HomeMy WebLinkAboutAppendix E.6 - Response to City CommentsProject No. 07516-42-02
May 10, 2023
Tri Pointe Homes
13520 Evening Creek Drive North, Suite 300
San Diego, California 92128
Attention: Mr. Allen Kashani
Subject: RESPONSE TO CITY OF SAN DIEGO REVIEW COMMENTS
NAKANO
SAN DIEGO, CALIFORNIA
References: 1. Project Issues Report, Nakano Discretionary Project, PRJ-1076302, City of San
Diego, Geology Review Comments prepared by Kreg Mills, dated April 21, 2023.
2. Update Geotechnical Investigation, Nakano Property, Chula Vista, California prepared
by Geocon Incorporated dated September 18, 2020 (Project No. 07516-42-02).
3. Addendum Geotechnical Report and Response to City of San Diego Review Comments,
Nakano, San Diego, California, prepared by Geocon Incorporated, dated February 9,
2022 (07516-42-02).
4. Nakano, Grading and Storm Drain, prepared by Civil Sense, Inc., dated May 12, 2022.
Dear Mr. Kashani:
We prepared this letter to respond to City of San Diego LDR-Geology review comments for the subject
project. The review comments pertaining to geotechnical aspects and our responses are presented below.
Issue 50:The project’s geotechnical consultant must submit a geotechnical addendum or update
letter for the purpose of an environmental review that specifically addresses the proposed
development plans, tentative map, and the following:
Response: Based on our review of the referenced plans, the recommendations presented in our
Update Geotechnical Investigation (Reference 2) remain applicable. This response serves
as the requested addendum/update report.
Issue 51:The limits of the proposed development appear to have changed since the submitted report
was prepared. Provide an updated Geologic Map (Figure 2) that shows the current
proposed development. Circumscribe the limits of anticipated remedial grading on the
updated map to delineate the proposed footprint of the project.
Response: Figure 1 is the requested updated geologic map using a CAD file of Reference 4 as the
base map. Figure 1 shows the proposed development and the disturbance limits and limits
of anticipated remedial grading. Cross sections are provided on Figures 2 and 3.
Geocon Project No. 07516-42-02 - 2 - May 10, 2023
Issue 52:The project’s geotechnical consultant should note that while the southern portion of the
site is in Geologic Hazard Category 22 and 52, most of the site appears to be in GHC 32.
Per the submitted Update Geotechnical Investigation, the northwest portion of the site is
underlain by compressible surficial deposits consisting of undocumented fill, topsoil,
colluvium, and alluvium that exceeds 18 feet thick and groundwater may be encountered
on the north side of the property adjacent to the Otay River channel, clarify how the data
from the geotechnical investigation demonstrations the site will not be impacted by
liquefaction potential.
Response: To evaluate the potential for liquefaction and groundwater impacting removals, we
performed three large-diameter borings on the norther edge of the development at the
locations shown on Figure 1 (Borings LD-3 through LD-5). We encountered
undocumented fill overlying alluvium and terrace deposits. Seepage was encountered near
a depth of 33 feet in boring LD-3. The seepage is below the expected removal bottom and
within the underlying terrace deposits. Logs of the borings are appended.
Recommendations provided in Reference 2 are for complete removal of undocumented
fill and young alluvial soils within the project limits and slopes supporting the project.
Based on our exploratory borings, complete removal of undocumented fill and alluvium
is possible within the project limits and along the northern property margin. As such, the
site is not subject to liquefaction provided the grading recommendations provided in the
referenced geotechnical reports are followed.
Issue 53:The project’s geotechnical consultant indicated that landslides are not mapped on the
property or at a location that could impact the site. However, per DMG Open-File Report
95-03, Imperial Beach Quadrangle, Plate 33G, the subject site is identified as Area 4
which is characterized as “most susceptible” to landslide hazards. Clarify how the data
from the geotechnical investigation demonstrates the subject site will not be impacted by
potential landslide hazards.
Response: The potential for landslides was addressed in References 2 and 3. For Reference 3, we
performed an additional large diameter boring and test pits in the southeast portion of the
site to evaluate the potential for landslides within the project limits. No slide planes,
bedding plane shears, or other geologic features indicative of landsliding have been
encountered within exploratory borings and test pits performed on the property. It is our
opinion there is a low risk for landslides impacting the project.
Issue 54:In general accordance with the Subdivision Map Act, the project's geotechnical
consultant should indicate whether or not there are any soil conditions within the area of
the Tentative Map which, if not corrected, would lead to structural defects.
- Indicate if critically expansive soils or other soils problems are present which, if not
corrected, would lead to structural defects.
-Indicate if rocks or liquids containing deleterious chemicals are present which, if not
corrected, could cause construction materials such as concrete, steel, and ductile or cast
iron to corrode or deteriorate.
- The project’s geotechnical consultant should clarify if the property that is proposed of
the tentative map is safe from geologic hazards.
Response: In general accordance with the Subdivision Map Act, we have performed a geotechnical
investigation to address soil and geologic hazards on the property. Geotechnical
Geocon Project No. 07516-42-02 - 3 - May 10, 2023
recommendations provided in the referenced geotechnical reports account for the soil
conditions encountered on the property and geologic hazards identified on or near the
property limits. Provided the recommendations in the geotechnical report are followed,
there is a low risk for impacts to the property from soil or geologic hazards. Specifically,
the grading and foundation recommendations in the referenced reports account for soil
conditions encountered on the property, including expansive soils (which are generally
low expansive). With respect to corrosion, laboratory testing performed during our
geotechnical investigation indicate the site soils have an “S0” sulfate exposure class (not
applicable severity) to concrete structures as defined by 2022 CBC and ACI 318.
However, Geocon does not practice corrosion engineering.
Issue 55:The provided slope stability analyses indicate planned cut and fill slopes, and the existing
native perimeter slope, will have a calculated factor of safety in excess of 1.5. The
project’s geotechnical consultant must also provide a professional opinion that the site
will have a factor-of-safety of 1.5 or greater for both gross and surficial stability following
project completion.
Response: As indicated in our addendum report and response letter dated February 9, 2022
(Reference 3), based on the results of our stability analyses, the slopes in and adjacent to
the proposed project have a factor of safety of 1.5 or greater for gross and surficial stability
following completion of the project, provided the grading recommendations in Reference
2 are followed.
If there are any questions regarding this correspondence, 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
(e-mail) Addressee
(e-mail) Civil Sense, Inc.
Attention: Ms. Maykia Vang
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T-16
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LD-3
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(5)
(26)
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF
PROJECT NO.
SCALE DATE
FIGURE
Plotted:05/10/2023 7:37AM | By:ALVIN LADRILLONO | File Location:Y:\PROJECTS\07516-42-02 (Nakano)\SHEETS\07516-42-02 Geo Map.60.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC 1AP
NAKANO
CHULA VISTA, CALIFORNIA
60'05 - 10 - 2023
07516 - 42 - 02
1 1 1
........UNDOCUMENTED FILL
........ARTIFICIAL FILL
........ALLUVIUM
........TERRACE DEPOSITS
(Dotted Where Buried)
........SAN DIEGO FORMATION (Conglomerate)
........MISSION VALLEY FORMATION
........APPROX. LOCATION OF GEOLOGIC CONTACT
(Queried Where Uncertain)
........APPROX. LOCATION OF BORING
........APPROX. LOCATION OF TRENCH
........APPROX. LOCATION OF INFILTRATION TEST
........APPROX. DEPTH OF REMEDIAL GRADING (In Feet, MSL)
........APPROX. LOCATIION OF GEOLOGIC CROSS SECTION
LD-5
D D'
GEOCON LEGEND
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Qudf
Qaf
Qal
Qt
Tmv
(5)
A-2
Tsdcg
T-24
0 12060 180 240 300 360 420 480 540 720600660 780 840 900 960 114010201080 1200 1260 1320
0 12060 180 240 300 360 420 480 540 720600660 780 840 900 960 114010201080 1200 1260 1320
D I S T A N C E
SCALE: 1" = 60' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION A-A'
D I S T A N C E
SCALE: 1" = 60' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION B-B'
0
60
120
180
240
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120
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240
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60
120
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GRADE
PROPOSED
GRADE
EXISTING
GRADE
EXISTING
GRADE
??
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF
PROJECT NO.
SCALE DATE
FIGURE
Plotted:05/10/2023 7:28AM | By:ALVIN LADRILLONO | File Location:Y:\PROJECTS\07516-42-02 (Nakano)\SHEETS\07516-42-02 XSection.60.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC CROSS SEC8ION
NAKANO
CHULA VISTA, CALIFORNIA
60'05 - 10 - 2023
07516 - 42 - 02
1 2 2
........UNDOCUMENTED FILL
........ALLUVIUM
........ARTIFICIAL FILL
........TERRACE DEPOSITS
........MISSION VALLEY FORMATION
........APPROX. LOCATION OF GEOLOGIC CONTACT
(Queried Where Uncertain)
........APPROX. LOCATION OF BORING
GEOCON LEGEND
?
Qudf
Qaf
Qt
Tmv
LD-5
Qal
0 12060 180 240 300 360 420 480 540 720600660 780 840 900 960 114010201080
0 12060 180 240 300 360 420 480 540 720600660 780 840 900 960 114010201080 1200
D I S T A N C E
SCALE: 1" = 60' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION C-C'
D I S T A N C E
SCALE: 1" = 60' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION D-D'
0
60
120
180
240
C
E
L
E
V
A
T
I
O
N
(
M
S
L
)
0
60
120
180
240
D
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A
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120
180
240
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60
120
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240
PL
PL
PL
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SECTION
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A-A'
SECTION
A-A'
SECTION
B-B'
LD-1
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NORTH
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EXISTING
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EXISTING
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(71)??
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LD-3
(Projected
36' West)
LD-5
(Projected
15' East)
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF
PROJECT NO.
SCALE DATE
FIGURE
Plotted:05/10/2023 7:29AM | By:ALVIN LADRILLONO | File Location:Y:\PROJECTS\07516-42-02 (Nakano)\SHEETS\07516-42-02 XSection.60.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC CROSS SEC8ION
NAKANO
CHULA VISTA, CALIFORNIA
60'05 - 10 - 2023
07516 - 42 - 02
2 2 3
........UNDOCUMENTED FILL
........ALLUVIUM
........ARTIFICIAL FILL
........TERRACE DEPOSITS
........MISSION VALLEY FORMATION
........APPROX. LOCATION OF GEOLOGIC CONTACT
(Queried Where Uncertain)
........APPROX. LOCATION OF BORING
GEOCON LEGEND
?
Qudf
Qaf
Qt
Tmv
LD-5
Qal
UNDOCUMENTED FILL (Qudf)
Medium dense, damp, light brown, Silty, fine SAND; trace clay
Firm, moist, brown, Sandy CLAY; trace rounded gravel
Loose to medium dense, damp, brown to olive brown, Clayey, medium
grained SAND; some angular gravel. asphalt and brick fragments up to 6" in
width. Plastic and metal also present
Loose to medium dense, dry to damp, reddish brown, Clayey, medium coarse
SAND with cobble; cobble is subrounded, up to 10" in width; minor caving
Loose to medium dense, damp to moist, yellowish brown, Silty, fine to
medium SAND; clear plastic debris present
TOPSOIL
Soft, moist, brownish black, Sandy CLAY; trace rounded gravel; some
charcoal and organic debris
ALLUVIUM (Qal)
Loose to medium dense, moist to wet, olive brown, Clayey, fine to coarse
SAND; few rounded gravel, trace cobble
Medium dense, moist, yellowish brown to grayish brown, Silty, fine SAND
and Clayey SAND; few subrounded gravel and cobble
TERRACE DEPOSITS (Qt)
Dense, moist, yellowish brown, Clayey, fine to medium SAND; some gravel
and cobble up to 18" in width
LB3-1
LB3-2
LB3-3
SM
CL
SC
SC
SM
CL
SC
SM/SC
SC
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
Figure A-3,
Log of Boring LD 3, Page 1 of 2
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING LD 3
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
R. ADAMS CO
N
T
E
N
T
(
%
)
SAMPLE
NO.05-08-2023
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)101'
07516-42-02 COMBINE.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
07516-42-02
-Groundwater at 33.5 feet: cemented zone, very difficult drilling
BORING TERMINATED AT 34 FEET
REFUSAL ON CEMENTED ZONE
Groundwater encountered at 33.5 feet
Backfilled on 05/08/2023
LB3-4
LB3-5
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
30
32
34
Figure A-3,
Log of Boring LD 3, Page 2 of 2
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING LD 3
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
R. ADAMS CO
N
T
E
N
T
(
%
)
SAMPLE
NO.05-08-2023
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)101'
07516-42-02 COMBINE.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
07516-42-02
UNDOCUMENTED FILL (Qudf)
Loose, dry, light brown, Silty, fine SAND; trace cobble and gravel
TOPSOIL
Loose, damp, dark brown to dark reddish brown, Silty, fine to medium
SAND; trace clay, trace gravel, charcoal observed, some pinhole porosity
-Switch to auger at 4 feet
TERRACE DEPOSITS (Qt)
Dense, damp, dark reddish brown, Clayey, fine to coarse SAND; some gravel
and cobble
BORING TERMINATED AT 5 FEET
PRACTICAL REFUSAL WITH AUGER AT 5 FEET
Groundwater not encountered
Backfilled on 05/08/2023
SM
SM
SC
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
Figure A-4,
Log of Boring LD 4, Page 1 of 1
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING LD 4
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
R. ADAMS CO
N
T
E
N
T
(
%
)
SAMPLE
NO.05-08-2023
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)98'
07516-42-02 COMBINE.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
07516-42-02
UNDOCUMENTED FILL (Qudf)
Loose, dry, light brown, Silty, fine to medium SAND; trace cobble and gravel,
some masonry and asphalt/concrete fragments
-At 4 feet: metal debris
-At 7 feet: becomes moist
Soft to firm, moist, dark grayish brown, Sandy CLAY with cobble; some
brick and clay pipe debris
TERRACE DEPOSITS (Qt)
Dense, moist, dark reddish brown, Clayey, coarse SAND with cobble; cobble
is subrounded, up to 12" in width
BORING TERMINATED AT 12.5 FEET
PRACTICAL REFUSAL ON COBBLE USING BOTH AUGER AND
BUCKET
Groundwater not encountered
Backfilled on 05/08/2023
SM
CL
SC
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
6
8
10
12
Figure A-5,
Log of Boring LD 5, Page 1 of 1
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING LD 5
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
R. ADAMS CO
N
T
E
N
T
(
%
)
SAMPLE
NO.05-08-2023
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)100'
07516-42-02 COMBINE.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
07516-42-02