HomeMy WebLinkAboutEngineer's OWTS Design PlanMarch 12, 2026
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313
S OPRIS E NGINEERING • LLC civil consultants
IRMW LLC
P O Box 1037
Carbondale CO 81623
C/O Jeff Parrington
President, Tally Ho Construction
www.tallyhoconstruction.com
"jeff" <jeff@tallyhoconstruction.com >
RE: Design Report–Onsite Wastewater Treatment System (OWTS), IRMW LLC Parcel 1 , 1058 County Road
100, Carbondale, CO, Garfield County, Colorado
SE Job No. 35122.01 Parcel No: 239335402001 . Garfield County OWTS Permit No._____________
Dear Jeff:
This letter presents the applicable findings regarding the design and construction of a new Onsite Wastewater
Treatment System (OWTS) at the above referenced Site, in support of your OWTS permit application to Garfield
County. The OWTS design is based on recent site assessment observations by Sopris Engineering of existing
physical site features, conditions, geotechnical soils evaluation with respect to the proposed commercial usage and
applicable regulatory design criteria in accordance with State and County OWTS Regulations. The design
recommendations, specifications and construction details are delineated on the attached OWTS permit/construction
plan “C1-OWTS-Plan”, dated 03-21-2026, that was prepared with GIS, LIDAR, Survey boundary information and
aerial mapping. The design criteria and system sizing information are summarized below.
Existing and Proposed Conditions
The proposed development to replace the existing garage to the southeast portion of the 10-acre parcel. The
proposed OWTS will serve the new garage/shop structure with a ½ bath that may have a future 2-bedroom small
apartment ADU addition in the future.
The subject portion of the 58-acre commercial industrial area existing topography and site conditions are derived
from county GIS database, aerial mapping, and lidar topography. The site is situated in existing commercial
industrial dev eloped and u ndeveloped land primarily consisting of construction storage and equipment parking
facilities . The proposed development area i s in the transition between two sloped areas (30% to 45%) and a broad
gently sloped partially filled area (6% to 10%.) with graded dirt and gravel surface with some native undist urbed
areas that generally trends downgradient to the north. The proposed OWTS field will be constructed in a native area
adjacent to a dirt and gravel drive way off the northeast corner of the proposed building.
The proposed development will consist of the construction of a 8400 S.F multi-unit shop/garage/office/ storage
facilities structure with 8 ½ bath restrooms . The facility has a 2nd story office facility with tow offic es. The proposed
improvements will include associated driveway, garage entrances, construction material storage areas, auto and
equipment parking. The building will be served with water, electric, gas utilities and a new onsite wastewater
treatment system. The development will be based on applicable site design criteria and include appropriate grading,
drainage, and site construction management. The proposed development improvements and site layout plan is shown
on the attached OWTS plan. Water service will be extended from an existing well on the IRMW LLC Parcel 1 site
located approximately 225 feet east and downgradient of the subject OWTS and proposed building site.
IRMW 11 OWTS
1058 County Rd 100, Carbondale, CO
SE Job No. 35122.01
March 12, 2026
Page2
Summary Design Criteria
The new OWTS is designed for a treatment capacity of 240 gallons per day. The new OWTS will utilize a 1,000
gallon two -compartment concrete septic tank. Sealed ribbed PVC risers with lids will be installed on the new septic
tank along with appropriate pipe connection to the new tank. The new 1,000 gallon 2-compartment septic tank will
be installed with appropriate sanitary tees, outlet effluent filter with risers and lids at the surface. A gravity schedule-
40 or SDR-326 sewer pipe section with two-way cleanout will be installed between the tank inlet on the gravity
sewer line adjacent to the structure.
The soil treatment area (STA) will consist of leaching chamber trenches that provide 288 S.F. of total absorption
area. The septic tank effluent will be gravity discharged through a new 4 -inch schedule-40 or SDR-26, installed at a
minimum 1.5% slope, to the STA via a distribution box. The effluent will be equally distributed from the
distribution box via 4” distribution pipes connected to the head end cap of each chamber trench. Observation ports
with caps will be installed on the proximal and distal ends of each chamber trench . The designed system meets all
required setbacks and will be installed within the general location indicated on the plan. Our design is outlined
below and delineated on the attached C-1 OWTS plan.
Design Flow
The design flow is calculated as follows for a commercial 6-unit shop/office contractor storage facility. The onsite
wastewater treatment system (OWTS) capacity is designed for daily employee /staff and transient contractor
employee restroom. Design flow is based on usage in 6 garage/shop/storage/offices units and 1 additional storage
and office unit on the second floor of the eastern unit. Maximum population for use of the facilities assumes1 full-
time worker per each unit plus an additional 4 persons for the eastern unit with the additional upper level office
spaces, for a total 10 daily office or shop staff. Additional usage is based on up to 18 transient employees/staff using
the 8 restrooms in the building.
From the Regulation 43 usage table 1:
Gallons per day per person =15 gal/employee/day,
Gallons per day per person =5 gal/transient/day,
Max. Design flow (Qd)gallons/day = (# of people) x (avg. flow)gal/person/day.
Design flow Qd = (10x15=150) + (18 x 5=90) = 240 gpd
The septic tank capacity required for a minimum 48 hour retention time is calculated as follows:
V = 240 gal/day * 2 = 480 gallons. Use a minimum 1,000 gallon 2-compartment septic tank. The tank to be installed
with risers and access lids set a minimum 3 inches above finish grade surface .
Sub Surface Conditions and Testing
A subsurface soil investigation and site assessment was performed by Sopris Engineering in on March 3, 2026. The
soils were sampled and characterized by application of the USDA visual/tactile soil texture method analysis from
samples in two profile pits. Two excavated profile pits 1 & 2 were observed in the East central portion of the site
within the proposed soil treatment area. The soils below 6 to 18 inches of topsoils and/or mixed surface fill &
gravels consist of medium dense sandy clay loam with moderate granular to slightly blocky structure with cobbles
and gravels to depths of 1 to 2.0 feet underlain by slighty sandy clay loam with less than 30% of total rock content
to the 8 foot depth explored in both pits. The soil appears to be generally consistent across the site. No evidence of
seasonal high ground water, redox conditions or any other limiting conditions were observed in the profile pits.
Groundwater levels are expected to be below 25 feet from the existing surface grades on the relatively flat terrain.
The soils are suitable for a shallow conventional absorption field consisting of gravelless infiltration chamber units.
IRMW 11 OWTS
1058 County Rd 100, Carbondale, CO
SE Job No. 35122.01
March 12, 2026
Page3
Profile Pit -1
The soils below approximately 12-18 inches of surface gravels and sandy silt loam fill consist of moderately dense
sandy silt loam texture soils that has blocky to granular shape of moderate structural grade with gravels and cobbles
to a depth of 4 -feet containing approximately 20% total rock content. Soils below 4 feet to 6 feet consist of
moderately dense slighty sandy silt loam texture soil that has granular structure of moderate structural grade with
less than 30% of total rock content underlain by silt loam with gravels with less than 20% rock content to the 8 foot
depth explored. The soils are characterized as a soil type 2 sandy silt loam. No free water or limiting condition was
encountered in the pit excavation.
Profile Pit -2
The soils below approximately 3 inches of surface fill consist of topsoil to a depth of 12 -inches underlain by
moderately dense sandy silt loam loam texture soils that has blocky to granular shape of moderate structural grade
with gravels and small cobbles to a depth of 4-feet containing approximately 25% total rock content. Soils below 4
feet to 5 feet consist of moderately dense slighty sandy silt loam texture soil that has granular structure of moderate
structural grade with gravels, cobbles and small boulders with less than 30% of total rock content underlain by silt
loam with gravels with less thant 20% rock content to the 8 foot depth explored. The soils are characterized as a soil
type 2 sandy silt loam. No free water or limiting condition was encountered in the pit excavation.
The native soils sampled from 2 -4 feet below the surface, in both profile pits, are characterized as a soil type 2 soil
type consisting of slighty sandy silt loam texture soil with granular to slightly blocky structure of moderate structural
grade. The brown sandy silt loam soil tactile test ribbons were ¾-1inch long. Soil type 2 has an effective loading rate
for conventional soil treatment of 0.60 gal/S.F./day for a level 1 conventional treatment system. The equivalent
percolation rate of these soils is assumed to be 20-30 minutes per inch.
Additional observations will be performed during construction to inspect the shallow trench chamber trench
excavations, absorptive surface preparation in the soil treatment area and provide guidance for installations of the
specified materials in the in-situ native soils. If any adjustments to design or installation recommendations are
necessary, notice will be made to County EHD and applicable revisions to design/construction plans and report will
be submitted. All conditions and installations will be included in the As -Constructed documentation.
Treatment-Soil Treatment Unit/ Absorption System Design
The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for
the native soils and the application of appropriate loading factors for a soil treatment unit system utilizing gravity
distribution to gravelless chamber trenches. The new treatment system and absorption field will consist of gravity
distribution of septic tank effluent via a distribution box to individual chamber trenches with treatment across the
native soil absorptive surface.
Long Term Acceptance Rate (LTAR):
Receiving Wastewater Treatment Level 1;
LTAR; (Table 10 -1 Soil type 2 loading rate for a sandy silt loam is (0.6 gal./S.F./day);
Design Flow; Qd = flow (gal/day) = 450 gpd
Loading factors; (Table 10-2, Gravity application trenches, L.F.1 = 1.0)
(Table 10-3, Gravelless chambers, L.F.2 = 0.7)
STA soil treatment area; A = Area S.F.;
IRMW 11 OWTS
1058 County Rd 100, Carbondale, CO
SE Job No. 35122.01
March 12, 2026
Page4
A(sf) = Qd x L.F.1 x L.F.2 .: A(sf) = 240gpd x 1.0 x 0.7 = 280 S.F.
LTAR 0.60 Gal/S.F./day
```
Number of Quick-4 Infiltrator chambers 4'x3'x12"chambers:
280 S.F. = 24 chambers; Use 24 chambers
12 S.F./Chamber
Number of Equivalent Arc-36 chambers 5'x3'x12"chambers:
280 S.F. = 19 chambers; Use 19 chambers
15 S.F./Chamber
Use 24 Quick-4 Infiltrator chambers in 3 trenches 34' long by 3' wide with 8 chambers units per trench plus two end
caps as delineated on the plan. Alternative use 19 Arc-36 chambers in 2 trenches 30' long by 3' wide with 6
chambers units per trench with ends caps and 1 35' long by 3' wide trench with 7 chambers units. The septic tank
effluent will be gravity distributed to the head of each chamber row via individual distribution pipes from a
distribution box.
Construction and Inspections
Prior to construction of the permitted system, the engineer should be contacted by the contractor and owner well in
advance to provide adequate time to discuss the system components with the contractor, answer questions, resolve
any conflict issues and schedule inspection site visits based on construction progress. A pre-OWTS construction
meeting is essential and required prior to installation of the OWTS. All septic system components shall be staked in
the field for approval by the Engineer prior to excavation.
Additional assessments and recommendations will be made by the engineer during initial stages of construction to
verify assumptions made for the OWTS design including verification of soils, STA layout, excavation depths, the
location of the sewer/distribution piping, components and installation of appurtenances.
During initial construction the engineer will evaluate the soils in the absorption treatment field excavations to
confirm soil conditions and make adjustments as needed. All septic system components and trench installations are
to be approved by the Engineer prior to backfilling. County Regulations require that the Engineers of record perform
site inspections of the permitted system during construction and provide “As-Constructed” documentation of the
installed system to the County after construction is complete . All installations will be inspected, field measured,
reported and delineated in the c ertification letter and record drawing. The contractor need s to photo document all
OWTS construction phases and supply photos to the Engineer.
The County Environmental Health department should be contacted at least 48 hours prior to final backfill of
components to provide advanced notice of construction schedule in order to perform a final inspection of the
in-place components. The County Environmental Health department should be contacted at least 48 hours prior to
final backfill of components to provide advanced notice of construction schedule in order to perform a final
inspection of the in-place components. The Garfield County contact is: Environmental Health Garfield County
Public Health; 970 -945-6614 x 8106 (main office)
OWS Operation and Maintenance
Ownership of the system and responsibility for maintenance and repair will remain with the property Owner. The
Owner is encouraged to retain the services of qualified personnel to inspect the OWTS and to perform all
maintenance and repairs necessary to ensure that the system components are maintained in good operating condition
IRMW 11 OWTS
1058 County Rd 100, Carbondale, CO
SE Job No. 35122.01
March 12, 2026
Page5
and suitable vegetative cover is established on the fields. The components of the OWTS system should be inspected
within 30 days of being placed into operation and should been inspected and maintained bi-annually. The tank,
absorption field and other system components should be visually inspected bi-annually for debris, damage, leaks, or
other potential problems. In general, for a properly utilized system, septic tanks should be pumped every 3 - 5years.
The effluent filter should be cleaned every six months and at the time of pumping. Absorption fields should be
maintained with suitable vegetative cover and kept free of root invasive plants. Positive surface drainage away from
the absorption field should be maintained.
If you have any question or need any additional information, please call.
Sincerely,
SOPRIS ENGINEERING, LLC
Paul E. Rutledge Yancy Nichol, PE
Design Engineer Principal
3/12/2026
L1.7
210.0 40.0
4''SS
4''SS
4''SS
4''SS
4''SS
4''SS
4''SS
APPROXIMATE DES LLC LOCATION
BUILDING TO BE LOCATED BY
CONTRACTOR
34.0
10.0
INSTALL 1000 GALLON 2-COMPARTMENT CONCRETE SEPTIC TANK
(USE VALLEY PRECAST ITEM # IM 1000-2CP) W/ SEALED RISERS AND
LIDS INSTALLED AT THE FINISHED GRADE SURFACE. INSTALL INLET
SANITARY TEE AND OUTLET EFFLUENT FILTER SANITARY TEE. DEPTH
TO TOP OF TANK FROM PROPOSED GRADE IS APPROXIMATELY 24".
4" PVC DISTRIBUTION PIPES (TYP.)
4" PVC EFFLUENT PIPE @ MIN. 1 %,
USE SCHD-40 OR SDR-35
ABSORPTION/TREATMENT FIELD
USE 24 QUICK-4 CHAMBERS IN 3 TRENCHES WITH 8 CHAMBERS PER ROW FOR A TOTAL
ABSORPTION AREA OF 192 S.F. THE SYSTEM SHALL BE PLUMBED FOR EQUAL GRAVITY
DISTRIBUTION. THE CHAMBERS SHALL BE INSTALLED ON LEVEL GRADE IN EACH TRENCH.
THE BOTTOM OF EACH TRENCH TO BE EXCAVATED TO A MAXIMUM AVERAGE DEPTH OF
30 INCHES BELOW THE EXISTING SURFACE GRADES, WITHIN THE UPPER HORIZON OF
THE NATIVE SILT LOAM SOILS & BACKFILLED WITH A MINIMUM 12-INCHES OF COVER
OVER THE CHAMBERS. THE FINISH GRADE ACROSS THE FIELD SHALL BE SLIGHTLY
MOUNDED A MINIMUM 3-INCHES ABOVE EXISTING ADJACENT GRADES.
CONCRETE DISTRIBUTION BOX WITH BAFFLE
INSTALLED LEVEL ON COMPACTED BASE
INSTALL RISERS AND LID TO SURFACE
4" PVC SEWER PIPE @ 1.5%,
USE SCHD-40 OR SDR-26
INSTALL 4" RISER PIPE INSPECTION PORT EXTEND RISER W/
PUSH ON CAP MIN. 4" BELOW FINISH GRADE & COVER WITH
6" DIA. VALVE BOX SET WITH LID 1" ABOVE FINSH GRADE
(TYP. EACH TRENCH CHAMBER END CAP)
INSTALL CHAMBER END CAP
ON ALL END CHAMBERS
4" TWO-WAY
CLEANOUT
INSTALL FULL BODY WYE
(TYP. EACH SEWER PIPE CONNECTION)
DATE REVISION
C-1.0
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OWTS DESIGN &
CONSTRUCTION
PLAN
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GRAPHIC SCALE
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35122JOB NO.
DATE:03-12-26
DESIGNED BY
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1.AN EFFLUENT FILTER SHALL BE INSTALLED IN THE DISCHARGE TEE IN THE SECONDARY
COMPARTMENT OF THE SEPTIC TANK. WE RECOMMEND THE INSTALLATION OF AN ORENCO
SYSTEMS 4" EFFLUENT FILTER FILTERED EFFLUENT THAT WILL DISCHARGE TO A CONCRETE
DISTRIBUTION BOX WITH RISERS AND LID AT THE SURFACE.
2.THE DISTRIBUTION SYSTEM WILL BE INSTALLED TO ALLOW FOR EFFLUENT TO BE EQUALLY
DISTRIBUTED TO THE ABSORPTION TRENCHES VIA INDIVIDUAL 4" DISTRIBUTION LINES
CONNECTED TO THE HEAD OF EACH CHAMBER TRENCH.
3.THE MINIMUM SLOPE OF THE DISCHARGE LINE FROM THE TANK TO THE DISTRIBUTION BOX
SHALL SHALL BE INSTALLED AT A MINIMUM 1% SLOPE. THE INDIVIDUAL DISTRIBUTION
LINES AT THE HEAD OF THE TRENCHES SHALL BE INSTALLED AT A MINIMUM OF 2% SLOPE.
1.ALL MATERIALS AND INSTALLATION SHALL CONFORM TO STATE AND COUNTY ONSITE
WASTEWATER TREATMENT SYSTEM (OWTS) REGULATIONS.
2.IT IS THE RESPONSIBILITY OF THE CONTRACTOR TO CONTACT ALL UTILITY COMPANIES FOR
FIELD LOCATIONS OF UTILITIES PRIOR TO CONSTRUCTION AND EXCAVATION.
3.ALL SEWER LINES TO BE SDR-35 OR SCHEDULE 40 P.V.C. PIPE UNLESS NOTED OTHERWISE.
4.INSTALL A TWO-WAY CLEAN OUT ON THE SERVICE LINE FROM THE STRUCTURE AND AN
ADDITIONAL CLEANOUT WITHIN 100' SECTION OF EFFLUENT DISCHARGE PIPE .
5.THE SEPTIC TANK SHALL BE INSTALLED LEVEL ON COMPACTED EARTH. INSTALL WATERTIGHT
RISERS AS NECESSARY TO BRING ALL REQUIRED ACCESS POINTS TO THE FINISHED SURFACE
GRADE. BACKFILL WITH SUITABLE NATIVE SOIL FREE OF BOULDER AND ROCK IN EXCESS OF 3"
DIAMETER.
6.A SANITARY BAFFLE TEE IS REQUIRED ON THE SEPTIC TANK INLET AND OUTLET. INSTALL THE
INLET AND OUTLET TEES PLUMB AND IN A POSITION TO ALLOW EASY INSPECTION AND
MAINTENANCE OF TANK FROM THE TANK RISERS.
7.INSTALL A 4" EFFLUENT FILTER ON THE 4" OUTLET TEE OF THE SEPTIC TANK. THE FILTER
SHOULD BE INSPECTED EVERY SIX MONTHS. THE EFFLUENT FILTER SHALL BE MAINTAINED AND
CLEANED WHEN THE TANK IS PERIODICALLY PUMPED OR AS NECESSARY. INSTALL A SUITABLE
EXTENSION ON THE FILTER WITH A HANDLE TO BE WITHIN 6" BELOW THE ACCESS LID.
8.THE CONTRACTOR SHALL ENSURE THAT THE SEWER LINES, SEPTIC TANK AND RISERS ARE
WATERTIGHT. ALL PLUMBING FIXTURES AND OWTS COMPONENTS SHALL BE INSTALLED AND
MAINTAINED TO AVOID SURFACE OR GROUNDWATER FROM ENTERING THE SYSTEM AND TO
PREVENT LEAKAGE FROM THE SYSTEM. IN-HOUSE PLUMBING FIXTURES SHALL BE MAINTAINED
TO PREVENT EXCESS WATER FROM ENTERING THE SEPTIC SYSTEM.
9.THE DIMENSIONS AND NOTES SHOWN ON THE PLAN INDICATE MINIMUM AREA, LENGTH,
WIDTHS AND SEPARATION DISTANCES FOR THE TRENCHES, BED OR MOUNDED ABSORPTION
FIELD.
10.THE ABSORPTION TRENCHES SHALL BE EXCAVATED TO LEVEL GRADE IN NATIVE EARTH. THE
TRENCH BOTTOM AND SIDEWALLS SHALL BE SCARIFIED AND/OR RACKED IF SMEARING
OCCURS. IF EXCESSIVE LARGE COBBLES OR BOULDERS ARE ENCOUNTERED IN ANY PART OF THE
EXCAVATION OVER 6" FROM THE PROPOSED TRENCH BOTTOM SURFACE, OVER EXCAVATE AND
BACKFILL WITH SAND.
11.THE LEACHING CHAMBERS SHALL BE INSTALLED LEVEL WITH A MINIMUM COVER OF 10 INCHES
NOT TO EXCEED 24 INCHES.
12.LEACHING CHAMBERS WILL BE PLACED IN THE EXCAVATION OVER THE NATIVE SOIL OR SELECT
SOIL REPLACEMENT OR ASTM-33 SAND LEVELING COURSE. END CAPS SHALL BE INSTALLED ON
THE END CHAMBERS IN EACH TRENCH.
13.VERTICAL INSPECTION PORTS SHALL BE INSTALLED FROM THE PRE MARKED HOLE ON THE TOP
OF EACH END CHAMBER CAP. (TYP. BOTH ENDS OF EACH ROW) THE PORTS MAY HAVE
THREADED CAPS AT GRADE.
14.THE CHAMBERS WILL BE BACKFILLED WITH EXCAVATED MATERIAL VOID OF ROCKS, THE
BACKFILL MATERIAL SHALL NOT EXCEED 2 1/2" DIAMETER AND SHALL BE PLACED TO AT LEAST
6 INCHES ABOVE THE TOP OF THE CHAMBERS. THE TOP OF THE PLACED BACKFILL SHALL BE
COVERED WITH A LAYER OF FILTER FABRIC. A MINIMUM 4" DEPTH OF TOPSOIL IS TO BE PLACED
ABOVE THE BACKFILL TO THE SURFACE & RE-VEGETATED.
15.INSTALLATION OF LEACHING CHAMBERS SHALL BE IN CONFORMANCE WITH THE
MANUFACTURERS INSTALLATION INSTRUCTIONS.
16.THE ABSORPTION TRENCHES/BED OR MOUND MUST BE GENERALLY MARKED AT THE FOUR
CORNERS WITH INSPECTION PORTS AND/OR BURIED REBAR. THE FIELDS MUST BE PROTECTED
FROM VEHICULAR AND LIVESTOCK TRAFFIC.
17.THE ABSORPTION FIELD SURFACES MUST BE SLOPED OR SLIGHTLY MOUNDED TO DIVERT
SURFACE DRAINAGE AWAY FROM THE FIELD.
18.THE ENTIRE ABSORPTION FIELD SURFACE MUST BE RE VEGETATED.
19.THE ABSORPTION FIELD SHALL BE INSTALLED PER THE REQUIRED SETBACK DISTANCES:
10 FEET FROM ANY PROPERTY LINE.
25 FEET FROM ANY POTABLE WATER SUPPLY LINE.
20 FEET FROM ANY OCCUPIED DWELLING WITH CRAWL SPACE .
100 FEET FROM ANY WELL, SPRING OR CISTERN.
50 FEET FROM ANY STREAM OR WATER COURSE.
NATIVE, YARD OR LANDSCAPED SURFACE
N.T.S.
TO 90% STANDARD PROCTOR
EXCAVATED MATERIAL COMPACTED
COMPACTED SUBGRADE
CHAMBER END CAP
CONNECT INDIVIDUAL 4" DISTRIBUTION PIPE
TO HEAD OF EACH CHAMBER TRENCH (TYPICAL EACH TRENCH).
INSTALL CONNECTION AS NEEDED FROM END OR SIDE INLET
PORT OF EACH INFILTRATOR CHAMBER END CAP.
N.T.S.
SUITABLE BACKFILL OR
CLASS 6 ROAD BASE
4" DISTRIBUTION
GRAVITY LINE
FROM SEPTIC TANK
INVERT IN
N.T.S.
4" SOLID PVC GRAVITY
DISTRIBUTION PIPES (TYP.)
TO ABSORPTION FEILD
BAFFLE
COMPACTED SUBGRADE
8" AGREGATE BASE COURSE
RISER SECTION
DISTRIBUTION BOX LID
AT GROUND SURFACE
N.T.S.
4" EFFLUENT PIPE FROM
DISTRIBUTION BOX
6" VALVE BOX LID
QUICK-4 INFILTRATOR
OR EQUAL BIO DIFFUSER
CHAMBER
QUICK-4 INFILTRATOR
END CAP
EXTEND 4" RISER PIPE
MIN. 3" THROUGH END
CAP OR CHAMBER PRE
FORMED PENETRATION
SECURE WITH SCREWS
THROUGH PENETRATION
FLANGE INTO PIPE
PUSH ON PVC CAP
6" VALVE BOX
FINISH GRADE
4" INSPECTION PORT RISER
VERT SAWCUT DEPTH OF CAP
Commercial Design Calculations OWTS
The design flow is calculated as follows for a commercial 6-unit shop/office contractor storage facility.
The onsite wastewater treatment system (OWTS) capacity is designed for transient contractor
employee restroom usage assuming 3 persons per each unit.
From the Regulation 43 usage table :
Design flow is based on usage in 6 garage/shop/storage/offices units and 1 additional storage and office
unit on the second floor of the eastern unit. Maximum population for use of the facilities assumes 1 full
time worker per each unit plus an additional 4 for the eastern unit with the additional upper level office
spaces, for a total 9 daily office or shop staff. Additional usage is based on up to 18 transient
employees/staff using the restrooms.
Gallons per day per person =15 gal/employee/day,
Gallons per day per person =5 gal/transient/day,
Max. Design flow (Qd)gallons/day = (# of people) x (avg. flow)gal/person/day.
Design flow Qd = (10x15=150) + (18 x 5=90) = 240 gpd
Septic Tank Design:
Use a 1000 gallon, two compartment concrete septic tank with an inlet sanitary tee and effluent filter
outlet sanitary tee in the second chamber. Extend new effluent filter handle to within 6" of access riser
lid. The tank shall be installed with ribbed PVC risers and fiber lids or sealed concrete risers and lids set
to approximately 3" above the finish grade surface.
Sub Surface Conditions and Testing:
A subsurface soil investigation and site assessment was performed by Sopris Engineering in on March 3,
2026. The soils were sampled and characterized by application of the USDA visual/tactile soil texture
method analysis from samples in two profile pits. Two excavated profile pits 1 & 2 were observed in the
East central portion of the site within the proposed soil treatment area. The soils below 6 to 18 inches
of topsoils and/or mixed surface fill & gravels consist of medium dense sandy clay loam with moderate
granular to slightly blocky structure with cobbles and gravels to depths of 1 to 2.0 feet underlain by
slighty sandy clay loam with less than 30% of total rock content to the 8 foot depth explored in both
pits. The soil appears to be generally consistent across the site. No evidence of seasonal high ground
water, redox conditions or any other limiting conditions were observed in the profile pits. Groundwater
levels are expected to be below 25 feet from the existing surface grades on the relatively flat terrain.
The soils are suitable for a shallow conventional absorption field consisting of gravelless infiltration
chamber units.
Profile Pit-1
The soils below approximately 12-18 inches of surface gravels and sandy silt loam fill consist of
moderately dense sandy silt loam texture soils that has blocky to granular shape of moderate structural
grade with gravels and cobbles to a depth of 4-feet containing approximately 20% total rock content.
Soils below 4 feet to 6 feet consist of moderately dense slighty sandy silt loam texture soil that has
granular structure of moderate structural grade with less than 30% of total rock content underlain by
silt loam with gravels with less than 20% rock content to the 8 foot depth explored. The soils are
characterized as a soil type 2 sandy silt loam. No free water or limiting condition was encountered in
the pit excavation.
Profile Pit-2
The soils below approximately 3 inches of surface fill consist of topsoil to a depth of 12-inches underlain
by moderately dense sandy silt loam loam texture soils that has blocky to granular shape of moderate
structural grade with gravels and small cobbles to a depth of 4-feet containing approximately 25% total
rock content. Soils below 4 feet to 5 feet consist of moderately dense slighty sandy silt loam texture
soil that has granular structure of moderate structural grade with gravels, cobbles and small boulders
with less than 30% of total rock content underlain by silt loam with gravels with less thant 20% rock
content to the 8 foot depth explored. The soils are characterized as a soil type 2 sandy silt loam. No free
water or limiting condition was encountered in the pit excavation.
The native soils sampled from 2-4 feet below the surface, in both profile pits, are characterized as a soil
type 2 soil type consisting of slighty sandy silt loam texture soil with granular to slightly blocky structure
of moderate structural grade. The brown sandy silt loam soil tactile test ribbons were ¾-1inch long. Soil
type 2 has an effective loading rate for conventional soil treatment of 0.60 gal/S.F./day for a level 1
conventional treatment system. The equivalent percolation rate of these soils is assumed to be 20-30
minutes per inch.
Additional observations will be performed during construction to inspect the shallow trench chamber
trench excavations, absorptive surface preparation in the soil treatment area and provide guidance for
installations of the specified materials in the in-situ native soils. If any adjustments to design or
installation recommendations are necessary, notice will be made to County EHD and applicable
revisions to design/construction plans and report will be submitted. All conditions and installations will
be included in the As-Constructed documentation.
Soil Treatment Unit/ Absorption System Design:
The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate
(LTAR) for the native soils and the application of appropriate loading factors for a soil treatment unit
system utilizing gravity distribution to gravelless chamber trenches. The new treatment system and
absorption field will consist of gravity distribution of septic tank effluent via a distribution box to
individual chamber trenches with treatment across the native soil absorptive surface.
Long Term Acceptance Rate (LTAR):
Receiving Wastewater Treatment Level 1;
LTAR; (Table 10-1 Soil type 2 loading rate for sandy silt loam is (0.60 gal./S.F./day);
Design Flow; Qd = flow (gal/day) = 240 gpd
Loading factors; (Table 10-2, Gravity application trenches, L.F.1 = 1.0 )
(Table 10-3, Gravelless chambers, L.F.2 = 0.7)
STA absorption treatment area; A = Area S.F.;
A(sf) = Qd x L.F.1 x L.F.2 .: A(sf) = 240gpd x 1.0 x 0.7 = 280 S.F.
LTAR 0.60 Gal/S.F./day
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Number of Quick-4 Infiltrator chambers 4'x3'x12"chambers:
280 S.F. = 24 chambers; Use 24 chambers
12 S.F./Chamber
Number of Equivalent Arc-36 chambers 5'x3'x12"chambers:
280 S.F. = 19 chambers; Use 21 chambers
15 S.F./Chamber
Use 24 Quick-4 Infiltrator chambers in 3 trenches 34' long by 3' wide with 8 chambers units per trench
plus two end caps as delineated on the plan. Alternative use 19 Arc-36 chambers in 2 trenches 30' long
by 3' wide with 6 chambers units per trench with ends caps and 1 35' long by 3' wide trench with 7
chambers units. The septic tank effluent will be gravity distributed to the head of each chamber row via
individual distribution pipes from a distribution box.
1.ADDITIONAL ASSESSMENTS AND RECOMMENDATIONS WILL BE MADE BY THE ENGINEER
DURING INITIAL STAGES OF CONSTRUCTION TO VERIFY ASSUMPTIONS MADE FOR THE
OWTS DESIGN INCLUDING VERIFICATION OF SOILS, STA LAYOUT, EXCAVATION DEPTHS,
THE LOCATION OF THE SEWER/DISTRIBUTION PIPING, COMPONENTS AND
INSTALLATION OF APPURTENANCES.
2.PRIOR TO CONSTRUCTION OF THE PERMITTED SYSTEM THE ENGINEER SHOULD BE
CONTACTED BY THE PROJECT MANAGER/CONTRACTOR WELL IN ADVANCE TO PROVIDE
ADEQUATE TIME TO DISCUSS THE SYSTEM COMPONENTS WITH THE CONTRACTOR,
ANSWER QUESTIONS, RESOLVE ANY CONFLICT ISSUES AND SCHEDULE INSPECTION SITE
VISITS BASED ON CONSTRUCTION PROGRESS. A PRE-OWTS CONSTRUCTION MEETING
WITH THE ENGINEER AND CONTRACTOR IS ESSENTIAL AND REQUIRED PRIOR TO
INSTALLATION OF THE OWTS COMPONENTS.
3.REGULATIONS REQUIRE THAT THE DESIGN ENGINEERS OF RECORD PERFORM SITE
INSPECTIONS OF THE PERMITTED SYSTEM DURING CONSTRUCTION AND PROVIDE
"AS-CONSTRUCTED" DOCUMENTATION OF THE INSTALLED SYSTEM TO THE THE
COUNTY LPHA AFTER CONSTRUCTION IS COMPLETE. THE ENGINEER SHOULD BE
CONTACTED AND NOTIFIED OF THE CONSTRUCTION SCHEDULE TO PERFORM TIMELY
INSPECTIONS, PROVIDE DIRECTION TO CONTRACTOR REGARDING THE INSTALLATION OF
THE OWTS COMPONENTS AND AT LEAST 48 HOURS PRIOR TO FINAL BACKFILL OF
COMPONENTS.
4.THE COUNTY ENVIRONMENTAL HEALTH DEPARTMENT SHOULD BE CONTACTED AT
LEAST 48 HOURS PRIOR TO FINAL BACKFILL OF COMPONENTS TO PROVIDE ADVANCED
NOTICE OF CONSTRUCTION SCHEDULE IN ORDER TO PERFORM A FINAL INSPECTION OF
THE IN PLACE COMPONENTS. THE GARFIELD COUNTY ENVIRONMENTAL HEALTH
DEPARTMENT CONTACT NUMBER IS 970-945-6614 X 8106 (MAIN OFFICE).
5.OUR DESIGN AND RECOMMENDATIONS ARE BASED UPON OUR EVALUATION OF THE
EXISTING AND PROPOSED SITE CONDITIONS, THE DEVELOPMENT PLANS AND
INFORMATION SUPPLIED TO US BY OTHERS. IF DEVELOPMENT PLANS OR SITE
CONDITIONS ARE FOUND TO BE DIFFERENT FROM CONDITIONS ASSUMED OR
INDICATED, WE SHOULD BE NOTIFIED TO EVALUATE ANY EFFECT ON THE PROPOSED
OWTS.
6.CONTRACTOR SHOULD REVIEW ANY CONDITIONS ON THE ISSUED PERMIT AND
COORDINATE WITH THE ENGINEER REGARDING CONSTRUCTION OF THE SYSTEM. IF YOU
HAVE ANY QUESTION OR NEED ANY ADDITIONAL INFORMATION, CALL THE ENGINEER,
PAUL RUTLEDGE, SOPRIS ENGINEERING, 970 704 0311.
FILTER FABRIC N-140
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1.THE OWTS AS SHOWN ON THE PLAN AND THE DETAILS WERE DESIGNED BY SOPRIS ENGINEERING.
2.THE EXISITNG LOT CONDITIONS PER COUNTY GIS DATA BASE, AERIAL MAPPING, LIDAR
TOPOGRAPHY. PLAT INFORMATION SHOWN IS BASED ON A EXISTING CONDITIONS SURVEY BY
SOPRIS ENGINEERING DATED 2014. PROPOSED LOT CONDITIONS BY CONTRACTOR.
3.PROPOSED STRUCTURE BY ALL DES LLC.
4.PRIMARY OWNER NAME AND ADDRESS: IRMW LLC, P O BOX 1037, CARBONDALE CO 81623
5.SITE ADDRESS: 1058 COUNTY RD 100, CARBONDALE, CO 81623
6.Legal Summary: IRMW LLC PARCEL 1 Lot: 1A AS PER MINOR SUBDIVISION PLAT RECEPTION
NUMBER 893462.
7.Parcel Number: 239335402001
8. COUNTY SEPTIC PERMIT #:
9.CONTRACTOR: MYRL SERRA, 5mconst.llc@gamil.com
YTN 03/12/26
3/12/2026