Shoal River RBF Evaluation Project Update

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Shoal River RBF Evaluation Project Update

• Erin Cox, CH2M HILL
• Jeff Littrell, Director Okaloosa County Water
  Sewer
• Steve Hubbs, WaterAdvice Associates

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Future Water Supply Options Under Evaluation for
Okaloosa County

• Riverbank Filtration (RBF)
• Direct Withdrawal
• Direct Withdrawal with Offline Storage Reservoirs

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Major Considerations and Constraints Related to
Project Feasibility

• Physical
• Geology, Hydrology, Soils, Topography
• Technical
• Engineering, Land Suitability and Availability,
  Legal and Political Issues
• Environmental
• Permits, Water Quality, Endangered Species
• Economic
• Cost/1000 Gallons, Resale Value, Ability to
  Finance
• Demands
• Ensure that existing and future demands justify
  project need

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Project Background

• Okaloosa County has purchased 353 acres of high
  quality riparian land along the Shoal River
• A comprehensive evaluation of RBF feasibility is
  underway

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Project Description

• The County is evaluating RBF and Direct Surface
  Withdrawal at Shoal River property
• Project is mainly focused on RBF first since it
  provides pre-treatment (potential cost savings
  for WTP)
• Comprehensive literature review performed for
  site, including geology, aquifer characteristics,
  wetlands, water quality, etc.
• CH2M HILL is performing geotechnical analyses
  such as borings, piezometers, and potentially
  near-capacity wells for further site suitability
  evaluation
• Test Boring and piezometer installation completed
• Slug testing performed to evaluate hydraulic
  conductivity of aquifer

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Site Characteristics

• Water Quality

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Site Characteristics

• Aquifer Characteristics
• Yellow shows extent of shallow sand and gravel
  aquifer
• Locally, aquifer exists in Citronelle Formation
  most important water-yielding formation in upper
  part of sand and gravel aquifer (USGS)
• Citronelle formation is characterized white and
  brown sand
• Alum Bluff low permeability

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Site Characteristics

• Shoal River Hydrogeology
• Substantial flow
• average flow from 1939 2003 was 717 mgd
• Fluctuates appreciably with respect to stage and
  flow, favorable for routine scour
• 7-day, 10 year low flow 300 cfs, or 200 mgd
• Characteristics acceptable for up to 20-mgd
  extraction

Flow 1997-2008
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Site Characteristics

• Geology
• The Citronelle Formation (Sand and Gravel
  Aquifer) is characterized as reworked alluvial
  sediments (sands, gravels, silts)
• The Alum Bluff Formation is predominantly clay
  (aquitard)

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Site Characteristics

• Streambed Slope
• The stream slope and hydrographs indicate that
  the Shoal River in the area of concern has
  adequate energy to maintain a clean coarse sand
  bed which is favorable to bank filtration

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Why Riverbank Filtration?
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Riverbank Filtration (RBF) Benefits

• Turbidity and pathogens
• NOM, taste and odor, biodegradable compounds
• Nitrates
• Trace organics
• Pesticides
• Pharmaceuticals and Personal Care Products as
  Pollutants (PPCPs)
• Endocrine disrupting compounds

Riverbank Filtration (RBF)
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RBF Removal Mechanisms
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Factors that Impact RBF

• Stream and Riverbed Characteristics
• Water quality and temperature
• Stream flow, velocity, and slope
• Area of exposure of the aquifer to the river
  bottom
• Riverbed sheer stress
• Riverbed media composition and conductance
• River bottoms width and configuration
• Biological processes taking place within river
  bottom
• Aquifer Transmissivity
• Site hydrogeology
• Total driving head available from the aquifer
• Wellscreen Dynamics

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Riverbed Characteristics
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Aquifer Characteristics
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Exploratory Geological Boring

• Objectives
• To evaluate the presence and general
  characteristics of the sands associated with the
  Citronelle Formation in the vicinity of the
  testing location along the Shoal River.
• Test borings constructed as part of these
  investigations penetrated the remaining
  Citronelle Formation at the site and to terminate
  at the top of the Alum Bluff Group.

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Exploratory Geological Boring

• Geotechnical borings have been completed in the
  power line corridor on both the East and West
  sides of the Shoal River

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Shoal River Preliminary Results

• Streambed Characteristics

• 10 streambed cores were taken, up to 4 feet deep
• Prevalent media was medium to coarse white sand,
  originating from Citronelle Formation
• Banks and low-flow areas contained alluvial
  deposits from upstream cuts into the Alum Bluff
• At every location probed, bed material favorable
  for RBF to at least 3 feet deep

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Shoal River Geotechnical Preliminary Results
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Shoal River Geotechnical Preliminary Results

• The upper zone of the Citronelle Formation is
  dark organic silty sands to sandy silts (0-8'
  bls)
• The lower zone of the Citronelle Formation is
  fine to course quartz sand with minor sub-rounded
  fine gravel (8-23' bls)
• The sand varies from 15 to 20 feet thick and the
  grain size coarsens with depth
• The elevation of the Citronelle contact with the
  Alum Bluff Formation is generally flat-lying
  perpendicular to the Shoal River

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Shoal River Geotechnical Preliminary Results
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Preliminary Field Investigation Results

• The formation isnt as deep as we would like (20
  to 25 feet saturated thickness as opposed to 35
  to 50 feet desired)
• The formation is better than anticipated with
  regards to sand size and gradation
• The results do not rule out RBF, but do point
  towards a low-head collection system
• Horizontal collector wells or siphon connected
  vertical wells are viable options

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Next Steps

• Compare the data from the pilot wells to the data
  from the I-10 bridge borings for consistency
• Develop the two piezometers and pump on a longer
  term basis to confirm a good connection to the
  river
• Develop conceptual designs from options
• Model to estimate capacity
• Confirm consistency in aquifer throughout the
  entire reach of stream (more test wells)
• Test-pump the most desirable location