HomeMy WebLinkAboutRevised OWTS Design 08.24.2023
Onsite Wastewater Treatment System Design
Revision
August 7, 2023
Revised: August 24, 2023
Gonzalez Project
591 County Road 259
Silt, CO 81652
Parcel No. 2127-33-101-003
Prepared By:
K-Cronk Engineering, Inc.
P.O. Box 140
Mack, CO 81525
970-250-0572
1
Site History
There is an existing four-bedroom residence on the site that is served by an existing onsite wastewater
treatment system (OWTS). The existing system is experiencing slow drainage and signs of failure, and the
owner would like to replace it. The OWTS will be designed for a four-bedroom residential loading.
The site consists of approximately 5.434 acres of cultivated native soil. Drainage is approximately 2% to
the east/southeast. A percolation (perc) test/soils evaluation and site study were conducted on the
property of reference on 07/31/2023 by Kachayla R. Cronk, registered professional engineer (R.P.E.).
The perc excavation trench was located approximately 210’ northeast of the southwest property line and
approximately 35’ southeast of the northwest property line.
A soils evaluation of a new excavation site closer to the proposed soil treatment area was conducted
on the property of reference on 08/23/2023. The perc excavation trench was located approximately
50’ south of the north property line and approximately 65’ southwest of the northeast property line.
This OWTS design has been prepared for the project based on information disclosed during the site studies
mentioned above. A discussion of the engineered OWTS design follows. The perc test/soils evaluation are
attached for reference as Appendix A. The locations of the perc excavation trench and soils evaluation
excavation are shown on the Plot Plan included in this report.
Development of Design Parameters
The 07/31/23 perc excavation trench was extended to a depth of 66" below ground surface (BGS). There
was no ground water present to a depth of 66" BGS. Evidence of high seasonal water table was observed
at a depth of 24" BGS. The soils evaluation indicates two distinct soil horizons underlie the site. A
lithological description follows:
depth (in.) description
0” – 24” silty clay loam, brown
(Soil Type 3A, USDA – silty clay loam, granular, weak structure)
24” – 66” sandy clay loam, brown
(Soil Type 3A, USDA – sandy clay loam, massive, structureless)
The 08/22/23 soils evaluation excavation trench was extended to a depth of 84" below ground surface
(BGS). Groundwater was present at a depth of 84” BGS. Evidence of high seasonal water table was
observed at a depth of 48" BGS. The soils evaluation indicates two distinct soil horizons underlie the site.
A lithological description follows:
depth (in.) description
0” – 24” loamy sand, light brown
(Soil Type 1, USDA – loamy sand, single grained, structureless)
24” – 84” sandy clay loam, light brown
(Soil Type 3, USDA – sandy clay loam, blocky, moderate structure)
Based on the results from the 07/31/23 perc test/soils evaluation and the 08/23/23 soils evaluation,
(Appendix A), an LTAR of 0.35 is chosen for overall system sizing for a pressurized infiltrator trench soil
treatment area design to discharge to subsoils below the 12” depth.
2
System Design
An INFILTRATOR trench soil treatment system is proposed for discharge of septic effluent at the site.
Construction of the system will consist of excavating level trenches in the area comprising the soil treatment
area. Grading during construction may affect slope, therefore contractor shall verify slope at time of
installation. Soil treatment area orientation may be adjusted per site variations to facilitate consistent
trench depth running parallel to final contours. The initial excavation shall be continued to a level depth
of 12" BGS (see Soil Treatment Area Cross Section). A lift station discharging into pressurized effluent
distribution laterals will be employed to discharge septic effluent into the soil treatment area.
Following completion of the initial excavation, INFILTRATORS (QUICK4 STANDARD or equivalent)
will be used to construct a septic effluent distribution system. The INFILTRATOR effluent distribution
system will be installed in accordance with the "Infiltrator Technical Manual", available from Infiltrator
Systems Inc., 123 Elm Street, Suite 12, Old Saybrook, Connecticut 06475. Adjacent INFILTRATORS shall
be fastened with a minimum of three (3) ¾” self-tapping screws to prevent movement and separation during
backfilling.
After the INFILTRATORS are installed, synthetic filter fabric (140-200 mesh) will be placed over the
INFILTRATORS and the system will be covered with a soil cap. The soil cap will consist of approximately
18” minimum of native soil backfill. The soil cap will be mounded 5% above the existing ground surface
to promote surface run off away from the soil treatment area.
Septic effluent will be introduced into the soil treatment area through pressurized distribution laterals
installed in each row of INFILTRATORS as shown in the included graphics. The injection laterals will
consist of 1" Schd 40 PVC pipe with 5/32" holes equally spaced 48" o.c. along each row of
INFILTRATORS. Holes in the injection laterals will be drilled at 12:00 o’clock to direct effluent up for
dispersal against the top of the chamber. Injection laterals shall be suspended from the top of the chamber
with all-weather plastic pipe strapping (min. 120 lbs tensile strength) at every chamber joint connection.
There is an existing tank on the site that has been used for sewage storage. The tank will be removed or
abandoned in place and replaced with a new tank described below. Abandonment shall consist of pumping
the tank of all solids and crushing the top and sides in before filling all void space with structural fill.
A 1,500 gallon, two compartment septic tank is required to provide a minimum of 48 hours retention time
for sewage generated from the proposed project in addition to the displaced volume from the pump vault.
A screened effluent pump will be placed in the final down-gradient compartment of the septic tank. The
effluent pump system will employ an OSI high head, non-clog (3/4” solids handling capability), effluent
pump (OSI model no. PF500511) and screened pumping vault (OSI model no. PVU57-1819-L).
A 2" Schd 40 PVC pressure transport line will be used to transfer septic effluent from the pumping system
to the STA. The pressure main will be self-draining or be buried a minimum of 36" below ground surface
to prevent freezing. All pressure piping and construction shall be completed in accordance with the attached
graphics.
As shown in the included graphics, the trench soil treatment system will consist of four (4) trenches 3' wide
x 12” deep x 72' long with eighteen (18) INFILTRATOR (or equivalent) units each for a total of seventy-
two (72) units. The soil treatment area will encompass an effective area of 1542.86 sq. ft.
3
DESIGN CALCULATIONS
DESIGN LOADING RATE OF 3 BEDROOMS @ 150 GAL./BEDROOM-DAY = 450 gal./day
PLUS 1 BEDROOM @ 75 GAL./BEDROOM-DAY = 525 gal./day
DESIGN LONG TERM ACCEPTANCE RATE (LTAR) = 0.35 GAL./SQ.FT./DAY
A = 𝑄
𝐿𝑇𝐴𝑄, WHERE,
A = SOIL TREATMENT AREA (SQ. FT.)
Q= DESIGN FLOW (GAL./DAY)
LTAR = LONG TERM ACCEPTANCE RATE (GAL./SQ.FT./DAY)
A = 525
0.35 = 1500 𝑆𝑄.𝐹𝑆.
SOIL TREATMENT AREA ADJUSTMENT FACTOR FOR PRESSURE TRENCH DESIGN = 0.8
SOIL TREATMENT AREA ADJUSTMENT FACTOR FOR USE OF CHAMBERS = 0.7
ADJUSTED SOIL TREATMENT AREA = 1500 SQ.FT. X 0.8 X 0.7 = 840 SQ. FT.
LENGTH OF 3’ WIDE TRENCH REQ’D = 840 SQ.FT. / 3 FT. = 280 FT.
USE 4 TRENCHES WITH 18 QUICK4 STANDARD INFILTRATORS (or equivalent) EACH, FOR A
TOTAL OF 72 UNITS
SOIL TREATMENT AREA SIZED AT 4 TRENCHES 3 FT. WIDE X 72 FT LONG = 864 SQ. FT.
4
Installation - Setbacks, Notifications, and Inspections
The owner and installer shall be aware of and comply with the following installation and system operation
requirements.
• The installer must be approved and licensed by Mesa County for installation of onsite
wastewater treatment systems.
• All installation activities shall be conducted in accordance with current Mesa County OWTS
Regulations. If at any time during construction, subsurface site conditions are encountered
which differ from the design parameters previously described, construction activities will stop,
and the design engineer and Mesa County will be contacted to address any necessary design
modifications.
• The final cover shall not be placed on sewer lines, septic tank, or the soil treatment area until
the system has been inspected and approved by the design engineer and Mesa County. The
installer shall provide 48-hour notice for all required inspections.
• Installation procedures including grade, location, setbacks, septic tank size, and soil treatment
size shall conform with the attached graphic details. Construction activities and system
components will not encroach upon existing easements or utility corridors. A minimum of 5
ft of undisturbed soil shall be maintained between individual absorption elements and the septic
tank. A minimum of 4’ of undisturbed soil shall be maintained between adjacent absorption
elements.
• The installer must maintain all setbacks to utility lines, easements, property lines, or other
adverse conditions, whether they are known and shown on the attached graphics or have been
disclosed during construction. Vehicle traffic and parking is to be prevented over the soil
treatment and repair area. Minimum setbacks for system components are:
Source Septic Tank Soil Treatment Area
domestic water line 10' 25'
domestic well 50' 100'
domestic water cistern 50' 100'
property lines 10' 10'
structure w/crawl space 5' 20'
structure w/o crawl space 5' 10'
irrigation ditch
open 50' 50'
intermittent irrigation 10' 25'
gated 10' 25'
solid pipe/lined 10' 10'
• All gravity flow sewer lines and effluent distribution piping shall be 4 inches in diameter and
have glued joints. All lines discharging sewage from the residence to the septic tank shall
maintain a minimum fall of 1/8 in. per foot and shall employ sweep 90's or 2-45's at all turns.
Sewer lines from the dwelling to the septic tank and at least 6 ft from the septic tank outlet
must meet minimum standard ASTM-3034. Lines discharging from the septic tank to the soil
treatment area shall maintain a minimum fall of 1/8 in. per foot. Sewer lines under driveways
shall meet the minimum Schedule 40 PVC standards. Additionally, effluent piping in traffic
areas with less than 24" of cover shall be encased in 6" CMP or flow fill and covered with
minimum 2" high density blue board insulation.
5
• Sewer lines or domestic water lines shall be encased in minimum SCHD 40 with water -tight
end caps or a minimum of 6” of flow fill at all points with less than 5’ separation between sewer
and domestic water lines.
• Four-inch clean outs shall be installed at maximum 100' intervals in all gravity flow effluent
lines exceeding 100' in length.
• A minimum of 12" of soil cover (18" recommended) shall be maintained over all gravity
draining OWTS components to prevent freezing of septic effluent (excepting septic tank access
ports which must be extended to the ground surface).
• A minimum of 36” of soil cover shall be maintained over all non-draining pressure effluent
line.
• The septic effluent pumping system shall consist of OSI components (OSI, non-clog (3/4”
solids handling capability) effluent pump model no. PF500511 and OSI screened pumping
vault model no. PVU57-1819-L) as detailed in the attached effluent pumping system detail.
The effluent pump control panel shall be Orenco model no. S1ETM. Electrical wiring shall be
continuous cable with all connections made in a weatherproof box. Limit switching shall
consist of: 1) low level/pump off, 2) high level/pump on, and 3) high level alarm/system failure.
The high-level alarm shall be both audible and visual and shall be easily detectable by
occupants. Emergency notification information (e.g., telephone numbers of owner, Garfield
County, service personnel) shall be posted near the high-level alarm.
• The effluent pump shall be configured with a minimum dose volume of 100 gal (3.20" float
differential for two-compartment, 1,500 gal. tank). Storage capacity in excess of the high-level
alarm shall be 6" above the pump-on float level.
• All access manholes on septic tanks and dosing chambers will be child proof and c ontain
appropriate warning labels if accessible to the public. Confined space entry precautions should
be observed by maintenance personnel.
• The system contractor shall be aware of the potential for construction activities to reduce soil
permeabilities at the site through compaction, smearing, and shearing. The following
precautions and construction procedures should be employed during installation to minimize
disturbance to native soils:
i. Excavation should proceed only when the moisture content of the soil is below the
plastic limit. If a sample of soil forms a rope instead of crumbling when rolled
between the hands it is too wet and should be allowed to dry before excavation
continues.
ii. Excavation and backfill equipment should work from the surface where at all
practical to avoid compaction of the soils at depth.
iii. The bottom and sidewalls of the excavation should be left with a rough, open
surface. The appearance should be that of broken or ripped soil as opposed to a
sheared, smeared, or troweled surface. Any smoothed or smeared surfaces should
be removed with a toothed rake or shallow ripper, taking care to remove loose
residues from the bottom of the excavation by hand if necessary.
iv. Care should be taken in placing fill materials in the excavation to avoid damaging
the exposed soil surfaces.
6
Operation - Maintenance and Inspections
• The owner shall install a structural barrier if necessary and take precautions to prevent vehicular
traffic, excessive surface watering, accidental flooding, or other activities in the vicinity of the
soil treatment area which may compact, saturate, or otherwise alter the subsurface soil
parameters used in designing the septic system.
• The owner will plant and maintain grass or other shallow rooted cover crop to prevent erosion
and promote evapotranspiration over the soil treatment area.
• The owner will inspect and maintain the required mounding and drainage away from the soil
treatment area to prevent saturation from precipitation and surface flows.
• To mitigate the generation of preferential flow channels which may compromise the operation
of the system, the owner will inspect and prevent intrusion of burrowing animals and deep-
rooted plants into the soil treatment area.
• The septic effluent pump and the effluent pump filter shall be inspected and cleaned as
necessary every six (6) months.
• The owner will conduct periodic maintenance of the septic system by removing accumulated
sludge from the septic tank every 3-4 years to prevent clogging of the soil treatment area.
7
Limitations
This report is a site-specific design for installation of an onsite wastewater treatment system and is
applicable only for the client for whom our work was performed. Use of this report under other
circumstances is not an appropriate application of this document. This report is a product of K-Cronk
Engineering, Inc. and is to be taken in its entirety. Excerpts from this report may be taken out of context
and may not convey the true intent of the report. It is the owner's and owner's agent’s responsibility to read
this report and become familiar with the recommendations and design guidelines contained herein.
The recommendations and design guidelines outlined in this report are based on: 1) the proposed site
development and plot plan as furnished to K-Cronk Engineering, Inc. by the client, and 2) the site conditions
disclosed at the specific time of the site investigation of reference. K-Cronk Engineering, Inc. assumes no
liability for the accuracy or completeness of information furnished by the client. Site conditions are subject
to external environmental effects and may change over time. Use of this plan under different site conditions
is inappropriate. If it becomes apparent that current site conditions vary from those anticipated, the design
engineer and Mesa County should be contacted to develop any required design modifications. K-Cronk
Engineering, Inc. is not responsible and accepts no liability for any variation in assumed design parameters.
K-Cronk Engineering, Inc. represents this report has been prepared within the limits prescribed by the
owner and in accordance with the current accepted practice of professional engineering in the area. No
warranty or representation, either expressed or implied, is included or intended in this report or in any of
our contracts.
SEAL
Kachayla R. Cronk, P.E.
Date
NOTE: This OWTS design is meant to include the following five pages:
1) plot plan
2) septic layout plan
3) notes for your installer
4) soil treatment area plan view
5) soil treatment area cross section
6) pump vault detail
7) pump curve
The plan is not to be implemented in the absence of these sheets. In addition, results from the
percolation test and soils evaluation are included for reference as Appendix A.
NOTES FOR YOUR INSTALLER
• Please verify slope at the time of system installation – the orientation of the
STA shown in this design has been determined based on existing site
conditions at the time of the original site investigation, but that may have
changed during construction and pre-construction grading of the site.
• The depth of the trenches is determined by percolation rates and soil
conditions relative to the existing ground surface at the time of the soils
investigation. If the site slope or grading of the ground surface at the time of
installation differs significantly from what was initially observed, the trench
depths may have to be adjusted to make sure the infiltrative surface remains
in the desired soil layer, and portions of the trenches don’t end up too deep or
too shallow. The depth of the soil cap relative to finished grading is not part
of the OWTS design criteria.
• Please provide K-Cronk Engineering with a copy of the septic tank
manufacturer’s specification sheet verifying maximum backfill depth. Tanks
must be backfilled according to manufacturer’s specification.
Pressurized System Notes
• Please provide K-Cronk Engineering a copy of the sand sieve analysis, if
relevant, dated within 30 DAYS of installation before purchasing/installing
the sand so we can check that it meets Garfield County OWTS standards.
• Pump floats do not come pre-set from the factory. Please refer to the Pump
Vault Detail for the distance needed between the on/off floats.
Please reach out at any time during the installation process if you have any questions!
____________________________
Kachayla Cronk – (970) 250-0572
Effluent Pumping System for Cold Weather Applications (cw style)
Orenco Systems
Incorporated
Effluent Pumping System - 2nd Compartment Drawdown
Pump Selection for a Pressurized System - Single Family Residence Project
GONZALEZ
Parameters
Discharge Assembly Size
Transport Length
Transport Pipe Class
Transport Line Size
Distributing Valve Model
Max Elevation Lift
Manifold Length
Manifold Pipe Class
Manifold Pipe Size
Number of Laterals per Cell
Lateral Length
Lateral Pipe Class
Lateral Pipe Size
Orifice Size
Orifice Spacing
Residual Head
Flow Meter
'Add-on' Friction Losses
2.00
160
40
2.00
None
10
39
40
2.00
8
32
40
1.00
5/32
4
5
None
0
inches
feet
inches
feet
feet
inches
feet
inches
inches
feet
feet
inches
feet
Calculations
Minimum Flow Rate per Orifice
Number of Orifices per Zone
Total Flow Rate per Zone
Number of Laterals per Zone
% Flow Differential 1st/Last Orifice
Transport Velocity
0.68
72
49.0
8
2.3
4.7
gpm
gpm
%
fps
Frictional Head Losses
Loss through Discharge
Loss in Transport
Loss through Valve
Loss in Manifold
Loss in Laterals
Loss through Flowmeter
'Add-on' Friction Losses
4.8
6.2
0.0
0.4
0.3
0.0
0.0
feet
feet
feet
feet
feet
feet
feet
Pipe Volumes
Vol of Transport Line
Vol of Manifold
Vol of Laterals per Zone
Total Volume
27.9
6.8
11.5
46.2
gals
gals
gals
gals
Minimum Pump Requirements
Design Flow Rate
Total Dynamic Head
49.0
26.7
gpm
feet
0 10 20 30 40 50 60 70 800
20
40
60
80
100
120
140
160
Net Discharge (gpm)
PumpData
PF5005 High Head Effluent Pump
50 GPM, 1/2HP
115/230V 1Ø 60Hz, 200/230V 3Ø 60Hz
PF5007 High Head Effluent Pump
50 GPM, 3/4HP
230V 1Ø 60Hz, 200/230/460V 3Ø 60Hz
PF5010 High Head Effluent Pump
50 GPM, 1HP
230V 1Ø 60Hz, 200/460V 3Ø 60Hz
PF5015 High Head Effluent Pump
50 GPM, 1-1/2HP
230V 1Ø 60Hz, 200V 3Ø 60Hz
Legend
System Curve:
Pump Curve:
Pump Optimal Range:
Operating Point:
Design Point:
Appendix A
Soils and Percolation Report
Soils and Percolation Report
July 31, 2023
Gonzalez Project
591 County Road 259
Silt, CO 81652
Parcel No. 2127-33-101-003
Lot 3 Dunlap Minor Subdivision
Prepared By:
K-Cronk Engineering, Inc.
P.O. Box 140
Mack, CO 81525
970-250-0572
- 1 -
Soils Evaluation
The site consists of approximately 5.434 acres of cultivated native soil. Drainage is approximately
2% to the east/southeast. A percolation (perc) test/soils evaluation and site study were conducted
on the property of reference on 07/31/2023 by Kachayla R. Cronk, registered professional engineer
(R.P.E.). The perc excavation trench was located approximately 210’ northeast of the southwest
property line and approximately 35’ southeast of the northwest property line.
The perc excavation trench was extended to a depth of 66" below ground surface (BGS). There
was no ground water present to a depth of 66" BGS. Evidence of high seasonal water table was
observed at a depth of 24" BGS. The soils evaluation indicates two distinct soil horizons underlie
the site. A lithological description follows:
depth (in.) description
0” – 24” silty clay loam, brown
(Soil Type 3A, USDA – silty clay loam, granular, weak structure)
24” – 66” sandy clay loam, brown
(Soil Type 3A, USDA – sandy clay loam, massive, structureless)
Perc holes were constructed at depths of approximately 24 in. and 52 in. The holes appeared to
be well saturated at the time of the test. Results of the percolation test are shown in Table 1.
TABLE 1
Percolation Test Results
591 County Road 259
Depth Time on 07/31/2023 Time
Drop
Perc
Rate
min/in 14:58 15:13 15:28 15:51 15:58
24” – 36” 4.75 5.0 5.25 5.625 5.75 60/1 60
52” – 64” 4.25 4.75 4.875 5.0 5.125 60/0.875 69
- 2 -
Limitations
This document is representative of the site conditions disclosed at the specific time of the site
investigation. Site conditions are subject to change from external events both manmade (irrigation
or water feature construction) and naturally occurring (flooding or excessive precipitation).
K-Cronk Engineering, Inc. is not responsible and accepts no liability for any future variation in
site conditions.
K-Cronk Engineering, Inc. represents this report has been prepared within the limits prescribed by
the owner and in accordance with the current accepted practice of professional engineering in the
area. No warranty or representation, either expressed or implied, is included or intended in this
report or in any of our contracts.
SEAL
Kachayla R. Cronk, P.E.
Date
Soils Report
August 23, 2023
Gonzalez Project
591 County Road 259
Silt, CO 81652
Parcel No. 2127-33-101-003
Lot 3 Dunlap Minor Subdivision
Prepared By:
K-Cronk Engineering, Inc.
P.O. Box 140
Mack, CO 81525
970-250-0572
- 1 -
Soils Evaluation
The site consists of approximately 5.434 acres of cultivated native soil. Drainage is approximately
2% to the east/southeast. A soils evaluation and site study were conducted on the property of
reference on 08/23/2023 by Kachayla R. Cronk, registered professional engineer (R.P.E.). The
perc excavation trench was located approximately 50’ south of the north property line and
approximately 65’ southwest of the northeast property line.
The soils evaluation excavation trench was extended to a depth of 84" below ground surface
(BGS). Groundwater was present at a depth of 84” BGS. Evidence of high seasonal water table
was observed at a depth of 48" BGS. The soils evaluation indicates two distinct soil horizons
underlie the site. A lithological description follows:
depth (in.) description
0” – 24” loamy sand, light brown
(Soil Type 1, USDA – loamy sand, single grained, structureless)
24” – 84” sandy clay loam, light brown
(Soil Type 3, USDA – sandy clay loam, blocky, moderate structure)
- 2 -
Limitations
This document is representative of the site conditions disclosed at the specific time of the site
investigation. Site conditions are subject to change from external events both manmade (irrigation
or water feature construction) and naturally occurring (flooding or excessive precipitation).
K-Cronk Engineering, Inc. is not responsible and accepts no liability for any future variation in
site conditions.
K-Cronk Engineering, Inc. represents this report has been prepared within the limits prescribed by
the owner and in accordance with the current accepted practice of professional engineering in the
area. No warranty or representation, either expressed or implied, is included or intended in this
report or in any of our contracts.
SEAL
Kachayla R. Cronk, P.E.
Date