LA-01286-14_RoseBowlPlumbing_UtilityRecsLtr_8-13-2026.pdf
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- Solicitation number
- 2026-RFP-0504
- Issued by
- Los Angeles County, California
About this file
This is a geotechnical engineering recommendations letter prepared by Earth Systems Pacific for the Rose Bowl Operating Company regarding utility infrastructure improvements at Rose Bowl Stadium in Pasadena, California. The letter, dated August 13, 2026, provides geotechnical input for proposed water, sewer, and gas distribution system replacements and rehabilitation work beneath the stadium concourse. The recommendations are based on previous geotechnical reports dating back to 2009 and the firm's experience with excavations and utility construction at the Rose Bowl since 2010. The project involves utility trenches for plumbing infrastructure rehabilitation, with work to be performed at an operating stadium that remains in continuous event use throughout construction. The document references three utility maintenance project plan sheets provided by Kimley-Horn dated August 6, 2026, covering water, gas, and sewer details.
The geotechnical letter identifies subsurface conditions consisting of undocumented artificial fill materials placed during the 1920s stadium construction, with varying depths and compositions including trash and debris-laden fill outside the stadium perimeter fence and relatively clean, poorly compacted fill within the stadium area. Key geotechnical recommendations include standard excavation techniques in accordance with Cal/OSHA standards, temporary trench laying back or shoring per Cal/OSHA type C soil requirements, over-excavation and recompaction of 12 inches beneath utility trench bottoms to 95 percent maximum dry density, use of geogrid in areas with debris-laden fill, clean sand pipe bedding, and backfill compaction procedures. The letter specifies that site soil may be reused for backfill after processing to remove deleterious materials and particles greater than 3 inches, with alternative options for flowable fill or controlled low strength material. Earth Systems Pacific representatives are to review utility plans and observe trench conditions prior to excavation, with compaction testing required during backfill operations.
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August 13, 2026 File No.: LA-01286-14 Project No.: 303128-008 Kimley-Horn 660 South Figueroa Street, Suite 2050 Los Angeles, California 90017
Attention: Mr. Patrick Wong
Subject: Geotechnical Recommendations for Utility Trenches Proposed Plumbing Infrastructure Rehabilitation Rose Bowl Stadium
1001 Rose Bowl Drive Pasadena, California
References: Preliminary Geotechnical Engineering Report, Proposed Press Box Additions and New
Tunnels, The Rose Bowl Stadium, Pasadena, California, by Earth Systems Southern California, LA-01286-01, dated August 28, 2009.
Addendum No. 1 Geotechnical Engineering Report, Proposed Press Box Additions and New Tunnels, The Rose Bowl Stadium, Pasadena, California, by Earth Systems Southern California, LA-01286-01, dated December 6, 2010.
Report of Density Test Results, Final Report, The Rose Bowl Stadium, Pasadena, California, by Earth Systems Southern California, LA-01286-03, dated August 3, 2016.
INTRODUCTION
Earth Systems Pacific (Earth Systems) has prepared this letter at your request to provide geotechnical engineering input for the proposed various utility infrastructure improvements at the Rose Bowl.
These recommendations are based on the information in the above-referenced geotechnical reports as well as Earth Systems’ experience in excavations and utility construction at the Rose Bowl since 2010. The following plan sheets were provided to Earth Systems:
Water Maintenance Project, Water Details, Sheet CW4.0, by Kimley-Horn, 8/6/2026.
Gas Maintenance Project, Trench Details, Sheet CG4.0, by Kimley-Horn, 8/6/2026.
Sewer Maintenance Project, Sewer Details, Sheet CS4.0, by Kimley-Horn, 8/6/2026.
August 13, 2026 2 File No. LA-01286-14 Project No. 303128-008
SUBSURFACE CONDITIONS
Undocumented artificial fill materials placed during and prior to the 1920’s construction of the Rose Bowl is present throughout the Rose Bowl and the surrounding parking lots. Fill present primarily outside the Rose Bowl stadium concourse/fence line were found to be relatively deep (potential over 20 feet in some areas) and contain large amounts of trash and debris. Sink holes and various areas of settlement are evident in pavements to the south and west of the Rose Bowl stadium. The soil portions of that fill are generally silty sand with gravel and cobbles, (SM soil type based upon the Unified Soil Classification System (USCS). The old debris-laden fill is unsuitable for support of structures and can be problematic for settlement sensitive utilities or any proposed infrastructure.
Undocumented artificial fill soils within the Rose Bowl area were mostly placed during the original stadium construction in the 1920’s and are generally free of debris. However, it was placed before current engineering compaction standards were developed, are poorly compacted and contain abundant oversize material (cobbles and boulders). The fill within the stadium area is primarily silty sand and gravelly sand with cobbles and some boulders (SW, SW-SM, and SM soil types). The thickness of the fill within the stadium is typically about two to four feet below field level based on the available subsurface data. Beneath the concourse, the fill is typically about two to 15 feet thick with the deeper fills toward the southern side.
The approximate depths of fill as observed in subsurface explorations and construction excavations are indicated on the Site Exploration Map (Plate I).
The compacted fills placed during recent construction activities since 2010 are generally free of debris and oversize material and were documented in the above referenced Report of Density Test Results by Earth Systems Southern California (ESSC, 8/3/2016).
The natural quaternary alluvial soils below the fill are predominantly gravelly sand with cobbles and boulders with some interbedded layers of silty sand (SW, SW-SM, and SM soil types). The natural soils were observed to be medium dense to dense. The gravel, cobbles and boulders were observed to be generally sub-rounded to well-rounded and up to three feet in maximum dimension.
DISCUSSION
Outside the concourse area (outside the perimeter stadium fence), particularly south and west of the Rose Bowl stadium, trash and debris-laden fills should be anticipated and have a severe potential for settlement of utilities and other infrastructure. There are less areas of trash and debris-laden fill within the concourse and the Rose Bowl stadium structure, and thus the potential for settlement of buried utilities is considered very low.
It is not necessary to over-excavate to the full depth of existing fills under the proposed utilities.
However, over-excavation and recompaction of at least one foot beneath the bottom of utility trenches will help mitigate some settlement potential. In areas of old trash and debris-laden fill
August 13, 2026 3 File No. LA-01286-14
(primarily outside the Rose Bowl stadium perimeter fence), placement of geogrid at the bottom of trenches (above recompacted zone but beneath bedding) will help mitigate the potential for settlement of underground utilities.
The fill and natural soils are very rocky and generally cohesionless; therefore, utility trenches will need to be laid back or shored to avoid caving.
GEOTECHNICAL RECOMMENDATIONS
A. Excavations
1. Standard construction techniques should be sufficient for temporary site excavations. All excavations should be made in accordance with applicable regulations (including Cal/OSHA).
Project safety is the responsibility of the contractor and the owner. Earth Systems will not be responsible for project safety.
2. Temporary trench excavations should be laid back or shored in accordance with Cal/OSHA standards for type C soil.
3. No excavation should be made within a 1.5H:1V (~34-degree) line projected downward from the toe of any existing footing or structure unless supported by properly engineered and installed shoring.
4. During the time excavations are open, vehicles or other surcharge loads (i.e. excavation spoils) should be allowed within a horizontal distance from the top of any slope equal to the depth of the excavation (both distances measured from the top of the excavation slope).
5. Adequate measures should be taken to protect any structural foundations, pavements, or utilities adjacent to any excavations.
6. The earth material anticipated to be exposed in the excavations is comprised of sandy and gravelly soil with rounded cobbles and boulders. The material may be excavated with conventional earth moving equipment; however, some breaking may be necessary and caving should be anticipated.
B. Utility Installation and Trench Backfill
1. The soil beneath the bottom of the trench may be over-excavated to a depth of 12 inches and recompacted as indicated. Over-excavation and recompaction is especially recommended where the base of the trench is in old undocumented fill. The fill should be compacted to 95% of maximum dry density per ASTM D1557. However, testing can only be accomplished if adequate safety measures (e.g., shoring and egress) are in place.
August 13, 2026 4 File No. LA-01286-14
2. The Earth Systems’ representative should review the utility plans prior to trench excavation and observe the bottoms and side walls of the trenches. Local variations in soil conditions may warrant increasing the depth of over-excavation. Any deeper areas of loose soils should be removed and be replaced as compacted, engineered fill.
3. In areas where poorly compacted trash and debris-laden fill is present beneath the utility trench, a layer of geogrid may be placed at the base of the trench to help mitigate differential settlement of the utility pipe. Geogrid should be a biaxial or triaxial product made of high-density polyethylene (HDPE) or polypropylene (such as Tensar BX or TX geogrids or similar).
4. Pipe bedding should consist of clean sand. Bedding consisting of washed concrete sand
(ASTM C33 Fine Aggregate or equivalent) as indicated is acceptable and typical.
5. After pipe installation, the pipe should be “shaded in” by backfill beneath the haunches of the pipe and over the pipe using the same or similar clean sand as the bedding. The sand should be densified by jetting or flooding. The densification should be observed by the geotechnical engineer’s representative but need not be tested for compaction.
6. The excavated site soils may be reused to backfill utility trenches above the pipe “shading” provided they are processed to remove any deleterious materials, debris, particles greater than 3 inches maximum dimension, and are properly moisture conditioned and compacted.
7. During replacement of excavated soils in utility trenches, the soils should be moisture-conditioned to near optimum moisture content and be uniformly compacted to at least 95% of the maximum dry density as determined by ASTM D 1557 test procedures using mechanical compaction equipment. To aid in the compaction operation, fill should be placed in lifts not exceeding 8 inches compacted thickness. Compaction should be verified by testing.
8. As an alternative to sand bedding and trench backfill, flowable fill consisting of “concrete slurry” or “controlled low strength material – CLSM” may be used. Slurry or CLSM should be a high-slump low-strength material to fill all voids beneath the haunches of the pipe. It should be excavatable when hardened and should conform to the requirements of the “Greenbook” Standard Specifications for Public Works Construction.
August 13, 2026 5 File No. LA-01286-14
CLOSURE
See the referenced Geotechnical Reports (ESSC, 8/28/2009 and 12/6/2010) for exploration logs, test results, and more detailed subsurface information.
Earth Systems trusts this report is sufficient at this time and meets your current needs. Earth Systems appreciates this opportunity to provide professional geotechnical engineering services for this project. If you have any questions regarding the information contained in this report, or if you require additional geotechnical engineering services, please contact the undersigned.
Respectfully submitted, Earth Systems
Mark L. Russell, P.E., G.E. Christopher F. Allen, P.G., E.G.
Project Geotechnical Engineer Project Engineering Geologist
Plate I - Site Exploration Map with Fill Depths Plate II - Recommended Utility Trench Detail
Distribution: Patrick Wong - Patrick.Wong@kimley-horn.com mailto:Patrick.Wong@kimley-horn.com
T U
N N
E L
A
T U
N N
E L 7A
T U
N N
E L
TUNNEL 10
T U
N N
E L
PRESS BOX STRUCTURE
BASE MAP FROM CENTRAL COAST AERIAL MAPPING, INC. PHOTO DATE 5/5/2009
LEGEND
SITE EXPLORATION MAP
APPROXIMATE BORING LOCATION
(ESSC, 2009)
APPROXIMATE TEST PIT LOCATION
(ESSC, 2009)
APPROXIMATE BORING LOCATION
(MACTEC, 2005)
APPROXIMATE BORING LOCATION
(LAW/CRANDALL, 1997)
APPROXIMATE BORING LOCATION
(LAW/CRANDALL, 1993)
APPROXIMATE BORING LOCATION
(LEROY CRANDALL, 1990)
APPROXIMATE TEST PIT LOCATION
(LEROY CRANDALL, 1990)
APPROXIMATE BORING LOCATION
(LEROY CRANDALL, 1982)
APPROXIMATE TEST PIT LOCATION
(LEROY CRANDALL, 1982)
APPROX. DEPTH OF NON-ENGINEERED
FILL BELOW EXISTING GRADE (FEET)
AND APPROX. TOP OF NATIVE SOIL
ELEVATION (FEET MSL) - AT BORING.
APPROX. DEPTH OF NON-ENGINEERED
FILL BELOW EXISTING GRADE (FEET)
AND APPROX TOP OF NATURAL SOIL
ELEVATION (FEET MSL) - OBSERVED
FROM RECENT GRADING.
N
APPROXIMATE
NORTH TP4
B1
APPROXIMATE SCALE
1 inch = 120 feet
60 120060 240
C
2 1
F~4+/797
F~11/808
Plate I
ROSE BOWL STADIUM
1001 ROSE BOWL DRIVE
PASADENA, CALIFORNIA
AUGUST 2026 303128-008
Earth Systems
F~4+/828
F~3+/821
F~5+/819
F~3+/812
F~5+/810 F~4+ / 825
F~7+/813
F>13 / <800
F~20+/800
F~20+/800
F~1+/799
F~3+/797
F~15+/805
F~2+ / 798
F>13/ <800
F~2+/798
F~2+/799
F~3+/819
F~7+/815
F~3+/797
F~6+/794
F~4+/796
F~3+/797
F~4+/797
F~2+/797
F~4+/795 F~2+/798
F~4+/797
F~3+/797
F~11/808
F~9/816 F~6/822
F~7/823
F~4/826
F~2/823
F~2/814
F>6/<804
F>6/<802
F>6/<810
F~9/810
F~9/811
F~7+/>800
F~15+/>795
A
C
B
2 1
B1
B2
TP1
TP2
TP3
TP10
TP8
TP9
TP5
TP4
TP7
TP6
TP11
B3
TP12
TP13
TP14
T U
N N
E L
B1(2013)
B2(2013)
REMOVE AND RECOMPACT
12-INCHES EXISTING SOIL
COMPACTED SAND BEDDING
“SHADE” PIPE WITH SAND
TO >3” ABOVE TOP OF PIPE
(DENSIFY BY JETTING
OR FLOODING)
BACKFILL ABOVE PIPE “SHADING”
WITH SITE SOIL SCREENED
TO REMOVE PARTICLES >3”
COMPACT IN LIFTS TO MIN 95%
OF MAX DRY DENSITY
REMOVE AND RECOMPACT
12-INCHES EXISTING SOIL
PAVEMENT SECTION
(ASPHALT OR CONCRETE AND BASE)
FINISHED GROUND SURFACE
UTILITY TRENCH DETAIL
Earth Systems
NOT TO SCALE
Plate II
BIAXIAL OR TRIAXIAL GEOGRID
(IN AREAS OF UNDERLYING
DEBRIS-LADEN FILL)
ROSE BOWL STADIUM
1001 ROSE BOWL DRIVE
PASADENA, CALIFORNIA
AUGUST 2026 303128-008
| LA-01286-14_Plate I Site Exploration Map with Fill Depths.pdf |
| Page 1 |
| LA-01286-14_Plate II RoseBowl_UtilityTrenchDetail_8-6-2026.pdf |
| Page 1 |
File details come from the government source that posted it. Updated .