Almost all water pumped for domestic use in Squaw Valley comes from the aquifer that underlies the upper part of the valley. That gravel-, sand- and silt-filled trough gets its water as “recharge” from the surrounding slopes.

That recharge is currently endangered by the KSL Capital/Squaw Valley Ski Holdings/Squaw Valley Real Estate proposal to allow the construction of houses and roads near the mouth of Squaw Canyon.

How do we know all this? First, all of the water-production wells in the valley are in its west end. Next, isotopic evidence cited below shows that water from snow melt and rain from near the valley, rather than from the upper mountain, is the major source of recharge.

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Finally, the new Specific Plan for the expansion of the “village” at Squaw Valley proposes re-zoning that would allow for construction on some-now-undisturbed slopes to the north and west of Olympic Valley Inn near the valley.

What is critical here is where the major recharge comes from. For years the common idea has been that snow and rain on the upper mountain provided the recharge, and not much thought was given to the lower slopes. However, recent isotopic studies of the water from the upper mountain, from the slopes, and from the aquifer itself by Dr. Jean Moran of Lawrence Livermore Labs and California State University show that the lower slopes produce the most recharge.

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Those studies also show that most of the water in the aquifer is new, meaning a year or less old, but some water in other parts of the aquifer is years older. What this means is that the aquifer’s plumbing system is really complicated.

Dr. Moran’s studies suggest that probably all of the lower slopes below about the 6,300-foot contour (about the elevation of upper Sandy Way on the north side of the valley) contribute the major precipitation to the aquifer. Those on the south side of the valley are relatively steep and hold their snow longer, while those on the north side are less steep, accumulate more snow, and the melt goes faster, especially with all the roads and houses.

The one area that is relatively flat (and thus accumulates more snow) and is undeveloped (and thus doesn’t have rapid run-off from roads and roofs) is that at the mouth of the valley near OVI. This is the area that Squaw proposes to zone and re-zone to enable a “neighborhood” of fractionally owned single-family-type houses. If this proposal succeeds, the aquifer may lose its primary source of recharge.

I, for one, judge that this could have a severe impact of the amount of recharge to the Squaw Valley aquifer.

All that said, one may wonder about Dr. Moran’s studies (reported in the Squaw Valley Public Service District’s recently released Creek Interaction Study Report) that discriminate between precipitation high on the mountain and that on the lower slopes. The studies are based on the fact that the isotopic composition of precipitation that falls at high elevations differs from that at lower elevations.

One may also wonder about what happens to the rain and snowmelt water from high on the mountain, inasmuch as it doesn’t make it to the aquifer. The answer is that some runs off as surface water directly or indirectly into the North and South Forks of Squaw Creek and into its main channel; some travels as underflow below the creeks; some is retained as soil moisture; and some travels through the soil, glacial deposits and fractured bedrock all the way to the Truckee River without ever having been noticed.

The same thing happens to the man-made snow. Some reports indicate that as much as 85 percent of the precipitation that falls in the Squaw Valley watershed follows these paths.

David A. Brew, Ph.D., is a California Licensed Professional Geologist and a part-time Squaw Valley resident.