HomeMy WebLinkAbout14. Engineering ReportDecember 8th, 2020
To: Vincent Hooper, Planner III
Garfield County Community Development Department
108 8th Street, #401
Glenwood Springs, Colorado 81601
RE: Engineering Report for the Limited Impact Review, 17352 Highway, Carbondale, CO 81623
SE Project #30201
Dear Mr. Hooper,
Sopris Engineering, LLC (SE) has prepared the following Engineer's Report to address the sewer, water,
drainage, access, and traffic impact to the proposed Land Use Change due to the conversion of the existing
single-family home and accessory dwelling unit, in accordance the Garfield County Land Use Code.
The site is located South of Highway 82 just East of mile marker 17, and is in Garfield County, Colorado.
The existing site is a four -bedroom single-family residential home with an accessory dwelling unit. To the
South of the parcel is the Highway 82 Frontage Road. The existing utilities, roads, and site conditions are
shown on the Improvement Location Certificate, dated July 8th of 2020, by Tuttle Surveying Services.
The proposed subject property is to be converted from a single-family home with an ADU to an office that
will house 12 employees and two one -bedroom apartments. The proposed conversion will not change the
footprint of the existing structure. It is proposed to add two covered decks to the existing structure and
remodel to accommodate the office and apartments, these changes can be seen on the Architectural Plans
dated October 9th, 2020.
Water System (7-104 Source of Water)
The proposed re -development will have a water usage as follows:
It is anticipated that 15 gallons of water per person per day will be used by each office employee. The total
number of employees is 12, so the total usage of water per day for the office is 180 gallons per day. The
Apartments would expect to use approximately 200 gallons of water per day, per each unit. Resulting in
580 gallons of water per day, for domestic use.
The existing lot is served by a well under the permit #48638. Please refer to the Balcomb and Green letter
for further information regarding physical and legal water supply.
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311• Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
SE#. 30201.01
12/08/2020
Page 2
Sanitary Sewer (7-105 Waste -Water System)
The existing residential structure has 4 bedrooms and a detached garage structure that can be considered
for use as a 1-bedroom ADU. In order to ensure adequate OWTS capacity for existing usage and potential
future usage the new replacement system is designed for the maximum design flow under anticipated re-
development scenarios. The residential facility design assumes a 4-bedroom single-family residence plus a
1-bedroom detached ADU.
The OWTS design is based on our evaluation of the site conditions for use in obtaining a Garfield County
OWTS construction permit. We have evaluated the existing and proposed site conditions with respect to
the operation and installation of a new OWTS in accordance with Garfield County OWTS Regulations and
State of Colorado Regulation 43. The new system meets all required setback requirements and operational
demands for the proposed usage. Based on the physical site features, soils, and proposed building layout,
we have prepared an OWTS design plan with construction details for Limited Impact Review and adequate
for a building permit approval also. The design drawing is based on a recent Improvement Location
Certificate (ILC), by Tuttle Survey Services, dated 7-8-20. The design and construction recommendations
with specifications are delineated on the civil design plan, Cl-OWTS Plan dated 12-08-2020, by Sopris
Engineering.
Traffic (4-203 Traffic Study)
The anticipated traffic impacts to the Highway 82 Frontage Road resulting from the proposed site
conversion were estimated utilizing the Institute of Transportation Engineers (ITE) Trip Generation
Manual, 9th Edition.
The Trip Generation Manual is based on information submitted voluntarily to ITE by public agencies,
developers, consulting firms and associations. It is a tool utilized by planners, transportation professionals,
zoning boards, etc. to estimate vehicle trips generated by a proposed development.
The anticipated number of Peak Hour Vehicle Trips (PHV) and Average Daily Trips (ADT) for the
proposed re -development are as follows:
Existing Average Daily Trips:
ITE Code 210 (Single Family Detached Housing):
Average Rate: 9.52 vehicle trips per Single Family House =>
(9.52) (1 Homes) = 9.52 ADT (10)
ITE Code 220 (Apatlinent):
Average Rate: 6.65 vehicle trips per Accessory Dwelling Unit =>
(6.65) (1 ADU) = 6.65 ADT (7)
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311• Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
SE#. 30201.01
12/08/2020
Page 3
Existing AM Peak Hour Trips:
ITE Code 210 (Single Family Detached Housing):
A.M. Peak Hour: 0.77 vehicle trips per Single Family House =>
(0.77) (1 Home) = 0.77 PHV (1)
ITE Code 220 (Apailinent):
A.M. Peak Hour: 0.77 vehicle trips per Accessory Dwelling Unit =>
(0.51) (1 ADU) = 0.51 PHV (1)
Existing PM Peak Hour Trips:
ITE Code 210 (Single Family Detached Housing):
P.M. Peak Hour: 1.02 vehicle trips per Single Family House =>
(1.02) (1 Home) = 1.02 PHV (2)
ITE Code 220 (Apartment):
P.M. Peak Hour: 0.77 vehicle trips per Accessory Dwelling Unit =>
(0.62) (1 ADU) = 0.62 PHV (1)
Proposed Average Daily Trips:
ITE Code 710 (General Office Building):
Average Rate per Employee: 3.32 vehicle trips per Employee =>
(3.32) (12 Employees) = 39.84 ADT (40)
ITE Code 220 (Apartment):
Average Rate: 6.65 vehicle trips per Apartment =>
(6.65) (2 One Bedroom Apartments) = 13.3 ADT (14)
Proposed AM Peak Hour Trips:
ITE Code 710 (General Office Building):
A.M. Peak Hour: 0.48 vehicle trips per Employee =>
(.48) (12 Employees) = 5.76 PHV (6)
ITE Code 220 (Apaitiuent):
A.M. Peak Hour: 0.77 vehicle trips per Apartment=>
(0.51) (2 One Bedroom Apartments) = 1.02 PHV (2)
Proposed PM Peak Hour Trips:
ITE Code 710 (General Office Building):
P.M. Peak Hour: 0.48 vehicle trips per Employee =>
(.46) (12 Employees) = 5.52 PHV (6)
ITE Code 220 (Apartment):
P.M. Peak Hour: 0.62 vehicle trips per Apaitruent =>
(0.62) (2 One Bedroom Apartments) = 1.24 PHV (2)
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311• Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
SE#. 30201.01
12/08/2020
Page 4
The existing average daily trip counts are found by using the original single-family home and ADU. The
average daily vehicle trips were calculated at 17 vehicle trips. The proposed average daily trip counts are
calculated by using an office building, with twelve employees and two apartments, resulting in 54 average
daily trips. The proposed re -development will result in an increase of 37 average daily trips.
The existing AM and PM peak hour trips are 2 and 3 respectively. The proposed AM and PM peak hour
trips are 8 and 8 trips respectively, resulting in a 6-trip increase in the morning and a 5-trip increase in the
evening.
Using the Garfield County Design Standards, under the Garfield County Land Use Code Table 7-107, the
existing subject property is categorized as Primitive Driveway, with 0-20 average daily trips. The
proposed re -development will increase the average daily trips to 54, categorizing the resulting re-
development as a Semi -Primitive Drive.
An Access Permit application has been submitted to CDOT, please refer to attached application.
Access (7-107 Roadway Standards)
In the section above, Traffic, it was found that the proposed driveway is classified as a Semi -Primitive
Driveway, from Table 7-107. Under the design standards for a Semi -Primitive:
➢ 40' ROW
➢ (2) 8' Lane
➢ 2' shoulder
➢ 4' Ditch
➢ Cross slope 2% with Chip/Seal or 3% with Gravel
➢ Minimum Radius 50'
➢ Gravel
Sopris Engineering has performed a site visit and reviewed the current survey, and it is our opinion that the
existing driveway and parking is in compliance with Garfield County's standards for a Semi -Primitive
Drive as listed above. Any further improvements will be controlled by the Colorado Department of
Transportation, with regards to the CDOT Access Permit Application.
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311• Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
SE#. 30201.01
12/08/2020
Page 5
Drainage and Erosion Control (7-204)
The existing property is not subject to any proposed grading or drainage improvements. The proposed
re -devolvement is utilizing the existing structure and only remodeling the interior to accommodate an
office for twelve employees and two (1) bedroom apartments.
Based upon our site visit the existing structure has good drainage away from the building in all directions.
If you have any questions or need any additional information, please call.
Sincerely,
SOPRIS ENGINEERING, LLC
Yancy Nichol, PE
Principal
Attachements:
• CDOT Access Permit Application
CC: Jack Albright
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311• Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants