The Meaning of Significance

First off: The Earth Day Accretionary Wedge is up, full of environmental musings from the geoblogosphere – check it out! Since it is still Earth Week here at Berkeley, I’ll follow up my carnival contribution with an observation from the trenches, where geology and environmentalism intersect in a series of excruciatingly dull technical documents.

Part of my job used to be telling the people of Sun County, California* how their ground water resources would be affected by proposed new developments. Your average housing development poses a couple of different potential risks to ground water supply. One is that paving a surface which was previously covered in permeable soil will reduce the amount of rainfall that ends up in the aquifer, sending it to the ocean instead in the form of stream and storm drain runoff. Another is that people will occasionally spill toxic chemicals on the ground (e.g., motor oil, pesticides) and if the soil is configured just wrong, those chemicals can potentially make it down to the water table and contaminate the aquifer. And of course, any development will require enough water for the people who live there, but evaluating the stability of the proposed water supply was someone else’s job.

So what I did was overlay a map of the proposed development with a geologic map of the area, check for potential problem spots where the water table was near the surface, and calculate the amount of ground water recharge that would be diverted away from the aquifer if the proposed new project was built. Oh, and I churned out some excruciatingly dull technical prose. It was all part of the larger environmental impact review required for all new construction in California under the California Environmental Quality Act (CEQA – we pronounced it “seequah”). CEQA requires that developers avoid or mitigate any significant impact to the environment caused by their proposed project.

What’s a “significant” impact? In many cases, local planning boards have drawn lines between “significant” impacts that require mitigation, and “insignificant” impacts that can be foisted worry-free on the people of California.

In other cases, “significant impact” means exceeding a threshold value that a subcontracting technical consultant, in the absence of concrete guidelines, pulls out of their a must use their professional judgment to determine.

The value of X for which eliminating X acre-feet/year of ground water recharge is “significant” enough to require mitigation is one of those fuzzy guideline cases (weirdo Imperial unit alert: one acre-foot/year is enough water to serve about three households). The City of Los Angeles says that any project resulting in a “demonstrable and sustained reduction of groundwater** recharge capacity” counts as a significant impact (i.e., X>0). Sun County was, at the time, keeping mum on the matter.

What we did as EIR-writers was to flap our arms, squint a little bit, hawk up a loogie, and say “gee, X sure is a lot smaller than the total recharge to Sun County Basin”. I don’t think that’s an acceptable planning strategy, and the only way to change it is to put decent leadership in local government.

A recent state supreme court decision requires developers to ensure that their projects have an adequate long-term water supply, but those who wish to pile a couple more straws on the camel’s back (or insert another little straw into the local milkshake, for all you who’ve seen There Will Be Blood) are still golden, so long as they can find a water supply somewhere – a local reservoir supplemented with water from the Sierras or the Colorado River, for example.

Climate change is going to screw over all of California’s water resources. Every time I think about this, I get depressed, because the system is already such a fragile web of carefully pumping every drop of sustainable yield from the ground and pumping more water through a rickety maze of old levees ready to crumble in the next Big One and hoping Arizona doesn’t need its full share of the Colorado River any time soon, how is it going to cope with endless drought?

*This may be overdoing the anonymizing, but many of the EIRs I worked on were confidential, and I am not sure how many of them made it past the initial stages to the point where the reports I helped produce actually entered the public record.
**When you’re dealing with the City of Los Angeles, “groundwater” is one word. For other clients, “ground water” is two words. Don’t ask me why, it just is.


  1. Anne J wrote:

    In Oregon, there was a similar there was a similar significance problem with streamflow. If you are going to use any water (surface or ground) within the Deschutes basin (and maybe others?) that has a 1% OR 1 cfs impact on streamflow, you have to mitigate. The problem is determining what’s going to have a 1 cfs impact, when the average discharge is several thousand cfs.

    (heh, I’m commenting under my real name for once!)

  2. Lab Lemming wrote:

    You lost your footnotes and possibly the end of your post, M.

  3. Maria wrote:

    Oops. Dratted quotes. Thanks.

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