INNOVATIVE IN-SITU DETERMINATION OF UNSATURATED HYDRAULIC PROPERTIES IN DEEP LOESS SEDIMENTS IN NORTH-WEST BULGARIA

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1 Poceedings of the 11 th Intenational Confeence on Envionmental Remediation and Radioactive Waste Management ICEM2007 Septembe 2-6, 2007, Oud Sint-Jan Hospital Confeence Cente, Buges, Belgium ICEM INNOVATIVE IN-SITU DETERMINATION OF UNSATURATED HYDRAULIC PROPERTIES IN DEEP LOESS SEDIMENTS IN NORTH-WEST BULGARIA Dik Mallants/Belgian Nuclea Reseach Cente (SCK CEN), B-2400 Mol, Belgium Doncho Kaastanev/Geological Institute, Bulgaian Academy of Sciences, Bulgaia Dimita Antonov/Geological Institute, Bulgaian Academy of Sciences, Bulgaia Janez Peko/ Belgian Nuclea Reseach Cente (SCK CEN), B-2400 Mol, Belgium ABSTRACT In the famewok of selecting a suitable site fo final disposal of low- and intemediate level shot-lived adioactive waste (LILW-SL) in Bulgaia, site chaacteization is ongoing at the Maichin Valog site, Noth-West Bulgaia. The site is chaacteized by a complex sequence of loess, clayey gavel, and clay layes, of which the fist m ae unsatuated. Pope knowledge about unsatuated wate flow and concomittant adionuclide tanspot is key input to safety assessment calculations. Constant-head infiltomete tests wee caied out at seveal metes below gound suface to detemine the unsatuated hydaulic popeties of silty loess, clayey loess, and clayey gavel layes. Individual infiltometes wee equipped with 0.5-m-long filte sections; the shallowest filte was fom 2 to 2.5 m depth, wheeas the deepest was fom 9.5 to 10 m depth. Infiltation tests povided data on cumulative infiltation and pogession of the wetting font in the initially unsatuated sediments suounding the infiltomete. A cylindical time-domain eflectomety TRIME pobe was used to measue wate content vaiations with time duing pogession of the wetting font. Access tubes fo the TRIME pobe wee installed at 0.3 to 0.5 m fom the infiltomete tubes. By means of an invese optimization outine implemented in the finite element code HYDRUS-2D, fieldscale soil hydaulic paametes wee deived fo all layes. Results show a geat consistency in the optimized paamete values, although the test sites wee seveal metes apat. Appaently the size of the affected volume of soil was lage enough to educe the effect of spatial vaiability and to poduce aveage field-scale hydaulic paametes that ae elevant fo lage-scale pedictions of flow pattens and adionuclide migation pathways. INTRODUCTION At pesent, the only nuclea powe plant in opeation in Bulgaia is located in Kozloduy. At Kozloduy, six eacto units exist, with fou in opeation, while two wee shut down in Decembe 2002 (WWER 440/230 units 1 and 2) as a esult of an ageement between the Bulgaian Govenment and the Euopean Union. Two futhe units ae planned to be shut down in the beginning of 2007 (units 3 and 4). Units 3 and 4 ae also 440 MW WWER eactos, while units 5 and 6 ae 1000 MW WWER eactos. Fo the Kozloduy plant, the total volume of LILW-SL fo suface disposal is estimated at ~ m 3. The Bulgaian State Entepise Radioactive Waste Management (SERAW) is cuently investigating the suitability of thee sites fo disposal of LILW-SL. Two sites ae located in the vicinity of the Kozloduy NPP, notably Bestova Padina and Maichin Valog. The thid site is located in Belene, along the Danube ive. Maichin valog is located at about 2.5 km to the west-southwest diection fom the Kozloduy NPP, while the othe sites ae located at a geate distance. 1 Copyight 2007 by ASME

2 At pesent the Maichin Valog site is the most extensively chaacteized site; this wok is mainly done by the Geological Institute of the Bulgaian Academy of Sciences. Because of the existence of elatively thick unsatuated loess/clay fomations at the potential epositoy site, detailed chaacteization of these layes is needed in view of a defensible site evaluation. This pape documents the initial steps of the chaacteization of the hydaulic popeties of the unsatuated loess/clay fomations. The esults epoted ae the outcome of collective effots of the Geological Institute of the Bulgaian Academy of Sciences and the Belgian Nuclea Reseach Cente (SCK CEN), in the famewok of a bi-lateal coopeation between both counties. SITE DESCRIPTION Topogaphy and statigaphy The Maichin valog site is located in an undulating landscape (Fig. 1) developed on Pliocene clay coveed with Quatenay sediments. The latte consists of two layes: silty loess and clayey loess with a vaiable thickness between 5 and 14 m, and a clayey gavel laye of about 2 m thickness whose base is the inteface with the Pliocene clay (Fig. 1). The epositoy is planned to be founded on the top of the Pliocene clay laye (at an elevation of ~85 m above mean sea level), afte the emoval of the Quatenay sediments. The inclination of the inteface between Pliocene clay and clayey gavel is in noth-west south-east diection. The pesumed outlet of the catchment is the Ogosta ive, which is at a distance of 8-9 km. A thin low-yield aquife is fomed in a m thick sandysilty intecalation within the Pliocene clay laye. A seepage zone exists at a distance of about m notheast of the site, whee the aquife is intesected by the neaby valley (Fig. 1). The top of the site (boehole BH 34) is at appoximately 100 m above mean sea level, wheeas the lowest point in the valley is at 64 m, and the goundwate table is at 63 m above mean sea level. Site 2 & 3 At Maichin Valog two sites wee equipped with infiltomete devices fo the detemination of unsatuated hydaulic popeties ([1], [2]). The sites ae at an elevation of 96 m (no. 1) and 88 m (no. 2) above mean sea level. The second site was subdivided into two subsites, i.e. site 2 and 3, with one infiltomete device being installed in each site. The two sites wee chosen in such a way that the fist site would have a maximum thickness of all statigaphic layes, wheeas in the second site the top layes would have a significantly educed thickness, o wee even absent, due to eosion. As a esult, the depth to the pesumed foundation laye fo epositoy constuction (Pliocene clay) would be about 3 m fo the second site vesus ~16 m fo the fist site. Since the pimay objective of this study was to hydaulically chaacteize the last few metes of the laye above the foundation laye, a much shote infiltomete device was necessay in the second site compaed to the fist. The pimay laye to be hydaulically chaacteized by in-situ tests was classified as clayey gavel, which was chosen because 1) the contast in hydaulic conductivity with the undelying Pliocene clay (i.e. ~ m/s vesus m/s) pesumably is lage enough to geneate an impotant lateal flow component (note the inclined inteface between Pliocene clay and clayey gavel) which could dominate the long-tem flow patten in the loess hill with much hoizontal longe flow paths compaed to flow paths associated with vetical dainage, (2) the pesence of gavel makes coe sampling and subsequent laboatoy detemination on coe samples poblematic. The objective of the in-situ test at the fist site was to hydaulically chaacteize the silty (2% sand (2-0.1 µm), 82 % loess ( mm), and 16 % clay (< mm)) and clayey loess layes (10% sand, 70% loess, and 20 % clay). Based on the paticle size distibution cuve, 50% of the paticles was lage than 1 cm. Fo this pupose an infiltomete was installed with filte sections at depths of 5.5 and 9.5 m (see futhe). The objective of the in-situ test at the second site was to hydaulically chaacteize the last few metes of the gavelly clay laye (66% sand, 30% loam, and 4% clay), fo which a much shote infiltomete device was sufficient compaed to the fist site. Site 1 Figue 1 Coss-sectional pofile of Maichin Valog site with appoximate location of test sites indicated. Infiltomete tests wee caied out at Site 1, 2 & 3. 2 Copyight 2007 by ASME

3 Obseved moistue pofiles fom TRIME measuements In the famewok of the chaacteization of the unsatuated sediments at the Maichin Valog site, a cylindical TRIME T3-44 moistue appaatus ([3]; [4]) was used. The TRIME appaatus is based on the Time Domain Reflectomete technique (TDR) ([5]), and should be used togethe with special polycabonate access tubes. The TRIME device geneates a high-fequency pulse (between 600 MHz and 1.2 GHz) which popagates along the wave guides geneating an electomagnetic field aound the pobe. At the end of the wave guides, the pulse is eflected back to its souce. The esulting tansit time (10 ps to 2 ns) and dielectic constant ae dependent on the moistue content of the medium. The moistue content was calculated by the TRIME device; we equied a custom made calibation because thicke access tubes wee used in ou expeiments compaed to the commecially available tubes fom IMKO. The TRIME pobe has the advantage that one single pobe can be used to detemine nealy continuous moistue pofiles within diffeent access tubes. Seveal tubes have been installed at the site, mainly fo the pupose of calibation of the pobe, fo detemining time seies of moistue pofiles, and fo caying out in-situ infiltation tests in undistubed soil at depths up to 10 m and moe. Usually applications with the TRIME appaatus ae limited to depths of a few metes ([5]), while in ou application the measuement depth is up to 10 m. TRIME access tubes installed as a component of the infiltomete set-up have also been used to obtain time seies of natual moistue pofiles. Details of the access tubes and the measuement depths ae shown in Fig. 2. The standad commecial length of access tubes is 3 m. Fo ou pupose, the total length of access tubes was extended until 10 m, using 2- m-long sections with SCK CEN-made povisions at both ends to allow two neighboing tubes to be smoothly attached and glued togethe. Fo the TRIME pobe to be useful at those depths, a special extension cable with a maximum length of 21 m was used togethe with the TRIME IPH module. Until pesent, moistue pofiles have been measued at fou diffeent times (see futhe). A second set of moistue pofiles was detemined on the basis of undistubed coe samples collected fom two boeholes. Caeful analysis of these coe samples also seved fo detemining a efined statigaphic desciption. 0 T1 ( ) T1 ( ) T1 ( ) T1 ( ) 2 Depth below suface (m) Volumetic wate content (cm 3 cm -3, %) Figue 2 Obsevation boehole T-1 fo wate content measuements using TRIME pobe, and infiltometes F-1a and F-1b. Elevations in m above sea level. Figue 3 Obseved wate content based on TRIME eadings. 3 Copyight 2007 by ASME

4 TRIME-based natual wate content measuements at diffeent obsevation times ae shown in Fig. 3. Fo boehole T- 1 dying of the pofile as time pogesses fom Febuay 2006 till Novembe 2006 is clealy seen, especially up to depths of 3 m. Deepe in the pofile wate content vaiations with time ae smalle. Fo the clayey gavel, aveage wate content inceased fom 26.6 % at 7.5 m was till 36.3 % at 10 m (Fig. 3). INFILTROMETER SET-UP infiltomete tube with the ecoding depth 1 cm below the level of the oveflow. When the wate level dopped 1 cm below the oveflow level, a signal was given and the pumping ate was inceased until the oiginal wate level was estoed. Such situation did almost not occu duing the measuements, since the pumping ate was put slightly lage than the infiltation capacity, with excess wate being evacuated though the oveflow device, then collected and finally ecycled. When steady-state flow conditions wee eached, wate application was stopped and the infiltation test was finished. At site 1 the deepest infiltometes wee installed at the depths of 5.5 m and 9.5 m (Fig. 2). The fist one is located in the silty loess laye, hence is used to detemine the hydaulic popeties chaacteistic of the silty loess. The second one is located in the clayey loess, and can be used to detemine the hydaulic popeties of that laye. Owing to the elatively geat depth of the filte sections, much highe constant head values will be applied fo infiltomete 1 compaed to the head values used fo the less deep filtes in site 2. Fo the installation of the infiltometes at site 1, a 150- mm-od boehole was dilled up to a depth of 6 and 10 m, espectively. The infiltomete was at 0.5-m distance fom the TRIME access tubes (Fig. 2). The infiltomete consisted of a 75-mm-OD PVC (72-mm-ID) tube with a sceened section of 0.5 m at its bottom end (sceen stated at 7 cm fom bottom). Vetically oiented sleeves wee made in the PVC to aange the filte section. Afte installation of the PVC tube, gavel was poued in the hole until the fist mete of the boehole was filled. Then loess fom the boehole was poued on the gavel until a laye of 0.7 m loess was obtained. Then bentonite powde was poued in the hole up to a thickness of 0.5 m. Next a 0.5-m-thick concete laye was made to seal off the filte section. The emaining space until the soil suface was filled with loess fom the site. Installation of infiltometes at the othe site was done in the same way. Each infiltomete was used as a so-called constant head infiltomete. Wate was injected into the PVC cylinde by means of a flexible tube, to which a heavy metallic weight was attached to keep the end of the flexible tube at a fixed position at the bottom of the cylinde. The flexible tube should be attached to a pump which povides a constant influx of wate fo the entie duation of the test. The PVC cylinde extended appoximately 2 m above the soil suface, whee an oveflow was povided. In this way a constant wate level could be maintained thoughout the entie infiltation test. CONSTANT HEAD INFILTROMETER TESTS: SUMMARY OF DATA AND ANALYSIS Constant head infiltomete tests wee caied out with infiltomete F-1a, F-1b, F-2 and F-3. The distance fom the diffeent filte sections to the soil suface and the extension was diffeent. As a esult, the constant head at the top of the filte section was, espectively 11.4, 7.3, 3.9, and 4.4 m fo infiltomete F-1a, F-1b, F-2, and F-3. Constant head was obtained by supplying wate though a flexible tube by means of an adjustable pump. A wate level ecode was put in the Cumulative infiltation (m 3 ) Maichin Valog site Infiltomete F1-a (2006) Best fit: F1-a Infiltomete F1-b (2006) Best fit: F1-b Infiltomete 2 (2006) Best fit: 2 Infiltomete 3 (2006) Best fit: 3 Infiltomete 2 (2005) Infiltomete 3 (2005) Time (days) Figue 4 Measued cumulative infiltation fo infiltomete F-1, F-2 and f-3. Best fit simulations using HYDRUS-2D ae also included. Cumulative infiltation fo all infiltomete tests is shown in Fig. 4. In total fou tests wee caied out in 2006: two tests in the shallow clayey gavel laye (infiltomete F-2 and F-3), and two tests in deepe loess sediments to evaluate the methodology fo deep sediments (F-1a and F-1b). Fo the fome infiltomete, initial tests caied out in 2005 wee epeated in 2006 to evaluate the epoducibility of such tests. Diffeent cumulative infiltation was obseved fo diffeent infiltometes (Fig. 4). The faste incease in cumulative infiltation fo infiltomete F-1a and F-1b is due in pat to the highe imposed heads: appoximately 12 m fo F-1a and 7 m fo F-1b, vesus appoximately m fo infiltomete F-2 and F-3. In less than 0.05 days (1.2 hous) a total amount of nealy 0.8 m 3 has infiltated. Appoximately twice as much time is needed to infiltate the same amount fo infiltomete F- 2. Fo infiltomete 3 a total amount of 0.5 m 3 had infiltated within 0.1 day. Fo all infiltometes a steady-state infiltation ate was obtained within the duation of the expeiment. 4 Copyight 2007 by ASME

5 Cumulative infiltation fo the 2005 and 2006 tests ae diffeent, with the smallest diffeence being obseved fo infiltomete F-2 and lagest fo infiltomete F-3. Fo the fome the same slope is obseved indicating a vey simila infiltation ate (6.55 m 3 /d in 2006 vesus 6.9 m 3 /d in 2005), while diveging slopes ae seen fo the latte esulting in slightly diffeent infiltation ates (2.46 m 3 /d in 2006 vesus 3 m 3 /d in 2005). Taking account of the diffeent initial wate content conditions (wette conditions in 2006), the epeatibility of the test is cetainly acceptable and the suitability of the test is theefoe confimed. NUMERICAL MODELING OF CONSTANT HEAD INFILTROMETER TESTS Invese estimation of hydaulic popeties using boehole infiltation data The pupose of the in-situ boehole infiltation test is the detemination of soil hydaulic functions at a measuement scale that is commensuate with the scale of modelling. The pocedue that will be used is outlined below. The paamete estimation by means of numeical invesion is demonstated using a conceptual model that was specifically developed fo the Maiching Valog site ([1],[2]). Initial values fo the hydaulic functions that had to be povided fo the numeical invesion wee estimated on the basis of neual netwok pedictions povided in HYDRUS-2D ([6]). In the pedictions we used paticle size distibution data as input paametes. Soil hydaulic popeties may be detemined by means of invese optimization techniques such as povided in HYDRUS- 2D. Numeical invesion with HYDRUS-2D allows detemination of van Genuchten ([7]) soil hydaulic popeties (see futhe) when sufficient and appopiate soil hydaulic data is measued, e.g. duing constant head infiltation in a boehole when cumulative infiltation and histoy of wate content in the undistubed sediment at seveal locations ae measued. Fo ou applications, invese optimization compises compute simulation of the expected soil wate edistibution histoy while adjusting the soil hydaulic paametes until the best possible ageement is obtained between measued and calculated cumulative infiltation and soil moistue pofile. The simulation stats with "guess" o "tial" values of the soil hydaulic popeties; these values may be estimated using neual netwok pedictions based on paticle size data, o by using some othe pio infomation, such as the optimized values fom laboatoy testing ([1]). In the optimization hydaulic popeties ae gadually changed until the calculated cumulative infiltation and soil moistue pofile agees well with the measuements. Application of the invese optimization equied developing an axisymmetic model in HYDRUS-2D fo each of the fou infiltometes. The vetical dimension of the model was limited to the soil layes that would be immediately influenced by the infiltating wate. The lateal dimension of the model was sufficiently lage such that lateal bounday conditions would not influence the simulation esults. Wate flow though the unsatuated sediments was descibed by means of the van Genuchten wate etention chaacteistic, o wate etention cuve, θ(h), defined as ([7]): θ s -θ θ + h <0 n m θ (h)= (1+( α h ) ) (1) θ s h 0 whee θ is wate content (cm 3 /cm 3 ), h is matic head (m), θ and θ s ae esidual and satuated wate content (cm 3 /cm 3 ), espectively, and α (1/m), n, and m ae constants which define the shape of the cuve, with m = 1-1/n (with the equiement n > 1 if Eq. 1 is used in combination with K(h)). In addition to the paameteisation of θ(h), desciption of wate flow though unsatuated soil also equies the paameteisation of the unsatuated hydaulic conductivity K(h). Most models fo K(h) assume that the wate-filled poe space consists of a set of capillaies with the distibution of poe adii being detemined by the soil wate chaacteistic. One vey attactive unsatuated hydaulic conductivity function is that deived by van Genuchten ([1]), and is based on the statistical poe size distibution of ([8]). The van Genuchten- Mualem K(h) model is defined as follows: whee K(h)= K = S τ e K K s s [1 - (1- S K (h) h <0 (2) h 0 1/m e and K s and K ae satuated and elative hydaulic conductivity (m/s), espectively, τ is an empiical constant assumed equal to 0.5 ([8]), and S e is satuation degee, defined as: θ θ ) m S e = (4) θ s θ whee θ is soil wate content (cm 3 /cm 3 ), θ and θ s ae the esidual and satuated wate contents (cm 3 /cm 3 ), espectively. As a fist appoximation and on intuitive gound, θ s = η (total poosity) and θ = 0. In eality, howeve, the satuated wate content θ s of field soils is geneally 5 to 10% smalle than the total poosity η because of entapped ai and the pesence of lage poes which dain too apidly to become satuated ([9]). The esidual wate content θ is likely to be lage than zeo, because of the pesence of adsobed wate. Futhemoe, the esidual wate content is an extapolated paamete, and may theefoe not necessaily epesent the smallest possible wate content in a soil. Most often θ is teated as a fitting paamete without physical significance ([9]). The advantage of the van Genuchten-Mualem K(h) model is that nealy all its paametes, except K s, can be detemined fom the soil wate chaacteistic. In othe wods, a complete desciption of θ(h) and K(h) may be obtained with fou paametes, i.e. θ, θ s, α, n, and one additional paamete, K s. ] 2 (3) 5 Copyight 2007 by ASME

6 In the optimization of the θ(h) and K(h) elationships, the θ and θ s paametes wee fixed to decees the degees of feedom and to educe poblems of non-uniqueness in the optimization. Paamete θ s was put equal to total poosity while θ was fixed at The automatic paamete optimization outine povided in HYDRUS-2D was invoked to futhe optimize the paametes α and K s. HYDRUS adopts the minimization of the sum of the squaes (SSQ) of the esiduals: N ( ) 2 q p, i qo, i SSQ = (5) i= 1 whee N is the numbe of calibation points (hee only the cumulative fluxes ae used), qp,i is the ith pedicted values, and qo,i is the ith obseved value. HYDRUS uses the Maquadt- Levenbeg optimization algoithm to minimize the objective function (Eq. 5), to come up with paametes that poduce the minimum diffeence between the obseved and pedicted values. In the optimization the paamete n was excluded fom being optimized because initial calculations whee n was included showed high coelation with paametes α and K s, and a high standad eo coefficient fo n indicative of nonuniqueness of the solution. The paamete n was theefoe kept constant and equal to 2 [2]. Results fom invese optimization Results fom paamete optimization fo infiltomete F1-a ae summaized in Table 1. Since the filte section of F1-a is in contact with clayey loess mateial, paametes fo this laye wee detemined fist. Best fit values fo α and K s with a low standad eo (SE) coefficient wee obtained fo the clayey loess. Afte five iteations the SSQ did not futhe decease (tue fo all infiltometes). A compaison between obseved and calculated cumulative infiltation is given in Fig. 4. Table 1 Paamete values fom invese optimization using HYDRUS-2D (infiltomete F1-b, silty loess). Paamete n was fixed at 2. Paamete Best fit value S.E. coefficient Lowe Uppe α (1/m) 0,0586 0, , ,0754 K s (m/day) 0,0449 0, ,0436 0,0463 SSQ 0,00281 R 2 0,99939 Optimized paamete values fo infiltomete F1-b ae given in Table 1, illustating again a vey good fit, with acceptable SE coefficients. Othe paametes (n, θ, and θ s ) wee fixed duing the optimization, with θ s = 0.44, the independently deived total poosity ([1]). Futhe compaison between obseved and fitted cumulative infiltation is given in Fig. 4. Results fo infiltomete 2 whose filte section was placed in the clayey gavel ae summaized in Table 2. A much highe α value was obtained compaed to infiltomete F1-a. This obsevation is in ageement with the geneal soil physical concept that coase mateials have lage α-values ([10]). Fo this mateial the satuated wate content, θ s, was also fitted, since no estimates of total poosity wee available. The fitting of θ s was done only afte α and K s wee fitted, and the latte two paametes wee kept fixed at thei optimal value while fitting θ s. Fitting of all thee paametes togethe esulted in non-uniqueness in the solution. A gaphical compaison between obseved and calculated cumulative infiltation is given in Fig. 4. Table 2 Paamete values fom invese optimization using HYDRUS-2D (infiltomete F-2, clayey gavel). Paamete n was fixed at 2, while θ = 0.05 and θ s = fitted. Values in squae backets fom 2005 campaign ([1]). Paamete Best fit value S.E. coefficient Lowe Uppe α (1/m) 3 [0,53] ,7014 5,298 K s (m/day) 0, , ,089 0,0927 [0,041] θ s 0,413 # 0, ,411 0,416 SSQ 0,00251 (0,000605) # R 2 0,99935 (0,99940) # # when θ s fitted sepaately CONCLUSIONS The Maichin Valog site located in the vicinity of Kozloduy NPP is consideed by the State Entepise Radioactive Waste (SE-RAW) a potential site fo final disposal of low-and intemediate level shot-lived adioactive waste. To pepae fo an in-depth evaluation of the suitability of the Maichin Valog site, site chaacteization was caied out in 2005 and 2006 by the Geological Institute of the Bulgaian Academy of Sciences and SCK CEN emphasizing on detemination of the unsatuated flow chaacteistics of the unsatuated geological mateials. Ove the past two yeas, the hydaulic chaacteistics of the vaiably satuated Quatenay sediments (a sequence of silty and clayey loess, ed clay and clayey gavel) at the Maichin Valog expeimental site have been detemined by means of laboatoy and field tests. The pesent document epots esults fom the constant head infiltomete field tests caied out in 2005 and The objective of in-situ field tests was to evaluate the feasibility of the infiltomete set-up fo seveal unsatuated layes with vaying depths below soil suface. Fo this pupose fou infiltomete tests wee caied out. The fist two to confim ealie esults fo infiltometes installed up to the depth of 3 m in vey heteogeneous clay laye mixed with gavel o cabonate concetions. The second two to test the technique in clayey and silty loess at depths up to 10 m. Testing the epeatability of the infiltomete test by compaing esults fom 2005 and 2006 was patly successful. Estimated satuated hydaulic conductivity values fo one and the same infiltomete wee in good ageement. The 2006 shape-cuve paametes α wee not in good ageement with the 6 Copyight 2007 by ASME

7 2005 values. Possibly the sampling of a diffeent pat of the soil mateial suounding the infiltomete could have caused this diffeence, in combination with lage spatial vaiability. Results fom the two deepe infiltation tests in clayey loess and silty loess wee satisfactoy: steady-state flow was obtained within a easonable shot peiod (i.e., less than 0.1 day), and no technical difficulties wee obseved. Cumulative infiltation cuves could be fitted well with simila unsatuated paametes, although the much lowe content of lage-sized paticles such as gavel and cabonate concetions esulted in much lowe α-values moe typical of loess o loam mateial. Diffeence in satuated hydaulic conductivity between diffeent mateials was elatively small, i.e. less than a facto of five between minimal and maximum value. One of the most difficult to chaacteize layes was the clayey gavel and cabonate ich laye. Owing to the lage-sized concetions and gavels, laboatoy detemination of hydaulic popeties is nealy impossible, leaving only fielddetemination as a viable option. The use of boehole infiltation data in the invese optimization outine of the compute code HYDRUS-2D is a pactical and eliable methodology to obtain such field-scale hydaulic popeties. The innovative featues of ou appoach compise use of constant-head infiltometes at elatively geat depth below suface wheeby in combination advancing wate fonts ae monitoed by means of cylindical TRIME TDR pobes and volumes of wate infiltated. All data may be integated in the paamete optimization outine of HYDRUS-2D fo invese optimization of hydaulic paametes. ACKNOWLEDGMENTS This study was financially suppoted by the bilateal coopeation pogamme Royal Decee 20 June 2005 and 2 June 2006 on Belgian suppot to impove the safety of nuclea installations in East and Cental Euope and in the CIS (yea 2005 and 2006, poject No. 8), (contact CO between SCK CEN and Fedeale Oveheidsdienst Economie, K.M.O., Middenstand, en Enegie). [4] Stachede, M., Blume, P., Köhle K., and Ruf, R. (2002). Pofiling soil moistue with a time domain eflectomety tube pobe. Poceedings of 17 th WCSS, August 2002, Thailand, Pape no [5] Intenational Atomic Enegy Agency (IAEA) (2000). Compaison of soil wate measuement using the neuton scatteing, time domain eflectomety and capacitance methods. IAEA-TECDOC [6] Šimůnek J., Šejna, M., and van Genuchten M. Th.(1999). The HYDRUS-2D softwae package fo simulating wate flow and solute tanspot in two-dimensional vaiably satuated media. Vesion 2.0, U.S. Salinity Laboatoy, Riveside, Califonia. [7] van Genuchten, M.Th. (1980). A closed-fom equation fo pedicting the hydaulic conductivity of unsatuated soils. Soil Sci. Soc. Am. J, 44: [8] Mualem, Y. (1976). A new model fo pedicting the hydaulic conductivity of unsatuated poous media. Wate Resou. Res., 12: [9] Van Genuchten, M. Th., Leij, F.J., and Yates, S.R. (1991). The RETC code fo quantifying the hydaulic functions of unsatuated soils. EPA/600/2-91/065. U.S. Salinity Laboatoy, USDA, Riveside, CA. [10] Casel, R.F., and Paish, R.S., Developing joint pobability distibutions of soil wate etention chaacteistics. Wate Resou. Res., 24(5): REFERENCES [1 ] Mallants, D., Kaastanev, D., and Antonov, D. (2005). The 2005 site chaacteization campaign at the Maiching Valog site (Kozloduy), Bulgaia. Assistance to selection and site evaluation fo low- and intemediate level waste disposal in Bulgaia. SCK CEN epot R-4285, SCK CEN, Mol, Belgium. [2] Mallants, D., Kaastanev, D., and Antonov, D. (2006). The 2006 site chaacteization campaign at the Maiching Valog site (Kozloduy), Bulgaia. Assistance to selection and site evaluation fo low- and intemediate level waste disposal in Bulgaia. SCK CEN epot R-4419, SCK CEN, Mol, Belgium. [3] IMKO GMBH (1996). Comments on the TRIME-tube access pobe, Abolat, T, Köhle, K. Gemany. 7 Copyight 2007 by ASME