The city's sewage treatment plant currently discharges 6.5 MGD (million gallons per day) of tertiary treated wastewater into the Santa Clara River Estuary, and has the capacity for 14 MGD. This is one of the last remaining estuary discharges in the state. Issues associated with this discharge include impacts of nutrient-rich water in the estuary and the artificial hydrology created by this volume of water. With this discharge, the lagoon fills up and breaches on a more frequent basis than it would under natural conditions. The estuary is habitat for a variety of threatened and endangered species, and wastewater flushing into the surf zone affects ocean water quality.
These studies are a requirement of the Regional Water Quality Control Board as a condition of the city's wastewater discharge permit. The aim is to investigate opportunities for enhancement of water quality. Information is available on the city website here.
The 'Special Studies' include 3 parts:
- Recycled Water Study
- Constructed Wetlands Study
- Estuary Monitoring and Assessment
The current system reclaims approximately 1 MGD which is reused on the two nearby golf courses and other urban landscaping.
The reuse study looked at potential markets for reclaimed water within a 5 mile radius. Possibilities include urban and agricultural reuse, as well as groundwater recharge.
The bottom line: cost is high to construct a system that would provide for any significant reuse, with estimates from $35M to $140M as summarized in this table.
Major piping and pumping infrastructure is needed to deliver reclaimed water, and agricultural reuse would require an expensive and energy intensive Reverse Osmosis (RO) treatment plant.
The city currently operates a series of ponds that help treat the effluent before it enters the estuary. Current effluent nitrate levels are over 15 mg/l. The city is planning on spending $22M at the treatment plant to remove nitrogen to the regulated limit of 10 mg/l.
The study identifies 3 potential sites for additional constructed wetlands. The aim would be to reduce nitrogen from the effluent.
There was discussion after the presentations.
Stakeholders were given an opportunity to place 'dots' on the chart below to express their preference for future discharge scenarios. The 'Volume' axis allows a sliding scale between all 'onsite' discharge as it currently exists, or all 'offsite' through reuse. Enhanced quality infers additional treatment wetlands. It seems the majority prefers enhanced water quality and at least half the volume discharged offsite.
According the the minutes of the meeting, I commented that:
'Would like to see more of the supply side as part of the equation/studies. There should be an integrated (regional) water management plan that could address issues across the board. (Paul Jenkins, Surfrider)'
What was not recorded was my comment that climate change and sea level rise may soon make the current location of the treatment plant infeasible - planning should consider opportunities to decentralize wastewater treatment to facilitate reuse without the need for complex pipelines and pumping systems.
Supply-side analysis should be conducted to consider on-site reuse of greywater throughout the city. For a relatively small investment, a greywater retrofit program would reduce the wastewater volume at the treatment plant, reduce the city's overall water demand, and create lots of local jobs in the process.
The next stakeholder meeting will be in February 2010.
The complete presentation and meeting notes are on the city website:
Other blog posts on this issue: