solving seawater intrusion in the central and west coast ... · proven deterrent to intrusion for...
TRANSCRIPT
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Solving Seawater Intrusion in the
Central and West Coast Basins of
Coastal Los Angeles County….for Now
Ted Johnson, PG. CHG.Chief Hydrogeologist
Water Replenishment Districtof Southern California
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5,700% increase in 110 years
LA County Population Growth
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1930s – 1950s Pumping Double
Natural Replenishment
160 foot drop (49 m)
50 foot drop (15 m)
Unsustainable.Severe Overdraft.Wells Went Dry.
Seawater Intrusion.Great threat to local
water supply.
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With Population Growth Came Groundwater Pumping Greater than Natural Replenishment… Overdraft and Seawater Intrusion
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By 1950s, groundwater was belowsea level in half of the basins,resulting in Sea Water Intrusion
Several miles inland along the Coast
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Silverado Aquifer
Lower San Pedro Aquifer
Pico Formation (“bedrock”)
200 ft. Sand Aquifer
Modified from DWR 1961, Cross Section E-E’
West East
Paci
fic O
cean
Sea Water Intrusion
1000
ft
(300
m)
Drinking Water Wells
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All coastal aquifers likely have minor seawater intrusion, even if not in overdraft
But heavy pumping can increase rate and distance of intrusion.
Seawater intrusion barriers can block the inflow of salt water and replenish the basins with fresh water
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Initial Barrier Tests 1952 - 1954
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Merged Silverado & 400 ft Gravel Aquifers
Lower San Pedro Aquifer
Silverado
400 ft. Gravel
Pico Formation (“bedrock”)
200 ft. Sand Aquifer
Modified from DWR 1961, Cross Section E-E’
West East
Seawater Barrier Wells
Injection Wells Build up pressure to overcome intrusion
Injected water also replenishes aquifers
Paci
fic O
cean
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West CoastBasin Barrier Project
1950sDominguez GapBarrier Project
1970s
Alamitos GapBarrier Project
1960s
Sea Water Barrier Wells - LACFCD
Nearly 300 injection wells, 16 mile overall length
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Water for the Barriers
n Treated Drinking Water (potable) from MWD (imported water): Ø Exclusive source 1953 – 1995.Ø Partial Source 1995 – Present.Ø 1.5 Million acre-feet to date.
n Advanced Treated Recycled Water:Ø Since 1995 at West Coast Barrier
(WBMWD).Ø Since 2005 at Alamitos Barrier (WRD). Ø Since 2006 at Dominguez Barrier (City
of LA). Ø 184,000 acre-feet to date.
n Goal is to move towards 100% recycled water at all three barriers (Water Independence Now–WIN).
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Secondary or Tertiary Wastewater
Advanced Treated Recycled Water for Barriers
To
Barriers
Advanced Oxidation
H2O2 Ultra Violet
Light Reverse Osmosis
Microfiltration
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Barrier Injection Amounts & Costs
n Injection Amounts (2016-17 estimate):n Potable Water: 6,260 afn Recycled Water: 26,040 af (81%)
32,300 af n Total Cost of Water:
n Potable Water: $ 8.5 million ($1360/af)n Recycled Water: $18.4 million ($ 707/af)
$26.9 million
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San Gabriel Valley
Palos Verdes Hills
Santa Monica Mtns
Long Beach
Los Angeles
San Gabriel Mtns
Pacific Ocean
San Fernando Valley
Torrance Carson
Going to 100% Recycled at Barriers
West Coast Barrier: Permitted for 100%
Dominguez Gap Barrier: Permitted for 50%. Moving towards 100% 2017
Alamitos Barrier: Permitted 100%
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Seawater Barrier Models
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Summaryn Seawater barrier injection wells have been a
proven deterrent to intrusion for over 60 years. Steep inland gradients caused by groundwater pumping are the main driver for the intrusion.
n Recycled water is an effective injection source for the barriers to offset the need for potable water use.
n WRD’s goal is to have the barriers at 100% recycled water in 2017.
n Impact of increased pumping and/or sea level rise may require additional injection and/or additional wells. Modeling can help predict the impacts.
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Thank You