HomeMy WebLinkAboutAttachment 8H - Supplemental Geotechnical Fault InvestigationGROCON
INCORPORATED
GEOTECHNICAL • ENVIRONMENTAL MATERIALSO
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone 858.558.6900 • Fax 858.558.6159
Project No. G2755-42-01
November 15, 2021
VWP-OP Nirvana Owner, LLC
2390 East Camelback Road, Suite 305
Phoenix, Arizona 85016
Attention: Mr. Steven Schwarz
Subject: SUPPLEMENTAL GEOTECHNICAL FAULT INVESTIGATION
NIRVANA PROPERTY
821 MAIN STREET
CHULA VISTA, CALIFORNIA
References: 1. Preliminary Geotechnical Investigation, Nirvana Industrial Buildings and Self-
Storage Complex, 821 Main Street, Chula Vista, California, prepared by Geocon
Incorporated, dated September 14, 2021 (Project No. G2755-42-01).
2. Update Geotechnical Report and Grading Plan Review, Energy Park, Chula Vista,
California, prepared by Advanced Geotechnical Solutions, Inc., dated September 29,
2014 (Report No. 1404-05-B-2).
Dear Mr. Schwarz:
In accordance with your request, we have performed a supplemental geotechnical investigation to
evaluate the presence or absence of a segment of the La Nacion Fault which is shown transecting the
site on regional fault maps and United States Geological Survey (USGS) databases.
The La Nacion Fault Zone is comprised of a series of north and northwest trending fault segments
mapped west and south of Interstate 805 and Interstate 8, respectively. The relative age of displacement
on all segments of the fault is listed in the USGS fault database as “Undifferentiated Quaternary (<1.6
million years). Active faults, as defined by the State of California, are faults with known displacement
within the last 11,700 years and are typically mapped within State delineated “Earthquake Fault
Zones.” Proposed development within an Earthquake Fault Zone requires a fault study to obtain
development approval from the local governing agency. The La Nacion Fault is not mapped within an
Earthquake Fault Zone, as defined by the State of California. Locally, the City of San Diego Seismic
Safety Study maps show all segments of the La Nacion fault as “Potentially Active” implying possible
displacement within the last 100,000 years, however, these maps are only applicable to areas within the
San Diego City limits.
The USGS database shows a segment of the La Nacion Fault transecting the western edge of the site
with the designation “location inferred,” implying that no direct field evidence is available supporting
the presence of the fault segment in the mapped location. The regional San Diego geologic map
(Kennedy and Tan, 2008) shows the fault segment mapped in the same location as the USGS database.
However, the regional geologic map depicts the fault as “concealed,” implying it is not visible at the
Geocon Project No. 06931-42-07 - 2 - November 15, 2021
ground surface (or inferred at the ground surface by juxtaposed unconformable geologic units) and is
buried by surficial geologic units such as the Older Alluvium or Terrace Deposits mapped at the site
(References 1 and 2). The Terrace Deposits at the site are interpreted as middle to late Pleistocene in
age, or between approximately 12,000 and 1.8 million years old, substantially older than the State
definition of an active fault.
Figure 1 shows the locations of fault trenches performed by Advanced Geotechnical Solutions (AGS;
Reference 1; TP-1), and by Geocon Incorporated (FT-1; excavated on November 4, 2021). Fault trench
locations and the fault trench log for FT-1 are presented on Figure 1. AGS did not provide a fault trench
log in Reference 1.
Based on our field logging, there is no evidence of faulting or offset in the Pleistocene age Terrace
Deposits exposed in our fault trench excavation. Our field observations support the conclusions
presented in the referenced geotechnical reports. Therefore, we opine that the La Nacion fault segment
depicted on regional maps and fault databases is not active as no evidence of faulting in Pleistocene age
sediments has been observed on the site. The La Nacion fault segment, if present at the site, is confined
to the Oligocene age Otay Formation (approximately 23 to 34 million years old) that underlies the
Quaternary Terrace Deposits at the site and will not impact site development. A fault setback for the
proposed development is not required.
If you have any questions regarding this letter, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Rodney C. Mikesell
GE 2533
Rupert S. Adams
CEG 2561
RCM:RSA:arm
Attachments: Figure 1
(e-mail) Addressee
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DISTANCE (FEET)
SCALE: 1" = 5' (Vert. = Horiz.)
FAULT TRENCH FT-1
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140
0
5
10
15
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35
145 150
1
1
1
2A-2
2D
2D
3
2B
2A-1
2A-1
2B
2D
2C
EXISTING
GRADE
EXISTING
GRADE
N55ºE
135.1
134.4
134.2
133.5
133.2
132.4
132.2
131.5
130.7
133.8
134.7
133.8
133.1
131.8
131.2
130.2
129.7
219.9
194.2
185.5
181.3
176.7
185.6
187.6
211.2
219.2
218.8
218.3
219.6191.7
190.5
187.7
179.2
180.9
168.7
175.2
144.4
142.3
166.9
165.3
164.7
166.3
165.4
163.9
165.5
163.7
218.7
LOT 23
MAP 8147 LOT 22
MAP 8147 LOT 21
MAP 8147
LOT 3
MAP 8147
PARCEL 1
PM 21587
1
2
3
3
4
4
5
N 87°34'46" W 1356.85'
(
N
8
7
°
3
4
'
0
8
"
W
1
3
5
6
.
6
6
'
R
2
)
N 02°25'25" E 0.13'
749.13'
N
0
0
°
2
7
'
0
5
"
E
4
2
4
.
2
3
'
(
N
0
0
°
2
7
'
2
8
"
E
4
2
4
.
2
4
'
R
2
)
L =2 9 9 .2 0 ' R =2 0 6 4 .0 0 ' D =8 °1 8 '2 0 " M &R 2
N 82°38'33" E
3
7
3
.
1
3
'
(
N
8
2
°
3
8
'
3
6
"
E
3
7
3
.
1
5
'
R
2
)
NW COR
SW 1/4 NW 1/4 SEC 20
2'1
2
0
'
1
4
24'13
24
'
12
24'2
3 4
34'
34'
12'
(131.82 FG)
183.0 TW
141.2 FG
H=41.8'
183.1
TW 162.5
FG
H=20.6'
186.9 TW
183.5 BW
H=4.4'
MAIN STREET
2
:
1
2
:
1
2
:
1
205.7 TW
184.5 FG
H=22.2'
184.00 TW
184.00 FG
H=0'
180.9
TW 155.6
FG
H=25.3'
180.9 TW
139.4 FG
H=41.5'
205.7 TW
183.5 FG
H=23.2'
187.0 TW
183.3 FS
H=3.7'
MOD. TYPE A-6
CO
135.32 TOP
183.75 FS
5%
INDUSTRIAL BLDG 2
185.25 FFINDUSTRIAL BLDG 1
184.25 FF
182.9 TW
141.4 FG
H=41.5'
183.0 TW
143.5 FG
H=40.5'
184.0 TW
184.0 BW
H=0'
H=3.6'
B
Qal
Qt
Qt
Qt
To
To
Qal
Qt
T-5 T-4
T-6
TP-2
TP-4
TP-3
TP-1
To
To
To
?
?
?
?
?
?
?
?
?
?
?
?
??
?
D
LB-3
LB-2
LB-1
TP-5
TP-6 APPROX. FRONT
LIMIT OF CLAYBED
REMOVAL
FT-1
Plotted:11/15/2021 12:34PM | By:RUBEN AGUILAR | File Location:Y:\PROJECTS\G2755-42-01 (Nirvana Self Storage)\SHEETS\G2755-42-01 FaultTrench.dwg
PROJECT NO.
SCALE DATE
FIGURE
SHEET OF
GEOLOGIC MAP AND FAULT TRENCH LOG
NIRVANA INDUSTRIAL BUILDINGS AND SELF STORAGE COMPLEX
821 MAIN STREET
CHULA VISTA, CALIFORNIA
50'11 - 15 - 2021
G2755 - 42 - 01
1 1 1 FLANDER7 DRI:E 7AN DIEGO CALIFORNIA
PHONE FA<
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
T-6
TP-7
B-2
........UNDOCUMENTED FILL
........ALLUVIUM
........TERRACE DEPOSITS
........OTAY FORMATION
........APPROX. LOCATION OF GEOLOGIC CONTACT
........APPROX. LOCATION OF EXPLORATORY LARGE DIAMETER
BORING (Current)
........APPROX. LOCATION OF EXPLORATORY BORING
........APPROX. LOCATION OF EXPLORATORY TEST PIT (Current)
........APPROX. LOCATION OF EXPLORATORY TEST PIT (AGS, 2014)
........APPROX. LOCATION OF EXPLORATORY TEST PIT (AET, 2008)
........APPROX. LOCATION OF GEOLOGIC CROSS SECTION
........APPROX. LOCATION OF PROPOSED SUBDRAIN
........APPROX. SURFACE EXPOSURE OF BENTONITIC CLAYSTONE
........APPROX. LOCATION OF FAULT TRENCH
GEOCON LEGEND
Qudf
G G'
Qal
Qt
To
LB-5
TP-8
FAULT TRENCH LEGEND
........Stiff to hard, dry to damp, dark brown to brownish-black Sandy CLAY (CH); trace subrounded gravel, abundant roots.
Strong ped development throughout. Stage II carbonate development along bottom contact with underlying Terrace Deposits.
Topsoil
2A-1 ........Stiff, damp, brown, reddish-brown to dark brown Sandy Clay (CH); massive, trace subrounded gravel, abundant caliche pods and
stringers, few roots. Interbedded with large horizontal lenses of olive brown to dark brown Clayey Gravel (GC) up to four feet thick.
Gravel and cobble is subrounded, up to 5 inches in max. dimension. Occasional discontinuous laminated medium to coarse grained
sand lenses are present within the gravel lenses. Boundary between 2A-1 and 2A-2 is gradational.
2A-2 ........Dense, damp, grayish brown to pale yellowish-brown, Silty, very fine Sand and Stiff Sandy Clay (SM/CL); moderately laminated,
occasional isolated fine gravel. Occasional horizontal caliche stringers present parallel to laminations. Boundary between 2A-1 and
2A-2 is gradational.
2B ........Firm to stiff, damp, light brown to olive brown Clayey Siltstone (ML-CL); massive, with occasional horizontal thin, coarse sand and
fine gravel lenses.
2C ........Dense, dry to damp, grayish brown to pale yellowish-brown, fine to coarse Sand (SP); laminated and cross-bedded. Low cohesion.
2D ........Medium dense to dense, brown to grayish brown Silty and clayey gravel (GM-GC); Cobble is moderately imbricated, up to 14 inches
in maximum dimension present. Represents a Lag Deposit. Caliche stringers present where close to existing grade at west end of trench.
........APPROX. LOCATION OF GEOLOGIC CONTACT
........APPROX. LOCATION OF INTRAFORMATIONAL UNITS
Terrace Deposits (Qt)
........Stiff to hard, dry, dark reddish-brown Claystone (CH); blocky, fractured with caliche stringers throughout.Otay Formation (To)
FT-1
1
3