22. CATHODIC PROP~CTION

The purpose d mthudk protection & ta protect metal pipe fm radd deterioration by electrolytfc cor'roslon or rlistlryl dire to contact with cotmslve'goils.

In Iowa t h resistivity of the mil [ohm-ern) Is the bast indicator of the potential for corrcsiwr of a mew glpe Installed in moist ts saturated mrrditiom, The relative affect 01 soil reslstiuity can be defined by ranges of mlativity as:

(1) Over 4,000 ohm-crn soil'has tittle or no adverse effect an zinc-coated CMP with life expectancy of ove'r 30 years.

(2) In 4,000 ohm-cm to '2,500 ohm-cm soils, ahc-costed CMP normally will bst 25 years or longer.

Asphalt coating rrr the "polymer* cwting, in addition to zinc. will .extend the Rfe 10. wars or .mote.. Cathodb protection should be cgnsitjtpd for wefut ife bayond 30 ts:40'years. when 4 plpe Is [nstaUed In soils In this resistivity roclga.

131 In. .2.M)O ohm-crn to 1,600 ohrn-crn :soils, C W . will require e coating.. In adGitCon to the zlnc coating for a 20- ta 25-yew life-expectamp.

Cathodic protection shodd be Installed at the, time of constrmtiorr to exlend Hfe beyond 20 to 28 years.

(4) Soils below 1,500 ohm-em sbhstluity ere quite corrwive: therefore* bath addittonal mating {either asphalt or polymer) a anodes are necessary to uwra a dfe byond 5 or 10 years for the zinc-coated CMP.

151 It la wcmrnended that ~ a t h o c t f ~ pmtectlon be c~nJid8red for welded %&el pipe (WGPI.

Cathsdk probction is designed et, protect th.e putside &face only of plpes which are in direat cmtact with the mil. It will not protect the pipe f r m corrosion from the inside to the- pipe exteriw. In amSs where there Is a history of low pH water or add diainagtt which has caused cotroded pipes, consideration should be given to using .some type of fully coated pipe+

The zinc cwtlng on CMP, In additim to protecting the ateel from direct contact with surt~unding:aoi~, acts as' a sacrificial mode to protaot tha 8tesL Asphalt of polymer coatings provide a further sagaration of pipe and soil along with some tfielectclc o p t s Anodes, usually pine w m a ~ n e i m alloy, sre generally used whare it is detwrnlned that corrosion may unduly limit the life of the.structure.

SCS TR No. 60, Earth D a m and Reservoirs, requres c~thodlc protectjm Qor corru~eted steel pipe and welded stael pipe in add whew wsistivlty in a saturated condition is less then 4000 ohm$- or whose pH is lower thm 5.0. The criteria for c.athdic protection is found in National -Handbook of Conservation Practices 430-FF. The theory of underground carrosion and the mechanics of cuthodtc protection are discussed in Dwlgn Note 1 2: 1993 revision.

Belsw reristivlties of 4000 ohm-cm, uphalt ot palyrnst coetingcr should not be used without cathodic potactiW; Areas whew ctm mating k .damaged.: dmrhmte fastar that pipe w l t h u coethq; Figw I and 2 show typical SCS mods i n e ~ l a t i o ~ far csthw3~ promtion of buried pipes.

t a t i o n

Anode

Sinals s node Instal lat ion - - - i q . I - Typical Anode lnst~llotion

Note: Anode$ .placed rride by $id& or ~ ~ r t l c a l l y shal l be spaced 20 feet apart.

Multiple Anode Instal la t ion

IEFM. Amend, lA41, April 1.9951

DESIGN PROCEDURE

1) Measure the soil resistivity, "Re" in ohm-cm, in proposed bwraw areas and/or along the proposed location of the principal spillway. If the pipe is already installed, measurements are to be taken of materials surrounding the pipe. Measurements shall begin at the ground surface and continue until the nominal pin spacing is greater than the borrow or pipe depth, whichever applies (see Soil Resistivity Measurements, form IA-ENG-36). The equipment needed for the soil resistivity test is a 4-pin direct current soil resistivity measurement kit. Select the value of resistivity for design based on the best e s t i m f , materials are or will be in place around the pipe.

2) Measure soil resistivity in the proposed anode bed location. Recommended pin spacing is 7 feet, assuming anode installation is 3.5 feet deep.

3) Estimate actual surface area of pipe which will be in contact with the soil, "A". Include any metal riser pipe, drawdown pipe, and anti-seep collars (see Table 1 ).

4) Estimate total protective current required.

a) For coated pipe (e.g. polymer coated CMP):

where: I = total current required, in milliamps (mA) C = pipe coating constant (see Table 2) A = surface area of pipe in contact with soil, in sq. ft. Reb = resistivity of backfill material around pipe, in ohm-cm.

b) For bare pipe (e.g. WSP or plain galvanized CMP):

where: I k = cathode current requirement, in mA/square foot. For galvanized pipe use l k = 0.2 to 0.3; steel pipe use I k = 0.5 to 1.0 for design. Use higher end of range where R% is low. Check with field measurements after construction.

5) Select anode material, size, shape, and potential. This may be a trial-and-error process to determine the most efficient anodes for the site. Zinc anodes are recommended where anode bed resistivity is less than 2000 ohm-em, or where design life is greater than 25 years. Magnesium is recommended where anode bed resistivity is greater than 3000 ohm-cm. Between 2000 and 3000 ohm-cm either may be used.

See Table 3 for a list of some commercially available prepackaged anodes.

Form IA-ENG-37, Cathodic Protection Data, may be used to record design and maintenance information and data.

I

(EFM, Amend. IA41, April 1995)

I,,, 4. Re,

whars: I, = current wltprt fey m g anode, in mA k = anode constant We T~ble 3) A% = mil rdetlvlty ill ?node b . d lwstten

81 D$tmhe ex@ected fife d anodes mlected.

when ' axpec~d~l i l~~r . j f mgnelliurn in&q! In Wars' W . - w81gt11 oj'shg~e brwano$e, in porn&.

It w@aed Ilte'is Jctadeqbrats. mlsct ,a d i f feht '@#e, mhjw dr p~mtiel of anqda and '#peat. aMps' 5l through 8). To get longer lib, :sdm an anode with-!a"m$lbr k value andldc gieater welght llawsr ratlo of kbNL

Nom..,ttlat mxtmm life qf a m Q n e 8 h y ~ d e 1s sbwt 25 para: m$.wrReds of 'burtent cequbammt .d;r b t b facmrs, dud to the relatively lw effklgrrq at'#$ rn~wlurrl allgy. A mlcul&td Hfq much hlgher than ;28 m g . $imply IrWcLW'tht Nrne ~f f)5B magmdurn will ' 'WL(B~W~"' f(o# intqrd mrmsim msohanlamb.

If ,alc,dptsd lik!L Jgnlflcemlv l o n ~ r than na~edlssry or much greatsr t b n 29 'yam; i e b ~ rn aridds with ,b high1 mio.:d k#V k~me.TaM@ 31,

For q ~ j & z t ~ l 35 to BQ'ymr da$igrr l f a , we1 of magnesium artodes meam the. mnef ar .aptmaw may need rb repwe the tlnoclett durirQ the dedgrr life ctf the .mmrec. If this i$ not fea$FWe, z1m grudas, m , y be 1) more al)prbg~ht$ .dhoice.

If 'mcpad lifm fs laadequate, add mom an;&$; cri try aq$Wi '&s with b Iamc rhtio of W+ It life is too Img, ~salwt:siza.with Kgkr W. '

9) Check wmpbmd. c s h d b .p to teah , system .sftet instalktiah m.~~ensucr that ctumnt &.po~enti#I a# Cfi thDI pmpw tarrge i6 prwldb:adqquate ~)ro@ktion. to tha pipe ::ISe.e MAINTEMNOE .seNon be!owJ.

SURFACE AREA OF METAL PlPE

Pipe Pipe Diameter Surface Area

Material (inches) (sq ft/ft)

WSP 6 1.73 WSP 8 2.26 WSP 10 2.81 WSP 12 3.34 CMP 112" corr. 12 3.57 CMP 1 /2" corr. 15 4.42 CMP 112" corr. 18 5.27 CMP 1 /2" corr. CMP 112" corr. CMP 112" corr.

:: iF :::: 30 8.69

CMP 1 /2" corr. 36 10.41 CMP 1 /2" corr. 42 12.1 1 CMP 112" corr. 48 13.82 CMP 112" corr. 54

60 y{ ;::: CMP 1/2" corr. CMP 1 " corr. 66 -L "21.75 CMP 1 rn corr. 72 q: L 23-70 CMP 1 " corr. 78 &, 25.65 CMP 1 " corr. 84 >, 27.59 -.. I

L. L; * All pipe, including drawdown, riser and principal spillway. * * Both faces of anti-seep collar after deducting the area of principal spklway pipe.

Area based on size on standard detail drawings 3-E-45956, 3-E-46967, and 3-E-46057.

TABLE 2 PlPE COATING CONSTANT, C

DESCRIPTION Fiber-bonded asphalt coated galvanized CMP Polymer coated galvanized CMP Class A coated steel pipe Class B coated steel pipe Tape-wrapped steel pipe

Anti-Seep Wlar Surface Area +

(sq ft)

C VALUE 1 20

I IEFM, Amend. IA41. April 1 995)

TABLE 3 PREPACKAGED ANQDES

ZINC ANODES: {EMF = -1.1 Vl

Bars Anode Weinht, Ib.

6 12 18 30 30 40 60

Packege Olmmirww Dism- x Len~th, in.

6 x 1 5 5 x 9 0 5 x 4 2 5 x 66 6 x 3 8 5 x a 1 5 x B 8

k Value. STEEL P i ~ e k#

18,000 3800 27,000 2258 33,000 1833 443,WO 1533 30,000 1000 38,000 844 46.000 787

k Valw, GALV- Roe

1 1.000 17,000 2 1 . o m 29,000 I s,ooo 24.000 as,ooo

'STANDAFlD POTENTIAL MAGNESIUM ANODES: lEMF .= -1 -55 Vl

bar^ Anode Weinht. lb+

1 3 5 9 17 32 50

Package Dimensinns R i m . x Lenath. 'In.

6 x 6 6 x 9 8 x 1 1 6 x 1 7

8.5 x 19 8 x 30 10 x 1B

k V a h , STEEL floe Nt'W 48.000 46.000 50,000 16,667 54.000 10.800 67,000 7,444 73,000 4.294

1 04,000 3,250 90.000 1.800

HIGH POTENTIAL MAGNESlUM ANODES: (EMF - ? -7 V)

.Bare Anode Weiaht. tb.

3 0 9

17 20 32 48

Peckage tXrnensians Piam- x Lemth. In,

6 x 9 6 x 1 1 6;x 17 6 x 30 6 n 82.5 8 x 30 B x 34

k Value, STEEL Pine kM( 62,400 20.667 67,000 1 9,400 B2,CJOD 9,Il I

1 14.000 6,706 I 0 8.860 1 23,QOO 4.000 138,000 9,878

k Val OALV.

28.0 31 ,0 39,O 41.0 45 .O 61,O 56 .0

~ n d d e size6 11sted arq tho88 avtjilable from Hereo Techndogtes as ot December 1993. The k v a l ~ ~ s wkrs caiwleted assuming pdarirsd plpe potenlid af -0.9 V for steal pips, -0.975 V for gelvsnimd pipe with rim anodes, -)+I5 V for galvanized with magnesium a~odes. VaILies of k for ather anodes may be emily calout~ted ~lsiw procedures in h s i g f i Noto 3 2.

IEFM. Amend. IA41, April 19951

EXAMPLE: Structure Design Life---------- 50 years

Given: Barrel length--------------- 154.33 ft. of 24" C.M. Pipe. ~)olymtar coated Riser length---------------- 10.1 2 ft. of 36" C.M. Pipe, polymer coated ~nt i -seep Collars------------------ 4 ea. ( 12 .12 '~ 7.67, polymercoated

Reb = 2200 ohm-cm Re, = 2000 ohm-em

Barrel Area = (6.97)(135.82)* = 947 sq. ft. Riser Area = 10.41)(10.12 = 105sq.ft Anti-seep collar area = (4)(189) - - 756 sa. f t

A = 1808 sq. ft. 'Excludes length of pipe not covered by fill material.

Trial 1 Current Required: It = = 5 2 0 ( 1 m = 98.6 mA

R=b 2200

Try 32 pound, standard potential, magnesium anodes k = 6 1,000 kMV = 1 906 (Table 3)

Current Output: 1, = - k = 61.00Q = 30.5mA R ea 2000

Number of Anodes Required: N = It I h, = 98.6 130.5 = 3'.5 SAY 4 Each

Expected Life: hag = 47(W1 = 47(321 = 49 years I m 30.5

Note: Exceeds expected 25 year life of magnesium. Try an anode with a higher k W ratio. (See the discussion about magnesium anode life under Design ~socedute above).

Trial 2 Try 32 pound, high potential, magnesium anodes

k = 88,000 kMI = 2750 (Table 3)

Current Output: Im = - k = B8,OOO = 44 mA Rea 2000

Number of Anodes Required: N = 4 1 = 98.6 / 44 = 2.2 SAY 3 Each

Expected Life: hag = 47iW) = 47(32) = 34 years I m 44

USE 3 Each 32 ~ound hiah ~otential mannesiurn anodes

(EFM, Amend. IA41, April 1995)

1. Anodeo should be placed kerkuntally in rsiation .to the qmnd surface mid aithw pw6llel er pecpemihbt h relatior, to the @pe+ Anoilks'ddl be placed at an elevation that will h u m the. anodes rm'ain moist. M a v 4 plaoe, .andea in fill ~ ~ ~ l .

2. Location of th4 rn0das.h &tion to the ~ipel iw 'is not cri-1 amp# In the cd'3e. .-of ,mgrsesium which must be piaced a minimum distaqcq of 50 kst aww from the pipeline or canduit.

3. Emi&ata hde @ verreh for anode W C ~ ~ W .

4, Pmpare b&lng for the anude.package.h thg W o r n af hcb m trench with well tamped. md8t dway dlt, clay t~am, silt or s i t loam, tn dandy and tysvslly arm?, fine mgtgtkl mwt be impprted, for bedding and lor w ~ r l n o the.mde$ to a. depth ot b in-

5- P~a.ce mOcM pacham in the prepared bod making rure that tha enode Is centered )n the packaae. b e -me caution not to .get the. an& pack- wet before it is pb&. . . Nsver lift the made by the lead . . wire-

6- After plrcemant, Irrmtq the made by pwrkrg water In the hale or m e h and let soah ih to iwia meistenins af the anode packaged backfill. TQ i w w the chemical backfill k irrfgrcted, the m.&a gackaga' may be punoturd with a pitchfork.

Complpte ba6kfllfing around mode d f h well tamped . f l a w $illln ppht 43 imhe) Qhua h m d a .

8, When aabdes zm p b c d in tight native clays, some prOvialm must be mu& t6 Inswe cmtlnued itrigatlm of the anode. This can be accomplhshed with sandy gravel "Fienoh drain*. TO insMII the: drain, backflll the trench st one end with mndy g r w l from enode depth to the surface of ths ground. The. trench length should extend sway $on, the anode 2 to 3 times the depth of the anmle, The gravel drain should not be placed kt contact with the amah as the gravel, wwld reduce the current amput 30 to 50 percent. Ptovide at least one Bquare foot of gravel drain am to the soil surface.

9. Where seueral ~anodb3 aie. to be installed. at s side locbtiori. the arrades may be connected to a A d e r wke. The header wire .may be connected dirgctly to the pipe, at, pwfembly, be #.a3ssd through a test box to p'tibmlt periodic measument of output currant and calwlatim of probsble life. Attach. lead wire to tha pipe by a powder weld. process rndldng sute that the .distuibed pipe costing i8 repelred.

It ls racomertded ti-m not more thao three sndba be connected to each haad&r wire. For hstdlktlw$ with more than 3 amd@s. two Qr mow hkder wims are recommsn&d. T ~ s : ~ I ~ ~ s $om8 anodes to be dlscmnected If voltage output i s found to be too h$h.

The lead wire From each anode shall ba cmnected to the header wim. preferably by tin-lead mldering. W m the I& wire around the header wire a minimum of 6 wraps prior to sddering, Tha conmtiott then needs to be mode waterproof by wrapping wlth three byera of rubber taps :and then three wraps d vi~yl electrical

!AM l&l {EFM. Amend. lA41, April 1995)

- tape. Prior to wrapping, the connection shall be thoroughly cleaned to remove all foreign material and moisture.

10. When using a test box, connect each header wire and the lead wire from the pipe to a separate stud in the test box. Complete the circuit between pipe and anodds) by using shorting bars or jumper straps between individual studs. These bars or straps are utilized to help eliminate problems of oxidation of the copper wires connected to the test station. Do not connect wires by just twisting the ends together around one stud. Oxidation at twisted wire connections over time can interrupt the current flow.

3 4 ill-] 11. Backfill remainder of trench with native soils leaving a 6 inch surface depression

for irrigating the anode. m MAINTENANCE

Cathodic protection systems need to be checked during installation and once every 2 to 4 years thereafter to make sure they are functioning properly. Testing of the system is straightforward but special equipment is needed. Each cathodic protection system has a test box installed to facilitate testing.

The anodes make a very low voltage-current flaw system with voltage and current flow less than that of a 2-cell flashlight. As the anodes corrode to supply the small current, they are being "sacrificed" to keep the pipe from corroding. Eventually, the anodes are used up to the point where, like a battery, they cease to function. The most likely problems in a system are a broken wire, broken connection,, or broken weld. A

I-; 'Fig. 3 - Schematic o f a Cathodic P r o t e c t i o n I n s t a l l a t i o n

(EFM, Amend. IA41, April 1995)

Bask!. equipmt wded to perform the tesa' is a$ follows:

a. 2W to 300 feet of rubbef-CmW. stranded R 1 8 wim with @el+

b A dt-&m-mlmamp (mMt memi with OC Wt range$ of d to 2 5 or 3 vdts, millimp ranges af 6 to $80 4th tw9:bwer mrrxinium deftection.ra.wm. and ohm isnges vu4th~~xparrdsd scale In the 1 to 6 + &rn range,

c. A wpfler-oopper sulfat~ halfdell with Wroua plug+

d. Twa or three 4 R+ to 8 . k beds of #1& wire with mall alligator cC[p&

The FIW tests.nomaly ussd for checking the system ere:

TKi. test .shcwtd alwdy$, Iptj dbm first ~ P W B 8w GkcuIta CUB dWmn&ted+ Orre reading at the inlet and me at tb outlet arrc rei;anmended. the half-ael .should btf at least five feet km the g@e; this test .Is pefforwb firat &nee. upon.dlsconrpecti~~. the system mn&.tt, begofaclze.and the voltaw . . hegln& to drop.

Fig. 4 - Schematid B f Usin Coppcr-Coppcr 5ulf-ate Half-CtI l Pips to S o i l PO 9 entcoj

The COPPBPU~~~BI $ultSt8 half-wll is a spachliztrd hall of e battery cell. W h it is plamad in .wntact with rnoistarltd aoil mi conmcted through h e VGM (volts DC mdel to s metal contatit with thO sad it win produce .a .carriparatim vdw8 fw the met81 to. soil, The cmper~adve voltage for s wrrupted iron or steel plpe t h t M pmtected 6hould be between Q;86 volg .mi 1.20 vdts Inagstrvs pottintiala). Less. tbrr (5.80 vdf memg thB pipe k 'wbddy ~6rrudhq 'hd additlmal anodes should be dtled, Voltages morn nugativa thsn -1 .S m y came the aim coating to separae Crm the steal pipe dm to the formstim of hydrogen gba'twBblw mdsc the surfaceA Shm anodes may need to be t e w r 8 r i l y tt1acmhBcmd Ifom the agwm. reducing the drivirlg voltage.

[EFM, Ammd. IA4 1, April 1888)

2. MEASURE THE CURRENT FLOW (from the anodes to the oiw, Fia. 5)

Because of the depolarizing process mentioned above, the current flow should be checked next. Connect the VOM (milliampere mode) to the lead wire from the pipe and the header wire from the anodes. During this test you will notice the current decrease as the pipe and anodes are disconnected. Record the maximum reading observed as the current flow. The current flow could vary from 5 me (0.005 amp) to 300+ ma (0.3 amp), depending on pipe area, soil resistivity, and soil moisture. A current flow larger than the design current usually means the pipe is protected to a higher level than needed. This wastes the anode and will result in reduced anode life. If the current is more than 1.3 times the design needs, a resistance should be added to the circuit. This is done with a length of special high-resistance wire connected to the circuit in the test box. Another method involves disconnecting an anodeis) from the system.

F ig . 5 - Schematic o f Anode to P i p e Current Flow

Test No. 1 should be repeated with the circuit open (anodes disconnected).

4. ANODE TO SOIL POTENTIAL (O~en Circuit. Voltaae ou t~u t of the anode. Fia. 61

This test is a comparative test using the copper-copper sulfate half-cell connected through the VOM (volts DC mode) to the lead wire from the anode. The normal anode voltage will be in the range of 1.4 to 1.8 volts for magnesium anodes, and around 0.85 to 1.2 volts for zinc anodes. A reading of 0 to 0.3 volts means the wire or a connection is broken between the test box and the anode. Sometimes this can be corrected by digging to the base of the post or the test box assembly (as applicable) and back toward the anode and checking the wire for breaks. The break is often at the base of the post because of the post having been knocked over. See the schematic drawina following in Figure 6.

(EFM, Amend. IA41, April 1995)

1% sat i t a p

Fig. 8 - Schen~tic of Y o J t ~ g e Potahfiol o f Anode t o Copge r-Cappe r Su l f g t i Ha l f -Ce l 1

The gipe. should act like one large wire from tha inlet to the last fully buried Joint so that current faadded fmm the anodea will flow through and pateet the total bngth of the pipe. Since a poor weld ursder the earth fll is nearly irnpoasibbe.to mrrsct, the pipa must be thcoughly checked bgha backfill k carnp!et#d, Thla can be don6 by two different methods. These w t s should be m d s during mrumuction and 6 ~ t ~ h time that the System 19 tested t h e r ~ f t e t .

M o d 4; C~nnect the pipe Inkt and lutlet in a circuit through a VUM. If the circuit 1s complete, the voltnge shuld be mra, Gnca tha pig@ Itself h ~ s ne driving voltage, Bee figwe 7A belaw:

Fig. 7A- Schematic o f l a s t s for Pipe C o n t i n u i t y

Method 8: A similar test is shown in Fig 7B. This test involves measuring the pipe to soil potential at both the inlet and the outlet with leads that are connected successively to the inlet and the outlet. The voltages measured at each location should be equal since the reference cell stays in the same position. The voltages may vaty slightly from inlet to outlet because of different soil conditions.

s u ~ f a t e lWSR I

I o k VOM set t o DC sca l e

i ngs

Test a t i n l e t

Test a t o u t l e t

F ig . 78- Schematic-of Tests f o r Pipe Con t inu i t y

Typical Continuity Check Readings Using Method B of Fig. 7

Wire Connected Reference Cell Reference Cell To P i ~ e At at Inlet at Outlet

1. Inlet 741 mv 708 mv

2. Outlet 741 mv 708 mv

Readings are equivalent, therefore the pipe is continuous.

(EFM, Amend. 1A41, April 1995)

United States tkwnment of Agriculture Natural ResourGes Censervation Service

IA-ENG-37 April 1995

CATHODIC PROTECTION DATA

Owner or Project Site District

Soil Resistivitv Measurement: (from IA-ENG-36)

Soil Resistivity at Pipe Depth - - ohm-cm Soil Resistivity Used in Design = ohm-cm = Reb Soil Resistivity at Anode Bed - - ohm-cm = Re,

I Anode Desian

I TYPE-STRUCTURE: i I#! I in. Diam. Pipe with Icier1 IhM) inlet

l and (cantilever) (Flume) outlet.

i Protective Coating: Coating Coefficient C (1

Area to be Protected in. Diam. Drawdown Pipe in. Oiam. Riser in. Oiam. Prin. Spwy. ea. Diaphragms ( in, , Diam.)

ft. @ ft. @ ft. @

@ sq (A) TOTAL

ft/ f t = ftfft = ft/ft = f t = - -

I Anode Material: - Zinc Anode Coefficient k: (2) - Standard Potential Magnesium

I - High Potential Magnesium USE (N) each of (W) Ib

Total Current Required I t = C(A/Re b 1 = It = Ik(A) = (coated pipe) (bare pipe)

Effective Life: Lmag = 47 N (W/Io) = yrs. Lzn = 31 N (W/lo) = yrs.

Date Installed: Structure Anodes

Potential Anode Date Inspector (-Volts w/Cu/CUS04 Current Effective Remarks

Electrode) (Milli- Life Pipe to Pipe to Anode to Circuit Amps) Years Soil Soil Soil Thru ANODE tc IClosed (Open (Open Pipe Pipe Circuit) Circuit) Circuit) OK lo Y .85 to 1.2 1.1 to 1.7

(1 See Design Note #12 & National Handbook of Conservation Practices 430FF I (21 See ~ e s i g n Note #12 i Rluesnr

(EFM, Amend. IA41, April 1995)