City of Coppell - Starleaf Pump Station Redundancy vs Cost Technical Memorandum
(Starleaf Pump Station Study)
Page 1 of 3
To: Jamie Brierton, CIP Coordinator
Jerry Davis, Water Operations Supervisor
From: Bryant Caswell, PE (Texas PE #91721)
Dorian French, PE, RPLS, DWRE (Texas PE #40453)
Jennifer Roath, EIT (Texas EIT #48676)
Date: July 19, 2016
Subject: Starleaf Pump Station – Water Distribution System Redundancy vs Cost
As part of the SPS Study, Brown & Gay Engineers Inc., (BGE) has performed a supplemental
hydraulic analysis of the City’s water distribution system with Village Parkway Pump Station
(VPPS) offline and only the proposed Starleaf Pump Station (SPS) running in order to analyze
three levels of redundancy. Reducing the capacity of the facility below fully redundant will offer
the City cost savings through smaller pumps, storage tanks, and possibly building size. The
purpose of this memorandum is to outline the levels of redundancy and cost savings so the City
can make an informed decision before moving into the pump selection and the design phases.
WATER DEMAND
Currently, the City receives all of their treated water from Dallas Water Utilities (DWU). They
are contracted to receive 18.5 MGD into the Village Parkway GST. Based on meter data from
the past two years, the demand fluctuates between 2.4 and 17.1 MGD between winter and
summer respectively. Figure 1 shows the daily DWU influent and VPPS discharge records from
January 1, 2014 to September 30, 2015.
Figure 1 – Daily Meter Data from 1/1/2014 ‐ 9/30/2015
0
2
4
6
8
10
12
14
16
18
20
1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1 10/1 11/112/1 1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1Flow (MGD)Date
DWU Influent VP Discharge
2014 2015
Technical Memorandum (Starleaf Pump Station Study)
Page 2 of 3
To achieve complete redundancy where the SPS is able to supply the entire system through peak
summer demand, SPS would require 18 MGD capacity. While complete redundancy would offer
the City the most protection, scaling back the pumps and storage would offer substantial cost
savings. If SPS is sized for 12 MGD capacity, then the redundancy would be reduced to seven
months, from about October to April based on 2104 & 2015 meter data. To provide an adequate
window for major maintenance to VPPS, a minimum six month window is recommended.
MODELING
Three redundancy scenarios were tested using the hydraulic model developed for Technical
Memorandum #2 – Hydraulic Study. These scenarios assumed VPPS was completely offline,
including all pumps and storage tanks. Supply from DWU was only entering the Starleaf GST
and SPS is the only source of supply for the City’s system. For each scenario, SPS had 3 pumps
of identical size varying from 4,000 gpm to 7,000 gpm. The GST was either 5, 6, or 8 Mgal.
Then demand was adjusted to model each redundancy level: 12, 14 and 18 MGD. Results of the
scenarios are described in Table 1 and discussed in the subsequent sections.
Table 1 – Modeling Scenario Results
Redundancy
Level
Pump Size
(gpm)
Tank Size
(Mgal) Comment
12 MGD
4,000 5 ESTs and GST below 5ft
4,000 6 ESTs and GST below 5ft
4,500 5 ESTs and GST cycle
4,500 6 ESTs and GST cycle
14 MGD
4,500 5 ESTs empty
4,500 6 ESTs and GST below 5ft
5,000 5 ESTs and GST below 5ft
5,000 6 ESTs and GST cycle
18 MG
7,000 5 ESTs empty
7,000 6 ESTs and GST below 5ft
7,000 8 ESTs and GST cycle
Redundancy Level 1 – 12 MGD
The lowest capacity level for pumping and storage redundancy recommended is 12 MGD. This
would provide the City with approximately 7 months in which to perform major repairs at VPPS
based on 2014 – 2015 meter data. When system demands reach 12 MGD, three pumps would be
required during peak hour flows to avoid the ESTs from nearing empty. The minimum pump size
required would be 4,500 gpm with a 5 Mgal tank.
Technical Memorandum (Starleaf Pump Station Study)
Page 3 of 3
Redundancy Level 2 – 14 MGD
14 MGD of pumping capacity with 6 Mgal of storage would provide approximately 9 months in
which to perform major repairs at VPPS. When the system demands reach 14 MGD three 4,500-
5,000 gpm pumps would be required during peak demand. The minimum pump size required
would be 4,500 gpm with a 6 Mgal tank.
Redundancy Level 3 – 18 MGD
Complete redundancy in the system would be achieved with 7,000 gpm pumps running during
peak hourly flow. A 6 Mgal tank almost emptied during the model run however, the model only
simulated a 72 hour period. More than three days of continuous peak demand would likely have
emptied the tank. Therefore, to achieve complete redundancy an 8 Mgal tank is recommended.
COST COMPARISON
The cost difference for the pumps and tanks at each redundancy level is summarized in Table 2.
This comparison only considers the direct cost of the pumps and tank, and does not include the
building, site work, yard piping, and other related costs.
Table 2 – Cost Comparison between Redundancy Levels
Redundancy
Level
Pump Tank
Total Size (gpm) Cost1 Size (Mgal) Cost1
12 MGD 4,500 $321,000 5 $2,900,000 $3,221,000
14 MGD 5,000 $345,000 6 $3,400,000 $3,745,000
18 MGD 7,000 $525,000 8 $4,200,000 $4,725,000
1. Costs shown are based on average vendor and contractor prices, see attachment
The building cost may vary based on the redundancy level, and will likely provide further cost
savings, but other uses such as maintenance and office space make it difficult to quantify at this
point. The type of pump, vertical turbine or horizontal split case, may have no significant impact
on the building cost. Although the building footprint for vertical turbine pumps will be less than
that required for horizontal split case pumps, significantly more excavation and subgrade
preparation would be required. Although detailed pump selections were performed for this
analysis, it is to be discussed further in Technical Memorandum 3 – Pump Type Selection, once
the stations capacity is determined.
RECOMMENDATIONS
It is recommended that the SPS be designed for a 14 MGD capacity to provide a 9 month
redundancy window to VPPS. The estimated savings by reducing the capacity from 18 MGD to
14 MGD would be approximately $980,000.
ATTACHMENTS: Contractor and Vendor Cost Comparisons
City of Coppell
Starleaf Pump Station Project - Pump Cost Comparison
Proj No. 3451
Pump*
Capacity
(gpm)
Horizonal Split
Case
Vertical
Turbine
Horizonal Split
Case
Vertical
Turbine
4,500 50,000$ 75,000$ 210,000$ 92,600$
5,000 75,000$ 75,000$ 210,000$ 95,500$
7,000 100,000$ 150,000$ 190,000$ 255,000$
*Costs shown are for a single pump. The pump station will have three (3) pumps of equal size.
Pierce Pump Solutions
Cost Comparison Table
$‐
$50,000
$100,000
$150,000
$200,000
$250,000
$300,000
4,500 5,000 7,000
Capacity (gpm)
Cost vs. Pump Size (gpm)
City of Coppell
Starleaf Pump Station Project - GST Tank Cost Comparison
Proj No. 3451
Tank
Vol (Mgal)Foundation Tank Total Tank Total Tank Total
1
2 500,000$ 1,025,000$ 1,525,000$ 950,000$ 1,450,000$
3
4
5 1,100,000$ 1,775,000$ 2,875,000$
6 1,200,000$ 2,250,000$ 3,450,000$ 2,045,000$ 3,245,000$
7
8 1,500,000$ 2,800,000$ 4,300,000$ 2,871,000$ 4,371,000$ 2,530,000$ 4,030,000$
DN Tanks Preload
Cost Comparison Table
Crom
$0
$500,000
$1,000,000
$1,500,000
$2,000,000
$2,500,000
$3,000,000
$3,500,000
$4,000,000
$4,500,000
$5,000,000
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Volume (Mgal)
Cost vs. GST Vol (Mgal)