HomeMy WebLinkAboutSP-23-040 - Supplemental - 1068 Williston Road (8)
Engineers Scientists Planners Designers
40 IDX Drive, Building 100, Suite 200, South Burlington, Vermont 05403
P 802.497.6100 F 802.495.5130 www.vhb.com
To:Marla Keene, PE
Development Review Planner
City of South Burlington
180 Market St.
South Burlington, VT 05403
Date:October 31, 2023
Project #:57913.01
From:Daniel Heil, PE Re: 1068 Williston Road- Holiday Inn Redevelopment Project
Site Plan Amendment for Phase 2A – NDMF I
LDR Section 12.03 – Slope Stability Analysis
On behalf of Champlain School Apartments Partnership (“Applicant”), this memorandum is being submitted to
accompany the application for Phase 2A of the Holiday Inn Redevelopment Project (“Project”). This memorandum
specifically addresses Section 12.03(C) - Steep Slope Analysis of the City of South Burlington Land Development
Regulations as related to a proposed footing drain outfall for North Dorset Multi-Family I (NDMFI).
Project Information
The proposal is to currently amend Site Plan Approval (SP-22-031) for minor construction related modifications to
Phase 2A of the Holiday Inn Redevelopment located at 1068 Williston Road in South Burlington. SP-22-031 approved
separating NDMF I and renovated building phase (Phase 2) into separate phases known as Phase 2A and Phase 2B,
adding nine (9) residential units to the mixed-use building, reducing the retail space to 5,800, and reconfiguring the
parking garage within it, 1068 Williston Road.
Since SP-22-031, a footing drain serving NDMF I was added to the plans. The outfall was originally intended to tie into
the proposed closed conduit storm drainage system on-site, however, when designing the footing drain it was
determined that the footing drain elevation would be too low compared to the proposed storm drain system. In
looking at existing grades and wetland / buffer restrictions around NDMF I, the most feasible option to daylight the
footing drain was just off-site, to the north-east of NDMF I. The footing drain has been designed to run at minimal
slope, and the limits of disturbance associated with trenching have been minimized to limit disturbance in this area.
Please refer to Sheet C3.01 – Grading and Drainage Plan for additional information.
Existing Soils and Slopes Analysis
Soils within the limits of disturbance associated with the footing drain outfall are Borrow Pit (BR) based on NRCS soils
mapping (see attached NRCS web soil survey). Existing slopes in this area average 23% and are classified as a Level II
resource per Section 12.01 of the LDR’s.
The NRCS BR soil classification is likely associated with the extraction of earthen material that was used as fill for the
construction of I-89 in the early 1960’s. NRCS does not provide a breakdown of soil properties and qualities for soils
mapped BR as the history of disturbance makes it difficult to characterize such features. Typically, NRCS will list an
erosion “K Factor” for soils which will indicate the susceptibility of a soil to sheet and rill erosion, but given the
previous disturbance on-site, and BR soil classification, NRCS does not provide an erosion “K Factor” for borrow soils.
Daniel Heil, PE
Ref: 1068 Williston Road- Holiday Inn Redevelopment Project
LDR Section 12.03 – Slope Stability Analysis
Page 2
Based on a visual inspection, the existing embankment is well vegetated and the existing slopes are stable with no
visual signs of erosion in the vicinity of the proposed footing drain outfall.
Recommendations
To mitigate this soil erosion risk associated with the proposed footing drain outfall, we recommend implementing the
following measures:
1. Erosion and Sediment Control: Install erosion and sediment control measures such as silt fences, temporary
and permanent stabilization, and outfall protection. Erosion and sediment control measures shall be in
accordance with Sheet C6.01- Erosion and Sediment Control Plan, Sheet C8.00 EPSC - Narrative and Notes,
and the VT Low Risk Site Handbook for Erosion Prevention and Sediment Control. These measures will help
to prevent soil erosion and sedimentation during construction activities. As the outfall is proposed
2. Limit Disturbance: Limit the area of proposed trenching to the minimum area required to install the
proposed footing drain and outfall. Immediately following installation install permanent stabilization per
Sheet C8.00 - EPSC Narrative and Notes.
3. Regular Monitoring: Conduct regular monitoring of the slopes during and after construction activities. This
will help to detect any signs of instability at an early stage and take corrective actions as necessary.
In conclusion, while the proposed temporary impacts for the installation of the footing drain outfall take place on
steep slopes, the slope stability and erosion risk can be effectively managed through the implementation of
appropriate mitigation measures.
8"
P
V
C
6
RIM=313.3
INV=308.2 OUT
7RIM=313.5
INV=308.4
INV=308.2
7B
OUT
CB
3
RIM=311.9
INV=306.6 OUT
CB
4RIM=311.9
INV=306.6 OUT
CB
15RIM=308.2
INV=304.8
INV=305.1 OUT
CB
12RIM=312.8
INV=306.2
INV=306.2
INV=306.1
13
RD3
OUT
CB
18
RIM=313.2
INV=308.3
INV=308.5
INV=308.5
INV=308.2
INV=308.5
17
21
6 IN
OUT
OUT
DMH
17
RIM=313.0
INV=309.0
INV=309.0
INV=309.0
INV=309.0
RD2
16
DS3
OUT
CB
19
RIM=312.5
INV=308.3
INV=308.2
INV=309.0
INV=308.5
20
OUT
OUT
DMH
20
RIM=312.1
INV=308.5 OUT
CB
REMOVE EXISTING PIPE
AND CONNECT TO
EXISTING STRUCTURE AT
INV=302.0
15"H
D
P
E
18"HDPE
18"HDPE
15"HDPE
15"PVC
REMOVE EXISTING GREASE
TRAP AND MANHOLE
21
RIM=312.6
INV=309.2 OUT
CB
1A
RIM=312.4
INV=302.3 1B
DMH
24
"
H
D
P
E
ELIMINATE EXISTING OUTFALL. PLUG
OUTLET. BACKFILL PIPE WITH
FLOWABLE FILL. COORDINATE ALL
WORK WITH VTRANS.
2%
M
I
N
.
SL
O
P
E
2RIM=312.4
INV=306.4
INV=306.4
INV=304.4
INV=304.3
4
3
5
OUT
DMH16RIM=313.1
INV=309.4 OUT
CB
13RIM=312.6
INV=308.6
INV=308.5
13 B
OUT
CB
12
"
H
D
P
E
15"HDPE
15
"
H
D
P
E
15
"
H
D
P
E
1
5
"
H
D
P
E
15"HDPE
22
RIM=312.4
INV=307.2
INV=305.0
19
OUT
DMH
15"HDPE
8
"
P
V
C
5
RIM=313.6
INV=307.5
INV=307.5
INV=308.1
INV=305.5
6
7
1 6
OUT
DMH
10"PVC
7B
RIM=313.3
INV=308.8
INV=308.6
7A
OUT
CB
12"
H
D
P
E
12" HDPE ROOF
DRAIN CONNECTION
15
"
H
D
P
E
SUBSURFACE
INFILTRATION
SYSTEM #1
SUBSURFA
C
E
INFILTRATIO
N
SYSTEM #2
1
5
"
H
D
P
E
13 B
RIM=312.0
INV=308.7 OUT
CB
6"PV
C
18"HDPE
14ARIM=309.9
INV=304.9
INV=304.8
INV=305.1
INV=304.8
11
OUT
OUT
OUT
CB
11
RIM=312.5
INV=306.0
INV=305.7
INV=305.6
RD4
12
OUT
CB
1B
RIM=312.4
INV=302.5
INV=302.4
2
OUT
DMH
12
"
P
V
C
18"HDPE
15"HDPE
15"HDPE
CORE NEW INVERT
AT 305.2 ADD RISER SECTION, MANHOLE FRAME,
AND COVER, AND ADJUST TO FINISH GRADE.
OUT
(W)
(E)
(N)
14B
RIM=310.0
INV=304.7
INV=305.7
INV=304.7
14A
OUT
OUT
DMH
(EX CB#1)
(N)
(S)
(E)
12"HDPE12"HDPE
12"HDPE
12"HDPE
12"HDPE
8"PVC
12
"
H
D
P
E
8"
P
V
C
8"PVC
8"
P
V
C
8"PVC
12"H
D
P
E
CO
CO
GMP TO HOLD EXISTING POLE AND
REINSTALL GUY WIRE. COORDINATE
DRAINAGE WORK WITH GMP.
RD INV=307.0
4"
S
D
R
3
5
P
V
C
@
1
%
M
I
N
.
CANOPY DRAIN
INV=309.5
WYE INTO 12" HDPE
BENDS AS NECESSARY
24
RIM=313.1
INV=300.1
INV=300.1
INV=300.0
23
OUT
DMH
12"HDPE
12
"
H
D
P
E
AS-BUILT INV
W/ CAP
= 300.6
FES
INV = 299.0
18
"
H
D
P
E
(2) 6" SDR 35 PVC.
INV. = 309.2
EXTEND 6" PVC 5'
BEYOND PHASE 2A
PAVERS AND WITNESS
FIELD VERIFIED LOCATION
OF CWD WATER MAIN
REMOVE EXISTING WATER SERVICE,
VALVES AND HYDRANT. SHUTDOWN
OF THIS LINE SHALL BE PERFORMED
BY CWD/SBWD PERSONNEL ONLY.
EXISTING HYDRANT
8" DI FIRE SERVICE.
COORDINATE WITH
MECHANICAL PLANS
FIRE DEPARTMENT CONNECTION
LOCATION (CONFIRM WITH
SPRINKLER DESIGNER)
4" DOMESTIC SERVICE.
FINAL SIZE PER
MECHANICAL PLANS
HYDRANT
8" GATE VALVE
CAP LINE FOR FUTURE
CONSTRUCTION
8x3 TEE
8" GATE VALVE
EXISTING 8" DI
WATER SERVICE
3" GATE VALVE
8x8 TEE
8X6 TEE
NEW HYDRANT
NEW 8" DI
WATER MAIN
REMOVE
EXISTING
WATER
SERVICE.
PROPOSED
8"x8"
CUT-IN-TEE
WITH VALVE
CLUSTER
NEW 8" D.I. CL52
WATER MAIN
6" GATE VALVE
NEW 8" DI
WATER MAIN
8" GATE VALVE
6" GATE VALVE
6" GATE VALVE
8" TO 6" REDUCER
INV
W/ CAP
= 307.61
7A
RIM=313.1
INV=310.0 OUT
CB
12
"
H
D
P
E
8" D.I. CL52 WATER MAIN STUB
(CAP WITH THRUST BLOCK)
8x8 TEE
10" SDR 35 PVC ROOF DRAIN
INV = 309.8
CAP FOR FUTURE CONNECTION
TEMPORARY 6"
PERFORATED SDR35 PVC
INFILTRATION TRENCH
8" SDR35 PVC
INV. = 307.5
STUB, CAP AND WITNESS
8x6 TEE
8" TO 4"
REDUCER
4" GATE VALVE
2%
M
I
N
.
SL
O
P
E
8" SDR35 PVC
INV. = 304.5
STUB, CAP AND WITNESS
CO
INV.=309.3
CANOPY
DRAIN
INV.=309.5
CANOPY
DRAIN
INV.=309.4
CANOPY DRAIN
INV.=310.0
CO
INV=309.8
6" SDR 35 PVC
@ 0.5% MIN.
15" HDPE INV. =
308.9. STUB, CAP
AND WITNESS
S
7
5
°
5
6
'
2
6
"
W
300
305
310
WIL
L
I
S
T
O
N
RO
A
D
TO I-89
5' DIA.
TOTAL GSF = 59,815 SF
FFE = 313.95'
TOTAL GSF = 136,561 SF
FFE = 313.9'
FUTURE PHASE
HOLIDAY INN
MULTI-FAMILY BUILDING
REMOVE EXISTING DRIVEWAY,
RESTORE TO PERVIOUS GRASS
SURFACE, GRADE TO DRAIN
12" MIN. TOTAL SOIL DEPTH
(4" MIN TOPSOIL)
TOTAL GSF = 59,815 SF
FFE = 313.95'
TOTAL GSF = 136,561 SF
FFE = 313.9'
FUTURE PHASE
HOLIDAY INN
MULTI-FAMILY BUILDING
(RENOVATION OF EXISTING
BUILDING)
LIMITS OF
PHASE 2A
312.2313.3
313 TC312.5 BC
310.5 TC
310 BC
309.5 TC
309 BC
308.5
309 TC
308.5 BC
312.8
313.65 TC/BC
314.3 TC313.7 BC
313.7
313.2
314.2 TC313.6 BC
313.8
313.7
313.7
313.9313.9 313.85313.85
310.5 TC
311.5 TC
313.3
GT
D
GT
D
313.3
314.1
314.7314.6
314.3314.2
312.15
313.3313.4
313.9
313.7 TC313.2 BC
313.8 TC313.3 BC
313.75
313.5 TC313.0 BC
313.9
310 TC309.5 BC
312.5 TC312 BC309 TC
313.9
313.9
313.9
313.75
313.75 TC313.25 BC
313.8 TC313.3 BC 313.8 TC
313.3 BC
312.6 TC
312.7
314.0
314.2 TC313.6 BC
313.45 314.0
313.65 TC/BC
313.7
312.8
313.0
312.6
312.7
312.6
313.4
313.1313.3312.7
312.5
312.5312.1
313.2 313.5
313.5
313.0
EDGE OF DELINEATED
WETLAND (TYP)
2013-3
50-FT WETLAND BUFFER (TYP)
Br
Fu
HlB
AdE
AdA
ScB
NRCS Soils Summary
SYMBOL SOIL NAME HYDROLOGIC GROUP HYDRIC SOILS FARMLAND SOIL
AdA ADAMS AND WINDSOR LOAMY SANDS, 0 TO 5 PERCENT SLOPES A NO STATEWIDE
AdE ADAMS AND WINDSOR LOAMY SANDS, 30 TO 60 PERCENT SLOPES A NO NPSL
Br BORROW PITS N/A N/A NPSL
Fu FILL LAND A N/A NPSL
HlB HARTLAND VERY FINE SANDY LOAM, 2 TO 6 PERCENT SLOPES C/D YES STATEWIDE, IF DRAINED
ScB SCANTIC SILT LOAM, 2 TO 6 PERCENT SLOPES C/D YES STATEWIDE, IF DRAINED
of
Project Number
Sheet
Drawing Number
Drawing Title
Issued for
Checked byDesigned by
Appvd.DateRevisionNo.
vh
b
.
c
o
m
Date
40 IDX Drive, Building 100
Suite 200
South Burlington, VT 05403
Holiday Inn
Redevelopment
1068 Williston Rd.
South Burlington, Vermont
Ph 2A Local Approval July 29, 2021
35
57913.01
Grading and
Drainage Plan
C3.01
4
CHS PBS
Feet6030015
Revised Phase 2A Utilites and Temp Drive Aisle 06/08/2023 DJH4
Revised Storm Drain per NDMFII Design 06/28/2023 DJH5
Revised Phase 2A Limits and Temp Drive Aisle 09/14/2023 DJH6
Temp Drive Aisle Grading 10/04/2023 DJH7
Added Existing Contours and Wetland Buffer 10/13/2023 DJH8
Area of Steep Slope
Impacts
Soil Map—Chittenden County, Vermont
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/23/2023
Page 1 of 3
49
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4
0
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8
9
0
644570 644620 644670 644720 644770 644820
644570 644620 644670 644720 644770 644820
44° 28' 19'' N
73
°
1
0
'
5
7
'
'
W
44° 28' 19'' N
73
°
1
0
'
4
4
'
'
W
44° 28' 6'' N
73
°
1
0
'
5
7
'
'
W
44° 28' 6'' N
73
°
1
0
'
4
4
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84
0 50 100 200 300
Feet
0 25 50 100 150
Meters
Map Scale: 1:1,940 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
Approximate Location
of footing drain outfall
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:15,800.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Chittenden County, Vermont
Survey Area Data: Version 27, Sep 10, 2023
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jun 18, 2020—Jun
20, 2020
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Chittenden County, Vermont
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/23/2023
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
AdA Adams and Windsor loamy
sands, 0 to 5 percent slopes
3.7 18.3%
AdE Adams and Windsor loamy
sands, 30 to 60 percent
slopes
1.5 7.2%
Br Borrow pits 2.0 10.1%
Fu Fill land 10.2 50.3%
HlB Hartland very fine sandy loam,
2 to 6 percent slopes
1.6 7.7%
HlE Hartland very fine sandy loam,
25 to 60 percent slopes
0.3 1.3%
ScB Scantic silt loam, 2 to 6
percent slopes
1.0 5.1%
Totals for Area of Interest 20.4 100.0%
Soil Map—Chittenden County, Vermont
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/23/2023
Page 3 of 3
Chittenden County, Vermont
Br—Borrow pits
Map Unit Setting
National map unit symbol: 9g36
Elevation: 300 to 2,000 feet
Mean annual precipitation: 36 to 50 inches
Mean annual air temperature: 37 to 46 degrees F
Frost-free period: 90 to 135 days
Farmland classification: Not prime farmland
Map Unit Composition
Pits, borrow:100 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Pits, Borrow
Setting
Down-slope shape:Convex
Across-slope shape:Convex
Typical profile
H1 - 0 to 60 inches: variable
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 8e
Hydric soil rating: Unranked
Data Source Information
Soil Survey Area: Chittenden County, Vermont
Survey Area Data: Version 27, Sep 10, 2023
Map Unit Description: Borrow pits---Chittenden County, Vermont
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/23/2023
Page 1 of 1