HomeMy WebLinkAboutOWTS ReportMOUNTåIN CROSS
ENGINEERINC. INE.
Civil and Environmental Consulting ãnd Dês¡gn
June 17,2021
Mr. Bruce Barth
Red House Architecture
815 Blake Avenue
Glenwood Springs, CO 81601
RE: McCarty Residenceo 280 Lariat Lane, Garfield Counfyo CO - OWTS Report
Dear Bruce:
The purpose of this correspondence is to inform you about the onsite wastewater treatment system
(OWTS) designed for the construction of the McCarty Residence. The project proposes to
construct a new residence. An existing residence exists on the site with its own OWTS. No
modification is proposed to that residence or system. The project is located in Garfield County at
280 Lariat Lane. The main and upper floors of the residence will be a gravity system to a
conventional septic tank where a pump will pressure dose to a leach field comprised of a sand
filter. The plumbing of the lower level will need a sewer ejector pump to lift into the gravity
system. The residence will be served by an existing well. The OWTS is not within a 1O0-year
flood plain boundary. There are practical constraints that you should be aware of when considering
the proper design, construction, and operation.
Subsurface
The soil was determined to be R0 soils with an LTAR value approximated as 0.80 gallons per day
per square foot (GPD/sq.ft.) based on using secondary sand media and a soil evaluation performed
by Kumar and Associates. A profile hole was excavated and an inspection revealed that no
bedrock or high groundwater table is within an 8' depth of the leaching area. A copy of the soils
report is attached.
Design Calculations
The residence is proposed to be 5 bedroonrs. Using Garfield County Table 6-l for a 5-bedroom
residence, this yields 600 gallons per day (GPD) total. The design calculations for sizing of the
septic system and the leach field follow:
o McCarty Residence: 5 bedrooms: 600 GPD
o Based on soil evaluation and sand media, LTAR: 0.80 GPD/sq.ft.
o Minimum absorption area: 600 GPD / 0.80 : 750 sq. ft.
o No reductions are allowed for rocky soils.
o Required septic tank volume : 1,500 gallons per Garfield County Table 9- I
o Dosing frequency : 4 doses per day; dose volume : 600 GPD / 4 doses : 150 gal./dose
. Pump(s) should provide 30 gpm at35' of Total Dynamic Head
o PVC lateral supply should be Schedule 40, l-l/2" in diameter.
o PVC lateral distribution pipes should be Schedule 40, 1" in diameter.
o Each lateral pipe should have ten /¿" diameter holes drilled in the lateral aL 6' spacing with
the first hole located at 51" from the start of the bed.
826"/zGrand Avenue, Glenwood Springs, CO 81601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
McCarty Residence
June,2021
Page 2 of3
The component manufacturers are typical for the area. Alternatives may be considered by
contacting this office. Construction must be in accordance with the speciÏications of Gartield
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. Calculations are attached.
Setbacks
The location for the septic and dosing tanks are limited by setback requirements per Garfield
County and the State of Colorado. These include:
o 50' FROM WELL
e 50' FROM WATER BODY
o l0'FROM WATER SLIPPLY LINE
o l0' FROM PROPERTY LINE
o l0' FROM LINED POND, DITCH, OR STREAM
o l0' FROM CREST OF BANK
¡ 5, FROM BUILDING WITH BASEMENT
o 5,FROM LEACH FIELD
The leach field setback requirements are
o 100'FROM WELL
o 50' FROM WATER BODY
o 25, FROM WATER SUPPLY LINE
o ZS'FROM CREST OF BANK
o 20' FROM BUILDING WITH BASEMENT
o l0' FROM PROPERTY LINE
r 10' FROM LINED POND, DITCH, OR STREAM
o 5,FROM SEPTIC TANK
The setback requirements deal primarily with buildings and potential contamination from the
septic tank, dosittg tank, and leach field to either culinary water or surlace water. These seibauks
have been included on the plans for reference.
There is an existing waterline that will need to be crossed. The pressurized sewer line will need
to be encased for 25' each side of the crossing. Contractor will need to pothole the water lirie to
determine its location so that the encasement can be centered on the water line.
Operation 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. No heavy equipment, parking of
machinery, or materials should be placed on the absorption area. Livestock should not graze on
Mountain Cross Engineering. lnc.
Civll and Envlronmental Consulting and Deslgn
826"/zGrand Averfue, Glenwood Springs, CO 81 601
P: 970.945.5544 F: 970.945. 5558 www.mountaincross-eng.com
McCarty Residence
June,2027
Page 3 of3
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 OïVTS. Grease should not be placed in drains and grease traps should be installed
upstream of the septic tank but downstream from any kitchen. 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 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:
l. 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 inforrnation 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. lnc.
Civil and EnvironmentalConsulting and Design
826 1/, Grand Avenue, Glenwood Springs, CO B'! 601
P: 970.945.5544 F: 970.945.5558 www.mountaincross-eng.com
MOUNT¡IIN EROSS
ENGINEERING, INE.
Oívil and Env¡ronmêñtal Oonlulting and Dcsigrr
8?6 1f? Gr¿nd Avenlle clanwood SÞrtntr, CO 81601
ph S70.9415544 f¡ 970,945.5ı58 M,meunta¡narosHn0.com
5 Bedrooms
600 gallons per day
4 doses perday
150 gallons per dose
DOSING DESIGN CALCULATIONS, for
280 Lariat Lane, Garfield County, CO
6t11t20?1
gallons: average day
Table 6-1
Step l: Flows
Step 2: BODS
75 gpd/person
8 persons
600 gpd used by residence
BODS for domestic uses:
0.2 lb/person/day from CDPHE
Step 3: Dosing Basin
4 foot diameter manhole
depth of dose volume =
lnvert in from septic tank
SumP = bottom of manhole
Pump "Off'
Pump On "Lead" Float
Pump On "Lag" Float
High LevelAlarm
12" from High Level to lnv ln
94.0 gallons per foot of depth
1.ô0 feet of depth in manhole
-3.35
-7.92
-6.92
-5.32
-4.82
-4.32
-3.32
5.0
1
2.60
3.10
3.ô0
4.60
minutes of run time per dose =
Step 4: Elevations, Orifices, and Head loss
Rim Elevation =
High Point Elevation =
lnvert ln at Manhole =
Sump =
Elev Diff = 1.4 feet
Length of 1-112" = 100 feet
Length of 1" = 260 feet
1-112" fittings in equivalent pipe length:
check 90 90 check 90
13.44413.44
Equivalent 1-1l2" Length from pump =
-0.5
-'1.5
-3.35
-7.92
to Leach field
ln Leach field
30 gpm
gate tee
1.1 8.1
171.6 feet
tee
8.1
tee
8.1 64.2 feel
from Fig F, using 8.27 flof friction head per 100'of 1-112" plastic pipe = 14.2 head loss @ 30 gpm
from Fig F, using 3.3 ft of friction head per 100' of '1" plastic pipe = 8.6 head loss @ 7.5 gpm
Plus operating head at end 5.0 feet
Dynamic Head (TDH) 35.2 system condition use TDH of 35 feet
Per Table 7-13 in OWTS Design Manual, 114 " dia. orifice @ I'of Head yields 0.75 gpm
4 Laterals 10.0 orifices per lateral 30 gpm
Step 5: Velocity verification
30 gpm in 1.5 inch pipe
0.012 = area
0.067 = flow in cfs
5.447 = velocity in feet per second, must be greater than 2.0 feet per second
but less than 10 feet per second
7.5 gpm in 1 inch pipe
0.005 = area
0.017 = flow in cfs
3.064 = velocity in feet per second
Step 6: Pipe Volume & Drain Back
assume only drainback from manifold
1.5 inch pipe
0.012 = cross sectional area
107 .4 = feet in length
1.3'18 = cubic feet
9.96 = gallons
1.26 = inches of drainback into dosing tank