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Home My WebLink AboutDRB17-0171 Geologic Hazard Assessment.pdfH-P~KUMAR Geotadlical Engtneemg I Engineering Geology Materials Testing I Environmenlal 5020 County Road 154 Glenwood Springs, co 81601 Phone: (970) 945-7988 Fax: (970} 945-8454 Email: hpkglenwood@lunaru.com Office Locations: Parker, Glenwood Springs. and Sunvnit County, Colorado RECEIVED GEOLOGIC HAZARDS ASSESSMENT LOT 30, VAIL POTATO PATCH SUBDIVISION 807 POTATO PATCH DRIVE VAIL, COLORADO PROJECT N0.17-7-193 FEBRUARY 23, 2017 PREPARED FOR: SCOITRYAN 2398 SW 76n1 LANE OCALA, FLORIDA 34476 srvanCa>.zefon.com JUN 16 Z017 Town of Vail TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY ....................................................................................... - 1 - PROPOSED DEVELOPMENT ..•....................................................................... -I - SITE CONDITIONS ................................................................................................................... - 1 - PROJECT AREA GEOLOGY ................................................................................................... - 2 - REGIONAL ROCKFALL INFORMATION ............................................................................. - 2 - GEOLOGIC HAZARDS ASSESSMENT .................................................................................. - 3 - EAR'lllQUAKE CONSIDERATIONS .................................................................................. - 3 - LIMITATIONS ........................................................................................................................... -4 - REFERENCES ........................................................................................................................... -5 - FIGURE 1 -PROJECT SITE LOCATION FIGURE 2 -SITE PLAN FIGURE 3 -PROJECT GEOLOGY H-P~KUMAR Project No. 17-7-193 PURPOSE AND SCOPE OF STUDY This report presents the findings of a geologic hazards assessment of Lot 30, Vail Potato Patch Subdivision, 807 Potato Patch Drive, Vail, Colorado. The purpose of our study was to evaluate the geologic hazards at the project site and assess their potential impact on the proposed development. A field reconnaissance of the project site was made on February 22nc1, 2017 to observe the geologic conditions and collect information on the potential geologic hazards present at the project site. In addition, we have reviewed relevant published geologic information, looked at aerial photographs of the project area, and reviewed previous studies in the area. This report summarizes the infonnation developed by this study, describes our evaluations, and presents our findings. PROPOSED DEVELOPMENT The proposed development is in tlie preliminary phase. Our understanding is that a single-family residence will be located approximately in the upper to middle part of the lot. When building location, type, and grading conditions have been developed, we should be notified so that we may reevaluate the information submitted in this report and perform additional analysis as ;:.:~:...:.:~~~~~~an~d~th,;;;;;.e.-uarcl~~ra=i~lal~on~g~P~o~ta~t~o~P~at~c~h~Dri~·v~e,=a=c=cess~=to=th=:e:;:t=is~'\&c- not currently feasible with drilling or excavation equipment without creatin cess trail into t ~ the building area or grading drill pads off of the road right-of-way. SITE CONDITIONS The 0.4-acre parcel is located about 0.35 miles to the north of Interstate 70 on the south side of Potato Patch Drive, as shown on Figure 1. The site was visited on February 22nc1, 2017. At the time of the visit, the site was mostly covered with around 6 inches of snow. The site is located on a very steep, south-facing hillside to the east of Red Sandstone Creek. The site lies at an elevation of around 8,590 feet. The existing topography is shown by the contour lines on Figure Project No. 17-7-193 -2- 2. ThQacross the proposed development @!Cl is about~. The hillside transition~ -to a moderately sloping bench with an average slope of about 20 percent to the north of the site. -Vegetation on the proposed development area is grass and scattered scrub oak with a few aspens near Potato Patch Drive. PROJECT AREA GEOLOGY The main geologic features in the project area are shown on Figure 3. This map is based on regional mapping by Scott and Others (2002). The project site is underlain by interbedded arkosic sandstone, conglomerate, and shale in the middle Pennsylvanian-age, Minturn Formation. The formation rock bedding in the area dips to the west to northwest at angles between around 15 to 40 degrees. The Red Sandstone syncline is to the north and east of the project site. At the project site the formation rock is mostly covered with pre-Bull Lake-age glacial till, but scattered outcrops of the sandstone may be present. The onsite rock blocks in the northern part of the site are associated with the till. REGIONAL ROCKFALL INFORMATION The Town of Vail (2000) regional rockfall map shows much of the Vail Potato Patch Subdivision in a high or medium severity rockfall area. Lot 30 is shown in a medium se11eri1y rockfall area, but based on our site-specific review, in our opinion, Lot 30 is not in a rockfall hazard area. The primary rockfall hazard is associated with the prominent sandstone outcrop located to the north of the subdivision. Lot 30 is not located in this potential hazard area A secondary rockfall hazard is associated with the local sandstone outcrops and till related rock blocks on the steep hillside in the vicinity of Lot 30. This secondary hazard does not present a ............ ------~-=-------~~----=----~ potential threat to development of Lot 30 because the proposed construction will be in the potential rockfall source area. Construction should reduce the potential risk to down slope ,building'.f precautions are takenluring construction to prevent dislodgement of the rock blocks» and unstable outcrops on the hillside near construction sites. Project No. 17-7-193 -3- GEOLOGIC HAZARDS ASSESSMENT Potential geologic hazards which could impact the project site consist of instability of the steep ;to~ and rockf~l. The site bas had a relatively stable recent geologic past and the steep slope should remain relativel stable provided site ev ment grading is pro rl desi and constructed. There will be a risk of construction induced instability. Surface grading and drainage normal for building on steep slopes should be used to protect the residence from surface runoff. Although Lot 30 is in medium severity rockfall area according to Town of Vail (2000), based on our site-specific review, in our opinion, Lot 30 is not in a rockfall hazard area. There is a potential for local instability of the scattered boulders when excavating for the project. Temporary rockfall protection should be placed downslope of the proposed construction in order to protect downslope infrastructure and buildingS from potential dislodged rocks. Geologic conditions in the project area should not present an unusual risk to the proposed development. EARTHQUAKE CONSIDERATIONS Historic earthquakes within 150 miles of the project site have typically been moderately strong with magnitudes ofMS.5 and less and maximum Modified Mercalli Intensities of VI and less. The largest historic earthquake in the project region occurred in 1882 (Kirkham and Rogers, 1985). It was apparently located in the northern Front Range and had an estimated magnitude of M6.2 ± 0.3, and a maximum Modified Mercalli Intensity of VII. Historic ground shaking at the project site associated with the 1882 earthquake and the other large historic earthquakes in the region does not appear the have exceeded Modified Mercalli Intensity VI (Kirkham and Rogers, 1985). Modified Mercalli Intensity VI ground shaking is felt by most people and causes general alarm, but results in negligible damage to structures of good design and construction. The project facilities should be designed to withstand moderately strong ground shaking with little or no damage and to not collapse under stronger ground shaking. For firm rock sites with shear wave velocities of2,500 fps in the upper 100 feet, the U.S. Geological Survey 2014 National Seismic Hazard Maps indicates that a peak ground acceleration of 0.06g has a 10% exceedance probability for a 50 year exposure time and a peak ground acceleration of 0.22g has a 2% exceedance probability for a 50 year exposure time at the project site (Peterson and Others, 2014). This corresponds to a statistical recurrence time of about 500 years and 2,500 years, H-P~ Project No. 17-7-193 -4- respectively. The soil profile at the proiect site appears to be Class C, as described in the 2015 International Building Code and §bould be.further eyaJuaiedas part of the site specific geotechnical study. LIMITATIONS This study was conducted according to generally accepted geotechnical and engineering geology principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based on our field observations, aerial photograph interpretations, published regional geology informatio~ the currently proposed development pl~ and our experience in the area. This report has been prepared exclusively for our client and is an evaluation of the geologic hazards and their potential influence on the proposed development We are not responsible for technical interpretations by others of our information. H-P~KUMAR Robert L. Duran, E.I. Reviewed by: cc: Pierce Architects -Bill Pierce (bill@lvailarcbitects.com) H-P~KUMAR Project No. 17-7-193 -5- REFERENCES Kirkham, R. M. and Rogers, W. P., 1985, Colorado Earthquake Data and Interpretations 1867 lo 1985: Colorado Geological Survey Bulletin 46. Scott, R. B., Lidke, D., J., and Grunwald, D. J., 2002, Geologic Map of the Vail West Quadrangle. Eagle County. Colorado: U.S. Geological Survey, Miscellaneous Field Studies Map MF-2369, Version 1.0. Peterson, M. D. and Others, 2014, Documentation for the 2014 Update of the National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2014-1091. Town of Vail, 2000, Official Rockfall Hazard Map, Town of Vail: Prepared by the Town of Vail, Vail, Colorado (Adopted by the Town Council on October 17, 2000). H-P~KUMAR Project No. 17-7-193 o,_-==300=-"""--===600 ft D 11-1-193 H-P ~KUMAR Lot 30, Vail Potato Patch Subdivision· Location Figure I I N Col a.. = 1:11 i.i: - - . I c cs 0:: !! i:ii -I c: .!2 .!!! .::: "'C .n ::I tll .:::. ~ c.. 0 ' • -r: ~ • .. --· -· .E __ ,. > 0 M 0 ...l - . --er. -----<( . ---2 . ::> .. ~ ! Ill ~ 0.. I ' i :::r:: ~ : - ; I"» ~ C\ . -. • .... . I ..... ~ -- • .......... w ................ ~ -..-.._ .... -.... ........... , 0.. ----t~J __ ...._ ...... -... _ _,_.._ Cll'o ,.... .. _____ ....._ __ ......... ~ .... .. c-.-·---,_ _ ..... Iii-----..... - 11-1-193 H-P ~KUMAR lllJlllO\~ • -, .._,_,_..._ ...... ..,_ •• I • ;-fi;I _,_ .... _' I I ~-----~. t----.... --. ... &p-. .. ----(__,..._... ...... ... _,_ Lot 30, Vail Potato Patch Subdivision -Project Geology Figure3