SEEPAGE CONTROL IN EXCAVATED EARTHEN RESERVOIRS

W. Nicholaichuk

Research Station, Research Branch, Agriculture Canada, Swift Current, Saskatchewan S9H 3X2

Received 15 March 1978

Nicholaichuk, W. 1978. Seepage control in excavated earthen reservoirs. Can. Agric. Eng. 20: 97-101.

Farm reservoirsoffer the only meansof water supply in manyareas wheregroundwater iseither unsuitableor unavailable.Insome areas there is excessive seepagefrom these reservoirs. This study was designed to test various methods of reducingthisseepage. The use of Na2C03 for seepage control was tested in the laboratory and field and was found to produce rapid andacceptable control.Thegleization method ofcontroladvanced byRussianworkerswasfound to bepromising. Thetextureof theoverburden covering the straw did not affect the gleizationprocess.Wheat, barleyand oat straw, and manure are materials thatcan be used to promote gleization. Oat straw was not quite as effective as the other two cereal materials.The use of partiallydecayed manure reduced the seepage rate more rapidly than straw but eventually both were equally effective.The laboratorystudy demonstrated that Na2C03 and bentonite providedthe most rapid reduction in hydraulicconductivityfollowedby manureand straw, respectively. Combining the gleization method with Na2C03 or bentonite resulted in an immediate seal upontreatment; furthermore neither Na2C03nor bentonite impededthe microbiologicalgleization process.Limitedfieldobservationsindicated that both the Na2C03 and gleizationmethods can beusedfor seepagecontrol withsuccess. Problems that arise withtheNa2C03 method indicate that treatment procedures must be strictly adhered to. Pockets of sand or sand lenses are specialproblems that must be dealt with carefully.

INTRODUCTION

Farm reservoirs offer the only means ofwater supply in many areas wheregroundwater is either unsuitable or unavailable. In some instances, particularly in areaswhere the soil tends to be calcareous, there isexcessive seepage from these earthenimpoundments. Many methods of seepagecontrol have been suggested. They includethe use of lining materials such as concrete,polymer films and butyl rubber. Apart fromcertain problems associated with each of theseepage control materials, they are generallyconsidered to be too expensive. Othermethods that may be advantageouseconomically, but are not as well publicized,include the use of chemical reagents andorganic matter liners.

The chemical characteristics of the soiloften influence its permeability. High concentrations of calcium cause clay particles toaggregate and to form a porous water-stablestructure with high permeability. Thisundesirable property can be rectified byreplacing the calcium with low concentrations of sodium. Sodium ions will disperseaggregates and thereby reduce the soilpermeability.

Reginato et al. (1968) described a methodof using Na2C03 to reduce seepage loss andgave the following equation for determiningthe amount of chemical required based onthe cation exchange capacity (CEC) of thesoil:

Na2C03 = 0.0428 DA (0.15 CEC — ES)

where Na2C03 = grams of sodiumcarbonate; D = depth of soil treated (cm);A = area to be treated (m2); CEC = cationexchange capacity (meq/100 g); ES =exchangeable sodium (meq/100 g).

This equation facilitates calculation ofthe quantity of Na2C03 required to raise theexchangeable sodium percentage from itsoriginal value to 15 (designated by the factorof 0.15) assuming complete replacement bysodium. Graveland and Olynyk (1973)found in a laboratory study that increasing

the application rate of sodium decreased thehydraulic conductivity. The exchangeablesodium percentage was 15%. This level wasachieved by using a coefficient of 0.25 in theapplication rate equation which will bereferred to as Reginato's modified equation.The shortcoming of the NA2C03 method isthat seepage may start to increase 2-3 yr aftertreatment as the calcium and magnesiumeventually replace the sodium applied in thetreatment (Reginato et al. 1968). As a result,reservoir maintenance may be required bywhich Na2C03 may be added to the pondedwater or incorporated with the soil.

As with Na2C03, Bowman (1967) hasshown that bentonite, when added to thesoil, provides an effective seal in permeablesoils. Bentonite, a clay containing montmorillonite as the essential mineral, ischaracterized by the ability to swell in water.It has been shown to reduce permeabilityeffectively when applied at rates of 4.5kg/m2 and 1.5 kg/m2 to extremely coarse(gravel) and normal soils, respectively.Apart from the relatively high cost,bentonite is somewhat difficult to keep inplace under field conditions.

A new method which appears to havedistinct possibilities is based on a gleizationprocess. It involves the use oforganic matterliners. Russian workers (Mirtskhulava et al.1972) report that under anaerobicconditions, the metabolic activities ofcertain anaerobes effect a chemical

reduction process in soil which results inincreased dispersity and plasticity, and adecrease in soil permeability to water. Intheir report of this USSR patented process,Mirtskhulava et al. (1972) did not providethe necessary details, such as suitability ofmaterials, rates of application, andassociated experimental results.

The objective of this study was todetermine how various additives might beused to control seepage from farmreservoirs. The study was carried outprimarily under controlled conditions in thelaboratory. An assessment of some of themethods studied was provided by observing

CANADIAN AGRICULTURAL ENGINEERING, VOL. 20 NO. 2, DECEMBER 1978

-•— Constant water level

-•— Plexiglass cylinder

**— Soil layer

-*— Organic layer

•*— Soil layer

&>!^2cS^i""^~ Sand layer

f*— Rubber stopperDrain tube

o

o

Beaker

Figure 1. Schematic of apparatus for seepagestudies.

the results obtained by farmers who used therecommendations.

MATERIALS AND METHODS

Laboratory StudiesThe soils used for test purposes consisted

of subsoils of two associations of the

Chernozemic Brown Great Group, viz.,Wood Mountain loam and Hatton fine

sandy loam series (Mitchell et al. 1944)which are known to seep. The clay fractionof these soils generally contained 45% illiteand the remainder montmorillonite (Warder1950). Kaolinite was absent or at most a veryminor constituent.

Soils were air-dried and passed through a2-mm sieve. A Wood Mountain loam

97

topsoil was used as overburden in anexperiment where straw was covered withtopsoil. Wood Mountain subsoil, uniformlymixed with various amounts of sieved sand,was used to simulate various textures of soils

for another test.

Duplicate hydraulic conductivity testswere conducted using 3.2-cm diam, 30-cmlong plastic cylinders. The bottoms of thecylinders were equipped with a fine metallicscreen that was covered with a 2-cm layerof fine sand (Fig. 1). For all tests exceptone, columns of soil were packed uniformlyto a depth of 15 cm and density of 1.3 g/cm3with a mechanical packer (Jackson et al.1962). For the test to evaluate sodiumcarbonate, soil was packed by the use of apacking block. The cylinder containing thesoil was dropped 20 times through a distanceof 2.5 cm onto the packing block. Theresultant bulk density was 1.25 g/cm3. Forthe gleization tests, 5 kg/m2 ofground strawwas added to create an organic layer duringthe mechanical packing operation asillustrated in Fig. 1.

The hydraulic conductivity as defined byDarcy's Law was determined by applying aconstant head (15 cm of water) to the soilcolumn and measuring the rate of outflow.The hydraulic conductivity that wasconsidered to be an acceptable measure of agood seal was 0.05 cm/h.

Field Studies

Several farm dugouts and ponds whichwere treated with Na2C03 and organicmatter liners were monitored for several

years. This consisted of observing the rate ofdrop of water levels for various treatmentconditions and correcting for evaporationand precipitation.

Prior to treatment with Na2C03, soilswere sampled and analyzed for texture,cation exchange capacity and exchangeablesodium. The rate of Na2C03 application wasdetermined using the modified Reginatoequation. The Na2C03 was broadcast overthe prescribed area and subsequentlyincorporated. Methods of incorporationincluded the use of hand-operated andtractor-driven rototillers as well as disc- and

cultivator-type implements. Some of thetreated soils were then compacted using arubber-tired tractor.

The method of lining reservoirs withstraw consisted of applying the straw using aforage harvester and subsequently coveringthe straw with a 10-cm layer of topsoil usinga backhoe. Other reservoirs were lined with

decayed organic matter by using a tractor-pulled, earth-moving bucket. Use of thismachine resulted in a layer of decayedorganic matter at least 5 cm thick on top ofwhich a 10-cm layer of soil was deposited.

RESULTS AND DISCUSSION

Laboratory StudiesThe precision of the seepage measure

ments was evaluated by comparinghydraulic conductivities for duplicate testruns. This showed that the use of the soil

98

WOOD MOUNTAIN LOAM

(28%C. 3l%Si,40%S)

x NO TREATMENT

o ^ AMOUNT OF NdgCOj

• Na,COx AS PER EQUATION

TIME(hrs)

Figure 2. Hydraulic conductivities for various rates of application of sodium carbonate using WoodMountain soil.

WOOD MOUNTAIN LOAM

(40%C,35%Si,25%S)

• STRAW LAYER COVEREO WITH SUBSOIL

(40%C,35%Si,25%S)

A STRAW LAYER COVERED WITH TOPSOIL

(l8%C.3l%Si,50%S)

TIME (weeks)

Figure 3. Effect of topsoil on the gleization method of seepage control.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 20 NO. 2, DECEMBER 1978

HATTON FINE SANDY LOAM

(IO%C, ll%Si,79%S)

o CHECK

• WHEAT STRAW

A OECAYED ORGANIC MATTER

TIME (weeks)

Figure 4. Comparison of decayed organic matter versus straw as an organic liner for seepage control using Hatton soil.

packer developed by Jackson et al. (1962)resulted in reproducible results.

In the interest of reducing cost, anexperiment was set up to determine whetherthe amount of Na2C03 incorporated in thesoil can be reduced without reducing theeffectiveness of the seal. It was found thatusing the amount of Na2C03 recommendedby Reginato's modified equation resulted ina complete and immediate seal (Fig. 2).Reduction in the Na2C03 application rateincreased the seepage rate.

The first of a series of experiments on theuse of straw as a lining material for thegleization method was designed todetermine whether subsoil would be as

efficient as topsoil in promoting thegleization process. It was suspected thatthere could be some differences between the

two sources because the microbial

population would be greater in the topsoil(Cook 1967). On the other hand, there mightbe a greater proportion of anaerobes andfacultative anaerobes in the subsoil (Cook1967). It is easier for the farmer and therancher to obtain topsoil to cover the strawlayer than subsoil.

The results indicated that the use oftopsoil neither enhanced nor impeded thegleization process when compared to straw

covered with subsoil (Fig. 3). At 7.5 wk, thehydraulic conductivity for each testcondition was similar even though initiallythe straw layer covered with topsoil tendedto cause a higher conductivity rate than thetreatment in which straw was covered with

subsoil. This difference was perhaps due tothe fact that the surface soil is usually morefriable because of the intimate intermixingof clay and organic matter in this layer, whilethe higher percentage of expanding-typeclay in subsoil would tend to promotesealing more rapidly.

The second gleization experiment wasdesigned to determine whether decayedorganic material (manure-), which is oftenmore readily available to the farmer, can besubstituted for straw as a lining material.Ranchers often find themselves with excess

manure for disposal but not excess straw.Results (Fig. 4) indicated that manure wasmore effective than straw in reducing theseepage rate during the first 10 wk of theexperiment and was equally effectivethereafter. The gleization process isenhanced by low oxygen and also highsoluble carbon concentrations (Russell1973). Both straw and manure are high incarbon, but the latter, being partiallydecayed, would likely be higher in soluble

CANADIAN AGRICULTURAL ENGINEERING, VOL. 20 NO. 2, DECEMBER 1978

carbon; thus its effect would be expected tobe more rapidly discerned. However, in timethe straw would decay and both materialsshould have a similar effect.

The third gleization experiment wasdesigned to evaluate various types of strawthat might readily be available to therancher. This test was carried out on the

Hatton fine sand. Wheat and barley strawwere equally effective as lining material (Fig.5). The seepage rate was reduced to 0.1 cm/ hafter 12 wk; this was not considered to be*quite low enough to be effective for fieldapplication. However, we suspect that thetest should have been extended to at least

100 wk as evidenced in the previous test. At100 wk, wheat straw as a liner was wellwithin the acceptable level of0.05 cm/h for asimilar type of soil.

The fourth gleization experiment wasdesigned to evaluate the lower limits of clay(or higher limits of sand) in which theprocess of gleization can be employed. It wasfound that the process occurred in preparedsoils containing a clay content as low as 10%(Fig. 6); silt content was 20% and sandcontent 70%. The rate of gleization wasgenerally uniform for all soil textures. Sincethe hydraulic conductivity was reduced asthe clay content increased, it was postulated

99

HATTON FINE SANDY LOAM

<IO%C,ll% Si .79 7.S)

4 CHECK

o BARLEY STRAW

. WHEAT STRAW

x OAT STRAW

TIME (weeks)

Figure 5. Comparison of wheat, oats and barley straw as organic liners for seepage control on Hatton soil.

that the amount of clay was correlated to theamount of Fe+++-sesquoxides which werereduced to Fe++-sesquoxides as gleizationoccurred. In addition, the higher the claycontent, the lower will be the oxygendiffusion rate and the better the conditions

for the proliferation of anaerobicmicroorganisms.

In order to obtain an immediate as well as

lasting seal, an experiment was carried outto determine whether the gleization methodcould be combined with the Na2C03 orbentonite methods to provide seepagecontrol. The gleization method of seepagecontrol was a time-dependent process whileNa2C03 or bentonite methods respondinstantaneously. It was hoped that Na2C03or bentonite would control seepage to anacceptable level until the process ofgleization could develop within the soil. Atthe same time, we were somewhatapprehensive that the Na2C03 might

100

increase thepH of the soil and that this mightdeleteriously affect the microbially mediatedgleization process.

It was found that Na2Co3 incorporatedwith the soil which covered the straw layer,or the use of bentonite over soil on top ofstraw were equally effective (results notshown). Both combinations resulted in anexcellent seal soon after application.Incorporation of Na2C03 or the use ofbentonite did not prevent the occurrence ofthe microbially induced process of gleization as was evidenced by gradual colorchange to blue-gray below the layer oforganic matter.

Field Observations

Field trials of the Na,CO, method ofseepage control have been conducted by anumber of farmers in Southwestern

Saskatchewan. Seepage was reduced in allcases but satisfactory control was achieved

on only three of the six reservoirs treated(Table I).

Several difficulties have been encoun

tered in the field treatments. The first wasdue to control of application rate. It isessential that Na2C03 be uniformly appliedover the entire area to be treated and at the

prescribed rate. Mechanical incorporationtended to move the Na2C03 downslope andleave areas partially untreated. InsufficientNa2C03 was found to be responsible whensuspect treated areas were sampled. Asshown in Fig. 3, insufficient Na2C03 will notprovide adequate seepage control.Furthermore, if some seepage does occur ina partially treated soil, the Ca++ and Mg++will replace the Na+ in the soil and reversethe reduction in seepage initiated by theaddition of Na2C03. On the other hand, toohigh a concentration of Na ions may behavelike Ca++ by reducing the hydrodynamicradius and increasing seepage. The other

CANADIAN AGRICULTURAL ENGINEERING, VOL. 20 NO. 2, DECEMBER 1978

TABLE I. FIELD OBSERVATIONS OF RESERVOIRS TREATED FOR SEEPAGE CONTROL

Subsoil

Location

Treatment

year

1973

Clay

Soil texture

Sand Silt

- Treatment

method

Gull Lake 27 29 44 Na2C03

Swift Current 1972 30 33 37 Na2C03

Ponteix 1971 28 29 33 Na2C03

Scottsbury 1972 42 24 34 |Na2C03Battrum 1972 Na2C03

Pambrun 1971 33 24 43 Na2C03

Swift Current 1975 47 28 25 Decayedorganicliner

White Bear 1974 17.5 16.5 66 Straw

liner

tObservations to date.

3Q

OO

-I

D<q:o

CLAY SILT SAND

• 10 20 70

x 14 27 59

o 18 33 49

A 21 40 39

TIME ( weeks)

Figure 6. Effect of soil textures on the gleization method of seepage control.

Remarks!

Reduced seepage to near acceptable levels;insufficient chemical was applied.

Reduced seepage but far from satisfactory; sand lenswas a problem. Good seepage control below sand lenslayer.

Good seepage control.

Excellent seepage control.

Reduced seepage; losses still occur through rockarea treated with bentonite.

Reduced seepage; sand lens a problem.

Using decayed straw, held water first year aftertreatment.

Reduced seepage to acceptable level after 2 yr.

difficulty encountered in the field was aresult of insufficient soil overlying porousrock or gravel bed and the low clay contentof the treated soil. Reginato et al. (1968)clearly demonstrated that the depth of soiloverlying any pervious layer should be atleast 30 cm. Also, the clay content of the soilshould be at least 15% or greater.

Consequently, the treated area should beproperly inspected and sampled to ensurethat all criteria are met.

Only two reservoirs were treated withorganic liners — one with wheat straw andthe other with partially decayed straw andbarnyard manure. Seepage controlsupported our laboratory results. Use of

decayed material resulted in an almostimmediate and satisfactory reduction inseepage. The use of straw required a longerperiod of time to allow for gleization tooccur. After 2 yr, the seepage rate in bothreservoirs had been reduced to an acceptablelevel. Field inspection indicated that a blue-gray layer had developed beneath theorganic layer to a depth of 15-30 cm.

BOWMAN, C.C. 1967. Bentonite and clay soilsunder extreme conditions. Bull. 610, MontanaAgric. Exp. Sta., Bozeman, Mont.

COOK, F.D. 1967. Some microbiological factors.Pages 177-192 in K.F. Nielson, ed. CanadianCentennial Wheat Symposium.

GRAVELAND, D.N. and G. OLYNYK. 1973.Laboratory tests on the use of sodiumcarbonate for reducing permeability in soilcolumns. Can. Soc. Agric. Eng. 15(1): 12-14.

JACKSON, R.D., R.J. REGINATO, and W.E.REEVES. 1962. A mechanical device for

packing soil columns. U.S. Dep. Agric. ARSpp. 41-52.

MITCHELL, J., H.C. MOSS, J.S. CLAYTON,and F.H. EDMUNDS. 1944. Soil Surv. Rep.No. 12, Univ. of Sask., Saskatoon, Sask.

MIRTSKHULAVA, T.E., G.B. ABELISHVILI,and M.N. TERLETSKAYA. 1972. Effect of

microbiological process on percolation ofwater through soil. Pages 713-721 in Fundamentals of transport phenomena in porousmedia. I.A.H.R.S.-I.S.S.S. Symposium,University of Guelph, Guelph, Ont.

REGINATO, R.J., L.E. MEYERS, andFRANCIS S. NAKAYAMA. 1968. Sodiumcarbonate for reducing seepage from ponds.Water Conserv. Rep. No. 7. U.S. Water Conservation Laboratory. U.S. Department ofAgriculture, Phoenix, Ariz. 85040.

RUSSELL, E.W. 1973. Soil conditions and plantgrowth. 10th ed. Longman Publications,London, England.

WARDER, F.G. 1950. Nature of clay minerals insome Saskatchewan soils. Unpublished M.Sc.Thesis. Univ. of Sask., Saskatoon, Sask.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 20 NO. 2, DECEMBER 1978 101