Capital Improvement Project 3 (CIP3) Sanitary Sewer Extension

iambert and Associates

CONSULTING GEOTECHNICAL ENGINEERS AND MATERIAL TESTING

GEOTECHNICAL SITE CHARACTERISTIC STUDY
PROPOSED CIP3 SEWER UPGRADE
MONTROSE, COLORADO

Prepared for:
CITY OF MONTROSE ENGINEERING DEPARTMENT

PROJECT NUMBER: M26005GE
MARCH 18, 2026

P.O. Box 3986 P.O. Box 45
Grand Junction, CO 81502 Montrose, CO 81402
(970) 245 6506 (970) 249 2154

Diambert and Associates

CONSULTING GEOTECHNICAL ENGINEERS AND MATERIAL TESTING

March 18, 2026
City of Montrose Engineering Department
P.O. Box 970
Montrose, Colorado

Attention: - Mr. Scott Murphy, P.E. PN: M26005GE

Subject: Geotechnical Site Characteristic Study for the
Proposed CIP3 Sewer Upgrade Project
Montrose, Colorado

Mr. Scott Murphy, P.E.:

Lambert and Associates is pleased to present our geotechnical site characteristic study for
the subject project. The field study was completed February 16, 2026. The laboratory
study was completed on March 11, 2026. The analysis was performed and the report
prepared March 11 through March 18, 2026. Our report is attached.

This report does not present site and structure specific design parameters. Lambert and
Associates is available to be the geotechnical engineer for the project and provide material
testing services to maintain continuity between design and construction phases.

If you have any questions concerning the information presented in this report for your
project please contact us. Thank you for the opportunity to perform this study for you.

Respectfully submitted; -_- YS

)
a oo
LAMBERT AND ASSOCIATES a

P.O. Box 3986 P.O. Box 45
Grand Junction, CO 81502 Montrose, CO 81402
(970) 245 6506 (970) 249 2154

M26005GE

TABLE OF CONTENTS
1.0 INTRODUCTION Page 1
1.1 Proposed Construction 1
1.2 Scope of Services 4
2.0 SITE CHARACTERISTICS 2
2.1 Site Location 3
2.2 Site Conditions 3
2.3 Subsurface Conditions 4
2.4 Site Geology 5
2.5 Seismicity 5
3.0 PLANNING AND DESIGN CONSIDERATIONS 5
4.0 ON-SITE DEVELOPMENT CONSIDERATIONS 7
4.1 Compacted Structural Fill 8
4.2 Backfill 9
4.3 Soil Corrosivity to Concrete 10
5.0 PRE-DESIGN AND PRE-CONSTRUCTION CONSIDERATIONS 10
5.1 Structural Fill Quality 11
6.0 LIMITATIONS 12
FIELD STUDY Appendix A
KEY TO LOG OF TEST BORING Figure A1
LOG OF TEST BORINGS Figures A2 - A8
LABORATORY STUDY Appendix B
GEOLOGY DISCUSSION SOUTHWEST
COLORADO GEOLOGY Appendix C

GENERAL GEOTECHNICAL ENGINEERING
CONSIDERATIONS Appendix D

M26005GE

1.0 INTRODUCTION

This report presents the results of the geotechnical site characteristic study we conducted
for the proposed CIP3 Sewer Upgrade project. The study was conducted at the request
of Mr. Scott Murphy, P.E., City of Montrose Engineering Department, in general
accordance with our proposal dated January 23, 2026.

The conclusions, suggestions and recommendations presented in this report are based on
the data gathered during our site and laboratory study and on our experience with similar
soil conditions. Factual data gathered during the field and laboratory work are summarized
in Appendices A and B.

1.1 Proposed Construction

It is our understanding the proposed construction will include approximately 4,800 feet of
sewer line upgrades/improvements.

1.2 Scope of Services

Our services for this Preliminary Geotechnical Site Characteristic Analysis and Pavement
Study included the following scope of our services as outlined below.

- The field study included observing, describing and sampling the soil materials
encountered in seven (7) small diameter continuous flight auger test borings in the
general vicinity of the proposed sewer line upgrades/improvements. Test boring
locations were determined and marked by City of Montrose Engineering
Department.

- The field study consisted of describing and sampling the soil materials encountered
in small diameter continuous flight auger test borings. Site conditions restricted and
somewhat dictated the location of the test borings.

- The soil materials encountered in the test borings were described and samples
retrieved for the subsequent laboratory study.

P.O. Box 3986 P.O. Box 45
Grand Junction, CO 81502 Montrose, CO 81402
(970) 245 6506 (970) 249 2154

M26005GE

- The laboratory study included tests of select soil samples obtained during the field
study to help assess:

the moisture content of samples tested, and
soil characteristics for soil classification (Atterberg Limits, % - #200).

- This report presents our general feasibility level geotechnical engineering comments
and suggestions for planning and preliminary design of the project improvements
including:

site subsurface soil conditions,

ground water elevation encountered and any special considerations,

trench excavation concerns,

geotechnical engineering considerations and recommendations for compacted
structural fill.

- Ourcomments, suggestions and recommendations are based on the subsoil and
ground water conditions encountered during our site studies.

- Our study did not address environmental or geotechnical engineering design level
issues. Our study did not address site and structure specific soil design
parameters.

2.0 SITE CHARACTERISTICS

Site characteristics include observed existing and pre-existing site conditions that may
influence the geotechnical engineering aspects of the proposed site development.

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING

M26005GE

2.1 Site Location

The site is located from the intersection of 6530 Road and North San Juan Avenue/Hwy
50 to the intersection of South Hillcrest Drive and East Main Street/Hwy 50, Montrose,
Colorado

=e Indicates Approximate
Project Location

Figure 1. Project Location Sketch

2.2 Site Conditions

The majority of the test borings were located adjacent to the existing paved roadways. The
test boring sites were generally landscaped and exhibited surface drainage away from the
paved surfaces.

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING

M26005GE

2.3 Subsurface Conditions

The subsurface exploration consisted of observing, describing and sampling the soil
materials encountered in seven (7) test borings. The approximate locations of the test
borings are shown on Figure 2.

@ Indicates approximate test boring location

Figure 2. Test Boring Location Sketch

The logs describing the soil materials encountered in the test borings are presented in
Appendix A.

The soil materials encountered in the test borings consisted generally of surficial fill
material underlain by native silty clay materials. The silty clay materials were underlain by
granular materials in Test Boring Nos. 2, 3 and 7 at approximate depths of eleven (11) to
eleven and one half (11-1/2) feet below existing site grades. The silty clay materials and
granular materials were underlain by formational shale materials. The formational shale
materials were encountered at approximate depths of seven (7) to eighteen and one half

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING

M26005GE

(18-1/2) feet below existing site grades.

Free subsurface water was encountered at approximate depths of five and one half (5-1/2)
to twenty seven (27) feet below existing site grades. Temporary slotted stand-pipe
piezometers were installed in each test boring to assist in future subsurface water level
measurements.

We anticipate that the free subsurface water may be shallower during wetter
seasons.

It is difficult to predict if unexpected subsurface conditions will be encountered during
construction. Since such conditions may be found, we suggest that the owner and
the contractor make provisions in their budget and construction schedule to
accommodate unexpected subsurface conditions.

2.4 Site Geology

A brief discussion of the general geology of the area near the site is presented in Appendix
C. The surface geology of the site was determined by observation of the surface
conditions at the site and observing the soils encountered in the test borings on the site.

2.5 Seismicity

According to the International Building Code, 2018 Edition, and ASCE Standard ASCE/SEI
7-10, Table 20.3-1 Site Classification, based on the subsurface conditions encountered
and the assumption that the soils described in the test borings are likely representative of
the top 100 feet of the soil profile, we recommend that the site soil profile be S,,, Stiff soil.

3.0 PLANNING AND DESIGN CONSIDERATIONS
A geologic hazard study was not requested as part of the scope of this report.

All of the suggestions and design parameters presented in this report are based on high
quality craftsmanship, care during construction and post construction cognizance of the
potential for swell or settlement of the site support materials, compacted structural fill
materials and appropriate post construction maintenance.

All construction excavations should be sloped to prevent excavation wall collapse. We

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING

M26005GE

typically suggest that as a minimum the excavation walls should be sloped at an inclination
of one-and-one-half (1-1/2) to one (1) (horizontal to vertical) or flatter. The area above the
excavations should be observed at least daily for evidence of slope movement during
construction. If evidence of slope movement is observed we should be contacted
immediately.

We anticipate that excavation and fill placement operations may be associated with the
proposed site development. Excavations in the area which generate vertical or sloped
exposures should be kept to a minimum.

Excavations which result in cut slopes with a vertical height greater than about four (4) feet
or with a slope or structure above should be analyzed on a site specific basis. Temporary
excavation cut slopes in competent material should not exceed a one-and-one-half to one
(1 -1/2 to 1) (horizontal to vertical) inclination. All construction excavations should conform
to Occupational Safety and Health Administration (OSHA) standards, Part 1926 Subpart
P App A and B, or safer. All permanent slopes should be constructed with inclinations of
three to one or flatter.

Slope and excavation surfaces should be protected by vegetation and/or other means to
prevent erosion. Surface runoff should not be allowed to cascade over the top of a slope
or to pond at the toe of any slope.

Generally, fill material placed on a site surface which will be used to support structures or
additional fill material should be placed so that the contact between the existing site
surface and the added fill material will be strong enough to support the added load. This
should be addressed on a site and fill area specific basis. The technique recommended
will be based on the site configuration, the finished fill configuration the actual material to
be used for the fill material and the size of the area thus constructed. Frequently the
preparation of the site area to receive fill material will include removing organic and loose
near surface native material in the area to receive fill material, placing the material in thin
horizontal lifts which are compacted at the appropriate moisture content. Some fill areas
could benefit from the installation of a subsurface drain system at the fill material/natural
material contact. We are available to, and recommend that, we discuss this with you and
provide site and fill specific recommendations when this portion of your development plan
merits the additional study.

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING

M26005GE

4.0 ON-SITE DEVELOPMENT CONSIDERATIONS

We anticipate that the subsurface water elevation may fluctuate with seasonal and other
varying conditions. Excavations may encounter subsurface water and soils that tend to
cave or yield. If water is encountered it may be necessary to dewater construction
excavations to provide more suitable working conditions. Excavations should be well
braced or sloped to prevent wall collapse. Federal, state and local safety codes should be
observed. All construction excavations should conform to Occupational Safety and Health
Administration (OSHA) standards or safer.

The site construction surface should be graded to drain surface water away from the site
excavations. Surface water should not be allowed to accumulate in excavations during
construction. Accumulated water could negatively influence the site soil conditions.
Construction surface drainage should include swales, if necessary to divert surface water
away from the construction excavations.

Organic soil materials in areas to receive fill material or structural components should be
removed. The organic soil materials are not suitable for support of the structure or
structural components.

Ithas been our experience that sites in developed areas may contain existing subterranean
structures or poor quality man placed fill. If subterranean structures or poor quality man
placed fill are suspected or encountered, they should be removed and replaced with
compacted structural fill as discussed under COMPACTED STRUCTURAL FILL below.

The soil materials exposed in the bottom of the excavation may be moist and may become
yielding under construction traffic during construction. It may be necessary to use
techniques for placement of fill material which limits construction traffic in the vicinity of the
very moist soil material. If yielding should occur during construction it may be necessary
to construct a subgrade stabilization fill blanket or similar to provide construction traffic
access. The subgrade stabilization blanket may include over excavating the subgrade soils
one (1) to several feet and replacing with aggregate subbase course type material. The
stabilization blanket may also include geotextile stabilization fabric at the bottom of the
excavation prior to placement of aggregate subbase course stabilization fill. Other
subgrade stabilization techniques may be available. We are available to discuss this with
you.

CONSULTING GEOTECHNICAL ENGINEERS
AND MATERIAL TESTING