HomeMy WebLinkAboutItem 6b. Authorize On-call Engineering Professional Services for Seismic Study and Geotechnical InvestigationCity of San Luis Obispo, Title, Subtitle
Whale Rock Commission Report
Whale Rock Commission Meeting – May 28, 2026
Agenda Item 6b – Authorize On-call Engineering Professional Services for a Seismic Study and Geotechnical
Investigation of Whale Rock Dam
FROM: Shawna Scott, Assistant Director of Utilities
PREPARED BY: Noah Evans, Whale Rock Reservoir Supervisor
SUBJECT: AUTHORIZE ON-CALL ENGINEERING PROFESSIONAL
SERVICES FOR A SEISMIC STUDY AND GEOTECHNICAL
INVESTIGATION OF WHALE ROCK DAM
RECOMMENDATION
Authorize selection of a consultant from the City of San Luis Obispo’s Qualified Civil
Engineering On-Call Consultant List to provide engineering professional services
including a seismic study and geotechnical investigation of the Whale Rock Dam, and
issuance of a purchase order, and any subsequent change orders, in an amount not
to exceed the total authorized budget of $550,000.
DISCUSSION
Background
In September of 2025 staff received a letter from the
Division of Safety of Dams (DSOD) requiring several
studies and assessments of the Whale Rock Dam
(Attachment A). In this letter, the DSOD directs the
Whale Rock Commission to perform a “high-quality
subsurface exploration” of the dam, followed by a
“static and seismic stability evaluation” using “modern
methods and standards for dams”.
Seismic and stability evaluations and subsurface
exploration of the dam have not been completed using
modern technology and staff understand that modern
methods for analysis and modeling will result in better
understanding of the stability of the dam during
emergency events such as an earthquake. The results
of these studies will be used to confirm the stability of
the dam and to identify potential safety improvements,
if necessary.
WHALE ROCK SPILLWAY WALL OFFSET
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City of San Luis Obispo, Title, Subtitle
Whale Rock Commission Report
Whale Rock Commission Meeting – May 28, 2026
Agenda Item 6b – Authorize On-call Engineering Professional Services for a Seismic Study and Geotechnical
Investigation of Whale Rock Dam
ENVIRONMENTAL REVIEW
The proposed study is exempt from the California Environmental Quality Act (CEQA)
pursuant to State CEQA Guidelines Section 15306 (Information Collection), because
the methods for data collection, evaluation, and analysis will not result in a serious or
major disturbance to an environmental resource and are necessary to inform future
action(s). This exemption includes studies leading to an action which a public agency
has not yet approved, adopted, or funded. The results of the study will identify
potential safety improvements, and these potential projects will be evaluated for
CEQA compliance.
FISCAL IMPACT
Seismic Study and Geotechnical Investigation of Whale Rock Dam
Funding
Category
Contribution
Source
Amount Budgeted Amount
Spent
Capital Asset
Expense
2026-27 CIP
Contributions
$550,000 $0
ALTERNATIVES
The Whale Rock Commission can request that staff issue a Request for Proposals
(RFP) for this work rather than utilize an on-call consultant. On-call consultants have
been selected through a competitive qualifications-based process and use of the on-
call consultant list expedites delivery of this work effort, with the intention of providing
these types of engineering services. Advertisement of an RFP requires additional
staff resources and would delay the project by approximately two months.
Attachments:
A - September 5, 2025, letter from the Division of Safety of Dams
Page 18 of 103
Docusign Envelope lD: E6966E92-1 D48-4478-8O37-AOB402B0FDEA
STATE OF CALIFORNIA - CALIFORNIA NATURAL RESOURCES AGENCY GAVIN NEWSOM, Governor
DEPARTMENT OF WATER RESOURCES
DIVISION OF SAFETY OF DAMS
2720 GAIEWAY OAKS DRIVE, SUITE 3OO
SACRAMENTO, CA 95833-3500
September 5,2025
Mr. Aaron Floyd, Deputy Director
Water Division
Whale Rock Commission
879 Morro Street
San Luis Obispo, California 93401
Whale Rock Dam, No. 1-40
San Luis Obispo Countv
Dear Mr. Floyd:
This is in reply to two letters dated June 14, 2019, and December 12,2024,with
multiple enclosures, from Whale Rock Commission (WRC) to the Division of Safety of
Dams (DSOD) in response to DSOD's letter dated May 24,2017, requesting a
comprehensive condition assessment of the spillway at Whale Rock Dam. The
enclosures reviewed for this response include the SpillwayAssessmenf report (Spillway
Report), by HDR Engineering, lnc. (HDR), dated May 20, 2019, and a final video survey
of the repaired spillway underdrain pipes by Nor-Cal Pipeline Services, dated October 5,
2023.
As discussed in an August 7,2025, call with Whale Rock Supervisor Mr. Noah Evans,
DSOD has reviewed the enclosures and has completed an independent comprehensive
review of the dam. From these reviews, DSOD has identified potential dam safety
concerns related to the dam's seismic stability and hydrologic capacity that will require
WRC to perfornr a comprehensive assessment of the dam system. At a minimum, this
comprehensive assessment must include the following:
1. A static and seismic stability evaluation of the dam using modern methods and
standards for dams.
2. A new high-quality subsurface exploration prior to the required seismic stability
evaluation since the past geotechnical investigations have not thoroughly
characterized the embankment and foundation alluvium.
DWR 9004 (New 8/25)
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Docusign Envelope lD: E6966E92-1 D484478-8O37-A6B402B0FDEA
Mr. Floyd
September 5,2025
Page 2
3. A hydrologic and hydraulic study to verify that the dam can pass the Probable
Maximum Flood (PMF) without overtopping. This needs to include visually
inspecting the condition of the stilling basin and evaluating the feasibility of
inspecting the spillway chute drains that were not previously inspected.
Following the hydraulic analysis, WRC must assess whether the current
condition of the spillway drainage system, given the observed presence of grout
intrusion, reduces the spillway's functionality to safely pass the PMF.
WRC must submit a plan and schedule for performing this comprehensive assessment
to DSOD by December 31 ,2025. This plan and schedule needs to incorporate a plan
for filing an alteration application for the required geotechnical exploration along with the
work plan and associated filing fees.
ln addition, HDR recommended several maintenance-level repairs in the Spillway
Report be performed, which include sealing of cracks and joints, repairing of spalls, and
grinding down wall offsets at joints. As documented during DSOD's recent periodic
maintenance inspection, these repairs have been satisfactorily completed with the
exception of grinding down adverse offsets at spillway walljoints. As required in the
recent inspection report, WRC submitted an August 19,2025,letter with a plan and
schedule to complete this work, which is currently under DSOD review.
HDR also identified an area of seepage in the spillway at Station 2+77. WRC must
inspect this area at least monthly, and any observations of seepage or turbidity must be
incorporated into the dam's annual instrumentation report. WRC needs to continue
performing regular spillway inspections and maintenance, including monitoring previous
repairs and sealing developing cracks to ensure that the spillway can safely pass flows,
and notify DSOD of any change to the spillway, including the projection of spill events.
lf you have any questions or need additional information, you may contact Dam Safety
Engineer Richard Keizer at (916) 612-4802 or Project Engineer lan Maki at
(916) 820-77e5.
Sincerely,
Sh."utu- h^rs for
Erik J. Malvick, Ph.D., P.E., G.E
Division Manager
Division of Safety of Dams
DWR 9004 (New 8/25)
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