HomeMy WebLinkAbout6_AdditionalPlatSupplements_12661.pdf Additional Subdivision Preliminary Plat Supplements
A. Surface Water
1. Mapping
The existing surface water resource within the proposed Westbrook Subdivision is Baxter
Creek. See Appendix A of this application for copies of the Gallatin County Ditch Map,
and the Flood Insurance Rate Map highlighting the subject property and existing
watercourses.
2. Description
One perennial waterway flows through the property in a northerly direction, eventually
draining to the East Gallatin River. Baxter Creek traverses the entire length of the property
from south to north. Montana Fish, Wildlife, and Parks (MFWP) classify Baxter Creek as a
stream/ditch.
As shown in the Wetland Impact Summary Map (Appendix A), the proposed road layout
involves one surface water crossing. Utility crossings will occur within the road right-of-
way as shown in the Utility Layout Map. All other construction will take place outside of
the surface water corridors.
Storm water detention and water quality ponds will be located throughout the subdivision
(see Drainage Map in Appendix E). These ponds will discharge storm water at the pre-
development runoff rate to Baxter Creek. The detention ponds will be designed to
minimize degradation of water quality in the receiving streams. Design of the detention
ponds will be in accordance with the City of Bozeman Storm Water Master Plan and
Design Standards and Specification Policy.
3. Water Body Alteration
Development of the property will include construction of roads across existing streams.
Three new culverts are proposed on Baxter Creek and one culvert proposed on Baxter
Ditch for road and utility crossings. Impacts to the stream channel and wetlands associated
with the road crossings will require a 310 Permit and 404 permit from the Gallatin County
Conservation District and the Army Corp of Engineers (USACE), respectively. 310 and
404 permits have been previously obtained for the stream crossings. A copy of the new
404 permit application revised in 2013 is attached in Appendix A. Also attached in
Appendix A are copies of the updated Waters of the U.S. Delineation Report and Wetland
Mitigation Plan which have been provided to the USACE. The 310 permit will need to be
obtained from the Gallatin Conservation District (GCD) prior to culvert installation. The
approved 310 and 404 permits are included in Appendix A.
4. Wetlands
Vaughn Environmental Services of Bozeman, Montana, completed a wetland delineation
and wetland mitigation plan for the original subdivision (Phases 1-4) in fall 2001. US
Army Corps of Engineers (USACE) Permit #2001-90-847 was approved on October 15,
2002, and expired on October 15, 2007. Over the five year period since the original
delineation was completed the wetland boundaries associated with Baxter Creek have
shifted as a result of the change in land use from flood irrigated pasture to residential. The
wetlands within Phases 3 & 4 were re-delineated on June 24, 2008. A copy of the 2008
Waters of the US Delineation Report is attached in Appendix A. The 2008 delineation is
still valid and acceptable by the USACE. The delineation report specifically addresses all
wetlands found within the boundaries of Westbrook Subdivision.
A new Wetland Mitigation Plan and 404 permit application have been prepared and
submitted to the USACE addressing all wetland impacts associated with the construction of
Westbrook. The only impact associated with Westbrook are a result of roads crossing the
existing wetlands. A 50 foot watercourse setback will be maintained from the edge of the
wetlands at all areas outside of the road crossings. Copies of the Mitigation Plan, permit
applications, and approved permit are attached in Appendix A.
B. Floodplains
A floodplain analysis was performed by Allied Engineering and approved by the City of
Bozeman Engineering Department for all phases of Westbrook Subdivision. Although the
layout of the lots has changed from the original preliminary plat submittal, no additional
alterations to the stream are being made. All proposed stream crossings will remain as
permitted. A floodplain delineation with the current lot layout is shown in Appendix A. A
copy of the floodplain analysis and related material is included in Appendix A.
C. Groundwater
General Information
1. Depth
Attached in Appendix B are test pit logs from 24 excavations on site along with a
groundwater depth map. The test pits indicate groundwater is found at depths ranging from
3.3 feet to at least 28 feet. Observation of construction over the past 4 years have
confirmed these groundwater depths and have shown seasonal fluctuation with seasonal
highs reaching close to 2 feet.
Soils information from the Natural Resources Conservation Service (MRCS) was utilized to
help confirm the site's seasonal water depths (see Appendix B). According to the NRCS,
many of the soil types mapped on the site are commonly found in areas exhibiting high
groundwater conditions. Approximately half of the site is covered by soils that typically
have high water tables extending within one to four feet of the ground surface. The
remaining 50 percent of the site's soils have estimated high groundwater tables of at least
six feet or below. Generally, the sites anticipated seasonal high groundwater depths
discussed above correspond with the groundwater characteristics of the mapped soil types.
However, it appears that some of the soils mapping is not entirely accurate, particularly in
the south-central portion of site.
Shallow groundwater between the depths of four and five feet was encountered throughout
much of this area, even though it was mapped as normally having high groundwater tables
greater than six feet.
Shallow groundwater conditions are prominent across the majority of the site. However,
many of the limitations and negative impacts posed by groundwater can be successfully
mitigated with the proper planning, design, and construction of the site's utility, street, and
building improvements. The geotechnical report included in this submittal (Appendix B)
presents detailed recommendations for site development in shallow groundwater
environments. A summary of these recommendations are provided in a following section
entitled "protective measures".
2. Steps to Avoid Degradation
The proposed development will be connected to the City of Bozeman's public drinking
water and sanitary sewer system. On-site wastewater treatment systems are not part of this
project and the project will not have an adverse impact on groundwater quality due to
impacts from domestic wastewater. Surface runoff will be controlled by channeling flows
into retention and detention areas which will limit discharges to pre-development rates and
allow for percolation and aquifer recharge. The basins will also filter sediments and oil
reducing the potential for contamination of down gradient aquifers.
D. Geology- Soils- Slopes
General Information
The site is located on the Bozeman alluvial fan complex, an extensive Quaternary-aged,
geologic formation covering much of the southeastern corner of the Gallatin Valley.
According to published literature, it is composed of a heterogeneous mixture of fine to
coarse-grained sediments (ranging in size from clays to boulders) eroded from the
southward lying Gallatin Range, transported into the valley by fluvial processes, and
deposited as a thick accumulation of intermixed materials. Well-graded, sandy gravels
(with abundant cobbles) predominately comprise the deposit; however, occasional lenses of
fine sands, silts and clays are encountered. Gravels are usually encountered at depths of
less than ten feet below the ground surface and are typically over lain by a variable thick
silt/clay layer of primarily flood-plain origin. The shallow fine-grained soils are often
blanketed by organic-rich topsoil. Underlying the alluvial fan deposit are semi-consolidated
beds of Tertiary-aged clays, silts, sands,and gravels, which are considered
to be "bedrock". In the vicinity of the site, the depth to bedrock is generally greater than
100 feet below the ground surface.
Based on 37 test pit excavations that were performed as part of the geotechnical evaluation
for the site, it appears soil conditions are consistent with the mapped geology as described
above. Generally, the soil stratigraphy (with increasing depth) consisted of the following
three distinct layers: black topsoil, brown silt, and gravel deposits. Depending on test pit
location, the topsoil thickness ranged from one to five feet, while gravel depths extended
between two and eight feet below the ground surface. The intermediate layer of silt had a
non-uniform thickness across the site. For a complete and detailed summary of the site's
soil conditions, see the geotechnical report in appendix B.
1. Geologic Hazards
The subdivision site is located in a valley that consists of flat-sloping topography (1.0 -
1.5%), upland terrain, and shallow gravelly soils. Therefore, there are no potential geologic
hazards present with respect to slope stability, mass movement, surface subsidence,or soils
bearing capacity. Westbrook is classified as Seismic Zone 3, considered to be a seismically
active zone. Since the entire Gallatin Valley is also classified as Seismic Zone 3 the
seismic risks at the site are no different than anywhere else in the Bozeman area. Based on
the subsurface investigation, the site's native gravels are most likely not susceptible to
liquefaction under seismic activity. This geologic issue is further discussed in the
geotechnical report (Appendix B). As addressed in a previous section, a high groundwater
table affects the site. However, the shallow groundwater conditions are simply an
inconvenience, not a geologic hazard. As long as the protective measures detailed below
are considered during the planning, design and construction of the subdivision
improvements, existing subsurface conditions will not greatly impact or limit site
development.
2. Protective Measures
a. Utilities
Due to the site's groundwater conditions, the intermediate silts, which are moisture
sensitive, will be the most problematic native material encountered during utility
construction. As the moisture content increases, these soils will substantially soften in
consistency, which subsequently wakens their support capacity. In addition, they will be
impossible to compact when overly moist. As a result of these soil characteristics, the
geotechnical issues that must be adequately addressed when these silts are involved are
foundation support (or utility lines), thrust restraint(of water mains), and the compaction of
trench backfill. IN all applicable locations, the use of Type 2 bedding for trench foundation
stabilization and the use of thrust restraints will be required. The inspection and testing of
backfill processes will be very important to ensure satisfactory soil compaction is being
achieved under roadways in order to reduce potential trench settlement concerns.
Dewatering will likely be required for most utility line installations.
b. Streets
Finished street elevations should closely match or exceed existing grades in order to limit
conflicts with high groundwater and reduce the potential for soft subgrade soils. Street
grades below the natural topography should be discouraged. The majority of the site's
subgrade soils will consist of the intermediate silts, therefore the use of a thickened
gravel section and a geotextile separator fabric under all paved surfaces is recommended
for adequate structural support. In locations where unstable subgrade materials are
encountered, the installation of structural geogrids or over-excavation/ replacement (with
gravel)practices may have to be incorporated into the construction of the streets.
C. Buildings
Buildings with full basements or interior slabs set below existing grades will not be suitable
due to shallow groundwater depths. In order to reduce the potential for moisture
related problems in crawl spaces, the depths to which they extend below the natural ground
surface should be minimized. As an added precaution against high groundwater in crawl
space applications, the installation of footing drains around the perimeter of the foundation
is recommended. In locations where these subsurface drainage improvements cannot be
feasibly implemented, all components that could be negatively affected or severely
damaged by water should be eliminated from the crawl space, particularly those essential to
the operation of the structure. The gravel deposits encountered at depths ranging between
two and eight feet below the ground surface are the most structurally competent material
under the site for use as foundation support. Therefore, they are the "target" bearing
material for all building improvements. All footings are recommended to either bear
directly on these native materials; or indirectly on them via structural fill (i.e. the structural
fill must be supported on the gravels and extend up to the base of the footing). None of the
silty soils that lie above the gravels are recommended for foundation support due to their
moisture sensitivity and the site's high groundwater environment. They have a much
greater susceptibility for non-uniform soils bearing capacity and the potential for settlement
is likely.
3. Unusual Features
The site contains no unusual topographic, geologic or hydrogeologic conditions limiting its
capability to be developed using standard engineering or construction practices. The site's
shallow groundwater environment is its most prominent limitation. Groundwater
dewatering will be required for most site work, including the construction of utilities,
streets, and structures. Based on previous development in areas having a similar
groundwater environment, construction dewatering operations for this project can be
successfully implemented.
4. Soils Map
According to NRCS soils data(see Appendix B), there are six mapped soil types within the
boundary of the site. These soil types are defined by a different map unit, but are all quite
similar with respect to their silt loam composition, topographic locale, and relatively
shallow seasonal high groundwater depths. For convenience, a summary of the site's soils
are presented in the following table.
Map Unit Soil Name Coverage Typical Slope Approximate
W/I Of Ground Depth To Seasonal
Subdivision Surface (%) High Groundwater
(%) (Ft.)
448A Hyalite-Beaverton 10 0.0-2.0 4.0-8.0
Complex
Map Unit Soil Name Coverage Typical Slope Approximate
W/I Of Ground Depth To Seasonal
Subdivision Surface (%) High Groundwater
457A Turner Loam 33 0.0-2.0 4.0-8.0
537A Lamoose Silt Loam 30 0.0-2.0 1.0-2.0
748A Hyalite-Beaverton 20 0.0-4.0 >6.0
Complex
453B Amsterdam-Quagle 0.0-4.0 >6.0
Silt Foams 5
509B Enbar Loam 2 0.0-4.0 2.0-3.5
Figure 4-3(Appendix B) is an aerial photograph of the site overlain with the NRCS soils
map. This figure illustrates the layout and distribution of the above referenced soil types.
Detailed soils reports, obtained from the NRCS database, are enclosed in Appendix B. The
information contained herein includes descriptions of each soil type's physical and
engineering index properties, water features, hydric characteristics, and site development
limitations.
5. Cuts and Fills
Fill within the right of way will primarily be composed of imported fill material. Where
cuts and fills are required outside of the right of way, material will generally be moved
from cut areas to fill areas.
The construction contract shall provide for landscaping, seeding, and fertilizing of all cut
and fill slopes. The overall storm water master plan/erosion control plan required by
MDEQ will detail all necessary erosion control measures. "Best Management Practices"
will be utilized to minimize erosion and any down gradient impacts. The Covenants and
Weed Control Plan include provisions to ensure that re-seeding and erosion control is
provided as individual buildings are being constructed.
E. Vegetation
1. Vegetation Map
The NRCS Soils and Vegetation Map has the Westbrook site listed as Shallow to Gravel
(map units 448A and 748A), Sub-Irrigated (map units 509B, 510B and 5UA), Silty (map
units 453B and 457A), and Wet Meadow (537A) (See Figure 4-3 for location of mapped
units). According to NRCS data (Appendix B), the area receives annual precipitation of
approximately 15 to 19 inches per year.
A recent aerial photograph with the proposed subdivision overlaid is attached in Appendix
A. The aerial photo show the nature of the site topography and vegetation.
The bulk of the pasture vegetation is comprised of timothy (Phleumpratense) wheatgrass
species (agropyron spp.) Kentucky bluegrass (Poa pratensis), meadow fescue (Festuca
pratensis), tall fescue (Festuca arundinacea), redtop (Agrostis alba), smooth brome
(Bromus inermus), dandelion (Taraxacum officinale) and quackgrass (Agropyron repens).
Small patches of Canada thistle (Cirsium arvense) and musk thistle (Carduus nutans),
Category I noxious weeds, were also observed. Pasture or upland plant species generally
correspond to NRCS map units 748 A, 448 A, 453 Band 457 A (Figure 4-3). The wetland
delineation completed for the proposed subdivision identified numerous wetland species
including meadow foxtail (Alopecurus pratensis), reed canary grass (Phalaris
arundinacea), beaked sedge (Carex rostrata), Nebraska sedge (Carex nebrascensis),
slender sedge (Carex tenera), water sedge (Carex aquatilis),creeping wildrye (Elymus
It-iticoides) tall mannagrass (Gyceria elata), Baltic rush
(Juncus balticis), common rush (Juncus tenius), various willow species (Salix spp.),
mountain alder (Alnus tenuifolia), red osier dogwood (Corpus stolonifera), small buttercup
(Ranunculus uncinatus) and watercress (Rorippa nasturitium-aquticum). NRCS map units
generally related to this type of vegetation include 509 B, 510 Band 511 A (Figure 4-3).
A noxious weed management plan has been approved by the Gallatin County Weed Office
for the control of weeds associated with development. A copy of the weed plan and Memo
of Understanding are included in Appendix C)
2. Protective Measures
Much of the site will be disturbed during the construction of the proposed project, either
during construction of the roads and other infrastructure, or during the development of each
lot. No critical plant communities will be disturbed. Existing woody species on the site are
associated with the Baxter Creek corridor and the depressional wetland. These trees and
shrubs will not be disturbed except at road crossings or in the wetlands
enhancement/mitigation areas.
For more information on critical plant species in and around the proposed subdivision, see
the response letter from Montana Natural Heritage Program included in Appendix C.
F. Wildlife
1. Species
The November 19, 2001:-"Wetland Delineation Report by Vaughn Environmental
Services, includes functional assessments of each wetland. The habitat assessment
addresses fish and wildlife habitat and discusses identification of species and/or indication
of species habitation (tracks, scat and etc.)
The field investigation performed as part of the wetland delineation revealed little to no
wildlife signs near the pond, Baxter Ditch, or the depressional wetland along the north
boundary. According to this report there are sparse food sources in adjacent uplands.
Similar observations were noted in the area around and including Baxter Creek. Wildlife
food sources and cover were limited to isolated areas on Baxter Creek and the depressional
wetland.
2. Critical Areas
There are no critical wildlife or habitat areas noted on the property. For more information
on critical wildlife in and around the proposed subdivision, see the response letter from
Montana Natural Heritage Program included in Appendix C.
3. Pets/Human Activity
The proposed subdivision was approved for annexation into the City of Bozeman and is
subject to city animal control laws that require licensing of pets and leashes on dogs.
Impacts from human activity will be minimal since the site does not contain significant
wildlife.
4. Public Access
Currently there are no public trails, hunting or fishing areas on or near the site. Public
access will be improved through the establishment of a trail system dedicated to the city of
Bozeman.
5. Protective Measures
The majority of site's wetlands will likely not be significantly impacted by project
development. The riparian systems associated with Baxter Creek will be protected within
continuous open-space corridors. Mitigation measures associated with the 404 Permit will
improve fish and wildlife habitat by removing the on-stream reservoir, creating pool and
riffle complexes on the tributary, and establishing woody plant species on both riparian
corridors. Trees and shrubs planted adjacent to the channels will provide food sources and
improved protective cover for wildlife. Woody plants also provide shade that will reduce
water temperatures, increase dissolved oxygen concentrations and increase invertebrate
insect populations. Woody species planted on the corridors may include willow,
cottonwood, alder, serviceberry,chokecherry,and currant.
6. Fish, Wildlife and Parks
Written comment was received from Montana Fish, Wildlife and Parks Fisheries Biologist,
Michael Vaughn. His concerns include impacts to fish in Baxter Creek. Mr. Vaughn
would like to see bridges used instead of culverts for stream crossings. He recommends to
avoid activity near surface waters,to avoid disturbing riparian or wetland vegetation,and to
avoid delivering pollutants to the surface waters (via storm drainage). Another concern is
preventing localized stream disturbances during construction. A copy of his letter dated
November 14, 2013 is included in Appendix D.
The proposed layout of Westbrook addresses the majority of Mr. Vaughn's concerns. The
proposed layout includes a large watercourse/wetland corridor with setbacks where impacts
to Baxter Creek are minimized. Wetland mitigation will occur within the corridor to
offsets the impacts from the proposed road and utility crossings. The mitigation measures
will increase the functional quality of the wetlands and enhance the fish habitat. A storm
sewer collection system will be designed to City of Bozeman standards, diverting the storm
drainage into detention and retention basins designed to remove sediment and pollutants.
Localized stream disturbance during construction will be minimized using "Best
Management Practices" outlined in the "Storm Water Pollution Prevention Plan' required
by MDEQ as a part of the General Permit For Storm Water Discharge Associated With
Construction Activity.
G. Historical Features
Written comments from Mr. Damon Murdo of the Montana Historical Society are included
in Appendix D. According to his letter, there are structures on the property that are over
fifty years of age. Any structure over 50 years of age is potentially eligible for listing on
the National Register of Historic Places. A cultural resource inventory was performed and
is included in Appendix M.
H. Agriculture
1. Number and type of acres in production
The 33.57-acre Westbrook Subdivision site currently consists of one single family
residence and vacant pastureland.
2. Agricultural operations in the vicinity
The area around the development consists of pastureland, hayfields and single-family
residences.
3. Productivity of the Land
Data from the Natural Resources Conservation Service(MRCS), and Gallatin County Soil
Survey indicates the proposed development contains the following mapping units (Figure
4-3) and associated forage species:
-448A &748A Hyalite-Beaverton - 15001bs/acre Idaho fescue(Festuca idahoensis). and
11001bs./acre arrowleaf balsamroot (Balsamorhiza sagittata).
-453B Amsterdam -2200 lbs. /acre Columbia needlegrass (Stipa columbiana)and 1400
lbs. /acre of Idaho fescue.
-457A Turner- 2200 lbs. /acre Columbia needlegrass and 1800 lbs. /acre of Idaho fescue
-509B Enbar-4500 lbs./acre Nebraska sedge (Carex nebrascensis) and 4000 lbs. /acre
basin wildrye (Leymus cinereus).
-537 A Lamoose- 5000 lbs. /acre Nebraska sedge and 3000 lbs. /acre bluejoint
(Calamagrostis Canadensis).
The above values are typical NRCS production based on soil series using native vegetation.
Vaughn Environmental performed a wetland delineation for the proposed subdivision on
November 19, 2001 and again in 2008. According to the report, the majority of pasture
vegetation consists of timothy (Phleum pratense) wheatgrass species (agropyron spp.)
Kentucky bluegrass (Poa pratensis), meadow fescue (Festuca pratensis), tall fescue
(Festuca arundinacea), redtop (Agrostis alba), smooth brome (Bromus inermus), dandelion
(Taraxacum officinale) and quackgrass (Agropyron repens), Canada thistle (Cirsium
arvense) and musk thistle (Carduus nutans), Category I noxious weeds, are present in
minor amounts. Pasture or upland plant species generally correspond to NRCS map units
748 A, 448 A, 453 Band 457 A (Figure 4-3). Plant species typical of moist sites include
meadow foxtail (Alopecurus pratensis), reed canary grass (Phalaris arundinacea), beaked
sedge (Carex rostrata), Nebraska sedge, slender sedge (Carex ten era), water sedge (Carex
aquatilis), creeping wildrye (Elymus triticoides) tall mannagrass (Gyceria elata), Baltic
rush (Juncus balticis), common rush (Juncus tenius), various willow species (Salix spp.),
mountain alder (Alnus tenuifolia), red osier dogwood (Corpus stolonifera), small buttercup
(Ranunculus uncinatus) and watercress (Rorippa nasturitium-aquticum). NRCS map units
generally related to this type of vegetation include 509 B, 510 B and 511 A (Figure 4-3).
After full development,the land would not be used for farming.
4. Farmland Viability
Due to the fractured ownership of the surrounding properties and encroaching development
the site is no longer considered a viable farming unit.
5. Containment of Family Pets
Covenants will include restrictions on the containment of family pets. Homeowners will be
required to meet City of Bozeman pet licensing requirements and leash laws.
6. Fencing
Fences found within the property will be removed as soon as development begins.
Perimeter fencing will be left in place for as long as possible during construction. After the
construction phase, the maintenance of fences adjacent to land under agricultural use will
be the responsibility of the individual lot owners.
I. Agricultural Water Use
1. Type, description, ownership,and users of facilities
Perennial surface water systems within the subdivision include Baxter Creek. Baxter Creek
flows through the entire property.
Baxter Creek originates approximately 2.8 miles south of the property in Section 22 of
Township 2, South Range 5 East, and flows approximately 1.4 miles to the north where it
is intercepted by Farmers Canal. Flow in Baxter Creek starts again downstream of ponds
located southwest of the intersection of Huffline Lane and Cottonwood Road in Section 16,
Township 2 South, Range 5 East and is supplemented by irrigation water from Farmers
Canal. Baxter Creek continues northward through the property and eventually discharges to
Hyalite Creek approximately 5.6 miles north of the property in Section 8, Township 1
South, Range 5 East. Baxter Creek carries water for private water rights users and
shareholders of the Farmers Canal Company.
Downstream water users of Baxter Creek include irrigation, stock water, recreation,
commercial, fish and wildlife.
There are no plans to alter stream/ditch corridors that will impact downstream water users,
although there will be temporary disturbances to the streams/ditches during construction
associated with the culverts and channel improvements. 310, 404, and Montana Pollutant
Discharge Elimination System (MPDES) permits will be obtained before construction
activities commence within the channels. Flow should not be disrupted during construction
and appropriate measures will be taken to prevent silting of waterways as required by
applicable permits. Flow to downstream water users will not be affected during
construction or after full development of the property. Culverts will be appropriately sized
and placed to accommodate anticipated peak flows and to prevent flow restrictions.
J. Water and Sewer Supply
1. Water Supply
i Water for domestic use and fire protection will be provided by connections to the City of
Bozeman water system. 8-inch water mains will be looped through the subdivision
connecting to existing 8" mains in Laurel Parkway and Annie Street. 8-inch mains will be
extended into the subdivision from the exterior roads and looped throughout. Hydrants will
be provided at intervals no greater than 500 feet throughout the subdivision as specified in
the Uniform Fire Code.
Water Usage is based on the following criteria:
Population Estimate
(R1 Zoning) = 62 dwelling units x 2.11 persons per dwelling unit =131 persons
(R4 Zoning) = 56 dwelling units x 2.11 persons per dwelling unit =118 persons
The overall annual average daily demand of 170 gallons per day(gpd) per person
is suggested for all future development. The demand estimate includes:
1.) Fire flows, flat rate accounts, leakage, under registering meters and other
unaccounted water usage such as street cleaning, hydrant and sewer
flushing. (Water Facility Plan, page 18)
2.) Base flow water.
3.) Increases in summer usage including lawn and garden irrigation, non-
commercial car washing, cleaning sidewalks, and other miscellaneous
metered uses.
Utilizing the 170 gpd per person,the predicted average daily water demand for the
Westbrook Subdivision is 42,330 gpd.
Preliminary analysis indicates that the Bozeman City water system can supply water to this
property. Final approval of water connections will be obtained through the normal
approval process of the preliminary plat, design report, and construction plans. Approval
will also be required from MDEQ.
2. SANITARY SEWER
Westbrook will require connection to the City of Bozeman's existing sewage collection
system. The subdivision will be serviced by existing 8" sewer mains located on Annie
Street, Laurel Parkway, and Oak Street. The existing mains flow to the West and North,
respectively, to an existing lift station on Oak Street installed with Laurel Glen Phase 1.
The lift station was sized with Phase 1 to handle the sewage from all Phases of Laurel Glen
Subdivision as well as Westbrook Subdivision. Sewage will be conveyed to and treated at
the City of Bozeman's Wastewater Treatment Plant located at Moss Bridge and Springhill
Road.
Design Requirements
The capacity of the 8-inch main at the intersection of Annie Street and Laurel Parkway to
serve the west section of Westbrook is checked as follows:
The peaking factor for the design area is determined by figtuing the equivalent population
and inserting the population into the Harmon Formula. The population to be served in the
west section of Westbrook is calculated as follows.
Population Estimate
(R1 Zoning) = 62 dwelling units x 2.11 persons per dwelling unit = 131 persons
Harmon Formula: Peaking Factor= (18 + P•5)/(4 +P•5) P=Population in
thousands
Peaking Factor= (18 + 0.131-5)/(4 + 0.131-5)
Peaking Factor= 4.21
Assumed infiltration rate = 150-gallons/acre/day = 150(26.51 acres =3976.50 gal/day.
The peak flow rate is calculated by multiplying the City's design generation rate of 89
gallons per capita per day by the population, multiplying by the peaking factor, and adding
the infiltration rate.
Peak Flow Rate= 89 gpcpd (131 persons)(4.21) + 3 976.5 0 = 53,060.89 gpd
36.85 gpm
0.0821 cfs
The capacity of an 8-inch main at minimum slope is checked using Manning's Equation:
Qruu = (1.486/0.013)AR2/35112
For the 8 inch main:
Manning's n= 0.013 for pvc
Minimum Slope(%)= 0.400%
Minimum Slope (S)= 0.004 (ft/ft)
Pipe Diameter(d) = 0.660 ft.
Area(A)=(pi/4)d^2 = 0.342 ft.^2
Wetted Perimeter(P) =2(pi)r 2.073
R=A/P 0.165
RA(2/3)= 0.301
S^(%)= 0.063
Qfu11 = 0.7592 cfs
Q= 0.0821 cfs
Q/Qfu11 = 10.80%
The 8-inch sewer main proposed to service this part of the subdivision will be more than
adequate to carry the design flows at frill build-out at minimum slope.
The capacity of the 8-inch main extending from Oak Street, serving the east portion of
Westbrook Subdivision is checked as follows:
The peaking factor for the design area is determined by figuring the equivalent
population and inserting the population into the Harmon Formula. The population of this
portion of Westbrook Subdivision at full build is calculated as follows.
Population Estimate
(R4 Zoning) = 56 dwelling units x 2.11 persons per dwelling unit = 118 persons
Harmon Formula: Peaking Factor= (18 +P•5)/(4+ P•5) P= Population in
thousands
Peaking Factor= (18 +0.118-5)/(4 + 0.118-5)
Peaking Factor=4.22
Assumed infiltration rate= 150-gallons/acre/day = 150(8.835acres) = 1325.25 gal/day
The peak flow rate is calculated by multiplying the City's design generation rate of 89
gallons per capita per day by the population, multiplying by the peaking factor, and adding
the infiltration rate.
Peak Flow Rate= 89 gpcpd (118 persons)(4.22) + 1325.25 = 45,643.69 gpd
31.70 gpm
0.0684 cfs
The capacity of an 8-inch main at minimum slope is checked using Manning's Equation:
Qfuli = (1.486/0.013)AR2'S"2
For the 8 inch main:
Manning's n= 0.013 for pvc
Minimum Slope (%)= 0.400%
Minimum Slope(S) = 0.004 (ft/ft)
Pipe Diameter(d) = 0.660 ft.
Area(A)=(pi/4)d^2 = 0.342 ft.^2
Wetted Perimeter(P) = 2(pi)r = 2.073
R=A/P 0.165
R^(2/3)= 0.301
S^(%)= 0.063
Qfu11 = 0.7592 cfs
Q= 0.0684 cfs
Q/Qfu11 = 9.00%
The 8-inch sewer main proposed to service this part of the subdivision will be more than
adequate to carry the design flows at full build out at minimum slope.
K. Storm Water Management
Storm water run-off from Westbrook Subdivision will be directed to multiple storm water
detention/retention areas on site. Allied Engineering's Storm Water Facilities Design
Report included a large portion Westbrook to be drained into the detention pond located to
the Southeast of the intersection of Glenellen Drive and Laurel Parkway. The layout of the
roads and lots for Westbrook has changed, and the areas to be drained to this pond are
depicted on the drainage map included in Appendix E.
The area to be drained to the existing pond, Area#1 = 13.66 acres, is smaller than the area
projected to drain to the pond in Allied's phase 1 report, 15.32 acres. Assuming a similar
drainage coefficient will be exhibited with Westbrook, the existing pond will be more than
adequate to handle that portion of the runoff from the proposed Westbrook Subdivision.
The rest of the site was divided into drainage areas which drain to detention ponds that will
release into Baxter Creek and Baxter Ditch at the pre-development now rate.
The storm water runoff rate was calculated with the rational formula as shown. A runoff
coefficient C) of 0.50 was applied to all residential lots regardless of zoning to be
conservative. A runoff coefficient of 0.73 was calculated for the right of way typical of the
roads in the subdivision. A runoff coefficient C) of 0.20 was used for all park land and
open space as well as the calculation of the pre-existing runoff.
The detention ponds were sized using the rational method to solve for the time of
concentration, then calculating the pre-development flow rate. The post development flow
rate was then calculated and a storm duration chart was developed indicating the maximum
amount of storage required for each drainage basin. The calculations for each basin are
included in Appendix E. More detailed calculations will be provided in the design report
required for city and MDEQ approval.
L. Streets, Roads, and Alleys
1. Description
Access to the site will be provided from Laurel Parkway, Annie Street, and Durston Road.
The project will include right of way dedications for all interior streets.
2. Access to Arterial
Lots within the proposed subdivision will not have direct access to any arterial streets or
roads. Durston Road is a minor arterial street that fronts the south side of the property and
will be accessed from local streets within the subdivision.
3. Modification to Existing Streets
a. Durston Road
Durston Road was constructed with Laurel Glen Subdivision Phase 1 with two 13' wide
drive aisles, a 5' wide bike path. A city standard sidewalk will be installed on the North
side of the road.
b. Annie Street
The easterly portion of Annie Street was constructed with Phase 1 of the Laurel Glen
development, dedicating 74 feet of right of way, with two eleven foot driving lanes, a five
foot bike lane, and a seven foot parking lane. This project will construct Annie Street to the
same specifications from the east boundary of Laurel Glen to the intersection Laurel
Parkway.
C. Local Interior Roads
All local roads will be constructed to the city standard with a 60 foot dedicated right of
way, 33 feet from back of curb to back of curb, an 7.5 foot wide boulevard strip between
the curb and sidewalk, and 5 foot wide sidewalks. See Appendix L for a drawings showing
the typical street cross section.
4. Dust
Dust will not be a problem because all interior and arterial roads will be paved. There will
be some dust during construction,but this will be mitigated with water.
5. Pollution and Erosion
Road maintenance for all streets will be provided by the City of Bozeman after the
improvements have been accepted by the City. On site runoff will be treated with
detention facilities. Erosion and siltation control will be exercised during construction by
using the appropriate best management practices as outlined in "Montana Sediment and
Erosion Control Manual"(May 1993) prepared by the MDEQ Water Quality Bureau.
6. Traffic Generation
A Traffic Impact Study for the subdivision has been prepared by Abelin Traffic Services
and is enclosed in Appendix G. See Appendix G for a detailed discussion of the
improvements recommended to mitigate additional traffic generated by this subdivision.
M. Utilities
Letters requesting comments on their ability to service this subdivision have been sent to
the following service providers:
Montana Fish, Wildlife, and Parks, Bozeman Fire, Charter Communications,U.S.
Postal Service, and NorthWestern Energy.
Response letters from all of those who chose to comment are enclosed in Appendix D.
N. Educational Facilities
A response letter was sent to Kevin Barre, Director of Facilities—Bozeman Public Schools.
His response letter is included in Appendix D.
O. Land Use
Westbrook Subdivision is proposed as a 63 lot major subdivision. The development is
proposed to contain 62 single family residential lots and 1 R4 Multiplex lot The property
has zoning designations of R-1, and R-3. A Zone Map Amendment is being submitted
concurrent with the preliminary plat to change the zoning on the R3 lot to R4. The
breakdown of the percentages is found on the Area Tabulation shown on the attached
preliminary plat.
P. Parks and Recreation Facilities
Parkland requirements for the subdivision will be met with the dedication of a large public
park located within the subdivision. The park is located on the northwest boundary of the
property and will be adjacent to the proposed park in the Boulder Creek Subdivision. This
will provide the public with one large contiguous park.
The required Westbrook parkland calculation is as follows:
62 single family lots x 0.03 acres/lot = 1.8600 acres
R-4 5.4111 Acres x 8 units/acre x 0.03 acres/lot = 1.2987 acres
Total = 3.1587 acres
Total Westbrook Parkland Required = 3.1587acres
Westbrook Parkland Proposed(Park A) = 3.8313 acres
0.6726 acres excess
Baxter Creek, its associated wetlands and setback corridor are incorporated into the
subdivision as "open space" running through the entire subdivision in a north-south
direction. A trail network is proposed within this open space corridor, providing
connectivity between adjoining properties and the centrally located parkland. The open
spaces and stream corridors running the length of the subdivision are not included in the
parkland calculation, nor are any of the areas with proposed or existing storm water ponds.
These open space areas amount to an additional 8.7493 acres.
A Park Master Plan is attached in Appendix H outlining the proposed parkland
improvements, maintenance responsibilities and irrigation plan.
Q. Neighborhood Center Plan
The 7.866 acre centralized park (areas of Westbrook and Boulder Creek parks) will serve
as the neighborhood center for Westbrook and Boulder Creek. A pavilion and playground
'facility is proposed at the northeast corner of Laurel Parkway and Annie Street within this
park area. The park master plan is attached in Appendix H.
R. Lighting Plan
Street lighting as required in Section 18.42.150 of the Bozeman Unified Development
ordinance will be installed with the Westbrook Subdivision. Street lights at intersections
with arterial steets(Oak Street and Durston Road) will be 250-watt High Pressure Sodium
shoebox style fixtures at approximately 24,000 lumens mounted at 35' on round, tapered
fiberglass poles. Street lights on interior streets will be 100-watt High Pressure Sodium
shoebox style fixtures at 9,500 lumens mounted at 25' on square fiberglass poles. Cut
sheets for the proposed lights and a street light location plan are attached in Appendix I.
Special Improvement Lighting Districts will be created in cooperation with NorthWestern
Energy, and the City of Bozeman for financing installation, maintenance, and electrical
costs.
S. Miscellaneous
1. Public Lands
Adam Bronken Memorial Park is the only adjoining public land which lies south of
Durston Road across from the southeast portion of this property. Pedestrian access will
be provided with a trail running through the open space and parkland in Westbrook from
Oak Street to Durston Road.
2. Hazards
The only construction hazards near the development are the existing power, gas, electric,
and phone lines found at the perimeter of the subdivision. The location of these utilities
will be considered in the design of all underground utilities. The construction plans will
require the contractor to have all underground utilities located prior to the initiation of
construction.
There are no known public nuisances on or around the subject property.
3. Existing House
The existing house will remain. The associated outbuildings will be removed. The lot
setback requirements will be met with the current lot layout. The house will be
connected to city water and sewer services and the current septic system will be pumped
and removed.