Ecological Modelling, 22 (1983/1984) 285--324 285 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

MODELING HEAVY METALS TRANSPORT IN AN ARCTIC FJORD SYSTEM POLLUTED

FROM MINE TAILINGS

NIELS NYHOLM i ' , TUE K. NIELSEN 2 and KNUD PEDERSEN 3 1 Water Quality Ins t i t u te , Agern All@ 11, DK-2970 H6rsholm (Denmark)

2 Danish Hydraulic Ins t i t u te , Agern All@ 5, DK-2870 H~rsholm (Denmark)

3 Greenex A/S, Landemerket 9, DK-1119 Copenhagen K (Denmark)

~Vis i t ing Scient is t at U.S. Environmental Protection Agency, Environmental Research Laboratory, Corva l l is , OR 97333 (U.S.A.)

ABSTRACT

Nyholm, N., Nielsen, T.K. and Pedersen, K., 1984. Modeling heavy metals transport in an arct ic f jord system polluted from mine ta i l i ngs . Ecol. Modelling, 22: 285-324.

A computerized mathematical model has been used to describe the dissolu-

t ion and transport of lead, zinc, and cadmium in the Agfardlikavsa Fjord,

Marmoril ik, West Greenland, where ta i l i ngs from the Greenex A/S lead/zinc mine

and concentrator are being deposited.

The hydraulic model basis is a quasi-stat ionary box model representation

which has been cal ibrated using s a l i n i t y pro f i les . The superimposed metals

model assumes equi l ibr ium between dissolved and par t icu la te metal forms using

Langmuir adsorption isotherms to calculate par t icu la te concentrations from

concentrations of dissolved metals and suspended sol ids, respectively.

Cal ibrat ion of the model parameters (sedimentation rates and dissolut ion rates)

has been made observing quite narrow constraints established by f i e l d observa-

t ions and laboratory experiments.

In the course of the time period being modeled, 1978-1980, the po l lu t ion

with heavy metals has been mitigated s ign i f i can t l y . The abatement measures

undertaken include: (1) a l te ra t ion of the lead f l o t a t i on process and lime

addi t ion to ta i l i ngs by June/July 1978; (2) alum coagulation of the e f f luent by

January 1979; and (3) establishment of a new ta i l i ngs discharge system in

December 1979. The model has been used to estimate the reductions brought

about in inputs of dissolved metals as well as to quanti fy the dynamics of the

heavy metals transport in the f jord system. A par t i cu la r important objective

was to estimate the net outf low of metals to the adjacent Quamarujuk Fjord and

to predict how the outf low responded to a decreased po l lu t ion load.

A fur ther resul t from the model study was the f inding that routine

monitoring of soluble metals in the discharged ta i l i ngs as assayed by a

speci f ic method did in fact approximate model estimates of metals discharge

rates i f ~H in the test was changed from pH 7.0 to pH 8.0.

0304-3800/84/$03.00 © 1984 Elsev ierSc ience Publishers B.V.

286

INTRODUCTION

Understanding and quant i fy ing the transport, pa r t i t i on ing , and ult imate

fate of heavy metals in aquatic environments has long been recognized as

essential for managing heavy metal po l lu t ion problems. In dealing with

pract ical s i tuat ions related to receiving waters, however, the state of the art

seems mostly to be the construction of rather simple budget models with only

l i t t l e mechanistic information incorporated. Although such input/output models

can be extremely useful, the i r appl icat ion may also be severely rest r ic ted

owing to the lack of mechanistic elements, which sometimes makes extrapolat ions

to, for instance, al tered input s i tuat ions, questionable. I t may also be

desired to quanti fy the internal dynamics of the system considered in more

deta i l than is possible using such budget models.

The model presented herein is a semi-dynamic (quasi-stat ionary) box model

representation of the heavy metals transport in the Agfardlikavsa (A-) Fjord,

West Greenland, which receives s ign i f i can t inputs of heavy metals dissolved

from mine ta i l i ngs being deposited on the f jord bottom. The metals considered

are lead, zinc, and cadmium. The model consists of a hydrographic module which

describes the water movements and a metals transport part which includes the

fol lowing processes: (1) adsorption of dissolved metals onto par t icu la tes; (2)

sedimentation of par t icu la te metals; (3) metals d issolut ion from ta i l i ngs

contaminated sediment; and (4) d issolut ion of metals from discharged ta i l i ngs .

Maintaining essent ia l ly constant parameter values, the model has been used

to simulate 3 consecutive annual cycles from January 1978 through August 1980,

during which period the metals po l lu t ion has been s ign i f i can t l y abated by

several measures undertaken by the mining company.

Details of the model study have been presented in a report prepared for

Greenex A/S (VKI, 1980a) and the presentation given at th is place is a summary

of this more comprehensive report. Results from prel iminary model calculat ions

were included in a paper by Pedersen and Nyholm (1979). I t must be emphasized

for the sake of completeness that this paper is based upon the knowledge

accumulated unt i l 1980 and that supplementary results from la te r invest igat ions

have not been taken into account.

BACKGROUND

The marine disposal of tai l ings from the Greenex A/S lead/zinc mine and

mill at Marmorilik, West Greenland, starting operations in 1973, has given rise

to unexpected high levels of metals in the receiving fjord system. The metals

levels observed were of a magnitude that caused the Ministry of Greenland to

take steps to demand the mining company to abate the pollution problems.

Consequently, in 1978, intensified surveys of the fjord system were in i t iated,

287

and in p a r a l l e l here w i th var ious abatement measures were evaluated and step by

step those measures which seemed most promising were e f fec ted .

The most s i g n i f i c a n t measures included a l t e r a t i o n of the lead f l o t a t i o n

process and enlargement of the lead f l o t a t i o n p lan t in June 1978 fo l lowed by

commensing the add i t i on of l ime to the t a i l i n g s in Ju ly , and subsequently alum

f l o c c u l a t i o n of the e f f l u e n t from January 1979. A new and improved o u t l e t tube

w i th an a i r separat ion system was i n s t a l l e d in December 1979. The new o u t l e t

system has t o t a l l y e l im ina ted an e a r l i e r upward-d i rected spreading of t a i l i n g

p a r t i c l e s , caused by a i r entra inment in the o ld system.

Data Sources

The model study has been a r e l a t i v e l y minor pa r t only of comprehensive

a c t i v i t i e s undertaken by var ious bodies and coord inated by Greenex A/S and the

M in i s t r y of Greenland, respec t i ve l y . A basel ine survey was ca r r i ed out in 1972

p r i o r to the s t a r t of mining and m i l l i n g a c t i v i t i e s in 1973, and since then

moni to r ing cru ises have been made twice a year by the M in i s t r y of Greenland.

This regu la r moni to r ing has included determinat ions of the metals contents in

seawater, in sediment, and in f l o r a and fauna. The i n t e n s i f i e d i nves t i ga t i ons

in 1978 were ca r i r ed out on beha l f of the Greenex A/S and headed by Professor

P. S ~ I t o f t of the Technical Un ive rs i t y of Copenhagen. Pa r t i c i pan t s in the

program included the A rc t i c Consul tant Group (ACG), The Cominco Chemical

Meta l lu rgy Group (Cominco), the Danish Hydraul ic I n s t i t u t e (DHI), the Water

Qua l i t y I n s t i t u t e (VKI) , and the mining company. During the f o l l ow ing year ,

i n ves t i ga t i ons were cont inued on a minor scale, but f requent moni tor ing of

d isso lved metals in seawater and so lub le metals in t a i l i n g s e f f l u e n t was

cont inued.

As many as 34 repor ts prepared by var ious i n v e s t i g a t o r s , reference to

which can be found in VKI (1980a) have served as a basis f o r the model study,

e i t h e r in p rov id ing q u a l i t a t i v e i n s i g h t or in c o n t r i b u t i n g data, or both. The

most impor tant data sources are l i s t e d in Table 1.

STUDY AREA AND ENVIRONMENTAL CONDITIONS

Figure I presents the study area, the Agfardlikavsa (A-fjord), dumpsite

for the mine tai l ings, and the adjacent outer Quamarujuk (Q-fjord) at

Marmorilik, West Greenland, located at approximate latitude 71°N, longitude

51°W, 50 km northeast of Umanak. Owing to a lack of physical possibi l i t ies of

land disposal, tai l ings are being discharged to the A-fjord. The outlet is

located at aproximately 40 m depth.

An important feature of the topography of the fjord system is the

existence of a s i l l at the north end of the A-fjord rising up to about 25 m

below sea level and thus separating the deeper parts of the A- and Q-fjords.

288

Table 1. Major data sources.

I ns t i t u t i on Data

Arct ic Consultant Group, Copenhagen

B. C. Research

Cominco, Ltd.

Danish Hydraulic Ins t i tu te

Danish Isotope Centre

Greenex A/S

Ministry for Greenland (Gr~nlands Geologiske Unders6gelse, Gr6nlands Fiskeri unders~gelse, Inst i tut for Petrologi)

University of Copenhagen (Insti tute for Ecological Botany)

Water Quality Institute, Denmark

Bottom topography. Hydrological data (freshwater runoff, s i l t transport).

Metals in seawater, metals release rates from tai l ings.

Metals data, metals release data.

Hydrographic observations.

Vertical diffusion coefficient.

Emission data. Hydrological and hydro- graphic data. Sediment trap data. Metals in seawater.

Metals in seawater. Sediment data. Hydrographic data.

Airborne metals emission data.

Water quality data (including metals). Sediment and sediment trap data. Metals release rates from sediments and tai l ings. Settling characteristics of s i l t and tai l ings. Metals adsorption data.

/ ,, /

/ , - "Q A U M A,,R U'J UK "FJO.R,,D eT" / /

" . . l o ,o, " , . , ' / - ~ ~ ' " . , / .

~ ~.~ ~_

Figure 1. Study area at Marmorilik. Numbers are sampling positions.

289

From November-December to May-June the f j o rds are covered by ice. During the

summer per iod cons iderab le quan t i t i e s of f resh water ( g l a c i e r me l t i ng ) enters

at the i n t e r i o r par ts of both A- and Q- f jo rd . Large amounts of s i l t are

ca r r i ed along w i th the mel t water each year , which in some per iods create a

great t u r b i d i t y in the surface waters.

The natura l sediments in the A - f j o r d (Bondam, 1978) are gray-green s i l t y

muds charac te r ized by a lack of c lay minerals and cons i s t i ng almost exc lus i ve l y

of do l om i t i c carbonates. A mean p a r t i c l e s ize has been determined to be in the

order of 2.6 N (VKI, 1979). The sediments are low in organic mat ter .

During 1978, in tens ive studies were ca r r i ed out by the VKI on the heavy

metals d i s t r i b u t i o n in the f j o rds system (VKI, 1978, 1979a) concur ren t l y w i th

hydrographical s tud ies undertaken by the Danish Hydraul ic I n s t i t u t e (DHI,

1979). Refer r ing to Figures 2-3, the f o l l ow ing c h a r a c t e r i s t i c resu l t s can be

s ing led out from these i n v e s t i g a t i o n s .

[ ' s s o e~ LecS ~ F_~ ,L 2.3~

JdN~ JLILI !~ c~ a " o

Depth m~

Figure 2. Variations of dissolved lead, June-July 1978 (VKI, 1979a).

Figure 2 presents the variation of dissolved lead in a cross section from

the bottom of the A-fjord across the s i l l to the Q-fjord, June-July 1978. I t

shows a general trend for the metals concentrations to decrease sharply from a

high level below the s i l l to a low level above the s i l l , where the action of

water exchange with the Q-fjord and freshwater runoff from the in ter ior of the

A-fjord maintains a low concentration level. This discontinuity layer for

metals concentrations is reflected by a similar marked discontinuity layer for

sal in i ty .

During the summer period, the water body below s i l l level is pract ical ly

stagnant. During this period, the mechanism for exchange of water from below

s i l l level to above s i l l level is treated as vertical diffusion in the

hydrographical model. Consequently, a buildup of high metals concentrations

below s i l l level occurs, which continues unti l the cessation of freshwater

290

Figure 3.

d~cth m

1 0 - . " ~ ' ~ x x \ • • • • • ° ° • • o °

. . . . . . . •

~ ~ ~ ~ ~ 5 0 ° " •

i I I / , 500 40 200

60 t I / l t 50 '

I0~ 1978 ~ 1 5 7 9

Variations in concentrations of dissolved lead (pg Pb/l) at position 4 in A-fjord, close to the tai l ings outlet, February 1978 - March 1979.

runoff and the formation of ice cover. During winter a drop off of the

concentrations of dissolved metals is observed. In the hydrographical model

description, this drop off is treated as caused by a displacement of botton

water. Figure 3 i l lust rates the annual cycle for dissolved lead in the A-fjord

during the time period February 1978 to March 1979.

The main ta i l ings deposit on the bottom on the A-fjord is rather l imited

in size, and i t is known that today the far greatest part of the discharged

ta i l ings end up in the main deposit area, in part icular after the instal lat ion

of a new outlet tube in December 1979. Previously, however, ta i l ings particles

have been spread rather widely and have contaminated the major part of the

A-fjord sediments. For i l l us t ra t ion , Figure 4 shows a sediment classif icat ion

according to metals content.

At an early stage of the environmental investigations, i t was believed

that the ta i l ings deposit on the bottom of A-fjord was the main source of

metals pollution. Laboratory assays (VKI, 1979b, c) and other investigations

revealed, however, that the dissolution of metals from these deposits was a

secondary metal source only. The main input source is, in fact, the dissolu-

t ion which takes place during the travel of the ta i l ings suspension stream from

the outlet tube down to the A-fjord bottom. Only a very small fraction of the

total contents of metals in the discharged ta i l ings is actually able to

dissolve in the sea water without further reactions taking place, such as

oxidative mineral erosion, and therefore only this small fraction of poten-

t i a l l y soluble metals is of practical interest to the pol lut ion problems. A

chemical assay technique has been developed by Cominco Technical Research

(Cominco, 1979) by which the amounts of available soluble metals (ASM values)

291

~Area Z, main deposit

~Area 2, conaentration revel superior ~,~ railings composivion

[ ]Ar~a 3, Zow m¢'tals concent~rabions

Figure 4. C lass i f i ca t ion of A- f jord sediments reproduced from ACG (1978).

in the discharged ta i l ings are measured. The ASM test is essentially a

leaching of ta i l ings solids in seawater for 1 hour at pH 7.0 (maintained

constant) and under deoxygenated conditions. These assays do not indicate,

however, how large quantities of metals are actually dissolved in the sea

water, but only how large quantities are available for dissolution. As a

matter of fact, one purpose of this model study was to estimate the dissolution

occurring.

In addition to the release from the bottom sediments, secondary metal

sources include metals already dissolved in the ta i l ings water pr ior to

discharge into the f jord. Also, airborne metals pollution is taken into

account as a minor source of metals input to the surface waters of the A-fjord.

Natural background sources comprise erosion of the surrounding rocks, atmos-

pheric precipitat ion, and metals contained in the glacier melt water. These

natural sources are re lat ively minor also. Like the airborne metal emission,

they are inputs to the A-fjord surface waters.

A large part of the metals which are dissolved in the water body of the

A-fjord is carried further on to the Q-ford by the moving water and, as pointed

out previously, this transport is by far largest during the winter period.

Sedimentation during summer and fa l l (July to October) has been identi f ied as

an important metal sink, on the other hand. I t is believed that both glacier

s i l t and particulate organic matter absorb dissolved metals, which in turn

precipitate. Other mechanisms such as chemical precipitat ion may play a role

as well for this metal sedimentation process, but no other specific mechanisms

have been identif ied.

292

In many other aquatic systems, freshwater or marine, heavy metal transport

occurs predominantly as a transport of par t icu la te bound metals, and usually

more metals are associated with the organic f ract ion of the par t icu lar

material. In the A-f jord, however, the major part of the metals in the water

body are present as dissolved metals, obviously because of the high concentra-

t ion levels preva i l ing, and consequently the outflow of metals from A-f jord to

Q-fjord is largely a transport of metals in a dissolved state.

In previous years, long distance transport of f ine ta i l i ngs par t ic les

appears to have been re l a t i ve l y s ign i f icant . During the period (1978-1980)

analyzed in this model study, however, th is transport has been found to be

rather l imi ted (VKI, 1978, 1980b), and has now been almost elminated a f ter a

new out le t tube was ins ta l led in December 1979. Therefore, only the metals

which are actual ly dissolved from the ta i l i ngs material are considered in the

model. The t a i l i n g part iculates are ignored and considered iner t material for

the purpose of the modeling.

Figure 5 gives a qua l i t a t i ve overal l picture of the metal transports in

the f jord system. This conceptual model forms the framework for the mathemat-

ical model which is presented in the fol lowing.

MATHEMATICAL MODEL

Model Structure

The mathematical model consists of a set of deterministic d i f ferent ia l

equations describing the metals concentrations in the A-fjord throughout a

specified number of years. In addition, another set of equations accounts for

the various mass transports in the system, such as outflow to Q-fjord or

sedimentation. All equations are integrated through each annual cycle

simulated and a detailed mass balance is set up for both the entire year and

for every 3-month period.

The metals transport model uses as a framework a quasi-stationary box

model of the water movements as shown in Figure 6. This model is based upon

hydrographic observations only and-has been calibrated largely on the basis of

sa l in i ty data.

Hydraulic Model Basis

A large number of hydrographic measurements carried out by several

inst i tut ions were used to identify the important water exchange mechanisms but

were not, however, used direct ly in the numerical model. Data used direct ly

for estimating model parameters include measurement of freshwater runoff during

1978 and 1979 and sal in i ty distr ibutions during 1978 and early 1979. Since

early 1979, sa l in i ty data were sparse, and the model cal ibration is therefore

293

SIMPLIFIED METAL TRANSPORT MODEL OF A-FJORD

, #

Abr born emission A-fjord ~ , - ' S Precipitahon

(~- fjOFd / ErOSIOn ~ J Lake

s u% m'~tal--~ I'-d,ssol metal . J O~ensh ~e r ",-~Y Sedimentation

~ plant i ~Lead e dn Zmk concentrctes

• Fme ore bin

Figure 5. General system description. The following dominant transport pathways are shown in the figure.

a. Discharge of t a i l i ngs into the bottom water of the A-f jord and immediate dissolut ion of metals (primary source).

b. Dissolut ion of metals from the ta i l i ngs deposit at the bottom of A-f jord (secondary source).

c. Freshwater runoff in summer carrying large amounts of g lac ier s i l t and providing a background input of metals (secondary source).

d. Inf low from Q-fjord.

e. Addit ional inputs of metals to the surface water from various sources, including airborne emission from the mining and mi l l i ng a c t i v i t i e s , background atmospheric p rec ip i ta t ion , and erosion of surrounding rocks (secondary source).

f. Sedimentation of metals which have become bound to par t icu la te material (g lac ier s i l t , phytoplankton, etc.) (primary sink).

g. Outflow to Q-fjord.

based upon data from early 1978 through early 1979. The water exchange in 1980

has tentat ively been assumed equal to the water exchange estimated in 1978.

Figure 7 shows the mass fluxes between water and sediments (sectioned in

three areas as i l lust rated in Figure 4) as represented in this model. The

state variables of the model appear from Figure 8.

294

I

B o x 5 I I

I I I I I I

Qp Surface 1"~ -! . . . . . . . . . . . 1 " Q~ l; .," -I---~ Box ~ r - t - - -

F-" =#~q~ I ~ ' ' ID=am ', \~ t t t t

, p, lO~ p io~ L. Q ' ID I I

- I - D- I ~ ~ I ~ . q35 I I ~ O X J I I ~ . ~ I , 1 ID= 25m

\ I I ~ I D : ~0m

I D - b o t t o m

Figure 6. Graphical i l lus t ra t ion of the hydraulic box model of water movements.

BOX _4

_[ BOX 3

P3, L ! BOX 2

A1 A2 A3

Figure 7. Graphical i l lus t ra t ion of the sectioning of the A-fjord into 4 boxes (drawn to scale).

295

toilin~s discharge

I ~ dissolved lead

t I particulate bed

g - &

~ E

i - -

"• d~ssolved zinc

particulate zinc

! d,sso,ved admium

T J porticoIo*e ~mium J

,I E

freshwater J run off

[suspended matler J

Figure 8. State var iables, sources, and sinks of the metals transport model. Transport of metals and suspended matter due to water flow not shown.

The model assumes equi l ibr ium between par t icu late and dissolved metal

forms using Langmuir adsorption isotherms to estimate approximately the

par t icu la te fract ions as functions of dissolved metal concentrations and gross

concentrations of suspended sol ids, respectively. Each compartment of

par t icu lates (lead, zinc, cadmium, sol ids) is represented in the model as an

en t i t y , i . e . , without regarding intensive properties such as par t i c le size

d is t r ibu t ion . Consequently, each of these compartments has been given i ts own

speci f ic sedimentation rate in the model, and the transport of each metal is

described independently of the other metals.

For the integrat ion of the d i f f e ren t i a l equations of the model, the

pseudo- or computational variables to ta l lead, to ta l zinc, and to ta l cadmium

are introduced as the dynamic variables together with the concentration of

suspended matter. This reduces the number of d i f f e ren t i a l equations to 4 for

each box, excluding equations for in tegrat ion of mass fluxes. Including

equations for mass f luxes, the to ta l number of d i f f e ren t i a l equations in the

model amounts to 39. Those mass fluxes of primary importance for the engin-

eering decision making are shown in Figure 9.

The model has been programmed in 360 CSMP (IBM) and implemented on the IBM

3033 computer of the NEUCC computing centre at the Technical University of

Copenhagen. Computing time for a 3-year simulation is approximately 30

seconds.

296

f r e s h ~ o t e r ~ 1 ~ F 3

d,sc~r e

:~!~:.:.:.:.:.:.:.:.:.:.:.:.:. :::::::::::::::::::::::::::::

F igure 9. Gross t r anspo r t s o f mat te r in the A - f j o r d system.

A q u a s i - s t a t i o n a r y d e s c r i p t i o n has been chosen, so t h a t the model

descr ibes successive t ime per iods w i th constant mix ing and f l ow ra tes w i t h i n

each per iod . These were se lec ted in such a way t h a t on ly a few water exchange

parameters a t a t ime were govern ing the s a l t and metal t r anspo r t s . For

example, a small v e r t i c a l mix ing is an impor tan t mechanism in a summer pe r iod

but not in a w i n t e r pe r i od , whereas a h o r i z o n t a l water exchange is o f impor-

tance dur ing the w i n t e r but not dur ing the summer. F igure 6 inc ludes the water

f lows from a l l t ime per iods . I f t h ~ : ~ d i f f e r e n t t ime per iods are viewed 1.1..

s e p a r a t e l y , the f l ow p a t t e r n w i l l appear much s imp le r as many of the water

cu r ren ts shown w i l l be zero.

For each volume and f o r each pe r i od , a s a l t balance was set up in o rder to

descr ibe the t ime v a r i a t i o n of s a l i n i t y as a f unc t i on of s a l t t r anspo r t s .

A f t e r t h a t , a c a l i b r a t i o n was c a r r i e d out f o r the e n t i r e model and f o r

successive per iods by f i t t i n g c a l c u l a t e d s a l i n i t i e s to measured va lues.

Comparisons between c a l c u l a t e d and measured s a l i n i t i e s f o r the four model

volumes are shown in F igure 10. The agreement appears to be f a i r and best f o r

the lower volumes (1 and 2) i n t o which the d i sso l ved metals are re leased.

Apparent d e v i a t i o n s in the upper volumes (3 and 4) are p a r t l y due to a crude

d e s c r i p t i o n of the boundary va lue o f s a l i n i t y in the model.

In o rder to i l l u s t r a t e the magnitudes of the va r ious mix ing and f low

ra tes , a t ime scale of mix ing T may be de f ined as

V T - 2q

where V is the model volume (m 3) and Zq is the sum of a l l mix ing and f l ow ra tes

(m3/sec) a f f e c t i n g the volume dur ing the pe r iod in view. Values of T are

l i s t e d in Table 2. A d e t a i l e d d e s c r i p t i o n of the hyd rau l i c model and the

hydrographic observa t ions made are found in DHI (1979). Supplementary cu r ren t

records are compi led in DHI (1980) and parameter va lues as es t imated f o r the

whole pe r iod s imula ted are inc luded in VKI (1980a).

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3

o measured

--

calc

ulat

ed

J

l I

~_

_

I I

I J

.~

J_

_ I

I I

I M

A

M

J J

A S

0 N

D

J

F M

A

~

197B

19

79

Fig

ure

10.

Sa

lin

itie

s:

measu

red

and s

imu

late

d v

alu

es.

298

Table 2. Time scales of mix ing de r i ved from model c a l i b r a t i o n .

Per iod Vol. 1 Vol. 2 Vol. 3 Vol. 4

1/13/78 - 3 /15/78 12 days 8 days 9 days 5 days 3/15/78 - 5 /15/78 49 days 33 days 18 days 7 days 5/15/78 - 6 /14/78 78 days 54 days 11 days 3 days 6/14/78 - 9 /13/78 98 days 72 days 2 days 1 day 9/13/78 - 11/27/78 98 days 43 days 3 days 2 days 11/27/78 - 1 /13/78 56 days 21 days 5 days 2 days 1/13/78 - 5/15/79 19 days 12 days 9 days 6 days

PROCESS DESCRIPTIONS

Metals D i s s o l u t i o n from Discharged T a i l i n g s

Immediate d i s s o l u t i o n of metals from the d ischarged t a i l i n g s ( i . e . , t h a t

d i s s o l u t i o n t ak i ng p lace before the t a i l i n g s have s e t t l e d on the f j o r d bot tom)

is modeled as an inpu t to box I and is c a l c u l a t e d as the d ischarged tonnage of

t a i l i n g s dry mater (month ly averages) t imes an es t imated con ten t ( g / t o n ) o f

immedia te ly so lub le metals. The l a t t e r f i g u r e is c a l c u l a t e d as analyzed

a v a i l a b l e so lub le meta ls , ASM (see above) , t imes a reduc t i on f a c t o r , XF, which

is the f r a c t i o n of a v a i l a b l e so lub le metals a c t u a l l y being re leased. The XF

fac to rs as es t imated by model c a l i b r a t i o n are l i s t e d in Table 3.

Table 3. Est imated f r a c t i o n s , XF, o f the a v a i l a b l e so lub le metals (ASM) in t a i l i n g s which are d i sso l ved in the f j o r d water .

Time Per iod XF Est imates

Lead Zinc Cadmium

01 Jan 1978 - 12 Jun 1978 2.5

12 Jun 1978 - 15 Jul 1978 1.5

15 Jul 1978 - 01 Jan 1979 0.80

O. 40 O. 50

01 Jan 1979 - Ol Dec 1979 0.80 0.20 0.35

01 Dec 1979 - 31 Dec 1980

Monthly ASM data on composite samples are a v a i l a b l e from l a t e 1978, wh i l e

p r i o r hereto data are more sparse. Before Ju l y 1978 lead values were ex t reme ly

v a r i a b l e (Cominco, 1979) and r e p r e s e n t a t i v e data are a v a i l a b l e f o r A p r i l on ly .

Presumably peaks w i t h e x c e p t i o n a l l y high so lub le lead contents occurred from

t ime to t ime, which may e x p l a i n the high XF f a c t o r es t imated f o r t h a t per iod .

The XF f ac to r s determined by model c a l i b r a t i o n are cons i s t en t w i th r e s u l t s

from exper iments c a r r i e d out in M a r m o r i l i k summer 1978 where t a i l i n g s were

299

washed a number of consecut ive t imes w i th seawater in o rder to s imu la te the

actua l d i s s o l u t i o n process (VKI, 1979c). For z inc , the d e v i a t i o n between the

exper imenta l values and the c a l i b r a t e d model es t imate was in f ac t less than 10

percent . Labora to ry exper iments conducted at VKI 's l a b o r a t o r y in Copenhagen

(VKI, 1980c) on t a i l i n g s sampled October 1979 agreed less we l l w i t h the model

c a l c u l a t i o n s . I t was assumed, however, t h a t the chemical c h a r a c t e r i s t i c s o f

the t a i l i n g s had changed dur ing t r a n s p o r t .

Metals Release from Sediments

Release of metals from the t a i l i n g s contaminated sediments are descr ibed

by s imple zero o rder k i n e t i c s owing to a lack of d e t a i l e d knowledge of re lease

mechanisms.

The re lease ra tes used in the model, as shown in Table 4, are maximum

values de r i ved from l a b o r a t o r y sed iment -water exchange assays (VKI,1979b). The

sec t i on i ng of sediments i n t o 3 areas w i th d i f f e r e n t degrees of t a i l i n g s

con tamina t ion has been descr ibed above.

Table 4. Release rates of metals from sediments.

Release Rates

Sect ion of Area Lead Zinc Cadmium Sediments 103 m 2 mg Pb-m-2.day - I mg Zn-m-2-day - I mg Cd-m-2-day - ;

1 150 3.2 17 0.056

2 465 0.7 I I 0.048

3 1325 0.5 5 0.033

The laboratory experiments used to establish the release rates were

carried out in 1978 and are presumably representative for that year. The lime

and alum additions to the ta i l ings as well as the fact that the contents of

soluble metals in the ta i l ings have been reduced may, however, have brought

about a reduction in the release from the main ta i l ings deposit in later years,

as i t is believed that owing to diffusional l imitat ions, a signif icant release

takes place only from the very top (and newly deposited) sediment layer.

Although s t i l l being a re lat ively minor source of dissolved metals, from

January 1979 the zinc release i f unchanged is no longer insignif icant (see

below) because of the decreased immediate dissolution of zinc from tai l ings.

No experimental data for this later period have been available, however, which

would jus t i fy an adjustment of the release rates established for 1978.

300

Sorption of Metals Onto Particulates

The model assumes an equilibrium between dissolved metals and particulate

bound metals, the la t ter concentrations being calculated as functions of

suspended solids concentrations and dissolved metal concentrations, respec-

t ively. The relationship used is a Langmuir adsorption isotherm:

Mds Mpt = SS • A • K + Md---- ~

where Mpt and Mds are concentrations of particulate and dissolved metal and SS

is the concentration of suspended solids.

For lead and zinc, the adsorption parameters have been estimated by

nonlinear regression of available data (VKI, 1980b) using a Gauss-Newton

optimization technique. For lead, the analysis could be performed direct ly ,

while particulate zinc concentrations had to be predicted from lead concentra-

tions using a regression equation. The adsorption isotherm for lead is shown

in Figure 11. For cadmium, no data were available and i t was tentat ively

assumed that 50 percent of the metal would be in a particulate state at a

suspended solids concentration of 2 mg/l and at a total cadmium concentration

of 0.4 pg/l. The half saturation constant K has been assumed to equal 1/100

times the figure estimated for zinc -- in analogy with the relat ive abundance

of these two metals in the A-fjord system.

25 m

E

20 v

(jr)

u~ IS

z

~- 10 Z lJJ

z

5 rr LLJ

m

In

O ~ I I I

0 200 400 600 800 LF~D CONCENTBRTION (pg/l)

Figure 11. Langmuir adsorption isotherm for lead onto suspended matter.

Table 5 l i s ts the parameters used for lead, zinc, and cadmium, respec-

t ive ly , together with standard deviations as determined by nonlinear regres-

sion.

301

Table 5. Parameters in Langmuir adsorpt ion isotherms fo r lead, z inc , and cadmium sorPed onto suspended p a r t i c u l a t e mat ter .

Hal f Adsorpt ion Satura t ion

Capacity Constant Metal A (Ng/mg) K ( p g / l )

Lead 15.0 ± (1 .6) 20.6 (± 6.5)

Zinc 22 (± 3) 40 (± 19)

Cadmium 0.2 0.4

I n t e g r a t i n g the d i f f e r e n t i a l equat ions of the model using t o t a l metal

concent ra t ions (M t = Mpt + Mds) as the dynamic va r i ab les , the p a r t i t i o n i n g in to

d isso lved and p a r t i c u l a t e metal forms is ca l cu la ted by so lv ing the the

equat ion:

Mpt2 - (A • SS + K • M t ) • Mpt + A • SS • M t = 0

The assumption of e q u i l i b r i u m between the d isso lved and p a r t i c u l a t e s ta te

of metals has been made fo r p r a c t i c a l reasons in order to avoid a s t i f f

d i f f e r e n t i a l equat ion system, and also because reac t ion ra tes are v i r t u a l l y

unknown. As to adsorp t ion , the assumption of a fas t reac t ion appears to be

j u s t i f i e d cons ider ing the t ime scales of the system. Desorpt ion, on the o ther

hand, may be less rap id , and the assumption of no k i n e t i c l i m i t a t i o n also fo r

t h i s process may the re fo re be quest ioned. However, the system s t ruc tu re is so

tha t the dominant p a r t i c u l a t e t r anspo r t takes place from the surface water low

in d isso lved metals concent ra t ions and downwards through water bodies, much

r i che r in d isso lved metals, where f u r t h e r so rp t ion accord ing ly takes place.

Possible slow rates of desorpt ion and the re fo re not l i k e l y to have much

in f luence on the mass balance ca l cu la t i ons .

Sorpt ion of d isso lved metals onto p a r t i c l e s fo l lowed in turn by sedimen-

t a t i o n of p a r t i c u l a t e metals are processes of dec is ive importance fo r the

metals t r anspo r t dynamics of the system. Therefore, a lso l abo ra to ry s tud ies

have been ca r r i ed out in order to determine the metal b ind ing capac i ty of the

s i l t (VKI, 1980c). However, these studies f a i l e d to demonstrate any s i g n i f -

i can t so rp t ion of z inc except in one assay where c o - p r e c i p i t a t i o n was be l ieved

to occur. Also, the uptake of lead was much less than expected, being in the

order of only 1.5 Ng Pb per mg of s i l t ( f r a c t i o n 0 - - 6 N (and 1.0 Ng/mg ( t o t a l

f r a c t i o n ) ) , both f igures r e f e r r i n g to excess and probably sa tu ra t i ng lead

concent ra t ions. These experiments were ca r r i ed out using bottom sediments from

an upstream lake. The c h a r a c t e r i s t i c s of the sediments may d i f f e r from those

302

of the A- f jo rd s i l t , but the resul ts were l a te r q u a l i t a t i v e l y confirmed by

experiments carr ied out in Marmori l ik on the very melt water s i l t suspension.

The above resul ts indicate that processes other than simple sorpt ion onto

native s i l t are l i k e l y to occur, which, re t rospec t i ve ly , is not surpr is ing

e i ther . During the course of the model study some doubt has been expressed,

however, as to the quant i t ies of dissolved metals ac tua l ly sedimenting a f te r

having been absorbed. I t has been questioned whether the metals sedimentation

as ascertained from sediment trap catches could in fact be t a i l i n g s pa r t i c l es

or perhaps airborne par t i cu la tes . This hypothesis could quickly be ruled out,

however, both based on mass balance considerations and regarding the fact that

sedimentation of metals has been found to take place v i r t u a l l y during the

summer and f a l l only, coincid ing with the occurrence of g lac ie r s i l t in the

f j o rd system. I t should be added also that , even before the s ta r t of mining

operations, se lect ive sorpt ion processes have been demonstrated (Bondam, 1978).

Some possible mechanisms of metal sorpt ion are discussed b r i e f l y in the

fo l lowing. F i r s t , sorpt ion of metals to carbonate minerals (which are major

const i tuents of the A- f jo rd s i l t ) should be at least in the order of magnitude

as observed for clay minerals (Suess, 1973). For zinc and cadmium, co-prec ip i -

ta t ion with carbonate may be a fur ther important e l iminat ion mechanism

(F~rstner and Wittman, 1979). While d i rec t sorpt ion, however, probably is of

minor importance as indicated by the laboratory studies, the major ro le of the

s i l t par t i cu la tes in metal sorpt ion may be that of a mechanical substrate for

the p rec ip i t a t i on and f loccu la t ion of organics and secondary minerals [Jenne

(1976) as quoted by F~rstner and Wittman (1979)]. Organic material is thus

also l i k e l y to play a s i gn i f i can t ro le for the metal sorpt ion, even in th is

a rc t i c f j o rd system r e l a t i v e l y low in organics. Greenland f jo rds may as a

matter of fact const i tu te considerable sinks for organic matter (Foged, 1980;

Petersen, 1978), most of which or ig ina te from outer waters, i . e . , f luxes may be

r e l a t i v e l y high despite that concentrations are low. Only l im i ted spec i f ic

data are ava i lab le for the A- f jo rd , but baseline observations of a r ich bottom

fauna p r i o r to the disposal of t a i l i n g s are consistent with a hypothesis of

s e t t l i n g organic mater ia l .

Settl ing

Settling of both particulate metals and suspended solids is described by

assigning a constant vertical sinking rate KS (m/day) to each compartment of

particulates (suspended matter, lead, zinc, and cadmium). For the upper 3

boxes which contain a free area as well as an area of bottom sediments, one

fraction of sett l ing particles proportional to the relat ive sediment area is

being retained within the box, while the rest is transferred to the next lower

box. In the bottom box, of course, al l ends up in the sediments.

303

S e t t l i n g ra tes have been determined by model c a l i b r a t i o n c lose l y observing

cons t ra in t s es tab l i shed from mass balance ca l cu l a t i ons and from sediment t rap

s tud ies , r e s p e c t i v e l y , and fo r suspended so l ids also from t h e o r e t i c a l ca lcu la -

t i ons and l abo ra to ry experiments.

Monthly averages of sedimentat ion rates in the A - f j o r d as est imated from

sediment t rap catches are i l l u s t r a t e d in Figure 12.

Mean sedimentation in A-fjord {uncorrected overage)

t Z l n c

200 I m g / m 2 / d ° Y '

lO

L 0 '~ 'f 5 I 6

1 } Lead 50 i m g / m 2 / d o y )

7 L._/, ~

' l 5 I 6 1

20 S u s p e n d e d m a t t e r C g / m 2 / d o y )

15

10

5

103) 0 q " I J

5 I 6

I[1 ! o!1, I ~0 I I I ~nth

11 I M~)n t h

Figure 12. Monthly averages in years 1974, 1975, 1978, and 1979 of sedimenta- t i o n rates in A - f j o r d as est imated from sediment t rap catches.

S e t t l i n g of Suspended Sol ids

Laboratory s tudies (VKI, 1980c) of g l a c i e r s i l t sediments from an upstream

lake showed tha t the s i l t undergoes a f l o c c u l a t i o n in sa l ine water , and tha t i t

contained a f r a c t i o n (30 percent by weight ) of s lowly s e t t l i n g p a r t i c l e s w i th a

s e t t l i n g ra te of less than 0.1 m/hr. The dens i ty of the s i l t was 2.79 g/cm 3.

The mean p a r t i c l e s ize of uncontaminated A - f j o r d bottom sediments was 2.6

p w i th 90 percent of the mater ia l being less than 8 p.

Averaging sediment t rap catch data from several years ( r e f e r to Figure

12), an est imated approximate amount of 2000 tons per year of suspended mat ter

s e t t l e s in the f j o r d . The runo f f from the g l a c i e r was found to be in the order

of 3600 tons in 1978 wh i le only 1700 tons in 1979. Runoff from the surrounding

rocks may con t r i bu te some suspended m a t e r i a l , too, however.

Owing to i n s u f f i c i e n t data i t was not poss ib le to es tab l i sh a d i r e c t

c o r r e l a t i o n between sedimentat ion rates and suspended so l ids concent ra t ion in

304

seawater. An average sett l ing rate for the aggregated model compartment termed

"suspended solids" has therefore been determined by t r i a l and error so that

running the model (1) agreement was obtained between simulations and the few

determinations of suspended solids available, and (2) the amount of suspended

material sett l ing was in the order of 2000 tons/year, the f inal result being

2200 tons in 1978 (and 1980) and 1500 tons in 1979. I t was found that the

sedimentation calculated was signi f icant ly influenced by the boundary concen-

trations assumed for the Q-fjord water (only sparse data were available).

Because of this interaction between sett l ing rate and boundary values, the

exact figure assigned to the sett l ing rate is appropriate only in combination

with the actual boundary concentrations used to feed the model (see section on

boundary values). Once established by cal ibrat ion, however, the suspended

solids prof i les can be regarded merely as a forcing function on the system, not

being affected by the metals load. Thus, the predictive value of the model

should be maintained.

The f inal set t l ing rate estimate is 0.4 m/day, which corresponds to a

sinking rate of 2.8 N sperical particles as calculated from Stoke's law

(particles of density 2.79 g/cm 3 sett l ing in seawater of 4°C and 32 °/oo

sal in i ty which has a viscosity of 1.653 x 10 -2 dyne-sec/cm 2 and a density of

1.027 g/cm 3 [data from Riley and Skirrow (1975)].

Se t t l i ng of Par t i cu la te Lead

The estimated lead sedimentat ion from averaged sediment t rap data

approximates 10 tons/yr . As was the case for suspended so l ids , the est imate

corresponds to a hypothet ica l average year.

Analyzing t rap catch data, i t was also found that the lead sedimentat ion

ra te , Vpb, cor re la ted ra ther wel l wi th the sedimentat ion rate of suspended

so l ids , VSS. The fo l l ow ing regressions were obtained (regression l ines forced

through the o r i g i n ) :

A - f jo rd data (high metals concentrat ions) :

Vpb (mg/m2/day) = (5.1 ± 0.4) • VSS (g/m2/day), r = 0.74

Q- f jord data (low metals concentrat ions) :

Vpb (mg/m2/day) = (1.0 ± 0.1) • VSS (g/m2/day), r = 0.73

A regression of lead sedimentat ion rates against concentrat ions of

p a r t i c u l a t e lead, Pbpt (few p a r a l l e l data a v a i l a b l e ) , y ie lded (A- f j o rd and

Q- f jo rd data pooled together) :

Vpb (mg/m2/day) = (1.8 ± 0.6) • Pbpt (Ng / l ) , r = 0.36

The low co r re l a t i on c o e f f i c i e n t is bel ieved mainly to be due to ana l y t i ca l

errors in pa r t i cu l a te lead determinat ions. Running the model, however, i t

turned out that the regression c o e f f i c i e n t was of a reasonable order of

magnitude, the f i n a l ca l i b ra ted estimate of the spec i f i c sedimentat ion rate

305

being KSpb = 2.0 m/day. Using t h i s parameter value, the model p red ic ted a lead

sedimentat ion of 8 tons in 1978, wel l in accordance w i th the t rap catch

est imate. The p red ic ted sedimentat ions in 1979 and 1980 a f t e r the lead

concent ra t ions had dropped were 5 and 6 tons, respec t i ve l y .

S e t t l i n g of P a r t i c u l a t e Zinc

Analyzing t rap catch data, the average yea r l y z inc sedimentat ion approx i -

mated 24 tons. Also, the z inc sedimentat ion ra te , VZn , co r re la ted reasonably

wel l w i th the sedimentat ion ra te of suspended s o l i d s , VSS. Regressions came

out as fo l l ows :

A - f j o r d data:

VZn (mg/m2/day) = (10.3 ± 1.1) • VSS (g/m2/day) , r = 0.65

Q- f j o rd data:

VZn (mg/m2/day) = (2.31 ± 0.24) • VSS (g/m2/day) , r = 0.78

As was seen fo r lead, the amounts of z inc being adsorbed to the p a r t i c -

u la te mater ia l are much less in the Q- f j o rd than in the A - f j o r d . I t was found

also tha t the l ead :z inc r a t i o in t rap catches assumed a v i r t u a l l y constant

value of 0.42 i r r e s p e c t i v e of l oca t i on .

Owing to an i n s u f f i c i e n t number of p a r a l l e l observat ions in combinat ion

w i th inaccurate determinat ions of p a r t i c u l a t e z inc in seawater in 1978, no

s i g n i f i c a n t d i r e c t c o r r e l a t i o n between z inc sedimentat ion ra te and p a r t i c u l a t e

z inc could be es tab l i shed.

Inc lud ing a number of data from previous years, however, the r a t i o of

p a r t i c u l a t e lead to p a r t i c u l a t e z inc was found to equal approx imate ly 0.61

( r e f e r a lso to sect ion on metals so rp t i on ) . Using t h i s in fo rmat ion in

combinat ion w i th the observed almost constant r a t i o of 0.42 between lead and

zinc in t rap catches, a t e n t a t i v e s e t t l i n g ra te fo r p a r t i c u l a t e z inc , KSzn , was

established from the set t l ing rate of lead:

KSzn = 0.61/0.42 • KSpb = 3.0 m/day

The f ina l , calibrated model estimate was KSzn = 3.2 m/day and the

corresponding estimate of zinc sedimentation equaled 19 tons in 1978, s l i gh t l y

lower than the 24 tons as estimated from trap catches. The predicted sedimen-

tations in 1979 and 1980 equaled 12 tons and 17 tons, respectively.

Sett l ing of Particulate Cadmium

No data were available on part iculate cadmium nor on set t l ing rates for

this metal. Measurements of dissolved concentrations were numerous, on the

other hand, and were found to be very closely correlated with measurements of

dissolved zinc, correlat ion coeff icients for separate time periods being as

high as 0.98 (March through December 1979). This close correlat ion was taken

to indicate that cadmium transport resembled zinc transport to some extent. A

306

calibrated sett l ing rate for particulate cadmium of KScd = 2.0 m/day was used

in lack of other information.

Resuspension

Resuspension from sediments was included in the model description but the

rate was set equal to zero in the f inal calibrated model. I t is believed that

most material resuspended at large depths w i l l remain rather close to the

bottom and thus w i l l not s igni f icant ly influence the overall material transport

in the f jord system.

FORCING FUNCTIONS

The model inc ludes a number of t a b u l a t e d f o r c i n g f unc t i ons which can be

d i v i d e d i n t o na tu ra l fo rces , not being i n f l uenced by the metal p o l l u t i o n , and

man-made inpu ts , r e s p e c t i v e l y .

Natura l fo rces comprise:

- - water t r anspo r t s

- - inputs o f g l a c i e r s i l t

- - background inputs o f metals in g l a c i e r mel t water

- - boundary concen t ra t i ons of suspended so l i ds

Man-made inpu ts are:

- - d ischarge of metals d i sso l ved from t a i l i n g s

- - re lease of metals from t a i l i n g s contaminated sediments

- - d ischarge of metals d i sso l ved in t a i l i n g s water

- - metals from a i rbo rne emission

Boundary concen t ra t i ons of metals are a lso descr ibed as t abu la ted

f unc t i ons , a l though they are i n f l uenced by the metal l e v e l s in the A - f j o r d ,

which f ac t obv i ous l y reduces the p r e d i c t i v e va lue of the model to some ex ten t .

A more comprehensive model d e s c r i p t i o n , however, which would inc lude a lso the

Q - f j o r d was beyond the scope of t h i s study. The i n f l uence of the boundary

cond i t i ons are f u r t h e r commented on in the sec t ion " S e n s i t i v i t y A n a l y s i s . "

The inputs o f metals d i sso l ved in t a i l i n g s water and those de r i ved from

a i r bo rne emission (P i l egaa rd , 1979) are r e l a t i v e l y i n s i g n i f i c a n t as are the

background inpu t from mel t water . They are inc luded in the model as f o r c i n g

func t i ons most ly f o r the sake o f completeness.

A l l t a b u l a t e d func t i ons are l i s t e d in VKI (1980a).

DATA FOR VERIFICATION

Data used for ver i f icat ion and cal ibration of the model were mainly

analytical data from sampling position No. 4 (Figure 1) which has been visited

regularly. The data were averaged over depth intervals corresponding to the 4

model boxes and subsequently corrected for longitudinal gradients by means of a

307

set of correction factors established on the basis of data from intensive

surveys in June and October 1978. Correction factors ranged from 0.65 to 0.88.

Ver i f icat ion data for dissolved metals as i l l us t ra ted graphically in

Figures 13-15 are comprehensive and are believed to be quite accurate except

for the very low concentrations sometimes measured in the two surface boxes.

Some problems arose though in estimating proper average concentrations for box

2, as sampling depths and model box l imi ts matched poorly. Therefore, the data

representing box 2 are considerably less re l iable than the data available for

the bottom box, in spite of a good precision of the analyt ical determinations

of the re la t i ve l y high metals concentrations prevail ing.

Data for part iculate metals and suspended matter representing the time

period being modeled are very sparse, unfortunately, and can be taken only as

indicating the levels encountered. For cadmium, no data on part iculate

concentrations are available at a l l . As pointed out already, a mass balance

can be ver i f ied largely on dissolved concentrations alone, and the fact that

data on part iculate fractions are sparse do not inval idate the results of the

model calculations, although more data had been highly desirable. I t should be

added that data used to establish Langmuir adsorption isotherms included

results from previous years not covered by the model simulations.

RESULTS

Results of the simulations are presented in Figure 13 showing the time

course of the state variables in the four boxes. Day No. O is 1 January 1978.

Dissolved Metals

Consider ing the approximat ions of the model d e s c r i p t i o n and the i n e v i t a b l e

a n a l y t i c a l e r ro rs at low metals concent ra t ions , the s imula t ions of d isso lved

metals agree ra ther wel l w i th the observed data. Dissolved lead and z inc in

box 1, r e c i p i e n t of the t a i l i n g s , are indeed s imulated e x c e l l e n t l y . In Autumn

1979, though, s imulated concent ra t ions exceed the measured values, probably due

to events of i n t rus ions of Q - f j o rd water not accounted fo r in the model.

Supplementary cu r ren t recordings (DHI, 1980) made subsequently to the

estab l ishment of the hydrau l i c model thus ind ica ted events of convect ive

in f lows e s p e c i a l l y in June 1979. The measurements, however, d id not a l l ow a

q u a n t i t a t i v e determinat ion of the volumes of bottom water in the A - f j o r d being

replaced.

As to d isso lved cadmium in box 1, s imulated and measured concent ra t ions

appear to be s l i g h t l y out of phase. Since phasing is e x c e l l e n t fo r lead and

z inc , a p l aus i b l e exp lanat ion fo r the discrepancy is hard to f i nd . I t might be

speculated tha t the d i s s o l u t i o n of cadmium from t a i l i n g s is descr ibed less wel l

in the model than is the case fo r lead and z inc.

r.~

i~ "

rl

~.z

~.

¢-e(

n (.

nr-

~

.o

~ ~

II fD

~ ~

° ~

~°

II

~

e-

N

o ¢4- .

,~

~.

OO

o o

o oo

o °

.o

o .o

.o

.

° I

,'

~'

°

.

tli

[]

l

0/

o

i i

I o

-0

C~

0

O-I

t

CO

0 C

,J

O~

0 U

1

C~

0 OO

C) -L

C

) .

CO

C~

O

Z

f

f

0 C

~

0 0

• -I

I~1

Z

'--"

-0

0 C

3

N

N

Z

Z

--I

(.I)

I B

O0

309

CDDS

10.

8,

6.

4.

2.

O.

CDDS m _~

CDPT l

CDPT

.50

r I

0

. ~ _J. ...._.~ m

180 360 540 720

• 4 0

.30

.20

. i0

" " ' 0.00 900 1080 DG

SUSP m

SUSP

5. O0

4. O0

3. O0

2.00

I. O0

O. O0 0 180 380 5ziO 720 900 1080 O6

Figure 13b. Box I . Model simulation, Jan 1978 - Dec 1980. Cadmium and suspended solids. CDDS = cadmium, dissolved (pg / l ) . CDPT = cadmium, par t icu la te (~g/ l ) . SUSP = suspended solids (mg/). Dotted l ines are metal part iculates.

310

ZND5

i000.

800.

600.

400.

200.

O.

ZND5 m

ZNPT • . . . . . . . . .

~NPT

50.

0 180 360 540 720 900 1080

40.

30.

20.

10.

O. DG

PBD5

500.

400.

300.

200.

100.

O.

PBD5 m

PBPT i . . . . . . . .

I ',1

0 180 360 540 720 900 1080

PBPT

50.

40.

30.

20.

10.

O. DG

Figure 13c. Box 2. Model simulation, Jan 1978 - Dec 1980. Zinc and lead. ZNDS = zinc, dissolved (Mg/l). ZNPT = zinc, par t icu late (Ng/l) . PBDS = lead, dissolved (Ng/ l) . PBPT = lead, par t icu late (pg / l ) . Dotted l ines are metal part iculates.

311

CODS

5. O0

4. O0

3. O0

2. O0

1.00

O. O0 0

CDDS m

COPT i . . . . . . . .

CDPT

• 5 0

[ ] [ ] / %,. []

[ ] [ ]

,,/"~ l ~ / - ' + \ d P [] [] /

• , : .

180

.40

.30

• 20

.I0

O. O0 360 540 720 900 1080 DG

SUSP m

SUSP

2.50

2. O0

i. 50

1.00

• 50

O. O0 0 180 360 540 720

J I

900 1080 DG

Figure 13d. Box 2. Model s imu la t i on , Jan 1978 - Dec 1980. Cadmium and suspended so l i ds . CDDS = cadmium, d isso lved ( H g / l ) . CDPT = cadmium, p a r t i c u l a t e ( p g / l ) . SUSP = suspended so l i ds (mg/). Dotted l i nes are metal p a r t i c u l a t e s .

312

ZNDS

250.

200.

150.

100.

50.

O.

ZNOS m

ZNPT u

ZNPT

0

50.

40.

30.

20.

10.

O. 180 360 540 720 900 1080 DG

PBD5

100.

80.

60.

40.

20.

O.

PBD5 m - -

PBPT i . . . . . . . .

t m

0

PBPT

20.

16.

12.

8.

4.

O. 180 360 540 720 900 1080 DG

Figure 13e. Box 3. Model s imu la t i on , Jan 1978 - Dec 1980. Zinc and lead. ZNDS = z inc , d isso lved ( p g / l ) . ZNPT = z inc , p a r t i c u l a t e ( p g / l ) . PBDS = lead, d isso lved ( p g / l ) . PBPT = lead, p a r t i c u l a t e ( p g / l ) . Dotted l i nes are metal p a r t i c u l a t e s .

313

COOS m

CDPT M

COOS

2.00

I. 60

1.20 ~

• 80

• 40

0.00 "- ~ 0

[ ]

,'I

180 360 540 720 900 1080

CDPT

, 2 0

,16

,12

,08

, 0 4

0.00 DG

SUSP m ..........

5USP

2.50

2. O0

I. 50

I. O0

• 50

O. O0 0

Figure 13f. Box 3. suspended solids. par t icu late (pg / l ) . part iculates.

I

I

J 180 360 540 720

J

900 1080 DG

Model simulation, Jan 1978 - Dec 1980. Cadmium and CDDS = cadmium, dissolved (pg / l ) . CDPT = cadmium, SUSP = suspended solids (mg/). Dotted l ines are metal

314

ZNOS

200.

160.

120.

80.

40.

O.

ZNOS m . . . .

ZNPT I . . . . . . . . .

0 180 360 540 720 900 1080

ZNPT

50.

40.

30.

20.

10.

O. DG

PBDS m -

PBPT I

PBDS

I00.

80.

I n [] 60.

1 []

O j • , , ~ • , - - ,

0 180 360 540 720 900 1080

PBPT

20,

16,

12,

8.

4.

O, DG

Figure 13g. Box 4. Model simulation, Jan 1978 - Dec 1980. Zinc and lead. ZNDS = zinc, dissolved (pg/ l) . ZNPT = zinc, part iculate (pg/ l) . PBDS = lead, dissolved (pg/l). PBPT = lead, part iculate (pg/ l) . Dotted lines are metal particulates.

• -.j

-,5

~ C

Ol

c g

~g~

--,m

x

0 0

C)

0 0

C~

C

3

C3

~

O~

(:

3

• C

3 C

) C

~ C

3

• .~

0

I I

I I

,I

, ,,

• N

N

o

----

~

N

-o,.

~

1

[]

B

~ 0

(--~

~,~

. ~-

.~

fo

-'.

c-t-

~ I:v

o~

CO

I

I I

! !

G'J

~

I

f (7

0 -0

--

I

oi

316

Many of the v e r i f i c a t i o n data fo r box 2 have been es tab l i shed only w i th

crude approx imat ion, and accord ing ly the s imula t ions cannot be expected to

descr ibe the data as wel l as fo r box 1. As to the two surface boxes low in

metals concent ra t ions , the water exchange w i th the Q- f j o rd has not been

determined w i th any great accuracy. Ana ly t i ca l de terminat ions of the lowest

metal concent ra t ions may be qu i te inaccurate a lso (VKI, 1980b). For these

reasons the model cannot be expected to reproduce the observed concent ra t ions

in great d e t a i l .

A somewhat b e t t e r agreement might have been obtained by r e c a l i b r a t i n g the

hydrau l i c model using metals concent ra t ions in add i t i on to s a l i n i t i e s . I t was

f e l t , however, t ha t the p r e d i c t i v e value of the model would appear more

p l a u s i b l e i f the hydrau l i c pa r t was c a l i b r a t e d independent ly. Another reason

fo r making no adjustments was the fac t tha t the mass balance ca l cu l a t i ons were

i n s e n s i t i v e to the water exchange rates in the surface boxes.

P a r t i c u l a t e Metals and Suspended Matter

The agreement between observed and s imulated concent ra t ions of p a r t i c u l a t e

metals and suspended mat ter is of a more q u a l i t a t i v e nature than fo r the

d isso lved metals, as very few rep resen ta t i ve f i e l d data are ava i l ab l e fo r the

former category of va r iab les .

I t should be noted tha t in the summertime, peak values of p a r t i c u l a t e

metals are p red ic ted to co inc ide w i th peak values of suspended mat ter . In the

two surface boxes, t he re fo re , e levated leve ls of p a r t i c u l a t e metals and

dissolved metals are occurring with di f ferent phasings.

Sedimentation Rates

Figure 14 shows simulated temporal variation of sedimentation rates of

lead, zinc, and suspended solids.

I t is noticed that sedimentation is pract ical ly zero in winter and spring.

The lower sedimentation predicted in 1979 relat ive to 1978 is a consequence of

the lower runoff that year. For 1980, the 1978 runoff was tentat ively assumed,

and consequently the sedimentation of suspended solids equals the 1978 value.

The metals sedimentations in 1980 are less than in 1978, however, because of

the reduced metals levels in the f jord system.

Management Applications

Figures 15-17 summarize those results which are considered most important

in a management context: the developments in time of (1) total metals contents

in the A-fjord; (2) discharge rates of dissolved metals; and (3) net outflows

of metals to the adjacent Q-fjord. The figures have been constructed from mass

balance calculations made at 3 month intervals.

317

SPBDT

100. kg/da~

60. 40. ~ 20. 0.

SPBDT

SZNDT -- -- - SZNDT

, ~ i 15S" L ~ i00. 50. 0.

O 180 3GO 5~0 720 900 I080 DG

5SSDT

50. T

SSSDT

4o I 30.

20, I 10. o.t

toTs/dqy

0 180 360 540 720 900 i080 DG

(b>

Figure 14. Model estimates of to ta l sedimentation rates in A-f jord of lead (SPBDT), zinc (SZNDT), both as kg/day, and suspended matter (SSSDT) (tons/day).

According to the model simulations, the alterations of the lead f lo tat ion

process and commensing lime addition in June/July 1978 has caused the discharge

of dissolved lead to drop off from approximately 130 kg/day to about 25 kg/day

throughout the rest of the period studied. Alum flocculation of ta i l ings by

January 1979 has brought about an estimated reduction of the zinc discharge

from about 145 kg/day to 40 kg/day. Also, the cadmium discharge was reduced as

a consequence of the alum flocculation, although not equally as much, model

estimates being in the order of 1.0 kg/day in 1978 and 0.5-0.6 kg/day in 1979

and 1980.

Figures 15-17 also i l l us t ra te how the mode] predicts the net outflow of

metals from A-fjord to Q-fjord to respond in a delayed fashion to the reduced

metals input owing to the hydraulic characteristics of the system. The outflow

is further influenced by the sedimentation of metals occurring in summer and

autumn which obviously causes the pollution load of the Q-fjord to drop off

re lat ively more than the reduction of the input to the A-fjord.

An important practical result from the model study was also that routine

monitoring of available soluble metals (ASM) in ta i l ings greatly overestimates

the amounts of zinc and cadmium actually being dissolved in the A-fjord water.

From January 1979, when alum flocculation was ini tated, the estimated fractions

of ASM test values actually being released were 20% only for zinc, 35% for

cadmium, while 80% for lead. Retrospectively, i t turned out that from 1979

Greenex A/S had also performed a number of ASM assays with pH changed from pH

7.0 to pH 8.0, the natural pH of seawater. The figures obtained at pH 8.0

corresponded much more closely to the discharge rates as estimated from the

model. Model estimates made up 87% (lead), 116% (zinc), and 74% (cadmium) of

318

16'

1 / .

12

10

8

6

140

120

100

80

6O

4.O

20

0

tons

A - f j o r d

L

2

I I I I I I I I I i I I 00 3 6 9 12 3 6 9 12 3 6 9 12 month

1978 I 1979 I 1980 I year

k g / d a y

Lead discharge rate (kg/day) ( 3 months average)

,D@

Fq I FTq I I 9 12 3 6 9 12 3 6

1978 I 1979 I 1980

enlarged (]) flotation plant (~) lime addition

I I

9 12 month I year

140

12C

10C

80

6E

4C

2C

0 i

- 2 0 ,

kg/day

Net outflow of Lead (kg/day) to Q- f jo rd (3 months average)

, I I , I I i I I I 1 limont h 3 6 ~ , ~ 9 IF ~ ~ 9

1978 1979 1980 year

Figure 15. Graphical p r e s e n t a t i o n o f 3 m o n t h s m a s s b a l a n c e s f o r l e a d ,

3O

25

20

15

10

5

o;

1AC

120

100

80

60

AC

20

3OO

250

2OO

150

100

5O

0

-50

tons Zinc content in A- fjord

I I . I I I I I I i i 3 6 9 12 3 6 9 12 3 6

kg / day Z in c disc:harge r a t e

( 3 months average

I I 9 12 month

( kg ' / doy )

k g / d a y

I I 6 9

1978

12 3

alum precipitat ion

I 6 9 12 6 9 12 month

Net ou t f low of Zinc ( k g / d o y ) to Q- f j o rd (3 months overage)

i ~ i I I I i I I 12 6 9 12 3 6 9 12 month I 1979 I 1980 { year

319

Figure 16. Graphical presentation of 3 months mass balances for zinc.

320

18o' 160

1LO

120

1 O0

8O

6O

z,O

20

0,8

0,6

OA

0,2

kg CQdmium content in A - fjord

1,8

1,&

1,2

].0

.0,8

0,6

O/.

0,2

0 ' 0

I I I L I °o ~ 6 ~ ~ ~ 6 ~ 1~ 3 ~ 9 11 month

I 1978 I ] 979 I 1980 I year

kg/ day

1 976

Cadmium discharge rate (kg/doy) ( 3 months overage)

slum precipitation

I I 9 12 3 6 9 12 month

I 1979 1980 I year

kg/doy Net outflow of cadmium (kg/day) to Q-fjord (3 months average)

3 5 9 12 12 1978 I 1979 I

I 6 9 12 month

1980 I year

Figure 17. Graphical presentation of 3 months mass balances for cadmium.

321

the discharges rates ca l cu la ted from the assays. Taking in to account tha t the

z inc discharge in 1979 and l a t e r could wel l be s l i g h t l y underest imated in the

model because the z inc re lease from sediments might have dropped o f f , and also

cons ider ing the more approximate nature of the cadmium model ing, the f igures

co inc ide s u r p r i s i n g l y we l l . I t was recommended, t he re fo re , t ha t cont ro l

e f f l u e n t moni tor ing should be performed by leaching at pH 8.0.

SENSITIVITY ANALYSIS

The dynamics of the model and the parameter i n t e r a c t i o n s were thoroughly

i nves t i ga ted dur ing the c a l i b r a t i o n phase and an add i t i ona l s e n s i t i v i t y

ana lys is was ca r r i ed out by running the model w i th se lected groups of para-

meters changed from the c a l i b r a t e d values. The parameters i nves t i ga ted

inc lude:

- - ho r i zon ta l c i r c u l a t i o n rates (Q1 and Q4,s in Figure 6)

- - v e r t i c a l w in te r mixing rates ( q l , 2 and q2,3 in Figure 6)

- - w in te r c i r c u l a t i o n rates (Q2 and q l , s in Figure 6)

- - boundary concent ra t ions of metals

- - metals sedimentat ion rates

- - metals discharge rates

I t was demonstrated tha t the net ou t f low of metals to the Q- f j o rd was

p r a c t i c a l l y unaf fected by a l t e r a t i o n s of the above water exchange rates. The

boundary concent ra t ions of metals had marginal in f luence on the net out f lows

through 1978-1979, but the in f luence was i n s i g n i f i c a n t f o r lead and z inc in

1980, at which t ime the leve ls in the f j o r d system of these metals were low

from the s t a r t of the year. Quite good est imates of the boundary metal leve ls

were a v a i l a b l e , though, p rov id ing conf idence in the model s imu la t ions . For

p r e d i c t i v e purposes, however, changes in the tabu la ted values must obv ious ly be

made, fo r instance by reducing the f igu res to background values, i f fo recasts

of an unpo l lu ted or s l i g h t l y po l l u t ed s i t u a t i o n were demanded.

While i t was des i rab le tha t the above groups of parameters exer t minor

in f luence on the model s imula t ions as unce r ta i n t i es in t h e i r est imated values

are causes of model u n c e r t a i n t i e s , the con t ra ry is in fac t des i red fo r

d ischarge rates and sedimentat ion ra tes , since an o b j e c t i v e of the model study

was to est imate these f igures by c a l i b r a t i o n . Figure 18 shows model runs w i th

d i f f e r e n t f i gu res being assigned to the released f r ac t i ons of ava i l ab le so lub le

metals (50% increase or decrease from the c a l i b r a t e d va lues) . As could be

expected, the model is indeed very sens i t i ve to these parameters, so the

f igures determined by c a l i b r a t i o n are probably qu i te accurate.

The model, however, was much less sens i t i ve to metal sedimentat ion rates

as judged from d isso lved metal p r o f i l e s . The e f fec t s of sedimentat ion were

g rea te r in box 2, where un fo r t un te l y v e r i f i c a t i o n data were less representa-

322

ZNDS 2000

1600

1200

800

~00

ibo ~o s~.o 7%-- 9'oo IG8~

PBDS 100(

80{

600

~00

200

iBO 360 5LO 720 900 1080 DG

Figure 18. Sensit ivity analysis. Dissolved zinc (ZNDS) (Ng/l) and dissolved lead (pg/ l ) in box 1 as calculated for specific discharge rates being increased or decreased by 50% relat ive to the calibrated estimates.

t i v e . Running the model, i t was obvious t h a t the sed imenta t ion could not be

1 .5-2 t ime as la rge as assumed, but i t was poss ib le to generate v i r t u a l l y

unchanged s imula ted curves by reducing sed imenta t ion ra tes and d ischarge ra tes

s imu l taneous ly . Thus, a s t r i n g e n t v e r i f i c a t i o n of the occurrence o f a

sed imenta t ion to the ex ten t assumed could not be ob ta ined from measured

p r o f i l e s o f d i sso l ved metals a lone.

CONCLUSIONS

The metals transport model has been shown to provide a good simulation of

dissolved lead and zinc concentrations in the Agfardlikavsa f jord and a fa i r

simulation of the dissolved cadmium. The agreement obtained between measured

and simulated concentrations of part iculate bound metals and suspended solids

was of a more qual i tat ive nature, as only very few representative f ie ld data

were available for the time period being modeled, 1978-1980. The overall metal

transports and in part icular the net outflow to the adjacent qaumarujuk f jord

are dominated by the dissolved transports, however, and the model estimation of

metal sedimentations were based on comprehensive data from sediment trap

323

studies. Therefore, in gross terms the model is concluded to have been

veri f ied by experimental data.

In the course of the time period being modeled, the pollut ion has been

mitigated signi f icant ly by several abatement measures, the effects of which

could be quantified by means of the model. Alteration of the lead f lo tat ion

process in combination with lime addition in June/July 1978 was estimated to

have brought about an approximate 80% reduction in the discharge of dissolved

lead which in turn caused the net outflow of lead from the f jord in 1980 to

diminish by 80% relat ive to the 1978 estimate and by more than 80% relat ive to

previous years. Alum flocculation of the effluent by January 1979 caused an

estimated reduction of the dissolved zinc discharge by 75% followed by a

reduction in the net outflow from 1978 to 1980 by 85%. The release of dis-

solved cadmium was also reduced although not equally as much. The model

estimate was a 45% reduction.

The model also demonstrated a nonlinear relationship between discharge

rates and future loadings of the Qaumarujuk f jord owing to sedimentation of

metals in the Agfardlikavsa.

A final practical result from the model study was related to routine

effluent monitoring. I t was found that soluble metals in ta i l ings, as assayed

by a specific method, were in fa i r agreement with model estimates of discharge

rates i f the test pH was changed from pH 7.0 to pH 8.0.

Acknowledgements

The model study was financed by Greenex A/S, who also kindly gave

permission to publish the results. This paper was written while the principal

author was on a sabbatical leave at the Environmental Protection Agency,

Corvallis Environmental Research Laboratory, Oregon, USA, who provided typing

aid. A major grant for the sabbatical leave was obtained from the Damish

Council of Technical and Scienti f ic Research.

REFERENCES

Arctic Consultant Group (ACG). 1978. Deponering of ta i l ings. Forunders6- gelser i Marmorilik, January/February 1978. Report prepared for Greenex A/S.

Bondam, J. 1978. Recent bottom sediments in Agfardlikavsa and Qaumarujuk fiords near Marmorilik, West Greenland. Bull. Geol. Soc. Denmark, 27 (Special Issue), 39-45.

Cominco Chemical Mellalurgy Group, Cominco Technical Research. 1979. The control of soluble metals associated with marine ta i l ings at Marmorilik, Greenland. Report for Greenex A/S.

Danish Hydraulic Inst i tute (DHI). 1979. Marmorilik, Hydrografiske unders#- gelser 1978. Report to Greenex A/S.

Danish Hydraulic Inst i tute (DHI). 1980. Current Recordings in Marmorilik, October 10-22, 1979. Report to Greenex A/S.

Foged, N. 1980. Danish Geotechnical Inst i tute. Personal Communication.

324

FSrstner, V., and G. T. W. Wittmann. 1979. Metal Pollution in the Aquatic Environment. Springer-Verlag, Berlin.

Jenne, E. A. 1976. Trace element sorption by sediment and soils -- sites and processes. In: Chappell, W., and K. Petersen (eds.), Symposium on Molybdenum, Vol. 2. Marcel Dekker, New York, pp. 425-553.

Pedersen, S. D., and Nyholm, N. 1979. Surveying and Mathematical Modeling of Heavy Metal Pollution in an Arctic Fiord System. International Confer- ence. Management and Control of Heavy Metals in the Environment. London, September 1979. CEP Consultants, Ltd., Edinburgh.

Petersen, G. H. 1978. Life cycles and population dynamics of marine benthic bivalves from the Disko Bugt area of West Greenland. Ophelia, 1__77, 95-120.

Pilegaard, K. 1979. Inst i tut for ~kologisk botanik, K~benhavns Universitet, Biologisk monitering af luftforureningen med metaller i omrBdet omkring Pb- og Zn-minen i Marmorilik, V. Gr~nland. Report to Greenex A/S.

Riley, J. P., and G. Skirrow. 1975. Chemical Oceanography. Vol. I, 2nd ed., Academic Press. London.

Suess, E. 1973. Interaction of organic compounds with calcium carbonate -- I I . Organo-carbonate association in recent sediments. Geochim. Cosmochim. Acta. 3_77, 2435-2447.

Water Quality Institute (VKI). 1978. Pilot Study. Marmorilik, Jan - Feb 1978. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1979a. Water Quality Studies. Marmorilik 1978. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1979b. Testing of methods to mitigate the release of metals from A-fiord sediments, Marmorilik. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1979c. Laboratory assays on metals release from tai l ings material from Marmorilik. Marmorilik duplication. 1978. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1980a. Mathematical modeling of the heavy metals release and transport in the Agfardlikavsa Fjord, M~rmorilik. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1980b. Compilation and Statistical Analyses of Water Quality Data. Marmorilik 1972-1979. Project report prepared for Greenex A/S.

Water Quality Institute (VKI). 1980c. Laboratory assays on the features of s i l t and tai l ings material from Marmorilik -- sedimentation, metal release, and metal adsorption. Project report prepared for Greenex A/S.