Cottonwood Water & Sanitation District September 2002
Arber
Indirect Potable Reuse at Cottonwood Water and Sanitation
District
Rick Arber, Ben JohnsonRichard P. Arber Associates
Pat MulhernMRE
Cottonwood Water & Sanitation District September 2002
ArberAgricultural & Industrial
• Exchanges• Recycle-process, cooling
Cottonwood Water & Sanitation District September 2002
ArberMunicipal
• Urban Landscape Irrigation• Indirect Potable Use• Direct Potable Reuse
Cottonwood Water & Sanitation District September 2002
ArberUnplanned Indirect Potable
Reuse
WTP
WWTP
WTP
WWTP
Cottonwood Water & Sanitation District September 2002
ArberPlanned Indirect Potable Reuse
WTP WWTP
AWT
Aquifer
Cottonwood Water & Sanitation District September 2002
Arber
Cottonwood Water and Sanitation District
Cottonwood Water & Sanitation District September 2002
Arber
CWSD….• Formed in 1981• 1200 Acres of residential
and commercial development
• Slow development in 1980s• Rapid development in 1990s
Cottonwood Water & Sanitation District September 2002
Arber
• Water Supplies• Deep wells (Dawson, Denver,
Arapahoe, Laramie Fox Hills)• Cherry Creek alluvium
• Wastewater • ACWWA Lone Tree Creek WWTP
Cottonwood Water & Sanitation District September 2002
Arber
• Deep Wells– 995 acre Feet
– Fe, Mn, H2S
• Alluvial Water– 141 acre feet senior rights– 585 acre feet junior rights– Upstream discharges (Pinery,
Parker, Stonegate)
Cottonwood Water & Sanitation District September 2002
Arber
• Deep Wells – non-renewing– draw down/capacities– require treatment
• Alluvial Wells– renewable– high capacity– require treatment
Cottonwood Water & Sanitation District September 2002
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CWSD SAFETY FACTOR DEMAND AND AVERAGE YEAR SUPPLY vs. TIME
* Includes 20% Additional Safety Factor Above Projected Demand
0
500
1000
1500
2000
2500
3000
1995 2000 2005 2010 2015 2020
Year
Dem
and/
Supp
ly (A
F/YR
)
YearlyDemand *
AverageYear Supply
Linear(YearlyDemand *)
Cottonwood Water & Sanitation District September 2002
ArberAlternatives
• Deep Wells– Non-renewing; eventual
depletion– Additional wells need with
draw down– Limited production– Treatment required
Cottonwood Water & Sanitation District September 2002
ArberAlternatives
• Dual Distribution $$$• Import Groundwater $$$
Cottonwood Water & Sanitation District September 2002
ArberAlternatives
• ReuseRenewable supplyExtend deep groundwater Greater production
Cottonwood Water & Sanitation District September 2002
ArberCentralized vs. Decentralized
Treatment
• Capital cost 10% less for centralized treatment.
• O&M cost similar for centralized treatment and decentralized.
• Centralized treatment easier to operate.
Cottonwood Water & Sanitation District September 2002
Arber
• Average daily demand 2 mgd
• Maximum daily demand 6 mgd
Cottonwood Water & Sanitation District September 2002
ArberTreatment
• Cartridge Filters• UV?• Anti-scalant• Nanofiltration• Degassifier• pH adjust• Alkalinity• Chlorine
Cottonwood Water & Sanitation District September 2002
Arber Indirect Potable Reuse
• Multiple Barriers– WWTP/AWT– Alluvium (3000 ft.,~
1.5 years travel)– Membrane water
treatment (100%)– Final disinfection
Cottonwood Water & Sanitation District September 2002
ArberConcentrate Disposal
• Cherry Creek Basin– PO4
• Split Flow– ACWWA WWTP (base flow)– Irrigation
Cottonwood Water & Sanitation District September 2002
Arber Objectives
• Evaluate effectiveness of NF on raw water
• Determine design criteria• Evaluate fouling potential• Evaluate feed, permeate, and
concentrate water quality• Select appropriate membrane
Cottonwood Water & Sanitation District September 2002
ArberPilot Testing Plan
• Three month duration– Test different membranes
• Sample water quality 6 times– At beginning and end of each
membrane test• Operate at 83% recovery
– 2.0 gpm permeate– 0.5 gpm concentrate
Cottonwood Water & Sanitation District September 2002
Arber Performance
• Tested two membranes– Osmonics– Filmtec (2 month test)
• Added anti-scalant chemical(Pro Treat)– Potential for sulfate precipitation
reduced
• No significant fouling was observed
Cottonwood Water & Sanitation District September 2002
ArberResults
• Both membranes performed well– Osmonics tighter - higher driving pressure– Filmtec looser - lower contaminant rejection
• Average Rejection– TDS
• Osmonics 68% Filmtec 62%– Hardness
• Osmonics 84% Filmtec 69%– TOC successfully rejected by both
membranes (BDL)
Cottonwood Water & Sanitation District September 2002
ArberProject Costs
• Treatment– $9.3 million
• Ancillary facilities– $2.3 million
Cottonwood Water & Sanitation District September 2002
Arber Public Education Program
• Consultant• Literature• CDPHE involvement• Public meetings
Cottonwood Water & Sanitation District September 2002
Arber
• Predesign underway• Design 2003• Construct 2004• Start up 2005
Schedule
Cottonwood Water & Sanitation District September 2002
ArberConclusions
• NF effective in removing TOC
• Multiple barriers provide public health protection
• Indirect potable reuse is viable, cost effective water supply for CWSD
• Public support is needed