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Lowe, Sorensen GUIDELINES FOR PREPARING HYDROGEOLOGIC AND SOIL REPORTS FOR WASTEWATER DISPOSAL SYSTEMS, WEBER COUNTY, UTAH UGS Circular 1021999GUIDELINES FOR PREPARINGHYDROGEOLOGIC AND SOIL REPORTSADDRESSING SUITABILITY FORALTERNATIVE WASTEWATER DISPOSALSYSTEMS IN WEBER COUNTY, UTAHbyMike Lowe,Utah Geological SurveyandDarwin Sorensen,Utah Water Research Laboratory,Utah State UniversityCIRCULAR 102UTAH GEOLOGICAL SURVEYa division ofUtah Department of Natural Resources


STATE OF UTAHMichael O. Leavitt, GovernorDEPARTMENT OF NATURAL RESOURCESKathleen Clarke, Executive DirectorUTAH GEOLOGICAL SURVEYM. Lee Allison, DirectorUGS BoardMemberRepresentingC. William Berge (Chairman) .......................................................................................................... Mineral IndustryD. Cary Smith .................................................................................................................................. Mineral IndustryCraig Nelson .................................................................................................................................. Civil EngineeringE.H. Deedee O’Brien ........................................................................................................................ Public-at-LargeRobert Robison ............................................................................................................................... Mineral IndustryCharles Semborski .......................................................................................................................... Mineral IndustryRichard R. Kennedy ................................................................................................. Economics-Business/ScientificDavid Terry, Director, Trust Lands Administration ...................................................................... Ex officio memberUTAH GEOLOGICAL SURVEYThe UTAH GEOLOGICAL SURVEY is organized into five geologic programs with Administration, Editorial, and ComputerResources providing necessary support to the programs. The ECONOMIC GEOLOGY PROGRAM undertakes studies to identify coal,geothermal, uranium, hydrocarbon, and industrial and metallic resources; initiates detailed studies of these resources including mining districtand field studies; develops computerized resource data bases, to answer state, federal, and industry requests for information; andencourages the prudent development of Utah’s geologic resources. The APPLIED GEOLOGY PROGRAM responds to requests fromlocal and state governmental entities for engineering-geologic investigations; and identifies, documents, and interprets Utah’s geologichazards. The GEOLOGIC MAPPING PROGRAM maps the bedrock and surficial geology of the state at a regional scale by county andat a more detailed scale by quadrangle. The GEOLOGIC EXTENSION SERVICE answers inquiries from the public and providesinformation about Utah’s geology in a non-technical format. The ENVIRONMENTAL SCIENCES PROGRAM maintains and publishesrecords of Utah’s fossil resources, provides paleontological and archeological recovery services to state and local governments, conductsstudies of environmental change to aid resource management, and evaluates the quantity and quality of Utah’s ground-waterresources.The UGS Library is open to the public and contains many reference works on Utah geology and many unpublished documents onaspects of Utah geology by UGS staff and others. The UGS has several computer data bases with information on mineral and energyresources, geologic hazards, stratigraphic sections, and bibliographic references. Most files may be viewed by using the UGS Library. TheUGS also manages a sample library which contains core, cuttings, and soil samples from mineral and petroleum drill holes and engineeringgeology investigations. Samples may be viewed at the Sample Library or requested as a loan for outside study.The UGS publishes the results of its investigations in the form of maps, reports, and compilations of data that are accessible to thepublic. For information on UGS publications, contact the Natural Resources Map/Bookstore, 1594 W. North Temple, Salt Lake City, Utah84116, (801) 537-3320 or 1-888-UTAH MAP. E-mail: nrugs.geostore@state.ut.us and visit our web site at http://www.ugs.state.ut.us.UGS Editorial StaffJ. Stringfellow ....................................................................................................................................................EditorVicky Clarke, Sharon Hamre...............................................................................................................Graphic ArtistsPatricia H. Speranza, James W. Parker, Lori Douglas...........................................................................CartographersThe Utah Department of Natural Resources receives federal aid and prohibits discrimination on the basis of race, color, sex, age, national origin, or disability. Forinformation or complaints regarding discrimination, contact Executive Director, Utah Department of Natural Resources, 1594 West North Temple #3710, Box145610, Salt Lake City, UT 84116-5610 or Equal Employment Opportunity Commission, 1801 L Street, NW, Washington DC 20507.Printed on recycled paper 2/99


GUIDELINES FOR PREPARING HYDROGEOLOGIC AND SOIL REPORTSADDRESSING SUITABILITY FOR ALTERNATIVE WASTEWATERDISPOSAL SYSTEMS IN WEBER COUNTY, UTAHbyMike LoweUtah Geological SurveyandDarwin SorensenUtah Water Research LaboratoryUtah State UniversityABSTRACTMany lots in Weber County presentlycannot be developed because adverse sitecharacteristics (such as soil that percolatesoutside of acceptable rate ranges or shallowground water) make them unsuitable forconventional wastewater disposal systems(septic tank soil-absorption systems). TheWeber-Morgan District Health Departmentand the Utah Division of Water Quality havedeveloped designs for alternative wastewaterdisposal systems that may be used in suchareas if hydrogeologic and soil conditions aresuitable, ground- and surface-water quality willnot be degraded, and humans will not beexposed to wastewater pathogens. Todemonstrate conformance with these criteria,hydrogeologic and soil studies of proposedsites will need to be conducted and resultssubmitted to the Weber-Morgan District HealthDepartment. Suitable hydrogeologicconditions include: (1) site slopes no steeperthan 4 percent, (2) soil percolation ratesbetween 60 minutes/inch and 1 minute/inch (5minutes/inch for both Ogden Canyon andOgden Valley), (3) depth to seasonal shallowground water at least 2 feet (0.6 m) below thebottom of soil-absorption drain-field trenchesor beds and 1 foot (0.3 m) below the originalground surface (location of trenches and bedswith respect to original ground surface varieswith alternative system type), (4) depth tobedrock or unsuitable soil at least 4 feet (1.2m) below the bottom of soil-absorption drainfieldtrenches, (5) topographic and geologicconditions that prevent wastewater fromsurfacing or reaching surface-water bodies orculinary wells or springs within 250 daysground-water time of travel, (6) ground-waterflow available for mixing in the zone of mixingin the aquifer below the site such that averagenitrate concentrations will not be increasedmore than 1 mg/L under the anticipatedwastewater loading, and (7) nitrate in highconcentration zones (plumes) will not exceed10 mg/L at any depth or location when itreaches the alternative wastewater disposalsystem owner’s property line, as determinedusing a defendable solute transport model.Additionally, soil conditions should be suchthat wastewater will be adequately treatedbefore reaching ground or surface water.INTRODUCTIONPurposeMany lots in Weber County (figure 1)presently cannot be developed becauseadverse site characteristics (such as soil thatpercolates outside of acceptable rate ranges,


Guidelines - Hydrogeologic Reports 3or shallow ground water) make themunsuitable for conventional wastewaterdisposal systems (septic tank soil-absorptionsystems). The Weber-Morgan District HealthDepartment and the Utah Division of WaterQuality have developed designs for alternativewastewater disposal systems that may beused if hydrogeologic and soil conditions aresuitable, ground- and surface-water quality willnot be degraded, and humans will not beexposed to wastewater pathogens (UtahAdministrative Code, R317-502-20; R317-507-7 to 9). To demonstrate conformance withthese criteria, hydrogeologic and soil studiesof proposed sites will need to be conductedand results submitted to the Weber-MorganDistrict Health Department.The purpose of this circular, prepared atthe request of the Weber-Morgan DistrictHealth Department, is to provide guidelinesfor: (1) geologists preparing hydrogeologicreports pertinent to the suitability of sites foralternative wastewater disposal systems, (2)soil scientists preparing soil evaluation reportspertinent to the suitability of sites foralternative wastewater disposal systems, and(3) geologists, soil scientists, and Weber-Morgan District Health Department officialsreviewing these reports. These guidelines areapplicable to other areas of Utah wherealternative wastewater disposal systems areused or are being considered to be used.These guidelines do not includesystematic descriptions of all availabletechniques, and do not imply that alltechniques be used on every project.Variations in site conditions or projectedwastewater loadings may require more orpermit less effort than is outlined here. Manysections of these guidelines have beenmodified from Utah Geological and MineralSurvey Miscellaneous Publication M,"Guidelines for preparing engineering geologicreports in Utah" (Utah Section of theAssociation of Engineering Geologists, 1986).Wastewater Disposal SystemsWastewater is disposed of in severaldifferent ways in Weber County, includingpublic sewer systems/wastewater treatmentplants in the East Shore area (locally knownas lower Ogden Valley), total-containmentsewage lagoons in Ogden Valley (locallyknown as upper Ogden Valley) and varioustypes of subsurface disposal systems in thewestern part of the East Shore area and in theOgden Valley drainage basin. The guidelinespresented herein apply to both community andindividual alternative on-site subsurfacedisposal systems.Subsurface wastewater disposal systemsgenerally consist of a building sewer(s), septictank(s), and a soil-absorption drain-fieldsystem (figure 2). The septic tank providesprimary treatment of wastewater. The volumeof solids is reduced in the septic tank, withnonfloatable solids removed from thewastewater producing a somewhat clarifiedeffluent that is then distributed to the soilabsorptiondrain-field system.Alternative wastewater disposal systemsdiffer from conventional wastewater disposalsystems (septic tank soil-absorption systems[figure 2]) primarily in the placement of thesoil-absorption drain fields (either trench orbed design). The drain fields of alternativewastewater disposal systems are generallyplaced at or above the original ground surface.Current alternative wastewater disposalsystem types include Low Pressure Pipe, At-Grade, Earth Fill, and Mound systems. Newpermits for Low Pressure Pipe systems thatdistribute effluent to a soil-absorption drainfield in sandy fill above the original groundsurface using a “demand-dosed” pumpmechanism, are no longer issued in WeberCounty and thus are not discussed further.At-Grade systems, like conventionalwastewater disposal systems, generally do notutilize dosing chambers and pumps to


4 Utah Geological SurveyFigure 2. Conventional wastewater disposal system (from R317-501 through 513, Utah Administrative Code).distribute effluent. Soil-absorption drain fieldsfor At-Grade systems consist of a series oftrenches, having the bottoms of the trencheslocated at the original ground surface (figure3). For Earth Fill (figure 4) systems,distribution pipes are placed at some distanceabove the original ground surface inengineered fill with a stabilized percolationrate between 15 and 45 minutes/inch afterone year; these systems generally rely ongravity flow and do not utilize dosingchambers and pumps to distribute effluent.Mound systems (figure 5) use a “time-dosed”pump mechanism to distribute effluent from adosing chamber to soil-absorption drain-fielddistribution laterals placed on sand fill(meeting American Society for Testing andMaterials C33 specifications) at some distanceabove the original ground surface and coveredwith fabric and soil. Slopes at At-Grade, EarthFill, and Mound system sites may not exceed4 percent.For all types of soil-absorption systems,the soil characteristics and percolation rates atthe soil-absorption drain-field location must fallwithin acceptable ranges; the acceptableranges of percolation rates are moreconservative (protective) in Ogden Valley(locally known as upper Ogden Valley) andOgden Canyon because the aquifers aregenerally more vulnerable to contaminationthan in the East Shore area (Anderson andothers, 1994; Snyder and Lowe, 1998). Forthe East Shore area (figure 1), percolationrates must be between 1 and 60 minutes/inchfor a depth of at least 4 feet (1.2 m) below thesoil-absorption drain field. For Ogden Valley


Guidelines - Hydrogeologic Reports 5Figure 3. Schematic diagram of an At-Grade system (from R317-501 through 513, Utah Administrative Code).Figure 4. Schematic diagram of a typical Earth Fill system (from R317-501 through 513, Utah Administrative Code).Figure 5. Schematic diagram of a Mound system (from R317-501 through 513, Utah Administrative Code).


6 Utah Geological Surveyand Ogden Canyon (figure 1), percolationrates must be between 5 and 60 minutes/inchfor a depth of 4 feet (1.2 m) below the soilabsorptiondrain field. Additionally, theseasonal shallow ground-water table cannotrise to a level of less than 2 feet (0.6 m) belowthe soil-absorption drain field or 1 foot (0.3 m)below the original ground surface, and theremust be sufficient suitable soils at the site forproper treatment of wastewater (table 1).GUIDELINES FOR PREPARINGHYDROGEOLOGIC AND SOIL REPORTSThe purpose of the hydrogeologic andsoil reports is to show that conditions aresuitable for an alternative wastewater disposalsystem. Suitable hydrogeologic conditionsinclude:(1) Site slopes no steeper than 4 percent.(2) Soil percolation rates between 60minutes/inch and 1 minute/inch (5minutes/inch for Ogden Canyon andOgden Valley) (figure 1).(3) Depth to seasonal shallow groundwater at least 2 feet (0.6 m) below thebottom of soil-absorption drain-fieldtrenches and 1 foot (0.3 m) below theoriginal ground surface.(4) Depth to bedrock or unsuitable soil atleast 4 feet (1.2 m) below the bottom ofsoil-absorption drain-field trenches.(5) Topographic and geologic conditionsthat prevent wastewater from surfacing orreaching surface-water bodies or culinarywells or springs within 250 days groundwatertime of travel.(6) Ground-water flow available formixing in the zone of mixing in the aquiferbelow the site such that average nitrateconcentrations will not be increasedmore than 1 mg/L under the anticipatedwastewater loading.(7) Nitrate in high concentration zones(plumes) does not exceed 10 mg/Lmodel (the ground-water-quality [health]standard) at any depth or location when itreaches the alternative wastewaterdisposal system owner’s property line.Nitrate concentrations at the property lineare to be determined using a defendablesolute transport model.Table 1. Suitable soil thickness and separation fromseasonal shallow ground-water requirements for conventional(septic tank soil-absorption), At-Grade, Mound, and Earth Fillwastewater disposal systems in Weber County, Utah.MINIMUMTHICKNESS OFSUITABLE SOILS(NOT INCLUDINGFILL)MINIMUM DEPTHTO MAXIMUMSHALLOW GROUND-WATER TABLEBELOW ORIGINALGROUND SURFACECONVEN-TIONAL60 inches(150 cm)36 inches(90 cm)AT-GRADE48 inches(120 cm)24 inches(60 cm)MOUNDAND EARTHFILL36 inches(90 cm)12 inches(30 cm)Site Description and General InformationThe report should describe the generalsite setting. The following items should beaddressed:(1) Site location, size, and general settingwith respect to major or regionalgeographic and geologic features. Asite-location map should be provided ona topographic base at a scale of 1:24,000or larger. Subdivision site plans, ifalready prepared, should also beprovided.


Guidelines - Hydrogeologic Reports 7(2) Topography and drainage within oraffecting the site.(3) General description of site geology,emphasizing the characteristics of theuppermost aquifer (including a watertableor potentiometric-surface map andone or more hydrogeologic crosssections).(4) Location(s) and description(s) ofproposed alternative wastewater disposalsystem(s) and any surface-water bodiesand/or culinary springs or water wells inthe general area or having the potentialof being affected.(5) List of references used and names(s),affiliations, and certifications ofprofessionals performing the study.InvestigationGeologic mapping of the site should beon a topographic base, at a scale preferably1:24,000 or larger, that shows sufficient detailto adequately define the geologic conditionspresent. Available geologic maps generallymust be supplemented with site-specificobservations. It may be necessary to studythe geology in adjacent areas to aid in defininggeologic conditions affecting the siting ofalternative wastewater disposal systems.The report should include descriptions ofthe types of rock and surficial materials,geologic structures, and show the threedimensionalrelationships on one or moreappropriately scaled cross sections or fence orblock diagrams. The locations of test holes(drill holes, test pits, and trenches) should beshown on maps and cross sections. Logs oftest holes should be included in the report topermit technical reviewers to make their owninterpretations.The following checklist is useful as ageneral, though not necessarily complete,guide for geologic descriptions.1. Geologic ConditionsA. Rock types (such as granite, siltysandstone, shale, schist) in the areashould be described, including age and,where possible, formation name (such asWasatch Formation and Tintic Quartzite).Descriptions should include: (1) pertinentphysical characteristics and variability ofrock units (such as color, grain size,voids, thickness, and stratification), (2)dip of beds and description of foldsshown on map and in cross sections, and(3) occurrence, distribution, dimensions,aperture, infilling, orientation, andvariability of faults and joints; andinfluence of clay seams, fault gouge, andother infillings on hydrologic conditions.B. Unconsolidated deposits at proposedsites should be described, includingdepositional environment (alluvial,colluvial, eolian, glacial, lacustrine,residual, mass movement, volcanic [suchas cinders and ash], and fill), grain size,stratification, sorting, compactness,cementation, relative age, distribution,and thickness. Cross sections should beincluded showing the above informationincluding, where possible, depth tobedrock.2. Hydrologic ConditionsA. Locations of water bodies such asrivers, streams, canals, land drains,ponds, swamps, springs, and seepsshould be clearly delineated on maps.B. Aquifers should be identified and theirproperties characterized, including: depthto ground water; seasonal fluctuations;type (confined or unconfined); potentialfor local perched aquifers above regionalaquifers; aquifer characteristics


8 Utah Geological Survey(permeability, hydraulicconductivity, and transmissivity);water quality; ground-water-flowdirection, gradient, and velocity;zone of mixing (nature andthickness); and recharge anddischarge areas.C. Topographic and geologic controls onthe ground-water system should bedescribed.3. Soil ConditionsA. Soil suitability, as described in UtahAdministrative Code R317-503-1, shouldbe characterized. The soil texture,structure, and depth of each soil horizonshould be logged (by depth andthickness) as described in UtahAdministrative Code R317-503-3.B. Soil horizon boundaries should bedescribed.C. Moist soil consistency in each horizonshould be described.D. Mottling should be identified anddescribed.Assessment Of Site SuitabilityTo show that a site is suitable foralternative wastewater disposal systems, thestudy must first demonstrate that conventionalwastewater disposal systems cannot be usedand all of the conditions listed below are met.We recommend that conditions be addressedin the order listed, and that the site beconsidered unsuitable and the studyterminated at any point where a condition isnot met.(1) Slopes at the alternative wastewaterdisposal systems are less than 4 percent.(2) There is no evidence of periodicsurface-water flooding of the site.Federal Emergency ManagementAgency (FEMA) floodplain maps areavailable for some drainages. Forsurface-water courses shown on FederalEmergency Management Agencyfloodplain maps, the site must be morethan 100 feet (30 m) from the streamchannel and more than 25 feet (7.6 m)from any surface water within thefloodway and floodway fringe.(3) There is no evidence of seasonalshallow ground water within 2 feet (0.6m) of the anticipated bottom of soilabsorptiondrain-field trenches and 1 foot(0.3 m) below the original ground surface(if the anticipated depth to ground wateris 34 inches (86 cm) or less, regularmeasurements of water levels in amonitoring well over a 1-year period, orfor the period of maximum ground-waterlevels as determined by the Weber-Morgan District Health Department, willbe required).(4) There is no evidence of bedrock orunsuitable soil within 4 feet (1.2 m) of theanticipated bottom of soil-absorptiondrain-field trenches.(5) Moist soil consistency of any horizonis firm or stronger than firm, but thehorizon is not cemented.(6) Soil horizon texture contains asufficiently high clay content to assureproper treatment of effluent, and the soilstructure is massive or weak.(7) Soil percolation rates are between 60minutes/inch and 1 minute/inch (5minutes/inch for both Ogden Canyon andOgden Valley).(8) Wastewater from alternativewastewater disposal systems cannot


Guidelines - Hydrogeologic Reports 9surface or reach culinary wells orsprings within 250 days groundwatertime of travel based onconservative (protective)estimates of aquifer propertiesand ground-water flow paths.(9) Ground-water flow available formixing in the zone of mixing in the aquiferbelow the site is of sufficient quantity toprevent average nitrate concentrationsfrom increasing more than 1 mg/L underthe anticipated wastewater loading. Theprojected average nitrate concentrationshould be determined using the methodsoutlined in Wallace and Lowe (1998).(10) A defendable solute transport modelindicates nitrate in high-concentrationzones (plumes) will not exceed 10 mg/Lat any depth or location when it reachesthe alternative wastewater disposalsystem owner’s property line.If information, such as seasonal shallowground-water depth or aquifer transmissivity,is not available, the information must becollected or the site will be consideredunsuitable. Explanations and supportingevidence from references and fieldobservations should be provided to allowtechnical reviewers to evaluate reliability ofdata, interpretations, and conclusions.Darcy’s Law and measured orconservative (protective) estimates of aquiferproperties and ground-water flow paths can beused to estimate the distance and directionwastewater could travel in 250 days. Mostpathogens found in wastewater die within 250days. The equation for ground-water seepagevelocity (Fetter, 1980), assuming laminar flow,is as follows:where:v s = (K/n e )(I)v s = seepage velocity (length/time),K = hydraulic conductivity (length/time),n e = effective porosity (dimensionless),I = hydraulic gradient (dh/dl =length/length = dimensionless).Measured aquifer properties should be usedwhen possible. If not available, ranges ofvalues for hydraulic conductivity and effectiveporosity are published in hydrogeologytextbooks and journals, and appropriatevalues may be used to calculate ground-watervelocity where site-specific values areunavailable. As a conservative approach, werecommend assuming an instantaneous traveltime downward to the regional water table,and then using the hydraulic gradient of theaquifer for the time-of-travel calculation.Hydraulic gradients may be estimated fromwater levels in wells completed in the aquifer.Similarly, ground-water flow available formixing (not including water in effluent) can becalculated using the following equation:where:Q=TLIQ= volume of water in aquifer belowsubdivision available for mixing (in mixingzone),T= transmissivity (length 2 /time),L= length of flow through aquifer parallelto hydraulic gradient, andI= hydraulic gradient (dimensionless).REVIEW OF REPORTSReports that conclude a site is suitablefor alternative wastewater disposal systemsshould undergo a technical review by ahydrogeologist and soil expert to determine ifthe scope of work was sufficient and if theconclusions and recommendations are valid.Prior to a technical review, the Weber-MorganDistrict Heath Department will perform


10 Utah Geological Surveyindependent soil studies and shallow groundwater-levelmonitoring. Prior to technicalreview by a hydrogeologist and soil expert,Weber-Morgan District Health Departmentofficials should also perform a preliminaryadministrative compliance review to determineif the report is complete and a technical reviewis necessary. The preliminary administrativecompliance review should determine that thereport:(1) concludes the site is suitable;(2) documents percolation between 1and 60 minutes/inch (5 and 60minutes/inch for Ogden Canyon andOgden Valley);(3) contains a site-location map on atopographic base at a scale of 1:24,000or larger showing water wells, if any, inthe area;(4) contains a site map or maps on atopographic base at an appropriate scaleshowing the location(s) of the proposedalternative wastewater disposalsystem(s) and percolation-rate test pit(s);(5) describes site geology and includes ageologic map;(6) describes hydrologic conditions of thesite; and(7) identifies the professionals(s)performing the evaluation.REFERENCESAnderson, P.B., Susong, D.D., Wold, S.R.,Heilweil, V.M., and Baskin, R.L., 1994,Hydrogeology of recharge areas andwater quality of the principal aquifersalong the Wasatch Front and adjacentareas, Utah: U.S. Geological SurveyWater Resources Investigations Report93-4221, 74 p.Fetter, C.W., Jr., 1980, Applied hydrogeology:Columbus, Ohio, Merrill PublishingCompany, 488 p.Snyder, N.P., and Lowe, Mike, 1998, Map ofrecharge areas for the principal valley-fillaquifer, Ogden Valley, Weber County,Utah: Utah Geological Survey Map 176,16 p., 1 pl., scale 1:75,000.Utah Section of the Association of EngineeringGeologists, 1986, Guidelines forpreparing engineering geologic reports inUtah: Utah Geological and MineralSurvey Miscellaneous Publication M, 2 p.Wallace, Janae, and Lowe, Mike, 1998, Thepotential impact of septic tank soilabsorptionsystems on water quality inthe principal valley-fill aquifer, OgdenValley, Weber County, Utah -assessment and guidelines: UtahGeological Survey Report of Investigation237, 11 p.The technical review of the report will beconducted by a hydrogeologist and soil expertwho are members of the Weber CountyWastewater Advisory Committee.

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