PlacerHandbook-SettlingPonds

8/12/2019 PlacerHandbook-SettlingPonds

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L SK DEP RTMENT OF ENVIRONMENT L CONSERV TION

PL CER MINING SETTLING PONDDESIGN H NDBOOK

L SK W TER QU LITYM N GEMENT PL NNING

PROGR M

his handbook ded l -...;j th th e consttu


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PLACER MINING SETTLING PONDDESIGN HANDBOOK

STATE OF ALASKADEPARTMENT OF ENVIRONMENTAL CONSERVATION

January 1983

Prepared By:R M CONSULTANTS INC.711 GaffneyFairbanks Alaska 997111

TABLE OF CONTENTS

IntroductionRecommendations Regarding Water UseSettling Pond LayoutsContainment Darns and Control Struc tures

Containment DamsPond InletsOutle t Struc turesOverflow SpillwaysRiser Outlets

Pond Sizing and DimensionsMaintenance and RestorationDesign ExampleStep-By-Step Worksheet Example

LIST OF FIGURES

112336789

101214

FigureFigureFigure

OneTwoThree

Example Placer Mine Settling Pond LayoutTypical Section of Containment DamOverflow Spillway Construction

Figure FourFigure FiveFigure SixFigure SevenFigure EightFigure Nine

Typical Riser Type OutletDesign Requirements for Riser Pipe and SpillwayOutlets from Settling PondsSettling Pond Surface Area RequirementsDetermination of Sluice Box FlowRelationship of Length Width and Surface AreaRectangular Settling and Presettl ing PondsRelationship Between Cleaning Interval and SurfaArea of Presettl ing Ponds


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EXAMPLESTEF-BY-STEP WORKSHEET

1) Sluice box:a} Slope in /f t )b) Width inlc) Depth-of-flow (in)d) Flow rate ( f igure 7 gpm)2 Daily volume of mater ial pro essed (cu. yrds.).3) .l Lesettl ing pond depth (f t) .

Desired ~ s t t l i n g pond cleaning in terval (days).5) .l Lesettl ing pond surface fre = resu l t s from figure 9 x (3depth) a ft ) 6) .l Lesettl ing pond length-to-width ra t io

Page 2EXAMPLE

17) Riser pipe diameter in) .or

spillway width (figure 5)and individual spillway widths to ta l(f t) 18) Dimension summary

7) .l Lesettl ing pond length (f igure 8) f t ) . .l Lesettling pond8) .l Lesettl ing pond width length L:W ra t io _______ f t ) .9

l l l )

11)

Percent recycleD e a i < ~ n volumetric flow rate [sluice box flow rate x[ \ recyc le+ lilll)] (gpml.

Se t t l i ng pond su r face area necessary to meet 11 2 ml/1set t leable solids l imi t without insta l l ing baffles (figure6 (acres).*12) Set t l ing pond surface area necessary to ob ta in maximumsedimenta t ion withou t i n s t a l l i ng ba f f l e s f i gu re 6)x (acres) .13) Settl ing pond length- to-width ra t io14) Settl ing pond length (f igure B f t ) .15) Settl ing pond width length L:W ra t io (f t) .16) Number of outle ts ( f igure 5)

In most cases the pond surface area wil l need to be the sizedetermined in th is s tep.

Cleaning in tervalLengthWidthDepth

Settl ing pondLengthWidthOutlets

NumberPipe diameterSpillway width(s)

(ft)number

(days)f t )f t)ftl

f t )ftl

(inlf t )


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SETTLING POND DESIGN H NDBOOK

This handbook presen t s recommendations for the designconstruc t ion and operation of set t l ing ponds to reduce the amountof soi l par t i c les in wastewater discharges from placer miningopera t ions .

The amount of sedimentation tha t occurs in a se t t l ing pond isaffected by many variables. Some of the most signif icant factorsinclude:

Surface area of the pondRate of flow through the pondThe grain size dis tr ibut ion of the incoming sedimentShort circui t ing of flow across the pondEntrance and exit effects

Other factors that can affect sedimentation include the specificgravity and shape of the incoming solids, the water temperature,and the turbulence within the pond as a resul t of wind, rainfalland other forces.

B C O ~ M E N D h T I O N S RG RQING ]WA minimum of water should be used. The less water used to mine,the less wastewater tha t needs to be t rea ted in the miningoperat ion. Any device or method tha t can be used to cut down

water qse and treatment helps. A reduced volume of water used inthe mining process resul ts in a reduced s ize of se t t l ing pondnecessary to achieve a given level of sediment removal.

Cla ss i f i c a t ion of s l u i c e feed mater ia l using g r i z z l i e strommels, screens, wobblers, vibrating tables, washing plants andconveyors) i s helpful in cutting down on the water used.Reuse of process water can also reduce the quan t i ty of water tobe t rea ted and discharged to the receiving stream. Reuse ofwater is pa r t i cu l a r l y advantageous where there is l i t t l e wateravailable. Normally, preset t l ing of the sluice discharge wouldbe desi rable to remove coarse sediments before the water i srecirculated back to the sluice.

SETtLING L YOUTS

For effective sedimentation, overburden should not be allowed toenter the settl ing pond and the mine discharge water and streamwater should not be allowed to mix upstream of the settl ing pond.Thus, construc t ion of a se t t l ing pond within a widened section ofthe stream is not recommended. Location of se t t l ing pondsoutside of the stream bed i s also an important consideration foravoiding washouts of the se t t l ing pond during periods of highstream flow or floods.


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I t should be noted tha t the cons t ruc t ion of a se t t l ing pondwithin a f ish stream would require a stream blockage permit fromthe Alaska Department of Fish and Game. AS 16.05.840, FishwayRequired

An example of a good layout of a mining operat ions is shown inFigure One.

CONTAINMENT CONTRQL STRUCTURES

ContainmentProper design and construction of settl ing pond containment damsi s a necessity to avoid dam failure. Factors to be considered inthe design of these dams include:

Height of the damCrest width and f i l l slopes of the damMaterials used in dam constructionConstruction proceduresAvoidance of flood damageDetails of outle t s t ructures

For safe ty reasons, dams should usual ly not exceed 10 feet inheight . I f t e r ra in condi t ions or other factors indicate tha t agreater height would be necessary to achieve the required ponds ize i t would often be more desi rable to construct several

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smaller ponds in ser ies that have lower dam height. Constructionof dams tha t have a height greater than ten fee t may require apermit from the Alaska Department of Natural Resources and s i tespecific engineering design if a downstream hazard to people orproperty exists .

Dam and pond s i t e s are l imi ted on a mining claim but ef for tshould be made to choose the best ava i l ab le si te . This wil lprevent fa i lure and subsequent rebuilding. Care should be takennot to locate a dam where i t s fa i lure would resul t in loss ofl i f e in ju ry to people or equipment, or in ter rupt ion of otheroperat ions . The s u i t a b i l i t y of a s i t e is also dependent on theabi l i ty of the soils to hold water.

Mining and explorat ion dr i l l ing provide an excellent opportunityfor s i te investigation. When borings or tes t p i t s are made theresulting samples should be viewed in terms of s i t e sui tabi l i tyas well as gold content. A record can be kept during explorat ionand/or mining showing locat ion depth and classes of mate r ia l .This i s l a t e r used to f ind the best locat ion for the se t t l ingpond.

An ideal dam/pond s i t e is on or underla in by a thick layer offa i r ly impervious consolidated material . Where these materialsoccur a t the surface or where bedrock has already been reached bymining, no special measures are required.

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I t is recommended tha t containment dams have c res t width of a tl e a s t twelve f ee t and upst ream and downstream s lopes of 2:1hor izon ta l :ve r t i ca l ) or f l a t t e r when cons t ruc ted of g r anu la r

t a i l i n g m ate r i a l . F l a t t e r s lopes 3:1 o r l e s s ) may beappropr ia te where dam he igh ts exceed t en f ee t , or where f inegrained mater ials are used in dam const ruct ion .

Granu la r t a i l i n g s ma t e r i a l i s u s u a l l y s u i t a b l e f o r damcons t ruc t i on , prov ided t h a t the inner co re o f the dam i scons t ruc ted of r e l a t i v e l y impervious mater ia l . This can beachieved by use of an impermeable bar r i e r of p la s t i c s hee t ingwithin the dam or by mixing s i l t y overburden materJala with thet a i l i ngs . The mixture sho-uld con ta in a t l e a s t 12 percen t , byweight , of silt sized par t ic le s as measured with respect to theweight of those t a i l i ng t h a t wi l l pas s a 3 inch mesh s ieve .

I t i s d e s i r a b l e t h a t the impervious m a t e r i a l in the dam extendthrough s u r f i c i a l pervious foundat ion so i l s in to under lyingbedrock or other impervious so i l s .

A typ ica l c ross sec t ion of a se t t l i ng pond containment dam i sshown in Figure Two

The dam should be cons t ruc ted by plad ing the t a i l i ngs in t h i nlayers less than twelve inches loose thickness) and thoroughly

compacting each l aye r before the next l aye r i s placed. As minimum compactive e f fo r t should cons is t of repeated passes oheavy ear thmoving equipment un t i l a dense, f i rm embankment i sachieved.

I t has been found tha t se t t l i ng ponds are more e f f e t i v ~ i fs lu iced mate r ia l is di s charged to a meander ing t a i l r ace thal eads to the pond. This a l lows t a i l i ngs and sand par t i c l e s tos e t t l e out before they reach the se t t l i ng pond, prolonging thel i f e of the pond before it becomes f i l l ed with sediment.

C ons t ruc t ion of a small prese t t l ing pond a t t he pond en t r ancewil l reduce inflow ve loc i t ie s and resu l t in addi t ional deposi t ioof coarse sediment before it reaches the pond.

The recommended prese t t l ing pond can of ten be cons t ruc ted withr e l a t i v e l y littl e f f o r t by placement of a shal low berm oft a i l ings across the t a i l race . Coarse sediments depos i ted behindthe berm can usually be removed wi thou t d i f f i c u l t y wi thbulldozer. Frequent removal of th i s mater ial would t yp ica l ly ber equ i r ed . C ons t ruc t ion of a prese t t l ing pond with a berm oft a i l i ngs can a lso serve to spread the en te r ing f low ac ross thee n t i r e width of the se t t l i ng pond, thus reducing the po ten t i afor f low to become concen t r a t ed in only a por t ion of the width o

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t he pond ( shor t c i rcu i t ing ) . Mul t ip l e i n l e t s t ruc tu ress e rve to reduce shor t c i r c u i t i n g and t hus could enhance pondef f i c i ency .

The su r face area of the p r e s e t t l i n g pond shou l d be about onesquare foo t for each gallon per ~ i n u t e of f low through the pond.

Structures

Out le ts shou l d be cons t ruc ted to l i m i t the l eve l of the watersu r face to a t l e a s t one foot be low the top of the dam. I t i srecommended t ha t , where a c o n t i n ~ e n t dam is subjec t to periodsof high flow an emergency overflow spi l lway be constructed in alow por t ion of the dam. This e ~ e r g e n c y sp i l lway shou l d bede s i gne d to re lease storm surges before over topping of the damoccurs. As such the required width of the emergency spi l lway iss i t e dependent , varying wi th the f l ood flow c h a r a c t e r i s t i c s ofthe s tream. The e leva t ion of the emergency ove r f l ow sp i l lwayshou l d typ ica l ly be about one ha l f foo t above the normal watersurface e leva t ion in the pond.

Out le t s t ruc tu res may be of the ove r f l ow sp i l lway type or maycons is t of a culver t pipe with r i se r , as descr ibed below.

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overflow Spillways

Overf low s p i l lways from se t t l i ng ponds need to be c a r e f u l ldesigned and cons t ruc ted to avoid eros ion or washouts froffi thpond di s charge . Spi l lway eros ion pro tec t ion on the downstreas lope of the conta inment dam and a t the toe of the s p i l lwashould cons is t of a minimum two foot thickness of angular rockaveraging e ight inches in i t s l eas t dimension. The cres t of dasp i l lway should be protec ted h a t l eas t a one foot th icknesof four inch angular rock. The width of the s p i l : ; ~ a y should ba t l e a s t one foot for each 4 1l ga l lons per min u te of f low th rougthe pond. This should l i m i t the v e l o c i t y of the pond di s chargs u f f i c i e n t l y to avoid eros ion of the containment dams i f thtibove recommended eros ion protect ion measures are provided. Al e a s t one s p i l lway shou l d be prov i de d for each 150 fee t of ponwidth t o l i m i t nonuniform f low v e l o c i t i e s ( shor t c i r c u i t i n g th rough the pond. I f a source of angular rock i s not ava i lab lfo r e ros ion pro tec t ion , a r i s e r type of o u t l e t should be usedAlternat ively, f i l t e r cloth, p las t ic shee t ing, t imber cribbingor other m a t e r i a l s may be used in the sp i l lway fo r pro tec t iofrom eros ion.

The recommended des ign de ta i l s are i l l u s t r a t e d in Figure Three.

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OutletsRiser ou t l e t s should be constructed of culver t pipes having adiameter of a t l eas t 18 inches to l imi t the potent ia l forobstruct ions from f loat ing debris . At l e a s t one inch of pipediameter should be provided for each 108 gal lons per minute offlow through the pond. At leas t one r iser should be provided foreach 150 feet of pond width to l imi t nonuniform flow veloci t iesthrough the pond.

Several cutoff col lars should be ins ta l led around the portion ofthe pipe that passes through the containment dam. These col larsare necessary to prevent erosion of f i l l mater ia ls by seepagealong the pipe. The cutoff co l l a r s may consis t of sheet metal,polyethylene sheeting or other impervious materials and shouldextend at leas t two feet beyond the pipe.

An apron of large rock approximately s min. dimension) or othersu i t ab l e mate r ia l should be provided at the pipe ou t l e t toprevent eros ion at the toe of the dam.

The recommended design deta i l s for a r i ser type of ou t l e ts tructure i s i l lus t ra ted in Figure Four.

The required number of r i ser or spi l lway out le ts the requiredsize of r iser pipes and the required to ta l spi l lway width can be

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determined from Figure Five, given the se t t l ing pond width anddischarge flow.

AND DIMENSIONS

Typical permit conditions for placer mining l imi t the amount ose t t l eable sol ids in the water leaving s e t t l i ng ponds to 0.2 mof solids per l i te r of water. Recent f ie ld tes ts of placer minse t t l ing ponds conducted in 1\laska showed tha t removal bysedimentation of suspended soi l par t ic les larger th,o;, ll.B2 ro isnecessary to consis tent ly meet th i s l imi ta t ion on se t t l eablesolids. Resul ts from these same f ie ld t e s t s ind ica te th asedimentation of 9.02 mm soi l par t i c les wil l occur i f thesettl ing pond overflow rate is 3799 gallons per minute per acreor less . The overflow ra te is the flow ra te through theset t l ing pond, divided by the surface area of the set t l ing pondFor example, a se t t l ing pond having a surface area of two acresand a flow of 1599 gal lons per minute through the pond would havean overflow rate of 759 gallons per minute per acre).

Sedimentation i s considered to be effect ive in removing onlythose suspended soi l par t ic les that are larger than 9.902 mmTherefore, to reduce the sediment concentration of the set t l ingpond discharge to i t s minimum at ta inable level the set t l ing pondshould be s ized to remove soi l par t i c les t ha t are 0.002 rom indiameter , or la rger . Results from se t t l ing pond f i e ld t es t s


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ind ica te tha t the sedimentation of par t i c les of th i s s izerequires a se t t l ing pond with an overflow ra te of less than 860gallons per minute per acre.

Sett l ing ponds should be designed to achieve the maximum removalof suspended part ic les that can be attained by the sedimentationprocess when receiving stream di lut ion is not su f f i c i en t topermit compliance with sta te turbidi ty standards. Since in manycases sedimentation wil l lUll be su f f i c i en t to meet s ta teturbidi ty s tandards add i t iona l t rea tment wil l be necessary tomeet these standards. Complete recycling would reduce the needfor any stream discharge or additional treatment.

The necessary se t t l ing pond areas to reduce se t t l eable sol idsconcentra t ions to l e s s than 8.2 ml/1 and to achieve maximumsedimentation can be determined from Fi rure Six given the flowra te through the s luice box and the P cent of water tha t isreused and not returned to the stream. The flow rate through thes luice box can be es t imated from measurements of the flow depthand the slope and width of the s luice box using Figure Seven.This Figure is based on a n n i n g ~ equation for uniform flowthrough an open channel with an effect ive roughness coefficientof 8.832 fee t 1/6 based on flow measurements through a number ofoperating s luice boxes. I f the effective roughness coefficientdi f fers from th i s value the flow est imate wil l be off to thatdegree.

In order to l imi t short ci rcui t ing of flow pond s sh ould beconstructed with a length tha t is at l eas t twice the width. Alength- to-width ra t io of 5:1 or greater i s des i rable wherepossible.

The insta l la t ion of baffles or other part i t ions that divide thepond in to several compartments will also reduce short circui t ing.A baffled pond can thereby be as effect ive in removing sedimentas a larger unbaffled pond.

The required dimensions of the pond needed to sa t i s fy neededsurface area and l ength- to-width ra t ios can be determined fromFigure Eight.

MAINTENANCE HQ RESTQBATION

Frequent removal of coarse sediments from preset t l ing ponds willnormally be necessary. This would be expected to be accomplishedwithout diff icul ty using a dozer.

The percentage of processed pay d i r t t ha t i s deposi ted bysedimentat ion in a preset t l ing pond is dependent upon the s ized i s t r i bu t i on of soi l par t i c les in the pay d i r t the length andconfigurat ion of the t a i l race between the s luice and the pondthe ra te of water use the surface area of the pond and othervariables . Typical ly however about 1/6 of the volume of pay

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dir t is composed of sand sized part ic les that would be too smallto be deposited in the ta i l race and too large to pass through thepreset t l ing p o n ~ Figure Nine shows the approximate relationshipbetween the surface area of a preset t l ing pond, the ra te ofprocessing of pay dir t , and the in terval between cleaningoperations in the p o n ~

Cleaning of settl ing ponds should be accomplished when the pondi s f i l led with suff ic ient sediment to lower the quality of waterdischarged from the pond below acceptable s tandards .Monitoring pond effluent on a regular basis with an Imhoff conei s the best method to determine i f the pond i s becomingineffect ive due to f i l l up or other causes such as shortcircui t ing.

Cleaning can usually be best performed with a dragl ine. I f adragl ine i s not ava i l ab le , t may be pract ica l to remove theaccumula ted sediment with a dozer during the spr ing while thesurface i s thawing but the underlying sediment i s s t i l l frozenand can support sediment removal equipment.

Sediment removed from se t t l ing ponds should be stacked to allowdrainage to occur and capped with a layer of t a i l ings or othergranular materials to prevent r o s i o ~

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If cleaning i s impract ical , or the s e t t l i ng pond i s to beabandoned for other reasons, i t should be drained and capped withsuff ic ient thickness of ta i l ings to form a firm, stable surface.

Draining can be accomplished by breaching the containment dike,provided tha t a lower conta inment dike of permeable granularmaterial is constructed downstream of the pond outle t to preventaccumulated sediments from enter ing a stream.

JlES IGli EX M PIE

A placer mine processes 750 cubic yards of pay d i r t per daythrough a sluice box having a slope of 1 1/2 inches per foot anda width of 42 inches. The depth of flow in the box is fourinches.

1. What i s the rate of water flow through the sluice box?Flow 3798 gal ./a in . (See Figure Seven)

2. What size should the preset t l ing pond be to remove sand sizedand larger part ic les?

Presettl ing ponds should have a surface area of at least onesquare foot for each gallon per minute of flow through thepond.1 sq. ft . /gal. /min.) (3788 gal. /min.) 3788 sq. f t .

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3. What s ize should the preset t l ing pond be to l imi t requiredcleaning to a two week in terval?

Ass ume a 2:1 length- to-width ratio .A surface area of approximately 14,999 square feet would berequired for the prese t t l i ng pond, assuming a uniform 3foot depth and sedimentation in the pond of 1/6 of the t o t a lvo l ume of the mater ial being mined. See Figure Nine}A 14,1HJ9 square foot surface area at a 2:1 length-to-widthra t io requires a length of 168 feet and a width of 84 feet .See Figure Eight)

4. What s ize should the se t t l ing pond be to reduce . se t t l e ab l esolids concentrations to 9.2 ml/1 no water reuse)?

To achieve set t leable solids concentrations of less than 9.2ml / 1 the se t t l ing pond should have an overf low ra te of notmore than 3790 gal lons pee minute per acre. The pond lengthshould be a t l eas t two t imes i t s width to l imi t sho.rtcircui t ing of flow through the pond.Minimum Surface Area, acres Flow Rate, gpm 3709 gpm peracre)

1.9 acre See Figure Six)Minimum Length (using the minimum 2:1 length- to-width rat io)

296 (See Figure Eight)Minimum Width = Length I 2 148 feet

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s. What s ize should the s e t t l i ng pond be to obtain maxiQumsedimentation (i.e. resul t in sedimentation of part ic les having adiameter of 9.992 mm and larger)?

6.

Assume no water reuse.To obtain maximum sedimentation, the s e t t l i ng pond shouldhave an overf low r a te of not more than 869 gallons perminute per acre.Minimum Surface Area, acres = Flow rate , gpm 869 gpm perace e)

4.3 ac.res (See Figure Six)Minimum Length (using the minimum 2:1 length-to-width ratio)

612 feet See Figure Eight}Minimum Width Length I = 306 feetBow many ou t l e t s should be provided and what s ize should

they be?

7.

At l eas t one r i ser pipe or spi l lway ou t l e t is required foeeach 159 fee t of pond width. Thus, for a pond having awidth of 396 fee t t h r ee ou t l e t s would be requiredconsis t ing of 18 r i ser pipes or spi l lways having a to ta lwidth of at least 10 feet. (See Figure Five}

What s ize of se t t l ing pond i s necessary to obtain maximumsedimentation i f half of the process water i s rec i rcula tedthrough the sluice box?

Assume a 2:1 length- to-width ra t io of the pond

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2 2 acresrea = surface (See= 432 feetond LengthFigure Six)See

Figure Eight)216 feetond Width =

A comparison ofrecirculationr J percent

d thecle case anfor the nonre y follows:d mensions i s asond l d above,Presentease, as

Pond widthPond LengthPond Area

culationiQ ecu_306 Feet61 2 Feet4 3 Acres

7

2 6 Feet432 Feet22 Acres

Containmentam

t dan forontainnenArea of b r e c ~ dewaterl og r TypeeOO of season Rise tructuresOJUet S

pm E OOE


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Water Surfac.:eSett l ing

Pond

. ."::,t ~ 1A ~ l i n g s )

Zone Having jm. U i l t Sizlkl ~ t i l e s 'tlervioll S ~ t i o a ~ t e l > i a ~/

TYPICAL SECl'ION CF


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~ ~ater Surface ...,..l ------.....~ t t l i . n gPord

TYPICAL RISER TYPE anu:T

FtaJRE f(1JR

Required futal Spillway Width, Feet

69 1 I 2 I 3 J I 5 . 6 7 8 9 10 11 12 l3114tl50 f >I59 0 IRiser Pipe Diameter, -nches fl'ypical)

{t 18 I 24I40 3@ KI --- _., GfI39 I 24" 39" 220 III

109 24 39" 36" 142"I 48" 54 69" 1i

0 1009 2990 3000 4900 5000 6090Sett l ing Food Discharge Flow, gal/min

Given:( ) Settli.ng Prod Dischal:ge Flow c 371 0 gpn@ Sett l ing Prod Width = 306 feetFind: Nuutler of required r iser or spillway outletsRequired total spi l lway width if spillway outlets are provided)Required diameter of r iser pipes if r iser outlets are provided)Q 3 Riser or spillway outlets required@ Required to tal spillway width 10 feet Required diameter of dse r pipes 18 inches(as indicated a t discharge flow and pond width intercepts)

FIGURE FIVEDesign Requirements For Riser Pipe ArxlSpillway CUtlets Fran Settli.ng Ptnis

Il l.j )

.j )

&'"'

0


15/16

"'0

1-'C00

......f.r:se.Q

w0g

w'0

;000 Q

;..

Required Sett l ing 1'ttld Surface Area ToCl>tain Haxim1.111 Sedimentation, Acres

0 C> 0.. ....

...IIIIIIIIIIIIIIIIIIIII

....Q

Required Settling Pald Surface Area To Redl.lceSettleable Solids O:llcentrations Below 0.2 ml/1, Acres

lji..

lir

....

..

89

' 60.540....:20f....."...


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Presettling Pond Length, Feet0 100 2llll 309 409 500 6006

49,1100.J

5 '.i.;Ql.:.4 39,1 l902l'3 211,990

Rs.-i

2 -------------w111,000

+.1+.1iA9

J 400 898 l l l l l l 12119 149a l6llllSe t t l ing Pond Length, Feet

Given: Given:( ) Preset t l ing Pond Area 14,1100 sq. ft @ Sett l ing Pond Area " 4.3 acresFind:

G

Length = 2 X Width Length 2 X WidthFind:

PJ:esettling Pond Dimensions Settling Pond DimensionsPald Length .. 168 fee t Pond Length 612 feetWidth " Lengtiv'2 Width I.erlcJtiV2.. 84 feet 3116 feet

FIGJRE EIGlTRelationship o f Length, Width an:1 SUrface AreaOf Rectangular Sett l ing an:1 Preset t l ing Ponds

0l i. -21_'.s ....

FIQJRE i lRelationship Between Cleaning Interval and Surface Area of P resettling Pond

Given: G Desired cleaning interval of presettling {XlOd 14 daysQ) 750 Ol yds. of material processed through sluice box perFind: ~ i r e surface area of presettling {XlOdQ Area - 14,009 aq. ft

310,000 20,000 30,

SUrface Area of Presett l ing Pond, Square Feet

Ass\qj" CllS;1. hifom 3 foot depth of pcesettling pll1d2. l /6 of totAl volliD& of te r ia l processed through sluice box depositepresett l ing pood.

PlacerHandbook-SettlingPonds

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