HomeMy WebLinkAbout02 - Design Report - Baxter Meadows Lift Station ALLIED
June 26, 2002 ENGINEERING
SERVICES, INC.
James Nickelson
Morrison-Maierle, Inc.
901 Technology Blvd South
Bozeman, MT 59715
RE: Baxter Meadows Subdivision
Final Response to Lift Station Review
Dear James:
The following comments from the final Baxter Meadows Subdivision lift station review have
been addressed.
JUNE 14, 2002 REVIEW
DEQ RELATED COMMENTS
Comment 1: The City will not support the deviation request for the lack of vertical separation
between the sewer force main and the water main. Since both of these facilities are proposed it
appears unreasonable that this separation issue cannot be designed within standards.
Response: As per your recommendation the force main has been redesigned to achieve
the required 18" separation between the water and sewer mains. See Sheet C5 of 7.
Comment 2: DEQ made a comment about cleaning the wet well hopper. Please review the
hopper configuration and consider alternate hopper layouts. Incorporating a flush valve on the
pump(s) may be an additional method of reducing concerns regarding wet well hopper cleaning.
Response: The hopper has been reconfigured to allow for a 1:1 slope on all sides. This
decreases the hopper area to 5' diameter, which will help facilitate the pumps in keeping
the hopper clean. Also the pumps will alternately run which will cover the entire area of
the hopper. See Sheet C6 of 7.
Comment 3:I Will forward a letter to the city addressing DEQ's comment regarding the City
approval.
Response: Not required.
32 Discovery Drive ♦ Bozeman, MT 59718 ♦ (406) 582-0221 ♦ Fax (406) 582-5770
James Nickelson Project: 01-241
June24 2002
DEQ RELATED COMMENTS
Comment 1:A pressure gage on the outlet of the Generator Building piping would be helpful for
the operator.
Response: A pressure gage has been added to the outlet of the Generator Building
piping. See Sheet C7 of 7.
Comment 2: Will the coupling (Item 5-Sheet C7) be adequately restrained?
Response: Yes, the couplings will be installed between two flanged spools, which
will restrain the couplings. The inlet and outlet pipes will be cast into the floor of
the Generator Building further restraining the pipes.
Comment 3:A supplier called requesting clarification on what lift station pumps are required by
the City. Discussions with City staff indicate that for submersible pump application they do not
have a set requirement.
Response: As per our meeting with the City on June 18, 2002, the decision was made
that Gorman Rupp pumps will be used on all lift stations.
Comment 4: The City hopes to have the radio control system in place by the time this lift station
is operational. Before this item is ordered please coordinate with the City Water Department.
Response: The specifications require a radio modem be used for the lift station.
However, John Alston at the City Water Department has not made a final decision about
the details of the radio use. The City is working closely with IAC, who will supply this
equipment, therefore the proper equipment will be ordered after the decision is made.
The recommended revisions have been completed. Please contact me if you have any questions
or comments.
Sincerely,
Josh McGibbon, EI Scott R. Smith, PE
Engineer Intern. Project Manager
cc: File
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ALLIED
May 16, 2002 ENGINEERING
SERVICES, INC.
James Nickelson
Morrison-Maierle, Inc.
901 Technology Blvd South
Bozeman,MT 59715
RE: Baxter Meadows Subdivision
Response to Lift Station Design Report Review
Dear James:
Enclosed please find a revised set of plans and specifications for the Baxter Meadows
Subdivision lift station and force main. As previously discussed, we are specifying a
submersible pump in lieu of the end suction pump.
The following comments from the lift station Design Report reviews have been addressed.
APRIL 16, 2002 REVIEW
DESIGN REPORT
Comment 1: The total development area (page2) appears to assume the 160 acres will also be
developed as a PUD with 30% open space. Is this certain? If the 160 acres is developed simply
as a subdivision the total developed area will increase.
Response: Total average daily flow has been recalculated based on 160 acres being fully
developed with no open space. This assumes the future subdivision will choose cash in
lieu of open space,which will cause the largest demand on the lift station.
Comment 2: City of Bozeman Design Standards call for
R-1 Density=2.3/acre Report uses 3.81/acre
R-3 Density= 27.61 acre Report uses 12.19/acre
It may be more appropriate to use the maximum densities proposed by the PUD submittal.
Response: The densities used in the Design Report were based of the 1998 Wastewater
Facility Plan for the City of Bozeman. We were informed by Bob Murray, that the City
of Bozeman Design Standard's density requirements were incorrect.
32 Discovery Drive ♦ Bozeman, MT 59718 ♦ (406) 582-0221 ♦ Fax (406) 582-5770
James Nickelson Project: 01-241
May 15 2002
Comment 3: There seems to be a discrepancy in the acreage number:
I"Paragraph-Page 1. 460 +160=620 total acres
Table 1- 367+115+139=621 acres
Table 2- 367+115+139+160=781 acres*
*(numbers adjusted for total acres)
Response: The acreage described in the first paragraph (460+160=620 acres) shall read
461+160=621. Table 1 (367+115+139=621) is incorrect. Table 1 shall read
207+115+139=461. The Table 2 column heading, "Number of Acres" shall read
"Number of Developed Acres." See revised Design Report for corrections.
Comment 4:Based on the above Total Average Daily Flow may need to be adjusted.
Response: The adjusted Total Average Daily Flow shall be:
160 acres x 12.19 people/acre x 72 gpcd= 140429 gpd
629,752 total gpd/ 1440 min/day=437 gpm
Comment 5: The design flows do not appear to account for infiltration. Response: According to
the City of Bozeman Deign Standards an infiltration rate of 150 gal/acre/day shall be added to all
flow calculations. Therefore the adjusted Total Average Daily Flow, including infiltration, shall
be:
150 gal/acre/day x 621 total acres= 93150 gpd
93150 gpd/ 1440 min/day-- 65 gpm
437 gpm+ 65 gpm=502 gpm
The adjusted Peak Hourly Flow Rate shall be:
629,752 total- gpd/ 72 gpcd= 8,747 equivalent population
F=(18+Po.5) / (4+Po.$)
F=(18+8.7o.$) / (4+8.7o.5)
F=3.01 peaking factor
437 gpm x 3.01= 1315 Urn+ 65 gpm(infiltration)= 1380 gpm
Comment 6: The City of Bozeman uses Suction Lift pumps for lift station applications. Be sure
to coordinate the type of pumps used with the Wastewater Department.
Response: Submersible pumps will be used in lieu of Suction Lift pumps as discussed in
the meeting with Mike Certalic on April 181h, 2002. It was determined that the depth of
the lift station would prohibit the use of suction lift pumps. See the revised drawings and
specifications for additional information.
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Comment 7: Based on items 1-8 above, the pump sizes may need to be reevaluated.
Response: See revised Design Report for new pump sizing.
Comment 8:Provide pump curves,pump selection data and design calculations showing that the
pumps will run at 850 gpm while pumping against 34.8 feet of head and also against 2 7.7 feet of
head,please review the pump curves.
Response: Pump curves and pump selection data have been attached with submittals for
your review. The pumps will run at 690 gpm while pumping against 36 feet of head.
Comment 9:Based on the above comments re-evaluate the cycle time and wet well size.
Response: See the revised Design Report and drawings for new cycle times and wet well
size.
Comment 10: Item 48.3 states that the force main will enter the gravity sewer system
approximately one foot above the flow line of the receiving channel. The plans show the force
main entering 0.1 feet above the receiving channel. The plans need to be modified accordingly
to provide a greater separation between the invert of the force main entering the manhole and
the invert of the receiving channel exiting the manhole.
Response: The force main has been raised to IE=4668.9 which is one-foot above the 24-
inch receiving channel. See Sheet C5 of 7, Section Manhole DVA.
Comment I1:An O&MManual needs to be provided with subsequent submittals.
Response: O&M Manuals will be provided during the submittal process.
PLANS
Comment 1: It appears that the 0.27 % slope may not allow for 18 inches of separation at the
water crossing at approximate Sta. 63+12. The grade of the force main may be adjusted or a
deviation requested for the separation.
Response: A deviation will be requested from DEQ for the separation of the water and
sanitary sewer at this location.
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Comment 2: Manhole DV-1 calls for the force main invert to be cored and sealed with non-
shrink grout. Review this connection to provide a gasketed, flexible, watertight connection.
Please coordinate with TDH to see if the manhole can be manufactured with provisions for the
connection.
Response: The manufacturing of Manhole DV-1 has been completed, therefore the force,
main invert will be cored. A field fit gasketed, flexible, watertight connection will be
installed per the revised plans and specifications. See Sheet C5 of 7, Section Manhole
DV-1 and Specification Section 00820- Special Provision#52
Comment 3: Manhole DV-1 calls for the invert of the force main to be 0.1 feet above the invert
of the 24-inch receiving channel. The design report states that the invert will be one foot above
the flow line of the receiving manhole. Review these inverts. At a minimum the manhole inverts
need to be set so that the 8110 depth of flow of each main is equal in elevation as with a gravity
main.
Response: See Design Reports Comment 10 for revisions.
Comment 4: The capacity of the 24-inch main should be reviewed in light of the lift station
producing a higher peak flow than a similar gravity system. Matching the pumping rate closer
to the peak hourly flow may be prudent.
Response: The 24-inch main was sized using a proposed peak hourly now rate of 1700
gpm. The actual peak hourly flow rate was found to be 1380 gpm, which is also the
pumping rate of two pumps. Therefore the capacity of the 24-inch main should be
sufficient.
Comment 5: The 24-inch outfall from Manhole DV-1 is not shown on the plan and profile.
Response: The 24-inch outfall from Manhole DV-1 has been added to the plan and
profile. See Sheet C5 of 7, Plan View and Profile View.
Comment 6:Design plans and specifications for the Generator Building need to be submitted for
approval with the lift station plans and specifications.
Response: Generator Building plans and specification are included in the revised lift
station plans and specifications. See Sheet C7 of 7 and Specification Section 11740-
Generator Building. As per conversations with you, the architectural plans and
specifications will be submitted by the facility architect at a later date.
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Comment 7: The Generator Building layout needs to be revised to account for the Suction Lift
Pump Station.
Response: A Submersible Pump Lift Station will be used.
Comment 8: Provide a site plan for the lift station site to be submitted with the plans and
specifications for the lift station.
Response: A site plan is included in the revised lift station plans and specification. See
Sheet C2 of 7, Lift Station Site Plan.
Comment 9: Modify the Finished View to account for the Suction Lift Pump Station.
Response: A Submersible Pump Lift Station will be used.
Comment 10: Modify the Plan View to account for the Suction Lift Pump Station.
Response: A Submersible Pump Lift Station will be used.
Comment 11: The stub for the 1 S-inch pipe entering the lift station from the south should be
provided at this time.
Response: The plans have been revised to require a stub for the 15-inch pipe entering the
lift station from the south. See Sheet C6 of 7, Lift Station Plan View.
Comment 12: A wall penetration pipe sleeve with flexible connections or gasketed, flexible,
watertight connection needs to be utilized between the wet well and valve pit. The valve pit can
be eliminated with the Suction Lift Pump Station.
Response: A Submersible Pump Lift Station will be used. The Generator Building will
replace the valve pit, which will store controls,pipes and valves.
Comment 13: Modify the Section Detail to account for a Suction Pump Lift Station.
Response: A Submersible Pump Lift Station will be used.
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Comment 14: An alternate to the concrete encasement needs to be considered for the gravity
pipes entering the wet well.
Response: Flowable Fill will be used for the gravity pipes entering the wet well. See
MPWSS Section 02225- Flowable Fill.
Comment 1 S: Reconsider the depth between the pumps off level and the inverts of the gravity
pipes entering the wet well. The existing configuration leaves very little room to adjust the
operating levels without permanently inundating the pipes entering the manhole.
Response: The depths between the pumps off level and the inverts of the gravity pipes
have been increased to 2.75 feet and 6 feet, from 0.6 feet and 3.85 feet. A minimum of
six-inches between switches has been designed. See Sheet C6 of 7, Lift Station Section.
SPECIFICATION
Comment 1: SP-29. COVER ON FORCE MAINS calls to maintain 6 feet of cover over the
sanitary sewer force mains. The required cover will be 6 '/ feet as called of on the plan
drawings.
Response: The specifications have been revised to require 6 '/z feet cover.
Comment 2: Section 11750 needs to be revised to account for a Suction Lift Pump Station.
Response: A Submersible Pump Lift Station will be used.
Comment 3: Section 13705, 3.04, c. calls for a redundant float switch. This switch is not
mentioned elsewhere in the specifications or shown on the plans.
Response: The float switch and redundant float switch have been deleted from the plans
and specifications. Two redundant ultrasonic level switches will be used in lieu of float
switches. See Specification Section 13705- Process Instrumentation and Controls.
Comment 4:All fittings and bends on the force main or yard piping shall be ductile iron.
Response: The specifications and drawings have been revised to require all fittings and
bends be ductile iron. See Specification Section 15210- Yard Piping.
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Comment 5: Electrical specifications covering basic electrical requirements, materials,
methods, service entrance, and distribution system, are not included.
Response: Electrical specifications have been included. See Specification Division 16-
Electrical and Sheet C7 of 7- Generator Building.
Comment 6:Motor control devices are not specified.
Response: The specifications have been modified to include the motor control devices.
See Specification Section 11750- Lift Station
Comment 7. Interior and exterior lighting has not been specified.
Response: The specifications have been modified to include the interior and exterior
lighting. See Specification Section 11740- Generator Building.
Comment 8: The heating unit is not specified.
Response: The specifications have been modified to include the heating unit. See
Specification Section 11740- Generator Building
Comment 9: No building specifications are provided.
Response: Generator Building plans and specification are included in the revised lift
station plans and specifications. See Sheet C7 of 7 and Specification Section 11740-
Generator Building. As per a conversation with you, the architectural plans and
specifications will be submitted by the facility architect at a later date.
APRIL 24, 2002 REVIEW
Comment 1: Section 0820- SP-18- This section conflicts with the plans on backfill requirements.
The type A backfill may be appropriate as a road is being constructed over the top of the force
main.
Response: The plans require Type A backfill be used over the top of the force main. The
special provisions allow for Type B backfill to be placed in "un-surfaced" areas only.
See Specification Section 0820- SP#17.
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Comment 2: Section 11750-
a. Manufacturer's Representative- Please provide additional detail on the experience
requirements for the representative.
b. Section 11750- Please consider utilizing a 10 feet diameter wet well. It would offer
additional operational flexibility in the future.
c. The city requests that all valves located in pits or buildings be fully epoxy coated.
d. 2.2.1- The contractor will need to warrant the pump unit for a full year following
acceptance of the lift station. This section includes a date of manufacture clause that
conflicts with the one year warranty requirement.
Response:
a. Additional requirements have been added for experience of the manufacturer's
representative. See specification Section 11750- Lift Station.
b. The wet well has been changed to 10-feet diameter. See Sheet C6 of 7, Lift
Station Details.
c. The specifications have been changed to require all valves in the pits and building
require a full epoxy coating. See Specification Section 11750-Lift Station.
d. The specifications have been changed to require a five (5) year warranty of the
pump unit following acceptance of the lift station. See Specification Section
11750- Lift Station.
Comment 3: Section 13705- The following comments and questions need to be addressed:
a. In the description of work afloat switch is noted. Is this a high alarm switch?
b. In many places there is a reference made to city supplied items. Please confirm that
the city is not required to provide any equipment that they do not now own as part of
their "central unit. " Any modifications to existing facilities will be the responsibility
of the developer.
c. It is anticipated that the city will switch from phone lines to radio signals by the time
this lift station is operational. Please coordinate with Industrial Automation
Consulting on this issue.
d. The alarm section specifies external station alarms. The city does not want alarms
(visual or audio) outside of the station.
e. The city wants a motion detector in the building in lieu of the magnetic door switch.
f. The backup run time for the UPS may be low. Please review.
g. The alternating operation of the 3 pumps and initial pump control scenario needs to
be specified.
h. Specify minimum experience levels for instrumentation subcontractor.
Response:
a. The float switch has been deleted from this system. The ultrasonic level switches
will handle the high alarm. See Specification Section 13705- Process
Instrumentation and Controls.
b. The City of Bozeman is not required to buy any equipment they do not already
own. This lift station will be added to the City's current PC Based Work Station.
The PC should have available, a one (1) GHz Pentium and 128 MB of available
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ALLIED
ENGINEERING
May 16, 2002 SERVICES. INC.
James Nickelson
Morrison-Maierle, Inc.
901 Technology Blvd South
Bozeman, MT 59718
RE: Baxter Meadows Subdivision,Bozeman, Montana
Revised Lift Station and Force Main Design Report
Dear James:
Please find enclosed revised design report, plans and specifications for the lift station and force
main at Baxter Meadows Subdivision. These materials have been submitted to Ryan Leland of
MDEQ for review.
Please contact me if you have any questions or comments. Thank you.
Sincerely,
Allied Engineering Services, Inc.
Jo cGibbon, EI Scott R. Smith, PE
Civil Engineer Intern. Project Manager
enc: Revised Design Report, Plans and Specifications for Baxter Meadows Subdivision
32 Discovery Drive ♦ Bozeman, MT 59718 ♦ (406) 582-0221 ♦ Fax (406) 582-5770
�A=-
ALLIE
ENGINEERING
May 15, 2002 SERVICES, IN(--.
Ryan Leland
Montana Department of Environmental Quality
P.O. Box 200901
Helena, MT 59620-0901
RE: Baxter Meadows Subdivision,Bozeman,Montana
Revised Lift Station and Force Main Design Report
Dear Ryan:
Please find enclosed revised plans and specifications for a lift station that will serve the proposed
Baxter Meadows Subdivision near Bozeman, Montana. The Baxter Meadows Subdivision is a
461-acre planned unit development consisting of both residential and commercial zoned areas.
The lift station is to be designed to serve the portion of the development that cannot flow into the
City's collection system by gravity, plus an additional 160 acres south west of the project. The
additional area to be served in the future has not been annexed at the present, but could be in the
future. The future expansion area is bordered by Oak Street on the south, Ferguson on the east,
Harper Puckett on the west and Baxter Lane to the north(NW 1/4 of Section 3, T2S, R5E). Baxter
Meadows is located in the NE 1/4 of Section 3, T2S,R5E and the SW & SE corners of Section 34,
T1S,R5E.
The subdivision will be provided water and sewer service by the City-of Bozeman, and all water
and sewer main extensions will be reviewed in accordance with certified check lists from the
City of Bozeman and the Montana Department of Environmental Quality. The homeowners will
be billed in their sewer rates for the City to assume the responsibility of operation and
maintenance of the lift station after it is constructed.
Robert Peccia & Associates (RPA) completed a preliminary sewer system design report for
Baxter Meadows in October, 2001 as part of their preliminary plat submittal. They calculated a
potential flow rate of 503,732 gpd from Baxter Meadows and an additional 97,022 gpd from the
adjacent 160 acre quarter section. These flows were calculated using flows and peaking factors
determined in the 1998 Wastewater Facility Plan for the City of Bozeman. Total flow was
estimated at 600,754 gpd.
Baxter Meadows has now been zoned, which helps refine the wastewater flow projections.
Additionally, the 160 acre 1/4 section adjacent to Baxter Meadows that could eventually tie into
the City system and be serviced by the Baxter Meadows lift station, was originally contemplated
by RPA to be zoned 50 percent R-1 (three units per acre) and 50 percent RS (one unit per acre).
The peak hourly flow of the lift station was determined in accordance with City of Bozeman
design requirements which in turn, are based on zoning classifications. The subdivision will be
32 Discovery Drive ♦ Bozeman, MT 59718 ♦ (406) 582-0221 ♦ Fax (406) 582-5770
MDEQ Project: 0� +1 Baxter Meadows Subdivision
May 16, 2002
developed in accordance with local planned unit development regulations (requiring 30% open
space). According to the 1998 Wastewater Facility Plan for the City of Bozeman, a density of
12.19 persons per acre and a flow of 72 gpd/capita should be used to estimate future flows for
un-zoned areas. Flows from the 160 acres adjacent to, but not included as part of Baxter
Meadows is estimated at 140,429 gpd. The total developed area is estimated below in Table 1.
Table 1. Total Developed Area of Baxter Meadows Subdivision
Total Area Developed Area (70%)
Zone Classification (acres) (acres)
R-3 207 144.9
R-S 115 80.5
BP 139 97.3
Totals 461 322.7
The total population served by the lift station is estimated below in Table 2. The facility plan did
not provide for wastewater flows generated by the BP zoning designation. The largest generator
of wastewater per acre in the facility plan was the B2 zoning designation at 3,495 gallons per
acre,which was used in lieu of a flow for BP.
Table 2. Population Served by Lift Station
Population Number of
Zone Classification (per acre) Developed Acres Total Po )ulation Flow d)
Baxter Meadows R-3 12.19 144.9 1766 127,176
Baxter Meadows R-S 3.81 80.5 307 22,083
Baxter Meadows BP 97.3 340,064
Ad `/a Section 12.19 160 1,950 140,429
Totals 1 482.7 1 629,752
The average daily flow rate, including infiltration, is then calculated as follows:
629,752 gal/day/ 1440 min/day=437 gpm
(150 gal/acre/day x 621 total acres) / 1440 min/day= 65 gpm
437 gpm+ 65 gpm= 502 gpm
An equivalent population was estimated in order to calculate a peaking factor. According to the
1998 Wastewater Facility Plan for the City of Bozeman, people generate 72 gpcd. The total flow
of 629,752 gpd has an equivalent population of 8,747 people.
Using the following equation from DEQ2, the peaking factor for the peak hourly flow rate was
estimated as follows:
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F= (18 +Pas)/(4 +PO-)
Where:
F =Peaking Factor
P =Population (in thousands)
F= (18 + 8.7o.$)/(4+ 8.7")
F=3.01
The peak hourly flow rate is then estimated to be 437 gal/min * 3.01 = 1315 gal/min + 65
gal/min (infiltration)=13 8 0 gal/min. A peak hourly flow rate of 1380 gpm will be used for all
calculations.
The proposed lift station will consist of three identical 13-HP submersible pumps. The peak
hourly flow will be handled with any two pumps, while most flows will be handled with a single
pump. All three pumps will be situated inside a ten-foot diameter concrete manhole with a total
inside depth of approximately 24 feet. The pumps are sized to service the peak flow with the
target pump out of service, as per MDEQ requirements.
Valves will be enclosed in the Generator Building in lieu of a valve pit. The pump discharge
assemblies will be six-inch diameter. Inside the Generator Building, all three pump discharge
assemblies will be connected together with a six-inch cross. The force mains will then transition
to 12-inch diameter PVC SDR 21 pipe, and will be approximately 1140 feet in length until it
discharges into a gravity sewer at the intersection of Dead Man's Gulch and Davis Lane.
Additional features of the lift station include:
♦ Permanent backup power generator;
♦ Continuous monitoring by a SCADA system in the City of Bozeman shop.
Pump Sizing. DEQ 2 requires the lift station pumps to meet the peak hour demand with the
largest pump out of service. Since all three pumps will be sized the same, each pump will need to
have a capacity of 690 gpm. DEQ 2 also requires use of the Hazen Williams equation to
estimate pipe friction (C value of 120). The pumps specified have a discharge of 690 gpm at 36
TDH.
The maximum total dynamic head for each pump is calculated as follows:
Friction: 3011 of 6" ductile iron @ 690 gpm, C=120 1.5 feet
11401.f. of 12"PVC @ 1380 gpm, C =120 6.8 feet
Elevation: from LWL to discharge into gravity sewer 22.0 feet
Minor Losses: 4 - 6" 90 degree bends @ 690 gpm (K= 1.2) 1.4 feet
1 - 6" gate valve @ 690 gpm (K= .2) 0.3 feet
1 - 6" swing check valve @ 690 gpm (K=2.3) 2.8 feet
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1 - 12" x 6"reducer @ 1380 gpm (K= 0.56) 0.5 feet
2 - 12" 45 degree bends @ 1380 gpm (K= 0.42) 0.4 feet
1 - 12"pipe exit(K= 1) 0.2 feet
Total Dvnamic Head: 36 feet
The total dynamic head for a single pump operating is calculated as follows:
Friction: 301.f. of 6" ductile iron @ 690 gpm, C=120 1.5 feet
114011 of 12"PVC @ 690 gpm, C =120 2.0 feet
Elevation: from LWL to discharge into gravity sewer 22.0 feet
Minor Losses: 4 - 6" 90 degree bends @ 690 gpm (K= 1.2) 1.4 feet
1 - 6" gate valve @ 690 gpm (K= 0.2) 0.3 feet
1 - 6" swing check valve @ 690 gpm(K=2.3) 2.8 feet
1 — 12" x 6"reducer @ 690 gpm (K= 0.56) 0.7 feet
2 - 12" 45 degree bends @ 690 gpm (K= 0.42) 0.5 feet
1 - 12"pipe exit(K= 1) 0.2 feet
Total Dvnamic Head: 31.4 feet
The selected pumps are 13 HP Gorman Rupp JS4 F60-X13 non-clog pumps, which can pass a
3.15 inch diameter solid.
In order to show adherence to the requirements of DEQ2, Chapter 40, each item within this
document has been individually addressed below.
DEQ 2, CHAPTER 40—WASTEWATER PUMPING STATIONS
41. GENERAL
41.1 Flooding. The wastewater pumping station is not located within any delineated
flood plain. The nearest surface water sources are irrigation ditches and the
capacity of the channels are adequate so that channel overtopping is not likely to
occur. No damage to the electrical controls or components will occur from
surface water.
41.2 Accessibility and Security. The pumping station will be located adjacent to
Dead Man's Gulch and will be accessible by maintenance personnel at all times.
The pumping station will be provided at a minimum with locking access lids.
41.3 Grit. It is not anticipated that significant amounts of grit will be present in the
wastewater since the collection system will not receive stormwater. Any grit
present in the lift station should be minimal and will either be pumped out or will
settle to the bottom of the manhole.
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41.4 Safety. The lift station will be equipped with pumps that will be removable from
the surface. There should be minimal requirement for maintenance personnel to
enter the pumping station. For those specific instances, an outside contractor will
be hired, since the lift station will be maintained by the property owner's
association.
42. DESIGN
42.1 Type. The proposed project will be a submersible wastewater pumping station.
42.2 Structures.
42.21 Separation. The proposed station is not a wet well/dry well type.
42.22 Equipment Removal. All pumps and electrical components can be
removed from the surface without entering the lift station.
42.23 Access and Safety Landings.
42.231 Access. Access to the wet well will be provided at the surface via
aluminum hatches.
42.232 Safety Landings. No safety landings are provided. The design is
intended to minimize/discourage the need for maintenance
personnel to enter inside the manhole. All pumps and electrical
equipment can be removed from the surface.
42.24 Buoyancy. Buoyancy calculations for the lift station wet well are
provided as follows:
7concrete= 150 pcf
7water= 62.4 pcf
ysoil = 120 pcf (for gravelly soils)
� =26' (backfill material)
The lift station has outside dimensions of 11.5 feet diameter with a height
of 24 feet, and a displaced volume of 2493 cubic feet. Assuming saturated
groundwater at the surface, the buoyant force is calculated to be 155,563
lb (2493 cf* 62.4 pcf).
The forces resisting buoyancy include the weight of the manhole and the
frictional forces along the failure surface. We also conservatively assume
the failure surface to be vertical along the manhole walls.
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The weight of the manhole is calculated as follows:
Vconeretein manhole= ((Tc*(11.5 ft)2—(10 ft)2)/4)*24 ft)+((7T*(10 ft)2)/4)*2 ft)
Veoncrete in manhole= 765 cf
Wconcrete in manhole= 765 cf* 150 pcf
Wconcrete in manhole= 114,750 lb
The shear forces acting along the failure surface are calculated as follows:
Fshear=7c*l l.5 ft * 0.5*(1-sin26°)*(120 pcf-62.4 pCf)*(24 ft)2 (tan 200)
(circ.of well) (resultant shear force acting upon failure surface g H 3)
Fshear= 122,1501bs
Including the frictional forces resisting buoyancy, the total force resisting
buoyancy is 236,900 lbs, which exceeds the calculated buoyant force of
155,563 lbs. We conclude that there is a factor of safety of approximately
1.5 against buoyancy given our stated assumptions.
42.25 Construction Materials. The lift station will be constructed of type I-II
SR cement capable of withstanding prolonged exposure to hydrogen
sulfide and other corrosive gases, greases, oils, and other constituents. All
metal components will be coated with corrosion resistant paints. Contact
between dissimilar metals will also be avoided.
42.3 Pumps and Pneumatic Ejectors
42.31 Multiple Units. Three identical pumps will be provided, with two
operating pumps capable of handling the design peak hourly flow.
42.32 Protection Against Clogging.
42.321 Combined Wastewater. The pumps will not handle combined
wastewater, therefore, no bar racks will be required.
42.322 Separate Sanitary Wastewater. The pumps will be handling
wastewater from 15-inch diameter sewers, therefore, no bar racks
are provided.
42.33 Pump Openings. The pumps will be capable of passing spheres greater
than three inches diameter. Pump discharge piping is four inches diameter
or larger.
42.34 Priming. The pumps will always operate under a positive suction head.
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42.35 Electrical Equipment. All electrical pumps, motors, controls, etc. will be
compliant with National Electrical Code requirements for Class I, Group
D, Division 1 locations. All equipment in the wet well will be suitable for
use under corrosive conditions. All flexible cables will be provided with
watertight seals and separate strain relief A fused disconnect switch
located above ground will be provided for the main power feed. None of
the control equipment will be located outdoors or exposed to weather.
42.36 Intake. Each pump has an individual intake.
42.37 Dry Well Dewatering. The proposed lift station is not a wet well/dry
well configuration. This requirement is not applicable.
42.38 Pumping Rates. The pumps and controls of the main pumping stations
will operate at constant delivery rates, with on/off cycles and alarms
controlled by an ultrasonic level sensor. The lift station design peak
hourly flow has been determined using the City of Bozeman criteria for
I&I rates of 150 gpd/acre and wastewater generation rates of 72
gpd/capita. The wastewater flows have been determined using the
proposed zoning within the development with a peaking factor as shown
in section 11.24. The velocity in the force main exceeds the minimum
requirement of two fps.
42.4 Controls. The ultrasonic level sensor will not be affected by turbulence in the
wet well. The pumps will also alternate automatically.
42.5 Valves.
42.51 Suction Line. There are no suction lines for the proposed lift station
configuration.
42.52 Discharge Line. Shutoff and check valves will be placed on the discharge
line of each pump. The check valve will be located between the shutoff
valve and the pump. The check valves will also be suitable for wastewater
and will be installed on a horizontal section of pipe. Valves will be
capable of withstanding normal pressure and water hammer.
All shutoff check valves will be operable from the floor level and
accessible for maintenance and provided with outside levers.
42.6 Wet Wells.
42.31 Divided Wells. The wet well will be a single chamber. The majority of
the maintenance will occur above ground and will not impact the
operation of the other pumps.
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Size. Both the design cycle time (fill time + drain time) and the minimum
pump cycle per hour for average flow and peak flow are considered in the
sizing of the wet well. The peak flows for the development are estimated
to be 1380 gpm at full buildout. Average flows are estimated at 502 gpm.
The design cycle time should not exceed 30 minutes for the design
average flow. During the initial phases of the development when flows
are less than the design flow rate, this requirement will be satisfied with a
timer operator which will signal the lead pump to operate at a frequency of
one start every thirty minutes. Thus, if the lead pump "on" switch has not
been activated for duration of thirty minutes, the timer will automatically
signal the lead pump to operate until the water level triggers the pump
"off' switch. The above DEQ2 criteria will be evaluated for both average
flow and peak flow. The following variables will be used to evaluate both
scenarios.
A ten-foot diameter manhole contains 78.5 cubic feet per foot of depth, or
588 gallons per foot of depth. Based on average flow, the pump on setting
should be 2.0 feet above the pump off setting. At 588 gallons per foot of
depth for 2.0 feet, a volume of 1176 gallons is available for filling.
Average Flow
At an inflow rate of 502 gpm, the fill time is 2.34 minutes. The cycle time
calculation is shown below:
Fill time = 1176 gallons/ 502 gpm=2.34 minutes
Drain time = (Volume between Pump One on and Pump off) + Inflow —
Pump out flow
Drain time= 1176 gallons + 502(x)—690(x) = 0 where x=time
Solving for time x, x= 6.25 minutes
Cycle time=fill time+drain time=2.34 min+ 6.25 min = 8.59 minutes
Since 8.59 minutes is less than 30 minutes, the cycle time meets DEQ2
requirements.
To verify cycles per hour for average flow,
1 cycle/8.59 minutes * (60min./hr)= 6.98 cycles per hour
Since pumps 1, 2 and 3 cycle between themselves as controlled by the
PLC, the pump cycles are actually 6.89 cycles / 3 pumps = 2.3 cycles per
pump per hour.
Since 2.3 cycles per pump per hour is less than 10 cycles per hour, the
cycle number also meets the requirements.
Peak Flow
The calculated peak hourly rate of 1380 gpm is equal to the pumping rate
of two pumps. If the peak hourly flow is used as inflow and the pumping
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rate is used as drain flow there will be a static state in the wet well.
Therefore, 90% of the peak hourly flow will be used to more accurately
represent the fluctuations in flow during the peak times.
At an inflow rate of 1242 gpm (1380 gpm* 90%), the fill time is 0.85
minutes for pump one to turn on. The fill time between when pump one
kicks on and pump two kicks on, is 0.85 minutes. The cycle time
calculation is shown below:
Fill time pump one= 1176 gal/ 1242 gpm=0.95 minutes
Fill time pump two =Inflow—outflow= 1242 gpm—690 gpm
=552 gpm
Pump 2's setting is 1.0 foot above pump 1's setting, so
588 gallons/foot * 1.0 feet= 588 gallons
588 gallons/ 552 gpm= 1.07 minutes
So the total fill time= 0.95 min+ 1.07 min=2.02 minutes
Drain time = (Volume between pump two on and Pump off) + Inflow —
Drain flow
Drain time = 3 feet * (588 gallons/foot) + 1242(x) — 1380(x) = 0 where x
=time
Solving for time x, x= 12.8 minutes
Cycle time= fill time+drain time=2.02 min+ 12.8 min= 14.9 minutes
Since 14.9 minutes is less than 30 minutes, the cycle time meets DEQ2
requirements.
To verify cycles per hour for peak flow,
14.9 minutes/cycle * (hr/60min.) =4.0 cycles per hour
Since two of the three pumps will be operating during a cycle, each pump
will be operating only 67% of the time.
67% * 4.0 cycles per hour=2.7 cycles per hour.
Since 2.7 cycles per pump per hour is less than 10 cycles per hour, the
cycle number also meets the requirements.
If all three pumps.are operational,the maximum pumping capacity is 2070
gpm. The pumps should be set so one pump is held in reserve, and the two
remaining pumps should pump at 1380 gpm. The pump in reserve should
be set to come on approximately 12 inches above the other two pumps.
The settings should be as follows:
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Redundant"Off'—set 18 inches above the bottom of the wet well
Pumps "Off'—set 6 inches above Redundant"Off'
Pump "On"—2 feet above pumps "Off'
Pump2 on— 12 inches above pump "On"
Pump3 on— 12 inches above pump2 "On"
Alarm— 12 inches above pump3 "On".
Per manufacturers recommendations, the pump cycles will not exceed ten
starts per hour. If it is assumed the peak flow of 1380 gpm occurs for at
least one hour the number of cycles per hour must not exceed ten.
42.62 Floor Slope. As required, the wet well floor has a slope of 1 to 1 to the
hopper bottom.
42.63 Air Displacement. Normal fresh air ventilation will be provided by two-
2" Ohio Green Vents.
42.7 Safety Ventilation
42.71 General. Adequate ventilation will be provided via vents located at the
surface of the lift station. Since there is no wet well/dry well
configuration, permanent mechanical ventilation is not provided. All
mechanical equipment that will require maintenance will be removable
from the manhole on a rail system which is operable from the surface.
42.72 Air Inlets and Outlets. Two vents are provided since the manhole does
exceed 15 feet in depth (even though the proposed project is not a wet
well/dry well configuration).
42.73 Electrical Controls. There. is, no ventilation equipment prtJvlderl for the
proposed lift station.
42.74 Fans, Heating, Dehumidification. There are no fans, heaters, or
dehumidifiers provided for the proposed lift station.
42.75 Wet Wells. The proposed project is not a wet well/dry well configuration.
42.76 Dry Wells. The proposed project is not a wet well/dry well configuration.
42.8 Flow Measurement. The proposed lift station will be continually monitored by a
SCADA system per City of Bozeman requirements which will be capable of
indicating, totalizing, and recording flow measurement with known pump flow
rates.
42.9 Water Supply. There is no physical connection between any potable water
supply and the proposed wastewater pumping station.
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43. SUCTION LIFT PUMP STATION
The proposed project is not a suction lift pump station configuration and the requirements in this
section are not applicable.
44. SUBMERSIBLE PUMP STATIONS—SPECIAL CONSIDERATIONS
44.1 The proposed submersible pumps and motors are designed specifically for raw
wastewater use, including totally submerged operation during a portion of each
pumping cycle, and meet the requirements of National Electrical Code. Shaft seal
failure or potential seal failure detection is provided within the control panel for
the proposed pumps.
44.2 Pump Removal. The proposed submersible pumps are readily removable and
replaceable without dewatering the wet well or disconnecting any piping in the
wet well using the pultruded rail system shown in the drawings.
44.3 Electrical.
44.31 Power Supply and Control. Electrical supply, control, and alarm circuits
will be removable from the surface as required.
44.32 Controls. The motor control center is located outside of the wet well in a
building that is readily accessible by maintenance/operation personnel.
44.33 Power Cord. The pump motor power cords are designed for flexibility
and serviceability under conditions of extra hard usage and are compliant
with applicable National Electrical Code standards. Ground fault
interruption will be used to de-energize the circuit(s) in the event of failure
in the electrical integrity of the cable. Power cord terminal fittings are
corrosion resistant and will prevent moisture from entering the cable and
will easily facilitate field connecting.
44.4 Valves. A gate valve and check valve for each pump will be located outside the
wet well in the same building as the electrical controls. The building will be
dewatered to the wet well through a drain line with a check valve.
45. ALARM SYSTEMS
An alarm system is provided for the pumping station. The alarms will be activated
upon power failure, sump pump failure, high wet well level, unauthorized entry, and
pump malfunctions. A redundant off level will be provided along with a low level
alarm. Telemetry will also be provided to the City of Bozeman offices which will
notify all necessary personnel of any problems experienced by the lift station.
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46. EMERGENCY OPERATION
46.1 Objective. The proposed facility will provide for emergency operation
during extended power outages with multiple pumps and a permanent
backup power source.
46.2 Emergency Pumping Capability. Emergency pumping capability will
be provided as needed by an on-site back up power generator. The backup
power generator shall be capable of running all pumps and electrical
equipment for the lift station. A temporary, portable, pump could be
installed in the lift station wet well if necessary through the hatch system
at the surface.
46.3 Emergency High Level Overflows. No emergency high level overflow
has been provided since the power source for the lift station has been
shown to be very reliable. In addition, a backup power generator will be
capable of handling all functions of the lift station during extended power
outages. The operator of the system will be responsible for the fuel supply
of the lift station.
46.4 Equipment Requirements.
46.41 General.
46.411 Engine Protection. The engine will be protected from
operating conditions that could result in damage to any
equipment. The engine will be located inside a building
that will be provided with adequate exhaust and ventilation.
In addition, no harmful gases will be present inside the
building that could result in explosion,
46.412 Size. The generator will have adequate power to start and
continuously operate under all connected loads.
46.413 Fuel Type. The fuel type shall be either propane, natural
gas, or diesel. If a diesel generator is chosen, the fuel
source will be heated to prevent gelling during extreme
cold conditions.
46.414 Design and Installation of Fuel Storage Tanks. Design
and installation of fuel storage tanks will comply with all
state and federal standards.
46.415 Engine Ventilation. The engine will be located in a
generator building with adequate exhaust/air ventilation.
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46.416 Routine Start-Up. The generator and transfer switch shall
undergo routine monthly testing to ensure their proper
function at all times.
46.417 Protection of Equipment. The emergency equipment will
be provided with an electrical transfer switch which will
sense restoration of normal power and transfer the power
source. The transfer switch will also cease operation of the
generator as required.
46.42 Engine-Driven Pumping Equipment. There are no engine-
driven pumps for the proposed project.
46.43 Engine-Driven Generating Equipment.
46.431 Generating Capacity.
a. Generating unit will be sized to provide adequate
power for pump motor starting current, lighting,
ventilation, and other auxiliary equipment necessary
for safety and proper operation of the lift station.
b. The generating unit will be sized to operate all three
pumps.
C. Provisions within the control panel will be made
such that a time delay between the starting of
pumps is provided.
46,432 Operation. The ability for automatic load transfer will be
provided using an automatic transfer switch.
46.433 Portable generating equipment. The generating
equipment will be permanent.
47. INSTRUCTIONS AND EQUIPMENT
An operation and maintenance manual will be provided to the operator of the system prior to
completion, which will include operational instructions, emergency procedures, maintenance
schedules, tools, and spare parts that may be necessary.
48. FORCE MAINS
48.1 Velocity and Diameter. The minimum velocity in the force main will occur with
one pump operating, in which the flow rate will be 690 gpm. In a 12-inch
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diameter PVC SDR 21 pipe, the velocity will be 2.2 feet per second. At the peak
hourly flow of approximately 1380 gpm, the velocity will be 4.4 feet per second.
48.2 Air and Vacuum Relief Valve. The force main will be installed with a high
point inside the Generator Building. Air and vacuum relief valves will be
required and placed at the highest point on the force main.
48.3 Termination. The force main will enter the gravity sewer system approximately
one foot above the flowline of the receiving manhole.
48.4 Pipe and Design Pressure. Pipe will be PVC SDR21 with gasketed joints. All
bends within the force main will be provided with restraint.
48.5 Special Construction. No force main construction will occur near streams or
water works structures.
48.6 Freeze Prevention. The minimum depth will be 6.5 feet to the top of the force
main pipe.
48.7 Design Friction Losses.
48.71 Friction Coefficient. As required, friction losses through the force main
were estimated using the Hazen and Williams formula with a "C" value of
120.
48.72 Maximum Power Requirements. The pumps were also evaluated at a
higher "C"value of 150 and found to operate satisfactorily.
48.8 Identification. The force main will be marked with a tape indicating the presence
of wastewater.
48.9 Leakage Testing. Leakage tests in the force main will be completed in
conformance with MPW standards for water main materials.
Please feel free to contact me with any questions or comments.
Sincerely, 11�l- t t'k- ��-SA
Allied Engineering Services,Inc. �°�� - •'T
Cott R. Smith, PE _ • Nc 125J3 PF ;u
Project Manager
enc: Lift Station Plans and Specifications
cc: File, James Nickelson
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