HomeMy WebLinkAboutEngineers Design Report 06.08.2018June 8, 2018
Mr. Andrew Braudis
1244 County Road 106
Carbondale, CO 81623
MOUNTAIN CROSS
ENGINEERING, INC.
Civil and Environmental Consulting and Design
RE: On -Site Wastewater Treatment System —1234 County Road 106
Dear Andy:
The purpose of this correspondence is to inform you about the onsite wastewater treatment system
(OWTS) for the residence located at 1234 County Road 106. The project proposes to replace a
common OWTS that serves two residences with separate OWTS systems. The residence at 1234
CR 106 was designed as a three bedroom residence. This is proposed to be a gravity system from
the house to a conventional septic tank where duplex pumps doses to a chamber bed dispersal
system. The residence is served by a water supply line from a potable water system. There is an
adjacent well located on the property of 1244 CR 106. 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
Percolation tests were performed on May 29, 2018 and the rate was congruent with evaluation of
site soils. These tests yielded an average percolation rate of 28.4 minutes per inch. Results are
attached. Based on these results and the soil evaluation, an LTAR value of 0.50 gallons per day
per square foot (GPD/sq. ft.) was used for design.
To achieve setback requirements, the irrigation ditch to the west will need to be piped. This will
prevent contamination from the OWTS but will also help reduce the saturation of soils from
irrigation water.
A profile hole was excavated at the time of excavation for the percolation tests. Evaluation of this
verified that there is no bedrock nor free water table within 4' of the infiltrative surface of the leach
field.
Design Calculations
The design calculations for sizing of the septic system and the leach field follow:
• 1234 CR 106 residence: 3 bedrooms
• Square footage is less than 6000 sq. ft.
• Design flow = 3 bedrooms, per Garfield County Table 6-1 = 450 GPD and
BODS = 1.2 lbslday.
• Based on soil evaluation and percolation tests results, LTAR used for design = 0.5.
• Soil treatment area = 450 GPD / 0.5 = 900 sq. ft.
• Required leach area: Soil treatment area * Factor for Chybers * and Dosing Bed per
Tables 10-2 and 10-3 = 900 sq. ft. * 0.7 * 1.0 = 630 sq. fl:
• Use 2 Chamber Beds of 30 by 11'-4" = 680 sq. ft. > 630 sq. ft.
826'/2 Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
1234 CR 106
June, 2018
Page 2 of 3
• Required septic tank volume for 3 bedrooms, per Table 9-1 = 1,000 gallons.
• Dosing frequency — 4 doses per day (DPD); dose volume = 450 GPD / 4 DPD = 112.5
gallons per dose.
• Pump(s) should provide 30 gpm at 15' of Total Dynamic Head
• PVC lateral distribution pipes should be Schedule 40, 1" in diameter.
• PVC supply and manifold pipes should be Schedule 40, 2" in diameter.
• Each lateral pipe should have six 1/4" diameter holes drilled in the lateral at 5' spacing with
the first hole located at 2.5' from the start of the bed.
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:
• 10' FROM WATER SUPPLY LINE
• 5' FROM BUILDING
• 10' FROM PROPERTY LINE
• 50' FROM UNLINED IRRIGATION DITCH AND POND
• 10' FROM LINED IRRIGATION DITCH AND POND
• 5' FROM LEACH FIELD
• 50' FROM A WELL
The leach field setback requirements are:
• 25' FROM WATER SUPPLY LINE
• 20' FROM BUILDING
• 10' FROM PROPERTY LINE
• 50' FROM UNLINED IRRIGATION DITCH AND POND
• 10' FROM LINED IRRIGATION DITCH AND POND
• 5' FROM SEPTIC TANK
• 100' FROM A WELL
The residence is served by a water supply line from a potable water system. There is no onsite
well but there is one located next door at 1244 CR106. Because of the leach field setback
requirements and its proximity to the well and an irrigation ditch, the irrigation ditches must be
piped. No buildings or automobiles may exist on top of the leach field. The setback requirements
deal primarily with buildings and potential contamination from the septic tank, dosing tank, and
leach field to either potable water or surface water. These setbacks have been included on the
plans for reference.
Mountain Cross Engineering. Inc.
Civil and Environmental Consulting and Design
826 '/z Grand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
1234 CR 106
June, 2018
Page 3 of 3
Operation Information and Maintenance
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,
Mountain Cross Engineering, Inc.
Chris Hale, PE
Mountain Cross Engineering, Inc.
Civil 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
Satank 1234
Date:
5/29/2018
Average = 28.4
Time
Beginning
Ending
Percolation
Average
Hole
Start
End
Difference
Minutes
Level
Level
Percolation
Rate
Rate
South
10:00
10:20
20:00
20.00
3.438
4.375
0.94
21.3
Depth
10:20
10:40
20:00
20.00
4.375
5.125
0.75
26.7
36"
10:40
11:00
20:00
20.00
5.125
5.750
0.63
32.0
12"
11:00
11:20
20:00
20.00
5.750
6.375
0.63
32.0
48"
11:20
11:40
20:00
20.00
6.375
6.938
0.56
35.6
33.19
Average = 28.4
Time
Beginning
Ending
Percolation
Average
Hole
Start
End
Difference
Minutes
Level
Level
Percolation
Rate
Rate
East
10:01
10:21
20:00
20.00
4.875
5.625
0.75
26.7
Depth
10:21
10:41
20:00
20.00
5.63
6.313
0.69
29.1
36"
10:41
11:01
20:00
20.00
6.313
7.06
0.75
26.7
11"
11:01
11:21
20:00
20.00
7.06
7.625
0.56
35.6
47"
11:21
; 11:41
20:00
20.00
7.625
8.19
0.56
35.6
33.40
Average = 28.4
Time
Beginning
Ending
Percolation
Average
Hole
Start
End
Difference
Minutes
Level
Level
Percolation
Rate
Rate
West
10:02
10:22
20:00
20.00
4.4375
6.125
1.69
11.9
Depth
10:22
10:42
20:00
20.00
6.13
7.50
1.38
14.5
39"
10:42
11:02
20:00
20.00
7.50
8.75
1.25
16.0
13"
11:02
11:22
20:00
20.00
8.75
9.75
1.00
20.0
52"
11:22
11:42
20:00
20.00
9.75
10.75
1.00
20.0
18.67
Average = 28.4