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HomeMy WebLinkAboutRevised OWTS Design - 03.17.2026*revised 03/17/26 to change lateral size and dose volume Onsite Wastewater Treatment System Design Revised: March 17, 2026* Revised: March 4, 2026 Original: October 7, 2025 Lucero Project 1000 CR 252 Rifle, CO 81650 Parcel No. 2129-014-00-050 Prepared By: K-Cronk Engineering, Inc. P.O. Box 140 Mack, CO 81525 970-250-0572 - 1 - Site History There is an existing residence on the site that is served by an existing onsite wastewater treatment system (OWTS) that will remain in use. The owner of the property wishes to construct a new one-bedroom accessory dwelling unit (A.D.U.) to be served by a separate OWTS. The site consists of approximately 4.19 acres of uncultivated native soil. Drainage is approximately 30% to the northeast. A soils evaluation and site study were conducted on the property of reference on 08/13/25 by Kachayla R. Cronka. Soils evaluation trench A was located approximately 75’ southwest of the northeast property line and approximately 50’ southeast of the northwest property line. 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 location of the soils evaluation trench is shown on the Plot Plan included in this report. Development of Design Parameters Soils evaluation trench A was extended to a depth of 60" below ground surface (BGS). There was no evidence of ground water or periodically saturated soils in the open excavation to a depth of 60" BGS. The limiting layer has been identified as Type R soils located throughout the soils profile. The soils evaluation indicates one distinct soil horizon underlies the site. A lithological description follows: depth (in.) description 0” – 60” loamy sand w/ pebbles to cobbles to boulders (>35% rock), brown (Soil Type R-1/1, USDA – loamy sand, single grained, structureless) Soils evaluation trench B was extended to a depth of 36" below ground surface (BGS) and showed the same soils lithology as described for trench A above. Based on the results from the 08/13/25 soils evaluations, Soil Type R-1/1 and corresponding long term acceptance rate (LTAR) will used for overall system sizing of a pressurized unlined sand filter soil treatment area (STA) designed to discharge to subsoils below the 48” depth. a Kachayla R. Cronk holds a Certificate of Attendance and Examination from the CPOW Visual and Tactile Evaluation of Soils Training. - 2 - System Design A pressurized unlined sand filter soil treatment area (STA) is proposed for discharge of septic effluent at the site. Construction of the system will consist of removing the native soil from the area underlying the bed of the proposed STA. 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 bed depth running parallel to final contours. The initial excavation shall be continued to a level depth of 48" BGS (see Soil Treatment Area Cross Section). If consistent bed depth cannot be maintained, excavation may continue to 36” minimum and 72” maximum BGS. A lift station will be employed to discharge septic effluent into the soil treatment area. Following completion of the initial push out, the open excavation will be backfilled with 24" (min. depth) of secondary sand (generally sold as ASTM 33 concrete sand) to a surface elevation of 24” BGS. 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 unlined sand filter must be completely settled prior to installation of components as approved by the design engineer. Septic effluent will be introduced into the soil treatment area through pressurized distribution laterals installed within chambers as shown in the included graphics. The orifices in the distribution laterals will be drilled at 12:00 o’clock to direct effluent up for dispersal against the top of the chamber. Additional holes will be drilled at the beginning and terminal ends of each laterals facing 06:00 o’clock to allow for effluent to drain out of the laterals and prevent freezing. Orifice shields must be installed at these holes to prevent the pressurized effluent from compromising the infiltrative surface of the STA. The distribution laterals will be suspended from the top of the chamber with all-weather plastic pipe strapping (min. 120 lbs tensile strength) at every chamber joint connection. Septic effluent will be transferred from the pump chamber to a manifold and then the laterals via a pressure transport main. All pressurized lines will be constructed of min. SCHD 40 PVC. Any non-draining pressure line shall be installed 36” or more below ground surface to prevent freezing. The pressurized distribution system will be installed in accordance with the manufacturer’s specifications, available here for Infiltrator Quick4 Standard Chambers: https://www.infiltratorwater.com/Customer-Content/www/CMS/files/chamber-manuals/Q04.pdf. After the chamber distribution system is installed, non-woven geotextile filter fabric will be placed over the chambers 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. A 1,000 gallon, two compartment, primary septic tank is required to provide a minimum of 48 hours retention time for sewage generated from the proposed project. A 500-gallon, single compartment pump chamber will be placed down-gradient of the primary tank. Alternatively, a 1,000-gallon, concrete, two- compartment septic tank may be used without the pump chamber. The tanks must be approved and accepted by CDPHE for use as a septic tank. A list of such tanks may be found here: https://cdphe.colorado.gov/OWTS under “Regulation 43: product acceptance lists”. Provide water-tight risers to surface with securely fitted lids for access to all compartments of the septic tank. If applicable, a non-corrodible filter shall be installed at the final outlet tee of the p rimary septic tank to limit the size of - 3 - solids and sludge passing into the pump chamber. The filter must be accessible for cleaning and replacement from the ground surface. A screened effluent pump will be placed in the pump chamber. According to Section 43.11.C.3(2), the maximum hydraulic loading rate for TL1 effluent to “Secondary Sand Media” in an unlined sand filter is 0.8 gal./sq.ft./day, or the long term acceptance rate (LTAR) of the receiving soil for TL3 (Table 10-1), whichever results in the larger area (design LTAR must be less than or equal to 0.8 gal./sq.ft./day). DESIGN CALCULATIONS DESIGN LOADING RATE OF 1 BEDROOM @ 150 GAL./BEDROOM-DAY = 150 gal./day DESIGN SOIL TYPE R-1/1 DESIGN LONG TERM ACCEPTANCE RATE (LTAR) TL3 = 0.80 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 = 150 0.80 = 187.5 𝑆𝑄.𝐹𝑆. REQ’D: UNLINED SAND FILTER SIZED AT ONE BED 9’ x 21’ IN SIZE MINIMUM DESIGN CALCULATION –AREA OF DISTRIBUTION MEDIA LTAR OF UNLINED SECONDARY SAND FILTER = 0.80 GAL./DAY-SQ. FT. A = 150 0.80 =187.5 𝑆𝑄.𝐹𝑆. SOIL TREATMENT AREA ADJUSTMENT FACTOR FOR PRESSURE BED DESIGN = 1.0 SOIL TREATMENT AREA ADJUSTMENT FACTOR FOR USE OF CHAMBERS = 0.7 SOIL TREATMENT AREA = 187.5 X 1.0 X 0.7 = 131.25 SQ. FT. REQ’D: 131.25 SQ.FT. / 12 SQ.FT. PER INFILTRATOR = 11 INFILTRATORS USE 3 ROWS OF 4 QUICK4 STANDARD INFILTRATORS (or equivalent) EACH, FOR A TOTAL OF 12 UNITS TOTAL BED AREA OF 9’ x 21’ As shown in the attached graphics, the unlined sand filter will consist of one bed 9’x21’ in lateral dimensions and encompass a total area of 189 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 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. • The installer must be approved and licensed by Garfield County for the 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. • 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. • 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. Minimum setbacks for system components are: Septic Tank, Dosing Tank Building Sewer, Effluent Lines STA spring/well/cistern 50 50 100 potable water supply line 10 5 25 structure w/ crawlspace 5 0 20 structure w/o crawlspace 5 0 10 property lines, piped or lined irrigation 10 10 10 subsurface drain, intermittent irrigation 10 10 25 lake, water course, irrigation ditch, stream 50 50 50 cut slope steeper than 3H:1V 10 10 25 septic tank -- -- 5 • Four-inch, 2-way SCHD 40 clean out must be installed within 5 ft of the outside of the building. • Gravity sewer lines that transport solid waste material must maintain a minimum fall of 1/4” per foot (2% slope); gravity effluent lines that transport only liquid waste material must maintain a minimum of 1/8” per foot (1% slope). • All gravity sewer/effluent piping shall meet minimum ASTM-3034 PVC standard, be 4-inch in diameter, and have glued joints. Gravity sewer lines that transport solid waste material shall employ sweep 90's or 2-45's at all turns. Sewer/effluent lines under driveways shall meet minimum SCHD 40 PVC standards. Additionally, sewer/effluent lines 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/effluent 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 sewer lines that transport solid waste material that exceeds 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. • 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. • 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. - 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. Every month: • Inspect backfill over the septic tank and soil treatment area for signs of settling – provide additional mounding as needed. • Inspect area of septic tank and soil treatment area for signs of intrusion by burrowing animals and deep rooted plants and take measures to prevent future intrusions as needed. Every year: • Remove tank lids and inspect outlet effluent filter in pump vault for damage and clean/replace as needed. • Inspect soil treatment area through the ports provided at the beginning and ends of bed for signs of excessive moisture or pooling water. • Log pump cycle number or pump run time. • Inspect pump components. • Perform squirt test and flush laterals to prevent excess buildup of material within pipe system. Every four years: • Remove accumulated sludge from the septic tank by pumping all compartments – interval may be adjusted to less than four years or more than four years depending on family specific usage and habits - 7 - OWTS Component Descriptions: Component: Model: Notes: Septic Tank Infiltrator IM-1060-2CP + IM-540-1CP pump chamber, or equivalents Alternative: 1,000 gallon, two compartment concrete septic tank Tank Riser Infiltrator EZsnap Riser SNAPIS-24## & Lid, or equivalent 2”, 6”, & 12” available Optional Safety Star: SNAPSAFT- 2400 Pump Package Orenco BioTube ProPak BPP30DD- CW-SX-ETMCT PF300011 pump PVU57-1819-L vault S1ETMCT control panel 48-gallon min. dose per cycle 19.1 Feet Total Dynamic Head 25.9 GPM Design Flow Rate Effluent Filter Orenco Model FTW0436-28 Pressure Main & Manifold 1-1/2” SCHD 40 PVC Lateral Size & Orifice 1-1/2” SCHD 40 PVC with 1/4” orifices spaced 36” o.c. Orifice Shield Orenco Model OS100 Distribution Media Infiltrator Quick4 Standard Chambers + endcaps, or equivalent Filter Fabric Non-woven permeable geotextile fabric (max. 2 oz. / sq. yd), or equivalent - 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 Schroeder, P.E. NOTE: This OWTS design is meant to include the following seven pages: 1) plot plan 2) septic layout plan 3) project notes 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. P R O F E SSI O N A L E N GINE E R61140 K A C H A YLA R E N E E S C H R O EDER COL O R A D O L ICEN S E DKachayla Schroeder 03/17/2026 Kachayla Schroeder NOTES FOR YOUR INSTALLER This is a STAMPED, ENGINEERED design – yes, septics are “simple” and water runs downhill. However, like anything that is engineered, it is critical that you follow the design so the system performs as intended – I cannot approve a system that was not installed to plans! If, FOR ANY REASON, you need to: 1. Change the location/rotation of the septic tank (i.e. plumbing was stubbed out of different wall, etc.) 2. Change the location/rotation of the soil treatment area (i.e. slope differed from the design, owner has changed the site plan, etc.) YOU MUST CONTACT THIS OFFICE FOR A REVISED DESIGN! The revision must be submitted and approved through the County (with a County $ revision fee) prior to calling in for inspection. Revisions take time, so please be prompt when contacting us to ensure the project is not delayed. Next, and I cannot stress this enough - DO NOT install the chambers DEEPER than the maximum depth stated in the design – the depth is determined by factors that the design engineer cannot control. This includes SATURATED/POOR SOIL CONDITIONS & COUNTY OWTS CODE. Our designs give the widest range of depth possible for the specific site – if the required depth cannot be met, other options may need to be explored. If the soil treatment area is installed at a depth greater than allowed, there are very few solutions to resolve the problem. Examples include: • Removing all components and reinstalling them in a different location at correct depth. • Backfilling trenches to an acceptable depth (using WASHED CONCRETE SAND ONLY), installing a pump chamber, effluent pump, and pressurizing the system. Please reach out at any time during the installation process if you have any questions – this office has experienced several installations that have failed County inspections due to issues described above – I would like to see every system PASS without comment as this makes everyone’s job easier. Kachayla Cronk, P.E. – (970) 250-0572 Effluent Pumping System for Cold Weather Applications (cw style) Model PVU57-1819-L Discharge Assembly Level Control Float Assembly Orenco Effluent Pump Biotube Pump Vault Scale: 1" = 2'Model S1ETMCT Control Panel Lid Riser(s) Tank Lid , Typ. Tank Shield (opt.)Conduit Seal PVC Splice Box w/Cord Grips Top View (NTS) Simplex Pumping System 1,000-gallon, concrete BPP30DD-CW-SX-ETMCT Pump Selection for a Pressurized System - Single Family Residence Project Lucero 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 1.50 50 40 1.50 None 10 6 40 1.50 3 12 40 1.50 1/4 3 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 1.73 15 25.9 3 0.2 4.1 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 2.0 2.0 0.0 0.1 0.0 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 5.3 0.6 3.8 9.7 gals gals gals gals Minimum Pump Requirements Design Flow Rate Total Dynamic Head 25.9 19.1 gpm feet 0 5 10 15 20 25 30 35 400 50 100 150 200 250 300 Net Discharge (gpm) PumpData PF3005 High Head Effluent Pump 30 GPM, 1/2HP 115/230V 1Ø 60Hz, 200V 3Ø 60Hz Legend System Curve: Pump Curve: Pump Optimal Range: Operating Point: Design Point: