February 4, 2026
Mr. Neema Ghanbari, PE
Public Works Director
City of Hawaiian Gardens
21815 Pioneer Boulevard
Hawaiian Gardens, CA 90716
Subject: Proposal to Provide Professional Engineering and Geotechnical Services for Citywide Infiltration Testing
Dear Mr. Ghanbari:
Willdan Engineering (Willdan) is pleased to submit this letter proposal to provide professional engineering and geotechnical services for citywide infiltration testing.
The City of Hawaiian Gardens is evaluating the feasibility of stormwater infiltration to support dry well implementation and related LID/GI (Low Impact Development/Green Infrastructure) objectives. The project requires (1) review of existing subsurface information (well logs, soils and geotechnical reports), (2) targeted field exploration and geotechnical/infiltration testing to characterize near-surface and intermediate-depth percolation potential, and (3) screening and selection of candidate dry well locations using the City’s Storm Drain Master Plan in conjunction with measured infiltration rates, utilities constraints, and site access/safety.
Key considerations include shallow groundwater conditions typical of the lower Los Angeles Basin, variable alluvial stratigraphy (including potential interbedded fine-grained soils), proximity to existing storm drain infrastructure, separation from utilities and foundations, water quality protection, and compliance with applicable County/Regional standards. The outcome will be a practical, defensible basis for dry well siting—prioritizing locations with sufficient infiltration capacity, appropriate vertical separation to seasonal high groundwater, and minimal conflicts with existing facilities—plus recommended design infiltration parameters and next-step design guidance.
The following is our proposed scope of work and fee: OF W O
Attachment A
Citywide Infiltration Testing
February 4, 2026
SCOPE OF WORK
Task 1 – Project Management and Meetings
1. Conduct all tasks necessary to complete the project, including day-to-day project management, meetings, progress reports, project communication and agency follow-up, project scheduling and tracking, invoicing, and overall administration of the project.
2. Attend a pre-design (kick-off) meeting with the City’s representatives to review the project, in detail, to determine the City’s specific requirements concerning the project.
3. Attend up to two (2) staff level meetings/conference calls to discuss project issues and status for the various design submittal stages.
4. Maintain continuous communication with the City Project Manager, including meetings to review project status at 100% completion.
5. Proactively initiate communications with the City Project Manager and/or staff when questions arise due to inconsistency in the flow of work production.
Task 2 – Geotechnical Report
Percolation testing will be performed at multiple locations to a depth of 50-60 feet each, following the County of Los Angeles Department of Public Works Administrative Manual GS200.2 (dated June 30, 2017).
Percolation testing will be conducted using the falling head method in 8-inch diameter borings, minimum 10 feet above detected water level. Each test hole will be equipped with a 3-inch diameter perforated PVC standpipe surrounded by a gravel filter pack. The holes will be pre-soaked to establish near-equilibrium moisture conditions before testing.
Water-level drops will then be measured and recorded at consistent intervals to determine the infiltration (percolation) rate.
Representative bulk soil samples will be collected from the borings for geotechnical laboratory testing to assess relevant engineering properties. After completing the field and laboratory work, a comprehensive geotechnical report will be prepared summarizing:
Site conditions and test procedures,
Laboratory test results,
Citywide Infiltration Testing
February 4, 2026
Calculated percolation/infiltration rates,
Historical groundwater information, and
Conclusions and recommendations relevant to the project design.
If groundwater is found between 15 and 50 feet, the drilling will be stopped and the percolation test performed at a depth 10 feet above the location where groundwater was found. If groundwater is found at shallower than 15 feet, drilling will be stopped and will proceed at the next location.
Task 3 – Hydrology Summary
Willdan will review the geotechnical results and utilize them to determine the feasibility of the dry well locations. If the dry wells are determined to be feasible Willdan will complete the following scope.
1. Willdan will review the locations adjacent to the percolation testing locations and determine the best locations for dry wells.
2. Willdan will perform hydrologic calculations based on the above tributary areas and determine the Water quality runoff flows. The confirmed runoff will be utilized to confirm ultimate LID improvements and discuss findings with Hawaiian Gardens.
Willdan will prepare an H&H memo consistent with Hawaiian Gardens and Los Angeles County Hydrology Manual Standards summarizing the results of the above analysis. The H&H Memo will outline the existing conditions and present the proposed dry well locations.
Exclusions
• We will not be completing any construction documents with this project. • We are not conducting a storm drain master plan. They hydrology analysis will be limited to 2-3 large drainage areas near each of the percolation tests that are successful.
• We anticipate 3 geotechnical borings only.
• We assume that we will not need Environmental permitting • We assume there is no hazardous soil
• Traffic control plans will not be required.
• Utility potholing is not required
Citywide Infiltration Testing
February 4, 2026
SCHEDULE
Willdan anticipates the draft geotechnical to be completed within 6 weeks from Notice-toProceed. This assumes that we will obtain the drilling permit from the LA County Department of Public Health and City of Hawaiian Gardens within 2 weeks of NTP.
FEE
We propose to provide the engineering design services outlined in our proposed Scope of Work for a time and materials not-to-exceed fee of $65,000.
Task 1 – Project Management $ 5,250
Task 2 – Geotechnical Investigation $ 51,500
Task 3 – Hydrology and Hydraulic Analysis and Memorandum $ 8,250 Total $ 65,000
As a time and materials contract, the city will only be billed for the effort actually performed. If infiltration is deemed infeasible in the field, we anticipate the costs will be substantially reduced.
Please indicate the City’s approval and authorization to proceed by either printing out and signing two originals and returning one hard copy to our office, or by scanning one signed original and returning it by e-mail.
Thank you for the opportunity to be of service to the City of Hawaiian Gardens. We recognize the importance of this project to the City and are committed to realizing its timely and successful completion. Should you have any questions regarding this proposal, please contact myself at (714) 393-1963 or Mr. Matt Crim at (714) 945-8477 or [email protected].
Respectfully submitted, Approval and Authorization to Proceed by:
WILLDAN ENGINEERING CITY OF HAWAIIAN GARDENS
Tyrone Peter, PE
Director of Engineer Ernesto Marquez, City Manager
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