Sea Water Intrusion in the Los Osos Groundwater Basin Presentation of Updated Technical Studies prep

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Sea Water Intrusion in theLos Osos Groundwater
BasinPresentation of Updated Technical Studies
prepared by Cleath Harris Geologists
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Definitions

• Acre foot 326,000 gallons, one single family
  home uses approximately 1/3 acre-ft each year
  (AFY)
• Safe yield the amount of water that can be
  pumped without creating adverse conditions
• Seawater intrusion an adverse condition wherein
  seawater degrades a freshwater groundwater basin,
  usually due to over pumping

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Downtown
Creek
Sand Spit
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Upper Aquifer (Zone C)
Lower Aquifer (Zone D)
Lower Aquifer (Zone E)
Bedrock
-700
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Los Osos Drinking Water

• Three water suppliers LOCSD, GSWC, and ST
  Mutual
• Much of the upper aquifer is high in nitrates,
  blending or treatment is required
• The lower aquifer currently supplies 77 of the
  water delivered by these suppliers

• Urban pumpers are exceeding the yield of the
  lower aquifer by over 40

77 Lower
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Lower Aquifer Ground Water Elevations - 2001
Creek Valley
Morro Bay Estuary
At Sea Level
10 below
5 below
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Extent of Seawater Intrusion into the deepest
zone (Zone E) is not shown.
Area of Sea Water Intrusion into Lower Aquifer
(Zone D)
LOCSD Palisades Well
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Creek
Downtown
Sand Spit
Ocean
Upper Aquifer (C)
Lower Aquifer (D)
Lower Aquifer (E)
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Sea water is the unwanted source in the lower
aquifer (values derived from 2002 Seawater
Intrusion study)
Los Osos Creek
Upper aquifer leakage
Sea Water Intrusion
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Current actions to combat seawater intrusion

• Purveyors reduction of water use (pumping) by
  approximately 15
• Purveyors shift in lower aquifer pumping from
  west to east
• SLO County retrofit-upon-sale ordinance
• Purveyors attempting to shift to upper aquifer
  through blending and future nitrate treatment

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Results of purveyor actions

• Sea water intrusion estimated in 2002 study
• 560 acre feet per year
• Current estimated sea water intrusion
• 420 acre feet per year
• Total purveyor pumping is approximately 2,050 AFY
  (5 year average)

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ISJ Agreement

• February 2004 - Basin adjudication initiated by
  LOCSD
• September 2007 - Water Purveyors and the County
  of SLO entered into an Interlocutory Stipulated
  Judgment (ISJ)
• August 2008 ISJ approved by court
• Current Conducting technical studies
  negotiating Basin Management Plan (BMP)

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BMP Components

• Hydrologic assessment of the basin
• Strategy for maximizing reasonable and beneficial
  use of the basin
• Balancing basin under current development and
  build-out
• Protect environment influenced by the basin
• Quantification of water rights
• Water conservation goals
• Well abandonment and construction program
• Equitable sharing of costs
• Coordination with LOWWP

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ISJ Work Program

• Task 1 Completed
• Update steady state hydraulic model
• Assess the potential of the upper aquifer before
  and after the wastewater project
• Update safe yield estimates
• Update demand estimates
• Task 2 - Completed
• Evaluate and determine creek compartment safe
  yield
• Assess water quality of creek compartment

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ISJ Work Program

• Task 3 Pending
• Determine location of future wells for each
  purveyor
• Run additional groundwater model scenarios
• Confirm the amount of water required at
  build-out, with aggressive conservation
• Update water conservation plan
• Define water supply infrastructure and cost to
  achieve a balanced basin at build out
• Tasks 4 and 5 - Future
• Further development of the groundwater model
• Monitoring and assessment of actual basin
  performance

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Relationship with the Los Osos Wastewater Project

• Balancing the Los Osos basin will be difficult
• The long term sustainability of the groundwater
  basin must be a priority for treated effluent
  produced by the LOWWP
• Quantity Enact cooperative management agreement
  to return treated effluent to the groundwater
  basin
• Quality Enact cooperative management agreement
  to address long term management of salt,
  nutrients and other contaminants
• If the wastewater project is delayed, the ISJ
  process will continue to move forward

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Relationship with the Los Osos Wastewater Project
ISJ Process
Tasks 1 2
Task 3 and BMP
Final BMP
2009
2010
Planning Comm.
BOS?
Coastal Comm?
Design/Construction
Wastewater Project Process
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Private Well Water Use Estimates

• Purpose to more accurately estimate the private
  domestic pumping in the basin
• Methodology
• - Irrigation / aerial surveys
• - Review of demand data
• - Development of demand factors
• Conclusion use estimates raised from 150 AFY to
  200 AFY

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Agricultural Water Use Estimates

• Purpose to estimate ag pumping in the basin in
  the Los Osos Creek valley
• Methodology
• - Detailed crop data submitted by farmers to SLO
  County
• - Estimates of water use by crop
• - Consideration of average-year climate
• Conclusion previous use estimates confirmed
  800 AFY

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Agricultural Water Use Estimates
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Agricultural Water Use Estimates
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Urban Area Basin Yield Update

• Purpose to estimate the yield of the urban area
  under current and future conditions
• Provides a tool for basin management and
  infrastructure planning
• Considers role of wastewater project in planning
  efforts

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Updated groundwater model

• Simulates seawater intrusion over time (dual
  density transient model)
• Calibrated to match current conditions with a
  50-year test run
• Future production wells can be added and
  optimized to determine safe yield.

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Key Conclusions

• Seawater intrusion can be mitigated through
  effective basin management including
  conservation, pumping shifts, and monitoring
• With effective basin management, adequate basin
  yield exists for current demand
• For build out demand, additional basin management
  strategies will be necessary (Task 3)

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Key Conclusions

• Even with promising modeling results, significant
  purveyor challenges and decisions lay ahead
• If pumping can be reduced below the maximum
  yield, water quality and infrastructure benefits
  would result
• Conservation, recycling, and other strategies can
  further enhance water quality and allow for
  unforeseen conditions (Task 3)

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Key Conclusions

• A sea level rise will result in a slightly lower
  sea water density (thermal expansion)
• A 2 sea level rise would reduce the safe yield
  by approximately 50 AFY

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Creek Valley Yield Analysis

• Purpose to estimate the yield of the creek
  valley portion of the aquifer
• Previous studies assumed that yield matched
  current pumping
• Stream data pointed to the potential for
  additional yield

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Creek Valley Yield Scenarios

• Purveyor wells west of Los Osos Creek
• - Adjacent to existing purveyor infrastructure
• - May be more straightforward to permit
• Purveyor wells west and east of Los Osos Creek
• - Requires more extensive infrastructure
• - May integrate with recycled water agricultural
  exchange programs

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Key Conclusions

• Yield increases by 250 AFY with purveyor wells on
  the west side of Los Osos Creek
• Yield increases by 500 AFY or more with purveyor
  wells on both sides of Los Osos Creek
• Significant decisions and challenges on well
  locations, pumping, and infrastructure still
  exist

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Key Conclusions

• Water quality information was not as extensive as
  desired, but potable quality expected based on
  test results
• Significant decisions and challenges on well
  locations, pumping, and infrastructure still
  exist
• Additional wet weather studies are recommended to
  review actual creek flows

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Next Steps

• Complete Task 3, with a focus on conservation and
  build-out supply infrastructure
• Implement a Basin Management Plan
• Move forward on a funding mechanism to finance
  water projects

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Next Steps

• Expedite conservation measures where possible.
• Continue to reduce demand on the lower aquifer
  through pumping shifts and blending
• Remain engaged in wastewater project discussions

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Questions?