Technical Memorandum 2
Water & Wastewater System Improvements
BACKGROUND
Parkhill, Smith & Cooper, Inc. (PSC) 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 second TM and will evaluate the current water system and
wastewater system through hydraulic modeling and determine deficiencies in the respective
systems. It will also present alternative for water and wastewater treatment systems.
Model Development
Parkhill, Smith & Cooper, Inc. subcontracted Treviño Land Surveyors to perform a survey of the
existing system by locating water valves, fire hydrants, sewer clean-outs and manholes. The
CAD drawings with the survey information were used to develop a hydraulic model of the water
system in H2ONet that includes all four of the pressure zones that the City of Marfa currently
operates. Well production and booster pump flows were provided by the City as well as overflow
elevations for the main legged tank and the standpipe. Flow capacities for the tomato farm
boosters, the Buena Vista Addition boosters and the boosters that serve the eastern part of the city
were also provided by the City. The methodology and details of the water system model are
contained in subsequent sections of this TM.
The wastewater collection system evaluation was performed using the manhole invert
information provided by the surveyor and the pipe diameter information provided by the City of
Marfa as well as interview with City personnel. More detailed explanation of the sewer
evaluation is presented later in this TM.
Evaluation of Hydraulic Model of Water Systems
A potable water system has to comply with Texas Commission on Environmental Quality
(TCEQ) regulations. These regulations include minimum line size for number of connections,
minimum operating pressure of 35 pounds per square inch (psi) within the distribution network
and minimum operating pressure of 20 psi under combined fire and drinking water flow
conditions. The most stringent of these regulations is the requirement to maintain at least 20 psi
pressure during emergencies such as fire fighting.
The peak day demand used was less than the fire flow demand of 600 gpm (864,000 gallons /
day) used therefore fire flow plus peak day conditions governed.
Table 2-1: Projected Average Water System Demands
Avg. Res.
Total Avg.
Year
Population
Demand
Demand
Gallons/day
Gallons/day
2000
2,121
398,748
591,759
2005
2,341
440,108
633,119
2010
2,585
485,980
678,991
2015
2,717
510,796
703,807
2020
2,855
536,740
729,751
2025
3,001
564,188
757,199
1
Technical Memorandum 2
Water & Wastewater System Improvements

The model, HM1, was set up using booster stations or transfer stations that represented
water transport between the two respective zones. The model was then run for peak day
demand (411 gpm) to determine the capabilities of the existing water system. Some of
the pressures in the existing water system dropped below the TCEQ allowable 35 psi for
the existing 2,001 peak flow condition. The model results also determined that velocities
were within the TCEQ requirements. This condition is depicted in Figure HM1-A.

A second model was then run for peak day plus 600 gallons per minute (gpm) fire flow
condition at node 22 to determine the capabilities of the existing water system. Some of
the pressures in the existing water system dropped below the TCEQ allowable pressure of
20 psi for the existing 2,001 peak flow plus fire flow condition. The model results also
determined that velocities up to 16.91 feet per second (fps) were present within the
system. This condition is depicted in Figure HM1-B.

A third model was then run for peak day plus 600 gallons per minute (gpm) fire flow
condition at node 488 to determine the capabilities of the existing water system. The
pressures in the existing water system meet the TCEQ requirement of 20 psi minimum
for the existing 2,001 peak flow plus fire flow condition. The model results also
determined that velocities up to 25.35 feet per second (fps) were present within the
system. This condition is depicted in Figure HM1-C.

Multiple models were run on the proposed water system improvements. The flow
conditions used in the computer model were the 2001, 2005, 2010, 2015, 2020, and 2025
peak day demand and peak day plus fire flow conditions at nodes 22 and 488. All TCEQ
pressure and flow regulations were met by the proposed improvements under these
conditions see attached HM’s in Appendix-Water.
ALTERNATIVES IDENTIFIED
Alternative 1
This alternative is based on leaving the system as is. No improvements would be done and the
town would continue to be out of compliance with TCEQ requirements and regulations.
Alternative 2
This alternative includes immediate improvements (shown in Figure 2-1) removing and replacing
2-inch and 4-inch waterlines with approximately 19,478 linear feet of 6-inch PVC pipe waterline
and 2548 linear feet of 8-inch PVC pipe waterline, 36 – 6-inch gate valves, 14 – 8-inch gate
valves, reconnecting 13 existing fire hydrants, reconnecting approximately 290 service
connections and approximately 9789 square yards of 2 ½ -inch hot mix asphaltic concrete
(HMAC). These improvements would maintain the water system in compliance with TCEQ
requirements and regulations for maintaining at least 20 psi pressure during emergencies such as
fire fighting through the year 2015.
Additional improvements required at the year 2015 are paralleling 850 linear feet of 6-inch PVC
pipe along Columbia Street from Aparejo Street traveling in the northeastern direction. Figure
TM 2-1 depicts the immediate improvements.
2
Technical Memorandum 2
Water & Wastewater System Improvements
Figure 2-1
3
Technical Memorandum 2
Water & Wastewater System Improvements
Opinion of Probable Construction Cost
Table 2-2
"Opinion of Probable Construction Cost"
Water Distribution System Improvements
Cost Component
6-inch PVC Pipe & fiitings in the distribution system
8-inch PVC Pipe & fittings in the distribution system
6-inch Gate Valves in the distribution system
8-inch Gate Valves in the distribution system
Reconnect Fire Hydrants in the distribution system
Reconnect Residents in the distribution system
Roadway Repairs in the distribution system
25% Contingency
Subtotal
15% Engineering
TOTAL CAPITAL COSTS
Unit Quantity Unit Price
LF
19478 $ 25.00
LF
2548 $ 30.00
EA
36 $ 1,803.64
EA
14 $ 2,500.00
EA
18 $ 1,500.00
EA
290 $ 300.00
SY
9789 $ 25.00
$
$
$
$
$
$
$
$
$
$
$
Total
486,950.00
76,440.00
64,931.00
35,000.00
27,000.00
87,000.00
244,734.00
255,514.00
1,277,569.00
191,636.00
1,469,205.00
Water Modeling Conclusions
The most stringent of the TCEQ regulations is the requirement to maintain at least 20 psi pressure
during emergencies such as fire fighting throughout the entire water system. Alternative 2 will
meet this stringent requirement for the improvements through the year 2025. Therefore, we
recommend Alternative 2 to upgrade the water system.
Wastewater System Evaluation
The wastewater system was evaluated using a combination of existing sewer maps, manhole
survey and interviews with City of Marfa operations personnel. Portions of the system have been
improved since 2001. The 2001 improvements were primarily in the southwest part of town. The
improvements targeted are located north of Washington Street up to the City Limits.
Improvements are to upgrade pipe sizes that are 4-inch with an acceptable pipe size to convey the
future flows. These locations are on second street between McMinn Street and Hill St, on fourth
Street between Capote Street and Ridge Road, the two alley ways located between Austin Street,
Third Street, Dean Street and First street, the two alley ways located between Austin Street,
Columbia Street, Dean Street and Washington and the three alley ways between Dean Street,
Washington Street, Aparejo Street and Central Street. Figure TM 2-2 depicts the system
improvements that are required. The existing system must be in compliance with TCEQ
requirements for minimum slope.
Opinion of Probable Construction Cost
Table 2-3
Opinion of Probable Construction Cost
Wastewater System Improvements
Cost Component
8-inch PVC Pipe
Furnish and Install Standard 4-foot Manholes
Roadway Repairs in the distribution system
25% Contingency
Subtotal
15% Engineering
TOTAL CAPITAL COSTS
Unit Quantity Unit Price
LF
12800 $ 32.00 $
EA
20 $ 2,500.00 $
SY
2778 $ 25.00 $
$
$
$
$
4
Total
409,600.00
50,000.00
69,444.44
132,261.11
661,305.56
99,195.83
760,501.39
Technical Memorandum 2
Water & Wastewater System Improvements
Figure TM 2-2
5
Technical Memorandum 2
Water & Wastewater System Improvements
WATER TREATMENT ALTERNATIVES (FLUORIDE REMOVAL)
Background
The City of Marfa currently has the well capacity and booster station capacity to handle the projected
2025 flows but the water quality does not meet the State Secondary Standard for Fluoride. Fluoride in
drinking water reduces the incidence of tooth decay however, it may cause mottling of teeth
depending on the concentration, the person’s age and susceptibility and the amount consumed. The
current secondary standard is 2 mg/L and the Cities wells contain between 2.5 and 3 mg/L of Fluoride.
This secondary standard is set to reduce the incidence of tooth mottling in those that are susceptible
since levels in excess of 2 mg/L can still cause problems. Since they meet the primary standard of 4
mg/L the City is not mandated to treat the water to meet the secondary standard but could elect to do
so to eliminate the health risks associated with concentrations in excess of the secondary standard.
Treatment Options
The treatment options for reducing fluoride are activated alumina adsorption and reverse osmosis
filtration. The third option in dealing with the fluoride is the do nothing alternative.
Activated alumina (AA) treatment is a proven technology for the removal of fluoride and it appears on
the United State EPA list of best available technologies (BAT). The activated alumina system also
has the side benefit of removing arsenic, a constituent that has recently had the maximum contaminant
level reduce from 50 to 10ug/L. In order to efficiently remove fluoride the pH of the water should be
in the 5.0 to 6.0 range which would require acid or CO2 addition to reduce the pH and then air
stripping or caustic addition after the filtration to return the pH to the normal level. Pilot testing of
this technology is recommended to determine if pH adjustment is warranted and to determine the filter
run times that can be expected before having to regenerate the media. If the removal efficiency is
good enough, it may be possible to split the raw water flow and only treat a portion of the flow and
blend it back with the raw water to get below the secondary standard for fluoride. A schematic plan
view for the implementation of this alternative is shown in figure 2-2.
Reverse Osmosis (RO) filtration will also remove fluoride and arsenic. An RO system will also
reduce other constituents in the water such as total dissolved solids as well. The high removal
efficiency of the RO system will also allow for blending raw water with treated water thereby
reducing the capital and O&M costs for treating the water. If RO is used, a pilot study should be
performed to determine whether there are other constituents such as silica in the raw water that may
cause fouling problems with the treatment system in the future. The space required for this process is
similar to that of the AA system.
Table 2-4
Opinion of Probable Cost*
Capital Expenditures for Water Treatment Plant Improvements
Description
Units
Quantity
Unit Cost
Total Cost
Treatment Equipment (0.5 MGD)
EA
1
$500,000
$500,000
Building to house equipment
EA
1
$30,000
$30,000
Site piping, valves and fittings
LS
1
$32,000
$32,000
Training for 2 Operators
LS
1
$5,000
$5,000
Subtotal
$567,000
Contingency (25%)
$141,750
Engineering & Administration (22%)
$155,925
Total
$864,675
*Cost opinion is based on treating 50% of the raw water stream and blending it back to reduce the Fluoride
concentration below the secondary standard of 2mg/L. Flow used is 2025 Peak day demand. Due to low population
growth, sizing for earlier year flows does not significantly reduce the capital cost.
6
Technical Memorandum 2
Water & Wastewater System Improvements
Figure 2-3
Treatment Schematic
7
Technical Memorandum 2
Water & Wastewater System Improvements
WASTEWATER TREATMENT ALTERNATIVES
Background
The City of Marfa currently operates two Imhoff tanks as their wastewater treatment plant. As a
condition of their TCEQ permit renewal, the City agreed to start looking at adding an effluent
storage pond to their system after the Imhoff tanks and prior to pumping the effluent to the
irrigation fields. According to the populations projections presented in TM-1, the City will have
to start looking at designing a new wastewater treatment plant (WWTP) some time between 2005
and 2010 to treat the effluent produced by the growing population. The current WWTP is based
on outdated technology that would most likely not be permitted if proposed today.
Treatment Options
The alternatives for treating the flows from the City of Marfa could be handled in several
different ways. The simplest technology would be a lagoon type system while the high tech
approach would most likely be a semi-package type activated sludge plant. The third option for
this TM is the do nothing alternative.
A lagoon system as shown in Figure 2-3 is very effective in treating wastewater to levels
acceptable for discharge to surface irrigation currently operated by the City. This treatment
option would consist of two smaller aeration basins (ponds) in series followed by a larger
sedimentation/stabilization pond and possibly an effluent storage pond. Because the detention
time in this type of treatment plant is around 20 days, this system would take a fairly large
amount of land (2.5 acres) to construct the lined ponds on but requires very little mechanical
maintenance and is relatively immune to upsets. Besides the maintenance on the aerators in the
first two basins, the majority of maintenance comes from keeping the areas around the ponds free
of growth and debris. The maintenance cost of this is not appreciably more than for the existing
plant.
Figure 2-4 – Typical Lagoon Treatment System
8
Technical Memorandum 2
Water & Wastewater System Improvements
Table 2-5
Opinion of Probable Cost*
Capital Expenditures for Lagoon Wastewater Treatment Plant Improvements
Description
Units
Quantity
Unit Cost
Total Cost
Construction of Lagoons
SF
52,650
$8.25
$434,366
Electrical Building
EA
1
$10,000
$10,000
Aerators/Controls
EA
4
$5,500
$22,000
Training for 2 Operators
LS
1
$5,000
$5,000
Subtotal
$471,366
Contingency (25%)
$117,841
Engineering & Administration (22%)
$129,625
Total
$718,833
*Cost opinion is based on treating the 2025 flows (113,138 gpd) with a lagoon type system. Due to low population
growth, sizing for earlier year flows does not significantly reduce the capital cost. Cost does not include land
acquisition.
An activated sludge type plant has a relatively small footprint (Figure 2-4) compared to that of the
lagoon system but it also has more maintenance associated with the upkeep of the plant and
depending on how drastic the change in influent quality it may be prone to upset. The mechanical
equipment needed for this type of plant includes blowers, submerged aerators and pumps.
Although not to difficult to operate, this treatment process is more complex than a lagoon system.
The one advantage of this type of treatment is that it gets the quality of the effluent much closer
to the Type I reuse standards which with the addition of particle filtration and chlorination
(shown in Figure 2-4) could be met. This water could be used for irrigation of parks, athletic
fields and other large landscaped areas that currently place a burden on the potable water system.
Figure 2-5 – Typical Activated Sludge Plant
The activated sludge plant without tertiary filtration and chlorination would cost approximately
22% less to build as shown in Table 2-5 but the annual operation and maintenance cost of close to
$5,000 per month would make it much more expensive to operate in the long run. The City
currently does not produce enough wastewater to support irrigation of the golf course to the east
of the City. The pumping costs to lift the reclaimed water over 100 feet from the plant to the golf
course would make reclaimed water use for the golf course cost prohibited.
9
Technical Memorandum 2
Water & Wastewater System Improvements
Table 2-6
Opinion of Probable Cost*
Capital Expenditures for Activated Sludge Wastewater Treatment Plant Improvements
Description
Units
Quantity
Unit Cost
Total Cost
Construction of plant
GAL
113,138
$2.12
$239,853
Electrical Building/Lab
EA
1
$24,000
$24,000
Blowers
LS
1
$115,256
$115,256
Training for 2 Operators
LS
1
$5,000
$5,000
Subtotal
$384,109
Contingency (25%)
$96,027
Engineering & Administration (22%)
$105630
Total
$585,766
*Cost opinion is based on treating the 2025 flows (113,138 gpd) with a lagoon type system. Due to low population
growth, sizing for earlier year flows does not significantly reduce the capital cost. Cost does not include land
acquisition. Activated sludge cost does not include filtration equipment to meet Type I reclaimed standards.
Recommended Alternative
The recommended wastewater treatment plant alternative is the lagoon system due to its lower
maintenance costs, reliability and resistance to upsets. The slightly higher capital cost will be
paid for in approximately 2.5 years with the savings on O&M costs over the activated sludge
option.
RECOMMENDED WATER AND WASTEWATER ALTERNATIVES TOTAL COST
Table 2-7 represents the total opinion of probable construction cost for the water and wastewater
improvements. The line items summarize the cost totals from the other sections in this technical
memorandum.
Table 2-7
Opinion of Probable Construction Cost
Water and Wastewater Improvements
Description
Units
Quantity
Water Distribution System Improvements
LS
1
Wastewater System Improvements
LS
1
Water Treatment Plant Improvements
LS
1
Lagoon Wastwater Treatment Plant Improvemnts
LS
1
10
Unit Cost
$1,558,632.71
$760,501.39
$864,675.00
$718,833.00
TOTAL
Total Cost
$1,558,632.71
$760,501.39
$864,675.00
$718,833.00
$3,902,642.10