HomeMy WebLinkAboutEngineer's OWTS Design-Original 08.07.2023
Onsite Wastewater Treatment System Design
August 7, 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. Installer shall provide a soils observation
trench within 50’ of the proposed STA at time of installation so design engineer can confirm soils
lithology is similar to that found during the initial site investigation and perc test.
This OWTS design has been prepared for the project based on information disclosed during the site study
mentioned above. A discussion of the engineered OWTS design follows. The perc test/soils evaluation is
attached for reference as Appendix A. The location of the perc excavation trench is shown on the Plot
Plan included in this report.
Development of Design Parameters
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)
Based on the results from the 07/31/23 perc test/soils evaluation (Appendix A), a design perc rate of 69
min/in. will be used for overall system sizing for a pressurized raised mound system designed to provide
the required vertical separation from the bottom of the treatment works to the water table.
2
System Design
A pressurized mounded soil treatment area (STA) is proposed for discharge of septic effluent at the site.
The STA will consist of one bed as shown in the included graphics. Construction of the system will
consist of removing the native soils from the area underlying the bed of the proposed STA. The initial
excavation will be continued to a level base at a depth of 24" BGS (see Soil Treatment Area Cross
Section).
The infiltrative surface of the mound will be a minimum of 12” above the existing ground surface. Side
slopes from the raised bed infiltrative surface to the native ground surface will consist of ASTM C33
concrete sand placed at a maximum 3:1 slope. ASTM C33 concrete sand will be continued from the toe-
of-slope footprint of the mound to a depth of 24” into the native soils to enhance the linear loading rate of
the treatment system. A gradation analysis done within 30 days of the installation date must be submitted
to the design engineer and Garfield County to assure the sand conforms to secondary sand standards
(Garfield County OWTS Regulations 43.11.C.d.3; effective size: 0.15-0.60 mm, uniformity coefficient: ≤
7.0, percentage fines passing #200 sieve: ≤ 3.0). The sand used to construct the mound must be
completely settled prior to installation of components as approved by the design engineer.
Following installation of the mound, QUICK4 STANDARD INFILTRATORS (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 12” min. of sandy loam. 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 2" Schd 40 PVC pipe with 1/4" 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).
3
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 attached graphics, the mound will consist of one bed 6.25’x105’ in lateral dimensions
and encompass a total area of 656.25 sq. ft.
Calculations and design parameters used to size the STA follow. Design parameters for sizing the mound
include:
• Design perc rate = 69 min./inch
• Soil Loading Rate (SLR) (LTAR TL3) = 0.55 gal./day-sq. ft.
• Soil Linear Loading Rate (LLR) = 5.0 gal./day-ft.
• Required vertical separation for pressurized distribution = 3 ft
• Site slope – 2% to the east
• Maximum mound side slope = 3:1
4
DESIGN CALCULATIONS – WISCONSIN MOUND
DESIGN LOADING RATE OF 3 BEDROOMS @ 150 GAL./BEDROOM-DAY = 450 GAL./DAY
PLUS 1 BEDROOM @ 75 GAL./BEDROOM-DAY = 525 GAL./DAY
MOUND INFILTRATIVE LENGTH = DESIGN LOADING/LINEAR LOADING RATE
MOUND LENGTH = 525 𝐹𝐴𝐿./𝐷𝐴𝑌
5.0 𝐹𝐴𝐿./𝐷𝐴𝑌−𝐹𝑆.= 105 FT.
MOUND INFILTRATIVE WIDTH = LINEAR LOADING RATE/SAND FILL LOADING RATE
MOUND WIDTH = 5.0 𝐹𝐴𝐿./𝐷𝐴𝑌−𝐹𝑆.
0.8 𝐹𝐴𝐿./𝑆𝑄.𝐹𝑆.−𝐷𝐴𝑌= 6.25 FT.
MOUND INFILTRATIVE SURFACE – 6.25’ WIDE x 105’ LONG
UPHILL MOUND SIDE SLOPE WIDTH 3:1 SIDE SLOPE DOWN FROM 1’ HEIGHT ABOVE
EXISTING GROUND SURFACE TO INTERCEPT WITH 2% SLOPE UP OF EXISTING GROUND
UPHILL MOUND SIDE SLOPE WIDTH = 1 𝐹𝑆.
0.33+0.02=2.83 FT.
DOWNHILL MOUND SIDE SLOPE WIDTH 3:1 SIDE SLOPE DOWN FROM 1.24’ HEIGHT ABOVE
EXISTING GROUND SURFACE TO INTERCEPT WITH 2% SLOPE DOWN OF EXISTING
GROUND
DOWNHILL MOUND SIDE SLOPE WIDTH = 1.24 𝐹𝑆.
0.33−0.02=3.96 FT.
MOUND BASIL AREA OF (2.83’+6.25’+3.96’)x(105’+2.83’+3.96’) ASSUMING ROUNDED FILL
CORNERS = 1457.74 SQ. FT.
ABSORPTION CAPABILITY OF NATIVE SOIL UNDER BASIL EXTENT OF MOUND IN
ABSENCE OF SATURATED SHEET FLOW CONDITIONS = SOIL LOADING RATE X BASIL
AREA
O.55 GAL./SQ. FT.-DAY X 1457.74 SQ. FT. = 801.76 GAL./DAY
ABSORPTION CAPACITY OF 801.76 GAL./DAY IS GREATER THAN THE OWTS DESIGN
CAPACITY OF 525 GAL./DAY
5
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 Garfield County for installation of onsite
wastewater treatment systems.
• All installation activities shall be conducted in accordance with current Garfield 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 Garfield 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 Garfield 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.
6
• 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 contain
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.
7
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.
8
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 Garfield 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
0
40
1.25
1
94
40
2.00
1/4
4
6
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
1.89
24
46.6
1
8.7
4.5
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
4.3
5.6
0.0
0.0
1.2
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
0.0
16.4
44.3
gals
gals
gals
gals
Minimum Pump Requirements
Design Flow Rate
Total Dynamic Head
46.6
27.2
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