HomeMy WebLinkAboutEngineer's OWTS Design PlanJune 24, 2024
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
S OPRIS E NGINEERING • LLC civil consultants
Anne and Laurence Sperry, West S Ranch LLC
33 Sunhill Lane,
Newton Center, MA 02459
lsperry@sperryinc.com
RE: Design Report–Onsite Wastewater Treatment System (OWTS), Sperry Residence, 0 102 County Road,
Carbondale, CO, Lot 2 Hunt Ranch, Garfield County, Colorado
SE Job No. 34042.01 Parcel No: 239120100278. Garfield County OWTS Permit #______________.
Dear Laurence and Anne:
This letter report 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, and geotechnical soils evaluation with respect to the proposed residential 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 “C6-OWTS Plan”, dated 06-21-2024. The design criteria and system sizing information is summarized below.
Existing and Proposed Conditions
The proposed OWTS will serve a new 4-bedroom single family residence with room for a two-bedroom ADU in the
future located in the central area of the property within an approximate 35-acre development area. The site is
vegetated with sagebrush, pinion/juniper, cedar and small grassland meadows.
The subject 35-acre parcel’s existing topography and site conditions are derived from county GIS data base, aerial
mapping, Lidar topography and survey information by Sopris Engineering. The central portion of the parcel within
the development area consists of relatively gentle slopes that generally trend down gradient to the west and north.
The proposed OWTS field will be constructed parallel to the contours on the slightly sloped terrain.
The proposed site improvements will include associated driveway, auto court, residential structure, utilities and a
new onsite wastewater treatment system. The property’s water supply is from a proposed domestic well located over
100-feet east of the proposed OWTS field. The proposed development improvements and OWTS layout is
delineated on the attached OWTS plan.
Summary Design Criteria
The new OWTS is designed for a treatment capacity of 675 gallons per day based on the design wastewater flow to
serve a minimum 6-bedroom residence in accordance with Table 6-2 values, Section 43.6, A.4. The new OWTS will
utilize a minimum 2,000 gallon two-compartment concrete tank to be installed off the northwesterly corner of the
garage. Sealed ribbed PVC risers with lids will be installed on the new septic tank along with appropriate pipe
connections to the new tank utilizing the appropriate fitting adaptor rings for the tank and riser. The new 2,000
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-35 sewer pipe section with two-way cleanout will be installed
between the tank inlet on the gravity sewer line and the residential structure.
The STA will consist of leaching chamber trenches that provide 960 S.F. of total absorption area in a trench
configuration. The septic tank effluent will be gravity discharged through a new 4-inch schedule-40 or SDR-35,
installed at minimum 1.5% slope, to the STA via a distribution box. The effluent will be equally distributed from the
OWTS, Sperry Residence
0 102 County Road, Carbondale, CO
SE Job No. 34042.01
June 24, 2024
Page2
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 and housed in valve boxes set just
above finish surface grade. The design is in compliance with the current County regulations with design calculations
based on the soil type, texture and structure with an appropriate long term acceptance rate (LTAR). The designed
system meets all required setbacks and will be installed within the general location indicated on the plan.
Design Flow
The design flow is calculated as follows for the minimum design capacity of an equivalent 6-bedroom residential
dwelling. The OWTS is designed for a treatment capacity of 675 gallons per day based on the design wastewater
flow in accordance with Table 10-1 values, Section 43.6, A.4. Regulation 43:
Minimum population based on 3 bedrooms at 2 persons per bedroom equating to 6 persons plus three
bedrooms at 1 person per bedroom equating to a total of 9 persons.
The Design flow is calculated based on residential usage of 75 gal/person/day,
Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day.
Design flow Qd = 9*75 = 675 gpd
Septic Tank Design
The septic tank capacity required for a minimum 48 hour retention time is calculated as follows:
V = 675 gal/day * 2 day = 1350 gallons. Use a minimum 2,000 gallon 2-compartment concrete septic tank. The tank
to be installed with ribbed PVC risers and access lids set a minimum 3 inches above finish grade surface.
Sub Surface Conditions and Testing
Subsurface soil investigations and USDA soil texture method tests were performed by Kumar, USA and Sopris
Engineering on May 29, 2024. The soils from three profile pits, in the vicinity of the proposed STA field area were
sampled and characterized by application of the USDA visual/tactile soil texture method analysis. The soils were
tested to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate,
absorptive surface level capacity and to assess appropriate treatment level design for the in-situ native soils. The
soils below 9 inches of topsoil consist of dense slit loam with less than 2% scattered gravel or rock content to 7 feet
below the surface grades. The soil appears to be generally consistent across the site.
The native soils sampled from 2-3 feet below the surface are characterized as a soil type 2A soil consisting of silt
loam texture with fine granular structure shape with massive grade. This soil has an effective loading rate for
conventional soil treatment of 0.5 Gal/S.F./day for a level 1 conventional treatment system. No rocky soils or
significant change of texture was encountered at depth. Some evidence of thin scattered lenses of calcareous deposits
at variable depths was encountered in Profile pit 1 and 3. A 6 to 9 inch layer of calcareous deposits at variable
pitched depth from 18 to 30 inches below surface grade was encountered in Profile pit 2 that was excavated from
existing surface grades approximately 3' below the other pits. Based on this evidence the proposed STA will be
situated on slightly higher ground. No free water was encountered in excavations observed on site. Evidence of flood
irrigation saturation (potential seasonal perched high ground water) was observed by the presence of redox mottling
slightly above and below the thin layer of calcareous deposits in Pit 2. Normal Groundwater levels are expected to
be below 8 feet from the existing surface grades. The soils are suitable for the installation of an STA consisting of
multiple gravelless chamber trenches. Additional soil evaluation will be performed during construction to verify the
soils in the entire field excavation.
OWTS, Sperry Residence
0 102 County Road, Carbondale, CO
SE Job No. 34042.01
June 24, 2024
Page3
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 2A loading rate for a massive silt loam is (0.50 gal./S.F./day):
Design Flow; Qd = flow (gal/day) = 675 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) = 675 gpd x 1.0 x 0.7 = 945 S.F.
LTAR 0.50 Gal/S.F./day
Number of Quick-4 Infiltrator chambers 4'x3'x12"chambers:
945 S.F. = 79 chambers; Use 80 chambers
12 S.F./Chamber
Number of Equivalent Arc chambers 5'x3'x12"chambers:
945 S.F. = 63 chambers; Use 64 chambers
15 S.F./Chamber
Use 80 Quick-4 Low Profile Infiltrator chambers in 4 trenches 82' long by 3' wide with 20 chambers units per trench
plus two end caps as delineated on the plan. Alternative use 64 Arc chambers in 4 trenches 80' long by 3' wide with
16 chambers units per trench with ends caps. 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
Additional assessments and recommendations will be made by the engineer during initial stages of construction to
direct installation in accordance with OWTS design, verify the soil conditions and location of the OWTS
components.
Prior to construction of the permitted system the engineer should be contacted by the contractor to provide adequate
time to discuss the system components, answer questions, resolve any conflict issues and schedule inspection site
visits based on construction progress. A pre-OWTS construction meeting with the engineer, the contractor, and the
qualified installer is essential and required prior to installation of the OWTS components. Pre-construction
consultation, and installation by SI Valley Pre-Cast, Inc. or Sopris Engineering will be coordinated by the contractor.
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24.0 80.0
4" PVC EFFLUENT PIPE @ MIN. 1 %,
USE SCHD-40 OR SDR-35
4" PVC SEWER PIPE
@ MIN 2%, USE
SCHD-40 OR SDR-35
CONCRETE DISTRIBUTION BOX WITH BAFFLE
INSTALLED LEVEL ON COMPACTED BASE,
INSTALL RISERS AND LID TO SURFACE
4" PVC DISTRIBUTION PIPES (TYP.)
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 FINISH GRADE
(TYP. EACH TRENCH CHAMBER END CAP)
INSTALL CHAMBER END CAP
ON ALL END CHAMBERS
ABSORPTION/TREATMENT FIELD, USE 80 LOW PROFILE QUICK-4 CHAMBERS IN 4
TRENCHES WITH 20 CHAMBERS PER ROW FOR A TOTAL ABSORPTION AREA OF
960 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 20" BELOW THE EXISTING SURFACE GRADES, WITHIN THE UPPER HORIZON
OF THE NATIVE SILT LOAM SOILS & BACKFILLED WITH A MINIMUM 12" OF
COVER OVER THE CHAMBERS. THE FINISH GRADE ACROSS THE FIELD SHALL BE
SLIGHTLY MOUNDED A MINIMUM 2" ABOVE EXISTING ADJACENT GRADES.
INSTALL 2,000 GALLON, 2-COMPARTMENT CONCRETE SEPTIC
TANK (USE VALLEY PRECAST ITEM #IM 2000T-2CP OR APPVD
EQUAL) 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".
EXCAVATION DEPTH 20" MIN. TO 48" MAX. BELOW
SURFACE GRADE, MIN. 12" COVER OVER TOP OF
CHAMBERS, FILL & GRADE FIELD AREA
APPROXIMATELY 2" ABOVE EXISTING SURFACE GRADES
PROPOSED 4" X 2-WAY
CLEANOUT, INV. TO BE
18" - 24" BELOW FINISH
GRADE SURFACE
INSTALL 4" FULL
BODY WYE
2" SCHD 40 PVC
SEWER PIPE
@ MIN 2%INSTALL 4" FULL
BODY WYE W/ 2" X 4"
REDUCER
INSTALL 4" FULL
BODY WYE
4" PVC SEWER PIPE @ MIN 1.5%
TO BE STUBBED FOR FUTURE USE,
PVC SCHD-40 OR SDR-35
4" PVC SEWER PIPE @ MIN 1.5%
TO BE STUBBED FOR FUTURE USE,
PVC SCHD-40 OR SDR-35
PROPOSED 4" X 2-WAY
CLEANOUT, INV. TO BE
18" - 24" BELOW FINISH
GRADE SURFACE
PROPOSED 2" X 2-WAY
CLEANOUT, INV. TO BE
18" - 24" BELOW FINISH
GRADE SURFACE
PROPOSED
PROPANE TANK,
SEE UTILITY PLAN
100-FT WELL
SETBACK
EXISTING
WELL
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DATE REVISION
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JOB NO.
DATE:
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34042.01
07/24/24
PER
WJB
C-3.2
OWTS DESIGN
NOTE: ALL CHAMBERS IN EACH TRENCH MUST BE INSTALLED ON
LEVEL GRADE OVER SCARIFIED NATIVE SOIL.
MAXIMUM DEPTH OF TRENCHES NOT TO EXCEED 36" BELOW
PROPOSED SURFACE GRADES. INLET AND END CAPS ARE TO BE
INSTALLED ON EACH END CHAMBER ROW. IF EXCESSIVE LARGE
COBBLES OR BOULDERS ARE ENCOUNTERED IN ANY PART OF THE
EXCAVATION, OVER EXCAVATE AND BACKFILL WITH SAND OR
SUITABLE SCREENED NATIVE SOILS.
BACKFILL WITH SCREENED
ONSITE SOILS FREE OF ROCKS IN
EXCESS OF 3" DIAMETER OR USE 3/4"
TO 1.5' SCREENED ROCK
CROWN FIELD TRENCH TO
DIVERT SURFACE WATER 4' MIN
LEACHING
CHAMBER
7"-12"
6"
N.T.S.
BACKFILL LAYER NATURAL ONSITE
SOILS FREE OF ROCKS
4" PVC INLET PORT
IN END CAP
SCARIFY/TILL BOTTOM SURFACE TO A
DEPTH OF 3"
1. ADDITIONAL GEOTECHNICAL EVALUATIONS AND INSPECTIONS BY THE ENGINEER SHOULD BE PERFORMED
DURING INITIAL STAGES OF CONSTRUCTION TO VERIFY SOIL CONDITIONS AND OWTS DESIGN.
2. THE EVALUATIONS AND INSPECTIONS MAY RESULT IN MODIFICATIONS TO THE DESIGN THAT MAY INCLUDE
FIELD SIZE REVISIONS AND POSSIBLE SOIL REPLACEMENT IN SELECT AREAS IF NEEDED. SUFFICIENT NOTICE
TO THE ENGINEER BY THE PROJECT MANAGER/CONTRACTOR NEEDS TO BE MADE IN ORDER TO SCHEDULE
THE SITE INSPECTIONS.
3. 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.
4. COUNTY REGULATIONS REQUIRE THAT THE DESIGN ENGINEERS OF RECORD PERFORM SITE INSPECTIONS
OF THE PERMITTED SYSTEM DURING CONSTRUCTION AND PROVIDE "AS-BUILT" DOCUMENTATION OF THE
INSTALLED SYSTEM TO THE COUNTY AFTER CONSTRUCTION IS COMPLETE. THE ENGINEER SHOULD BE
CONTACTED AND NOTIFIED OF THE CONSTRUCTION SCHEDULE.
5. 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:
Ted White, P.E., Environmental Health Specialist III.Garfield County Public Health;
twhite@garfield-county.com, 970-945-6614 x 8106 (main office) or 970-230-2442 (mobile)
6. OUR DESIGN AND RECOMMENDATIONS ARE BASED OUR SITE ASSESSMENT, SOIL EVALUATION AND UPON
INFORMATION SUPPLIED TO US BY OTHERS. IF SUBSURFACE 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. IF THE COUNTY REQUESTS CHANGES OR MODIFICATIONS TO THIS
DESIGN, WE SHOULD BE CONTACTED TO EVALUATE AND RESPOND TO THE REQUEST.
7. CONTRACTOR SHOULD REVIEW ANY CONDITIONS ON THE ISSUED PERMIT AND COORDINATE WITH THE
ENGINEER REGARDING CONSTRUCTION OF THE SYSTEM. THE CONSTRACTOR AND/OR SYSTEM INSTALLAR
SHOULD PHOTO DOCUMENT ALL PHASES OF OWTS CONSTRUCTION AND INSTALLATION OF COMPONENTS.
8. IF YOU HAVE ANY QUESTION OR NEED ANY ADDITIONAL INFORMATION, PLEASE CALL PAUL RUTLEDGE AT
SOPRIS ENGINEERING, (970) 704-0311.
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.
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" NOT TO EXCEED
24".
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 OR END CAP. (TYP. BOTH ENDS OF EACH ROW) THE PORTS MAY HAVE THREADED CAPS AT
GRADE OR HOUSED IN A 6" VALVE BOX.
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" ABOVE THE TOP OF
THE CHAMBERS. THE TOP OF THE PLACED BACKFILL SHALL BE COVERED WITH A LAYER OF FILTER FABRIC. A
MINIMUM 3" 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 MANUFACTURES
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 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.
COMPACTED SUBGRADE
4" SDR35
3" DIA
4" SCH40
4" SCH404" SDR35
3" DIA
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
1. THE OWTS AS SHOWN ON THE PLAN AND THE DETAILS WERE DESIGNED BY SOPRIS ENGINEERING.
2. THE PROPOSED LOT CONDITIONS BY SOPRIS ENGINEERING AND SURVEY/PLAT INFORMATION SHOWN IS
BASED ON AN ISP BY SOPRIS ENGINEERING, 10-11-23.
3. PRIMARY OWNER NAME AND ADDRESS: WEST S RANCH LLC, 33 SUNHILL LANE, NEWTON CENTER, MA
02459
4. SITE ADDRESS: TBD COUNTY ROAD 102, CARBONDALE, CO 81623
5. Legal Summary: SECTION: 20 TOWNSHIP: 7 RANGE: 87 A PARCEL OF LAND SITUATE WITHIN SECTION 20
BEING MORE PARTICULARLY DESCRIBED PER SPECIAL WARRANTY DEED RECEPTION NO. 969596 35.11
ACRES
6. Parcel Number: 2391-201-00-278
7.COUNTY OWTS PERMIT #: ________________________
8. CONTRACTOR: _____________________________
6" MIN.
4" MIN.
6" MIN.
4"4"
4" DISTRIBUTION
GRAVITY LINE
FROM SEPTIC TANK
INVERT IN
N.T.S.
BAFFLE
COMPACTED SUBGRADE
8" AGREGATE BASE COURSE
RISER SECTION
DISTRIBUTION BOX LID
AT GROUND SURFACE
EXCAVATED MATERIAL COMPACTED
TO 90% STANDARD PROCTOR
UNDISTURBED EARTH
SILTY LOAM SOIL.
REVEGATATION
TOPSOIL LAYER
4.0
0.7
Quick4 Plus Low Profile Endcap Detail
(to scale)
0.7
1.5
0.9
1.1
LP- 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
6" VALVE BOX
4" INSPECTION PORT RISER
PUSH ON CAP
6" VALVE BOX
COVER EACH CHAMBER ROW
W/ FILTER FABRIC COVER
Pena Design Calculations OWTS
The proposed onsite wastewater treatment system (OWTS) will be installed to serve a 4-bedroom single family
residence. A possible future 2-bedroom ADU in the adjacent barn/shop structure may be considered in the
future. In order to ensure adequate OWTS capacity for current proposed usage and potential future usage the
new system is designed with a design flow based on a total residential population of 9 persons. Therefore
design flow treatment capacity is calculated as follows for a minimum equivalent 6-bedroom single family
residence.
From the Regulation 43 usage table :
Minimum population based on 6 bedrooms = (2 persons * 3 bedrooms) + (3 bedrooms * 1 persons)= 9 persons.
Gallons per day per person = 75 gal/person/day, No peaking factor
Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day.
Design flow Qd = 9*75 = 675 gpd
Septic Tank Design:
Septic Tank Design: 2-Day detention time = 675 x 2 = 1350 gallons required. Use a 2000 gallon, two
compartment concrete septic tank with an effluent filter outlet sanitary tee in the second chamber. The tank
shall be installed with sealed PVC risers and lids set to the finish grade surface.
Sub Surface Conditions and Testing:
Subsurface soil investigations and USDA soil texture method tests were performed by Kumar, USA and Sopris
Engineering on May 29, 2024. The soils from three profile pits, in the vicinity of the proposed STA field area
were sampled and characterized by application of the USDA visual/tactile soil texture method analysis. The soils
were tested to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic
loading rate, absorptive surface level capacity and to assess appropriate treatment level design for the in-situ
native soils. The soils below 9" of topsoil consist of dense slit loam with less than 2% scattered gravel or rock
content to 7 feet below the surface grades. The soils appear to be generally consistent across the site.
The native soils sampled from 2-3 feet below the surface are characterized as a soil type 2A soil consisting of silt
loam texture with fine granular structure shape with massive grade. This soil has an effective loading rate for
conventional soil treatment of 0.5 Gal/S.F./day for a level 1 conventional treatment system. No rocky soils or
significant change of texture was encountered at depth. Some evidence of thin scattered lenses of calcareous
deposits at variable depths was encountered in Profile pit 1 and 3. A 6 to 9 inch layer of calcareous deposits at
variable pitched depth from 18 to 30" below surface grade was encountered in Profile pit 2 that was excavated
from existing surface grades approximately 3' below the the other pits. Based on this evidence the proposed
STA will be situated on the slightly higher ground. No free water was encountered in excavations observed on
site. However evidence of flood irrigation saturation (potential seasonal perched high ground water) was
observed by the presence of redox mottling slightly above and below the thin layer of calcareous deposits in Pit
2. Normal Groundwater levels are expected to be below 8 feet from the existing surface grades. The soils are
suitable for the installation of an STA consisting of multiple gravelless chamber trenches. Additional soil
evaluation will be performed during construction to verify the soils in the entire field excavation.
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 2A loading rate for a massive silt loam is (0.5 gal./S.F./day);
Design Flow; Qd = flow (gal/day) = 675 gpd
Loading factors; (Table 10-2, Gravity application trenches, L.F.1 = 1.0 )
(Table 10-3, Gravelless chambers, L.F.2 = 0.7)
STU absorption treatment area; A = Area S.F.;
A(sf) = Qd x L.F.1 x L.F.2 .: A(sf) = 675 gpd x 1.0 x 0.7 = 945 S.F.
LTAR 0.5 Gal/S.F./day
Number of Quick-4 Infiltrator chambers 4'x3'x12"chambers:
945 S.F. = 79 chambers; Use 80 chambers
12 S.F./Chamber
Number of Equivalent Arc chambers 5'x3'x12"chambers:
945 S.F. = 63 chambers; Use 64 chambers
15 S.F./Chamber
Use 80 Quick-4 Infiltrator chambers in 4 trenches 82' long by 3' wide with 20 chamber units per trench plus two
end caps as delineated on the plan. Alternative use 64 Arc chambers in 4 trenches 80' long by 3' wide with 16
chambers units per trench with ends caps. The septic tank effluent will be gravity distributed to the head of
each chamber row via individual distribution pipes from a distribution box.
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