SS9901A-SY010413WASTEWATER FLOW EVALUATION
SANDY LAKE WASTEWATER LIFT
STATION AND FORCE MAIN
IMPROVEMENTS
For
CITY OF COPPELL
DEPARTMENT OF ENGINEERING & PUBLIC WORKS
TCB JOB NO. 15-31124-001
Prepared by
lurner Collie ~.~Braden lnc
APRIL 2001
Turner Collie f._ffB den Inc.
Engineers · Planners · Project Managers
April 13, 2001
Mr. Kenneth M. Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
255 Parkway Boulevard
P.O. Box 478
Coppell, Texas 75019-4409
17300 Dallas Parkway
Suite 1 O10
Dallas, Texas 75248
972 735-3000
Fax 972 735-3001
Re:
Sandy Lake Wastewater Lift Station and Force Main Improvements
Wastewater Flow Evaluation
Dear Mr. Griffin:
This Wastewater Flow Evaluation summarizes our investigations for the existing and estimated
flows in the Year 2020 for the Sandy Lake Wastewater Lift Station.
We are available to meet with you to discuss our findings during your review of this evaluation.
Thank you for the assistance provided by you and the members of the public works staff in
performing this investigation and preparing the report.
Sincerely,
E. Mt:Lean, P.E.
Engineer
Ted B. Sug~g~P.E.
Project Manager
N-EM
Engineering Excellence for Over One-Half Century
ENGINEERING DESIGN REPORT
SANDY LAKE WASTEWATER LIFT
STATION AND FORCE MAIN
IMPROVEMENTS
For
CITY OF COPPELL
DEPARTMENT OF ENGINEERING & PUBLIC WORKS
TCB JOB NO. 15-31124-001
Prepared by
Turner Collie ~Braden lnc
APRIL 2001
TABLE OF CONTENTS
EXECUTIVE SUMMARY
SECTION I INTRODUCTION
General ................................................................................................................................. I - 1
Project Description ............................................................................................................... I - 1
Project Area .......................................................................................................................... I - 1
Project Scope ........................................................................................................................ I - 1
Data Collection .................................................................................................................... I - 2
Design Meeting ................................................................................................................... I - 2
SECTION H EVALUATION
Current Wastewater Flows .................................................................................................. II - 1
Existing Pumping Records ................................................................................................. II - 3
Peak Wet Weather Flows ................................................................................................... H - 3
Ultimate Development of Basin ......................................................................................... II - 4
Comparison of Flows ......................................................................................................... II - 6
SECTION m CONCLUSION ....................................................................................................... IH - 1
TABLES
Table 1 - Summary of Dry Weather Flow Rates ................................................................ II - 1
Table 2 - Existing Dry Weather Flow Rates ....................................................................... H - 2
Table 3 - Ultimate Build-Out Dry Weather Flow Rates ..................................................... II - 5
Table 4 - Comparison of Flow Projections ......................................................................... H - 6'
EXHIBIT
Exlfibit 1 - Location Map
Exhibit 2 - Ultimate Build-Out Land Use
EXECUTIVE SUMMARY
The City of Coppell selected Turner Collie & Braden Inc. (TC&B) to conduct a study to determine
the existing wastewater flows received at the Sandy Lake Wastewater Lift Station and to estimate
future flows for the year 2020. The Sandy Lake Wastewater Lift Station is located in the southeast
quadrant of the City of Coppell off of Sandy Lake Road. The Sandy Lake drainage basin consists of
the majority of the eastern side of the City of Coppell from the City's boundary on the east to Samuel
Boulevard on the west. The Sandy Lake Wastewater Lift Station receives flow from both the
DeForest Wastewater Lift Station and the Sandy Lake drainage basin.
Based on this study, TC&B has determined that the Sandy Lake Wastewater Lift Station currently
receives an estimated peak fl0w of 10.20 MGD, and future peak flows are estimated to roach 18.40
MGD by the year 2020. The flow from the Sandy Lake drainage basin alone, without the flow from
the DeForest Wastewater Lift Station, constitutes an estimated peak flow of 3.80 MGD, with future
estimated peak flows of 4.24 MGD.
SECTION I - INTRODUCTION I - 1
GENERAL
The Sandy Lake Wastewater Lift Station is located in the City of Coppell near the southeast comer of
Sandy Lake Road and MacArthur Boulevard, as shown on Exhibit 1. The wastewater lift station was
designed and constructed in 1975. The original design peak flow capacity of the lift station is 10.30
MGD. Based on this study, it is estimated that the lift station is currently operating at an average
base flow of 2.55 MGD with estimated peak flows of at least 10.20 MGD. The base flow for the lift
station consists of 1.60 MGD from the DeForest Wastewater Lift Station and 0.95 MGD from the
Sandy Lake drainage basin. The capacity of this lift station should be designed to meet future
demands anticipated with the current rate of growth and development in the community.
PROJECT DESCRIPTION
The City of Coppell Department of Engineering and Public Works selected Turner Collie & Braden
Inc. (TC&B) to evaluate the existing flows into the lift station and to determine the ultimate build-out
development and associated wastewater flows for the basin.
PROJECT AREA
The project area lies entirely within the City of Coppell. The drainage basin is bounded by DeForest
Road to the north, Coppell city limits to the east, Tupelo Drive to the South, and Samuel Boulevard
to the West, as shown on Exhibit 1.
PROJECT SCOPE
TC&B was contracted to provide the following services for the City:
Prepare an estimate of current wastewater flow based on existing land use.
· Compare estimated flow rates with current pumping records provided by the City.
· Review peak wet weather flows based on available past rainfall data and wastewater flows.
Estimate peaking factors based on rainfall data and lift station pumping records provided by the
City.
· Estimate flows based on projected full development of the basin, using the peaking factors
established above.
· Compare year 2020 wastewater flows, ultimate peak flows, and pumping requirements with the
1994 Master Plan projections and TNRCC regulations.
· Prepare a task report and review the findings with the City.
I-2
DATA COLLECTION
Existing utility and lift station plans were obtained from the City of Coppell Engineering and Public
Works Department. These plans provided information about the lift station and sanitary sewer line
locations, sizes, and slopes. CAD maps provided from the City of Coppell were used as the
background for exhibits presented in this report.
The "Wastewater Collection System Master Plan" prepared in December 1994 by Rady and
Associates, hereinafter referred to as the 1994 Master Plan was obtained from the City of Coppell.
The 1994 Master Plan summarized existing flows, projected future population, industrial growth, and
associated wastewater flows to the year 2014.
Design regulations were obtained from the "Design Criteria for Sewerage Systems, 30 TAC Chapter
217" published March 3, 2000 by the Texas Natural Resources Conservation Commission (TNRCC).
Population data was obtained from the "2000 Current Population Estimates" published in April 2000
by the North Central Texas Council of Governments.
Aerial photographs from the "1999 Dallas Photo Atlas" by Landiscor Aerial Information were used
to help identify development in the City of Coppell and current zoning information.
DESIGN MEETING
A meeting was held between the City of Coppell and TC&B on Feb 1, 2001 to discuss the results of
the preliminary design report prepared for the DeForest Wastewater Lift Station. The final
recommendation was to address the DeForest Wastewater Lift Station improvements and the Sandy
Lake Wastewater Lift Station improvements as one project to find a solution that minimizes total
project construction and operating costs. This wastewater flow evaluation is the beginning of the
Sandy Lake Wastewater Lift Station Improvements evaluation.
SECTION H - EVALUATION II - 1
CURRENT WASTEWATER FLOWS
Wastewater flows were estimated for the Sandy Lake drainage basin using the method recommended
in the "Design Criteria for Sewerage Systems, 30 TAC Chapter 217', page 18, published March 3,
2000 by the Texas Natural Resources Conservation Commission (TNRCC). The annual average
wastewater flow was established by multiplying the per capita flow by the number of people in the
service area. The average number of people per home used in this study was established by dividing
32,640, the known population of the City of Coppell, by 9920, the number of billed water meters.
The number of people in the service area was estimated by multiplying 3.29, the average number of
people per home, by 2,783, the number of dwelling units. The number of dwelling units was
estimated from existing maps and verified by field visits. Commercial flows were calculated
separately, by multiplying the estimated square feet of each business by the average flow rates for
each type of business. The Commercial flows were then added to the total flows for the drainage
basin. Existing records were used to establish unit dry weather flow rates for the drainage basin, as
shown in Table 1. Wastewater from the DeForest drainage basin is currently pumped to the Sandy
Lake Wastewater Lift Station.
Table 1: Summary of Dry Weather Flow Rates
Use Flow Rate (GPD) Unit of Measure
Animal Hospital 600.00 EA
Apartment Unit 250.00 EA
Bank 0.07 SF
Car Wash 1250.00 EA
Church 0.06 SF
Fire Station 1000.00 EA
Head Start or Day Care Facility 0.06 SF
Homes 300.0~ EA
Library 0.06 SF
Light Industry 0,05 SF
Office 0.10 SF
Restaurant 0.91] SF
Retail 0.07 SF
Schools 0.06 SF
Service Station 1250.0~ EA
An inventory of the homes, schools, churches, and commercial buildings within the drainage basin
was performed. For commercial buildings, a unit flow rate per square foot was used to estimate the
wastewater flows. The individual flows were summed to obtain an existing base flow of 0.95 MGD
for the drainage basin, as shown in Table 2.
II -3
EXISTING PUMPING RECORDS
Existing water pumping records were obtained from the City of Coppell. These records established a
water use rate of 128 GPD per capita in the service area. The estimated average dally wastewater
flow rate is 104 GPD per capita. This average wastewater flow rate is approximately 81 percent of
the average water use rate and is consistent with flow rates for this region.
The flow from the Sandy Lake Wastewater Lift Station is not metered. The wastewater level in the
wet well and pump activity at the lift station are monitored and recorded. Dimensions of the wet well
are known and were used to establish the volume of the wet well.
Daily flow information was provided for April 11, 2000. The time between pump activity was
measured to calculate the average flow rate into the lift station of 2.09 MGD. These estimated flow
rates represent 80 percent of the estimated dry weather flow rates established by TC&B in the
previous section.
The average flow rate into the wet well and the time each pump was running were used to calculate
the pumping rate out of the wet well. The calculated pumping rates were then checked against the
design conditions of the pumps. The estimated pumping rate for both Pump No. 2 and Pump No. 3
running simultaneously was 5750 GPM. The design flow conditions for Pump No. 2 with a 35 Hp
motor and 17-inch impeller is 3,000 GPM at 23 feet of head. The design flow conditions for Pump
No. 3 with a 50 Hp motor and 18-inch impeller is 3,850 GPM at 33 feet of head. The pumps are
operating below design conditions. Some decrease in flow is due to normal wear on the impellers.
In addition, a larger force main has been installed downstream of the lift station changing the
operating conditions since the original pumps were installed. New pumps are recommended at the
lift station to handle current and future flow conditions.
PEAK WET WEATHER FLOWS
The "Design Criteria for Sewerage Systems, 30 TAC Chapter 217", page 18, recommends using a
minimum peaking factor of four applied to estimated dry weather flows to determine peak flows.
Peak two-hour flow rates are used as design flows for the lift station and force mains to allow added
capacity for fluctuations in daily flow and seasonal flow variations.
A 5.1 inch storm event occurred on the evening of April 11, 2000. The flow into the wet well during
this event was estimated by multiplying the pumping rate calculated for each pump by the time each
pump was running to establish the peak 2-hour flow rate. The estimated peak 2-hour flow rate was
5.36 MGD. This established a known peak event at a factor of 2.10 times the estimated average daily
flow rate.
This one peak event is not reliable as the basis for determining the peaking factor to be used in
designing this lift station. Diurnal peak flows occur in the early morning and early evening hours of
the day. A storm event of this magnitude occurring at the same time of day as the peak diurnal flow
would be expected to generate a greater peak event.
II-4
The estimated flows of the storm event do support using the TNRCC recommended peak factor of
four. The design flow is obtained by multiplying the peak factor of four times the average daily flow
of 0.95 MGD. A design flow of 3.80 MGD is estimated for the drainage basin.
ULTIMATE DEVELOPMENT OF BASIN
The ultimate development of the drainage basin was determined using land use and zoning
information provided by the City of Coppell and aerial photographs obtained from Landiscor Aerial
Information. The City Planner was contacted for current information on residential development.
The City Planner estimated full residential development within the next few years followed by
continued growth in commercial and industrial development.
Ultimate flows were estimated by multiplying a unit flow rate for each land use area by the total area
zoned for that land use. The land use areas were divided into three categories: residential multi-
family, residential single family, and commercial development. Unit flow rates for each land use
category were estimated from current land development practices. Land use areas were measured
from zoning maps and electronic maps of the drainage basin provided by the City. Table 3 was
developed to show the relationship of future development and flow rates in each land use area
between the year 2000 and predicted full development in the year 2020.
Residential multi-family homes are typically apartment complexes in the City of Coppell. The
current housing density of apartment units is 25 dwelling units per acre. Each apartment unit is
assumed to have an average flow rate of 250 GPD. A unit flow rate of 6,250 GPD/acre was
established for each acre of land zoned for residential multi-family development. The City Planner
stated that one apartment complex is currently under construction, and this will complete the
construction of multi-family dwellings. Two other parcels are currently zoned for residential multi-
family development. Single family homes are being developed on these parcels. The City Planner
suggested that we designate these areas as residential single family development to follow with the
current development of these parcels. The designation of these parcels was changed on maps and the
total area used to calculate future wastewater flows for residential multi-family development.
Residential single family homes are currently being constructed at a density of three homes per acre. '
It is assumed that home construction will continue with this density in the undeveloped lots zoned for
residential single family homes. Each home is assumed to have an average flow rate of 300 GPD. A
unit flow rate of 900 GPD/acre was determined for each acre of land zoned for residential single
family development.
Commercial development is widely mixed with offices, fast food restaurants, strip malls, gas stations,
and various other businesses operating within a concentrated area. An average flow rate was
calculated based on the types of businesses and current density of development. TC&B and the City
Planner agree that similar development density can be assumed for the undeveloped land. A unit
flow rate of 1,500 GPD/acre was determined for each acre of land zoned for commercial
development. This rate is consistent with an average unit flow rate calculated for the existing types
of businesses.
II - 5
Table 3: Ultimate Build-Out Dry Weather Flow Rates
Single Family Multi-Family Commercial Total
Flow
Year Acres Flow Rate Acres Flow Rate Acres Flow Rate (GPD)
(GPO) (GPO) (GPO)
2000 967.75 870,975 9.60 60,00C 12.00 18,000 949,000
2001 1034.69 931,221 9.60 60,00C 32.0~ 48,000 1,039,000
2002 1034.69 931,221 9.60 60,00~ 40.29 60,435 1,052,000
2003 1034.69 931,221 9.60 60,00~ 40.29 60,435 1,052,000
2004 1034.69 931,221 9.60 60,00~ 40.29 60,435 1,052,000
2005 1034.69 931,221 11.23 70,1881 40.29 60,435 1,062,000
2006 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,000
2007 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2008 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,000
2009 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,000
201~3 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2011 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2012 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,000
2013 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00(3
2014 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00(3
2015 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2014 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2017 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2018 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00~
2019 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00C
202C 1034.69 931,221 11.23 70,188 40.29 60,435 1,062,00C
The ultimate base flow is estimated to be 1.06 MGD. This is based on the eventual full development
of residential and commercial land use areas. Ultimate development is estimated for completion in
the year 2020. Ultimate development assumes growth to continue at a rate of 600 residential lots and
20 acres of commercial development per year. These rates are consistent with estimates by the City
Planner and the current rate of growth in this area. The recommended peaking factor of four was
multiplied times the base flow to determine the design flow. An ultimate build-out design flow of
4.24 MGD is estimated for the Sandy Lake drainage basin.
II - 6
COMPARISON OF FLOWS
The flows estimated in this investigation were compared with the flows presented in the 1994 Master
Plan. The two studies targeted different years and used a different method for estimating flows.
Therefore, to allow a comparison of the two studies, peak flows and base flows were calculated for
each year to present and compare the findings of the two studies, as shown in Table 4.
Table 4: Comparison of Flow Projections
1994 Master Plan Year 2000
Year Population Base Flow Peak Peak Flow !Population Base Flow Peak Peak Flow
(MGD) Factor (MGD) (MGD) Factor (MGD)
1994 6,120 2.34 1.97 4.61
1995 6,250 2.32 1.97 4.57
1996 6,370 2.30 1.97 4.53
1997 6,500 2.28 1.97 4.49
1998 6,630 2.26 1.97 4.4~
1999 6,760 2.24 1.97 4.4(3
2000 6,880 2.21 1.97 4.36 9,156 0.95 4.00 3.80
2001 7,010 2.19 1.97 4.32 10,770 1.134 4.00 4.16
2002 7,140 2.17 1.97 4.28 10,770 1.05 4.0(1 4.20
2003 7,260 2.15 1.97 4.2~1 10,770 1.05 4.00 4.20
2004 7,390 2.09 1.97 4.12 10,770 1.05 4.00 4.20
2005 7,390 2.05 1.97 4.0,~ 11,130 1.06 4.00 4.24
2006 7,390 2.01 1.97 3.95 11,130 1.06 4.00 4.24
2007 7,390 1.96 1.97 3.87 11,130 1.06 4.00 4.24
2008 7,390 1.92 1.97 3.78 11,130 1,06 4.00 4.24
2009 7,390 1.88 1.97 3.7C 11,130 1.06 4.00 4.24
2010 7,390 1.83 1.97 3.61 11,130 1.06 4.00 4.24
2011 7,390 1.79 1.97 3.53 11,130 1.06 4.00 4.24
2012 7,390 1.75 1.97 3.4zl 11,130 1.06 4.013 4.24
2013 7,390 1.70 1.97 3.315 11,130 1.0~ 4.013 4.24
2014 7,390 2.59 1.97 5.11i 11,130 1.0~ 4.013 4.24
2015 7,390 2.59 1.97 5.11 11,130 1.015 4.0t3 4.24
2016 7,390 2.59 1.97 5.11 11,130 1.015 4.0~ 4.24
2017 7,390 2.59 1.97 5.11 11,1313 1.061 4.0t2 4.24
2018 7,390 2.59 1.97 5.11 11,1313 1.06 4.012 4.24
2019 7,390 2.59 1.97 5.11 11,1313 1.06 4.012 4.24
2020 7,390 2.59 1.97 5.11 11,1313 1.06 4.012 4.24
The two studies were performed using different methodology and therefore, produced different
results. The two methods used different primary assumptions for conducting the wastewater flow
11-7
studies. The method used to derive the base flows for the 1994 Master Plan assumed an average
daily flow for residential use of 117 GPD per capita. Commercial and industrial flows were assumed
to contribute to more than 50 percent of the wastewater flows for a combined unit dry weather flow
rate of 330 GPD per capita. For this study, a combined unit flow rate for residential and commercial
use of 104 GPD per capita was established from existing water usage rates. In addition, commercial
and industrial development was verified to be less than 30 percent complete at this time from maps,
field visits, and information provided by the City Planner.
The peak factor used for the 1994 Master Plan was approximately two. This peak factor is not
considered high enough for current wet weather and daily flow fluctuations. The base flow
estimations in the 1994 Master Plan were considerably higher than current base flows based on
existing water records and wastewater pumping records. This study estimated a lower base flow and
recommends using a peak factor of four to account for both wet weather and daily fluctuations in
flow.
The recommended peak design flow of 4.24 MGD is justifiable based on existing water and
wastewater records, land development, and established design criteria. The 1994 Master Plan
derived an estimated peak flow of 5.11 MGD. This conclusion is similar, but the data to justify the
conclusion is not available to support this conclusion. Therefore, use of the estimated peak design
flow of 4.24 is recommended, as presented in this study.
SECTION HI - CONCLUSION IH - 1
CONCLUSION
The base wastewater flow rate into the Sandy Lake Wastewater Lift Station is estimated to be 0.95
MGD. Flow from the DeForest Wastewater Lift Station is pumped to the Sandy Lake Wastewater
Lift Station for a combined base flow rate of 2.55 MGD. Peak flows at the Sandy Lake Lift Station
are estimated to reach 10.08 MGD. Present conditions at the lift station are adequate for the existing
flows. Future flows for the Sandy Lake drainage basin have been estimated to increase to a base
wastewater flow rate of 4.24 MGD and a peak flow rate of 18,40 MGD by the year 2020. TC&B is
evaluating the feasibility of redirecting the flow from the DeForest Wastewater Lift Station and
reducing the total flow received at the Sandy Lake Wastewater Lift Station to improve the operating
efficiency of the wastewater system. Future flows to the Sandy Lake Wastewater Lift Station would
reduce the required finn pumping capacity to 4.24 MGD.
PROJECT LOCATION &lAP
CITY OF COPPELL
SANDY LAKE WASTEWATER LIFT STATION
& FORCE&lAIN I&IPROVE&IENTS
Turner Collie ~Braden Inc.
ENGINEERS · PLANNERS · PROJECT MANAGERS