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Feasibility of Stormwater Harvesting in Southern California
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Feasibility of Stormwater Harvesting in Southern California

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  • 1. Richard Lucera, PE RBF Consulting November 3, 2010
  • 2.
    • Rainwater Harvesting Concept
    • Historic Applications
    • Notable Nationwide Programs
    • Evolution of California MS4 Regulations
      • Bay Area MRP
      • Involves Inherent Challenges to Implementation Not Faced Elsewhere
  • 3.
    • Technical Feasibility
      • Water Balance Considerations, Stormwater Supply Versus Demand
      • Water Quality Considerations
    • Economic Feasibility
      • Cost Data Residential Installation
      • Operational Cost
      • Valuating Harvested Water
      • Return on Investment
    • Conclusions and Recommendations
  • 4.
    • Golden Rule of Rainwater Harvesting
      • Supply Must Equal or Exceed Demand
        • Urban Landscape Demand – Seasonally Influenced
          • Turf is Major Traditional Dictating Driver of Demand
          • 1 Inch Per Week Traditional Rule of Thumb
          • On Going Evolution of Landscape Ordinances in California
  • 5.
    • Golden Rule of Rainwater Harvesting
      • Supply Must Equal or Exceed Demand
        • Acceptable Household Demands – Non Influenced Seasonally
          • Toilets, Laundry, Car Washing, Dish Washing
          • “AWWA Residential End Use Study”
            • 1.6 Gal/Flush, 6 Flushes Per Day
            • 18-25 Gal/ Wash Load, 2.6 Wash Loads Per Week
            • 8 Gal/Dishwashing Cycle, 0.7 Cycles Per Day
        • Typical Household Range Indoor Use 2,000 – 3,000 Gal/Month
  • 6.
    • No System is 100% Efficient
        • Precipitation Losses
          • High Intensity Rainfall Losses – Gutter Splash-out, Capacity Limitations on the Collection System
          • Infiltration within Pervious Areas
          • Evaporation (Applicable to “Rough” Collection Systems)
          • Overflow When Storage is Full
        • Traditional Rule of Thumb 75% - 90% Capture Rate (“Texas Manual on Rainwater Harvesting”)
          • Southern California Could Realistically Be Lower
  • 7.  
  • 8.  
  • 9.  
  • 10.  
  • 11.  
  • 12.  
  • 13.  
  • 14.  
  • 15.  
  • 16.  
  • 17.
    • Advantages of Rainwater
      • Naturally “Soft”
        • Benefit for Appliances
      • Sodium Free
        • Benefit if Intended for Potable Use
      • Promotes Healthy Plant Growth
      • Generally Suitable for Irrigation and Potable Use (When Incorporated with Adequate Treatment, Testing, and Dependable System Maintenance Plan)
  • 18.
    • General Challenges Associated with Rainwater
      • Tends to be Slightly Acidic
      • Contact and Transport of Pollutants within Catchment Area
        • Dust, Dirt, Fecal Matter, Plant Debris
  • 19.
    • Southern California Challenges with Rainwater Harvesting
      • No Specific Federal or State Standards for Harvested Rainwater
        • Not Addressed in AB 1420 or AB 1560
      • Large Scale Implementation Would Prove Problematic for Compliance with Local Hydromodification Standards
  • 20.
    • Dependant Upon Location and End Use
      • Geographic Location, Which Dictates Size of Required Storage
        • Tank Size and Material Are Largest Factors in Overall Cost
        • Other Typical Minimum Requirements
          • Collection/Gutter System
          • Roof Washers (Necessary for Drip Irrigation)
          • Pumps and Potentially Separate Pressure Tanks
  • 21.
    • Potable or Contact Uses Also Require Additional Filtering and Disinfection
      • Typical Filters
        • Cartridge Filter, 3 micron or greater removal
        • Reverse Osmosis Filter, 0.001 micron or greater removal
      • Disinfection Techniques
        • UV Light – Effective for Low/Moderate Coliform Influent
        • Chlorine – Potential Health Risk From Overdose
        • Ozone - Requires Frequent Testing and Monitoring, Also a Circulation Pump
  • 22.
    • Typical Initial Cost Range 10,000 Gallon System
      • Fiberglass Tank…………………………....$20,000
      • Vinyl Gutters/Collection………………....$1,500
      • “Smart Valve” Roof Washer………………..$200
      • Pump and Pressure Tank………………....$1,000
      • RO Filter…………………………………….$2,000
      • UV Disinfection………………………...….$1,500
      • Backflow Prevention (Cross Connection)…$500
      • Total $26,700
  • 23.
    • Approximate Annual Operation and Maintenance Cost
      • Replace UV Bulb (One Time)……..……...$500
      • Clean Gutters/Collection Pipe.…………..$500
      • Clean “Smart Valve”……………...............$200
      • Allowance for Other Miscellaneous..……$100
      • Total $1,300
  • 24.
    • San Diego $1.79 (OMWD)
    • Austin $0.75 (Austin Water Utility)
    • Sydney $1.15 (Sydney Catchment Authority)
  • 25.
    • Stormwater Supply Versus Demand
      • Overall Rainwater Supply in Southern California Cannot Realistically Meet Traditional Landscaping (i.e. Turf) Needs
      • Residential Application for “Indoor Only” Needs Much More Technically Feasible, However…..
      • Potable/Contact Use Not Advisable Given the Risks Versus the Rewards
      • High Density/Commercial Use Can Become Highly Problematic Due to Limitations on Storage Necessary for Increased Per Capita Demand – More Suitable to Address Limited Irrigation Needs
  • 26.
    • Water Quality Considerations
      • Southern California Faces Similar Water Quality Challenges as Other Parts of the Country Plus…..
      • Lack of Technical Guidance or Regulation at State Level
      • Potential Risk Associated with High Particulate Matter
      • Conflict Between Local Hydromodification Discharge Standards and Large Scale Rainwater Harvesting
  • 27.
    • Economic Feasibility
      • Capital Cost Residential Household – Approximately $25,000
      • Operation and Maintenance – Conservative Range $1,500
      • Return on Investment - Southern California (Like Other Regions) Requires a Capital Investment that Far Exceeds the Retail Value of “Harvestable” Water, Even When Based Upon Local Rates
        • Local Rates Would Have to Escalate to Approximately 25 Times Current Levels to Justify Use Annually, Assuming 20 Year Life
  • 28.
    • “ Texas Manual on Rainwater Harvesting”, Texas Water Development Board, Third Edition, 2005.
    • “ City of Tucson Water Harvesting Guidance Manual”, City of Tucson Department of Transportation Stormwater Management Section, October 2005.
    • “ Managing Wet Weather with Green Infrastructure, Municipal Handbook, Rainwater Harvesting Policies”, Christopher Kloss, Low Impact Development Center, December 2008.
    • “ Rainwater Harvesting with Cisterns for Landscape Irrigation”, Florida Rainwater Harvesting Initiative, First Edition October 2009.
    • “ Water Use Classification of Landscape Species, A Guide to the Water Needs of Plants”, L. R. Costello and K.S. Jones, University of California Cooperative Extension, April 1994.
    • “ San Diego County Water Authority Agricultural Water Management Plan”
    • “ Operation H2O Annual Report 2009”, San Diego County Water Authority.
    • “ Ohio Department of Health Final Rules, 3701-28-09 Continuous Disinfection”, www.odh.ohio.gov/Rules/Final/Chap28/Fr28_lst.htm
    • “ Guidelines on Rainwater Catchment Systems for Hawaii”, Manoa (HI): College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.
  • 29. Richard Lucera, PE RBF Consulting 9755 Clairemont Mesa Blvd, Suite 100 San Diego, CA 92127-1324 858.614.5000 [email_address]