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Richard Cowen, a professor emeritus in geology, told me: "A city the size of Davis (and it will increase in population) will locally deplete almost any aquifer. That will draw water inward to replace it. That situation can continue for a while, but in the end is not sustainable.
"The useful life span of a deeper aquifer depends on its geology and its source of recharge, neither of which I know. We are talking years rather than decades, I would imagine, without knowing the facts.
"Careful monitoring would give warning that an aquifer’s life is limited. But given the difficulty of finding an alternative, we might find ourselves in a bad bargaining position as time begins to run out. In other words, if we have a better alternative right now, why go to the trouble and expense of drilling into a new aquifer that has to be a diminishing resource?
"The Sacramento River is the biggest and cleanest water source in the region, and could certainly supply municipal water for Davis forever because its water is renewed from rain and snow every year. It would be much more reliable in the long term than any aquifer."
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Gregory Pasternack, a professor of Watershed Hydrology in the Department of Land, Air and Water Resources, told me: "If you look at the facts on face value with no questioning of assumptions, then sure, Davis uses a lot of water and will be using ever more, so more supply and better supply is needed. A number of shallower wells in Davis are contaminated now and the good, deep aquifer varies in depth and water quality from East to West. Davis has spent a lot building one or more wells and then decommissioning without production due to manganese in the east, so that is a problem. The vision of getting high-quality surface water makes sense in that view. Deep groundwater can supply a lot, but do we really want to use that so heavily and ignore future generations? I think more deep groundwater wells would work for a while, as every community in the region is now probing for that same sweet spot at ~800-1000' depth."
"What bothers me is that we need to get serious about changing our water system more radically to get to where we need to go in terms of quality and quantity. If we were starting from scratch, we would never build the system like this, emptying all our best water onto lawns (or maybe they would, but shouldn't!). We would use low-quality water from shallower, cheap wells to irrigate, preserving the good, deep groundwater for household use only. Well, we are not starting from scratch, but the opportunity is here now just the same. We only get one shot to make this major investment in infrastructure, and what happens if the surface water conditions or water quality don't pan out over time due to climate change or legal rights issues? In fact, many neighborhoods have extensive greenbelts and buffer lands that could be used to run independent irrigation pipes OR we could open up the roads and run the pipes underground- just get it done one time and never have to worry about treating all that lawn water. Then retrofit the houses to take irrigation water from the new lines and leave the deep groundwater for household use."
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Thomas Harter, a Cooperative Extension specialist in the Department of Land, Air and Water Resources and holder of the Robert M. Hagan Endowed Chair in Water Management and Policy, told me: "The issue, as I understand it, is not about the availability of groundwater, it is mostly about its quality and suitability a) for drinking and b) for meeting wastewater discharge requirements. I defer to the experts of Davis groundwater quality to speak to that topic and what future trends they may see. As to the question, whether groundwater will suddently change it's quality or will suddenly disappear in an unforeseen event - the answer depends on your perspective. Indeed, neither of these events will happen overnight or from one week to the next - the change is gradual. But when it takes a decade or more to develop an alternative water supply, "sudden" means: less than ten years. In that sense, we may indeed "suddenly" see changes that we cannot accurately predict today; water quality standards - which classify drinking water quality to be either "bad" or "good" may also change "suddenly", i.e., over the next decade. So, I do understand the need for planning ahead."
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I asked Steve Grattan, a water specialist who studies "Salinity effects on plants at the plant and field scale; agricultural drainage water reuse and management; salinity-trace element interactions in plants; evapotranspiration" this:
Do you believe deep aquifer well water is a reliable, long-term source of water for Davis? Why or why not?
"This question is best answered by ground water hydrologists. However, my feeling is that if the Sacramento River is a viable option, the water will be of better quality than many of the ground water aquifers that supply the city of Davis. What is uncertain is the dependability on surface water supply over the long term. Certainly there will be continued droughts in California where various water users will compete for its (river) use. Another issue that needs to be considered is the gradual shift in peak water flows in many California rivers to earlier times. With climate change, not only is the snow pack in the Sierra Nevada mountains moving to higher elevations, snow melt is generally occuring earlier where peak flows are now occurring earlier in the year. This affects how much of this water is stored in dams vs how much is released down stream. With that trend, there may be merit in trying to re-capture that early flows in ground water aquifers by diverting it to flood plains. How this may affect water supplies for the city of Davis I am not sure but it is something important to consider."
If and when the deep aquifer dries up or no longer produces good water, will we have a number of years of advanced warning, or will we be shocked to find over night that we can no longer rely on our deep wells?
"If and when the deep aquifer dries up it will likely be a gradual process. It will not be something that happens over night. There will be a warning with sustained drop in aquifer depth over time. The water quality may also become progressively worse in quality over the years.
Based on what you know about the alternatives, would you recommend Davis go forward with its surface water project? Or do you think we are just as well off to wait 10 or 20 or more years before we spend the money it will take to bring Sacramento River water to Davis? Why or why not?
"It is never too early to begin to think about alternate water supplies. Ideally it would be valuable for the city of Davis if it had both sources available. The top priority would be Sacramento river water and during prolonged droughts, rely on ground water supplies. Ultimately it comes down to economics and water demand among the various water users."
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By email, I asked Professor of Hydrogeology Graham Fogg if the deep aquifer was sustainable:
"This is poorly understood because of (a) the unknown future changes in groundwater quality due to downward movement of poor quality groundwater from agricultural and urban sources (Davis is not unique in this regard), (b) the unknown effects of increased pumping by the City in the so-called deep aquifer, from which UCD already withdraws drinking water, and (c) the unknown (to me at least) future demands for water in Davis when one considers growth and possible conservation measures. Of course, even if the groundwater quality continues to degrade, there is always the option of treating the groundwater to remove dissolved substances, much like we do routinely with surface water; but this costs."
How many years will the deep aquifer last?
"It's best to think of it as an "aquifer system" rather than an aquifer, because most of it consists of a complex network of aquifer materials (sands and gravels) and non-aquifer materials (silts and clays), and the latter are by far most prevalent. The groundwater levels appear to be recovering more or less fully every year following the dry season, indicating it is not yet in overdraft with respect to water quantity. In most any city where groundwater is the sole source of drinking water and landscape water, however, it is possible for demand to grow to the point that groundwater overdraft occurs. In that case, the aquifer system would not dry up and blow away, but there would be more severe restrictions on water use, like vastly reducing landscape watering, which is a large but non-essential part of the water demand. (I realize, it's an uphill battle in N. CA to get people more accustomed to lack of green grass, but since landscape watering in this part of the world is the largest part of the urban water budget, this issue will be receiving more and more attention.)
Will we have advanced warning before the aquifer dries up?
The changes in groundwater quality will not be sudden, but will likely continue on a decades to centuries time scale.
Do you believe that the Sacramento River water is a reliable and sufficiently safe long-term source for our municipal water?
Hydrologically, the Sacramento River water would be a reliable long term source. Legally, not sure because that is not my area of expertise.
Based on what you know about the alternatives, would you recommend Davis go forward with its surface water project?
"I am not sufficiently up to speed on the latest information (and related economics) to answer the big question. However, I would keep in mind the following guideposts:
"(a) The groundwater system is vulnerable due to long term degradation of water quality and potential for future overdraft. Many cities that rely solely on groundwater seem to eventually reach overdraft conditions.
"(b) Based on (a) and the water quality vulnerability, any planner in his right mind should jump at the chance to secure surface water sources that can be used in conjunction with the groundwater (i.e., use more of the surface water when you have it, keeping the groundwater in the 'bank'; use more of the groundwater during drought). Especially if that can be accomplished reasonably economically.
"(c) The common sense in (b) looks even better when you consider the wastewater discharge limitations that the Regional Board is apparently enforcing strictly. If the Board really will be requiring that Davis reduce drastically its salt load from wastewater discharged into the Delta watershed, then the only viable alternative I am aware of is for Davis to reduce the salt content in its drinking and landscape water by using substantially more Sac. R. water, which is much lower in dissolved salts.
"(d) The common sense in (b) also looks even better if the opportunity to secure the surface water is arising now and is unlikely to ever arise in the future.
"(e) The question probably hinges mostly on the wastewater discharge issue. If this will be strictly enforced, then Davis seems to have little alternative but to bring in more Sac. R. water if it can. If this discharge is not strictly enforced and never will be (big ifs), then Davis could probably make do just with groundwater. If they go groundwater only, then when the quality worsens, they will have to invest in water treatment in the coming decades. If and when they reach serious overdraft conditions, their only recourse would be to eliminate most lawn watering entirely. Such a measure would possibly be used to manage or reverse overdraft, but would require a major shift in attitudes of the citizenry."
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I asked Qingfu Xiao, a research water scientist at UC Davis, if the deep aquifer was reliable:
"This is totally depends on how we (are) managing and using this resource. As more and more lands are used for buildings, streets, and parking lots, one problem, to make (the) deep aquifer well water reliable, is to use new technology and management to balance the groundwater withdraw and recharge. And the technologies are there at reasonable cost USGS has been testing recharge groundwater at relatively large scale in L.A."
How many years do you think deep aquifer water will last?
"It depends on how we pumping and recharging rate. It is a management issue. It will last longer than predicted because the fresh water line from Lake Berryessa (UCD), and water conservation from both technology and education."
Based on what you know about the alternatives, would you recommend Davis go forward with its surface water project?
"We should go forward with this surface water project. But, at the same time, we need rethink how we keep our groundwater system healthy, change our landscape design to increase groundwater recharge (water banking?). Multiple water resources will improve water quality and reliability for Davis."
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