch pipe into the
existing grit tank. The pipe is to be rerouted to direct flow into the new grit system.
Overflow ITom the grit washer would flow into the channel leading to the grit tank.
Currently, flow ITom the grit classifier underdrain and the upper level floor drain are
routed to the sump pump. Both of these pipes are to be rerouted into the overflow line to
teed directly into the grit channel. The overflow line needs to be lowered to meet the
underdrain and floor drain pipes, and to increase ground cover over the pipe.
Sludge Waste Pipe
A 4-inch sludge pipe ITom the control building currently flows into the grit tank. The
sludge pipe directs waste sludge from the biological systems into the grit tank and
consequently, primary clarifiers. The sludge pipe needs to be rerouted into the new grit
system Sludge would flow through the line into the grit tank approach channel.
Digester Overflow Pipe
A 4-inch overflow pipe ITom the digesters feeds into the grit tank. Digester supernatant
flows to the grit tank through this pipe. This pipe needs to be rerouted into the new grit
system
Plant Water Pipe
A 4-inch pipe accommodates flow ITom a lift station, which pumps wastewater ITom the
plant into the existing grit tank. Wastewater and drain water generated by the plant flow
into this lift station. This pipe also needs to be rerouted into the new grit system
9
SCREENINGS DISPOSAL
Buildin~ Addition Option
Screenings ITom each mechanical screen could
be collected and conveyed toward the west
wall. An enclosed, shaftless screw conveyer
would exit through a small access in the west
wall, north of the screening room door, shown
on the right. The screening room door would
be moved to the southwest side of the building
for easy access to the west side of the
mechanical screens. A building addition is
proposed to house a dumpster for screenings
west of the existing Pretreatment Building
(Figure 2). The addition would be 18'-0" long by 8'-0" wide, and the elevation would be
set to match the floor elevation of the grit building. A door would be installed for
personnel to access the south side of the addition. An overhead door would be installed
on the north side of the addition to allow a waste hauler to empty the screenings
dumpster. Ventilation would be provided to maintain a safe environment when occupied.
The cost for weekly collection is estimated to be $150 per month. For future design flow
conditions, the cost of collection is expected to increase due to an increase in screenings.
.t'
;!Ii~~'F.,~
,:'!i.l-'--- F ~
;"','" <i"'!,_
t!]:.i l~;_ i
\;11:1 \"i."\."
t, :1". '
. : ~ -
~ i
--
Conveyance to Grit Room
A conveyance system can be installed to collect screenings ITom both mechanical bar
screens and transport the screenings to a dumpster located in the grit room It is feasible
to convey screenings through the north wall into the grit room of the Pretreatment
Building, and dispose of screenings with grit. A series of three conveyors are needed to
convey the screenings. First, the screenings need to be collected ITom the bar screens on
a conveyor that runs ITom south to north inside of the building. Then, screenings would
be discharged into a conveyor that tr<U1SpOrts the screenings west along the north wall of
the screenings room Finally, screenings would drop into a third conveyor that runs
through the north wall into the grit room. A small access would be cut through the north
wall, and a conveyor would pass through the access. The grit room is currently not rated
as explosion proof, and the electrical equipment that is ITeely exposed to air ITom the
screenings room would need to be explosion proof For this alternative, a wall could be
built between the east and west halves of the grit room to isolate the east half of the grit
room. Double doors for access would be installed on the east side of the east half of the
grit room. The east half of the grit room would not need to be explosion proof The
MCC, electrical panel, and sampler would then be moved to the east half of the grit room
Electrical equipment remaining in the west half of the grit room would be replaced with
explosion proof equipment. Lighting, wiring, junction boxes, and the grit classifier motor
would need to be explosion proof
Compactor Option
The screenings collected ITom both screens could be compacted in the conveyance
system for either of the above alternatives. Once compacted, screenings would be 40
10
percent solids and water buildup in the dumpster would be less of a problem The
volume of screenings is reduced 1T0m 50 to 70 percent, which would reduce wasted
dumpster volume.
Grinder Option
Grinding of screenings is another option that
could save considerable expense. The bar screen
would operate as previously described, but instead
of discharging onto a conveyor, it would
discharge into a grinder as shown in the photo to
the right. This is different 1T0m in-channel
communitor equipment. Screenings would be
ground to 5/8-inch solids and returned to the
wastewater flow stream. Ground screenings
would be captured in the grit tank and primary
clarifiers. A potential drawback of grinders is the increase of solids loading to the
digesters, which could affect land application. Grinder manufacturers include Muffin
Monster (Disposable Waste Systems, Inc.) and Franklin Miller.
GRIT DISPOSAL
A dumpster is needed to collect grit and screenings. Two options are available for dumpster
location. The frrst option is to locate the dumpster outside of the Pretreatment Building, and
construct an overhang to protect it 1T0m weather. Alternatively, a cheaper alternative would
be to locate the dumpster inside of the overhead door to collect grit directly 1T0m the
classifier. In this case, the waste hauler would be contracted to lift the dumpster out of the
building and empty it. Additional padding would need to be added to the overhead door and
building for protection ITom the waste hauling truck. Ace Solid Waste is the current
contracted waste collection service for the City. Ace can provide a 2-yard dumpster, with
wheels, that is roughly 7'-0" long by 3'-0" wide by 4' -0" deep to collect grit. The electrical
control panel located on the north side of the grit room needs to be moved prior to dumpster
placement. The cost for collection has been estimated to be $150 per month for a weekly
pick-up based on the current flow conditions. For the design average flow rate, more
lTequent collections would be required resulting in an increased cost of around $500 per
month. A reevaluation of the collection method may be investigated at that time.
MISCELLANEOUS
Retaining Wall
Site grading north of the Pretreatment Building and proposed grit system could be
facilitated by construction of a retaining wall. A retaining wall could be constructed
north of the building extending towards the existing primary clarifiers. The retaining
wall would allow leveling to grade, provide stability to the soil, and reduce erosion.
II
Pavement
The area west of the Pretreatment Building needs to be paved to facilitate pickup and
li;op"o,,] of screenings and grit. A &ont-end loading garbage truck would require
adequate pavement for turning and maneuvering. Pavement would be extended iTom the
south edge of the driveway to the edge of the proposed building addition and roughly
20' -0" to the west of the Pretreatment Building.
Ladder Safety Cage
Grit pumps are located in the north half of the Pretreatment Building in the lower level.
Operators must climb a ladder down to the grit pump level. The 1995 facility upgrade
included plans to replace the ladder with stairs. The ladder can be instal1ed as part of this
project in a similar arrangement to those plans.
Exterior Ladder
Plant staff are required to maintain ventilation equipment housed on the roof of the
Pretreatment B,.ilding. It is recommended that a ladder be added to the south side of the
building for easier access.
Primary Clarifier #1 Guardrail
The guardrail surrounding the west circular primary clarifier is weathered and due for
replacement. Original installation of the guardrail occurred in 1975. It has deteriorated
along its entire length and is completely corroded in numerous spots. Painting provides
little benefit in its current condition and causes future maintenance issues. As part of this
project, the guardrail should be replaced for safety reasons to match the guardrail
surrounding the adjacent primary clarifier.
Electrical Panel Removal
The existing Sylvania motor control center (MCC-2), located on the north side of the
Pretreatment B'lilding, should be replaced during this proj~ for the following reasons:
. Sylvania no longer manufactures MCC's, making replacement parts difficult or
impossible to obtain.
. MCC-2 is full; leaving no space for the larger motor starters required for the
proposed headworks improvements.
Motor starters that are in good working condition would be salvaged iTom the existing
MCC and turned over to the plant staff to use for spare parts in other Sylvania MCC's at
the plant. The replacement MCC would be relocated to the northeast side of the grit
room to allow a dumpster to be set next to the overhead door. A small concrete slab is to
be constructed over part of the grit pump pit to support the MCC.
CONSTRUCTfON STAGING
Construction of the proposed headworks upgrades is to be phased and flow bypassed during
construction. Detailed analysis of construction staging will be performed during the design
phase, but general observ<ltions hav~ been made based on preliminary design.
12
Bar screen channels need to be empty to allow demolition of the existing channels and
subsequent replacement with new channels. Wastewater flow needs to be bypassed around
the flow channel that is under renovation.
Flow would be routed into the existing grit tank until completion of the new grit system.
Once complete, flow would be routed into the new grit system while the existing grit tank is
demolished.
Northem Dewatering, Inc. provides bypass pumping, and evaluated bypassing wastewater
flow at the Elk River WWTF ITom the influent force mains to the primary clarifiers. A
temporary wet well with adequate reservoir capacity is needed for Northern Dewatering to
provide bypass pumping effectively and safely using grinder pumps. Based on their
evaluation, the budget price for bypassing flow is $31,000 for the first month and $8,000 per
month after that.
RECOMMENDED ALTERNATIVE
Howard R. Green Company recommends upgrading the Elk River WWTF Headworks to
meet an average day flow of3.5 MGD and a peak hourly flow of 7.0 MGD. to meet the
flow demands, HRG proposes widening bar screen channels, replacing the existing bar
screens, providing conveyors and compactors to dispose of screenings in a small building
addition, installing a vortex grit tank, installing a primary clarifier splitter structure,
construction of a chemical building for phosphorus removal, and rerouting yard and process
piping to the upgrades.
To minimize costs, HRG proposes to use the existing building and modify as required.
Specific manufacturers may be required to meet the limited space in some cases. The items
listed below are recommended by HRG for specific process upgrades.
Screens: US Filter I Envirex bar screens fit into existing Pretreatment Building.
Grit Tank: One 7.0 MGD unit; several models are available for competitive bid.
Grit Pwnps: Several manufacturers available for competitive bid.
Screening Disposal: Multiple screw conveyors, compactor, building addition for screenings
disposal.
Grit Disposal: Dwnpster located inside the existing grit room.
Chemical Building: Chemical building and piping to flow splitters to meet future
phosphorus regulations.
13
OPINION OF PROBABLE COST
A preliminary Engineer's Opinion of Probable Construction Cost for the Headwork:s project
has been prepared based on equipment manufacturer's costs using the recommended
alternative and typical construction expenses, The opinion of probable cost fur the project is
presented in Table 4,
14
TABLE 4. OPINION OF PROBABLE COST
~CRIPll0N TOTAL COST $
REQUIREMENTS
Mobilization 12%) $19 000
Site Work $20 000
T Facilities $20 000
Miscellaneous $50 000
BAR SCREENS
Demofition (manual & mechanical bar
screens, concrete oioes, etc.) $15 000
Bar Screens (2) $70 000
Bar Screen Installation 140%) $28 000
ChanneVFloor Concrete $30 000
Slide Gates l'A $1$ 000
GRIT TANK
Demolition lexistina arit basin oioina) $11 000
Vortex Grit System (1) $62 000
Grit Pumas (2)Nalves $40 000
Grit Installation 140%) S25 000
Concrete Tank $10,000
Slide Gates (3) $15 000
PRIMARY CLARIFIER SPLITTER
Demofition (existina rectanaular clarifier) $20 000
Solitter Structure & Installation 140%) $50 000
SCREENINGS & GRIT DISPOSAL
Comoactor $42 000
Convevor saD 000
Buildina Addition $60 000
MISCELLANEOUS
Yard Pioina $30 000
ProceS$ . . 000
Aluminum Gratina $20,000
Guard Rail $21 000
Retainina Wall $10 000
Stairs - grit room $10 000
Buildina Ladder/Installation $5 000
Crack Repair $5 000
Paintina $10000
CHEMICAL PHOSPHORUS REMOVAL
Buildino Addition $40 000
Tanks $20 000
Feed $9,000
ELECTRICAL MODIFICATIONS
Demolish Svlvania MCC $2 000
Electrical $9aOOO
HVAC/PLUMBING $24 000
SUBTOTAL Headworks Renovations $984 000
CONTINGENCY 115%) $148000
ENGINEERING/ADMINISTRATION (15%) $148,000
TOTAL ESTIMATED CO C110N COST . $1 280 000
O:\PROJ\822560J\ReportIER Headworks Tech Memo.doc
15
n n ,. 0
"""'11 ,..,
00"'11 1I1
""1 0 ~ .5
r.;~;ii8
.. 0
<:) g ~ ~
" .
"
00
c .
~~
~ ~
e ~
::IJ iO r.. ~
011 U. ill >
3. ~ ~ ~
~ 3 ~ ~
" "
,
; Ii I~
o
ji z.
. ,\1
8 ~~
. .
~
~t!~
';:~~
.I~.,,~
!;!;o.~~
~~;~
~C:I:%
~ei~
!;!~c:~
I~!~
~13"~
i"'i2,.,
,l!:Rg
,.,...e:
.~,
i~~
gii
!i:'ii$!
hi
O.
c 0
n >
r i
I
~
Q
::0
GJ
iD
CD
::J
n
o
:3
D
CD
::J
'<
q~
I Sj1 "
I ~ 1)
> ~ ~
L.~
z
~
~
[]"11 \1
fi) a
.... ~
.
o
/1'
~1~;
./ ~I :111
./ I!!!
/ ,II!:
/ Iii
, ~' :;
,/ ..:-":!i
/ ':',
mil:i! ~_,-~ I Ii
~~il~ijf / ~~ '\ ~~~ \ i i! !
.~ i I, ;;J: ~Oi/!2 ~ g~6 )1 / (.I.!. '..! ,.1
/::!~ i \. ~ ~~i~- ~ 'I , I
At ~' ~Ir--~ l :' E~n!mi J' '-- -~-~I' ~~Oi': ( ~I i II!II 'I' 1
__ ___ _ ~I I !i;;JM I oi:1~ ~ _, Co" gF~i!I ' , "
, I i( '~\ I i!i ]1 /v~,' ilil ~ -~ ;Ih II!!
/ /'1 I I \ liil ~ ;/. ) - I, ~I~ /111' ~i~ \V~ 11.1-1;~~mjIILII
I" \. '. ~>~,' ~~~~:>:J~'
,,/ --~.-l --- I~I :IJ~ Ii;;: ,.., b';'~ 11 11
. I . ~ I '" ',.,1 :a 3 z~z\';11
__ .' _ ______ ' EXISTING I I~l O~o! I, i
P
z>_
p;l)z
(,J~~
"
.\ ~ ~ ~, '
r---~ - > "
e rr---- I i Ol __ \. ~/J ~ MOl i 1/
\ .---. II T I l <) =-r--L______ I '- --- "O~ ~~": ~--
__ ___-- r __~----l! !!i_ ~i!I!!~ III
\\ -; _ -1i'- 1/ [/ - ',-$~I_o ~!-.ti;l
I~: < ''1 I ( ~~> III ~i~ \ I Ig ~ ~~d l~j\
~~
\ I _IL~ 11 'c_J "~ ,,-"Y, ~ ..~t
"\ l : c:I~-~;~~~'~. --------1 r ( - ~-~ f f i
I I~!~I I I z::J:!!"" , , ,
\'~ J!~=-----t~ 11 \ .'!i ) :::
\ ~h I .! AER...A..TION TANK jJ.' f01:J~::--::::: f;l~ i
. 6F ~~ I ,_._.n . . " ~ '
Zr;} .---~...--.~"'II :':!~';;' i OI&'~ r~ ';
::,~---------~_.__._----':' I ~ ~ ~ ~ ~ ! ~g~ j~! :
'I " ~"'II ;I)~~ "r o~i ~0!~ ~
'I :'UTUR' AERATION TANK! ,---- ........ ~\!~ I ,t'.~1
\ II ____... r~~~~-~~~~~-;:~: I ,If ,Ii ,Ii
\ -=--v ---
\ ,--.;; ...
II '\ .-'\ 0~,' ------- III
..___.___._______________ 0 -0. ''';,
~~ ~~~ :!I~~g___ __u "
~ ii!l i~i!I UU Q I ~
\ \ II' 1~ 1 ~~ ~ i ~ '
\ \ (1110 m~ i I i I'
I \ i ~ ~ U~ ~ I ~ I
IL _ _ _ _ _ _ _ _ _ _ _ _ ~ C__mnmnmnn !~ ______J___~___J
->--_x__
--.----~-
.....----.---<--
UU~iin ~
Ui~~;~;~ ~
i~ US~i~ i
i~~~Ji~;~ ~
<ilii 1;i'''i .
~<IiU~~.~ I
....6.. S~:"". 8
t.o. _ . _at ::!I
~1i;; : i
:"'8
0_
~~
...
8
o
>
"
.
.
.
.
.
\1
~
~
!/
-"
" '"
LiI
.. "
q ~
@I
~ ~
ii
,
r
,
~
"
ii
~
II
, ,
I I
6'
~
~
~ ~ ~ ~
o " ~
p ~ ;g fl
~ ~ 8 8
~ if ~ ~
<.n 16 '0 '"
f! ~ ~ '"
0'
. ;:;
" N
o
" 0
0.... '- 0
~ ::: ~ ~
~ ::. 2 ~ ~
n~~~
~; I; 12 i
.., ~;:o
e
11'-4"
".
~
N ~;
,- ~
0, ~
.
%
~
~
/.:',
N t
" N
0 "
. 9 .
2 ~ N
~ " ~.
. 0
% ~
B
~
g~
.~
"~
~~
~%
.0
~
.."
"
,-
~
J .
~ 51 i!i!:I-
Q ~ "'~~i!i
z ~ '; -.,,~
i a~~~
~)o~f;I
~~~~
<<<
~R~~
Plzi'"
~~c~
I~a~
~~~~
~~~g
~;;~
~~.
~~i
.2"
.~~
~"'"
?i j;
i r
~
~~
.'
.
~
~
.
-::;~
~~
~~
~
p
.
N
~
".
"
<
"
.
.
2
.
~
~.
~Q
N>
_z
n
~
~
z
-"
~ ."
~ ~
'i;
~
~
z
"
~
n
o
z
~
~
-.
,
0,
::r:
~
CD
a.
::0
GJ
([)
(j)
::J
o
o
:3
D
CD
~
g
! r
a
~
t ~
~
>
~
.
~
.
o
"
>
~
>
F
~
p
.
;;
N
~.
E
~
~ 0 ~
~ ~ ~
!~:D
~ ~ ~
;>JI
~ ~
~ ~
> CJ)
I
"~
i i ~ N
E "
E x ~
~ CJ) . 3 ~
~ ~ ~
-i . ~
i
,
~ (11:I!
0-
z NUl
z-o
o~ ~~
"TIfT!
o~ "TIfT!
<!!:I: ~r
Q)> 8;c:
ZUI
)>
rtD Z
O~ UI
OZ ;jjZ
(") C)>
c~ (") N
;c:fT! :::I~ "
I ~ ~I fT!O ~-< ~o
ZC
-/(") "
,r
"0
tJ ..
N ~