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United States Department of AgricultureNatural Resources Conservation Service344 Merrow Road, Suite A * Tolland, Connecticut 06084-3917 * (860) 871-4011 * www.ct.nrcs.usda.govSoil Potential RatingsSubsurfaceSewageDisposalSystemsfor SingleFamilyResidencesSTATE OF CONNECTICUTFebruary, 2009

TABLE OF CONTENTSPageINTRODUCTION . 1PURPOSE . 1DEFINITION . 1SOIL POTENTIAL RATINGS . 2USE CONSTRAINTS . 2PERFORMANCE STANDARD . 2RATING CLASSES . 3EVALUATION CRITERIA . 4SOIL POTENTIAL RATINGS BY MAP UNIT . 6CORRECTIVE MEASURES . 6SOME SITE CONDITIONS AND DESIGN CONSIDERATIONSNOT REPRESENTED IN THE RATINGS . 7REFERENCES . 37TABLESTABLE 1 – Evaluation Factors . 9TABLE 2 – Corrective Measures for Slope . 10TABLE 3 – Corrective Measures for Soil Percolation Rates . 11TABLE 4 – Saturated Hydraulic Conductivity and Percolation Rate . 12TABLE 5 – Corrective Measures for Depth to Seasonal High Water Table . 13TABLE 6 – Corrective Measures for Flooding. 14TABLE 7 – Corrective Measures for Depth to Bedrock. 15TABLE 8 – Soil Potential Ratings Map Unit . 16TABLE 9 – Map Units Grouped by Potential Rating . 30The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, nationalorigin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, geneticinformation, political beliefs, reprisal, or because all or a part of an individual's income is derived from any public assistance program. (Notall prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of programinformation (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file acomplaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 202509410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.0

IntroductionThe Soil Survey of the State of Connecticut is a modern soil survey, unifying theseparate eight county soil legends to a single statewide legend, incorporating currentsoil taxonomy and standards, addressing land use changes and urbanization, andcompiled onto planimetric orthophoto base.The soil survey provides information on the location and characteristics of variouskinds of soils within the state. The soil survey report also contains interpretations orratings of the soils for various land uses. The interpretations are based on the soilproperties that affect the intended use. These interpretations are dynamic. They mustbe periodically revised to reflect improved soils data, new technology and the needsof the soil survey report users.PurposeThe purpose of this document is to update and expand the interpretations in the soilsurvey report for subsurface sewage disposal systems (SSDS). These updatedinterpretations are in the form of soil potentials, which are interpretive ratings thatstress soil suitability.The soil potential ratings may be used to determine the relative suitability of soilswhen installing a SSDS as well as possible ways soil limitations may be overcome.*These soil potentials were developed for planning purposes and are not intended asrecommendations for soil use.The information presented here will be useful to groups or individuals involved withurban development such as local officials, builders, engineers, sanitarians, realtors,homebuyers, and other decision makers. It may also be utilized by local, regional,and state planning and zoning agencies.DefinitionSubsurface sewage disposal systems (SSDS) are systems consisting of a housesewer, a septic tank followed by a leaching system, any necessary pumps and siphons,and groundwater control system on which the operation of the leaching system isdependent. This interpretation focuses mainly on the septic tank leaching field andgroundwater control system.*The special requirements identified to overcome soil limitations are a guide to planning andare not to be applied at a specific location without on-site investigation for design andinstallation.1

Soil Potential RatingsSoil potential ratings are classes that indicate the relative quality of a soil for aparticular use compared to other soils in a given area, in this case the state ofConnecticut.The rating criteria were developed by a committee of state and local sanitarians,engineers, and installers. The soils information was provided by the USDA NaturalResources Conservation Service (NRCS). Then the performance and site conditionsfor a typical system were defined (see Performance Standard). This provided astandard against which various combinations of soil properties for the soils withinConnecticut could be compared.The engineering and installation practices used to overcome various soil limitationswere listed and their costs estimated. This information was used to identifylimitations and costs associated with installing a SSDS on each of the soils inConnecticut. Soils with no or minor limitations for the installation of a SSDS wererated the highest. Conversely, soils requiring extensive site modification and designwere rated the lowest. The ease of system installation, and hence cost, formed thebasis of the rating scheme.Use ConstraintsIn obtaining this data from NRCS, it is understood that you and/or your organizationhave the right to use them for any internal purpose. This data is not designed for useas a primary regulatory tool in permitting or citing decisions, but may be used as areference source. This data is not suitable for site-specific studies or litigation.Inappropriate applications would include a regulatory or policy decision requiring onsite verification or prejudicial judgment based on the soil potential ratingsinformation alone.Performance StandardThe performance standard is composed of two parts. First, it identifies the capabilitiesof a typical SSDS. A typical system is assumed to be for a single family, 4-bedroomhome on a 1-acre lot with a private well, or a ½-acre lot with public water supply. Thesystem has a 1250 gallon septic tank and a 660 to 1000 square foot leaching field.Second, it addresses soil and landscape characteristics. This identifies the soilcharacteristics that are present in order for a typical system to be constructed.2

The soil characteristics are:1. Slope is less than 15 percent.2. Soil percolation rate is 1 to 30 minutes per inch.3. Depth to seasonal high water table is greater than 36 inches below the soilsurface.4. Depth to bedrock is greater than 60 inches.5. The soils do not flood.Rating ClassesThe rating class definitions refer to installing a SSDS that will meet state and localhealth code regulations. Soils with high potential have characteristics that meet theperformance standard. A typical system can be installed at a cost of x. The cost of xrepresents the going rate for installing a SSDS. The actual value of x variesdepending on many factors independent of soil properties.The cost of installing an leaching field is expressed as a multiple of x and is called thecost factor.** The cost factors of 3x and 3.5x mean that the estimated cost of aleaching field ranges from 3 to 3.5 times more than a field installed in a soil with highpotential. These cost factors provide relative estimates of the costs in installing aSSDS. Soil potential ratings are listed in Tables 2 and 3.The soil potential ratings and associated cost factors, assuming a typical system, aredefined below.High Potential –These soils have the best combination ofcharacteristics or may have limitations that can beeasily overcome using standard installation practices.The cost factor is 1x to 2.0x.Medium Potential –These soils have significant limitations, such as lowpercolation rate, that are generally overcome usingcommonly applied designs. The cost factor rangesfrom 2.0x to 2.5x.Low Potential –These soils have one or more limitations, such as lowpercolation rate and depth to seasonal high watertable, that require extensive design and sitepreparation to overcome. The cost factor ranges from2.5x to 3.5x.**Cost factors are only a guide. Actual costs will vary both above and below the rangesgiven. Actual costs will be influenced by on-site features and other variables independent ofsoil properties.3

Very Low Potential –These soils have to overcome major soil limitations,such as depth to bedrock, that require extensivedesign and site preparation. A permit for a SSDS maynot be issued unless the naturally occurring soils meetthe minimal requirements outlined in the state healthcode. It is unlikely these soils can be improvedsufficiently to meet state health code regulations. Thecost factor ranges from 4.25x to 6.0x.Extremely LowPotential –These soils have multiple major limitations, such asflooding and depth to seasonal high water table,which are extremely difficult to overcome. A permitfor a SSDS may not be issued unless the naturallyoccurring soils meet the minimal requirementsoutlined in the state health code. It is unlikely thesesoils can be improved sufficiently to meet state healthcode regulations.Not Rated –Areas labeled Not Rated have characteristics thatshow extreme variability from one location toanother. The work needed to overcome adverse soilproperties cannot be estimated. Often these areas areurban land complexes or miscellaneous areas. Anon site investigation is required to determine soilconditions present at the site.The estimated percent of land in the state of Connecticut that fit into each of the soilpotential ratings is as follows:High PotentialMedium PotentialLow PotentialVery Low PotentialExtremely Low PotentialNot Rated15.3%12.4%30.7%7.2%13.7%20.7%Evaluation CriteriaThe evaluation criteria are soil properties that can significantly affect the cost ofinstalling a SSDS. These soil properties correspond to criteria identified in theConnecticut State Health Code Regulations, as well as factors deemed significant byNRCS who developed these soil potential ratings. The evaluation criteria are listed inTable 1 and detailed in Tables 2 through 7.4

The criteria listed in Table 1 are broken up into several ranges of values. These valuesare assigned classes. The values defining each rating class were chosen based on threeconsiderations:1. Is the data compatible with state health regulations?2. Can the information be obtained from presently available soil survey data?3. Do these values identify significant differences in the cost of installing aSSDS that meets the performance standard?The five evaluation criteria are:Percent Slope –Slope is the inclination of the land surface from thehorizontal. Percentage of slope is the vertical distancedivided by the horizontal distance, multiplied by 100.Thus, a slope of 20 percent is a drop of 20 feet in 100feet of horizontal distance.Soil Percolation Rate – A percolation test is intended to measure the rate atand Saturatedwhich the soil will absorb effluent. MeasurementsHydraulic Conductivity are made in minutes per inch and called thepercolation rate. These rates are utilized by the CTPublic Health Code. The percolation rate is not ameasure of any one property of the soil. Instead, it isrelated to many factors including soil texture, kinds ofclay minerals, bulk density, structure, size andconfiguration of pores, number and size of rockfragments, depth to water table, antecedent moistureconditions, chemical composition, etc.Soil surveys generally measure saturated hydraulicconductivity (Ksat) to convey the rate of watermovement through the soil under (field) saturatedconditions as the preferred parameter in the NationalCooperative Soil Survey. Percolation rates have alsobeen used to express water flow through soils,particularly for soil interpretations for septic drainfields. For this planning document, percolation rateswere estimated for soil types based on saturatedhydraulic conductivity values (Table 4). Althoughthese two parameters are different, determined bydifferent methods, and yield different results, they canbe considered to be functionally equivalent for thisapplication. Consequently, percolation rates may,with prudence, be used as a proxy for Ksat in this case.5

Depth to SeasonalHigh Water Table(SHWT) –This is the depth from the soil surface to a zone ofsaturation at the highest average level during thewettest season. The depth to a water table isdetermined primarily through the presence of rustcolored and/or gray soil redoximorphic features.Flooding –Flooding is the temporary covering of the soil surfaceby floodwater from streams overflowing their banks,inflow from high tides, or any other combination ofsources. The frequency or how often, typically, that itfloods is an estimate of the current condition, whethernatural or human-influenced (such as dams or levees).Depth to Bedrock –Depth to bedrock is the depth from the soil surface tothe contact with coherent (continuous) bedrock.Ledge rock is another term used for bedrock by theConnecticut Public Health Code.Soil Potential Ratings by Map UnitConnecticut’s statewide soil survey identifies and displays the dominant soils in thestate. The symbols on the maps identify map units, each map unit representing aunique combination of soils. Areas within the same symbol have similar composition.The soils were mapped at a scale of 1:12000 with a minimum size delineation ofapproximately 3 acres. Maps enlarged from the soil survey report do not providemore detailed soils information. More detailed information can only be obtainedthrough on-site investigations.The soil survey is not a replacement for on-site investigation. The survey identifiesthe probability of finding a particular soil or combination of soils.Table 8 assigns a potential rating to each map unit. The list of map units is in orderby soil map unit symbol. The potential rating is based on the ease of installing aSSDS in the dominant soil(s) of the map unit. The majority of map units arecomposed of one dominant soil or of several soils with similar characteristics. Asingle potential rating is listed for each map unit. Other map units are composed oftwo kinds of contrasting soils. In these cases, an overall potential rating is listed forthe map unit.The limiting soil characteristics for each map unit are identified in Table 8 under thecolumn labeled Concerns. The table also identifies state regulations which may beapplicable if particular soil features are present on the site. This information islocated in the column labeled State Regs. The numbers in this column reference thefootnotes provided at the end of the table.6

Corrective MeasuresCorrective measures are any design or construction practices that may be required ona site. The kinds of measures identified are dependent on the limiting soilcharacteristics and are commonly used solutions for dealing with those soillimitations. Some soil limitations have no practical corrective measure identified inthe CT Public Health Code. Without an on-site investigation, it is impossible topredict exactly what improvements a site will need in order for the subsurface sewagedisposal system to work. For this reason, the site improvements are divided into twocategories:Probable CorrectiveMeasures –These are on-site improvements that are most likelyto be needed on a site having a particular kind of soil.Possible AdditionalThese improvements may be necessary on some sites.Corrective Measures – Whether they are needed depends on the degree of thelimiting soil and site characteristics.The commonly applied corrective measures are identified in Tables 2, 3 and 5through 7. In these tables, the column labeled Concerns identifies why correctivemeasures are needed on a site having the specified soil feature. The tables alsoidentify the state regulations that may be applicable if a particular soil feature ispresent on a site. This information is located in the column labeled State Regs. Thenumbers in this column reference footnotes provided at the end of the each table.The column labeled Other Considerations lists the practices or site requirements thatmay be needed to construct a SSDS. These measures may be needed to allow for theinstallation of a system or to determine the most practical solution to a soil or siteproblem.Some Site Conditions and Design Considerations NotRepresented in the RatingsThe soil potential ratings for SSDS were determined based on the ease of overcomingthe soil limitations listed in Table 1. In many cases, the ease of constructing a systemand cost is determined by other factors that may be site specific or result from localtown requirements. A partial list of these factors that may influence cost, but are notrepresented in the rating scheme, follows: Small areas of contrasting soils too small to delineate at the scale of the SoilSurvey of the State of Connecticut.Boulders that cannot be moved by customary construction equipment.Topographic configuration of the property.7

Fill needed to compensate for the volume of material lost through the removalof stones and boulders.Measuring depth to water table during the spring months.Local health department practices.Inland wetland setbacks.Time needed for approvals from regulatory agencies.Easements.Access to site for testing, construction, and system maintenance.Landscaping.Maneuvering around site features to be preserved such as stonewalls and trees.Tree and stump removal.Hauling costs of fill and gravel.Proximity of proposed leaching field to neighboring wells.Time of year of construction.Construction stakeout and supervision by an engineer or sanitarian.8

Table 1Evaluation FactorsEvaluationCriteriaNot LimitedSomewhat LimitedVery Limited 1515 to 25 251 to 30 1; 30 to 60 60Depth to Seasonal HighWater Table (inches) 3618 to 36 18Flooding (frequency)noneDepth to Bedrock (inches) 60Percent SlopeSoil Percolation Rate(minute/inch)very rare, rare, occasional,frequent, very frequent40 to 609 40

Table 2. Corrective Measures for SlopeSlopeConcernsProbable CorrectiveMeasures 15%NoneNone15-25%Difficulty ofinstallation (access,machinery, etc.)BreakoutDesign and installation toaccommodate for slope.Serial distribution of effluentthrough the use of high leveloverflow. 25%Difficulty ofinstallation (access,machinery, etc.)BreakoutDesign and installation toaccommodate for slope.Serial distribution of effluentthrough the use of rectiveMeasuresSelect t and/orconstructionmethods.Select fill means clean bank run sand, clean bank run sand and gravel, or approved manufactured fill having agradation which conforms to the specifications stipulated in Section VIII A of the Technical Standards. Note:See Standard VIII A for manufactured fill approval requirements. Section I of the Connecticut Public HealthCode – Regulations and Technical Standards for Subsurface Sewage Disposal Systems, Technical Standards(Pursuant to Section 19-13-B103). January 1, 2004.1Identified as an area of special concern. Section 19-13-B103d (e) (1) of the Connecticut Public Health Code.10

Table 3. Corrective Measures for Soil Percolation RatesSoilPercolationRateConcerns 1 min/in(fast perc)Inadequateeffluentrenovation due tofast movementthrough the soil.1 to 30 min/inNone30 to 60 min/in(slow perc) 60 min/in(slow perc)Probable CorrectiveMeasuresDouble horizontalseparating distancebetween well and easuresSelect fillOtherConsiderationsHydraulic analysisor pollutantrenovationanalysis may berequired.3Slow acceptanceof effluent intothe soilDesign leaching field todistribute effluent over alarger area.Curtain drain anddrainage swale to divertsurface and subsurfaceflows of water.Slow acceptanceof effluent intothe soil.Special design of largerleaching field.Curtain drain anddrainage swale to divertsurface and subsurfaceflows of water.Need drainageoutlet. Hydraulicanalysis may berequired.1,31, 2Select fillNeed drainageoutlet.Select fill means clean bank run sand, clean bank run sand and gravel, or approved manufactured fill having agradation which conforms to the specifications stipulated in Section VIII A of the Technical Standards. Note:See Standard VIII A for manufactured fill approval requirements. Section I of the Connecticut Public HealthCode – Regulations and Technical Standards for Subsurface Sewage Disposal Systems, Technical Standards(Pursuant to Section 19-13-B103). January 1, 2004.1Identified as an area of special concern. Section 19-13-B103d (e) (1) of the Connecticut Public Health Code.2No permit or approval shall be issued where there is an impervious soil or where there is less than 18 inchesdepth of suitable existing soil over impervious soil. An impervious soil has a minimum percolation rate slowerthan one inch in sixty minutes when the groundwater level is at least eighteen inches below the bottom of thepercolation test hole. Section 19-13-B103e (a) (3) of the Connecticut Public Health Code.3Identified as a suitable soil. A suitable soil means having a minimum percolation rate of one inch in one tosixty minutes when the groundwater level is at least eighteen inches below the bottom of the percolation testhole. Section 19-13-B103 b (h) if the Connecticut Public Health Code.11

Table 4. Saturated Hydraulic Conductivity andPercolation Rate***Saturated Hydraulic Conductivity (Ksat)cm/day 3.312.011.010.09.1 8.3 .610.550.500.460.420.38 0.35*** 541.391.271.161.05 0.96PercolationRatemin/in 1510152025303540455055 60Adapted from the State of Virginia, Virginia Department of Health, September 20, 2001, FootprintCommittee Meeting. See references at the end of this document.12

Table 5. Corrective Measures for Depth to Seasonal HighWater TableSoil DepthTo SHWTConcernsProbable ctiveMeasuresOtherConsiderationsCurtain drain orshallow trenchesmay be neededwhen the watertable is near the3-foot depth. 36 inchesNoneNone18 to 36inchesGroundwaterinterference witheffluentdispersal.Curtain drain anddrainage swale to divertsurface and subsurfaceflows of water, and/or0-3 feet of select fill. 18 inchesGroundwaterinterference witheffluentdispersal.Curtain drain anddrainage swale to divertsurface and subsurfaceflows of water, and/or3-5 feet of select fill.1Need drainageoutlet. Hydraulicanalysis may berequired.1, 4, 5Need drainageoutlet. Hydraulicanalysis may berequired.Select fill means clean bank run sand, clean bank run sand and gravel, or approved manufactured fill having agradation which conforms to the specifications stipulated in Section VIII A of the Technical Standards. Note:See Standard VIII A for manufactured fill approval requirements. Section I of the Connecticut Public HealthCode – Regulations and Technical Standards for Subsurface Sewage Disposal Systems, Technical Standards(Pursuant to Section 19-13-B103). January 1, 2004.1Identified as an area of special concern. Section 19-13-B103d (e) (1) of the Connecticut Public Health Code.4No permit or approval shall be issued where the ground water level is less than 18 inches below the surface ofthe ground for a duration of one month or longer during the wettest season of the year. Section 19-13-B103e (a)(3) of the Connecticut Public Health Code.5Identified as an area of special concern. Designated as wetland under the provisions of Sections 22a-36through 22a-45 of the Connecticut General Statutes, as amended. Section 19-13-B103d (e) (1) (G) of theConnecticut Public Health Code.13

Table 6. Corrective Measures for FloodingSoil FloodingFrequencyConcernsProbable CorrectiveMeasuresNoneNoneNoneVery Rare, RareOccasionalFrequentVery frequentSystembackup.Erosion ofraised system.Maintain separatingdistance to areas ofconcentrated OtherConsiderations1, 5The very rare class floods more than or equal to 1 time in 500 years, but less than 1 time in 100 years.The rare class floods 1 to 5 times in 100 years. The occasional class floods 5 to 50 times in 100 years. Thefrequent class floods more than 50 times in 100 years. The very frequent class floods more than 50 percent ofall months in a year1Identified as an area of special concern. Section 19-13-B103d (e) (1) of the Connecticut Public Health Code.5Identified as an area of special concern. Designated as wetland under the provisions of Sections 22a-36through 22a-45 of the Connecticut General Statutes, as amended. Section 19-13-B103d (e) (1) (G) of theConnecticut Public Health Code.14

Table 7. Corrective Measures for Depth to BedrockSoil Depthto BedrockConcernsProbable CorrectiveMeasuresStateRegs 60 inchesNoneNone40 to 60inchesInsufficient soildepth for effluentrenovation.1 to 3 feet of selectfill.1, 6 40 inchesInsufficient soildepth for effluentrenovation.Possiblegroundwaterpollution.3 to 5 feet of selectfill.1, ationsSelect fill means clean bank run sand, clean bank run sand and gravel, or approved manufactured fill having agradation which conforms to the specifications stipulated in Section VIII A of the Technical Standards. Note:See Standard VIII A for manufactured fill approval requirements. Section I of the Connecticut Public HealthCode – Regulations and Technical Standards for Subsurface Sewage Disposal Systems, Technical Standards(Pursuant to Section 19-13-B103). January 1, 2004.1Identified as an area of special concern. Section 19-13-B103d (e) (1) of the Connecticut Public Health Code.6No permit or approval shall be issued where there is less than four feet depth of suitable existing soil overledge rock, two feet of which is naturally occurring soil. Section 19-13-B103e (a) (3) of the Connecticut PublicHealth Code.15

Table 8. Soil Potential Ratings forSubsurface Sewage Disposal System by Map UnitMapSymbolMap y fine sandy loamExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,53Ridgebury, Leicester, and Whitman soils,extremely stonyExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,54Leicester fine sandy loamExtremely lowpotentialDepth to SHWT1,4,55Wilbraham silt loamExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,56Wilbraham and Menlo soils, extremely stonyExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,57Mudgepond silt loamDepth to SHWT1,4,5Depth to SHWT, lowpercolation rate1,2,4,5Extremely lowpotentialExtremely lowpotential8Mudgepond and Alden soils, extremely stony9Scitico, Shaker, and Maybid soilsExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,510Raynham silt loamExtremely lowpotentialDepth to SHWT, lowpercolation rate1,2,4,512Raypol silt loamExtremely lowpotential13Walpole sandy loamExtremely lowpotential14Fredon silt loamExtremely lowpotentialDepth to SHWT1,4,515Scarboro muckExtremely lowpotentialDepth to SHWT,high percolationrate1,4,516Halsey silt loamExtremely lowpotentialDepth to SHWT1,4,517Timakwa and Natchaug soilsExtremely lowpotentialDepth to SHWT,high percolationrate1,4,518Catden and Freetown soilsExtremely lowpotentialDepth to SHWT1,4,520AEllington silt loam, 0 to 5 percent slopesLow potentialDepth to SHWT121ANinigret and Tisbury soils, 0 to 5 percent slopesLow potentialDepth to SHWT116Depth to SHWT,high percolationrateDepth to SHWT,high percolationrate1,4,51,4,5

MapSymbolMap UnitNamePotentialRatingStateRegs.Concerns22AHero gravelly loam, 0 to 3 percent slopesLow potentialDepth to SHWT122BHero gravelly loam, 3 to 8 percent slopesLow potentialDepth to SHWT123ASudbury sandy loam, 0 to 5 percent slopesLow potentialDepth to SHWT124ADeerfield loamy fine sand, 0 to 3 percent slopesLow potentialDepth to SHWT,high percolationrate125ABrancroft silt loam, 0 to 3 percent slopesLow potentialDepth to SHWT, lowpercolation rate1,225BBrancroft silt loam, 3 to 8 percent slopesLow potentialDep

Soil Percolation Rate – A percolation test is intended to measure the rate at and Saturated which the soil will absorb effluent. Measurements Hydraulic Conductivity are made in minutes per inch and called the percolation rate. These rates are utilized by