Septic Tank Design Concept

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State of KansasDepartment of Healthand EnvironmentBulletin 4-2, March 1997

MINIMUM STANDARDSFOR DESIGN ANDCONSTRUCTION OF ONSITEWASTEWATER SYSTEMS

Bureau of WaterNonpoint Source SectionForbes Field, Bldg. 283Topeka KS 66620(785) 296-4195

In Cooperation withK-State Research and Extension


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Table of ContentsIntrod uction ........................................................................ 1Wastewater Flows ................................................................ 2Site and Soil Evaluation ...................................................... 2Sept ic Tank .......................................................................... 6

Septic Tank Design/ Construct ion Specification s .............. 7Septic Tank Placement Specification s ................................ 9Absor pt ion Field Size ........................................................ 10Absorp tion Field Material Specification s ......................... 12Field Construction Specificat ions .................................... 13Maint ainin g On site Wastewater Systems ......................... 13Waste Stab ilizatio n Ponds ................................................. 13Alternative Systems Guidelines ........................................ 14Appen dix A Conduct ing a Perc Test ................................. 14Appen dix B Sou rces of Addit ional Informat ion .............. 16KDHE District Boundaries and

District Offices ................................. Inside back cover

Tables

1 Soil Limitation Ratings Used by NRCSfor Wastewater Absorp tion Fields .............................. 2

2 Design Septic Tank Effluent Loading Rates forVarious Soil Textu res and Structu res ........................ 3

3 Recommended Absorption Reductions... .. .. .. .. .. .. . .. .. . 44 Soil Absorption Field Loading Rate

and Area Recom mend ation for Sept ic Tank Effluen t Based on Perc ............................................... 4

5 Minimum Required and MinimumRecommended Separation Distancesfor On site Wastewater Systems .................................. 4

6 General Alternative Option Guidefor Moderate or Severe Limit ingSoil Condit ions .......................................................... 5

7 Minimum and Recommended SepticTank Capacities Based on theNumb er of Household Bedroom s ............................. 6

8 Trench Separation Distances ....................................11

Figures

1 Compartmen talized Septic Tank ............................... 62 Design Details for a Precast,

Concrete Septic Tank ................................................. 73 Septic System Reference Sketch ................................ 84 Typical Step Down or Serial

Distribu tion System ................................................. 105 Standard Lateral Trench Design ............................... 11


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IntroductionKansas Administrative Regulations (K.A.R. 28-5-6 to

9) auth orize the Kansas Departmen t of Health and Envi-ronment (KDHE) to establish minimum standards forseptic t an klatera l fields. KDHE bulletin 4-2: Min im umStandards for Design and Construction of Onsite Wastewa-ter Systems fulfills that purp ose. The minimu m standardspresented in th is document are intended to ensure do-mestic wastewater is managed so that:

Qualit y of surface and grou ndwater is protected fordrinkin g water, recreation, aqu atic life supp ort, irri-gation , and ind ustrial uses.A breedin g place or h abitat will not b e created forinsects, roden ts, and ot her vectors that may latercontact food, p eople, pets, or drin king water.Wastewater will not b e exposed on the grou nd su r-face where it can be contacted by children and/orpets, creatin g a significant health hazard.State and federal laws and local regu lations governingwater po llution or wastewater disposal will be met.Nuisance conditions or obnoxious odors and un -sightliness will be avoided.

Bulletin 4-2 is not intended to provide an in-depthdiscussion o f the ration ale for th ese standards. For m oreinformation, see the Environm ent al Healt h Handbook an dresources identified therein as well as other references inAppen dix B (page 16). Most coun ty health d epartmen tshave a copy of th is handb ook, o r copies are available atcost from Kansas State University, Extension Biologicaland Agricultural Engineering (see Appendix B).

Local governments have the authority to adopt mini-mum requirements (codes) for onsite wastewater man-agemen t systems, to app rove individu al plans, to issuepermits for construction, to issue permits for operation,and to grant variances. County sanitary (environmental)codes specify local design and permitting requirements.Compliance with these requirements helps preventillness caused by environmental contamination andprotects surface and groun dwater.

So m e lo ca l r eq u i r emen t s , su ch a s t h o se i nw e ll h e a d p r o t e ct i o n o r s e n si t i ve g r o u n d w a t e ra r e a s , m a y b e m o r e st r i n g en t t h a n t h o se est a b -l i sh ed i n Bu l l e t i n 4 -2 . Of t en , t h e se s t r i c t e r r e -q u i r e m e n t s p r o v id e g r e a t e r p r o t e c t i o n o f p u b l ich e a l t h a n d t h e e n v i r o n m e n t , esp e ci a ll y w h e r ew a t e r r e so u r c es a r e v u l n e r a b l e t o co n t a m i n a t i o n .

Sanitary codes are adopted and administered bylocal governmen t usually through count y health depart-ments. The local administering authority should alwaysbe contacted before any time or money is invested insystem d esign, plan s, installation , or repairs.

If there is no local code, landown ers are required tocomply with Kansas Administrative Regulations(K.A.R.) 28-5-6 to 9 and minimum standards in thisbulletin. If no assistance is available from the healthdepartment or other local authority, contact yourcounty Extension Office or KDHE, Bureau of Water,phon e (785) 296-4195, o r th e n earest KDHE District

Office

(see in side back cover).K.A.R. 28-5-6 stip ulates th at all do mest ic wastewatershall be d ischarged to an appro ved sewage collectionsystem o r an ap proved lagoon , septic system, o r alterna-tive system. Domestic wastewater mean s all waterborn ewastes produced at family dwellings in con nect ion withordinary living including kitchen, toilet, laundry,shower, and bath tub wastewater. It also includes similartype wastewater, pro duced at businesses, chu rches,indu strial, and commercial facilities or establishm ents.

Wastewater from a hom e shall be d ischarged to aproperly designed and maintained septic tanksoil ab-sorption field or wastewater pond, an approved alterna-

tive treatment and disposal system, or a permittedsewage treatment plant. Seepage pits, cesspools, and drywells (rat holes) are not permitted. This bulletin pro-vides information on conventional soil absorption fields,wastewater pond s, and altern atives that may be consid-ered when conventional absorption fields or ponds arenot suitable.

Bulletin 4-2 covers five basic elements of properseptic t ankla teral field system design:

1. wastewater flow,2. soil and site evaluation,3. septic tank standards, for design, construction and

installation,4. lateral field design and construction, and5. system maintenance.

This bulletin also addresses basic principles for waste-water p onds.

This bulletin is intended to provide information ontreatment of domestic wastewater. Domestic wastewaterexcludes surface run off from roof, paved areas, or oth ersurfaces; subsurface drainage from springs, foundat iondrains, and sump pump; or cooling water. Industrial orcomm ercial wastewater (from shops, man ufacturin g, carwashes, etc.) is not p ermit ted to be discharged to anonsite soil absorption system, so it shall not be mixedwith domestic wastewater.

By following the standards established in Bulletin4-2 and your countys sanitary code, you actively con-tribute to p rotecting the environment and qu alityof life for your family, your neighbors, your community,and other Kansan s. You r cont ribution is appreciated!


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Wastewater FlowsOne major concern in the design of household

wastewater systems is the quantity of wastewater gener-ated daily. The system mu st have enou gh capacity toaccommodate and treat this total flow. Normal contribu-tions to this flow will come from bathroom, kitchen,and laundr y facilities. Kansas regulation s require th at alldomestic wastewater be treated and disposed thro ughthe on site system. Surface runo ff from roofs and p avedareas, subsurface drainage from footing drains and sumppu mp s and coolin g water are not domestic wastewaterand must be excluded from soil absorption systems.Such water may be used to help maintain the operatingwater level in wastewater ponds.

Design flow is estimated by multiplying the numberof household bedrooms by 150 gallons per day (gpd).This is based on 75 gallons per person per day for twopeople in each b edroom 1. This accoun ts for the n um berof people that can occupy the home for extendedperiods rather than how many actually live there whenthe system is in stalled. Hou ses frequen tly experience achange in ownership or occupancy over the life of thewastewater system. When calculating wastewater flow,no te th at a water soften er may increase water use by asmuch as 10 gallon s per capita per day or p ossibly morewhere water is very hard.

Site and Soil EvaluationAlthough the septic tank is important for removing

solids from the wastewater, more of the wastewatertreatment is provided b y the soil. Microorganisms livingin th e soil profile feed on o rganic matter in the waste-water, treatin g and pu rifying th e water as they grow.Four feet of aerated soil below the bottom of the absorp-tion field is necessary to ensure adequate treatment of the wastewater before it reaches the water table or flowslaterally due to a restrictive condition .

In sandy soil, it is recommended that as muchvertical separation as possible be provided. An und er-standin g of the soil is necessary to assess the ability of the site to provide good wastewater treatment. Soil mu stabsorb th e septic tank effluent , treat the wastewater, andtransm it treated wastewater away from the soil absorp-tion areas.

The site evaluation begins b y reviewing availableinformation such as a published soil survey and thenevaluating the soil on site. County soil survey reportsare usu ally available from the local Natu ral ResourceConservation Service (NRCS, formerly Soil ConservationService). Contact you r local NRCS office, cou nt y conser-vation district or Extension office for a copy of the report.

The soil survey provides general information andserves as a guide to t he soil cond ition s. Sites characterizedby slow permeability, restrictive subsoil layer, shallow soilover rock, high groundwater, poor drainage, or steepslopes, as iden tified in the soil survey, have moderate to

TABLE 1Soil Lim it ati on Ratin gs Used b y NRCS For Wastewater Absor pt ion Fields

LIMITS

Propert y Sligh t Moderate Severe Restrict ion or Feat u re

USDA Texture Ice Permafrost (not found in Kan sas)

Flooding None, Protected Rare Com mon Flood water in undates site

Depth to Bedrock (in.) >2 72 4072 72 4072 < 4 0 Red uces water an d air movem en t

Depth to H igh Water Table, > 6 46 < 4 Sat urated soil, poor aerat ion ,

(ft. below surface) anaerobic soil, restricted movement

Permeability, (in./hr.)2460 in . la yers 2.06.0 0.62.0 < 0.6 Slow p erc rate, p oo r d rain ageless th an 24 in . layers > 6.0 Poor filter

Slope, (percent) 08 815 > 15 Difficu lt to con struct an d h old in place

Large ston es greater th an 3 in ., < 25 2550 > 5 0 Restricted water an d air m ovem en t(percent by wt.) results in reduced treatment capacit y

1The 150 gallons per bedroom, or 75 gallons of wastewater produced daily by each person, assumes at least some water using appliances such as clotheswasher, dishwasher, water softener, etc.2> means greater than3< means less than


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severe restrict ions for convent ional septic tan ksoilabsorption systems and o ther option s may be preferred orrequired.

A site and soil evaluation shou ld be completed inorder to locate the area to be used for the absorptionfield, to verify t he soil ch aracteristics, and to size thesystem. Areas with slopes steeper than abou t 20 p ercent

will cause considerable difficulty du ring con structionand are not recommended for lateral field installations.Rock ou tcropp ings warn of shallow soils and maysuggest the probable direction of grou ndwater flow. Therange of values for each of several prop erties that cau sethe soil to be placed in slight, mo derate, and severelimitation rating for soil absorp tion systems is shownon Table 1.

The wastewater system area should be cho sen priorto any construction on a site and shou ld be an integralpart o f the hom esite design and development . A soilprofile analysis is highly recommended to ensuresuitability of the area and to establish the loadin g rate

so th at adequate space is available for the ab sorpt ionfield and its replacement.

To perform a soil profile analysis, an excavator isusually used to open a pit, which exposes the soilprofile. The soil evaluation , performed b y a trained an dqu alified person 4, includes examin ing th e soil profile,determining the soil texture, structure, color, consis-tence, measuring soil depth, and looking for evidenceof a high or perched water table or other restrictions.

The soil profile should be an alyzed to a depth of at least4 feet below the bot tom of the absorpt ion area or atleast 6 feet below the surface.

Because OSHA regulation s requ ire shorin g fortrenches deeper than 5 feet for some soils, it is recom-mended th at the pit be constructed so a person is no trequired to go deeper. Soil below 5 feet can be examinedfrom cut tings, observation from a distance, and byshovel or auger without entering a deeper pit.

At least th ree pits should be dug surrou nding th earea to establish the range of soil characteristics that arepresent on the site, and to determine the b est locationfor the absorpt ion field. Sanitarians, usually thro ugh local

health or environmental departments, or environmentalhealth specialists, are available to assist in the site and soil

TABLE 2Design Sep tic Tank Eff luen t Loadin g Rates for Vario us Soil Textu res an d Struct ur es

Wastewater Loadin gGroup Soil Ch aracterist ics (in / day) (cm / day) (gpd / ft 2)

I. Gravelly coarse sand and coarser. Not Recommended for convent ion al soil absorption system 5

II. Coarse sands (not cemented). 1.8 4.6 1.1

III. Medium sand with single grain structu re and loose tofriable con sistence (not cemented). 1.5 3.7 0.9

IV. Other sands and loamy sands with single grain or weak structu re (not extremely firm or cemen ted consistence). 1 2.5 0.6

Sandy loams, loams and silt loams with mo derate or strongstructure (except platy and loose to friable consistence).

V. Sandy loams, silt loams and loams with weak structure(not of extremely firm or cemented consistence). 0.7 1.7 0.4

Sandy clay loams, clay loams and silty clay loams with moderateto stron g structure (n ot o f platy, of firm, o r of cemented con sistence).

VI. Sandy clay loams, clay loams and silty clay loam s with weak structu re (not massive, not of firm , or of cemented consistence.) 0.4 1 0.25

Some sandy clays, clays and silty clays with moderate and strongstructure (n ot platy, not of firm, or of cemented con sistence).

VII. Other soils of h igh clay con ten t with weak or massive struct ure, Not Recom mended for conven tion alextremely firm or cemented consistence or platy, clay pan , soil absorption system 6

fragipan, and caliche soils.

NOTE: The above descriptions are estimates and assume that the soil does not have large amounts of swelling clays. Soils withplaty structu re, massive, comp acted or h igh den sity should b e used with extreme caution or avoided.4 A t rained an d qu alif ied person w ould include a soil scient ist, such a s one workin g for NRCS, environm ent al h ealth specialist, san itari an, or oth er personwho has received appropriate soil training and through experience is competent .5Soil is too coarse for conven t ional soil absorption d esigns, use pressure dist ribut ion dosing or other alternat ive system to prevent too rapid inf iltrat ion.6 Soils wit h these cond it ions may be acceptable for wastewater stabilizat ion ponds or possibly other alternat ive systems. (See Table 6).


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evaluations. A few consultants, either engineers or design/ installation contractors, also provide this service.

Table 2 gives the recommended loading rates basedon soil texture, structure, and consistence information.These loading rates are based o n research that h as shownthat soil characteristics provide a strong basis for waste-water system design loading rate. Results show system

design should be based on the most limiting soil textu refound in the first 4 feet of soil below the bottom of theproposed absorption lateral.

Once the wastewater flow (num ber of bedrooms) andloading rate for the soil are known, th e absorption fieldarea needed for the lateral system can be calculated. It ishighly recommended that the absorption field and anequal area reserved for fu tu re use be marked and fenced sothey will not b e disturbed du ring construction. Requiredsetback distances to property lines, wells, surface water, andbuildings mu st be checked and included in the site plan.

Where evaporation substantially exceeds precipitation ,as in central and western Kansas, a reduction in soil

absorption area may be used when th e soil is well suited towastewater absorption. A well suited soil has medium tocoarse textu re, perc rates less than 45 minutes per inch and

TABLE 4Soil Abso r pt ion Field Load in g Rate and AreaRecomm endation for Septic Tan k Effluent Based on Perc

Recomm endedPerc Rate Absor pt ion Area Loadin g Rate

(m in u tes/ inch ) (ft 2 / bed ro om ) (gp d / ft 2)

Less than 5 minutes Not recommended for convent ionalsoil absorption system 5

510 minutes 165 0.91

111 5 minutes 190 0.79

1630 m inut es 250 0.6

314 5 minutes 300 0.5

4660 min ut es 330 0.45

Greater th an 6 0 m in u tes No t reco m men ded fo rconvention al soil absorpt ion system 6

TABLE 5Minim um Requir ed an d Minim um Recom men ded Separat ion Distan ces for On site Wastewater Systems

Minimum Distance (ft.)

Separat ion Distances Requ ired Recom mended 7

Sept ic Tank to foundat ion of house or other bu ildin gs 10 10

Soil Absorpt ion System to dwellin g foundat ion 20 50

Any p art o f a wastewater system t o:

public potable water lin e 25 8 25private potable water line 10 25property line 10 50public water supply well or suct ion lin e 100 9 20 0private water supply well or suction lin e 50 9 100surface water course 50 100

Wastewater Lagoon s to :property line 50 10 20 0dwelling foundat ion 50 10 20 0

wastewater loading rates of 0.5 gallons per square foot perday or more. For marginal, high clay, soil that has lowloading rates, no reduct ion should be u sed regardless of location in Kansas. Recommended allowable soil absorp-tion system reductions and percent of total absorpt ion areafor central and western Kansas is shown on Table 3.

Since about 1970 considerable research about onsite

wastewater systems has occurred. New information,including design p rocedures, operating characteristics, andmany new products, has been and continues to be devel-oped to help improve onsite wastewater systems.

The soil profile evaluation provides a comprehensiveassessment of soil characteristics and is the preferred

5Soil is too coarse for conven t ional soil absorption d esigns, use pressure dist ribut ion dosing or other alternat ive system to prevent too rapid inf iltrat ion.6 Soils wit h these cond it ions may be acceptable for wastewater stabilizat ion ponds or possibly other alternat ive systems. (See Table 6).7 Th ese recom mend ed separation distances help assure a min im um of problems, but are no assurance th at problems w ill not result .8 Th e m inim um distance specified by K DHE guidelines for public water supplies9The minimum distance required by KAR 28-30-8(a).10W hen lot dim ension, topography , or soil condition m ake main tainin g the required 50 feet separation distance impossible, a w ritt en variance from th eaffected property ow ners shall be obtained and f iled with deeds.

TABLE 3Recom men ded Absor pt ion Reduct ion s

Western Cen tral EasternKan sas Kan sas Kan sas

Actu al absorpt ionarea (in percent) 65 80 100

Recommendedreduct ion (in percent) 35 20 0


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method for determinin g the suitability of the soil to acceptand treat wastewater and establish the design loading.

Some local sanitary cod es require the p erc test andother codes require both a perc test and a soil profileevaluation . Perc is short for percolation and h asbecome the preferred term for this test to evaluate soilsuitability to accept wastewater. Percolation means water

movement through a soil. Since the driving force isgravity, most of th e mo vement will be down ward. Theperc test really measures an infiltration rate for waterinto a wet but unsaturated soil at the depth of expectedsystem placement. The procedu re for doing a perc test isdescribed in Appendix A (page 14). Once the perc rate isknown , refer to Table 4 to determ ine th e loading rateand absorption field area, or use another metho dspecified by the local sanitary co de.

Separation o f the soil absorpt ion field from buildings,structu res, and boundaries is essent ial to maint ain system

performance, to permit repairs, to maintain requiredseparation from wells, and to reduce undesirable effects of underground wastewater flow and dispersion. The struc-tu res and bou ndaries to consider include easements,buildings, property lines, utilities, wells, and com pon entsof the wastewater disposal system. Minimum required andrecommended separation distances for private wastewater

systems are given in Table 5.Many soils, especially in eastern Kansas, have proper-ties that restrict their suitability for soil absorption fields.When limiting prop erties occur in th e soil profile, avariation of conventional laterals, wastewater ponds oralternative treatment systems may be used to compen satefor the limiting cond ition. Variations and alternatives thatmay be considered are summarized in Table 6. Whenpossible, sites with these restrictive conditions should beavoided due to higher cost, larger land area, and greatermaintenance requirements for the alternative systems.

TABLE 6Genera l Altern ative Option Guide for Mod erate or Severe Limit in g Soil Cond ition s

I. Shallow Permanent, Perched or Seasonal Groundwater Subsu rface drainage system at least 50 feet from t he soil absorp tion area to lower the water tablesuit able for m od erate

or m ore p ermeable soil condit ions. This alternative creates drainage that mu st be d ischarged away from the area Variation o f conven tion al lateral trench

- Sha llow in-groun d tren chsuit able for gro un dwater at 4 3 4 feet or deeper- At-grade lateral systemsuit able for gro un dwater at 4 feet or deep er

Enhanced wastewater treatment 11 by ro ckp lant filter 12, sand filter 13, or aerated tan k 14 or other equivalent system 15followed by shallow soil absorpt ion or wastewater p ond

Wisconsin (en gineered) mo und suit able for grou ndwater or o ther restriction at 1 foot or deep er Rockplan t filter 12suit able for gro un d water at 1 foot or d eeper followed by soil absor pt ion

II. Shallow Bedrock Wastewater po nd suit able for sites with bed rock at an y dept h wh en o verexcavated an d at least 1 1 2 feet of com pacted clay

lining is installed

Variation o f conven tion al lateral trench- Shallow in-ground trench systemsuit able for b edrock at 4 3 4 feet or deeper- At-grade lateral systemsuit able for be dro ck at 4 feet or d eeper

Enhanced wastewater treatment 11 opt ions (see I above) followed b y shallow soil absorption Wisconsin (en gineered) mo und suit able for bedro ck at 1 foot or d eeper

III. Rapid Perc Rate ( < 5 m pi) or very permeable soil ( > 20 in/hr) Pressurized distribut ion do sing system to un iform ly distribute wastewater thro ugho ut the absorpt ion field On e foot linin g using loam soil to botto m and sides of the trench to limit water absorption rate

IV. Slow Perc Rate (60 to 120 mpi) or slow soil permeability (0.20.6 in/h r) Dual shallow lateral systems in permeable surface soils (each with 60% to 80% of conventional lateral area) with a diversion

valve and alternatin g use of systems Wastewater pond provided sufficient site area is available to meet all setback requirements Wisconsin (en gineer ed) mo un dsuit able for n early level sites with m ore per meable surface soil Enhanced wastewater treatment 11 opt ions (see I above) followed by sh allow soil absorption into permeable surface soil

V. Very Slow Perc Rate Soil ( > 120 m pi), very slow soil permeability ( < 0 .2 in/h r) Wastewater pon dsuit able for sites with en ou gh site area to meet all setback requ iremen ts Wisconsin (en gineer ed) mo un dsuit able for level sites with perm eable surface soil Enhanced wastewater treatment 11 opt ions (see I above) followed by sh allow soil absorption into permeable surface soil

11 Enhanced t reatm ent is higher qua lity than septic t ank eff luen t and m ay be equiv alent to secondary treatm ent in w astewat er treatment term inology, or insome cases even h igher qual ity, comparable to advanced wastewat er treatm ent 12 Rockplan t f ilter provides a higher level of treatm ent th an sept ic tanks. Due t o higher qua lity ef f luen t, th e soil absorption f ield size m ay be sm aller th an f or a conventional absorption field system.13Sand filters provide a very high level of treatment. Due to this high quality effluent, the soil absorption field may be smaller than that required for aconventional absorption field.14 Aerobic tan ks have poor operating records so an operating/m aint enance agreemen t w ith a reliable supplier is strongly recomm ended to en sure system

performance.15Promising technology is underdevelopment that may meet enhanced treatment requirements.


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TABLE 7Minimum and Recommended Septic Tank Capaci-ties Based on th e Num ber of Household Bedro om s. 16

Numb er of Bedrooms Septic Tank Capacity (gallons) 17

150 gpd/ bed room Min im u m Recom mended13 1,000 18 1,350

4 1,200 1,800

5 1,500 2,250

Figure 1Comp artm entalized Septic Tan k

OUTLET

LIQUID LEVELLIQUID LEVEL

SLUDGE

SCUM

VENT

INLET

ACCESS MANHOLES

GAS DEFLECTOR

Septic TankThe septic t ank separates the settleable and f loatable

solids, contains an anaerobic environment wherebacteria part ially decompo se the solids, and p rovidesstorage for the accum ulated sludge and scum. The septictank is sized so that wastewater flow through the tank takes at least 24 hours even with sludge and scumaccumu lation. This detention time p ermits the settlingof solids heavier than water and allows scum, grease andoth er materials lighter th an water to float to th e surfacebefore the water is discharged to the absorption field.

Septic tanks are designed to h andle all the daily flowa hou sehold will normally produce and m ust have suffi-cient capacity for the minimum recommended volume of at least two times the d aily wastewater flow. Larger capacitytanks usually mean less carryover of solids, resulting inprolonged life of the soil absorption field. Larger tanksrequire less frequent cleaning and allow for fut ure expan-sion of the home or times when guests visit. They also havea good cost-benefit retu rn. Table 7 gives min imum andrecommended capacities for sizing septic tanks.

Less solids exiting the septic tank helps extend the lifeof the soil absorption field because less clogging of the soilpores will occur. Septic tank effluent filters are effective inreducing solids and providing an added measure of protection for the soil absorpt ion field so their use ishighly recommended.

Two com partment tanks or two tanks in series alsomay help. If a mult iple comp artment tank is used, the firstcompartment shall be sized to contain from one-half totwo-thirds of the tot al tank capacity. The total tan k capacity is important and should be sized to retain at leasttwo-to-three times the total daily wastewater flow as shownin Table 7. Figure 1 shows a design concept for a two

compartment septic tank.Tanks shall never be closer th an 50 feet from anywater supply and greater distances are preferred if possible.However, a 100-foot separation is required if the watersource serves a public water supply. The septic tan k shallnot be located closer than 10 feet from any building, inswampy areas, or in areas located within the 100 year floodplain. Table 5 gives minimum required and recommend edseparation distances for on site wastewater systems.

There shall be no perman ent structure (patio, building,driveway, etc.) over the tank, lateral or other part of anonsite wastewater system. Consideration should alsoinclude easy access of trucks and equipmen t for pum ping,

maintenance, and repair. To avoid damage to the system,heavy equipment should not have to cross any portionof the wastewater system when servicing the septic tank.

A sketch of the wastewater disposal system as con -structed, showing measurements should be made anddelivered to th e homeowner for future reference, andfiled with the permit at the county health department.Figure 3 shows an example septic system reference sketch.

Septic tan ks and soil absorption systems are anexpensive and long-term investment. Material selection,design, and con struction should be don e with long life inmind . When located in suitable soil, well designed, p rop-erly constructed, and adequately maintained, th ey shou ldlast several decades.

All abandoned or unused septic tanks, cesspools,seepage pits or other h oles that h ave received waste-water shall be emptied and plugged following proce-dures described in K-State Research and Extensionbulletin MF-2246.

16 For each addit ional bedroom, add 30 0 gallons to the m inim um value and 450 gallons to th e recom mend ed value.17 Volume held by the tank below the liquid level (invert of the outlet pipe).18 Min im um tan k size is 1 ,000 gallons.


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19W here locally available product s cannot presently m eet th ese requirement s, man ufactu rers will have u nt il July 1 , 2002 to comply.20 If t ank is deeper than 12" add exten sion riser as shown so top of riser is no m ore th an 12 " from surface

Septic Tank Design/ConstructionSpecifications 19

General RequirementsFigure 2 shows the dimensions included in this

section for a ty pical precast concrete septic tan k. Thefollowing factors are requ ired of all septic tan ks regard-less of the con struction material:

A. The septic tank including all extensions to thesurface shall be watertight to prevent leakage into orout of the tank. It shall be structurally sound andmade of materials resistant to corro sion from soiland acids pro duced from septic t ank gasses. Becauseof corrosion, steel tan ks are not acceptable.

B. The tank liquid depth (distance from ou tlet invert tobottom of tank) shall be at least 3 feet but shall notexceed 6 1 2 feet. The effective inside length of tan ksshall not be less than 1.5 nor greater than four t imesthe effective inside width .

C. The minimu m septic tank capacity is two timesthe daily wastewater flow using 150 gallons perbedro om or 1 ,000 gallons, whichever is larger. SeeTable 7 for min imu m tan k sizes. Tanks sized at th reetimes daily flow are recommended and shall berequired when garbage disposals are u sed.

D. The top of all tanks shall be designed and con-

structed to suppo rt a minimu m u niform load of 400 pou nds per square foot plus 2,500 pou nd axleload. When buried mo re than 2 feet deep, the tank,especially the top, shall support an additional100 pounds per square foot for each foot of soil orport ion th ereof in excess of 2 feet.

E. If the tan k is placed in an area subject to any vehicu-lar traffic it shall be cert ified to meet H-20 h ighwayloading by a Kansas licensed struct ural en gineer.

F. Space above the liquid line is required for thatportion of the scum that floats above the liquid.For vertical sidewall tanks, the distance b etween thetop of the tan k and the ou tlet invert should be at

least 15 percent o f the liquid d epth with a min imumFigur e 2Design Det ails for a Precast Concr ete Septic Tank

k

b

he

f

d

w

l

g

m

yn

a

x

x

c

Name Measu remen t Min . Max.

a. access manhole smallest dimension 20" b. in let baffle penetrat ion 8" 0.2 dc. cover 20 surface to manhole surface 12"d. liquid depth outlet to tank bot tom 3' 6 1 2'e. difference in let to outlet inverts 3" 4"f. outlet baffle outlet to bot tom 0.35 d .g. th ickn ess wall 2 1 2"

Name Measu remen t Min . Max

h . open space outlet invert to top 7" 0.15 dk. space gap 1" l. tank length inside of walls 6' 4 w

m . rein forcement per en gin eerin g design as n eededn. extension riser length 20 to 1' from su rface gradew. tan kwidth inside of walls 4'x. in spect ion riser inside diameter 6"y. locat ion riser inside diameter 1 1 2"


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Figur e 3Sept ic System Referen ce Sketch

of 7 inches. In ho rizontal, cylindrical tan ks, an areaequal to approxim ately 12 1 2 percent of the totalvolume sho uld b e provided above the liquid level.This condition is met if the space above the liquidlevel (distance from outlet invert to top of tank) is15 percent of the tank diameter .

G. Sewage lines carrying solids from the source to th e

tan k should h ave sufficient slope to main tainvelocities that keep solids moving. For householdsize lines, a slope o f between 1 percent ( 1 8 inch perfoot) and 2 percent ( 1 4 inch per foot) is usuallybest. The last 15 feet of sewer line preceding thetank shall not slope more th an 2 percent ( 1 4 inchper foot).

H. The inlet and outlet baffle or tee and compartmentbaffle shou ld extend above the liquid level to on einch below the top of the tank. This space at the topof the t ank is essent ial to allow gas to escape fromthe tank th rough the house stack vent.

I. The invert of the inlet pipe shall be located at least

3 inches above the invert of the outlet when the tank is level. This space allows for temporary rise inliquid level durin g discharges to the tan k, andprevents liquid from standing in the sewer linebetween the hou se and th e septic tank, which maycause stopp age or backup .

J. The septic tank or pu mping tank inlet shall be asanitary tee, elbow or long sweep elbow with low headinlet or baffle to direct incoming sewage downwardand prevent flow from distu rbing the floating scumlayer. It should extend at least 8 inches below the liquidlevel, but shou ld not penetrate deeper than 20 percentof the liquid depth.

K. The out let tee or baffle prevents scum from beingcarried out with effluent, but limits the depth of sludge that can b e accommod ated. The ou tlet device

should generally extend below the liquid surface adistance equal to 35 percent of the liquid depth. Forhorizontal, cylindrical tanks, th is distance shou ld bereduced to 30 percent of liquid depth.

Example: Horizontal cylindrical tank 60 inchesin d iameter, liquid depth = 52 inches, outlet teepen etrates 52 .30 = 15.6 inches below liquid level.

L. Inlet and outlet openin gs shall be designed andconstructed to be water tight for at least a 20 -yearlife of the system.

M. The dividing baffle in two comp artment tan ksshall extend from th e bottom of the tank to at least6 inches above the liquid line. The open ing in thedividing baffle may be any shape and shall be at least2 inches minimu m d imension with a tot al area of atleast 12 square inches. The baffle opening is to becentered 35 percent o f liquid depth (30 percent forcylindrical tanks) below th e liquid level.

N. Septic tanks shall have an access manhole with20 inches min imum dimension for each comp art-

ment. If the manh ole does not extend to surfacegrade, a small diameter (at least 1 1 2 inch d iameter)pipe shall extend to surface from the cover to mark the location of the manhole. This pipe shall notpenetrate th e lid of th e tan k. Inspection risers at least6 inch diameter shall extend to surface grade centeredover the in let and outlet tees. All below grade att ach-ments to the t ank, conn ections, riser, extensions andlid shall be water tight. When any opening largerthan 8 inches extends to the surface, that op eningshall be child and tamper resistant. Ways to accom-plish th is include lids weighing at least 65 pou nds,locks, or anchors th at are not removable withou tspecial tools .

O. The sewer line from the house to the tank, allfitt ings and pipe in t he tank, all extensions to the

SepticTank

HouseWaterWell

LateralLines

Not to Scale


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surface from the top of the tank and the first 10 feetexitin g the tan k shall be schedule 40 pipe o r heavier.

P. Septic tan ks shall be designed for at least a 20-yearlife. They shall be designed an d con structed towithstand extremes in loads result ing from adverseconditions without excessive deflection, deforming,creep, cracking or breaking. Change in shape shall

be limited t o 5 p ercent. Loads shall be based on 62.4pou nds per cubic foot for water and water satu ratedsoil. Top loads for d esign shall be in un iform 400pound s per square foot plus 2,500 pou nd axle pointload. Design shall be based on a 2 foot placementdepth to top of the tank. If the tank will be placeddeeper th an 2 feet or subject to vehicular traffic overthe tan k, a design by Kansas licensed structu ralengineer shall be done for the specific conditions.

Special Considerations for Concrete TanksThe anaerobic environment of a septic tank pro-

duces gases that combine with moisture to produce

acids. Concrete above the liquid level is subject tocorrosion and deterioration from these acids. Thiscorrosion is best resisted by high quality concrete mix.Concrete septic tan ks shall meet the following req uire-ments in addition to those above:

A. The concrete design mix shall be for a compressivestrength o f at least 4,000 pounds per square inch at 28day cure. The watercem ent ratio shall not exceed 0.45.

B. Baffles or other interior concrete units shall notbe u sed for precast or po ured in place concreteseptic tan ks unless they are cast or built into th etank wall at the time the tank is constructed.

C. Air entrainm ent additives shall be added t o

5 percent volume. Other chem ical admixtu resare encouraged to redu ce water conten t, imp rovecement placement in forms and wet handling of incompletely cured concrete.

D. Concrete tanks and lids shall receive proper careduring the hydration (h ardening) period by: 1)monitoring and controlling temperature of theconcrete and gradients (i.e. maintain 50 to 90 degreesFahren heit for convention al cure and u p to 140degrees Fahren heit un der low pressure steam cure.) 2)monitoring and controlling humidity to preventadverse moisture loss from fresh concrete (i.e. preventor replenish loss of essent ial moistu re durin g the earlyrelatively rapid stage of hydration .)

E. Reinforcing steel shall be placed as designed by aKansas licensed structural engineer to ensure floor,wall, and top do not crack from moisture, frost, soilload, water loads, axle loads, or other stresses. Loads asspecified above shall be used for the design condition.Reinforcing steel shall be covered by a m inimu m of 1inch of concrete and shall be placed within 1 4 inch.

F. Pouring the floor and walls of the septic tank at thesame time (monolithic pour) is the preferredconstruction procedu re. Very large tan ks are oftencast in 2 p ieces and assemb led in t he field. All tan ksshall meet the same structural strength standard asspecified earlier. Two piece tanks shall have perma-nently sealed structurally sound joints and shall

be water tested after assembly. A Kansas Licensedstructural engineer shall determine if the tan k meetsthe strength specification.

G. In areas of high sulfate water (greater th an250 mg/L) more acid producing gases are likelyand additional corrosion resistance is appropriate.Recommended measures include ASTM C150 Type IIcement (moderate sulfate resisting), ASTM C150Type V cement (highly sulfate resisting), or coatinginterior concrete surfaces above the water line.Coatings that provide additional protection of theconcrete include asphalt, coal tar, or epoxy. Theproduct used should be acid resistant and provide

a moist ure barrier coating for the concrete. Theproduct mu st not bleed into the water and th us risk groundwater contam ination.

H. Manufacturers are strongly urged to follow guide-lines and meet standards of American ConcreteInstit ute, Nation al Precast Con crete Association, andAmerican Society for Testing and Materials. Manu-facturers should identify and advertise their prod-ucts that meet applicable standards.

Special Considerations for Fiberglass,Fiberglass Reinforced Polyester,and Polyethylene Tanks

A. All tanks shall be sold and d elivered by the m anu-factu rer com pletely assemb led.

B. Tanks shall be structurally sound and supportexternal forces as specified above when empt y andinternal forces when full. Tanks shall no t deform orcreep resulting in deflection m ore than 5 percent inshape as a result of loads imposed.

C. Tanks and all below grade fittings and connectionsshall be water t ight.

Septic Tank PlacementSpecifications

A. Durin g the process of placing th e septic tan k, avoidcausing compaction in the absorption field by no tentering the absorption field area.

B. Where natu ral soil is not suitable tanks shall beplaced on a bed of at least 4 inch es of sand, peagravel, or crushed granu lar non corrosive material forprop er leveling and bearing. Material shall be n olarger than 2 inches in diameter and bed depth shallbe at least four t imes the largest material diameter.


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C. Access manh oles shou ld be at surface grade, butshall not be more than 12 inches below surfacegrade. Where top of the tank m ust be more th an 12inches below surface grade, a water t ight exten sioncollar shall be added as required t o raise the cover.Inspection openings placed over inlet and outlet teesor baffles shall be at least 6 in ches in d iameter and

extend to the surface to permit easy tank inspection,cleanin g of effluent filter, checking condition of teeor baffle and sludge accumulation.

D. Septic tanks should not be placed into the water table(including perched or seasonal water table) because of the tendency of the tank to float, especially whenempt y, as when pum ped for maintenance. In any areasubject to h igh water table or seasonally high watertable, plastic and fiberglass tanks shall no t be u sedunless precautions are taken to drain groundwater.

E. Septic tanks shall be water tight. An adequate test forwater tightness is to fill the tank with water and let itstand for 8 hou rs to allow concrete to absorb water and

plastic tanks to adjust. Then the tan k is topped off andan in itial measurement made with a hoo k gauge withvernier scale. After an hour, another measurement ismade. Any loss is cause to reject the tank. Observations

of the ou tside of the tank can also give clues aboutleakage losses. Any trickle, ooze, or exterior wet spot isreason to reject the tan k. Precast one piece tanks arebest tested at the plant before delivery. Two piece tanksthat are assembled on-site must be tested followingplacement but before back filling.

F. The hole that the tank is placed into shall provide

ample space around the tank for access to do com-paction . Backfill shall be in un iform , comp actedlayers not exceeding 2 feet thick and surroundingthe t ank. Because of p otent ial soil collapse, it isun safe and m ay be illegal for a person to en ter atrench deeper th an 5 feet without adequate shoring.Compaction should b e done from the surfacewithout entering trenches deeper than 5 feet.

Absorption Field SizeAbsorption field area is dependent on two factors:

wastewater flow and soil loading rate. The wastewaterdesign flow is based on the nu mb er of bedrooms

allowing 150 gpd per bedroom (75 gpd per person) asdiscussed previously. The wastewater flow assumes thehou se is fully occupied with t wo persons per bedroom.

Elevation contours

9 4 '

9 6 '

9 8 ' 1

0 0 '

2" 2"

Figure 4. Typical Step Down or Serial Distribution System


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Inspection pipe with removablenspection pipe with removablecoverover

Earth Backfillarth Backfill

Barrier Materialarrier Material

Ditribution pipeitribution pipe

Clean Rock 3/4" to 2" sizelean Rock 3/4 to 2 size

Anchor using Rebar ornchor using Rebar or Teee

Bottom of trenchottom of trench

Aerated soilerated soil

Groundwaterroundwater , bedrock, bedrock,impervious layer or othermpervious layer or otherrestrictionestriction

Inspection pipe with removablecover

Earth Backfill

Barrier Material

Distribution pipe

Clean Rock 3/4" to 2" size

Anchor using Rebar or Tee

Bottom of trench

Aerated soil

Groundwater, bedrock,impervious layer or otherrestriction

4 F T

. M I N

1 2 " M I N

6 " M I N 1 2 " M A X

6 " M I N

2 " M I N

Figur e 5St an da rd Lateral Tren ch Design

Table 8Trench Separ ation Distances

RecommendedTren ch Wid th Min im um Distance Between

(inches) Trench Cen terlin e (feet)182 4 8.0

2430 8.5

303 6 9.0

The site and soil evaluation previously discussed inth at section is essent ial for good design. The loading rateis determined from the soil profile using Table 2 or fromthe perc rate using Table 4 or by using another methodas specified in the local code. The soil absorpt ion area isobtain ed b y dividin g the wastewater flow in gallon s perday (gpd) by the loading rate (gpd per squ are foot (ft 2)).

The maximu m gravity lateral run shall not exceed 100feet and preferably should be less than 60 feet. If a lateralis supplied from the center, the total length shall notexceed 200 feet (100 feet to each side) and a maximum of 120 feet is preferred. Lateral systems on level sites with alllaterals on the same elevation shall be connected at eachend with a level manifold or conn ector pipes as shown inFigure 3 so there are no dead ends.

Loading rate exampleThe following example illustrates how to choose

and u se the loading rate for design: four-bedroom home Harney soil. Light silty clay loam with mediu m

subangular blocky structure at 17 to 40 inches greater than 6 feet to restrictions of rock or

perched water table perc rate 40 minutes per inch trench width 3 feet undisturbed soil width between trenches is 6 feet

Wastewater flowSize of house (number of bedrooms) flow rate (gpd)per bed room = total d aily wastewater product ion

4 bedrooms 150 gpd/bedroom = 600 gpd

Loading rateFrom soil evaluation Table 2 = 0.4 gpd/ft 2 and fromperc test using Table 4 = 0.5 gpd/ft 2

Use the smaller of these or 0.4 gpd /ft 2 for design.

Absorpt ion AreaWastewater flow loading rate = absorpt ion area

600 gpd=

600 ft 2= 1,500 f t 2____________________________________________ _________________________0.4 gpd/ft 2 0.4

Trench LengthAbsorption area trench width = length of trench

1,500 ft 2 = 500 lineal feet of trench length

3 feet

Field AreaOnly the bo ttom area of the trench is considered

in d etermining absorption area. The absorptiontrench width sho uld b e 18 to 36 inches, preferably 24inches. For 3 feet wide t renches as in th is example, thetot al lateral length need ed is 500 feet. If trenches are 2feet wide, the tot al lateral trench length is 750 feet.Assum ing th at a 3 feet wide tren ch will be used and100 feet is the length of each trench , 5 trenches, 100feet long will be needed for 1,500 ft 2 total trenchbot tom . To calculate the total area n ecessary for thefield, include the min imum 6 feet of undisturbed soilbet ween trenches. For th is example the to tal width is(5 3 ft) + (4 6 ft) = 15 ft + 24 ft = 39 feet The totalfield area is 39 100 or 3,900 ft 2. An area equal to this

same size should be reserved for fut ure expan sionand/or replacement.

For sites that slope more than about 1 percent, a levellateral system installed without shaping the surface oftenrequires more than a half foot difference in soil coverfrom one side of the area to the other. On slopes greaterthan 1 1 2 percent there is enou gh slope to u se a step down(or serial) distribution. This results in the top lateral


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being filled before effluent bu ilds up and flows to thenext lateral down slope. Step down or serial distributionas shown in Figure 4 is recommended for all sites thatslope 1 1 2 percent or more and/or result in more than6 inches difference in cover for a level lateral system.

Adjacent absorpt ion field trenches shou ld be sepa-rated by at least 6 feet o f und isturb ed soil. Table 8 shows

the m inimu m spacing for trench widths ranging from18 to 36 inches. Individual trenches shou ld be con -structed on contour with the surface grade and with alevel trench bot tom to keep the trench cover a uniformthickness.

A min imu m of 6 inches of rock or gravel shall beplaced in th e trench under t he distribution pipe, fol-lowed by enou gh gravel to cover the pipe b y 2 inches.The soil cover over the tren ch shou ld no t be less than6 inches to provide adequate water ho lding capacity forgrass nor more than 12 inches to maximize water andnu trient use by vegetation . Generally, the tot al trenchdepth should be as shallow as possible, but not less than

18 inches. Perforated distribution pipe shall be used and,where pressure dosing is not required, 4-inch diameterpipe is adequate. See standard lateral trench design anddimensions shown in Figure 5. Wh ere pressure do sing isrequired, the p ipe size should be just large enou gh toavoid excessive pressure loss (no more th an 10 percent)in the distribut ion lines.

Variations from the standard lateral design describedabove allow the designer additional flexibility in somerestrictive soil situations and are discussed in the site andsoil evaluation section and in cluded in Table 6. Many soilsin eastern Kansas h ave a friable, moderately permeablesurface soil layer of up to 15 to 18 inches in th ickness.Many subsoils have high clay conten ts and a very re-stricted permeabilit y. Laterals placed into the t ight, veryslowly permeable subsoil frequently do not performsatisfactorily.

Shallow in-ground laterals dug 6 to 12 inches into thesurface soil layer and covered with imported topsoil maybe a viable option to achieve a workable soil absorptionsystem for some soil conditions. Shallow in-groundsystems may overcome marginal conditions such asgroundwater or rock over 4 1 2 feet but less th an 6 feetrequired for conventional laterals.

The shallow, rock-filled trench shall be covered witha synthet ic geotextile barrier material (at least 3 o un cenylon or 5 ounce polypropylene nonwoven filter fabric)before the lateral and interval between laterals is coveredwith top soil brought to the site.

In soils with st ill more restrictive or shallow soilconditions (4 to 4 1 2 feet to restrictions) an at-grade lateralsystem may be an opt ion. The at-grade lateral involvespreparing the soil surface on a level contour in stripsmuch as the first step in constructing a Wisconsin

mound. The rock, normally placed in a trench, is placedon the surface. Pressure dosing distribution is used toensure even water distribution and help prevent horizon-tal flow at the natural soil surface resulting from tempo -rary ponding in the lateral. The rock lateral shall becovered with barrier material before the lateral andinterval space is covered with top soil brought to the site.

Loading rates and other d esign criteria are basicallythe same for shallow in-ground and at-grade systems asfor convent ional lateral trenches. The at-grade lateralrequires tilling the soil strip under the lateral on a levelconto ur. A pressure dosing system shall be included as apart of the at-grade design. Distribution lateral linepressure should not exceed 5 feet of head. Orifices in thepipe shall be sized and spaced to evenly distribute flowthroughout the lateral system. If the area is too large topressurize the ent ire system, a m ultizone d esign andsequencing valve shall be used to dose zones in sequence.

The use of an effluent filter on the septic tank outletis strongly encouraged to prevent solids from plugging

the absorpt ion field. This will prolong the life of theabsorption field and improve performance of the system.It also helps reduce the stren gth of wastewater effluen t.

Absorption FieldMaterial Specifications

Rigid PVC or corrugated polyethylene plastic pipemeeting American Society for Testing and Materials(ASTM) standard ASTM D2729-93 and ASTM F405-93or latest edition respectively meet minimum standardsfor use as solid or perforated gravity distribut ion lines.All materials used in the plum bin g, wastewater line, an d

lateral fields shall meet standards specified by ASTM.In gravity lateral p ipes, perforations are circular, 1 2-inchdiameter and are placed at 4 and 8 oclock position s onthe pipe circumference. In no circumstance is slottedpipe acceptable as the narrow slot o pen ings plug easily.

Washed gravel or crushed stone is commonly used asthe po rous med ia for the trench. The media gradationshall be 3 4 inches to 2 inches in diameter, with the smallersizes preferred to reduce masking of the infiltrationsurface. Uniform size is preferred because more voidspace is created. Rock having a hardn ess of threeor more on the Mohs Scale of Hardness is required. Rock that can scratch a pen ny without crum bling or flaking

generally meets th is criterion. Larger diameter and smallerdiameter material, or soft aggregate such as calcitelimestone are not acceptable and shall not be used.

Fines should be elimin ated as much as po ssible.Fines shall not exceed 5 percent by volume, so un-washed material is generally unacceptable. A simple testis to wash a volume o f material into a clear contain er of the same d iameter and measure fines (5 inches of gravelshould produce no more than 1 4" of fines).


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When suitable rock or gravel is not locally available,is expensive, or access to the site is restricted, gravellesscham bers are good choices for laterals. They have theadvantage of mo re liquid sto rage capacity, reducing theeffect of high flows or loadings on weekends or ho li-days. Cham ber systems are lightweight m aking installa-tion easier at sites with restricted heavy eq uipm ent

access. Cham bers also may be recovered for reuse in thefuture. Before using chambers, consult the local author-ity to identify requirements.

Chu nks of recycled t ires are a suitable substitu te forrock. Ninety percent of the pieces should be 1 / 2 to 4inches in size with no fin es. Wire strands shall no textend more than 1 / 2 inch from the pieces.

The porous media shall be covered with a filterfabric (at least 3 ounce nylon or 5 ounce polypropylene)before backfilling to prevent soil from sifting throu gh th emedia. Traditional u ntreated buildin g paper or 3-inchlayer of straw are in ferior second cho ices or are no trecomm ended. Filter fabric is required when t ire pieces

are used as th e poro us med ia. Materials relatively imper-vious to air and moisture are not permitted.

Field Construction SpecificationsProtection of the absorption field area begins before

any activity on the site. The site and soil evaluationidentifies the best lateral field area and reserve area.Heavy equipment, such as loaded trucks, should be keptaway from the ab sorpt ion field by marking th e site. Theweight of such equipment can permanently alter soilcharacteristics due t o com paction. Excessive equ ipmen tor foot traffic can comp act even relatively dry soils.

Construction of septic tankla teral field systemswhen the soil is too wet causes compaction and smear-ing of th e soil structure, greatly reducing the waterabsorption and treatment efficiency of the system. Agood test for this is to work the soil into a ball and rollbetween the hands. If it can be rolled out into a soilwire 1 4 inch in diameter or smaller without falling apart,it is too wet and construction should no t proceed.

Before beginn ing construction, contou rs shou ld bedetermined and level lateral locations should be markedby flags or stakes on the contour. Trenches shall not beexcavated deeper th an th e design depth or wider than thedesign width . Following excavation , the tren ch sides andbot tom shall be raked to remove any smearing andgraded to assure a bottom with no m ore than 1 inchdifference in elevation along the entire lateral length orthe complete field for a level system. The lateral pipe androck cover shall not vary more than 1 inch in elevationalong th e lateral length using a surveyor level or laser.

The trench bot tom should then b e immediatelycovered with at least 6 inches of rock or th e cham ber.Distribution pipes are carefully placed on the rock,

and leveled with perforations at 4 oclock and 8 oclock position s. Rock is placed arou nd an d over the p ipe to acover depth of at least 2 in ches.

After rock and p ipe h ave been placed in the tren chthe filter fabric or o ther barrier shall be placed to p rotectfrom soil movement into the ro ck. Finally, earth backfillshall be carefu lly placed to fill the trench cavity.

The backfill shall be mounded above the trench about20 p ercent of th e soil fill height to allow for settling.If a variation in the tren ch d epth is used, top soil alsomu st be placed between laterals as well as over thelateral to level the site.

Maintaining OnsiteWastewater Systems

The ho meown ers respon sibility for on site wastewa-ter treatment and disposal does not end when thebackfill is placed over the trench lines and wastewaterintrod uced. Mainten ance of the system is a critical factorto ensure long life and continued effectiveness of thesystem. Minimum annual maintenance criteria include:

check the sludge and scum in the tan k to d eterminepum ping requirements; tanks need to be pu mpedregularly depending on wastewater flow and tank size, (often 3 to 5 years),

check the baffles or tees to en sure they are intact,secure, and in good condition,

check the septic tank and soil absorption areamon th ly for indication s of leaks or failure,

check observation port s in each lateral to en sureeffluent is reachin g all parts of the system,

check effluent filter and clean as needed.

Refer to K-State Research and Extension bulletinslisted at the end of this document for additional infor-mation . A file contain ing records of repairs, pum ping,site plan of the system, annual checklist, and otherpertinent information should be m aintained for easyreference and for information when ownership changes.

Wastewater Stabilization PondsWastewater pond s, somet imes called lagoons, are a

viable sewage treatment method and should be consideredfor individual household wastewater where soil conditionshave severe limitations for conventional lateral absorp-tion field systems. Single family wastewater pon ds shou ldnot be con sidered if septic tan klateral field systems arefeasible as determined by local requirements or recom-mendations contained in t his bulletin. Wastewater pond sare especially applicable on sites with very restrictivepermeability, h igh clay subsoil, (i.e. slow perc rates) orshallow bedrock where adequate area is available.

A wastewater pond is a small pond with a maximum5-foot operational water depth, which receives domesticwastewater. Size, as in a soil absorption field, is deter-


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min ed by the nu mb er of occupan ts and thus the waste-water flow, the soil, and evaporation.

Wastewater enters the pond by a pipe outlet near thebot tom close to the center of the lagoon. All privatewastewater ponds must be nondischarging and must befenced. Wastewater ponds require a sizable area, includ-ing water surface, emban kment , and separation d is-

tances. Mainten ance is required to remove vegetation atthe waters edge, to mow vegetation on embankments,and to remove trees that will shade the pond. Odorsfrom a properly designed, installed, and maintainedpond are infrequent and minimal.

Individuals considering wastewater ponds for sewagetreatment should first check with count y or other localautho rities to determine requ irements. Proceed with anyprivate sewerage facility only when pub lic sewers are n otavailable and all applicable local requirements are met.Refer to K-State Research and Exten sion bulletin s onwastewater pon ds for more information and guidance.

Alternative Systems GuidelinesKansas Administrative Regulations (K.A.R. 28-5-9)authorize coun ty health departments, or other autho-rized local agency, in cou nt ies that have local codes, togrant a variance for alternative onsite wastewatertreatment and disposal systems. Most county codescontain a variance clause th at autho rizes the localadmin istrative agency to grant req uests for variancesprovided that certain conditions are met. The requestfor variance is filed with the cou nt y administrativeagency. The local agency can consult with KDHE fortechn ical assistance in evaluatin g the system, bu t h asthe au tho rity to issue t he variance locally if there is alocal code.

No p r i v a t e o n s i t e was t ewa t e r sys t em sh a l lh av e a su r face d i sch a r g e .

When there is no local code KDHE is authorized byregulation to grant a variance. On site wastewatertreatment options that might be considered for varianceinclude enhanced wastewater treatment options such asaerated tan k, sand o r media filter, rockp lant filter, orother equivalent system. Design, construction, opera-tion, and maintenance criteria or guidelines are plannedbut are not yet available for use in Kansas.

Some county codes require that design and specifi-cations for alternative systems be com pleted b y alicensed p rofessional en gineer. Engin eers should beadequately trained or have experience under adequatesupervision, b efore d esignin g alternative systems.Results show that design by an inexperienced engineercan n ot p roduce a more reliable or long life alternativeth an con vention al systems. Some altern ative systemsinvolve complex design and specific constructioncriteria that can result in dramatic failure when violated.

Appendix AConducting a Perc Test

Water movement through soil in response to gravityis called percolation. For wastewater soil absorption fieldevaluation, the absorption of water from a post-typehole is a method for the evaluation for soil suitabilityand loadin g rate design. The absorption of water fromth is hole involves water movement in 3 dimen sions andforces other th an gravity. The term perc test is appliedto this evaluation. The purposes of this test include:

Obtaining the rate at which wet, unsaturated soilwill absorb water,

Helping assess suitability of soil on a specific siteto absorb septic tank effluent,

Helping select fro m amon g alternative on site sewagesystems an d establish a design loading rate.

To en sure the b est evaluation, all available soilinformation should be u tilized. This would includeassessment o f restrictive condit ions such as h igh watertable, perched water table, shallow depth of soil, andrestrictive layers such as clay pan ; soil pro file evaluationfrom the site, including history of high water tables; anddescription of soil profiles from county soil surveys.

Brief DescriptionA minimum of four to six holes are placed through-

out the proposed site of the absorption field and at thedepth of the pro posed laterals and soaked with waterun til th e clay is swelled, usually for at least 24 h ou rs.The perc rate is measured in each hole and reported asthe number of minutes it takes for an inch of water to beabsorbed in t he hole. The optim um time to conduct aperc test is in th e spring when the soil is normally wet.An accurate perc test durin g a dry period when the soilis cracked m ay not be p ossible.

Materials Needed to Conduct the Perc Test1. Site plan including proposed absorpt ion field and

location of tests. Dimensions help ensure the testholes are properly located in and around the field.

2. One batter board1 in ch by 2 inch board of 18 inches lon g for each p erc test hole.

A. Numb er each board so that each test hole willbe distinguishable.

B. Mark a center line on the side of each batterboard. This will provide a consistent referencepoint for the measuring device.

3. Durable measuring device (1 to 2 feet long) and away to reproducibly locate the water surface, such asa pointed h ook or float on a stiff wire or rod.

4. An adequate supply of water to soak the hole andconduct the t est. Water usually has to be t ranspo rtedto the site. Two hundred to 300 gallons is usuallyadequate.


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Procedure1. Identify Proposed Site of Absorption Field The

site preferably shou ld be located downslope fromthe septic tan k. If effluent will no t flow by gravity,an effluent pu mp may be used to move effluent toa suitable absorption field. For n ew hom esites, theproposed area reserved for future use should also

be checked for suitability.2. Num ber an d Location of Tests Loca te a m in imu mof four to six holes uniformly over the proposedabsorpt ion field site. If the site is sloping, it isespecially impo rtant to have test holes at all eleva-tion s to be u sed so th at any differences in soil willbe evaluated.

3. Typ e of Test Ho le Dig or b ore each ho le to th edepth of the prop osed trench (usually 18 to 24inches) and with a con sistent d iameter (8 inchesis recom mended ). All test h oles shall be the samesize to help en sure consistency in results.

4. Prepare the Test Hole Scrat ch the sides and b ot tom

of the hole to eliminate any smeared or compactedsoil surfaces and remove loose material from thehole. Place 2 inches of washed gravel in t he bo tto mof the hole. The gravel can be contained in a meshbag for easy removal and reuse at other sites. Thisgravel protects the bottom of the hole from erosion,scourin g, and sediment as water is introd uced.

5. Wet Hole to Allow for Soil Swelling Saturationmeans that the voids between the soil particles arefilled with water. This happens fairly quickly for soilimmediately surround ing the portion submerged inwater. Swelling is caused by intrusion of water intothe clay particles and can take many hours andpossibly days when the soil is qu ite dry.

A. Carefully add 12 to 14 inches of water. Using ahose will prevent soil washing down from thesides of th e ho le.

B. Maintain the water level for at least 24 h ou rs toallow for swelling to occur. In most cases it willbe n ecessary to add water periodically from areservoir. A float supplied by a hose from areservoir simplifies the procedu re.

C. If the soil appears to be sandy or init ially verydry, plan to check the condition of the holewetting after 12 hours or overnight. If there isno water left in t he ho le and th e reservoir is dry,refill the reservoir and holes. After the full24 hou rs have passed since soaking was initi-ated, begin measurin g as described in #6.

6. Perc Measu remen tA. Remove the apparatu s used to add water to the

hole.B. Place the batter board across the to p of each

hole and secure with weights, spikes or attach

to stakes. Be sure th at the centerlin e mark iscentered over the hole and each board isnumbered.

C. Align th e measuring rule with mark on theboard and use the hook gauge or the float androd to read the level when it just touches thewater surface. Record th e measurement and

time. Fill the ho le to abou t 6 inches over therock and make the initial measurement.D. Measure at 30-minu te intervals (does not have

to b e exact) recording both level and t ime. If the water level in the h ole drop s too rapidly, itwill be necessary to red uce the tim e interval formeasurement. The time interval should be shortenough that the water level should n ot dropmore th an 25 percent of the wetted ho le depth.

Note: If the water drops more than 1 to 2 inches in30 m inu tes, it will be necessary to add water to th ehole after each reading until it is the same depth asrecorded in itially. Be sure to record the measure-

ment of the refilled perc h ole.7. Calculate Perc Rate . Divide t ime interval by drop

in water level to find the perc rate in m inu tes perinch (mpi).

Examples:If the drop is 5 8 inches in 25 minutes:

25 = 25 8 = 40 mpi___ ___5 8 5If the drop is 1 1 2 inches in 12 minutes:

12 = 12 = 12 2 = 8 mpi_____ _____ ____11 2 3 2 3

A. Continu e measurements unt il each o f threeconsecutive calculated rates varies by n o mo rethan 10 percent from the average of the threerates. Use the average of three rates as the valuefor that hole

Example:Rates of 26.0, 28.0, and 3 0.5 m pi average 28.2 mp i

B. Measure and calculate the rate for each h ole inthe application field. Average th e rates for allholes as the value to u se for loading rate andbot tom area sizing.

8. Compare with Permeability in the NRCS SoilSurvey . The field measured p erc (mpi) shou ld be n osmaller than about one third the inverse of thepermeability rate shown in the t able of physicaland chem ical properties of soils in the soil surveyreport. If it is, suspect a problem with the perc test,soil mapping or other cause. A well aggregated,undisturbed soil may have a good perc rate.


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16

Appendix B Sources of Additional InformationKansas State University, Agricultural Experiment Stationand Cooperative Extension Service Bulletins 21 (exceptas noted)

Wastewater Systems and Related Information Design of Submerged Flow Wetlan ds, Special Repo rt 457,

Missouri Small Flows Education and Research Center,Agricultu ral Experimen t Station, University of Missouri, Columbia, MO 65211

Environm ent al Healt h Handbook, First Edition, Aug 1992,Kansas Association of San itarian s, KDHE, and K-StateResearch and Extension cooperatin g, available fromK-State, Extension Biological an d Agricult ural Engi-neerin g, Cost: $20.00 22

Get to Know Your Septic System, MF-2179 How t o Run a Percolation Test, FO-0583-C, (Revised 1993),

Minn esota Extension Service, University o f Minne-sota, St. Paul, MN 55108Onsite Domestic Sewage Disposal Handbook, MWPS-24,

Midwest Plan Service, Iowa State University, availablefrom K-State, Extension Biological and AgriculturalEngin eering, Cost: $6.00 22

Plugging Cisterns, Cesspools, Septic Tanks, and Other Holes,MF-2246

RockPlant Fi lter Design and Installat ion, expected 1997 RockPlant Fi lter Operat ion, Main tenance and Repair ,

expected 1997Septic Tank Maintenance, MF-947Sept ic TankSoil Absorpt ion System , MF-944

Soil Evaluat ion for Home Sept ic Systems , MF-945Wastewater Pond Design and Construction, MF-1044Wastewater Pond Operation, Maintenance, and Repair,

MF-2290W hy Do Septic Systems Fail? MF-946Your W astewater System Owner/Operator Manu al, S-90 For

sale bu lletin , cost 35

Other Helpful BulletinsKinds and Types of Levels , LR-17 22

Land Judging and Hom esite Evaluat ion , S-34Operating, Checking and Caring for Levels, LR-101 22

Safe Domest ic Wells, MF-970Soil Water Measurements: An Aid to Irrigation Water Management, L-795

Using a Level, AF-19 22

Standards Related to Onsite WastewaterSystem Materials and ProceduresACI 23212.3R Chemical Admixtures for ConcreteACI 350R Environ ment al Engineering Concrete Structu resASTM 24C150-95 Standard Specification for Portland

Cemen t. Vol. 04 .01ASTM C267-82 Stand ard Test Method for Chem ical

Resistance of Mortars, Grouts, an d MonolithicSurfacings. Vol 04.05

ASTM C452-95 Stan dard Test Metho d for Poten tialExpan sion o f Portland Cemen tCem ent MortarsExposed to Sulfate. Vol. 04.01

ASTM C890-91 Standard Practice for Minimum Struc-tural Design Loading for Monolithic or SectionalPrecast Concrete Water and Wastewater Structures.Vol. 04.05

ASTM C1227-94 Standard Specification for PrecastConcre te Septic Tan ks. Vol. 0 4.05

ASTM D1600-94 Stan dard Term ino logy for AbbreviatedTerms Relatin g to Plastics. Vol. 0 8.04

ASTM D2321-89 Standard Practice for Undergrou ndInstallation of Thermoplastic Pipe for Sewers andOther Gravity-Flow Application s. Vol. 08.04

ASTM D2729-93 Standard Specification for Poly(VinylChloride) (PVC) Sewer Pipe and Fitt ings. Vol. 08 .04

ASTM F481-94 Stand ard Practice for Installation of Thermoplastic Pipe and Corrugated Tubin g in SepticTank Leach Fields. Vol. 08.04

ASTM F405-93 Standard Specification for Co rrugatedPolyethylene (PE) Tubin g and Fitt ings. Vol. 08 .04

ASTM F412-94a Standard Termino logy Relatin g to PlasticPiping Systems. Vol. 0 8.04

ASTM F449-93 Standard Practice for Subsurface In stalla-tion of Corrugated Thermoplastic Tubing for Agricul-t ura l Drainage or Water Table Cont rol. Vol. 08 .04

ASTM D3385-94 Standard Test Metho d for In filtrationRate of Soils in Field Using Double-Ring Infiltro meter.Vol. 04.08

ASTM F789-89 Standard Specification for Type PS-46Poly(Vinyl Chloride) (PVC) Plastic Gravity Flow SewerPipe and fit tin gs. Vol. 08.04

ASTM F810-93 Standard Specification for SmoothwallPolyethylene (PE) Pipe for Use in Drainage and WasteDisposal Absor pt ion Fields. Vol. 08 .04

ASTM ASTM F949-93a Standard Specification for Poly

(Vinyl Chloride) (PVC) Corrugated Sewer Pipe With aSmo oth Interior and Fitt ings. Vol. 08.04NPCA25 Durable, Watertight Precast Concrete, TECH

notes, April 1996NPCA Sept ic Tan k Manufactur ing: A Best Practices

Manual. Anticipated by Summer 1998NPCA Underground Watertight Systems (video)

21Product ion Services/Dist ribut ion, Kansas State University, 28 Um berger Hall, Manh att an, KS 665063 402, Phone: (785) 532-115022 Available th rough Extension Biological and Agricultural Engineering, Kansas State University, 237 Seaton Hall, Manhat tan, KS 66506 2917, Phone: (785) 532-581323 American Concrete Inst itu te, P.O. Box 9094 Farmington Hills, Mich igan 48333, Phone: (810) 848-3808 24 American Society for Test ing and Materials, 100 Barr Harbor Drive, West Conshohocken , PA 194282959 Phone (610) 832-950025 Nat ional Precast Concrete Association , 10333 N orth M eridian Street, Suite 272, Indian apolis, Indiana 46290 Phone (317) 571-9500


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Rawlins

Rice

McPherson Marion

Chase

Cheyenne Norton Phillips Smith Republic Marshall Nemaha Brown

Doniphan

AtchisonJacksonPottawatomieClay

CloudOsborne

Dickinson Geary

Morris

Lyon

Wabaunsee

Ottawa

RooksGrahamThomasSherman

Wallace Logan Gove Trego Ellis Russell

Saline

BartonScottWichitaGreeley

Hamilton Kearny Finney

Gray

HodgemanPawnee

Edwards

Stafford

Reno HarveyButler

Shawnee

Jefferson

L e a v e n w o r t

h

Wyandotte

Douglas Johnson

MiamiFranklin

Osage

LinnAndersonCoffey

Bourbon

Crawford

Cherokee

Allen

Neosho

Labette

Wilson

Montgomery

WoodsonGreenwood

Sedgwick

Chautauqua

CowleySumner

Kingman

Harper

Pratt

Barber

Kiowa

Comanche

Ford

ClarkSeward

HaskellGrant

StevensMorton

Stanton

Lane

Ellsworth

Jewell

Mitchell

Lincoln

Washington

Sheridan

Decatur

Meade

Riley

Elk

RushNess

KDHE District Boundries and District Offices

KDHE, Division of Enviroment , Nonpo int Source Section

Forbes Field, Bldg. 283Top eka, Kan sas 66620(785) 296-4195

KDHE District Offices

Kan sas Dept Health & Environ men tNorthwest District Office2301 E. 13th StreetHays, KS 676012 651(785) 625-5663

Kan sas Dept Health & Environ men t

North Central District Office2501 Market Place, Suite DSalina, KS 67401(785) 827-9639

Kan sas Dept Health & Environ men tNortheast District Office800 W. 24th StreetLawrence, KS 660464417(785) 842-4600

Kan sas Dept Health & Environ men tSou thwest District Office302 W. McArtor RoadDod ge Cit y, KS 67801609 8(316) 225-0596

Kan sas Dept Health & Environ men tSouth Central District Office

130 S. Market, 6th FloorWich ita, KS 672023802(316) 337-6020

Kan sas Dept Health & Environ men tSou theast District Office1500 W. 7th StreetChan ute, KS 667209701(316) 431-2390


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