Promising Solution or Potential Problem?

As we near the end of Palo Alto’s dewatering season, October 31st, we face a dilemma. Do we support the use of cut-off walls for underground construction where the water table is high or not?  We’d like you suggestions and comments.  Save Palo Alto’s Groundwater is hosting a table at this Sunday’s, October 1st, Midtown Ice Cream Social, Hoover Park, 1 – 4 pm. Either in the comments section below or at the Ice Cream Social we would like to know what you would like the City to do about construction dewatering.

The City’s Public Works Department released the chart below that shows the results of three finished 2017 City of Palo Alto dewatering projects. Item number 3 shows a project that used cut-off walls. Not only did this project pump out less than 2% of the amount  of groundwater pumped by the other projects that used conventional dewatering methods, it was able to percolate back all this groundwater so that this process didn’t waste any groundwater! This project also had less impact on neighboring properties, the canopy and infrastructure because of the smaller groundwater drawdown.

Terrific, isn’t it? What’s not to like? One of our concerns about all underground construction is its impact on flooding. Underground construction means the removal of soil – soil that we depend on to retain and slowly release storm water on its way to the Bay. Not only is the removed soil unavailable for storm water management but, also, all those underground basements and garages can act like sticks in a stream. If beavers could speak they would tell us that with a few sticks we can build a dam – a dam to the underground flow of storm water during heavy rains.  With the loss of this soil and underground construction acting as dams, the City will have to build ever more expensive  infrastructure to handle heavy rains and reduce flooding.

But if we are building basements and underground garages already anyway, what’s wrong with using cut-off walls?  To be effective, cut-off walls need to be built down to a non-water bearing layer (clay layer).  In our area this depth is roughly twice the basement’s depth. This means we essentially double the amount of soil unavailable to absorb storm water and block water flow through much of the lot   Do we understand the impacts of basements or cutoff walls on flood risks?  We think not.

Thank you for your interest and your support.

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Too many regulations?

The stories and photos coming from Texas (and likely soon from Florida) are sobering and, some, heartbreaking – they are a reminder of what can happen and what did happen in a much smaller way in Palo Alto  during the February 1998 winter storm.

Although unprecedented amounts of water fell on the Houston area, experts say [1], [2] that among other measures, having and implementing zoning regulations could have minimize the impact of the storm.

A neighbor mentioned that she is opposed to regulating dewatering for basement construction because “we already have too many regulations”.  While too many regulations might feel like being “nickeled and dimed”, what if those regulations actually improve our lives and our safety?

In the case of dewatering for underground construction, regulations that limit or eliminate the waste of shallow groundwater can protect this resource for use in future droughts. Additionally, instead of pumping this shallow groundwater and shunting it to the Bay, a sustainable amount of this groundwater could be used for current non-potable needs such as irrigation. This would decrease our use of ever more scarce and expensive potable water.

Beyond dewatering and with the floods in Houston in mind, we know that soils regulate the flow of stormwater (plus sequester carbon dioxide, a greenhouse gas). With ever more underground construction, we are removing this soil and it will no longer be available to retain stormwater and release it slowly over time. Thus, we increase the chances of flooding in our neighborhoods. As the failure of the Oroville dam demonstrates, flood protection infrastructure can be overwhelmed, despite the assurances of planners. And, when overwhelmed, the damage can be extreme.

With expected sea level rise the groundwater level will concurrently rise. As with underground construction, there will be less soil available to retain stormwater and release it slowly over time. This means that areas not currently in the FEMA flood zone are more likely to have flooding in the near future. Should we be building basements and underground garages in these areas? According to the USGS, underground construction in which the groundwater level is currently at 13 feet or less is at risk of flooding within its lifetime. For these reasons, shouldn’t we be regulating underground construction to ensure it’s in the right place and impacts are minimized?

Times and circumstances change.   We should eschew regulations that are no longer applicable and enact regulations that reduce risks to public safety and protect our properties, infrastructure and natural resources such as shallow groundwater and soil. These resources are vital to our safety and well-being and that of future generations. We believe we all have a responsibility to see that these resources are not squandered and that private development doesn’t increase public risks.



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City Council will vet Marriott Plans on June 12, 6 pm, City Hall

No one has failed to notice there’s a building boom in Palo Alto. And there are several projects with two levels of underground construction already started or in the pipeline. So what is unique or different about the Marriott hotels proposed for San Antonio Road and why should we be concerned?

Marriott proposes to open two hotels with a two level garage on a 1.9-acre site at 744-750 San Antonio Road (between Leghorn and Middlefield). The Courtyard by Marriott and AC by Marriott Hotels would total 294 rooms and each would be five stories high. The neighborhood is primarily residential and one-story businesses such as Summerwinds Nursery. The proposed underground parking garages fill the property and allow little room for trees, shrubs or landscaping.

Save Palo Alto’s Groundwater is specifically concerned about the plan to build two levels of underground garage – a total of 82,660 ft² – in an area where the groundwater level is 7 – 11 feet below ground surface, according to their geotechnical report. Last year a single-level residential basement of 3, 500 ft² with a similar groundwater level pumped out more than 30 million gallons during construction. This area is more than twenty times larger, and part of the underground construction is twice as deep. Maybe they’ll be extra careful when pumping and not discharge 600+ million gallons of groundwater but it’s still going to be a lot of water. At the same time over a million cubic feet of soil will be removed to accommodate the two-level garage. The Final Environmental Impact Report (FEIR) does not quantitatively analyze the impacts on groundwater at all, but rather summarily dismisses such concerns as “no significant impact.”

We believe that this project requires much more careful vetting of its underground construction plans than it has received thus far. The amount of soil and groundwater to be removed under the proposed construction is significantly large enough to impact our aquifer, infrastructure, neighboring properties and the amount of soil available for future storm water mitigation.

City Council will discuss and decide whether to approve the Final Environmental Impact Report for 744-748 San Antonio Road on Monday, June 12, 6 pm at City Hall, 250 Hamilton Ave. We plan to be there and voice our concerns. Please join us and the neighbors from Greenhouse One and Greenhouse Two and let City Council know your opinion about this project. If you can’t attend, you can contact the City Council at [email protected]

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City 2017 Dewatering Map Now Online

The City has updated the online map of dewatering sites.  You can easily find the location of Palo Alto’s 2017 dewatering sites by clicking the Maps link on the right-hand side of this page.  As of May 31st, yellow marks indicate pending, green indicates pumping, red indicates completed.

Palo Alto Dewatering Site Map, 5/31/0217

Note that dewatering impacts can extend 200 – 400 feet (about 1 city block) from the dewatering site.  See the graph on our Feb. 5, 2017 blog, “Building basements without wasting water”.  Neighbors have mentioned cracked walls, cracked windows and cracked walkways, doors that stick, trees that died a few months after dewatering ended, etc.  If you notice any such impacts on your property, please let us know by entering a reply/comment at the bottom of this page, or send us an e-mail at [email protected]

Also, we consider dewatering to be “localized drought” for the neighboring properties. This article in the Mercury News  and this article in the Business Insider explain drought mitigation for properties.  Caveat emptor!


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Palo Alto’s new dewatering policy effective May 4, 2017

Palo Alto’s new dewatering policy takes effect on May 4, 2017.  The stated goal for this new policy is to minimize the discharge of groundwater from construction dewatering; it applies to projects that do not have their building permits as of May 4th.  Application forms and information for applicants and contractors are available in the section titled “Construction Dewatering Plan Guidelines” on the City’s website.  You can see the City’s map of pending dewatering sites for 2017 here. The new dewatering policy is summarized below.

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