Practical Considerations for Stormwater Harvesting and Use

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"Rainfall Harvest or Stormwater CaptureYour
Nuisance or Our New Water Supply?"

• Practical Considerations for Stormwater
  Harvesting and Use

Eric Strecker, P.E. Geosyntec Consultants
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Overview

• We should assertively look for opportunities to
  responsibly use runoff for water supply
  augmentation
• Infiltration into managed aquifers is the key
  large scale harvest and use
• Carefully evaluate other opportunities to ensure
  that they are effective

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Effectiveness of Stormwater BMPs

• Function of
• Runoff Patterns
• Pollutant types and forms
• Storage Volume/Treatment Rate
• Hydraulics of recovering storage
• Deeper infiltration
• Evapotranspiration
• Harvest and use (irrigation/toilet flushing)
• Draw-down/discharge rate
• Treatment Process for released flows
• Physical/Biochemical (settling/adsorption
  filtering, etc.)
• Operations and Maintenance

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Factors Affecting Stormwater Management in
Southern California (and west coast)

• Weather
• Precipitation events arrive in clusters
• High pressure ridge down, then series of storm
  until ridge re-established
• High pressure ridge up no or very little
  precipitation for long periods
• Most rainfall/runoff occurs in December/January/Fe
  bruary/March
• Results
• Makes harvest and use for irrigation difficult at
  best
• If Infiltration rates slow, then infiltration is
  limited
• Rainfall pattern results in large storage
  requirements for capturing significant amounts of
  runoff

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Pelican Hills Resort A Low-Impact Approach in
Southern California

• Eric Strecker
• Geosyntec Consultants
• Sat Tamaribuchi
• The Irvine Company

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Project Overview
New tourist-serving fractionalized ownership
condominiums
New club house and restaurant
A new hotel (the Inn)

• Total project area of almost 118 acres
• Part re-development (7 acres of impervious area)

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Client Specified Desired Project Water Quality
and Hydrology Goals

• No changes in pre/post in hydrology
• No increase in runoff volume
• No increase in infiltration
• Show an improvement in water quality
• No irrigation runoff
• Eliminate all runoff to Morning Canyon
• Project area drains to ASBS

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No Change in Hydrology!(Surface or sub-surface)

• Necessitated a detailed analysis of
  precipitation,
• runoff,
• shallow soaking and drying, and
• deeper infiltration
• to ascertain what conditions to match

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Pre- and Post-Hydrology No BMPsWater Balance
-SWMM Model 40 year record
About 83 Evapotranspiration Pre-Development!
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What to do with the water?Golf Course
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Pelican Hills Development
Cisterns
Golf Course Water Features/Reservoirs
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Water Balance for All Years Modeled
Acre-Feet/per year
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Tanks Under Construction and Post
600,000 gallon cistern
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Pelican Hills Results

• Water balance would be maintained for the project
  area with the planned 1.26 inch design depth
  cisterns and other runoff reducing BMPs.
• Water Quality was enhanced over existing
  conditions
• Captured runoff replaced about 20 percent of
  average annual reclaimed water use no potable
  water demand reduction

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Retain on site - Choices

• Infiltrate
• Evapotranspirate
• Harvest and Use

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Infiltration

• Can you do it?
• Where should you do it?
• If you do, do it carefully
• Proper pre-treatment

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North Orange County (Green areas are AB Soils)
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North Orange County (Green areas -AB Soils
Hatched 10 feet or less Depth to GW)
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North Orange County (Green AB Soils
Contaminated Sites/Plumes)
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Contaminated Soils/Plumes, Depth to GW A/B
Steep Slopes
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Adapted from
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Monthly Precip vs. ET
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Weekly Precip and ET
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General Water Balance Impacts
ET fraction estimated as 83-97 in Southern
California Chaparral.1
1 Ng and Miller (1980) Soil Moisture Relations in
the Southern California Chaparral. Ecology, Vol.
61, No. 1. (Feb., 1980), pp. 98-107
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Harvest and Use (re-use)

• Key factors for success of harvest and use
• Having a use for the water irrigation, toilet
  flushing, process water
• Being able to use the water Code issues/human
  health
• Being able to use the water fast enough to
  recover storage (due to back-to-back storm
  events) so that subsequent storms are captured
  and overall capture meets goals
• Replacing reclaimed?

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EPA Headquarters'- Harvest and Use Cistern

• Visited on April 28th, 2009 (about 80 degrees
  that day)
• Cisterns were empty as flows were being bypassed
  due to lack of irrigation demand

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Example Cistern Scenario Modeling Inputs

• 100 ac Residential Catchment _at_ 60 impervious
• Tank sized to DAMP (0.8 storm) 1.3 MG
• Indoor non-potable demand (Toilet Flushing) 65
  gpd/du, assumed 4.5 du/ac
• Outdoor ET demand monthly average ETo x assumed
  30 ac of irrigated area (irrigation always on
  regardless of rainfall)
• Rainfall and Eto data from Irvine CIMIS station
  (WY 1988-2008), ETo simulated as monthly averages
  (not normals)

Irrigation of landscaping and toilet flushing
Stormwater Inflow
Stormwater Overflow/ Bypass
Schematic for illustration purposes only, not to
scale
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Modeling Results

• Overall capture efficiency 48
• Capture efficiency for individual water years
  ranges from less than 30 to 100
• Potable water demand reduction about 3 to 4
• Doubling tank size (to 1.6 inches 2.6 million
  gallons up capture to about 58 and potable
  demand reduction of about 7 to 8
• Following charts illustrate temporal patterns of
  tank storage conditions and bypass conditions

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Individual Water Year Performance
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Capture and Reuse - Effect of Sequential
Storms(100 acre residential development with
Cistern 1.6 inches of runoff -2.6 Million
Gallons and use for irrigation and toilet flushing
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Pollutant Loading/Concentration Example

• Example 100-acre residential development with 0.8
  inch (OC DAMP size) Cistern and use for
  irrigation and toilet flushing
• Results Bioretention with underdrains showed
  better TSS loading reductions

Cisterns and Re-Use 55
Bioretention with Underdrains 63
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Pollutant Loading/Concentration Example

• Results Biotention with underdrains had lower
  average concentrations

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Commercial Office Building Example

• Oregon Clinic medical office bldg, Portland,
  Oregon
• 33,000 sf roof area (only roof water to Cistern)
• 20,000 gallon cistern
• Water used in toilets and urinals 650-1,200 gpd
• Supplemented by non-potable and potable water

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Oregon Clinic System Components
Photo 1 Building Rooftop and Drains
Photo 4 Non-Potable Water Mixing Tank
Photo 3 Filter Cartridge and UV Light
Photo 2 Bag Filter Housing
Photo 5 Booster Pump and Expansion Tank
Sustainability?
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Oregon Clinic Improving Performance?
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Stormwater Capture/Harvest and Use

• Must drain tank relatively fast (similar to
  ED/Infiltration System Drawdown rates)
• Irrigation use limited
• Seasonal issues
• Zeroscaping push
• Competition with reclaimed water
• Toilet flushing possible with high enough
  densities (TUTIA Toilet Users To Impervious
  Area Ratio)
• Building becomes ½ occupied during recession?
• Competition with reclaimed water
• Combine with Grey Water Systems?
• Positives of using infrastructure better

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Stormwater Capture/Harvest and Use

• Must drain tank relatively fast (similar to
  Extended Detention/Infiltration System Drawdown
  rates)
• Irrigation uses are limited
• Seasonal issues
• Zeroscaping encouragement/requirements
• Competition with reclaimed water
• Toilet flushing possible with high enough
  densities (TUTIA Toilet Users To Impervious
  Area Ratio)
• Competition with reclaimed water
• Low flush toilets?
• Combine with Grey Water Systems?
• Positives of using infrastructure better

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Rainwater harvesting and Reuse Systems
Sustainability? Carbon Footprint?
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Summary/Recommendations

• Infiltration should be maximized where
  appropriate- i.e. Central Valley, Inland Empire,
  LA River Forebay) and with proper control
• Cistern based harvest and use of runoff has
  limited applications where it can be effective
  due to runoff patterns and demand considerations
• should be considered where it is effective- i.e.
  Pelican Hills Resort large buildings with lots
  of toilet flushers
• There needs to be more technical vetting of
  retain on site and stormwater harvest/use as
  these are considered or made mandatory

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Orange County MS4 NDPDES Permit DraftTechnical
Guidance Document
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Infiltration Techniques
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Infiltration Techniques