Not all storage is created equal: Groundwater banking at Semitropic

It’s been hot these past few days. So hot that those in the water industry have been worried that the snowpack is melting too fast. This, they say, is a sign of what will become more common. Climate change equals weather whiplash and hotter temperatures, all of which are concerning even when we have good rain years.

This potential new normal makes how we plan to meet water supply needs more tricky. The amount of water over the course of a year that falls from the sky (either rain or snow) may be the same but if nature delivers it in stronger, shorter bursts or it can’t stay frozen until we need it, what does that mean?

There are three main options:

1.        Capture it and store it for when we need it.

2.        Use less through conservation, in particular for outdoor landscaping.

3.        Make our own through purified water and desalination, both of which are extremely expensive due to regulatory costs and the energy costs to operate.

In this blog I want to talk about #1 as I recently visited a place where we store a whole bunch of water, Wasco California.

Semitropic Groundwater Banking

Santa Clara Valley Water District stores water in many reservoirs, including 10 in the county that we own and operate. We also store water underground in Santa Clara County. In fact, we store more water underground than we do in all of our ten reservoirs. And, while our current storage capacity can meet our hydration needs in normal years, when there are multi-year droughts, it cannot.

That’s where additional storage comes into play. In this case, the Semitropic Water Storage District where we store 350,000 acre feet of water. For comparison, our biggest reservoir, Anderson, holds 89,000 acre feet or 29 billion gallons.

Here are a couple things to know about Semitropic:

We’ve been storing water there for about thirty years and hope to continue to do so. Our contract with them is coming to an end and we will start the renegotiation process but there are some complications, namely that Semitropic will need to meet new and more stringent regulatory standards. So, it is not assured that we will renew that contract and/or renew it at the same level.

Even if we did though, it doesn’t solve all our problems. This is because of where the basin is located (South of the Delta) and the ability to get stored water out. Here’s how it works.

Photo credit to Director Beall. : )

We ship some of our excess water via the California Aquaduct to Semitropic. Once it’s there, if we need it, we can’t just ship it back. As a sidenote, we’re only permitted to put in around 30k acre feet a year and take 30k acre feet a year. This is called the “put” and “take.”

With that in mind, once the water is in Wasco, which is close to Bakersfield, there’s no way to physically get the water back. There’s no canal that can move water in reverse. So instead, Semitropic gives us some of their water when we need it that hasn’t yet been delivered to them from the Bay Delta. That water then gets diverted to us in Santa Clara County. Semitropic then keeps the water we’ve previously shipped to them. This is called an “exchange.”

Storage Problem Solved? 

Phew! We have a solution for those drought years. But not so fast. Here’s an added complication. The times when we most likely need to call on that water (during a drought) are also the times that everyone else needs water, including Semitropic. So, we could ask for our water back when we need it but there might not be enough “exchange capacity” to accommodate our request since everyone else also needs water during that time.

So, yay, we have a place to store excess water. And it’s underground, minimizing evaporation losses. But boo, getting it back is not as simple as it might seem.

Which brings me back to the first point. We have three things we need to do:

1.        Store water (and store it in ways that we can have it when we need it)

2.        Use less

3.        Make water

The point I want to make is that all storage is not equal. When water is in our own reservoirs or our groundwater basins here in Santa Clara County, that’s best. We can access that and are the masters of our own destiny.

So how do we plan to store water?

We recently adopted the Water Supply Master Plan where we outline the different storage options. As a reminder, one option that was in the previous plan was pulled, Pacheco reservoir. It would have been about 1.5 times larger than our largest reservoir, Anderson. I supported pulling the plug as I was concerned about the environmental and economic costs but that means we need to find other storage options.

Included in the plan are ideas around potentially increasing the capacity of our existing dams but it is unknown how much additional storage that could yield and at what cost. In the meantime, half of our reservoirs are currently under seismic restriction, meaning, they are not storing as much water as they could. Over the course of the next five years, we will beginning to fix those dams so that they will hold in an earthquake and we can then fill them to capacity. (I wrote about that here.) Other options in the plan include raising Sisk Dam (that's the San Luis Reservoir off of Highway 152) and finding other groundwater banking opportunities. You can read the plan here. The storage options start on page 82 and the entire report is an easy read of 428 pages!

Planning for our future water needs is complicated and hotter temperatures have created an unanticipated wild card in all of this. In the meantime, we continue to build, grow, and behave in ways (big green lush lawns) that ignore these realities. If you haven’t yet swapped out your landscaping for something more drought tolerant, linked here is information about the Water District’s landscape rebate program.

Below are some pictures of the tour of Semitropic. Thank you to their General Manager, Jason Gianquinto, and Isela Medina, their District Engineer for taking the time to show off all the great work that they are doing to store our water.

Jason, the GM of Semitropic explains the recharge ponds to us. This is actually pretty cool because they did a deal with High Speed Rail to get these ponds built. HSR needed dirt. Semitropic needed recharge ponds. So, HSR built the ponds and kept the dirt they excavated. Can you think of any projects in Santa Clara County where we might do a similar exchange?

Pictured here is how Semitropic treats the water for arsenic, which is naturally occurring in the groundwater.

This is a stand tank. A stand tank helps regulate water pressure.