HomeMy WebLinkAboutVAIL VILLAGE FILING 7 TRACT B GOLDEN PEAK 1995 REDEVEOLPMENT ENVIRONMENTAL IMPACT LEGALVtuJv \ \IT,,JR t"tJ^?,-l.Ro[^*[1.J t-n-."^*b l{rru
ET-IVIRONMENTAL IMPACT REPORT
ENVIRONMENTAL IMPACT REPORT
GOLDEN PEAK REDEVELOPMENT
Revised October 18. 1995
Prepared for:Vail Associates, Inc.
P.O. Box 959
Avon, CO 81620
Alpine Engineering, Inc.
P.O. Box 97
Edwards, CO 81632
(970) 926-3373
Prepared by:
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TABLE OF CONTENTS
1.0 INTRODUCTION ..... 1
l'l scoPE ........ 1
I.2PROJECTDESCRIPTION. .....1
2.0 MILLCREEKCULVERTEXTENSION .......I
2.1 CULVERTDESIGN ....2
2.2 FLOODPLAINALTERATION. ........3
3.0 CONSTRUCTIONIMPACTS .........3
3.1 ATRQUALITY ........3
3.2 EROSIONANDSEDIMENTATION. ....4
3.3 CONSTRUCTIONDEWATERING... .........4
3.4 STREAMDIVERSION ........4
4.0 EXTERIORDRAINAGEPLAN .......5
5.0 NON-POINTSOURCESTORMWATERDISCHARGES . ....... 5
5.I PARKINGSTRUCTURE.. .....5
5.2 SNOWSTORAGE ......6
6.0 MILLCREEKDIVERSIONSTRUCTURE ......6
7.0 MUDANDDEBRISFLOWHAZARD ,...,...6
8.0 REFERENCES. ......8
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GOLDEN PEAK REDEVELOPMENT
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EIWIRONMENTAL IMPACT REPORT
I 1.0 TNTRODUCTION
1.1 SCOPE
Alpine Engineering, Inc. was retained by Vail Associates, Inc. (VAI) to prepare an
I Environmental Impact Report to be submitted to the Town of Vail with an application forI Development Plan approval for the Golden Peak Base Area Redevelopment. The scope of
this report was defined through discussion between Alpine, VAI and Mr. Russell Forrest,
I Environmental Planner for the Town of Vail. Environmental issues identifted include:I
1. Impacts of the Mill Creek cuivert extension;
2. Definition of an exterior drainage plan;
3. Mitigation of non-point source stormwater discharges;
4. Determination of the adequacy of the existing diversion structure; and
5. Mud and debris flow mitigation plan.
I.2 PROJECT DESCRIPTION
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VAI is proposing to redevelop the Golden Peak Base Area. A development plan for this
I project was submitted and approved in 1984; the current submittal constitutes an amendment
I to the 1984 plan. The redevelopment plan includes: l) replacing the existing Golden Peak
building with an improved ski portal; 2) improving skier access and traffic flow to the
I facility; and 3) modifying the base area with improved lifts, access and outdoor space.
f Modifications to the lifts and planned increase in skier use of the base area will require
moving the existing stormsewer inlet out of the planned skier maze located near the bottom of
I Lift 6. The stormsewer inlet is fed by the East Branch of Mill Creek, an anificial rectangular
I channel which carries water diverted from Mill Creek for the purpose of flood protection.
VAI proposes to convert 378 feet of the open channel of the East Branch to buried
I stonnsewer and constructing a new inlet structure further up the ski slope out ofthe way of
I converging ski traffic near the base area.
I 2.0 MILL CREEK CULVERT EXTENSION
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The East Branch of Mill Creek is an artificial stream created to abate flood levels during the
I spring runoff and summer stormflows along the West Branch of Mill Creek as it runs through! the center of the Town of Vail to Gore Creek. From the point of diversion, located above the
Golden Peak Base Area (see Site Plan. Exhibit 1). the East Branch of Mill Creek flows
f through the base area between Lifts 6 and 12 and enters the existing stormsewer near theI
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bottom of Lift 6. Currently, the East Branch consists of a rip-rap-lined rectangular channel
with drop structures for energy dissipation near the entrance to the stormsewer.
The East Branch of Mill Creek is aligned across t}re Golden Peak base area at an angle to the
general flow of skier traffic. In order to allow skier and snowcat traffic across the open
channel, VAI places half culvert sections over the channel bed during the ski season and
plows snow over the culverts to provide a passable surface. This temporary piping of the
East Branch flow is problematic for several reasons: 1) frequent maintenance is required to
allow safe skier passage through this area of high traffic and skier convergence; 2) snow is
packed into the channel, decreasing the flow capacity; and 3) the half culverts cause
significant disnubance to the stream bed.
VAI is proposing reconstruction and regrading of the Golden Peak base area. As part of this
redevelopment, the lifts will be realigned and the existing stormsewer inlet will be located in
the area of a planned skier maze. In order to accommodate these changes, and to eliminate
maintenance and traffic problems related to the artificial channel, VAI proposes to extend the
stormsewer culvert up the course of the East Branch of Mill Creek approximately 378 feet
from the existing stormsewer entrance (see Proposed Stormsewer Extension Plan, Exhibit 2).
This extension will be sized at a minimum to accommodate the 100-year snowmelt event
which was determined in a previous hydrologic study (Hydro-Triad, Ltd., 1983). The existing
stormwater culverts which carry flows from the East Branch of Mill Creek to Gore Creek are
oversized for the 100-year snowmelt event (95 cfs) and the 100-year thunderstorm event (160
cfs); the proposed extension will be designed commensurate with the existing system.
One altemative to the stormsewer extension was considered: replacing the existing
rectangular channel with a broad swale. This alternative would have many of the same
disadvantages as the existing artificial channel including: l) frequent maintenance required to
allow safe skier passage through this area of high traffic and skier convergence; 2) snow
packed into the channel, decreasing the flow capacity; and 3) potential overflow or escape of
flow from the artificial channel would result in damage to property. Extension of the
stormsewer with regrading to eliminate the channel cutting across the hill slope would allow
greater skier safety in the area of traffic convergence and greater control of the flood waters.
This alternative is more expensive. but is balanced bv decreased maintenance costs over time.
2.I CULVERT DESIGN
The proposed stormsewer extension will consist of a headwall with a 66-inch conugated metal
pipe (CMP), which then reduces to a 54" CMP aligned approximately along the existing
stream course. The existing stormsewer inlet located near the bottom of Lift 6 will be
removed along with the concrete bulkhead. Stormsewer manholes will be located for change
in alignment or grade of the pipe. A new storrnsewer headwall and inlet wiil be located at
the top of the extension with a series of drop structures for energy dissipation and to provide
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some sediment removal. With the exception of the stormsewer inlet, the extension will be
located entirely at or below grade.
The proposed extension will be capable of transmitting 210 cfs, slightly in excess of the 100-
year snowrnelt event and commensurate with the existing stormsewer capacity. Hydraulic
velocities within the stormsewer extension have been calculated to exceed current velocities in
the East Branch of Mill Creek. The use of comrgated metal pipe is recommended over
smooth pipe as its increased roughness will partially abate velocity increases within the
stormsewer extension. Energy dissipating structures have been included within the design of
the stormsewer extension to mitigate increased velocities due to the replacement of rip-rap-
lined channel with culvert (see details, Culvert Extension Plan, Exhibit 2).
The capacity of a stormsewer is related to its cross-sectional area which may be affected by
debris and sediment accumulation within the pipe. To maintain the full capacity of the
proposed sewer extension, a sedimentation structure and trash screen will be provided at the
storrnsewer inlet. In addition. VAI will clean and maintain the as needed.
2.2 FLOODPLAIN ALTERATION
The East Branch of Mill Creek is not mapped on Federal Emergency Management Agency
Flood Insurance Rate Maps. The proposed constructioh is therefore not located within a
jurisdictional flo ill Creek is an artificial stream originally
created by the(lt4ill Creek Diversion Structure flr the purpose of abating flooding on the West
Branch of Mill i at the Golden Peak site has sufficient
capacity to carry the 100-year flood event. In keeping with its intended use, the design ofthe
stormsewer extension will accommodate the same event as the existing system.
The East Branch of Mill Creek is classified as a "navigable waters of the United States" and
is within the jurisdiction of the U.S. Army Corps of Engineers (ACE) as mandated under the
Clean Water Act. Conversion of a portion of the East Branch of Mill Creek to below-grade
stormsewer requires notification of the ACE. As part of this environmental impact report.
Alpine prepared a letter ofnotification including a project description and site plan for review
by the ACE. The ACE will provide review and comment on the project and will make a
determination whether a 404 permit application is required. A copy of this notification is
presented in Attachment B. No response was received prior to submittal of this report.
3.0 CONSTRUCTION IMPACTS
3.1 ArR QUALTTY
An increase in diesel emissions and fugitive dust will result in air quality impacts during
construction activities. The proposed area of disturbance for the Golden Peak redevelopment
is less than 25 acres and therefore is exempt from fugitive dust permitting requirements.
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Fugitive dust and diesel emissions will be controlled in accordance with standard construction
practices. Construction roadways used by heavy machinery will be watered three times per
day or as needed to control dust. The redevelopment of the Golden Peak base area will cause
no permanent degradation of air quality.
3.2 EROSION AND SEDIMENTATION
Areas disturbed by construction activities are subject to erosion and subsequent sedimentation
impacts downstream during storm events. Prior to the commencement of construction
activities, VAI will apply for a Colorado Department of Health, Water Quality Control
Division Stormwater Discharge Permit. The permit application will include current Best
Management Practices for erosion control and stormwater detention as required during the
proposed construction. Following issuance of the permit, construction activities at the site
will conform to all requirements of the permitting authority.
3.3 CONSTRUCTION DEWATERING
A geotechnical investigation (CTl/Thompson, Inc., 1983) of the Golden Peak site identified
the groundwater table to be as shallow as l0 feet below ground surface. It is anticipated that
free groundwater may be encountered during excavation activities during the proposed
redevelopment, Prior to commencement of excavation activities at the site, VAI will apply
for a Construction Dewatering Permit under the Colorado Wastewater Discharge Permit
System. The permit application will include current Best Management Practices for
groundwater discharge and sediment control. Following issuance of the permit, construction
activities at the site will conform to all requirements of the permitting authority.
3.4 STREAM DIVERSION
During construction of the stormsewer extension, discharge to the East Branch of Mill Creek
rvill be diverted at the Mill Creek Diversion Structure to the West Branch of Mill Creek. In
keeping with the purpose of the East Branch diversion as flood abatement, diversion of flow
will not occur during spring run-off or during the summer thunderstorm season. Construction
of the extension will be scheduled for the late summer or earlv fall when the likelihood of a
flood event is remote.
Diversion of East Branch flow may potentially impact wildlife and fish habitat along the
course of the stream. The Colorado Department of Wildlife (DOW) has been notified of the
proposed Golden Peak redevelopment construction activities in a letter requesting DOW
review and comment. A copy of this letter of request and the DOW response is presented in
Attachment B. VAI will coordinate all changes in streamflow in the East Branch of Mill
Creek due to construction activities with the DOW throughout the life of the redevelopment
project. VAI will conform to all requirements of the DOW.
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4.0 EXTERIOR DRAINAGE PLAN
An exterior drainage plan for the proposed redevelopment of the site is provided on the
Proposed Drainage Plan, Exhibit 3. In general, surface run-off generated from impervious
surfaces, including roadways, plaza and roof areas, will be directed to the stormsewer system
via drains, swales or gutters, as appropriate. The proposed parking structure is situated
below-grade with a landscaped surface. Subsurface drains will convey soil water from the
landscaped surface to surrounding native soils. Stormwater run-off from the landscaped
parking structure surface will be directed to the stormsewer system via drains, swales or
gutters. A detailed drainage plan will be submitted for approval by the Town of Vail as
required for the issuance of a building permit. In general, stormwater run-off following
redevelopment of the site will not increase over current levels. The existing stormsewer has
been determined to be adequate at this time.
A potential altemative to the below-grade parking structure, dependant upon market conditions
at the time of construction, is a 30-space surface parking lot (see Alternative Surface Parking
Lot. Exhibit 4). The detailed drainage plan for this alternative will address the mitigation of
the increase in stormwater water run-off due to the impervious parking lot area.
5.0 NON.POINT SOURCE STORMWATER DISCHARGES
5.I PARKING STRUCTURE
A recent study conducted by the Northwest Colorado Council of Govemments and the Town
of Vail (Draft, March 1995) indicates that levels of pollutants, including sediment, dissolved
solids and oil, are found in stormwater run-off from parking surfaces and roadways in the
Town of Vail in similar proportions found in highly urbanized areas. The proposed
redevelopment of the Golden Peak base area will not significantly increase the area of
roadways associated with the site. In addition, traffic management to the site is anticipated to
result in no significant increase in vehicuiar use or trips to the site. The proposed below-
grade parking structure will have a landscaped surface. contiguous with the surrounding land
surface. Amounts of pollutants from vehicles will accumulate in the below-grade parking
areas at the same rate as in a surface parking area. However, a great advantage to a covered
parking area is that the removal and disposal of accumulated pollutants can occur under
controlled conditions as opposed to occurring with unpredictable storm events. Drainage
within the stmcture will capture run-off from all parking areas. The parking structure will be
provided with a drain system with integrated sediment and oil traps for the removal of
accumulated pollutants. A periodic inspection, cleaning and maintenance program rvill be
implemented by VAI to ensure that the traps are working properly.
The alternative 30-space surface parking lot will not have the advantage of being covered, but
will accommodate far fewer vehicles resulting in a decrease in total pollutant accumulation on
impervious surfaces. Mitigation of non-point source pollutants from this parking surface will
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be provided. Potential mitigation measures may include drainage to a subsurface sediment
and oil trap, or a grassed swale filter strip. VAI will conduct a periodic inspection, cleaning
and maintenance program to ensure that the mitigation measures are working properly.
5.2 SNOW STORAGE
Snow removed from roadways and parking areas also contain sediment, dissolved solids, and
oil. It is expected that snow removed from roof areas and plazas will contain significantly
lesser amounts ofpollutants than areas subject to vehicular traffic. In general, snow removed
from roof areas and plazas will be stored where evenfual melt water can either infiltrate into
soil or be diverted to the stormsewers. Snow removed from roadways and parking areas will
be placed in a designated snow storage area. Mitigation of non-point source pollutants from
this storage area will be provided. Potential mitigation measures may include drainage to a
subsurface sediment and oil trap, or a grassed swale filter strip. VAI will conduct a periodic
inspection, cleaning and maintenance program to ensure that the mitigation measures are
working properly.
6.0 MILL CREEK DII'ERSION STRUCTURE
The Mill Creek Diversion Structure, located approximately 1,000 feet south of the existing
Golden Peak base area was designed to split the flow of Mill Creek approximately 40Vo to the
East Branch and 600/o to the West Branch. Upon inspection of the diversion structure by
Alpine on May 22, 1995, it was observed that these gates are now absent. Discussion with
Mr. Paul Testwuide, VAI revealed that the structure has removable gates and that they have
been removed for the spring run-off to allow maximum flow through the structure. In the
absence of the gates, flow is controlled by an approximately two-tenths-of-a-foot difference in
invert elevations. At the time of inspection, flow to the two branches was split approximately
60-40 as intended. Both culverts branching from the diversion structure headwall were free of
sediment and debris, and appeared to be properly maintained.
The adequacy of the Mill Creek Diversion Structure is addressed in an engineering analysis
and schematic design prepared by Alpine as part of this Environmental Impact Report, and is
presented in Attachment C. The diversion structure appears to be adequate to accommodate
the 1O0-year flood.
7.0 MUD AND DEBRIS FLOW HAZARD
Mud and debris flow hazard areas are mapped on Town of Vail Hazard Maps. A portion of
the Golden Peak base area is located within an area designated "moderate debris flow hazard".
This delineated hazard area has been overlaid on the Golden Peak redevelopment site plan
(see Debris Flow Hazard Map, Exhibit 5). A debris flow within the delineated hazard area
could cause the blockage of the Mill Creek Diversion Structure or blockage of the proposed
stonnsewer inlet, potentially causing diversion of flood waters towards homes or to the
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Golden Peak base area. A debris flow is a catastrophic and highly unpredictable event, both
in time and space. Engineering mitigation is generally very expensive with no guarantee that
the mitigation structure has been placed in the path of the next major debris flow.
VAI will be responsible, in the case of a debris flow causing blockage to the Mill Creek
Diversion Structure or the proposed stormsewer irilet point, for removing the blockage and
restoring flow to the East and West Branches of Mill Creek.
A Geologic Hazard Study dated September 15, 1995, was prepared by R.J. Irish Consulting
Engineering Geologist, Inc., which is attached in Attachment C, Engineering Analysis.
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8.0 REFERENCES
I "Design Report Improvements to East Branch of Mill Creek, Golden Peak Development, Vail
Colorado," Jan. 1985, Hydro-Triad, Ltd.
t "Soils and Foundation Investigation, Proposed Golden Peak Building, Vail, Colorado",
_ November 22, 1983, CTl\Thompson.
I "Vail Non-point Source Water Quality Management Plan", Draft, March 1995, Northwest
Colorado Council of Govemments.I
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II Mr. Bill Andreei.' .June.i,ll995 :' : -
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L.'- jIr ..-.I , , ' , : Plg4se provide your comments concerning this proposed diversion.
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I STATE OF COLOFADO
3:',ff ff l'ff ffih" ot R Esou R.EE
ii.Mtst-o-ry-*o,f w I L D L I F E
Prtry D. Obo$ Dlrocbr
006 Bordwly
Dcnver. Colorarb 802.|6
ToDPndF: (3og) 297'1r sz
Aucrust- 20. 1995
RuF.r.. t-he CDow ayrprcciates the
ir"rr"'anY qn:estioni Please feel
si ncerelY.'
= fu-J|J A'"L.u--
Rill Andreciiliti"t wi ldl ife Hanaser-VaiI
Toun of Vail
A'PTN: RuFs Forrest
iS-souttt Frontaoe Road
vail. CO- 91657
Lraar RusE r
The. cnlorad.o Divjsion of l{iLdljfe (cDot{l has re.viewed the plan for
the. de.velopnent oi-Eirc"" Peak and-hll the' tol.lowltrg connenf'3'
Any ingracts frorn the dewaterinq of the alternat-e l-rl'arrch of llill
craak Fhnrrtc, be hinor. rhis-"""iioi"-n"*-ut"tt <iewat-ered severa]
time-s in the po"i""'-lrirl creek "i:i'n"'si-rirery^r'er'e[Jt
front o'11
thc pater heing Jnntojn"'a in.on9 "i"i""i' The cDoi{ does not Fee
;; ;;;;iticani I'oa"t' at this tj'me'
Tt shoulr! be noted that dewaterino the remaining n!ll creek channel
oftcr thic proiaJt- "iir r,"ve tigliificant impacts'
REFERTO
For NiUfift"
For PeoPlcI
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chance to revlew this Plan if Yott
free to cal I rne ' 9?'rl--1424 '
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oEP^RTT,ENT oF MTuRAL RESoUFCES. Jarm.s S. Loc*ficed, Exeo.,li.. 9,jf1 .
tYll,DL1FE COMMtSSTOX. fncmalM'-iuitLi-"n'ruub r' slrtll' vict'chrli'rn;ln ' A?^old srlttat' st'crDlafv
Jde. r:nlslen Boya',i..L-t-u"i'?i"t w' coopot' Membet' Rebcc'ca L' Frank' Membsr
W,l|ia; n. Hegb3€. Matnber. Mett Lrv8lls'' Membcr
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I One alternative to the stormse\\€r extension rvas consi
rectangular channel wjth a broad sl,ale; . This alremari
rclered: replacing rhe exisrin-q '
This altemative qould hat'e many of the same -
lil1c:: * the.existing artificiar recungurar channer incrudingr if#equent maintolsaovankges as the existing artifici
required to allorv safe skier passage.through this area of high traffic and skier convergence; 2)
enance
".i . , .' g'v J'\'^'rJr'rl.r- wrur.rsgldolng Io ellmlnate ihe channel cutting across the hill slope tyould. I . , '' :t ' 4llo1v gleateT skier.safety in the area of traffic convergence --d gr."r., control of flbod. :.-.: ' ..^r!,.tt 6lvsrel r.r\Jq )4rsly rn tne area or uallic convergence and greater control of flbod. ..
'aters."'This alternarive is more expensive, but is batincea u" a..i.r*J;;j;;;;:, :".,.- 1.. '-:-.by decreased maintenarce costs
thb artificial charurel
: . :.lover timd. r.
, snow packed.ir.tto,$e channbl, decrlasing rhe florv capacithe florv capacity; and 3) potential overflow or
u'ould result in damase 1o orrinertv F-*rpncinr er{damage to propeny. Extension cjf
' Please Doliry me of your determination of rhe need for' a 404 permit foi rhis projeit. If i,ouha'e any questions conceming rhis request, do not hesitate to cair n:e.
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7l0l Wesl Yale
Avenue. No 601
Denter Colorado 80227
303.986.6658
R. J. lrish
Consulting Engineering
Geologist, Inc.
September 15, 1995
KOECHLEIN CONSULTING ENGINEERS
1?354 West Alameda Parh,vay,
Suite 103
Lakewood, CO 80228
Attn.: Mr. William Koechlein
President
Re: Geologic Hazard Study, Golden Peak Base Facilities Site, Vail, Colorado.
Job No. 376
Gentlemen:
As requested by your Mr. \,Jilliam Koechlein, the undersigned has investigated engineering
geologic conditions pertinent to the Golden Peak Base Facilities site in Vail, Colorado. Our
objectives have been to outline those conditions generally, and to predict and assess their
probable impacts on the planning, construction and operation of the planned facility, including
any potential or existing geologic hazards that should be considered. That facility is to be a
multi-story building with an underground parking garage constructed on a lot that is about 450
feet long east to west, and about 350 feet wide north to south. This propefty, sited on the floor
of the Gore Creek Valley south of Gore Creek near its confluence with Mill Creek, is bounded by
Gore Creek Drive on the north, the Vail Village First Filing of single-family residences on the
\ryest, open land to the east, and the Golden Peak ski slope and run-out area to the south and
southeast.
During the course of our investigation we have researched published and open-file geologic
reports (including our own) and maps pertinent to the project area, and geologically recon-
noitered the site and vicinity (today, September 'l 5, 'l 995).
Sedimentary rock strata of the Minturn Formation of Pennsylvannian-age (about 280 to
320 million years ago) constitute bedrock across the floor of the valley and the adjacent
mountain sides. These strata include interstratified sandstones, siltstones, and shales, along
with thin and thick layers of limestones and dolomites. On the slopes south the project site those
strata appear to strike generally eastward subparallel to the trend of the Gore Creek Valley, and
Coisulant tc Des'gners. Con!racio|s. P!anners
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R. J. lrish
Consulting Engineering
Geologist, Inc.
appear to dip southward into the mountain. The Gore Creek Valley has been glaciated repeatedly
during the past 2 million years or so (the lce-Age ended in this valley about 8000 to 10,000
years ago), thus the lower slopes and the floor of the valley commonly are underlain by soils
deposited by glaciers or glacial meltwaters. Across the higher elevations of the valley slopes the
bedrock strata are blanketed by slopewash and residual soils, although several thick strata of
stronger bedrock stand out as rock bluffs several tens of feet high.
The Golden Peak Base Facilities site is located on about the longitudinal centerline of a large
alluvial fan created by discharges of the bed load of Mill Creek onto the floor of the Gore Creek
Valley . The project site is about two.thirds of the way down the fan from the mouth of the Mill
Creek Valley to the perimeter of the fan, the deposition of which has pushed Gore Creek almost
over to the other side of the floor of its valley. This fan, fully 2500 feet across its toe, and
about 2000 feet long, with its surface sloped at about 15:l (vertical to horizontal), is not a
debris fan, and does not evidence, therefore, repetitive high energy debris flows, past or future.
The material of a debris fan was debouched from a steeply sloped ravine as very fast-
moving water highly charged with soil and rock debris, and the surface of the fan is sloped as
steeply as 2 to 4:'1. Many debris fans are apparent along both sides of the Gore Creek Valley in
the Vail area, but the fan at the mouth of Mill Creek is not one of them. The floor of the Mill
Creek Valley is shallow-sloped along its course for at least 3 miles upstream from its mouth,
thus the floods that have emanated from it have been much lower energy events, mainly of water
carrying much less soil and rock debris than their sister events, the debris florvs; and the
surface of the fan is sloped at a low angle (about l5:l ) typical of alluvial fans. The fan
probably was constructed mainly during the first few thousands of years after the end of the
lce.Age, thus is a geologically old feature (relative, certainly, to the time of modern habitation
of the valley), for the most paft, although periodic flooding of Mill Creek since then no doubt
has contributed soils to build this oeolooic structure.
Moreover, the risk of debris flows coursing down the Mill Creek Valley after discharge
from streams occupying steep ravines tributary to that valley is low because the slopes of the
valley, although typically steep, are densely forested, mainly with evergreens. The geologic
hazard associated with an alluvial fan is stream flooding, and that risk should be evaluated by an
hydrologist. However, the Mill Creek alluvial fan has not been invaded by flood water, to our
knowledge (admittedly meager), since the founding of the town of Vail, a large section of which
has been constructed on this fan.
The Mill Creek alluvial fan soils, likely several tens of feet thick, probably include poorly
stratified, cobbley and bouldery, silty to clayey sands and gravels that probably are underlain
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R. J. lrish
Consulting Engineering
Geologist, lnc.
by morainal and/or glaciofluvial soils tens of feet thick. The alluvial fair soils may be subject to
differential settlement, hence that should be considered in the development of foundation designs
for the building.
Othenn ise, geologic conditions pertinent to the Golden Peak Base Facilities site appear to be
benign. We found no evidence to suPPort any affirmation of geology-related hazards that should
be consi.dered in the design, construction, or operation of the planned facility, including rock
fall/rockslide risk, debris flow risk, landslide risk, or avalanche risk (provided, of course,
the slopes ofthe adjacent Golden peak ski Areaareproperly groomed and protected). so long as
the natural ground stability across the project area is not significantly disturbed by large cuts
and fills-and we understand the cut slopes for the building basement will be geotechnically
engineered-the ptanned construction activity and the operation of the planned facility should
have a negligible impact on site geologic conditions and should not trigger any geology-related
hazards. consequently, that activity, in my opinion will not increase the geology-related hazard
to neighboring properties or structures, or to public buildings, roads, streets, rights-of-way,
easements, utilities, or facilities.
I hope my evaluations and conclusions rvill be of some service to you' lf you have any
questions, please call.
Yours truly,tutuw
Consulting Engineering Geologist
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Comments on EIR Russ Forrest, Senior Environmental Policy Planner
The following axe comments on the Golden Peak Environmental Impact Report. There are still
some significant issues that need to be resolved. However, I feel that the information has been
generated to address these issues, but simply need to be incorporated into the EIR. There are
sigdficant discrepancies between an Alpine Engineering letter dated August 7th to Greg Hall and
the EIR. On November 16th, I spoke with Lynn Schoor of Alpine Engineering and she stated that
a correction would be made to the EIR prior to the December 4th PEC meeting. However, staff
had not received a copy of the revised EIR at the time these comment were prepared.
Culvert extension/Ileadwall:
The Army Corps of Engineers has provided verbal comments to the affect that the Corps
would prefer to maintain flows in the main stem of Mill Creek and only use the east branch
for flood control. In discussions with the applicant an idea was discussed to create a small
berm at the headwall were tle main stem and the east stem of Mill Creek diverge. This
berm would be designed so that flows would be focused down the main stem while
allowing some flow down the east branch, primarily for aesthetic reasons. This would also
allow the east branch to be used for flood events witlout any operation of flood gates. A
recommendation to this affect was in the August 7th letter to Greg Hall from Alpine
Engineering. This letter states that the 100 year flood is not contained in the existing
culvert on the west side. In addition this letter stated that the inlet capacity should be
increased to the 100 year nrnoff event of 480 cfs, or 240 per side. The letter further
states that this could be accomplished by increasing the headwater depth by I foot. The
information and conclusions from the August 7th letter need to be incorporated into the
EIR.
F'loodplain Alteration :
There is a floodplain issue even if the mapping does not extend up the east branch of Mill
Creek. There have been recent flooding and debris flow events on Mill Creek which
conflicts with Mr. Irish's conclusions "the Mill Creek alluvial fan has not been invaded by
flood water to our knowledge..". Mr. Irish does recommend that strearn flooding should
be evaluated by a hydrologist We also asked the applicant to look at a 500 year flood
event when determining whether the culvert would have an impact on other property
owners. Again the letter dated August 7th discusses the 100 and 500 year flood.
Recommendations from this letter need to be incorporated into the EIR.
Construction Dewatering:
The ACE asks for 0 fines discharged in dewatering activity. The Town will monitor
dewatering activity to ensrue that water quality in Gore Creek is not impacted from
increased sedimentation or turbidity from construction activity. It is assumed" although not
clearly stated in the EIR, that the detention ponds will be used to mitigate this discharge.
Please provide a more detailed discussion of how dewatering will occur and be mitigated.
This could be a condition ofapproval.
Stream Diversion:
I agree that the best way to reduce erosion & sedimentation is to divert flow to the main
stem. The only concern I would have is reopening the east branch once construction is
completed. Additional sedimentation traps may need to be installed to prevent the
discharge of sediment that will a,ccumulate in the east branch during construction.
Nonpoint Source Impacts
Creation of a sediment and oil tap does adequately address impacts from the parking area.
However, the mitigation of impacts from surface nrnoff is unclear. The EIR basically
states that this will be addressed when a building perrnit is required. This is acceptable if it
is clear tlat mitigation will be required to address any increase in flow of the site from
snow storage or nrnoff.
Debris Flow:
It is necessary, as per section 18.69.052 of the Town code, to demonstate that a
structure in a geologic hazard area does not need special engineering to protect public
safety, Mr Irish states that there is no significant hazard on the site and that the creation
of the development does not exacerbate the hazard. In discussing this section with Greg
Hall we noted several times in recent history where there have been debris flow incidents
in Mill Creek. The knowledge that there have been debris flow incidents within the last l0
to 15 years seems to contadict the conclusions made by Mr lrish. I would recommend
that the debris flow analysis in this report be reviewed by a third party who is a qualified
geologist or engineer. A third party review oould occur as a condition ofapproval which
could also require mitigation if it was found be necessary to comply with the Town's
hazard regulations.
As per section 18.56.110, the PEC should review the EIR within 30 days and approve,
disapprove, or request sfuanges in the project in writing. The PEC "shall approve the project
unless it finds that either the project will have sipificant long-temt adverse effects on the
envhonment or will have short-term adverse effects on tle environment so detrimental that public
health safety or welfare considerations preclude approval ofthe project.
F :\cveryonewsshemos\golden.eil