Seawater Desalination and Water Supply Reliability in Marin County Louis Armstrong, URS Corporation

MMWD Founded in 1912 – California’s first municipal water district Founded in 1912 – California’s first municipal water district Serves 185,000 residents of Central and Southern Marin County Serves 185,000 residents of Central and Southern Marin County Primary supply is local reservoirs (5 on Mt. Tamalpais watershed, 2 in West Marin) Primary supply is local reservoirs (5 on Mt. Tamalpais watershed, 2 in West Marin)

Current MMWD Supplies

Marin’s Demand for Water Operational Yield † 1987 Demand

Projected Demand Increase (120AF Per Year) Yield

Utilizing North Marin Pipeline Projected “Decay” of Excess Delivery Capacity Loss of 2,300AF by 2015

Projected 2015 Scenario Current supply deficit: 3,200AF Current supply deficit: 3,200AF Demand increase: 1,560AF Demand increase: 1,560AF Projected loss of NMWD capacity: 2,300AF Projected loss of NMWD capacity: 2,300AF Total projected deficit: 7,060 AF Total projected deficit: 7,060 AF

Possible Solutions: Soft Path Increased Conservation: 2,000 AF Increased Conservation: 2,000 AF Increased Recycling: 1,800-2,100 AF Increased Recycling: 1,800-2,100 AF Adjust Service Levels: 869 AF Adjust Service Levels: 869 AF TOTAL: 4,669 to 4,969 AF TOTAL: 4,669 to 4,969 AF

So what about Desalination…..

The Process

Desalination By Reverse Osmosis 2 gallons of seawater = 1 gallon of high quality drinking water 2 gallons of seawater = 1 gallon of high quality drinking water Pre-treatment and RO removes contaminants, including mercury and other contaminants in the Bay Pre-treatment and RO removes contaminants, including mercury and other contaminants in the Bay MMWD will use “dual pass” RO MMWD will use “dual pass” RO

Reverse Osmosis 

Flow at the Membrane

Effectiveness of Reverse Osmosis

World-Wide Installed Capacity

Desalination Highlights Advantages Advantages –reliability (drought proof) –independence/self- sufficiency –possibly smaller environmental footprint –high quality water taste test taste test Challenges Challenges –siting of plant –energy consumption - improved technology, green power options, environmental management system plan –discharge (CMSA) –intake (Rod & Gun Club pier) –sludge disposal

Preferred Plant Location

Option for Discharge of Brine Mix with existing WWTP outflow Considerations: –Need existing outfall with sufficient capacity –Potential to reduce dilution due to buoyancy in receiving water, or increase momentum mixing –Potential for in-pipe dilution of constituents in wastewater

Next Steps... Draft EIR released : Late Summer 2004 Draft EIR released : Late Summer 2004 Certification of the EIR : Late 2004 Certification of the EIR : Late 2004