HomeMy WebLinkAboutOWTS DesignGnnTIELD COUNTY OWTS RrpONr
4756 Couurv Ro 309
GnnnELD CoururY, CoLoRADo
November 2021
Prepared by
SsGtï{
118 West Sixth Street, Suite 200
Glenwood Springs, CO 81601
970.945.7004
970.945.5948 Ía><
GnnTIELD CoUNTY OWTS Rrponr
4756 Courury Rono 309
Gnnr¡ELD Courury, CoLoRADo
"l hereby affirm that this Onsite Wastewater Treatment System (OW|S) report for 4756 County
Road 309, Garfield County, Colorado was prepared by me, or under my direct supervision, for the
Owners thereof in accordance with the provisions of Garfield County's OWTS Regulations and
approved variances and exceptions listed thereto. I understand the County does not and will not
assume liability for OWTS facilities designed by others."
l,*. .(. ß.*¿-a;
License ''-.Licensed Professional Engineer, State of Colorado (Affix Seal)
PRepRneO BY:
Tennv Beruoern, P.E.
SGM Project # 2018-47 1 -OO1
2
Tnelr Or COTIENTS
1.0 lntroduction
2.0 Preliminary lnvestigation
2.1 Propertylnformation
2.2 Topography
2.3 Soil Data
2.4 Location of Physical Features
2.5 Additionallnformation
2.6 Landscape Position
2.7 Natural and Cultural Features
2.8 Current and Historic Land Use
3.0 Detailed Soil Investigation
3.1 Visual Evaluation
3.2 Tactile Evaluation
4.0 Recommendations
5.0 Installation Observations
6.0 Operation and Preventative Maintenance Schedule
7.0 Limitations
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Appendix
Site Plan Sheet 1
Layout Plan Sheet 2
OWTS Plan Sheet 3
OWTS Details Sheet 4
NRCS Soils Map
NRCS Absorption Field Soils Data
NRCS TexturalTriangle
SGM Soil Observation Logs
SGM SoilTexture by Feel
OWTS Design Spreadsheet
4
1.0 lntroduction
The subject property encompasses 6.59 acres +/- and had two existing residential structures on the
property, one constructed in 1909, the otherin 1969. The residence constructed in 1909 has been
demolished and removed from the property. lt is proposed that the removed residence be replaced
with a three bedroom modular home.
The purpose of this report is to present the preliminary investigation, reconnaissance information and
design to meet the requirements for an onsite wastewater treatment system (OWTS) as required by
the County's Regulation 43 (Reg43).
SGM personnel contributing to this report are:
. Terry Bendetti- PE/CPOW Certified Competent Technician/NAWT Certified Designer. Ryan Stowe - EI/CPOW Certified Competent Technician
2.0 Prelim¡nary Investigation
2.1 Property lnformation
PhvsicalAddress: 4756 County road 309, Garfield County, Colorado
Leqal Description: Located in Section 1, Township 6, Range 95, a tract of land in the SESW cont.
1.73 acres; a tract cont.4.863 acres as described in book 1700, pages 619 and 623; a total of
6.593 acres. Garfield County's Parcel Number for the property is 217336300017, the County's
account number is R270093.
Existinq Structures: There will be one existing residential structure on the subject property, which
is a four bedroom single family residence.
Domestic Water: Water to the residence will be provided by an existing tank located upslope on
the mountainside, south of the subject residence. All minimum setbacks requirements stated in
Table 7-1 of the County's Regulation 43 are met under existing and proposed conditions.
Sepfib; There is one existing septic system on the property, which serves the existing four
bedroom single family residence. The approximate location of the STA for the existing system is
shown on sheet 1. Per Water Quality Site Application Policy 6, published by the Colorado Water
Quality Control Division, the existing OWTS serving the four bedroom residence and the proposed
OWTS for the three bedroom modular are considered separate systems, having no influence on
the other.
2.2 Topography
Topography in the vicinity of the new OWTS slopes from south to north at grades between 2 to 5
percent. Grades increase in steepness towards the north and west of the bench where the
proposed OWTS will be located.
2.3 Soil Data
According to the Web Soil Survey for the Natural Resources Conservation Service (NRCS), soils
associated with the subject property are classified as map unit 55 and 59. NRCS soil unit 55 is
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Potts Loam and 59 is Potts -lidefonso complex. Unit 55 has grades of between 3 to 6 percent
and 59 between 25 to 45 percent. These grades agrees with field observation
Both units are classified as being very limited for septic tank absorption fields due to slow
movement of water. This agrees with field observations during excavation of test pits, texture of
the excavated soils exhibited clayey characteristics.
Plotting the percentages of clay, sand and silt published by the NRCS for these soil units on the
USDA Textural Triangle indicates the soils would classifo as a loam, soil type 2 or 2A. Soils
having a classification type of 2 or 2A are suitable for absorption fields. The long term application
rates (LTAR) for type 2 and 2A soils are 0.60 and 0.50 gallons per day per square foot of area
(gpd/ft2), respectively
2.4 Location of Physical Features
Physical features on the subject property thatwill require minimum horizontal setbacks are shown
in the following Table and on sheet 1 of the design drawings. All distances are in feet.
FillArea (from crest)
Potable
Water Supply
Line
Structure without
basement, crawl
space or footing
drains
Property
Lines
Septic
Tank
Septic Tank 10 10 5 10
Effluent Line 10 5 0 10
STA 25 25 lo 10 5
2.5 Additional lnformation
a. Floodplain Maps: According to FEMA (Federal Emergency Management Agency), FIRM
Panel 0802051320B, 1211511977 is not printed. The project is not within any floodplain.
2.6 Landscape Position
The landscape position for the STA is considered summit. The slope shape is linear - linear (LL)
towards the north.
2.7 Naturaland Cultural Features
No natural or culturalfeatures were identified in the site reconnaissance
2.8 Current and Historic Land Use
The subject property is in Garfield County's Agricultural Zone. Current and historic land use has
been agricultural, its future use is expected to also be agricultural.
3.0 Detailed Soil lnvestigation
A detailed soil investigation to determine the depth to the limiting layer, if any, and properly classify
the soil type was conducted on October 21,2021. Visual evaluation of two soil profile test pits were
conducted in the field and samples collected from each test pit. The soil texture by feel method was
utilized in the field to classify the soiltype that will receive wastewater effluent.
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Test pits were excavated adjacent to the proposed location for the STA, see sheet 1 for locations.
Visual evaluation of both test pits was conducted under adequate light conditions, with the soil being
in an unfrozen state.
3.1 Visual Evaluation
The owner for the project site excavated two test pits, TP-1 and TP-2, with SGM personnel being
on site.
TP-1 did not exhibit topsoil. TP-2 did exhibit topsoil for the first 0 to 6 inches. One layer horizon
from the bottom of the topsoil zone to the bottom of each pit was observed. Rocks were
encountered in both test pits, however by visual observation their percentages were determined
to be less than 35 percent.
Excavation was terminated at a depth of I feet for both test pits and neither pit showed signs of:
o A limiting layer.¡ Presence of groundwater
Soil observation logs and photos can be found in the Appendix.
All measurements are from ground surface.
3.2 Tactile Evaluation
On 1012212021 SGM conducted the soil textural by feel evaluation on the soil samples collected
during the visual evaluation of the test pits.
Results of the soilgradation revealed:
1. Total sample size = 1,000 ml; both samples.
2. Volume of rock > 35 mm (314"¡ = minimalfor both samples.
3. Volume of rock < 35 mm (314") > 2 mm (0.079") = 75 ml for sample 1;140 ml for sample
2.
4. Percent rock in sample = 7.5o/o sample 1; 14o/o sample 2.
Soils are not type "R".
Performing the soil texture by feel methodology on the non-rock portion of the sample are shown
in the following table.
SAMPLE
Sample
Depth from
Ground
Surface (ftì
Does Soil
Form a Ball
(yes/no)
Does Soil
Form a
Ribbon
(yes/no)
*Type of Ribbon
Formed (Weak,
Moderate,
Stronq)
How Does the
SoilFeel
(Gritty/Smooth/
Neitherl
TP-1 4.0 Yes Yes Stronq Grittv
TP-2 4.0 Yes Yes Stronq Grittv
*Weak < 1 inch; Moderate 1-2
Results shown in the above table indicate a USDA soil classification of sandy clay, soiltype 4 or
44.
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To determine the proper soil type; the USDA soil structure type and grade were used. The
following Table shows the soil's USDA structure type and grade determined for the sample.
SAMPLE
USDA Soil
Structure
Tvoe
USDA Soil
Structure
Grade
TP-I Blockv Moderate
TP-2 Blocky Moderate
According to Table 10-1, section 43.10 of Reg43, soil types 4 and 4A can have a blocky structure
type, but only soiltype 4 can have a moderate soil structure grade. As such, the soilto receive
the effluent waste is classified as soil type 4. Soil type 4 has a LTAR of 0.20 gpd/ft2 for the
application of effluent treated to treatment level 1 (TL1).
These findings correlate fairly wellwith the NRCS septic tank absorption data.
4.0 Recommendations
An OWTS as a wastewater treatment system is suitable for this site. At a minimum, the OWTS shall
have:
. A septic tank.¡ Three, bed type STAs.. Category 3 distribution media in the STAs.o A distribution box.. 4" diameter perforated distribution laterals.. 4" diameter influent and effluent lines.
lnfluent from the residence will be conveyed through piping by gravity to a new septic tank. From the
septic tank, effluent will be conveyed through piping to a distribution box. The distribution box will
divide the effluent flow into proportioned volumes to be delivered to each distribution lateral manifold.
Each manifold will distribute effluent to the bed's distribution media. All effluent flow will be by gravity
and influenleffluent lines shall be installed per associated plans and details.
The proposed residence is a 3-bedroom single family residence. Per Table 6-1 of Reg43 the design
flow rate will be 450 gpd (gallons per day).
# Bedrooms Occupancy (# of
Persons)
Wastewater Flow per
Person Design Flow (gpd)
4 6 75 450
The OWTS STA site elevation is approximately 5,300 feet above sea level (USGS Topo) and it will
be located north and west of the proposed residence. The septic tank will be installed east of the of
the residence. See design drawings.
Sewer Pipe: Sewer influent pipe shall be 4-inch solid wall SCH 40 PVC installed per plans, but may
be adjusted in the field, as field conditions warrant. lf adjustments are made, a minimum grade of
1%o, must be maintained for all pipes. Joints shall be solvent welded. Cleanouts are required:
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1) Within 5 feet of the existing building.
2) At spacing not to exceed 100 feet.
3) Upslope of two or more bends closer than 10 feet.
All 90 degree bends shall be constructed using two, 45 degree fittings. The pipe shall be properly
bedded per the typical trench detail on sheet 4.
Septic Tanks: One new 1,000 gallon septic tank with two bays will be required. The tank must be on
the Colorado Department of Public Health and Environment's accepted septic tank list. The tanks
and lids shall conform to current County OWTS regulations and be traffic rated. The tanks shall be
installed with insulated, watertight access risers having lids that can be secured. Risers shall meet
the tank manufacturer's requirements for type and installation. There shall be an effluent filter and
its handle shall extend to within twelve inches of the lid.
The septic tank shall:
1) Be located down gradient of the home.
2) lnstalled per the design drawings unless field conditions require modifications. lf modifications
are necessary, covering over the tank cannot be more than 4.0-feet nor less than O.5-feet in
depth, measured from the top of the tank lid to finished surface
3) Be at a location accessible for pumping and maintenance.
Prior to installation of the tank, the installer must ensure tank placement as shown on the plans will
allow connection of the tank's inlet invert to the influent piping from the residence. lf tank installation
can't be accomplished as shown on the plans, the tank can be set to have between 0.5 to 4.0 feet of
cover over its lid, measured from the top of the lid to surface grade. lf the tank needs to be relocated,
the design engineer should be notified to aid in relocating the tank. lt should be stressed that a septic
tank having a cover thickness less than 0.5 feet or greater than 4.0 feet will not be allowed.
lf the tank is raised higher than shown on the plans and a minimum cover of 42-inches over the
influent or effluent piping cannot be achieved, insulation must be installed over the pipe per the detail
on sheet 4 until the minimum cover can be met.
Distribution Box: The distribution box shall be centered as shown on sheets 1 and 3 in a manner to
distribute effluent proportionately to the distribution lateral manifolds. Speed levelers shall be used
to divide flows proportionately.
The Engineer should be contacted if alignments or locations change in order to verify regulation
requirements are maintained. The box should be capable of one inlet pipe having an insertion point
a minimum of 2-inches above outlet openings and 3 outlet openings.
SoilTreatment A¡ea: The soiltreatment area was sized using criteria found in section 43.10 of Reg43
for a 3-bedroom residential home using:
¡ Beds for the soil treatment area.. Effluent application by gravity.
. Chambers for the distribution media.
I
The following table summarizes sizing of the STA.
No.
Bedrooms
Daily
Design
Flow (qpd)
LTAR
Method of
Application
Adiustment Factor
Distribution Media
Adjustment
Factor
STA
Size
(sf)
No. Chambers
(15sf/chamber)
3 450 0.20 1.2 0.7 1890 126
The STA shall be excavated as field conditions require using the following guidelines.
1. Three beds sized per sheet 3.
2. Beds shall be no wider than 12-feet.
3. Bed lengths shall be no greater than 100 feet, 75 feet shown.
4. A minimum of 6-feet, measured sidewall to sidewall, shall separate beds.
5. The infiltrative surface shall be no greater than 4-feet from existing surface
6. Bed floors shall be level and set at the infiltrative surface.
7. Chambers shall be placed per the manufacturer's directions.
Chambers shall have a minimum of 90% of the required square footage area calculated for the STA,
per Reg43 requirement 43.13.
The STA shall have a final soil cover as described in the Final Soil Cover Material Notes found on
sheet 4 of the design drawings. This may mean that the STA cover will need to be 16-inches +/-
when initially placed to allow for settlement over the freeze-thaw of a winter season. The surface of
the STA shall be seeded after installation of the system. A native, upland seed mix should be used.
These mixes do not require irrigation and develop a growth 10 to 15 inches high. No automatic
sprinkler system shall be installed over the STA. Vehicular traffic and livestock shall be kept off of
the STA. No landscaping, impervious surfaces or plastic sheeting can be installed over the STA,
which will reduce performance of the STA.
5.0 lnstallation Observations
An installation observation inspection of the OWTS tank, influent lines, effluent lines, distribution box
and infiltrators shall be conducted by the design engineer prior to backfilling. lnstallation of these
components shall be substantially complete and ready to be backfilled prior to requesting individual
or simultaneous observation inspection(s). Our office shall be notified at 970-945-1004 to schedule
an observation inspection at least three days in advance.
6.0 Operation and Preventative Maintenance Schedule
The goal of an operation and maintenance schedule is to observe the operation, and perform minor
maintenance to the onsite wastewater system to allow for proper, long-term functioning of the system.
Septic tanks: The scum and sludge accumulation in the septic tanks shall be monitored yearly. Once
the cumulative scum or sludge thickness reaches 25o/o of the tank depth, the entire tank shall be
pumped. A pumping frequency of 1 to 3 years is expected at design flows. An alternative is a regular
pumping frequency of every 2 years.
Effluent Filter. The effluent filter at the septic tank discharge shall be cleaned (hosed off) at the time
of pumping or as needed.
General: System users must realize that an on-site wastewater treatment system is different from
public sewer service. There are daily considerations, such as not putting plastic or other non-
biodegradable material into the system. Water use shall be monitored so that toilets are not allowed
10
to leak when seals malfunction. Allowing fixtures to flow continuously to prevent water lines from
freezing is not acceptable. Although the proposed system can accommodate variable flows,
spreading water use over several hours and eliminating peak flows is recommended. To illustrate
the point, a malfunctioning toilet can discharge in excess of 1,000 GPD. Excessive daily loading
could flood and irreparably harm the STA.
SGM recommends against installation of a water softener. The chemical and hydraulic loading from
the backwash of a water softener would be damaging to the STA, so if a softener is installed, a
separate drywell shall be constructed for the backwash waste. No landscaping or plastic can be used
over the STA, which would reduce the performance of the STA. The design of the OWTS is based
on the treatment of domestic sewage only. Swimming pool or spa water is not to be discharged into
the OWTS. The proposed OWTS design is based on the regulatory flows noted in the attached
calculations. lncreased flows may hydraulically or organically overload the OWTS, causing
premature failure.
7.0 Limitations
Our investigation, layout, design, and recommendations are based on site visits and the best
information available at the time. The contents of this letter shall not serve as the basis for any third
party engineering design. lf conditions that are considerably different from those described in this
report are encountered, SGM shall be called to evaluate the conditions. lf the proposed construction
is changed, SGM shall be notified to evaluate the effect of the changes on the OWTS prior to the
changes being made. All construction shall be in accordance with the Garfield County OWTS
Regulations. Pipe type and size, burial requirements, septic tank construction, and other
specifications, which are not depicted in our report, shall conform to the requirements of the County's
OWTS Regulations. The installer of the system shall be acceptable by the County's Environmental
Health Department.
11
Appendix
Site Plan Sheet 1
Layout Plan Sheet 2
OWTS Plan Sheet 3
OWTS Details Sheet 4
NRCS Soils Map
NRCS Absorption Field Soils Data
NRCS Textural Triangle
SGM Soil Obseruation Logs
SGM Soil Texture by Feel
OWTS Design Spreadsheet
12
NRCS Soils Map
=f^bÀ3LRSoil MafRifle Area, Colorado, Parts of Garfield and Mesa Countþs(4756 County Road 309, Garfield County, CO)2/M26fl0ÆbVÊb Soil SurveyNational Cooperative Soil Survey216Ên2ÆåÆÆEÐNatural ResourcesConservation Serulce2¡mzEg)2ffi2¡ÍÐ3!P 28¿l'| Ng39P 2g¿ClNEEsEPpeEsg2680243sDæo261t0lvlæ Scaþ: 1:4,0S f pinÞd m A bndcpe (11' x 8.f) *:ef0sil)01ÐÐ@sflbp p?o¡¡dim: \tÊb lvlerabr CorfEræorúraG: Iì/GS84 Hgeths: ttlì4 A'E üf'¡ \¡l,GS842'lÍÐ11t4t2021Paç 1 of3=RnBrôlrÀNA9 2d24NI.5DA:Æn2ããt2tgn39o 242¡f N
I.5DA7-Natural ResourcesGonservation SewlceSoil Map-Rifle Area, Colorado, Parts of Garfield and Mesa Counties(4756 County Roâd 309, Garfield County, CO)Vvbb Soil SurveyNational Cooperative Soil Survey11t4t2021Page 2 of 3MAP LEGENDMAP INFORMATIONThe soil surveys that comprise yourAOl were mapped at1:24,000.Waming: Soil Map may not be valid at this scale.Enlargement of maps beyond the scale of mappir€ can causemisunderstanding of the detail of mapping and accuracy of soilline placement. The maps do not show the small areas ofcontrasting soils that could harc been shown at a more detailedscale.Please rely on the bar scale on each map sheet for mapmeasurements.Source of Map: Natural Resources Conservation ServiceWeb Soil Survey URL:Coordinate System: Web Mercator (EPSG:3857)Maps from the VVeb Soil Survey are based on the \A/eb Mercatorprojection, wÌrich preserves direction and shape but distortsdistance and area. A projection that preserves area, such as theAlbers equal-area conic projection, should be used if moreaccurate calculations of distance or area are required.This product is generated from the USDA-NRCS certified data asof the version date(s) listed belor.Soil Survey Area: Rifle Area, Colorado, Parts of Garfield andMesa CountiesSurvey Area Data: Version 14,Sep2,2021Soil map units are labeled (as space allows) for map scales1:50,000 or larger.Date(s) aerial images were photographed: Dec 31, 200Hct12,2017The orthophoto or other base map on which the soil lines werecompiled and digitized probably difiers from the background¡magery displayed on these maps. As a result, some minorshifiing of map unit boundaries may be evident.Area of lnterest (AOl)Area of lnterest (AOl)So¡lgSoil Map Un¡t PolygonsËl SPoil Area0 StonySpotlB VeryStonyspotV v!þtspot& Other+' Special Line FeaturesWater FeaturesStreams and CanalsTransportat¡ont# Rails4 lntertate Highways* USRoutes:iyi Maþr Roads1¡"{ Local RoadsBackgroundI Aerial Photographytw Soil Map Unit L¡nesI Soil Map Unit PointsSpecial Point Features(9, Blor/outE Borfow Pitxi Clay Spott Closed DepressionX Gravel Pit".. Gravelly SpotÊ LandfillA Lava FloYv& Mersh orsurampæ Mine orQuarryû Miscellaneous \r\åþrO Perennial V\hterV Rock Outcrop+ Saline Spot:.: Sandy Spotë Severely Eroded SpotS SinkholeÞ Slíde or SlipE Sodic Spot
Soil Map-Rifle Area, Colorado, Parts of Garfield and Mesa Counties 4756 County Road 309, Garffeld
County, CO
Map Unit Legend
lldofonso stony loam, 25 to 45
percent slopes
3.1 4.3o/ø34
65 Potls loam, 3 to 6 percent
slopec
20.8 28.9%
56 Potts loam, 6 to 12 percent
slopes
9.0 12.404
39.2 54.3%59 Potts-lldefonso complex, 25 to
45 percent slopes
72.2 100.0%Totals for Area of Interest
t͡fxt Natural Resources
Consoryatlon Servlce
Web Soll Survey
National Cooperative Soil Survey
11t4t2021
Page 3 of 3
NRCS Absorption Field Soils Data
=hÈSeptic Tank Absorption Fields-Rifle Area, Colorado, Parts of Garfield and Mesa Counties(4756 County Road 309, Garfield Coung, CO)2¡6ED?Ætþ26t€2æ3lôbR]P 2g¡lzNg3!P 2g¡tlNReEüEeEgEPBgqg$e245itaÐxwlbp Scale: 1:4p$ f pti{¡d mAbnbøpe (11" x&5¡) dæettvþÞs0ÐfæTnoftet0l$00slbp polrclion: Vrbb liþrcabr GrErcodffi: W684 Rlgetts: UfMZone 13N\¡lGS842¡ß6t)11t4t2021Page I of5=¡!R=fı18NANatural ResourcesConsewation Sery¡ceVrëb Soil SuweyNatimal Cooperative Soil Surveyg 2a2qr{I..6DA-æÐ2ıF2æto39o 292¡rN
Natu¡al ResourcesConse¡vation Sery¡ceSeptic Tank Absorption Fields-Rifle Area, Colorado, Parts of Garfield and Mesa Counties(4756 County Road 309, Garfield County, CO)ìÂ/eb Soil SurveyNational Cooperative Soil Survey11t4t2021Page 2 of 5MAP LEGENDMAP INFORMATIONArea of lnter€st (AOl)Area of lnterest (AOl)SoilsSoil Rating Polygonsf VerylimitedE Somãr/hatlimitedI Notl¡mitedBackgroundI Aerial PhotographyThe soil surveys thal comprise yourAOl were mapped at1:24,000.Waming: Soil Map may not be valid at this scale.Enlargement of maps beyond the scale of mapping can causemisunderstanding of the detail of mapping and accuracy of soilline placement. The maps do not sho¡r the small areas ofcontrasting soils that could have been shown at a more detailedscale.Not retèd or not eve¡lablêSoil Rating Linest# Verylim¡þd. t Someìr/hat limitedÐ Notlimited. .t Not raþd or not availableSoil Rating Polntsf Very limitedtr Someìr/hat limitedI Notlimiþdtr NotratedornotavailableWater FeaturesStrcams and CanelsTransportation|+} Reilsfl lnÞrstate Highwaysfl USRoutes::ìi; Major Roads--.4 Local RoadsPlease rely on the bar scale on each map sheet for mapmeasurements.Source ofMap: Natural Resources Conservation Serviceì¡1þb Soil Survey URL:Coordinate System: Web Mercator (EPSG:3857)Maps from the \Â/eb Soil Survey are based on the Web Mercatorprojection, which preserves direction and shape but distortsdistance and area. A projection that preserves area, such as theAlbers equal-area conic projection, should be used if moreaccurate calculations of distance or area are required.This product ¡s generated fom the USDA-NRCS certified data asof the version date(s) listed below.Soil Survey Area' Rifle Area, Colorado, Parts of Garfield andMesa CountiesSurvey4¡s¿ Data: Version 14,Sep 2,2021Soil map units are labeled (as space allows) for map scales1:50,000 or larger.Date(s) aerial images were photographed: Dec 31, 2009-oct12,2017The orthophoto or other base map on which the soil lines werecompiled and digitized probably difiers fom the backgroundimagery displayed on these maps. As a result, some minorshifting of map unit boundaries may be evident.TJSDA-
Septic Tânk Absorption Fields-Rifle Area, Colorado, Parts of Garfield and Mesa Count¡es 4756 County Road 309, Garfield
County, CO
Septic Tank Absorption Fields
Map unlt
symbol
Map unit name Ratlng Component
name (percent)
Rat¡ng reasons
(numerlc
values)
Acres in AOI Percent of AO¡
34 lldefonso stony
loam, 25 to 45
percent slopes
Very limited lldefonso (907o)Slope (1.00)3.1 4.3o/o
Large stones
(1.00)
55 Potts loam, 3 to
6 percenl
slopes
Very limited Potts (85o/o)Slow water
movement
(1.00)
20.8 28.9o/o
56
59
Potts loam, 6 to
12 percent
slopes
Very limited Potts (85%)Slow water
movement
(r.00)
9.0 12.4o/o
Slope (0.04)
Potts-lldefonso
complex, 25 to
45 percent
slopes
Very limited Potts (607o)Slope (1.00)39.2 54.30/o
Slow water
movement
(1.00)
lldefonso (30%)Slope (1.00)
Large stones
(1.00)
Totals for Area of lnterest 72.2 r00.0%
Rat¡ng Acree ln AOI Percent of AOI
Very limited 72.2 100.0%
Totals for Area of lnterest 72.2 100.0%
USDA
-
Natural Resources
Gonservation Service
Web Soil Survey
National Cooperative Soil Survey
11t4t2021
Page 3 of 5
Septic Tank Absorption Fields-R¡fle Area, Colorado, Parts of Garfield and Mesa Count¡es 4756 County Road 309, Garfield
County, CO
Description
Septic tank absorption fields are areas in which effluent from a septic tank is
distributed into the soil through subsurface tiles or perforated pipe. Only that part
of the soil between depths oi 24 and 60 inches is evaluated. The ratings are
based on the soil properties that affect absorption of the effluent, construction
and maintenance of the system, and public health. Saturated hydraulic
conductivity (Ksat), depth to a water table, ponding, depth to bedrock or a
cemented pan, and flooding affect absorption of the effluent. Stones and
boulders, ice, and bedrock or a cemented pan interfere with installation.
Subsidence interferes with installation and maintenance. Excessive slope may
cause lateral seepage and surfacing of the effluent in downslope areas.
Some soils are underlain by loose sand and gravel or fractured bedrock at a
depth of less than 4 feet below the distribution lines. ln these soils the absorption
field may not adequately filter the effluent, particularly when the system is new.
As a result, the ground water may become contaminated.
The ratings are both verbaland numerical. Rating class terms indicate the extent
to which the soils are limited by all of the soil features that affect the specified
use. "Not limited" indicates that the soil has features that are very favorable for
the specified use. Good performance and very low maintenance can be
expected. "Somewhat limited" indicates that the soil has features that are
moderately favorable for the specified use. The limitations can be overcome or
minimized by special planning, design, or installation. Fair performance and
moderate maintenance can be expected. 'Very limited" indicates that the soil has
one or more features that are unfavorable for the specified use. The limitations
generally cannot be overcome without major soil reclamation, special design, or
expensive installation procedures. Poor performance and high maintenance can
be expected.
Numerical ratings indicate the severity of individual limitations. The ratings are
shown as decimal fractions ranging from 0.01 to 1.00. They indicate gradations
between the point at which a soil feature has the greatest negative impact on the
use ('1.00) and the point at which the soil feature is not a limitation (0.00).
The map unit components listed for each map unit in the accompanying
Summary by Map Unit table in Web Soil Survey or the Aggregation Report in Soil
Data Viewer are determined by the aggregation method chosen. An aggregated
rating class is shown for each map unit. The components listed for each map unit
are only those that have the same rating class as listed for the map unit. The
percent composition of each component in a particular map unit is presented to
help the user better understand the percentage of each map unit that has the
rating presented.
Other components with different ratings may be present in each map unit. The
ratings for all components, regardless of the map unit aggregated rating, can be
viewed by generating the equivalent report from the Soil Reports tab in Web Soil
Survey or from the Soil Data Mart site. Onsite investigation may be needed to
validate these interpretations and to confirm the identity of the soil on a given
site.
USDA
-
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
11t4t2021
Page 4 of 5
Septic Tank Absorption Fields-Rifle Area, Colorado, Parts of Garfield and Mesa Counties 4756 County Road 309, Galield
County, CO
Rating Options
Aggregation Method: Dominant Condition
Aggregation is the process by which a set of component attribute values is
reduced to a single value that represents the map unit as a whole.
A map unit is typically composed of one or more "components". A component is
either some type of soil or some nonsoil entity, e.9., rock outcrop. For the
attribute being aggregated, the first step of the aggregation process is to derive
one attribute value for each of a map unit's components. From this set of
component attributes, the next step of the aggregation process derives a single
value that represents the map unit as a whole. Once a single value for each map
unit is derived, a thematic map for soil map units can be rendered. Aggregation
must be done because, on any soilmap, map units are delineated but
components are not.
For each of a map unit's components, a corresponding percent composition is
recorded. A percent composition of 60 indicates that the corresponding
component typically makes up approximately 60% of the map unit. Percent
composition is a critical factor in some, but not all, aggregation methods.
The aggregation method "Dominant Condition" first groups like attribute values
for the components in a map unit. For each group, percent composition is set to
the sum of the percent composition of all components participating in that group.
These groups now represent "conditions" rather than components. The attribute
value associated with the group with the highest cumulative percent composition
is returned. lf more than one group shares the highest cumulative percent
composition, the corresponding "tie-break" rule determines which value should
be returned. The "tie-break" rule indicates whether the lower or higher group
value should be returned in the case of a percent composition tie. The result
returned by this aggregation method represents the dominant condition
throughout the map unit only when no tie has occurred.
Component Percent Cutoff: None Specified
Components whose percent composition is below the cutoff value will not be
considered. lf no cutoff value is specified, all components in the database will be
considered. The data for some contrasting soils of minor extent may not be in the
database, and therefore are not considered.
Tie-break Rule; Higher
The tie-break rule indicates which value should be selected from a set of multiple
candidate values, or which value should be selected in the event of a percent
composition tie.
USDA5 Natural Resources
Conseruation Service
Web Soil Survey
National Cooperative Soil Survey
11t4t2021
Page 5 of 5
NRCS Textural Triangle
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450
Mahaffey Single Famility Residential OWTS Design
Design
Flow
(GPD)
Bedrooms
Bldngs 0
Design Flows
SITE CRITERIA
Soil Type LTAR
1
2
2A
3
3A
4
4A
5
Soil Loading Rate =on Table 10.1
T¡eatment Area = STA = Deslgn F|oøLTAR 2250 ft2
Adjustment Factors for Method of Appllcatlon in STA
Type of Absorption
Area Method of Effluent Applcation
Dosed
(siphon or Pressure
Grav¡ty PumP) Dosed
Trench
Bed X
Adjustment Factors for Types of Distribution Media in STA
Category2 Category3-
Categoryl- - Other Chambersor
Rock or Tire MFG Enhanced
Chips Media Media
Type of D¡str¡bution
Media x
Ad¡ustment for Method of Application =
Adjustment for Type of D¡stribution =
L.2
0.7
STA Size =1890 ft2
of lnfiltrators =
3
r
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IIIII
x
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Tank Size =1000 gallons
126
Proposed 3-Bedroom Residence
HIA = 100 + {(DF - 1000)/100} X 8; Where
HIA =74
Existing 4-Bedroom Residence
HIA = 100 + {(DF - 1000}/100} X 8; Where
DF = Design Flow = 1.5 X DC
DC = Total Average Daily Flow for System
ft
DF = Design Flow = 1.5 X DC
DC = Total Average Daily Flow for System
ftHIA =83