Old-fashioned water filtration

On the path up to Chabot Dam, you pass this row of big tanks (click for big version).

water filtration

They were used to filter the water from Lake Chabot reservoir, and they’re still filled with fine sand plus, I suppose, the decades’ worth of slime and crap they kept out of Oaklanders’ stomachs and food.

This is roughly the same purification method we rely on when we use well water. The fine pores between mineral grains purify groundwater in two ways. First, of course, they physically trap the crap. Second, the minerals themselves chemically attach to many dissolved contaminants. Clay minerals are especially important for that.

The days are long gone when Oakland was served by wells. The water table has been pulled down all over the city by human intervention. The headwaters of Lion Creek were once called Laundry Canyon because there was so much good water coming down. Fruitvale irrigated orchards for many years. The rains we get here can’t keep up, so now we pipe our water in from the Sierra.

One important feature of the new state water compact, if they can ever get it nailed down, will be a new, wide-scale program of monitoring groundwater. We need that to get a handle on the whole resource. Everyone knows, except the statutes, that surface water and groundwater are intimately connected. Western water law is an ass.

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7 Responses to “Old-fashioned water filtration”

  1. Mike Says:

    Do Oakland residents realize that every time they turn on their tap, they cause desertification in the Sierra Nevada?

  2. Andrew Says:

    I wouldn’t say that. The Sierra water harvest doesn’t hurt the Sierra. It bypasses the Valley, whose water table has been lowered so much over the years that it would be unrecognizable to the original Mexican vaqueros who cleared it of elk and grizzlies to manage vast cattle herds there. Today’s Valley and Delta are badly degraded that they can never be restored while civilization exists here. The new water plan aims to stop degradation and maybe reverse it slightly in a few places. Oaklanders’ tap water would desertify the Valley if they didn’t pump up so much groundwater there.

  3. Mike Says:

    Ag water pumped is returned to the same aquifer. City water in the valley is returned to the local river. Here in Placerville, we steal water from Caples lake.

    Los Angeles dried up Mono Lake, and has to maintain the lake at a specified level. And water is taken from Trinity River that should flow to the Kalamath. I don’t know the destination of that water, but you can bet it negatively affects the Salmon.

    19% of California’s Electricity, 30% of Natural gas, and 80M gallons of diesel is used transporting water. Hetch Hetchy actually produces more power than it consumes. But pumping valley water to LA requires the same energy as desalinating ocean water.

    http://www.energy.ca.gov/2005publications/CEC-700-2005-011/CEC-700-2005-011-SF.PDF

  4. Andrew Says:

    I appreciate those facts, and thanks for bringing them up. I do disagree about the Valley, where many shallow aquifers are given water that comes from deeper aquifers. And certainly the salmon suffer and the Sierra rivers suffer. But the rest of the mountains–the trees and wildlife–don’t feel it when the rivers run low. It’s a small point in the big picture, but that’s the point I was making. I didn’t realize your point about the energy costs of pumping versus desalinating before!

  5. Andrew Says:

    Here’s a recent article in Science News about the unsustainable depletion of the Central Valley’s aquifers.

  6. phaed Says:

    I like this content so much.Thanks.

  7. clew Says:

    “Ag water pumped is returned to the same aquifer. ”

    A lot of it is transpired through the plants to the air, and may not fall to ground again until it’s a continent away. Irrigation would be a lot less worrisome if we really returned the water.

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