Arresting Leakage in Ponds

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Water loss from a p ond is a seri-ous p roblem. For the farm er, it canmean little or no w ater for fish,irrigation or cattle. For the hom e-owner, a leaking or empty p ond isunattractive and detracts from thelandscape. Leaky p onds alsoincrease water u se, reduce fertiliz-er effectiveness, and can pollutegroundwater.

The most common causes of leak-age are:

1) improper pond construction;2) perm eable soils or layers w ith

high sand or gravel content; or

3) thin layers of soil with frac-tured or layered bedrock orsolution cavities (sinkholes) astheir substrate.

Known problem locations includ eareas in n orth Alabama andGeorgia, and parts of Kentuckyand Tennessee, where thin soilmantles lie on top of cavernouslimestone. Another area where

pond s are prone to leaks is theSouthern Coastal Plain region,wh ere soils are sandy and usuallyhave a limestone base. In aridparts of Texas and Oklahoma,subsu rface caliche h igh in calciumcarbonate or gypsum is associatedwith leaky pond s.

The keys to repairing a leakypond are properly identifying thecause of the seepage p roblem an dselecting an app ropriate methodof sealing the p ond. Though sometreatments are suggested forund rained pond s, these are gener-ally less effective. In most cases, apond will need to be drainedbefore repair. The p ur pose of thepond and th e cost that the pondowner is willing to bear w ill influ-ence treatmen t d ecisions. Because

effective treatm ents often requirean in-depth knowledge of soilcharacteristics, the pond ownershould consult the Natu ralResources Conservation Service(NRCS) or the CooperativeExtension Service for assistance.

Repairing a leaky pond is oftenexpensive (Table 1). When it is aviable option, re-working andcompacting a pond is the cheapestalternative at about $300 to 1,000per acre. Treating a pond with a

minim al rate of ben tonite (i.e., 1pou nd per squ are foot) will cost$3,500 to 4,000 per acre for th ebentonite alone. Other treatmentscost still more. The h igh cost of treating a leaky pond may leadthe owner to aband on it, or donothing in hopes that the pondwill seal natur ally.

Identify the Problem

In some cases the cause of a seep-age problem may be app arent; inother cases, the cause may beun know n (Table 2). When there isexcessive seepage, the first step isto carefully examine the ponddam or levees. Seeps, wet spots orwetland vegetation on or belowthe dam are indicators of leakagethrough or under the dam or lev-ees. Water also can leak th rough

mu skrat or crawfish burrow s orthrough channels left by rottentree roots. Older pond s can d evel-op leaks around drain or overflowpipes. If the water d rops rapidlyto a certain level, carefully check the perimeter of the pond at thewaterline for holes or discontinu-ities in the soil.

In addition to inspecting thepond , gather as much informationas possible about the p ond histo-ry, site characteristics, and con-struction practices used.Important qu estions includ e:

s Was the site properly preparedby removing the existing vege-tation an d topsoil?

s Was the pon d levee built prop-erly, in comp acted layers of 6inches or less?

VIPRJanuary 1999

SRAC Publication No. 105

Renovating Leaky Ponds

Nathan Stone*

*Universit y of Arkansa s at P ine Bluff.



s Were the levee and pond bot-tom areas ad equately comp act-ed ?

s Is the area known for sand orgravel lenses or sinkholes?

s How deep is the soil?

s Is there fractured or jointedbedrock in the p ond basin?

If possible, ask the person who

built the pond about potentialproblem areas. This may helpidentify the problem area andreduce treatment costs.

Before undertaking expensivepond renovation, consider thatthe problem may n ot be seepage.If the pon d’s watershed has beenaltered or reduced in size lesswater may be flowing into it. Thiswou ld give the misleading

impression that water is being lostfrom the pond.

Sometimes ponds on ly appear tobe leaking, or they may leak onlytemporarily. Ponds built in shrink-swell clays will develop deepcracks when dry. As they arerefilled water ru ns through thecracks until the soil swells again.A considerable volum e of water

may also be lost during the initialfilling of a p ond as it soaks intothe surrou nd ing soil, giving th eimpression of a leak. It is notuncommon for new ponds to havehigh initial seepage rates thatdecrease as m icrobial activity andthe accumulation of fine sedimentand organic matter help seal thepond bottom. If pond s that havesealed in this mann er are dried orre-worked , they may again leak

excessively u ntil the seal re-estab-lishes.

Spot Treatments

If seepage ap pear s localized, digout the susp ect area and coverthat section with a 1-foot-thick layer of compacted clay soil. Formthe clay blanket with two layers of soil, compacting each layer sepa -

rately. When repairing leaks indam s or levees avoid m aking ver-tical cuts, as they are difficult toseal. Dam or levee cuts should bemad e in a broad V shape so thenew fill will bond with existingsoil as it is compacted.

If spot treatment will not work orif leakage cann ot be localized, theentire pond basin will requiretreatment. Methods for complete

Table 1. Approximate costs of certain seepage treatments. Prices vary with quantity and location. Costshould not be the only factor in selecting a treatment, as treatments are neither equally effective norsuitable in all cases.

Approximate cost

Treatment per sq. ft. per acre

Compaction $0.01-0.02 $300-1,000

Bentonite (cost of chemical alone–compaction is required) $0.08-0.25 $3,500-11,000

Dispersants (cost of chemical alone–compaction is required)

salt >$0.01 $240-395

soda ash ($0.15-0.27/lb.) $0.02-0.05 $650-2,400

TSSP ($0.82-0.92/lb.) $0.04-0.09 $1,800-4,000

STPP ($0.61-0.64/lb.) $0.03-0.06 $1,300-2,800

ESS-13 $0.15 $6,500

Liners (site preparation required at extra cost)

HDPE (price per roll for liner only—installation is extra)

12 mil $0.08 $3,500

20 mil $0.11 $4,80030 mil $0.165 $7,200

40 mil $0.24 $10,500

Reinforced HDPE—custom shape

16 mil $0.27 $11,800

20 mil $0.38 $16,600

24 mil $0.55 $24,000

40-mil HDPE (includes professional installation) $0.35-0.40* $15,200-17,400

Textured 40-mil HDPE (as above) $0.37-0.42* $16,000-18,300

*Price quote for 5.8-acre pond

Liquid urethane rubber. (60-mil coating, preferably appliedover polyester fabric) $1.24 $54,000



pond basin work-overs includ esimple compaction, compactionaided by ad ditives, or the add i-tion of a liner.

Compaction

For man y soils, comp action is crit-ical to redu cing leakage.Compaction works well when thesoil has a w ide and well-gradedrange of soil particle sizes. Withsoil containing sand, silt and atleast 10 percent clay, water acts asa lubricant and the force of com-paction squeezes air from the soiland locks the d ifferent size pa rti-

cles into th e sma llest possiblearran gemen t. This leaves littlespace for water to m ove throughthe compacted layer. For adequatecompaction be certain to:

1) comp act thin layers;

2) use sufficient compactive force;an d

3) make sure that the soil has theright amou nt of moisture.

Compact no m ore than 8 to 9inches of loose soil at a time. Thiswill give a compacted layer about6 inches thick. This is critical, asthe force of compaction diminish-

es quickly with soil depth.Compacting only the top of a piledoes little to reduce the perme-ability of the soil underneath.

Using specific equipm ent is essen-tial. A bulldozer alone will notcompact adequately, as the broadtracks on a d ozer are designed tospread out the w eight of themachine to keep it from sinkinginto the soil. A sheepsfoot rollerbehind a bulldozer compactsmu ch better (Fig. 1). As the rollermakes repeated passes, compact-ing the soil and making it firm,the roller begins to “walk” out of

Table 2.

PossibleSpecific problem reason for leakage Treatment options Requirements

Seepage through a well- Poor initial compaction. Compaction Drain; dry pond enough forgraded soil (one with a equipment to enter.wide mix of particle sizes– Sand lenses or other areas Plow and mix soil, cover

sand, silt and clay), more of high seepage. suspect areas with fresh mix,than 15% clay. compact.

Exposed layer of porous Poor initial compaction. Compaction Requires at least 10% clay.soil, sand/silt/gravel mixes,usually with less than Too little clay Clay blanket Requires local source of15% clay. (less than 10%). clayey soil to be cost

effective.

Bentonite Requires supporting foun-dation soil; must be keptwet or will crack and leakagain.

Liner Requires prepared site,professional installation.

Thin layer of soil on top Poor initial compaction. Compaction Requires at least 10% clayof undesirable foundation– and soil thickness of 12 torock fractures, jointed 18 inches.bedrock, solution cavities.

Too little clay; pond Compacted clay blanket Requires nearby source ofbottom soil layer too thin. suitable clayey material.

Liner Requires prepared site,professional installation.

Clayey soil that leaks. Seepage through clayey Compaction Requires strong compac-Typically high calcium soil because of aggregated tive force at near optimum

soils. soil structure. soil moisture to changesoil particle structure,reducing permeability.

Soil dispersant with Requires dispersants tocompaction change soil particle

orientation.



Bentonite

Sodium bentonite is a highly plas-tic clay that exp and s 8 to 20 timesin volume w hen w et. It is used tofill in voids in p orous soils.Bentonite has been used success-fully on relatively sandy soil (at

least 10 to 15 percent sand ) wherethere is adequ ate supp ort for thebenton ite-treated layers. Calciumbentonite does not swell to thesame extent as sodium bentoniteand should not be used.

The amoun t of bentonite neededvaries with soil type an d laborato-ry testing is recommend ed todetermine optimu m ap plicationrates. Given its high cost, ben-tonite is more suited to spot treat-ments or small ponds. Typicalapplication rates are:

Application rate

Soil type lbs./ sq.ft. tons/acre

sandy silt 1.0-1.5 22-33

silty sand 1.5-2.0 33-44

sand 2.0-2.5 44-54

For best results, spread bentoniteover the pond bottom at the rec-ommend ed rate and m ix it in w itha disk or tiller to a depth of 6inches. Moisten the soil if neces-

sary, and compact the pond bot-tom as described in the section oncompaction. Seepage will notdecrease immediately because theclay sw ells slowly. Once treated ,the pond bottom should be keptmoist to p revent the clay fromcracking and shrinking.

If a pon d cannot be d rained, gran-ular bentonite can be u sed as aspot treatment over a suspectedseepage area. The granular formallows the bentonite to sink to thepond bottom before dispersing.

The proprietary compound ESS-13(Seepage Control, Inc.), a resinouspolymer emulsion, also can beapplied to und rained pond s toreduce seepage.

Soil Dispersants

There is a comm on m isconceptionthat soils with ad equate amoun tsof clay will not leak. In fact, not

the soil on the feet extending fromthe dru m. Adequate compactionwill require at least four to sixpasses of the roller over a ll of thepond bottom and sides. Tractor-draw n wh eeled d irt pans also canbe used over the dam or levee,although they d o not compact aswell as a roller.

The amoun t of water in the soilwhen it is compacted affects theresulting perm eability, esp eciallyfor clay soils. Though determiningthe optimu m moisture content fora soil requires laboratory tests, agood indication in the field is soilthat is too wet for good tilth butnot so wet that water oozes outwhen it is comp acted. If the soil istoo wet, it can be disked to speedthe d rying p rocess. If the soil istoo dry, spray water over the siteand allow it to soak in before pro-ceeding.

When compacting an existingpond, the bottom m ust be dry

enough to support the weight of the equipm ent. Remove any vege-tation, tree stumps, roots andlarge stones. Disk the pond bot-tom to a dep th of 16 to 20 inches,mixing the soil and ensuring thatthe soil moisture is near optimumbefore comp action.

Seepage increases prop ortionallywith w ater depth. For ponds less

than 10 feet d eep, a 1-foot-thick layer of comp acted soil is usu allysufficient. This layer shou ld becomposed of tw o separate layers,each comp acted separately. Soilwill need to be stockpiled to oneside or “borrowed” from a nearbysite in order to apply a secondlayer to a comp acted p ond bot-tom. For each foot of water depthbeyond 10 feet, an additional 2inches of comp acted fill is recom-mended.

Clay Blanket

Comp acted blankets of clay soilhave been used successfully toseal areas of exposed, fracturedrock or other permeable material.The best soils are those w ith awid e range of soil particle sizesand with 20 percent or m ore clay.Again, a minimu m thickness of 1foot is recommen ded . When su it-able soils are available nearby, it isrelatively inexpen sive to cover the

pond bottom with compacted soillayers. Hau ling in soil from a d is-tant site adds greatly to the cost.The failure of clay blankets isoften associated w ith on-siteapp lication p roblems. If the soil isdry, clods should be broken ap artand water w orked into the soil toachieve proper moisture content.

Figure 1. Sheeps foot roller.



all clays are alike, and thearran gemen t of clay particles in asoil greatly influences perm eabili-ty. Dispersants can be added tosoil to reduce aggregation andperm eability. As the nam e implies,dispersants aid in changing thesoil structure from the open,

aggregated form to a d ispersedform that is less permeable towater. They work best on calcium-satur ated clay m inerals; therefore,soils derived from limestone arethe likeliest candidates for theeffective u se of a dispersant.Dispersants will work only withaggregated soils (with an open,honeycomb arrangem ent of soilparticles) with more than 50 per-cent silt and clay-sized p articlesand at least 15 percent clay.Because of the technical natu re of

soil dispersants and clay mineral-ogy, pond own ers should seek expert ad vice in selecting anapp ropriate dispersant, if the useof one is ind icated.

Common salt is recomm ended asa dispersant only for soils with ahigh cation exchange capacity(CEC), typically mon tmorilloniteclays. Soda ash (sodium carbon-ate) is also used as a sodium-based dispersant. For kaolin clays(low CEC), sodium polyphos-

ph ates are more effective thanplain salt because of the addition-al reaction of clay w ith the p hos-phate. Three comm only usedpolyphosph ates are tetrasodiumpyrophosphate (TSPP), sodiumtripolyphosphate (STPP), andhexametaphosphate (SPP). Theproprietary compound ESS-13also functions as a soil dispersant.

A field test for the effectiveness of a polyphosp hate dispersant is toadd a pinch of the dispersant to ahan dfu l of moist soil. If the soil

becomes noticeably wetter a s it isrolled between the fingers, thedispersant should be effective.

Dispersants are app lied in th esame way as bentonite. Disk thepond bottom and spread the d is-persant evenly over the surface.Mix the soil and compact it as out-lined in the section on com-paction. Again, a m inimu m of two , 6-inch-thick comp acted lay-

ers is recommended . Adequatecompaction is an important p artof the treatment, as the disper-sants work with the force of com-paction to change the soil struc-ture.

Typical application rates are:

Application rate

Dispersing lbs./ tons/agent sq. ft. acre

salt 0.2-0.3 4.4-7.2

soda ash 0.1-0.2 2.2-4.4

sodiumpolyphosphates 0.05-0.1* 1.1-2.2

*Higher rates are indicated for high CEC

montmorillonite clays.

When ponds treated with disper-sants are filled, the w ater w ill

probably become muddy andmay take w eeks to clear. (Alum orlime shou ld not be u sed to treatfor this tur bidity, as they w illcounteract the effect of the disper-sants.) Dispersan t salts might alsoleach out into the water and affectits suitability for use as a w atersource.

Liners

Properly installed, a liner is 100percent effective in stopping seep-age. For soils with high gypsumcontent, a liner is the only option.Because of the relatively highcost, liners have been used pri-marily for ornamental pon ds,water storage, fish hatcheries, andresearch facilities. However,advances in liner technologyachieved through their wide-spread use for landfills, haz-ardou s waste, and w ater storagefacilities have cau sed prices tofall.

Proper liner installation is impor-

tant. A liner’s edges usually areanchored into a trench bu iltaround the pond perimeter.

Many factors influence the selec-tion of a liner m aterial, and con-sumers h ave a w ide choice of prod ucts. Modern p lastics areenvironmentally safe, withstandfreezing, and are U V-stabilizedfor long-term exposure to the su n.With care, a pon d liner can last 20to 25 years.

Liner thickness is measured inthousandths of an inch (mils).Twelve- to 20-mil liners can beused in sandy soils, while thickerliners are required to preventpunctures in rocky soils. In somecases, an inexpen sive geotextilemat is app lied u nd er the liner to

protect against punctures. Liners20 mils or less in thickness aremore suitable for temp orary u ses.For permanent aquaculture facili-ties, 30- to 40-mil liners are recom-mend ed. Thin liners will be pun c-tured by plant sprouts along pondedges unless a sterilant is appliedbefore the liner is installed.Obviou sly, even thick liners m ustbe protected to a reasonabledeg ree. For examp le, cattle shou ldnot be allowed to tram ple linedponds.

Liners can be made from high-density polyethylene (HDPE) orlow-den sity polyethylene(LDPE).LDPE is more flexible and is usedwhere there is more shifting ormovement of the soil, whileHDPE is more resistant to chemi-cals. Polyethylene is both econom-ical and du rable and can be fiber-reinforced for greater streng th.Seams on polyethylene liners arebest sealed by heat w elding orextrusion, w hich calls for custom

fabrication for smaller ponds orprofessional installation on largerpon ds. Vinyl can also be used forliners and, though less resistant toaging than polyethylene, it can besealed and patched w ith solventadhesives.

For smaller, ornamental ponds,butyl rubber is typically used as aliner material. A prop rietary, liq-uid u rethane rubber produ ct isalso available. It conforms to anypond shape and seals aroundpipes and other structures.

Professional in stallation is recom-mend ed but gallon kits and aninstructional video are av ailable tohomeowners.

Liners will become slippery withtime, wh ich can create a safetyhazard where pond slopes aresteep. Using a textured plasticliner, or embedding small stonesin the liner ’s sides with a liquidurethane rubber p rodu ct will pro-vide a non-slip surface.



The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 94-38500-0045 fromthe United States Department of Agriculture, Cooperative States Research, Education, and Extension Service.

Other Treatments

Other method s of sealing pond sinclude the use of animals, pu d-dling, and gley (organic matter).

A traditional remedy has been tofence pigs, cattle or other anima lsin the pond basin. Livestock

manu re aids in sealing the p ondbottom, and an imals tramp lingthe pond bottom compacts adeep er layer of soil. This methodgives mixed results and can causenutrient pollution of surface orground water un til the pond sealsup .

Pud dling refers to th e d eliberatechurning of soupy wet soil. Finesreleased from the soil during themixing form a barrier of low per-meability as they settle out on topof heavier par ticles. Soils mustcontain some clay and silt parti-cles in order for pu dd ling towork. Pud dling forms a seal thathas little strength, so it is not su it-able for thin soil layers over rock.Pud dling is used primarily insmall du gout pon ds or to createzones of low permeability withinlarger d ams that are otherw iseconstructed to structurally su p-port the weight of impoun dedwater.

Bur ying a 6-inch-thick layer of

organic matter, typically straw ora man ure-straw mixture, in apond bottom has been used as asealing method. Once the organicmatter is spread over the p ondbasin, it should be covered with

soil and comp acted firmly.Microbial action converts th emater ial to a “gley,” an organiclayer of low perm eability. Thismethod does not form a sealquickly and unwanted nutrientsmight flow into surface watersuntil a seal is formed.

Prevention

Proper site selection and pondconstruction methods will helpprevent pond leakage.Landow ners should consult withthe Natural Resources Conser-vation Service before building apon d. The Service has soil sur-veys with valuable informationon soil properties and their suit-ability for water m anagement.Taking core samp les from a p ro-

posed pond site will help id entifyareas of high permeability andprevent future p roblems.

Cutting too deeply du ring con-struction is a common cause of leaky ponds. As adequate com-paction an d suitable moisturecontent are critical, a pond basinshould be in the m iddle layer of asoil profile. This midd le layer iscalled th e B horizon and typ icallyhas the maximum accum ulationof clay. The parent m aterialun derneath the B horizon mayhave little clay.

Finally, pond mainten ance isimportant in p reventing leaksfrom developing. Levees shouldbe mow ed to prevent tree growth

and to discourage burrow ing ani-mals. Trees growing on levees area frequent cau se of leaks in olderpond s. How ever, once trees withsubstantial root systems becomeestablished it is better not to cu tthem down, as leaks typicallydevelop w here dead roots decay.

Sources of Information

Allred , J. 1996. Pond sealing withbentonite. Alabama FishFarming Cen ter, Fish Farm ingNews, Vol. 8(1). Greensboro,AL.

Haman, D.Z., A.G. Smajstrla, F.D.Zazu eta and G.A. Clark. 1990.Selecting a m ethod for sealingpon ds in Florida. Circular 870,Florida Coopera tive ExtensionService, Institute of Food an d

Agricultur al Sciences,University of Florida ,Gainesville, FL.

Pfost, D.L., D. Williams and R.Koenig. 1997. Reducing pon dseepage. AgriculturalPublication G01555, UniversityExtension, Un iversity of Missouri, Columbia, MO.

USDA-NRCS. 1997. Ponds - plan-ning, design, construction.Agricultural Hand book Number 590, United States

Department of Agriculture,Natural ResourcesConserva tion Service,Washington, DC.

Arresting Leakage in Ponds

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