4-6-DA27008-2619055 Approved Fault Line Study.pdf

FAULT STUDY

PROPOSED EVIDENCE WAREHOUSE

4451 SOUTH 2700 WEST

TAYLORSVILLE, UTAH

PREPARED FOR:

DFCM - STATE OF UTAH

4315 SOUTH 2700 WEST, 3 FLOORRD

TAYLORSVILLE, UTAH 84129-2128

ATTENTION: ROB ROBINSON

PROJECT NO. 1250534 SEPTEMBER 30, 2025

AGC.,CAGC.,C

Applied Applied GeoTechGeoTech

600600 WWesest t SSandy andy Parkway Parkway • • SSandy, andy, Utah Utah 84070 84070 • • (801) (801) 566-6399 566-6399 • • www.agecinc.comwww.agecinc.com

TABLE OF CONTENTS

PURPOSE AND SCOPE OF INVESTIGATION. . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1

GEOLOGIC AND SEISMOTECTONIC SETTING. . . . . . . . . . . . . . . . . . . . . . . . . Page 1 A. Regional Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1 B. Tectonic Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2

SITE DESCRIPTION AND CONDITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2

OFFICE METHODS OF INVESTIGATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3

FIELD METHODS OF INVESTIGATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 A. Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 B. Subsurface.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4

CONCLUSIONS AND RECOMMENDATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5

LIMITATIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7

FIGURES

GEOLOGIC MAP FIGURE 1

FAULT TRENCH AND MINOR FAULT LOCATIONS FIGURE 2

TRENCH LOG FIGURES 3-6

PURPOSE AND SCOPE OF INVESTIGATION

This report presents the results of a fault study for the proposed building to be constructed at 4451 South 2700 West in Taylorsville Utah. The site is located in an area recommended for fault study by the Utah Geological Survey (Utah Geological Survey, 2025).

The study was conducted to determine if there is evidence of potentially active faults extending through or near the proposed building area. The study included a review of geologic literature, aerial photographs and lidar data, site reconnaissance, subsurface exploration and geologic analysis. This report has been prepared to summarize the data obtained during the study and to present our conclusions and recommendations. The study was performed in general accordance with our proposal dated July 21, 2025.

GEOLOGIC AND SEISMOTECTONIC SETTING

A. Regional Geology

Taylorsville is located in the Basin and Range province. The province is made up of north/south elongated mountain blocks and valleys. Taylorsville is located on the eastern edge of Basin and Range province with the Oquirrh and Wasatch Mountains partially bounding the valley on the west and east, respectively.

The site is located within the Salt Lake Valley. The valley was once occupied by a large lake known as Lake Bonneville during the Wisconsin glaciation of the

Pleistocene. The present day Great Salt Lake is a remnant of ancient Lake Bonneville.

Stillstands of Lake Bonneville formed benches along the Wasatch Front. The highest level of Lake Bonneville is marked by a bench, the Bonneville Shoreline, at approximate elevation 5160 to 5200 feet. The lake remained at this high level from approximately 18 to 17 thousand years before present, until it dropped

APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC. 1250442

approximately 350 feet during a catastrophic flood known as the Bonneville Flood

(Currey and Oviatt, 1985; Jarrett and Malde, 1987). Two lower still stands of Lake

Bonneville are the Provo and Gilbert, which formed at approximate elevations 4850 and 4250 feet, respectively (Personius and Scott, 1992). There is no evidence that the lake has risen above the site elevation since at least 13,000 years ago (McKean, 2019).

Based on topography from the US Geological Survey 7½ minute Salt Lake City South quadrangle map, the approximate elevation of the site is 4304 feet, placing the site approximately 54 feet above the Gilbert shoreline.

B. Tectonic Setting

The site is located southeast of the Great Salt Lake along the Granger Fault of the

West Valley fault zone, which is considered an active fault system. The closest mapped surface trace of a fault, part of the Granger Section of the West Valley fault zone, is located approximately 167 feet west of the western edge of the proposed building (McKean, 2019).

SITE DESCRIPTION AND CONDITIONS

At the time of our field study, the site consisted of a grass covered field.

The ground surface at the site is relatively flat with a gentle slope down to the northeast.

Vegetation at the site consists of grass. There are some trees along the western edge of the property.

There are sheds and paved storage areas to the east, a parking lot to the west, a State building to the north and a continuation of the field to the south.

OFFICE METHODS OF INVESTIGATION

Geologic conditions at the site were evaluated by a review of geologic literature, aerial photographs and lidar data. Aerial photographs reviewed were downloaded from the Utah

Geological Survey Aerial Imagery Database. Stereo-pair photographs reviewed are dated

September 19, 1937 with Photo Numbers 10-AAL 1-103 and 104, May 27, 1958 with

Photo Numbers AAL 11V-62, 63 and 64, and low-sun-angle photographs dated 1970 with

Photo Numbers WF-N 5-6-98 and 99. Lidar data used during the investigation were downloaded from the Utah AGRC website. The lidar data is 0.5-meter bare-earth DEMs acquired for the State in 2023. Geologic literature reviewed includes the Utah Geological

Survey Geologic Hazards Portal, surficial geologic maps by Personius and Scott (1992) and

McKean (2019).

The general geology of the area is presented on Figure 1. The surface geology is mapped by McKean (2019) to consist of Quaternary silt and clay of upper Pleistocene age (Qlf). The

1958 aerial photos show a quarry or borrow pit to the west of the site. The 1970 photos show the quarry expanding eastward toward the site. The sediment encountered consisted of lake sediments consistent with mapping by McKean (2019). Thus, we interpret at least the deeper sediments exposed in the trench to have been deposited in Lake Bonneville.

McKean (2019) shows the surface trace of a fault, part of the Granger Fault located approximately 167 feet west of the eastern edge of the proposed building. Fault offset is down to the east. The mapped surface trace of the fault appears to be consistent with that identified by review of the aerial photographs. The ground has been modified north and south of the site, obscuring evidence of the fault scarp.

FIELD METHODS OF INVESTIGATION

A. Surface

A site reconnaissance was performed to evaluate the surface geology at the site and vicinity, but due to development of the project site and surrounding areas, we found no evidence of the fault scarps.

B. Subsurface

A trench was excavated on August 28, 2025 at the approximate location indicated on Figure 2 using a backhoe. The location of the trench was determined using a tape measure. The trench was logged by geologists from AGEC. A log of the subsurface conditions encountered in the trench is presented on Figures 3 through 6.

The soils encountered in the trench consist of approximately ½ to 4 feet of fill overlying lean clay with thin silt and sand layers. Some of the sand layers were logged for the length of the trench and found to be continuous across the full length of the trench. Offsets of the sand layers were up to approximately 2 inches, typically down to the east. Locations of offset sediments projected up to the ground surface are presented on Figure 2. The trend of the offset sediments appear to generally be consistent with the mapped orientation of the Granger Fault.

The natural soils encountered in the trench are interpreted to represent Lake

Bonneville sediments that were deposited in the lake at least 13,000 years ago.

CONCLUSIONS AND RECOMMENDATIONS

There were thin sand layers with offsets up to approximately 2 inches encountered in the trench. Salt Lake County defines an active fault as having offset of 4 inches or greater. No building setback is required for faults with offset less than 4 inches. Thus, no building setback is required for the proposed building from these offset sediments, but the structural engineer should design the building to withstand similar type movements as presented on the trench logs. Should this not be practical then a different site should be considered for the proposed building. The sediments encountered in the fault trench are considered to be at least 13,000 years old and thus old enough to identify Holocene faults that may be of concern for siting the proposed building. Based on our findings, placing the proposed building at the location indicated on Figure 2 should avoid fault rupture hazard of greater than those identified in the trench. Fault movements similar to those observed in the trench can be expected at the site during a major seismic event on the Granger Fault.

LIMITATIONS

The analysis and report findings are based on published geologic maps and reports, aerial photographs and lidar data of the site, the trench excavated at the approximate location indicated on Figure 2 and our interpretation of geologic conditions at the site. Our conclusions are based on currently accepted geologic interpretation of this information. The geologic log of the trench presented in this report depicts geologic conditions only along the specific corridor and to the depth excavated. The log does not necessarily reflect geologic conditions at other locations or at greater depths. No attempt has been made to predict earthquake ground motions or to determine the potential magnitude for earthquakes associated with faults in the area.

The trench was backfilled without compactive effort and not placed uniformly or tested for compaction. The backfill in the trench should be removed and be properly compacted where it will support proposed buildings, slabs, pavements and other settlement-sensitive features planned for the site.

APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC.

Trae D. Boman, G.I.T.

Reviewed by Douglas R. Hawkes, P.E., P.G.

TDB/rs

9-30-2025

REFERENCES

Currey, D.R. and Oviatt, F.G., 1985; Durations, average rates and probable cause of Lake Bonneville expansion, stillstands and contractions during the last deep-lake cycle 32,000 to 10,000 years ago; in Diaz, H.F. (ed.), Problems of and prospects for predicting Great Salt Lake levels, Proceedings for NOAA conference; Center for Public Affairs and Administration, University of Utah, Salt Lake City, Utah.

Jarrett, R.D. and Malde, H.E., 1987; Paleodischarge of the late Pleistocene Bonneville Flood, Snake River, Idaho, computed from new evidence; Geological Society of American Bulletin,

v. 99, p. 127-134.

Lund, W.R., Christenson, G.E., Batatian, L.D., and Nelson, C.V., 2020; Guidelines for evaluating surface-fault-rupture hazards in Utah, in Bowman, S.D., and Lund, W.R., editors, Guidelines for investigating geologic hazards and preparing engineering-geology reports, with a suggested approach to geologic-hazard ordinances in Utah, second edition: Utah Geological Survey Circular 128, p. 31–58.

Machette, M.N., Personius, S.F. and Nelson, A.R., 1987; Quaternary geology along the Wasatch fault zone; segmentation, recent investigations and preliminary conclusions; U.S.

Geological Survey Open-file Report 87-585, p. B1 - B124.

McKean, A.P., 2019; Geologic map of the Salt Lake City South quadrangle, Salt Lake County, Utah, Utah Geological Survey Map 283DM. 1:24,000 scale.

Personius, S.F. and Scott, W.E., 1992; Surficial geologic map of the Salt Lake City segment and parts of adjacent segments of the Wasatch fault zone, Davis, Salt Lake, and Utah Counties, Utah, US Geological Survey Miscellaneous Investigations Series Map I-2106.

1:50,000 scale.

Salt Lake County, 2002; Surface Rupture and Liquefaction Potential Special Study Areas Map, Salt Lake County, Utah, adopted March 31, 1989, updated March 2002, Salt Lake County Public Works - Planning Division, 2001 South State Street, Salt Lake City, Utah.

Utah Geological Survey, 2025; Geological Hazards Portal accessed August 27, 2025 at https://maps.geology.utah.gov/hazards/.

SITE

Qlf

Qlf

1250534 Geologic Map Figure 1

EXPLANATION OF SYMBOLS AND GEOLOGIC UNITS IN AREA OF PROPOSED DEVELOPMENT

Qh - Fill and disturbed land (Historical).

Qlf - Lacustrine silt and clay (upper Pleistocene).

Qlg - Lacustrine gravel and sand (upper Pleistocene).

Geologic contact between units, dashed where approximate.

Normal fault, bar and ball on down thrown side, dashed where approximate, dotted where concealed.

10000 2000 feet Approximate Scale from McKean (2019)

PROPOSED EVIDENCE BUILDING

4451 SOUTH 2700 WEST

TAYLORSVILLE, UTAH

AutoCAD SHX Text N

AutoCAD SHX Text N

El ev at io n/ fe et

Distance/feet

100 20 30 40 50 60 70

WESTEAST

Top of Trench

11A 1A

Bottom of Trench FAULT 1 Displacement: 1" Dip: 65° Strike: 170° SE

FAULT 2

Displacement: 1" Dip: 95° Strike: 5° NE

1250534 Trench Log Figure 3

LEGEND:

Topsoil; 0-6", lean clay, moist, medium stiff, dark brown, roots.

Silty Sand; slightly moist, light brown, slight iron oxide staining.

Fill; lean clay, medium stiff to stiff, slightly moist to moist, brownish gray.

Lean Clay; cemented with calcium carbonate in upper approximately 2 feet, moist to very moist, medium stiff to stiff, dark brown to brownish gray, slight iron oxide staining.

Silty Sand; medium stiff to stiff, orangish brown, slight iron oxide staining.

1A

1B at io n/ fe et

Distance/feet

8070 90 100 110 120 130 140

WESTEAST

Top of Trench

1 1

1A 1A

Bottom of Trench

FAULT 3

Displacement: 1.5" Dip: 80° Strike: 145° SE

FAULT 4

Displacement: 1¼" Dip: 80° Strike: 10° NW

FAULT 5

Displacement: 1½" Dip: 80° Strike: 35° NW

See Figure 3 for Legend and Notes

1250534 Trench Log Figure 4 at io n/ fe et

Distance/feet

150140 160 170 180 190 200 210

WESTEAST

Top of Trench

FILL

1A

1A

Bottom of Trench

FAULT 6

Displacement: ½" Dip: 75° Strike: 210° SE

FAULT 7

Displacement: 1" Dip: 85° Strike: 0° N

FAULT 9

Displacement: 1" Dip: 75° Strike: 170° SE

FAULT 8

Displacement: ½" Dip: 80° Strike: 170° SE

FAULT 10

Displacement: 2" Dip: 80° Strike: 10° NW

1250534 Trench Log

Figure 5 at io n/ fe et

Distance/feet

220210 230 240 250 260 270 280

WESTEAST

Top of Trench Top of Trench

Gap due to waterline

1B 1A

Bottom of Trench Bottom of Trench

1250534 Trench Log Figure 6