Attachment 4: Geotechnical Recommendation TM

Technical Memorandum

Geotechnical Recommendation Report
Date:

May 30, 2025

Jacobs Government Services Company

Project Name:

Replacement of South Rim
Wastewater Treatment Plant (GRCA 257282)

Project No.:

D3167666

Attention:

Mike Ryan/NPS
Christopher Carpenter/NPS

4 Embarcadero Center

Suite 3800
San Francisco, CA 94111
United States

Client:

National Park Service- Grand Canyon National Park

Prepared by:

Maddie Heidari/Jacobs

Reviewed by:

Nason McCullough, PE/Jacobs
Kathy Rosinski, PE/Jacobs

T +1.415.356.2040
F +1.415.356.2055
www.jacobs.com

Expires: 3/31/2027

1.

Introduction

This report was prepared for the GRCA 257282 Replace Wastewater Plant South Rim Village project. As part of the geotechnical evaluation, two geotechnical explorations were conducted for the project, one focused on wastewater treatment plant area, and one based on the access road improvement. The Preliminary Geotechnical Recommendation Report for Replace Wastewater Plant South Rim Village was prepared by Shannon & Wilson in April 2022 (Attachment 1) for the wastewater treatment plant area. The report summarizes:
 Subsurface conditions encountered during the exploration program completed on January 17 and 18, 2022
 Laboratory test results
 The geotechnical engineering recommendations
Shannon & Wilson completed the work as a subconsultant to Jacobs Government Services Company (Jacobs) under Professional Service Task Order 148027714 dated October 1, 2021. The Preliminary Geotechnical Report (Shannon & Wilson 2022) was prepared during the early phase of the project. Because Jacobs is the engineer of record for the final design, Jacobs has reviewed the Preliminary Geotechnical Report and prepared this technical memorandum (TM) to document updates and design decision changes that affect the Preliminary Geotechnical Report. The following items in the Preliminary Geotechnical Report have changed, and are documented herein:  The list of proposed new facilities in the Preliminary Geotechnical Report was updated to the current facility list documented in Table 1 and Figures 1 and 2.  The Construction Considerations - Earthwork recommendations of the Preliminary Geotechnical Report have been modified as discussed in Section 3.
All other engineering recommendations are as presented by Shannon & Wilson.

Jacobs Government Services Company
240620104000_c797e258

Technical Memorandum
The Geotechnical Report for South Rim WWTP Access Road was prepared by Shannon & Wilson in January