HomeMy WebLinkAboutLift Station StudyLift Station Study
FOR
Creek Meadows Subdivision
Section 7, Phase One & Two
College Station, Brazos County, Texas
March 27, 2015
Prepared For:
Creek Meadow Partners, L.P.
c/o Oldham Goodwin Group, LLC
2800 South Texas Avenue, Suite 401
Bryan, TX 77802
Prepared By:
RME Consulting Engineers
Texas Firm Registration No. F-4695
P.O. Box 9253
College Station, TX 77845
RME No. 260-0551
Lift Station Study
FOR
Creek Meadows Subdivision
Section 7, Phase One & Two
College Station, Brazos County, Texas
March 27, 2015
Prepared For:
Creek Meadow Partners, L.P.
c/o Oldham Goodwin Group, LLC
2800 South Texas Avenue, Suite 401
Bryan, TX 77802
Prepared By:
RME Consulting Engineers
Texas Firm Registration No. F-4695
P.O. Box 9253
College Station, TX 77845
RME No. 260-0551
Lift Station Study
Creek Meadows Subdivision
Section 7, Phase One & Two
College Station, Brazos County, Texas
TABLE OF CONTENTS: PAGE
1.0 General Information ...................................................................................................................................... 1
1.1 Scope of Report ....................................................................................................................................... 1
1.2 Site and General Location ....................................................................................................................... 1
1.3 Description of Existing Sanitary Sewer Conditions ................................................................................ 2
2.0 Sanitary Sewer Flow ...................................................................................................................................... 2
2.1 Sanitary Sewer Demands ......................................................................................................................... 2
2.2 Outfall Capacity ....................................................................................................................................... 3
3.0 Lift Station Design .......................................................................................................................................... 3
3.1 General Information, Methodology & Design Criteria ............................................................................ 3
3.2 General Site Conditions ........................................................................................................................... 5
3.3 Wet Well & Storage Capacity ................................................................................................................. 5
3.4 Pumping Requirements ............................................................................................................................ 7
3.5 Force Main Evaluation ............................................................................................................................ 8
ATTACHMENTS:
Section 1.0
Schematic Phase Layout
Creek Meadows Subdivision -Preliminary Plan
Vicinity Map
Section 2.0
CMSSLS -Service Area Map
Section 3.0
LS-01: Lift Station Site Plan
Geotechnical Investigation
LS-02: Lift Station Details
Lift Station Design Worksheet
Tank Floatation Worksheet
Bearing Capacity Worksheet
System & Performance Curves
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Lift Station Study
Creek Meadows Subdivision
Section 7, Phase One & Two
College Station, Brazos County, Texas
1.0 GENERAL INFORMATION
1.1 Scope of Report:
This report addresses the lift station system improvements, for the Creek Meadows
Subdivision, Phase One & Two. The purpose of this study is to evaluate (1) outfall
capacities and expected sanitary sewer demands (lift station flows being received by the 8"
sanitary sewer collection line located in Creek Meadows Subdivision, Section 5, Phase 3),
and (2) evaluate the proposed design of the lift station pumping, wet well storage, and
forcemain piping. The ultimate desire, illustrated in this design report, is generally as
follows:
(1) Provide adequate service capacity for Creek Meadows Subdivision-Section 7, Phase
One & Two, and other phases discharging to this lift station;
(2) Verification that the outfall capacity of the existing collections systems is not
overwhelmed.
The proposed Creek Meadows Southside Lift Station (CMSSLS) improvements are
generally described as follows and are in further detailed within the body of this report.
Schematic Phase Layout, illustrates graphically these improvements is contained within
the "Attachment -Section 1.0" portion of the report. Also reflected in this report, and the
before mentioned schematic drawing, is information from the Creek Meadows Lift Station
(CMLS) study (dated 9/11/13) and the Castlegate 2 Lift Station (CG2LS) study (dated
2/4/15).
The proposed development's sanitary sewer improvements are analyzed in accordance
with the criteria outlined in the "B/CS Unified Technical Specifications and Design
Guidelines" (UTSDS) manual of the City of College Station (CoCS) and Chapter 217 of
the Texas Commission on Environmental Quality (TCEQ) Rules & Regulations.
1.2 Site and General Location:
The Creek Meadows Subdivision has access to Greens Prairie Road West, near its north
property line, and is bisected by Greens Prairie Trail through its southern third. Adjacent
existing developments generally consist of the Estates of Royder Ridge to the west,
Turnberry Place and Benjamin Graham subdivisions to the north, Woodlake to the
southeast, and Wellborn Oaks to the east. Originally all of these subdivisions were located
in the College Station E.T.}. However, since the time of the original report much of these
developments have been annexed by the CoCS. Currently sewer services, for these ETJ
subdivisions, are still being provided by on-site sewerage facilities (OSSF's) on an
individual bases. The Creek Meadows subdivision is further illustrated on the attached
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Creek Meadows, Section 7, Phase One & Two
Lift Station Study
RME Consulting Engineers
March 27, 2015
Creek Meadow Preliminary Plan, which is contained within the "Attachment -Section
1.0" portion of the report.
Also a Vicinity Map, for this project site, is provided and is located in the "Attachment"
portion ofthis manual. This map is being provided as an aid in locating the site. Drawings
describing the work and its specific locations are contained in the Construction Drawings
prepared by RME Consulting Engineers, College Station, Brazos County, TX. These
Construction Drawings are included as part of this Lift Station Study by reference.
1.3 Description of Existing Sanitary Sewer Conditions:
The Creek Meadows Subdivision is currently partially developed. An existing 8" sanitary
sewer collection line, which will be the discharge point for CMSSLS, was installed with
Section 5, Phase Three. This collection line discharges to the Creek Meadows Subdivision
Lift Station.
2.0 SANITARY SEWER FLOW
2.1 Sanitary Sewer Demands:
The sanitary sewer requirements, for all contributing phaeses, were derived by
implementation of Method 2 -"Land Use Determination" from the UTSDS. Lot totals,
for the Creek Meadows Subdivision, are based on the latest approved Preliminary Plan
(see "Attachment -Section 1.0" portion of report) and the CMSSLS Service Area Map
(see "Attachment -Section 2.0" portion of report) Average daily sanitary sewer flow
values were calculated and the results are summarized in Table #1 -"Sanitary Sewer
Flows" shown below. Assumptions for these calculated sanitary sewer flow values are
reported following Table #1.
TABLE #1 -SANITARY SEWER FLOWS
Average Average L-ttour
Daily Flow Dwelling Daily Flow Peak Flow Peak Flow
Section/Phase (gpd/cap) Units (gpd) (gph) (cfs)
Section 6, Phase I 100 33 8,811 1,469 0.05
Section 6, Phase 2A 100 9 2,403 401 0.01
Section 6, Phase 3 100 28 7,476 1,246 0.05
Section 7, PhaseTwo 100 48 12,816 2,136 0.08
Section 7, Phase Three 100 14 3,738 623 0.02
Section 7, Phase Four 100 32 8,544 1,424 0.05
TOTAL EXPECTED FLOWS= 164 43,788 7,298 0.27
Flow Determination Assumptions:
I) Residential density is at 2.67 capita/Dwelling Unit (D.U.);
2) Average Daily flows, for each use, were assigned per Table III-"Average
Wastewater Generations" per the UTSDS;
3) A Peaking Factor of 4.0 will be utilized;
Utilizing the flow data in Table #1 the minimum required Firm Pumping Capacity of the
CMSSLS will be 121 gpm. The actual Firm Pumping Capacity is expected to be 133 gpm.
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Creek Meadows, Section 7, Phase One & Two
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2.2 Outfall Capacity:
RME Consulting Engineers
March 27, 2015
As discussed in Section 1.3 of this report the proposed outfall for the CMSSLS is the
existing 8" sanitary sewer collection line (located in Section 5, Phase 3 -Identification of
MH #22). The existing 8" sanitary sewer collection line has been laid at a slope of 0.40%
slope. This equates to a capacity of approximately 350 gpm (0.78 cfs) for the 8" line
(n=0.013). The before mentioned 8" sanitary sewer line discharges directly into the CMLS.
Prior to discharging sanitary sewer into the lift station the sanitary sewer line will collect
an additional 81 gpm (0.18 cfs). Thus the total flow intercepted by this 8" sanitary sewer
line will be as follows. As illustrated there is a surplus of 136 gpm (0.30 cfs) capacity in
this collection line.
8" Sanitary Sewer Collection Line (Capacity = 350 gpm)
Downstream areas of CMLS
Firm Pumping Capacity CMSSLS
TOT AL EXPECTED FLOW TO 8" SS:
3.0 LIFT ST A TI ON DESIGN
3.1 General Information, Methodology & Design Criteria:
81 gpm
133 gpm
214GPM
Utilizing the proposed lift station layout, design conditions, expected flows from Table #1,
the Creek Meadows Southside Lift Station (CMSSLS) was designed for compliance with
proposed anticipated improvements. The applicable design criteria, from the TCEQ -
Chapter 217, are briefly listed below:
1. §217 .59 -Lift Station Site Requirements;
2. §217.60-Lift Station, Wet Well, and Dry Well Designs:
(b )(7) -Minimum pump cycle time· based on peak flow and pump horsepower
requirements;
( d) -Lift Station Ventilation;
3. §217.61 -Lift Station Pumps:
( c) -Lift Station Pumping Capacity;
( d)(3) -Friction Coefficient;
(d)(4)-System Curves;
(e)(2)-Total number of pumps;
4. §217.63(d)(l)-Retention Capacity (Emergency Provision);
5. §217.64(b)-Material for Force Main Pipes;
6. §217.67 -Force Main Design:
(a) -Velocities;
( c) -Water Hammer;
( d) -Connection to Gravity Main;
(h) -Valves;
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Creek Meadows, Section 7, Phase One & Two
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3.2 General Site Conditions:
ROADWAY ACCESS:
RME Consulting Engineers
March 27, 2015
The CMSSLS will take access via the pubic street Crooked Creek Path. This public street
is located in a 50' right-of-way with a 27' street section (laydown curb/gutter, 6" lime
stablished subgrade, 6" limestone base & 2" HMAC surface) that has finished grades
above the 100-year flood elevations. The adjacent nearby flooding source would be Peach
Creek Tributary 16.4.3 with a maximum flood elevation of 288.18' during the 100-year
rainfall event (per Limited Flood Study prepared by RME and dated 3/27/15).
SECURITY FENCE & GATE:
The CMSSLS is secured by means of an 8' high solid wood privacy fence. The site will
be accessed by a 16' wide, 2-panel, swing gate. Also, the site will be 30'x 35' in size
which will allow a minimum of 1 O' separation between the security fence and any portion
of the wet well or vault box.
SUBSURFACE EXPLORATION & GEOTECHNICAL STUDY:
Gessner Engineering was retained and prepared a Geo technical Investigation (dated
1121/15) (see "Attachment -Section 3.0" portion of report) and will be utilized to assist
in design of the wet well. Generally speaking the recommendations are based from a
single bore (approximately located at the center of the proposed wet well) and extended
30' below existing grade (bottom of bore at an elevation of ~255'). Generally speaking it
is estimated that the CMSSLS wet well foundation will be founded on stiff and moderate
fat clays and that the water table is below the bottom elevation.
3.3 Wet Well & Storage Capacity:
RETENTION STORAGE:
The CMSSLS wet well is proposed to be a 6-foot in diameter with a minimum storage
elevation of 272.00' and a maximum storage elevation of 287.00'. Further details of the
CMSSLS wet well, and operation system, are illustrated on both the LS-02: Lift Station
Details sheet and the Lift Station Design Worksheet contained in the "Attachment-Section
3.0" portion of this report.
Emergency storage capacity was accounted for in the design of the wet well and is in
accordance with TCEQ §217.63(d)(l). This information is as follows and is based on Peak
Flow (PF) conditions.
);>-Wet Well= 3,171 gallons;
);>-Available line storage ~ 3,480 gallons;
The CMSSLS collection system has a maximum storage elevation of 287. 00 ' before
wastewater backs-up into any residential service line;
);>-Available Retention Storage = 6,651 gallons (accommodates PF=229 gpm);
);>-Required Retention Storage = 3,527 gallons (calculated PF=122 gpm);
The longest power outage, provide by Bryan Texas Utilities (James Tanneberger -
emailed 1120115), within the past 24 months is 29 minutes.
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Creek Meadows, Section 7, Phase One & Two
Lift Station Study
RME Consulting Engineers
March 27, 2015
Additional volume checks were performed utilizing Equation C.5, per TCEQ
§217.60(b)(8), which utilized the reported Pump Cycle times below in Table #4 of Section
3.3 during the Ultimate Design Conditions. As illustrated below in Table #2 the combined
wet well and available line storage will be adequate for this project.
TABLE#2
MIN. EFFECTIVE VOLUME
Firm Peak Flow Storage Volume
Pumping Cycle
Capacity Time Storage Storage
m min (cu.ft.) (gal.)
133 40.7 180.9 1,353
WET WELL DESIGN DATA:
Flood Protection: Per TCEQ §217.59(c) the design of the lift station shall provide flood
protection during the 100-year flood event. However, the CoCS Lift Station Design
Guidelines exceeds this requirement by requiring the top of the lift station to be equal to or
greater than 3' above BFE. Thus the lift station flood protection is as follows:
~ 288.18' = 100-year pool elevation of adjacent detention facility (maximum pool
elevation of Pond #8);
~ 291.25' =Top of Wet Well (required 291.18');
~ 290.75' = Finish grade elevation (Top of lift station vault shall be set 6" above
finish grade);
Wet Well Piping & Mechanical: Addition data outlined in TCEQ §217 .60 or the CoCS
Lift Station Design Guidelines are highlighted below.
~ Minimum of 6" clearance with flanges and wet well wall;
~ 15% bottom slope and grout doesn't extend up into "All Pumps Off'' (Top of grout
is 9" above FFE and "All Pumps Off' is 18" above FFE);
Passive Venting: Per TCEQ §217.60(d)(l) and the CoCS Lift Station Design Guidelines
an 8" diameter vent pipe, with stainless steel screen, will provide up to 600 :tpm at the lift
stations firm pumping capacity.
STRUCTURAL DETERMINATIONS:
Information and calculations shown in this subsection are based upon data provided in the
Geotechnical Report (prepared by Gessner Engineering-dated 1/21/15).
Buoyancy Calculations: The wet well shall be designed to resist the effects of buoyancy
assuming full saturation of the surrounding soils to the finish grade of the wet well. No
surface friction was provided in the attached Geotechnical Investigation therefore this
measure of "resistance" to buoyancy will not be included in the calculations. Details of
this information is contained on the Tank Floatation Worksheet contained in the
"Attachment -Section 3.0" portion ofthis report. A brief summary is as follows. Please
note this approach and resulting Factor of Safety (FOS) are conservative calculations (i.e.
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Creek Meadows, Section 7, Phase One & Two
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RME Consulting Engineers
March 27, 2015
analyzed with an empty wet well, "anchoring" created by yard piping, no considerations
for attached vault box, wet well lid, etc ... ).
~ 12" truck concrete bottom;
~ Buoyancy Resistance no Skin Friction -FOS = 1.53
The CoCS Lift Station Design Guidelines requires a FOS of 1.1 with surface friction
not considered.
Bearing Capacity: Calculation shown below consider 100% buoyant soils (less the 6" of
lift station elevated above the finish grade). This is a conservative approach since no
groundwater was present during the drilling operations and will thus result in smaller
contribution with the "compensated foundation" system. Calculations are detailed on the
Bearing Capacity Worksheet which is contained in "Attachment -Section 3.0" of the
report.
~ Maximum allowable Bearing Capacity = 3,000 psf (FOS = 3)
~ Applied Stress = 1, 192 psf
Predicted Settlements: Per the Geotechnical Report the total expected settlement is
predicted to be minimal using the above Maximum Allowable Bearing Capacities.
Lateral Earth Pressures: The following equation was utilized to calculate the maximum
exerted Lateral Earth Pressure on the side wall of the wet well. This data will be reported
on the construction drawings and verified by the wet well manufacture that the structural
strength of the wet well will be sufficient.
P1 = (100 pct) x d where,
P1 =lateral earth pressure (pst);
100 = equivalent fluid unit weight;
d =depth below ground surface (ft);
therefore,
P1 = (100 pct) x 21.25 ft = 1,850 pounds per foot of width of wall
Utilizing a FOS = 3 then P1 = 6,375 pounds per foot of width of wall
LEVEL CONTROL SETTINGS:
The CMSSLS wet well will be equipped with PVC ball-type floats with mercury switch
for each pump "on'', "off", and alarm elevations. Spacing of the level control points have
been established to provide adequate pump cycle times, pumps "off' is no closer than
twelve-inches (12") from the finished floor, and such that no level setting is closer than six
inches (6") apart. Also the "high level" alarm has been set at an elevation two-feet (2')
above the lag pump "on" elevation. These control settings are summarized below in Table
#3.
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Creek Meadows, Section 7, Phase One & Two
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RME Consulting Engineers
March 27, 2015
TABLE#3
LEVEL SETTINGS
Elevation
Condition (ft)
FFE 270.50
ALI Pumps "Off' 272.00
Lead Pump "On" 274.00
Lag Pump "On" 274.95
Influent Pipe 274.95
High Level Alarm 276.95
Conditions Satisfied:
l. Minimum sump required of 12" (18" provided);
2. Lead Pump "On" setting below influent tlowline
(l l" difference provided);
3. Minimum float separation of6" (11" provided);
3.4 Pumping Requirements:
PUMP INFORMATION:
As discussed in Section 2.1 the required minimum Firm Pumping Capacity of the CMSSLS
will be 121 gpm (133 gpm provided). In order to accommodate this required pumping
capacity system curves where develop. System Curves utilized a friction coefficient of
C=130 & C=150. These System & Performance Curves are contained within the
"Attachment -Section 3.0" portion of the report.
PROPOSED PUMPS:
~ Two Flygt Pumps (CP-3085 MT 3---434);
~ Duty Point -133 gpm at 30.3' TDH;
~ Pump efficiency at approximately 61 %;
~ Rated 3 hp with 460V (3 phase) 25 Amp starter service;
Below in Table #4 are the Cycle Times during Average Daily Flows (ADF) and Peak Flow
(PF) for CMSSLS improvements. Per Table C.4 of §217.60(b)(7) the minimum pump
cycle time of 6 minutes is required for this system. This cycle time is analyzed between
the "pump-on" and "pump-off' elevations report earlier in Table #3. The pump "on"
elevation may need minor adjustments to obtain a more desirable pump cycle time.
TABLE #4 -PUMP CYCLE TIMES
CM:S:SL:S
Firm Pump Cycle Time
Pumping
Capacity ADF Peak Flow
PHASE (gpm) (min) (min)
Ultimate Design 133 18.0 40.7
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Creek Meadows, Section 7, Phase One & Two
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3.5 Force Main Evaluation:
VELOCITIES:
RME Consulting Engineers
March 27, 2015
TCEQ §217.67(a) (2) requires that a minimum velocity of 3.0 fps be met in a duplex pump
system with one (1) pump in operation. Therefore utilizing the Hazen-Williams equation
the 4" forcemain will experience a velocity ofV=3.4 fps during pumping of 133 gpm.
WATER HAMMER & PRESSURE:
TCEQ §217 .67( c) requires that a forcemain with a velocity greater than 6.0 fps be designed
to manage pressure and that the working strength of the forcemain not be exceeded due to
water hammer. As reported above the 6.0 fps threshold will not be surpassed.
As required in the UTSDS the pressure in a force main shall not exceed 1/2 of the maximum
working pressure of the piping. The minimum working pressure of any type of force main
is 160 psi. Therefore the maximum allowable pressure is 80 psi (185' TDH). As noted
previously in Section 3.4 the "duty point" for the pumping capacity will not exceed this
allowable pressure (maximum design = 30.3 ' TDH when C=130).
CONNECTION TO GRAVITY MAIN:
As previously mentioned the 4" forcemain will discharge into Manhole #22 which was
installed with the development of Section 5, Phase 3.
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SECTION 1.0
GENERAL INFORMATION
CREEK MEADOWS:
SECTION 7, PH . 1
VICINITY MAP
NOT TO SCALE
N
NOTTO
SCALE
SECTION 2.0
SANITARY SEWER FLOW
SECTION 3.0
LIFT STATION DESIGN