Notice to Owners/Applicants planning to Dewater and Construct Basements in Palo Alto in 2016

News Release

Notice to Owners/Applicants planning to Dewater and Construct Basements in Palo Alto in 2016

The City of Palo Alto is considering changes to requirements associated with basement dewatering and construction for the 2016 construction season. The new requirements, if adopted, will likely require applicants to provide additional information in order for the Grading Permit to be issued when dewatering is anticipated during construction. To avoid delays in the issuance of such Grading Permits, City Staff are recommending that Owners/Builders who expect to process applications for construction in 2016 begin to assemble this additional information now. It is anticipated that the required information would need to be submitted in a report prepared by a qualified professional, and would at a minimum, include the following:

1. Describe alternative construction methods considered by the owner/applicant and explain why dewatering is proposed for the project.

2. Submit the following information:

  • Depth to groundwater, maximum depth of excavation (including utilities, pits, shafts, etc.) and proposed maximum depth of dewatering wells/pumping.
  • Description of dewatering technique, including:  location of dewatering wells, size and anticipated flow from each pump. Include a schematic diagram showing pipe and pump sizes and locations and sizes of all tanks, fill station,  pipe route to nearest storm drain inlet (including flexible and rigid pipe locations), and all street and sidewalk impacts including trenching, sawcuts, and asphalt patching between project site and storm drain inlet.
  • Anticipated dewatering flow rate and total dewatering duration.
  • Controls to be utilized (e.g., settling tank, turbidity curtain, etc.)
  • Location of anticipated discharge including final receiving water (Creek name or Bay)
  • All wells and other dewatering sites within a 400 foot radius (roughly one City block) of the property that may interact with dewatering activity, using information available from the City. State or show the exact location of these dewatering sites.
  • Determine the radius of influence (i.e. extent of cone of depression) from each dewatering well as a function of time, based on local soil and groundwater conditions. Prepare a map and cross sections of the cone(s) of depression.  State whether it is reasonably likely that the proposed dewatering will cause effects (including settlement or movement) on off-site structures or infrastructure, including the right or way, easements, and utilities within public utility easements. State whether it is reasonably likely that the proposed dewatering will reduce the amount of water taken up by any vegetation or trees to a level that will affect the health or viability of the vegetation or trees. Utilize an Urban Forestry Sub Consultant (certified arborist) to verify any such effects on trees.

3. To the extent that the qualified professional states that off-site effects are reasonably likely tooccur, identify avoidance measures to be implemented that will minimize the type and severity of those effects. Avoidance measures are also to be employed to the extent practical to minimize the flow rate and duration of the pumping, even when off-site effects are not specifically identified.Avoidance measures may include, for example: reducing well count, well depth, well location, pumping rate, and/or duration of pumping; supplemental irrigation of trees or vegetation, soil amendment, or other plant protection methods recommended by a certified arborist; alternative dewatering or construction methods.

4. Develop a monitoring plan to assess any actual effects on vegetation, trees, structures and infrastructure.

5. The geotechnical study and description and extent of the cone of depression must be stamped by a California licensed Geotechnical Engineer and submitted to the City. This report will be made available for public review.

In addition to this determination the following new requirements will apply, if adopted, to basement construction dewatering:

6. Construction of a fill station per Public Works Specifications and public outreach/signage to encourage its use. The City will expand fill station specifications that must be implemented by contractors to address water pressure issues from multiple concurrent users, including separate pumps for neighbors where needed, a flow meter with data logger and sidewalk bridges for hoses to reduce tripping hazards.  City inspectors will inspect fill stations to ensure compliance with specifications.

7. The City will implement additional requirements for Groundwater Use Plans.  These additional requirements include maximizing on-site water reuse (e.g. watering on-site and nearby vegetation), at least one day per week water truck hauling service for neighbor and City landscaping, and piping to nearby parks or major users where feasible.

The Palo Alto City Council is currently scheduled to discuss basement dewatering requirements at its February 1, 2016 meeting. For more information please contact the Public Works Department at 650.329.6951

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Peter Pirnejad
Director, Development Services Department