HomeMy WebLinkAboutEngineer's Design Report 08.09.2016August 9, 2016
Mr. Mike Simpson
P.O. Box 1281
Glenwood Springs, CO 81602
MOUNTAIN CROSS
ENGINEERING, INC.
Civil and Environmental Consulting and Design
RE: On -Site Wastewater Treatment System - Simpson Residence
Dear Mike:
The purpose of this correspondence is to inform you about the onsite wastewater treatment
system (OWTS) for your residence. The project proposes to construct on OWTS to serve a four
bedroom residence on a vacant lot. The project is located at an approximate elevation of 5,780
feet above sea level and the lot is located on Midland Avenue; the residence will be constructed
between Midland Avenue and the Roaring Fork River. The parcel ID# is 218516200008. This is
gravity system from the house to a conventional septic tank where a siphon doses to a leach field
comprised of infiltration chambers. The residence will be served by a water supply line from a
public potable water system. The OWTS is not within the 100 -year flood plain boundary. There
are practical constraints that you should be aware of when considering the proper design,
construction, and operation of the OWTS.
Subsurface
The LTAR was determined from tests performed by HP-KUMAR and the results are reported in
the Subsoil Study dated July 12, 2016. The LTAR was determined to be 0.60 gallons per day per
square foot based on USDA rating of very gravelly sandy loam and this rate was used for the
OWTS design. The project design is thus far based on soil boring logs. A profile hole will need
to be excavated and an inspection performed to verify boring logs are congruent with the site
soils, water table, and bedrock date. This can be performed either by HP-KUMAR or this office.
It is recommended that these tests and the profile hole be performed during excavation and
earthmoving operations to minimize the costs of mobilizing excavation equipment. This
inspection may require revisions to the design.
Design Calculations
The water use is based on a flow rate of 75 gallons per person per day. Using Garfield County
Table 6-1, which associates 7 people to a 4 bedroom household, this equates to 525 gallons per
day (GPD) total. The design calculations for sizing of the septic system and the leach field
follow:
• Simpson residence: 4 bedrooms
• Square footage is less than 6000 sq. ft.
• Design flow = 4 bedrooms, per Garfield County Table 6-1 = 525 GPD and BODS
=1.41bs/day
8261/2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
Simpson Residence
August, 2016
Page 2 of 3
• USDA soil type = very gravely and loam, LTAR = 0.60
• Soil treatment area = 525 GPD / 0.60 = 875 sq. ft.
• Reduction in soil treatment areas for chamber/trench treatment with dosing
= 875 sq. ft. * 0.7 * 0.9 = 552 sq.ft required leach area
• Required chambers = (552 sq.ft)/(12.34 sq.ft/chamber)
= 45 chambers, 5 rows of 9 chambers
• Required septic tank volume for 4 bedrooms, per Garfield County Table 9-1
=1,250 gallons
The components manufacturers are typical for the area. Alternatives may be considered by
contacting this office. Construction must be in accordance with the specifications of Garfield
County Environmental Health, the OWTS permit, and this design.
Topsoil should be placed over the OWTS and planted with native grasses. No large vegetation
and/or plants with taproots should be planted over the absorption area nor grasses that require
excessive irrigation.
Setbacks
The location for the septic and dosing tanks are limited by setback requirements per Garfield
County and the State of Colorado. These include:
• 50' FROM WELL
• 10' FROM WATER SUPPLY LINE
• 5' FROM BUILDING
• 10' FROM PROPERTY LINE
• 50' FROM STREAM
• 5' FROM LEACH FIELD
The leach field setback requirements are:
• 100' FROM WELL
• 25' FROM WATER SUPPLY LINE
• 20' FROM BUILDING
• 10' FROM PROPERTY LINE
• 50' UNLINED FROM DITCH OR STREAM
• 5' FROM SEPTIC TANK
The setback requirements deal primarily with buildings and potential contamination from the
septic tank, dosing tank and leach field to either culinary water or surface water. These setbacks
have been included on the plans for reference.
Operation Information and Maintenance
Mountain Cross Engineering, Inc.
Civil and Environmental Consulting and Design
826'/2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
Simpson Residence
August, 2016
Page 3 of 3
The homeowner will need to be responsible for the operation and management of the OWTS.
Geo -fabrics or plastics should not be used over the absorption area. No heavy equipment,
parking of machinery, or materials should be placed on the absorption area. Livestock should
not graze on the absorption area. Plumbing fixtures should be checked to ensure that no
additional water is being discharged to OWTS; for example, running toilets or leaky faucets can
discharge hundreds of gallons of water a day and harm the absorption area.
Garbage disposal use should be minimized, and non -biodegradable materials should not be
placed into the OWTS. Grease should not be placed in household drains. Loading from a water
softener should not be discharged into the OWTS. No hazardous wastes should be directed into
the OWTS. The OWTS is engineered for domestic waste only.
The Homeowner will likely need to contract with a septic system cleaner to clean the septic tank
every two years, or as needed gauged by measurement of solids in the tank. The standards of
performance for the septic system cleaner are recommended to be the following, at a minimum:
1. The Systems Cleaner shall be licensed.
2. The Systems Cleaner, when cleaning a septic tank, shall remove the liquid, sludge, and
scum, leaving no more than three (3) inches depth of sewage in a septic tank.
3. The Systems Cleaner shall maintain his equipment so as to ensure that no spillage of
sewage will occur during transportation, and that its employees are not subject to undue
health hazards.
4. The Systems Cleaner shall dispose of the collected sewage only at a designated site
recognized by the Board of Health.
Construction Observation
Prior to being backfilled, the construction of the OWTS and all of the components will need to
be observed by representatives of Mountain Cross Engineering, Inc.
The conclusions and opinions that are expressed above are based on the information available at
the time of preparation of this report. Any additional information presented afterward may
require that these opinions and the design be modified.
Thank you for the opportunity to provide this report. Feel free to call if you have any questions,
concerns, or comments.
Sincerely,
Mountai/7 Cross E gin CP' ng, Inc.
6iILA:"A
-wilHale, PE
Mountain Cross Engineering, Inc.
Civil and Environmental Consulting and Design
826'Y2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com