Transcript South Texas Water Supply

WATER
Benefits and
Challenges of
Developing Brackish
Groundwater Supplies
Presented by:
Kevin J. Spencer, P.G.
R.W. Harden and Associates, Inc.
Supply
Objectives
• The Need to Develop Brackish
Groundwater Supplies
• Potential Advantages
• Practical Considerations
Rio Grande
Regional
Water
Southmost
Regional
WaterPlanning
Authority Group
•City of Los Fresnos
•Indian Lake
Valley MUD #2
•Port of Brownsville
Surface Reservoir Conditions
Water Levels Amistad and
Falcon Reservoirs (U.S.Ownership)
Acre Feet in
Millions
Reservoir Capacity
4.0
3.5
3.3
Water Level at 100% Capacity
3.0
2.5
2.0
1.5
1.0
Water Level at 50% Capacity
Summer 2002 – 25% Capacity
0.5
Source: TNRCC Watermaster
What Can We Expect?
• Increased demand/less
water
• Implementation of
drought management
strategies
• Irrigation shortages
– “Piggy Back” by
municipalities
– Hydrilla/ Hyacinth
blockage
Alternative Sources
• Conservation
• Reuse
• Desalination
– Sea Water
– Brackish
Groundwater
Brackish Groundwater Desalination
• Significant brackish groundwater
reserves in Gulf Coast aquifers
• Independent of river flows
• Not subject to water rights
purchases*
• Cost of treatment comparable to
surface water
• Improved water quality
Cost Trends
$7
$6
$5
Surface
Brackish
Sea Water
$4
$3
$2
$1
$0
1980 1985 1990 1995 2000 2005 2010
Cost per 1000 gallon including
debt service and operations
Source: NRS Consulting Engineers
Cost Factors
• Degree of total dissolved solids
• Power costs
• Economies of scale
• Location
• Concentrate disposal
Brackish Groundwater
• Advantages over sea water
– Significant reduction in plant
capital and O&M
– Reduced environmental impact
• Advantages over surface water
– Drought tolerant
– Improved water quality
– Water rights savings
Brackish Groundwater
• Advantages over fresh groundwater
– New Supply Resource
– Less Competition
– Less Regulation
– Positive Public Perception
Regional Water Supply
• Establish economies of scale
• Favorable to funding agencies
– Texas Water Development Board
policy statement
– Infrastructure financing
Allocation of Water
Los Fresnos
2.3%
BND
2.1%
Indian Lake
0.2%
VMUD
2.5%
7.5 MGD Phase I
PUB
92.9%
Southmost Regional Water Authority
Capacity Provided
Total Water Sales
6,316,998,573
Annual Availability from Authority
2,737,500,000
Remaining Supply from Participant
3,579,498,573
Remaining
Supply from
Participant
57%
Annual
Availability
from
Authority
43%
Southmost Regional Water Authority
Planned Brackish GW Projects
• North Alamo WSC (5-10 MGD)
• City of Edinburg (5 MGD)
• City of Raymondville (~2 MGD)
• City of Combs (~0.5 MGD)
• Laguna Madre WD (2-3 MGD)
Implementation Challenges
• Proving up the supply
• Concentrate Disposal
• Well Design Considerations
Proving Up the Supply
• Initial Modeling
• Test Drilling
• Development of Geologic Framework
• Long-Term Aquifer Testing
• Refinement of the Model
• Locating Suitable Well Sites
Concentrate Disposal
• Discharge to brackish surface water
• Discharge to ocean
• Injection
• Waste water systems
• Evaporative
Well Design Considerations
• Corrosion Protection
• Casing Design
–
–
–
–
–
Stainless Steel
PVC
Carbon Steel
Fiberglass
Coatings
• Pump Column Design
– Stainless Steel
– PVC
– Fiberglass
• Pump Construction Materials
– Bowls and Motors - Stainless Steel
– Impellers - Brass/Stainless Steel/Ceramic
Summary and Conclusions
• Brackish groundwater is the least
cost alternative for each entity
• Regional Advantages
– Economy of Scale
– Personnel cost savings
– Common well field
– Potential for additional partners
– Favorable grant potential
Summary and Conclusions
• Cost Factors
– Improvement in Membrane
Technology
– Operation of RO at peak capacity
– Increasing expense of surface
water treatment and water rights
• Water Quality Improvement
• Decreased Competition
Questions?