Loading...
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 2 5 5 4 0 49 2 5 5 9 0 49 2 5 6 4 0 49 2 5 6 9 0 49 2 5 7 4 0 49 2 5 7 9 0 49 2 5 8 4 0 49 2 5 8 9 0 49 2 5 5 4 0 49 2 5 5 9 0 49 2 5 6 4 0 49 2 5 6 9 0 49 2 5 7 4 0 49 2 5 7 9 0 49 2 5 8 4 0 49 2 5 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