Technical Memorandum 1
Water System Demands and Wastewater Flows
BACKGROUND
Parkhill, Smith & Cooper, Inc. has been retained by the Border Environment Cooperation
Commission (BECC) to develop a facility plan for the City of Marfa that covers improvements
needed for 5, 10 and 20 year time periods. This plan is broken down into two technical
memoranda (TM). This is the first of the TM’s and will evaluate the current water system
demands, population projections and wastewater contributions.
EXISTING CONDITIONS
Population and Location
The City of Marfa is located in Presidio County, on Highway 90 between Valentine to the
Northwest and Alpine to the East as shown in Figure 1-1. The City is approximately 72 km from
the US/Mexican border. The City has a population of 2,121 people according to the 2000 census.
An aerial map of the City is shown in Figure 1-2.
Figure 1-1 – Location Map
Water System
The City supplies potable water to its residents from a series of three water wells located on the
same site as a 0.5 million gallon ground storage tank, 3700 gpm booster pump station and a
75,000 gallon elevated storage tank. Well 2 and 3 pump 1,100 gpm each and well 4 pumps 400
gpm. The water plant booster station has two 1,850 gpm pumps installed. The City also has a
stand pipe and 2 booster pump stations and two hydro-pneumatic tanks located at other sites.
Both of the booster pump stations are designed to pump 350 gpm. The total treated water storage
capacity is 812,000 gallons. TCEQ has requested that the City construct a new potable water well
at some point away from the existing three wells so they have some redundancy in the event that
the site where the existing three wells are located becomes contaminated.
As of the end of 2001 the City had a total of 1059 residential water meters. The City delivered an
average of 603,578 gallons per day to a total of 1204 meters. This flow equates to a per capita
supply of 279 gallons per day based on a population of 2,163. The Cities water meter data that
shows the large amount of
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Technical Memorandum 1
Water System Demands and Wastewater Flows
Figure 1-2 Aerial Map
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Technical Memorandum 1
Water System Demands and Wastewater Flows
water (350 gpm) sent to a Hydro-ponic Tomato Farm to the north of the City. By subtracting
these flows from the supply number leaves a per capita consumption of 188 gallons per day. The
peak day per capita flow reported by the City is 279 gpm which equates to 1.48 times the average
day. Dividing the total population by the number of connections reveals a population density of
2.04 people per connection. The standard population density per Texas Water Development
Board is 2.36 people per connection.
A review of water supply records supplied by the City of Marfa revealed an unaccounted for
water volume that averaged 22 percent of the total water supplied. This water is either lost due to
line breaks, line maintenance or hydrant testing/flushing.
The following issues and concerns related to Marfa’s water system were identified during the
RAP:
 The water supply contains fluoride concentrations above the secondary standard
contaminant level allowed by TCEQ.
 Areas of the system do not meet TCEQ standards for minimum water line sizes.
This includes areas served by 2” lines that have more than 10 connections.
 Areas of the system experience pressure problems; primarily due to small diameter
and dead-end lines – approximately 17 dead-end locations throughout the system.
 The small and dead ends lines leave areas of the system with low or no chlorine
residual. Line looping and increased line size will help resolve this problem.
 Fire flow capacity is a concern in these areas.
Wastewater Treatment and Collection System
The City of Marfa has an old Wastewater Treatment Plant (WWTP) that treats sewage for the
entire city. The WWTP consists of a parshall flume for metering the influent, a submerged bar
screen, two Imhoff Tanks, two sludge pits, and a sludge drying bed. The first Imhoff Tank was
built in 1929. The second tank was added in 1945. The permitted capacity of the plant is 0.120
MGD. Current average daily flow is approximately 0.080 MGD or 37.7 gallons per capita per
day. Effluent disposal is via irrigation of 62 acres of non-public pasture land located adjacent to
the plant. The sludge from the Imhoff tanks is pumped to sludge drying beds next to the tanks
where the moisture evaporates and is absorbed by the ground. During wet weather, the drying
beds do not work properly and have on occasion overflowed into the creek where the plant
effluent is discharged. Sludge from the dying beds is taken to the regional landfill in Alpine.
Issues and concerns related to Marfa’s WWTP initially identified during the RAP are as follows.
 The plant is approaching 75% of its permitted capacity. This is the point where TCEQ
requirements to begin planning for new or expanded facilities kick in. The existing plant
is outdated technology and has well outlived the normal useful life of such facilities,
which the industry considers to be 50 years. The TCEQ has encouraged the City to look
at alternative treatment methods since the technology currently used would not be
allowed to be installed today.
 TCEQ is currently requiring the City to build an effluent storage pond after the plant to
allow for buffering of peak and wet weather flows and to provide for more controlled
land application of effluent discharge.
The City of Marfa’s collection system is comprised of 4-, 6-, 8-, and 10-inch lines and two
sanitary lift stations. Portions of the system date back to the late 1920’s. Issues and concerns
related to Marfa’s collection system initially identified during this RAP are as follows.
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Technical Memorandum 1
Water System Demands and Wastewater Flows


The existing collection system has many small (4”), old vitrified clay lines. These lines
are undersized and would not be allowed to be installed today under TECQ guidelines.
The condition of some of these lines is suspect – deterioration, root intrusion, etc. – as
evident by past backups, surcharged manholes, and maintenance problems.
FUTURE POPULATION AND DEMAND PROJECTIONS
Projected Population
In 2002 the Texas Water Development Board reviewed and revised population projections for a
number of cities and counties in Texas. The revised population projections for Marfa as approved
by the Texas Water Development Board are as follows:
TWDB Approved Population Projections
Year
Population
2000
2,121
2010
2,585
2020
2,855
These projections indicate a growth rate between 2000 and 2010 of two percent per year and from
2010 to 2020 of one percent per year. Applying these growth rates give the following interim
year populations:
Intermediate Population Projections
Year
Population
2005
2,341
2015
2,717
2025
3,001
It is projected that this growth will take place in and around currently developed areas within the
City of Marfa.
Projected Water System Demands
Using the TWDB approved population projections reveals the following residential demand
projections given the 188 gallons per capita per day (gpcd) average. The total average demand
includes flows to the tomato farm north of the City. The peak day demand uses the 279gpcd flow
rate established from the City water records and also includes flow to the tomato farm.
Year
2000
2005
2010
2015
2020
2025
Projected Average Water System Demands
Avg. Res.
Total Avg.
Population
Demand
Demand
Gallons/day
Gallons/day
2,121
398,748
591,759
2,341
440,108
633,119
2,585
485,980
678,991
2,717
510,796
703,807
2,855
536,740
729,751
3,001
564,188
757,199
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Peak Day
Demand
Gallons/day
784,770
846,150
914,226
951,054
989,556
1,030,290
Technical Memorandum 1
Water System Demands and Wastewater Flows
The current well and booster station facilities are sufficient to handle the projected future
demands.
Projected Wastewater Flows
The following table is based on the average per capita wastewater contribution of 37.7 gallons per
day. The peak flow is based on the American Society of Civil Engineers WCPF Manual of
Practice No. 9 – Design and construction of Sanitary and Storm Sewers, 1974. The equation
relates peaking factor to population as follows:
2-hour peaking factor = 18.051 x (population)-0.187
The peaking factor multiplied by the average flow yields the peak 2-hour flow to the plant.
Year
2000
2005
2010
2015
2020
2025
Projected Wastewater System Contributions
Wastewater
Population
Contributions
Gallons/day
2,121
79,962
2,341
88,256
2,585
97,455
2,717
102,431
2,855
107,634
3,001
113,138
Peak 2-hour
flow rate
Gallons/day
344,605
373,394
404,739
421,462
438,786
456,942
This table shows that the Cities current wastewater plant capacity of 0.120 MGD will handle the
2020 flow as currently permitted. The States 75/90 rule which says that when a WWTP reaches
75% of its permitted capacity the owner must undertake planning for a plant expansion and that it
must be constructed when the current plant reaches 90% of its permitted capacity. The City of
Marfa will reach the 75% capacity between 2005 and 2010 but this project could upgrade the
currently outdated facilities to span beyond the 2010 mark.
Summary
The data presented in this TM shows that Marfa has the potable water capacity to meet the 2025
projected demands. The TCEQ would like the City to develop additional groundwater resources
away from the current water plant site. The current wastewater treatment plant needs to be
upgraded with an effluent storage pond to comply with a current TCEQ condition of permit for
the City. Even without this effluent storage pond, the plans for a plant expansion will be needed
between 2005 and 2010. The current technology used by the City to treat wastewater is outdated
and has outlived its life expectancy of 50 years.
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Technical Memorandum 1
Water System Demands and Wastewater Flows
APPENDIX A
Water Production and Meter Data
Wastewater Flow
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