We will never run out of water on Earth, but we run out of fresh water, locally and globally. Each of the water agencies around Monterey Bay is exploring several alternatives to provide water to customers in this second year of major drought and beyond.
The recommendations of the Santa Cruz Citizens Water Supply Advisory Committee in 2015 included 1. water exchange with nearby water agencies, including the Soquel Creek Water District; 2. store excess surface water (when available) in a groundwater basin; 3. recycle wastewater treated by advanced treatment for specific uses; and 4. desalination, as an option for customers of the city of Santa Cruz water utility. The first two of these, however, depend on average or above average precipitation and runoff, which has been lacking in the past two years.
Storing any excess water in the ground through the city’s existing Beltz groundwater wells in Live Oak or new wells in the Central County Groundwater Basin for later use has been studied extensively since 2015. Short for ASR, or Aquifer Storage and Recovery, this project involves pumping treated water from the Graham Hill water treatment plant on Graham Hill Road to the Beltz wells where it would be stored in the basin and pumped later.
The goal of current studies is to understand any operational or water quality constraints of this strategy, including having enough excess water in Santa Cruz to pump to the wells, which ultimately would be used. to meet the needs of the city when rainfall and runoff are low.
Recycling of the city’s treated wastewater for beneficial uses such as irrigation, groundwater replenishment, increasing surface water and direct use of drinking water is also under assessment. These types of projects have the distinct advantage of not requiring any new water source and instead reusing an existing source. The barriers with recycled water are primarily psychological as the technology has been proven successful with facilities around the world, in the United States and California (like Orange County and Monterey).
One approach would be to send our existing secondarily treated wastewater, currently discharged to the ocean, from the Neary’s Lagoon plant to the Soquel Creek Water District’s PureWaterSoquel project for advanced purification. This treated water could then be used for parks, golf courses, groundwater recharge or pumped to Loch Lomond where it would mix with a much larger volume of water and ultimately be pumped to the treatment plant. from Graham Hill Road to be processed and distributed in the city. .
Alternatives to recycled water would require an investment in expanding the advanced PureWaterSoquel purification system. This project has a planned capacity of 3,000 acre-feet / year, double the current capacity, a volume determined by the Santa Cruz County Groundwater Sustainability Agency, necessary to ensure the sustainability of basin operations. . If this volume of water could be achieved, the city would receive half of it, or 1,500 acre-feet / year.
An acre-foot (approximately 326,000 gallons) is a volume difficult to imagine; think of a soccer or football field covered with a foot of water. This will meet the annual indoor and outdoor water needs of four to five families in our area, so that the 1,500 acre-feet that could be taken out of the city’s project, if successful, could meet the annual water needs. about 6,000 to 7,500 on average. households.
In other words, that’s about 6% of the volume of our only large reservoir, Loch Lomond, or about two months of typical city water consumption. If this turns out to be successful, it would be a significant addition to the city’s water supply. This is however a big if, which is the subject of the pilot project and feasibility studies.
The two groundwater storage options (using excess surface water and purified wastewater) avoid chemical interactions and changes in water quality when introducing a new source of water. water in the groundwater basin, and just as important, the quantity of recharged water can actually be recovered or pumped out of the aquifer of the middle departmental basin following recharging when the city has needs in times of drought?
The remaining option, seawater desalination, faces serious obstacles. The main advantages are that it does not require precipitation and that there is a lot of water in our ocean backyard, 97.5% of all the water on the planet, or about 332,000,000 cubic miles. . The most popular desalination technology, which pushes seawater through a semi-permeable membrane, has been in use for years and is applied in 120 different countries around the world.
The list includes a number of countries in the Middle East (Saudi Arabia, Oman, United Arab Emirates and Israel), Mediterranean countries (Greece, Portugal, Spain, Italy, Gibraltar, Cypress and Malta), as well as Australia, China, Japan and the United States. States. Globally, desalination covers the water needs of about 300 million people, or about 4% of the world’s population. By volume, however, this represents only about 0.5% of the planet’s total freshwater use.
Gary Griggs is Professor Emeritus of Earth and Planetary Sciences at UC Santa Cruz. He can be contacted at [email protected] For previous Ocean Backyard reviews, visit http://seymourcenter.ucsc.edu/about-us/news/our-ocean-backyard-archive/.