SS9901-SY001116WASTEWATER FLOW EVALUATION
DEFOREST WASTEWATER LIFT
STATION AND FORCE MAIN
IMPROVEMENTS
For
CITY OF COPPELL
DEPARTMENT OF ENGINEERING & PUBLIC WORKS
TCB JOB NO. 15-30041-001
Prepared by
Turner Collie(._~Braden inc.
NOVEMBER 2000
Turner CollieF. Braden Inc.
Engineers - Planners · Project Managers
17300 Dallas Parkway
Suite 1010
Dallas, Texas 75248
972 735-3000
Fax 972 735-300]
November 16, 2000
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
Re:
DeForest 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 DeForest 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
Sincerely,
N~a nZ~E ~b~ c [ e~a'n ,~e~
Project Engineer
Ted B. Sugg, PTET.
Project Manager
NEM
Engineering Excellence for Over One-Half Century
WASTEWATER FLOW EVALUATION
DEFOREST WASTEWATER LIFT
STATION AND FORCE MAIN
IMPROVEMENTS
For
CITY OF COPPELL
DEPARTMENT OF ENGINEERING & PUBLIC WORKS
TCB JOB NO. 15-30041-001
Prepared by
Turner Collie~Braden lnc
NOVEMBER 2000
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 II EVALUATION
Current Wastewater Flows .................................................................................................. II - 1
Existing Pumping Records ................................................................................................. II - 3
Peak Wet Weather Flows ................................................................................................... II - 3
Ultimate Development of Basin ......................................................................................... II- 4
Comparison of Flows ......................................................................................................... II - 6
SECTION III CONCLUSION ....................................................................................................... III - 1
TABLES
Table 1 - Summary of Dry Weather Flow Rates ................................................................ II - 1
Table 2 - Existing Dry Weather Flow Rates ....................................................................... II - 2
Table 3 - Ultimate Build-Out Dry Weather Flow Rates ..................................................... II - 4
Table 4 -Comparison of Flow Projections ......................................................................... II - 6
EXHIBIT
Exhibit 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 DeForest Wastewater Lift Station and to estimate future
flows for the year 2020. The DeForest Wastewater Lift Station is located in the northeast quadrant of
the City of Coppell off of DeForest Road. The DeForest drainage basin consists of the majority of
the north half of the City of Coppell from the City's boundary on the west to Samuel Street on the
east.
Based on this study, TC&B has determined that the DeForest Wastewater Lift Station currently
receives an estimated peak flow of 6.40 MGD, and future peak flows are estimated to reach 13.72
MGD by the year 2020.
SECTION I - INTRODUCTION
I-1
GENERAL
The DeForest Wastewater Lift Station is located in the City of Coppell near the intersection of
Samuel Street and DeForest Road, 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 6.90 MGD.
Based on this study, it is estimated that the lift station is currently operating at an average base flow
of 1.60 MGD with estimated peak flows of at least 6.40 MGD. The capacity of this lift station
should be increased to meet future demands anticipated with the current rate of growth and
development in the coramunity.
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 the
Coppell city limits on the west, Denton Creek on the north, Samuel Street on the east, and Sandy
Lake Road on the south, as shown on Exhibit I.
PROJECTSCOPE
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 land use, 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.
The "Wastewater Collection System Master Plan" (hereinafter referred to as the 1994 Master Plan),
prepared in December 1994 by Rady and Associates, 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. The 1994 Master Plan also contained land use and
utility maps which were used as the basis for this report.
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 by the North
Central Texas Council of Governments in April 2000. Aerial photographs and zoning information,
dated February 1999, were obtained from Landiscor Aerial Information.
DESIGN MEETING
A meeting was held between the City of Coppell and TC&B on April 28, 2000 to review the existing
conditions of the lift station and obtain record drawings of the lift station and force mains. In a
separate meeting on May 5, 2000, Doug Newport and Steve James of TC&B met with Kenneth
Griffin, Glenn Hallowell, and Chuck Hancock from the City of Coppell to discuss the proposed lift
station and force main alternatives.
CURRENT WASTEWATER FLOWS
Was,~ewater flows were estimated for the DeForest drainage ~,si,,n,,using the method recommended in
the Design Criteria for Sewerage Systems, 30 TAC Chapt~ ~ 217", page 18, published March 3, 2000
by the Texas Natural Resources Conservation Commission
wastewater flow was established by multiplying the per cai:
service area. The average number of people per home used
32,640, the known population of the City of Coppell, by ~
The number of people in the service area was estimated by
ITNRCC). The annual average
ita flow by the number of people in the
.a~his study was established by dividing
t0~, the number of billed water meters.
aultiplying 2.89, the average number of
people per home, by 4,318, the number of dwelling units. The number of dwelling units was
estimated from existing maps and verified by field visits. Commemial and Light Industry flows were
calculated separately, by multiplying the estimated square feet of each business by the average flow
rates for each type of business. The Commemial and Light Industry 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.
Table 1: Summary of Dry Weather Flow Rates
Use Flow Rate (GPD) Unit of Measure
Animal Hospital 600.00 EA
Apartment Unit 250.0C EA
Bank 0.0'7 SF
Car Wash 1250.0C EA
Church 0.015 SF
Fire Station 1000.0C EA
Head Start or Day Care Facility 0.015 SF
Homes 300.0C EA
Library 0.015 SF
Light Industry 0.05 SF
Office 0.1 ~2 SF
Restaurant 0.9C SF
Retail 0.0'7 SF
Schools 0.015 SF
Service Station 1250.0~2 EA
An inventory of the homes, schools, churches, commercial buildings, and light industrial areas within
the drainage basin was performed. For commercial and light industry 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 1.60 MGD for the drainage basin, as shown in Table 2.
) 1 1 1 1 I 1 1 -1 -1 ! 1 1 1 ! '! I 1
II -2
Table 2: Existing Dry Weather Flow Rates
Land Use Flow Rate Number of Units by Sheet Map Number* Total Flow Rate
Category Unit (GPD/uni0 B2 C2 D2 A3 B3 C3 D3 A4 B4 C4 D4 AS Units (GPD)
Animal EA 600.00 I I 2 1,000
Hospital
Apartment EA 250.00 738 (73~8 185,000
Unit
Bank SF 0.07 20,000 20,000 1,000
Car Wash EA 1,250.00 1 1 1,000
Child Care SF 0.06 80,000 37,500 117,500 7,000
Facility
Church SF 0.06 164,300; 38,300 202,600 12,000
Fire EA 1,000.00 1 1 1,000
Station
Homes EA 300.00 262 83 504 605 1,106 358 207 341 114 (..3,5'~8~0 1,074,000
Library SF 0.06 27,500 27,~ 2,000
Light SF 0.05 292,400 117,600 1,188,200 37,80~ 171,00~3 1,807,000 90,000
Industry
Office SF O. I 0 99,000 40,800 139,800 14,002
Restaurant SF 0.90 18,100 9,800 27,900 25,00C
~,etail SF 0.07 162,400 90,60~ 111,600 364,600 26,00~
Schools SF 0.06 505,000 1,100,00(3 450,000 357,50~ 202,500 2,615,000 157,000
Service EA 1,250.00 2 I 3 4,000
Station
TOTAL 1,600,000
* City of Coppell, City-Wide Mapping System - Topographic / Base Map
II -3
EXiSTiNG PUMPING RECO~~'~'~ ~~ ~
Existing water pu~were obtained from the City of Coppell. These records established a
water use rate of 8 G~..~_~ er capita~i.n_~e_s_e_rvice area. This water use rate was used to establish
the estimated wastewater flow rate of 128 GPD per capita. The average water use rate and estimated
wastewater flow rates are consistent with flow rates for this region.
The flow from the DeForest 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 1.77 MGD. These pumping rates
are consistent with the estimated dry weather flow rates established by TC&B in the previous
section.
The daily flow information for April 11,2000 was also used to estimate the current capacity of the
pumps. 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 Pump No. I was 4,360
GPM. The design flow conditions for Pump No. 1 with a 125 Hp motor and 17-inch impeller is
4,300 GPM at 72 feet of head. The estimated pumping rate for Pump No. 3 was 3,145 GPM. The
design flow conditions for Pump No. 3 with a 94 Hp submersible motor and 17-inch impeller is
3,140 GPM at 72 feet &head. The estimated flow rates are close to design flow conditions, so the
estimated flow rates are reasonable for this analysis.
PEAK WET WEATHER FLOWS
The "Design Criteria for Sewerage Systems, 30 TAC Chapter 217", page 18, recommends using a
minimum lseaking 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
4.60 MGD. This established a known peak event at a factor of 2.88 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 1.60 MGD. A design flow of 6.40 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 four categories: residential multi-
family, residential single family, commercial development, and light industry. 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 fol'low 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 acm 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
Light industry is mixed with various operations and population densities. An average flow rate was
developed from the existing density of industry development. A unit flow rate of 725 GPD/acre is
equivalent to the current estimated flow rates for the developed areas.
Table 3: Ultimate Build-Out Dry Weather Flow Rates
Single Family Multi-Family Commercial Light Industrial Total Flow
Year Acres Flow Rate Acres Flow Rate Acres Flow Rate Acres Flow Rate (GPD)
(GPD) (GPD) (GPD) (GPD)
2000 1193.30 1,073,970 29.52 184,500 169.31 253,965 125.00 90,625 1,603,000
2001 1400.0£ 1,260,000 41.12 257,000 190.00 285,000 175.00 126,875 1,929,000
2002 1600.0C 1,440,000 41.12 257,000 210.00 315,000 225.00 163,125 2,175,000
2003 1800.0C 1,620,000 41.12 257,000 230.00 345,000 375.00 271,875 2,494,000
2004 1918.13 1,726,317 41.12 257,000 250.00 375,000 425.00 308,125 2,666,000
2005 1918.13 1,726,317 41.12 257,00£ 270.00 405,000 475.00 344,375 2,733,000
2006 1918.13 1,726,317 41.12 257,00C 290.00 435,000 525.00 380,625 2,799,000
2007 1918.13 1,726,317 41.12 257,00C 310.00 465,000 575.00 416,875 2,865,000
2008 1918.13 1,726,317 41.12 257,0012 330.00 495,000 625.00 453,125 2,931,000
2009 1918.13 1,726,317 41.12 257,00C 350.00 525,000 675.00 489,375 2,998,000
2010 1918.13 1,726,317 41.12 257,000 367.43 551,145 725.00 525,625 3,060,000
2011 1918.13 1,726,317 41.12 257,00C 367.43 551,145 775.00 561,875 3,096,000
2012 1918.13 1,726,317 41.12 257,000 367.43 551,145 825.00 598,125 3,133,000
2013 1918.13 1,726,317 41.12 257,000 367.43 551,145 875.00 634,375 3,169,0001
2014 1918.13 1,726,317 41.12 257,000 367.43 551,145 925.00 670,625 3,205,00C
2015 1918.13 1,726,317 41.12 257,000 367.43 551,145 975.00 706,875 3,241,00C
2016 1918.13 1,726,317 41.12 257,000 367.43 551,145 1025.00 743,125 3,278,0QC
2017 1918.13 1,726,317 41.12 257,000 367.43 551,145 1075.00 779,375 3,314,00C
2018 1918.13 1,726,317 41.12 257,000 367.43 551,145 1125.0t2 815,625 3,350,00t3
2019 1918.13 1,726,317 41.12 257,000 367.43 551,145 1175.0C 851,875 3,386,000
20201 1918.13 1,726,31~ 41.12 257,000 367.43 551,145 1231.43 892,787 3,427,000
The ultimate base flow is estimated to be 3.43 MGD. This is based on the eventual full development
of residential, commercial and industrial 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, 20 acres of commemial development, and 50 acres of industrial development per
year. These rates are consistent with estimates by the City Planner and the current rate of growth in
this ama. The recommended peaking factor of four was multiplied times the base flow to determine
the design flow. An ultimate build-out design flow of 13.72 MGD is estimated for the DeForest
Wastewater Lift Station.
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 9,510 3.14 1.97 6.18
1995 10,180 3.36 1.97 6.62
1996' 10,850 3.58 1.97 7.05
1997 11,520 3.812 1.97 7.49
1998 12,190 4.02 1.97 7.92
1999 12,850 4.24 1.97 8.36
20013 13,520 4.4~ 1.97 8.79 12,480 1.60 4.00 6.40
2001 14,190 4.68 1.97 9.23 15,110 1.93 4.00 7.72
2002 14,860 4.91 1.97 9.66 16,845 2.18 4.00 8.72
2003 15,530 5.13 1.97 lO. lO 18,580 2.49 4.00 9.96
2004 18,700 6.1' 1.97 12.16 19,600 2.67 4.00 10.68
2005 18,700 6.22 1.97 12.24 19,600 2.73 4.00 10.92
2006 18,700 6.26 1.97 12.33 19,600 2.80 4.00 11.212
2007 18,700 6.30 1.97 12.41 19,600 2.87 4.00 11.48
2008 18,700 6.34 1.97 12.50 19,600 2.93 4.00 11.72
2009 18,700 6.39 1.97 12.58 19,600 3.00 4.00 12.012
2010 18,700 6.43 1.97 12.67 19,60t2 3.06 4.00 12.24
2011 18,700 6.47 1.97 12.75 19,6012 3.10 4.00 12.412
2012 18,700 6.52 1.97 12.84 19,6012 3.13 4.00 12.52
2013 18,700 6.5{ 1.97 12.92 ' 19,6012 3.17 4.00 12.68
2014 18,700 6.60 1.97 13.32 19,6012 3.21 4.0£ 12.84
2015 18,700 6.65 1.97 13.32 19,60t3 3.24 4.0¢ 12.96
2016 18,700 6.69 1.97 13.32: 19,6013 3.28 4.0£ 13.12
2017 18,700 6.73 1.97 13.32 19,6013 3.31 4.0t2 13.24
2018 18,700 6.77 1.97 13.32 19,6013 3.35 4.012 13.413
2019 18,700 6.82 1.97 13.32 19,6013 3.39 4.012 13.56
2020 18,700 6.76 1.97 13.32 19,600 3.43 4.012 13.72
II - ?
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
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 128 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 13.72 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 13.32 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 13.72 is recommended, as presented in this study.
SECTION III - CONCLUSION
III - 1
CONCLUSION
The base wastewater flow rate into the DeForest Wastewater Lift Station is estimated to be 1.60
MGD. Present conditions at the lift station are adequate for the existing flows. Future flows for the
DeForest drainage basin have been estimated to increase to a base wastewater flow rate of 3.43 MGD
and a peak flow rate of 13.72 MGD by the year 2020. TC&B recommends designing and
implementing upgrades to the current lift station and force mains to a firm capacity of 13.72 MGD in
preparation for these future flows.
DRAINAGE
BOUNDARY
SV I LL£
DEFOREST LIFT STATION
PROJECT LOCATION MAP
CITY OF COPPELL
DEFOREST WASTEH/ATER UFT STATION
Tumer Collie ~den I~