ML20206E065

Forwards Groundwater Transport of Sr-90 in Glacial Outwash Environ, Describing Development of one-dimensional Transport Model Used to Predict Sr-90 Cleanout from Groundwater

ML20206E065
Person / Time
Site:	Wood River Junction
Issue date:	05/19/1986
From:	Johnston H INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
To:	Crow W NRC
References
27022, NUDOCS 8606230078
Download: ML20206E065 (14)

Text

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2 RETURN TO 396-SS p,m

/ 4i United States Department of the Interior 76-dd c

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_,_j GEOLOGICAL SURVEY o

Water Resources Division 237 J.O.

Pastore Federal Bldg Providence, Rhode Island 02903 I

1. 1. N May 19, 198 e Mr. William T Crow 8/

g' U.S.

Nuclear Regulartory Commission m

Mail Stop SS396 P

Washington, D.C.

20555 6- # 29 od ;3 k

g,s.H0Cth ed i

'O Dear Bill-

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gas #*

Enclosed is a paper that describes the development of a\\ g>

d dimensional transport model for strontium 90 that was used'toEl predict cleanout of this constituent from ground water at the UNC plant at Wood River Junction, Rhode Island. The article was written by USGS research hydrologists Ken Kipp, Ken Sto11enwerk and Dave Grove who work at.USGS regional headquarters in Denver, Colorado.

It was published in the April, 1986, issue oC Water Resources Research.

This model predicts that it will be of the order of a decade until natural groundwater flow and radioactive decay have reduced the strontium-90 contamination to drinking water standards.

This would place the cleanout time in the mid 19 90 's.

The authors note, however, that future monitoring-of the plume will be necessary to to assess the accuracy of model predictions.

Barbara Ryan and ken Kipp are still working on the final site report, which will provide more comprehensive discussion of 2-D ground water flow modeling'"and a discussion of cleanout of constituents other than strontium 90.

Barb is doing her part on her own time, since funding for the project ended in September 1985.

I couldn't contact Ken Kipp' this weck' to determine future

~

sampling plans at UNC, because he is on vacation.

Ilowever, so far as I know, he still plans to do follow up sampling in FY 87 or 88 to check the accuracy of his model predictions.

We are not doing any work at UNC at tbc present time.

If you have any questions, call me at FTS 838 5135.

\\ *I @

Sincerely your

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e WATER RESOURCES RESEARCli, VOL 22, NO. 4, pAGES 519-530, ApRll 1936 Groundwater Transport of Strontium 90 in a Glacial Outwash Environment KENNETit L Kirr, JR., KENNErlt G. STOLLENWERK, AND DAVID B. GROVE U3 Geological Surrey, Deruvr, Colorasia As part of the investigation of groundwater contamination at a uranium-scrap recovery plant at Wood Riser Junction, Rhode Island, laboratory experiments led to the development of a model for predicting the transport of strontium 9o in glacial outwash sediments based on an approx mate mechanism for ion exchange. The multicomponent system was simphfied to two components by regarding all exchangeable cations other than strontium 90 as a single component. The binary ion-exchange parameter was a function a f the variable, total ion concentration. A one-dimensional solute transport model was formu.

lated to evaluate the time necessary for natural groundwater flow to remove the strontium 90 contami-nati,>n plume from the groundwater system to the pawcatud River. The finite difference transport equations were sobed sequentially for total ion concentrations, then strontium 90 concentrations. Ctay-free quarts and feldspar sands at the study site hase little potential for stronnum 90 sorption, and high calaum, magnesium, and sodium concentrations compete for the few ion exchange sites. As the totalion concentration plume moses out of the system, ion eschange of strontium 90 mcreases, reducing the strontium 90 concentration in the groundwater. Cleanout times predicted using the binary ion exchange mechanism were about two thirds of those predicted using a constant distribution coeflicient. It is suggested that this type of model can simulate solute transport more realistically in many groundwater sptems uhere the totalion concentration is not constant.

INuoDUCtf0N PattfrSon and Spoel[198!] also measured an increase in the in the course of investigation of a groundwater contam.

strontium distribution cocmcient with a decrease in excliange-nation plume at a cold-scrap uranium recoscry plant at Wood able calcium. This suggested that a constant equilibrium.

distribution coemeient would not be able to characterize re-Riser Junction, Rhode Island, strontium 90 concentrations as large as 250 pCi/L were measured [Ryan and Kipp,1984].

alistically the strontium interaction with these glacial outwash, Since these concentrations were well above the epa drinking sand, and grasci sediments. To account for the presence of the water standard of 8 pCi/L [U.S. Enrironmental Protection other major cations in the contamination plume, we took the 4cncy, 1976], a major objectise of the study was to approach of developing a simplified, mass-action relation for characterite the strontium transport rate to estimate the time ion exchange of strontium 90 whose parameters could be de-required for natural ground water flow to reduce strontium 90 termined from laboratory experiments. This relation could concentrations to the drinking water standard.

then be used in the formulation of a strontium transport model.

IkcLqroun) and Purpose Site Description This piper presents the results of the part of the investi-The study site. located at Wood River Junction in south-

. is gation whose objectises were to (1) quantify the strontium 90 interaction with these sediments,(2) develop a simplified, one-ern Rhode Island (Fi;;ure 1). Liquid wastes containing radio-nuclides and chemical solutes from an enriched uranium cold-dimensional transport model for this nuclide, (3) estimate a time range for natural groundwater flow to transport the scrap recovery plant base leaked from ponds into the highly strontium 90 contamination to the Pawcatuck River which permeable, sand and gravel aquifer. The plant was operated drains the area; and (4) evaluate the sensitivity of the stron.

from 1964 to 1980; liquid wastes were discharged to various tium transport rate to uncertainties in the parameters.

ponds and trenches from 1966 to 1979. Pond and trench bot.

The groundwater contamination plume at this study site toms were 0.3 to 4 m above the highest level of the water resides in glacial outwash sands and gravels with very httle sil table. Data are not available to quantify the contamination and clay [Manheim et al.,1984). The concept of a constant nource. In addition to nitric and hydrofluoric acids, tributyl equilibrium-distribution cocmcient commonly has been used phosphate, and kerosene, smaller amounts of the following to characterire strontium solute-sediment interaction. Compi.

chemicals were used in the recovery process: aluminum ni.

lations of distribution cocmcient values can be found in works trate, calcium hydroxide, mercury, sodium carbonate, sodium by Borg et al. [1976] and Ishcrwood [1981]. Patterson and hydroxide, and potassium hydroxide. Although primarily non.

SporI[1981] determined distribution cocmcients for strontium irradiated fuel elements and fuel fabrication equipment were in the laboratory on sediments from their site at Chalk River, processed, some slightly irradiated fuel elements were pro.

Ontario, Canada, with clean, quartz sand sediments that are cessed from 1967 to 1980. It is assumed that these fuel ele-quite similar to those at the Rhode Island site. These authors ents wcre the source of strontium 90 in the ground water.

found evidence that electrostatic forces control the adsorption The study area is underlain by the llope Valley Alaskite U "'I" II". Pr ter 20ic Age. Glacial till deposits of poorly of strontium. These I'mdings correlated with the results of Jacle s rted clays,inits, sands, gravels, and boulders form a thin (! css son and Inch [1980,1983], who observed that most (about than 6 m) mantle over the bedrock [LaSala and llaim,1960]

80%) of the strontium in the contamination plume at the "PP'"'.at land surface cast f the plant site. Glacial out-Chalk River site was readily exchangeable on the sediment.

wash deposits of medium to coarse-grained sands and grav-cls, with line grained sands and silts at depths lower than about 24 m below land surface, are deposited in the bedrock This paper is not subject to U.S. copyright. published in 1986 by valley. The line-grained sands and silts are cohesise in places:

Ihe American Geophysical Umon.

clay s. ire particles compose only about 3% of the material. An paper number SWJI711.

average of 1.5% clay-size particle content has been measured 519

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Location map and generalized surfwial geologic map of the study area. (Adapted from Ryan and Kipp [1984].)

in the coarse sand and gravel unit. htineralogy of the outwash been estimated to range from 0.3-1 m/d [Ryan and KIpp, deposits is predominantly quartz (3647%) and feldspars (43-1984].

56%). Iliotite and hornblends are more abundant t9-12%)in "fhe plume of contamination extends froin the pond area the finer sediments [Manheim er al.,1984].

northwestward about 500 m to the Pawcatuck River, then The groundwater aquifer in the study area is unco,1 fined southwestward about 250 m in the downstream direction and has a saturated thickness of about 2746 m. Afedium to-through the swampy area west of the river (Figure 2). Ground.

coarse sands and gravels occupy about 15-24 m of the upper water discharges into the river and swamp, where dilution saturated thickness and contain virtually all of the contami-precludes detection of any contaminant concentrations greater nation plume. Generally, groundwater flows from the upland than background lescis. The plume is approximately 90 m till areas to the Pawcatuck River and the swamp west of the wide and is contined to the upper 25 m of saturated thickness riser (Figure 1). The Pawcatuck River flows southwestward to (Figure 3). 'Ihe top of the contamination plume is depressed Long Island Sound, flydraulic conductisity values for the below the water table, and its depth increases as it moves medium to coarse sands and gravels in the vicinity of the away from the source area. Then it rises to the discharge area study site range from 30 60 m/d. The interstitial selocity has at the river and adjacent swamp. Freshwater recharge on top 4

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EXPLANATION e

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--Dashed wtiere approximately located.

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800 700.

600 500 400 300 200 100 0

Distance from source area in meters VERTICAL EXAGGERATION: X10 Fig. 3.

Cross-sectional map of strontium 90 concentrations in groundwater, October 1982.(Adapted from Ryan and Kipp [1934).)

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KIPPfT Al:GRoDNDWAnn TRrmront or StRoNilt'M 90 32)

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of the plume is considered to be responsible for the plume sediments. Of these, calcium is the dominant cation, com-depression, as fluid density effects have been shown to be prising about 90% of the equivalents in the cation mixture.

negligible [Ryan and Kipp,1984]. The rone of high strontium The term strontium refers to all strontium that is not stron-

)

90 concentration about 500 m from the source is believed to tium 90, w hich essentially is equal to the total strontium in the I

be the result of h'storical variations in the source con.

system.

centration.

As the first step in the development of an ion exchange Chemical and radiochemical constituents in the contami.

relation for strontium 90 in this sytem we reduced the six ionic nated water include nitrate (5-600 mg/L), boron (20--100 components to three by considering the calcium, magnesium, pgjL), potassium (3-25 mg/L), strontium 90 (4-250 pCi/L), s dium, and potassium as a single chemical component re.

t t

calcium (1.5-720 mg/L), and technetium 99 (75-1350 pCi/L).

ferred to as C, Component C could be regarded as pure cal.

Complete tables of measured chemical data appear in the cium to a good approximation. In this ternary system, we work by Ryan et al. [1984). Concentrations of gross-beta base the ion exchange of(1) comp (ment C with strontium 90, emitters range from 5 to 500 pCi/L. No gamma emitters hase (2) component C with strontium, and (3) of strontium with been detected. Specific conductance of the water ranges from strontium 90. Since the ratio of strontium to component C in 53 to 5000 pmhos/cm at 25'C. Dissolved solids concentrations the contaminated groundwater is about 0.001, we neglected are as large as 3500 mg,L, and these concentrations interfere the exchange of strontium with strontium 90 because it will be with the detection of alpha emitters.

much less than the amount of strontium 90 exchanged with l

component C. The two remaining ion exchange reactions were Tumny assumed to be chemically equivalent. In fact, the component C i

exchange with strontium was used to determine the parame-Strontium Interaction Irith the Sediments ters for the component C exchange with strontium 90.

The aqueous chemistry of strontium is similar to that of the The second step was to combine the strontium with compo.

other alkaline-earth elements. Adsorption of strontium is af.

nent C to form componer t H. This reduced our ion exchange fected by pil and by the type and concentration of other ions system to a binary system, with component A being strontium in solution [Mcifenry,1958). Partitioning of strontium be.

90.

j tween water and sediment is sensitive to the concentration of For a binary, divalent, ion exchange mechanism with stron.

other alkaline-earth elements [Chittenden,1983]. Kinniburgh tium 90 as the species of interest, the equilibrium sorption i

et at [1975] determined that sodium had no significant efTect isotherm is [Valocchi et al.,1981; Grore,1984]

j on adsorption of strontium by iron and aluminum hydrous g,ancj W, " c ' + ( K * ' - 1 )cd' l

oxides. Adsorbed strontium can be removed from soil by a

r

! caching with calcium solution [Lagerwerff and Kemper, 1975]. Divalent ion exchange of two species can be described w here l

by a mass action equation:

c/ strontium 90 lluid concentration (meq!L);

A * * + BX ss A X + B * *

(1) w/ strontium 90 sorbed concentration (meq/g);

where A and B represent the ion species in solution and AX Q cation exchange capacity (meq/g);

and BX represent the ion species sorbed onto the porous Ka, sekctidy cocmaent F);

total ion concentration (meq/L).

cr matrix at the stationary divalent anionic sites, X. At equilibri.

um, a selectivity cocmcient K,4 can be defined with respect to Since the concentration of strontium 90 is much less than the the concentrations [ Rubin and James, 1973: Schwelch and concentration of each of the other cations, the isotherm equa.

Sardin,1931; Grorr,1984]

tions (3) can be simplified to Ka' "

(2) w/ -

cf (4) j where c4' and c,' are the concentrations of A and B in the with slope i

fluid phase (millicquivalents per liter) and w/ and w,' are the dw/

K,dQ concentrations of A and B in the sorbed phase on the porous (5)

- - - =

I matrix (milliequivalents per gram). Other units of con.

dc e,

a r

centration can be used, but equivalents are the most con

• This is in the form of a linear-equihbrium isotherm,if K,d, Q senient for our purposes. It is often assumed that the selec*

and c ' are constants. That is, r

tisity coemcient is a constant. Ilowever, Valocchi et al. [1981]

indicate that K,' can be variable in natura. soil systems. If n g#, Ka'O ' 1000 g

exchangeable ions are considered, there is an equilibrium c'r equation for each pair, and n - 1 are independent. For two i

ions an isotherm curse relates the ionic concentration in the where K, is the distribution cocmcient (milliliters per gram) fluid phase to that on the porous medium, at a gisen temper, and the numerical factor converts liters to milliliters. The dis.

ature and normality (equivalents / liter) of the fluid phase tribution cocmcient can also be defined as the ratio of sorbed

[Schwelch and Sardin,1981]. If the normality of the solution c ncentration to solution ccacentration under a gisen set of or the exchange capacity of the porous medium is not con-measurement conditions [Schwelch and Sardin,1981]:

stant, or if more than two ions are considered, a single iso.

e therm curve does not exist. This is the case at the Rhode K," 4,#

(7) j island site being studied.

d Calcium, magnesium, sodium, potassium, and strontium are Equation (6) relates the distribution cocmcient to binary lon the major cations in the contamination plume that undergo exchange parameters provided there is low concentration of lon exchange with strontium 90 and with each other on the the eschanging species of interest. In this case, K, represents i

3 524 Kwe rr AL: Gummow Au n Tumnar tw Smownm <m i

t the slope of the exchange isotherm and is a constant only if and where A is a suitable measure of the amount of the species l

the isotherm is linear and if the total ion concentration is of interest (mass, activity, equivalentsL constant. Equation (5) is the ion exchange relation that was 1:quations Na and 8h are combined to eliminate the transfer used in the formulation of the strontium transport model, rate S, gising:

Strontium Transport Simulation SloJeling Ec iw 2*c

?c

- - Ac - zAw (9)

A one-dimensional solute transport model was formulated, 5 + x it~ = y Ox 2 2x which included the following transport mechanisms: ad v ec-Strontium 90 transport simulation was based on the as-tion, 6spersion, sorption or ion exchange, and radioactise sumption of binary, divalent ion exchange described pre.

1 decay. The model was based upon the following assumptions:

viously, with component Il consisting of all the other exchang-(1) one-dimensional now and solute transport and (2) constant l

and uniform pore velocity, dispersion coefficient, and sorption ing cations. This great simphtication climinates determining parameters. Continuity of solute aux determined the bound.

the parameters and solsing the transport equations for all six ary conditions. The inlet boundary condition as taken to be a exchangeable cation species known to be present at this site, j

decaying source, initially at background concentration. The Simulation of solute transport with a multiplicity of chemical reactions and interactions and with the concentration distri-1 initial condition was assumed to be a uniform solute distri, butions of several species computed concurrently has been

]

bution over the flow path length for all simulations except demonstrated only recently with the CilEMTRN numerical two,in w hich a stepwise variable distribution was used.

model of Afiller und licnum (1983). Valoccid er al. (1981)

The solute transport equation for the fluid phase in dimen-showed concentration profile development for binary and ter-I sionless form is i

nary ion eschange systems with constant and variable total dc, d#c tc ion concentration. The modeling approach taken in the pres-I 3 3 is Ox2 Ox ent work is similar to their bmary case with variable total ton concentration; however, the additional mechanism of radioac-i The transport equation for the sorbed phase in dimensionless tive decay is included here, and the boundary conditions are j

Irmis ditrerent. All of these models account for competition among j;

ditTerent 6ations for ion eschange or sorption sites.

tw l

2 y = - S - 21*

(8h)

The transport equation for strontium 90 is obtained by con.

verting (5) into dimensionless form and using the relation:

'I where tw (w ic Ew fer (10) t'r (c it + ter 08 dimennonless time; rt 4

1. =L 1

Combining (9) and 00) and the dimensionless form of(5), we

)

g j

x=7 dimensionless distance down the now path; obtain n

(I * &a) ic < $nca fc

?*c Ec4 r

a a 7,' " ~qr ~ ~q y = g dimensionless dispersion coefficient;

\\

c / ff r

er

~I

+

UU A

S=

dimensionless solute transfer rate from sorbed to duid phase; i

w here the dimensionless ion exchange factor is l'

i

-L dimensionless radioactive decay rate; do = p ga q 02) j C clo c'

c = -- dimensionless fluid phase concentration; and w.here co dimensionless strontium 90 concentration.cqual to o' ;

c w'

dimensionless sorbed phase concentration; ca w=-

can i

w e dimensionless total ion concentration, equal to dimensionless sorption factor relating Huid and cr f

sorbed concentrations; and the dimensional variables and parameters are as follows:

The boundary conditions are I

f distance down the flowpath (1.);

b

,.a x=0 (13a) e interstitial velocity (t/T);

0x l

L How path !cngth (1,);

and c'

duid phase concentration (A/ll);

c' duid phase scaling concentration (A/ll);

tc, w'

sorbed phase concentration (A/Al);

~Q = 0 x=l (136) w*

sorbed phase acating concentration (A/Al);

o D dispersion coefficient (11/7);

where c is the dimensionless initial background concen.

i S solute transfer rate from porous medium to fluid phase tration of strontium 90. The initial condition is I

tAlTV

1. d"#N

1. ~U N

d 1

A decay constant O/T);

j p bulk density of porous medium (Al/l!);

w here cm is the dimensionless initial concentration distri-e porosity ( -);

bution of strontium 90(not necessarily backgroundk l

i 4

Kn r si As,: Unot sowania Terwmmt or Stuownou 90

$25 i

t TAHl.li 1.

Grain-Sire Dmribution of the Three Sedunent Samples and Cation linchange Capacuy i

Percent ihmbuhon Cation eschange j

Sediment capacuy 9

Sample

Pebble, Granule.

Sant, Sitt and Clay,

< 2 mm fracnon,

)

idenufication 4-64 mm 2-4 mm 0 06-2 mm

< 0 06 mm meq/100 g

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2. t 1:43 fi n 0.18 i

$ $9-4t 0 42 0.9 R4.$

I4.3 0.23

$76; o

D 99 N 02 030 1

l

' Determined as the sum of cubangeable canons (f%iv.1932, p.1601 l

tCollected from uncontammated part of aquifer.

j

Collected from partially contaminated part of aqu

fer.

k i

j llecause of the small amount of strontium 90 in the system passed through columns packed with sediment. Ihcess solu-j we neglected changes in the total ion concentration resulting. tion then was drained from the column; the sediment was i

i from radioactive decay. Then, because all the concentrations remmed; and adsorbed cations were estracted with IN am-f are espressed in equisalents, there is no change of total ion monium acetate at til 7. Adsorbed strontium 90 was estrac.

i concentration from other eschanges that take place, ted from sediment sampic 576 using IN Nil,OAc at til 7 and l

l The transport equation for the total ion concentratmn is analy/ed according to Thatcher et al. [1977). This procedure obtained by dropping the sorption and radioactise decay allows measurement of adsorbed ions in situations where the i

terms from (9). Thus quantity remosed from solution is too low to be detected by consentional batch esperiments. Cations were determined l

[h,,y'M#r Nr with a Jarrell Ash AtomComp 975 inductisely coupled atomic I

(15)

Pt A

eminion spectrophotometer.

I The boundary conditions are The two uansport equations can be solved sequentially at each time step because the transport of strontium 90 depends 1,

on the total ion concentration, but not vice sersa. The equa.

-y^3+e i

r = c,.

x-0 (16a) j tion for total ion concentration must be snhed first, then the i

5 p,,,

ion eschange parameter in the strontium 90 equation is a

-=0 (16h) determined function of space and time, l'inally, the liniear h

]

strontium 90 equation is solsed. A finite ditTerence algorithm j

where e. s the dimensionless background total ion con, was used to solve equations ill) (17) numerically, with central r

centration. The irJtial condition is thfrerencing in both space and time. One hundred nodes in the spatial domain were used, with a time step of 0001 dimension-i c = r b) t-0 (17) less time units. This avoided numerical oscillations from spa-e e

where e,is the dimensionless initial distribution of total ion hat or temporal thscretiration.

l r

concentration.

IllM11.ts AND IhW OulON The three sediment samples used in this study were cores S'ro"'ium lon I:vchange collected by a spht spoon sampler from three hwations that The composition of groundwater associated with the three i

i included both contaminated and uncontaminated zones of the sediment samples studied is listed m Table 2. Dnsohed sohd j

aquifer. Grain site distribution and cation eschange capacity concentrations in the uncontaminated groundwater were low.

of these samples are listed in Table 1. The sediment predomi-llackground strontium 90 was 0.5510,83 pCliL based on 31 nantly is sand slie. The cation eschange capacity is a rela-measurements: total strontium was 0.02 mrJL in the uncon-

'l tisely low 0.18 0.30 meq/100 g as determined by estraction laminated sample. Calcium and nitiate are the major lons in with l N ammonium acetate at t l 7 [l'auc,1982, p.160).

the contaminant plume. T he higher.t obsersed concentration i

j Standard petrographic techniques and

• ray difTraction were of strontium 90 was 250 f. 25 pCi/L with an associated total

]

used to determine the mineral constituents of the sediment suontium of 1.6 mg/L Composition of a groundwater sample

)

[3fanheim et al.,1984]. Approsimately 90-95% is comprised taken from a sone ofintermediate contamination also h ghen i

of quartz and feldspar; 5-10% is composed of sermicuhte, in Table 2.

}

blot te, chlorite, and muscovite. Average mineral grain specific itelatively httle strontium was adsorbed by the sediment gravity is 2.65 g/cm', determined by a lleckman air pyc*

used in these esperiments, as shown in Table 3. Approsi.

nometer using helium as a flushmg gas [Afanhcin et al,1984j.

n.ately 0 2% of the ewhangeable cations on the sediments was (Any use of trade names is for descriptise purpmes only unti strontium. Calcium accounted for approsimately R$% of the does not comtitute endorsement by the Lt.S. Geologic I cubangeable cations; magnesium plus wdium accounted for

]

Survey )

about 10%. Potanium was not measured on escry sample l

The masimum adsorption capacity of the sediment for dif.

because of.malytied thmculties; however, the few reliable ferent ionic strengths of groundwater was determined by analpes indicated that potanium accounted for as much as column esperiments. Uncontaminated groundwater was used 5% of theeschangeablecations.

to dilute a synthetic contaminated groundwater with the same Selathity coefikients were calculated for the euhange of j

major ion composition as in the contaminated ground *nter of strontium with calcium, magnesium, and mdium, according to i

Table 2. Dilutions of 20: 1,10: 1, 5 : 1,1 : 1 (uncontaminateil:

(21. As shown in Table 3, they range from 1.$ to 2.2, with a i

contaminated) amt umbluted, contaminated groundwater were mean of 11 The ratio of adsorbed f a + Mg & Na to ad.

I used to simulate solute concentration ranges in the aqui.'er.

sorbed Sr aseraged $00:1, which can be ati?ibuted to the j

Seseral pore solumes of these grounitwater solutions were relatisely low contentattion of strontium in mlution. The j

,i

m a

f

$26 Kwr e t As :Gnomnwrita Ta4wunt a SimoNnou 90 I

TABLE 2, Groundwater Compostion amount of strontium adsorbed essentially was constant for each sediment sample; howeser, the concentration of stron-Groundwater Sample tium and the other cations in solution increased as the per-centage of contanunated water in Ow sarnpk inacased M a Camilituent Uncontam.

partially hiont 1

or property mated

• Contammatedt Contammated g result N,salues decreased The strong dependence of the distribution coefficient on the 4

i pil 56 33 46 total cation concentration in the groundwater indicated the

""" W ' " between strontium and other cations for es.

,p 0 55 On4 2

change sues..Ihe greatest proportion of strontium was sorbed Ca. mg L 30 150 770 hig. mg L 0 73 30 26 from the uncontaminated groundwater w here the con-K, mg L l.5 40 21 centrations of the other cations were the lowest. Thus the use Na,mg1.

36 N6 27 of a constant distribution coefficient to characterne strontium 90 inteuctmn woh gWal outwash sana n not tcahstie, i

r,'mg i n

Cl. mg L 60 96 23 Most of the esperimental results were obtamed for total l

ItCo,, mg L 9

4 7

strontium, Correspondmg concentrations for strontium 90 in N, mg Lt

0. t R 120

$80 the solution phase also were measured. The concentration of We mgL 13 14 M

strontium 90 adsorbed on the tiediment samples can be calcu-j

• Uncontammated groandwater collected from same 6ntersal as sed, lated from 17); results are presented in Table 4 Concentrations iment samples $39 3 and $59 4.

of strontium 90 adsorbed by the sediments were, for the most 4

trarnally contaminated ground water collected from same intersa!

part, less than 3.1 x 10~ 8 pCi!g, which is the detection hmit of T

as sediment sample $76.

the radiochemical prmedure for the sample slic obtamable.

l Ground water from most contammated part of plume,CllW 350.

T hus dired measurement of the amount of strontium 90 ah-Oscan and variance of 31 measurements over the study area.

1 INitrogen contenirnoon from mtrale plus mtrne, notbed was not practical.1he one esception was sample $76, at a ddubon ratio of 5 4:1. Iloth solution and sorbed con.

j eentrations of strontium 90 were measured on a core collected j

ratio of Ca + Mg + Na to strontium in solution ranged from from a partly contamincted mne of the aqmfer. The K, from 800: 1 for uncontaminated groundwater to 1000: 1 for con.

the strontmm 90 measurements agreed quite well with the j

taminated grounda ater.

salue obtained from total attontmm measurements.

The selectisity cocmcient euentially was constant for each A stronttum 90 omtamination plume at Chalk Riser, On.

sediment sample for all ration of uncontaminated to contami.

tario, Canada, has been estensisely studied by Jachon anil nated groundwater. Ihlierences in selectivity cocmcient and im h [1980,19N31, l'attmon on,I Nrorf I19 Nil, and 1% Arns er adsorbed strontium concentration between sediment samples ul. (19Ni]. The geology of the Rhode bland and Chalk River resulted from dilTerent cation eschange properties (Table 1) sites is similar; thus one would espect that the strontium 90 Calculated cation eschange capacities on the three samples solute / sediment intera6 tion would be similar, lloweser, this

{

used in the present study ranged from 0.lR to 0 30 meq'100 g uas not the case, because the corresponding concentrations of i

with a median salue of 0.24 megfl00 g, whereas Ryan und the other cations hi the omtamination plumes were signifb j

Opp [1984), reported cation eschange capacities from 0.1 to cantly ddlerent.

I 4.2 meq'l00 g, with a median value of 0.5 mcq/100 g measured Cation eschange capacities ranged from 0.1 to 4 2 meq!!00 on fhe sediment samples.

g at the Rhode blamt site [Nyan et al.1984), compared to the i

Distribution coemeients for strontium were calculated from range of 0 3 to I N meq/100 g at the Chalk Riser site measured I

the data in TaWe 3 based on 17). The range of K,* salues in by Ja< bon and Inch (19N0). The selectisity cocmcient values Table 4 was a function of the concentration of strontium and K.,*, calculated for the Rhode Island site from the esperi.

)

the other cations in solution. As can be seen in Tahte 3, the mental data in Table 3, ranged from 1.5 to 2 2 and were TAllt.1:.1.

Concentratmns of Catcium, Magnesium. Noihum, aml Sirontmm, Adsoebed by Mediment j

%amples Se timent itatio of Adioibed Contentratmn, Motuhon Contentrallon, 5 ample t!nsontammated ruey ' 800 g meq 'ml.

Meles tmty hiennn. to Contaminated wettkient I

cahon Groumtwater Ca + his + Na Mr C,e + his + Na Mr K.....i.."

l I

$$9.)

Uncontanunated 0 19 3 9 = 10

• 17 u10'*

4 5 a 10 ' '

2.1 i

20.1 0 16 4 2 = 10 '

• 2.7 s 10- s 12 10

• 22

)

10: 1 0 17 3 4 = 10

• A n = 10 '

$ 6 = in

• 17 hl O lN 1 s = 10

• 9 2 w 10 ' '

91 a 10

• 19 I;l 0 19 17 e 10 *

2. 2 = 10

• 8 2 2 w 10

• 19 Contaminated 0 19

)$ = 10-*

4 2 = 10 8 4l = to

• 19 4

$$9 4 Uncontaminaird 0.'6 48 = 10'.*

37 = 10'*

4 5 = 10 1.3 s o.,0 u.,0 a n.,0

,6 20a ou 10 1 0 23 4 5 = 10 "

• 4 R = 10 - 8 3 6 = 10

• 13 i

I:1 0.27 4 7 m 10 -

• 2 2 m to a j ), in e g,7 l

Contaminated 0 21 17 = 10

• 4 2 = 10 ' 8 41 m 10

• 16

$76 20 1 0.10 6 4 = 10

• 47 = 10

• 4 5 s 10 '

In j

10: 1 01) 69 m 10'*

2J =10'8 3 2 m 10

• lR 34;l 0 2x 4 2 10 ^

• A s = 10 ' '

3 6 = 10

• 13 i

l.1 0 10 39 m 10

• 2 2 = 10 ' 8 2 2 m 10 '

20 l

Contanunated 0 11 6 2 = 10 *

• 4 2 = 10 - 8 4l = 10 '

20 f

I

l Kirr T at : Gnousowaina TRANSPoaf oF SnoNittas 90 327 l

TADLE 4.

Equil brium Distnbution Cocmcients for Strontium, and Calculated Strontium 90 Concentrations Adsorbed by Sedirnent sampics Sediment Ratio of Strontium Measured Calculated j

Sample tJncontaminated Distribution

• • Sr in "Sr Adsorbed Identifi-to Contaminated Cocmcient

Solution, by Sediment.

cation Groundwater K,a',ml/g PCi/L pct /s

$$9-3 Uncontaminated 8.5 0.S$

4.7 x 10-8 20:1 1.3 12 16 x 10-8 10:1 0 61 25 15 x 10-8 5:1 R38 So 19 x 10'8 1:1 0.17 123 21 x 10-s Contaminated 0.08 $

250 21 x 10'8

$$9 4 Ifncontaminated 10.4 0.$$

5.7 x 10-8 20:1 1.5 12 t8 x 10-8 10:1 0.81 23 29 x 10*8 1:I 0.22 125 28 x 10-8 Contaminated 0 090 250 22 x 10*8

$76 20: 1 2.0 12 24 x 10

• 8 10: 1 1.2 23 30 x 10-s

$.4 :1 0.69(.71)*

46 32(33)' x t0*8 1:1 0.27 12$

34 x10-s 1

Contammated 0.13 250 32 x 10 - s,

' Measured value for '*St.

similar to the range at the Chalk River site of 1.5-2.1 calcu.

Flow path length for this one-dimensional analysis was lated by Patterson and Spoci(1981). At the Chalk River site, taken to be 610 m (Figure 3). Interstitial velocity was assumed calcium comprised approximately 75% of the exchangeabic to be 0.30 m/d. Laboratory and field measurements led to the cations, compared to 85% at the Rhode Island site, following ranges for the various parameters:

Values of the distribution cocmcient for strontium ranged from 4 to 20 mL/g for contaminated sediments and coexisting y 0.02 to Oh A EI333; groundwater at the Chalk River site [ Jackson and Inch,1980; Patterson and SpocI,1981]. The range at the Rhode Island c.

n0022; era noll; site, given in Table 4, was 0.08$ to 10. mL/g with a mean value of 1.7 mL/g. This is somewhat lower than the mean values at &n a $4 to a SL the Chalk River site of 10. mL/g (Patterson and Sport,1981]

A uniform strontium 90 concentration of 230 pCi/L was and 4.9 ml./g [Pktens et al.,1981). Our data from the Rhode used as the initial condition for most of the simulations. For Idand site confirmed the effect of an increase in strontium two of the simulations (run numbers 12 and 13) the initial dntribution coefficient with a decrease in each.tngeable cal. condition was a distributed concentration down the flow path, cium found by Patterson and Sport (1981) at the Chalk River initial concentration was set at 200 pCl/L for the first $% of site.

the path length, to $0 pCi/L for the nest 73% of the path Calcium concentrations in the groundwater system of the length, and to 200 pCl/L for the final 20% of the path length.

Rhode Island study site were as much as 2 orders of mag. This appro Imates the measured concentration distribution nitude greater than those of the Chalk Riser site. Magnesium, along the amis of the contamination plume,as shown in Figure sodium, and potassium concentrations were about I order of 3-magnitude greater. As a result, there is greater competition for ion exchange sites, and this could account for the smaller amount of strontium 90 interaction with the sediments at the TAllLE $.

predicted strontium 90 Cleanout Times for Various Rhode Island site relative to the Chalk River site.

Transpon Parameter Values Strontium Transport Simulation Time to Cleanout l'arameter Values (c ac 0.032)

Results from the laboratory measurements were used to es.

tablish parameter ranges for the sediment interaction of stron*

Simulation y

4, A

i t', years llum 90. Ilackground strontium 90 concentration was 0 $$

pCl/L (Table 21, and background total lon concentration was I

o 0

0 t

1 0 43 meq/L. Cation exchange capacity ranged from 1.M x 10-a 2

0 02 0

0.8 ))

1.4 7.7 to 3.0 x 10-8 men'g. The mailmum strontium 90 con.

j

[n]

$254 St33 O

N centration measured was used as a scaling concentration:

0 02 0.731 0.133 1.5 a.2 c e' = 250 pCl/L. The associated totalion concentration used 6

0.1 0

0.133 19 to as the scaling concentration for c ' was 42.3 meq/l.. The ion 7

0.1 0

0 2.0 11 r

enchange selectivity cocmcient was taken to be the average "l

jj ll

'12 g

d esperimental value: Ke = 2. ~ihe halflife of strontium 90 it 10' nl n 254 nt33 2.4 13 28.$ ) ears. Previously measured data [R)an rf al.,1984; Ryan li' O. I 0 731 0 l33 3.2 la and Kipp,19R4] were used to determine lhe other hydrological 12t 01 0 711 0 133 16 AR l

parameters for the transport simulations. Ilutk density and 13t 01 n234 ni))

16 ts porosity measurements gave a range of values of p/s of 310 econstant linear equihbrium distribution coeMetent.

s

$.$ g/cm,

t Ihree step 6niti.it conditton dntribution.

.b

$28 Ktrr 27 At : GaotmowATi.a TnANaront nr SrRoNTIUbe 90 LO t-u______,.

f,o*

Q

~

0.8 /-

2 ' *,

/,

i

,i i

a i

i 6,*,o**..

~

~

y l

/

/

• j 0.6 '/

,/

f

-t t'

/

e w

/

/

o*,*

g l.

l

,,,o*,

/

e 0.4

,o*,*,

o l

,/

• ,o**

EIPcANATION

/

Strontium-90 in ground water

-.....Totasson 0.2

.-.- Strontium 90 on porous medium e

• • ,,e*,

[ Strontium 90 t. e.0 Drinking water standard

.a,,... _., _...... _. -

7,,

0.0 0.2 0.4 0.6 0.8 1.0 Dimensionless distance along nowpatn Fig. 4.

Concentrations of strontium 90 and total lons in groundwater and concentration of strontium 90 on the porous medium whh distance along the now path, at selected times 1. All quantities are dimensionless. Dispersion parameter, y = 0,t;sorpuon passmeter,& = 0.73ti uniform initialconcentrations.

The time required for the one dimensional flowpath column dispersion, which is quite unrealistic. Including dispersion and to become decontaminated was taken to be that at which no radioactive decay resulted in a range of 7.7 to 10 ) ears. Al.

calculated strontium 90 concentration etceeded the drinking though the low cation exchange. capacity values that were water standard of 8 pCi/L [U.S.1:m*onmental Protection measured and the presence of high calcium concentrations hency,1976). In dimensionless form this translates to e4 s initially led us to believe that essentially no strontium.

0032. The time to cleanout was calculated in dimensionless sediment interaction was occurring, the constant linear iso.

time (column volumes), then conserted to years. Cleanout. therm calculations showed a significant retardation of the times were calculated for various combinations of dkrersion transport rate by the slight exchange that took place at the and ion eschange parameters, with and without radioactive high total lon concentrations. Radioacthe decay under the decay.

binary exchange mechanism had only a minor influence, since Results of the calculations are summarised in Table S. The cleanoot times were il years or less, which is 0.4 of the half.

times necessary for the strontium 90 groundwater contami-life for strontium 90, nation to meet drinking water standards along the entire flow Cleanout times were insensitive to the range of binary es.

path ranged from $.$ to la years. The minimum value resulted change sorption parameter used but were somewhat senstthe from the unrealhtic assumption of only advecthe transport to the range of dispersion parameters estimated to apply to with no ion etchange, no dispersion, and no radioactive this site. The reasons for this can be deduced from an under.

decay. The masimum value was based upon the greater sorp, standing of the transport rates of the total ion concentration tion parameter value and a constant, linear, ion exchange dis, and the strontium 90 and their binary exchange interaction tribution cocmcient. The cleanout time was estimated at 13-1R under the conditions assumed to esht for ihn simulation years, for constant sorption, whereas the binary,lon exchange

• study. To illustrate, concentration profiles in space at selected times fa the strontium 90 concentration and the total ion calculation gave results of R.2 Il years. Note that the time necessary to reduce strontium 90 from its initial uniform con, concentration in the groundwater and the strontium 90 con.

centration to the drinking water standard by radioactive centration sorbed on the porous medium are shown in l'igure decay alone was about 141 years. 'the more realistic, three, 4 for simulation run 9 (parameters are given in Table $1. All step initial concentration distribution with the maximum con.

variables are in dimeniloniens form. The concentration profiles centration at 200 pCi/l. gave a cleanout tima of 8.8 years, are shown at dimensionless time values of 0.2,0.7, and 2.0.

using the higher dispersion cocmcient and the same range of Initial condition profiles are all at a dimension! css con.

sorption parameters as before, scntration of 1.0, and the dimensionless concentration corte.

The range of cleanout times was $.5 to ll years when no sponding to the drinking water standard for strontium 90 is solute. sediment Interaction mechankms were included, llow. shown as a dashed line at the value of 0.032.

eser, the minimum time is based on the assumption of no During the numerical simulations invohing binary lon ex.

s*

Kirr it AL: Gneiesowsirn Tasstront or Stitovmm 90

$29 change, most of the strontium moved with the plume of high duction in peak solute concentration in the groundwater while total ion concentration. At a gisen pomt along the flow path, not mereasing the sorbed concentration above the initial con.

the strontium 90 concentration and the total ion con-dition level.

centration in the flowing phase and the strontium 90 con-Uncertainties in the dispersive and sorptive transport pa-1 centration in the sorbed phase all decreased with time. Ilow-tameters and their etrect on the predicted strontium 90 clea.

ever, the ratio of sorbed to flowing phase strontium 90 con-nout times have been discussed. Ilowever, variations in as-centration increased with time as the decreasing total ion con-sumed interstitial groundwater velocity and flow path length centration caused the ion exchange of strontium 90 to in-will hase a primary elTect on calculated cleanout times. If the crease. The etiectise distribution coefficient changed by almost flow path length and the interstitial selocity are changed from 2 orders of magnitude. The increased amount of strontium 90 the assumed values of 610 m and 0.3 mfd, respectisely, the that was sorbed on the sediments disappeared primanly by simulations must be recalculated because the dimensionless radioactne decay, as shown in Figure 4 by the horizontal decay rate and the dimensionless dispersion coefficient change.

portions of the sorbed-strontium 90 curses that drop with Three-dimensional flow and transport clTects are escluded time. The lower sorbed concentrations near the beginning of from this analysis, as are variations in interstitial groundwater the flow path are caused by the teaching of strontium 90 that velocity along the flow path. These uncertainties and limi-took place as a result of the relatisely uncontaminated tations must be kept in mind when interpreting the predicted groundwater entering the sptem, cleanout times at this groundwater contamination site.

The sorbed strontium 90 concentrations that decreased with time indicate that the increase in strontium 90 ion eschange is too small to cause the sorbed strontium 90 to eser eseced the egyng3,gy3 irutial concentration. The same results uere obtained when the radioacthe decay calculation was suppressed. This indicates The clay-free quartz and feldspar sands at. t(iguranium that it is the relatisely small amount of ion exchange that scrap recovery plant site at Wood Riser Junctian, Rhode occurs on these clay free quartz and feldspar sands that pre.

Nand, base hule potential for strontium 90 sorption com-pared to sediments with strongly sorbing clay mineralogy. The sents the total ion concentration plume from mosing com, pletely ahead of the high strontium 90 contanunation plume, high calcium, magnesium, and sodium concentrations in the in the fashion of separation chromats graphy. The range of the contamination plume monopolire the few sorption or ion ex.

sorption parameter calculated for these sediments is too small change sites that are present. Ilowever, the ion eschange that to mke it a senutive parameter for the cleanout time calcula, does take place retards the transport rate of strontium 90 tion. Strontium 90 concentratmns in the groundwater de.

through the system and reduces the peak concentrations in the cresed shghtly faster for the lower salue of the sorption pa.

groundw ater.

rameter, but the time to cleanout was reduced by less than 0 5 Ws esperimental work and the previous work of others scars The time for the totat ion concentration plume to reach hase shown that a constant equilibrium distribution coef.

background salue was 4 2 dimenyonlew time units, wherea, ficient is inadequate to characterve the sorption of strontium the strontium 90 concentration in the groundwater decreased 90 onto glacial outwash sandy sedimentt fly including the to drmk ng water standards by 2.0 dimensionicu time umts, dependence of the strontium 90 ion eschange on the total ion The ellects of reduemg the dnpetuon parameter from 0.1 to concentration in the groundwater, numerical simulations show 002 were a quicker reduction of the totalion concentration to that the contamination plume of total ion concentration background lesel (2.1 nstead of 4 2 dimennonicu time unitst moves slightly ahead of the strontium 90 plume Reduction in and a faster cleanout of the strontium 90 (1.$ mstead of 2.0 concentration of competing ions causes an increase in stron.

dimensionien titue umtn With reduced dispersion, the change tium 90 eschange, which reduces the strontium 90 con.

j from the lower to the higher value of the sorption parameter centration in the groundwater. This enables the drinking

(

occurred more abruptly as the high total ion concentratmn water standard for strontium 90 to be reached rnore quickly plume mmed out of the system and more of the strontium 90 than if equdibrium sorption under conditions of constant total mmcd out with it. Note that the solute dnpersise fluses were ion concentration were taking place. The cleanout times nec.

l in the oppmite direction to the adsectne Huset essary for groundwater flow to reduce the strontium 90 con.

I Transport umulatmni made using a constant knear equihh. centration to drinking water standard, predicted by a one.

rium sorption r. rameter for the strontium 90 showed that dimesnional transport model using binary ion eschange with fluid. and sorbed. phase concentrations decreased with time at total lon concentration dependence, were about two thirds of a gnen point along the flow path but with a constant con, thme predicted using a comtant equihbrium distribution coef.

centration ratio as required b) this mechanism. Strontium 90 licient.

concentrations in the groundwater were higher than the corte.

't his rather simphfied transport model has predicted that it sponding ones for the binary eschange mechanism until the will be of the order of a decade untd natural groundwater flow time when, under the binary eschange mechanism, the stron, and radioactise decay have reduced the strontium 90 contami.

tium started leaching cli the porous medium back into the nation to drinking water standards at this Rhode Idand site.

Howing Froundwater. The shorter cleanout omes predicted by llowever, the restricthe auumptions on which these predic.

the binary eschange mechanism were camed by the increased tions ure based must be kept in mind, l'uture monitoring of ion eschange, relathe to the constant. parameter eqmhbrium, the phime udl be necewary to anen the accuracy of these sorption mechanism, cauung more strontium 90 to be sorbed (leanout time forecasts. It h suggested that this type of model onto the porous medmm. The resuhmg deshne in strontium with binary ion euhange and parameter dependence on the 90 concentratien in the groundwater enabled the drinking total ion concentration simulates solute transport more te.

water standard to be achiesed all along the flow path more alistHally in many groundwater contamination systems. The quickly. llowever, the time neceuary to reduce both tiowing anumption that ion eschange h described by a single iso.

and sorbad phase strontium 90 concentrations to background therm is avoided. T his makes the model suitable under con.

was longer under the bmary eschange mechanism. Thus we ditiom of variable total lon concentration that are usually hase a ca of increased sorption prmidmg a benetical re.

encountered at actual groundwater contamination sitet l

• p

$30 Kier er Ai : GnoeNowArtit Tu Awimi m Sinowinat 90 Rt rl RI'NCIS Agronomy, Inc., and Soil Science Society of America, Inc., Ntadi-Dorg, I., R. Stone,11. Levy, and L Ramspott, Information pertment son, Wie,1981 to the migration of radionuclides in groundwater at the Nevada Patterson, R.1, and T. Spocl, Laboratory measurements of the stron-test site, I, Reuew and analyus of eintmg information, Rep.

tium dntribution memeient N/ for sediments from a shallow sand UCRL-52073, Law rence Livermore Lab., Livermore, Cahf.,1976, aquifer, ll' uter Rcwur. Rcs.,173L $13-520,1981.

Chittenden. D. Al., II, Factors atTecting the soluble-suspended distri-Pickens, J. F., R. E. Jackson, K. J. Inch, and W. F. Nierritt, Nfeasure-bution of strontium-90 and cesium 137 in Dardanelle Reservoir, ment of distribution coefUcients using a radial mjection dual tracer Arkansas, Enr ron. Sct Technol, 17,26-31,1933, test, Water Rcwur. Res., 170),529-544,1981.

Grose, D. B, Computer model of one-dimensional equthbrium con-Rubin, J., and R. V. James, Dnpersion-airected transport of reacting trolled sorption processes, U.S. Geol. Surv. Water Resour. Insest.,

solutes in saturated porous media: Galerkin method aptshed to 84-4039,1984 equihbrium-controlled eschange in umdirectional steady w ater hherwood, D., Geoscience data base handbook for modchng a nu-Ilow, ll'arer Rcsour. Rcs.,9,3,1332-1356,1973.

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