(a) Compliance with regulations. Where temporary construction-related groundwater dewatering will be required, applicants shall conduct dewatering in full compliance with the provisions of this chapter, including this section, the regulations established by the city engineer, and all permit conditions. Applicants shall promptly implement corrective actions identified and required by the city engineer, including, but not limited to, directives requiring immediate cessation of discharge.
(b) Types of dewatering. Temporary construction-related groundwater dewatering may be conducted using 1) groundwater exclusionary techniques (e.g., secant wall), or 2) controlled groundwater pumping.
(c) Groundwater exclusionary technique submittal requirements. When groundwater exclusionary techniques will be required or utilized, applicants shall submit to the city engineer a street work permit application, and a dewatering plan and traffic control plan in a form approved by the city engineer.
(d) Groundwater exclusionary technique operational requirements. Temporary construction-related groundwater dewatering through groundwater exclusionary techniques shall be conducted in compliance with the following:
(1) The rate of discharge of groundwater shall be limited to thirty gallons per minute or less.
(2) Groundwater discharge shall be percolated onto the same property where pumping is occurring rather than discharged into the storm drain system, if feasible.
(3) The approved dewatering plan and traffic control plan for the project, approved by the city engineer, shall be followed during dewatering activities. The traffic control plan shall include, among other provisions, an appropriate schedule for an attendant to be present on the street during the period of the installation of groundwater exclusionary technique.
(4) Discharge of groundwater to the city storm drain or sanitary sewer systems shall only occur from April 1 through October 31. The city may grant an exemption and allow discharge from November 1 through March 31, upon application, if:
(A) The discharge is limited to an average of ten gallons per minute over a twenty-four hour period and other conditions warrant allowance of discharge; or
(B) It is demonstrated that a ten year storm event can be accommodated by the receiving storm drain system and water system to the satisfaction of the city engineer.
(C) Any such exemption granted under subsections (A) or (B) above shall be subject to immediate cessation orders from the city. A cessation order may be issued for reasons including, but not limited to: capacity issues in the storm drain or sanitary sewer systems; the discharge is causing or contributing to surcharging in the storm drain or sanitary sewer systems; the storm drain or sanitary sewer systems fail; excess flow entering the Palo Alto Regional Water Quality Control Plant; emergency or routine maintenance of city infrastructure; and protection of the environment, public health, safety and welfare. The applicant shall immediately comply with any cessation order issued.
(5) The applicant shall install a groundwater monitoring well, and during the construction period of the underground structure, submit periodic groundwater level and other measurements and reports as required by the city engineer. During pumping, the groundwater monitoring water level shall be measured at a monitoring well located at a farthest feasible point on the subject site from the underground structure. This monitoring shall be conducted daily for the first two weeks, then weekly thereafter.
(6) Designs and plans submitted to the city engineer for approval shall incorporate all of the requirements hereinabove.
(e) When controlled groundwater pumping required. If the rate of groundwater discharge is greater than thirty gallons per minute, the requirements of subsections (f) and (g) below shall be followed.
(f) Controlled groundwater pumping submittal requirements. When controlled groundwater pumping will be required, applicants shall submit the following to the city engineer:
(1) The applicant shall prepare and submit a street work permit application, a dewatering plan and a groundwater use plan, all in a form approved by the city engineer. The groundwater use plan shall show how the groundwater will be used to the maximum extent practicable and incorporate the operational requirements of subsection (h) below.
(2) The applicant shall submit a dewatering hydrogeological study conforming to the regulations issued by the city engineer, adhere to the study's findings, and make modifications as directed by the city engineer. Avoidance measures identified in the study shall be employed to the maximum extent practicable to minimize the flow rate and duration of the pumping, even when off-site effects are not specifically identified. The dewatering hydrogeological study shall be stamped by a California licensed hydrogeologist or equivalent and submitted to the city.
(3) The applicant shall submit a pre- construction building condition survey and report on structures on adjacent parcels prepared by a qualified professional and meeting the standards established by the city engineer. The survey shall include a photographic and narrative report on the interior and external condition of each structure and surveyed and marked elevations of adjacent parcels, with particular attention to the condition of concrete foundations, structural connections, brickwork, plasterwork and other architectural finishes that are susceptible to cracking. The report shall assess the likelihood that the proposed dewatering would cause effects (including but not limited to settlement or movement) on off-site private or public structures or infrastructure, including the right-of-way, easements, and utilities within public utility easements, and the health or viability of vegetation or trees. To the extent that report concludes that off-site effects are reasonably likely to occur, the applicant shall identify avoidance measures to be implemented that will minimize the type and severity of those effects, and shall develop a monitoring plan to assess any actual effects on vegetation, trees, structures and infrastructure.
(g) Controlled groundwater pumping operational requirements. Temporary construction-related groundwater dewatering through controlled groundwater pumping shall be conducted in compliance with the following:
(1) Dewatering shall only occur April 1 through October 31, if discharge to the storm drain or sanitary sewer system is required. The city may grant an exemption and allow discharge from November 1 through March 31, upon application, if it is demonstrated that a ten year storm event can be accommodated by the receiving storm drain system and water system to the satisfaction of the city engineer. Any such exemption shall be subject to immediate cessation orders from the city, which shall be complied with immediately upon issuance.
(2) Groundwater pumping for underground residential structures shall be limited to ten weeks, with an additional two week start-up period. At the end of the start-up period, the applicant must demonstrate compliance with all performance and water quality standards established by the city engineer.
(3) The applicant shall verify the anticipated drawdown curve in the dewatering hydrogeological study with a pump test performed on monitoring wells installed on the project site, as specified by the city engineer. Following the two-week start-up period, the dewatering, pumping rates and maximum amount of water pumped on a daily basis shall be limited to the values calculated in verification study.
(4) Fill station(s) shall be designed to provide the minimum delivery flowrates and incorporate instructional and public safety signage in accordance with the regulations issued by the city engineer.
(5) The applicant shall deliver pumped groundwater to any nearby parks and schools as requested by the city.
(6) The applicant shall truck water one full day (eight hours) per week from the project site to irrigation sites as directed by the city during the first six weeks of dewatering activities (not including the two-week start-up period). The applicant shall truck water five days per week (eight hours per day) during the remainder of the dewatering period.
(7) The applicant shall allow adjacent properties to use hoses connected to the fill station(s). If used, applicant must set up hoses with bridges along sidewalks. Hoses shall be placed in a manner that is safe to the public and does not cause damage to neighboring or city property, and shall not cross the street. The city engineer may modify these requirements as circumstances require.
(8) Prior to the commencement of dewatering activities, the applicant shall notify occupants of neighboring properties of the temporary construction and availability of water.
(9) The applicant shall use the pumped groundwater on-site for dust suppression and other construction needs.
(10) Prior to pouring a basement slab, groundwater may be pumped no deeper than three feet below the depth of the slab, measured at the center. After the slab is poured, groundwater may be pumped no deeper than one foot below the center.
(11) The applicant shall install a groundwater monitoring well prior to the commencement of dewatering, and during the construction period of the underground structure, submit periodic groundwater level and other measurements and reports as required by the city engineer.
(A) During pumping, the groundwater monitoring water level shall be measured at a monitoring well located at a farthest feasible point on the subject site from the underground structure. This monitoring shall be conducted daily for the first week, then weekly thereafter. At the end of the start-up period or thereafter, if drawdown results are greater than anticipated, the applicant shall submit a revised dewatering hydrogeological study and any revised conclusions on impacts of the groundwater drawdown.
(B) Survey and mark land elevations on structures on adjacent parcels weekly, if allowed by the adjacent property owners. These locations should coincide with the pre-construction building condition survey. If permission is not granted, inform the city immediately.
(12) While discharging to the storm drain system, construction work on the underground structure shall be continuous, occurring daily, and make progress towards completion of the underground structure without delay.
(h) City engineer authority to issue regulations. The city engineer is authorized to establish and from time to time revise regulations to implement this section and related provisions of this chapter and to advance the goals of minimizing temporary construction-related dewatering and reducing its impacts.
(Ord. 5425 § 5, 2018: Ord. 5410 § 5, 2017)