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IS : 2470 ( Part 2) l 1985Indian Standard

CODE OF PRACTICE FORINSTALLATION OF SEPTIC TANKS

PART 2 SECONDARY TREATMENT AND DISPOSALOF SEPTI C TANK EFFLUENT( Second Revision )

First Reprint APRIL 1990

UDC 628352 : 00676

0 Copyrtght 1985BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARGNEW DELHI 110002

Gr 6 December 1985

( Reaffirmed 1996 )

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IS : 2470 Part 2 ) - 1985Indian Standard

CODE OF PRACTICE FORINSTALLATION OF SEPTIC TANKS

PART 2 SECONDARY TREATMENT AND DISPOSALOF SEPTIC TANK EFFLUENT( Second Revision 1

Water Supply and Sabitation Sectional Committee, BDC 24czhaimlan RQWS~ntitlg

SHRI J. D Cavz Wate; ~p~p~;h,ik Sewage Disposal Undertaking,eMembers

CHIEF ENoINEEB ( CIVIL I ) ( .#temats toShri J. D Cruz ) \A~VISIER ( PHE ) Ministry of Works and HousingDEPVTY ADVISEB ( PHE ) ( Alfcrnut~)_Soar M. S. ASNAN~ Pub]; Delhi Administration,epo:lsh,Department,

SHRI P. C. SIWASTAVA ( Altern& )Sang N. S. BHAI~AVAN Public Health Engineering Department, Govern-ment of Kerala, TrivandrumSVP~RINTEI&NO ENQINEEB ( Al:rra&_)SHRX I. CHANDBA Pubk;anp;ks Department ( 2blic HealthGovernmentChandigarh Haryana,SHRK K. IL. GANDHL ( ALrra&)CHIEEBENCINEE~ ( CONST~VCTION ) Uttar Pradesh Jai Nigam, LucknowSV~~~NTENDIN~ ENQINEEB ( Altrraatc )SH~I R. C. P. CEAVDHARYSHRI H. V. RAO ( Altcrnatr )

Engineers India Ltd, New DelhiSHBI S. K. DAS~V~TA Calc~,;uf;tropolitan Development Authority,

Snar S. R. MVKEEBJEE (Al&n&)PROF J. M. DAVESaar S. G. D~OLALIKAR Institution of Engineers ( India), CalcuttaIn personal capacity (Flat No. 403, So&i CinemaCemm&el Con&x, &a& Kaikzsh II, NewDelhi )( Cmrinued .n pope 2 )

BUREAU OF INDIAN STANDARDSThis publication is protected under the fadian Gm& Act ( XIV of 1957 ) andreproduction in whole or in part by any means except with written permission of thepublisher ehall be deemed to be an infringement of copyright under the said Act.

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IS : 2470 (Part 2 ) - 1985( Gntinuedfromp4gc 1)

MembersHYDBAULI~ ENQINEEB

RepcmtingMunicipal Corporation of Greater Bombay,Bombay

CHIEF ENQINEEB ( SEWEBAQEPBOJECTS ) ( z&mate )SEBI R. A. KH~A Public Health Engineering Department,Government of Madhya Pradesh, BhopalSHBI D. K. MITBA ( Alfcmete I )SERI I. S. BAJA ( Alfcrnate II )9~~1 P. K~~ISHANAX Central Public Works Department, New DelhiSWVEYOlX OF WOBKS-l( ND2 )( Alternate )SIZBI S. R. KSHIRSAQ~B National Environmental Engineering ResearchDE P.V.R.C. PAXICKEB ( Alfevate ) Institute ( CSIR ), Nagpur

SEBI M. Y. MADAN The Hindustan Construction Co Ltd, BombaySR~I C. E. S. RAN (Alternate )SHaI S. L. MAIN Punjab Public Works Department ( Public HealthBranch ), Government of Punjab, PatialaMANAQIXQ DIRECTOR Punjab Water Supply & Sewerage Board,ChandigarhSas~ R. NATARAJAN Hindustan Dorr-Oliver Ltd, BombaySH~I SUB~ASH VEBJ~A ( Alternate )&tar K. J. NATE All India Institute of Hygiene h Public Health,CalcuttaSHBI D. GUIN ( Alfernafe )Sasr A. PONNAMBALAM TamMaf$ Water Supply & Drainage Board,SHEI RANJIT SINQH Ministry of RailwaysDB A. V. R. RAO National Buildinga Organization, New DelhiSHBI 0. P. RATRA ( Alternate )PBOF Y. N. RA~~ACHANDIXAno Engineer-in-Chiefs Branch (Ministry of Defence ),New DelhiMAJ B. S. PABYAB ( Alternate )SEcrt33~AaF Indian Water Works Association, BombaySECBET~BY GENERAL Institution of Public Health Engineers India,Calcutta

SHBI R. N. BAXERJEE ( Altcrnatr)SRBI L. R. SEEQAL L. R. Sehgal St Co, New DelhiSEBI S. K. SEABMA Central Building Research Institute ( CSIR ),Sanr B. N. THYAQABAJA Roorkee -Bangalore Water Supply & Sewerage Board,BangaloreSHRI H. S. PUTTAKEBII=A~NA Altemafs)SBBI V. VABADAIUJAH Madraa Metropolitan Water Supply & SewerageBoard, MadrarSEXI S. D~IVAIKAXU Alternute )&RI G. RAMAN, Director General, IS1 ( Ex-o&i0 Member )Director ( Civ Engg )

Secre avSEBI A. K. AVASTHYAs&ant Director ( CivEngg ), IS1

(C&itweden~~ 21)2

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ma4i8(?kt2pla85him Stantthtd

Cpl?!l q pK#JcgcBFoRINSTALLATION OF SEPTIC TANKS

( SecondRevisionJ& FOREWORD

6A This bdian kmderd ~Part 2) (Second Revision) was qopted bJhe hdian Staidar& titutiom on 28 Febru*ry 1985, efler the dr tik&ad by the W- SUPPIY ~d ~t8&~8ti&.iom&Coutmittee hadh *ggmuve&&y the CM Ib@newq q. .&2xn& z c tank, eyen if of 4hqtu@ ~ and iqmcity, ~y apartiol! of auepeoAd eolide eettk k the tank, tlte disidved o~cnaattlw.88dSemw,ofheWspddedInq - dA4utwJboIn thetaxlkim the eifbeai =md will cawse,a :&eak&:bu@ iftk:diiuent ia,satdeqm@e@~du. , :,-, >,., ,;.. ~ . In tllie revisiow *diepmal ,of eeptic tank efihmatby b>logtcal Slier have been coverwI hdetails. IJpflow amrobic dk~ fir the dispoeakof efiluent from the-m+ tank, which ~- pre&ged in My 8reU, - slso, covered in.3

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gh ag70chet ~wmU For the purpose of deaiding whether a particular reqa ofthis atandard ir complied with, the &nal value, observed or calculated,expmkng the ,msult of a test, shall be roundkd off in accordance. witbIS : 2-lSo*. The msrnber of signi6aaq plqae~ retaked in the rouadecloff value shouk! be the same aa ihat of the specified value in thisstandard.0.7 This Code of practice represents a #andard of good practice andtherefore takes tbc fatln of reckniepdation.

1. SCOPE1.1 %bb code lays down recommeadatioua for the methods of treatmentand disposal of effiuent from septic tanks.- . ;L p Li. TsuAlnNomy I -

3.9 Diw Tremeh-A trench k Which open j&ted pipe8 areiaid aud surrounded by coarse aggqate media and overlaid b+ Sacagregate. TbeeHwntgetadispersedthroughtheopenjointsaaw3iraf!o rbed in the neighbokii soil.2asImmmt8

a) Fz l@amt - The supernatmt-liquid dkharge fiotn .a rpic.b) El&e-Theiiquiddischargedfionraklogkal@lter.

clinker, broken stone and gravelrrtl*#ofwbkh w f3h1~

-We?.@. Pa.4 F&hi!fkatiralkWdQ?Z.L.~IB Tbe liquid was+tif i h&+&&&k 6ammuzAy including.

gl*reWouad~e@aamwkl nl=(rirwj.4

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IS : 2470 ( Part 2) - 19852.7 Subsoil Water - Water occuring naturally below the surface ofthe ground.23 Sarfacc Water - The run-off from precipitation and other waterthat flows over surface of the ground.3. PRELIMINARY DATA\FOR DESIGN3.1 In order to design secondary treatment works of the treatment ofeffluent from septic. tanks, information on the following items should becollected.

[a)zNature oftsoil and subsoil condition1)

2)

3)

The fullest possible information on the nature of the soil andsubsoil conditions should be obtained, as well1 as theapproximate water table and any available records of goodlevels or information as to the variation, seasonal or otherwise,in the water table.The soil should be explored to a sufficient depth to ascertainthe soils horizons and the soil types, grading, structure andpermeability. The external drainage factors, such as slopeof ground and position of surface water drains, if any, shouldbe, ascertained. Exploration of the soil to a significant depthshould be made because casual or visual inspection may failto reveal unsuitable conditions, such as an impervious granitelayer under sand, or on the other hand suitable conditions,such as permeable schist overlaid by clay.Soil Ty#es - An approximate field identification of the soilsshould be made in accordance with the methods given inIS : 1498-!970*. Trial bores or boreholes should be sunkalong the line of the proposed filter and data there fromtabulated. In general, the information obtained from trialbores is more reliable than that from boreholes. Thepositions of trial bores or boreholes should be shown on theplans together with sections showing the strata found and thedates on which the water levels were recorded. Fullinformation should be given as to the structure, type, colour,permeability, depth and horizons of the soil, as well as anyimpedances to drainage such as rock bars.

- *Classification and identification of soils for general engineering purpose (jirJ~rhiwl ) .5

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IS : 2470 ( Part 2 ) - 19854) Percolation Test - To decide on the details of B soil absorptionsystem a soil absorption test as given in Appendix A shallbe conducted. The percolation rate, that is time requiredin minutes for water to fall 25 mm in the test-hole shall be

determined. A test in trial pits at more than one place inthe area should be undertaken to permit deriving an averagefigure for percolation rate.b) Site plan showing the proposed or existing buildings as well asreduced ground levels over the site.

/ c) Discharge from the septic tank.d) The position and nature of outfall ditches, wells, tanks or smallstreams in the vicinity, if any.

3.2 When assessing the feasibility of a proposed effluent disposal schemeinvolving absorption of effluent in soil, consideratian should be given tofactors such as:a) The area of land available for the absorption.b) The risk of prejudicing adjoining property, underground watersupplies, swimming and wading pools and the like, by seepagefrom the area.c) The permeability and depth of the soil on the proposed site forthe absorption area. Percolation tests are useful but the seasonof the year when the tests are made and many other factorshave to be taken into account when assessing the results of thetests. Long-term efficiency of an absorption area can be

adversely affected by high concentrations of chlorides andsulphides in the soil.d) Any seasonal changes in ground water level and absorptivecapacity of the site.e) The climate and its effect on the evaporation from the site, forexample, distribution of rainfall, hours of sunshine, prevelanceof wind.f) The effect of seepage ano surface water from surrounding areasat higher levels than the proposed absorption area.

3.3 Before any work is started, the approval from the AdministrativeAuthority should be obtained.6

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SS:2470(Part2)-19W4. METHODS OF TREATMENT AND DISPOSAL OF EFFLUENT4.1 The following methods of disposal are describgd in this Code:

a) Soil absorption system,b) Biological filters, andc) Upflow anaerobic filters

4.2 Depending on the position of the subsoil water level, soil and subsoilconditions, the recommended method of disposal of the effluent is givenin Table 1.

TABLE I RECOMMENDED METHOD OF DISPOSALFOR SEPTIC TANK EFFLUENT

POSITION OB TEESUBSOIL WATERLEVEL FROXGROUNDLEVEL

Within 18 m

Below 1.8

( %lauses4.2, 6.0 and 7.0 )SOIL ANDSUBSOILCONDITION,-------~* --------mm-_Porous oil with Percolation Rate--A -----Not exceeding30 min Exceeding30 min but not exceed-

ing 60 min

Dense and clays so

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IS : 2470 ( Part 2 ) - 1985with Appendix A ) and the values obtainable from the graph given inFig. 1 may be used for guidance; the allowable rate of effluentapplication for certain selected values of percolation rates are given inTable 2.

SIANDARD PERCOLATION RATE, MINUTES (t 1Q=$p

FIG. 1 ALLOWABLE RATE OF EFFLUENT APPLICATION FORSTANDARD PERCOLATION RATE5.2 Construction of the Soil Absorption System - Two types ofsoil absorption system have been covered:

a) Seepage pit, andb) Dispersion trench.

5.2.1 Seepage Pit - The seepage pit may be of any suitable shape withthe least cross-sectional dimension of 0.90 m and not less than 1.0 m indepth below the invert level of the inlet pipe. The pit may be linedwith stone, brick or concrete blocks with dry open joints which shouldbe backed with at least 75 mm of clean coarse aggregate ( see Fig. 2A ).The lining above the inlet level should be finished with mortar. In thecase of pits of large dimensions, the top portion may be narrowed to

8

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RS : 2470 ( Part 2 ) - ~985reduce the size of the RCC cover slabs. Where no lining is used, speciallynear trees, the entire pit should be filled with loose stones. A masonryring may be constructed at the top of the pit to prevent damage byflooding of the pit by surface run-off ( see Fig. 2B ). The inlet pipe maybe taken down to a depth of 0.90 m from the top as an anti-mosquitemeasure. Illustrations of typical constructions of seepage pit are givenin Fig. 2

TABLE 2 ALLOWABLE RATE OF EFFLUENT APPLICATIONS TOSOIL ABSORPTION SYSTEM(Cluuss 5.1 )

PEROOLATION ATEMin MAXIE~UYRATE OBEFFLUENTAPPLICATIONl/ma/day1 or less 2042 1433 1184 1025 90

10 6515 5230 3745 3360 26

NOTE 1 -The absorption area for a dispersion trench is the trench bottom area.NOW 2 -The absorption area for reepage pits is the effective side wall area,

effective depth being measured from 150 mm below invert level of inlet pipe to thebottom of the pit (see Fig. 2 ).NOTE 3 - If the percolation rate exceeds 30 minutes, the soil is unsuitable foraoakaways. If the percolation rate exceeds 60 minutes, the soil is unsuitable for anysoil absorption system.

5.2.2 Dispersion Trench -.Dispersion trenches shall be 0.5 to 1.0 m deepand 03 to 1.0 m wide excavated to a slight gradient and shall beprovided with 150 to 250 mn+of washed gravel or crushed stones. Openjointed pipes placed inside the trench shall be made of unglazedearthen-ware clay or concrete and shall have minimum internaldiameter of 75 to 100 mm. Each dispersion trench should not be longerthan 30 m and trenches should not be placed closer than 2.0 m.

9

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IS : 2470 ( Part 2 ) - 1985

INLE

OUTER CASIYGNITif COrRSiAGGREGr.7 E C

2A EMPTY PIT WJITY l.iNiNGBRICtt,STtlNE OR CONC BLOCKLIYfNG WITH MORTAR JOINTS

b-- 90rm MIN ------rl

OUTER CA&NGWITH COARSE SAM?

2F3 PIT WITH FILLING WITHOUT LININGFIG. 2 TYPICAL ILLUSTRATIONSOF SEEPAGE PITS

10.

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IS : 2470 ( Part 2 ) - 19855,2.2.1 The covering for the pipes on the top should be with coarseaggregate of uniform size to a depth of approximately 150 mm. Theaggregate above this level may be graded with aggregate 12 to 15 mmto prevent ingress of top soil while the free flow of water is in a wayretarded. The trench may be covered with about 300 mm of ordinarysoil to form a mound and turfed over. Dispersion trenches are notrecommended in areas where fibrous roots of trees or vegetation are likelyto penetrate the system and cause blockages. The finished top surfacemay be kept at least 150 mm above ground level to prevent directflooding of the trench during rains. Illustration of a typical soilabsorption system through dispersion trenches is given in Fig. 3.

5.3 Location of Subsurface Absorption System - A subsoildispersion system shall not be closer than 18 m from any source ofdrinking water, such as well, to mitigate the possibility of bacterialpollution of water supply. It shall also be as far removed from thenearest habitable building as economically feasible but not closer than6 m, to avoid damage to the structures. The actual distance, however,shall be based on the soil conditions in relation to both percolation andbearing capacity. Care should be taken that the ground below theadjacent building is not likely to be affected by the effluent seeping intothe soil. In lime stones or crevice rock formations, the soil absorptionsystem is not recommended as there may be channels in the formationwhich may carry contamination over a long distance, in such case, andgenerally where suitable conditions do not exist for adoption of soilabsorption systems, the effluent, where feasible should be treated in abiological filter or upflow anaerobic filters. _

5.3.: It is an advantage if the area avaiiable for disposal of effluentis large enough to permit relocation of absorption trenches whenreplacement of trenches become necessary.6. BIOLOGICAL FILTERS6.0 Biological filters are s.uitable for treatment of septic tank effluentwhere the soil is relatively impervious ( SEI Table 1 ), water logged areasor where limited land area is available. In a biological filter, theeflluent from septic tank is brought into contact with a suitable medium,the surfaces of which become coated with an organic film. The filmassimilates and oxidizes much of the polluting matter through theagency of micro-oganisms. The biological filter requires ampleventilation and an efficient system of underdrains leading to an outlet.6.1 Construction - The depth of medium should be 1 400 mm butnever less than 900 mm. The medium should be retained in positionby walls of adequate trench. The filter should have a concrete floor,

11

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IS : 2470 ( Part 2 ) - 1385laid to falls with a system of underdrains laid on it and consisting of F.rlddrains half channels laid upside down and open jointed, or special tilesdischarging to the outlet.6.2 Distribution - The septic-tank effluent should be distributed evenlyover the surface of the biological filter through which it percolates tothe floor. Biological filters may be either rectangular ( seeFig. -1.1; orcircular ( see Fig. 4B ) in shape and a series of fixed channels or rotatingarm distributor may be used for distributing efiluent on the medi-urn.6.3 Filter Media - The filter sand and gravel shall conform 10IS : 8419 ( Part 1 )-1977*.6.4 Ventilation - Adequate ventilation of biological filter is essential.Air vents communicating with the floor level of the filter should beprovided. Where the filter is below ground level, the vent pipes fromthe ends of the underdrains should be carried to 130 mm above groundlevel outside the fi!ter. Normally the filter should not be covered, butwire netting may be used to prevent falling of leaves fouling the surfaceof the filter or blocking the ends of the vent pipe.6.5 Volume of Filter - It is essential that the volume of filter mediumprovided is sufficient to allow for sewage flow which occurs with s:naIlinstallations, such variation being more pronounced it the smaliernumber of persons are ser:.ed. For populations of up to 10 persons thevolume snouldbe 1 m3 of medium per head, of resident population forover 10 and up to 50 persons, 0.8 ms and for over 50 and tip to 300persons, O-6 m3.

If pumping of the septic tank e;liuent forms part of scheme,recirculation of final effluent to dilute the septic tank effluent may beintroduced to reduce the volume of the filter.6.6 Treatment of Filter Effluent - The filter effluent is eitherdischarged into surface drain or evenly distributed over a grass plotfrom the system of channeh. ItThere the eflluent is likely to contaminatethe watercourse, the effluent should be adequately disinfected.7. UPFLOW ANAEROBIC FILTER7.0 Upflow type of filters ( reverse filter) operating under submergedconditions is a method for disposal of septic tank effluents in areas wheredense soil condition (see Table 1 ), high water table and limitedavailability of open land are factors to be considered for successfull equirements for filtration equipment : Part 1 Filtration media sand and gravel.

13

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ISt2470(Part2)-1985P--A

TWO-WAYTIPPER I +

t-APLAN

, UNDERDRAINSSECTION AA

SECTION 88All imensions io millimetres.

NOTE - Flexibleointsay be required oh ink or outlet connectiona,Twhercrigid pipes are used.FIG. 4A RECTANCWLAR BIOLOGICAL FILTER

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lSt2470(PartP)-1985

PLAN

ROVE GFiOUhD LEVEL

-f1100_-LUNDERDRAINS \ CENTRE PILLAR

IF REWIREDSECTION A AAll dimensiona in millimetres.

NOTE -Flexible joints may be required on inlet or outlet connection% wheresigid piper are used.

FIG. 4B CIRCULAR BIOLOGICALFILTRR

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IS:247O(Pltt2)-l985disposal of effluents by secondary treatment. Jbe septic tank effluentis introduced from the bottom and the microbii growth is retained onthe stone media making possible higher loading rates and efficientdigest&A The capacity of the unit is 094 to @05 m* per capita or l/3to l/2 theliquid capacity of the septic tank it serves. BOD removalr of70 percent can be expected and the effluent is clear and-free from odourrpd-nuisance. The flow sheets of the filter system are shown in Fig. 5.7.1 Types - Upflow anaerobic filters areof the following types:

a) Single chamber&l rectangular type, Tb) Double chambered rectanguIar type, andc) Circular type.

7.2 Constnaction Featprcs- In an upflow filter, the tank effluententers at the bottom through a system of underdrains, flows upwardsthrough a layer of coarse material generally 0.6 to l-2 m deep and isdischarged over a weir or trough at the top. The driving head in thefilter, that is, the difference between the water level and the filter may beas low as 25 to 150 mm during normal functioning.7.2.1 Single Chambered Rectangular Type-In this type ( Fig. 6 ) anupflow filter with a rectangular chamber is constructed to treat the

etlluent from a normal domestic septic tank. The chamber is packedwith coarse material and the size of the packing media should be 20 mm.The medium rests on a perforated concrete false bottom slab. Theeffluent from septic tank enters the bottom of the filter chamber througha 150 mm pipe and is distributed upward through the media from aperforated slab at the bottom.The vertical inlet is fitted with a tee at the bottom, one branch ofwhich leads to the filter and the other branch is kept plugged while thefilter functions. The plug can be removed to facilitate emptying into an

adjoining chamber and cleaning the filter where required. The effluentfrom the top of the bed is allowed to escape over a V-notch. The silllevel is kept 150 mm above the top of the medium.7.2.2 Double Chambered Rectangular 7j@ - The filter consists of twointerconnected compartments ( Fig. 7)* The first chamber is filled to adepth of O-55 m with 20 mm coarse medium. The second chamber isfilled to a depth of O-45 m with 20 mm size coarse aggregate. The septictank effluent falls through a perforated tray over the medium in the firstcompartment and enters the second compartment directly from the

bottom. The effluent passes up through the medium in the secondchamber and escapes over a V-notch placed 75 mm above the top of the. 16

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WASTE WATER . c SEPTIC TANK - ANAEROBIC ) GRASSFILTER PLOT. _EF:LOUENTGRAINL k \ -

(1)GAS POSSIBILITY1 OF GASCOLLECTION 1

& t ,, _WASTE WATER L _ ANA,E ROBI%F 1CTp.R c GRASSPLOT -eFF:aUENTDRAINI) ,(2)

\ 1 r , ,OISPOSAL BYWASTE WATER m SEPTIC TANK ANAE ROBlCFILTER * SOAKPIT ORTILE FIELDh

(3)FIG. 5 ANAEROBICILTER SYSTEM

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ls:2470(lpt2)-1983medium. By this arrangement, the time of travel of the effluent throughthe filter is lengthened. The two chambers are each fitted at the bottomwith a 75 mm galvanized iron pipe leading to an adjacent chamber. Avalve in these pipes allows the filters to be partly desludged into thecollecting chamber.

REMOVABLESEPTIC TANK \

SLABEFFLUENT,

FILTERCHAMBER

+EFFLUENt

I-WIRE MESU. SUPPORT ORPERFORATED CONCRETE BLOCK

FIG. 6 UPFLOW ANAEROBIC FILTER ( SINGLE (CAMBEREDRBCTANCWLAR TYPE ),-REMOVABLESLAB

-EFF LUENT

FIG. 7 UPPLOW ANAEROBIC FILTER ( DOUBLE CHAMBEREDRECTANGULAR TYPE )

7.2.3 Circular Filter - A circular filter O-9 m in dia may also beconstructed. Medium of aggregate of uniform size 20 mm should be.18

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ISr247O(Patt2)-1985packed to rest on a perforated concrete slab. Thi effluent may be madeto escape over the top of the medium through equally placed notchesalong the periphery of the filter. The sill level is usually 100 mm abovethe top of the medium.7.3 Filter Media - The filter media shall conform to IS: 8419 ( Part 1 )-1977.7.4 Treatment of Filter Effluent - The filter effluent shall be treatedas given in 6.6.

APPENDIX A( Clause 5.1

DETERMINATION OF THE SOIL ABSORPTION CAPACITYA-l. PERCOLATION TESTA-l.1 Percolation test should be conducted as descrit>ea in A-I.2 to A-l.6to .determine the permeability of the soil at any depth at which it isintended to dispose of the effluent.A-1.2 A square or a circular hole with side width or diameterrespectively 100, to 300 mm and vertical sides shall be dugged or boredto the depth of the proposed absorption trench. The bottom and sidesof the holes shall be carefully scratched in order to remove any smearedsoil surface and to provide a natural soil interface into which water maypercolate. All the loose material shall be removed from the hole andcoarse sand or fine gravel shal1 be added for a depth of about 50 mm, toprotect the bottom from scouring and sediment.A-1.3 Water shall then be poured up to a minimum depth of 300 mmover the gravel. In order to ensure that the soil is given ampleopportunity to swell and to approach the condition it will be in, duringthe wettest season of the year, the percolation shall be determined24 hours after the water is added. If the water remains in the test holeafter the overnight swelling period, the depth shall be adjustedto 150 mm over the gravel. Then from fixed reference point the dropin water level shall be noted over a 30 minute period. This drop shallbe used to calculate the percolation rate.

Requirements for filtration equipment:Part 1 Filtration media-Sand and gravel.19

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16:2470(Part2)-1965A-1.4 If no water remains in the hole, water shall be added to bring thedepth of the water in the hole till it is 150 mm over the gravel. From atied reference point, the drop in water level shall be .measuredat 30 minutes intervals for 4 hours, re-filling 150 mm over the gravelas necessary. The drop that occurs during the final 30 minutes periodshall be used to calculate the percolation rate. The drops during priorperiods provide information for possible modification of the procedureto suit local circumstances.A-l.5 In sandy soils or other porous soils in which the first 150 mm ofwater seeps away in less than 30 minutes after the overnight swell&gperiod, the time interval between measurement shall be takenas 10 minutes and the test run for one hour. The drop that occursduring the final 10 minutes shall be used to calculate the percolationrate.A-l.6 Percolation Rate -Based on the final drop, the perccilationrate, that is, the time in minutes required for water to fall 25 mm, shallbe calculated.

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IS t 2470 ( Part 2 I - 1985( Continwd from page 2 )

Water Supply and Plumbing Subcommittee, BDC 24 : 1Members R8fircsenfin~

SERI J . D CruzSHRI S. A. SWAMY (Altarnate) Municipal Corporatixr of DelhiSHRISG. DEOLALIKAR In personal capacity ( 403, Sauitri CinemaCommercial

SHRI S. K. DHORI Complex, Greater Kailask IZ, .hfcw Delhi )Delhi Fire Service, New DelhiSXIRI R. K . BHARDWAJ (Alternate)SHRI DEVENDRA SINQH In personal rapacity ( 16 A, Maya Mahal, 17th Road,Khor, Bombay )HYDRAULIC ENGINEER Municipal Corporation of Greater Bombay,BombayGRIEF ENQINEER ( SEWERAOE ) (~~;;cu(lts )SERI R. A. KHANNA Health Engineering Department,SHRI D. K. MITRA (Alternate I ) Government of Madhya Pradesh, RhopalSHRI I. S. BAWEJ A ( Alternate I I )SARI S. T. K~ARE Public Health Engineering Department,Government of Maharashtra, BombaySRRI A. S. KULKARN~ Municinal Corporation of Greater BombaySHR~ V. B. NI KAY ( Alternarc ) ( Bombay Fire Brigade ), BombayDR R. P. MATXUR University of Roorkee, RoorkeeSHRI U. L. TOSHNIWAL ( Alternatr )SHRI K . GOVINDA MENON Tarn&z:; Water Supply & Drainage Board,SRRI T. G. SRINIV~SAH ( Altcrnatc)SHRI V. A. MHAI~ALKA~ National Enviroamentai Engmecring ResearchInstitute (CSIR), NagpurSHRI C. V. CEALPLTIRAO ( Alternate)SHRI K . GOVINDAN NAIR Pubiic Health Engineering Department,Goverrment of Kerala, TrivandrumSERI N. S. QHAIKAVAN I Alternote jHRI P. K. NAGAREARSHRI J . N. KA~DILE ( Altcrnutr )PROF. Y. N. RAMACHANDRA RAOMAJ B. S. PAW&AR ( Alternuts )SHRK 0. P. RATRASRBI S. K. SEARMA

Mah;;;tra Engineering Research Institute,

Engineer-in-Chiefs Branch ( Ministry ofDefence ), New DelhiNational Buildings Organization, New DelhiCent;~or~e~ding Research Institute (CSI R),

21

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INTERNATIONAL SYSTEM OF UNITS ( SI UNITS )Base Unit0

QUANTITYLengthMassTimeElectric currentThermodynamictemperature

Luminous intensityAmount of substanceSapplementaty Units

QVANTITYPlane angleSolid angleDerived Units

QUANTITYForceEnergyPowerFluxrlux densityFrequencyElectric conductanceElectromotive forcePressure, stress,

UNITmetrekilogramsecondamperekelvincandelamole

UNITradianateradian

UNITnewtonjoule .wattwebeiterlahertzsiemensvoltPascal

SYYBOLmkgsAKcdmol

SYMBOLradsr

SYMBVL

JWWbTHZSV

Pa

DEFINITION1N - I kg.m/ss1J - 1 N.mIW - 1 J/s1 Wb - 1 V.sIT = 1 Wb/m1 Hz - 1 c/s (s-1)IS = 1 A/V1v - 1 W/A1 Pa - 1 N/m*

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BUREAU OF IN DIAN STANDARDSHeadquarters;Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 110002Telephones : 331 01 31, 331 13 75 Telegrams : Manaksanstha( Common to all offices )

TelephonesE331 01 313311375

36 24 99Regional Ofices;Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg,NEW DELHI-1 10002*Eastern : l/14 C.I.T. Scheme VII M, V. I. P. Road,Maniktola, CALCUTTA 700054Northern : SC0 445-446, Sector 35-C,CHANDIGARH 160036Southern : C. I. T. Campus, MADRAS 600113tWestern : Manakalaya, E9 MIDC, Marol, Andheri (East),BOMBAY 400093Branch Offices:Pushpak Nurmohamed Shaikh Marg, Khanpur,AH M EDABAD 380001SPeenya Industrial Area, 1 st Stage, Bangalore Tumkur RoadBAN GALORE 560058Gangotri Complex, 5th Floor, Bhadbhada Road, T. T. Nagar,BHOPAL 462003Plot No. 82/83, Lewis Road, BHUBANESHWAR 75100253/5, Ward No. 29, R. G. Barua Road, 5th Byelane,GUWAHATI. 7810035-8-56C L. N. Gupta Marg ( Nampally Station Road),HYDERABAD 500001RI4 Yudhister Marg, C Scheme, JAIPUR 302005117/418 B Sarvodaya Nagar, KANPUR 208005Patliputra Industrial Estate, PATNA 800013T.C. No. 14/1421, University P.O., PalayamTRIVANDRUM 695035lnspecfion Ofice (With Sale Point) :Pushpanjali, 1st Floor, 205-A West High Court Road,Shankar Nagar Square, NAGPUR 440010Institution of Engineers ( India ) Building, 1332 Shivaji Nagar,PUNE 411005

*Sales Offxe in Calcutta is at 5 Chowringhee Approach, P-0. PrincepStreet, Calcutta 700072tSales Office in Bombay is at Novelty Chambers, Grant Road,Bombay 400007

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