HomeMy WebLinkAboutEngineered OWTS System Design Report 04.08.2018April 8, 2018
Ms, Deanna Spracher and
Mr. Ryan Beringer
2607 Woodberry Drive
Glenwood Springs, CO 81601
MOUNTAIN CROSS
ENGINEERING, INC.
Civil and Environmental Consulting and Design
RE: On -Site Wastewater Treatment System — Creek Residence
Dear Deanna and Ryan:
The purpose of this correspondence is to inform you about the onsite wastewater treatment system
(OWTS) for the Creek Residence. The project proposes to construct on OWTS to serve a four
bedroom residence in Garfield County. This is a gravity system from the residence to a
conventional septic tank where a siphon doses to a leach field comprised of infiltration chambers.
The house will be served by a shared well. The OWTS is not within a 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 January 05, 2018. The LTAR was estimated to be 0.60 gallons per day
per square foot based on USDA rating of gravelly sandy loam and was used for the OWTS design.
No high water table or bedrock was encountered within 8'.
Design Calculations
Using Garfield County Table 6-1, which associates a 4 bedroom household with 7 people and a
flow rate of 75 gallons per person per day, this equates to 525 GPD. The design calculations for
sizing of the septic system and the leach field follow:
• Residence: Square footage is less than 6,000 sq. ft.
• Design flow = Four bedrooms, per Garfield County Table 6-1 = 525 GPD
• USDA soil type = gravelly sandy 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 Chamber Rows to be three rows of 3' wide by 65' wide:
= 3 rows * 3' * 65' = 585 sq.ft > 552 sq. ft. required leach area.
Number of leaching chambers per row is to meet or exceed the 65' length.
• Required septic tank volume, per Garfield County Table 9-1 = 1,250 gallons
• Four doses per day = 525 GPD / 4 DPD = 132 gallons per dose 16" in a 4' manhole
8261/2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
Creek Residence
April, 2018
Page 2 of 3
The septic tank to be chosen from the CDPHE WQCD approved list. The distribution box shall
be a precast concrete box with 1 inlet and 7 outlets. 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.
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 POND
• 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. The OWTS is
over 100' away from the well and over 50' from the stream. These setbacks have been included
on the plans for reference.
Aeration Information and Maintenance
The Owner 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. 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. 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
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
Creek Residence
April, 2018
Page 3 of 3
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 Owner 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,
Mountain Cross Engmeal pg, Inc.
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iris Hale, PE
Mountain Cross Engineering, Inc.
CMI and Environmental Consulting and Design
8261/2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com