Proposed 2018 dewatering regulations for below ground construction are on City Council’s consent calendar for Monday, Dec. 11th, 7 pm, City Council Chambers, 250 Hamilton. City Council accepts written and oral comments from the public on any item on the consent calendar. It does not, however, discuss items on the consent calendar. It will therefore vote on, but not discuss, revisions to the dewatering ordinance this coming Monday.
In 2017 cut-off walls for three residential basements were successfully used with zero to minimal amounts of groundwater placed in the City’s storm drains. While these work very well to reduce the waste of groundwater, Save Palo Alto’s Groundwater does not request that cut-off walls be mandated for all below ground construction that requires dewatering. Cut-off walls have disadvantages, including use of potable water during construction, construction impacts, increased amount of soil unavailable for stormwater retention and possible interference of the cut-off walls with groundwater flows, these last two leading to increased risk of flooding.
Staff’s proposed 2018 dewatering regulations add the following requirements that address some impacts of construction dewatering to the current ordinance : a) Construction work must be continuous during the dewatering period, b) A pre-building survey and report on structures on adjacent parcels must be submitted, c) After an 8-week dewatering period trucking of water to irrigation sites increases from 1 to 5 days/week.
We have heard from various neighbors, builders and other stakeholders that the proposed Dewatering Ordinance needs improvement in several areas:
- According to the Oct. 23, 2017 Public Meeting Groundwater Assessment Use slides, the estimate of the “safe yield” of groundwater for Palo Alto is 2,500 acre ft. /year. This “safe yield” is the total amount of groundwater that may be pumped for any purpose per year, including groundwater for emergency situations, and should be incorporated in any Ordinance and Plan that allows groundwater pumping.
- Require large commercial and residential sites to install cut-off walls to dramatically reduce required pumping. Specifically address the coming Marriot hotels on San Antonio Road that could conceivably pump up to 2,900 acre-feet of groundwater with broad area dewatering.
- Require sites in or near contaminated ground water plumes to install cut-off walls (to reduce the spreading of the contaminant plume).
- Improve the use of broad area dewatering by specifying “Best Practices” when designing pumping systems (such as a limit on flow rate of 60 gpm).
- Include clear metrics and avoid case-by-case requirements and exemptions in the regulations.
- Require data in the hydrogeology report that helps design a dewatering system with lower flow rates.
- Address pumping and impacts to groundwater flows for railroad trenches and tunnels.
- Consider the cumulative impact of all below ground construction and dewatering.
The following is an excerpt from Staff’s response to some of our concerns: “In response to the issues raised by Save Palo Alto’s Groundwater, Staff believes that the appropriate course of action is to adopt the proposed Ordinance enhancements now, and consider the other suggested changes after the New Year. We concur that more work on this topic is needed, especially with respect to large commercial sites. But it is critical to get the proposed changes in place now for residential sites, to provide certainty for designers, and to avoid more “grandfathering “ of residential sites as has occurred in the past. Most of the new sites will be residential, not commercial, as in past years.”
We are requesting Council to a) approve the ordinance revisions on the consent calendar and b) as proposed by Staff, direct Staff to follow-up with additional amendments to the Dewatering Ordinance in Q1 2018.
Whether you are a homeowner whose property has been impacted by dewatering, an environmentalist who believes we should protect our groundwater, an emergency services volunteer who believes we’ll need groundwater for future droughts, a homeowner/builder who believes regulations are too onerous, etc. we invite you to attend the City Council meeting on Dec.11th at 7 pm and make your voice heard.
Thank you for your interest and your support.