In February 2020 the USFS issued a Notice of Proposed Action that MMSA wants to expand their snowmaking activities and cover much more of the mountain with man-made snow than it currently does. The Environmental Assessment (EA) that came out along with the notice states that on average only 100 acre-feet of water is needed to cover these 29 additional runs and that it would be a 43% increase in how much water is currently used for the ski season. One hundred af/yr is not a significant amount of water, but is it a realistic projection, especially in drought years? Since the EA doesn’t state how many acres have been covered by snowmaking in recent years so it is hard to determine how much of an increase in water the additional 206 acres will require. Covering 29 more runs with snow seems like a significant increase over the number of runs above the Main Lodge that are equipped with snowmaking equipment now. The Heavenly Mountain Resort 2017 Capital Improvements Project states that about 4 acre feet of water is consumed per acre to cover rocks, obstacles, and hazards with 5 feet of snow at the start of the season. For 206 acres, that would be 824 af of water.
Many of the proposed runs to be covered with man-made snow will be at lower elevations and will require more water to maintain them with multiple, repeated applications than those at higher elevations on the north face. Snowmaking equipment at the lower elevations means the runs could be kept opened the full duration of the season and do not have to close prematurely in spring. That also increases the amount of water to be used. Has this been factored in? How much water was used in the 5-year drought to make snow? That might be more representative of future water usage.
An article by Brad Rassler mentions that experts estimate that 10-15% of the water sprayed sublimates and never hits the ground. In addition to that, a measurable amount of the snow on the ground evaporates from wind and sun. The article states that it could add another 10-15% of water loss. This can be calculated with data from the weather stations on Mammoth Mountain and worked into the model. However, the EA points out that modeling will come after this decision is made. The need for snowmaking should increase as temperatures rise with climate change. The 2001 Breibart hydrology study of the Dry Creek watershed states the evaporative loss could be 50% in a dry year and 35% in a wet year. In an age of declining precipitation and precious water resources snowmaking may need to give way to higher priorities e.g. natural resources and domestic use. It is not be an issue now, but it will be as climate change worsens. (Here is another interesting article by Mr. Rassler on the future of the ski industry and on the impacts of dust on snow.)
Monitoring Groundwater Usage in Dry Creek
MMSA operates five wells on USFS land that tap the Dry Creek aquifer. Three of those wells are used for snowmaking. With this project MMSA is asking to put in two more wells. The USFS isn’t subject to the California’s Groundwater Sustainability Act nor is the Dry Creek basin a priority basin or even on the state’s radar. However, the USFS has control over the groundwater in the Dry Creek basin and it is in the USFS’ best interests to voluntarily manage it sustainably to preserve the aquifer and to maintain a healthy forest cover. Unsustainable groundwater pumping impacts surface vegetation, local springs, and wildlife. The 2012-2015 droughts stressed the trees in the Dry Creek basin. For the next two years following the drought, trees died from bark beetle infestations. This increased the risk of wildfire.
Based on the Breibart study both the surface runoff and the groundwater flow from the north face of Mammoth Mountain, down the Dry Creek drainage and onto the flats around Deer Mountain. The surface snow on the flats percolates down into the ground and contributes to the aquifer too. The Burak 2015 thesis states that Dry Creek contributes to Big Springs, when in 2001, the connection wasn’t clear. Depending upon the amount of water pumped, extractions from the Dry Creek basin could impact Big Springs to some unknown degree.
A rigorous groundwater inventory and monitoring program should be implemented with adaptive management, if it isn’t already. There should be a plan in place that places caps on the amount of water that MMSA can extract in dry years and that sets trigger points for when pumping should stop. This type of data would provide a baseline of water use before water use increases with the expansion of the Main Lodge facilities. With the Base Land Exchange, MMSA will be able to tap into the Dry Creek aquifer independently. A report should be published annually on groundwater levels and recharge modeling.
The EA states that additional groundwater pumping will be needed during drought years. If the EA underestimates the projected amounts of water to be used for snowmaking, then it underestimates the impacts to groundwater levels and connected springs. There should be full disclosure in the EA about how many and which wells have already dried up on Mammoth Mountain due to snowmaking. The EA argues it would put enough snow on the surface during a drought year to create a normal year of run-off and recharge. True, but leaving all of it in the ground might be even better. The EA estimates that the recharge rate would be 80%. This means 20% of what would be extracted would be lost. With a prolonged drought, there would be a continuous depletion of groundwater. Plus the amount would be extracted from the Dry Creek drainage but spread around the mountain in both the Mammoth Creek drainage and the Dry Creek drainage. It wouldn’t all return to the Dry Creek drainage. Rain on snow events will seep in less.
The Breibart study explains that twenty years ago (2001), MCWD and MMSA both want to tap the Dry Creek aquifer: MCWD wanted 2,000 af and MMSA wanted 685 af. The study calculated how much groundwater could be sustainably extracted. Using the 1992 drought year data, the study calculated the recharge fell between 2,800 af and 10,500 af and recommended that only 2,000 af be withdrawn during drought years. Based on that study, there is plenty of groundwater for MMSA to be able to increase their pumping. However, if the MCWD needs to tap the Dry Creek aquifer in the future, there wouldn’t be enough groundwater to meet both their needs in drought years. By monitoring the groundwater levels now and collecting data on the impacts of MMSA’s snowmaking and domestic water usage on the aquifer, the USFS would be better prepared to manage the aquifer in the future.
We recommend the USFS perform periodic water quality tests on all the wells on its property and at Big Springs to monitor how much salt used on the runs is seeping into the groundwater. A USGS study of the tributaries to the San Joaquin River and springs in the Devils Postpile states that MMSA applies an average of 120,000 lbs/yr of salt to the ski area. That USGS study identified salt in the Upper Dry Creek groundwater along with emerging contaminants e.g. caffeine, sunscreen chemicals, DEET. Using water from the ponds year in and out increases the salinity of the ponds. With increased recycling of groundwater pumping-snowmelt-recharge, would these chemicals become more concentrated?
Update: The Forest Service approved the project in July 2021. Click on the file labeled "Decision".