Spigots throughout the basin are not going to run dry for decades, if ever.
This largely has to do with being at the top of the watershed, a geological composition that is conducive to capturing and storing groundwater, a ginormous lake to store water and draw from, conservation measures reducing use, and limits on growth.
Even with the forecast for less snow and more rain (hard to imagine with snowfall records breaking this year), the basin is in good shape, according to South Tahoe Public Utility District.
“Seven of the last 17 years were below normal precipitation. Despite a decrease in total storage in the basin, the groundwater remains stable,” Shelly Thomsen, STPUD director of public and legislative affairs, said. “Our lake fluctuates a lot in levels. We do not see that same level in groundwater fluctuations. It is more stable.”
Groundwater is collected via snow literally melting into the ground, and with runoff reaching Lake Tahoe. The lake is a groundwater basin because its bottom absorbs water. These groundwater components are hydrologically connected.
STPUD applied for a $2 million state grant to help address groundwater and climate change issues. STPUD wants to better understand how threats to the greater ecosystem might alter groundwater. More rain and less snow could impact tree mortality and wetlands significantly.
“The biggest concern for our community with regards to climate shifts is what does it do for the groundwater dependency systems,” Julie Ryan, engineering manager, with the district, said.
STPUD collects groundwater data twice a year. Desert Research Institute in Reno helps with projection models.
“We are constantly imputing the most up-to-date climate projects so we don’t end up like the Colorado River,” Ryan said.
Ryan explained there is a limit to groundwater capacity, though. “Generally you hit groundwater about 15-feet deep and then it’s saturated below that. Our groundwater basin is really quite full. There is not a lot of room for more water below ground.”
STPUD, Lukins and Tahoe Keys water districts rely completely on groundwater—or wells. Lakeside on the California side and many Nevada water purveyors draw directly from Lake Tahoe. (Lakeside uses a well in emergencies.)
STPUD is looking into securing surface water rights through the state, meaning it would be able to use lake water.
“We would be more resilient if we had surface water,” Ryan said. “If you have PCE (tetrachloroethylene) it can take decades to resolve that. Surface water quality you have to deal with on a daily basis, but there are fewer surprises. But when there are surprises, they are easier to manage.”
STPUD has long said the largest threat to its water supply is contamination, not the lack of water to pump. Lukins and the Keys districts continue to deal with PCE. Arsenic and uranium are two naturally occurring contaminants groundwater purveyors must contend with.
In the early 2000s STPUD won settlements against Chevron and Shell regarding MTBE (methyl tert-butyl ether) seeping into the groundwater; with some of that money being spent on new wells.
STPUD started a groundwater management plan after the MTBE brouhaha.
California has only been regulating groundwater since 2014. A that time, STPUD with El Dorado County Water Agency became the overseers of the newly created Tahoe South Subbasin. They manage the groundwater with the help of an advisory group that meets twice a year. The boundaries are from the state line west to Eagle Point and south to Christmas Valley. So, it includes the smaller California water districts, along with nearly 700 private wells.
State law mandates plan updates every five years. STPUD did so in 2022. The state Department of Water Resources in March discussed districts that are overdrafting, which means using more water compared to what is replenished each year.
The Tahoe South Subbasin isn’t even close to being in this category. More water is collected compared to what is used.
Notables from 2022 the report:
- Approximately 1.8 million acre-fee of groundwater storage is available. (An acre-foot is the equivalent of 1 acre being covered with 1 foot of water.)
- Average annual recharge from 2010-19 was 48,300 acre-feet per year (AFY) and the average from 1983–2019 was 41,600 AFY.
- Groundwater withdrawals averaged 7,660 AFY and 7,150 AFY from 1983–2019 and 2010–19, respectively.
- Between 2010-19 groundwater storage increased an average of 1,700 AFY.
- The state allocates a maximum of 12,493 AFY to be pumped.
- Maximum pumpage is expected to be 11,800 AFY using El Dorado County’s 50-year population growth rate.
Note: This story first appeared in the March 2023 issue of the Tahoe Mountain News.
Continuing to provide comprehensive information is greatly appreciated.