EPA/60 0/R

! 00/ 081 Sept ember, 2000 Revi sion G (May2004)


# Exposu re Analys is Mod eling System (EXAMS): User Manu al and System Docu mentatio n

By
La wren ce A

. B ur ns , P h. D. Ecol ogist , E cosyst ems Research Div isi on U.S . E nvi ronment al P rot ecti on Ag ency 960 Col lege St ati on Road At hens, Georgi a 30605 -2700

Nati onal Ex posure Re search La borat ory Office of Research a nd Dev elop ment U.S . E nvi ronment al P rot ecti on Ag ency Research T rian gle P ark, NC 27711ii 

## N oti ce

The U. S. E nviron mentalProt ection Age ncythrough it s Offi ce of Re search and Deve lopm ent funded and m anage d theres ear ch de scribed here u nder GPRA Goal4, Preve ntin g Po llution and Redu cing

Risk in C om mu ni ti es, Ho mes, W

or k pl ac es an d Ec os

y ste ms , Obje ct ive 4.3, SafeHandling and Use of C ommerc ial C he mi c al s an d M i c ro or ga ni sm s , Subobje ct ive 4.3.4, Human Healt h and Ecos

ystem s, T ask 6519, Advanc ed Pes ti cide Ri

sk Asse ssme nt T echnology . It has been subje ct ed to t he Agency ’s pe er and admini strative re vie w and a pproved for publ ic at ion as an EPA docum ent . Mention of tr ade nam es or com m erc ia l product s doe s not constit ute endors em ent

or re comm endation f

or use .iii 

## F orewo rd

Environm ent alprot ection e ffort s a re incre asingly

directed toward pre ven ting adv erse healthand ecol ogic al ef f ec ts as so ci at edwi thsp e c i f i c c h emi ca l co mp o un d s o f na tur al orhu manor ig in . A s p art o f th e E co sy st ems Res ear ch Di vis ion’s res ear ch on the occ urrenc e, m ovem ent , t ransf orm at ion, im

pact , and cont

rol of envi ron mental cont aminants , t he Ec osys te m s Ass ess m ent Branch s tudi es com

ple xes of environm ent al proce sse s t

hat cont rol the tran spo rt, tr ansfor m at ion, degra dat ion, fat e, and i m pact of pol lut ant s or othe r m at eri al s in soi l a

nd wate r and devel ops m odel s for ass ess ing the ris ks a ssoc iate d wit h expos ures to c hemic al cont aminants
. Conce rn about en viro nme nta l e xposure to s ynt het ic organi c c hemic al s ha s incre ase d thenee d for te chni ques t o predic t the behavi or of chemic al s ent eri ng theenvironm ent as a result of

them anufa ct

ure, use, an dd is p o sa l o f

co mmer ci al pr o du ct s. Th e E xp o sur e A n al ys is Mo d el in g Sy st em ( EXAMS ), whi ch ha s be en undergoi ng continual devel opm ent , evaluat ion, and re vis ion at t his Divi si on since 1978, provi des a c onveni ent toolto ai d in judging the environm ent alcons equenc es shoul d a spec ifi c chemic alcont aminant e nte r a nat ural aquatic sy st em . B eca

use EXAMS requir es no che m ic almoni toring data , i t c an beuse d for ne w che m ic al s not ye t introduc ed into c omm erc e a s wel l a s for thos e whosepatte rn and volume of us e areknown. EXAMS and o th e re xp o sur e a ss es sme nt mo d el s s h o u ldco ntr ib ute si g n if ic an tl y to ef

f o rts to an ti ci p at e p o te nti al pr o b le ms ass oci at ed wi th e nvironm ent alpollutants
. Rose m ari e C . R usso Dire ct or Ecos yst em s R ese arc h Divi si on Ath ens , Geo rg iaiv 

## A b st ract

The E xposure Analysi s Mode ling System, first publi shed in 1982 ( EP A -600/3- 82-023), provide s inte rac tive com pute r soft ware for form

ulating aquati c e cosy st em m odel s and rapi dly

eva luating the fat e, transport , and exposureconc ent

rations of s ynt

het ic organi c c hemic al s – pe st ic ide s, industria l m at eri al s, and le achate s from dis posalsi te s. EXAMS co nta in s anint eg r at edDatab as e M an ag eme nt S ys te m ( DBMS ) spe ci fic al ly des igne d for stor age an d mana gement of pr oj ect d ataba ses r equ iredby the so ftw are. Userinterac tionis pro vid ed b y a fullfeature d Com

m and Line Int erfa ce ( CLI ), co ntex t-sen sitive h elp menu s, anon- line da ta diction ary and CLIuse rs’ guide , and plot

ting ca pabi li ti es for re vie w of out put data
. EXAMS provides 20 output t abl es t hat docum ent

the input dat ase ts and provideint egrate d res ult s sum m ari es for a id in ec ologi calri sk a sse ssm ent s. EXAMS ’ cor e i s a

se t of proce ss module s t

hat link fundam ent alche m ic alproper ti es to t he l im nologi cal param et ers that c ontrolthekinetics of fate and transport

in aquatic sy st em s. T he c hemic alproper ti es are m eas urabl e by

conventi onalla

boratory method s; most are require d un dervario us re gu latory aut horitie s. EXAMS li mnologi caldat a are c om posed of el em ents hist oric al ly of inte rest

to aquatic sc ie nti st s worl d-wide , so gen eratio n of

suitab le env iron mental datase ts can g ener al lyb e acc omplish ed w ith minimal pr oj ect-sp ecific fie ld investigati ons. EXAMS prov i de s fa c i l i ti e s fo r l on g- t e rm ( ste a dy -s t at e ) analy si s of

c hron i c c he mi c a ldi sc ha

rg e s, initia l-va lue approa ches for s tudy

of s hort- te rm

che m ic alrel eas es, and fullkine ti c s im ulati ons t hat al low f or m onth ly vari at ion in m ean cl im at ologi calparam et ers and al te ration of che m ic alloa dings on da ily tim e s cal es. EXAMS has been writte n in gener al iz ed (N-dim ensi onal ) form in it s i m ple m ent ation of a lgori thm s for repre senting spatia l de ta iland chemic aldegra dat ion pathways; thecomplexity o f the envi ronm ent aldes cripti on and the num ber of che m ic al s i s ful ly

use r-cont roll ed. This im

ple m ent at ion al lows for dire ct a cce ss fil e ( UDB ) st orage of fi ve inte rac ting chemic alcom pounds and 100 environm ent alsegm ent s; mor e com ple x confi gurations can be c reate d and subse quent ly st ored us ing EXAMS ’ WRI TEcom m and. EXAMS provi des analyse s of Exposu re : t

he e xpect ed (96- hour ac ute , 21-day and long-term chroni c) e nvironm ent alconc ent rations of synt het ic che m ic al s and the ir transform at ion product s, Fate : t he s pat ia l di stribution of che m ic al s in the aquatic ec osys te m , and a sens itivi ty ana ly si s of the relativ e importan ce of each trans fo rmation andtransp ort proces s (important in establish ing the accep table uncer ta int y in che m ic alla

borat ory dat a), and Per si sten ce : t

he tim e re quire d for natura l purifi cation of the ec osys te m

(vi a e xport and de gradati on proce sse s) onc e c hemic alrel eas es end.
EXAMS inc lude s file-transfer int erfa ces to the PRZ M t erre stria l modeland the FGETS and BASS bi oacc um ulati on m odel s; it

is a com ple te im ple m ent at ion of EXAMS in Fortran 95. This repor

t c overs a pe riod from

Dec em ber 1, 1999 t o S ept em

ber 15, 2000 and work was com ple te d as of Septe m

ber 17, 2000. T his ve rsi on of theManualref

le ct s c ontinuous m ai nte nanceand upgrade of EXAMS .v 

## C o n ten ts

F o r e w o r d
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . iii Ab s tr a c t
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . i v 1 .0 I ntr o du ct io nto th e E xp o sur e A n al ys is Mo d el in g Sy st em ( EXAMS )
. .... .... .... .... .... .... .... .... .... .... .... .... . . 1 1
. 1 B a c k g r o un d
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 1 1
. 2 E xp o s ur e An a l y s i s i nA qu at i c S y s t e m s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 1 1
. 2
. 1 E xp o s ur e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 1 1
. 2
. 2 P e r s i s t e n c e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 1 1
. 2
. 3 F at e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 1 1.3 T he EXAMS p r o g r am .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 2 1
. 4 S e n s i t i v i tyAn a l y s i s an dE rr o r E v a lu at i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 3 1.5 E XAMS P r o c e s s M o d e l s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 3 1
. 5
. 1 I o n i z at i o nan dS o r

p t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 4 1
. 5
. 2 T r an s f

o rm at i o nP r o c e s s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 4 1
. 5
. 3 T r an s p o rt

P r o c e s s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 5 1
. 5
. 4 C h e m i c a lL o a d i n g s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 5 1
. 6 E c o s y s t e m s An a l y s i s an dM ath e m at i c a lS y s t e m s M o d e l s . .... .... .... .... .... .... .... .... .... .... .... .... .... . 5 1.6.1 EXAMS D e s i g nS tr at e g y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 5 1
. 6
. 2 T e m p o r a lan dS p at i a lR e s o lut i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 1
. 6
. 3 A s s um

p t i o n s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 7 1
. 7 F urth e r

R e a d i n g . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 8 2
. 0 E xp o s ur e A s s e s s m e nt : M e c h an i s m s an dP r o c e s s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 1 0 2
. 1 C o m p artm e nt M o d e l s an dC o n s e rv at i o no f M a s s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 1 0 2
. 2 E qu i l ib r i um

P r o c e s s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 1 1 2
. 2
. 1 I o n i z at i o nR e a c t i o n s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 1 1 2
. 2
. 2 S e d i m e nt

S o r p t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 1 3 2
. 2
. 3 B i o s o r

p t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 1 5 2.2.4 Com

ple xat ion wi th DOC . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 1 6 2.2.5 Com

putati on of E quil ibrium

Dis tributi on Coe ffi ci ent s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 2
. 3 K i n e t i c P r o c e s s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 2 0 2
. 3
. 1 T r an s p o rt
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 2 0 2
. 3
. 1
. 1 H y dr o l o g yan da dv e c t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 2 1 2
. 3
. 1
. 2 A dv e c t e dw at e r

f l o w s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 2 3 2
. 3
. 1
. 3 A dv e c t i v e s e d i m e nt tr an s p o rt
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 2 5 2
. 3
. 1
. 4 D i s p e r s i v e tr an s p o rt
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 2 7 2.3.1.4. 1 Dis persi on wit

hin t he wate r column (28) 2.3.1.4. 2 Dis persi on wit

hin t he botto m

se dim ent s (28) 2.3.1.4. 3 Excha

nges bet ween bed s e dim ent s and overlyi ng wat ers (29) 2
. 3
. 1
. 5 T r an s p o rt

o f s ynth e t i c o r g an i c c h e m i c a l s . .... .... .... .... .... .... .... .... .... .... .... .... .... ... 3 2 2
. 3
. 2 V o l at i l i z at i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 3 3 2
. 3
. 2
. 1 C h e m i c a lD at aE ntry . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 3 6 2
. 3
. 2
. 2 E x c h an g e C o n s t ant s f o r W at e r V ap o r . .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 3 6 2
. 3
. 2
. 3 E x c h an g e C o n s t ant s f o r M o l e c u l ar

O x y g e n . .... .... .... .... .... .... .... .... .... .... .... .... .... . 3 7vi

2
. 3
. 2
. 4 V a l i d at i o nan dUn c e rt a i ntyS t u d i e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 3 8 2.3.2.4. 1 Ra don in sm al l l akes in the Canadi an Shi el d (38) 2.3.2.4. 2 1,4-Di chl orobenz ene in L ake Zuric h (39) 2
. 3
. 3 D i r e c t

P h o t o l y s i s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 4 3 2
. 3
. 3
. 1 D i r e c t

p h o t o l y s i s i na qu ati c s y s t e m s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 4 3 2
. 3
. 3
. 2 L i g ht

att e nu at i o ni nn at

ur a lw at e r s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 4 7 2.3.3.2. 1 Dis tributi on functions (D) in natura l wa te rs (47) 2.3.3.2. 2 Absorption c oeffi ci ent s (a) in nat uralwat ers (48) 2.3.3 .3 R eac ti on quant

um yi el ds ( Ö ; Q y i e l d )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 4 9 2.3.3 .4 Absor

pti on spe ct

ra ( ABSORG )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 5 0 2
. 3
. 3
. 5 E f

f e c t s o f s o r p t i o no np h o t o l y s i s r at e s ........ .... .... .... .... .... .... .... .... .... .... .... .... . . 5 2 2.3.3.5. 1 Sens itivi ty

ana ly si s of sorp ti on eff

ect s on direc t photoly si s (53) 2
. 3
. 3
. 6 N e ar - s ur f

a c e s o l ar b e am an ds kyi rr a d i an c e . .... .... .... .... .... .... .... .... .... .... .... .... .... . 5 4 2.3 .3 .7 I np ut dataandcomputa tion al mechanics – Summ ary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 2.3.4 Spec ifi c Ac id, Spec ifi c B ase , and Neut ralHydrolysi s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8 2
. 3
. 4
. 1 T e m

p e r at ur e e f f e c t s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 5 9 2
. 3
. 4
. 2 I o n i z at i o ne f

f e c t s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 6 0 2
. 3
. 4
. 3 S o r

p t i o ne f f e c t s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 1 2
. 3
. 5 I n d i r e c t

P h o t o c h e m i s try , O x i d ati o nan dR e du c t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... 6 3 2
. 3
. 5
. 1 O x i d at i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 3 2
. 3
. 5
. 2 S i n g l e t

O x y g e n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 4 2
. 3
. 5
. 3 R e du c t i o n . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 5 2
. 3
. 6 M i c r o b i a lT r an s f

o rm at i o n s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 6 7 2
. 4 I np ut P o l lut ant L o a d i n g s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 7 1 2
. 4
. 1 P r o du c t

C h e m i s try . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 7 3 2
. 5 D at aA s s e m

b l yan dS o lut i o no f

E qu at i o n s . . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 7 4 2
. 5
. 1 E xp o s ur e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 7 4 2
. 5
. 2 F at e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 7 5 2
. 5
. 3 P e r s i s t e n c e . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 7 6 3
. 0 T ut o r i a l s an dC a s e S t u d i e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 8 0 3.1 T utori al1: Intr oduct ion to Exposur e Ana ly si s wi th EXAMS – L ab o r at o ry1
. .... .... .... .... .... .... .... .... .... ... 8 0 3.2 T utori al1: Intr oduct ion to Exposur e Ana ly si s wi th EXAMS – L ab o r at o ry2
. .... .... .... .... .... .... .... .... .... ... 8 4 3
. 3 C o mm an dS e qu e n c e s f o r T ut o r i a l1 , L ab
. 1
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 8 9 3
. 3
. 1 L ab
. 1 , E x e r c i s e 1 : S t e a dy - S t at e An a l y s i s ( M o d e 1 )
. .... .... .... .... .... .... .... .... .... .... .... .... ... 8 9 3.3.2 Lab. 1, E xerc is e 2: Mode 2 Analysi s of Initia l Va lue Probl em s – S ixt y Day R Un Ti m e. . . . . . . . . . . . . . . . . . . . . . . . . 9 1 3.3.3 Lab. 1, E xerc is e 3: Ti m e-va rying se asona l a

nalysi s using Mode 3.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 3.4 I ntroduc ti on to EXAMS – La b. 1 E xerc is es wit

h Com ple te EXAMS R e s p o n s e s . .... .... .... .... .... .... .... .... .... . 9 5 3
. 4
. 1 L ab
. 1 , E x e r c i s e 1 : S t e a dy - S t at e An a l y s i s ( M o d e 1 )
. .... .... .... .... .... .... .... .... .... .... .... .... ... 9 5 3.4 .2 Lab. 1, Ex ercise 2: EXAMS i nM o d e 2
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 104 3.4 .3 Lab. 1, Ex ercise 3: EXAMS i nM o d e 3
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 111 3
. 5 T ut o r i a l2 : C h e m i c a l& E nv i r o nm e nt a lD at aE ntry . .... .... .... .... .... .... .... .... .... .... .... .... .... .... 117 3
. 5
. 1 E x e r c i s e 4 : p - D C B i nL ak e Z ur i c h
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 117 3.5.2 Exerci se 4 (Lake Zuric h) wi th i llustrative EXAMS R e s p o n s e s . .... .... .... .... .... .... .... .... .... .... ... 120 4.0 E XAMS C o mm an dL an g u a g e I nt e r f a c e ( C L I ) U s e r ’ s Gu i d e . .... .... .... .... .... .... .... .... .... .... .... .... .... . . 129 4
. 1 C o nv e nt i o n s U s e di nth i s C h ap t e r . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 129 4
. 2 O v e rv i e w . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 129 4
. 3 E nt e r i n g C o mm an d s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 129 4
. 4 C o mm an dP r o m

p t i n g . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 130 4
. 5 E XAMS M e s s a g e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 131 4.6 T he HELP C o mm an d
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 131 4
. 7 C o mm an dP r o c e dur e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 131 4
. 8 W i l dC ar dC h ar a c t e r s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 131 4
. 9 T r un c at i n g C o mm an dN am e s an dK e yw o r d s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 132vii

4.10 Summ aryDesc ription of EXAMS ’ S y s t e m C o mm an d s . .... .... .... .... .... .... .... .... .... .... .... .... .... . 132 5
. 0 S y s t e m

C o mm an dD e s c r ip t i o n s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 133 AUDI T . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 133 CATA LOG . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 135 CHAN GE . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 137 CONT INUE . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 139 DE SC RIB E . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 143 DO . . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 145 ECHO . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 148 ERAS E . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 149 EXIT . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 151 HELP . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 152 LI ST . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 154 NAM E . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 157 PLOT . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 158 PRIN T . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 163 QUIT . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 164 READ . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 165 REC A LL . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 167 RUN . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 169 SET . . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 170 SHOW . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 172 STORE . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 175 WRIT E . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 177 ZERO . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ... 178 6.0 E XAMS D at aD i c t i o n ary . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . 180 Ap p e n d i c e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... . . 196 Appe ndix A P art i t i o n i n g t o N at

ur a lO r g an i c C o l l o i d s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 196 Appe ndix B EXAMS dat a e ntry

te m plate for c hemic alm olar abs orpti on spe ct ra ( ABSOR)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 Appe ndix C Im ple m ent ing t

he mic rocom

pute r runtim e EXAMS . .... .... .... .... .... .... .... .... .... .... .... .... .... .... 201viii1



## 1 . 0 I n t r o d u c t i o n t o t h e E x p o s u r e A n a l y s i s Mo d e l i n g S y s t e m ( E XA MS 

## ) 1.1 Background Indust ria l product ion of

agri cul tura l c hemic al s, pl astic s, and pharm aceuti cal s ha s incre ase d st eadi ly over the pas t f

ive deca des. Morerec ent ly , growt h of the c hemic alindus try has been acc om

pani ed by inc rea si ng c oncer n ove r the e ffects of synt het ic che m ic al s on t

he e nvironm ent . Thesuspi ci on has ari sen that, in s om e c ase s, t he be nefit s ga ine d by usi ng a chemic alma

y not off set the cost of inci dent aldam age to m an’s nat uralli fe-s upport sys te m

– the b iosphere. The toxi ci ty of a chemic aldoes not

of i ts el f indi cat e that the e nvironm ent alri sks ass oci at ed wi th i ts use areunac ceptable, however, as it is the dose that m akes the pois on. A rati onaleva luati on of t he ri sk po sedby the us e anddisp osa l of s ynth etic ch emicals must beg in fro m a kn ow ledg e of th e per sisten ce an d mob ility of che micals in t he e nvironm ent , whi ch in tur n es ta bli sh t he c on ditions of exposurele adi ng to absorption of toxi col ogic aldose
. Th e E xp o sur e A n al ys is M o d el in gSy st em ( EXAMS ), de vel oped at the U.S. E nvironm ent alProt ection Age ncy ’s re search la borat ory in At

hen s, Georgi a, is an int era ct ive com pute r program int ended to give de ci si on-m aker s in industry and governm ent

ac ce sst o a

r e sp on sive , ge ne ral , and cont roll abl e t ool fo r read ily deriv ing andevalu ating the beh avio r of synth etic chemic al s in theenvironm ent . Theres ear ch anddeve lopm ent effort has focus ed on the cre at ion of theint eractive c omm and lang uage and user ai ds t

hat arethecoreof EXAMS , and onthe genes is of re li abl e EXAMS m at hem at ic almodels
. EXAMS was desi gned prim ari ly

for the ra pid s cre eni ng and ide nti fic at ion of synth etic org anic ch emical s likely to adver sely impact aqu atic systems. Th is re po rt is inten dedto acqu aint po tential us ers w ith th e un d er ly in g th eo ry, cap ab il it ie s, an dus e o f th e s ys te m. 

### 1. 2 E xp os ur e A na lys is i n A qu ati c S ys tem s EXAMS was conce ivedas an aid to those wh o mus t ex ecute hazard eva luati ons sol ely from l aboratory des cripti ons of the chemis try of a newl y s ynt hesi zed toxi c c om

pound. EXAMS estim at es exposure , fate , and pers is te nce foll owing r el eas e of an o r g an ic ch emi ca l into anaqu at ic ec o sy st em. Ea chof th es e te rms was give n a

f orm a lop e rat i on a lde fini t i onduringthe i ni t i al d es ig nof th e s ys te m. 

### 1. 2. 1 E xp os ure W hena pollu tant is relea sedinto ana quatic eco system, it is ent rai ned in the t

ranspor t fie ld of the s yst em

and beg ins to sprea d to l ocations beyond t he originalpoint

of rele ase . During the cours e of the se m ovem ent s, c hemic aland biol ogical proce sse s t

ransf orm thepare nt c om

poun d into da

ughte r product s. In the f

aceof c ontinuing emis si ons, the rece iving sys te m evolves toward a “st eady -state” condi ti on. At st eady st at e, the pol lut ant

c oncent rations are in a dynam ic equi librium in whi ch t

he l oadi ngs are ba lanced by t he trans port and transform at ion proces ses . R esi dualconc ent rations can be co m pare d t o tho sep os i nga

d ang e r t o l i vi ngo rg ani sm s. T he com pari son is oneindic at ion of the ris k e nta il ed by the pres ence of a chemic alin nat

uralsy stems or in drinking-wat er s uppli es. Thes e “expect ed e nvironm ent alconc ent rations ” ( EEC s), or exposurele vel s, in rec ei ving wate r bodie s are onecom ponent of a hazar d eva luati on. 

### 1. 2. 2 P ers ist en ce Toxic ologi caland ecol ogic al“ effe ct s” st udie s are of

t wo kinds : inv estigation s of sh ort-term “acute” exp os ur es , as op po sedto longe r-t erm

“c hronic ” experim ent s. Acut e s tudi es are oft en us ed to determ ine theconc ent ration of a chemic alres ulting in 50% mortality of a test p op ulatio n ov er ap er io d of hours. Ch ro nic stud ies examine sub

- le th al effe cts onpop ulatio ns expo sedto lowe r conce ntrati ons over ext ended periods . Thus , for exam ple , an EEC that i s 10 tim es le ss t han t he a cut e l eveldoes not affirm that a quat ic ec osys te m s wi llnot be affe cted, bec ausethe probabi li ty

of a “c hronic ” i m

pact inc rea ses wit

h expos ure duration. A c om

pute d EEC thus m

ust be suppl em ent ed wi th a

n estim at e of “per si st ence ” in theenvironm ent . (A c ompound im m une to al l transform at ion proce sse s is by de fini ti on “per si st ent ” in a globa l sens e, but even in thi s cas e trans port pr oces ses w ill eventu ally redu ce thepolluta nt to negl igiblelevels shoul d theinput

l oadi ngs cea se. ) The noti on of “pe rsi st ence ” c an be gi ven an expl ic it

defini ti on in the cont ext of a partic ular cont aminate d ec osys te m : s hould t he pol lut ant

loa dings ce ase , what tim e s pan would be requi red for dis sipat ion of m ost of t he resi dualcont aminati on? (For exam ple , gi ven t

he hal f-l ifeof a chemic alin a “ fir st -order”sy st em, the tim e re quire d to reduc e the che m ic alconcent

ration to any

spe ci fie d fra ct ion of

it s initia l value c an beea si ly

com pute d.) Wit

h thi s inform at ion i n hand, the appropriate duration a nd pollutant l evel s for c hronic st udie s can be m ore rea dily deci ded. More det ai le d dynam ic si m ulati on stud ies can elicit the pro bab le magnitud e anddur ationof acute even ts as well. 

### 1. 2. 3 F ate Thet ox i c ol og i st

a l so n e e ds t o kn owwhi c h po pu l at i on s in the sy st em ar e “ atri sk .” Po p u lati o n s at r is kcanbe de du ce dto so me ext ent from thedis tributi on or “ fat e” of t he c om pound, t hat is , by an es ti m at e of EEC s in dif fere nt ha bit at s of si ngle ec osys te m s. EXAMS r e po rt s as e parate EEC for ea ch c om partm ent , and thus ea chlo ca l p o p u lati o n , u se dto de f in e th e s ys te m. The c oncept

of the “ fat e” of a chemic alin an a quat ic sy st em has an a dditiona l, equal ly

signifi cant

m eaning. Ea ch t

ranspor t or transform at ion proces s a ccount s for only part of thetot al behavi or of the pollutant. The r el at ive im portance of ea ch proce ss c an bedet ermine d from theperc ent age of t

he t ota l sys te m loa dings c onsum ed by theproce ss. The r el at ive importan ce of

the tran sfo rmations indica te wh ich pr oces s is2 dom inant in thesy st em , and thus in g reate st nee d of a ccur acy and pre ci si on in it s kinet ic param et ers. Overall dominance by transport proce sse s m ayim

ply a cont aminati on of downs tre am sys te m s, los s of si gnifi cant am ounts of

t he pollutant to the atm osphere , or polluti on of ground- wat er a quife rs. 

### 1. 3 T he E XA MS 

### program The ne ed t o predi ct

che m ic alexpos ures from limited data

has st im ulate d a vari et

y of rec ent advances in environm ent al m odel ing. Thes e a dvance s fa llinto thr ee gener alcate gorie s:
! Pro cess mod els giv ing a quantitative , often t heoretical, ba sis for pre dic ting therat e of transpo rt and t ransf orm at ion proce sse s a s a

function of

environm ent alvari abl es.
! Proce dures for e st im at ing t he c hemic alparam et ers requi red by pr oces s m odel s. E xam ple s include l inear fr ee energy rel at ions hips , and corr el at ions sum m ari zi ng largebodie s of experim ent alche m ic aldat a.
! Sy st ems models th at combine unit p ro cess mod els with desc riptions of the environm ent alforc es det ermining the strengt h and spee d of t

heseproce sse s in rea l e cosy st em s. The vocabul aryus ed t o des cribe e nvironm ent alm odel s includes m anyte rm s, most

of whi ch re flect t

he unde rly ing inte nti ons of the mode lers. Mod els may be pred ict iv e, stoc has tic, empirical, mechan istic, theo retical, deterministic, exp lanato ry, co ncep tual, caus al , desc riptive , e tc . The EXAMS program is a det ermini st ic , pr edictiv e systems model, bas ed ona cor e of mec h an istic proce ss e quat ions derived fr om fundam ental t

heore ti cal concepts . The EXAMS com pute r codeal so includes desc riptive em piri calcorrelati ons t

hat ea se the use r’s burden of param et er cal cul at ions , and an int era ctive c omm and l anguagethat fac il it at es the appl ic at ion of thesy st em

to spec ifi c probl em s. EXAMS “pre dic ts ” in a som ewhat l imit ed sens e of the t erm . Many of t he pre dic ti ve wate r-qual it y model s c urrently in use inc lude site-sp ecific p arameters that can o nly be f oundvia field cal ibrati ons. Af

te r “va li dation” of t

he m odelby com

pari son of it s c al ibrate d output s wit

h additiona l fi el d m eas urem ent s, t hese m odel s are often used to e xplorethem eri ts of a lt ernati ve m anagement pl ans. EXAMS , ho wev er, d eals withan entir ely diff eren t class of probl em . B eca use newly synth esizedchemicals m ust be evaluat ed, li ttle or

no fie ld dat a m aye xis t. Furtherm ore, EEC s at a ny parti cul ar s it e are of

l ittl e dire ct

inte rest . In thi s c ase , the g oal, at least inprin ciple, is to pred ict EEC s for a widerange of ec osys te m s unde r a vari et y of geogr aphi c, m orphom et ric , and ecol ogic alcondi ti ons. EXAMS inc lude s no direc t c al ibrati on paramet ers, and it s input e nvironm ent aldat a c an bedeve lope d from a var iet y of sourc es. For e xam

ple , i nput data

can be synth esizedfro m an analysis o f the o utp uts o f hydro dyn amic m odel s, f

rom pri or fi el d inve st igati ons c onduct ed wi thout ref eren ce t o tox ic chemicals, o r fro m t he ap pr op riate li mnologi calli terature. The EEC s gen eratedby EXAMS arethus “eva luati ve” (Las si te r et a l. 1979) predic ti ons desi gned t o ref le ct ty pic alor avera ge c onditions
. EXAMS ’ environm ent aldat abas e can be us ed t o des cribe s peci fic loc al es, or a s a gen eralized desc ription of

theproper

ti es of aquati c s yst em s in broad geogra phic regi ons. EXAMS relies onmechanistic , r atherthan empir ical, con stru cts fo r its cor e proc ess equ ation s wher everpossib le. Me chan istic (phys ic al ly

det erminate ) m odel s are m ore robust pr edi ct ors t

han are purely e m

piri calm odel s, whi ch c anno t s afe ly be ext ended bey ond therangeof pri or obse rvations
. EXAMS cont ai ns a few em piri calc orrel at ions am ong che m ic alparam et ers, but the se are not i nvoked unl ess theuse r appr oves. For e xam ple , t he parti ti on coef ficien t of t

he c om pound on t

he s edi m ent

phas es of t

he system, as a fun ctionof the or g an ic carbo n co nten t of its sedi m ent s, c an be es ti m at ed from thecom pound’s oc tanol-wate r partition c oeffi cient . A direc t l oad of the partition c oeffi ci ent ( KOC , se e t

he EXAMS Dat a Di ct ionary begi nning on page 180) overri des the em

piri caldefa

ult es ti m at e, however. (Because EXAMS is an intera ct ive program in whic h theuse r has dir ect acc ess to the input

dat abas e, m

uch of thi s doc um ent at ion ha s been writte n us ing the c om pute r vari ables (e.g., KOC above ) as ide nti fie rs and as quanti ti es i n the proce ss e quat ions . Al though this approa ch poses s om e diff ic ultie s for the c asua l rea der, it all ows t he pot ent ia l us er of

theprogram

to seetheconne ct ions betw een p ro gr am variab les andthe un de r lyin g pr oces s theo ry. The EXAMS dat a di ct ionary in thi s docum ent (begi nning on page 180) inc lude s an alphabetic all is ting and defi nitions of EXAMS ’ input vari abl es. )
EXAMS is a det ermini st ic , rathe r t han a st ochas ti c, m odelin the se n se th ata g iv ense t o f

inp uts w i l l a lw ay s p r o du ce th e s ame output . Uncont

roll ed variati on is pres ent both in ecos yst em s and in c hemic alla

borat ories, and e xperi m ent alres ult s from ei the r m il ie u are o ften r eport ed a s m ean values and t hei r as soci at ed var iance s. Pr ob abilistic modeling techn iqu es (e. g., Mon te Carlo si m ulati ons) c an a ccount , i n pri nciple , for thi s var iation a nd atta c h an e rr or

bo un d o r c on fi de nc e i nt e rv a lt o e a c h im po rtant output vari abl e, al though the s tati st ic aldi stributions of che m ic al and e nvironm ent alparameters are not ofte n known i n the requi si te det ai l. Input tim e s eri es that include e cophy si ologi cal andhydr olo gic var iatio n dir ectly trans ferthese v ariab ilities to the outc om es of

sim ulati ons. S tandard EXAMS tim e-se rie s and summary outp uts re flect variationin resp on se to meteor o log y, and find use in s tati st ic alanalyse s of the e xpect ed freque ncyand m agni tude of t oxicologi cal ly si gnifi cant

eve nt dur at ions . One object ive of

thi s ki nd

of m od e l i ng , i n t

he c a seof

haz ard evaluat ions , i s t o es ti m at e t he e ffec t of

param et er e rrors on the overa llc onclusi ons to be drawn from t he m odel
. This goal can ofte n be effi ci ent ly

m et by som e for

m of s ensi ti vit

y analysi s. 

### 1.4 Sensitivit y Analysis and Error Evaluation EXAMS doe s no t pro vid e a f ormal sensitiv ity ana lysis among its3 opti ons: thenum

ber of s ub-si m ulati ons ne eded to f

ully a ccount fo r in teractio ns among ch emical anden viro nmental v ariab les is prohibi ti vely l arge (Be hrens 1979) . W hen , for exam ple , t he sec ond -o rd e r rat e c on stant f or al kal ine hydr oly si s of a c om pound is des cribed t o EXAMS via an A rrh eniu s f un ctio n, th e rate constant com

pute d for e ach com

partm ent in the ec osys te m depends on at

l eas t si x param et ers. T heseinclude the fre quency fac tor and a ct ivati on ene rgy of t he re action, the parti ti on coef fic ient of t he c om pound ( KOC ), t

he organic carbon cont ent of t he sedi m ent

pha se, t he t em perature , and theconc ent

ration of hydroxi de i on. Theovera llrat e estimate is thus as depe ndent up onthe accuracy o f the system defin ition as it is uponthe skill of the labo rato ry ch emist; in this example, the rate co uldvary six order s of m a gn i t ud e a s af

un c t i onof

di ff e re nc e s am ong ecos yst em s. I n order

to fully m ap t

he par amet er inte rac ti ons affe ct ing a

proce ss, al l c om

binati ons of param eter c hanges wo uldhav e to be simulated . Eve n this ( simplified ) example would r equi re 63 si m

ulati ons (2 -1, whe re n i s thenumbe r (6) of

n par ameters) merely to d etermine sen sitivities o f a sing le compo nen t pro cess ina single ecosys tem compartment. Sensi ti vit y analysi s re m ai ns an attra ct ive tec hnique for answe ring a c ruci alques ti on that a ris es during hazard evaluat ion. This ques ti on can be si m ply st at ed: “Arethe chemic aldat a a ccurateenough, and prec is e e nough, t o support an an alysis of

the riskenta il edb y r eleases of the chemical into the environm ent ? ” Like m anysi m ple questi ons, t

his ques ti on does not have a

si m ple , de fini ti ve answer. It can be broken down, howeve r, into a

se rie s of expl ic it , m or e tr act abl e que st ions whose a nswers sum

to a re asona

bly com ple te eva luati on of t

he si gnifi canc e t

hat shoul d be at

ta ched t o a report ed e rror bound or confi denceint erva l on anyinput dat um . Using theoutput

ta ble s andcommand lang uag e utilities pr ov idedby EXAMS , t hese questions can be posed, and answe red, in t he fol lowi ng order
. ! Which ge ographi c area s, and which ecos yst em s, de vel op th e l ar g e s t

c h e m i c a lr e s i du a l s ? EXAMS a ll ows a user to l oad the dat a for

any environm ent

cont ai ned in his fi le s, s peci fy a l oadi ng, and run a

si mulation , t

hrough a si m

ple se rie s of one-l ine Engl is h com

m ands.
! Whi c h p ro c e ss i s do m i nant in t he m os t s e ns i t ive ecos yst em (s)? The dominant proces s, i .e. , the proces s m ost respons ibl e for

thedec om

posi ti on of t

he compound in the sys te m , i s t

he proc ess requiring the greate st ac cura cyand prec is ion in it s c hemic alparam et ers. EXAMS pr od uc e s two output ta ble s t hat indi cat e t

he re lati ve i m

portance o f eac h proce ss. The f

irs t i s a “ kine ti c prof

il e” (or fre quency sca ling), whi ch gives a c om partm ent -by-c om

partm ent li st ing wi th a llproce sse s re duced to e quiva le nt (hour ) -1 terms. Th e seco ndis a tabulatio n of the o ver all steady- state fat e of the com

pound, giving a li st ing of theperc ent age of the loa d cons um ed by ea ch of the tr ans po rt and transform at ion proces ses at st eady st at e. Give n thedom inant proces s, t he input data aff ecting t his proce ss can be varie d over the repor te d err or bounds, and a s im ulati on can be e xecut ed for ea ch va lue of t he param et ers. The effe ct of param et er e rrors on the EEC s and pers is te nce of t he compound can the n be document ed by com pil ing t he re sul ts of t

hese si m ulati ons. This se quenceof ope rations is, in e ffec t, a s ensi ti vit y analysi s, but t he e xte nt of

the analysi s i s c ontrol le d and dire ct ed by the use r. In som e c ase s, f

or exam ple , one proce ss wi llalways acc ount f or m ost of t he de com posi ti on of t

he c om pound. When the dat abas e for thi s dom inant proce ss i s ina dequat e, the obvious answe r t o theori gina l que st ion i s that the data do not ye t s upport a riskanalysis. Conver sely, if the dominan t pro cess is w ell def ined, and t

he e rror l imit s do not

subst ant ia lly a ffec t t

he estimates of expo sur e and pe rsisten ce, the data may be ju dg ed to be a de qu at e f

or the e xp os ur e ana l y si s po rti onof ahazar d evaluat ion. 

### 1.5 E XA MS 

### Pr oc ess Mo de ls In EXAMS , t

he l oadi ngs, t

ranspor t, and t ransf orm ations of a com pound arec om

bine d into dif

fere nti alequati ons by

using the m ass cons ervati on la

w as an a ccounting principle. This l aw acc ounts for al l the c om

pound ent eri ng and le avi ng a sys te m as the a l gebr a i c s um

of ( 1) e xt e rn a ll oa di ng s, ( 2) trans po rt proce sse s e xporting the com pound out of t

he s yst em , and (3) transform at ion proces ses wit hin t he s yst em t

hat degra de t

he com pound to it s daught er pr oduct s. T he fundam ent alequati ons of t he m odeldes cribe t

he rate of

change in che m ic al conce ntrati ons a s a

bal ancebet

ween inc rea ses due to l oadi ngs, and de cre ase s due to t

he t ranspor t a nd tr ansfor

m at ion proces ses r emo v in g th e c h emi ca l f

r o m th e s ys te m. The s et of uni t proces s m odel s use d to com pute thekinetic s of a com pound is the ce ntra l c ore of EXAMS . Thes e unit m odel s are al l “ sec on d- order”or

“ sy st em -independent”model s: ea ch proc ess equation includes a direc t s tate m ent of t he inte rac ti ons be twe en the che m is try

of a com pound and the environm ent alforc es that shapeit s be havi or i n aquati c s yst em s. T hus, e ach rea li zation of the pr oces s equ ation s implemented by th e userin a specif ic EXAMS si m

ulati on is tai lore d to t

he uni que c hara ct eri st ic s of that ecos yst em . Mos t of

theproce ss e quat ions arebas ed on st andar d the oretic alcons truct s or acc ept ed e m piri calrel at ions hips . For example, light inten si ty in the watercolumn o f the sys tem is com pute d using theBe er-L am bert law, and t em

perature corre ct ions for r at e c onst ants are c om pute d using Arrhenius functio ns. Detailedexp lanatio ns o f the p ro cess mod els i nc or po rat e d in EX AMS , and of t he m echanic s of the com putati ons, are pr ese nte d in Chapt er 2. 

### 1.5.1 Ionization and Sorption Io nizatio n of

org anic acid s andbases , complex ationwith dis sol ved organic carbon ( DOC ), and sorption of the com pound withsediments an d bio ta, are tre ated as th ermodynamic pr op erties o r (lo cal) e qu ilibria that a lter th e o per ationof kinetic4 p r o ce ss es . F o r

ex amp le , anor g an ic ba se inth e w at erco lumn m ayocc ur i n a

num ber of m ole cul ar spec ie s (as dis sol ved i ons, sorbed wit

h s edi m ent s, e tc .), but only t he unc harge d, di ssolved spec ie s c an bevolati li zed acr oss the air-wat er inte rfac e. EXAMS al lows f or the s i m ul t ane ou s tre atm e nt

of up t o 2 8 mol e c ular spec ies of a chemic al . The se inc lude thepare nt unc harge d m ole cul e, and s ingly, doubly , or triply c harge d cati ons and ani ons, e ach of whi ch can oc cur in a dis sol ved, sedi m ent -sorbe d, DOC -com ple xed, or bios orbed form . The program com pute s t he fra ctionof the total con centr ationof co mpoundthat is pre sen t in eac h of the 28 m ole cul ar s truc ture s (t he “ dis tributi on coef fic ie nts ,” á ). Thes e ( á ) values ent er t

he kinet ic equati ons a s m

ultipl ie rs on the rat e c onst ant s. In thi s way, theprogram ac count s for diff

ere nces in reac tivity that dep endon th e molecularform of the che mical, as a function of t

he s pat ia l di stribution of environm ent al param et ers cont

roll ing mole cul ar s peci at ion. For e xam ple, the la bil it y of a partic ular m ol e c ul e t o hy drolyti c de com posi ti on m ay depend on whet

her i t i s di ssolved or is sorbe d wit h these dim ent phaseof t

he s yst em . EXAMS m akes no i ntrinsi c a ssum pti ons about therel at ive tr ansfor

m at ion r eac ti vitie s of the 28 m ole cul ar spec ie s, wi th t

he s ingl e e xception t

hat bios orbed s pecie s are unavai la ble to inorganic rea ct ions . Thes e a ssum pti ons are cont roll ed t hrough the s truc tureof

t he input data de scribing t

he spec ie s-spe ci fic che m is try of t he c om pound. 

### 1. 5. 2 T ra ns for mat ion Proc ess es EXAMS compute s the kine tics of transf ormations attribu table to direct photolysi s, hy droly si s, bi oly si s, and oxidati on rea ct ions
. The input c hemic aldat a for hydr olyti c, biolytic , and oxidative rea ct ions can be ent ere d ei the r as single -valued s econd- order rat e c onst ant s, or

as a pai r of values def

ining therat e c onst ant

as a fu nc ti on of e nv i ro nme nta lt e m

pe rat ures. For e xam

ple , t he input dat af or a l ka l in e hy dr oly si s of

thec om po un d c on si st s of

two compu ter var iables : KBH , and EBH . When EBHis ze ro, t he program int erpre ts KBHas these cond-orde r rate cons tant. When EBHis non-ze ro, EBHis int erpre te d as the ac ti vat ion e nergyof the reaction, and KBHis re- int erpre te d as thepre- exponentia l (freque ncy ) fa ct or i n an Arrhenius e quat ion giving t he secon d- order rate cons tant a s a function of

theenvironm ent al te m perature( TCEL ) in ea ch s yst em com partm ent . ( KBHand EBH are both act

ual ly m at ric es wit h 21 e le m ent s; ea ch e le m ent of t he m at rix corre sponds t o one of the 21 possible mol ecul ar s peci es of t he c om pound, i.e ., the7 i onic spe ci es occur ring in di ssolved, DOC -com ple xed, or se dim ent -sorbedform --as note d above , bios orbed f

orm s do not

partic ipate in ext

ra-c el lul ar r eac ti ons.)
EXAMS inc ludes two a lgori thm s for com puting therat e of photolytic tr ansfor

m at ion of a synthe ti c organic che m ic al . The se al gorit hm s accom

m odat e t he t wo m ore c omm on kinds of la borat ory dat a and che m ic alparam et ers used to describe photolysi s re actions . Thesi m ple r al gorit

hm requ ires only

an av er age p seu do -fir st-o rd er rate con stant ( KDP ) app licable to near -surfa ce wat ers under cl oudle ss condi ti ons at a spe ci fie d refe renc e l at it ude ( RFLAT ). To c ontrolrea ct ivi ty as sum pti ons, KDP is coupl ed t o nom ina l (norm al ly unit-value d) re action quantum y i e l ds ( QY IELD ) for eac h m ole cul ar s peci es of t he com pound. Thi s a

pproac h m akes possible a fir st approxim at ion of phot ochemic alrea ct ivi ty , but negl ect s t

he ve ry im

portant eff ects of chan ges in the sp ectral quality of sun ligh t with inc rea si ng dept

h in a body

of wate r. T he m ore c om ple x photoc hemic alal gor it

hm com pute s photoly si s ra

te s direc tly f

rom the abs orpti on spe ct

ra ( m olar extinc ti on coe ffi ci ent s) of the com pound and it s i ons, m eas ured values of t he re action qua

ntum yi el ds, and the envi ronm ent alconc ent rations of c om

pet ing l ight absorbe rs (c hlorophy ll s, s uspende d se dim ent s, DOC , and w at er it sel f). When using a KDP , pl eas e beaware t hat dat a fr om la borat ory photore act ors usual ly are obta ine d at int ensiti es as much as o ne tho usandtimes larg er th an that of normal sunligh t. The total rate o f hydro lytic transf ormation of

a chemical is compu ted by EXAMS as the sum of threecont

ributing proces ses . Eac h of t heseproce sse s c an beent ere d via s im ple rat e c onst ant s, or as Arrhenius func ti ons of te m perature . Therat e of spec ifi c-acid-cat alyz ed re actions is com pute d from

thepH of eachsectorof the ecos ystem, an d sp ecific- bas e catalysis is com pute d from

theenvironm ent alpOH dat a. The rate data for neut ralhydr oly si s of the compound are ent ere d as a set of pseudo-f irs t-or der r at e coef

fic ie nts ( or Arrhe nius functions ) for reacti on of t

he 28 (pote nti al ) m ole cul ar s peci es wit h thewat er m ole cul e. EXAMS com

pute s bi otransform at ion of thechemic alin thewat er column and inthe bo tto m sed iments of th e system as entirely separat e functi ons. B oth f unct ions arese cond-orde r equati ons that r el at e t

he rate of bi otransform at ion to thesi ze of t he bact eri alpopulati on a ct ive ly degra ding t

he c om pound (Paris et al . 1982) . Thi s approa ch is of de m onstrat ed val idi ty

f or at le ast som e b i oly si s pr oc e ss e s, and pr ov i de s the us e r wi th a m i nim al semi-e m piri calm eans of di st ingui shi ng bet ween eut rophic a nd olig otro ph ic ecosys tems. The sec on d- or derrate con stants ( KBACWfor the wate r column, KBACS for be nthi c s edi m ent s) c an be e nte red e it

her as single- valued c onst ant s or as functions of 10 te m peratu re. When a non-z ero va lue is ent ere d for t he Q of a bio transform ation (para

m et ers QTBAW

and QTBAS , re spec ti vely), KBAC is int erpre te d as therat e c onstant at 25 de gree s C el sius, and t he biolysi s rat e in ea ch s ector of t he e cosy st em

is adjus te d for t he l ocalte m

perature( TCEL ). Ox idatio n rea ction s are computed fro m the chemical inp ut data and t he tot ale nvironment alc oncent rations of r eac ti ve oxi diz ing spec ie s (alky lpe roxy and a lkoxy l r adi cal s, e tc .), corre ct ed for ult ra-vi ole t l ight

extinc ti on in thewat er c olum n. Theche m ic al data canagainbe ente r ede ith er as simple seco nd -o rd er rate const ant s or as Arrhenius func ti ons. Oxi dation s due to si ngle t oxyge n arecom

pute d from

che m ic alr eac ti vit

y data and si ngle t oxyge n conc ent

rations ; s ingl et

oxygen i s estim at ed as a

function of t he c oncent

ration of DOC , ox ygentens ion , an d ligh t intens ity. R e du c t i oni s i nc lud e d in t he pr og ram

a s as i m pl e s e c ond-order5 rea ct ion proces s drive n by t he user ent

rie s for conce ntrati ons of reduc tants in t

he s yst em . As wit

h biolysi s, t

his provi des the use r wit h a mini m ale m

piri calm eans of

a sse m bling a simulati on model th atinclud es spe cific kn ow ledg e of th e reductan ts im portant to a partic ular che m ic alsa fet y e valuat ion. 

### 1. 5. 3 T ra ns po rt P ro cesses Inte rnaltrans port and e xport of a c hemic aloccur i n EXAMS via a dv e c t i ve a nd di sp e rs i ve m ov e m e nt of di ssol ved, sedi m ent -sorbe d, and bios orbed m at eri al s and by vol at il iz at ion los ses at theair-wat er inte rfac e. EXAMS provi des a s et of ve ct ors ( JFRAD , etc.) th at specif y the lo catio n an d stre ng th of both advec ti ve and

di sp e rs i ve tr ansport

pat hways . Advec ti on of wate r through the sy st em

is the n com

pute d from

thewat er ba lance, usi ng hydr ologi c data

( rai nfal l, evapor at ion r at es, st ream fl ows, groundwat er s eepa ges, et c.) supplied to EXAMS as part of t he def initionof eachenv iron ment. Dispe rsi ve inte rchanges wit hin t he s yst em , and ac ross sys te m boundari es, arecom

pute d from

theusual geochemic al spec ifi cation of thecha

rac te ris ti c l engt

h ( CHARL ), c ross- sec ti onal are a ( XSTUR), and dis persi on coe ffi ci ent ( DS P ) for eac h ac ti ve exchange pat

hway. EXAMS can com

pute tr ansport

of s ynt hetic chemic al s vi a whole-sedim ent bed loa ds, s uspende d se dim ent wash-l oads, exc hanges wi th f ixe d-volum e s edi m ent

beds , ground-wat er infiltrati on, trans port through the the rm ocl ine of a l ake, los ses in efflue nt s tre am s, e tc . Vol at il iz at ion l osse s are compu ted us ing a two -re sistan ce model. Th is computationtreats the tot alres is tance to t

ranspor t a cross theair-wat er inte rfac e a s the sum of re si st ance s in theli quid a nd vapor phase s im m edi at ely a djace nt to theint erfa ce. 

### 1.5.4 Chemical Loadings Exte rnalloa dings of a toxi cant can ent er t

he e cosy st em

via point source s ( STRLD ), non-point s ource s (NPSLD ), dry fal lout or a eri al dr ift ( DRFLD ), atmosph eric w ash -o ut ( PCPLD ), and ground-wat er seepage ( SEELD ) ent ering the sys te m . Anyty pe of loa d can be ent ere d for any s yst em

com partm ent , but t

he progr am

wil l not im ple m ent a loa ding that

is inc onsi st ent

wit h thesy st em defi nition. For e xam

ple , t he progr am

wil l a utom at ic ally c ance l a ra infa llloa ding ( PCPLD ) entere d forthe hyp olimnionor ben thic sedi m ent s of a l ake ecos yst em . W hen t his ty pe of corre ct ive action i s e xecuted, t

he c hange is repor

te d to the use r vi a an err or m ess age. 

### 1.6 Ecosystems Analysis and Mathemat ical Sy ste ms M od els The EXAMS pro gr am was con structedfro m a systems analysis per sp e c t i ve . Sy st e m s ana l y si s be gi ns by de fini ngas y st em ’s goal s, inputs , e nvironm ent , re source s, and thenat ure of the sys tem’s com

ponent s and the ir int erc onnections . Thesy st em goal s de scribe t

he out puts produce d by the s yst em a s a result of operating on its input stream. The system env iron ment com pris es thos e fa ct ors a ffec ting sy st em out puts ove r whic h thesy st em has li ttle or no cont

rol. Thes e fa ct ors are often c al le d “for ci ng functions” or “e xte rnaldri ving va ria ble s.” Exam

ple s for an aqu atic ecos ystem includ e run of f andsediment ero sionfro m i ts wat ershe d, i nsol at ion, and ra infa ll
. Sys te m r esourc es are defined as thos e fac tors a ffec ting pe rform anceove r whic h t he syst em exer ci ses som e c ontrol . R esourc es of an aquatic ecosy st em inc lude , for exam

ple, the pH t

hroughout the sy st em , l ight int ensi ty in the wat er column, and di ssolved oxy gen c oncentrati ons. The leve ls of t

heseint erna l driving vari abl es are det ermine d, at l eas t in part, by the st at e of the sy st em it sel f. In othe r words, the se fac tors arenot nece ssarily s ingl e-va lue d functions of t

he s yst em environm ent . Ea ch of the com ponent s or “s ta te variables” of a system can b e desc ribe d in terms of its local inp ut/ ou tput behavio rs an d its cau sal con nectio ns w ith oth er elements of th e system. The sys tems appr oachlends itself to t he for m ulati on of m at

hem at ic alsy stems m odel s, whi ch are si m ply tools for encoding knowle dge of transport and tran sfo rmation p ro cesse s andderiv ing the implic atio ns o f this kn ow ledg e in a log ical andrepe atable w ay. A sy st em s m odel , when buil t a round re le vant

st at e varia

ble s (m eas urabl e prope rti es of system com ponent s) and ca

usal proce ss model s, prov i de s a m e t ho d f or e xt ra po lating fut

ure s tate s of sy st em s from

knowle dge ga ine d in the pas t. In order for s uch a m odelto be ge nera lly us eful , howeve r, m ost of i ts param et ers m ust posse ss a n int rins ic int ere st

tr ansc endi ng the ir rolein any partic ular comput er pr ogram . For thi s re ason, EXAMS was desi gned to use chemic alde scriptors (Arrhe nius functions , pKa, va po r pr e ss ur e , e t c .) and wat e r qu a l i tyvari abl e s (p H, chl orophyl l, bi om ass , et c.) t hat are i ndepende ntly m eas ured f or m anyche m ic al s and ec osys te m s. 

### 1.6.1 E X A MS

### Design Strategy The conceptua l vie w a dopted for EXAMS begins by defining aquatic e cosy st em s as a seri es of dis tinct subsys te m s, int erc onnect ed by

phys icaltr ansport

proce sse s t

hat m ove synt het ic che m ic al s into, through, and out of thesyst em . The se subsy st em s include t

he epil im nion a nd hypolimnion of

lakes, li tt oralzone s, be nthi c s edi m ent s, e tc . Thebas ic arc hitecture of a c om pute r m odelal so depends, howeve r, on it s int ended uses . EXAMS was d esign ed fo r use bytox icolo gists an d de cisi on-m aker s who m

ust eva luate theri sk pose d by use of a new chemic al , ba sed on a forec ast from the mode l. The EXAMS program is it self p art of a

“hazar d eva luati on sy st em ,” and t he struct ure of t he program

wa s nece ssarily strongly

inf lue nced by the nic he pe rce ive d for i t in thi s “ sys te m .” Many int erm edi at e t echni calis sues ari sedu ringt hedeve l opm ent of as ystems m od el. Us ually thes e issue s can b e reso lvedin sev eral w ays; the mo d elin g “style” o r des ignstrateg y usedto b u ildthe model gu ides th e cho ices take n among the ava ilable al te rnative s. The s trate gy us ed t o form ulate EXAMS begins from a prim aryfocus on t

he ne eds of

the int ended user and, othe r things be ing e qual , re sol ves m ost t echni cali ssue s in favor of t he m ore effi ci ent

c om putati on. For exam

ple , al l transport and transform at ion proces ses aredri ven by int erna l r esourc e fa ct ors6 (pH, t em perature , water m ovem ent s, s edi m ent depos ition a

nd scour, etc .) in t

he sy st em , and eac h deser ves separat e t

reatm ent in the modela s an indi vidua l st at e vari abl e or function of se vera l st at e varia

ble s. T he s trate gy of

m odel dev el opm ent

use d for EXAMS sugg ests, however, that t he only s tate vari abl e of any transce ndent

int ere st to the use r is the conc ent ration of the chemic alit sel f i n thesy st em com partm ent s. EXAMS thus treats al l e nvironm ent alst at e varia ble s a s c oeffi ci ent s de scribing t he st at e of the e cosy st em , and only com pute s t he i m pli cations of th atst at e, as re si du al co n ce ntr at io n s o f ch emi ca ls in th e s ys te m. Alt hough thi s a

pproac h vas tly s im

plifi es the m at

hem at ic al m odel , with corr esponding gains in eff ic ie ncyand spee d, t

he sys te m definition i s now s om ewhat im proper. Sy st em

res ource s (fac tors aff

ecting pe rform ancethat a re s ubject

to fee dback con trol) have b een r edef

inedas part of the system envir on ment. In fa ct , t he “ sys te m” repres ent ed by them odelis no l onger an aqu atic ecos ystem, but merely a che mical pollutan t. Pos sible fai lurem odes of the modelareim m edi at ely a

ppare nt. For exam ple , i ntroduc ti on of a

che m ic alsubj ect to a lka line hydro lysis andtoxic to p lant life into a pro du ctive lak e wo uld ret ard prim aryproducti vit y. The de cre asein prim ary productivi ty

woul d l ead to a decr eas e in thepH of the s yst em and, conse quent ly , a

de cre asein the rat e of hydrolysi s and an incr ease inthe residual co ncen trationof the toxicant. Th is seque nce of eve nts would repe at it sel f indefi nit ely, and con stitute s a po sitive fe edb ack lo op that cou ld in re ality badly dam age an ecos yst em . Gi ven t he c hemic albuffe ring and functio nal redun d an cy pre sen t in most real ecos ystems, this exam ple is inhe rently

im probabl e, or at

le ast se lf- li m iting. More importan tly, give n the in itial EEC , t heenv i ro nment altoxi col ogis t coul d antic ipate thepote nti alhaz ard. Thereis a m ore telli ng advant age, m oreove r, t o theuse of env iron mental de scri ptors i n pr efe rence to dyna mic envi ronm ent alst at e varia

ble s. P redi ct iveec osys te m model s t hat inc lude al l the fac tors of potentia l i m portance t o thekine ti cs of toxi c pollutants are only now bei ng devel oped, and wil l r equi re val idati on befor e any e xte nsi ve us e. Furtherm ore, al though ext remely fine- reso lution(tem poraland spatial) m odel s a re of te n con sider ed anultimate ideal, th eir u tility as co mpon ents o f a fate m odelfor synt

het ic c hemic al s rem ai ns sus pect . Ec osys te m s are dr iven by meteor olo gical ev ents, andare themselv es sub ject to inte rnalst ochas ti c proc ess es. Det ai le d weathe r fore cas ts are limit ed to ab ou t nine d ays, b ec au se at the en d of this per iodall possible st at es of t

he system

areequa lly pr obabl e. Det ai le d ecos yst em

fore cas ts aresubje ct

to si m il ar c onstrai nts (Pl att e t a l. 1977 ) . For the se rea sons, EXAMS was d esign ed p rimarily to fo recas t t he pre vai ling cl im at e of chemic alexpos ures, rat her than to givedet ai le d loc alfore cas ts of EEC s in spe ci fic loc at ions
. 

### 1.6.2 Temporal and Spatial Resolution W hena synthe tic org anic c h emical is releasedinto anaqu atic ecos yst em , t

he e ntire array

of transport and t

ransf orm at ion proce sse s be gins at

onc e to ac t on the che m ic al . Them ost effi ci ent way to accomm odat e t

his para ll elac ti on of t he proce sse s i s to com

bine t hem into a m at

hem at ic aldes cripti on of the ir tot aleff

ect on t he rate of change of che m ic alconc ent ration in the sys tem. Systems that includ e trans po rt pr oces ses leadto partial di ffere nti alequati ons, whi ch us ual ly m ust be sol ved by num eri calint egrati on. Thenume ric alte chni ques in oneway or ano therbreak up the syste m, w hichis continuo usly v aryin g in spa ce andtim e, in to as et of discr ete elements. Sp atial discr ete el em ent s are often re ferre d to as “grid poi nts ” or “ nodes” , or, as in EXAMS , a s “ com

partm ents.” Cont inuous tim e i s oft en repr e se nt e d by

f i xi ngt he s y st e m

d ri vi ngf un c t i on s fo r a short int erva l, int egrating over the int erva l, and t hen “ updat ing” the forcing functions befor e e valuat ing t he ne xt tim e-st ep. At any given mome nt, the behavior of t he c hemic alis a com

pli cat ed function of

both prese nt a

nd pas t inputs of

the com pound and st at es of th e s ys te m. EXAMS is ori ent ed t oward e ffi ci ent sc ree ning of

a m ultitude of newl y invent ed industria l c hemic al s and pes ti ci des. Idea lly, a fulleva luation o f t

he pos sible ri sks pos ed by m anufa ct

ure and use of a new chemica l woul d begin from a det ai le d tim e-se rie s des crib ing the exp ectedrelease s of th e compo un d into aqu atic sys te m s ove r t

he e ntire pr oject ed history of i ts m anufa ct ure. Give n an equi val ent ly

det ai le d tim e-se rie s for envi ronm ent al vari abl es, m achine inte gration woul d y ie ld a det ai le d pic tureof EEC s in therec ei ving wate r bodyover the entireperi od of conce rn. T he gre at

cos t of thi s a pproach, howeve r, mil it at es against it s usea s a

sc ree ning tool. Fineres olution e valuat ion of synt het ic che m ic al s c an proba bly be used only f

or com pounds that are s ingul arly de le te rious and of exc ept iona l e conomic si gnifi canc e. The simplest situatio n is that in w hichthe che mical loading s to sys te m s are known only as single es ti m at es pert ai ning ove r inde finit e p eriods. Thi s si tuati on is them ore l ike ly for t he va st m ajori ty of ne w che m ic al s, and was chose n for deve lopm ent of EXAMS . It has an additiona l a dvant age. The ultim at e fate and exposure of

chemicals often enc om

pass es m any

dec ades , making det ai le d tim e t

rac es of EEC s fe asible only for s hort- te rm evaluat ions . In EXAMS , the en viro nme nt is rep rese ntedvia lon g- term avera ge v alues of the for cing fun ction s that control t he behavi orof

chem ic al s. B y c om

bining theche m is try

of t he com pound wit

h ave rage proper

ti es of the ec osys te m , EXAMS reduc es the scree nin g pr ob lem to m anag eable proportions . The se simplified“first- or der ” equ ation s are so lvedalge b r ai cally in EXAMS ’s s te ady -st at e M ode 1 to give t he ul ti m at e (i .e. , st eady -st at e) EEC s t

hat wil l e vent

ual ly res ult from theinput loa dings . In addi ti on, EXAMS pr ovide s a ca pabi li ty to st udy ini ti alvalue probl em s (“pu ls e l oads”in Mode 2), and se asona l dynam ic s in whic h environm ent aldri ving f orce s are update d on a m onth ly

bas is (Mode3). Mode 3 is partic ularly valuabl e for coupl ing to the out

put of t he PRZMm odel , whi ch c an provi de a le ngthy tim e-se rie s of cont am ination event s due to runoff and erosi on of s edi m ent s from agri cul tura l l ands.7 D ai lype st ic id e e xp o rt v al u es fr o m PRZMare tran sferredto EXAMS as “pu lse load ing ” even ts at the beg inn ing of the day. The peakcon centr ationon th at day is th en re po rtedby EXAMS as the av erag e of th e start
- of -d ay andend -o f-d ay valu es. Th is approxi m ation of PRZMrunoff event s does not introduce a gross dis tortion of

thefac ts : F or a 1-ha 2-m deep pond wit

h an ini ti al conce ntrati on of 1 m g/L of a pestic ide wit h a 2-dayhalf-life, EXAMS rep o rts a f

ir st
- d aype akof

0. 8 5 4 mg/L . I f

the s ame am ount of

pe st ic ide is permitte d to ent er t he pond as a s te ady loa d over 24 hours, t

he pe ak va lue is 0.849 mg/L, occ urri ng at the end of t

he 24 hour period. If the load wereto ent er ove r a run-off dur at ion of

four hour s, t

he pond would achi eve a pe ak conce ntrati on of 0. 989 m g/L. Trans port of a c hemic alfrom a loa ding point into t

he bulk of t

he sy st e m t ake s pl a c e by

a dv e c t e d f

l ow s and

by t ur bu l ent disp ersio n. The simultaneo us transf ormations p rese ntly resu lt in a c ontinuously varying dis tributi on of t he c om pound over the physi calspa ce of t

he s yst em . Thi s c ontinuous di stribution of the com pound can be des cribed via partia l di ffere nti alequati ons. I n sol ving t he e quat ions , t

he phy si calspaceof the s yst em m ust be broken down int o dis cre te el em ent s. EXAMS is a com partm ent al or “box”m odel . The physi calspa ce of t he s yst em

is broken do wninto a ser ies of

p h ysica lly homog eneo us elements (com partm ent s) c onnect ed by

adve ct ive and dis persive fluxes. Ea chco mp artme nt is a p arti cu lar vo lume e le men t o f

th e s ys te m, cont ai ning wa te r, s edi m ent s, bi ota , di ssolved and sorbe d chemic al s, et c. Loadings and export s are r epre sent ed as m ass fluxes ac ross the boundari es of t he volum e e le m ent s; rea ct ive propertie s are t

reate d as point proces ses wit hin e ach compartment. In charac te riz ing a quat ic sy st em s for use wit h EXAMS , parti cul ar attentio n must be g iventhe gr id

- size of the spatial ne t usedto repre sent the sy st em . In effe ct , the com partm ent s m

ust not be s o large t hat int erna l gradi ent s have a m ajor effe ct on t he e st im at ed tran sformati on rat e of the com pound. In othe r words, the com partm ent s are a ssum ed t o be “we ll -m ixe d,” that i s, t he rea ction p roce sse s are not sl owed by

del ay s in tr ansporting t

he com pound from

le ss r eacti ve t o m ore r eac ti ve z ones in t he vo lume element. Ph ysical b ound aries that c an be use d to d elimit sys te m com partm ent s include the air-wat er inte rfac e, the the rm ocl ine , t

he be nthi c inte rfac e, and perha ps t he depth of biot urbation of

se dim ent s. Som e proce sse s, howeve r, aredri ven b y e nv ir o nmen ta l f

ac to r s th atoc cur

as gr a d i e n t s i nth e s ys te m, orare most active at in te rfa ces. F orexample, irr adian ce is dis tribute d expone nti al ly throughout t

he wate r column, and volati li zation occur s only at the air-wat er inte rfac e. The r at e of the se transform at ions may be overe st im at ed in, for exam ple , quie sce nt l akes in which the rate of supply of che m ic alto a rea ct ive zonevia

vertic altur

bule nce cont

rols t he ove ral l r at e of tran sfo rmation, unles s a r elativ ely fine- scale seg mentationis used to describe thesy st em . B eca use com partm ent m odel s of str o n g lyadv ec te dwa te rmas se s ( r iv er s) intr o du ce so me numerical dis per sioninto the calcu lation s, a relativ ely fine- scale segm ent at ion i s oft en a dvis abl e for highly r esolved e valuat ions of fluv ial systems. In manycases the erro r inducedby hig hly reactiv e compo un ds will b e o f little moment to the pr ob able fa te of t he c hemic alin t

hat sy st em , howeve r. For

exam ple , i t m akes little differ ence wheth er the pho tolytic half- life of a chemical is 4 or 40 m inut es; in ei the r cas e it willnot long survi ve e xposure to sunlig ht. 

### 1.6.3 Assumptions EXAMS has be en desi gned t o eva luate thecons equenc es of longe r-t erm , pri m ari ly

tim e-avera ged c hemic alloa dings that ultim at ely res ult

in tra ce- le velcont aminati on of a quat ic sy st em s. EXAMS gene rat es a s te ady -st at e, ave rage fl ow fi el d (l ong-te rm or month ly) fo r the e co sys tem. The pr og ram thus cann ot fu lly evaluat e thetrans ie nt, conce ntrate d EEC s t hat ari se, for e xam

ple , from che m ic alspi ll s, or

fr om runoff event s t

hat induc e sign ifican t hydr olo gi c tr an sients in the rec eivin g wa ter bo dy. This lim it at ion de rive s from two factors. Fir st , a

st eady fl ow fie ld i s not

always appropriat e for

eva luating thespre ad and decay of a m ajor pul se (spi ll ) i nput. Sec ond, an a ssu mption of trace- level EEC s, whi ch can be viol at ed by spi ll s, ha s be en us ed to desi gn theproce ss e quat ions use d in EXAMS . Thefol lowi ng as su mp ti o n s w er e u se dto bu il dth e p r o g r am.
! A usef

ul e valuat ion c an beexe cuted in dependently of t he chemic al ’s a ct

ualeff ect s on t he s yst em . In othe r words, the chemi cal i s a ssum ed not to it sel f ra dic al ly

change t

he envi ro nme nta lva

ri a bl e s t hat dri vei t s t ra ns form at ions . Thus , fo r example, ano r gan ic acid orbase is ass umed no t to changethepH of the sy st em ; the com pound is as sum ed not to i ts el f abs orb a si gnifi cant f rac ti on of t

he l ight ent eri ng the sys te m ; ba ct erial populations do not si gnifi cantly

inc rea se (o r dec line) in resp on se to the pres ence of the chemical.
! EXAMS use s l ine ar s orp tion i sotherm s, and se cond-orde r (rat her t han M ic hael is -Ment en-Monod) expre ssi ons for biot ransf orm at ion kinet ic s. T his approa ch is known to be val id for t he low conce ntrati ons of ty pic alof e nvironm ent al cont am inan ts; it s va li dit y at hi gh conc ent

rations is le ss cer ta in. EXAMS cont

rols it s c omputati onalrangeto ensure that t he a ssum pti on of t

rac e-l evelconcentrati ons i s not grossly violated. T his cont rol is key ed t o aque ous-phas e (dis sol ved) resi dualc oncent rations of

t he c om pound: EXAMS a borts any analysi s gen erat ing EEC s in whic h any dis sol ved spec ie s exce eds 50% of i ts aque ous solubil it y ( see Chapte r 2.2. 2 for a dditiona l de ta il ). T his res tra int inc ide nta lly a ll ows t

he progr am

to i gnore pr ecipit at ion of th e co mpoundfro m solutionandprec lud es inp uts o f solid partic le s of the che m ic al . A lthough sol id pr ecipit at es have occa si onal ly

bee n tr eat ed as a

separ at e, non-re active phas e in c ontinuous e qu i l ibrium wit h di ss olve d form s, t

he e ffi cac y of thi s fo rm

ul at i onha s ne ve r be e n a de qu at e l ye va luat ed, and t he e ffec t of

saturate d concent

rations on t

he l ine ari ty

of sorptio n iso therms wou ld intr o du ce sev eral pr ob lematic com ple xitie s t o thesi m

ulati ons.8 ! Sorpt ion i s t

reate d as a the rm odynam ic or c onst it uti ve propert y of ea ch s egm ent

of t he s yst em , t

hat is , sorptio n/d eso rp tionkinetics are assu med to be rapid comp aredto oth er pr oces ses. T he ad equ acy of this ass um pti on is partia lly c ontrol le d by propertie s of the chemic aland sys te m

being evaluate d. Ext ensi vely s orbed chemic al s t end t o be sorbed and de sorbed m ore s lowly t han weakly s orbed c om

pounds; de sorption ha lf- li ves m ay approa ch 40 day s for the most ext ensi vely bound com pounds. E xperi encewit

h the program

has indi cat ed, however, that s trongly sorbe d chemic al s te nd to be c apt ured by be nthi c s edi m ents, whe re t hei r re le aseto the wat er column is contr olledby theirav ai lability to be nth ic exchange proc ess es. Thi s phe nom enon ove rwhelm s any ac ce ntu at io nof

th e s p ee dof

p r o ce ss es inth e w at erco lumn th atmayb e cau se db y th e a ss ump ti o nof lo ca l equ il ib r ium. 

### 1.7 Further Reading Baughm an, G. L. , and L. A. Bur ns. 1980. Transport and trans fo rm at i onof

c he m i c a l s: ape rs pe c t i ve . pp . 1 -1 7 I n: O. Hutz i ng e r (E d. ). T he Hand bo ok of E nv i ro nm e nt al Chemis try , vol .2, part A. Springer-Ve rla g, B erl in, Fede ral Republic of

Germany. Burn s, L . A. 1989. Me thod 209- -ExposureAnalysi s Mode ling S ys te m ( EXAMS --V ersio n 2. 92 ) . pp . 10 8- 11 5 In : OECD Envir onm ent

Monographs No. 27: Com pendium of Envir on mental Ex po sur e A ssess ment Methods for Chemic al s. E nvironme nt Direc torate , Organiz at ion f or Economic Co-Ope ration a nd Deve lopm ent , Paris , France. Burn s, L. A. 198 5. Mod els for pr edictin g the fate of syn thetic chemicals in a qu atic systems. pp . 17 6- 19 0 In : T.P. Bo yle (Ed.) Val idati on and Predi ct abi li ty of L aboratory

Me thods fo r As sessin g the F ate andEffe cts of Con taminan ts in Aquat ic Ecos yst em s. A STM STP 865, Ame ric an Soc ie ty for Tes ting and Mat eri al s, P hil adelphia , Pe nnsylvani a. Burn s, L . A. 1983a. Fate of c hemic al s in aquati c s yst em s: proce ss model s and com pute r code s. pp. 25- 40 In: R. L. Swann and A. E sche nroede r (Eds .) Fat e of Chemic al s in the Envir onm ent : C om

partm ent aland Multim edi a M odel s for Predi ct ions . Sym

posium Serie s 225, Am eri can Chemic al Soci et y, Washingt on, D.C
. Burn s, L
. A. 1983b. Val idati on of e xposure m odel s: therol e of conceptua l ve rif

ic at ion, sens itivi ty

ana ly si s, and al te rnative hyp othe ses . pp. 255-281 In: W.E. B is hop, R .D. C ardwell, and B .B. Heidolph (Eds.) Aquatic Toxic ology and Haz ard Asse ssm ent . ASTMSTP 802, Am eri can Soci et y f or T esting and M at eri al s, P hil adelphia ,, P ennsy lvania
. Burn s, L . A. 1982. Ide nti fic at ion and eva luati on of fundam ent al transport and t ransf orm ation proce ss m odel s. pp. 101-126 In: K.L. Dic kson, A. W. Maki , and J. Cairns, Jr. (Eds. ). Mo d el ing the Fate o f Che micals in the Aquatic Envir onm ent . Ann Arbor Sci encePubl ., Ann Arbor, Mi chi gan. Burn s, L . A., an d G . L. Ba ughm an. 1985. Fate m odel ing. pp. 558-584 In: G.M. Ran d and S.R. Pet roce ll i ( Eds.) Fundam ent al s of Aquati c Toxi col ogy: Me thods and Ap pl i c at i on s. He m i sp he reP ub l
. C o. , Ne w Y ork, NY
. Gam es, L. M. 19 82 . Fieldvalida tionof Ex po sur e An alysis Mo d el in g Sys te m ( EXAMS ) i n a flowing st ream . pp. 325-346 In: K. L. Dic kson, A. W. Maki , and J. Cairns, Jr. (E ds.) Mod eling the Fate of Chemicals in the Aq u atic Envir onm ent . Ann Arbor Sci encePubl ., Ann Arbor, Mi chi gan. Gam es, L. M. 1983. Pra ct ic alappl ic at ions and com pari sons of envir on mental exposure a sse ssment model s. pp. 282-299 In: W. E. B is hop, R . D. Car dwel l, and B. B. Hei dolph ( Eds.) Aquati c T ox i c ol ogy

and Haz ard As se ssm ent , ASTM STP 802. Am eri can Soci et

y for Te st ing and Mate ria ls , Phi la delphia , Pennsy lvania
. Kols et , K., B. F As chjem , N. Chri st opherson, A. Heiberg, and B
. Vige rust . 1988. Evaluat ion of som e c hemic alfate and transport m odels. A case st

udy on the polluti on of t he Norrsunde t B ay(Swede n). pp. 372-386 In: G. Angel ettiand A. Bjø rseth(E ds. ) Or gan ic Micro po llutan ts in the A qu atic Envir onm ent (Procee dings of t he Fi fth European Sym posium , he ld in Rom e, Ita ly Octo ber 20- 22, 1987). KluwerAcad emic Publish ers, Dor dr echt. Lass iter, R. R. 198 2. Te sting models of the fate o f ch emicals in a qu at i c e nv i r o nm e nt s . p p . 2 8 7
- 3 0 1 I n : K
. L
. D i c k s o n , A
. W. Maki , and J. Cairns, Jr. (Eds. ) Modeling theFat e of Chemic al s in the Aquati c Envir onm ent
. Ann Arbor Sc ie nce Publ. , Ann Arbor , Mi chi gan. Las s it er, R. R., R. S. Parris h, and L. A. Burns . 1986. D ec o mp o si ti o nbypl an kto n ic an datt ac h edmicr o o r g an is ms im proves chemic alfat e m odel s. Envir onm ent alToxi col ogy and C hemis try

5:29- 39. Mul k ey , L. A., R. B. Am brose, an d T . O. Barnwel l. 1986. Aquati c f

at e and trans po rt

m od e l i ngt e c hn i qu e s for predi ct ing e nviro nme nta le xp os ur e t o o rg ani c pe st ic ide s and othe r t oxic ants--a c om

parati ve s tudy . In: Urban Runoff Polluti on. Springer-Ve rla g, New York. Paris , D . F ., W. C . St een, and L. A. Burns . 1982. Mi crobi al transform at ion kinet ic s of orga ni c c om po un ds
. pp . 73-81 In: O. Hutzi nger ( Ed.). TheHandbook of Envi ronm ent al Chemistry, v.2 , pt. B. S pr ing er- Ver lag, Be rlin, Germany. Plane , J. M. C., R . G. Zika , R . G. Zepp, and L. A. Bur ns. 1987. Photoc hemic alm odel ing a ppli ed t o nat

uralwate rs. pp. 250- 267 In: R. G. Zika and W . J. C ooper ( Eds.) Phot ochemis try of Environm ent alAquaticSystems. ACS Symposium Serie s 327, Am eri can Chemic alSoci et y, Washingt on, D.C
. Poll ard, J . E. , and S. C. Hern. 1985. A fi el d te st of t he EXAMS m odelin the Monongahel a Rive r. E nvironm ent al Toxic ology

and Chemis try

4:362- 369. Platt , T., K . L. Denm an, and A.D. Ja ssby . 1977. Model ing t he pr od uc t i vi tyof

phyt op l ankt on . pp . 807-8 56 I n: E .D
. Goldbe rg, I. N. M cCave, J. J . O’B rian, and J. H. St eel e, Eds. Marine Modelin g: Th e Sea, V ol. 6 . W iley -Int ersc ie nce: New York. Rein ert , K. H., P. M. Rocchi o, and J. H. Rodge rs, Jr. 1987. Par ameterizationof p red ictive fate models: a case stu dy.9

Envir onm ent alToxi col ogy and Che m is try 6:99- 104. Rein ert , K.H. , and J. H. Rodge rs, Jr. 1986. Vali dat ion t ria l of predi ct ive fat e m odel s using an aquatic herbi ci de (Endot hal l). Envi ronm ent alToxi col og y and Che m is try 5:449-461. Ri tt e r, A.M ., J .L. Shaw, W.M. Wil li am s, and K.Z. Travis . 2000. Charac te riz ing a quat ic ec ologi calri sks f rom pes ti ci des usi ng a di quat

brom ide casest

udy. I. Pr obabi li st ic expos ure es t i m at e s. E nv i ro nm e nt a lT ox i c ol og yand C he m i st

ry 19:749-759. Sand ers, P. F., and J . N. Seiber. 1984. Organophosphorus pestic ide volati li zation: Mode l s oilpit s and eva po ration ponds. pp. 279-295 In: R. F. Kreuge r and J. N. Seiber ( Eds.) Treatm ent an d Dis posalof Pe st ic ide Waste s. AC S Sy mpo sium Series 259 , AmericanChemical Soc iety, Washingt on, D.C
. Schn oor, J . L. , C . Sato, D. Mc Ket chni e, and D. Sahoo. 1987. Pro cesse s, C oef

ficien ts, andMod els fo r Simulating Tox ic Organi cs and He avyM et al s in S urfac e Wat ers. EPA/ 600/3- 87/015, U.S. E PA, At

hens, Georgi a. Sat o, C. , and J. L. S chnoor. 1991. Appl ic at ions of t hree complet ely mixe d com

part m ent model s to the long -term fate of di el drin in a

res ervoi r. Wat er Rese arc h 25:621- 631. Schr amm , K.-W., M. Hirsch, R. T wel e, and O. Hutz inge r. 1988. Mea sured and m odel ed fate of Di spers e Yellow 42 in a n outdoor pond. C hem osphere17:587- 595. Slim ak, M. W ., an d C. D elos. 198 2. P red ictive fate models : their ro le in the U.S. Envir onm ent alProt ection Age ncy ’s wate r program . pp. 59-71 In: K. L . D ickson, A. W. Maki, and J
. Cai rns , Jr
. (E ds .) M od e l i ngthe F at e of C he m i c a l s i n t

he Aquat ic Envi ronm ent . Ann Arbo r Sc ie nce Publ. , Ann Arbor, M ic higan. Sta pl es, C. A., K. L. Dicks on, F. Y. Sal eh, and J . H. Rodger s, Jr. 1983. A m ic rocosm

st udy of Li ndane and Na

phtha le ne for m od e lva l i dat ion. p p. 26 -4 1 I n: W. E
. B i sh op , R
. D. Car dwel l, andB.B. Hei dolph ( Eds.) Aquatic Toxi col ogy and Hazard Asse ssm ent : S ixt h Sym posium , ASTM STP 802, Am eri can Soci et

y f or Tes ting and Mate ria ls , Phi la delphia , Pennsy lvania
. Will i am s, R
. J., M. D. Jürge ns, and A> C . Johns on. 1999. Initia l predi ct ions of t

he c oncent

rations and dis tribu ti on of 17 â

oest radiol, oest

rone and et

hiny l oe stradi ol in 3 Engl is h rive rs. Water Res ear ch 33: 1663-1671. Wolf e, N. L. , L. A. Burns, and W. C. Ste en. 1980. Use of linear freeene rgy rel at ions hips and an evaluat ive mode l t o as ses s the fate andtr an spo rt of phth alate ester s in the aquatic envi ronm ent . C hem osphere9:393- 402. Wolf e, N. L. , R . G. Zepp, P. S chl otzhauer , and M. Sink. 1982. Tran sfo rmation path ways of he xach loro cylcop entad iene in the aquati c e nvironm ent . C hem osphere11:91- 101. R ef ere nces f

or C hapt er 1. Behr ens, J. C. 1979. An exe m pli fie d se m i-analytic alapproa ch t o the tr ansi ent

se nsi ti vity of non- linear sy st em s. Appl ie d Mat hem at ic alMode ll ing 3 :105-115. Las s it er, R. R. , G. L. Ba

ughm an, and L. A. B urns. 1979. Fate of toxi c organic s ubst ance s in t he a quat ic environm ent . Pa ges 219-246 in S. E. J orgensen, edi tor. St at e-of-t he-Art in Ecol ogic alMode ll ing. Pr ocee dings of t he C onfere nce on Ecol ogic alMode ll ing, Copenha gen, Denm ark 28 August

- 2 Sep tember 19 78 . I n te rn ation al Socie ty forEcolo gical Model ling, C openhage n. Par is , D. F ., W . C. Steen , andL. A. Burn s. 1 9 8 2 . Micro bial transform at ion kinet ic s of organic com pounds. P ages 73-81 in O. H utzin ge r , edito r. Th e Han db oo k of Env iron mental Chemis try , Volum e 2/Part B. Springer-Ve rla g, B erl in. Platt , T. , K. L. De nm an, and A. D. Ja ssby . 1977. Modeling the producti vit

y of phyt oplankton. Page s 807-856 in E. D. Gold be rg , I. N. M c C ave , J. J
. O' B ri e n, and J
. H. S t eel e, edi tors . MarineMode ling. Wil ey -Int ersc ie nce, New York.10 

## 2. 0 E xp osu re A ss es sm ent: M ec h an i sm s an d P roce ss es Many exc el le nt books, revie w artic le s, and journalrepor ts have beenwrittenon th e sub

ject o f the fa te andtransp ort of ch emicals in t he e nvironm ent . Thi s report is not int ended as an e xhaustive summ aryof t

he i deas and fac tua l i nform at ion ava il abl e fr om the li te rat ure. EXAMS is a di st il lati on of that l it erature , e ncoded in a c om put e r progra

m . Th i s c ha

pt e r (2 ) sum

m ari zes thefundam ent al ide as that we re us ed t o cons truc t t he EXAMS prog ram. The refe re nc e s c i t e d repr e se nt o nlyt he k e yf i nd i ng s or

p ape rs that dire ct ly inf luenced t he EXAMS code . Addi ti onaldet ai l a nd backgr ound inform at ion c an befound in theworks li st ed in the bib liog rap hy fo r this re po rt. 

### 2.1 Compartm ent Models and Conservation of Ma ss EXAMS ’ environme nta l data arecont ai ned in a fil e (t he “canonic alenvironm ent s fi le ”) t hat includes a se rie s of conci se descr iptions of t

he a quat ic sy st em s of int ere st to a us er. (The te rm “c anoni cal ” s im

ply me ans t hat the dat a in t

he fi le inc lude s only thos e quanti ti es bearing dire ct ly on t he fate and transport

of synthetic organi c c hemic al s.) Eac h wat er-body is repr ese nte d via a set of N com partm ent s or dis tinct

z ones in t he s yst em . The program is bas ed on a s eri es o f mass bal ance s, whi ch gi ve ri se to a single dif fere nti ale quat ion for eac h c om partm ent . Working from the transport

and transform at ion proces s e quat ions , EXAMS com pil es an e quat ion f

or t he net rate of change of chemic al conce ntrati on in eac h com partm ent. The r esulting sy st em of N diff ere ntial e quat ions des cribes a m ass bal ancefor t he e ntire e c os y st e m . Th e see qu at i on s ha ve the ge ne ra lf

orm of E qu at i on (2-1): ( 2- 1) where: V is thevolum e of wat er in thecom partm ent (l it ers) , [ C ] is thetot alche m ic alconc ent ration a s mg/l it er of V

, Leis thetot alext erna l l oadi ng on t he c om partm ent (mg/h), Liis thetot al internalloa ding on the com partm ent (mg/h) resul ting from

cont aminate d fl ows among sy st em com partm ent s, and K i s an overa llpse udo-fi rst -order (/h) los s c onst ant that expres ses th e co mbinedeff ect o f transport

and tra nsf orm at ion pr oces ses tha t de cre ase che m ic al conce ntrati on. The “ canoni calenvironm ent s fi le ” c urrently suppl ie d wit

h the EXAMS com

pute r program

is i nte nded prim ari ly

as a seri es of t est valu es to estab lish that the pr og ram is op er atin g co rre ctly. Alt hough thedata s uppli ed in thi s fi le arewit hin t he range of observe d va lue s, thi s fil e is not inte nded for production runs of the program . EXAMS has bee n des igne d to accep t s tandard wat er-qua li ty

param et ers and s yst em charac te ris ti cs that a

re comm only

m eas ured by

limnologi st s t

hroughout the worl d. EXAMS a l so i nc lud e s ade sc ript or l angua ge (param e t e rs JFR AD , JTURB , e tc .) t

hat si m plifi es the spe ci fic at ion of sy st em geom et ry and c onnect edness. The proce dure f or def ining an EXAMS environm ent

is il lus trate d in Chapt er 3. The EXAMS code has been writte n in a ge nera l (N-co mpart m ent) form ; t

he program al loc at es m em ory as requi red by thecurr ent

des cripti on of the wate r bo dy. The c hemic al data

bas e s uppli ed wi th t

he progr am

inc lude s 11 com pounds investigate d by Sm it h and coworke rs (1 97 8)
. As wit h EXAMS ’ no min al en v ir o nmen ta l d at a b as e, th es e d at a sho uld no t be reg ard ed as immutably f ixed . Inmany instanc es the d ata of S m i th e t a l. ( 1 97 8) were aug mented in o rd er to illus trate EXAMS ’ data en try capabilities, an d the assu mptions usedto fill gaps in the c hemic aldata

ba se are ope n to revi si on as addi ti onal experim ent aldat a be com e avai la ble
. Refer enc es for Chap ter2.1. Sm ith, J. H ., W . R . Ma

bey , N. Bohonos, B. R. Holt , S. S. Lee , T. -W. C ho u, D. C
. B om be rg e r, and

T
. Mi l l
. 19 78. Envir onm ent alPat

hways of Se le ct ed C hemic al s in Fres hwat er S yst ems: Part II. Laboratory

St udie s. E PA600/7-78- 074, U.S. Environm ent alProt ection Age ncy , Athe ns, Ge orgia
.11 

### 2. 2 E qu ili br iu m P ro ces ses The kinetic p ro perties of o rg anic ch emicals are o f te nstron gly influence d by the m ole cul ar s tate of t he c om po un d. C onsi der, for exam ple , a c om pound t hat c an bot h ioni ze and s orb t o suspe nded sedi m ent s. I n thi s c ase , t he c om pound wil l bepres ent in the wat er column in ioni zed, unioni zed, and sorbed st at es. In inland wat ers, where a erosol for m at ion c an benegl ect ed, only the uni on i z ed, unsorbed m ole cul e wi llvola ti li ze acr oss t

he a ir- wat er int erfa ce. An accurate eva luati on of t he t endenc y of

the com pound to volati li ze thus cannot beobt ai ned untilioni zation and s orpti on areinc orporated in the e st im at ion m et hod. Io nizatio n an d so rp tionalso aff ect the rea ctivity of

chemicals to transform at ion

proc e ss e s, a l t

ho ugh them agni tude of t

he c hanges cannot be as rea dily pr edi ct ed. Laboratory deter

m inati ons of kine ti c rate cons tants areoft en li m it ed t o hom ogeneous phas e (c le an wate r) i nvestigations
. Mode ling the behavi or of a com pound in rea l s yst em s re quire s som e knowl edge, or

som e a ssum

pti ons, a bout t he e ffec ts of sorption a

nd ioni zation on a c hemic al ’s be havi or i n the environm ent
. EXAMS doe s no t conta in “hard -w ired” ass um pti ons that so rp tioneither “p ro tects” the co mpound , e nh an ces its reactiv ity, or h as no effec t. Ins tead, the inp ut ch emi cal data in c lud e s e parat e r at e c on st ant s fo r e a c h mol e c ul ar fo rm of the compo un d. Th is data array allow s a userto inclu de un iqu e rate const ant s for ions and s orbed mole cul es when t heseareknown. When het eroge neous phase(or pH depende nt) chemic aldat a are not avai la

ble , t he ne ces sary

as sum pti ons are l eft

to the use r’s dis cre ti on. Ioniz ationand sorpt ion of synthe ti c c hemic al s are t reate d as the rm odynam ic or constit uti ve prope rti es of ea ch c om putati onal el em ent in EXAMS . EXAMS tr eats t heseproce sse s a s l ocal (within -co mpartment) rev ersib le equilibri a, rat her t han cal cul at ing a

globa l ( sys te m -wide ) equi librium partitioning of the com po und am ong it s poss ibl e m ole cul ar s peci es. The inc lus ion of

partitioning to col loi dal“ dis sol ved” organi c c arbon pr eclud es any n eed t o explicitly acco un t for“particle conce ntrati on” e ffec ts or de sorption hy st eresis (Gschwe nd and Wu 1985) , (More l a

nd Gschwe nd 1987)
. Ioniz at ion e quil ibri a are us ual ly achieved wit

hin a very short ti m e, com pare d t o t he tim e-sc al e of transport and transform at ion proce sse s, s o a

( l oc a l ) e qu i l ibrium

a ssum pti on is usua lly jus ti fie d in natural systems. D eso rp tionof n eutr al molecu les bo un d to sedi m ent s, howe ver, m ayber el at ive ly s low f or com pounds t hat are ext ensi vely bound (l arge partition c oeffi ci ent s). EXAMS ’ evaluat ions do not

expl ic itly include t he e ffec ts of sorp ti on/de sorption kinet ic s on t ranspor t or tr ansfor m at ion proce sse s. T he progr am does , howeve r, c om

pu te t he m ajor transport eff ect of s low de sorption, as an i m pli ci t function of int era ct ions bet

ween bent

hic s edi m ent s and the ove rly ing wate r column. Exte nsiv ely sorbedcompou nd s are u sua lly pred ominan tly capt ured by thebottom

se dim ent s (be nthi c c om

partm ent s) in an aqu atic system. Release o f the co mpoundto th e watercolumn is thenlimited by th e turn ov err ate o f the b otto m sediments the m selves. The turnove r tim es of bent hic se dim ent s, e xcept during st orm

eros ion, are longe r than t

he desor pti on hal f-l ive s of or gan ic chemicals. Co nse quently, theint rins ickine ti c l imitations im posed byres ide nce in bot tom se dim ent s ge nera lly e xcee d thos e att ribut abl e t o des orpti on kine ti cs as such.
EXAMS allows forthe exis tence of six ionize d sp ecies, in ad di t i ont o the p are nt

uni on i z e d m ol e c ul e . Ea c h of t hese can com ple x wi th “di ssolved” organi c m atte r ( EXAMS vari abl e DOC ), and s orb wi th t

he s edi m ent

pha se and the bi ota

in an e cosy st em com partme nt ( com

putati onalel em ent). T he progr am com pute s the fra ct ion of

thetot alche m ic alconc entration pr ese nt in ea ch m ole cul ar st

ruct ure. The se di stribution c oeffi ci ent s ( á ) ar e us ed as multipliers on th e user -sp eci f ie d tran sfo rmation r ate coef fic ie nts for e ach decom

posi ti on proce ss. 

### 2.2.1 Ionization Reactions According to the Brönsted-Lowry conc ept of i oniz at ion r ea ct io n s, ac id s an db a se s r ea ctwi thso lv en t ( w at er ) to fo rm a con ju gate acid -b ase pa ir (S t

um m and M organ 1970) . The EXAMS program r egar ds anysynthe ti c organic as pote nti al ly ca pabl e of acting as an ampholyte, forming bo th singly, doub ly, and trip ly charged c at ions and ani ons in theaqueou s m edium . The un ion ized molecu le is takenas the pare nt compo un d, an d is 3 denot ed in thepr ogram

docum ent at ion a s “ RH .” The pote nti al aci d-baserea ct ions arethe n: (1) B asi c re actions : ( 2- 2) ( 2- 3) ( 2- 4) (2) Aci dic rea ct ions : ( 2- 5) ( 2- 6) ( 2- 7) This se t of

che m ic alrea ct ions des crib es the si m ult aneous exi st enceof s even chemic alspe ci es of t he c om pound: ! the un ion ized p aren t m olecu le , ! a s ingly c harge d cati on , ! a doubly c harge d cati on , ! a t riply c harge d cati on , ! a s ingly c harge d ani on ,12 T( E C ) a2 K (×10 10 ) 0 4.45 5 5.20 10 6.03 15 6.92 20 7.85 25 8.85 30 9.89 35 10.9 40 12.0 45 13.1 50 14.2

a2 T a b le 1 . K o f P h e n o lS u lfo n ic A c id ! a doubly c harge d ani on , and ! a t riply c harge d ani on . (A gain , be caus e EXAMS i s an int e ra c t i ve pr og ram i n whi c h t

he use r h as d ir ec t access to the inp ut database, much of this docum ent at ion has been wri tt en usi ng theinput dat a varia

ble s a s ide nti fie rs and as quant itie s in theproce ss e quat ions . Al though this ap p r o ac hp ose s some diff iculties fo r the cas ual rea der , it al lows the potentia l us er of theprogram

to seetheconne ct ions betw een p ro gr am variab les andth e un der lying pro cess th eory. The Data Dictionary

cha pte r of t his docum ent

(beginning on page 180) cont ai ns an alphabetic alli st ing a nd defin itions of EXAMS ’ i nput variabl es. Input dat a are nam ed wi th a

te rm ina l “G” (“Gl obal ”), and varia ble s inte rnalto the EXAMS program it sel f ar e nam ed wi th a

te rm ina l “ L” ( “Loc al”) . For exam ple , “ KP SG ” can b e spec ifiedby th e user ; “ KP SL ” i s i ts int erna l equi val ent .) Most com pounds do not

e xhibi t t he ful l r ange of behaviors give n in E q. (2-2) –(2-7). EXAMS ’ chemic alinput dat a stream c arri es, for e ach chemic al , a

vec tor ( SPFLG ) o f 7 flags that t el ls the program whic h of t

he i oniz at ion r eac ti ons are a ppropri at e for that compou nd . (A “flag” in this usag e m eans a sign al usedto cont rol exec ution of the progr am .) Setting an el em ent of t he SPFLGvec tor to “ 1" indic at es that t he c orres ponding c hemic al spec ie s in fac t e xis ts ; setting an el em ent of SPFLGto “0" (ze ro) indi cat es theche m ic alspe ci es does not e xis t. S PFLG (1 ) sho uld usual ly be set to indi cat e t

he e xis te nce of t

he parent m ole cul e. When, for exam

ple , t he re m ai ning f

la gs ( SPFLG (2 ...7 )) ar e all zero, EXAMS tr eat s t

he c hemic alas a neut

ral(uni oniz abl e) organi c c om

pound. When SPFLG (2) is s et ( =1), and SPFLG (3... 7) are 0 , the co mpoundis takento be anorg anic b ase forming on ly 4 a s ingly c harge d cati on (RH ). + The e quil ibrium

cons tants for t

he ioni zation rea ct ions provide a measure of t

he s tre ngth of

theorgani c a ci d/ba se rel at ive to wat er. The ba si ci ty

cons tants corres ponding t o Eq. (2-2), (2-3), and (2- 4) ar e: ( 2- 8) ( 2- 9) ( 2- 10)
The a ci dit y c onst ant s c or

re sponding to Eq. ( 2-5), ( 2-6), and (2-7) are : ( 2- 11) ( 2- 12) ( 2- 13) Thes e i oniz at ion cons tants are“mixe d” c onst ant s (St umm and 3 3 Morgan 1970:82) , whi ch t akepH=- l og{H O } ({ H O } or {H } + + + is hydr ogen ion activi ty , IUPAC c onvent ion), and the com pound is expre ssed in conce ntra ti on unit s. ( Sal t e ffec ts on pK va lue s, andchan ges in pKwwith temper atur e, are curre ntly neg lected in EXAMS .)

2 In di lut e a queous solutio ns (unit wat er a ct ivi ty , { H O}=1), the wat er t erm s in theequi librium cons tants can be neglec te d. In b en th ic se d ime nts , h o w ev er , mu chof th e c o mp artme nt v o lume is occ upie d by sol ids , and thedec rea sedactivity of wate r m

ust be c onsi dere d. In EXAMS , thi s proble m is over com e by

ref erring all co ncen tration s to the aqu eou s ph ase of the compartment (no te dim ensi ons of vari abl es in E q. (2-1) ). Bas ic it y and ac idi ty

cons tants are entere d to EXAMS as the negative of their Bri ggsi an logarit hm s, that is, as pK va lue s. T he com pute r varia

ble s are PKB (1), P KB(2), and PKB (3) for the 4 fir st , se cond and third bas ic it y c onst ant s (ge nerating RH , + 5 6 RH , RH and respe ct ively) and PKA(1), P KA(2), and 2+ 3+ P KA (3 ) fo r the fir st, seco ndandthirdacidity con stants 2 (gene rating R

H , RH , and R res pective ly). The e quil ibrium ! 2

! 3

! const ant s c an beent ere d ei ther as s ingl e (t em pera ture -indepe ndent) pK value s or as functions of t em perature
. Tem peraturedepe ndencie s of the equi librium cons tants are compu ted fr om a ninteg ratedform of the Gib bs- Helmho ltz equation (Ca st el lan 1964: 215-217)
. Eac h com pute r i nput datum (PKB, PKA) has a co rre spo nd ing entha lpy var iable (E PK, EPK). When the ent

halpy te rm

(EPK) is zero, the PK dat um is taken a s a t em perature -independent

pK. When t

he EPK te rm

i s non-z ero, the PK datum

is int erpre te d as thecons tant in theequati on

describing t

he e quil ibrium

cons tant as a func ti on of te m

perature . For exam ple : The Ha ndbo ok of Chemi st ry and Phys ics, Ed. 51 p. D122 (Weast

1971) , gi ves the a2 sec ond ac idi ty

cons tant ( K ) of phenol -sul fonic ac id f

or 0 E to 50 E C ( Tabl e 1 ).

EXAMS coul d be loa ded wi th a typical va lue dr awn fro m t his d ata a2 se t , fo r e xam

pl e , at 25 E C, K = 8.85×10 and PKA(2) =9.05 ( al so

! 10 loa d E PK(2) = 0.0). The pKa will the n be taken a s 9.05 reg ardless of the wate r te mperature of the compartment. Alternativ ely, the vi sibledependence of t he a ci dit y c onst a nt on temperature co uldbe de scrib ed to EXAMS via

PKA(2) and a non-zero va l ue o f EP K( 2). St at is ti cal13 a regre ssi on of t

hesedat a on the m odelK = A exp(-B /RT), where R is the gas con stant ( 1 .9 8 7 2 cal/d eg mol) an d T is abs olute te m perature , y ie lds theparam et ers A = 8. 27 24×10 and (B/R)
! 7

a = 2.0466× 10 and acc ounts for 99. 7% of the variati on in K
.

3 EXAMS requires the loga

rit hm of A, and B in kcal/m ol, as input

a2 dat a. There fore, thedepe ndenceof K on t em peraturewould be desc ribe d to EXAMS via PKA(2) =log A =

! 6.082 and EPK(2) =(B/R)×R ×0.001(kc al/c al ) = 4.067 kc al/m ol

a2 EX AMS w i l lt

he n c om put e a l oc a lv a lue o f K a s af

un c t ion of the wat er t em

perature( TC EL ) in eac h system compartment, usi ng theequati on:

a log(K )=PKA(2)- [1000×EPK( 2)/{ 2.303×R ×(TC EL+273. 15)}] 

### 2.2.2 Sediment Sorption EXAMS com

pute s a (l ocal ) equi librium

va lue f or the partitioning 3 4 of ea ch c hemic alspe ci es (RH , RH , etc.) to s ediment p has es in + the sy st em . Theche m ic alinput data includes a vect or of parti ti on coef fic ie nts ( KP SG ) whoseel em ents apply t o ea ch of the corre spondi ng c hemic als peci es. T hat is , KP SG (1) i s t

he parti ti on

3 coef fic ie nt f or neut ralorganic s or the unioni zed m ole cul e (RH ),

4 KP SG (2) a ppli es to t he RH m ole cul e, et c.

+
EXAMS us e s l i ne ar i so t

he rm s fo r al l s orpti on com putati ons, r at

her than thenon-lin ear

Fre undli ch or Langm

uir form ulati ons. ( A linear is othe rm is equiva le nt t o a partition c oeffi ci ent .) Li near is otherm s are us ual ly

an adequate des criptor of t he c apt ure of neut ralorgani cs by sedi m ent s, at l eas t up to 50% of t

hei r wat er solub i l i ty( Kari c kh of

f 19 99 (pe rs . c om

m .) ) re si du a lin the aqu eou s ph ase. F orcompou nd s w h o se melting poin t ( EXAMS input par am et er MP ) i s gre at er t han t he am bie nt t em peraturea cry st alene rgy term is adde d (com pare Eq. 12 in (Kari ckhoff 1984) ):

f in whi chX

i s m ol e f ra c t i ons olub i l i ty, Ä S is the solute ent ropy

m of fusi on, T is t

he m el ting point

in K, T is abs olut e t em

perature , f and R is thegas cons tant. Ä S is bet ween 12 and 15 eu (ent

ropy unit s, c al/mol K) , so, for c om pounds t hat aresol ids at

the am bie nt tem perature EXAMS com

putes the limiting co ncen tration l C as

in whi ch SOL, MP

, and TCEL are EXAMS input param et ers; the f f ac to r 6. 5 re su lt s f

r o m Ä S /R. (Fo rliquid s, this co rre ctionis ignore d.) EXAMS res tri ct s it s ope rating r ange to e nsure that t he a ssum pti on of i sotherm

linearit y i s not viol at ed. Thes e re stric ti ons are im posed by e valuat ing t

he e xte rnalloa dings to ensure that t he input s t o thesy stem are not exce ssi ve, and by a pre-out

put evaluat ion of

thecom pute d EEC s in al l c om

partm ent s. L oadi ngs via rain fall andgro un dw ater see pag e may no t exceedsolubility of t he ne utra l s peci es, evaluated usi ng thepH and te m perature of the r eceiv ing seg ment. S tream-b orne andNP S lo ads , as with l cal cul at ed EEC s, m aynot exce ed C in t he di ssolved neutra l molecule. Upo nd et ec ting erro rs in lo adin gs o r in fin al EEC s, EXAMS repor

ts theprobl em

an d retur

ns c ontrolto the use r for corre ct ions
. The uptak e of n eutr al org anic ch emicals b y soils an d aquatic sed iments app aren tly invo lves d isso lutionof the compo un d into the org ani c m atri x o f the s oi l/ se di m e nt , rathe r than a pur e physi cal(surf

ace) ads orpti on (see , for exam ple , C hiou e t a l. 1979) . Sorpt ion of thi s cl ass of chemic alprobably takes pla ce by a hy dr op ho bi c m e c hani sm , i n whi c h t he c om po un d ( or

m ore 3 gener al ly the RH m ole cul e of aci ds and bas es) is dri ven fr om the wat er pha se of t

he s yst em by a l arge fu gaci ty . Thi s proc ess is conc ept

ual ly si m il ar t o theext

rac ti on and rec overyof an or gan ic pollu tant fr om water u sing an or gan ic solv ent. The partitioncoef

ficien t ( KP S ) for a parti cul ar c om pound can be norm al iz ed t o theorgani c c onte nt of soi ls (Chi ou et al . 1979) or, equ ivalen tly, to the o rg anic carbo n con tent of aqu atic sediments (Kari ckhoff et

al . 1979) . The res ulting param et er ( KOC ) i s a rel at ive ly st abl e, sys te m -independent m eas ure of

an int rinsic propert y of organi c c om

pounds. KOC can be used to c om pute a local p artitioncoef

ficien t ( KP SL ) for sedi m ent pha ses of an aquatic sy st em , a s a

function of

theorgani c c arbon conte nt ( FROC , organic carbon as frac ti on of dr y we ight) of t

he s edi m ent ph ase of each co mpartment. K OC is s trongly

corr el at ed wi th t

he oc tanol-wate r par

ti ti on coefficien t ( KOW ) (K arickho ff et al. 1 97 9) . Fo r wh ole sed iments, as use d in EXAMS , KOC c an be estim at ed (wit hin a fac tor of 2.5) as 35% of KOW (Se th et al. 19 99 ) . The pref err ed ap pr oachis to inclu de at least ameasuredKow andKoc measuredon aquatic sed iment, as sed iment Ko c ten ds to be abo ut twice that of soil Koc (Chi ou et

al . 1998)
.
3 EXAMS computes the RH partitio n co eff icient ( KP SL (1 )) for eac h sys te m com partm ent via evaluat ion of

the se input

dat a ( KP SG (1), KOCG , KOWG ). T he KP SGdatum is use d as a sys te m -wide partition coef

fic ie nt wheneve r it

i s non-z ero, giving prec edenc e to expl ic it

use r ent rie s. KOCGis , h o w ev er , th e p r ef err edda tum, as it pro vid es a system-ind epen den t m easure of sorp tionaffin ity that c an beta il ored t o the spe ci fic proper ti es of e ach com partm ent . When KP SGi s z e ro , and KOCGnon-ze ro, a loc al (com partm ent -spec ifi c) KP SL ( 1 ) is co mp ute dfr o m KOCGand the or gan ic carb onc o nten t ( FROC ) of t he s edi m ent

phas e of eac h compartm ent . When KOCGis ze ro, but the KOWGentry is14 non-ze ro, KOC is com

pute d as 0.35× KOWG , and c onverse ly
. KOW and KOC areal so use d to estim at e KP B (se e C hapter 2. 2.3) and KPDOC (Cha

pte r 2.2. 4). Organi c i ons c an e xchangewit h thenorm alsoi l ion s, to an ext ent probably governe d by the ion exchange c apac it y of a sed iment. The particle siz e d is tribu tionof the sediment, ho wev er, ap par ently also gov ern s the ability o f th e sediment to take up organi c i ons (Kari ckhoff and Bro wn 1978) . The com ple xit y of thi s proc ess has hindere d thedeve lopm ent of robust , sy st em - i ndepende nt a nal ogs of KOC for organi c i ons. EXAMS inc lude s a seri es of “ sys te m - independent” m eas ures of ion s orpti on that c an be invoked at theuse r’s option. Thes e param et ers rel at e t

he (inte rnal ) KP SLfor t

he organi c i ons t o the ion e xchangeca

pacities of

se dim ent

phas es in e ach sys te m com partm ent . Thecom

pute r varia

ble s are:
KIEC (1) for sorption of – KP SL ( 2 ) co mp ute dfr o m CEC KIEC (2) for sorption of – KP SL ( 3 ) co mp ute dfr o m CEC KIEC (3) for sorption of – KP SL ( 4 ) co mp ute dfr o m CEC KIEC (4) for sorption of – KP SL ( 5 ) co mp ute dfr o m AEC KIEC (5) for sorption of – KP SL ( 6 ) co mp ute dfr o m AEC KIEC (6) for sorption of – KP SL ( 7 ) co mp ute dfr o m AEC The uni ts of KIE C are ((mg/kg)/(mg/L) )/( m eq/ 100 g dry wei ght); thecati on ( CEC ) and ani on ( AEC ) exc hange capa ci ti es of syst em se dim ent s are e nte red a s mil li equi val ent s (m eq) pe r 100 gram s dry weight of t he s edi m ent . When a si ngle partition coef fic ie nt i s pre ferre d for a llse dim ent s in t he sy st em , it

m ust be loa ded vi a t

he a ppropri at e e le m ent

of theKPSG vec tor and t he corre spondi ng el em ent

in KIEC or KIEC m

ust be set to zer o. EXAMS uses th e intern al va lue o f th e p artitioncoef ficien t ( KP SL ) for e ach chemic alspe cies, howe ver c om pute d, t o ca lc ulate the equi librium

sedi m ent

sorption of

ea ch s peci es on ea ch parti c ul at e s e di m e nt

ph a se( P) thr ou gh out

the s y st e m . The chemic alequations and equil ibrium expre ssi ons are s imil ar f or eac h che m ic alspe ci es:
( 2- 14)

( 2- 15)

( 2- 16) ( 2- 17)

( 2- 18)

( 2- 19)

( 2- 20) Sedi m ent parti ti on coeffi ci ent s are usual ly report ed as a

rati o of the conc ent

ration of so rb ed c hemic al(mg com pound/g dr

y wei ght of s edi m ent) to the res idua l a queous phaseconc ent ration (m g/lit er), in “di m ensi onle ss” unit s ((mg/kg)/ (m g/L) ). T he sorption e quil ibrium

cons tants areequi val ent to con vent iona l partition c oeffi ci ent s only s o long as the concentr at ion of partic ulate m atte r [P] is expre sse d as a “se dim ent :wate r rati o” ñ (kg dry wei ght/li te r of wate r), and theche m ic alconcentrations 3 3 (e.g. , [RH P] and [RH ]) are ref erre d to the aque ous pha se of t he sys te m and expre sse d as (m g com pound/l it er of wate r). EXAMS stric tly a dhere s to thi s convention for i ts int erna l c om putati ons. EXAMS ’ out

put t abl es, however , are c onvert ed t o conve nti onal reporting uni ts . For exam

ple , conce ntrati ons of se dim ent -sorbe d chemic al s are r eportedto theuse r as m g/kg dr y we ight of sedi m ent , but

arecarri ed inte rnal ly

as (sorbe d m g)/( li te r of wat er). The need for stric t adher encet o t his conve nti on ari ses from the verylarge sedi m ent

/wate r rati os of bent

hic se dim ent s. Wat er co lumnco mp artme nts canbe ass umedto h av e a w at e rv o lume ess ent ia lly t

he s am e a s t

hei r environm ent alvolum e (VOL) . For the se com

partm ent s, EXAMS ’ i nte rnalvariable (SEDCOL , t he sed im ent /wate r rati o ( ñ , kg/L)) i s sim ply com pute d as 10 ! 6 (k g/mg) times the inpu t datum (SU SED , susp end ed sediments in m g/L)
. Bec ausethesol id phase occupi es a s igni fic ant fra ct ion of

the tot alenvironm ent alvolum e of bed s edi m ent s, ñ (SED COL ) is com pute d qu ite dif

fer ently for bent

hic (TYPE“B ”) com partm ent s. F or bent

hic com partm ents, theinput

dat um BULKD i s thebulk densi ty of the se dim ent

(g/cc environm ent al vo lume). Th e sediment:w ater ratio is compu te df r om the bu lk densi ty and wat er cont ent

( PCTWA, 100 × thefre sh wei ght/ dry wei ght r at io) of t

he s edi m ent , and thetot alenvironm ental volum e (VOL, cub ic m et ers) of t he c om partm ent . (T he

w computati on takes ñ , the d e ns i tyo f wat e r, a s 1 g/ c m .) The 3 equations (using theint erna l c ode varia ble s) are: ( 2- 21) where15

TO TM AS = BUKLD × VOL ×1000. S EDMSL = TOTMAS /( PCTWA/100.) , and

w WATVOL = ( TO TM AS - SE DM SL )× ñ Here TOTMAS i s t

he t ota l c om

partm ent m ass (kg), SE DM SLis the m ass of s edi m ent in the c om partm ent (kg), and WATVOLis the volum e of wat er c onta ine d in the com partm ent (l it ers)
. The s edi m ent

/wate r rati o can als o be com pute d dir ectly

from the wat er c onte nt of

these dim ent

(Eq. (2-22)):
( 2- 22) Eq. ( 2-21) i s t

he m ore e ffi ci ent

com putation for EXAMS , however, be caus e t

he re sul ts of t

he inte rm edi at e c om

putati ons ( W A TV O L, SE D MS L) ar e u se dels ew h er e inth e p r o g r am. 

### 2.2.3 Biosorption The uptak e of ch emicals by livi ng org anisms is rep rese ntedin EXAMS via

se ven s im

ple bioc oncent

ration f act ors or bio m ass partition c oeff

icient s ( KPBG ). KPBGis a vect or of 7 el em ent s, eac h of whi ch a

ppli es to t

he c orres ponding che m ic alspe ci es 3 4 (RH , RH , e t c .)
. Th e c he m i c a le qu at i on s and e qu i l ibri um + expre ssi ons are anal ogous t o thos e for se dim ent sorption:

( 2- 23)
( 2- 24)
( 2- 25)
( 2- 26)
( 2- 27)
( 2- 28)
( 2- 29)
Bi oconce ntration f

act ors ( BCF , EXAMS input vari abl e KPBG ) shoul d be ent ere d to EXAMS on a drywei ght ba si s. T he e xpect ed un i t s of KPBGare (μg /g(dry)) / (mg/L), o r the numerically equi val ent

unit (mg/kg( dr

y )) / (mg/L). EXAMS es ti m at es KPB from KOWif theinput dat a i s not

pres ent. The e st im at ion e quat ion (Bau gh man andParis 1 98 1) is As wi th s edi m ent sorption, EXAMS conve rts it s input data for com partm ent biom ass es t o an i nte rnalvari abl e ( BIOTOL , “B” in Eq. (2-23)–(2-29) ) wit

h dim ensi ons of kg drywei ght pe r l it er of wat er in thecom

pa rtm ent
. EXAMS ’ inp ut d atum fo r wa te r co lumn com partm ent s ( PL MA SGin mg dry w eigh t per liter) is simply m ultipl ie d by 10 (kg /mg) t o yi el d BIOTOLin it s prope r uni ts
.

! 6 For be nthi c c om

partm ent s, t

he be nthi c bioma ss ( B NM AS G ) is ent ere d to EXAMS wit

h dim ens ions of gram s (dry wei ght) per squarem et er of

bottom se dim ent surfa ce. EXAMS con verts this dat um t o i t s i nt e rn a lv ari abl e (B ( BIOTOL ), kg per l it er of int erstitia l wate r) vi a Eq. (2-30):
( 2- 30) wh e re AREAG

isthe(use r-suppl ie d) t ota l s urfac e area of t he bent hic com partm ent (square m et ers)
. Thea c t ua lq uanti t i e s of

s ynt he t i c o rg ani c s c apt

ur e d bythe bio mass are of

te nr elativ ely small, comparedto the amoun ts sorbed wit

h se dim ent s or dis sol ved in the aque ous phaseof rea l sys te m s. T hus, t

he bi om ass oft en plays a re lati vely minor roleas a trans po rt orcapture medium af f ec ti n g the f

ate of anorg anic pollutant. The role of t

he bi om ass as a fo od-chai n vec tor can, howe ve r, ha ve gr e a t e c ot ox i c ol og i c a l s i gnifi canc e. (Bi otransform ation of c hemic al s i s, of cours e, anot

her m atte r al toge the r (se e 2. 3.6).) EXAMS doe s no t inc lud e a mobile com ponent of t he bi om ass , t

hat is , vol itiona l movem ent s of fis hes (et c.) am ong com partm ent s are not

as ses sed. The plankton, however, is t

ranspor te d in a ccor d wi th t

he hy drology of t he a quat ic sy st em , c arry ing a ssoc iate d chemic alwith it . (T he transport equati ons are di scus sed in C hapt er 2. 3.1.) The KPB vect or for organi c com pounds estim ates organi sm al body-burde ns from

si m ple bioc oncentrat ion f

act ors. Note , ho wev er , th at EXAMS ’ com putati ons are ba sed on partitioning ratios to dis sol ved s pecies of theche m ic al
. EXAMS does not attempt to evalu ate suchthing s as the expo sur e of f ishes to vari abl e c hemic alconcentrati ons a s t heym igrate am ong diff eren t zones of the eco sy st em, or fo od -ch ain biom agni fications . If desired, m eas ured f is h bioc oncent

ration fa c t or s or e sti m at e s base d on Ko w (Mey lan et al . 1999) can be ent ere d via KPBGand used as for prel iminary eva luati on of fi sh cont aminati on, but

tr ansfe r of EXAMS output

expos ur e f

i l e s t o t he B AS S model is the pr eferredmethodo log y. 

### 2.2.4 Complexation with DOC EXAMS tr eat s c om

ple xat ion wi th t

he “ dis sol ved” (i. e., col loi dal andfiltrab le particu late) or gan ic matt er of natur al water s via com ple xat ion c onst ant s for eac h of t he ioni c spec ie s (E q. (2-31) – (2-37)) In t

heseform

ulati ons, DOC is in kg/L, com ple xed spec ie s are in m g/kg ( DOC ), and dis sol ved c hemic alspeci es are16 in mg/L; Kpdoc i s c onvent iona lly r egar ded a s be ing “di m ensi onle ss” or a s having uni ts of (mg/kg)/( m g/L) or L/kg, as in t he di scus si on of s edi m ent sorption in Cha

pte r 2.2. 2.

( 2- 31)

( 2- 32)

( 2- 33)

( 2- 34)

( 2- 35)

( 2- 36)

( 2- 37)

Kpdoc shoul d be m eas ured on the m at eri alas it nat ural ly occ urs, rath er than onhumic acid or f ulv ic acid ex tracts. If, as is u sua lly the c ase , a

m eas ured Kpdoc is not avai la ble , EXAMS estimates it from Kow as Kpdoc=0.074Kow. This value wa s de rive d from analys is of th e data p rese ntedin Ap pen dix A. Th is tabu lationis a c om pendium of l it eraturevalues for Koc measurem ent s on nat uralwat e r sa

m pl e s. Me asure m ent

m et hods include, inter a lia , dia ly si s (Carte r and Su ffet 1982) , re verse d-phaseseparati on (Lan drum et al. 198 4) and so lub ility enhan cement (Chi ou et al
. 1986) ; values devel oped usi ng f luore sce nce quenching m et hods (G auth ier e t a l. 19 86 ) were exclu dedbecau se this metho d is subjec t to int erfe renc es that of te n l ead to ove r-es ti m at es of Koc (Laor and Rebhun 1997) , (Dani el son e t a l. 1995) , (Ti ll er and Jon es 1 997) . Parti ti oning to DOC in ben thic seg ments is cal cul at ed us ing t

he ge nera l Koc of t

he c om pou nd , a s t

he avai la ble li te rat ure indi cat es a gre at er a ffi nit y of bent hic DOC , a s exp ress ed v ia a m ean Kp/K ow(0. 46 , Ap p en d ix A) th at is well wit hin t he unc ert ai nty

(0.14Kow – 0.89Kow) of observati ons for partic ulate organi c c arbon (Set h et al . 1999)
. 

### 2.2.5 Computation of Equilibrium Dis tribution Co eff ici en ts EXAMS com

pute s t he di strib ution of t

he c hemic alam ong it s 28 3 3 possible m ole c ul ar st

ru c t ur e s (R H , RH P, e t c .)
. Th i s di stribution is expre sse d as a vect or of c oncent ration r at ios ( á ). E ach el em ent of á is theratio of

theconc ent

ration of a partic ular m ole cul ar spec ie s, to thetot alconc ent ration of che mical in t

he s yst em t com partm ent (S , mg che m ic alper li te r of wat er in the com partm ent). T hese áva lue s ent er the kinet ic e quat ions as m ultipl i e rs on

t heus e r- suppl ie d rat e c onst ant s for transform at ion of ea ch m ole cul ar s peci es. The logic of these computation s can best be seen via a sample calcu la ti o n. F orexample, co nsid er the b ehav ior o f an o rg anic aci d in pure wate r, subjec t to thefol lowi ng ioni zation r eac ti ons: ( 2- 38)
( 2- 39) In orde r t o eva luate theeffects of ioniz at ion on transform at ion and transport

of t he ch emic al , EXAMS requires thre e conce ntrati on ratios ( CR ): (1) t he fr action pr ese nt a s , or ( 2- 40) (2) t he fr action pr ese nt a s ,or ( 2- 41)17 (3) t he fr action prese nt a s , or ( 2- 42) The e quil ibrium

cons tants for the chemic alEq. (2-38) and ( 2-39) are : ( 2- 43)
( 2- 44)

3 As has alrea dy be en m ention ed, EXAMS c om pute s { H O } a s

+ 10 . Thee qu i l ibrium

e xp re ss i on s, t og e the r wi th a conc ent ration -pH condi ti on, provi de enoug h inf ormation for com

puting thedes ire d concen trati on ratios CR (St umm and Morgan 1970:102) . The conce ntrati on condi ti on is si m ply a st at em ent

of the l aw of conse rvation of

m ass : ( 2- 45) The c on cent

ration c ondition ( Eq. ( 2-45)) and thedefinition of 1 the fi rst conc ent ration r at io CR (Eq. (2-40)) com bine to give :

( 2- 46)
The e quil ibrium

expre ssi ons c an now besolved for and in te rm s of To wi t, Eq. ( 2-43) c an berearrange d to give : ( 2- 47) and, from Eq. (2-44), ( 2- 48)
Substit uting Eq. (2-47) into E q. (2-48) yi el ds:

( 2- 49)
Substit uting Eq. (2-47) and Eq. (2-49) into E q. (2-46 ), and

3 canc el ing [RH ] from

num erator and denom inator, yi el ds t he des iredresu lt: ( 2- 50)

2 The s econd dis tributi on coe fficient CR can be com

pute d in an 2 anal ogous fa shi on. From

thedefinition of CR in E q (2-41), and the conc ent

ration c ondition ( Eq. ( 2-45)), ( 2- 51)
Solving Eq. (2-43) for , and Eq. (2-44) for , yi el ds t he re quire d expre ssi ons in : ( 2- 52)

( 2- 53) Substit uting Eqs. (2-52) and(2-53) int o Eq. (2-50)2.33, and canc el ing from nume rat or and denominator, the n give s
2 an e xpress ion f

or CR :
( 2- 54)

This con ven tion al solutionforthe distr ibutioncoef ficien t is som ewhat

unsati sfy ing f

or dire ct im ple m ent at ion in a com

pute r a1 program , howeve r. Wheneve r t he a ci dit y c onst ant

( K ) is ze ro, the ma chi ne wil l, nonet

hel ess , att em

pt t he di vis ion a

nd m ake an error. Of c ourse, a separat e segm ent of c ode coul d bewri tt en for eac h possible subse t of

the28 pot ent ia l m olecular spe ci es, and the machi ne c ould beguide d to the appropriate se ct ion of the code by a logi c tre e. Obse rve, however, that E q. (2-54) can al so be wri tt en a s:

( 2- 55)

This equ ivalen t e xp ress ioncan be gen eratedby simply substit uting these condterm

in the denominator of Eq. (2-50) into its ow n numerato r. Eq. (2 -5 5) now has the adv antag e that a a1 zer o va lue f

or K wi llnot

c auset he com pute r to atte m

pt a “ zer o 2 divi de,”and wil l nonet

hel ess yie ld the proper va lue for CR , t hat is , z ero. Inthe sam e way, substit uti on of t

he t hird te rm

in the denominator int o thenum erator of Eq. (2-50) give s:18 ( 2- 56)

3 Eq. ( 2-56) i s e quiva lent to the e xpress ion f or CR obtain ed v ia sub st ituti o no f

exp r es si o n s f

o r an d (i nterms
3 of ) i nto t he for m ula for CR givenby:

( 2- 57) Rearranging Eq. (2-54) gi ves in te rm s of : ( 2- 58)
and Eq. (2-43) give s: ( 2- 59) or, s ubst it uting Eq. (2-58) into E q. (2-59) , ( 2- 60) Substituting Eq s. (2 -5 8) and(2- 60 ) into Eq.( 2- 57 ), and ca ncel ing from num erator and de nom inator, the n yi el ds:
( 2- 61)

whic h is equi val ent

to Eq. ( 2-56). This exam

ple dem onstrat es that an al gorit hm for c om puting the dis tributi on coe ffi ci ent s ( á ) of any m ulti-s peci es mixt

ure can be con stru cted inthe fo llow ing way.

t (1) Wri te a conce ntrati onconditi on for [ S ] that e xpress es the law of c onservati on of m ass (Eq. (2-45)). (2 ) Def ine the distrib utio n co eff icient fo r the p aren t m olecu le 3 3 T (RH ) as [RH ]/ [R ] (Eq. (2-46)). (3) S olve theequi librium expre ssions for t

he ful l s yst em

(Eq. (2-43) and Eq. (2-44)) f

or ea ch m ole cul ar s peci es, expre ssing 3 eac h spe ci es in t erm s of [RH ] (Eq. (2-47) and Eq. (2-49)). 3 (4) C ance l [ RH ] from

ea ch of the se expre ssi ons (E q. (2-47) and (2-49)), the rebyobta ining thecont ribution of

ea ch s peci es (DISFC T(I)) to t

he de nom inator of Eq. (2-50). (5) C om pute a tota l de nom inator (SUMFC T) a s ( 1 + t hese te rm s), as in E q. (2-50) (t hat is , 3 3 DISFCT (1) =[RH ]/ [RH ] = 1).

i (6 ) Compu te each d is tr ib u ti oncoef ficien t ( á ) as DI SFC T(I )/SU MFCT , wher e DISF CT(1 ) = 1 and , inth is exam ple ,
a1 DISFCT (2) =K /{ H } and +

a1 a2 DISFCT (3) =(K )(K )/{ H }{H } + + This com putati onalpr ocedur e is ge nera l for al l i ts subse ts : whe n
a anyK = 0, the com

pute d dis tributi on coe ffi ci ent is ze ro. Furtherm ore, the ávalue s always sum to 1 .0 , as they must in order to c onform

to the la w of c onservati on of m ass . The EXAMS algori thm

for com puting dist

ribution c oeffi ci ent s of the 28 (pot ent ia l) m ole cul ar s peci es of an organi c c hemic alwas con stru cted o n this mod el. Refer enc es for Chap ter2.2. Baughm an, G. L. , and D. F. Pari s. 1981. CRC C ritic alRe vie ws in Micro bio log y 8 :205. Carte r, C . W., and I. H. Suff et . 1982. Bi nding of

DDT t o dis sol ved humic mate ria ls . Environm ent alSci enceand Tech no log y 16 :735-740. Caste llan, G . W . 19 64 . Phys ic al Ch emistry. Ad diso n- W esley Publ. Co. , R eading, Ma ssa chuse tt s. Chi o u, C . T. , R . L. Ma lc olm , T. I. Brint on, and D. E. Ki le . 1986. Water solubil it

y e nhance m ent

of s om e organic pollutan ts and pe sti c i de s by

di ss olve d humi c and

f ulvi c a ci ds. Env iron mental Scien ce andTechn olo gy 20 :502-508. Chi o u, C
. T. , S. E
. Mc Gr od dy , and D. E
. Ki l e . 19 98
. Parti t ion character istics of

polycyc lic aromatic hydro carb on s onsoil s andsediments. Env iron mental Scien ce an d Tech no log y 32 :264-269. Chio u, C. T., L. J. Peters , andV. H
. Fre ed. 197 9. A phys ical concept of

soi l-wate r equi libria

for noni onic organi c com pounds. S ci ence 206 :831-832. Dani el son, K. M., Y.-P. Chin, J. S. But erba ugh, T. L. Gusta fson, and S. J. Traina. 1995. Solubil it y enhancem ent

and fluor esc encequenc hing of py reneby hu mi c s ub st ance s: The effe ct of dissolved oxy gen on quenching proce sse s. Env iron mental Scien ce andTechn olo gy 29 :2162-2165. Gauthie r, T . D., E. C. Shane , W. F. Gueri n, W. R. Si etz, and C
. L. Grant. 1986. Fluoresc encequenc hing m et hod for determining equi librium

cons tants for polyc yc li c arom at ic hy dr oc arb on s bi nd i ngt o d i ss olve d humi c m at e ri a l s. Env iron mental Scien ce andTechn olo gy 20 :162-1166.19 Gschwend, P . M. , and S.-c . Wu. 1985. On the const ancy of sed iment-w ater partitioncoef ficien ts of h ydr op ho bic organi c pol lut ant s. E nvironm ent alSci enceand Tec hnology 19 :90-96. Kar ic kh of

f, S. W . 19 84 . O r g an ic po llutan t sorp tionin aqu atic sys te m s. J ournalof Hy draul ic Engi neering 110 :707-735. Kari c khoff, S . W., and D. S
. Brown. 1978. Paraquat s orpti on as a f un c t i onof

parti c l e s i z e i n n at

ur a ls e di m e nt s. J ourn a lof Env iron mental Qu ality 7 :246-252. Kari c khoff, S . W., D. S. Brown, and T. A. Scott. 1979. Sorpt ion of hy drophobic pollutant s on natura l s edi m ent s. Wat er Res ear ch 13 :241-248. Landrum, P . F. , S. R. Nihart, B. J. Eadi e, and W. S. Gardne r. 1984. R ever se-pha se separation m et hod for de te rm ining pollutant binding to Aldri ch humic ac id a nd dis sol ved organi c c arbon of natura l wate rs. Envir onm ent alSci ence andTechn olo gy 18 :187-192. Lao r , Y., andM. Rebhun . 199 7. Co mplexatio n- floc culatio n: A new method to determine b ind ing coef ficien ts of o rg anic cont amina

nts to disso lvedhumi c s ubst ance s. Environment al Scien ce andTechn olo gy 31 :3558-3564. Me y l an, W. M ., P. H. How ard , R
. S. B oe thl i ng , D. Ar on so n, H. Pri ntup, and S. Go uchie. 1999. I m proved m et

hod for estim ating bi oconce ntrati on/bi oacc umul at ion f act or from oct anol/water pa rtition co eff icie nt. Envir onm ent al Tox icolo gy an d Ch emistry 18 :664-672. More l, F. M . M. , and P. M. Gschwe nd. 1987. The role of col loi ds in thepartitioning of s olut es innat uralwat ers. Page s 405-422 in W. Stum m , e dit or. Aquatic Surfa ce Chemis try

-- C hemic alProc ess es at thePar ti cl e-Wate r Inte rfac e. John Wil ey& Sons , New York. Seth , R ., D. M a c kay , and J
. Munc ke
. 19 99
. Es t i m at i ngthe organi c c arbon parti ti on coe fficient and i ts vari abi li ty for hydrophobi c c hemic al s. E nvironm entalSci enceand Tech no log y 33 :2390-2394. St umm , W
. , an dJ
. J
. M o r g an . 1 9 7 0
. A qu at i c C h e m i s try : An Intr oduct ion E m

phasi zi ng Che m ic alEqui libria in Nat ural Waters . Wil ey -Int ersc ie nce, New York. Til le r, C . L. , and K. D. Jone s. 1997. Effe ct s of dis sol ved oxy gen
oc and l i ght e xp os ur e o n de t e rmi nat i ono f K va lue s fo r PA Hs usi ng fluoresc enceque nching. Environm ent alSci enceand Tech no log y 31 :424-429. Wea st , R
. C., e dit or. 1971. Handbook of Che m is try and Phys ic s. 51st edi ti on. TheChe m ic alRubbe r Co. , C le vel and, Ohio. 

### 2. 3 Ki ne ticPr oc ess es “Ki net ic ” proc ess es, unlike ra pid ( loc al ) equi librium

proce sse s such as ioni zation a

nd sorption, occur

on ti m e s cal es that m ake the ir ti m e-dependent

behavior of di rec t conce rn i n a hazard evaluat ion. (Very

sl ow proce sse s, at t

he fur therext

rem e of the tempor al spectrum, ar e u sua lly treatedby modeler s as abs olute const ant s. F or exam

ple , change s in t

he emis si on of l ight

by the sun (t he s olar “c onst ant ”) are us ual ly m odel ed only

by astro ph ysicists.) The kinetics of the trans po rt regime in aqu atic sys te m s, and thekine tic s of the tr ansfor m at ion proces ses that degra de a

che m ic alto innoc uous form s, are the pri m ary constit uent s of EXAMS ’ eva luati ve c apabi li ti es. 

### 2. 3. 1 T ra ns po rt EXAMS ca lc ulate s st eady -st at e avera ge t ranspor t of wat er, sedim ent s, a

ndplankton ic org anisms thr ou gh ou t the sys te m . The flows of wate r, s edi m ent s, and plankton act a s sim ple carri ers for the dis sol ved, sedi m ent -sorbe d, DOC -com ple xed, and bi osorbed form s of the synthe ti c organic chemic al . Thes e car rie r flows are ultim at ely r educe d to coeffici ent s t hat expre ss t

he e ffec ts of transport proce sse s on the kinet ic s of the che m ic al ; t he ve ct or of conce ntrati ons of the synthe ti c organic che m ic alit sel f t hereby rem ai ns t he only t rue tim e-dependent

st at e varia

ble in EXAMS . A hydrol ogic sub-progr am was cre at ed for EXAMS in ord er to m ini m iz e t

he l abor nec ess aryto spec ify , or m odify , t he phy si cal transport se ct ion of EXAMS ’ env iron mental data base. This data bas e is comp o se d pr imarily of read ily availab le andeasily com prehe nded param et ers, such as the volum e, m ean dept h, and surfa ce are a of the sy st em compart m ent s. Any

of t hese param et ers c an be m odifi ed by theuse r as des ire d. EXAMS the n rec om pute s t he e xchange s of m at eri al s am ong com partm ent s, and t he ne t t ranspor t of m at eri al s t

hroug h th e sy st em , i n eff ect cre at i ngane w hy dr ol og i c m od e la c c or di ngt o t he us e r’s m odifi cations
. The hy drologi c proc edure operat es on thr ee sub-se ts of EXAMS ’ envi ronm ent aldat a ba se. The fir st is a desc ription of

the v o lumes of

wa te r en te r in g eac hzo n e o f

th e s ys te m fr o m external source s. T he s econd cate goriz es t he geom et

ry of the sy st em , and the proper

ti es and di stribution of

biom ass and sedi m ent s. T he third sub-s et

cont ai ns st

ruct uralpr op ertie s of the ec osys te m it sel f. T his la st

(varia ble s JFRAD , JTURB , e tc.) sp ecif ie s t he dire ct ion and st

rengt h of t he flow pat

hways int erc onnecting t

he syst em com partm ent s. T he fl ow of wate r t hrough t he s yst em com partm ent s i s c ompu ted from a m ass bal anceon wat er enter ing andleavin g eachsegment. EXAMS ’ fl ow pat

hways can be spec ifi ed via advective or dis persive e quat ions , or both. (Advection i s li ke a fre ight tr ai n, dis persi on is them acr o-sca le ana logue of di ffusi on, operating li ke a drunken wal k.) The program uses conve nti onalequati ons for bot h proce sse s. F or compartm ent s of const ant volum e, the law o f con serv ationof m ass demand s that the hydro log ic inpu ts to a c om part m e nt beba l anc e d b ya dv e c t e d f l ow s l e avi ngthe20 com partme nt. The e xpress ion us ed for dis persive or turbul ent exchanges acr oss c om

partment boundari es is , a s usua l, ( DS P × XSTUR /

CHARL ) where XSTUR

is thecros s-se ct iona l a

rea of t he exchange boundary (in squarem et ers) , CHARLis the “charac te ris ti c l engt

h” (m et ers) along t

he flow path (t

hat is , t he aver age leng th of the com partm ent s or the dis tance bet ween com partm ent ce nte rs, m eas ured a long the e xchangeaxi s), and DS P i s the e ddy dis persi on c oeffi ci ent ( squarem et ers/

hour). F or exam ple , in a sim

ple (t wo surfa ce wat er c om

partm ent s) m odel of a s trat i fi e d l ake , when XSTUR is theare a of the the rm ocl ine and C HA RL is one -h alf the mean d epthof the lake, th is expre ssi on describe s therateof exc hange of wat er be twe en t he epi li mnion a

nd hypol im

nion.
EXAMS al so c om

pute s sediment

tr ans po rt via

thegene ral advec ti ve and dis persive e quat ions , but an addi ti onalse t of transport rul es is supe rim

posed on these dim ent

equati ons. F or ex amp le , anadv ec ti v e p ath w aybe tw ee nwa te r co lumn compartments is permitted to carry alo ng susp end ed sed iments (and pl ankt on) from

one com partm ent to the next. An adve ct ive pat hway from

thewat er c olum

n into a bent

hic se dim ent

is not al lowe d to c arry

partic ulate m atte r wi th i t, however: Thi s kind of pat hway i s rese rved for wat er se epageint o the sedi m ent (al ong wi th d i ss ol ve d and DOC -co mplexed ch em ic al s), and ground-wat er r echarge l eaving thesy stem . These dim ent transport rul es give EXAMS the abi li ty to inc lude ri veri ne sedi m ent wash- loa ds and bed-l oads, groundwater seepageand rec harge , and com

ple x exc hanges bet

ween the wat er c olum

n a nd bent hic se dim ent deposi ts dri ven by phys ic aland biol ogic al proce sse s dominant in non-fluvia l s yst em s. EXAMS does not expl ic itly repr ese nt s equenti aldepos ition a nd scour of benthi c sedim ent zones, nor does it

all ow in m ost

ca ses for a se cul ar a ccum

ulati on of bottom

se dim ent s wit

h cons equent buria l of sorbe d che m ic al s. I n one sense, thi s l imit s EXAMS ’ uti li ty in evaluat ive sa fet

y investigati ons. F or exam ple , run-of-t he-ri ver f lood c ontrolres ervoi rs are very comm on in t

he USA, and ma

ny of the m

rapidly ac cum

ulate sedi m ent s and bury chemicals in th eir dep ths. The b otto ms of many, if not most, fre e-f low ing river s andlargerlakes accumulate sediments quite sl owly , howeve r. In addi ti on, t he s ynt het ic che m ical s c apt

ured by be nthi c s edi m ent s proba bly arefre quent ly

re- expose d to the overlyi ng wat er column vi a wate r t urbule nce, phys ic al dis turbance by de m ersa l f is hes, and the int erna l s tirring of sedi m ent s by

bent hic org ani sm s (biot

urbation). EXAMS the refore tre at s be nthi c s edi m ent s a s bottom zonecom

partm ent s wi th a fixe d vo lume, sub

ject to co ntinual (alb eit slow ) exc han ges with the ov e rly i ngwat e r c olum n. At l e a st f or e va luat i onand scre eni ng purpose s, i t seem ed unwi se to s uppose that burie d synt het ic che m ic al s wi llneve r re appear. Where appr opriate, ho wever, ne t s edi m ent at ion a nd buri alof synt het ic che m ic al s c an berea dily e valuat ed, for t he buri al proce ss c an berepr ese nte d via a first -order dis appearanc e of the com pound from

bent hic sedi m ent s. For exam

ple , gi ven an ac ti ve sedi m ent dept h of 10 cm , and a n et buri alof 1 mm /yr, t he l oss coef fic ie nt f or a synt het ic com pound in the se dim ent

would be 0.1/10 = 0.01 /yr wi th a hal f-l ifeof 69 yea rs. This approa ch shoul d, howeve r, only beuse d when t he be nthi c z one i s m odel ed as a s ingl e s edi m ent

la ye r. EXAMS was desi gned for eva luati ve purpos es, rat her t han for de t a i l e d s i t e -s pe c i fi c a

pp l i c at i on s. F or

thi s re a so n, EX AMS ’ transport al gorit hm s wer e wri tt en in a verygene ral fo rm that uses an input

des cription of the transport condi ti ons in the sys te m , rathe r than att em

pting t o c om

pute hy draul ic s and sol ids transport from fi rst pri nciple s. S ever alca

uti ons t o theuse r def inin g anecosys tem for e ntry to th e p ro gr am are theref or e in order. Firs t, beca

use EXAMS i s a

c om partm ent m odel , t he represe ntati on of adve ct ed fl ows necessarily introduc es som e num eri cal disp ersio n into the comp u tatio ns. Altho ug h this p ose s little proble m for ge nera l e valuat ions , i t shoul d berec ogniz ed t hat the concentrations co mputedby the pr og ram fora particu la r l ocation are to a d eg r ee dep end ent onthe spa tial reso lutionusedto repre sent thesy st em . For exam

ple , EXAMS com

pute s t he avera ge conce ntrati ons in a rive r re ach, rat her t han t he de ta il s of the (u sually dec rea si ng) profi le of c oncent rations within therea ch. As t he num ber of com partm ent s use d to desc ribetherea ch incr eases , the co mpartmentalizedrepr esen tatio n be gin s to app ro ach th e m or e detailed pro file pred ictable fro m an analytic soluti on to the governing partia l di ffere nti alequations. In gener al , for si te -spec ifi c a ppli cations , sim

pli fie d tr ansport rep rese ntatio ns canbe adju sted o r “calib rated ” to more faith fu lly dep ict trans po rt detai l, v ia initial matchin g of pro gr am outpu ts to a con serv ative tra ce rsub stanc e. Chlo ride con centr ationis ofte n use d as a cal ibrati on tracer in e st uari es; te m

peratureand diss olv eds ubstan ces canbe us ed fo r calibr ationstud ies in la cust rinesyst em s. Of

cours e, if desired, EXAMS c ould be l oaded via an analysi s of the output s of det ai le d hydr aul ic and sedi m ent transport m odel s. Sec ondly , EXAMS does not im pose a segm ent -by-s egm ent m ass bal anceon t

he s oli d phas es (sedim ent s and biot a) t hat tr ansport sorbed chemic al s t

hrough t he s yst em . In m ost

ins tances , sedi m ent (det rit alm at erial s), “di ssolved” organi c m atte r, and b io taar e s ub

j ec t to si g n if

ic an t cr eati o nan dde str

u ct io ninso me are as of aquati c systems, so t hat , unl ike wat er, the se quant itie s cannot be tre at ed a s sim

ple m ass-conse rvative entitie s in a gener al iz ed a lgori thm . Thus , for exam ple , m ass balances for suspe nded sedim ent s in EXAMS are l eft to the use r’s di scre ti on. The EXAMS pro gr am, how ever , do es no t permit a failure to con serv e sedim ent

m ass to perturb the mass balan ce fo r synth etic organi c c hemic al s. Exchanges wit

h se dim ent

beds aredes cribed prim ari ly via a dis persive exchange t erm (Cha pte r 2.3. 1.4). This approa ch involves a s tati st ic alsum m aryof t he m ultitude o f phy si caland bio log ical trans po rt mec h anisms that h ave n ot bee n fu lly21 char act eri zed in t

he l it erature . I t has dis advant ages in that t he appropri at e m agni tude s for the input param et ers (e.g. , DS P ) ar e only approxim at ely know n. The m agni tude s of the des cripti ve param et ers neede d for a

m ore m echanis ti c c hara ct eri zation of the se m ultipl e phy si caland biol ogicaltr ansport pat hways are , however, stil l l ess perf

ectly known. In gene ral , t

he s ensi ti vit

y of EXAMS ’ out

puts to vari at ion in se dim ent -wat er c olum n e xchange par am et ers shoul d probably beroutine ly exam ine d, at l eas t f

or ext ensi vely s orbed c om

pounds. 2.3.1.1 Hydrol ogy and advect ion Hydrol ogic input s are s peci fie d in EXAMS ’ env iron mental data bas e via fo urvariab les: ST FLO (st ream fl ow), NPSFLO (non-p oint-s ource fl ow), SE EP S (ground-wate r i nflows ), and RAIN (ra infa ll ). Aft er s ubtra ct ing e vaporati ve wate r l osse s ( EVAP ), t he s um of t hesete rm s is t

he tot alwate r flow ent eri ng a com partm ent from ext erna l s ource s. EXAMS adds to t his sum the advec te d fl ows ent eri ng the com partm ent via othe r com partm ent s in thesy st em . Thi s grand sum is t he t ota l am ount of wat er a dvect ed into the c om partm ent from al l ( int erna l a

nd ext ernal) source s c om

bin ed. The to tal adv ective f lowthrough the com partm ent is the n dis tribute d am ong thefl ow pat hs spe ci fie d for t hat com partm ent in the JFRAD and ITOAD struc tura l ve ct ors. Three of the hydrol ogic input vari abl es ( STFLO , NPSFLO , and SE EP S ) ar e ve ct ors t

hat inc lude a separat e e ntry for e ach com partm ent of t he a quat ic sy st em

des cribed by the dat a ba se. The STFLO vect or is used to e nte r poi nt s ource s, t ribut aryfl ows, stream flows ent eri ng a lake, and t he di scharge e nte ring the upperm ost

rea ch of a river s yst em . The NPSFLO s are use d to ent er non- po int-f

lows and ove rland runoff flowing into the com partm ent s. G ro und- wat er s eepa ge or subsurf acefl ows ar e enter ed vi a SE EP S . STFLO , NPSFLO , and SE EP S a l lh ave unit s of cubi c m et ers per hour; EX AMS allows each co mpartment to receiv e an en try fro m each catego ry. Th es e hydro log ic inpu ts can in a ddition bespe ci fie d for e ach m onth of theye ar. Rai nf all ( RAIN ) i s a

sc al ar varia

ble in EXAMS , t

hat is , t he envi ronm ent aldes criptor is a singl e (m onthly) value rathe r t han a c ompart m ent -speci fic vec tor. RAIN has unit s of m il li m et er/

m onth. EXAMS con verts this clim atolo gical d atum to a volum e of wat er e nte ring eac h com partm ent having an ai r-wat er inte rfac e. EXAMS detects the air-wat er inte rfac e, and decide s whet

her t o admit

rainfal l into t

he c om partm ent , ba sed up onthe stru ctur e of th e sy st em. Ra infa ll is not permitted to e nt e r c om

part m e nt t ypes ( TYP E ) “ B ” (be nt hi c ) or “ H” (hypol im nion). The deci si on m echanis m for L (it tora l) and E(pi li mnion) com

partm ent s i s m ore c om ple x. For the se com partm ent ty pes, EXAMS checks thecom partm ent num bere d one l ess tha

n thecom partm ent under consi derati on (t

hat is , i f t he curre nt c om

partm ent is J, thedeci si on is bas ed on t he prope rti es of com partm ent (J-1) )
. If the pr ece ding com partm ent i s anothe r el em ent of t he wate r column, ra infa lli s not al lowe d t o e nte r t he curren t (Jth) compartment. At fir st glan ce, this decisio n seems triv ial: a f te r all, rainonly fal ls on the wat er s urfac e, the reforeonly the se com

partm ent s c an rec ei ve ra infa ll . Theprobl em is com plicated, howe ver, by t

he fact tha t EXAMS was d esign ed to allo w a us er to in te r ac ti v ely m od i fy any vari abl e i n t

he e nv i ro nm e nt a ldat aba se . EXAMS the reforem

ust be able to dete ct

any change in thesy st em struct ure and ac curate ly

rec om pute , i n thi s c ase, a ne w hydrol ogic r egi m e. Change s in sy st em st ruct ure a ffec t a

num ber of ot her pr oces ses as wel l. For e xam ple , i n com

puting vertic al li ght e xtinct ion t

hrough the wate r column, EXAMS det ect s t he t op of t he watercolumn, c om pute theli ght l evel s in ea ch su c c e ss i ve ly

de epe r wat e r- column com partm ent , and the n res tart the com putati on for e ach adjac ent vertic alse ct ion. The prob le m , t

hen, is som ewhat

m ore ge nera l t

han i t f irs t appears, and is not

e ntirely trivia l: the t

hree -dim ensi onal struct ure of thesy st em

m ust be decode d as an im

pli ci t f unct ion of t he input e nvironm ent aldat a. The de coded struct ure t hen serve s as a gui de for

com puting thekine ti cs of t

he t ranspor t a nd transform at ion proces ses . The decoding proble m coul d, of course, be eliminated b y requ iring that the en viro nmental da ta inclu de a more co mplete set o f s tru ctur al descr ipto rs. T his approa ch, however, le aves the u ser inthe un comfo rtab le pos ition of having to mem or ize a larg e set of arbitrary, m od el- sp ec if

ic com partm ent des criptors of l ittl e intrinsi c inte rest
. EXAMS ins te ad re li es on a

s et of s im ple c onvent ions for num

beri ng and n ami n g th e c o mp artme nts us edto de sc r ib e anaqu at ic sy st em. Thes e c onvent ions can be st at ed a s 4 de fini ti on rul es: (1) Com partm ent s c an benam ed ( TY PE ) ei the r “L” (l ittora l), “E” (epi li mnion), “H” (hy

poli mnion), or “B”(bent

hic ). Thes e nam es car ry the ir usualim

pli cations : an “H” c om

partm ent la cks an ai r-wat er inte rfac e, a “ B” com partm ent is a bott om

se dim ent , e tc
. A ll sy st em z o n e s c anbe en te r edas ve rti ca l s ta ck s o f th e s ame TY PEforadd ed sp atial detail. (2) Com partm ent numbe r 1 mus t be par

t of a wat er c olum

n and m ust be of TY PE“E”or “ L”. (3) E ach vertic als egm ent m ust benum bere d in inc rea si ng order withincrea sing dep th. Th at is, wh ena vertical se gment is divi ded into, say , 4 c om

partm ent s, if the topmost com partm ent is num bere d 5, t he bottom

com partm ent wil l benum

ber 8. (4) E veryvertic alse gm ent m ust te rm inate in at

le ast one bott om sed iment (“B”) co mpartment. EXAMS ’ com

putati ons are s om ewhat

m ore e ffi ci ent

if one m ore ruleis obse rved: (5) Ve rti calbloc ks of com partm ent s are arrange d, and numb er ed , a lo n g th e ma inadv ec ti v e f lo wpa th s i nth e s ys te m. EXAMS ’ i nte rnaldec oding of the ( im pli ed) s yst em

st ruct ure t hus avoi ds t he probl em

of m ultipl e m odel -spec ifi c param eters, but22

Fi gu r e 1. I m pr op er s eg m en t at i on a nd nu m be r i ng : c om pa r t m en t nu m be r 1 i s ( B) en t hi c, be nt hi c se di m en t s ar e i nc om pl et e, a nd nu m be r i ng i s ho r i z on t al l y r at he r t ha n v er t i ca l l y or ga ni z ed .

F ig u r e 2 . P r o p e r s e g m e n ta tio n : ve r tic a lly o r g a n iz e d n u m b e r in g , a ll v er t i ca l s eg m en t s i nc l ud e a bo t t om s ed i m en t , a nd c om pa r t m en t n u m b e r 1 is o f s u rfa c e w a te r typ e (“ L ” o r “ E ” ). CMPT STFLO AREA EVAP VOL DEPTH 1 10 1000 146.1 2000 2 3 10 800 146.1 1600 2 5 200 146.1 400 2 7 1000 146.1 2000 2 Ta bl e 2. Hy dr ol og i c i np ut da t a f or Nona m e Sl ou gh at some cost: EXAMS must assume that the userhas scrup ulo usly adh eredto these rules . Supp ose , fo r example, that a 10 -mile stretch of ri ver we re de scribed a s 10 s ucce ssi ve “ L” compartments, andthe ben thic sed iments were omitted: EXAMS w o u ldsup p o se th e s ys te m to b e a v erti ca l, 10

- mile

- d ee p co lumn of wate r. Aga in, shoul d a surfa ce- wat er c om partm ent be desi gnat ed “ H”, EXAMS will no t allow rainto fa ll, no r che micals to volati li ze, f

rom t he c om partm ent . Exam

ple s of im proper and proper segm ent at ions of a sm al l rive r and la

ke s yst em aregive n in Figu re 1 and Figu re 2
.

EXAMS ’ fi nal hydr ologi cal input quant it y is a com partm ent -spec ifi c ve ct or of monthly eva porative wat er l oss rat es, EVAP , wi th uni ts (mil li m et er/ m onth). A value of EVAP can be en teredforany compartment, bu t EXAMS ignor es ina ppropri ate en trie s, t

hat is , e vaporati on is al lowe d only for com partm ent s wi th a

n air-wat er inte rfac e. EXAMS can be operate d wit h very gene ralized de scripti ons of aqu atic systems typical of b r o ad g eog rap hic reg ion s, orwith m ore de ta il ed de scripti ons of partic ular sites and loca le s. T he mechanic s of EXAMS ’ trans po rt c om put at i on s c an be stbe appre ci at ed vi a a

spe ci fic exam

ple . Thi s e xam

ple w illbe dev elop ed in so me (site-sp ecific) detai l, so as to illustra te m et hods for preparing envi ronm ent aldat a for EXAMS , computationa l m echanic s, and therangeof t ranspor t proces ses th atcanbe ac co mmo d at edbyth e p r o g r am. 2.3.1.2 Advect ed w aterfl ows EXAMS ’ adve ct ive fl ow com putati ons are a

dir ect appl ic at ion of the l aw of conse rvation of m ass . Bec ausec hanges in storage volum es are not permitte d in M odes 1-3, t he t ota l inputs to eac h com partm ent m ust be bal ance d by advected out flows . The advec ti ve t

ranspor t r egi m e t hus c an bec om

pute d by im

posi ng a wat er ( m ass ) bala

nce on t he hy drologi c inputs to the sy st em . The logi c of the se com

putati ons can be st

be see n within thecont ext of a spec ifi c e xam

ple : Figu re 3 is a 9-co mp artme nt model o f a po rtionof a slo wly movin g slo ug h orriversystem. Ups tream disch arg e into com partm e nt 1 i s 10 c ub i c m e t e rs /h. T he f l owi s sp l i t

b y an islandinto co mpartments 3 an d 5; 7 5% of th e f lo w go es to com partm ent 3, theremai nder t o com

partm ent 5. C om partm ent 3 also receiv es a tribu tary disc har ge o f an ad ditio n al 10 cubic m et e rs /ho ur . Ea c h se gm e nt i s 10 0 m l on g and 2 m d e e p. The se g men t w idth s ar e 1 0 m fo r 1 an d7 , b ut c o mp artme nt 3 is 8 m, and c om partm ent 5 i s 2 m , wide . Therat e of evapor at ive wat er los s ( EVAP ) i s 146.1 mm

/m o for al l s egm ent s; no ra in f al ls on t he sys te m . EXAMS ’ hy drologi c input data , thus far, l ooks li ke t his :

EXAMS now conve rts STFLO and EV AP (using AREA ) t o thenet li t e rs /ho ur

e nt e ringe a c h c om

pa rt m e nt f ro m e xt e rn a ls ourc es (WATINL), and sum s t

he t ota l avai la

ble fl ow (TOTIN) , arri ving at thehydr ologi c analysi s shown in Tabl e 3
.23

Fi gu r e 3. Ni ne - co m pa r t m en t m od el ofNona m e Sl ou gh .

CMPT STRMFL EVAPL WATINL 1 10,000 200 9,800 3 10,000 160 9,840 5 0 40

! 40 7 0 200

! 200 TOTIN 19,400 Ta bl e 3. A dv ec t i v e i np ut s t o Nona m e Sl ou gh

Name of environment: Noname Slough - Advection Test Data Total number of segments (KOUNT) = 9 Segment Number: 1 2 3 4 5 6 7 8 9 Segment "TYPE": L B L B L B L B B

--------------------------------------------------------------- Table 9. Input specifications -- advective transport field.

--------------------------------------------------------------- J FR AD 1 1 3 5 7 I TO AD 3 5 7 7 0 ADV PR 0.750 0.250 1.00 1.00 1.00 Path No.: 1 2 3 4 5

--------------------------------------------------------------- E x a ms O u t p u t T a b l e 1 . P a r t i a l a d v e c t i v e s t r u c t u r e o fN o n a me Sl ou gh . JFRAD WATFL TOTIN 1 3 5 7 I T O A D 1 1.00 0.0 0.0 0.0 0.505155 3 -0.75 1.0 0.0 0.0 0.507216 5 -0.25 0.0 1.0 0.0 -0.002062 7 0.00 -1.0 -1.0 1.0 -0.010309 Ta bl e 4. Nor m al i z ed c oe f f i ci en t m at r i x, a dv ec t i on e qu at i on s The s truc tureof the a dvective f low f ie ld i s gi ven by

param et ers JFRAD , ITOAD , and AD VP R . The se nam es are ac ronym s for J FRom ADvect ion ( JFRAD ), I TO ADvec ti on ( ITOAD ), and ADvection P Roportion ( AD VP R), respe ct ive ly. Ve ct or JFRAD is the li st of t he s ourcecom

partm ent s fo r ea ch fl ow. The corre spondi ng m em

ber of ITOAD hold s the num ber of the com partm ent rec ei ving t

he fl ow, and AD VP R

give s t he fraction of the to tal flowthro ug h co mpartment JFRAD that f oll ows t he pat h to ITOAD . A z ero (0) e ntered in ITOAD denot es an e xport from thesy st em . EXAMS ’ report o f th e (parti al ) st ruct ure given for t he s lough s yst em

in Figu re 3 wou ld app ear as inExa ms Output Tabl e 1. EXAMS now com bine s the inform at ion giv en in Tabl e 3 and Exam s Out

put T abl e 1 int o a set

of inpu t/ou tput equations refl ecting t

he conse rvation of wat er m ass in the sy st em . Taking X(I) to denot e thetot aloutput fl ow from

com partm ent (I), the se equations can be writte n as : OUT PUT = SUMOF IN PUT S X( 1) = 9 800 X( 3) = 9 840 + 0. 75 X(1 ) X( 5) = -40 + 0. 25 X(1 ) X( 7) = -20 0 + 1. 00 X(3 ) + 1. 0 X (5) This is a set

of 4 si m ult aneous equati ons in 4 unknowns; it can be solv ed by succes sive eliminationof terms in the us u al way. Inthis case, it is easy to see that: X(1 ) = 98 00 X(3 ) = 98 40 + 0 .75 (98 00) = 171 90 X(5 ) = - 40 + 0 .25 (98 00) = 24 10 X(7 ) = -2 00 + 1 719 0 + 24 10 = 194 00
EXAMS was writte n to acc omm odat e N e quat ions in N unknowns. In othe r words, the pr ogram s olve s t he input/ output advec ti ve e quat ions for an arbi trary num ber (N) of com partm ent s, any of

whic h can rec eive, del ive r, or exchange advec te d fl ows wi th any

or allof the other com

partm ent s in the sys te m . TheN input/ output equati ons are s olve d by a Ga ussi an el imin at io nalg o r ithm (Stu art 1 97 0:3 04 -3 11 ) . This algor ithm is a m at rix soluti on of a

norm al ized form

of t he input/ output equ ation s. Th e matrix (A MAT ) is load ed in three stage s: Firs t, eac h va lue of

WATINL i s di vide d (norm al iz ed) by TOTIN, and loa ded on the (N+1) column of AMAT. Next , t he c oeffi ci ent s on the output

(X) t erm s (whi ch are a lways unit y (1)) ar e loa ded on the dia gonalof AM AT. Final ly , t he AD VP R values are ent ere d into AMA T witha rowindex givenby ITOAD an da co lumn ind ex giv en b y JFRAD . (T he s yst em export te rm s ( ITOAD = 0) are not r equi red f

or t his part of t

he analysi s.) Leaving a si de No name Slou gh ’s be nth ic compartments, the co eff icient matrix would be( Tabl e 4 ):

The s olution of

thi s sy st em

of e quat ions is :24 JF RAD 1 3 5 7 I T O A D 1 0 0 0 0 3 7350 0 0 0 5 2450 0 0 0 7 0 17190 2410 0 WATOUL 0 0 0 19400 Ta bl e 5. Exa m pl e W A TF L m at r i x an d W A TOU L v ec t or ( L/ h) CHEMICAL: Unspecified Chemical ECOSYSTEM: Noname Slough - Advection test data

------------------------------------------------------------------------ TABLE . TRANSPORT PROFILE OF ECOSYSTEM.

------------------------------------------------------------------------ CP T* VOLUME SEDIMENT WATER FLOW SED. FLOW RESIDENCE TIME (DAYS) Y (CUBIC M) MASS (KG) (CU. M/DAY) (KG/DAY) WATER SEDIMENTS

------------------------------------------------------------------------ 1L 2.0000E+03 235. 8.50 2B 3L 1.600E+03 413. 3.88 4B 5L 400. 57.8 6.92 6B 7L 2.000E+03 466. 4.30 8B 9B

------------------------------------------------------------------------ * COMP. TYPE: “L”=LITTORAL; “E”=(EPI) AND “H”=(HYPO)LIMNION; “B”=BENTHIC Exa m s O ut pu t Ta bl e 2. Par t i al t r an sp or t pr of i l e f or Nona m e Sl ou gh .

( 2- 63) ( 2- 62) X(1) = 0.505155 X(3) = 0.886082 X(5) = 0.124227 X(7) = 1.000000 where “X” is now the frac ti on of TOTIN passing through ea ch compartment. For e ach com

partm ent , EXAMS com

pute s t he a ct ualdis charges al ong eac h f

l owpath a s the pr od

uc t of X, T OT IN , and

the AD VP R forthe path way. This in fo rmation is enter ed in a matrix ( W A TF L) of

fl o w s amo n g s eg men ts . T h e r o wan dco lumn indi ces of WATFL are t

he s am e a s t

hose of AMAT, that is , t

he WATFL indi ces givethesource and des tinat ion c om partm ent num ber f or ea ch fl ow. Export s from the system

(i n li te rs pe r hour) are e nte red int o a

ve ct or (WATOUL) of export s from ea ch com partm ent . Theexport s from ea ch ( JFRAD ) com

partm ent are com pute d as theproduct

of X, TOTIN, and AD VP R fo r those pat hways having ITOAD = 0. In t he Nonam e Sl ough example, thedis charges from se gm ent num ber 1 are : WATFL(3,1) =(0.505155)( 19400)(0.75) = 7350, and WATFL(5,1) =(0.505155)( 19400)(0.25) = 2450. The only n on -zer o ou tlet flowis WATOUL(7) = (1. 0)(19400)(1.0) = 19400. The WATFL m at

rix and t he WATOUL vec tor for the se sec ti ons of Nonam e Sl ough areshown in Table5
. EXAMS ’ ou tputs inc lude a “t

ranspor t profil e” of the s yst em , showing theadve ct ed flows through ea ch segme nt. EXAMS also co mputes a (lo cal) turnove r or “ wat er r enewa l” ti me (the volum e/ dis charge rati o) for e ach compar

tm ent
. EXAMS ’ tr an sp o rt p r o f il e f o r No n ame Slough, as defined t

hus far, i s gi ven in Exam s Out put T abl e 2. 2.3.1.3 Advect ivese dim ent trans port

Sedi m ent arym at eri al s (de tri tus ) can be produce d and dest roye d bioge nic al ly

wit hin a n aquatic ec osys te m . Se dim ent tr ansport thus is not com

pute d in EXAMS via

thesi m ple mass bal ance const rai nts use d to com

pute thetr ansport

of a dvect ed wat er m ass es. EXAMS i ns t e a d t re at s a dv e c t e d s e di m e nt as a non-conse rvative subst ancewhose transport is si m ply driven by the hydr odynam ic s of the sy st em . The p oint- ( STFLO ) and non-point - (NPSFLO ) external hydro log ic inpu ts do co ntain coupl ed s edi m ent

loa ds ( STSED and NP SED , kg/ h). T hese vari abl es are use d t o e valuat e the che m ic alloa dings (se e C hapt er 2.4); the y do not e nte r t

he c hemic altr ansport

equati ons. EXAMS c om

pute s advec ti ve sedi m ent

t ranspor t a s t he produc t of the rate s of w ater tran sp o rt andthe sed iment/waterratio (SEDCOL , Eq. (2-2 1) ) of the s ource com partm ent s. WATFL and WATOUL ar e us ed t o loa d an anal ogous se dim ent fl ow m at rix (SEDFL) and export vector (SEDOUL), both having unit s of kg sedim ent

tr ansport ed pe r hour. The e quat ion f or advec ti ve s edi m ent

tr ansport am ong com

partm ent s i s (2-62) :

andthe equ ationforadv ectedsediment expo rt is

Th es e equ at io n s ar e n o t bl in d lyex ec ute dfo r the enti r e s y st em, however: The exec uti on of the se dim ent tr ansport

equati ons (Eqs. (2- 62 ) and (2-63)) i s c onstrai ned by a seri es of spe ci al con ditions, whic h can be expre sse d as a set of 5 sedi m ent transport rul es: ( 1 ) A nadv ec te d

wa te r mas s l eav in g any w at erco lumn com part m ent ca rri es an entraine d se dim ent w ashl oad, unle ss the fl ow ent ers a b enthic c om partm ent . A fl ow from

the wat er c olum

n into a be nthi c sedi m ent

is an infi lt

ration f low that doe s not

tr ansport se dim ent s.25 Fi gu r e 4. Nona m e Sl ou gh be dl oa d, w as hl oa d, a nd gr oundw at er f l ow s. (2) B e nt hi c s e di m e nt

( “ B ” ) c om

part m e nt s c an a l way s e xp ort wateracro ss syste m b o und aries, andcan advect w ater to an y o th erco mp artme nt inth e s ys te m. (3 ) Aben thic co mpartment can expo rt sed iment (in ad ditionto wat er) only

when i t occupie s t

he s edi m ent -wat er inte rfac e (that i s, t he (J -1) c om

partm ent is not of TY PE“B ”). (4 ) S ediment canno t be adv ectedfro m a ben thic co mpartment to anyel em ent

of t he wate r column. (5) When be nthi c c om

partm ent s are not verti cal ly adja cent (ac tua lly, when t

hei r com partm ent num bers differby 2 or m ore), se dim ent s c an beadve ct ed fr om one to a nothe r (for exam ple , a long a

bedl oad t ranspor t path). Th e ses e di m e nt

trans po rt r ul e s a l l ow EXAMS to inc lude se dim ent was hlo ads andbed load s, andseep age of gr oundwaterbothinto and out of the sy st em . One addi ti onalsystem definition r

ule m ust be o bse rv ed, how ever , wh en a gr oundwaterrech arg e is po rtraye d: The gro un dw ater fl o wp ath must inclu de at least 2 vertical ben thic sed iment compartments . If th is def initionrule is ignore d, EXAMS will interp ret the exp ort flowleavin g the b enth ic com partm ent as a bedl oad (rul e 3) rat

her than as a groundwat er rec harge
. Thes e c oncept s can be il lus trate d by expanding thedefinition of Nonam e Sl ou gh . In the expande d definition of Figu re 4 , one seg ment receives a gr oundwaterinput (SE EPS ) of 0. 2 cub ic meters/ho ur . The gro un dw ater see p pa sses th ro ug h be nth ic com partm ent 6 and is a dvect ed int o t

he overlyi ng wat er ( rule2); by r ule 4 t he wate r fl ow does not entrain a sedi m ent fl ow. The downstr eam

se gm ent (7) l oses wate r to a groundwat er r echarge. The infiltrati on fl ow is 2% of the tot aladve ct ed flow t hrough compartm ent

7 ( AD VP R

=0. 02 ). B yr

ul e 1, the i nf

i l trat i ondo es not e ntra in t

he s uspende d s edi m ent s. The groundwat er r echarge mustbe carrie d onfro m compartment 8 into compartment 9 beforeit can be export ed fro m

thesy st em , howeve r, or EXAMS would inte rpret

theexport

as a bedl oad (r

ule 3) rathe r t

han a s a flow of w ater only (ru le 2). The b edlo ad p ath (co mpartment 2 to 4 to 8) , b y ru le 5 , carr ie s b o thw at eran ds ed ime nts do wn str eam. The be dloa d export

at com partm ent 8 i s e nabl ed unde r rul e 3. The wa shl oad (com

partm ent s 1 to 3, 5 t o 7) m oves through the system und er ru le 1; EXAMS com pute s thedownstre am

tr ansport of sus pended sedi m ent

from Eq. (2-62). To com ple te this exam

ple , som e a dditiona l propertie s of the sedi m ent s m

ust be spec ifi ed. Let , t

here fore , Nonam e Sl ough have a s uspende d sedi m ent concent ration (washl oad, SUSED ) of 100 ppm , and st

ream -borne sedi m ent

loa dings ( STSED (1) and (3)) of 1.0 kg/

h. (Not e t

hat thi s t reatm ent im po ses a m ass bal anceon su spe nded s edi m ent s.) Thedept h of t he s urfi ci al sed iments (co mpartments 2, 4, 6, and8) is 5 cm; each h as a bu lk den sity ( BULKD ) of

1 .2 g/cc, an d a water con tent ( PCTWA ) of 180%. Se gm ent

9 i s a 30 cm l ay er of sand wit h a bulk de nsi ty

of 1.95 g/ cc, and a wate r cont ent of 115%. The be dloa d is , of cour se, anot her m eas urabl e prope rty

of t he Slough. Suppose , for exam ple , t he m eas ured be dloa d le avi ng the downstr eam

se gm ent of t he Sl ough were100 kg/

h. The AD VP R for t he c rosse d inf

il trati on and bedl oad t

ranspor t t hrough com partm ent 8, and theupst

ream bedl oad inputs , c an be devel oped from

thi s dat um and an ass um ed sol ids bal ancefor t he sy st em. The sedi m ent

/wate r ratio for the s urfi ci als edi m ent s is 1.25 kg/l it er ( Eq. ( 2-2 2)); thewat er e xport ass oci at ed wi th t he bedl oad i s, t

here fore, (100)/ (1.25) =80 l it ers per hour = 0. 08 cubi c m et ers/

h. Thegroundwat er infiltrati on wa s give n as 2% of the ava il abl e di scharge pa ssing through se gm ent 7 ( Figu re 4 ). The t ota l se gm ent

7 discharge is 19.4 c ubic m /h ( Tabl e 5 ), plus the gro undwater

se ep e nte ring via

se gm ent 6 (Fi gure ) , or 19.6 cubi c m et ers/

hour. The 2% infi lt

ration is the refore(0.02)( 19.6) = 0.3 92 cub ic m/h, andthe total f lowthro ug h co mpartment 8 is 0.392 + 0.08 = 0.472 cubi c m /h. The AD VP R

for t he t hroughput of i nf i l trat e d w at e r i s the re fo re( 0. 39 2) / (0 .4 72 ) = 0. 83 ; the AD VP R for t he be dloa d is 0.17. Fina lly, presuming t

he be dloa d ori ginate s in equalm eas ure f rom the i nf lue nt f l ow s t o c om

part m e nt s 2 and

4, th e be dl oa d inf

l ow s to bot h se gm ent s are 0. 04 cubic mete rs of wat er pe r hour26

Name of environment: Noname Slough - Advection Test Data Total number of segments (KOUNT) = 9 Segment Number: 1 2 3 4 5 6 7 8 9 Segment "TYPE": L B L B L B L B B

--------------------------------------------------------------- Table 9. Input specifications -- advective transport field.

--------------------------------------------------------------- J FR AD 1 1 3 5 7 I TO AD 3 5 7 7 0 ADV PR 0.750 0.250 1.00 1.00 0.980 Path No.: 1 2 3 4 5 J FR AD 7 2 4 6 9 I TO AD 8 4 8 5 0 ADV PR 2.000E-02 1.00 1.00 1.00 1.00 Path No.: 6 7 8 9 10 J FR AD 8 8 I TO AD 9 0 ADV PR 0.830 0.170 Path No.: 11 12

--------------------------------------------------------------- E x a ms O u t p u t T a b l e 3 . F u l l a d v e c t i v e s t r u c t u r e o fN o n a me Sl ou gh .

CHEMICAL: Unspecified Chemical ECOSYSTEM: Noname Slough - Advective transport regime

------------------------------------------------------------------------ TRANSPORT PROFILE OF ECOSYSTEM.

------------------------------------------------------------------------ CP T* VOLUME SEDIMENT WATER FLOW SED. FLOW RESIDENCE TIME (DAYS) Y (CUBIC M) MASS (KG) (CU. M/DAY) (KG/DAY) WATER SEDIMENTS

------------------------------------------------------------------------ 1L 2.000E+03 200. 235. 23.5 8.50 8.50 2B 50.0 3.333E+04 0.960 1.200E+03 27.8 27.8 3L 1.600E+03 160. 413. 41.3 3.88 3.88 4B 40.0 2.667E+04 1.92 2.400E+03 11.1 11.1 5L 400. 40.0 62.6 6.26 6.39 6.39 6B 10.0 6.667E+03 4.80 0.000 1.11 7L 2.000E+03 200. 470. 46.1 4.25 4.34 8B 50.0 3.333E+04 11.3 2.407E+03 2.35 13.8 9B 300. 5.087E+05 9.40 0.000 8.12

------------------------------------------------------------------------ * COMP. TYPE: “L”=LITTORAL; “E”=(EPI) AND “H”=(HYPO)LIMNION; “B”=BENTHIC Exa m s O ut pu t Ta bl e 4. A dv ec t i v e t r an sp or t r eg i m e i n Nona m e Sl ou gh . ( STFLO (2) and (4)), wit

h a para ll else dim ent

loa d ( STSED ) of 50 kg/h. EXAMS ’ retr ieval o f the fu ll adve ctive sp ecificatio ns is sho wn in Exam s Out

put T abl e 3, and EXAMS ’ c om pute d advec ti ve “t

ranspor t profil e” is give n in Exam s Out put T abl e 4.

2.3.1.4 Disp ers ivetran sport The m ean advec te d fl ow is no t the only proce ss gove rning the transport of synt het ic c hemic al s in a quat ic sy st em s. Turbule nce and sh e ar fl owin ri ve rs , fo r e xam pl e , c om bi ne t o ge ne rat e a wid e spec trum o f meso -sca le advectiv e p ro cesse s. S imilarly, in stratifi ed l akes exc hange across t he t hermocl ine is dri ven by m ole cul ar di ffusi on, wi nd-induc ed mixing, storm surges , and int erna l waves and s eiches. The se m eso-s cal e proc ess es can usual ly bede sc ribe d v i aas t at i sti c a ls um m ary ( the di sp e rs i on equation) of t

heir effect s on t

he avera ge t

ranspor t of dis sol ved and e ntra ine d suspended subs tances (see , for exam ple , Fi sche r et al . 1979)
. EXAMS ’ envi ronm ent aldat a ba se inc lude s 5 ve ct ors that s peci fy the dir ection ( JTURB , ITURB ), and stre ngth ( DS P , XSTUR , CHARL ) of

disp ers iv e trans po rt path ways in an aquatic sys te m ; di spers ivi ty

can be vari ed by

m onth. The c orres ponding m embers of the JTURB and ITURB vec tors spe cify the p air of

compartments that are ex chan gin g materials via ea ch di spers ion pathway. For e xam ple , t he 4t h ent ry in t he vect ors coul d be used to s peci fy an e xchangebet ween com partments 7 and 10, by

se tting JTURB (4) =7, and ITURB (4) = 10. Bec ausedis persi on , u nlike a dvection, is a sym m et ric al proce ss, thi s pathwaycoul d al so be spe ci fie d as JTURB (4) =10 and ITURB (4) = 7. B oundarycondi ti ons (di spers ive exc hanges wit h theext erna l world) are specifi ed by a 0 se tting on ei the r vect or. In othe r words, the ve ct ors can spec ify a turbulent exchange of, for exam

ple , c om partm ent 10 (an em

baym ent), wit h an exte rnalrese rvoir , via ei the r ( JTURB = 10; ITURB =0) or ( JTURB = 0; ITURB =10). EXAMS c om pute s the boundary exchanges as a s im

ple dis pla cem ent

of c ontam inate d, by chemic al -free , wat er and sedi m ent s. Non-zer o chem ic al bo un dary cond itions are loadin gs, andthus wou ld inter fer e with EXAMS ’ es ti m at es of persi st ence(def ine d as thetim e t o cl eans e the sy st em

aft er a llloadings te rm inate ) i n Mode 1. Non-z ero (dis persive) c hemic alboundary conditions can if

des ire d be intro du c e d v i aan arti fi c i a lpo i nt -s ourc e or no n- po i nt -s ourc e advec ti ve input, coupl ed wi th a symm et ric aladve ct ive export from thecom partm ent , or via

a DRFLD (se e C hapt er 2. 4). The conve nti onaldispe rsi on equation us ed in EXAMS des cribes the rat e of e xchangeof envi ronm ent alvolum e a cross a boundary bet ween two c om

partm ent s. EXAMS ’ form

ula is : ( 2- 64) In thi s e quat ion, XSTUR

is t he cros s-se ct iona l a

rea of t he pathway (in squarem et ers) , CHARLis the“c hara ct eri st ic le ngth” of t he pat h (m), and DS P is th e d isper sioncoef ficien t or ed dy dif

fu sivity (squar e m et ers/

hour). F is the n a

f low of envi ronm ent alvolum e, withdimensio ns o f cub ic meters per h our. Equat io n(2- 64 ) is hom ologous wi th the m at hem at ic s of si m

ple Fi cki an m ole cul ar diff usi on. Thedis persi on equati on, howeve r, i s a st at is ti cal summ aryof t

he l arge -sca le eff

ect s of m eso-scal e a dvective proce sse s; it

is use d when t

he m eso-s cal e proc ess es are so com ple x or s poradi c t

hat a det ai le d t

reatm ent is int rac ta ble . The net res ult of t he m eso-sc al e proc ess es is si m il ar t o m ole cul ar diff usi on in that di ssolved constit uent s are trans porte d along the gradi ent s of conce ntrati on in the sy st em . Th e apparent rat e of trans po rt of m at e ri a ls fr om

are a s of hi gh , t o are a s of

l ow , conce nt rat i oni s m

uc h f a st e r than r at e s of

m ol e c ul ar di ff

us i on, however. For t

his rea son, t

he kinet ic param et er in Eq. (2-64) ( DS P ) i s usua lly cal le d a “di spers ion c oeffi ci ent ,” “t urbule nt diff usi vit y,”or “ eddydif

fusi vit y,”rat her t han a “di ffusi on” con stant (Bi rd et

al . 1960: 629) . The events de scribed by dis persi on are not ful ly

hom ologous wit

h Fi cki an di ffusi on, however, and the use of di spersi on te rm s t o depi ct che m ic al transport in sedim ent s requi res c are ful adj ustm ent for e ffec ts of porosi ty , t ortuos it

y, sorption, and i on exc hange (Be rner 1976)
.27 ( 2- 65) From the dis persi on equati on (2-64), EXAMS com pute s a flux of waterandsediments alo ng the path way sp ecifiedby JTURB and ITURB . Thefluxes bet

ween com

partm ent s are a dded t o the advec ti ve flows in m at

ric es WATFL and S EDFL , thereby com ple ting EXAMS ’ de sc ripti onof the s y st e m ’s i nt e rn a lfl ow field . The bound ary flu xes are adde d to the ap pr op riate elements of WATOUL and S ED OUL; t he e xchangebri ngs in a repl ace m ent

volum e of uncont aminate d wat er and se dim ent s. The “char acteris tic length”( CHARL ) of a pat hway conventionally repre sent s t

he dis tance bet

ween com

partm ent c ent ers, m eas ured al ong theaxi s of the exc hange. A si ngle s egm ent t hus m ayhave sev eral ch aracte ristic leng ths, dep end in g onthe geo metric orie nt at i onof

i t s l i nk a ge s t o a dj oi ni ngs e gm e nt s. T he cross -sec ti onalare a ( XSTUR) for the exc hange pat h al so depends upon theori ent at ion of thecom

partm ent s. F or a vertic al exchange, as for e xample t ranspor t a cross thethe rm ocl ine of a lake, XSTUR

i s usual ly

the AREAof t

he hy poli mnion compartment. Lon gitu din al disper sionin a rivercon ven tion ally takes the fl ow cross se ction as XSTUR , howeve r, and thi s doe s not c orres pondto any va lue of AREA . Adher enceto the se conventions is a responsibil it y of m odelcons truc ti on. EXAMS does not attem

pt to eva luate thegeom etry of t he s yst em , but si m ply ins ert s t he user’s e ntri es for CHARLand XSTUR into Eq. (2-64). Alt hough EXAMS does not evaluate t he ori ent at ion of

the disp ersiv e exch ang e p athw ays, the pro gr am does ad ju st its com putati ons a ccor ding to thenat ure ( that i s, t

he TY PE ) of t

he exch ang ing compartments . The se adj u stments ar e primarily im portant for t

he exchanges ac ross t

he be nthi c boundary laye r, beca use of t he ve ry diff

ere nt phys ic alproper

ti es of t he wate r column and a sed iment bed. Inthis ca se, a simple symmetric exchange of envi ronm ent alvolum es would t ranspor t ve ry diff ere nt s edi m ent

m ass es and volum es of wat er. EXAMS a l l ow s for t he pos sibil it

y of bioge nic production and decay of det rit al sedi m entary m at eri al s, and thus gene ral ly does not im

pose expl ic it int erna l m ass -b alance cons tra int s on t he t ranspor t of sedi m ent s in thesystem. In t his ca se, howeve r, t

he m ass ive inje ct ion of

bed sedi m ent s into t

he wate r column, w ith littl e or no res ettl em ent , woul d am ount to a gross di st orti on of s edi m ent tra nsport dyna mics beyon d the r ealm of bio gen ic pos sibility . The si m ple dis persi on equati on (2-64) thus requi res si tuati onal adj ustment s. EXAMS the re fo re d i vi de s it s di spers ion com putati ons into 3 dis tinct

ca ses : ( 1) di spers ion be twe en wate r column compartments , (2 ) disp ersio n be tweenben thic com partm ent s, and (3) di spers ion be twe en a benthi c s edi m ent and t he ove rly ing wate r column. 2.3.1.4. 1 Dis

pers ion wi

thi n t he water c olumn The volum et

ric dis pla ce m e nt

of s uspe nd e d se dim ent s c an a lm ost always be negl ected, so t he wate r volum es and e nvironm ent al vo lumes of w ater c olumn compartments c an be ass umed no t to diff er. For exam

ple , a 15,000 m g/L was hloa d with a de nsi ty of 1.5 g/ cc would pe rtur

b thi s a ssum

pti onby only

1%. EXAMS the reforecom pute s th e e xchangefl ow of wate r bet ween wat er-c olum

n com partm ent s (in li te rs/

hour) a s:

This va lue is ad dedto the advectiv e flow s already in WATFL (I ,J) and

WAT FL (J ,I ). ( I i s the c om part m e nt num ber hel d in ITURB ; J

is thecom

partm ent num ber he ld in JTURB .) The dis persive exchange i s e quiva le nt to a sym m et ric pair of a dv e c t e d (ps e ud o) f

l ow s be twe e n t

he c om part m e nt s. If F LO W is a bound ary c on dition , it is add ed to W AT OU L(J ), w her e J is the com partm ent num ber he ld by

thenon-ze ro m em

ber of the ( JTURB , ITURB ) coupl e. The SED FL matrix is up datedvia SEDFL(I ,J) 

# 7 SEDFL (I,J) + ( FLOW)×(SEDC OL(J)) and SEDFL(J ,I) 

# 7 SEDFL (J,I) + ( FLOW)×(SEDC OL(I)); the SE DO UL vecto r is up datedvia SEDOUL(J) 

# 7 SEDOUL(J) + (FLOW)×(SEDC OL(J)) (SEDCOLis these dim ent /wate r rati o, Eq. (2-22)). In t his ca se, sedi m ent m ass nee d not be c onserve d. When t he e xchanging com partm ent s have di ffering concentrations of s uspende d sedi m ent s, EXAMS pe rmi ts a net fl ow of s edi m ent s a long t he conce ntrati on gradi ent
. EX AMS a ss ume s t hat bi og e ni c prod

uc ti on and de cay

of de tri ta l m at eri al s wi thin the c om partm ent s se rves to maintain th e gra dien t. EXAMS co mputes lateral, vertical, an d h or izon tal dis per sionvia thi s proc edure . Theequati ons t hus a ccount

for s ever alrat

her diff ere nt proces ses . Theeff ect s of shear fl ow in ri vers are com pu ted v ia a “ lon gitu din al di spers ion c oeffi ci ent .” Depending upon t

he ge om et

ry and sl ope of the c hannel , ri veri ne lo n g itu d in al di sp er si o nco ef f ic ie nts canvary f

r o m 27 0 0 (Y uma Mesa A Canal (Schus te r 1965) ) t o 5.4×10 (Mi ssouriRi ver ne ar 6 Blair, N ebr ask a; (Yots ukura e t a l. 1970) ) square m et ers per hour (ci te d from

Fisc her e t a l. 1979:126) . Som e s m al l l akes deve lop nearly unif orm vertic aldensit

y gr adi ent s t

hat inhibit vertic al exchange, whil e a ll owing r api d late raldis per sion, at al l depths inth e lake. Usu ally, ho wev er, th e most im po rtan t barr ier to vertic altr ansport

in lakes is a loc al iz ed regi on (t he t herm ocl ine or m et al im

nion) wi th a st eep te m

perature(dens it

y) gradi ent . The excha nge of epi lim

netic an d hyp olimnetic wa ter masses is driven by wind- induc ed e ddie s, s torm surge s, and int erna l s ei ches (see , fo r e xam pl e , Wetz e l19 75 : 89 -1 22 )
. Th e ne t e ff e c t of the se proce sse s c an us ual ly

be summ ari zed via

a dispe rsi on equati on. For e xam

ple , Snodgra ss (1 97 7) used a “vertica l d if fu sivity coe ff ic ie nt” to “i nte grat e t

he e ffec ts of m ole cul ar di ffusi on, e ddy diff usi on, i nte rnalwave s, s ei ches, st andi ng wave s, [ and]28 hypol im net ic ent rai nm ent
... into a net

tr ansport proce ss” ac ross the the rm ocl ine of L ake Ontario. The aver age DS P duri ng the stratifi ed pe riod (Aprilto Novem ber) range d from

1.0 t o 4.1 squarem et ers per day , over 6 ye ars of m eas urem ent s. A useful summ aryof t

he obs erved values of di spers ion c oeffi ci ent s c an be found in (Schnoor et

al . 1987)
. 2.3 .1. 4.2 Disp ersio n within thebotto m sed imen ts In som e c ase s, exc hanges am ong benthi c c om partm ent s re quire adjust m ent for s trongly di ffering proper ti es of t he e xchanging segm ent s. T he s urfi ci alse dim ent s of Nonam e Sl ough ( Figu re 4 ) are late ral ly

hom ogeneous , for exam ple , but thedeeper s andy laye r (c om

partm ent 9) di ffers substant ia lly f rom the s urfi ci al laye rs in bulk densi ty , wat er cont ent , and organi c c arbon cont ent . These dim ent

/wate r rati os of the se laye rs can be com pare d by ins erting thei r wat er c onte nts ( PCTWA ) i nto E q. (2- 22). In the surfi ci alse dim ent s, t he gi ven wate r conte nt i s 180%, and SE DCOL = 1.25 kg sedi m ent per li te r of wate r. T he s andy laye r has a water cont ent of 115%; it s SE DCOL (6. 67 kg/l it er) is 5 times that of

the sur ficial layers . Disp ersio n be tweenben thic com partm ent s t

her efore m

ust al low f or exc hanges bet

ween segm ent s of verydif

fere nt phy si calproper

ti es. Further m ore, the wat er volum e and theenvironm ent alvolum e of a benthic se dim ent

areby no m eans thesam e. The s urfi ci al sedi m ent s of Nonam e Sl ough, to c ontinue t he e xam ple , have a give n bulk densi ty

of 1. 2 g/c c. The volum et ric ( li te r/l it er) wat er cont ent (“por osi ty ”) c an becom pute d via Eq . (2-21); the surfi ci alse dim ent s c onta in only 0. 53 li te rs of w ater per l it er of env iron mental volu me. The po ro sity of the san dy layer ( bu lk densi ty 1.95 g/cc) is only 0.25 L/L. Equation(2- 65) thus c annot be us ed for

a dire ct com putati on of di spersive tr ansport of a synt het ic che m ic albet

ween bent

hic se dim ent

com partm ent s. The di stribution of

che m ic al s wi thin la cus trine and m ari ne sedi m ent s ha s be en s ucce ssfully model ed vi a a vertic al one-di m ensi onaltr eat

m ent of t ranspor t and chemic aldynam ic s inth is sub sy st em (Be rner 1976, Im boden and Lerm an 1978, Jones and Bowser

1978) . The se one-di m ensi onal(“di agene ti c”) equations include the usua l di spers ive , a dvective , and rea ct ion terms. The adv ective terms in these equatio ns are oftenused to desc ribethenet

depos ition of

se dim ent ary materia ls , and the effe ct ive vertic alfl ow of inte rstitia l wate rs produc ed by com paction of

thedepos it s. EXAMS p re c lud e s depo si t i onand perm anent

burial o f synth etic org anic ch emicals as inap pr op riate to a n eva luati ve m odel , so i ts adve ct ive te rm s (C hapt er 2. 3.1.3) repre sent ground-wat er f

lows and, wher e a

ppropri at e, irrigati on of bent hic depos it s by

burrowi ng organi sm s. The a ct ivities of burr owing organi sm s (bi oturbati on), phy si cal dis turbance by de m ersa l f ishes , and int ermitte nt s trong wat er turbul encete nd to physi cal ly mix s oli ds deposi te d on t he sedi m ent surface t o appre ci abl e depths . The se active ly m ixe d zones gene ral ly

ext end from about 2, to a s de ep a s 50, centim et ers in natur alsy st em s (Jones and Bowse r 1978 and refe renc es the rei n)
. This phys ic alreworking m odifi es observe d conce ntrati on profi le s in s edi m ent s, and has le d Schink and Guina sso (1977) to propose the use of e xplicit solids m ixing terms in the on e-d imension al treatment of early dia gen esis in sedi m ent s. EXAMS m ake s us e o f ac om part m e nt a l i z e d re a l i z at i ono f the se one-di m ensi onalequati ons, but does not per

m it expl ic it m ixing of se dim ent

sol ids bet ween bent

hic com partm ent s. T he depth of the sed iment compartments usedto desc ribe a system is t akento be a dept h th rough which the se dim ent can be regarded a s “we ll-mixed. ” The mixing of so lids is thu s implicitly inc orporated i nto t

he s peci fic at ions of t

he s truc tureof t

he sys te m , rathe r t

han a s direc t t erm s inthe sim ulati on equati ons. Ineffect, therefore , EXAMS a ss um e s that ve rti c a lc on c e nt

rat i on gradi ent s wit

hin the be nthi c com

partm ent s do not greatly di st urb the res ult s of it s e valuat ions
. There is som e e xperi m ent alevi dencethat t he s peed of i nte rnal mixing p ro cesse s in surficia l sediments is su fficie nt lyr ap id to ju stify EXAMS ’ di scre ti zed tre atm ent . For exam ple , McC al l a

nd Fis her ( (1 97 7) , quo tedfr o m (Jones and Bowse r 1978) ) have shown t hat ty pic alpopulati on densi ti es of t ubifi ci d oli gochae te s can com ple te ly rework the top 5 cm

of sedi m ent s ever

y 2 wee ks in a labo rato ry se tting. Van derbo rg ht andW ollast (1977) found that t he upp er 3 c m

of m ari ne (Nort

h Sea) se dim ent s e xhibi te d an inte rnaldispers ion c oeffi ci ent of 1× 10 cm /s ; t

his value ! 4 2 im pli es a re working ti m e of only 25 hours
. When a d i sp e rs i ont e rm

( l at e ra lo r ve rti c a l ) i s sp e c i fi e d f or exchange bet

ween bent

hic com partm ent s, EXAMS c om

put e s a symm etri c a l e xc hang e o f wat e r (o nl y ) be tween the com partm ent s. T his exc hange f low is use d to updat e t he W AT FL matr ix . Gen erally the inpu t dispe rsio n co eff icient in such a cas e shoul d be corre ct ed only for t ortuos it

y; theprogram itself co rre cts fo r the av erag e p o ro sity of th e 2 compartments involved , and for s orpti on of t he c hemic alto sol id pha ses . EXAMS im

poses no l imit at ions on t he m agni tude of DS P . Irri gat ion of

deep se dim ent

zone s by burrowing organi sm s c an thus be repre sent ed via

dispe rsi on te rm s, i f des ire d. A boundary con ditionfora botto m sediment compartment is co mputedin m uch t he s am e way, except, of cour se, theporosi ty of t he spec ifi ed c om

partm ent i s t he only datum

ava il abl e for

corr ection of the no minal DS P .

2.3.1.4. 3 Exchangesbet ween bed sedi

ment s and over

lying wat ers Cap ture of o rg anic ch emicals by sediment b eds can oc curvia several processe s. A dis sol ved pha se can sorb direc tly t o the surfa ce of the bed, wit

h thesorbe d m at eri albeing the n subduc te d int o thebed via

biot urbation. Irri gat ion of

these dim ent s by tube -dwel ling ani m al s c an directly entra in a fl ow of con taminated w ater thr ou ghthe bed ; th e se diment so lids w ill29 ( 2- 66) the n te nd to strip chemic alfro m the wat er f low. Filte r-fee ding organi sm s c an a ggregatec om po un ds s or

be d wi th s uspende d fi ne partic le s and add m at eri alto the bed, as m aythese quent ia l deposi ti on, i nte rnalm ixing, and sc our eve nts char acte ris ti c of rive rines yst em s. In lakes and oceans, sedi m ent “bursting” (Heat hershaw 1974) res ult s in fre quent sa lt at ion of

bed sol ids , le adi ng to sorption/ desorption e vent s and ent rapm ent of fr ee boundarywat ers in t

he re deposi te d se dim ent

m at rix. Alt hough dir ect

sorption/ desorption to thesedi m ent surfac e i s a cont inuous proces s, m anyof t he inte rac ti ons be twe en t

he wate r column and bent

hic se dim ent s are highly inte rm itte nt. For e xam pl e , He athe rs haw (1976) has es ti m at ed t hat , i n wel l-mixe d areas of the IrishSea, as muchas 70 % of the Reyn old s stress in the be nth ic bou nd ary l ayerresu lts fro m events o ccup ying only 5% of the total time of

record . Interactio ns mediatedby the bio ta are p resu mably also intermittent and h igh ly v ariab le in their int ensi ty . Themos t prac ti caland effi ci ent me ans of represe nting this arr ay of interactio ns b etwee n the w ater co lumn andben thic sed iments is to use a statistica l summary of th ei rmacro-s cale effe ct s, that is , a dis persi on equation (Berner197 6) . This strat egywas adopt ed for EXAMS . A dis persive e xchangebetwe en a wat er c olum

n (L, E, or H) and a be nthic (B) com

partm ent is des cribed t o EXAMS via spec ifi cation of

a chara ct eri st ic lengt

h ( CHARL ), c ross- sec ti onal are a ( XSTUR), an d dis per sioncoef ficie n t ( DS P ) for the wat er col umn–ben thic element ex chan ge p athw ay. Th e vo lumetric exchange gi ven by

FL OW (Eq.(2-65)) can be regarded (heuri st ic al ly) as thesaltation of a unit volum e of the bed (cont ai ning wate r and sol ids ), fol lowe d by e quil ibrati on wit h the wat er column and res ettl em ent on t he be d. EXAMS thus separate s the rat e of exchange of enviro nmenta l volum e gi ven by ( DS P )( XSTUR)/( CHARL ) i nto dis tinct wat er and sol ids exc hange compo nen ts. Th e po ro sity of th e ben thic s ediment is coupledto the disp ersi on equati on to give a wat er-e xchangete rm , vi a t he expre ssi on:

This waterflowterm (units o f liter s/ho ur ) is thenusedto up date sym m et ric loc at ions in the W AT FL m at rix, giving an appar ent rat e of exchange of flui ds be twe en t he wate r colu mn and the inter stitial por e water s of th e ben thic sed iment compartment. Chemic altr ansport

c an the n be com

pute d by tre at ing t

hesewat er flows as s im

ple carri ers for t

he di ssolved fr action r esi dent on ei the r si de of the bent

hic boundary

la ye r. In som e c ase s, e xchange s a cross thebent hic boundary

la ye r can be t re at e d a s be i ngdri ve n b ygr a di e nt s i n d i ss olve d c he m i c al conce ntrati ons a lone . Many s ynt het ic organic che m ic al s, however, havevery high partition c oeffi ci ent s, s o that s orpti on onto t he s urfac e of the bed followe d by biot urbationa l subduction i s proba

bly a si gnifi cant

m echanis m

of c hemic al tr an sp o rt f

o r th es e co mp o un d s. Th e re mai n in g ex ch an g e v o lume is therefore t aken to r epre sent a dire ct int era ct ion of

thebed sol ids wit h thewat er column com partm ent . First , an apparent “re suspe nsi on” or “bursting” term for t he e xposure of t

he be d sol i ds t o the w at e r c olum n i s c om put e d a s the p ro du c t of

the sedi m ent :wate r rati o (SEDC OL) of the bent hic zoneand the flui d exc hange rat e. The S EDFL m at rix is thus updat ed by

an appar ent fl ow of be d se dim ent s (T EMSE D, un i t s ki logram /hour) int o thewat er c olum

n via theexpre ssi on:

A nai ve “ sol ids bal ance ” now r equires th at an e qualm ass of sedi m ent r ese ttle on the be d, in order to m ai nta in the notio n of a s ta ble (st eady -st at e) be d thi cknes s. T he tra nsport of a c hemic al acr oss t he be nthi c boundary laye r coul d the n be com pute d by regarding the sol id pha se as a si m ple carri er of

sorbe d che m ic al s, usi ng sorbe d conc ent

rations (mg/kg s oli ds) on ei the r sideof t he bo un dary. The f oregoi ng is , for the m ost

part , c onvent iona l c om

partm ent m odel ing. Sti ll , because a m ultit ude of proce sse s have be en summ ari zed in a

single kine ti c e xpress ion, a c are ful independent tri alof t he a pproac h seem ed warrant ed. Alt hough a num

ber of exp erimental tests o f the equatio ns can be imagine d, in itial tests were conduct ed by

com par ing t he out put f rom the EXAMS program to a e xam

ple si tuati on cons tructed on t heore ti cal grounds a lone . Thi s t est

was conduct ed on a reduc ed s ubsys te m of t he Nonam e Sl ough ec osys tem . C onsi der, for e xam ple , t he vertic alse gm ent

of Nonam e Sl ough that includes a 2 m wat er column u nderl ai n by a 5 cm m ud depos it

and a 30 cm

la ye r of sand ( Figu re 4 ). If

thet ranspor t c hara ct eri st ic s of thi s subs yst em are rede fined t o el iminate thebedl oad and groundwat er infi lt ration, the dis persi on equati on can be used to de scribe v erti ca l mo v eme nt o f

a ch emi ca l inth e s ub sy st em. Ret ai ning t

he phys ic alsedi m ent

chara ct eri st ic s ( BULKD , PCTWA ) devel oped in Cha

pte r 2.3. 1.3, t

he s orptive prope rti es of the sedi m ent s m

ust now al so be spec ifi ed. For the e xam ple, let t he organi c c arbon c onte nt of thewashl oad be2% ( FROC = 0.02), that of them ud la ye r 5%, and l et

thesandco ntain only 0. 1% organi c car

bon. The charac te ris ti c l engt h ( CHARL ) and e xchange cross se ct ion ( XSTUR) fo r th e d isper sive ex chan ges can in th is in st an ce be de v el o p eddi r ec tl y f r o m the ge o metry of

th e s ys te m. Thes e va lue s, al ong with t he kinet ic exc hange coef

fic ie nts ( DS P ) are give n in Exam s Out

put T abl e 5. Vande rborght and Wolla st (1977) , working with rhodamine dyein North Sea se dim ent s, found t hat phys ic altur

bule nce induc ed be nthi c boundary laye r30

Name of environment: Noname Slough - Dispersion Equation Test Data Total number of segments (KOUNT) = 9 Segment Number: 1 2 3 4 5 6 7 8 9 Segment "TYPE": L B L B L B L B B

--------------------------------------------------------------- Table 10.13. Mean dispersive transport field.

--------------------------------------------------------------- J TURB 7 8 I TURB 8 9 XS TUR m2 1.000E+03 1.000E+03 CHARL m 1.02 0.175 DSP m2/hr* 1.500E-04 3.600E-05 Path No.: 1 2

--------------------------------------------------------------- * Average of 12 monthly mean values. Exam s O ut put Tabl e 5. D i sper si v e i nt er connect i ons – t est dat a. CHEMICAL: Unreactive neutral compound -- Koc = 3.E5 ECOSYSTEM: Noname Slough -- Dispersion equation test data

------------------------------------------------------------------------ DISTRIBUTION OF CHEMICAL AT STEADY STATE: IN THE WATER COLUMN:

------------------------------------------------------------------------ COMP STEADY-STATE RESIDENT MASS **** TOXICANT CONCENTRATIONS **** 2 TOTAL DISSOLVED SEDIMENTS BIOTA G/M KILOS % MG/* MG/L MG/KG UG/G
--- ------ ------ ------ --------- --------- --------- --------- 1 2.000E-03 2.0001E-03 100.00 1.000E-03 6.250E-04 3.75 SUBTOTAL: 2.0001E-03 1.21 AND IN THE BOTTOM SEDIMENTS: 2 0.125 0.1250 76.61 3.75 2.500E-04 3.75 3 3.818E-02 3.8176E-02 23.39 7.505E-02 2.500E-04 7.501E-02 SUBTOTAL: 0.1632 98.79 TOTAL MASS (KILOGRAMS) = 0.1652

------------------------------------------------------------------------ * TOTAL CONCENTRATION AS MG/L IN WATER COLUMN, AS MG/KG IN SEDIMENTS. Exa m s O ut pu t Ta bl e 6. Te st ofdi sp er si v e ex ch an ge e qu at i on . exch ang e coef

ficien ts o f 2 .9× 10 to 6.2 × cm /s. Th e test DS P ! 6

! 4 2 for Nonam e Sl ough werese le ct ed fr om thi s range of values.

In orde r t o t est

thedis persive t

ranspor t a lgori thm

in is olati on, t

he te st che m ic alcan be spec ifi ed a s a co mpl et ely unr eac ti ve, non-volati le neut

ralcom pound, wi th a

Koc of 3×10
. 5 When the te st

che m ic alis int

roduce d into the sy st em , an equi librium

st at e c ould berapidly gene rat ed by suspe nding t he bent hic la ye rs in thewat er c olum

n, and thoroughly a git at ing t he mixture. At equ ilibrium, this 4-p has e syste m wouldexh ibit a si ngle aque ous c oncent

ration, and s orbed-pha se conce ntrati ons diff erin g as the r atio of the ir partition co eff icients ( i.e., in proport ion wi th t

he organic carbon contents of t he s edi m ent phase s). If t

he be d sol ids were then al lowe d to rese ttle , t he si m ple separati on of the m at eri al s woul d not result in any change in the di ssolved (m g/L of wat er) or sorbed (m g/kg dry soli ds) conce ntrati ons. T he e nvironm ent alconc e nt rati on s (mg/L of

tot al envi ronm ent alvolum e) c ould, of cour se, diffe r bet ween the wat er c olum

n and the (re st ored) bed l ay ers. This situationalso ap plies to an op en syst em ina dynamic equilibrium

or s te adyst at e. Suppose, for e xam ple , t hat wat er cont aminate d to a l evelof 1 μg/L (ppb) with the te st che m ic al flows continuous ly

through t he Nonam e Sl ough subsy st em . The dis persi on equationcont rols only therat e of exchange of ch emi ca l b etw ee nthe wate r co lumnan dth e b en th ic sub sy st em. At s te adyst at e, no conc ent ration gr adi ent

rem ai ns to drive further ne t c hemic alexchange . In t his ins tance of an unrea ct ive com pound, t he finaldynam ic equi librium is equi val ent

to the st at ic ca se. The resu lting compu ter outp ut is sho wnin Exams Outp ut Tab le 6. Thecom

putatio ns lead to a

st eady -st at e e nd point

of e qual sorbe d conc ent rations for t

he wa shl oad and the m

ud l ay er, rat

her thanequ al dissol

ved concent rations . Alt

hough theconc ent

ration dis tributi on bet

ween the bed sand and m ud la ye rs fol lows the the oretic alexpe ct at ions , t his res ult for the washl oad and them ud layer is ex actly op po site the expecte d ou tcome of th e test. Alt hough thecom

pute d outcom e c ould berationa li zed in m any ways , t he fa ct rem ai ns that the program output did not r efl ect

the ass um pti ons and rea soni ng use d to buildthe m odel ; a nai ve “se dim ent

balanc e” fai le d to providean acc urat e s im ulati on of chemic albehavior and t

hus re quire d revi si on. Close r con sider ationof the heuristic log ical stru ctur e usedto adapt thedis persi on equati on to thi s a ppli cationsu ggeste d an appropri at e re vis ion. At le ast nom ina lly, in t

he c aseunder consi derati on thesuspende d and bedded sol ids need ne ver e ven com e in cont act , so the re i s no pl ausible way for s orbed c hemic al to e xperi encea dire ct

conc ent rationgradie nt. The c apt ure of chemic alby the bed is drive n by flui d exc hange, and by s al tati on of the bedsolids , wh ich allow s them to in te r ac t directly w ith chemic aldis sol ved in thewat er c olum n. Theroot of

theprobl em thus se em s t o li e wi th t

he di ffere nce in organi c c arbon c onte nt (i. e., partition c oeffi ci ent) of t he suspended and bedde d sedi m ent s. The s orbed c oncent

rations com

pute d for eac h com

partm ent are base d on prope rti es of t he s edi m ent s spe ci fie d for the com partm ent , rat

her than on the pr opertie s of a sa lt at ory transi e nt
. Th e re fo re , i t

m i ght s e rv e the c a set o s i m

plya djust chemic altr ansp ort acc ording to t he rati o of t

he parti ti on coef fic ie nts (Kp). In t

his way, for e xam

ple , if the Kp of t

he be d sed iment were 5 times tha t of the susp end ed sed iment, the rate of ca ptureof c hemic alby the bed woul d be proport iona lly l arge r than tha t sugge st ed by

Eq. (2-66) s im

ply coupl ed t o the con centr ationon th e wash load , andcon ver sely. Alt hough organi c c arbon c onte nt g ov erns t he a bil it y of a sed iment to sorb neutral (unch arg ed) molecu les, anorg anic acid or bas e wi llocc ur as both neutra l a nd charged s peci es, wit

h a spec iati on governe d by the pH of t he s yst em . The sorptive capa ci tyo f

a sediment may thus d epen d onits carbo n co nten t, ion e xchangeca

paci ty , and thepH o f t

he c om partm ent . Thus whe n n e c e ss ary , the r e l at i ve s or pti ve c apa c i tyof

s e di m ent phase s c an becom

pute d via thedis tributi on coeffi ci ent s ( á ) and sedi m ent :wate r ratios ( SEDCOL) of t he wat er-c olum

n and31

CHEMICAL: Unreactive neutral compound -- Koc = 3.E5 ECOSYSTEM: Noname Slough -- Dispersion equation test data

------------------------------------------------------------------------ DISTRIBUTION OF CHEMICAL AT STEADY STATE: IN THE WATER COLUMN:

------------------------------------------------------------------------ COMP STEADY-STATE RESIDENT MASS **** TOXICANT CONCENTRATIONS **** 2 TOTAL DISSOLVED SEDIMENTS BIOTA G/M KILOS % MG/* MG/L MG/KG UG/G
--- ------ ------ ------ --------- --------- --------- --------- 7 2.000E-03 2.0000E-03 100.00 1.000E-03 6.250E-04 3.75 SUBTOTAL: 2.0000E-03 0.49 AND IN THE BOTTOM SEDIMENTS: 8 0.313 0.3125 76.61 9.38 6.250E-04 9.38 9 9.543E-02 9.5428E-02 23.39 0.188 6.250E-04 0.188 SUBTOTAL: 0.4079 99.51 TOTAL MASS (KILOGRAMS) = 0.4099

------------------------------------------------------------------------ * TOTAL CONCENTRATION AS MG/L IN WATER COLUMN, AS MG/KG IN SEDIMENTS.

Exa m s O ut pu t Ta bl e 7. Te st ofm od i f i ed di sp er si v e ex ch an ge pr ocedur e. bent hic com partm ent s spe ci fie d for

an e xc ha ng e pa t hw ay . Gi ven á (d ,w ) and á (d ,b) as the tot aldis sol ved fr action in thewat er column (w) and bent

hic (b) c om

partm ent s, r espe ct ive ly , and á (s,w) and á (s,b) as the sediment-sorbe d fra ct ions , t he re turn “flo w” (S ED FL) of su spe nd ed se diment acro ss the b enth ic boundarylayer to t

he s edi m ent

com partm ent can be com

pute d as:

This calculatio n yields the ratio of the sorp tive capac ity (ov erall partition c oeffi ci ent , Kp) of the be nthi c sedi m ent , to that of the wa sh l oa d. T hu s fo r e xam pl e , i f the be nt

hi c s e di m e nt s have aKp twi ce that of

thewashl oad, the rat e of capt ure of che m ic alby the bed (t hat is , the appare nt ps eudo-se ttle m ent rat e of saltatory

bed m at eri al s) must occur at

twi ce the rat e t

hat would be inferre d dire ct ly from theproper

ti es of t he wa shl oad i ts el f. The e ffec t of thi s revi si on c an now bet est ed by exec uti on of t he te st ca se des cribed a

bove; theres ult s are given in Exam s Out put Tab le 7. Th e con sequen ces of the ca lc u la tio n are now quite satis fac tory : T he cal cul at ed dis sol ved conce ntrati ons are unifor m ly 0.62 5 ppb, and thesorbe d conc ent rations ref

le ct the diff ere nces in organic carbon c onte nt of thesy st em

se dim ent s. Note , howeve r, that thi s com putati on is val id wi thin thecont ext of t he EXAMS pr ogram

only beca

use sedi m ent

t ranspor t i s not an exp licit state variab le in the pr og ram, i.e., th e SEDF L matrix is no t a desc ription of sedi m ent t ranspor t per se, but

m erely a compu tation al dev ice forcomputin g the ex chan ge o f synth etic organi c c hemic al s a cross the benthi c boundary laye r. “ Soli ds bal ance s” and st abl e bed thi cknes ses are the res ponsibil it y of the user when ass em

bling an e nvironm ent alde scripti on t o drive the pr og ram; EXAMS si m

ply processes the se dat a (vi a t he SE DFL m at rix) to arri ve at a

proper charac te riz at ion of

che m ic al tr an sp o rt inth e s ys te m.

2.3 .1. 5 Tra nsp ortof sy nth etic or ga nic chem icals EXAMS use s t he t ranspor t f ie ld de fine d by WATFL, SEDFL , W AT OU L, an d SE DO UL to compu te f irst-o rd er co eff

icients th at de scribe t

ranspor t of che m ic althrough theec osys te m . The se co ef f ic ie nts de sc r ib e th e exp o rt of ch emi ca ls fr o m th e s ys te m, and t he inte rnaltr ansport

of t he c om pound among the com partm ent s used to define di ffere nt phy si calse ct ors of the sy st em. The WA TO UL and SED OU L vector s are used to co mpute exports from

ea ch c om

partm ent . A va lue of EXAMS ’ i nt e rn al vect or EXPOKL, wit

h dim ensi ons of (li te rs/

hour), is ca lc ulate d for e ach com

partm ent as EXP OKL = ( á (29)+ á (31)+ á (32))×WATOUL + á (3 0) ×S ED OU L/ SE DC OL where á (29), ( 30), (31) , and (32) are t he t ota l f rac ti ons of the chemic alin dis sol ved, sedi m ent -sorbe d, DOC -com ple xed, and plan kto nic bio sorbedstates, res pectiv ely. Pollutants al so l eaveeach c om part m ent via wat er and sedi m ent flow pat hways that c onnect

thec om partm ent to othe r se ct ors of the eco system. Fro m t

he p ersp ective o f the do no r compartment, the se flow s c an berepr ese nte d as a pure e xport of che m ic al acr os s the b ound ari e s of

t he c om part m e nt , de sp i t e t

he f a c t that the m at eri alm aybe ret

urned f rom therec ept or com

partm ent at som e l at er tim e. Ea ch row of the WATFL and SEDFLm at ric es giv es the flo ws o f wate r and sed iments leaving a compartment, an dthe ro wsums ar e th e to ta l lo ca l (th atis, w i th in

- sy st em) outfl ows from

thecom partm ent s. F or ea ch c om

partm ent , EXAMS com pute s a value of an int erna l va

ria ble (INTOUL, li te rs/

hour) anal ogous to the e xport vect or EXPOKL. Thi s c om putati on can be represe nte d as INT OUL =( á (29)+ á (31)+ á ( 3 2 ) )×S UMW AT + á (3 0) ×S UM SE D/ SE DC OL

wh er e S U MW A T an dSU MS ED ar e th e ap p r o p r iate ro wsums in t he WATFL and SED FL m at ric es, and SEDCOL is the sed iment:waterratio fo r the d on orcompartment. Thes e t ranspo rt te rm s (E XPOKL and INTOUL) m ust now be con verted to p seu do -fir st-o rd er co eff icien ts tha t expr ess the ir effe ct on t he c oncent

ration of che m ic alin t

he s ource (donor) compartment. Th is coef

ficien t (CON OU L, dimens ion s /ho ur ) is com pute d as : C ON OU L = (E XP OKL + IN TO UL )/WAT VO L wher e W ATVOL is the volum e of wat er ( li te rs) pr ese nt in the donor com

partm ent . Thi s c oeffi cient (C ONOUL) i s t he cont ribution of

tr anspo rt p roce sse s t o theovera lllos s c onst ant “K” of Eq. (2-1).32 Intr a-system

tr ansport al so i m poses che m ic alloa dings on t he compartments receiv ing the con taminated flo ws (fa ctor“Li” in Eq. ( 2-1)). EXAMS c om

bine s the WATFL and SE DFL m at ric es int o a new m at

rix (INT INL, dim ensi ons l it ers/ hour) ne eded for com puting theint erna l l oadi ngs (L i) on ea ch com partm ent . Ea ch el em ent of INTINL i s first

ca lc ulate d from

thesum

of c or re sp on di nge l e m e nt s i n WAT FLand S ED FLv iathe expre ssi on: ( á (29)+ á (31)+ á (32))×WATFL + á (3 0) ×S ED FL/ SE DC OL usi ng values of á , andSED COL forthe do no r compartment. Mul tipli cation of eac h e le m ent of INTINL in a

give n row, by

the con centration of

che m ic alin the donor c om partm ent give n by the suc ces si ve column indic es of the row, y ie lds them agni tude of t he l oadi ngs pa sse d to the rec ept or com partm ent by eac h of the d on or s. Th e sum of the se load ing s is the internal loa d (L i, m g/h) on therec ei ving c om partm ent . Lim

ust als o be divi ded by the aque ous volum e of the r eceptor ( V in Eq. (2- 1) ), in o rd er to expre ss t he e ffec t of

theint erna l l oadi ngs on t he c oncentration of che m ic al s in therec ept or. EXAMS the reforedivi des eac h elemen t o f

IN TI N L b y th e v o lume o f th e r ec ei v in g co mp artment:
IN TINL 

# 7 INT IN L/WAT VO L and re ta ins theres ulting m at rix of pseudo-fi rst -order (d imensio n s /h ) co ef

f ic ie nts fo r sub se qu en t u se inits steady-state and kinet ic si m

ulati on equati ons (C hapt er 2. 5). Refer enc es for Chap ter2.3.1. Bern er , R
. A. 19 76
. Th e be nt hi c bo un dary

l ay e r fr om

the view point

of a geoc hemis t. Page s 33-55 in I. N. Mc Cave , e di t or . Th e B e nt

hi c B ound ary

L ay e r. P l e num

P re ss , Ne w York and London. Bird , R. B., W . E. Stew art, an d E. N . Ligh tfoo t. 19 60 . Tran spo rt Phenom ena. John Wil eyand Sons, Inc., New York. Fis ch er, H. B. , E. J. List, R. C. Y. Koh, J. Im berge r, and N. H. Brooks. 1979. M ixing in Inland and Coas ta l Wat ers. Acade mic Pre ss, New York. Heat her sha w, A. D. 1974. "Bur st ing" phenom ena in t he s ea. Nat ure 248 :394-395. Heat hershaw, A. D. 1976. Mea surem ent s of turbulence in the Iri sh Sea benthi c boundary laye r. Pa ges 11-31 in I. N. Mc Cav e, ed it o r . T h e B en th ic Bo un d ary L ay er . P le num Pres s, Ne w York and London. Im bo den, D. M., and A. Lerm an. 1978. C hemic alm odel s of lakes. Page s 341-356 in A. L erm an, editor. Lake sChemis try , Geol ogy, Phys ic s. Springer-Ve rla g, New York. Jon e s, B
. F. , and

C
. J. B ow se r. 19 78
. Th e m i ne ra l og yand rel at ed c hemis try

of l ake sedi m ent s. P ages 179-235 in A. Lerm an, edi tor. Lake s-Che m is try , Geol ogy, and Phy si cs. Spri nger-Ve rla g, New York. McC al l, P. L ., andJ. B. Fis her. 1977. Ver ti caltr ansport

of sed iment solids by Tubif

ex tubi fe x(Ol igoc haet a) ( abst

rac t). in 20th Conf. Great

Lake s R es. Schi nk, D. R., and N. L. Guina sso, Jr. 1977. Eff ects of biot urbation on sedim ent -seawat er inte rac ti on. Marine Geo log y 23 :133-154. Schn oor, J . L. , C . Sato, D. Mc Ket chni e, and D. Sahoo. 1987. Proce sse s, C oeffi ci ent s, and Mode ls for S im ulating Toxi c Organi cs and Heavy

Met al s in Surfa ce Wate rs. EPA/ 600/3- 87/015, U.S. Envir onm ent alProt ections Agenc y, Offic e of Res ear ch and Deve lopm ent , At hens, Georgi a. Schu st er, J. C . 1965. Cana l di scharge m eas urem ent s wi th radi ois otope s. J ournalof t he Hy draul ics Divi si on, Proc
. ASCE 91 :101-124. Snod grass , W. J. 1977. Rel at ions hip of ver ti caltr ansport

ac ross the therm ocl ine to oxyge n and phosphorus regi m es: Lake Ontario as a prot oty

pe. Page s 179-202 in R. J. Gibbs, edi tor. Tran sport Proc ess es in L akes and Oceans. P le num Pre ss, New York and London. Stuart, F. 1970. FORTRAN Program m ing. John Wil eyand Sons, Inc., New York. Vand erborght, J. P., and R . Woll ast . 1977. Mas s t ransf er propertie s in se dim ents near thebent hic boundary

la ye r. Pag es 209-219 in J. C. J. N iho ul, ed itor. Bottom Turbul ence . Proc eedings of the 8th Inte rnationa l L ie ge Col loquium

on Oce an Hydrodynamic s. E ls evi er S ci ent ifi c Publi shi ng Co. , Am st erdam . Wetz el , R . G. 1975. Limnology. W.B. Saunde rs C o., Phil adelphia
. Yots ukura, N., H. B . Fi sche r, and W. W. Sayre. 1970. Measurement of

Mixing Char acteris tics of th e Misso ur i Ri ver be twe en Si oux Ci ty , Iowa and Platt smout

h, Nebra ska. U.S. Ge ologi calSurve y Wat er-Supply P aper 1899-G. 

### 2.3.2 Volatilization EXAMS use s a two-r esi st ancemode l t o com pute trans port acr oss the a i r- wat e r i nt e rfac e. EXAM S cal cul at es the rat e of int erpha se transpor t by

com puting these quent ia l r esi st anceto m ovem ent through an a queous and a gas eous “fi lm ” at t

he a ir- wat er int erfa ce. Alt

hough ori gina lly de veloped for indus tri al appl ic at ions (Whitm an 1923) , the se m odel s have been ada pte d to en vironm ent alprobl em s (Li ss 1973, Li ss a nd Sl at er 1974, Mac kayand Lei nonen 1975, Mac kay1978, B urns 1982, 1985)
. Whitm an (1923) vis uali zed the aquati c inte rfac e a s “ st agnant film s” of ai r and wat er, bounded by wel l-mixe d bulk phase s on eithersi de of the int erfa ce. Figu re 6 i l lus trat e s the c on c e pt ua l m odelof c hemic altr ansport ac ross the air-wat er inte rfac e.33

F ig u re 6 . W h it m a n (1 9 2 3 ) tw o -re s is ta n c e o r tw o -fi lm m o d e l o f a g a s -l iq u id in te rfa c e (a fte r L is s a n d S la te r 1 9 7 4 ).

( 2- 67)

( 2- 68) ( 2- 69)

( 2- 70)

( 2- 71) l Spec ifi cal ly , in Figu re 6 , C i s the c oncent ration of cont aminant g (m ol @ m ) in the bulkwaterpha se; P is it s parti alpres sure

! 3 sl (atmosp her es) in the bu lk air ab ov e the inter face; C is it s a quesg ous conce ntrati on at t

he inte rfac e; and P isit s parti alpres sure

on t he atm ospheri c s ide of t

he inte rfac e. The f

lux of com pound F (m ol @ m @ h ) through the a queous film can be desc ribe d using ! 2

! 1 Fic k’s first

la w

where D is t

he aqueous dif

fusi on cons tant of

theche m ic alin the film (m @ h ), C

is theconc ent

ration of unioni zed, unsorbe d 2

! 1 com pound (m ol @ m ), and dC/ dZ is the con centr ationgrad ient in
! 3 th e f il m. Similarly, the flu x of chemical throu ghthe stagn ant atmosp her ic layer is

where D is now the dif

fu sioncon stant o f the compoundin the air laye r, dP/dZ

is thepartia l pr ess ure ( atm osphere s) gradi ent in the film , R is thegas cons tant (8.206×10 m -atm /m ol-K), and T

is -5 3 Kel vin t em

perature
. Env iron mental ga s exch ang e pro cesse s are o ftenformulated in te rm s of an exc hange c onst ant “k” , that i s, a s a con du ctivity(t he inv erse of the film tran spo rt res is tanc e ). The e xchangecons tant h as dime n si o n s o f

ve lo ci ty(m @ h ); i t i s a ls o known as the“m ass

! 1 tran sfercoef

ficient,” “pe rmeability coef ficient,” “ad sorp tion/exit coef fic ie nt,”and “pi st on vel oci ty .” The flux of ga s F through the st agnant

la ye rs i s t hen in t he l iqui d phas e, and

in t he g as phase , wher e dC

is t he conce ntrati on diffe renc e a cross the fi lm , dP

is theparti alpressur e diff ere nce acr oss t

he fi lm , and ( @ ) ( @ ) ( @ ) ( @ ) k = D / z , z thefi lm

thi cknes ses . Therec iproc al s ®= k ) of -1 the e xchangecons tants givethetr ansport res is tances r

of t he aquatic and atm ospheri c fi lm s. Give n negl igible dynamic st orage ca paci ty in the fi lm s and conse quent

st eady -st at e t

ranspor t of gas through t

he inte rfac e ,

1 the m ass fluxes through the st agnant la ye rs of ai r and wat er ( see l g Figu re 6 ) m

ust be t he s am e. There fore, F / F , and we can se t ( 2- 69) equa l t o (2-70) and substit ute the conce ntrati on dif

fere nces ( Figu re 6 ), obt ai ning

l g where k is theliqu id p hase , and k thegas phas e, exchange coef fic ie nt. The pa

rti ti oning of

theexc hangi ng (uni oniz ed) subst anceac ross the air-wat er inte rfac e i s gi ven by Henry ’s
sg sl Law : P = H C , wher e H i s the He nry’s L aw constant

sl sg (atm -m /m ol). Usi ng Henry ’s L aw, C and P can be el iminate d

3 from (2-71), yi el ding a

n equati on rel at ing t

he t ranspor t f lux F to the bu lk ph ase co ncen tration s on ly: ( 2- 72)

l where K , t

he t ranspor t c onduct ance , i s de fine d by ( 2- 73)
The tota l r esi st ance to t ransf er of a gas acr oss t

he a ir- wat er l l int erfa ce (R = K ) is thu s the sum of the series of resistan ces in -1 l g the li quid ( k ) and gas (RT /(H k )) phase s of the int erfa ce. The -1 two-re si st ancem odelas sum es that t ranspor t r esi st ance at

the int erface canbe negl ect ed; al though ge nera lly t his is theca se, under ve ry turbul ent

condi ti ons or inthepres enceof surfa ce- active c ontam inants ( surfa ct ant s) thi s ass um pti on is le ss te nabl e (Bi rd et

al . 1960: 652) ). The “ two-fi lm ” pi ct

ure of the air-wat er inte rfac e ( Figu re 6 ) is physi cal ly

ine xact , a lt

hough eve nts at

mol ecul ar s cal es

N ot e t hat t hi s i s a m icr o sc op ic , ra t her t han a m a cr o sc op ic , ass um pt i on -- t hat 1 is, the se ex trem ely th in in terfac ial film s a re m er ely as su m ed to m ain tain a r ap id equil i bri um w i t h t he adja cent , t hem sel ves ful l y dyn am i c, bu l k l ayer s.34 ( 2- 75) undoubte dly

aff ect int erpha se transport. Bot h at m ospheri c and hydrodynamic eddy

tur bule nce ofte n ext end to t he a ir- wat er int erfa ce, howeve r, s o theide a of a di scontinuous tr ansi ti on from turbul ent fl ow to a s ta gnant film ne ar t he a ir- wat er inte rfac e cannot be seri ously e nte rta ine d. Thesupposition t hat the int erfa ce is com

posed of sta ble , uni form

fi lm s i s stil l l ess plau sible. The tw o- resis tance models d o, h ow ever , exp licitly reco gnize that t

ranspor t r esi st anceocc urs bot

h in the aque ous and in theatm ospheri c regi ons of the air-wat er inte rfac e. There is ample prec eden t (see, fo r exam ple , Fi sche r et

al . 1979) for am al gam at ing the effe ct s of int ermitte nt t urbule nt a nd adve ct ive transpo rt events occ urri ng in the int erfa ci alzone , i nto a n empirical dis per sioncoef ficien t D or ex ch ang e con stant k
. Furthe rmore, pred iction s der ivedfro m t wo - r esistan ce models usual ly dif fer veryli ttle from

thepredi ct ions of more com ple x (e.g. , sur fac e-re newalthe ory) m odel s (Danckwerts 1970)
. Laboratory

st udie s of t he vol at il iz at ion of

chl orohydroc arbons from di lut e a queous soluti on (Dil ling et al . 1975, Dil ling 1977) have pr ovide d furt

her e vide nce that t

wo-res is tance m odel s are good pr e di c t or s of

f lux e s of organi c c he m i c a l s a c ro ss the ai r-wat er inte rfac e. A two-res is tance m odelhas bee n used to com pute thetr ansport of atm ospheri c c ontam inants (sul fur di oxid e, car bon te tra chl oride , etc. ) i nto t

he worl d oce an (Li ss a

nd Sl at er 1974)
. g Su c h an app l i c at i onr e qu i re s ak no wl e dge of P , the bu lk
g atm ospheri c partia l pres sure. Lacking a m eas ured va lue of P , it can in s om e c irc um st ance s (ge nera l c irc ulati on m odel s of the atm osphere , plum e (s ta ck ga ses ) di spers ion models) be cal cul at ed and coupl ed t o a two-re si st anceint erpha se transport m odel . Usua lly, however, bulk atm ospheri c t ranspor t of synth etic org anics volatilizedfro m aquatic systems rap idly
g remov es th em fro m the v icinity o f th e inte rfa ce, so that P can be negl ect ed (Mac kay andLeinon en 19 75 , Mackay 19 78 ) . T h is approa ch wa s a do ptedfor EXAMS , re sul ting in a s im pli fic at ion of (2-71), yi el ding ( 2- 74) Bec ause EXAMS was desi gned, am ong other th ings , for pre -m anu fa c t

ur e e va luat i onof

ne w c he m i c a l s and

pe sti c i de s, the re was, in anycase , li ttle li kel ihood t hat m eas ured va lue s of
g P would be re adi ly

ava il abl e for

usein the m odel
. EXAMS does no t entirely pr eclude atm ospheri c inputs , howeve r. EXAMS ’ load ing fun ction s allowfo r en try o f spr ay drif t ( DRFLD ), and for rain -o ut ( PCPLD ) l oadi ngs, whe re t hesecan be com

pute d. For usein EXAMS , (2-74) m ust be rephra sed to give t

he e ffec t of volati li zation on t

he conce ntrati on of pollut ant in e ach sec tor of the e cosy st em

(com partm ent , se gm ent) having an ai r-wat er int erfa ce. EXAMS ’ conc ent ration va ria ble [C ] i s the total conce ntrati on of pol lut ant in unit s of m g/Li ter of a queous vo lume. Multip licationof b othsides o f (2- 74 ) by MWT A/V

, where MWT

is th e gram

m ole cul ar we ight

of t he c om pound, A is theare a of the air-wat er inte rfac e (s quare m et ers) , and V is the volum e (m ) of t

he c om partm ent , gives 3 1 The f act or á is thefra ct ion of the tot alpollutant c oncent ration [ C] prese nt a s a

volati li zable (unioni zed, unsorbe d) che m ic al l 1 spec ie s. The group K A á /V is a pseudo-f

irs t-or der r at e c onst ant withuni ts h . This rate con stant is co mputedby EXAMS in a

-1 spec ifi c m odule , a

nd t he vol at il iz at ion c ontributi on is the n adde d to t he t ota l ps eudo- firs t-or der r at e c onst ant s use d int erna lly by EXAMS to simulate po llutan t dynamics with in env iron mentally st abl e tim e s egm ent s. EXAMS ’ t

wo-res is tance m odel re duces at thi s point to a com putati on of t

he tra nsport resi st ance s (or exchange c onst ant s)

l of che m ic alpol lut ant s in t he l iqui d ( k ) and atm ospheri c ( RT/(H -1
g k ) ) zone s of the air-wat er inte rfac e. Thes e transport res is tances are governe d by the int ensi ty and duration of

phys ic altur

bule nce and c onvective m oti ons in theinte rfac e zones . Expanding upon a s uggestion of Li ss a

nd Sl at er (1974) , EXAMS inde xes the transport res is tance of che m ic alpollutants agai nst theexc hange propertie s of wel l-s tudi ed environm ental substances: oxygen and wat er va por. The trans po rt of oxyg en acro ss the air-w ater interf ace of aquatic sys te m s (re aer at ion) has been st udie d fo r many y ear s. Oxy gen transport is cont ro lle d by resi st ancein the li quid pha se (Li ss 1973) . Theexc hange const ant for di ssolved oxygen thus provide s a m eas ure of turbul enceon the liqu id si de of the ai r-wat er inte rfac e. Water it sel f, a s t he s olve nt f

or chemic al pollutants in a quat ic syst em s, has no trans port resi st ancein the liqu id ph ase of

the inter face: its tran spo rt is con trolledby even ts in t he atm osp her iczoneof t

he inte rfac e. Giv en exch ang e co nstan ts fo r o xyg en andfo r w ater vapo r (n ote that t he l atte r i s not

thesam e as the eva

poration r at e), it

rem ai ns to index t he t ranspor t r esi st ance s of t

he pollutant t o thoseof t

he envi ronm ent alref

ere nts . Se vera l indexi ng me thods havebee n proposed. Kine ti c t

heorysugge st s t

hat theens em

ble m olecul ar kine ti c e nergi es KE of al l c hemicals pr ese nt in a give n zoneof the int erfa ce are thesam e, and t hus, a s ave rage m ole cul ar ve loc itie s in a m ulti -c om po ne nt mi xturem

ust be dis tribute d in pr oporti on t o t he squarer oot of the molecular wei ghts of t

he c om ponent s. EXAMS use s t

his m et hod for r el at ing t

he e xchangecons tant f

or wat er va por t o thevapor- phasevolati li zation r esi st anceof pollutants . Thetem

per ature of t

he va por fi lm is as sum ed t o be the same as the watertempera ture specif ied fo r the ap pr op riate aquatic com

partm ent
. EXAMS thus com pute s t he va por-phas e g transport res is tance R from

theequati on ( 2- 76)35 ( 2- 77)

( 2- 78) ( 2- 79)

( 2- 82) w where T is Kel vin t em

perature , V i s the wat er va por exc hange co n st an t ( p is to nve lo ci ty , m @ h ), H the Hen ry’s Law con stant, ! 1 the m ole cul ar wei ght of wat er i s t aken as 18 g/mol, and MWT is the molecu lar we igh t of the volatilizin g ch emical. To arrive at the total tran spo rt resis tance , we must also compute the li quid-pha se re si st ancein theint erfa ce zone. Re asoning from the St okes -Einst ei n equati on, Ts ivogl ou (1967) sugge st ed t hat the (l iqui d-phasedominate d) exchange const ant s for m ole cul ar oxyge n vs . t

he norm al atmospheri c ga ses (Kr, Ra, He, etc. ) ar e linearly rel at ed t o the ir rel at ive m ole cul ar di am et ers or, equi val ent ly , t

hei r m ole cul ar di ffusi on const ant s in wat er. A li te ralint erpre tati on of the Whit m an “t wo-film ” deri vat ion gives m uch t he s am e re sul t. In cont rast , m odel s based on sur face- ren ewa l theor ie s s u gg est that relative ex chan ge co nstan ts shoul d vary as the s quare r oot of diffus ivi ti es (Danckwe rts 19 70 : 10 0)
. Do bbins (1 96 4) con stru cted anelegan t hybr id of film and s urfac e-re newalthe ory that c oll apse s t o a Whitm an m odel under qui esc ent

condi ti ons, and to a s urfac e-re newalm odel under more t

urbule nt c onditions . He al so found, via la borat ory st udie s, t hat theappropriate root

of t he di ffusivit

y r at io f or t he nitro gen/helium gas pair ten dedfro m 0.98 5 t o 0. 64 8 with inc rea si ng wat er t

urbule nce, as expe ct ed fr om his the or etic al equati ons. Given t

he unc ert ai nti es in e st im at ing or ave ragi ng oxyge n exc hange const ant s, howe ver, a ful l de vel opm ent of t he Dobbins m odelfor inclusi on in EXAMS has thu s far se em ed unwarrante d. The mole cul ar di ffusi vit

y of a new organi c chemic alis not ofte n known, although i t c an bees ti m at ed fr om othe r che m ic al propertie s (Reidet al. 197 7) . Th e molecu lar w eigh t of anorg anic com pound i s al m ost

a lways avai la

ble , however, so EXAMS use s Lis s and Sl at er’s (1 97 4) molecu lar we igh t corr ectoras its defau lt te chni que for

rel at ing t he liqui d-phasetr ansport res is tance of a pollutant to exc hange const ant s of dissolved oxyge n ( EXAMS input param et er K

O2 , a pis tonve loci ty

for mole cul ar oxy gen). l The l iqui d-phasetr ansport res is tance R is then simply

O2 wh e re K is theoxyge n (m ole cul ar we ight 32) e xchange con stant. The tota l t

ranspor t r esi st anceof t

he pol lut ant

is t he si m ple sum l g of t he indivi dualphas e t

ransport res is tances , R + R . The

l exch ang e con stant o f the co ntaminan t ( K , the co nductiv ity) is th e r ec ip r o ca l o f

th atsum:

Thus, EXAMS com

ple te s c om

putati on of the ps eudo-first -order l 1 volati li zation r at e c onst ant as K á A/V

. 2.3.2.1 Chemi calData E ntry The c hemic alparam et ers gove rning vol at il iz at ion of a pollutant from a quat ic sy st em s c an beent ere d into EXAMS ’ ch emical data basein seve ralway s. T he gram m ole cul ar weight

of t he po llutan t MWT

( EXAMS param et er MWT) i s requi red , for com putati on of

t he vapor-pha se transport index (2-76). The Hen ry’s Law co nstan t (

H , i nput parame te r HENRY) can be loa ded, however, ei the r as asinglevalue of HENRY (atm -m /m ol), or a s a

function of te m

perature . When i nput 3
H param et er E (input

datum EHEN) is loa ded a s a

non-ze ro value, EXAMS com

pute s t heHenr y ’s Law const ant

at loc alte m perature s T (TCEL ) fro m t

he re lation ship

When no dat a for

theHenry ’s L aw c onstant is avai la ble at run time, but EXAMS de te ct s the pr ese nce of a non-z ero va lue of t he vapor pr ess ure of

thecont aminant, EXAMS int erna lly c omput es the H enry’s L aw con stant fr om the vap orpres sur e/solubility ratio (Mac kayand Wolkoff 1973, M ackay and Leinonen 1975)
. If e it her t he va por pre ssureor t

he s olubi li ty

of t he c om pound have been ent ere d as functions of t em perature , these d at a are adjust ed t o loc al(TC EL) t em perature s (vi a Eq. (2-80) and/ or Eq. (2 -8 1) ), pri or

t o c om put at i onof

HENR Y. ( 2- 80) ( 2- 81) No t e that , a l tho ug h a

s i m pl e ( t e m pe rat ur e i nv ari ant) po llutant solubil it y i s e nte red in unit s of m g/L (ppm), EXAMS ex p ec ts solubil it y a s a function of

te m peraturet o be ent ere d via

theide al solubil it y l aw, t hat is , as the dependenc e of m olar solubil it y on te m perature
. 2.3.2.2 Exch ange Cons tants for Wat er Vapor W The watervap orexch ang e con stant ( V , Eq. (2- 76 )) u sedto com pute thevapor- phasetr ansport res is tance of pol lut ant s i s not it sel f a dire ct

use r i nput to EXAMS . Li ss (1973) , in a series of wind-t unnelexpe rim ent s, f

ound thepiston veloci ty of wate r vapor t o be a linear

function of

wind spee d. EXAMS takes, as its user input vari abl e, the avera ge wind spe ed at a hei ght of 10 c m above the wat er s urfac e (input va ria ble W IND , m @ s ). T he
! 1 W exchange c onst ant

for wate r vapor

( V ) is computedsepar ately for e ach com

partm ent from the se dat a. Lis s’ re sults can be repre sent ed vi a a

linear regr ess ion e quat ion t

hat inc lude s t

he sh if t inun it s f

r o m m @ s fo r

wi n dsp ee dto m @ h for t he wate r ! 1

! 1 vapor e xchangecons tant

in whi ch c hanges in win d v el oci ty at 10 c m abovethewat er surfa ce (W IND ) ac count for 98. 3% of t

he variance in t

he36 ( 2- 83) W exchange const ant

for wate r vapor

( V , m @ h ) over

a range of
! 1 w in dsp ee d s ( at10 cm h ei g ht) fr o m 1. 6 to 8. 2 m @ s . ! 1 Wind spee ds obse rved at

ot her hei ghts c an be conver te d to wind spee d at 10 c m via the usu al a ssum

pti on of a loga rit hm ic wind profi le 1 2 (Isra el sen and Hanse n 1962) . Wind s peeds U and U at 1 2 hei ghts Z and Z arerel at ed by

1 2 1 2 U / U = l og( Z /Zo ) /

log(Z /Zo ) where Zo isthe“e ffec ti ve roughne ss hei ght.”Theroughnes s hei ght i s ge nera lly on the order of mil li m et ers; wind measure ment heigh ts can co nv enien tly be ex pr essedin mm in order to a chi eve a vertic altr ansl at ion of an observe d wind spee d dat um . For exam

ple , m anyte rres tri alUSA weathe r stati ons measure windspeed s at18 -2 0 fee t (6 m) abo ve g ro un d leve l. W indspeedat 10 cm

can be estimated by multiplicationof this dat um by (log 100)/( log 6000) , t hat is , by

reduc ing t

he observati on by a fa ct or of 1. 89. Thest andar d obse rvationa l hei ght f or wi nd spe ed data

in oceanographi c investigati ons i s 10 m, in this cas e requirin g reductio n of the data b y a factorof 2 , to gener at e va lue s of W IND for EXAMS . Wind s peeds read by EXAMS from

a PRZMmet eo ro log ical file are au tomatically tran slatedto 10 cm heig ht. 2.3.2.3 Exch ange Cons tants for Mol ecu larOxygen Hydro dyn amic turbu lence nearthe air -w ater inter face is gener at ed by

a vari et y of m echanis m s. In s wiftly f lowi ng stream s and ri vers, bed shear st ress on t he m ov ing wate rs g en er at es ed dy tur

b u le n ce th atcanke ep the enti r e w at erco lumn in a st at e of const ant

agit at ion. Where ri vers wi den into c oast al est uari es, adve ct ion ve loc itie s de cre ase , but them oti on of t

he ti des te nds t o m ai nta in s trong turbulenc e in thesurfa ce wat ers. In lakes and in the ope n oc ean, wind s tre ss is a primary force produci ng tur

bule nt moti ons in theupper p art of t he wate r co lumn . W in dwav es tr av e l f arbe yo n dth e s to rm sy st ems produci ng the m

in the larges t l akes and in t he oc eans , and the great oc ean curre nts and upwel ling z ones gener at e uppe r wat er turbul encebey ond t

hat attributa ble to the winds al one. In sm al le r lakes, wind stress m aybe dire ct ly res ponsible for m ost

of t he hydr o dyn ami c mo ti o ninth e s ys te m. EXAMS requires an oxyge n e xchangec onst ant as an input

dat um for e ach com

partm ent from whic h a pollutant can volatil iz e. The i np ut dat um ( KO 2, cm @ h ) i s a ssum ed t o be the exc hange

! 1 const ant m eas ured at 20 E C, o r cor rec te d to that t em

perature
. EXAMS use s t

he conventiona l engi neering c orrec ti on (equival ent to a n Arrhenius e xpress ion) for c onverting KO2 to the temperature (T CEL) of eachcompartment (Kram er 1974)
(KO2 is al so di vide d by 100 to conver t c m @ h to m @ h )
.

! 1

! 1 Rea eration rat es can be m eas ured in thefi el d in a num ber of ways , i ncluding t

rac er t echni ques (Tsi voglou et al. 1972) and oxy ge n r e l e a sei nt o a

ni tro ge n- sp arg e d d om e (Cope land and Duffer 1964, Hal l 1970) . La cki ng m eas ured va lue s, oxy gen exchange c onst ant s c an in m anyinstances be estim at ed fr om ot he r pr op e rti e s of

the s y st e m . Kr am er (1 97 4) has b riefly revi ewed the avai la

ble predi ct ive equati ons for estim at ing oxyge n exc hange coeffic ie nts in stream s and ri vers. Most of the se cont ai n te rm s for flow vel oci ti es and depth. Many al so inc lude longi tudinaldispe rsi on coeffi ci ent s, ene rgy grade lines, and c hannel widt

hs. Although pr edi ct ive equati ons have be en succ ess fully us ed for ri veri ne s yst em s, ge nera lly t heseequati ons si gnifi cantly

under- predi ct

rea erati on in est

uari ne s yst em s. Oxygen exchange const ant s in rive rs are ge nera lly on theorder of 5 t o 20 c m @ h . In est

uaries, e xchange c onst ant s of 4 to 25 ! 1 cm @ h , and as large as 100 cm @ h , have bee n observe d. Li ss a nd
! 1

! 1 Slate r (1974) es ti m at ed an ave rage exc hange constant f or t he open s ea of 20 c m @ h .
! 1 In t he m ore quie sce nt wat ers of lakes and ponds , re aer at ion m ay be prim ari ly

de te rm ine d by the loc alwinds . B anks (1975, B anks and He rrera

1977) s howed that t

he e ffec t of

wind on rea erati on rat es can be s epar at ed int o two dis tinct zones. At wind spe eds (at 1 0 m h e i g h t ) l es s th anab o ut 5 .5 m @ s , exch ang e con stants ! 1 corre late wit

h thesquare r oot of

wind spee d. At

highe r wi nd spee ds, t he e xchangeconstan t i ncre ase s a s t he s quare of t

he wind ve loc it

y. Banks (1975) give s, f

or U < 5 .5 m @ s , ! 1
( 2- 84)

an d , f o r 5. 5 m @ s # U

< 3 0 m @ s , ! 1

! 1 ( 2- 85) where KL is th e o x yg enex ch an g e c o n st an t ( inm @ s ) and U is
! 1 w in dsp ee d(m @ s ) at

10 m abovethewat er s urface. O ver a ! 1 r an g e o f win dsp ee d s fr o m 1 to 30 m @ s , the oxyge n exc hange
! 1 const ant thus would changefrom 1.5 t o 104 c m @ h . When t he
! 1 oxyge n pi st on ve loc it

y is not ent ere d, EXAMS use s Eq. (2-84) or Eq. (2 -8 5) to c al cul at e i ts value. Banks ’ equati ons are not te m perature -spec ifi c; the y we re de rive d as an am al gam of st udie s at m anyte m

perature s. E xam s t akes theres ult of Banks’ equations and adjust s for the am bient wate r t em

peratureusing (2-83) 2.3.2.4 Vali dati on and Uncer tain ty Stud ie s A num ber of r eport s on vol at il iz at ion from nat uralwat er bodi es have been publi shed. T heses tudi es providegood i llustrations of the gene raluti li ty

and le velof

reli abi li ty

of t he t wo-res is tance m odeldeve lope d for EXAMS . 2.3 .2. 4.1 Rad

on in sma ll lakes in the Can ad ian S hield Em erson (1975) conduc te d an e xperi m ent alinve st igati on of t he 222 los s of radon ga s (R

n ) fro m sm al l l akes in Cana da’s Ex p er ime nta l L ak es Ar ea(E LA ) . H e r ep o rte dhi s r es ults in terms37

T E C 10 X 1 0 H

4 2 0 4. 24 4. 25 5 3. 40 5. 31 10 2. 77 6. 50 15 2. 31 7. 81 20 1. 95 9. 24 2 5 1 .6 8 1 0 .8 3 0 1 .4 6 1 2 .3 3 5 1 .2 9 1 4 .0 4 0 1 .1 6 1 5 .6 4 5 1 .0 5 1 7 .2 5 0 0 .9 6 1 8 .8 T a b le 6 . R n S o lu b il it y

( 2- 88) of exc hange const ant s for Rn ga s; the“be st e st im at e” was 0. 16 to 0. 40 m /d. Averagewind velo ci ti es, m eas ured 1 m abovethe w at ersur f

ac e, we r e ab o u t1 .5 m @ s . Sum m er epil im

nion
! 1 te m perature s in the se lakes are about 20 E C (Sch indl er 1971)
. Wind spee d and te m

peraturesuffi ce, given the Henry ’s L aw const ant for R n, t o derive an i ndepende nt e stim at e of the Rn ex ch an g e c o n st an t f

r o m EXAMS ’ two -re sistan ce model.
EXAMS com

putes both a gas- and l iqui d-phasetr ansport resi st ance . R

n tr ansport

is usua lly c ontrol le d by t

he l iqui d-phase resi st ance . Under

a suffi ci ent ly

st agnant ai r m ass , howeve r, gas-pha se resi st ancec an be greatly m agni fie d. In thi s inst ance , compu tati o no f the g as-p has e resistan ce serv es to illustr ate EXAMS ’ pr ocedur e, andto demon strate th at Rn tran spo rt is cont roll ed by eve nts in the li quid phas e of t he a ir- wat er inte rfac e of t heselakes. Wilhe lm , B attino, and Wilc ock (Wi l he l m e t a l
. 19 77 ) give the aqu e ou s so lub i l i tyof

r a do n g as as the m ole fra ct ion X

under 1 atm parti a lpr e ss ur e ( Tabl e 6 ). Th e Hen ry’s Law co nstan t ( H , atm -m m ol ) of R

n gas bet ween 3

! 1 0 and 50 E C can be com pute d from t hesedata. Regr ess ion of

the se dat a on the model H = A exp (-B /R T

) where R is t he gas const ant

(1.9872 cal/de g m ole ) and T

is Kelvin te m perature , y ie lds A = 660.5 andB/R =2615, a ccounting f or 99% of t

he variation i n the Hen ry’s Law co nstan t with te m perature
. EXA MS ’ inp ut data thus coul d inc lude HENRY = l ogA = 2.82, and E H E N = (B/R)×R ×0.001 ( kcal/c al ) = 5.197 kc al/m ol. EXAMS would the n com puteloc al(com

part m ent -spec ific) values of t

he He nry’sLaw const ant for r adon, as a func ti on of envi ronm ent alte m perature s (TCE L), via

Eq. (2-79). In what fol lows, theHenry ’s L aw const ant at 20 E C will be tak en as 0 .09 23 9 atm-m /mol. 3

W A pi stonv e l oc i tyf

or w at e r va

por ( V , Eq. (2-82)) c an be co mp ute df

r o m th e o b se rv edw in ds p ee d( 1 .5 m @ s at 10 0 0 mm ! 1 hei ght). EXAMS ’ i nput ( W IND ) i s re fere nced to a 10 cm hei ght above the wat er s urfac e. The obs erve d wind spee d can be corre ct ed t o a 10 cm

hei ght by

as suming a

logari thmic wind velo city pro file, giving W IND =1. 5 (lo g 10 0 /l o g 10 0 0 ) =1 .0 m @ s . ! 1 W The wat er vapor exchange const ant ( from E q. (2-82)) is the n V = 0 .1 8 5 7 +( 1 1 .3 6 ) ( 1 .0 ) =1 1 .5 m @ h , and thegas -phasetr ansport ! 1
g resi st ance(R in Eq. (2- 76 )) is ( 2- 86) = 0.079 h @ m ! 1 Em erson’ s ( 1 97 5) inves tigatio ns w ere co nductedin small (3 .6- 5.6 ha ), sha llow(mean dep th 3 .6- 5.6 m) dimictic lak es with rel at ive ly l ong hy draul ic r esi dencetim es (3.2-4.2 yr) (Brun skill andSchin dler197 1) . The hydr odynamics of these lak es is cl early dominat ed by

wind stress , and Banks’ (1975) equati ons (Eqs.(2-84) and (2- 85)) c an beuse d to estim at e an exc hange const ant for mole cul ar oxy gen. The inp ut datum for t hese equations shoul d be refe renc ed t o a hei ght of 10 m abovethe watersurf

ace. Th e o b se rveddatum thu s must be tran slatedto 10-m hei ght vi a U

= 1 .5 ( lo g 10 0 0 0 / lo g 10 0 0 ) = 2 .0 m @ s . U ! 1 is les s th an5. 5 m @ s ; E q.(2-84) the reforeappl ie s and
! 1 = 5 .9 3 ×1 0 m @ s . -6

! 1
EXAMS ’ input

dat um (KO2) ha s di m ensi ons of cm @ h ; the units
! 1 conversion yiel ds KO2 =2.13 c m @ h fordirect en try. (Re call,
! 1 ho wev er, th at EXAMS w i l lus e B ank s’ e qu at i on s t o g e ne rat e KO 2 wh enon lyth e w in dsp ee dis en te r ed(1 .0 m @ s at 10 c m).)
! 1
EXAMS ’ es ti m at es the li quid-pha se t ranspor t res is tance usi ng the m olecularweight

of t he pol lut ant

as an inde xing f

act or. T he tem peratureof t

he epil im nion ( 20 E C ) i n t

hi s c a seob vi at e s the need for c onversi on of KO2 t o a diff ering va lue at

the te m peratureof t

he e nvironm ent (E q. (2-83) ). T he l iqui d-phase

l Rn t ranspor t r esi st ance(R in Eq. ( 2-77)) c an becom pute d as ( 2- 87) = 123. 66 h @ m .

! 1 Res is tance in t

he li quid phas e thus am ounts to 99.9% of t he t ota l Rn t ranspor t r esi st ance ( Rt =Rg + Rl =123.74 h @ m ). T he
! 1 estim at ed e xchangecons tant f or Rn gas is the reforeRt = -1 8
. 0 8 × 1 0 m @ h = 0.1 9 m/d, wh ich va lue canbe comparedto

-3

! 1 Em erson’ s (1975) expe rim ent ales ti m at e of 0.16 - 0.40 m /d. Oth er models con sider ed fo r ind exin g ox ygenpiston velo city to a s tudy co mpound us e t

he re lati ve di ffusi vitie s of oxyge n and the m at eri alof inte rest

(se e page 3 6) . Under

the se m odel s, E q. (2-77) for theli quid pha se transport res is tance becom es

VO Where K is a li quid-pha se transpor t index m eas ured by

the te chni ques of Hi llet

al
. (1976) , or estim at ed fr om theaque ous diff usi vit y of thepolluta

nt, expre sse d as a rat io of dif fusi vitie s or as som e fractiona l powe r of t hat ratio. A com

pari son of results from

the se m odel s a

pplied to Rn evas ion provide s a m easu re of “ m odelunce rta int y; ” he re wewil l c ontra st the sens itivi ty

of e st im at ed vol at il iz at ion t o th e m odelchos en, as38 ag ainst th e valu es cho senforthe par ameters use d to calcu late m odelres ult s (i .e. , param et er unc ert ai nty). Em erson (1975) , c iting Rona (1918) via Peng (1973) give s a diff usi on cons tant f

orRnof 1.37×10 cm @ s at

25 E C. The -5 2

! 1 diff usi on c on st ant

of m ole cul ar oxy gen in wat er at 25 E C is 2.41×10 cm @ s (Vi vian and King

-5 2

! 1 (1964) , ci te d f ro m Re id, Praus nitz, and She rwood (1 97 7:5 76 ) ). The diff usiv ityratio 2 (D(Rn)/D(O )) is thus 1.37/2.41 = 0.568. Appli cation of Eq. (2- 88 ) thenyields a liqu id-p has e trans po rt resis tance in these small

l lakes of R =1/( 0.0213×0.568) = 82. 6 h @ m and a Rn exchange ! 1 l g const ant (1/ (R +R )) of 0.29 m

/d. Appli cation of surfa ce rene wal l the ory woul d give R = 1/ (0.0213× % 0.568) =62.3 h @ m and a Rn ! 1 exchange c onst ant

of 0. 38 m @ d .

! 1 Tsivoglou (1967) m eas ured s im ultaneous exc hange co nstants f or ox ygenan dRninlabor atory exp eriments, arriv ing at a ratio bet ween t hem of 0.70. (Thi s va lue corr esponds to the 0.63 r oot of t he diffusivi ty

ratio.) Appl ic at ion of

Eq. (2-88) in thi s c ase l yi el ds R = 1/(.0213×0.70) =67.1 h @ m , and a Rn e xchange
! 1 const ant of 0.36 m

/d. The modeles ti m at es of t he R n exc hange const ant (0.19, 0.29, 0.36, and 0.38 m /d) thus allfallwit

hin t he range of E m erson’ s (1975) e xp e rim e nta l“best es ti m at es”of 0. 16 to 0. 40 m/d; ther e is no b asis to p ref er on e model to an oth er in thi s a ppli cation. Lis s and Slater (1974) havees ti m at ed avera ge e xchange const ant s for oxy gen (20 cm @ h ) and wat er vapor (3000 cm @ h )
! 1

! 1 appl ic abl e t o thesurfa ce of t he ope n se a. Thes e va lue s have on occa si on bee n rec omm ended as appropri at e t o es ti m at ion of the volati li zation of

pollutants from

inl and wate rs. For Rn t

ranspor t in t heses m al l E LA l akes , useof L is s and Sl at er’s (1 97 4) ocean ic exchange c onst ant s woul d give

g R = ( 293.15×8.206× 10 )/( 30.0×0.09239× % [1 8/2 22 ]) -5 = 0.0305 h @ m ! 1

l R = 1/ (0.2× % [32/222] ) = 13.17 h @ m ! 1
tgl R = R + R = 13. 2 h @ m ! 1 and a Rn exchange c onstant (1/R t) of 1.8 m

/d. The da

ngers of un critical extrapo lationof env iron mental driv ing for ces (inthis cas e the r eae ration rat e or oxyge n pi st on ve loc it y) betw een sys te m s i s a

ppare nt: TheE LA Rn exchange const ant , e st im at ed from oxyge n and wat er vapo r t ranspor t in theopen sea , i s an order of m agni tude too large , a s c om pare d wit

h ei the r t

he measuredvalue s, orto estimates fro m volatilizationmodels param et eri zed via

wind s peed and B anks’ (1975) com pil at ion of oxyge n exc hange rat es as a func ti on of wind vel oci ty . The cri ti calel em ent

in an a ccur at e a

ppli cation of EXAMS to this si tuati on is the refore , t

he s el ection of

appropriate values for t

he envi ronm ent aldri ving va ria ble s (W IND and KO2), rathe r t han the choi ce of a m odelfor indexi ng Rn li quid-pha se transport resis tance again st EXAMS ’ environm ent aldes criptors
. 2.3.2.4. 2 1,4-Dichl orobenzene

in Lake Zuri

ch Schwarzenba ch e t a l. (1979) conduc te d a one-y ear st udy of the fat e and tr ansport

of 1, 4-dic hlorobe nzene(DCB ) i n L akeZ uri ch, Switzerla nd. C onta minate d eff

lue nts from was te-w ater treat m ent plants arethepri m arysourc e of DCB loa dings ent eri ng thelake (them at eri alis use d as a re si dent ia l toil et cl eans er). The conce ntrati on of DCB in t heseeff lue nts is rel at ive ly

cons tant among treatment plan ts andov er time, p ro vid ing anopp ortun ity for a ca se-hi st ory tri alof EXAMS ’ us e ( i n Mo de 1 ) as a steady-state ev aluativ e model. DCB is not subjec t to appre ci abl e de gradati on by chemi calor bioc hemic alproce sse s in aquati c s yst em s (Ca ll ahan et al . 1979) ; its beh avio r is ther efo re go vernedby vo latilization , tran spo rt, and sorpti on phenom ena. EXAMS in thi s inst ancerequires 4 chemical des crip tors : the molecularweig ht (MW T), so lubility (SOL), oct anol -wat er partition coef fic ie nt ( KOW), and Henr

y’s Law c onst ant

(HENRY) . Them olecular wei ght of

DCB 6 4 2 (C H Cl ) i s 147.0. The aqueous solubility and oct anol -wat er partition coef

fic ie nt of DCB have been m eas ured by Banerje e e t al
. (1980) . DCB i s soluble to 0.502 mM in wat er at 25 E C ( SO L = 73 .8 p pm). Its o ctan o l- waterpartitio n co eff icient (K OW ) is 2340. The Henry ’s Law cons tant of DCB has not bee n m eas ured, but it c an bees ti m at ed (f

or 25 E C, the temper atur e of th e solubility observati on) from

thevapor press ure/ solubil it y r at io (Mac kay andWo lko ff 19 73 , Mackay andLeinon en 19 75 ) . Par a- D CB is a sol id at

nor m ale nvironm ent alt em

perature s (mp 53.1 E C (Weast 1971)
. The va

por pre ssure(Pv) of sol id 1, 4-DCB at 10, 30, and 50 E C is 0.2 32 , 1.6 3, an d 8.4 35 torr, re spe ctively (Darki s e t a l
. 19 40 )
. R e gr e ss i ono f the sed at ao n the mod elPv =A exp(-B /T) yi el ds A =9.63×10 , B = 8223, and acc ounts for 11 99.99% of t

he variati on in Pv wi th t em perature
. EXAMS coul d be loa ded wi th t

he re sul ts of thi s re gress ion a nalysi s, i .e. , VA PR=lo gA =11 .98 , andEVP R=(B) (R) (0 .001)=16.34 kc al/mol. Alterna tiv ely, the H enry’s Law con stant canbe estimated via int erpol at ion of the obs erve d va por pre ssureto 25 E C. The l atte r proce dure wa s use d for t his ana ly si s of DCB in L ake Zuri ch. The inte rpolate d value of Pv i s 1.011 torr at 25 E C. The He nry’s Law c onst ant

is the refore (1.011/ 760)/0. 502 = 2. 66×10 -3 atm-m /mol.

3
EXAMS al so re quire s e nvironm ent alinput dat a de scribin g Lake Zuri ch. In t

his ca se, a “canonic al ” data se t ne ed only inc lude infor m at ion r el evant

t o t ranspor t, sorption, and volati li zation of neut ral organi cs. Schwarze nbach et al
. (Schwarze nbach et

al
. 1979) r est ric te d t hei r inve st igati on t o t

he cent ralba si n of

Lake Zuri ch. Bot

h theupper and t

he c ent ralbas ins rece ive DCB-c ontam inate d wast e- wate r ef flue nts . Thece ntra l ba si n can be m odeled in i sol at ion, however, by tre at ing inputs from the upper ba si n as adve ct ed l oadi ngs t o the(downst ream) cent

ral basin. Exc ept

a s note d ot

herwi se, t he e nvironm ent aldes cripti on give n bel ow was drawn from Schwarze nbach et

al
. (1979)
.39 Par am et er C om par t m ent N um ber 1 2 3 T y p e E H B Ar ea, m 6. 8×10 6. 8×10 6. 8×10

2 7 7 7 D ept h, m 10 40 0. 02 Vol , m 6. 8×10 2. 72×10 1. 36×10

3 8 9 6 Sused ( m g/ L) 5 5 B u lk d (g /c m ) 1 .5 -3 Pct wa, % 150 Fr oc 0. 02 0. 02 0. 02 W i nd, m @ s @ 10cm ! 1 1. 38 Tabl e 7. Env i r onm ent al D at a f or C ent r al B asi n ofLake Zur i ch The c ent ralbasi n has an ave rage hydraul ic resi dencetim e of 1.2 ye ars. Banks’ (1975) m et hod for e st im ating K O2 from wind spe ed thu s seems most appr opriate, lack ing exten sive d irect field m eas ur ement s of the oxyge n exc hange const ant . Theannua l meanwi n d

sp ee dfo r th e p er io d19 5 5
- 6 3 , 1 9 6 5
- 6 9 wa s 2 .6 m @ s ! 1 (5.1 knot s) (unpubl is hed data for Zuri ch, Switzerland/Kl ote n, summ ari zed by t

he U.S . Ai r Force E nvironm ent alTec hnic al Appli cations Cent er, suppl ie d courte sy of NOAA). Although a stationhistory was n o t ava ilable, th ese da ta wer e in all probabi li ty

coll ect ed at

the conve nti onalm et eorol ogic alsc ree n hei ght ( 6 m). Wind s peed at 10 m hei ght woul d be 2.6(l og 1 0 0 0 0 /l o g 6 0 0 0 ) = 2. 7 5 m @ s . C om putati on of KO2 vi a Eq. (2-
! 1 84) t hen gi ves 2.5 c m @ h via
! 1 Av erag e win d sp eed a t 1 0 cm heigh t ( EXAMS ’ i nput pa ram et er W IND ) wo u ldbe 2. 6 ( lo g 10 0 /l o g 60 0 0 ) = 1 .3 8 m @ s . ! 1 The m ean dept

h of the c ent

ralbas in i s 50 m , and thesurfa ce are a is 68 km , gi ving a total volum e of 3.4×10 m . Thelake

2 9 3 stratifi es during the sum m er ( May

through Sept em

ber); the the rm ocl ine se ts up at a dept h of 10 m by early May and rem ai ns at a bout that dept

h untilf al l t urnover (Li1973) . A s im ple “box” m odelof t

he l ake can be const

ruct ed for EXAMS by divi ding t he lake into 3 vertic alzone s, e ach wit h an are a (AREA) of 68 km2 or 6. 8× 10 m . Fo r the epi l i mni ons e gm e nt ( c om part m e nt 1, 7 2 TY PE (1) = “ E”), DEPTH (1) =10 (m), and VOL (1) =6.8×10 (m ). 8 3 The hy polimnion ( com

partm ent 2, TY PE (2) =“H” ) t

hen ha s DEPTH (2) = 4 0, and VOL (2) =6.8×10 ×40 =2.72×10 m . 7 9 3 Assuming a

2 c m dept h of active be nthi c s edi m ent s ( com partm ent 3, TY PE (3 ) = “ B ” ) gi ves DE PTH (3) =0.02, and VOL (3) =1.36×10 m . 6 3 Li (1 97 3) compute d th e v ertical ed dy dif fu sioncoef

ficien t in Lak e Z uri c h, a s af

un c t i onof

dept h and s e a so n, f ro m ob se rved m onthly t em

peratureprofi le s avera ged ove r 10 ye ars of rec ord. The a nnualm ean te m

peratureof the epil im

nion (0-10 m

dept h, TCEL (1)) wa s 11 E C; t

he m ean hypol im

nion te m peraturewas 5.6 E C ( TCEL (2 )). The ed dy dis per sioncoef ficien t at 1 0 m depth aver aged 0.058 c m @ s duri ng the str ati fie d peri od and was 2

! 1 about 1 c m @ s duri ng thebal anceof t he y ear . Theannua l m ean 2

! 1 value ( DS P for param et eri zi ng ave rage tr ansport betwe en t

he epi li mnion a

nd hypol im

nion) was 0. 6 cm @ s ; EXAMS ’ i nput 2

! 1 value of DS P = 0. 2 m @ h . The dispe rsi on coe ffi ci ent for 2

! 1 exchange be twe en t

he hy poli mnion a

nd bent hic se dim ent s was taken a s 10 m @ h .

-4 2

! 1 In order t o com

pute sorption of

DCB to sedi m ent

phas es, EXAMS require s a desc riptio n o f th e ben thic an d su spe nd ed sed iments in th e s ys te m ( FROC , BULKD , PCTWA ). Gi ven t he s iz e of Lake Zuri ch (i .e. , t

he relative ly

sm al l ove ral l s edi m ent :wate r rati o), and t he s m al l oc tanol: wat er parti ti on coe ffi ci ent of DCB (2340), DCB wil l oc cur prim ari ly in the dis sol ved s tate in thewat er column of t

his lake. The va lues chose n for FROC , BULKD , and PCTWAarethe reforenot critic alto the outc om e of the sim ul at i on , so l on g a s the yarer e pr e se nt at i ve. Tabl e 7 summarizes the o bse rv ed an d assu med valu es that w ere u sedto desc ribethece ntra l ba si n of L ake Zuri ch t o EXAMS . The c om bine d fl ow from

theupper basin ( 2,5 00), sm al l c ree ks

drai ning into t

he c ent ral ba si n (100), and t

reatm ent pla nt effluent s (28) was 2,628× 10 m /yr, gi ving STFLO (1) =3×10 m 6 3 5 3

@ h . Thetot alloa d of DCB on thece ntra l ba si n was 88 kg/yr, of
! 1 whic h 25 kg derive d from the upper basi n, 62 kg from

tr eat m ent plan t efflu ents d isch ar g edinto the centra l basin , and1 kg /yr from ot her minor source s. F or t he EXAMS s i m

ul at i on , the se loa dings weresum

m ed t o g ive a STRLD (1) t o theepi li mnion of the c ent ralbas in of

0.010 kg @ h . (Cha

pte r 3.4 dem onstrat es the
! 1 ent ry of t hese data into EXAMS , and thecom m and s equenc es used to c onduct

theana ly si s.)
EXAMS (Exam s Out

put T abl e 8 and Exam s Out put T abl e 9) predi c t e d a

t ot a lm a ss of

37 kgDC B r e si de nt

i n t he wat er column (DCB conc ent

ration 10. 7 ng/L ), a

flux of DC B t o the atm osphereof 59.4 kg/yr, and wate r-borne export of 28. 2 kg/yr. Bycom pari son, S chwarz enbac h et al
. (1979) es ti m at ed a resi dent m ass of 38 kg ( 11.2 ng/L) in t he lake, and, from

a m ass bal ancef or DCB , e st im at ed t

he flux to the at

m osphereto be 60 kg/yr, wi th a

wat er-borneexport

of 28 kg/yr. During the st

ratifi ed pe riod, cont aminated tre atm ent pla nt effluent s spr ead late ral ly through them et al im

nion of the lake and mix wi th bot

h thehypol im

nion a nd theepi li mnion ( S ch w ar z e nb ac het a l. 19 7 9 ) . A ss umin g th atth e s ummerti me loa dings mix upward and downward in e qualm eas ure, EXAMS ’ loa dings c an bem odifi ed t o ac count for t his phenom enon. The summ er ( 5 m onth) DCB loa d to the hypol im nion woul d am ount to ( 5/12)( 62) /2 kg/

yr, whic h can be ent ere d to EXAMS as a “dri ft”loa d ( DRFLD (2)) of 1.5×10 kg @ h . Pro po rtion ate -3

! 1 reduc ti on of theDCB loa d on t he epil im nion gives STRLD (1) = 8.5×10 kg @ h . Gi ven thi s m odifi cation, EXAMS predi ct ed a

-3

! 1 larger conce ntrati on of DC B in thehypol im nion ( 13.5 ng/L) , and40

M et hod C onc n g /L M ass

kg V o la til e

k g / yr E x p o rt

k g / yr M ea s ur ed 11

. 2 38

. 60

. 27 +1 1 0 .7 3 7

. 5 9 .4 2 8 .2
Par t i al l oad hy pol i m ni on 1 0

. 7 ( E)

1 3

. 5 ( H) 4 4

. 5 9 .4 2 8 .2

DCB O 2 D /D 1 2 .9 4 4 .2 5 3 .7 3 3 .9 9 .1 3 1 .3 6 3 .7 2 4 .0

O 2 K = 2 0 c m /h
W V = 3 0 m /h 1. 95 6. 69 82. 5 5. 13 T a b le 8 . R e s u lt s o f EXA MS si m ul at i ons oft he behav i or ofD C B ( 1, 4- di ch l or ob en z en e) i n L ak e Zu r i ch , Sw i t z er l an d Ecosystem: Lake Zurich - central basin (Untersee) Chemical: 1,4-Dichlorobenzene
--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.
--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 7.3 20.00 1.074E-05 1.074E-05 1.759E-04 0.00 2 29. 80.00 1.074E-05 1.074E-05 1.759E-04 0.00 ======== ====== 37. 99.33 and in the Benthic Sediments: 3 0.24 100.00 1.798E-04 1.065E-05 1.744E-04 0.00 ======== ====== 0.29 0.78 Total Mass (kilograms) = 36.75
--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics. Exa m s O ut pu t Ta bl e 8. Pr ed i ct ed c on ce nt r at i on a nd r es i de nt m a s s o fDC B.

Ecosystem: Lake Zurich - central basin (Untersee) Chemical: 1,4-Dichlorobenzene
--------------------------------------------------------------- Table 20.01. Exposure analysis summary.
--------------------------------------------------------------- Exposure (maximum steady-state concentrations): Water column: 1.074E-05 mg/L dissolved; total = 1.074E-05 mg/L Benthic sediments: 1.065E-05 mg/L dissolved in pore water; maximum total concentration = 1.798E-04 mg/kg (dry weight). Biota (ug/g dry weight): Plankton: Benthos: Fate: Total steady-state accumulation: 36.8 kg, with 99.33% in the water column and 0.67% in the benthic sediments. Total chemical load: 0.24 kg/ day. Disposition: 0.00% chemically transformed, 0.00% biotransformed, 67.79% volatilized, and 32.21% exported via other pathways. Persistence: After 216. days of recovery time, the water column had lost 50.52% of its initial chemical burden; the benthic zone had lost 19.55%; system-wide total loss of chemical = 50.3%. Five half-lives (>95% cleanup) thus require ca. 35. months. E x a m s O u tp u t T a b le 9 . E XA MS su m m ar y ofDC B i n L ak e Zu r i ch . a re si dent m ass of 44 k g D CB; the predi ct ed fluxes and DC B conce ntrati on in the epi li mnion ( 10.7 ng/L) we re unc hanged. A te st of ot her t ranspor t indic es requires kn owle dge of DCB diff usi vity. The aque ous di ffusi vit y of DCB can be estim at ed

b b from m olar volum e at

t he norm alboil ing point ( V ), and V can

c it sel f be estim at ed fr om V , molar volum e at t he c ritic al te m perature c (Re id e t al
. 1977) . V for p- DCB is 372 c c/ g-m ole ; b c V =0.285(V ) (Tyn and Ca lus m et hod) = 140.9 c c/ g-m ole
. 1.048 The a queous diff

usi vit y of p-DCB at 25 E C, com

pute d via the Hayduk -Lau die rev isionof the Othmer- Th ak ar relation ship , is (13.26×10 ) (0.8904 )(140.9 ) = 8.46 ×10 cm @ s ,

! 5

! 1.4

! 0.0589

! 6 2

! 1 taking the visco sit

y of wat er at 25 E C a s 0.8904 cp (W east 2 1971:F- 36) . Thedif

fusi vit y r at io D( DCB)/D( O ), gi ven t he 2 diff usi vit y of m ole cul ar oxyge n D(O ) as 2.41×10 cm @ s , is
! 5 2

! 1 0.35; it s squa

re r oot i s 0.59. Substit uting t heseva lue s for EXAMS ’ m ole cul ar we ight tr ansport inde x gave estim at ed re si dent

DC B m ass es of 43.8 kg ( 12.9 ng/L), and 31.0 kg ( 9.1 ng/L), respe ct ive ly . Si m ulati on using Liss and Slate r’s (1974) open-s ea transport param et ers (wit

h the m ole cul ar weight transport inde x) pre dic te d a resi dent m ass of on ly 6.6 kg ( 2.0 ng/L ). Th ese co mpariso ns ar e su mm arizedin Tabl e 8
.

Predi ct ed c oncent

ration, res ide nt m ass in wat er c olum n, and fluxe s vary as a func ti on of loa d r outing, m et hod use d to inde x int erpha se transport

aga inst its envi ronm ent alref ere nts , and envi ronm ent altr ansport

paramete rs. The de faul t mole cul ar wei ght t ranspor t i ndex provi ded t

he m ost ac curate predi ct ion of the volati li zed flux of DCB f rom L ake Zuri ch. As was the ca se for R n tr ansport

in ELA l akes , howeve r, t he s el ection of

proper values for e nvironm ental driving forc es see m s t o be m ore

cri ti cal , t han i s t he choi ce taken am ong m et hods of inde xing po llutan t transp ort acros s the air- waterinte r f ace again st its envi ronm ent alref

ere nts
.

Refer enc es for Chap ter2.3.2. Bane rjee , S. , S. H. Yal kowsky, and S. C. Valvani . 1980. Water solubil it y and oct anol/water parti ti on coe ffi ci ent s of or gan ics. Limitations of the so lub ility-partition co eff icient correlatio n. Env iron mental Science andTechn olo gy 14 :1227-1229. B ank s , R
. B
. 1 9 7 5
. S o m e f e at ur e s o f w i n da c t i o no ns ha l l ow lakes. Journal of theEnvironm ent alEngine eri ng Divi si on, Proc. ASCE 101(EE 5) :813-827. Bank s, R . B ., and F. F. Herre ra. 1977. Ef fec t of wind and rai n on sur face reae ration. Journal of the En viro nmental Engine eri ng Divi si on, Proc . ASC E 103(EE 3) :489-504. Bird , R. B., W . E. Stew art, an d E. N . Ligh tfoo t. 1 96 0. Tr ans po rt Phenom ena. John Wil eyand Sons, Inc., New York. Brun ski ll , G. J., and D. W. Schindl er. 1971. Geogr aphyand bathym e try

of s e l e c t e d l ake ba sins , Expe ri m e nt a lL akes41

Area, nort

hwest ern Ont ari o. Jour nalof t he Fi sheri es Res ear ch B oard of

Canada 28 :139-155. Burn s, L . A. 1982. Ide nti fic at ion and evaluat ion of fundam ent al tra nsport and tra nsformation process mode ls . Pages 101-126 in K. L. Di ckson, A. W. Maki, and J . C ai rns, Jr., edi tors
. Mod eling the F ate of Ch emicals in the Aquatic Envir onm ent . Ann Arbor Sci encePubl ., Ann Arbor, Mi chi gan. Burn s, L. A . 1 98 5. Mo dels f orpred icting the fate o f synth etic chemic al s in aquatic s yst em s. P ages 176-190 in T. P. Boy le , edi tor. Val idati on and Predi ct abi li ty of Laboratory

Me thods fo r Asses sing the Fate andEffects of Con taminants in AquaticEcos ystem s. AS TM S TP 865. American So ciety for Tes ting and Mat eri al s, P hil adelphia , Pe nnsylvani a. Cal lahan, M. A. , M. W. Slim ak, N. W. Gabel, I. P. May , C . F. Fowle r, J . R . Fre ed, P. J enni ngs, R . L. Durfee, F. C. Whitm ore, B. Mae stri, W . R. Mabe y, B. R. Holt , and C. Gould. 1979. Wate r-Re late d Envi ronm ent alFat e of 129 Prio r ity Pollutants. Vol. II: Ha log enate d Alip hatic Hydroc arbon s, Hal og e nat e d Et he rs , Mo no c y c l i c Aromati cs, Phtha late E st ers, P oly cy cl ic Arom at ic Hydrocarbons, Nit rosamine s, and M is cel laneous Com pounds. E PA-440/4- 79 -0 29 b. U .S. Env iron mental Pr otectio n Ag ency, Washingt on, D.C
. Cop e land , B. J., andW . R. Du ffe r. 1 96 4. U se of a cl ear p lastic dom e t o m eas ure gas eous di ffusi on rate s in nat uralwat ers. Limnolo gy an d Oc eano gr aph y 9 :494-499. Dan c kw erts, P. V. 197 0. G as-L iqu id Reactio ns. McGr aw- Hill Book C o., Ne w York. Darki s, F
. R ., H
. E. V e rmi l l i on , and P
. M. Gro ss . 19 40 . pDic hloro- benzene as a vapor f um igant. Phys ic aland chemical stud ies. In du strial En gin eerin g Ch emistry 32 : 94 6- 949. Dil ling, W. L. 1977. Int erpha se transfer proce sse s. I I. Evaporati on rat es of chl oro m et hanes , e thanes , e thy le nes, propane s, and propy le nes from dilute aque ous soluti ons. Com pari sons wi th t

heore ti calpredic ti ons. E nvironm ent al Scien ce andTechn olo gy 11 :405-409. Dil ling, W. L., N. B. Tefertil le r, and G. J . Kal los . 1975. Evaporati on rat es and re activi ti es of m et hyl ene chlor ide, chl oroform , 1,1,1-tric hloroe thane , tri c hl or oethyl ene, tetrach loro ethylen e, andotherchlor inatedcompou nd s in diluteaque ous soluti ons. E nvironm ent alSci enceand Tech no log y 9 :833-838. Dobb ins , W. E. 1964. Mec hani sm of ga s a bsorption by

tur bule nt li quids . Pa ges 61-76 in W. W. E c ke nf e l de r, e di t or. Advance s in Wate r Pol lution Res ear ch. Proce edi ngs of the Inte rnationa l C onfere nce hel d in London S ept em ber 1962. Vol. 2. TheMa cMi ll an C om pany , New York. Eme rso n, S . 19 75 . Gas ex chan ge ra tes in small Canad ian Sh ield lakes . Limnolo gy an d Oc eano gr aph y 20 :754-761. Fi sc h e r, H. B ., E
. J. L i st , R
. C
. Y. Koh, J. Im ber ge r, and

N. H. Brooks. 1979. M ixing i n Inl and and Coa st alWate rs. Acade mic Pre ss, New York. Hal l, C. A. S. 1970. M igrati on and Met abol is m in a St ream Ecos yst em . Ph. D. Uni versi ty of Nort h C arol ina , C hapel Hill. Hi l l , J., IV. , H. P
. Ko l l i g, D. F
. Pari s, N. L
. Wol fe , and R
. G. Ze p p . 19 76 . Dyn amic Behavio r of Vinyl Ch lorid e in Aquat ic Ecos yst em s. E PA-600/3- 76-001 . U.S. Envir onm ent alProt ection Age ncy , At hens, Georgi a. Isra e ls en, O. W., and V. E . Hans en. 1962. Irrigati on Principle s and Pr actic es. John Wil eyand Sons, Inc., New York. Kram er, G. R. 1974. Predi ct ing r eae ration c oeffi ci ent s for pollute d est

uary . Jour nalof t he Environm ent alEngi neering Divi si on, Proc . ASC E 100 (EE 1) :77-92. Li, Y .-H. 1973. Vertic aleddy dif fusi on coe ffi cient in Lake Zuri ch. Schwei zeris che Zei ts chri ft fue r Hydrologi e 35 :1-7. Lis s, P. S. 1973. P roce sse s of gas exc hange acr oss a n air-wat er int erfa ce. Deep-Sea

Re search 20 :221-238. Lis s, P. S., and P. G. Sl at er. 1974. Flux of gases ac ross the airsea int erfa ce. Nat

ure 247 :181-184. Mac k ay , D. 1978. Volatil iz at ion of pollutants from wat er. Page s 17 5- 185 in O. Hutzinger, I. H. v. Le lyvel d, and B. C. J. Zoet em an, edi tors . Aquatic Pol lut ant s: Transf orm at ion a

nd Bi ologi calEffe ct s. P ergam on Pre ss, Oxford. Mac k ay , D., and P. J . Le inone n. 1975. Rat e of evaporation of low -so lub ility contaminan ts fro m water bo d ies to atm osphere . Environm ent alSci enceand Tec hnology 9 :1178-1180. Mac k ay , D., and A. W . Wolkoff. 1973. Rate of e vaporati on of low -so lub ility contaminan ts fro m water bo dies to atmosph ere . E nv ir o nmen ta l S ci en ce an d Techno log y 7 :611- 614. Peng , T. -H
. 19 73
. De t e rmi nat i onof ga s e xc hang e r at e s a cross sea -ai r i nterfac e by

theradon m et

hod. Ph. D. The si s. Colum bia Unive rsi ty , New York. Rei d , R . C ., J . M. Pra

usni tz, an d T . K. Sherwood. 1977. The Pro perties of G ases andLiquid s, 3rdedition . McG raw -H ill Book C om

pany , New York. Rona , E. 1918. Di ffusi onsgross e u nd Atomdurchm ess er de r Radiu m-emanation . Zeitsch rift f uerPhysik alisch e Chemie (Leipzi g) 92 :213-218. Schi n dle r, D. W. 1971. Li ght, te m perature , and oxy gen re gim es of se le ct ed l akes in the Experim ent alLake s Are a, northwe st ern Ont ari o. Jour nalof t he Fi sheri es Res ear ch Boar d of C anada 28 :157-169. Sc hw arz e nb a c h, R
. P. , E. M olnar- Ku bi c a , W. Gi ge r, and

S
. G. Wakeham . 1979. Dist

ribution, resi dencetim e, and fluxe s of te tra chl oroet

hyl ene and 1, 4-dic hlorobe nzenein Lake Zuri ch, Switzer land . Environm ent al Sci ence and Tech no log y 13 :1367-1373. Tsi vo glou, E. C . 1967. Tracer Me asure m ent of St ream Rea erati on. PB -2 29 923, Fed. Wate r Pol l. Cont r. Admin., Washingt on, D.C
. Tsi vo glo u, E. C., M. A. Mc Cl anahan, and W. M. Sande rs, III, edi tors . 1972. Proce edi ngs of a Symposium on Di rec t Tr ac erMe as ur eme nt o f

th e Re ae r at io nC ap ac ity o f Str eams42

andEstuar ies. U .S. Env iron mental Pro tectionAge ncy, Washingt on, D.C
. Vivi an, J. E., and C. J. King. 1964. AIChE J. 10 :220. Wea st , R. C. , edi tor. 1971. Handbook of Che m is try

and Phys ic s. 51st edi ti on. TheChe m ic alRubbe r Co. , C le vel and, Ohio. Whitm an, W. G. 1923. A pre l i mi na ry e xperi m ent alconfirm at ion of t he t wo-film theory of gas absorption. Chemic aland Met al lurgi calEngi neering 29 :146-148. Wilh el m , E. , R. Bat

tino, and R. J. Wil cock. 1977. L ow-pres sure so lub i l i tyof

ga se s i n l i qu i d w at e r. C he m i c a lR e vi e ws 77 :219-262. 2.3 .3 D irect Pho tolysis EXAMS includes t

wo entire ly

separate m et

hods t o com

pute rat es of dire ct photolysi s. The se m et

hods are m

utua lly e xclusi ve, and accep t diffe ren t kin d s of inpu t data. Th e first, mechanize d in proce dure “ PHOTO 1,” beg ins fr om a pseu do -fir st-o r d errate con stant ( KDP ) rep rese ntin g the ph oto lytic dec ompo sitionrate in near -surfa ce water s unde r cl oudle ss c onditions at a spec ifi ed ref eren ce latitud e (RFL AT )
. Th is inpu t rate con stant d atum is taken a s t he annualm ean value avera ged over t he entiredie l ( 24- hour) c yc le
. The second m et

hod, i n proce dure “ PHOTO 2, ” wo rk s from m eas ured l ight

abs orpti on s pectra and re action qua ntum yi el ds of t he c om pound. B eca

use thi s m ethod i s intrinsi cal ly m ore acc urat e, it

is to be pre ferre d whene ver pos sible
. EXAMS se le ct s t

he a ppropriate procedurevia an audi t of

the stru ctur e of th e chemical inp utd at a. Fo r the ex isting ionic

3 spe cies (RH et

al . – s ee SPFLG a

nd Cha pte r 2.2. 1), whe n at le ast one value of ABSORG , the l ight a bsorption s pect

rum of t he m ole cul e, is non-ze ro, EXAMS ca ll s o n procedure PHOTO 2 to comput e the phot oly si s rat e of the c hemic al
. (Tec hnic al ly this te st is exe cuted o n a sum

m at ion of the ABSORGvec tor of t

he ion ic specie s; ap o sitiv e valu e of th is sum (internal variab le ABSTOL ) i nvokes the ca llto PHOTO 2.) Not e that t he s truc tureof thi s de ci si on in effe ct

give s ABSOR

a highe r com

putational priorit y t han KDP , that is, if any ABSOR areposi ti ve, EXAMS will use PHOTO 2 and the abs orpti on spe ct rum for i ts com

putati ons, and wi llignor e a llent

rie s in theKPD ve ct or. The t echni ques used wit

hin EXAMS for c om

puting rat es of di rec t photolysi s have be en de rive d in large part from thework of Zepp and c oworkers (Zepp et al. 1975, Zepp et al . 1976, Zepp a

nd Cl ine 1977, Zepp et

al. 1977, Zepp 1978, Zepp a nd Ba ughm an 1978, Mi ll er and Zepp 1979a, b, Zepp 1980) . Zepp (1980) and Zepp and Ba

ughm an (1 97 8) s um

m ari z e d t e c hn i qu e s for predi ct ing dir ect phot oly si s in nat uralwat ers; a com

pute r code for e valuat ing t

his tr ansfor

m at ion pathway wa s described by Zepp a nd Cl ine (1977)
. 2.3.3.1 Dir ectphotolysi s i n aquati c s ystem s Dire ct photoc hemic alrea ct ions area conse quenceof t he absorption of

el ect rom agneticene rgy by a

pollutant m ole cul e. In thi s “prim ary ” phot ochemic alproce ss, absorption of a photon pr omotes th e m olecu le from i ts groundstate to an electro nically exci te d st at e. The exci te d mole cul e the n e it her rea ct s t o yi el d a photopro du ct , or decays via som e ot

her m echanis m (fluo resce nce, phosphore sce nce, et c.) back to t he ground st at e. The effic ie n cyof eachof the se ene rg y con ver sionpro cesse s is cal le d it s “ quant

um yi el d” Ö ; the law of conse rvation of ene rgy requi res that the pri m aryquant um eff ic ie nci es sum

to 1.0. T hese ideas are exp ress ed b y two fund amental laws o f ph oto chemistry. The fi rst , t

he “ Grott hus-Dra per” la w, st at es: “Only t

he l ight whic h is abs orbed by

a m ole cul e c an beeff

ective in produci ng photoc hemic alchange in the m ole cul e.”Si m ple ir radi at ion of a sy st em does not nec ess ari ly

resul t i n photoche m ic alrea ct ions ; the li ght m

ust be of wavel engt

hs t hat can be absorbe d by the chemical. Co nv erse ly, labo rato ry irra diatio n o f a ch emical with wavel engt

hs t hat arenot found i n nat

uralwat ers (<280 nm) i s of li ttle value fo r predi ct ing t he be havi or of t

he c om pound in the envi ronm ent . These cond l aw of photoc hemis try , t he “St ark-E ins te in” la

w, was form

ulate d aft er t

he discovery t

hat inter action s of lig ht andmatter are restr icted to d is crete ( qu an ti ze d ) ev en ts . T h is se co n dlaw inits mo d ernfo rm (Calv ert andPitts 19 66 :20 ) states: “Th e abso rp tionof ligh t by a molecule is a one-quantum

proce ss, so that the sum

of the pri m aryproce ss quant um yi el ds m ust be unit y.” Th e r at e o f

ph o to lyti c tr an sf

o rmat io n s i naqu at ic sy st ems depends upon bot

h theligh t inte nsi ty

in the m edium

(i n othe r words, the dose rat e), and on the res ponse of t he irrad iate d pollutant. The c hemic alres ponse is com posed of t wo fac tors : t

he ë p o ll utant’ s ab so r

p ti o nsp ec trum å ( EXAMS ’ inp ut ABSORG ), and it s quantum

eff ic ie ncyfor photochemic altr ansfor m at ions Ö (rea ct ion quant

um yi el d, EXAMS ’ inp ut QYIELD ). T he l ogic of t he situatio n canbe dev elop ed in t erm s of m on och ro matic light, with spec tra l e ffec ts subse quent ly inc orporat ed via integr at ion or summ at ion a cross thesol ar s pect rum . In EXAMS , t

he s olar spec trum i s subdi vide d into 46 wave le ngth inte rval s ( Tabl e 9 ), and t he t ota l r at e c onst ant

is com pute d as the sum

of cont ributions from

ea ch spectral int erva l. In what fol lows, however, thespe ct

ralsubsc ript s have in m ost ca ses bee n omitted, in th e intere st of n otatio nal simplicity. Light int ensi ty

dec rea ses expon ent ia lly wi th depth in any absorbing medium. T his phenom enon i s known a s t he Bee r-Lam

bert la w, and can be s tate d m at

hem at ic al ly

as :
( 2- 89) where Eo = photon sc al ar irradi ance , phot ons c m s ! 2

! 1 z = d ep th , m ( EXAMS vari abl e DEPTHG ) K = di ffuse atte nuat ion c oeffi ci ent for irradi ance , /

m , and ( 2- 90) (Smit h and Tyl er 1976) , wher e D is them ean opti calpat h per unit z (dim ensi onle ss),43 a is theabs orpti on coe ffi ci ent for t he m edium

(/m), and (Bb ) is the ba ck- scatter ing coef ficien t. Photon sca la

r i rradi ance( Eo) is t

he sum of t wo c ontributing li ght fie lds in n aturalwat ers, thedownwel ling (Ed) and upwe ll ing (Eu) irradi ance s. F ie ld m eas urem ent s, al though for t he m ost part restr icted to marin e systems, hav e in almost all cases resu lted in m eas ured va lue s of Eu of only 2% or le ss of

Ed. Upwelli ng irrad iance can, h ow ever , con tribu te significantly to Eo at visib le wavel engt

hs in thecl ear est

oce an wate rs, wher e m ole cul ar b ac k

- sc atte r in g canbe sig n if ic an t, an dov erwh it e s an dy b o tt o ms of high albedo (Jer lov197 6) . Alth ou ghseldo m m easuredin fres hwat er s yst em s, t

hesest udie s in m ari ne wate rs indi cat e t hat back- scatt eri ng is gene rally ve ry sm al l a nd can sa fely be neglec ted (Jerlov 1976) . In the fol lowi ng dis cuss ion, photon irr adi anceis the reforedes ignate d E and i s tre at e d as bei ng ide nti calwit

h Ed or Eo; Eu i s ne gle ct ed. Inte gration of

Eq. (2-89) y ie lds an expre ssi on for t he re si dual irr adi anceaft er t

ransmis si on through a hom ogeneous la ye r of dept h z: ( 2- 91) wh ere E( 0) i s the irr a di anc e at

t he t op o f the l ay e r. T he r ate of li ght a bsorption Ew(ph oto ns c m s ) in the layer is
! 2

! 1 (E( 0)

! E( z) ), or ( 2- 92) For ph ot oc he m i c a lpurp os e s, i t i s m os t c onve ni e nt

t o e xp ress li ght a bsorption on a volum et ric m olar bas is (Ba il eyet al
. 1978:223) (one m ole of phot ons i s an Ei nst ei n, E). Th e rat e of li ght a bsorption I w, i n EL s , i s: ! 1

! 1
( 2- 93) where A = 6. 023×10 photons /m ole (Avogadro’ s num ber). 23 Den otin g E( 0) /A as Io (Eins teins cm s ) , the vo lumetric
! 2

! 1 absorption r at e Iw (in E L s ) i s t hus
! 1

! 1
( 2- 94) The electron ic absorptio n spectr a of synthetic or gan ic chemicals are usua lly r eport ed as (decadi c) molar abs orptivitie s or ext inc ti on coe ffi ci ent s å , wi th uni ts (cm (m ole/liter) ) or
! 1

! 1 (cm M ) ( EXAMS ’ i nput va ria ble ABSORG ). T he de fining ! 1

! 1 equation i s: ( 2- 95) where Ab is the abs orbanc e m eas ured in a spec trophot om et er, l is t he pat h l engt h in c m , and [P ] is theconc ent ration of the chemic alin m ole s pe r l it er. The prese nce of t he c hemic alin a natural wa ter bo dy incr eases the ab so rp tio n co eff icient (units m ) of th e w at erfr o m ( a ) to ( ). T he
! 1 tot alr at e of li ght absorption in thewat er body the n bec om es, by substit uti on into Eq. (2-94),
( 2- 96)

where D is therel at ive opti calpat h in the water body (Eq. (2- 90)). T he fr action of

thi s l ight abs orbed by

thepollutant it sel f i s:

and t he rate of l ight

abs orpti on by the pollutant Ia, in E L s , ! 1

! 1 is :
( 2- 97)
At trace levels o f the p ollutant ( EXAMS ’ oper at ing r ange) , by defi nition t

he quanti ty

(230.3 å [P ]) << a , and (a + 230.3 å [P] ) can be a ppr ox im at ed by

thenat uralabs orpti on coe ffi ci ent of t he water bo dy, a . Equati on (2-97) in t hesecircum st ance s re duces to:
( 2- 98)
Th e quan tity Ia/[

P] is ca ll ed t

he “ spec ifi c s unli ght a

bsorption rat e” of t he pol lut ant , Ka (Zepp 1980)
.44

ë ce nte r ( nm) Ä ë

( nm) w p doc

ç ç ç ë ce nte r ( nm) Ä ë ( nm) w p doc

ç ç ç 280.0 2.5 0.288 145 8.35 380.0 10.0 0.0220 46 1.96 282.5 2.5 0.268 138 8.05 390.0 10.0 0.0191 42 1.69 285.0 2.5 0.249 132 7.77 400.0 10.0 0.0171 41 1.47 287.5 2.5 0.231 126 7.49 410.0 10.0 0.0162 39 1.27 290.0 2.5 0.215 120 7.22 420.0 10.0 0.0153 38 1.10 292.5 2.5 0.194 115 6.97 430.0 10.0 0.0144 35 0.95 295.0 2.5 0.174 109 6.72 440.0 10.0 0.0145 32 0.82 297.5 2.5 0.157 106 6.48 450.0 10.0 0.0145 31 0.71 300.0 2.5 0.141 101 6.25 460.0 10.0 0.01566 28 0.61 302.5 2.5 0.133 95 6.03 470.0 10.0 0.0156 26 0.53 305.0 2.5 0.126 90 5.81 480.0 10.0 0.0176 24 0.46 307.5 2.5 0.119 85 5.61 490.0 10.0 0.0196 22 0.40 310.0 2.5 0.105 80 5.41 503.75 17.5 0.0295 19 0.33 312.5 2.5 0.0994 78 5.21 525.0 25.0 0.0492 14 0.24 315.0 2.5 0.0952 75 5.03 550.0 25.0 0.0638 10 0.17 317.5 2.5 0.0903 72 4.85 575.0 25.0 0.0940 8 0.12 320.0 2.5 0.0844 70 4.68 600.0 25.0 0.244 6 0.08 323.1 3.8 0.0793 68 4.47 625.0 25.0 0.314 5 330.0 10.0 0.0678 64 4.05 650.0 25.0 0.349 8 340.0 10.0 0.0561 59 3.50 675.0 25.0 0.440 13 350.0 10.0 0.0463 55 3.03 706.25 37.5 0.768 3 360.0 10.0 0.0379 55 2.62 750.0 50.0 2.47 2 370.0 10.0 0.0300 51 2.26 800.0 50.0 2.07 0 w p Ta bl e 9. Spe ct r al i nt er v al s us ed i n EXA MS , a n d s p e c tr a l a b s o rp ti o n c o e ff i c i e n ts o f w a ter ç ( m ) , chl or ophy l l s + pheophy t i ns ç (m (m g /L ) ), ! 1

! 1

! 1
doc s ( hu m i c) di ss ol v ed or ga ni c ca r bo n ç ( m ( m g/ L) ) . Suspended sedi m ent s ç ta k e n a s u n ifo r m ly 0 .3 4 m (m g /L ) . S e e s e c tio n 2 .3 .3 .2 ! 1

! 1

! 1

! 1

Ka can al so be com

pute d from

the ave rage li ght inte nsi ty in any layer of the wate r bo dy (MillerandZepp 197 9a) . Inthis app r o ac h , the av erag e light in tensity Em (ph oto ns cm s ) is
! 2

! 1 found byint egrati on of Eq. (2-91) over the dept h of t he l ay er z , foll owed by

divi si on of t

he re sul ting int egra l by

z: ( 2- 99) where E( 0) i s the inte nsi ty

at the t op of

t he laye r. Em

(ph otons cm s ) canbe con verted to molarunits ( Im, E cm s ) via
! 2

! 1

! 2

! 1 divi si on by Avogadro’s num ber A :
( 2- 100)45 whic h, a s Io = E(0)/A ,

Th e te rm Io (1-exp(

Daz))/az in thi s e quat ion i s e m

bedded in E q. (2-98); Ia and Ka can thus be com pute d from t

he avera ge l ight inten sity Im vi a the e quiva le nt expre ssi ons (2-101) and (2-102): ( 2- 101) ( 2- 102) Light absorption i s a

one-quantum

proce ss, so Ia

(E L s ) al so ! 1

! 1 give s t he rate of e le ct

ronic ac ti vat ion of

t he pol lut ant

(M/ s). Ka , the s peci fic s unli ght absorption rat e, thus ha s unit s s . If each
! 1 ph oto n ab sorbedby the ch emical pollutant res ultedin photoc hemic altr ansfor

m at ion of

one m ole cul e, Ka wo uld am ount to a pseudo-f

irs t-or der r at e c onst ant

for photoly si s of the pollutant. This , howeve r, i s ra rely t he case in soluti on-phase sys te m s. The e ffi ci ency

of t he (s econdary) photoc hemic altr ansfor m at ion pr oces s i s c al le d the“re action qua ntum yi el d” Ö ( EXAMS input par ameter QYIELD ), w i th (“ dim ensi onle ss” ) uni ts of m ole s/Eins te in. Zepp (1978) ha s described proc edure s for m eas uring Ö of organic ch emicals in dilute air -saturatedaque ous soluti ons; them eas urem ent of Ö is des cribed in EPA Gui del ine OPPTS 835.2210 (

Dire ct Pho tolysis Rate in W ater b y Su nlight, repo rt E PA7 12 -C -9 8- 06 0, J anu ary 1 99 8)
. Th e r at e of ph oto chemical tran sfo rmation o f a po llutan t is givenby:
( 2- 103)
The quantity ( Ö )(

Ka ) is the ps eud o- firs t-or derp h o to lysis rate const ant . Multipli cation of this quanti ty

by 3600 s/

h give s t he ph oto lytic contr ibutionto the ov erall tran sfo rmationrate const ant K i n Eq. (2-1). Alt hough thefore going di scus si on has bee n phras ed in te rm s of m onochrom at ic li ght, the eff ect of s pectral differ ence s c an be read ily incorpo ratedvia integ ratio n orsummation ( in disc rete wavebands) ac ross t

he sol ar spe ct

rum . The rat e of photolysi s of a s ynt het ic organi c com

pound thus can be com

pute d from

the absorption spe ct

ra and rea ct ion qua

ntum yi el ds of the se vera l ioni c s peci es of t

he c hemic al , vi a a

coupl ing of

the se param et ers to the ( spec tra lly-dependent) behavi or of l ight in nat uralwat ers ( EXAMS ’ proc edure PHOTO 2). When the abs orpti on spe ct rum of a com pound has not been qu an ti f ie d(al th o u g hth e s p ec tr al po si ti o nof ab so r p ti o nmax ima m aybe known). EXAMS provi des an a dditiona l procedur e, PHOTO 1, d esign edto accep t pseu do -fir st-o rd er ph oto lysis rate con stants as its primary inp ut data
. Fo r example, Smith et al. (1978) atte m

pte d t o m eas ure the a

bsorption spec trum

of M ire x, b ut the abs orptiv ity was be lowthe detec tionlimit of their instrument (0. 1 cm M ). Ex per imental stud ies, co nductedvia
! 1

! 1 cont inuous expos ure of

an aqueous soluti on of M ire x t o am bie nt sunl ight at Me nlo Park , CA for a peri od of 6 m onths , dem onstrat ed t

hat Mire x is phot ochemic al ly reac ti ve in aque ous soluti on wit

h a pseudo-f

ir st -o rd e r rate cons tant of

3.7×10 d . (A

-3 -1 pseudo-f irs t-or der r at e c onstant deter m ine d via

a brie f experim ent , for exam

ple at m ids umm er l ocalnoon, m ust be adjust ed for

annua l m ean sunl ight

int ensi ty and day le ngth prior to e ntry in EXAMS .) So l ong as therea ct ion mixt ures a bsorb a ne gli gibl e fr action of 0 D P the am bie nt l ight

(I . I ), t his obs erve d rat e c onst ant (K (0), i .e. , K at z= 0) i s e quiva le nt to:

DP K (0) = Ö Ka =2303 Ö åIo D integ ratedacr oss the solarsp ectrum. The av erag e p ho tolysis ra te

DP con stant K (z

) in a l ay er of

appre ci abl e depth z

is the n
( 2- 104)
wh ere the abso rp tioncoef ficien t ( a ) fo r

the wate r bo dy is so me appropri at e s ingl e va lue
. EXAMS al so com pute s a corr ection t erm for effe ct s of cl oudine ss and geogra phic lati tude
. EXAMS ’ i nput vari abl e ( KDP , u nits h ) i s t aken as the near-surf ace , 24-hour
! 1 annualave rage pse udo-fi rst -order photolysi s rate cons tant unde r cl oudle ss c onditions at

a spec ifi ed l at it

ude RFLAT . RFLATis expre ssedin degre es + t ent hs. F or exam

ple , Me nlo P ark, Cal ifor nia , is at 37 E 27 ' N; EXAMS ’ i nput woul d be RFLAT= 37. 4. 2.3.3.2 Li ght atte nuati on i n natur al w ater s The att enuation of

ir radi ancein nat

uralwat ers is des cribed by the di ff us e att e nu at i onc oe ff

i c i e nt or “ K- func t i on ,”K (E q. ( 2- 90)), wi th uni ts m . Thenum eri calvalue of K depe nds upon
! 1 b o thth e ab so r

b an ce of th e me d ium ( a ), and upon the r el at ive op tical pathin the w ater bo dy (D ). T he a bsorbanc e of a natura l wat er body

res ult s from

abs orpti on of l ight by thewat er i ts el f, plus a bsorption by gree n pl ant s, dis sol ved organi c matte r (pri m ari ly

hum ic mat eri al s), and s uspende d se dim ent s. T he opti calpat

h param et er D depe nds on t he angle of incid enceof the ligh t source( s), an d onforwar d scatter ing of the l igh t within the wat er body

it sel f. 2.3.3.2. 1 Dis tribut

ion funct ions(D) i n nat ural wat ers The optic alparam et er D isthem ean opti calpat h per unit vertic al dep th in the system; D ma y be cal le d a “di stribution f unct ion” as proposed by P rie sendorf

er ( (1 95 8b , 19 58 a) , quo ted fro m Smith and Ty le r (1976) ), or an “ inve rte d value of an avera ge c osi ne” where the average cosine i s de fine d as a/K (Jerlov 1976) . (T he te rm “in v erte dva lu e o f

anav er a g e co si n e” or ig in at edfr o m a46 gener al iz at ion of

thefac t t hat t he pat h le ngth of

thesol ar be am is give n by the se cant

(1/ cos) of t

he angle of re frac ti on of t he beam.) In the case of a collim ated light b eam inciden t normal to the wat er s urfac e, D = 1.0. In the c aseof a com ple te ly dif fused li ght f ie ld, D rea ches it s m axi m um value of 2.0 (L e i ghton 1961:24ff )
. Inthe cleare st natural wa ters, the distr ibutionfun ctio n is dom inate d to appre ci abl e depths by the ge om et ry of i nci dent

sky radi at ion a

nd thesol ar be am . When t he sun is in theze nit

h, t he sol ar D = 1.0 ; D inc rea ses wit h increasi ng ze nit

h angl e. When the s un i s near

t he hori zon, D reac hes a l imiting value of about 1.5, be caus e of refra ct ion of thesol ar be am

as it cros ses the ai r-wat er inte rfac e. At l ow sol ar e le vat ions , howeve r, t he underwat er li ght fie ld in thephotoc hemic al ly si gnifi cant

portion of t he sol ar spec trum

i s dom inate d by cont

ributions from

dif fuse skylig ht. The c oll im at ing effect of t ransmis si on ac ross the air-wat er int erfa ce reduc es the dis tributi on function f or di ffuse sky li ght from a D of 2. 0 in the at

m osphere , t o a subm ari ne va lue of a bout 1.19 ( ( P o o le an dAtk in s 1 9 2 6 ) , qu o te dfr o m (Hut c hi nson 1957:391) ). T his value corresponds t o an equi val ent sol ar el evation of

about 44 E . Thet ota linc i de nt

ph otoc he m ic al ly

ac ti ve irr adi ance (wavel engt

hs # 370 nm) i s dominate d by skyl ight at sol ar a ltit udes le ss t han 45 E , and irr adi anceat wavel engt hs # 330 nm is dom inat ed by

sky radi at ion at a llsol ar e le vat ions (Lei ghton 1961: 23ff)
. A di stribution function of 1.19 i s t hus an ad equ at e ap p r o x imati o nfo r th e n ear - sur f

ac e zo n e, an dto so me consi dera ble dept h for t he c le are st

nat uralwat ers. In m ost nat uralwat ers, and in t

he de eper part s of cl ear

wat ers, the rad iance distrib utio n ap p ro ache s an asympto tic value in whic h forward scat

te ring bysuspende d parti cl es i s ba lanced by ligh t abso rp tion , and the distrib utio n coef ficien t attains a stab le value. At s hal low depths in nat uralwat ers cont ai ning s cat te ring partic le s, D is usually l arge r t han t he va lue sugge st ed by

the sol ar e le vat ion. For e xam ple , i n theBa ltic Sea and in t he Mediterranean, D has bee n m eas ured at 1. 40 and 1.25, resp ectively ( (Jerlov ( Johnson) and Li lje quis t 1938, Hojers le v 1 9 7 3 , 1 9 7 4 ) ; qu o te dfr o m (Jerlov 1976: 88) ). T he c orres ponding so lar be am D va lues w ere o nly 1. 14 and1.0 4 res pectiv ely, indicating a

st rong ef fec t of partic le sc atte ring in t

hesewat ers. Mi ll er and Zepp (1979a) me asure d li ght sc atte ring by6 natura l sedi m ent suspe nsi ons. T he dis tributi on functi on ranged from 1.3 t o 2 .0 , but

s ho we d l i tt l e c or

re l at i onwi th t

he s us pe nsi on conce ntrati ons of the se dim ent s (17–105 m g/L)
. The distrib utio n functio n fo r eachelement of the wa ter b ody is an (e nvironm ent al ) i nput pa ram et er t o EXAMS . The se param et ers ( DFACG ) can bes et

at anyva lue be twe en 1.0 and 2. 0. If an input va lue i s <1 or

> 2, ho we ve r, EXAMS res et s t he di stribution function of

these gm ent

to DFACG= 1. 19 f

or surfi ci al(t

ype L, E) wat ers, and to 1. 50 for pr ofundal(H) s egm ent s. 2.3.3.2. 2 Abs orpt ion coef ficients(a) i

n nat ural wat ers EXAMS com

pute s separate values of the spec tra l a bsorption coef ficien ts (a) f

oreach sec tor o f the waterbody. Abso rp tionis com pute d from

thesum of t he c ontributi ons of wat er i ts el f, pl ant p ig ments, dis solv ed o rg anic carbo n (p rimarily attribu table to hum ic mate ria ls of m ole cul ar we ight >1000 (Mick le andW etzel 1978) ), and suspended se dim ent s. Abs orpti on coe ffi ci ent s for wat er it sel f, and t

he s peci fic abs orpti on coe ffi ci ent s for the othe r absorbing spe ci es, aregive n in Tabl e 9
. EXAMS com

pute s t he t ota l absorption coef

fic ie nt (a, unit s /m) for eac h s pect

ralinte rvalin e ach wat er c olum n com partm ent via Eq. (2-105): ( 2- 105) The s pect ral s peci fic abs orpti on coe ffi ci ent s suppl ie d wit h the wpd o c s p r o g r am ( ç , ç , ç , ç ) ar e gi ven in Tabl e 9 . The envi ronm ent alconc ent

rations of t

he a bsorbi ng spe ci es (CHL, DOC , and SUSED (m g/L) ) ar e e nte red a s part of t he envi ronm ent aldat a basef or eac h wat er-c olum

n com partm ent of ea chec o sy st em. Ab so rp t i onb yp l ant

p i gm e nt s i s ke y e d t o the c on c e nt rat ion of tot al chl orophyl l-l ike pigm ent s (c hlorophy ll s +pheopi gm ent s) in eachsectorof

the wate r colu mn (inp ut var iable CH L, un its mg/L). Un dervery eu trop hic co nd itions , Chl a can attain2 mg/L ( ( Ta ll in g et a l. 19 7 3 ) , qu o te dfr o m (Wetze l 1975: 337) ). In oli gotrophi c a lpine and arc ti c l akes , pi gm ent conc ent rations can be a s l ow as 0.001 mg/L (Wetzel 197 5:334) . Smit h and Bake r (1978, B aker

and Sm it h 1982) det ermine d thecont ribution of tot alchl orophyl l-l ike pigm ent s ( CHL ) t o the K- function of marine systems via re gr essio n analysis; the resu lting spe ctral K values diff

ere d l ittl e from

s pect rophotom et

ric al ly dete rm ine d abso rbance of phytopl ankt ers. EXAMS ’ spe ci fic abs orpti on

p coef fic ie nts ( ç in Eq. ( 2-105) and Tabl e 9 ) weredeve lope d by divi si on of Smit

h a ndBaker’s ( (1978) ) “k2" by an a ssum ed aver age dis tributi on function of 1.20.

doc EXAMS ’ spe ci fic abs orpti on c oe ff i c i e nt s for DOC ( 

### ç ) ( Tabl e 9 ), repre sentati ve of fres hwat er a quat ic hum us, we re c al cul at ed from theexpre ssi on

doc 

## ç = 0. 71 exp (0.0145(450- ë)) where ë is th e w av el en g thinnm (Zepp and Sc hlotzhaue r 1981)
. Light abs orpti on by suspended se dim ent s m ayvary ac ross the sol ar s pect

rum , but int erfe renc e by

pa rticlesc atte ring has ham pere d inve st igati on of t

his phenom enon. Mill er and Zepp (1 97 9a) determinedbothD- and K- functio ns for331 nm light, via ac tinom et er e xperi m ent s c onduct ed on a s eri es of 6 nat ural sedi m ent suspe nsi ons. T he s peci fic abs orbanc e c oeffic ie nt ((K/D) /[S], where [S] (i .e. , SUSED ) i s t he c oncent

ration of suspe nded s edi m ent s in mg/L) va rie d f rom 0.19 t o 0.59, wit

h a m ean value of 0.34, m (m g/L)
. EXAMS inc lude s a 46-el em ent ! 1

! 147 s vect or of speci fic sedi m ent abs orpti on coe ffi ci ent s ç ; t his vec tor is curr ent ly

unif orm ly fi ll ed wi th a

value of 0.34. W henthe abso rp tionspectrum of the compo un d is not av ailable fo r coup ling to the abso rp tionspectrum of the w at erbody, procedure PHOTO 1 requires appropri at e s ingl e a bsorption coef fic ie nts “a ” for

ea ch a quat ic segm ent . The se values are cal cul at ed from

( 2-105). The wavel engt

h inte rvals el ect ed for this co mp u ta ti oncan be specif ied viathe inp ut che mical data desc ribing thecom

pound: T he c hemicaldat a ba se inc lude s a vari abl e ( LAMAX , nm) t

hat can be used to sp ecifythedes ire d wavel engt

h int erva l f

or com puting a . Theregi on of gre at est overl ap of t

he absor pti on spect

rum of the che m ic alwit

h thesol ar spec trum is perha ps t he m ost appropriate value for LAMAX . Usual ly , howeve r, i t i s t

he spec tra l loc at ion of peak absorbance that i s re adi ly

avai la ble , in whi ch c asethi s va lue can be used for LAMAX . If LAMAXis outs ide therel evant portion of

thesol ar spec trum (t hat is , <280 or >825 nm), EXAMS com pute s LAMAX via (2-105) at

300 nm (i nte rval9 i n T ab le 9 ). Input values of LAMAXneednot b e restr icted to th e center s of th e wav eban ds in Tabl e 9 ; EXAMS se le ct s t he spec ifi c a

bsorption c oeffi ci ent s for com puting LAMAXvia

a m at chi ng of LAMAXto the app ro pr iate spe ctral int erva ls in the Tabl e. For e xam ple , i f LAMAX=30 6, EXAMS selects ab sorptio n co eff icients f ro m waveb and11 in Tabl e 9 ; a LAMAXof 442. 2 se le ct s waveband 30; et c. 2.3.3.3 Reacti on quan tum yi el ds ( Ö ; Qyi el d) A photoa ct ivate d or ganic m ole cul e c an undergo a vari et y of sec ondary(t

herm al) transf

orm at ions , i ncluding photoaddi ti on and s ubst it

uti on rea ct ion s, c yc loa dditions , i som eri zations and rearrange m ent s, and photofra gm ent at ions and el iminati ons (T urro 197 8) . The efficien cy of p ho toch emical proc esses is expre sse d in te rm s of the “quantum yi el d” Ö , t

hat i s, t he num ber of m ole s of photoc hem ic alac ti vit y pe r m ole of phot ons (Ein steins ) abs orbed . Ph o to ac tivatedmolecules ar e sub ject to num erous physi caland chemic alproce sse s, and thee ffi ci ency of eachof the se pr oces ses canbe exp ress ed as a quan tum yield (exa mpl e s i nc l ud e the f luore sce nce quantumyi el d, phosphores cenc e quant

um y ie ld, quant

um yi el d for f

orm at ion of a s peci fic product

m ole cul e, et c.) The quant um yi el d of si gnific ancefor EXAMS is the “disapp earan ce” qu antum yi eld (input param et er QYIELD ), that is , the num ber of m ole s of pare nt com pound transfor

m ed to daug hterpro du cts permole of ph oto ns absorbe d. The ( sec ondary ) t

ransf orm at ion proce sse s ofte n involve t herm al rea ct ions , and thedis appearanc e quantum yie ld there fore can be sl ightly te m perature depe nd e nt
. Thes e t herm alrea ct ions arevery fast , a s t heym ust be in order to c om

pet e wi th t

herm alreve rsi on of the uns ta

ble int erm edi at es to t

he ori gina l pol lut ant

m ole cul e. The a ct ivati on ene rgie s of the the rm altr ansfor m at ion r eac ti ons are o n the o rd er of

only 1- 2 kc al/mol; EXAMS the reforedoes not inc lude an opti on for de scripti on of t em perature eff

ect s on dis appearanc e quantum

yi el ds. Unli ke va por-phas e phot ochemic alr eac ti ons, the dis appearanc e quant um yi el ds of organic molecul es in a queous soluti on are gener al ly independent

of t he wavel engt

h of incide nt r adi at ion, at le ast wit hin t he e nvironm ent al ly

si gnifi cant

portionof

the sol ar s pect

rum . Thi s di ffere nce ari ses from theenhanced op po rtun ity for en erg y trans ferto the s olvent in condens ed-pha se sys te m s. I n soluti on-phaseir radi at ion, the rapi d ( radi at ionl ess ) decay of exc it ed m ole cul es from se cond or hig herelectro nic st at es , to theirfirst ex cited state, normally pr ecludes rea ct ion f

rom thehighe r st at es ( Ze p p 19 7 8 ) . S o me or gan ic dyes, stable und er vis ible lig h t b u t pho toch emically labile un derUV , are n otab le excep tion s to this ru le. Th is ph eno menonsho uldbe su spe cted w hena >10 0 n m g ap is prese nt in thecom

pound’s a bsorption s pect

rum . In suc h a cas e the as sum ed l ack of wave le ngth dependenc e of Ö shoul d be te st ed by expe rim ent s c onduct ed in both a bs or bingr egi ons of the spec trum . If nece ssary, the photoc hemic al ly ina ct ive se ct ion of the com pound’s absor

pti on spe ct

rum can be om itte d from

the input dat a ( ABSORG ) . V ery s mal l o r g an i c mo le cu le s, an dso me coordi nat ion c om

pounds, c an e xhibi t a

wave le ngth dependenc e of Ö . Thephotoc hemis try of iron (II) cy ani de com

ple xes is one exam ple of t his phenom enon ( (Ba lz aniand Car ass iti 1970) , qu o te dfr o m (Zep p 19 78 ) ). Mo st small organ ic molecu les in aqu eou s solu tionare ph oto chemically unreactiv e in sun ligh t, ho wev er. Th e disap pear ance quantum yi elds u sedas inpu t to EXAMS shoul d in al l c ase s be derived fr om ex perim ent s using wavel engt

hs t hat arepa rt of theenvironm ent al ly

rel evant portion of t he s olar spe ct

rum , rathe r t

han far UV (<280 nm). Ö can a l so bea ff

e c t e d b ythe c he m i st

ry of the wat e r so lut ion itself. Th e qu antum yi elds o f th e ion ic sp ecies o f an o rg anic acid or bas e ge nera lly di ffer. Thi s phe nom enon l eads to an a ppare nt depende nce of Ö on t

he pH of them edium . EXAMS al lows for the entry of a separat e va lue of Ö ( QYIELD ) fo r eachionic spec ie s of the com

pound. Thi s inform at ion c an bededuc ed fr om a knowle dge of the pK(s ) of the c om pound, absorption spectra of i ts ioni c spec ie s, and quant um yi el d expe rim ent s c onduct ed at seve ralpH values. For ex ampl e, Zepp (1978) has des cribed method s fordeterminin g dis app earan ce quan tum yields via compar isonof the r ate of tr ans fo rmation o f a test po llutan t P to that of a ref eren ce co mpoundR, of

kn ow n ab sorptiv ity å (R) and quant um yi el d Ö (R). The m ethod depends on a com pari son of the sl opes S

of t he (ps eudo- f

irs t-or der) ln[P ] and ln[R] dis appearanc e c urves over tim e, under irradi at ionat a sel ect ed wav eleng th (e. g., 313 nm). The r ef er ence compou ndserv es to norm al iz e t

he e xperi m ent

for l ight int ensi ty and the geom et

ry of the photoc hemic alapparat us. F or a neut

ralm ole cul e, ( 2- 106) The app aren t Ö of an organi c a ci d or basewilldepend on t he pH of the system. Fo r a fixe d pH , Eq. (2- 10 6) can be rewr itten to inc lude theioni zation e quil ibri a and s epar at e a bsorptivi ti es and quant um y ie lds of t he vari ous ioni c spec ie s of the pol lut ant P. For e xam ple , a monoproti c organic ac id wil l di stribut e be twe en 3 2 its uncharged RH m ole cul e and it s anion RH (se e C hapt er !48 2.2.4) as: ( 2- 107) and ( 2- 108) wh e re áis thefra ct ion of thetot alpollutant pr ese nt a s e ach of the mol ecul ar spe ci es (Ka he re is t he aci dit y const ant). E quat ion (2-106) t hen be com es
( 2- 109) Suppose, for e xam

ple , t hat P is a m onoproti c organic ac id whos e pK a = 5.0. At pH 5, t

he c om pound would dis tribute equa lly 3 2 bet ween RH and the RH ani on. At pH 4.5, thecom

pound
! 3 2 would di stribut e a s 76% RH and 24% RH . G iven, for
! 3 2 e xample , å of

RH as 5000, and åof RH as 10 0 0 0 at 3 1 3 nm, ! and e xperi m ent al ly

det ermine d values f

ortheri ght s ide of E q. (2-109) a s 10 and 20 at

pH 4.5 and 5.0 respe ct ive ly ; the quant um yields o f the molecu lar sp ecies canbe calcu lated v ia si m ult aneous soluti on of t

he e quat ions :

3 2 1: (0.76)(5000)( Ö (RH )) +(0.24)( 10000)( Ö (RH )) =10 !
3 2 2: (0.50)(5000)( Ö (RH )) +(0.50)( 10000)( Ö (RH )) =20 ! giv ing a re action qua

ntum yi el d Ö for t

he unc harge d m ole cule 3 2 RH of 1. 5×10 , and Ö (RH ) = 3.9×10
.

! 4

! ! 3 Zepp a nd Ba ughm an (1 97 8) havedis cuss ed t he e ffec t of

othe r diss olv ed sp ecies onthe dir ect ph oto lysis of synth etic o r g anic m ole cul es. Dis sol ved oxy gen in som e inst ance s “ quenche s” photoc hemic alrea ct ions via energy t ransf er f rom a pollutant m ole cule to the oxy gen m ole cul e at t he e xpenseof tran sfo rmation path ways . Disapp earan ce qu antum yi elds sh ou ld be d eterminedin air-s atur ated pure waterto allowforthis eff ect; EXAMS does not include an expl ic it al gorit hm to m ake al lowances for varying dis sol ved oxy gen c oncent rations (as sunl it wat ers are very rare ly ana erobi c). Phot ochemic al rea ct ions wit

h diss olve d nucle ophil ic speci es suc h as hydr oxide , chl oride , bromide , and s ulfi de can changet he rea ct ion qua

ntum yi el d of a

pollutant f

rom thevalue de te rm ine d in pure wate r sys te m . Theconc ent

rations of t

hesespe ci es in natura l f resh water s are, h o w ev er, typ ically much too small fo r them to com pet e wi th nuc le ophil ic dis pla cem ent s by wa ter i ts el f. In m ari ne s yst em s, c hlori de and bromide occ ur at conc ent rations (0 .6 an d 0. 00 1 molar, resp ectively) hig h e no ug h to co mpete, in princ ipl e, wit

h wat er. Som e organic com

pounds t hat arenot photoreactive i n pure wat er are photoactive when c om ple xed wi th m et alions . For exam ple , NTA a

nd EDTA are phot ochemic al ly ac ti vat ed by com ple xat ion wi th iron (III ). Photoactive co-di ssolved sub stanc es (e. g., disso lvedhumic materi al s) can also mediate photore actions of pol lut ant che m ic al s vi a direc t e nergytr ansfe r to t he pol lut ant

m ole cul e, or bygene ration of reac ti ve int erm edi at es (e.g., single t oxy gen). Thes e phe nom ena are properly t erm ed “i ndire ct ” or “se nsi ti zed”photolysi s, howe ver, as opposed to t

he “ dire ct ” phot otransform at ions that a re t he subjec t of thi s C hapt er. 2.3.3.4 Absorp tion spe ctr a ( ABSORG) The a bsorbanc e of organi c aci ds and base s in aqueous soluti on vari es wit h pH, a s a res ult of di ffere nti alli ght a

bsorption by

the neu tral mol ec u le andits ions. The ra te of p ho tolytic transform at ion of

an organi c a ci d or basein nat uralwat ers thus depends on t

he pH of thesy st em . EXAMS ’ com putati ons are key ed to t he spec ie s-spe ci fic absorption s pect ra of thepollutant chemic al(uncharged pare nt mole cul e and it s i onic spe ci es), m eas ured in pure wat er. EXAMS links the avera ge spec tra l s olar intensi ti es in e ach laye r of t he wate r bodyto the abs orpti on sp e c tra of thec om po un d, and

the reby c om put e s ava lue of

Ka (Eq. (2-102)) f

or ea ch di ssolved m ole cul ar s peci es. EXAMS ’ dyn am ic st at e varia ble is thetot alconc ent

ration of pollutant in ea ch e cosy st em se gm ent , re ferre d to the aque ous phaseof t

he c om partm ent . Thefracti on of t his tot al con centr ationpres ent a s eachmolecular sp ecies is co mputedvia the e qu ilibrium ionizatio n andso rp tiondis tribu tioncoef ficien ts á(Cha pte r 2.2. 4). Onc e in posse ssi on of Ka (Eq. ( 2-102)) va lue s for the s ever ali onic spe ci es, EXAMS com pute s t he c ontributi on of each to the total ps eud o- firs t-or derdirect p h o to lysis r ate const ant via theexpre ssi on (com

pare Eq. (2-103)) where the subsc ript

(i ) re fers in turn to eac h of t he i onic spe ci es. This com putati onalloop is ac tua lly i te rat ed 3 ti m es for eac h i on i c s pe c i e s, be caus e EXAMS incorpo rates th e effe cts of sorption to s edi m ent s and com

ple xat ion wi th DOC via

a set of 3 values of QYIELD foreach io nic sp eci es . I notherwor ds, foreach io nic spec ie s i , EXAMS com

pute s t he t ota l c ontributi on of t

hat spe ci es to t he overa lldirec t photolysi s rat e const ant by fixing thevalue of i , and sum

m ing t he e xpress ion { á (i, k) × QYIELD (i, k) × Ka(i )} over t he k= 1 (di ssolved), k=2 (s edi m ent sorbe d), plus k= 3 ( DOC com ple xed) f orm s of the com

pound in eac h sector

of t he ecos ystem. The m echanics of this compu tationallow th e userto con trol th e p ho tore activity o f so rb ed molecules via th e entrie s in the QYIELD che m ic alinput vec tors
. Sorpt ion of

thepollutant to suspended sedi m ent s and com ple xat ion wi th “di ssolved” organic carbon ( DOC ) can induc e com ple x changes in bot

h theli ght a

bsorpti on spe ct

ra and the rea ct ion qua

ntum yi el ds of the com

pound, and c an “prote ct ” t he m ole cul e from

exposure to sunl ight

via m igrati on or di ssoluti on int o the(dar

kened) int eri or of s edi m ent partic le s. EXAMS ’49

C enter Sp ect r al A bsorpt i on C oeff i ci ents å , cm M

-1 -1 ë , nm p H 5 .1 p H 7 .0 p H 8 .9 3 2 RH RH

- p H 7 .0 297. 5 14 18 193 14 3767 16 3 0 0 .0 3 .8 7 .2 1 7 3 3 .8 3 5 5 1 6 .0 3 0 2 .5 2 .4 3 .8 1 5 0 2 .4 3 0 9 7 4 .4 3 0 7 .5 0 2 9 2 .6 0 1 9 4 1 1 .2 3 1 0 .0 2 6 3 .5 1 3 3 1 0 .8 3 1 2 .5 1 4 0 .3 8 4 5 0 .5 3 1 5 .0 0 2 4 .1 5 0 5 0 .3 3 1 7 .5 1 3 .0 2 7 2 0 .2 320. 0 6. 2 130 0. 08 323. 1 3. 8 80 0. 05 330. 0 0 T a b l e 1 0 . L i g h t a b s o rp ti o n s p e c tr a o f p -C re s o l i n p u re w a ter. M easur ed v al ues at pH 5. 1, 7. 0, and 8. 9 f r om Sm i t h et al . 197 8. Ca l c u l a t i o n o fmol e c u l a r s p e c i e s a b s o r b a n c e a n d e s t i m a t e d p H 7 s o lu tio n a b s o r b a n c e d e s c r ib e d in te x t. p K a = 1 0 .2 firs t -o rd e r e valuati on s us e t hequ a nt um yi el d param et er ( QY IELD ) as a m echanis m

for a pproxim at ing t

he e ffec ts of s orpti on on t he photore activi ty

of pollutant chemic al s; thephenom ena involved are dis cuss ed in greate r det ai l in Cha pte r 2.3. 3.5. In orde r to com

pute the ef

fec ts of pH on li ght abs orpti on and on photolytic r at e c onst ant s, EXAMS requires a s peci fic abs orpti on sp ec trum ( å , EXAMS ABSORGvec tor) for e ach (dis sol ved) m ole cul ar speci es of t

he pol lut ant

che m ic al . The se absorption spec tra can bededuc ed fr om

thepK(s) of t

he c om pound and the abs orptio n sp ectra o f aqu eo u s so lution s of th e chemical, m eas ur ed at seve ralpHs. The procedur e i s anal ogous t o that des c ribe d fo r re a c t i onq

uant um y i e l ds in C ha

pt e r 2. 3. 3. 3. For e xa m pl e , Smi th a

nd coworke rs ( (1 97 8) ) measure d theabs orpti on spec trum of p-C resolat

pH 5.1, 7.0, and 8. 9 ( Tabl e 10 ). Para -cre solis a weak organi c a ci d (pKa = 10.2); at pH 5. 1, 7.0, and 8. 9 theani on is pres ent as only 0.00079, 0.063, and 4.77 perc ent of t he tot alconcent

ration. The obs erve d spe ct ra ( Tab le 10 ) cl early

indi cat e t hat the ani on is the m ore s trongly a bsorbi ng spec ie s.

The obs erv ed ab sorptio n coef ficien t at any fixedwav eleng th is 3 the sum of a bsorbanc e att

ribut abl e t o theuncharged ( RH ) 2 m ole cul e, plus that att

ribut abl e to th e ani onic (RH ) spe ci es. ! Denot ing t

he obs erve d abs orpti on coe ffi ci ent as , t

his sum can b e exp ress ed alg ebr aically: ( 2- 110) This equati on can be used to e st im at e t he s epar at e a

bsorbanc es 3 2 of t he RH and RH mole cul es. F or exam ple , at 297. 5 nm , for
! pH 7.0: 3 2 å o = 18 = (0.99 9 3 6 9 ) å (R H ) + (6.31 × 1 0 ) å ( RH ) ! 4

! and a t pH 8. 9, 3 2

å o = 19 3 = (0.95 2 ) å (R H ) + (0.04 7 7 ) å ( RH ) ! Si m ul t aneous s ol ut i on of t hes e e quat i ons yi el ds

3 å ( R H ) = 15. 6 and 2 å ( RH ) = 3734.

! The u nc ha r ge d mol ec ul e i s p r es en t a s 9 9. 99 92 % o f t he t ot al conce nt r at i on atpH 5. 1, s o t he pH 5. 1 s pect r um ca n be t aken as 3 a d i rec t ex p erim en t al m ea su rem en t of å ( R H )
. G i ven t hi s, t he 2 a b s o r p t i o n s p e c t r u m o f t h e ( RH ) a ni on c an be ca l cul at ed us i ng

! t h e p H 8
. 9 s p e c t r u m a n d E q . ( 2

- 1 1 0 )
. F o r e x a mp l e , a t 2 9 7
. 5 n m,

2 1 9 3 = (0.95 2 )( 1 4 ) + (0.04 7 7 ) å ( RH ) !

2 gi ves å ( RH ) = 3767. The acc ur acy of t hi s pr ocedur e c an now ! be e val uat ed by us i ng E q. ( 2- 110) t o pr edi ct abs or bance of t he sol ut i on atpH 7. 0: ( 0. 999369) ( 14) + ( 6. 31×10 ) ( 3767) = 16 ( cm M ) ! 4

! 1

! 1

as compar ed t o the exper i m ent al val ue of 18 c m M
. The

! 1

! 1 3 com put ed a bsorpt i on s pect r a of t he unchar ged R H m ol ecul e a nd 2 t h e RH ani on of

p- C r es ol ar e als o sh ow n i n T abl e 10 , al ong ! w i t h t he pr oj ect ed a bsorpt i on coe f f i ci ent s at pH 7. 0. The a b so rp tion sp e c tra o f th e in d iv id u a l m o lec u l es are the ap p rop ri a te dat a f or ent r y i nt o E X A M S ’ ch em i ca l d a ta b as e (i n p u t ve cto rs ABS ORG ). 2. 3. 3. 5 E f

f ect s of s orpt i on on photol ysi s rat es The ef f ect s on di r ectphot ol ysi s of s or pt i on t o s uspe nded mat er i al ar e i nc orpo r at ed i nt o E X A M S vi a s epar at e di sa ppear ance quantum yi el ds ( QY I EL D ) f

or t he s or bed f

or m s of ea ch di ss ol ved s peci es 3 2 ( RH , RH , et c. ) of

t he c om pound. A l t hough s or pt i on ca n ! pr oduce subt l e a nd compl ex c hanges i n t he phot ochemi st r y of pol l ut ant s, l i ght e xt i nct i on by sus pended par t i cul at e mat t er , and cap t ure of

sor pt i on - prone ch em i cal s by bo t t om sedi m ents, r el egat e t he e f

f ect s of s or pt i on t o a s econda r y r ol e. I t s houl d not be a ss um ed, how ever , t hat s or pt i on i nevi t abl y “ pr ot ect s” a chemi cal f

r om di r ecti nt er act i on w i t h s ol ar r adi at i on, s o E X A M S al l ow s f or al t er nat i ves t o t hi s as sum pt i on vi a t he Q YI EL D chemi cal i nput vec t or . ( Thi s capa bi l i t y i s onl y ava i l abl e f or c o m p o u n d s fo r w h ic h th e a b so rp tion sp e c tru m is k n o w n .) T h e “s o rp tion ” p ro c e ss in c lu d e s a d so rp tion o f a c h e m ic a l o n to p a rticle su rfa c e s, d iss o lu tion o f u n c h a rg e d sp e c ie s in to sus pended or gani c mat er i al s, and m i gr at i on i nt o t he i nt er i or of p a rticle s v ia d iffu sio n a lo n g p o re c h a n n e ls. T h e p a rticle m i cr oenvi r onm ent i s of t en ve r y di f

f er ent f r om t hat of

t he50

sur r oundi ng aque ous m i l i eu. Fore xam pl e, t he sur f ace ac i di t y of cl ay mi ner al s can r es ul t i n pr ot onat i on of or gani c bas es beyond t h a t p r e d i c t e d b y s o l u t i o n - p h a s e p H a n d p K ( K ar i ckhof f and B ai l ey 1976)
. Thi s ef

f ectcan, atl eas t i n pr i nci pl e, be r epr es ent ed vi a E X A M S ’ s epar at ed pa r t i t i on coe f f i ci ent s f or t he i oni c s peci es of a pol l ut ant ( C hapt er 2
. 2. 2)
. The e xt ent of t he so rp tion /p ro to n a tion p ro c e ss is in flu e n c e d , h o w e v e r, b y p a rticle si ze, i nt er act i ons w i t h t he sol ut i on- phas e carbonat e s yst em , and i no r gan i c cat i on s adso r bed on t he cl ay surf ace . T h ese com pl exi t i es , and t he f

actt hat m i ner al cl ays const i t ut e a va r yi ng p ro p o rtion o f n a tu ra l se d im e n ts, re stric t E X A M S t o t he phenom enol og i cal appr oach des cr i bed i n C hapt er 2. 2. 2. The phot or eac t i vi t y of

an or gani c aci d or bas e c an be af f ect ed by i oni c s peci at i on att he sur f ace of adsorbent par t i cl es . B ai l ey a nd K ari ck h o ff (19 7 3 ) de m o n str ated t h i s effec t via i t s conv ers e: t hese aut hor s show ed t hat U V s pect r osc opy ca n be us ed t o m oni t or sur f ace aci di t y o f

cl ay mi ner al s vi a t he s hi f t i n t he a bsorpt i on spe ct r um of

ads or bed or gani c bas es f r om t hat of

t he unc har ged, t o t he p r ot on at ed, m ol ecu l ar species. The di ss ol ut i on of

neut r al organi c pol l ut ant s i nt o s uspe nded or ga ni c mat t erors ur f ac e or ga ni c f

i l ms a l s o r emov es t he chem i cal f

r om aque ous sol ut i on t o a ve r y di f f er ent m i cr oenvi r onm ent
. Thi s or ga ni c m i cr oenvi r onm ent m ay a l t er t he abs or pt i on s pect r um , quantum yi el ds, and phot ochemi cal re a c tion s o f a so rb e d m o le c u le , f o r o rg a n ic so rb e n ts u su a lly di f f er f r om w at er i n bot h r ef

r act i ve i ndex and pol ar i t y. A cha nge i n t he r ef r act i ve i ndex of

t he abs or bi ng m edi um i m pl i es cha nges i n s pect r al r adi at i on dens i t y ( er g c m pe r uni t f r equenc y r ange) ! 3 i n t he medi um , and t her ef or e i n t he appar ent abs or pt i on s pect r um of a pol l ut ant c hem i cal
. A l t hough t he e f f ect s of s uch phe nom ena can be c om put ed i n s om e c as es ( Str i ckl er and Ber g 1962) , t he het er ogenei t y of

na t ur al s uspe nded or gani c m at t er def i es des cr i pt i on. Par t i cl e s i ze di st r i but i on ( i
. e. , l i ght ext i nct i on i n t he i nt er i or of

t he pa r t i cl e) w oul d al so af f ectt he a ver age r adi at i on d e n sity e x p e rie n c e d b y a so rb e d -p h a se p o lluta n t. In a d d iti o n , rea c tion c o n d iti o n s w ithin a su sp e n d e d p a rticle m i cr oenvi r onm ent m ust di f f er f r om t hose of

aque ous sol ut i on; t hes e di f f er ence s can al t er t he r eac t i on qua nt um yi el ds and t he ki nd s o f p ho t oc he mi ca l p r od uc t s t ha t r es ul t f r om i r r ad i at i on of t h e s y s t e m ( M i l l er a nd Zepp 1979b)
. Sus pended se di m ent s m ay al so r et ar d sorbed- phas e phot or eac t i ons by quenc hi ng exc i t ed sta te s o f th e m o le c u le , an d m a y e n h a n c e p h o to re a c tion v ia i ndi r ectpr ocesses or “ se nsi t i zed” r eac t i ons. Poss i bl e i ndi r ect re a c tion s in c lu d e th e p ro d u c tion o f e x c ited sta te s o r fre e ra d ic a ls vi a i r r adi at i on of

t he or gani c mat r i x of

t he s uspe nded pa r t i cl es, and phot oel ect r i c e xci t at i on of s em i conduct or s, s uch a s Ti O 2, w h ic h a re a c o m m o n c o n stitu e n t o f m a n y n a tu ra l se d im e n ts (O l i v er et al. 19 7 9 )
. A f ew phenom enol ogi cal i nves t i gat i ons of t he e f f ect s of natur al sus pended se di m ent s on phot ochemi cal ki net i cs have a ppear ed in th e li te ra tu re ; t h e c o m p le x ity o f th e p h e n o m e n a h a s le d th e ir aut hor s t o des cr i be t hei r f i ndi ngs vi a a ppar ent ef

f ect s on r eac t i on quant um yi el ds. O l i ver , C osgr ove, and Car ey (O l i v er et al. 19 7 9 ) com par ed t he ef f ectof pur i f i ed Ti O 2 s em i conduct or t o t he phot ochemi cal ef

f i cacy of Ti or es ( i l m eni t e a nd r ut i l e) and nat ur al r i ver suspens oi ds. A l t hough pur i f i ed Ti O 2 w as an ef f i ci ent phot ochemi cal ca t al yst , t he Ti or es an d t he na t ur al sedime nt s al i ke si m pl y su pp r essed the p ho t och em i st r y of t he t est m at er i al s vi a c om pet i t i ve l i ght abs or pt i on. M i l l er and Zepp ( 197 9b ) , f

r om s t udi es of

t he phot ol ysi s of

D D E and m - t r i f l uor omet hy l pe nt ad ec an op he no ne ( TPP) i n nat ur al suspen ded sedi m ents, con cl ud ed t hat t he sedi m ent m ic ro e n v iro n m e n t i s s im ilar to a sa tu ra te d h y d ro c a rb o n so lv e n t. These aut hor s r epor t ed a n a ppar ent i ncr eas e i n t he di sa ppear ance qu antum yi el d of

s or bed D D E t o 1. 5 t i m es i t s val ue i n aque ous sol ut i on, and a f

act or of 2 t o 6 dec r eas e i n t he a ppar ent quantum yi el d of TPP
. B ot h r es ul t s w er e c onsi st ent w i t h t he be havi or of t hes e c om pounds i n or gani c s ol vent s. M i l l er and Zepp (19 7 9 a) concl uded t hat t he co m peti t i ve ab sorpt i on of l i gh t by s uspe nsoi ds i s nonet hel es s t he domi nant ef f ect of sus pended par t i cl es on ph ot ol ysi s i n na t ural w at ers . 2. 3. 3. 5. 1 Sensiti vi t

y anal ys is of sor

pti on ef f ect s on di re ct p h o to ly sis Phot ol yt i c t r ans f

or m at i on of

pol l ut ant c hem i cal s i s an i m por t ant pr oces s i n m any a quat i c s yst em s, m ostes peci al l y w hen ph o t o che m i cal t r ansfor m at i on i s t he o nl y de gradat i on process capa bl e of

l i m i t i ng or gani sm exposur es underenvi r onm ent al condi t i ons. T hi s pr oces s i s cr i t i cal l y depe ndent on compet i t i ve l i ght abs or pt i on by sus pended m at er i al s, and on t he e f f ect s of sorpt i on on t he a vai l abi l i t y of a pol l ut ant t o phot ochem i cal processes. In a na tu ral w ater bo d y , ca p t u re of a po l l u t an t by b e n th ic se di m ent s r em oves t he c om pound t o a phot ochemi cal l y i nact i ve (da rk) sec t o r of t h e e co sy stem
. T h e n et p h o to c h e m i str y of a po l l ut ant che m i cal t hu s depe nd s on so l ut i on - and sor bed

- ph ase phot or eac t i vi t y, c ompe t i t i ve l i gh ta bs orpt i on by s uspe nsoi ds, and ca ptur e of

t he p ol l ut an t b y t he b en t hi c s ub s ys t em. The i nt er act i ons among t hes e pr oces se s can be e xpl or ed vi a E X A M S . For t he e xam pl e si m ul at i ons, t he e cos yst em w as a s m al l ( 1 ha) st at i c pond, 2 m deep, w i t h a 1 cm ac t i ve bent hi c s ubsys t em of b u lk de n sity 1.7 5 g/c c an d w a te r co n te n t 1 5 0 % . T h e e x a m p le com pound had a nea r - sur f ace ha l f

- l i f e of 1 houri n s ol ut i on, but w as a f ul l or de r of

mag ni t ud e mor e ph ot or ea ct i ve w he n s or bed w i t h susp end ed sed i m ents ( QY I EL D (1 ,1 ) = 1 .0 , QY I EL D (2,1) = 10. 0)
. The di st r i but i on f unct i on ( DF ACG ) w as t aken as 1. 20; E X A M S us ed t he s um of l i ght abs or pt i on by w at er i t se l f ( at 300 n m ), p lu s th e a b so rb a n c e a ttri b u ta b le t o su sp e n d e d se d im e n ts, to com put e t he aver age l i ght i nt ens i t y i n t he w at er c ol um n ( Eq. ( 2- 10 4) )
. S ys t ema t i c ch an ge s i n t he p ar t i t i on c oe f f i ci en t of t he c h e m ic a l ( K PS ) a n d th e c o n c e n tra tion o f su sp e n d e d se d im e n ts ( SUS ED ) w er e t hen used t o el uci dat e t hei r netef f ecton t he ph ot och em i st r y of t he co m po un d, un der cond i t i on s m ost f avor abl e f

or enha ncement of

phot ot r ans f

or m at i on ki net i cs by sorpt i on. The r es ul t s of

s i mul at i on s us i ng a s us pe nd ed s edi m ent c o n ce n t rati o n of 1 0 m g / L an d va rying pa rt i t i o n co effi cie n ts51

Kp L/ kg % of W at er

C o lu m n in D i ss ol ved S ta te % of To t al

R e s id e n t in B e n th ic Zone P seu d o -Fir st -O rder H al fliv e s , h W at er Col u mn W h o le

Syst em 0 100 0. 29 8. 50 8. 52 1 100 0. 87 8. 50 8. 57 10 100 5. 8 8. 49 9. 01 1 0 0 9 9 .9 3 6 .9 8 .4 2 1 3 .4 1 0 0 0 9 9 .0 8 5 .2 7 .8 0 5 2 .9 10000 90. 9 98. 2 4. 68 253 100000 50. 0 99. 7 1. 55 452 1000000 9. 09 99. 8 0. 93 492 Tabl e 11 . Ef f ect ofpar t i t i on coeff i ci ent K p ( L/ kg) on net phot or eact i v i t y w hen suspe nded sedi m ent concent r at i on = 10 m g/ L ( A v er age l i ght i nt ensi t y i n w at er col um n 11. 8% of sur f ace v al ue) [ S] m g /L % of W at er

C o lu m n in D i ss ol ved S ta te % of To t al

R e s id e n t in B e n th ic Zone M ean

Iz/Io ( % ) Pseud o-Fi r st
- O r der

H a lf liv e s , h W at er Col u mn W h o le

Syst em 0 100 36. 96 84. 8 1. 18 1. 87 1 100 36. 96 59. 3 1. 68 2. 67 1 0 9 9 .9 3 6 .9 3 1 1 .8 8 .4 2 1 3 .4 100 99. 0 36. 73 1. 22 75. 2 119 1000 90. 9 34. 77 0. 12 449 688 10000 50. 0 22. 67 0. 012 1484 1918 Tabl e 12 . Ef f ect ofsuspende d sedi m ent concent r at i on [ S] on net phot or eact i v i t y w hen par t i t i on coeff i ci ent K p = 100 L/ kg

Kp L/ kg S u s p e n d e d S e d im e n t C o n c e n tra tio n , m g /L

0 1 10 100 1000 10000 0 1. 18 1. 69 8. 52 82. 2 819 8182 1 1. 19 1. 70 8. 57 81. 8 749 4157 10 1. 25 1. 79 8. 93 79. 1 437 861 100 1. 87 2. 65 12. 3 65. 4 125 209 1000 8. 06 10. 5 29. 1 51. 7 63. 3 137 10000 69. 9 50. 0 45. 9 49. 0 56. 6 130 100000 689 89. 6 49. 2 48. 6 55. 9 129 1000000 6876 97. 4 49. 6 48. 6 55. 8 129 Tabl e 13 . Effe c t of

s us pe nde d s e di m e nt c onc e nt r at i on ( m g/ L) and pa rt i t i on coeff

i ci ent ( K p, L / kg) on syst em - l evel pseud o-f i rst - ord er ph otochem i cal ha l f

- l i fe ( ho urs) w hen sorbed chem i cal i s 100 t i m es m ore react i ve t ha n d i ss ol ved speci es ( 0–1×10 L/ kg) ar e gi ven i n T abl e 12 . T h e se re su lts a re g iv e n in

6 t e r ms o f p s e u d o - f

i r s t
- o r d e r h a l f

- l i v e s f o r t h e wa t e r c o l u mn subs yst em al one, and f or t he e nt i r e pond e cos yst em . ( The w hol e- sys t em hal f

- l i ves assum e t hat t he r at e of t r ans por t f

r om t he be nt hi c s ubsys t em i nt o t he w at er col um n does not l i m i t t he r at e of phot ochemi cal t r ans f

or m at i on of

t he c om pound. ) U nder t hes e e nvi r onm ent al condi t i on s, l es s t han 1% of t he c om pound i n t he w at er col um n i s i n t he s or bed s t at e f or a pa r t i t i on c o e ffic ie n t l e ss th a n 1 0 0 0 L /k g . W h e n th e p a rtit io n c o e ffic ie n t i s gr eat er t han 1000, how ever , m or e t han 85% of t he r es i dent m at er i al i s captur ed by t he ( dar k) bent hi c s ubsys t em . The sy ste m -le v e l h a lf-life o f th e c o m p o u n d in c re a se s s te a d ily w ith i ncr eas i ng K p, des pi t e t he gr eat er phot or eac t i vi t y of t he s or bed m a te ria l. T h e e ff ec tof co m p eti t i v e li g h t ab so rp tion b y su sp e n d e d m a te ria ls w as exa m i ned by f

i xi ng t he par t i t i on coef

f i ci ent at 100 L/ kg, and sys t em at i cal l y i ncr eas i ng t he c oncent r at i on of s uspe nded s e d i me n t s f

r o m 0 t o 1 0 0 0 0 mg / L ( T abl e 12 )
. I n t hi s cas e, l i ght abs orpt i on by t he s us pe nd ed s ed i ment s r ap i dl y i nc r ea s ed t he phot ochemi cal ha l f

- l i f e of t he com pound. Thi s eff ect

over w hel m ed t he e nhance d phot or eac t i vi t y of t he s or bed m at eri al , des pi t e t he f actt hat m or e t han ha l f of t he t ot al com pound i n t he s yst em r es i ded i n t he w at er col um n ( at s t eady state). The s yst em - l evel ps eudo- f i r st
- or der ha l f

l i f e i ndi cat es t he out com e of

t he i nt er act i on bet w een com pet i t i ve l i ght abs or pt i on by s uspe nded mat er i al s, ca pt ur e of t he c om pound by bot t om se di m ent s, and e nhance d phot or eac t i vi t y in t he s or bed s t at e. T abl e 13 giv es t h e sy stem -l ev el ph o t o ch em i ca l ha l f l i fe o f a c o m p o u n d th a t i s 1 0 0 ti m e s m o re re a c tive in t h e so rb e d , th a n in t he di s s ol ve d, s t at e, f ora r an ge of

K p a nd s ed i ment conce nt r at i ons unl i kel y to be excee ded i n natur e. A s com par ed w i t h the 1. 18 hour hal f

- l i f e of t he uns or bed, cl ean- w at er bas el i ne, an i ncr eas e i n s or pt i on l eads t o a ne t s uppr es si on of t he r at e of ph ot och em i cal t r an sfor m at i on of t he co m po un d i n al l cases, des pi t e t he uni quel y ( and unr eal i st i cal l y) f avor abl e c ondi t i ons as sumed f

or t he anal ysi s. I n sum, t he e f f ect s of r es i dence i n t he sorbed s t at e on phot or eac t i vi t y ar e of s econda r y i m por t ance , and can be a dequa t el y sum m ari zed vi a a si m pl e descr i pt i ve pa r am et er ( QY I EL D ).52

The ef f ect s of sorpt i on t o or gani c sl i cks at t he a i r - w at er i nt er f ace ar e noti ncl uded i n E X A M S f or s i m i l ar r eas ons: A l t hough t he conce nt r at i on i n t he s l i ck c an be l ar ge, t he t ot al f r act i on of

t he pol l ut ant r es i dent i n t he f i l m i s pr obabl y t oo s m al l t o have m uch eff ect on t he syst em - w i de ki neti cs of po l l ut ant che m i cal s ( Zepp an d B au g h m an 19 7 8 )
. E X A M S re p re se n ts th e p h o to c h e m ic a l effe c ts o f so rp tion to sus pended se di m ent s, and c om pl exat i on w i t h DOC , v ia se p a ra te ent r i es i n t he Q YI EL D vect or s. N ot e t hat t hes e ve ct or s r epr es ent t he e f f ectof r es i dence i n t he bi osorbed s t at e on t he di r ect phot ol ysi s of t he pol l ut ant ; t hey a r e noti nt ended t o r epr es ent phot ose nsi t i zat i on or p ho t ob i ol og i ca l t r an s f or mat i on of pol l ut ant s by phyt opl ankt on. A l t hou gh qual i t at i ve s t udi es have i ndi cat ed t hat t hi s pat hw ay exi st s, a s yet a qua nt i t at i ve ba si s f or pr edi ct i ng i t s m agni t ude a nd i m por t ance i n natur al syst em s has n o t be en de v elo p ed (Z ep p 19 8 0 ). 2. 3. 3. 6 N ear- surf

ace sol ar beam and sky i rradi ance The spe ct r al l i ght f

i el d i s cal cul at ed by E X A M S as a ve ct or ë ë ( “W LA M ” for W ) of 46 phot on i r r adi ance s. W i s t he t ot al ( sol ar bea m p l u s skyl i gh t ) i r r adiance un der cl ear ( cl ou dl ess) condi t i ons, j ustbel ow t he a i r - w at er i nt er f ace ( t hat i s, af

t er su b t rac t i n g refl ec t ed l i g h t fr o m t h e li g h t i n cid en t on t h e su rf ac e). E X A M S cor r ect s t he i nput i r r adi ance f or ef f ect s of cl oud cove r usi ng t he e m pi r i cal r el at i onshi p: ( 2- 111) ( Bü t t n e r 1 9 3 8 ) , c i t e d f r o m ( Zepp 1980) ; s ee al so ( Sc hul t z a nd G räfe 1 9 6 9 )
. The cl oudi ness ( E X A M S ’ in p u t CL OUD ) t er m i s t he a ver age opaque sky coveri n t ent hs, w i t h a r ange f r om 0 ( cl earsky) t o 10 ( f ul l cove r )
. O paque sky coverm ay a l so be r epor t ed i n okt as ; an okt a i s one e i ght h of

t he cel es t i al dome. C onver si on f r om okt as t o t enths m ay b e m ade as f ol l ow s: WMO C ode O kt as Tent hs 0 ( cl ear ) 0 0 1 1 ok t a or l ess,

b u t no t ze ro 1 / 1 0 or less, bu t no t ze ro
2 2 okt as 2/ 10 - 3/ 10 3 3 okt as 4/ 10 4 4 okt as 5/ 10 5 5 okt as 6/ 10 6 6 okt as 7/ 10 - 8/ 10 7 7 okt as or m or e, but not 8 okt as 9/ 10 or m or e, but not

10/ 10 8 8 okt as 10/ 10 9 sky obsc ur ed by f og or ot her m et eor ol ogi cal phenom enon 15 cl oud cove r i ndi sc er ni bl e f or r eas ons ot her t han f og or ot her m et eor ol ogi cal phenomenon, or obse r vat i on not m ade

C l ear - sky i r r adi ance att he e ar t h’ s sur f ace depe nds on l at i t ude, si t e e l evat i on , at m osph eri c turbi di t y an d w at er vapor cont ent , and t he oz one c ont ent of t he s t r at osphe r e (L eig h t o n 19 6 1 )
. C om put at i onal m et hods f or es t i m at i ng s pect r al i r r adi ance have b een exp l ored by a num ber of aut ho r s (e .g ., L e ig h to n 1 9 6 1 , G r een etal
. 1974, D ozi er 1980, G r een et al
. 19 80, G r een and Schi ppni ck 1980, G r een and Schi ppni ck 1982)
. Zepp and Cl i ne ( (19 7 7 ) ), us i n g a c o m p u t er p rog ram (“ S OL AR ”) ava i l abl e on r eques t f r om t hose aut hor s, ca l cul at ed phot on s cal ar i r r adi ance ë W at 39 of the w av elen g t h i n t erv als ad o p t ed for E X A M S . ( They r epor t ed “ m i dse as on, ” “ m i dday” spect r al i r r adi ance at40 E N l ati t u d e. F o r E X A M S , s uch va l ues m ust be reduced by a day l engt h f act or( dayl i ghthours / 24 ) , and si nu soi d av eragi ng ove rt he phot oper i od ( i
. e. , m ul t i pl i ed by 2/ð ). Pr ocedur e PHO TO 1 begi ns f r om nea r - sur f

ace pr e- com put ed ph ot ol ysi s r at e con st ants ( KDP ) , and t hus does not use t he ë sp e c tra l i rra d ia n c e v e c to r W in i t s co m p u t atio n s. PHOTO 1 a d ju sts KDP via a cl ou di ness corr ect i on ( 2-111 ) , and al so corr ect s KDP f or t he ge ogr aphi c t r ans l at i on f r om t he l at i t ude a t w hi ch e ach KDP w as m eas ur ed ( R FL A T) t o t he l at i t ude of t he e cos yst em ( LA T). The cor r ect i on t er m i s com put ed f r om t he t ot al annua l s o l a r + s k y r a d i a t i o n r e c e i v e d a t l a t i t u d e s R FL A T a n d LAT. G r ound- l evel r adi at i on w as comput ed as a f unct i on of

l at i t ude a t 1 0 d e g re e in te rv a ls v ia p ro c e d u re s d e sc rib e d b y L ist ( 1966) us i ng an at m osphe r i c t r ans m i ss i on coe f f i ci ent of 0. 90. Est i m at ed t ot al ra d ia tion in c re a se d fro m 1 .0 3 8 × 1 0 c a l cm y r a t t h e p o le , t o 5

! 2

! 1 2.744× 10 l angl ey yr at theequator. Re gress ion of the(8) 5

! 1 estim at es on: Y = a

+ b cos(2L ) where L i s t

he l at it ude in radi ans, yiel ded a = 1. 917×10 , b =

5 8.7 05 ×10 , and ac count ed for 99.7% of t

he variati on in tot al 4 irr adi ance(Y) w i t

h l ati tude . In proce dure PHOTO 1, t he c orrec ti on te rm for KDP is com

pute d as :

For e xam ple , for a rate c onstant

m eas ured at t

he e quat or and a p o lar ec o sy st em,53 Fi gu r e 7. I m pr op er s eg m en t at i on : i nc om pl et e v er t i ca l de f i ni t i on This proce dure i s ba sed on tot alsol ar energy input , and t hus m ay undere st im at e t

he l at it ude dependence of photoc hemic al tran sfo rmation o f po llutan ts that abs orb s unlig ht most stro ng ly atwav el en g th s < 32 0 nm. 2.3.3.7 In put data and comp utati onal me chani cs – Summary Proce dure PHOTO 1 was desi gned to evaluat e c hemic al s whose abso rpti on spe ct

rum has not been quant ifi ed. Its pri m aryinput dat um , KDP , is a ve ctorof p seu do -fir st-o rd er ph oto lysis rate const ant s. A separat e va lue of KDP can be ent ere d for e ach 3 4 exi st ing i onic spe ci es (RH , RH , e tc .). KDP mus t be cal cul at ed + as an annualave rage value a ppli cabl e t o near-s ur face wat ers, under c loudl ess condi ti ons and ful l-day avera ge s olar i rradi ance . EXAMS the n adjus ts therat e c onst ant for l ight extinc ti on in the wat er c olum

n, e ffec ts of clou d cove r, and departur e of the lati tude of t

he e nvironm ent

( LAT) from

t he lati tude at whic h the rat e c onst ant

was m eas ured ( RFLAT ). Effects of sorpt ion a nd DOC -com ple xat ion c annot

be represente d; only t

he di ssolved form of t he c hemic alphotolyz es. The c om putati ons exec ute d by proce dure PHOTO 1 are inher ently le ss a ccur at e t

han wavel engt

h-spec ifi c c om

putati ons ba sed on th e c h emi ca l’ s ab so r

p ti o nsp ec trum ( PHOTO 2), be caus e PHOTO 1 cannot eva luate theeffect s of spec tra lly di ffere nti at ed l ight ext inc ti on in the wat er c olum n. Proce dure PHOTO 2 c ouple s the a bsorption spec tra

of the c om pound ( ABSORG (1 -4 6,k )) to the irra dian ce spe ctrum inci dent on t he wat er body ( W ë). T he QYIELD matri x conta ins m eas ured dis appearanc e quantum

yi el ds; i t i s a ls o use d in EXAMS to acc ount f or ef fec ts of s orpti on and com ple xat ion wi th DOC . Bothpho tolysis p ro cedures op erate onthe in ciden t light fieldto com pute theave rage l ight

inte nsi ty in e ach com

partm ent of t he ecos yst em . (In PH OTO 1, t he inci dent

li ght f ie ld ha s a nom ina l value of 1.0, be caus e KDP has built into i t t he c le ar-s ky irr adi anceat

lati tude RFL AT.) PHOTO 1 use s a spe ct ral com posi te l ight

a bsorption coef

fic ie nt for eac h s ector of the wat er body co m

pute d via Eq. (2-105) at t

he us er-s peci fie d wav eleng th( L AM AX ); PHOTO 2 comput es t he a bsorpt i on coef f i ci ent f or eve r y s pect r al w aveba nd ( T abl e 9 ) f r om t he pi gm ent ( C H L), di ss ol ved or gani c c arbon ( DOC ) , and s uspe nded se di m ent ( SU SE D ) conc ent r at i ons i n ea ch c om par t m ent (E q u ati o n (2-10 5 ))
. The w at er col um n ( “E” a nd “ H ” c om par t m ent t yp es) ca n be su b d iv id e d in to a s m a n y h o riz o n ta l s lice s a s s e e m s a p p ro p ria te fo r a p a rtic u la r w a te r b o d y . E X A M S t r ace s l i ght ext i nct i on ver t i ca l l y t hr ou gh t he s l i ce s b y co mput i ng i r r ad i an ce a t t he bot t om of

e ac h c ompa r t ment , a s w el l a s t he a ve r ag e i r r ad i ance use d f or comput i ng photol ysi s r at e c onst ant s. W hen t he ( J- 1) com par t m ent i s anot her E or H s egm ent , i r r adi ance att he bot t om of t he ( J- 1) com part m ent i s t aken as t he s t ar t i ng poi nt f or i r r a d i a n c e c o mp u t a t i o n s i n t h e c u r r e n t ( J ) s e c t o r . T h i s s c h e me w i l l f ai l , how ever , i f

t he s yst em def

i ni t i on r ul es gi ven i n C hapt er 2. 3. 1. 1 ar e di sr egar ded. A n e x a m p le o f a lo g ic a l, b u t i m p ro p e r, se g m e n ta tion sc h e m e is show n i n Fi gure 7
.

Cal ls to EXAMS ’ pho tolysis p ro cedures ar e exec utedin com partm ent order . For thi s e cosy st em , t he first cal l c om

pute s p h o to ly si s i nco mp artme nt 1 , a(L ) itto r al wa te r co lumn com partment . Theinc ide nt l ight fi el d at theair-wat er inte rfac e is iden tified as the ligh t intens ity at the top of the compartment, and EXAMS c om

pute s both aver age li ght int ensi ty and ir radi ance at th e b otto m of compartment 1. Compartment 2 is a (B) enth ic compartment; EXAMS si m ply se ts thephotolysi s rate to 0 and does not c al l a

photolysi s proc edure . Upon re aching com partm ent 3, EXAMS che cks the com partm ent ty pe of the (J-1) com partment . As com

partm ent 2 i s “ B” (bent

hic ), t he inci dent ligh t f ie ldis us ed to start the co mputatio ns. A ph oto lysis proce dure i s not

invoked for (B )ent

hic com partm ent 4. When EXAMS now ca ll s for irr adi ancecom putati ons for the (H)ypol im

nion c om

partm ent (5), an e rror occ urs. EXAMS insp ects (J- 1) compartment 4 , find s it to be (B) enth ic, and starts it s c om putati ons for t

he hy poli mnion us ing t

he s urfac e inci dent li ght f ie ld, rat her t han inte nsi ty

at thebottom

of t he epil im nion. The proper s yst em

definition i s shown in Figu re 8
.

Fi gu r e 8. Pr op er s eg m en t at i on : c om pl et e v er t i ca l de f i ni t i on .54 In t his c ase , upon initiati on of c om putati ons for the hypol im

nion (now num

bere d 6), EXAMS finds t

hat the (J -1) c om

partm ent (5) is not ( B )e nt hi c , a s i t i s an ( E) pi l i mni ons e gm e nt
. Th e l ight inten sity at the bo ttom of compartment 5 (in tern al variable BOTLI T i n PHOTO 1, ve ct or BOTLAM in PHOTO 2) i s t here fore ret rie ved and use d to st art

their radi ancecom

putati ons for t

he hypol im nion.
EXAMS repor

ts the ave rage li ght inte nsi ty in eac h se ct or of t

he ecos yst em

as part of i ts “c anoni calprofi le ” of the sy st em . The se report s are give n a s a perc ent age of t he l ight fi el d inc ide nt on the wat er body , i nte grat ed ove r t he ul traviol et

portion of

the spec trum (278.75–395 nm). Refer enc es for Chap ter2.3.3. Baile y, G. W. , and S. W . Karickho ff. 1973 . An ultr avio let spe ctro sco pic methodformonito ring surfa ce ac idity of clay min er als un dervaryin g wa ter con tent. Clays andClay Mi nera ls 21 :471-477. Bai le y , R
. A. , H. M
. C l ark e , J. P
. Fe rri s, S
. Kr aus e , and R . L. Str ong. 1978. Chemis try of t he Environm ent . Academic Pres s, Ne w York. Bake r, K. S., and R . C . Smit h. 1982. Bi o-opti calcl ass ifi cation and m odelof natura l wate rs. 2. Lim nology and Oce ano gr aph y 27 :500-509. Bal z ani, V., and V. Carass iti. 1970. Phot ochemis try of C oo rd i nat i on

C om po un ds
. Ac a de m i c P re ss , Lo nd onand New York. Büt tn er, K. 1938. Phys ikal Bioklimatologi e (P hysik. B iokl imat .), Leipzi g. Calv ert , J. G., and J . N. Pitt s, J r. 1966. Phot ochemis try . John Wile y and Sons, Inc. , New York. Dozi er, J. 1980. A cl ear -skyspe ct ral solar ra diati on m odelfor snow-cove red mounta inous terrai n. Wate r Re source s Res ear ch 16 :709-718. Gree n, A. E. S., K. R. Cross , and L. A. Smit h. 1980. Im

proved ana l y t i c c ha ra c t e ri z a t i on of ult ravi ole t s kyl ight
. Ph oto chemistry an d Ph oto bio log y 31 :59-65. Gree n, A. E. S., T. Sawada , and E. P. She ttle . 1974. The middl e ult ravi olet r eac hing t

he ground. Phot ochemis try and Ph oto bio log y 19 :251-259. Gree n, A. E. S ., and P. F. Schippni ck. 1980. UV-B rea chi ng the ground. in Confe renc e in Ult rav iol et Li ght in Marine Ecos yst em s, C openhage n. Gree n, A. E. S., and P. F. Schippnic k. 1982. UV-B re aching the surfa ce. Page s 5-27 in J. Calkins , edi tor. The Rol e of Solar Ult ravi ole t Radi at ion i n Mari ne Ecos yst em s. Pl enum Pre ss, New York. Hoje rsl ev, N. K. 1973. Inhe rent and appar ent

opti calproper

ti es of t he we st ern M edi te rrane an and t he Hardange rfjord. 21, Univ. Copenha gen, Inst . Phy s. Oc eanogr ., C openhage n. Hoje rsl ev, N. K. 1974. Inhe rent and appar ent

opti calproper

ti es of t he Balti c. 23, Univ. Copenha gen, Inst . Phy s. Oc eanogr . Hutc hins on, G. E. 1957. A Tre at ise onLimnol ogy. Vol. I. Geography , Phy si cs, and Chemis try
. John Wile y and Sons, Inc, New York. Jerl o v (Johns on), N. G., and G. Lil jequi st
. 1938. On t

he angular dis tributi on of s ubm arine dayl ight and the tot alsubm ari ne il luminati on. Sve n. Hy drogr.- Bi ol. Komm. Skr., Ny S er. Hydrogr. 14 :15. Jerl o v, N. G. 1976. Marine Optic s. E ls evier Sci. Publ . C o, Am st erdam -Oxford-New York. Kari c khoff, S . W., and G. W. B ai le y. 1976 . P ro tonati on of or gan ic bases in clay-w ate rs ystems. Clays andClay Mi nera ls 24 :170-176. Lei g hton, P. A. 1961. Sol ar r adiation and i ts abs orpti on. Pa ges 6-41 in Phot ochemis try o f Ai r Pol lution. Acade m ic Pre ss, New York and London. Lis t, R. J. 1966. Smit

hsoni an M et eorol ogic alTabl es, 6th edi ti on. Sm it hsoni an Ins ti tution, Washingt on, D.C
. Mi ck le , A. M., and R . G. Wetze l. 1978. Eff ectivenes s of subm erse d angi osperm -epiphyt e c om ple xes on exc hange of nutri ent s and organi c c arbon in li tt oralsy st em s. I I. Diss olv ed o rg anic carbo n. A qu atic Botan y 4 :317-329. Mille r, G. C. , and R. G. Z epp. 1979a. Effe ct s of suspe nded sedi m ent s on photoly si s rate s of dis sol ved pol lut ant s. Wat er Res ear ch 13 :453-459. Mi ll e r, G. C., and R. G. Zepp. 1979b. Phot orea ct ivi ty of aquati c po llutan ts sorbedon su spe nd ed sed iments. En viro nmental Scien ce andTechn olo gy 13 :860-863. Oli ve r, B . G., E. G. Cos grove, and J . H. Car ey . 1979. Effe ct of suspe nded s edi m ent s on the phot oly si s of organi cs in wate r. Env iron mental Scien ce andTechn olo gy 13 :1075-1077. Pool e, H. H., and W. R. G. At kins
. 1926. On t

he pe net ration of li g h t into sea-w ater. Jo urnal of the marine bio log ical Assoc iati on of t

he U.K. 14 :177-198. Pre i s e nd or fe r, R
. W. 19 58 a . Di re c t l yo bs e rv abl e q uanti t i e s for ligh t fields innatur al hydr oso ls. Vis ibility Labo rato ry Repor t S IO Re fere nce 58-46, Sc ripps Instit uti on of Oceanography , La

Jol la , C al ifor

nia
. Prei s endorfe r, R . W. 1958b. Unifi ed Ir radi anceEquations
. Visibil it y Labor at ory Report SIO Re fere nce 58-43, Sc ripps Instit uti on of Oc eanogr aphy , La Jol la , C al ifor

nia
. Schu ltz, R., andK. G räf

e. 19 69 . Con sider ationof sky ultrav iolet radi at ion i n the m eas urem ent of sol ar ultraviol et

radi at ion. Page s 359-373 in F. Urbach, edi tor. The Bi ologi c Ef fec ts of Ult ravi ole t Radi at ion. Pergam on Pre ss, Oxford. Sm i th, J
. H. , W. R
. Ma

be y , N. B oh on os , B
. R
. Ho l t , S. S. Lee , T.-W. Chou, D. C . B om berge r, andT. Mil l. 1978. Envir onm ent alPat

hways of Se lect ed C hemic al s in Fres hw at e r Sy st e m s: P art I I. L abo rat or

yS t ud i e s. E PA

600/7-78- 074, U.S. Envi ronm ent alProte ct ion Age ncy , Athe ns, Ge orgia
. Sm it h, R . C ., and K. S. Baker. 1978. Opti calcl ass ifi cation of natural wa ters. Lim

no log y and Oc eano gr aph y 23 :260-267. Sm it h, R . C ., and J. E. T yl er. 1976. Tr ansmission of solar radi at ion into natura l wate rs. Photoc hemis try and Photobi ology

Re vie ws 1 :117-155. Stric kler, S. J ., and R. A. B erg. 1962. R el at ions hip be twe en absorption inte nsi ty

and fluore sce nce l ife ti m e of m ole cul es.55

Journalof C hemic alPhy si cs 37 :814-822. Tal ling, J. F., R. B. Wood , M. V. Prosse r, and R. M. Baxt er. 197 3. T he u

pp e r l i m i t

o f ph ot os ynt

he t i c p ro du c t i vi tyby phyt op l ankt on : E vi de nc e f ro m E thi op i an s od al akes
. Fre shw ater Bio log y 3 :53-76. Turro , N. J. 1978. M odern M ole cul ar P hotoc hemis try . The Benjam in/ Cumm ings Publ . C o., I nc., Me nlo P ark, Cal ifor nia
. Wetz e l , R
. G. 19 75
. Limno l og y . W.B
. Sa un de rs C o., Phil adelphia
. Zep p , R. G. 197 8. Q uan tum yields f o rr ea ctio n of

pollu tants in dilute aqueous soluti on. Environm ent alSci enceand Tech no log y 12 :327-329. Zep p , R. G. 198 0. A ssess ing the ph o to ch emistry of o rg anic pollutants in aquatic environm ent s. P ages 69-110 in R. Haque, e dit or . Dyna

mi c s, E xp os ur e and Haz ard As ses sm ent of Toxi c C hemic al s. Ann Arbo r Sc ie nce Publi shers , Ann Arbor. Zepp , R . G., and G. L . B aughm an. 1978. Pre dic ti on of ph oto chemical tran sfo rma tionof p ollutants inthe aqu atic envi ronm ent . Pa ges 237-263 in O. Hutzi nger, I. H. v. Lelyv eld, an d B. C. J. Zoeteman, editor s. Aquatic Pollutants: Tr ans fo rmation and Biol ogic alEffe ct s. Pergam on Pre ss, Oxford. Zep p , R. G. , andD. M. Clin e. 19 77
. Ra te s of direct p ho tolysis in aquatic environm ent . Environm ent alSci enceand Tech no log y 11 :359-366. Zepp , R . G., and P. F. Schl otzhauer . 1981. Com pari son of ph oto chemical beh avio r of vario us humic sub stanc es in water: III. Spe ct

roscopi c prope rti es of humic subst ance s. Chemosphere 10 :479-486. Z e p p , R
. G. , N. L
. Wo l f

e , L
. V
. A z arr a g a , R
. H
. C o x , an dC
. W. Pape . 1977. Photoc hemic altr ansfor m at ion of theDDT and m et hoxyc hlor degra dat ion product s, DDE and DMDE, by sunl ight . Arc hive s of Envir onm ent alCont aminati on and Tox icolo gy 6 :305-314. Zepp , R . G., N. L. W olfe , J. A. Gordon, and G. L. Ba ughm an. 19 75 . Dynamic s of 2,4-D e st ers in s urfac e wate rs: hydrolysi s, photoly si s, and vapori zation. Envir onm ent al Scien ce andTechn olo gy 9 :1144-1150. Zepp , R . G., N. L . Wolfe , J. A. Gordon, and R. C. Finc her. 19 76 . Ligh t-inducedtrans fo rmations of meth ox ychlo r in aquat i c s y st e m s. J ourn a lof Agri c ul t

ur a land F ood Chemistry 24 :727-733.


### 2.3.4 Specific Acid, Specific Base, and Neutral Hyd ro lys is Many organi c c om

pounds re act

dir ectly with wat er in the aqu eou s solv ent system. Inadd ition, waterdisso ciates into hydronium

and hy droxidei ons, and the c oncent rations of the se subsi diary spec ie s ofte n a ffec t the r at es of chemic al transform at ions
. EXAMS inc lude s kinet ic const ant s for thre e 3 kinds of hy drolyti c pathways: spe ci fic -ac id ( H O ) cata lyzed, + neut ralhydr oly si s, and spe ci fic -base(OH ) cat alyz ed
! transform at ions
. The br eakdown of es te rs t o yi el d a carbo xyli c a ci d and an al coholis a conveni ent

exam ple of hy drolyti c tra

nsform at ions
. The ove ral l r eac ti on is : ( 2- 112) where R and R’

can be any alkyl o r acyl mo iety. A ltho ug h this equati on a c c urat e ly

depi c t s t he s toi chi om et

ry of es te r hy droly si s, it do e s no t

s e rv e a s ade fini nge qu at i onf or c om put i ngthe vel oci ty of the reaction. The r at e of transform at ion of any spec ifi c e st er i s fundam ent al ly depe ndent

on i ts che m ic al struct ure. The s peed of t

he re action of

te n depe nds on t

he pH of the m edium

as wel l, however, bec ausees te r hy drolys is can pr ocee d via th ree distin ct pa thw ays (acid/base catalysis, n eutr al) withidentica l net stoich iometry. Bec ausechemic alrea ct ions involve s hift s in el ect ronic bonding orbit al s, organi c c om

pounds are most

rea dily att acke d by groups that can donat e or acc ept el ect rons from

theta rget m ole cul e.

3 Ele ct ron-deficie nt che mical species (e. g., hy dronium ions , H O )

+ are ca ll ed “ el ect rophil es. ” El e c t

ro ph i l e s arepa

rti c ul arly attra ct ed to atoms with neg ative char ge, to a lone pair o f electro ns, andto the el ect ron-dens e re gion of

a double bond. Chemic algroups wit h ext ra non- bonding el ect

rons are c al le d “nuc le ophil es. ” The el ect ronegati ve hy droxideion i s a rel at ive ly st rong nucl eophi le
. The wate r m ole cul e i s itself nuc le ophil ic , be caus e t he oxy gen at om of t his “pol ar” m ole cul e ha s a lonepair of e le ct

rons. The mechanisms of

the fo rmation an d hydro lysis of org anic esters have beenrev iewedby K irby ) . Tins ley (Ti nsl ey1979:105 ff) has sum

m ari zed the rout es and m echanis m s of est er hydro lysis un derenv iron mental con dition s, wh ere in all pr obabil it y only t he “ A(AC)2” and “ B(AC) 2”m echanis m s are si gnifi cant . Al though al l thre e route s of est er hydrolysi s involve nu cleo p h il ic phe no mena, the mechanism of th e path way is som ewhat

dif fere nt in ea ch c ase . Acid -catalyze d esterhydr olysi s is a true “catalysis” rea ctionin that t he hy dr on i um

i onp arti c ipat e s i n the r e a c t i onbut is not con sumed b y the reac ti o nsequen ce. Inthe firs t step of this pat hway, theel ect

rop hilic hydr onium

ion protonate s t

he car bonyl(C= O) oxy gen. The protonate d e st er t hen unde rgoes a nucl eophi li c a ddition of

wat er t o give a

te trahedra l inte rm edi at e; thi s st ep i s c at alyz ed by

a sec ond wat er mole cul e a ct ing as a ge ne ra lba se . Fina l l y , the te trahe dr a li nt e rm e di at e br e aks do wn via two add itiona l (fast) steps to yieldthe pr oduct carbo xylic aci d and alc ohol, and to rege nerate the cata lyti c hy dronium ion. Bec ausetwo wat er mole cul es are involved in t he for m at ion of the te trahedra l inte rm edi at e, the spe ci fic -ac id c at alyz ed56 hydro lysis of

the esterbon d is “s eco nd -o rd er” in w ater. W ith wat er a s t

he s olve nt m edium

for t he di ssolved pha se of t

he com po und, however, thewat er c oncent ration doe s not

change during the course o f the re actionan d n eed no t be inco rp or ated in the kine ti c e xpress ion. The observed r at e c onst ant s are nonet hel ess subje ct

to sol vent

effect s and shoul d be m eas ured usi ng pure wat er a s t

he s olve nt whe never

possibl e. The direc t involvem ent

of t he wate r m ole cul e in t

he rea ct ion a ls o im

poses a needforcare in th e ex trap olatio n o f hydro lysis rate co nstan ts (m eas ured in pure wat er) to c om pounds sorbed wit

h se dim ent s. In EXAMS , a llconc ent

rations areref

eren ced to t

he wate r phas e of ea ch c om

partm ent (Eq. (2-1)). The tot alpollutant conce ntrati on [ C] (unit s m g/l it er of wate r), whe n m ultipl ie d by the ap pr op riate dis tribu tioncoef ficien t á , gi ves the di ssolved conce ntrati on of pol lut ant in th e aqueous phas e of eac h com partm ent , inc luding t

hat in t he int erstitia l pore wat er of a bent hic se diment . Thi s fra ct ion of t he pol lut ant

hydr olyzes at

the rat e m eas ured vi a a homogene ous pha se (pure wat er) experim ent
. EXAMS com

pute s t he e ffec ts of resi dencein a sorbe d st at e (where wate r conce ntrati on c an be quit e sm all) on the rea ct ivi ty of t he c om pound via

an addi ti onalset of input param et ers (Cha

pte r 2.3. 4.3). Neutralhydr oly sis of

organic est ers proce eds via a m echanis m similar to that of

the seco ndstage o f the acid -catalyze d pa thw ay. Two m ole cul es of wat er are a gai n involve d in theform at ion of a t et rahe dralinte rm edi at e, wit h one m ole cul e of wat er a ct ing a s the nucl eophi le and a s econd wat er mole cul e acting a s a gene ral basecat alyst . Alt

hough the neut

ralrea ct ion i s usua lly t

reate d as a s im ple fi rst -order proce ss (W olfe 198 0) , it is in fact tech nically sec ond-order in wate r concent ration. This rea ct ion i s t

hus a ls o sub ject to solv ent eff

ects, an d require s the same cautio n in ext rapol at ion to sorbe d st at es as was m ent ione d abovefor aci d-cata lyzed hydrolysi s. Alka line hydrolysi s, t

he t hird hydrolytic m echanis m cons ide red in EXAMS , i s not

st ric tly s peaking a hydroxide-“ cat alyz ed” rea ct ion, for hy droxideion i s c on su m e d in the rea ct ion s equenc e, yieldin g the e st er ’ s co nstitu ent alco ho l and th e anio n of its car boxyl ic ac id. At t

rac e c oncent

rations of t

he est er in buffe red nat uralwat ers, howeve r, this dis tinct ion i s of no prac ti cal si gnificance. As in the neut raland aci d-cata lyzed pat hways , a te trahedra l inte rm edi at e spec ie s is probably invol ved in al kal ine hydro lysis. Inthis case, how ever , the intermediate is usu ally envi si oned a s re sul ting from a dire ct nucl eophi li c att ack of hydroxi de i on on t

he c arbony l c arbon, wit

h formati on of t

he te trahedra l i nte rm edi at e as the rat e-l imiting s tep in the rea ct ion path way. The tetrahedral intermediate thenbreaks d ow n via releas e of anR’O anion, and rapidproto n tran sfer(to R’O ), to
! ! yi el d theproduct s of the rea ct ion ( R’OH and RC OO ).
! The ove ral l rat e of hydrolytictrans form at ion i s thus thesum of obs thre e competin g rea ction s, andthe ob serv ed ra te con stant (K , unit s /h) can be com

pute d a s the s um

of c ontributi ons from aci d-cata lyzed ( KAH ), n eutr al ( KNH ), and bas e-c at alyz ed ( KBH ) rea ct ions (Wolfe 1980) : ( 2- 113)
obs K i s a pseudo-f

irs t-or der (h ) rat e const ant unde r the spe ci fie d
! 1 envi ronm ent alconditi ons (pH, pOH) i n pure wat er. Afte r inc orporation of

the eff ect s of ioni zation a

nd sorption on obs rea ct ivi ty , K beco mes the hydro lytic contribution to the o ver all p se u d o - f ir st
- o r d errate co n stant K

of E q. (2-1) . These cond-orde r transform at ion r at e c onst ant s are part of EXAMS ’ input che m ic al dat a ba se. KAHand KBHhaveunit s of rec iprocal molarit y and rec iproc alhours (M h ). KNH , th e neu tral hydro lysis rate
! 1

! 1 con stant, h as un its h . The env iron mental data fo r this
! 1 com putati on areent ere d as a separat e pH an d pOH for ea ch sec tor (com

partm ent) of t

he e cosy st em ; t

he EXAMS varia

ble s are “ PH ” and “ POH ,” res pectiv ely. The util it y of thi s approa ch i s not , of course , l imit ed t o che m ic al transform at ions of c arboxy li c aci d e st ers. F or exam ple , am ide s, carb amates, an d or gan op ho sph ates br eak d ow n via h ydr olytic mechanism s (T i ns l e y19 79 )
. Al so , m any ha loge nat ed com pounds are s ubject

to unim olecul ar and bimole cul ar 1 2 1 nucl eophi li c s ubst it

uti on (SN and SN ) or e liminati on (E and 2 E ) reac ti ons whose ki net ic s can be repres ent ed vi a Eq. (2-113). Experim ent al stud ie s of the rat e of hydrolysi s in buffe red obs aqueous soluti on can be used to de te rm ine K at fi xed pH levels. In m anyca ses KAHand KBHc an be d e t e rmi ne d at l ow andhighpH, resp ectively, whe re on ly one r eactionpa th w ay is obs si gnifi cant . ThepH-rat e profile , a plot of l og K vs. pH, t

hen inc lude s a des cending (ac id cata lyzed) and asc endi ng (alkal ine ) li m b, wi th s lope s of -1.0 and +1 .0, respective ly ( Figu re 9 ). Thes e lines int erse ct

at the t heore ti calr at e m ini m

um , giving the best pH for an e xperime nta l de te rm inati on of any neutra l cont ribution ( KNH ). One or m ore of therea ct ion pathways m ay be unde te ct ably s low f

or a partic ular com

po und, re sul ting in a si m pli fie d pH -rate profil e. The us e of pH-rat e prof il es for cal cul at ing hy droly si s rate cons tants has bee n des cribed in m ore detail by K irby (K irby 1 97 2:1 53 ) andby M ab eyandMill (1978)
.57

Fi gur e 9. H y dr ol y si s pH- r at e pr of i l e ofpheny l ace t at e at 25 E C. Pr of i l e co ns t r uc t ed v i a r at e co ns t an t da t a su m m ar i z ed by M abey and M i l l 197 8 . Repor te d chemic alrateconst ant s are often ba sed on t he s econd or minut e as the uni t of ti m e. For use in EXAMS , suc h dat a m ust be conver te d to unit s base d on the hour. For exam ple , t he ne utra l hydrolysi s rate cons tant of pheny l a cet at e i s 6.6× 10 s ( Figu re -8

! 1 9 ). EXAMS ’ che m ic alinput param et er ( KNH , uni ts /h) would be 6.6×10 (s )×3600 ( s/

h)=2.38× 10 h
. -8

! 1 - 4

! 1 2.3.4.1 Tem per atureeff ect s Eac h hydr olytic rate cons tant in EXAMS ’ che m ic aldat a ba se ( KAH , K

NH , KBH ) h as a pai red input pa ram et er t hat al lows for al te rnative ent

ry of the chemic alinform at ion as an (Arrhe nius ) function of te m

perature
. The pa irings are KAH

–EAH , KNH

–ENH , and KBH

–EBH , re spective ly . Therat e c onst ant vari abl es ( KAH et c.) are int erpre te d as the(Briggs ian lo gar ithm of t he) “preexponentia l” or “ freque ncy ” fa ct or i n an Arrhenius func ti on, only when t he paral le l ac ti vat ion e nergi es ( EAH etc .) are non-ze ro. When t

he input ene rgy param et er i s se t to ze ro, EXAMS acc ept s t he kinet ic para me te r ( KAH , e tc .) a s t he rate cons tant it sel f (c om

pare Cha pte r 2.3. 2.1) . For exam

ple , an ac ti vat ion ener gy (Ea ) for the neut

ralhydr oly si s of pheny l a cet at e ( ENH ) of, say , 20 ,0 00
. c a l/m ol e wo ul d im plya f re qu e nc yf

a c t or A = KNH / e xp(-Ea /RT), ( T in Ke lvin) or, give n KNH= 2. 38×10 h at -4

! 1 25 E C ( Figu re 9 ), A= 2.38×10 /e xp(-20000./ (1.99×298. 15)) = -4 1.04×10 h , and log A, t he EXAMS inpu t ( KNH ) =11.02 h
. 11

! 1

! 1 In t his ins tance, if EXAMS wereloa ded wi th KNH =2.38× 10 and
! 4 ENH= 0. 0, KNHwould be us ed a s t he ra te c onst ant

for neutra l hydrolysi s irr espe ct ive of the t em perature(environm ent alinput param et er TCEL ) obt ai ning in thesy st em com partm ents. Alt ernati vely, EXAMS co uldbe loade d wit h KNH= 11. 02 and ENH=20. 0. In the l atte r case EXAMS would com pute loc al (co mpartment spe cific) value s of th e neu tral hydr o ly sis rate con stant KNHvia : log KNH= KNH

! ((1000× ENH )/4. 58( TCEL +273.15)) or , at TCEL = 25 E C, log KNH = 11.02

! (1000×20)/ (4.58×298. 15) =

! 3.626 and KNH = 2.36×10 h
. -4

! 1 Inmany cases the te mp er ature de pen den ce of a chemical rate const ant is repor te d in t erm s of transi ti on st at e t heory , t hat is , a s an en thalp y (H) andentro py (S ) of activa ti o n . G ivenH in cal orie s/m ole and S in ca l/ deg/m ole (al so c al le d “e ntropy unit s,” e.u .), data rep orted un derthis con ven tioncan be con verted to Arrhenius func ti ons vi a (Bunne tt 1961) : ( 2- 114) and ( 2- 115) in whi ch Ea has unit s of cal orie s/m ole , and A i s in h
. ! 1 (Be cause the RT te rm

is only about 600 c al/m ol at room temperature, h ow ever , in many cas es r epo rtedvalue s of H are in fac t unc orrec te d Arrhenius a ct ivati on ene rgie s ( Ea ).) For e xam ple, Wolfe and coworker s (Wolfe e t a l. 1977) found that malathio n ( O,O -d imethyl-S- (1,2-dica rb etho xy) et hylphosphorodit

hioate ) bre aks down via an aci d cata lyzed degra dat ion wi th a

n ent halpy of ac ti vat ion (

H ) of 22. 3 kca l/

m ol and an ent

ropy of ac ti vat ion ( S

) of - 4.1 e u. Using 15 E C as the te m peraturefor c onversi on, Eq. (2-114) gi ves Ea =22300 + (1.987)(288. 15) = 22872 ca l/ m ol a nd an EXAMS inp ut

o f EA H = 22.87 kcal/m ol. Thefrequenc y f act or A (Eq. (2-115)) woul d be: log A = ! 4. 1/4. 58 +l og(288. 15 ) + 14 .3 19 , y i e l di ngl ogA = 15.88 h = KAH .

! 1 When a c om

pound is subje ct

to m ore t

han onedegradati on p ath w ay , th e rate co nstan ts must be combin ed p riorto entry in EXAMS ’ che m ic aldata

ba se. F or exam

ple , m al at hion unde rgoes 2 an a lka line c arboxy l e st er hy droly si s plus an E el iminati on rea ct ion kinet ic al ly

depe ndent

on hy droxideion conce ntrati on [O H ] ! (Wolfe e t a l. 1977) . The se authors com pute d ent ropie s and(un corrected ) enth alpies of activation fo r bo th reac tion s; this inform at ion c ould beuse d to gener at e an Arrhenius approxi m at ion f

or t he tot ala lka line dis appearanc e rat e c onst ant KBHvia thetr ansi ti on st at e t

heoryequati on KBH(h ) = (7.5018×10 )(T)× exp(-H/RT)× exp(S/R),

! 1 1 3 wher e H = Ea

- RT, a s i n E q. (2 -1 14 ). Whe ne ve r po ss ibl e, however, it

is probably be tt er t o rely on experim ent al det ermi nati on s of

t het ota ldi sa

pp e ara nc e r at e c on stant , m eas ured at environm ent al ly

rel evant te m perature s. I n thi s c ase , t

he t ota l (sec on d- or der ) disap pear ance rate con stant w as measur ed at 0 E and at 27 E C; it

was 0.067 an d 5.5 M s , re spec ti vely. The
! 1

! 1 activationene rgy and fr equenc y f act or can be eas ily c om

pute d from the se dat a, giving KB H = 23.67 h and EBH= 26. 6 ! 1 kcal/mol.58

Fi gur e 10 . H y dr ol y si s pH- r at e pr of i l e f or a subs t i t ut ed 2- Ph eny l - 1, 3- D i oxane. D at a f r om B ender and Si l v er 196 3. 2.3.4.2 Ioniz ationeff

ect s Anions and cations of organi c a ci ds and bas es can hydrolyz e at rat es di ffering greatly f rom thos e of the pare nt uni oniz ed spec ie s. T his phenom enon can give ri se to pH- rat e prof il es very un like the archet

ypa l e xam

ple of phe nylac et at e ( Figu re 9 ), inc luding an appar ent

kine ti c depende nce on f

rac ti onalpowers 3 of {H O } or {OH }. In orde r t o encom pass the se phenom ena, +

! eac h of EXAMS ’ input

kinetic param et ers (and paral le l a ct ivati on energie s) i s se t up as a 3× 7 m at rix of varia

ble s. T he s econd inde x of t heseparam et er m at

ric es spe ci fie s t

he i onic spe ci es for wh i c h a parti c ul ar rat e c on st ant

ap pl i e s. T he f

i rs t i nd e x a l l ow s for spec ifi cation of the e ffec ts of s edi m ent s orp tionand DOC c om pl e xat i ononr e a c t i vi ty ; thi s a sp e c t of EX AMS ’ inp ut datais dis cuss ed in Cha

pte r 2.3. 4.3. Consi der, for e xam

ple , the hydrolysi s of t

he s eri es of subs ti tut ed 2- pheny l-1, 3-dioxanes st udie d by B ender and Silver (1 96 3) . All the ac et al s in the seri es showed t he us ualac id-c at alyz ed hy dr oly si s, but

tho sem e m

be rs c ont a i ni ngan o - or p -p hen olic sub stituen t were reactiv e at alkaline pH as well. Th e pH -rate profi le for onem ember of t his se rie s, 2- (4-hydr oxy-5- nit ropheny l)- 1,3-di oxane (“HND”), is shown in Figu re 10 . This pr of ile include s a

des cending lim

b of s lope -1.0 at

low pH, a obs zo n e o f littl e c h an g e inK su g g es ti v e o f an eu tr al mec h an is m, foll owed by

a sec ond desce nding l im

b in the alkal ine pH range, whic h begins in thevic ini ty of pH =pKa.

Fr om ac om pari so n o f the kine t i c s of o - and p -p hen olic substit ute d ac et al s, and from

theeff ect of de uterium oxide on thesekine ti cs, Be nder and Si lve r (1 96 3) c on c lud e d that the hydrolysi s of thesecom

pounds doe s not

in fac t procee d via

a neut ralm echanis m . Ins te ad, the ini ti aldes cending lim b is the result of theusua l a cid-catalyzed hydrolysi s of the unioni zed spec ie s, and thedes cending lim b in the alkal ine pH region resu lts fro m a similar acid- cata lyzed h ydr olysis o f the p hen olate ani on ( Figu re 10 ). T he anion i s 860 tim es m ore r eac ti ve t han t he obs unioni zed spec ie s. T he uni formit y of K at int ermediat e pH results from theinc rea si ng im

portance of t

he phe nolate ani on, a s a fr action of

thetot alconc ent

ration, in t

his pH range. The hydr olytic kin etics of HN D canbe complete ly specif ied in EXAMS ’ che m ic aldata

base vi a thepKa of the com pound and the rat e const ant s for a ci d hydr oly si s ( KAH ) of t he unc harge d and the ani onic spe ci es. The e xis te nce of the unioni zed spec ie s and the phenol at e ani on i s si gnal ed by s etting SPFL G(1) and SPFLG(5) to 1 (Cha pte r 2.2. 1), and thepKa of HND is s peci fie d via PK (1) = 6.63. The sec ond-order rat e c onst ant s are 540 and 4. 68×10 5 M h forthe par ent co mpoundandthe anio n res pectiv ely
! 1

! 1 ( Figu re 10 ). T his inf

orm at ion is loa ded t o EXAMS by setting KAH (1,1) t o 540, and KAH (1,5)= 4.68E5. The f irs t index (C hapt er 2.3.4.3) sim

ply denotes the fo rm of the co mpound(1=d isso lved). The s econd inde x s peci fie s the i onic s peci es to be t ransf orm ed. Subscript (1,1) t hus spe ci fie s t

he uni oniz ed di ssolved HND a s 3 rea ct ing at r at e (540) [H O ] h , and subsc ript (1,5) spec ifi es the +

! 1 3 ph eno late anio n as re acting at rate (4. 68 ×10 )[H O ] h
. 5 +

! 1 2.3.4.3 Sorpti on ef

fec ts Sorpt ion of

a com pound wi th s edi m ent

phas es or com

ple xat ion wit h DOC removes the com

pound to a m ic roenvi ronm ent that can be ve ry diff

ere nt f rom thefre e wate r phase of the syste m . For exam ple , Mi ll er and Zepp (1979) found t hat thedaught er product yi elds r esulting from

photolysi s of DDE shi fte d from p,p’-di chl orobenz o p h e none t oward DDMU (1,1-bi s(p-c hlorophe nyl )- 2- chl oroet hyl ene) when thepare nt DD E wa s so rb e d wi th su sp e nd e d se di m e nt s. P ho t oly si s of DD E dis sol ved in hexane a ls o gaveenhanced yi el ds of DDMU. The aut hors c oncluded t

hat the sorbed com

pound expe rie nced a m ic roenvi ronm ent

si m il ar t o that of

an organic solvent , ve ry diff ere nt f rom that of theaque ous pha se. Simil ar e ffec ts ca

n be post ulate d for t

he m ajori ty

of m odes of chemical reac tionof o rg anic co mpound s in the en viro nment. Pre sumably re action s like the n eutr al hydr olysis o f carb ox ylic aci d es te rs, in w hich t

he wate r m ole cul e parti cipat es in t he rea ct ion, would besubst ant ia lly inhibi te d by resi denceof t he 1 1 target m ole cul e in a sorbed st at e. An E or S N r eac ti on m ight

be li ttle aff ect ed, however. Furt

herm ore, t

he pos sibil it

y of acc el erate d (se dim ent

“catalyz ed”) rea ct ions cannot be dis regarded. Alt

hough no defi nitive st

udie s on t

he e ffec ts of resi dencein a sorbe d state on chem ic alreac ti vit y haveappe are d in the l i t e rat

ur e , su c h e xp l or at or

ye xp e ri m e nt s a s have bee n undert aken indi cat e t

hat sorption “prote ct s” m anycom pounds from hydr olyti c t

ransf orm at ion. This is not a uni versa l phenom enon, however, for in som e cas es the rea ct ivi ty of comp o un d s was not af

fectedby resid ence in a sorbedstate (Mac al adyand Wolfe 1985)
. Obviously, the n, t

he diff ere nces be twe en the s orbed form of an organi c com

pound and it s dis sol ved phasecan beas profound a s the dif fer ence s betw een, for

examp le, an o rg anic acidandits ani ons (C hapt er 2. 3.4.2). EXAMS the reforeprovi des for t he e ntry of rate cons tants (or Ar rhenius func tions) that

spe ci fy the59 kine ti cs of sorbe d form s c om ple te ly independent ly

of t he rea ct ivi ty of t he aqueous diss olve d phase of t he c om pound. Ea ch nam ed kinet ic param et er i s a m at rix wit h 21 e le m ent s, a ll owing for up to 7 i onic spe ci es wit h 3 form s (di ssolve d, se dim ent -sorbe d, and DOC -com ple xed) of theparent (uncharged) com pound and of i ts ions
. EXAMS com

pute s t he rat e of rea ct ion of the s orbed s peci es under the as sum pti on that t

he re action is f

irs t-or der in sorbe d subst

rat e. The modeluse d t o c al cul at e t heserea ct ion r at es can be de scribed via a si m pli fie d exam

ple . Ingene ral , t

he rate of t

ransf orm at ion of disso lvedcompou ndis givenby: ( 2- 116)

W W where [ C ] i s a qu e ou s c on c e nt rat i on( m g/L) and K is a fir st -order (or pseudo-f

irs t-or der) rat e const ant (unit s h ).

! 1 Simil arly, the rat e of tra nsform at ion of thesorbe d phas e of the com pound can be taken a s: ( 2- 117)

S where [ C ] is theconc entratio n of thesorbe d phas e of the S com pound (mg/kg dr

y s edi m ent) and

K is a firs t-o rd er rate con stant. Under EXAMS ’ as sum

pti on that a

rapi d (i .e. , faster than the W S rea ct ion rat es) sorption e quil ibrium ism ai nta ine d, [ C ] and [ C ] T T are in const ant

proportion t o [ C ], where[ C ] is thetot al con centr ationof p ollutant in th e system. ( I n this co ntex t, “system ” i s e quiva le nt to a si ngle ec osys te m se ct or ( compartment), a we ll-mixed ch emical appar atus, etc.) W ithin EXAMS , c hemic alconc ent rations arecarri ed int erna lly in uni ts of m ass /uni t a queous volum e. Conse quently thetot alrat e of transform at ion of

a com pound is repr ese nte d as : ( 2- 118) where ñ is the sediment/w ater ratio (k g/L) , that is, SED COL in the la nguage of Cha

pte r 2.2. 2. Give n that the as sum

pti on of a rapi d loc alsorption e quil ibrium holds good, howe ver, ( 2- 119) and ( 2- 120)

1 p 2 p p p where á =1/ (1+ ñ K ), and á = ñ K /(1+ ñ K ) , K thepartition coef fic ie nt a s de scribed in Cha pte r 2.2. 4. Subs ti tution of Eq. (2- 119) and Eq. ( 2-120) i nto E q. (2-118) give s: ( 2- 121) Equation ( 2-121) i s (a

sim pli fie d form

of) the de fining equati on used to bui ld EXAMS ’ al gorit hm for c om bining therea ct ivi ty

of diss olv ed an d so rb ed fo rms into a sin gle ps eud o- firs t-or derrate con stant. This form

ulati on m akes theconve rsi on o f expe rim ent al observati ons into a

form sui ta ble for EXAMS relatively str ai gh tforwar d. S up po se, fo r example, that a neu tral or gan ic compound ( “NO C”), su bj ect to a pH-i ndepende nt transform at ion, is obse rved t o havea hal f-l ifein pure wate r of 33 hours. T h e r at e con stant d escr ibin g this p ro cess is

w K =-(ln0.5)/ 33=0.021 h
. ! 1 This rat e c onst ant

ent ers EXAMS ’ che mical data base v ia KNH (1,1) = 0.021. The fir st s ubscript of KNHdenot es the dis sol ved for

m (1) of t

he c om pound; t he s econd denot es an un char gedmolecule. (A s NO C is a neutr al compo un d, o nly SPFLG (1) i s se t ( i.e., = 1), and SPFLG (2... 7) ar e 0, denoting t he non-exi st enceof any i onic spe ci es. ) Suppose, now, t

hat NOC ha s a

partition c oeffi ci ent

on a partic ular se dim ent

of 90000 (m g/kg)/ (m g/L) , and an exp e ri m e nt a lde t e rmi nat i oni s m a de of the ha l f- l i feof

the com pound aft er s orpti on

equi libration on a 100 m g/L suspe nsi on of the sed iment. (So long as local so rp tio ne qu ilibrium i s m ai nta ine d, t

he ha lf- li fe c an beas cer

ta ine d by fol lowi ng ei the r W S T C or C over tim e.) The f rac ti on of C pres ent

as dis sol ved and

p as sorbed NOC ca

n be com

puted us ing ñ and K . The sedim ent /wate r rati o ñ is (100 mg/L) ×(10 kg/ml) = 10 kg/L ; -6 -4 1 p the dis solve d f

ra c ti on i s t hu s á =1/ (1+ ñ K ) = 1/(1+ (90000×10 )) -4 2 p p = 0.10. Si m il arly, the fra ct ion s orbed i s á = ñ K / (1+ ñ K ) = (90000×10 )/( 1+(90000×10 )) =0.90.

-4 -4 This exp erimen t h as three o bv iou s po ssib le outc omes. Fir st, sorption m ayhaveno effe ct on t he re activi ty

of t he c om pound. Sec ond, t he obs erve d hal f- l ifem aybe incr eased in stric t

1 proport ion wi th á , t

hat i s, s orpti on m ay“prot ect” t he c om pound. Fina lly, an a lt ere d hal f-l ifem aybeindic at ive of an al te red, but non-ze ro, re activi ty

of t he s orbed pha se of t

he c om pound. In t he first case , when theprese nce of t he s edi m ent

suspe nsi on

S has no eff ect on t he rate of transform at ion of the com pound, K W is identic al ly

the sam e a s K
. EXAMS could thenbe load ed w ith KNH (2,1) =0.021; thesubsc ript “2" denot es the se dim ent -sorbe d form of NOC
. When resi dencein a s orbed s tate inhibit s t he t ransf ormation re ac ti o n, th e ob serv ed ra te con stant K ob s will dec reas e in proport ionwith the res idua l wate r conc ent ration of the 1 2 com pound. From

Eq. (2-121), Kobs = á Kw + á Ks. In this 1 exam ple , á = 0.10, and, i f Ks = 0, the n Kobs =(0.10)( 0.021) = 0.0021 h
.

! 1 The pos sibil it

y t hat sorption “prote ct s” the compound can thus be e valuat ed vi a t

he c om pound’s ha lf- li fe in a sedi m ent suspe nsi on. Her e, give n Kobs =0.0021, the hal f-l ife ôis give n by: ô= - (ln 0.5)/ (0.0021) =330 hours
.60 Inotherwor ds, an ob serv ed h alf-lif e that wa s no t signif

icantly diff ere nt fr om 330 hours woul d be a c le ar indic at ion t hat Ks = 0, and EXAMS coul d be loa ded wi th KNH (2,1) =0. Fina lly, the obse rved ha lf- li fe m aybe neit her 33 nor 330 hours, indi cating th at t

he s orbed s tate , whi le rea ct ive , doe s not transform at thesam e rate as the a queous-pha se dis sol ved com pound. (In theevent

that the obse rved hal f-l ifewerelonge r than330 hours, K s wo uldbe neg ative. T h e most pro bab le expl anation of

suc h an event , howeve r, i s t hat e it her t he sed iment was co ntaminatedwith th e study compou ndprio r to the expe rim ent , or that

the ass um

pti on of ra

pid l ocalequi librium ha s be e n v i ol at e d. ) Anyha l f- l i fe> 0 and # 330 hours can be conver te d to a va lue of Ks via

Eq. (2-121). If t

he hal f-l ifewere le ss t han 33 hours, t

he t ransf orm at ion m

ust havebee n acc el erate d in the se dim ent ph ase and Ks > Kw. Suppose , however, that t

he ha lf- li fe of

NOC in the 1 00 mg/L se dim ent sus pen sionwas 15 0 h ours. The first- or derrate con stant K ob s is the n: Kobs = -(l n 0.5)/ (150) =4.621×10
. -3

obs 1 W 2 S Give n K = á K + á K , t hen 4. 62 1× 10 =( 0. 1) (0 .0 21 ) + (0 .9 ) Ks

-3 and Ks = 2.80× 10 . Therat e of rea ct ion of N OC in t he s orbed -3 st at e was th us 13.3% of that of thedis sol ved pha se of t he com pound. This inf

orm at ion c ould now be e nte red into EXAMS via thecom m and SET KNH (2,1)= 2.8E-3. Sec ond-order pH-m edi at ed re actions occ urri ngon se dim ent s are acc omm odat ed in EXAMS in a whol ly ana logous way. EXAMS uses thesolution -phase pH and pOH to c om pute rat es of rea ct ion, so of courset

he input dat a m ust al so be deve lope d from thi s perspe ct ive . The ful l 21-el em ent m at ric es of KAH , KNH , and KBHal low f

or t he s peci fic at ion of

eff ect s o f bot

h se dim ent 3 sorption a nd DOC com

ple xat ion on first -order, [H O ] m edi at ed, + and[OH ] m ediatedreactio ns. In ad dit ion , any o f thes e rate

! param et ers can al te rnative ly be spec ifi ed vi a an Arrhenius function, as desc ribe d in Chapt er 2. 3.4.1. Refer enc es for Chap ter2.3.4. Bend er, M. L ., and M. S. Si lver . 1963. The hy droly si s of substit ute d 2-phenyl -1,3-di oxanes . Journalof theAm eri can Chemical So ciety 85 :3006-3010. Bunn ett, J. F . 1961. The i nte rpret at ion of rat e data . Pa ges 177- 283 in S
. L. F ri e ss , E. S
. Le wi s, and A. We i ss be rg er, edi tors . Te chni que of Organi c C hemis try Vol. VIII Part

I. Inte rsci encePubl . Inc ., Ne w York. Kirb y, A. J. 1972. Hydrolysi s and form at ion of es te rs of organi c aci ds. P ages 57-207 in C. H. B am ford and C. F. H. Tipper, edi tors . C om

prehe nsi ve C hemic alKinetic s Vol . 10--E st er Form at ion a

nd Hydrolysi s and Rel at ed Reac ti ons. E ls evi er Publi shi ng Co. , Am st erdam -London-New York. Mab ey , W., and T. Mi ll . 1978. Cri ti calrevi ew of hydrolysi s of or gan ic compo un ds inwaterund er en viro nmental cond i t i on s. J ourn a lof

P hy si c a land

C he m i c a lR e fe re nc e Dat a 7 :383-415. Maca lady, D . L., an d N. L. W olfe . 19 85 . Eff ects of sediment sorption on abi oti c hydrolyse s. I. Organophosphor othi oat e esters . Journal of Ag ricu ltura l and Foo d Ch emistry 33 :167- 173. Mi ll e r, G. C., and R. G. Zepp. 1979. Photor eac ti vit y of aquati c po llutan ts sorb ed onsuspen dedsediments. En viro nmental Scien ce andTechn olo gy 13 :860-863. Tins l ey , I. J. 1979. C hem ical C oncept s in Pol lut ant Be havi or. John W ile y and Sons, New York- Chi ches te r-Bri sbane

Toront o. Wolf e, N. L. 1980. De te rm ining t he rol e of hydrolysi s in thefat e of organic s in nat

uralwat ers. Pag es 163-178 in R. Haque , edi tor. Dynam ics, Exposure and Hazar d Asse ssm ent of Toxic Che m ic al s. Ann Arbor Sc ie nce Publi shers, Ann Arbor. Wol f e , N. L ., R
. G. Z e pp , J. A
. Go rd on , G. L
. B aug hm an, and D. M. Cl ine . 1977. Kine ti cs of che m ic aldegradation of malathionin water . Env iron ment alSci enceandTechn olo gy 11 :88-93.



### 2.3.5 Indirect Photochem istry, Oxidat ion and Reduction Dire ct photolysi s i s not

the sol e pollutant t

ransf orm at ion proces s drive n by the sol ar f

lux in aquati c s yst em s. T he s im ult aneous occur renc e of pla

nt de com posi ti on product s (“humic m aterials” ), dis sol ved oxyge n, and sunl ight of te n r esults in an a cce le ration of the rat e of transformation of organi c pol lut ant s (Zepp 1988a)
. Zepp e t a l. (1 97 7a) , fo r example, fo un d that metho xych lor, with a direc t photoly si s ha lfl ifeof m ore t han 300 hours, had a ha lfl ife of as li ttle as 2.2 hour s unde r i rradiation in nat uralwat ers cont ai ning di ssolved humic m at eri al s. F urthe r, Ross a nd Cros by (1975) found t

hat a soluti on of a ldrin in wat er from a taro paddy can be photoc hemic al ly

c onvert ed to die ldrin, despi te the fa ct that aldr in do es no t abso rb sun ligh t. Thes e kinds of rea ct ions are u sual ly te rm ed “ indirec t” or “se nsi ti zed”photolysi s. I ndire ct photoly si s c an besubdi vide d int o two gener alcla sse s of rea ct ions . First , “ sens itiz ed photolysi s” per seinvo lves sunlig ht abs orptio n an d electr on ic exci tati on of a

se nsi ti zer

(humic ) m ole cul e, foll owed by dir ect chemical int era ct ion be twe en t he e xci te d st at e of the se nsi ti zer and a pollutant mole cul e. Possible che m ic alrea ct ions inc lude a dire ct ene rgy transfer

to the pol lut ant

mole cul e, hydroge n at om transfer from pollu tant to sens itiz er t o givefre e ra dic al s, and un ionof sen sitizer an dp ollutant yieldin g anexcited -state complex or “ exciple x” (Z e pp and B aug hm an 1 97 8)
. The resulting fre e ra dic al s or exc ipl e xe s c an t hen re act wit h dis sol ved m ole cul ar oxy gen, a process te rm ed “ ty pe I sens itiz ed photooxi dat ion” by the se aut hors.61 So urc e Si ng l et O xyg en ( M ×10 )

13 Peroxy R adi cal

( M ×10 )

9 H ydroxyl R adi cal

( M ×10 )

17 A u c illa Ri ve r , FL 1 8 2 .8 1 .8

O kefenokee S wa m p , GA 22

M i s s i s s i ppi Ri v e r , LA 5

C o y o te Cr e e k , CA 9 .1 , 5 .0 1 .6

B or onda L a k e , CA 9. 5, 0. 45 0. 15 T a b le 1 4 . S te a d y- s ta te c o n c e n tr a tio n (m o le s /lite r ) o f o x id a n ts in s o m e n a tura l w a ters The s econd cl ass of

indire ct phot oly si s involves the f

orm at ion of chemic aloxida

nts in natura l wat ers, prim ari ly via the int era ct ion of sunl ight , humic material s, and dis sol ved oxy gen (t ype II sens itiz ed phot ooxidati on (Zepp and B aughm an 1978) ). T he pr imary oxid ants kno wnto occur inna tura l wa ters ar e hydro xyl (O H C ) and

pe ro xy ( R OO C ) ra dic al s (Mi llet al. 1978) , single t 2 oxyge n O )

(1 (Zep p et al. 19 77 b) . Alk ox y radica ls anddirad icals mayals o co ntr ib u t e to en v ir o nmen ta l o x id at io nof so me com pounds, but t

hei r pre senc e in nat

uralwat ers has not be en conclusi vely de m onstrat ed (Mi ll1980, M il l e t a l. 1980)
. 2.3.5.1 Oxidat ion EXAMS repr esen ts the ox idativ e trans fo rmation o f po llutan ts via a phe nom enol ogic alcoupl ing of a sec ond-orde r rat e c onst ant ( KOX , uni ts M h ) t o them olar conc ent ration ( OXRADL , ! 1

! 1 m ole s/ li te r) of oxidan ts in eac h ec osys te m com partm ent . The pseudo-f irs t-or der c ontributi on of oxi dat ion pr ocesse s t o the overa lltr ansfor

m at ion r at e c onst ant

K of Eq. (2-1) i s c om

pute d for e ach (J) c om

partm ent via : K (h ) = KOX× OXRADL (J)
! 1 The input pa

ram et er KOXis a 3×7 matrix, allow ing forsepar ate ent ry of ratecons tants of i onic spe ci es andfo r cont rol of t he ef f ec ts of so r p ti o nonre ac ti v ity. Th e s ub sc r ip t s h av e th e s ame si gnifi canc e and use as de scribed for KAHet c. in C hapt er 2. 3.4. Effe ct s of te m

peratureareent ere d via a par al le l m at

rix of Arrhenius a ct i vati on

e ne rg i e s EOX(kca l/

m ol), aga in a s de scribed in C hapt er 2. 3.4 for hydrolytic rea ct ions
. The oc curre nce and c oncent ration of oxidants in natura l wate rs has beeninves tigatedvia the irrad iationof ch emical “pr ob es” in al abo rat or

ys e tt i ng . Zepp e t

a l
. (1 977b) st

udie d thegene ration of s i ng l e t oxy ge n u sings oluti on s of 2, 5- dim e thy l furan ( DM FN ) in natural wa ters. DMF N giv es 1, 2- diacetyleth ylenes via 1,4-addi ti on of s ingl et

oxyge n. Thespeed of t

his rea ct ion upon irr adi at ion of

thesoluti on give s a

quantit at ive m eas ure of the st eady -st at e conce ntrati on of s ingl et oxy gen in the solu tion. Simil arly, Mi ll et al
. (1978, 1980) haveuse d cum ene (is opropylbenze ne) and pyridine as che m ic alprobes for t he steady-state co ncen tration s of p ero xy an d hydro xyl r adica ls in irr adi at ed natura l wate rs. Som e re sul ts of the se st

udie s are given in Tabl e 14 ( D at a f r o m Zepp et al . 1977b, Mi llet

al . 1980) . The se conce ntrati ons wer e det ermine d via

photolysi s of thin la

ye rs of soluti on, and are presum ably depende nt on t he inte nsi ty

and spec tra l di stribution of t he s olar flux in the solution. The avera ge s te ady -st at e m olar conce ntrati ons of oxidants we re on the order of 10 for s ingl et ! 13 oxyge n, 10 for pe roxy radi cal s, and 10 for hy droxylradi cal s.

! 9

! 17 More rec ent

inve st igati ons have found surfa ce conce ntrati ons of si ngle t oxyge n from

about 9×10 M down to 4× 10 M

! 13

! 15 (Haag and Hoigné 1986)
. Even at t hesel ow c oncent

rations, singlet oxyge n can be a s igni fic ant fac tor in t

he e nvironm ent alfat e of substit ute d alke nes, phe nols , ani lines, andmerc apt ans (Weber 1998) . Hy droxylradi calconcent rations have m ore r ece ntly be en rep orted to r ang e fro m 10 to 10 M, withreactio n with
! 15

! 18 hydroxy l r adi calpote nti al ly ac count ing fo r as m

uch a s 15% of to ta l car b aryl di ss ip at io ninso me s h al lo wwa te r sy st ems (Arm brust 2000)
.

Car bonat e ra dic alis a sec ondaryoxida nt, produced i n nat

ural wat e rs b yr e a c t i ono f hy dr oxy lr a di c a lw i th c arb on ate or bic arbonate ion. Ste ady -st at e c oncent rations in Ontario, Canada have been observe d ranging from 5×10 to 10 M ! 15

! 13 (Huang and Mabury 2000) ; in theGr eife nsee(Swi tz erl and) s umm er car bonat e ra dic alconc ent

rations areabout

3×10 M

! 14 (Lar son and Zepp 1988)
. Bec auseli ght e xtinction in t he wate r column reduc es the volum et ric ave rage sol ar f

lux be low t

hat at t he a ir- wat er int erfa ce, theoxida

nt c oncent

rations give n in Tab le 14 app ly only to the surfa ce zone of nat uralbodie s of wat er. The e ffec t of li ght e xtinct ion c an becom pute d from

theequati on: I/I o = ( 1-exp(-kZ ))/kZ where I/I o is theavera ge l ight int ensi ty expre sse d as a frac ti on of i ts surfa ce value (Io ), k is a diff use atte nuat ion c oeffi ci ent (/m), and Zis thedept

h of t he c om partm ent (m). T he fa ct or I/Io is calculate d by EXAMS f

or the UV li ght im

portant in gene rating ph oto chemical ox idan ts (28 0- 39 5 nm), an d then used to gen erate dept h-corre ct ed oxi dant

conc ent rations : OXRADL= OXRAD × ( I/I o)
EXAMS al lows for theentry of environm ent alconc ent rations of on ly one k indof o xid ant o th erth ansing let oxyg en, whic h is tre at ed sepa rate ly

(Cha pte r 2.2. 5.2). For a

com pound rea ct ive wit h m ore t han oneoxida

nt s peci es, therate constant a nd environm ent alconc ent

ration giving t

he m ost si gnifi cant transform at ion r at e can be ent ere d, or a c om posi te rat e c onst ant and e nvironm ent aloxida

nt c oncent

ration can be c om

pute d and62 loa ded in thedat a ba ses . 2.3.5.2 Sin gle t Oxygen 2 Si ng l e t o xy ge n ( O ), an e l e c tro ni c a l l ye xc i t e d st at e of the

1 2 dioxy gen m ole cul e (O ), i s form ed in nat uralwat ers by t

he transfer of solar energy

from il luminate d DOM . EXAMS ca lc ulate s 2 the conc ent

ration of O in eac h surfa ce wat er seg ment , using

1 m et hods de scribed by

Zepp and c oworkers (Z e pp e t a l
. 1985, Zepp 1988b) , c orrec ts for depth a nd couple s theresul t to a 3×7 m at rix of se cond -o rder re action r at e c onst ant s K 1 O 2 for 2 appl ic at ion in them ass bal anceEq. (2-1) . Generation of O 1 begi ns wi th t

he produc ti on of e le ct

ronic al ly e xci te d tripl et

st at es ( S* ) via ab sorptio n of

su n li g ht ene rg y by diss olv ed o rg anic m atte r ( S ). T he wavel ength-s peci fic quant um yi el ds ö usedin EXAMS forthis pr oces s we r e co mputedfro m t he re lation ship ö =0.015 e xp(0.01(366- ë), whe re ë i s t he wavel engt

h in nm . The pre-e xponent ia l f

act or i n thi s re lati onship wa s deri ved fr om the aver age value of ö ( 0.015) report ed for 11 natura l wat ers at 366 nm (Zepp et

al . 1977b) , c orrec te d as per (Haag et al . 1984a)
. The slop e (0. 01 ) was calculatedfro m t he o bse rv ationthat ö at 31 3 nm i s app ro xi m at e l y0.025 (H aag et al . 1984b, Zepp e t a l. 1985) . Exam

ple values are give n in Tabl e 15 . Co mputation of li ght absorption by DOC use s t he s peci fic abs orpti on coef fic ie nts åof Tabl e 9
.

ë (nm ) ö ë (nm ) ö 280 0. 035 400 0. 011 300 0. 029 450 0. 006 312. 5 0. 026 490 0. 004 350 0. 016 650 0. 0009 Tabl e 15 . Exam pl e quant um y i el ds f or pr oduct i on oft r i pl et s e n s i ti z e r S*

f r o m DOC

S*decays b ac kto its gr oundstate by spo ntan eou s decay (with 3 firs t-or derrate con stant Kdec S , wi th uni ts s ) and sel f-
! 1 qu e nc hi ng i nt e ra c t i on s wi th o the r c om po ne nt s of

the DO M (sec o n d- or derpro cess ra te con stant Kqnch wit h unit s M s ).

! 1

! 1 The secon d- or derrate con stant (Kox ) f or t he produc ti on of si n g le t o x yg enbyen er g y tr an sf erto d is so lv edox yg enfr o m S* is bet ween 1×10 and 3×10 (R. G. Z epp 2000, oralcom m .), for 9 9 EXAMS i t is t aken as 2×10 M s 9

! 1

! 1 (Zepp et

al. 1985) . Single t oxyge n undergoe s ra

pid phy si calquenchi ng by wat er to ground 2 state dio xyg en w ith a pse ud o- firs t-or derrate con stant Kdec O of 2.5×10 s (

5

! 1 ( Ro d g er s an dSn o w d en19 8 2 ) cit edfr o m (H aag et al . 1984a) ). T heserea ct ions can be summ ari zed by Eq. ( 2-122)- (2-124), where D is thedis tribu tion function a nd Iaveis the aver age lig ht inten sity. Th e qu an ti ty ( ö åIave ) i s inte grat ed acr oss t he s unli ght s pect

rum duri ng EXAMS ’ com

putati ons. ( 2- 122) ( 2- 123)
( 2- 124)

2 The steady- state con centr ationof O in sun lit surf ace wa ters is 1 give n by ( 2- 125) where
( 2- 126)

In creas ing the ox ygencon centr ati o nfro m 2.6×1 0 M (air
! 4 sat urat ed) t o 1.2×10 M (oxy gen s at urat ed) de cre ase s [S * (s s)]
! 3 by s om e 4× (Zepp et

al . 1985) . Gi ven K

ox[ O 2 ], thesum

of t he 3 othe r t erm s in thedenominator of Eq. (2- 12 6) (K decS and K qn c h[ DOC] ) i s 1.6× 10 . T heseexpe rim ent s wer e c onduct ed 5 usi ng [DOC] of about 20 m g/L (R . G. Zepp 2000, oralcom m .). For EXAMS , t

he t erm s wer e e qual ly pa rti ti oned, thus giving 3 KdecS = 8. 0×10 (s ) and Kqnch = 4, 000 (s (m g/L) ) for 4

! 1

! 1

! 1 cal cul at ing s te ady -st at e c oncent rations of t

riplet se nsi ti zer

and si ngle t oxygen. M odelperf orm ancecan be gauged by com pari son of EXAMS ’ cal cul at ed values to publi shed estim at es 2 of surf aceconc ent

rations of O

1 (Zepp et al . 1977b, Haag and 2 Hoigné 1986)
. The cal cul at ed O c oncent rations ( Tabl e 16 ) ar e 1 accep tab le e x ce pt in the case of the thr ee US A riv ers w ith [DOC] < 15 m g/L; the se wat ers (from theWakulla, S t. Marks , and M is si ssippi rive rs) c onta ine d si gnifi cant quantitie s of noncol ored DOC (R. G. Z epp 2000, oralcom .).63 2 Water [DOC] [ O ]s s × 10 M 1 1 4 mg/L Lit Val EXAMS Lent ic Türl erse e 8.3 2.8 9.7

1 Grei fense e 3.5 3.3 4.5

1 Lütz el see 7.9 5.4 9.3

1 Etan g de la Gruère 1 13 11.6 14.
Okefenoke e 24 17.8 6.9

2 Lot ic Rhi ne 3.2 2.4 4.1

1 Kle ine Em

m e 3.2 4.1 4.1 1 Glatt 4.1 4.6 5.2 1 Auci ll a 24 14.6 6.9

2 Ecofina 41 15.4 9.0

2 Fenhol loway 77 13.8 11.

2 Wakull a 6 0.16 2.4

2 St. Marks 9 0.49 3.3

2 Mi ssi ssippi 14 0.41 4.8

2
1 . Ju n e S w iss v a lu e s fr o m H a a g a n d H o ig n é 1 9 8 6 , co rre c te d to f ul l day val ues by da y l engt h and f ac t or of 2/ ð 2. D ecemb er U SA val ues f r om Z epp et al
. 19 77 b, cor r ect ed as above , nor m al i ze d t o f l at w at er body by di vi s i on by 2, and c o rr e c te d f

o r u p d a te d D M F ra te c o n s ta n t v ia d iv is io n b y 1 .6 T a b le 1 6 . C o m p a ris o n o f EXA MS ’ si ngl et oxy gen est i m at es w i t h l i t er at ur e v al ues

2.3.5.3 Reduc tion Anaerobi c (r educing) environm ent s are c omm on in nat ure, inclu din g many gr oundwater s andsatur ated so ils, aqu atic sed iments belo w the surf ace oxid ized layer , water log gedpeats and m arshl ands, and, at

le ast peri odic al ly , the hypol im nion of stratif ied lak es. Ch emicals noto riou sly per sisten t i naero bic env iron ments can b e re markab ly less so und er an aero bic condi ti ons (Macaladyet

al . 1986) . In anae robic se dim ent s, t he transform at ion hal f-l ive s of nit roarom at ic s c an befrom

m inut es to hour s, wi th form at ion of arom at ic amine s a s hazar dous daught er pr oduct s (Weber 1998) . Theres ponsible reduc ing agent s m ayinc lude fer

rous ir on, iron sul fide s and dis sol ved sulfi dic spe ci es (Si m on et al . 2000) , bi ochemic alagen ts produce d by the bent hos, and dir ect b iolysi s. Reductive transform at ions enc om

pass a vari et

y of rea ct ion t

ype s and chemic alcl ass es, including r eductive dec hlorinat ion, (or, more gen erally, r edu ctive d ehalo gen ation ), re du ctionof n itroaro matic and azo compo unds, r eduction of N-ni tros amine s a cross ei the r the N-N or N-O bond, reduc ti on of s ulfoxi des to t hioe the rs, of quinone s, and reduc ti ve de al kyl at ion (Lar son and Weber 1994)
. Predi ct ion of

theenvironm ent alconc ent rations of re duci ng agent s ha s t

hus far pr oved intra ct abl e. The s it uat ion i s furt

her complicatedby the ob serv ationth at , alth ou ghsorp tioninhib its reductio n rea ction s, the v el o ci ty of the reac tionincrea ses w ith inc rea si ng se dim ent

conc ent ration. This res ult

sugge sts that rege nerati on of t

he re duci ng age nt by

“e le ct ron-transf

er mediator s” may play in im po rtan t role in go vernin g the velo city of re duct ion pathways (W ebe r19 98 ) , andthat reducin g ag ents m ai ntai n st abl e l evel s in thepres enceof l ow conc ent rations of rea ct ing pol lut ant s. As wi th oxi dant s, EXAMS provi des a pheno m e no l ogic alcoupl ing bet ween a re action r at e c onst ant st ruct ure ( the 3×7 m atri ces KRED ) andanarray (month ly foreach en viro nmental seg ment) of m olar conce ntrati ons of reduc ing a gent s ( REDAG ). Effe ct s of te m per ature areent ere d via a para ll elm at

rix of Arrhe nius activati on ene rgie s ERED ( k cal/mol) , againas desc ribe d in Chapt er 2.3.4 for hy drolyti c re actions
. EXAMS doe s not inc lude nom ina l va lue s for REDAG . Refer enc es for Chap ter2.3.5. Arm brust, K. L. 20 00 . Pesticid e hydro xyl rad ical rate co nstan ts: Mea surem ent s and es ti m at es of their i m portance in a quat ic env iron ments. En viro nmental To xico log y andCh emistry 19 :2175-2180. Haag , W. R. , an d J . Hoigné . 1986. Singl et oxyge n in surfa ce wat ers. 3. P hotoc hemic alfo rm at ion a nd st eady -st at e con centr ation s in var iou s types o f wa te r s. En viro nmental Scien ce andTechn olo gy 20 :341-348. Haag , W. R. , J. Hoigné , E. Gass m an, and A. M. Bra un. 1984a
. Sing let oxyg en in s ur face water s - Part I: Furfuryl alcoh ol as a t rappi ng age nt. Chemosphere 13 :631-640. Haag , W. R. , J. Hoigné , E. Gass m an, and A. M. B raun. 1984b. Singl et oxyge n in s urfac e wat ers - Part II: Quant um yi el ds of i ts production by

som e natura l humic m at eri al s a s a function of

wave le ngth. Chemosphere 13 :641-650. Huan g, J. , and S. A. Mabury
. 2000. Steady -st at e c oncent rations of carb on ate rad icals in fieldwa ters. Env iron mental Tox icolo gy an d Ch emistry 19 :2181-2188. Lars o n, R . A., and E. J . Weber. 1994. Reac ti on Me chani sm s in Environ mental Org anic Ch emist ry. CRC Press , B oca Raton, Florida
. Lars o n, R. A., and R. G. Zepp. 1988. R eac ti vit y of thecarbonat e rad ical with anilin e d eriv atives . Env iron mental Tox icolo gy andChemistry 7 :265-274. Mac a la dy, D. L. , P. G. Tratny ek, and T. J. Grundl. 1986. Abi oti c reduc ti on rea ctions of a

nthro po gen ic chemicals in an aerobi c systems: A critical re vi ew . Jo urnal of Con taminant64

Hydro log y 1 :1-28. Mi ll , T. 1980. C hemic aland p hoto oxi dat ion. Page s 77-105 in O. Hutz i ng e r, e di t or . Th e Hand bo ok of E nv i ro nm ent al Chemis try . Volum e 2 Part A-Re actions and Proce sse s. Spri nger-Ve rla g, B erl in-He ide lbe rg-New York. Mi ll , T., D. G. Hendry , and H. Ric hard son . 1980. Free -radi cal oxidants in nat

uralwat ers. Sci ence 207 :886-887. Mi ll , T., H. Ric hardson, and D. G. Hendry . 1978. Oxidati on of organi c c om

pounds in aquati c s yst em s: thefre e ra dic al oxidati on of cum ene. Page s 223-236 in O
. Hutz i ng e r, I
. H. v. Lelyvel d, and B. C. J. Zoet em an, edi tors . Aquatic Pollutants: Tr ans fo rmation andBiol ogic alEffe ct s. Pergam on Pre ss, Oxford. Rodg ers, M. A. J., and P. J. Snowden. 1982. Jour nalof t he AmericanChemical Soc iety 104 :5541-5543. Ross , R . D., and D. G. Crosby . 1975. The photooxidati on of al drin in wate r. C hem osphere 4 :277-282. Simo n, R ., D. Col ón, C . L. Tebe s-St evens , an d E . J. Webe r. 2000. Ef

fec t of redox zonation on the reduc ti ve transform at ion of p -cy anoni trobenzene in a la borat ory sedi m ent column. Environm ent alSci enceand Tec hnology 34 :3617-3622. Web er, E. J . 1998. Abiotic t ransf orm at ion r eac ti ons. P ages 259- 281 in G. Sc hüürm ann andB. Markert , e dit ors. Ecot oxic ology : E col ogic alFundam ent al s, C hem ic al Exposure , and B iol ogic alE ffec ts
. John Wile y & Sons, Inc., New York, andSpektrum Akade m is cher

Verl ag, Hei delberg. Zepp , R. G. 1988a . Environm ent alphotoproces ses involving nat uralorgani c m atte r. Pa ges 193-214 in F . H. Fri mm eland R. F. Christmam, edito rs. Hu mic Substances andTheirRole in t he Environm ent . John Wile y & Sons, New York. Zepp , R . G. 1988b. Fa ct ors a ffec ting thephotoche m ic al treatm ent of hazar dous was te . Environm ent alSci enceand Tech no log y 22 :256-257. Zepp , R. G., and G. L . B aughm an. 1978. Pre dic ti on of ph oto chemical tran sfo rmation o f po llutan ts in the aquatic envi ronm ent . Pa ges 237-263 in O. Hutzi nger, I. H. v. Lelyv eld, an d B. C. J. Zoeteman, edito rs. A qu atic Pollut ant s: T rans fo rm at i onand Bi ologi calEffe ct s. Pergam on Pre ss, Oxford. Zepp , R . G., P. F. Sc hlotzh auer , and R. M. Sink. 1985. Photos ensiti zed tra

nsformations involving e le ct ronic energy transf e r i n n at ur a lwat e rs : R ol e of

hum i c s ub st anc e s. Env iron mental Scien ce andTechn olo gy 19 :74-81. Z e p p , R
. G
. , N
. L
. Wo l f

e , L
. V
. A z arr a g a , R
. H. C o x , an dC
. W. Pape . 1977a. Phot ochemic altr ansfor m at ion of theDDT and m et hoxyc hlor degradation product s, DDEand DMDE, by sunl ight . Arc hive s of Envir onm ent alCont aminati on and Tox icolo gy 6 :305-314. Zepp , R . G., N. L . Wolfe, G . L. B aughm an, and R . C . Hol li s. 1977b . Singl et

oxyge n in nat

uralwat ers. Nat

ure 267 :421- 423. 

### 2.3.6 Microbial Transformations Micro bial co mm

un ities are a ub iqu itou s con stituen t of almost all aquatic ec osys tems. Them ic robiot a pl aya cent ralrol e in the remine ral iz at ion of

pla nt a nd ani m aldebri s; the y have e volve d the ca paci ty to transform

and harve st

ene rgy from an i mm ense arr ay of n atur ally occurring organ ic compound s. Th e op timistic hope that “t

he soluti on t o pol lution is di lution” to some ext ent had i ts ori gin in a nai ve fai th in the a bil it y of sa probic m ic robes to utiliz e any an d all synth etic org anic co mpound s in their m et abol ic m il ls
. Total fai th in theabi li ty of natura l s yst em s t o abs orb and det oxify synt

het ic che m ic al s was , of course , shaken by the dis cover y of t he world-wi de di spers al(and bioc oncent ration) of synt het ic bioc ide s, not ably DDT and t he re late d com

pounds DDE and DDD . I t i s now “ axi om at ic that mic ro-organi sm s are fal lible and that m any synthetic organi c c om pounds are rec al ci trant . .. and ac cum ulating in som e e nvironm ent s” (Ale xander 197 9b )
. In c on se qu e nc e , qua li ta ti ve “bi odegra dabi li ty ” t est s (Sw isher 1970) arenow routine in the det erg e nt i nd us try , and

“ slud ge ” t e st s have be e n s ug ge st ed (B uz z e l le t

a l
. 19 69 ) a s ar out i ne pr oc e duref or e va luat i ng indus tri alsynthe ti c organic c om pounds. The latt er t est s c an a ls o providesom e ass uranc e that the com pound willnot dest

roy the m ic robia l c omm

unitie s t hat se rve man i n se wage tre atm ent plan ts, as we ll as pro vid ing an evalu ationof the biod egr adab ility of t he c om pound (e.g. , B ai rd et

al . 1974)
. The dis cover

y of m ic robia l fal libil it

y has le d t o a

more critical andquantitativ e view of microb ial metabolism of syn thetic or gan ics; it no lon gersuff ices to kn o wthat a compo un d is “bi od e gr a da

bl e .”I ns t e a d t

he r at e s, pr od

uc t s, m i c ro bi al populati ons, and environm ent alcondi ti ons sur rounding an observe d biode gradati on areof incre asing int ere st to the m ic robiol ogic aland ecologi calcom m unit y. Give n that t

he nat uralmic robia l subst

rat es can m ass ive ly

a ccum ulate in spec ia l ci rcum st ance s (e .g., peat bogs and swam

ps), a de gree of ske pticism is obviously wa rranted toward any claim of univ ersa l, uncondi ti onalbiode grada bility of a syn thetic or gan ic com pound. The r at es at

whic h a com

pound is biode grade d must depend up onboththe stru ctur e of the compo un d, andon the metabolic ca pa c i tyof the m i c ro bi a lc om

m un i tyr e si de nt

i n t he e c osy st em rec ei ving t

he c om pound. Mi crobi alcom

m unitie s de rive energy

for m et abol is m

and growth from

thebreakdown of organic com pounds, an d the kine ti cs of growt

h and s ubstrat e uti li zation have been of i nte rest to mic robiol ogis ts for m anyyears. Bot h populati on growth and subst rate uti li zation r at e have be en de scribed vi a M onod’s (1942) ana logy

wit h Mi chae li s-Me nte n enzym e kinet ic s (Sl at er 19 79 ) . Inthis ap pr oach , th e gro wthof a microb ial pop ulatio n in a non-l imiting e nvironm ent is des cribed by ( 2- 127)65 where μ is ca ll ed t

he “ spec ific growth r at e” and N is m ic robia l biomass or populati on si ze. The Monod e quat ion modifi es Eq. (2-127) vi a t

he recogn ition t

hat cons um pti on of re source s in a fini te environm ent

m ust at s om e point c urta iltherat e of inc rea se ( dN/ dt) of the po pu lation . This fact is typically incorpo ratedinto Eq. (2- 12 7) via ( 2- 128) in whi ch [ S] is theconc ent ration of thegrowth lim iting s ubstrat e,

max μ is the“maxi m

um spe ci fic growth rat e” obta ining when [ S] S is pres ent

in excess (i. e., non-l imiting), and K , t he “ hal fsat uration cons tant” is that va lue of [ S] al lowi ng thepopulati on

max to grow at rat e μ /2. An equati on describing thebehavior of t he growth subst

rat e [ S] over tim e, andthus by im pli cation t

he dynam ic s of a biode grada ble synt het ic com pound, foll ows vi a a si m ple derivat ion (Sl at er 1979) : Assuming t hat a fixe d am ount of gr owth res ult s from

m et abol is m

(and the reforelos s from soluti on) of a

unit quantit y of S, t hen dN = -Y dS, wher e Y

is the “yield co eff

icient” incells or b iomass pr oducedper unit S m et abol iz ed. Taking
( 2- 129) give s d S /dt = -( μ/ Y ) N , or, substit

uting Eq. (2-128) for μ , ( 2- 130)
The obse rved m ic robia l growt h yi el d Y is oft en c al cul at ed fr om the am ount of m ic robia l biom ass produce d duri ng thecours e of transformation of

a m eas ured quanti ty

of s ubstrat e. Bec ausea microb ial pop ulatio n must satisf y maintenan ce require ments beforeany growt

h can occ ur, theapparent yi el d Y can fall quite drast ically at l ow conc ent rations of S . Exp ress ion s with separat ed growt

h and m ai nte nancey ie lds have be en de vel oped by Pirt (1 97 5) andit is p o ssib le to compu te the sep arate m agni tude s of growth and m ai nte nance y ie lds from m ic robia l growth experim ent s (Sl at er 1979)
. The Mon odformulation(Eq . (2 -1 30 )) h as bee n su ccess fu lly appl ie d to biot

ransf orm at ion of

synthe ti c c hemic al s in a labo rato ry setting . Th ese stu dies h ave d emonstr ated th at a Monod ana l y si s ne e d n ot

ber e st ri c t e d t o s i ng l e -s pe c ie s po pu lation s, th at is, the Mo no d equatio ns canserv e as adequate desc ript ors of subst

rat e t ransf orm ation by “ m ixe d” or “het erogeneous” (i .e. , m

ulti-s peci es) m ic robia l popul at ions . In one e xam

ple , Paris , Le wis, and Wolfe (1975) is olate d a 4- spe cies con sortium o f

org anisms able to use malathio n as its sol e s ource of c arbon. Anal ysi s of the grow th r espons e of the populati on andof co ncurre nt m al at hion t ransf orm ation rat es the n

max S gave the Monod param et ers μ =0. 37 /h, K = 2. 17 ìmol/L (0.716 mg/L) , and Y

= 4. 1×10 ce ll s/ ìm ol ( 1.2×10 ce ll s/m g).

10 11 In a si m il ar s tudy , Sm it h and coworker s (1978) inve st igate d the degra dat ion of

p- cre solby m ixe d m ic robia l c ult ures abl e t o use the com pound as a sol e car

bon source . Thes e a

uthors expre sse d

max the ir results in te rm s of Monod param et ers, fi nding μ = 0. 62 S /h, Y = 1. 8×10 ce ll s/m g, and K = 0. 84 m g/L.

9 Unfortunate ly , theseel e gant a ppl ic at ions of c la ssi cal m ic robiol ogic alm et

hods t o thebiotransf

orm at ion or

“bi oly si s” of synt het ic organic com

pounds are diffi cul t t o extra polate to a broade r ec ologi calcont ext . Thefi rst dif fic ult y, whic h has receiv ed so me attentionin the microb iolo gical literature, is pr imarily m echanical: Th e M on odformulation(Eq .(2 -1 30 )) is no n- linearin its parameters, an d thu s impo ses a hig h co st in com putationtim e whe n use d in a c om pute r program

or m at hem at ic almode l. For

trac e conce ntrati ons of pol lut ant s (i .e. , S S [ S] << K ) , h o w ev er , th e te rm ( K + [ S]) inthe denom inator of

S Eq. (2 -1 30 ) canbe app ro ximated by K , gi ving t he l ine ar approxi m at ion
( 2- 131)
This form ulati on is si m il ar to t

he “se cond-orde r” e quat ions use d to de scribe t

he kinet ic s of chemic alrea ct ions, andthe te rm

max S μ /(Y K ) can by analo gy be termed a second -o rd er bio lysis rate B2 con stant K , wi th uni ts /h/ (ce ll s/L) whe n population s iz es N are expre sse d in cel ls /L. The proprie ty

of t his substit

uti on can be rea dily e valuat ed. For

max S m al at hion, μ /(

Y K ) = 0.37/ (4.1×10 ×2.17) =4.16× 10 10 -12 /h/ (ce ll s/L). Pari s e t a l. B2

(1975) a ls o c om

pute d va lue s of K from microb ial pop ulatio n sizes andm alathio n trans fo rmation rates in B2 the ir experim ent alst

udie s, f inding a m ean value for K of (2.6±0.7) ×10 (9 5% conf ide nce int erva l) /h/ (ce ll s/L) for a -12 seri es of 8 e xperi m e nta lde t e rmi nati on s sp ann i nga conc ent ration range from

0. 0273 t o 0.33 ìm ol/L i n m al at hion. The m eas ured B2 max S K di f f er edfr o m μ /(Y K ) by le ss t han a fac tor of 2, sug ges ting that simplifiedkin etic exp eriments co uldbe us ed to devel op s econd- order rat e const ant s, in li eu of a detail ed

max S el aborati on of μ , Y, and K , wh en the regio no f c o n cernis S rest ric te d to le vel s of com

pound << K
. Furtherm ore, dis sol ved pe st ic ide conc ent rations in surfa ce wat ers are oft en ve ry low inde ed. For exam ple , di el drin, lindane, andDD T have bee n found prim ari ly at ng/Lle vel s bot

h in the USA (1972) and in Bri ta in (Brooks 1972) . For indus tri al chemic al s, howe ver , the situ ationcan be somewh at diff ere nt. For exam ple , t he re le aseof

phenol ic wast es int o theSt . Lawrence Riverresu lts in rive rine con centratio ns o f 0. 01 to 0.1 5 mg/L (Vis ser et

al . 1977) . A lt

hough the se high c oncent rations are res tri c t e d t o ad i sp e rs i onc on e imm e di at e l yd owns tre am o f the S effluent s, K for p-cr eso l (0.84 mg/L) is un comfo rtab ly close to the highe st

m eas ured c oncent

rations
. The need for a

thorough eva luati on of t he proprie ty

of E q. (2-66 131) as an adequate approxim at ion to theMonod form ula (Eq. (2-130)) di sappe ars, however, upon exam inati on of t he conceptua l di ffi cul ti es st andi ng in the way of the appl ic at ion of ei the r equati on to envi ronm ent alsi tuati ons. A nat uralm ic robia l community d er iv es its ener gy fr om a large v ariety of org anic det rit alm at eri al s. A m ic robia l spec ie s rest ric te d t o a tr ace -le vel synth etic compo un d as its so le c arb onsource w ou ld be at a sev ere com

pet itive dis advant age; the re i s no way of predi ct ing a pri orithepopulati on dens itie s t he de grade r coul d atta in in rea l sys te m s. E ven whe n a synthe ti c com pound is suffi ci ent ly

si m il ar to natura l s ubstrat es t

hat it can be i ndiff

ere ntly de grade d by the microb ial community as a wh ole, th e pre sen ce of multip le energy-y ie lding subst

rates in t

he e nvironm ent

viol at es a fund ament alas sum

pti on underlyi ng theMonod a pproac h, t

hat is, that [ S], thesynthe ti c c om pound, l imit s growt

h. In m any ins tances , m oreove r, a com pound maybet

ransf orm ed or degra ded in an e nergy -requiring det oxifi cation proces s, m aki ng the conc ept

of c el l y ie ld ( Y

) o f dubi ous util it

y. When the com pound, for what ever

rea son, i s de grade d in theabs enceof a c hang e i n p op ul at i ons i z e , the a pp are nt z e ro y i e l d f

or c es abandonme nt

of E q. (2 -1 30 ) and

( 2-131) a li ke. This phenom enon is som et im es cal le d “c om et abol is m ,” e.g. , (Alexander 1979a , Jac obson e t a l. 1980)
. Des pite thes e diff

iculties, th e rate of

trans fo rmation o f or gan ic pollutants m

ust depend on the st

ruct ure of thecom pound and the m e t abo l i c c apa c i tyof

m i c ro bi a lc om

m un i t i e s. T he s i m

ple st expre ssi on of t

his dual it y i s t he s econd- order equation
( 2- 132)
whic h as sert s t

hat the rate of bi oly si s ( d[S]/dt ) is firs t-or derin com pound conc ent

ration [ S] and in m ic robia l a ct ivi ty , bi om ass , B2 or popul at ion s iz e B , and in whic h theide nti fic at ion of K with

max S μ / (Y K ) i s di sc ount e d. T hi s app ro a c h r e qu i re s that the sec ond-order rat e const ant bede te rm ine d via

la borat ory st

udie s of re lati vely undi st

urbed s am

ple s drawn from

nat uralm ic robia l communities. It also requ ires d emonstr ationthat d[S]/dt is linearly proportiona l to [ S] f

or f i xe d l e ve l s of B , and that appropri at e m eas ures of B be found. One conventiona l mic robiol ogic alte chni que for charac te riz ing m ic ro bial popul at ions is si m ple populati on si ze, m eas ured, for exam ple , by col ony c ounts on pour-pl at e a gars (APHA 1976.)
. To t he e xte nt t

hat p op ulati on si ze is an adequate m eas ure of comm unit y m etabo lic cap acity, sim ple m ic robiol ogic al te chni ques coul d se rve t o charac te rize the rate of biotransf orm at ion of

synthe ti c c om

pounds i n nat

ural envi ronm ent s. T his hypot hesi s ha s been expl ored f or t hree com pounds – t

he but oxye thy l e st er of 2,4-D ( 2,4- DBE), m a l athi on , and

c hl or pr op ham – by P ari s and

c ow orke rs (Ba ughm an e t a l. 1980, Paris et al . 1981) . The se aut

hors inv estigated bio tran sfo rmationof the ir study compou nd s in sam ple s of nat

uralwat ers drawn from 40 locations in the cont ine nta l US A. Am bie nt wat er te m

perature s at

thecol le ct ion p o in ts ran g edfr o m 1 E to 29 E C, and t he l aboratory

st udie s wer e conduct ed at t

he obs erve d am

bie nt t em peratureof t

he s am ple d envi ronm ent s. Am

bie nt ba ct eri alpopulati ons, a s m eas ured by 48-hour incubat ion on TGE (t rypt one glucoseext

rac t) agar at 22 E C, ran gedfro m 4×10 to 9×1 0 cells/ml 2 5 (Pari s e t a l. 1981)
. Biolysis of these chemicals was demons trab ly first-or d erin com pound conc ent

ration a nd in populati on si ze, and was rel at ive ly independent

of t em perature . The95% c onfide nce

B2 int erva ls (bas ed on am on g- sit e va ri ati on) for K (/

h/(c el l/L)) and the num ber of si te s for the se com

pounds wer e (5. 42±0.97)×10 -10 (2,4-DBE , 31 si te s), (4.54±0.74) ×10 ( m al at hion, 14 si te s), and -11 (2.63±0.72) ×10 (chl orpropham , 11 s it es). -14 Eva luatio nof b iolysis insuch“riverdie-aw ay” stud ies is partic ularly

dif fic ult when a com bination of sm al l popul at ions and s low r at es of bi odegradati on le ads to inconveni ent ly long biolysi s ha lfl ive s. I n suc h ca ses populati on dens itie s must be augm ent ed vi a c ent

rif ugat ion or

suppl ement alnutrie nt broth. The l att e r pr oc e durec an h avethe di sa dv ant a ge of f avo ring opportuni stic heterotrophs at theexpe nse of organis m s be tt er equipped t o degra de m ore r eca lc it rant com pounds. F or exam

ple , B2 the s econd- order biolysi s rat e const ant (K ) for chl orpropham is unaf fectedwhenpopu lationdensities are aug ment edvia B2 nu tri ent brot h suppl em ent at ion, but t he m eas ured K for phenant hrene dec rea ses in approxi m at e propor tion wit h the populati on inc rea se (Pari s 1982, oralcom m .). Baughm an, Pari s, and St een (1980) a ls o repor te d se cond-orde r rat e c onst ant s for biot

ransf orm at ion of synthe ti c c hemic al s by po pu lation s der ivedfro m aqua tic sediments. The o bse rv ed ra te const ant s for 2,4-DBEand m al at hion we re c onsi st ent

with the B2 rate of deg rad ationby water -co lumn po pu la ti on s, at K of 2.3 ×10 and4. 0×1 0 /h/( cell/L) resp ectively. Aero bic bio lysis

-10 -11 of chl orpropham

by the se dim ent -deri ved popu lati ons was , B2 however, a lm ost

an order of m agni tude fas te r ( K = 1. 42×10 )

-13 B2 than biolysi s by

thewat er-c olum

n populati ons (

K =2.4×10 -14 /h/ (ce ll/L) ). B y varying these dim ent /wate r rati o, t

heseaut hors al so de m onst

rat ed t hat chl orpropham, m etho xych lor, andseveral phtha late e st ers were unavai la ble t o bi olyti c organi sms when sorbed to s uspende d se dim ent s. Plate -count

es ti m at es of bac te ria l popul at ion de nsi ties are ext rem ely se le ct ive and can undere st im at e t ota l popul at ion s iz es by thre e or m ore orders of m agni tude (Janna sch and J ones 1959, Wetzel 1975: 571, Fl et cher 1979) . Furt

herm ore, al though inc rea ses in pollutant f lux ( that is, kg m s or m ass -3 -1 degra ded/ti m e) with incr easin g c hemical conce ntrati on (consonant wi t

h p seudo-fi rst -order kine ti cs) have been observe d in nature (e.g., Sherri lland Say le r 1980) , i t i s a ls o tr ue t hat , at el evat ed pollut ant

conc ent rations , bot

h a reduc ti on in the app aren t first-o rd er rate con stant (Ti nsl ey1979:149f f) , and zer o-order kine ti cs (Vis ser et al . 1977) havebee n obse rved. The latt er phe nom ena areconso nant (m at hem at ic al ly) wi th E q. (2- 130). It is not cl ear , howeve r, whe ther thes e kinetic s are a67 refl ection of

them axi m

um growth rat e of a s peci al iz ed sub-populat ion of

degra ders or re sul t f

rom toxi c e ffec ts of elevated co ncen tration s onthe microb ial community. In any ca se, it iscl ear that t he s tudi es of se cond- or der kinet ic s ci te d abovearea usefulbeginning in thedet ai le d quantit ati ve study of rates of bio tran sfo rmation of

pollu tant ch emicals. Little m ore e xtra

polati ve powe r can be devel oped untilsuc h tim e a s the en viro nmental co up ling variab les that go vern th e metabolic capa ci ty of natura l and laboratory m ic robia l popul at ions have been rigor ously de te rm ine d and m eas ured in both kinds of sys te m s. As a fir st approxim at ion, EXAMS uti li zes a si m ple se cond-orde r equation (Eq.(2- 132)) to c om pute therat e of biot

ransf orm at ion of pol lut ant

che m ic al s. M ic robia l popul at ion densi ti es (as “col ony forming unit s” (abbre v. c fu)) for ea ch s ect or of t

he ecos yst em

ent er EXAMS ’ environm ent aldata base vi a t he B AC PL and BNBACve ct ors. For wat er column com partm ent s, B AC PLhas un it s of cfu/mL; BNBACfor be nthi c c om partm ent s ha s uni ts cfu/ 100 g dry

we igh t of s edi m ent . (A us efulsum m aryof observe d bac te ria l popul at io n d e ns i ti es in a quat ic sy st em s c an be found at pp. 571-596 of (W etzel 1 97 5) . ) Seco nd -o rd er bio lysis rat e c onst ant s e nte r EXAMS ’ che m ic aldat a ba se via separat ed param e t e rs f

or wat e r- c olumn ( KBACW ) and bent hic ( KBACS ) populati ons. T he nomina l uni ts areh (cfu/ mL) in both c ase s. -1 -1 EXAMS int ernally c onvert s be nthi c mic robial popul ation densi ti es to uni ts (cf

u/mL of wat er) comm ensurate wit h theunit s of the rat e c onstan t KBACS . Thi s c onversi on is exe cut ed vi a t he expre ssi on (

BNBAC × SEDMSL

) /( 100× W ATVOL ) where SE DM SLis the m ass of s edi m ent

in the com

partm ent (kg), WATVOLis t

he volum e of wat er c onta ine d in thecom partm ent (Lit ers) (Eq. (2- 21)), and thenum eri calfac tor (1 00) is a uni ts conve rsi on te rm (1000(mL/L )/10( deca gram s/kg). Despit e t

he rut hle ss pa rsi m ony im

posed on EXAMS ’ rep rese ntatio n of

biolysis kinetics , the de gr ee of ch emical detail pr ov idedby EXAMS ’ al lowance for i onic and sorptive spe ci at ion le ads to f

ai rly subst ant ia l oppor

tuni ti es for t

he inclusi on of biolytic kinetic det ai l. Bot h KBACWand KBACS are4×7 e le m ent matrices f oreachch emical und er stu dy; eachelement repr esen ts a s epar at e rate cons tant f or t he i onic and sorbed spec ies o f the pollutant. (The use of the m at rix indi ces t o s pecify c hemic al spe cies is des crib ed in Chap ter 2.3 .4. ) Inaddition , bio lysis rate const ant s c an be ente red e it her a s t em

perature -independent 10 si ngle values, or a

Q fun ction can beinvoke d to depi ct the effe ct s of te m

peratureon bi oly si s rate s.

10 The Q values (i.e ., inc rea se in bi oly si s rate per 10 E C change in t em perature ) for KBACWand KBACS oc curas t he paral le l m atrice s QTBAWand QTBAS , re spec ti vely. When the value of param et er QTBAWor QTBAS is non-ze ro, EXAMS takes the corre spondi ng m em

ber of KBACWor KBACS as the bio lysis rate const ant at 25 E C ( in acc ordanc e wit

h Subpar t N guide lines), and

10 rec al cul at es the second- order rate const ant via the Q equati on: ( 2- 133)
Becau se micr o b ia l co mmun it ie s f r equ en tl y a d ap t th ei r

metabolic capa ci ty t o ke ep pacewit

h sl ow sec ular (e .g. s eas onal ) changes in e nvironm ent alt e m

pe rat ures, te m peratureres ponses m eas ured in a la borat ory setting do not always a pply t o environm ent al condi ti ons. T his lim it at ion s hould berec ogniz ed whe n int erpre ting t

he re sul ts of EXAMS si m ulati ons t

hat inc lude te m peratureeff

ect s on bi oly si s rate cons tants
. Alt hough thenom ina l uni ts for bact eri alnumbe rs and for KBAC inc lude bac te ria l popul at ion de nsi ti es expre sse d a s num be rs /mL, clearly the se var iables can in b othinstan ces be red ef in edto enco mpass any env iron mental c o up ling variab le of utility in estim at ing bi odeg radati on rat es in a quat ic ec osys te m s. I t i s, however, e spec ia lly im

portant t hat the se unit s be com

m ensurate : Fo r example, if the rate con stants were determinedvia viab le plate c ounts , and the natura l populati on e st im at ed via dire ct count s, bi oly si s rat e s wo ul d p ro ba blybegr os slyov e rs t at ed. Furtherm ore, the si m

ple se cond-order equation a ll ows for a m ultipl ic it y of es ti m at ors of m ic robia l c apac it y. For e xam

ple , Nee ly (1980:117f

f) ) l is ts 7 c omm only us ed e st im at ors of m ic robia l bi om ass or a ct ivi ty , i ncluding c ounting te chni ques, ATP and DNA analyse s, and oxyge n uptake. Bysui ta ble (use r) rede fini ti on of

t he nomina l uni ts of KBAC s, B AC PL , and BNBAC , EXAMS can be usedto compu te pseu do -fir st-o rd er rate con stants as a func ti on of e nvironm ent alvariation in t he pre sum ed governi ng vari abl e, so long as the rat e c onst ant s and thebac te ria l po pulati on si zes areent ere d into EXAMS ’ dat a base s in comm ensurate unit s. The m echanic s of EXAMS ’ con ver sionof sec on d- or derbiolys is rat e c onst ant s and thecom partm ent -spec ifi c e nvironm ent al couplin g variab les to ps eud o- firs t-or derfo rm are completely hom ologous wit

h t he e quat ions use d for c hemic alrea ct ions . The total pseu do -fir st-o rd er biolysis rate co nstan t K is ac cum ulate d as the s um

of expre ssi ons of the form

K = á × KBAC × B , wher e á is the frac tionof the total po llutan t conc entr ationpres ent in eac h existing ioni c or sorbed chemic alspe ci es, KBAC is the appropri at e e le m ent

of m at rix KBACWor KB AC S (correct ed a s 10 neede d for envir onm ent altem perature s usi ng the Q equati on), and B is the deg rad er po pu lationde nsity ormetabolic cap acity of the microb ial community ine ac h eco system compartment. The s um of t hesepse udo-fi rst -order (/h) expre ssi ons the n becomes t he biolysis contr ibu tion to the ov erall (co m pa rt m e nt -spe c i fi c ) pseudo-fi rst -order rat e c onst ant K of E q. (2-1). Biolysis r at e data canalterna tively be supp lied as A qu atic Aerobi c and Anae robic Me ta bo lism hal f-l ive s (in day s). When no KBAC value i s non-zero, the se vari abl es (AerM et and AnaerM ) re spec ti vely) are conve rte d to KBACWand KBACS . A er M et and A naerM ar e a vai l abl e f or ea ch c hem i cal under68

study. A t R U N t i m e t hey ar e conver t ed t o i nt er nal s econd- or der bi ol ysi s r at e c onst ant s usi ng pr oper t i es of t he w at er body. For aer obi c met abol i sm, t he a ver age bact er i opl ankt on popul at i on dens i t y i s cal cul at ed a nd A er M et i s conver t ed t o KBACW . For anae r obi c m et abol i sm, t he a ver age sur f i ci al bent hi c ba ct er i al p o p u la tion d e n sity is c a lc u la te d a n d A n a e rM is c o n v e rte d to KBACS . I n bot h cases, t he r es ul t i ng KB AC is a p p lied to a ll d i sso l v ed form s (i .e., pH i n d ep en d en ce i s p resu m ed ); DOC -c o m p le x e s a n d s o rb e d fo rm s a re p re s u m e d to b e u n a v a ilab le f or bi ol ysi s. I n M OD E 1 and M ODE 2, t he pa r t i cul ar t em por al el em ent of

t he w at er body dat a s el ect ed f or t he RU N i s use d i n t he co n v ersion (i .e., on e o f M ON TH s 1 -12 o r 13 (av era g e v alu es ))
. In M ODE 3, t h e b ac t erial p o p u l ati o n s o f Jun e, Ju l y , an d A u g u st are cons i der ed. A quat i c met abol i s m i np ut s a r e on l y c onsi der ed w hen use r - ent er ed s econd- or der bi ol ysi s r at es a r e not al r eady pr es ent i n t he c hem i cal dat a. Refer enc es for Chap ter2.3.6 Ale x ander , M. 1979a. B iode gradati on of t oxic che m ic al s in water and soi l. Page s 179-190 in R
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al lible m ic roorgani sm s. P ages 246-253 in J. M. Lynch and N. J . Pool e, edi tors . Mi crobi alEcol ogy: A Conceptua l Appr oach. Bl ackwe llSci ent ifi c Publ ic at ions , Oxford. APH A. 1976. Standard M et hods for the Examinati on of Wat er and Wastewater

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nd Fat e of Chemi cals in the Aquat ic Envi ronm ent . Am eri can Soc ie ty for Mi crobi ology , Washingt on, D.C
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pounds in nat

uralwat ers. Appli ed and Env iron mental Micro bio log y 41 :603-609. Pir t, S. J. 1975. Pri nciple s of m ic robe and ce llcul ti vat ion. Bl ackwe llSci ent ifi c Publ ic at ions , Oxford. Sherrill , T. W., and G. S. Say le r. 1980. Phenanthre ne bi od e gr a dat i oni n f

re shwat e r e nv i ro nm e nt s. Ap pl i e d and Env iron mental Micro bio log y 39 :172-178. Slate r, J. H . 19 79 . Micro bial po pu latio nan d co mm un ity dynam ic s. P ages 45-63 in J. M. Lync h an d N . J. Poole , edi tors. Mi crobi alEcol ogy: A Conc ept ualApproac h. Bl ackwe llSci ent ifi c Publ ic at ions , Oxford. Sm it h, J. H., W. R. M abey , N. Bo ho no s, B. R. Holt , S. S. Lee , T.-W. Chou, D. C . B om berge r, and T. Mill. 1978. Envir onm ent alPat

hways of Se le ct ed Chemic al s in Fre shwat e r Sy st e m s: P art I I. L abo rat or

yS t ud i e s. E PA600/7-78- 074, U.S. Environm ent alProt ection Age ncy , Athe ns, Ge orgia
. Swis her, R. D. 1970. Surfac tant B iode gra dati on . Ma rc e lDe kker, Inc., New York. Tins l ey , I. J. 1979. C hemic alConc ept s inPol lut ant Be havi or. John Wil eyand Sons, New York-Chi ches te r-Bri sbane

Toront o. Viss e r, S. A., G. Lam ontagne, V. Zoul al ian, and A. T ess ie r. 1977. B act eri a a ct ive in the degra dation o f phenol s in pollute d w aters of t

he St . LawrenceRi ver. Archi ves of Env iron mental Con taminationandTox icolo gy 6 :455-469. Wetz el , R . G. 1975. Limnology . W.B. Saunder s C o., Phil adelphia
. 

### 2.4 Input Pollutant Loadings The flux of a pollutant chemic ale nte ring an ecosystem (term “Le” inEq. ( 2- 1) ) is a primary d eterminan t of the ultimate exposureexperi ence d by resi dent organi sm s. EXAMS does not69 ( 2- 134) compu te pollu tant loadings . Loa din gs may be dev elop ed v ia projec te d or m eas ured industria l e ffluent fluxes, agri cul tura l runoff, by t

ransf er f rom the PRZMmodel , landfil l s eepa ges, et c., but t hesecom putati ons m

ust be exec ute d ext erna lly t o EXAMS . EXAMS provi des input

vec tors for 5 kinds of l oadi ngs t o ea ch com partm ent of t he s yst em . The se are : point-source or stre am -borne loa dings ( STRLD ), non-point-s ource loa dings (NPSLD ), c ontam inate d ground-wat er s eepage ent eri ng the sy st em ( SEELD ), pre cipit at ion wa shout from theat m osphere ( PCPLD ), and spray-dri ft (or miscellane ous) l oadi ngs ( DRFLD ). The l oadi ngs have uni ts of kg (of c hemical)/hour i n al l c ase s. Thes e loa dings are taken as ti m e-i nvari ant cons tants in EXAMS ’ st eady -st at e com

putati ons, or a s m onthly va lue s when EXAMS is run i n mode 3. In addi ti on, both M ode 2 and M ode 3 providefor event loa dings by spec ifi cation of thedat e, chemic al , and kg mass of the even t. Eachnon -zer o pollu tant loadin g must con fo rm to the hydro log ic defi nition of

theec osys te m , or EXAMS wi llnot im ple ment the loa ding. For e xam

ple , EXAMS wil l c ance l a STRLD , NPSLD , or SEELD for a give n com

partm ent , i f t

hat com partm ent does not re c e i ve an a

pp ro pri at e c arri e r fl ow STFLO , NP SF L , or SE EP S resp ectively. (Defin ition andentry of the hydro log ic variab les is dis cuss ed in Cha

pte r 2.3.1.1. ) Pre cipit at ion ( RAIN ) is a monthly cl im at ic vari abl e in EXAMS ; a PCPLD is ther efo re allow ed o nly for c om partm ent s poss ess ing a

n air-wate r i nte rfac e. Non-zer o PCPLD s areaut om at ic al ly cancel ed in theca se of B (bent hic ) or H ( hy po li mni on ) c om

part m e nt s. A PCPLD is unco nd itiona lly permitte d for com

partm ent numbe r 1, whi ch wi llalways havean air-w ater inter face if

the sys tem definitio n ru les discu ssedin Ch ap te r 2. 3 .1 .1 ar e f

o ll o w ed . F o r

a l l oth erwa te r - co lumn com partm ent s, EXAMS si m ply looks bac k at

the(J-1) com partm ent . If thi s (J-1) com partm ent i s a ls o part

of t he wate r column, i t i s a ssum ed t o be dire ct ly abo ve the current

(J) c om partm entand anynon-ze ro PCPLD is removed. Com partments with an a ir- wat er inte rfac e are a lways prec eded by a bent hic (B) com

partm ent when EXAMS ’ system de fini ti on conventions (Cha

pte r 2.3. 1.1) are obs erve d.
EXAMS ’ subrouti ne CKLOAD evaluate s t he proprie ty

of t he four kinds of loadings t

hat ent er vi a c arri er f

lows. Thes e l oadi ngs are evaluat ed a gai nst

thevolum e of the carri er fl ows and the wat er qual it y c hara ct eri st ics of the ta rget com partm ent . The se evaluat ions weredes igne d to preve nt inadver te nt s peci fic at ion of a loa ding out si de EXAMS ’ o per ati ng range . In partic ular, EXAMS m akes no provi si on for crys ta ll iz at ion of thecom pound from s oluti on , no r do e s the pr og ram a l l owf or agr a dua l dis soluti on of chemic alf

rom a conde nsed (sol id or

li quid) phase
. In addi ti on, t

he non-l inearitie s pot ent ia lly pr ese nt at hi gh chemic alconc ent

rations (non-l inear s orpti on is othe rm s, appre ci abl e l ight

abs orpti on by the com pound, z ero-orde r biolysi s, et c.) are not

incorporate d in the code
. EXAMS ’ l oadi ng chec k com

putati ons are divided int o two groups: che cks base d on carri er f

lows of wat er a lone ( PCPLD and SEELD ), and c hecks base d on carrier flows of wate r plus an ent rai ned s edi m ent loa ding ( STRLD and NPSLD ). Ground-wat er s eep and ra infa llloa dings aresi m ply cons tra ine d to aqu eous solubil it

y. In t hesecom putati ons, t

he t em perature ( TCEL ) and

pH( PHand POH ) of t

he c ompartm ent

rec ei ving t

he loa d areuse d to com

pute (as appropri at e) thesolubil itie s of eac h ioni c s peci es of t

he c om pound, and the di stribution of the pollutant am ong it s i onic sp eci es (dis tributi on coe ffi ci ent s á , com pute d as des cribed in Chapte r 2.2). EXAMS the n com pute s the c on centr ationof

po llutan t in the c arr ier f

low . If th e solubility cri te rion is exc eede d, EXAMS reduces the loa d to the ext ent nece ssary to c onform

to the upper li m it

of EXAMS ’ operating range , notifi es the use r of t he m odifi cation(s ), and ret urns cont rol to t he us er wi thout

exe cut ing a

si m ulati on. Theloa dings are rec om pute d as theproduct

of t he l imiting c oncent

ration a nd the carri er f

low r at e, that i s,

where Load

is in kg/h, Inf

low in L/h, Lim it

(kg/L) i s one -hal f t

he solubil it y of thele ast soluble che m ic alspe ci es, and â is the fra ct io n of

the total co ncen trationpres ent in th e least soluble d is so lv edfo rm. Ea c h s tre am fl ow( STFLO ) or non- point -sourc e wate r fl ow (NP SF L ) enteri ng a com

partm ent m ayhavean ass oci at ed s tre am sed iment ( STSED ) ornon -p oin t-so ur ce sed iment (NPSED ) l oadi ng (kg se dim ent

/h) to the com

partm ent
. STSED and NPSED arenot us e d i n trans po rt

c om put at i on s (s e e C ha

pt e r 2. 3. 1. 3) . In the courseof e valuat ing s tre am-borne and non-point -sourc e pollutant l oadi ngs, EXAMS c om pute s a sorption e quil ibrium

for capt ure of thepollutant by

ent rai ned s edi m ent s in t

he stream or non-point -sourc e fl ows ent eri ng ea ch c om partm ent . The se com putati on s usethete m

perature , pH, and s edi m ent partitioning par ameters (e. g., org anic carbo n co nten t ( FROC ) and i on exchange c apac itie s ( AEC and CEC )) of the receiving c om part m e nt
. Fr om

t he s e di m e nt

/wat e r rat i o o f the c arri e r fl ow , EXAMS com

pute s t he di stribution c oeffi ci ent s ( á ) of t hec he m ic al i n t he c arri e r fl ow . If t he re si dualaque ous c oncent ration of any dis sol ved s peci es exce eds it s c oncent

ration l imit , t

he offending loading is reduc ed via Eq. (2-134), the s im

ulati on i s abort ed, and c ontrolis ret urned to t he us er f or eva luati on. EXAMS ’ m et hod for calcul at ing co n ce ntr at i o nlimi ts th aten sur e li n ear ity o f so r p ti o nis o th erms is des cribed in Cha

pte r 2.2. 2. Afte r che cki ng theloa dings and m aki ng any nec ess ary m odifi cations , sum

m ing a llext erna l loa ds and unit s c onversi on from kg/h to mg/h y ie lds term Le of Eq. (2-1). “Dri ft”loadings ( DRFLD ) are initially implemented un critically.70 If, howe ver, EXAMS ’ compu tation s re sult in f inal steady-state chemic alc oncent

rations above EXAMS ’ oper at ing r ange, any DRFLD s are thensequen tially reduceduntil the computatio nally inva li d es ti m at es are corr ected . (If MODE >1, or no dri ft loa ds were spec ifi ed and theres ult s are out si de t he ope rating range, EXAMS abort s t

he run and re turns cont rol to t he us er f

or corre ct ive ac ti on.) The DRFLD vec tor can be used to s peci fy m is cel laneous loa dings not e ncom

pass ed in EXAMS ’ four other monthly l oadi ng ty pes. EXAMS , for exam

ple , doe s not

all ow for entry

of pol lut ant

ac ross the air-w at er inte rfac e fr om a pollute d at

m osphere(Cha

pte r 2.3.2). Th e im

pact of a pollute d at

m ospherecan, howeve r, be com pu ted from

thebulk atm ospheri c parti alpres sure of t he cont aminant, and e nte red into EXAMS via the DRFLD ve ct or. T he net flux of pollutant acr oss t

he a ir- wat er inte rfac e (

F , m ole s m ! 2 l g l l h ) is giv en (see Eq . (2 -7 1) ) by F = K ( P /H - C) whe re K is
! 1 g l the e xchangec onst ant

(m h ), and both (P /

H ) and have C units
! 1 of (mole s m ). B y a ssuming t he bulk at

m osphereto be
! 3
g g uncont aminate d (P / 0. 0 ) , th e te rm ( P / H ) was dis car ded in the devel opm ent

of EXAMS ’ al gorit

hm for c om puting volati li zation lo ss es o f p o l lutants fr o m aqu at ic sy st ems . I nmuc hth e s ame way, thegross pollutant l oadi ngs i m posed by a

cont aminate d l atm ospherecan be com

pute d by taking C / 0.0. Non-zer o boundary condi ti ons can be loa ded into EXAMS via the DRFLD vec tor. EXAMS ’ environm ent alinput data can inc lude a char act eri st ic le ngth ( CHARL ), cros s-se ct iona l are a ( XSTUR), and disp er sioncoef

ficien t ( DS P ) at

any boundary

of t he s yst em

(by se tt i nge i the r JTURB or ITURB to zer o, a s de scribed in Cha pte r 2.3 .1. 4) . The exch ang e flow of water acros s the boun d ary is give n by FLOW (li te rs/

h) = (1000)( DS P )( XSTUR)/( CHARL ) If t he inle t e xchangefl ow is cont aminate d to a l evelof [C ] m g/L, the loa din g (k g/h ) onthe system of inte rest is simply: LOAD = FLOW × [C ] ×10 (kg/m g)
! 6 This load can be im

posed on therec ept or com partm ent via the appropri at e e le m ent

of t he DRFLD vec tor. The f ina l t erm in Eq. ( 2-1) i s “ Li, ” t

he s um of t he inte rnal loa dings on the sy st em

com partm ent s. Int erna l l oads aris e fr om two s ource s: chemic aland biol ogic altr ansfor m at ion proces ses , and inte rnaltr ansport

proce sse s. T he t

ranspo rt loa dings ari se from f lows of cont aminate d wate r, sedi m ent s, andpla nkton amo n g th e p hys ic al se c t o r s ( co mp artme nts ) of th e e co sy st em. Their m agni tude s can be com pute d f rom t he m agni tude s of the flows , t he di stribution of

thec om pound am ong i ts dis sol ved and sorbed spec ie s, and theconc ent ration o f the pollutant in the sourcecom

partm ent s (e xpress ed a s m ass /uni t a queous volum e). EXAMS use s t

he WATFL ( L/h) and S EDFL (kg/h) f low m at ric es (seeCha pter 2. 3.1.5) to c om

pute a m at

rix of i nte rnalloa ding fac tors ( EXAMS ’ i nte rnalvari abl e INT INL), by a ssoc iating car rie r flows wi th a

ppropri at e e le m ent s of

the ám at rix (Cha pte r 2.2.4). Thi s com

putati on r esults in t erm s whic h, when m ultipl ie d by t he t ota l c oncentration of pol lut ant in the sourc e com partm ent s (mg/L) , y ie ld t he m ass loa dings Li(mg/h) on the target com partm ent s, c onst it

uent s of the finalterm

in Eq. (2-1). 

### 2. 4. 1 P ro du ct C he mis try Trans form ationpro du cts are anadd itiona l element in the int ernal loa dings of som e com

pounds. The se are spe ci fie d to EXAMS by setting theac ti vit

y data base( ADB ) num

ber of thepare nt a

nd daught er within thecurren t simulation sp ecificati ons, t he proc ess gener at ing t

he produc t, the rea ct ive f

orm of t he pare nt mole cul e, the p ro c e ss y i e l d, and , i f de sire d, t he e nt ha lpy o f the transforming proce ss. The EXAMS input param et ers are CHPAR , the ch emical paren t ADB num ber, TP ROD , the t

ransf orm at ion pr oduct ADB num

ber, NPROC , t

he num ber of theproce ss, RFORM , the rea ct ive form

of thepare nt mole cul e, yi el d, t he (M/M ) proce ss y ie ld, and EAYLD , t he e ntha lpy

(kca l). The ge nerating proce ss i s spe ci fie d using thefol lowi ng c ode s for NPROC : 1 = sp ecific acidhydr olysis 2 = ne utra l hydr olysis 3 = sp ecific b ase hydro lysis 4 = dir ect ph oto lysis 5 = s ingl et

oxyge n 6 = fr ee rad ical ox idatio n (e. g., hydr ox yl radica l) 7 = wa ter colu mn bacter ial biolysis 8 = be nth ic sediment b acterial b iolysis 9 = r eduction Twent y -e i ght r e a c ti vef or m s areavail abl e for

spe ci fying RFORM , in a ddition to whi ch tot aldi ssolved e tc . c an bespe ci fie d using an RFORMof 29 = a lldis sol ved s peci es 30 = a llse dim ent -sorbe d spe ci es 31 = all DOC -com

ple xed s peci es 32 = a llbios orbed s peci es (The com ple te li st of RFORMspe ci fic at ions is give n at the RFORM e nt ry i n t he EX AMS data dictio nary in Chap ter 6 o f this docum ent .) T he proc ess YIELD may be en teredas the simple m ole of produc t pe r m ole reacted, or as an Arrhenius func ti on, in whi ch c asetheent

halpy of therea ct ion i s e nte red a s EAYLD . Ente ring transform at ion proce ss chemis ty r equi res spec ifi cation of t heseparam et ers using a “pat hway num

ber” as theinde x for each c om

ple te rea ct ion path. For e xam ple , i f t he parent compound (parathi on) i s re cal le d as ADB che m ic al1, and the product (paraoxon) is rec al le d as ADB c hemic al2, t hen a rea ct ion sche m e in whic h dir ect

photolysi s of DOC -com

ple xed parat

hion yi el ds a50 % ge ne rat i onof para ox on, and

hy dr oxy lr a di cal oxidati on of di ssolved parat hi on produc es para oxon in m ole -for-71 m ole form at ion, would bespe ci fie d to EXAMS as fol lows:

CHPAR 1 1 TPROD 2 2 NPROC 4 6 RFORM 3 1 YIELD 0.5 1 EAYLD 0 0 Path way: 1 2 Give n the se spec ifi cations , EXAMS ca lc ulate s t he re sul tant gener at ing flux (in thi s cas e of para oxon, chemic alnum ber2) from thebreakdown of t

he parent m at eri al (s) ( in t

his example, parath ion , chemical number 1) , andadd s the res ulting terms to the m ass loa dings Li(mg/h) in e ach segm ent , t hus c ompl et ing Eq. ( 2-1).
EXAMS al lows for m

ultipl e t ransformations; any

one of t he chemic al s be ing s tudi ed c an ge nerate any of theothe rs. Am ong the possibil itie s t

hus avai la

ble arerege nerati on of paren t from product , ge nerati on of m ultiple product s from

a si ngle st arting m at eri al , re action c hai ns, e tc
. 

### 2.5 Data Assembly and Solution of Equations EXAMS includes t

hree “m odes”of ope ration: dir ect ca lc ulati on of t he “ st eady -st at e” out c ome of l on g- t e rm

c ont ami nation ( Mode 1), s tep-wis e c om

putati on of t

he tim e course of cont aminant e xp os ur e un de r as pe c i fi e d s e t of e nv i ro nm e nt a lc on di t ions , (Mode 2), and com

putati on of daily e xposure conce ntrati ons usi ng m onthly update s of envi ronmental condi ti ons (M ode 3). The num eri calinteg ration t echni ques are thesam e, and t he output sum m ari es anal ogous, for e ach operating “m ode” of t he p r o g r am. 

### 2. 5. 1 E xp os ure Afte r computing a llte rm s in Eq. (2-1), the res ulting s yst em of mas s- b al an ce equ at io n s c anbe di v id edthr o u g hbyth e v o lume of the compartments to give a set of equ ation s desc ribin g the r ate of change of chemic alconc ent ration ove r tim e:

( EXAMS al lows the volum es of sy st em el em ent s t o be al te red by the use r duri ng thecourse of an analysi s (exc ept in Mode 1), and m akes appropriate modi fi cations to exposurele vel s. T his feature is dif fic ult to use, howeve r, and requires car e in int erpret at ion. A vers ion of EXAMS that includes dynam ic changes in st orage volum es (Mode 4) i s in preparation.) As time passe s, th e system evolv es tow ardan ultimate “st eady -st at e” condi ti on at which the conc ent

rations ac hie ve st abl e va lue s. T his endpoint i s de fine d by t he c ondition d [C] /dt = 0.0 for e verycom partm ent . At

steady stat e, the n, t

he con centr ationof p ollutant i ne achsectorof the ecosys tem is give n by ( 2- 135)
Num eri calint egrati on to st eady st at e is notorious ly

profl igate of com putati onalres ource s, s o EXAMS con tains anexp licit proce dure ( subroutine STEADY ) des igne d to sol ve t he e quat ions fo r thes e co n ce ntr at io n s, wh ic hde f in e lo n g - te rm exp o sur e le v els of t he pollutant and can serveas a usefuladjunc t to any expos ure analysi s. The l ogic of t

he s it uat ion c an beillustrated via an el em ent ary exam ple . For the exam

ple , c onsider the be havi or of a no n- sorbin g ch emical, sub ject to n eutr al hydr ol ysis as its sole transform at ion proces s, in a stati c one -hec tare pond. The pond is 1 m et er deep, wit

h VOL V the refore10,000 m (10 L). The 3 7 bent hic subsy st em

cons is ts of a

5 cm ac ti ve depth of

m at eri al witha bulkden sity ( BULKD ) of 1. 5 g/c c and awa ter cont ent ( PCTWA ) of

150 %. Th e env iron mental volu me of the be nth ic zone ( VOL ) i s 500 m ; i ts aque ous volum e i s 250,000 li te rs of 3 water(Eq . (2 -2 1) ). D ef inin g ex chan ge b etwee n the b enth ic subsy stem and thewat er c olum n via XSTUR = 10,000 m , 2 CHARL =(1.05/2) = 0.525 m , and DSP =10 m /h, the rat e of
! 4 2 exchange of flui d volum e be twe en t he water c olum

n and the inter stitial por e water(Chapter2.3 .1. 4) is

This exchan ge flow of water can be redu ced to its pse ud o- firs t-or dereffect onchemical con centr ation s (Kt, /h) in the wat er c olum

n (w) and thebent

hic (b) s ubsys te m

via : Kt(w) = 952.4/ 10 = 9.524×10 / h, and 7

! 5 Kt( b) = 952 .4/2 50 ,00 0 = 3. 81 0×1 0 /h
! 3 As t he c om pound does not sorb, transport of s edi m ent

and plankton c an in thi s inst ancebe ignore d. The int ernal loa dings on the s yst em aris e from

pollutant cont aminati on of t

he 952. 4 L/

h exc hange flow bet

ween the sys te m com partm ent s. Allthe com

pound is pres ent

in dis sol ved form in thi s e xam

ple ; s orbed and com

ple xed exchange proc ess es are hereim

m at eri al
. EXAMS com

pute s i ts int erna l l oad fa ct ors Li/V bydivi di ngthe e l e m e nt s of INT IN L by

the vo lum e of

the target com partm ent . In thi s inst ance , t he l oad fa ct or on t

he bent hic subsyst em

res ulting f

rom cont aminati on of t

he wate r column is INTINL(b, w) 

# 7 (95 2.4 × 1.0 0) /25 0,0 00 = 3.8 10 ×10 /h
! 372

Ecosystem: Static 1-hectare pond, 1 meter deep Chemical: Unsorbed chemical subject to neutral hydrolysis
--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.
--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 2.0 100.00 0.199 0.199 0.00 0.00 ======== ====== 2.0 99.32 and in the Benthic Sediments: 2 1.37E-02 100.00 2.740E-02 5.479E-02 0.00 0.00 ======== ====== 1.37E-02 0.68 Total Mass (kilograms) = 2.000
--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics. E x a m s O u tp u t T a b le 1 0 . E XA MS o u tp u t ta b u la ti o n o f s te a d y-s ta te concent r at i ons. and the load fac tor on thewat er c olum n res ulting f

rom con taminationof the ben thic inter stitial wateris INTINL(w, b) 

# 7 (95 2.4 × 1.0 0) /10 = 9.5 24 ×10 /h 7

! 5 (IN TIN L and Kt are equa l in this much simplifiedexample; this is not usual ly

theca se. ) Fina lly, give n an external load on t he wate r column (her e a DRF LD ) of

, say, 0 .0 2 k g /h , anda neutr al hydr olysis r ate con stant o f 0. 01 /h, the b ehav ior o f the ch emical in the sys tem is giv en b y: d[ Cw ] / dt =( 0. 02×10 / 10 ) +9. 524×1 0 ( Cb )
- ( 0. 01 + 9

. 524×1 0 ) Cw 6 7

! 5

! 5 d[ Cb ] / dt = 3. 810×1 0 ( Cw ) - ( 0. 01 + 3

. 810×1 0 ) Cb ! 3

! 3 where Cwis theaque ous conce ntrati on in thewat er c olum n and Cb is theaque ous c oncent ration in the inte rstitia l por e wate r (m g/L) . At

st eady st at e, d[ Cw ]/dt =d[ Cb ]/dt = 0.0 , resu lting in 2 equati ons in 2 unknowns:
- 0. 010095 24 Cw

+ 0. 000095 24 Cb= - 0. 002 0. 00381 Cw

- 0. 01381 Cb= 0.0 This el em ent ary e xam

ple can be eas ily s olve d to give Cw= 0.1986 and Cb = 0.0548 mg/L. EXAMS solves the si m ult aneous linear equat ions that de scribe s te ady -st at e c oncent rations by Gauss ian el imination (Cha pte r 2.3. 1.2). EXAMS ’ out put f or t he example sys tem describ ed ab ove is give n in Ex ams Outp ut Tab le 10.

As Gaus si an e li m inati on is not an infallible m echanis m for execu ting the se com

putati ons, EXAMS inc lude s a se cond te chni que for com

puting t he s olution to thesy st em

of e quat ions (Eq. (2-135)), whic h is invoke d in thos e c ase s for whic h Gauss ian el iminati on fai ls . Thi s al gorit hm i s an it erati ve “ linear cas cade ” m et

hod t hat a ppli es Eq. (2-135) to e ach com partm ent in t urn, and t hen repeat s t

he e ntire pr oces s untilsuc h tim e a s t he succ ess ive es ti m at es for e ach com partm ent c hange by l ess tha

n 0.0001%. EXAMS allows forup to 10 0,0 00 iteratio ns o f the fu ll “l ine ar cascade” com

putati on. If the linear

ca sca de t erminate s wit hout f ullconver gence, EXAMS abort s t he run; thi s e vent gen erall y can be takenas an ind icationthat steady-state conce ntra ti ons a re unbo un ded. For exam ple , a non-tr ansfor

m abl e chemic alin a st at ic pond without any export pat hways wil l a ccum

ulate inde fini te ly ; in thi s si tuati on no “st eady -st at e” condi ti on can be computed. The de gree of con ver gen ce ach ievedby EXAMS for t he ful l ecosys te m

can be examine d in the m ass bal anceche ck printe d as thefi nalent ry (“R esi dualAcc um

ulati on Rate ”) in EXAMS ’ output ta ble entitle d “Analysi s of Ste ady -St at e Fate of Organic Toxi cant .” In t he e le m ent aryexamplegive n above , t he l ine ar c asc ade soluti on would proce ed: Ite ration 1, st ep 1: solve for Cw ( com partm ent num ber 1)
C w = ( Le/ V + Li / V) / K = ( 0. 002 + 9. 524×1 0 ( C b) ) / 0. 0100 9524 ! 5 giving, a s C b at

them om ent

= 0. 0,
C w = 0. 002/ 0. 0100 9524 = 0. 1981 1 Ite ration 1, st ep 2: solve for Cb (com partm ent num ber 2)
C b = ( Le/ V + Li / V) / K = 0. 0038 1( C w) / 0. 0138 1 = ( 0. 0038 1×0. 1981 1) / 0. 0138 1 = 0. 0546 7 Fro m t he ini ti al estimates, the seco nditerationpro ceed s to com pute a refined e st im at e of Cw and Cb:
C w=( 0. 002+( 9. 524×1 0 ×0. 0546 7) ) / 0. 0100 9524 =0. 1986 3 ! 5 C b=( 0. 0038 1×0. 1986 3) / 0. 0138 1 = 0. 0547 99 The c onverge nce test

is com pute d for e ach com

partm ent by cal cul at ing t

he re lati ve c hange in the estim at e. The change in Cw was 1 - 0. 1981 1/ 0. 1986 3 = 0

. 0026 and t he c hange in C b was
1 - 0. 0546 7/ 0. 0547 99 = 0. 0026 As t he set e st v a lue s aregre at e r than EXAMS ’ conve rgenc e cri te rion (10 ), EXAMS continue s wi th a third i te ration of

the
! 6 linear ca sca de. EXAMS ju dg es co nv erg ence to be co mplete only when t he re lati ve c hange in e veryc om partm ent i s l ess tha

n 10
. -6 In m ode 2, EXAMS int egrate s from tim e “ TINIT ” t o tim e “ TFINAL ”73 with output

and int erva ls of “ CINT ” i n uni t s sp e c i fi e d by
“ TCODE .” At the end of an inte gration ( “ RUN ”), the si m ulati on is paused and the us er can evaluat e the r esults and c hoose to
“ CONTINUE ” t

he simulation to som e ne w value of TFINAL . In Mod e 3, the minimum runtime is on e year, w ith month ly updat es of environm ent alpropertie s. Mul tiple ye ars (“ NYEAR ”) can be run as a si ngle unit , or the continue com m and c an beuse d to run bloc ks of ye ars. When EXAMS is us ed in co nj un ctionwith the PRZMm odel , EXAMS read s the climate tim e-se ries u sedwith PRZMand buil d a

c li m at ic data

s et c onsi st ent

wit h the PRZMdat a. 

### 2. 5. 2 F ate Afte r com

puting expos ure c oncent

rations , EXAMS eva luate s t he im pact of e ach transport

and transport ation p roce ss on the beh avio r of

the compo un d. D ur ing the co ur se of redu cing its input data to pseudo-f

irs t-or der f

orm , EXAMS pres erve s t

he va lue of ea ch proc ess ’ contributi on to the overa llpse udo-fi rst - orde r rat e c onst ant

K (Eq. (2-1)) for each com partm ent . Theflux of chemic altr ansfor

m ed or t ra nspo rte d (m a ss /ti m e ) i s t

hen gi ven by the product

of t he proc ess rat e c onst ant , the concent rations , and the aque ous volum e of e ach com partm ent . In the ins tance under revi ew, t he c hemic alfluxes at

tributa ble to neut

ralhydrolysi s are Fw = Khy d × Cw × WATV OL(w) × 10 (kg/ mg) -6 = (0 .01) (0.1 986 )(1 0 )(1 0 ) = 0 .019 86 k g/h 7 - 6 in t he wate r column, and Fb = (0.0 1)( 0.05 479 )(2 .5×1 0 )(1 0 ) = 0 .000 137 kg/h 5 - 6 inth e b en th ic sub sy st em. EXAMS sum s thefluxes(by proce ss) over the ent iresy st em , and com pu tes t he s igni fic anceof t

he proc ess via

divi si on of t

he p r o ce ss fl uxbyth e sum of the ex te rn al loa d in g s o nth e s ys te m, foll owed by conver si on of t his r esult to a perc ent age basi s. I n the exam ple , t he t ota l f lux i s (0. 01986 + 0. 000137) kg/ h, t he t ota l load ing was 0.0 2 kg/h , thu s hydro lytic transf ormation acco un ts for 100(0. 01986 + 0. 000137)/0. 02 = 100% of the i nput l oadi ngs, as of cour se it

m ust in thi s e le m ent aryexam

ple
. EXAMS ’ out

put t abl e c onta ining ther esults of t he flux analysi s, ent itle d “Se nsi ti vit

y Ana ly si s of Chemic alFat e,”al so includes estim ated hal f-l ive s for rem ovalor di ssipat ion of theche m ic al from thesy st em . The se hal f-l ive s are c om puted under t

he ass um ption that inte rn al trans po rt delays are insigni fic ant , giving a s upple m ent alvie w of t

he ge nera l s igni fic anceof e ach proce ss. The ha lf- li fe com

putati ons are execut ed via divi si on of the tota l proce ss f luxe s by thetot alm ass of pollut ant res ide nt in the sys te m to give a sys te m -widepse udo-fi rst -order rate const ant Kp r. Th e half- life is thensimply T1⁄2 = - l n(0. 5)/ Kpr In t he e xam ple case , t

he t ota l r esi dent

m ass (com

pute d as the sum of volum es and c oncentrations ) i s 2.00 kg (Exam s Out put Tabl e 10), and the projec te d hydr olyti c ha lf- li fe i s t here fore T1⁄2 = ( 0. 6931 5 × 2

. 00) / ( 0. 0198 6 + 0

. 0001 37) = 69

. 3 hou r s. EXAMS does not infl exibly repor t f luxe s and ha lf li ves in hour s, fo r in many instan ces th e ho uris an inco nv enien tly small reporting uni t. Inst ead, the p rogram m akes a prel iminary evaluat ion of thetot altrans port and t ransf orm at ion f

lux t hrough the ec osys te m , and com

pute s a fi rst -order estim at e of the total hal f-l ifeof the c om

pound. Thispr el iminary estim at e is the n use d to s el ect them ost appropriate (ho ur s, days, m onths , or ye ars) ti m e scal e for

repor ting theres ult s of al l s ucce edi ng ti m e-de pendentcomputa ti ons. T his es t i m a te of the “sy st em -le vel ” hal f-l ifei s al so used to set t he ti m e inte rval s for EXAMS ’ Mod e 1 “p ersis tence ” computation s, as de scrib ed in Chapt er 2. 5.3.
EXAMS ’ flux com

putati ons, a long wi th its t abl e of com partm ent -spec ifi c ps eudo-first -order rate cons tants (out put ta ble “Ki net ic Profi le of Synthe ti c C hemical”) providea sens itivi ty

a nalysi s of the be havi or of the pol lut ant in the partic ular ec osys te m

under st udy. Thes e t abl es indi cat e t he rel at ive st

rength of t

he t ransf orm at ion proces ses , and the reby indi cat e whic h pr oces ses are in nee d of t he m ost sc rupulous and exac t e xperi m ent aldet erminati ons of rat e c onst ant s. I n addi ti on, EXAMS interac tive cap abilities allo w a us er to v ary the inpu t data over a report ed e rror bound, and thus det ermine , for exam ple , the degre e of uncer

ta int y im pli ed for expos ure c oncent

rations
. 

### 2. 5. 3 P ers ist en ce EXAMS ’ fi nalround of com putations de aldir ectly

wit h a third (af ter expos ure a

ndfate) asp ect of ex po sur e evalu ationin aqu atic sys te m s, t hat of the“pe rsi st ence ” of the com pound. (T heseare a fe at ure of Mode 1 only.) It

shoul d perhaps be em

phasi zed that EXAMS com

pute s l ocal , rathe r t

han gl obal , pe rsi st ence , t hat is , EXAMS ’ compu tation s address the per sisten ce of compoun ds in the spe ci ficec osys te m

under revi ew, a nddo not addre ss t he globa l i ssue of t

he pe rsi st enceof a com

pound afte r it

le aves the loc alec osys te m . Thus , for example, a com pound that i s not subjec t to any

tr ansfor m at ion proces ses is ips o facto (glo bally) persi st ent
. Withi n t

he m ore li m it ed cont ext of a parti cul ar ecos yst em , howeve r, export proces ses willult im at ely res ult in a “cl eanup”of t

he s yst em , and thetim e re quire d for t his cl eanup proce ss c an becom

pute d. (As the ult im at e e xposure conce ntrati ons for a t

ransf orm at iona lly persi st ent

che m ic alin a st at ic (clos ed) sy st em

areunbounded, EXAMS ne ver e ncount ers the res ulting infini te cl eanup ti m es. )
EXAMS begins i ts M ode 1 persi st encecom putati ons by

using the st eady -st at e c oncent

rations of pol lut ant

in the sy st em

as a se t of st arting va lue s o r “ini ti alcondi ti ons.” The se ini ti alcondi ti ons are p resent ed t o thenum eri calint egrati on pac kage (subroutine DRIVER et se q.). The r el evant

se t of differe nti alequati ons,74 Ecosystem: Static 1-hectare pond, 1 meter deep Chemical: Unsorbed chemical subject to neutral hydrolysis
----------------------------------------------------------------- Table 19. Summary time-trace of dissipation of steady-state chemical mass following termination of allochthonous loadings.
----------------------------------------------------------------- Time Average Chemical Concentrations Total Chemical Mass
----- ------------------------------- ------------------- Hours Water Column Benthic Sediments Water Col Benthic
-------------------- ------------------- --------- -------- Free-mg/L Sorb-mg/kg Pore-mg/L Sed-mg/kg Total kg Total kg
----------------------------------------------------------------- 0 0.20 0.0 5.48E-02 0.0 2.0 1.37E-02 12 0.18 0.0 5.43E-02 0.0 1.8 1.36E-02 24 0.16 0.0 5.30E-02 0.0 1.6 1.32E-02 36 0.14 0.0 5.11E-02 0.0 1.4 1.28E-02 48 0.12 0.0 4.87E-02 0.0 1.2 1.22E-02 60 0.11 0.0 4.62E-02 0.0 1.1 1.15E-02 72 9.63E-02 0.0 4.34E-02 0.0 0.96 1.09E-02 84 8.53E-02 0.0 4.06E-02 0.0 0.85 1.01E-02 96 7.56E-02 0.0 3.78E-02 0.0 0.76 9.44E-03 108 6.70E-02 0.0 3.50E-02 0.0 0.67 8.75E-03 120 5.94E-02 0.0 3.23E-02 0.0 0.59 8.08E-03 132 5.27E-02 0.0 2.97E-02 0.0 0.53 7.43E-03 144 4.67E-02 0.0 2.73E-02 0.0 0.47 6.82E-03 E x a m s O u tp u t T a b le 1 1 . S a m p le EXA MS ou t pu t f or di ss i pa t i on of chem i cal af t er r em ov al ofext er nal l oadi ngs. des crib ing the behavio r of the pollutant ove r tim e, is essen tially Eq. ( 2-1) wi th t

he e xte rnalloa dings (L e) set to zer o or s truc k from theequati ons:

InM od e 1, EXAMS com

pute s t he di ssipat ion of

thecom pound over tim e, taking the tim e re quire d to encom pass 2 (e st im at ed) sys te m -le velhal f-l ive s as t he e ndpoint

of t he s im ulati on. The results of t

his si m ulati on aresum

m ari zed in EXAMS ’ ou tput table ent itle d “Expos ure Ana ly si s Sum m ary .”
EXAMS m akes use of t

wo int egrati on pac kages (Mal anchuk et al
. 1980)
. EXAM S in itially calls up ona variab le step size, variab le order (1-12) Adam s PE CE m et hod. In the event

that t he 2 equ ation s pro ve to b e mathematically “stiff,” th e p artially complet e inte gration i s re m anded to a n al te rnat e pa ckagethat int egrate s stiff

equati ons by

a vari abl e-orde r, varia

ble st ep s iz e code em ploy ing m

ulti-s tep bac kward di ffere nti at ion m et hods of order 1 through 6. T he Adam s m et hod codewas taken fr om (Sham pine and Gordon 1975) ; the stiff equati ons m et

hod was deri ved fr om

an algor it

hm ori gina lly de vel oped by

Gear (Gear 1971c, b, a)
. EXAMS lim it s t

he e xpenseinc urred in th e inte gration vi a a li m it at ion on the tot alnum ber of s teps whic h t

heseroutine s are permitte d to exec ute
. EXAMS wri te s out the s ecul ar dis sipat ion of the com pound at 12 e qual ly spaced tim es, up t o theendpoint ( TFINAL ) def

ine d b y 2 estim at ed s yst em -le velhal f-l ive s. I f t he integ rato rs ex ceedtheir allo tted expen se allo w an ce pr ior to int egrati on to TFINAL , c ontrol is rel inqui shed by t he inte grat or fo r eva luatio n of

the situatio n. I f the in tegr ator s hav e failedto reachthe firs t ou tput poin t ( TFINAL/12), EXAMS abort s a llfurt her persi st encecom

putati ons and so noti fie s theuse r. If at le ast one ou tput point ha s be en pa sse d, EXAMS us e s the l at e st po int re a c he d by

t he int e gr at or s i n i t s pe rs i st e nc e c om put at i on s, and noti fie s t he us er that the di ssipat ion s im ulati on was abbre viate d. Inte gration e xpenseis al so influe nced by t he pre cision dem anded. Thi s c an becont roll ed by theuse r byal te ration of ABSER and RELER , the a

bsolute and rel at ive err or crit eri a us ed by the num eri calint egrati on pac kage. The sm al le r t hei r values, the greate r the prec is ion of theanaly si s, but

thegreate r t

he perform ancecos ts incurred. The se param et ers cannot be m ade arbi trarily s m al l dueto the intrinsic l imit at ions of di git al com puting m achinery ; upon invoc at ion EXAMS eva luate s t he num eri calprec is ion l imit at ions of t he c om puting platfor

m and est abl is hes l imit s for ABSER and RELER . If the se are t oo la rge, the int egrators wil l e ncount er s ta bil it y pr oble m s, s o it

is som et im es worth experi m ent ing wi th ABSER and rel er t o optim iz e t he condi ti ons of an analysi s.

In t he va st m ajori ty of c ase s, EXAMS ’ dissip ati on si m ulati ons conclude wi th a

succe ssfulint egrati on to TFINAL . EXAMS ’ out put summary of th e time course o f diss ipatio n via n eutr al hydr olysis in t he static pond use d as an exam ple in Chapt er 2. 5.1 i s gi ven i n?.

EXAMS pri nts a summary of theexpos ure and fat e inform at ion gener at ed by

theprogram

and al so e stim ates and report s t he le ngth of tim e re quire d for c le anup of the ec osys te m . EX AMS report s, in the f

irs t inst ance , t

he pe rce nta ge of the ini ti al chemical m asses in the entire wate r column andbe nth ic subsy st em

t hat ha d be en dis sipat ed by

tim e TFINAL . EXAMS the n wei ghts the se dis sipat ions ac cordi ng to the ini ti aldi stribution of the che m ic alin thesyst em , and report s a first -order estim at e of the tim e re quire d for t

he s yst em to cl eans e i ts el f of t

he c hemic al m ass ac cum

ulate d at st eady st at e. This e st im at e is com pute d as 5 (ps e ud o- firs t -o rd e r, we i ght e d) ha l f- l i ve s; i n a tru e f i rs t -o rd er sys te m thi s would corr espond t o diss ipati on of 97% of t he m ass of che m ical initia lly pr ese nt in thesy st em . (T he a ct ual (m at hem atical) “ order”of t

he s yst em is defined by

thenum ber of com partm ent s use d to de scribe t he e cosy st em . For exam

ple , when a wat er-body

is des cribed t o EX AMS via 20 se gm ent s, EXAMS com

pil es 20 linked fir st -order diff ere nti alequati ons, and solv es this sys tem of equ ation s to ge ner ate its ou tputs. Th e data used in EXAMS ’ per si st ence tim e c om putati ons i s ge nerate d by summ ing t

he re si dualche m ic alm ass es ov er c om partm ent s, the rebyfo ll owing t

he di ssipat ion of

theche m ic alin the entire sys te m . Thecom

putati ons are in thi s se nse reduc ed orde r approxi m at ions ; t

hu s EXAMS repor

ts aregive n as “rough” estim at es (e.g. , Exam s Out put T abl e 12). ) This computa tioncan be illustratedvia the r esu lts of th e sample si m ulati on given in ? . At t he e xpirati on of 144 hours, the resi dent pollutant m ass ha d f

al le n f rom 1. 986 t o 0. 467 kg in t

he S o call ed fr o m t h ei r s u ccessive o p erat i o n s o f pr edi ct i on , 2 der i vat i ve ev al uat i on , c o r r e c tio n, and fi nal der i vat i ve ev al uat i on .75 Ecosystem: Static 1-hectare pond, 1 meter deep Chemical: Unsorbed chemical subject to neutral hydrolysis
--------------------------------------------------------------- Table 20.01. Exposure analysis summary.
--------------------------------------------------------------- Exposure (maximum steady-state concentrations): Water column: 0.199 mg/L dissolved; total = 0.199 mg/L Benthic sediments: 5.479E-02 mg/L dissolved in pore water; maximum total concentration = 2.740E-02 mg/kg (dry weight). Biota (ug/g dry weight): Plankton: Benthos: Fate: Total steady-state accumulation: 2.00 kg, with 99.32% in the water column and 0.68% in the benthic sediments. Total chemical load: 2.00E-02 kg/ hour. Disposition: 100.00% chemically transformed, 0.00% biotransformed, 0.00% volatilized, and 0.00% exported via other pathways. Persistence: After 144. hours of recovery time, the water column had lost 76.49% of its initial chemical burden; the benthic zone had lost 50.21%; system-wide total loss of chemical = 76.3%. Five half-lives (>95% cleanup) thus require ca. 14. days. E x a m s O u tp u t T a b le 1 2 . E x a m p le s u m m a ry o u tp u t ta b le (M o d e 1 ). wat er column. Thi s di ssipat ion of thepollutant r epre sent s a los s of 100 (1 - (0.467/ 1.986)
or76. 5% of the orig inal material. Simi lar ly, the be nth ic subsy st em

has los t (0.0137 - 0.00682) = 0.00688 kg or 50.2% of its ori gina l m ass of c hemic al . (T he be nthi c s edi m ent exhibit s a sl ower l oss of

chemic alas a res ult

of continuing rec ontam inati on (Li , Eq. 10) of thi s subs yst em from thewat er c olum

n.) In a fir st -order sys te m , t

he de cre aseof an ini ti alma ss of m at eri al Qo over ti m e i s gi ven by Q(t) = Q(0) exp(-k × t), or ln(Q(t)/Q(0) ) = -k×t where k is thefi rst -order rat e c onst ant and t i s ti m e. The ha lf- li fe is defined as th e tim e re quire d for Q( t) to r eac h Q(0)/2 or for Q(t)/Q(0) = 0.5, t

hat is , H = -ln (0 .5) /k The fir st -order hal f-l ive s (H) for t hesewat er-c olum

n (Hw) and bent hic (Hb) s ubsys te m s are, the refore : Hw = (0. 69315)(144) /

ln( 0.467/1. 986) =69.0 hrs, and Hb = ( 0.69315)(144) / ln(0.00682/ 0.0137) =143.4 hr s At s te adyst at e, 99.32% of the c om pound is pres ent

in the wat er co l umn , an don ly0. 6 8 % is inth e b en th ic sub sy st em ( Ex ams Output Table 10). EXAMS thus es ti m at es the tim e re quire d for dis sipat ion of

theche m ic alas : Td = 5 (0.9932 (Hw) + 0.0068 (Hb)) = 5 ( 0.9932 (69. 0) + 0.0068 (143. 4)) =347.5 hr s or 14.5 day s. EXAMS out

put s umm aryfor t

his exam ple is give n in E xam s Out

put T abl e 12. If th e majority o f the ch emical had b een p rese nt in the ben thic zone, EXAMS would of co urse have give n com putati onal pr eced ence to dissip ationin the sed iment sub system f o rits estim at e of decont aminati on tim e. A m ore de ta il ed e valuat ion of thepers istenc e of the che m ic al can be e xecut ed vi a a

graphi calana ly si s of the tim e c ourse of pollutant di ssipation, plotte d from theres ult s of EXAMS ’ num eri calsi m

ulati on of thi s phe nom enon (?). In inte rpreting EXAMS ’ estimate of th e time require d to dis sipate the che mical, it shou ld be r emem

ber ed tha t EXAMS ’ estim at e repre sents fi ve half -live s, orabo ut 97 % remov al of th e initial mass. If this rem ovalsugge st s t

hat the chemic alwould st il l oc cur at un ac ce p tab le co n ce ntr at io n s, a f ir st
- o r d erev al u at io nof

th e ti me requi red t o a chi eve a spec ifi ed re duct ion c an becom pute d from EXAMS ’ out

puts . Suppos e, for e xam

ple, that thetim e t o reduc e the che m ical to 0.01% of i ts ini ti alvalue we re t he tim e of int ere st . Thi s tim e i s gi ven by theexpre ssi on (-ln(Q/Q(0))/K), where Q/Q(0) is in thi s c ase0.0001. EXAMS ’ es ti m at e of decont aminati on tim e i s c om pute d as ( 5)(0.69315)/K, wher e K can be re garde d as a weigh te d whole -sy st em fi rst -order decay const ant
. EXAMS ’ es ti m at e of dis sipat iontim e Td can thus be expande d via

theapproxim at ion:

In t his ins tance, Q/Q(0) = 0. 0001, -ln(Q/Q(0) ) = 9.21, and the time to reduce th e chemical to 0. 01 % of its steady- state valu e is approxi m at ely day s. No te, ho wev er, th at a continu ed first- or derdecay of chemical in the bent hic subsy st em

woul d, at 37 day s (888 hours), result in a resi dualof 100 exp(888 ( ln 0.5 / Hb) ) or 1.4% of the origi nalbenthi c pollutant m ass . Thesy st em -wide76 dis sipat ion of

theche m ic alm ayle ave pocket s of highe r con centr ationin zon es of restricte d ph ysical tran spo rt. Extr apol at ions of EXAMS ’ results beyond the des igne d operating ran ge o f the pr og ram are pr ob ably ill-advised . If n ecess ary, however, a plot

of the r esults of EXAMS ’ dis sipat ion s im ulati on shoul d be used to e valuat e t he propri et

y of a fir st -order ext rapol at ion of

sy st em se lf- purif

ic at ion tim es. Refer enc es for Chap ter2.5. Gear , C . W. 19 71 a. Al gorit hm 407: DIFSUB for soluti on of ordinary diff

ere ntia l e quat ions . C omm unic at ions of t

he ACM 14 :185-190. Gear , C. W . 19 71 b. Th e auto matic in tegr ationof o rd inary diff ere nti alequations . C omm unic at ions of t

he AC M 14 :176-179. Gear , C . W. 1971c. Num eri calIni ti alValue Pro blem s in Ordinary Di ffere nti alEquat ions . Prentic e-Hal l, Engle wood Cl iff s, N. J. Malanchuk , J., J. Otis, an d H. Bouver . 19 80 . Eff icient A lg o rithms fo r So lvin g Syste ms of Or din ary Dif fer ential Equations for E cosy st em Mode ling. EP A-600/3-80-037, U.S. Environm ent alProt ection Age ncy , At hens, Georgi a. Sham pine , L. F., and M. K. Gordon. 1975. Com pute r Solution of Ordi naryDif

fere nti alEquat ion s: TheIni ti alValue Probl em . W.H. Fre em an, San F ranc is co.I t hank Dr. Fri eda B. Taub of theUnive rsi ty

of Washington S choolof Aquati c and Fi shery Sci encefor 3 hermaterial contr ibution s to the d evelo pment of these in troducto ry EXAM S la borat orie s.

EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 77 

## 3. 0 T u t ori al s an d C ase Stud i es 3 

### 3.1 Tutorial 1: Intr oduction to Exposure Analysis with E XA MS 

### – Laboratory 1 I. Fir st com pute r run of EXAMS (t

he ove ral l L ab pl an)
! Foll ow thedir ections in the “La b 1, E xerc is e 1: St eady -St at e Analysi s (Mode 1)”(page 89) t hrough l ine 30. T his wil l introduc e y ou to th e b as ic s o f

runn in g th e p r o g r am.
! Revi ew t

he principle s of running the program in “Mode1” (thedefa

ult m ode, st eady -st at e analysi s).
! Stop and re vie w theinput s, out puts , and int erre lati onships, c om ple te theworkshe et s on pa ges 82 and 83 , and prepare f or La b. 2 by ent eri ng theLab. 1 data

for m et hylparathi on che m is try

and it s be havi or i n thest andar d pond on pa ges 86 and 88. Ia. Run nin g the p ro gr am: Inpu ts EXAMS has “Use r Dat a B ase s”(UD B ) fo r C he mi c a l s, E nv ironm ent s, L oads, and Product s (i .e. , produc ts of t ransf orm at ion proces ses ). E ach ent ry in t he UDB is ac ces sed by i ts num ber, e.g. , C HEM 11. To r un a si m ulati on, y ou m

ust
! R e c a l lan e nv i ro nm e nt ( ENV) ! Rec al l at l eas t oneche m ic al(CHE M) ! Rec al l or

se t a n input LOAD (i .e. , t

he am ount of

pes ti ci de a dded ove r tim e, or an event loa ding f rom spray drift

or runof f). ! Set a MODE (de faul t i s Mode1, s te ady -st at e analysi s) Th e REC AL L c om

m and ( REC ) l oa ds dat af

ro m the UD B i nt o t

he Ac t i vi tyDat aBa se(AD B ), an d c hang e s t he UDB num

be r t o an A DB num ber. For e xam

ple , when you RECALLCHEM11, i ts num ber in the AD

B bec om es CHEM 1. Only one ENVIR can be active at a ny tim e. More than one CHEM can be a ct ive ; t his is es peci al ly

use ful when y ou spe ci fy the gene ration of a transform ationpr oduct, e.g. , produc ti on of 2, 4-D by hydrolysi s of 2,4DBE, thebutoxy et hyles te r of 2, 4-D. In addi ti on to the cont inuous long- te rm

loa ds of Mode 1, you can al so spec ify l oad event s (as dire ct

ini ti alcondi ti ons in Mode 2, or from PRZ M t ransf er fil es in M ode 3) and pi ece -wis e (monthly) cont inuous loa ds. Once you have s peci fie d therequired inform at ion, the RUN c omm and e xecut es a s im ulati on.EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 78 Ib . Run nin g the p ro gr am: Outpu ts EXAMS pr o du ce s at le as t 2 0 ou tp ut tab le s f o r ea c hs i mu l at io n . F o r

co mp le x , mu lt i- ye arstu d ie s th e to ta l o utp ut canrap id lybe co me overwhelm ing. In m ost

ca ses , you wil l want

to examine the ec otoxi col ogic alexposure inform at ion in one or a few t abl es and gra phic s, as you di d in the int

roduct ory tut oria l. Warning: when r eques ting a plot , m ake note of t he varia ble s y ou haveas ked for

and the ir unit s, beca use the graphi c wil l not providet he la bel s. The cont

rol vari abl e “OUTFIL ” is us ed to spec ify whi ch output

f il es are t o be produce d. Thes e m ayinc lude both ecot oxic ologi calexpos ure f il es (EcoT oxC.xm s or EcoToxR .xm s) and order ed s et s of annualm axi m um se rie s of st andar d, or user- spec ifi ed (s ee vari abl e “ EventD”) e xposure event durations (fi le s Ec oRi skC. xm s or EcoRis kR.xm s.) Typ e L I S T H EL P to di sp lay alis t o f th e av ai lab le inp ut an dou tp ut tab le s ( as at lin es 18 an d19 of the fi r stintr o du ct o ry e x er ci se ) . O nso me compu ters, [Sh ift][Pr intSc rn ] will prin t the list.
! Note that T abl e 1 is an echo of t he c hemic alinput

dat a. ! Becau se tran sfo rmation p ro du ct chemistry wa s no t entere d, Table 2 is empty. ! Becau se no puls e load s wer e spec ified(andare in any case irre levan t to steady- state ana lyses) , Tab le 3 is also empty. ! Tab le s 4 thr o u g h13 ar e th e e nv ir o nmen ta l mo d el , a g ai nanec h o of th e inp u td at a a lth o u g hTab le 12 an dTab le 13 co nta inso me infe rred values. You wi llnee d to examine the se ta ble s to seewhat kind of

an envi ronm ent

ENV 2 i s so you c an l abelyour dia gram on page4. T he EXAMS “data dic ti onary ” (pa ges 180 ff.) inc lude s de scripti ons and unit s for the param et ers give n in the ta ble s. ! Tabl e 14 cont ai ns l oad inform at ion. ! Tabl es 15 through 20 are out put r esults
. For re fere nce, you can PRINT ALL to get a pa per copyof

a lltheinput

and output

ta ble s (T abl es 1-20, whi ch m ayin som e inst ance s have seve ralsub-t abl es). Warni ng: T he ou tput f

il e “r epor t.xms” is overwritten each ti me you makean EXAMS run . Once you have c om

ple te d theworkshe et s on pa ges 82 and 83 , y ou m ayret urn t o theint

roduct ory exer ci ses to exp lore Mo de 2 (ini ti al value a pproac hes) and M ode 3 (sea sonaleff ect s).EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 79 

## N am e EX AM S 

## Lab A s s i gnm e nt– I nt r oduc t i on 1. Working f

rom theMode 1 analysi s, m ake a half -p age dia gram

of t he EXAMS pond e nvironm ent (on t he ne xt pa ge). Include t

he co mp artme nts , th ei r

si ze s, nu mb er s, an dtyp es , an dth e g eo metry an dhy dr o lo g y o f th e s ys te m. 2
. W h at i s th e w at e r

s o lub i l i tyo f

m e thy lp ar ath i o n ? 3. What m ass (kg) of

che m ic alis res ide nt in theli tt oralwat er c olum n at st eady st at e? 4. W hat co ncen tration(mg/L orppm) of the che mical is dissolv ed in th e littoral? 5
. W h at i s th e b u l km a s s ( k g ) o f

th e c h e m i c a li nth e b e nth i c s e d i m e nt ? 6
. W h at i s th e an a l yt i c a lc o n c e ntr at i o n( m g /k g dryw e i g ht) i nth e s e d i m e nt ? 7. What is theexpos ure of bent hic organi sm s (i .e. , ppm

dis sol ved in pore wat er)? Do thedif fe rent locationsof

t he chemi cal

and i tsconc ent

ration in thevariousmedia ( water column, bent

hicse dime nts, porewater) make sens e to you? If not, ple ase dis cusswi th y our inst ructor – t hisisan important

part of theex erc is e. 8. O f the p ro cesse s con sider ed, whic h two were resp on sible fo r the g reates t loss of chemical? (1) (2) 9. O f the p ro cesse s con sider ed, whic h two were least resp on sible fo r loss of ch emical? (1) (2) Go back and e xamine t he properties of

theche mic al and t

he e nvironment

and de te rminewhy

the se processes had t

he rel ative import

ance the y did. Give n theproper

ti es of m et

hylparat hion and thepond e nvironm ent , propos e at l eas t t hree ques ti ons t

hat them odelcoul d help you st udy (fo r methyl parath ionora r elated chemical, fo r th e p on d o r a r elated en viro nment) . Fo r example, if the p on d we re more o ligo trop hic w ith le ss num erous bact eri a, what would be t

he s te ady -st at e e xposure?EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 80 

## D i ag ram o f EX AM S 

## ’ C ons t r uc t e d Far m Pond

Your ques ti ons: (1)

(2)

(3)EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 81 

### 3.2 Tutorial 1: Intr oduction to Exposure Analysis with E XA MS 

### – Laboratory 2
EXAMS ’ se cond t

utori al(beginning on page 117) i s a subst ant ia l e xerc is e in as sem bling che m ic aldat a, buil ding a n environm ent al m odel(of t

he l ower ba si n of L ake Zuri ch, Switzerland), va li dat ing t he m odelaga ins t obs erve d dat a and expl oring the dynam ic s of an env iron mental pollu tant. H ere w e will use the firs t part o f that tuto rial (ch emistry of 1 ,4 d ichlo ro ben zene ) to illustr ate chemical data ent ry and ba si c s tudi es of t

he e nvironm ent albehavior of pes ti ci des and ot her organi c c hemic al s. 1. Res tart EXAMS from

theDOS prom

pt. (It is som et im es safe r t o re- st art theprogram

when be ginning a new probl em to ensurethat al l pr evi ous re sul ts aredel et ed.) 2. R evi ew what

you did in Lab1. Notethat t he only r equi red

EXAMS com

m ands were SET M ODE=1 REC ALL C HEM 11 REC AL L ENV 2 SET S TRL( 1,1,13)= .01 SET OUT FIL(1)=Y SET OUT FIL(2)=Y Alltheothe r com

m ands you us ed (e .g., HELP, SHOW, CATALOG C HEMIC AL, e tc .) we re optiona l e ntri es to t eac h you how to use th e p r o g r am. 3. Add anothe r che m ic alto the use r dat abas e (UDB ) and use it in the st andar d pond. Typethefol lowi ng se rie s of comm ands (notethesi m il ari ty to the fi rst

part of t he La ke Zuric h tutoria l). Pre ss t he Ent er ke y a fte r ea ch line. EX A MS ( To re - st art th e p r o g r am) REC CHEM1 (T his ent

ry in t he UDB is an em

pty te m plate for l oadi ng new data .) CHEM NAME IS 1,4-Di chl orobenz ene set mwt(1)= 147.0 changesol (1,1) to 73.8 set kow(1)=2340 set henry (1)=2. 66e-3 cat che m (T o se e how m anyche m ic al s are in theUDB) sto c he m 12 ( As sum i ngy ouhave no C HE M 12 no w) REC ENV2 SET S TRL( 1,1,13)= .01 SET OUT FIL(1)=Y R UN PRINT 15 PRINT 18 PRINT 20 If y our com

pute r does n’t print , usethesc ree n li st ings (LIS T 15, et c.) to s tart fil ling out the ta ble s on pa ges 86 and 88.

4. Modi fy (eut

rophy) the pond t o inc rea se the organi c c arbon c onte nt of these dim ent

(bot h thesuspe nded s edi m ent in the wat er column and the bent

hic se dim ent). SHOW FROC(1,13) (Writ e down what y ou se e) SHOW FROC(2,13) (Writ e down what y ou se e) Look i n the EXAMS User ’s gui de for an expl anation of

theFROC param et er. SET F ROC(1, 13)=0.4 SET F ROC(2, 13)=0.4EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 82

SHOW FROC(1,13) (Writ e down what y ou se e) SHOW FROC(2,13) (Writ e down what y ou se e) SH OW CHEM (Che ck tha t the valu es youadd ed fo r the ch emical are there ; EXAMS m ayhaveadde d addi ti onalproper ti es base d on it s unde rst andi ng of pe st ic ide che m is try . If so, y ou can use theHELP function to gain an underst andi ng of t hesenew va lue s. SHOW LOAD (Chec k to seethat t he l oad i s what

you expec t i t to be. ) R UN LIST 15 (Fi llin som e of the ta ble dat a on pages 86 and 88) LIST 6 LIST 1 LIST 18 LIST 20 EN V N AME IS Hyp er- eutr op hic Po nd(Yo u are naming an d will sto re this en viro nment) CAT ENV (To s ee how m anyyou have) STOR ENV 6 (As suming y ou have5) CAT ENV (To m ake sure it took) 5. Det ermine how t

he first che m ic al(m et

hylparathi on) woul d behave in thehype r-eut rophic pond. REC CHEM11 REC ENV6 SET S TRL( 1,1,13)= .01 R UN LIST 15 (Writ e y our ans wers on theTabl es) LIST 6 LIST 1 LIST 18 LIST 20EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 83 

## N am e
1. C om pare theche m ic alproper

ti es of m et

hylparathi on and p-DCB. Provi de num ber and unit s. a. In what ta ble arethe se vari abl es found? b. Where are theunit s l is te d? c. Fil l in theta

ble . If nece ssary, use EXAMS ’ “he lp” functio ns to gen erate a co nsis tent da ta set. Chemic alPrope rty Unit s Met hylPar at hion 1,4-Di chl orobenz ene Mol ecul ar Wei ght So lub ility

ow K (n-Oct anol :wate r solubil it y r at io) Henry ’s L aw C onst ant KBACW KBACS If a v alue h as no t beenentere d orcalculatedby EXAMS , t he EXAMS ta

ble ent ry is bla nk and it s va lue is ze ro. d. Li st them ajor di ffere nces bet ween the se chemic al s t

hat aff ect the ir fat e and expos ure. I.

II.

III.

2. C om pare thest andar d and the hype r-eut rophic ponds. a. Defi ne FROC ( , ) uni ts Vari abl e Standard P ond Hyper -Eut rophic Pond FROC (1,13) FROC (2,13)EXAMS L ab o r at o ryE x e r c i s e s . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 84 3. C om pare thedis tributi on and transform at ion of thetwo chemic al s in thetwo envi ronm ent s.
Var iable EXAMS

Tabl e No. Met hylPar at hion 1,4-DCB Std. Pond Eutr pond Std. Pond Eutr pond % inwa te r

co lumn Kg in watercol. % i n bent hic zone Kg in bent

hic zone Tota l m ass (Kg) Conc in pl ankt on (μg/g) Conc in be nthos (μg/g) Flux (%l oad) f

rom Bac te riopl ankt on
Water- borne e xport Volati li zation
Pers is te nce: tim e t o 95% dis sipat ion 4. Using thenum

bers you f

il le d in above, expl ai n why inc rea si ng theorgani c c arbon c onte nt of thesuspe nded and bed sedi m ent had a m ajor im pact on 1,4- DCB, but not on m et hylparathi on. Is thi s re al is ti c? If you t hink not , re -run t

he analysi s and revi se your conclusi ons.

5. Which of t

heseche m ic al s woul d havea diff ere nt e nvironm ent alfat e and expos ure i f t he num bers of bac te ria

in the wat er c olum

n or ben thic zo ne w ere ch ang ed. W hy?E X A M S I ntr o du c t o ryL ab o r at o ry( M o d e 1 )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 85 

### 3.3 Command Sequences for Tutorial 1, Lab. 1 3.3.1 Lab. 1, Exercise 1: Steady-State Analysi s (Mode 1) Intr oduct ion to EXAMS. Exec ute thefol lowi ng com m ands at the EXAMS pro mpt. The o bj ect of th e exer cises is to g ain a ba sic famil iarit y wi th t he EXAMS com

m and inte rfac e. 1 HELP 2 HELP HE LP 3 HELP USE R 4 HELP P AGES 5 SHOW VAR 6 HELP M ODE 7 SET M ODE t o 1 8 CATALOG C HEMIC AL 9 CATALOG ENVIRONMENT 10 CAT 11 LO 12 HELP RECALL 13 REC CHEM11 14 REC ALL ENV 2 15 HE LP L OA D 16 SH OW L OA D 17 SET S TRL( 1,1,13)= .01 18 SE T OU TF IL (1 )=Y 19 SE T OU TF IL (2 )=Y 20 R

UN 21 LIST 22 HELP 23 20 24 LIST 18 25 LIST 15 26 HELP P LOT 27 PLOT 28 KI 29 PL 30 3 31 6 32 0 33 0E X A M S I ntr o du c t o ryL ab o r at o ry( M o d e 2 )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 86



### 3. 3. 2 L ab. 1 , E

xerci se 2 : Mo de2 A na lys is o

f In iti al V alu e P ro blems –

Si xty Da y R Un Ti me
1 REC CHEM11 2 REC ENV 2 3 SET S TRLD( 1,1,13)= 0.01 4 SET M ODE=2 5 SHOW TI FR 6 HELP T CODE 7 SET T CODE=2 8 SET T END=60 9 SET C INT=1 10 SHOW TI FR 11 SE T OU TF IL (1 )=Y 12 SE T OU TF IL (2 )=Y 13 R

UN 14 PLOT KI PL 15 3 16 6 17 0 18 0 19 SH OW L OA D 20 ZE R O L OA D 21 SH OW L OA D 22 SET I CHEM( 1)=1 23 SET I SEG(1)= 1 24 SET I MASS(1)= .1 25 SH O P U 26 SET T END=14 27 R

UN 28 PL KI PL 29 3 30 6 31 0 32 0 33 CONTINUE 34 28E X A M S I ntr o du c t o ryL ab o r at o ry( M o d e 2 )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 87 35 CONTINUE 36 60 37 PL KI PL 38 3 39 6 40 0 41 0 42 PL KI PL 43 6 44 0 45 0E X A M S I ntr o du c t o ryL ab o r at o ry( M o d e 3 )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 88 

### 3. 3. 3 L ab. 1 , E

xerci se 3 : T ime-va ryi ng seaso na l an aly

sisus in g M od e 3

1 REC CHEM11 2 SET M ODE=3 3 REC ENV 2 4 SET I CHEM( 1)=1 5 SET I SEG(1)= 1 6 SET I MASS(1)= .1 7 SET I MON(1)=5 8 SET I DAY(1)=15 9 SET I CHEM( 2)=1 10 SET I CHEM( 3)=1 11 SET I SEG(2)= 1 12 SET I SEG(3)= 1 13 SET I MASS(2)= .1 14 SET I MASS(3)= .1 15 SET I MON(2)=6 16 SET I MON(3)=6 17 SET I DAY(2)=1 18 SET I DAY(3)=15 19 SH O P U L O 20 SE T OU TF IL (1 )=Y 21 SE T OU TF IL (2 )=Y 22 R

UN 23 PL KI PL 24 3 25 6 26 0 27 0 28 PL KI PL 29 3 30 0 31 0 32 CONTINUE 33 PLOT KI PL 34 3 35 0E X A M S I ntr o du c t o ryL ab o r at o ry( M o d e 3 )
. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 89 36 0 37 LIST 20 38 Y 39 QUITIntroduction to EXA MS . ................................... Page 90 

### 3.4 Introduction to E XA MS 

### – L ab . 1 Ex erc ise s with C omp let e E XA MS 

### Re sp on ses These t hr ee exer ci se s i l l ust r at e t he E X A M S co m m an d l i n e interfac e, da t a e n t ry, an d op era t i o n s “m o d es .” T h e c o m m an d s in t h e su m m ary l i st i ngs ar e gi ven he r e i n BO LD/ IT A L IC . N o te th a t E X A M S s t ar t s i n M ode 1 w hen i t i s i ni t i al l y i nvoked, i
. e. , t he de f aul t “ M ode” i s 1. 

### 3.4.1 Lab. 1, Exercise 1: Steady-State Analysi s (Mode 1) To begi n, att he D O S pr om pt , ent er C:> EXAMS Welcome to EXAMS Release <current release number> Exposure Analysis Modeling System Technical Contact: Lawrence A. Burns, Ph.D. U.S. Environmental Protection Agency 960 College Station Road Athens, GA 30605-2700 USA Phone: (706) 355-8119 (Fax) 355-8104 Internet: burns.lawrence@epa.gov Latest Maintenance <da te of lat est ma int ena nce > Type HELP and press the RETURN key for command names, HELP USER for a summary of command functions, HELP PAGES for a list of information pages, or HELP EXAMS for introductory information. Please stand by while EXAMS checks the computational precision of this computer and initializes the Activity Data Base.

EXAMS-> HELP EXAMS includes these system commands: AUDIT CATALOG CHANGE CONTINUE DESCRIBE DO (@) ERASE HELP LIST NAME PASSWORD PLOT PRINT QUIT READ RECALL RUN SET SHOW (?) STORE WRITE ZERO Help pages describe the commands and additional topics: ADB, COMMAND, EXAMS, INPUTS, LOADS, LODNAM, NEWDAT, TABLE, TABNUM, TUTOR, UDB, USER, WILD Text describing the commands, and the text of the additional topics, can be seen by entering HELP <topic>, where <topic> is either a command, one of the additional topics above, or the name of one of EXAMS' input data parameters. USER gives a summary list of EXAMS' command functions. PAGES gives an annotated list of EXAMS' information pages. TUTOR is an introduction to using the HELP facility. TABNUM describes EXAMS’ table numbering scheme.

EXAMS-> HELP HELP The HELP command invokes EXAMS' HELP facility to displayIntroduction to EXA MS . ................................... Page 91

information about a particular EXAMS topic. For a tutorial explanation of the HELP command, now type HELP TUTOR and press the RETURN key. For more detail on the available information, now type HELP USER or HELP PAGES and press the RETURN key. Related topics: DESCRIBE Syntax: HELP [command], or [EXAMS parameter] HELP is also available from the interior of most EXAMS commands. A list of the "parameters" available through HELP can be invoked by typing "SHOW VAR". HELP provides definitions and dimensions of all these input data and control variables.

EXAMS-> HELP USER Command Summary Description =========== ================================================ AUDIT Start/Stop user notepad for recording procedures CATALOG List the contents of User Databases (UDBs) CHANGE/SET Enter/reset input data and program controls CONTINUE Resume integration (Modes 2 and 3 only) DESCRIBE Report dimensions and data type of parameter DO Execute file of EXAMS commands (file.EXA) ERASE Clear section of stored database (UDB) HELP Describes access to EXAMS on-line HELP facility LIST Show tabular results on the screen NAME Specify the name of a UDB, e.g., CHE NAME IS ... PASSWORD Restrict Recall/Store access to UDB datasets PLOT Plot results on the screen PRINT Queue tabular results for hardcopy printing QUIT Abort command, or End interactive session READ/WRITE Upload/download data from non-EXAMS disk files RECALL Activate data from stored database (UDB) RUN Begin simulation run SHOW Display current data values or control settings STORE Download current data into stored database (UDB) ZERO Clear loadings, pulses, or current concentration EXAMS-> HELP PAGES ADB defines the term "activity database" COMMAND tells how to use EXAMS' system commands EXAMS describes the scope and operation of the program INPUTS describes EXAMS input data and data manipulation LOADS explains how to specify chemical loads on the ecosystem LODNAM gives EXAMS' special names for the chemical loadings NEWDAT tells how to begin entry of a new dataset HELP gives more explanation of the HELP facility TABLE explains why your initial outputs seem to disappear TABNUM explains the numbering system used for EXAMS' outputs TUTOR introduces EXAMS' HELP utility UDB defines the term "user database" USER gives a general command summary. WILD describes the use of wild cards in SET/CHANGE commands Enter HELP and the name of a topic for further information. EXAMS-> SHOW VARIntroduction to EXA MS . ................................... Page 92

CHEMNA ECONAM LOADNM PRODNM TYPE AIRTY FIXFIL IUNIT MCHEM KCHEM MODE PRSW MONTH NYEAR YEAR1 TCODE CINT TEND TINIT ABSER RELER SPFLG MWT SOL ESOL PK EPK KOC KOW KPB KPDOC KPS KIEC MP HENRY EHEN VAPR EVPR QYield KDP RFLAT ABSOR LAMAX KAH EAH KNH ENH KBH EBH KOX EOX K1O2 EK1O2 KRED ERED KBACW QTBAW KBACS QTBAS KOUNT JFRAD ITOAD ADVPR JTURB ITURB XSTUR CHARL DSP SUSED BULKD FROC CEC AEC PCTWA TCEL PH POH OXRAD REDAG BACPL BNBAC PLMAS BNMAS KO2 DOC CHL CLOUD DFAC DISO2 OZONE VOL AREA DEPTH XSA LENG WIDTH RAIN EVAP LAT LONG WIND ELEV RHUM ATURB STFLO STSED NPSFL NPSED SEEPS STRLD NPSLD PCPLD DRFLD PRBEN SEELD IMASS ISEG ICHEM IMON IDAY IYEAR SPRAY CHPAR TPROD NPROC RFORM YIELD EAYLD EXAMS-> HELP MODE MODE is an integer scalar. MODE sets the operating "mode" of EXAMS. Three operating modes are available; these are selected by SETting MODE to 1, 2, or 3. MODE Operational characteristics of EXAMS
---- --------------------------------------------------- 1 Long-term (steady-state) analysis. 2 Pulse analysis--specifiable initial chemical mass (IMASS) and time frame, time-invariant environment. 3 Monthly environmental data, daily pulse loads IMASS and monthly chemical loadings of other types. EXAMS-> SET MODE to 1 EXAMS-> CATALOG CHEMICAL UDB # Name of Chemistry Dataset ===== ================================================== 1 Chemical Data Entry Template 2 p-Cresol [CAS# 106-44-5] 3 Benz[a]anthracene [CAS# 56-55-3] 4 Benzo[a]pyrene [CAS# 50-32-8] 5 Quinoline [CAS# 91-22-5] 6 Benzo[f]quinoline [CAS# 85-02-9] 7 9H-Carbazole [CAS# 86-74-8] 8 7H-Dibenzo[c,g]carbazole [CAS# 194-59-2] 9 Benzo[b]thiophene [CAS# 95-15-8] 10 Dibenzothiophene [CAS# 132-65-0] 11 Methyl Parathion [CAS# 298-00-0] 12 Mirex [CAS# 2385-85-5] 13 Heptachlor [CAS# 76-44-8]

EXAMS-> CATALOG ENVIRONMENT UDB # Name of Environmental Dataset ===== ================================================== 1 Environmental Data Entry Template 2 Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) 3 Georgia OPP Farm Pond (MLRA P136, WBAN 13873) 4 Mississippi OPP Farm Pond (MLRA P134, WBAN 03940) 5 Index Reservoir, IL (MLRA M115, WBAN 13994) 6 Lake Zurich (Untersee), Switzerland: annual meansIntroduction to EXA MS . ................................... Page 93

EXAMS-> CAT Enter Environment, Chemical, Load, Product, Help, or Quit-> LO Catalog of Chemical LOADings UDB No. Name of Entry Volume ======= ======================= 1 Load Data Entry Template 2 Test input loadings for Exams <version number>

EXAMS-> HELP RECALL RECALL transfers data from permanent storage (UDB) to activity databases (ADB). The data to be used by EXAMS for an analysis are held in a foreground memory bank or ADB (activity database). When EXAMS is started, the ADB is empty. Use the RECALL command to transfer data from the User Databases (UDBs) to foreground memory (ADB). Be sure to STORE all new data before you QUIT from EXAMS: the ADB is discarded at the end of each session!! =========================================== Related topics: CATALOG, ERASE, NAME, STORE Syntax: RECALL <datatype> <UDB#> [AS ADB#] where <datatype> can be CHEM, ENV, LOAD, or PRODUCT EXAMS uses these four kinds of datasets: 1. CHEMICAL reactivity and partitioning (up to MCHEM sectors), 2. ENVIRONMENTal physical and chemical parameters, 3. allochthonous chemical LOADings, and 4. PRODUCT chemistry for generating interconversions among multiple chemicals in an analysis. For more information: ADB, AS, UDB EXAMS-> REC CHEM 11 Selected compound is "Methyl Parathion [CAS# 298-00-0]" EXAMS-> RECALL ENV 2 Selected environment is "Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136)" EXAMS-> HELP LOAD Enter allochthonous loadings of synthetic chemicals either as instantaneous pulses, or as stable (or average) values that persist for at least one month. SHOW PULSE displays pulsed loadings; SHOW LOADS displays the steady loadings. Steady loadings are entered by specifying the type of load (STRLD, etc.), the segment, ADB number of the chemical, month of the loading, and the mass loading (kg/hour). For example, command: EXAMS-> SET STRLD(1,2,8) TO 0.01 sets an August load of 0.01 kg/h of chemical #2 on segment #1. Pulse loads are entered by "event number." Each event includes the ADB # of the chemical, the month and day of the event, the target segment, and the mass (kg) of the pulse. If, during a RUN, a loading violates assumptions of the modelIntroduction to EXA MS . ................................... Page 94

(e.g., by super-saturating an incoming flow), or is found to be impossible (e.g., a PCPLD to a (B)enthic segment), the load is reduced or deleted. The corrected loadings are stored in the LOADS matrix and returned to the user, i.e., the unusable loadings are discarded and the new values are substituted.

EXAMS-> SHOW LOAD Name of environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Total number of segments (KOUNT) = 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 1 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: 1) Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Mean of year 2000: allochthonous chemical loads (kg/hr).

--------------------------------------------------------------- Load data-- Seg Streams Rainfall Seeps NPS Loads Drift
--- --------- --------- --------- --------- --------- 1 2 3 4 5 6

--------------------------------------------------------------- EXAMS-> SET STRL(1,1,13)=.01 Command processing complete; ready for input. EXAMS-> SET OUTFIL(1)=Y Command processing complete; ready for input. EXAMS-> SET OUTFIL(2)=Y Command processing complete; ready for input. EXAMS-> RUN Simulation beginning for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] RUN command completed. EXAMS-> LIST At the prompt, enter a Table number, "Quit," or "Help" to see a catalog of the output tables. Enter Table Number -> HELP 1 Chemical inputs: FATE Data 2 Chemical inputs: PRODUCT Chemistry 3 PULSE Chemical Loadings 4 Environmental Input Data: BIOLOGICAL ParametersIntroduction to EXA MS . ................................... Page 95 5 Environmental Input Data: HYDROLOGIC Parameters 6 Environmental Input Data: SEDIMENT Properties 7 Environmental Input Data: PHYSICAL GEOMETRY 8 MISCellaneous Environmental Input Data: Wind, D.O., etc. 9 Input specifications: ADVECTIVE transport field 10 Input specifications: DISPERSIVE transport field 11 Environmental Input Data: GLOBAL site parameters 12 KINETIC PROFILE of Synthetic Chemical 13 Chemical REACTIVITY PROFILE of Ecosystem 14 Allochthonous Chemical LOADS and Pulses 15 DISTRIBUTION of Chemical in Environment 16 Chemical SPECIATION of Dissolved Concentrations 17 Chemical Concentration MEANS, Maxima, and Minima 18 Sensitivity Analysis of Chemical FATE 19 Summary TIME-TRACE of Chemical Concentrations 20 Exposure Analysis SUMMARY ALL Entire Report At the prompt, enter a Table number, "Quit," or "Help" to see a catalog of the output tables. Enter Table Number -> 20 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Table 20.01. Exposure analysis summary.

--------------------------------------------------------------- Exposure (maximum steady-state concentrations): Water column: 7.393E-02 mg/L dissolved; total = 7.405E-02 mg/L Benthic sediments: 6.586E-02 mg/L dissolved in pore water; maximum total concentration = 3.32 mg/kg (dry weight). Biota (ug/g dry weight): Plankton: 27. Benthos: 24. Fate: Total steady-state accumulation: 2.44 kg, with 62.72% in the water column and 37.28% in the benthic sediments. Total chemical load: 0.24 kg/ day. Disposition: 2.30% chemically transformed, 81.86% biotransformed, 0.06% volatilized, and 15.78% exported via other pathways. Persistence: After 12.0 days of recovery time, the water column had lost 85.24% of its initial chemical burden; the benthic zone had lost 29.47%; system-wide total loss of chemical = 64.4%. Five half-lives (>95% cleanup) thus require ca. 58. days. EXAMS-> LIST 18Introduction to EXA MS . ................................... Page 96

Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Table 18.01. Analysis of steady-state fate of organic chemical.

--------------------------------------------------------------- Steady-state Values Mass Flux % of Load Half-Life* by Process Kg/ day days
--------------------- ---------- --------- ---------- Hydrolysis 4.0378E-03 1.68 418.6 Reduction Radical oxidation Direct photolysis 1.4853E-03 0.62 1138. Singlet oxygen oxidation Bacterioplankton 0.1686 70.23 10.03 Benthic Bacteria 2.7911E-02 11.63 60.56 Surface Water-borne Export 3.7872E-02 15.78 44.63 Seepage export Volatilization 1.3355E-04 0.06 1.2656E+04

--------------------------------------------------------------- Chemical Mass Balance: Sum of fluxes = 0.2400 Sum of loadings = 0.2400 Allochthonous load: 100.0 Autochthonous load: 0.0 Residual Accumulation = 0.0 0.0

--------------------------------------------------------------- * Pseudo-first-order estimates based on flux/resident mass. EXAMS-> LIST 15 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.

--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 1.5 96.84 7.405E-02 7.393E-02 3.70 27.5 3 1.07E-02 0.70 7.152E-02 7.140E-02 3.57 26.5 5 3.76E-02 2.46 6.263E-02 6.253E-02 3.13 23.2 ======== ====== 1.5 62.72 and in the Benthic Sediments: 2 0.61 66.71 0.898 1.783E-02 0.892 6.62 4 6.72E-02 7.39 3.32 6.586E-02 3.29 24.5 6 0.24 25.90 2.91 5.768E-02 2.88 21.4 ======== ====== 0.91 37.28 Total Mass (kilograms) = 2.438

--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics. EXAMS-> HELP PLOT Use the PLOT command to display results of the current analysis. Three kinds of PLOTs are available on-line from EXAMS: POINT, PROFILE, and KINETIC. Each PLOT requires the specification ofIntroduction to EXA MS . ................................... Page 97

several options; these can either be entered on the system command line or entered in response to EXAMS' prompts. You can enter HELP in response to any of these prompts; EXAMS will then describe the available options. Related topics: LIST, PRINT Syntax: PLOT <option1 option2 option3> For more information on option1: type HELP POINT, HELP PROFILE, or HELP KINETIC HELP for options 2 and 3 is available inside the PLOT command. EXAMS-> PLOT The following options are available: POint - Vertical concentration profile PRofile - Longitudinal concentration profile Kinetic - List or plot kinetic outputs Help - This message Quit - Return to the EXAMS program prompt Option-> KI The following KINETIC options are available: List - lists selected KINETIC output parameters Plot - plots selected KINETIC output parameters Help - this message Quit - return to the EXAMS prompt Option-> PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B

The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 6Introduction to EXA MS . ................................... Page 98

Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 1.53 I* I I * I I * 1.02 I I+ + + + I + + + + I * + + + + I * + 0.510 I * I * I * * * I * I 0.00 I +----+----+----+----+----+----+----+----+----+----+ 0.00 2.40 4.80 7.20 9.60 12.0 1.20 3.60 6.00 8.40 10.8 Time, DaysIntroduction to EXA MS . ................................... Page 99 

### 3. 4. 2 L ab. 1 , E

xerci se 2 : E X A MS

### in Mo de2 U si ng E X A M S t o s ol ve i ni t i al val ue pr obl em s. M ode 2 c an be us ed t o s t udy det ai l s of expos ur e dur i ng br i ef

( 60 days i n t he e xam pl e) per i ods, or t hr ough a s er i es of epi sodi c c ont am i nant r el eas es . I f you have not cont i nued on di r ect l y f r om Exer ci se 1, af

t er s t ar t i ng EX A M S you s houl d f

i r sti ss ue t he c om m ands t o “ R E C A L L C H E M 11 ” (m e th y l p a ra th io n ), “ RE C E NV 2 ” , “ S ET S TRLD ( 1, 1, 13) =0. 01 ”, “ S ET O U T F IL (1)= Y ” , S E T O U T F IL (2)= Y ” , and “ RUN ” t o begi n t hi s exer ci se . EXAMS-> SET MODE=2 Command processing complete; ready for input. EXAMS-> SHOW TI FR A RUN will integrate from 0 to 1 Days with output at intervals of 1 Days. CINT = 1, TINIT = 0 TEND = 1, TCODE = 2 EXAMS-> HELP TCODE TCODE is an integer scalar. The value of Time_CODE sets the units of TINIT, TEND, and CINT SET TCODE to 1 (hours), 2 (days), 3 (months), or 4 (years). TCODE is under full user control only in Mode 2. In mode 2 TCODE controls the time frame of the study: e.g., given TINIT=0, TEND= 24, and CINT=2; CHANge TCODE from 1 to 3 to convert a 0-24 hour study into 0-24 months (bimonthly reports). In mode 1, EXAMSselects the units for reporting results from the probable halflife of the study chemical(s). In mode 3, a RUN encompasses one year or longer, and the timing is set to produce standard output EXAMS-> SET TCODE=2 Command processing complete; ready for input. EXAMS-> SET TEND=60 Command processing complete; ready for input. EXAMS-> SET CINT=1 Command processing complete; ready for input. EXAMS-> SHOW TI FR A RUN will integrate from 0 to 60 Days with output at intervals of 1 Days. CINT = 1, TINIT = 0 TEND = 60, TCODE = 2 EXAMS-> RUN Simulation beginning for: Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) RUN command completed. EXAMS-> PLOT KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L BIntroduction to EXA MS . ................................... Page 100

The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 6 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 1.52 I ******************************* I ******* I *** I ** I * 1.02 I * I * I * +++++++++++++++ I * ++++++++ I * ++++++ 0.508 I +++++ I * ++++ I ++++ I * ++ I ++++ 0.00 I++++ +----+----+----+----+----+----+----+----+----+----+ 0.00 12.0 24.0 36.0 48.0 60.0 6.00 18.0 30.0 42.0 54.0 Time, DaysIntroduction to EXA MS . ................................... Page 101

EXAMS-> SHOW LOAD Name of environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Total number of segments (KOUNT) = 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 2 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: 1) Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Mean of year 2000: allochthonous chemical loads (kg/hr).

--------------------------------------------------------------- Load data-- Seg Streams Rainfall Seeps NPS Loads Drift
--- --------- --------- --------- --------- --------- 1 1.000E-02 2 3 4 5 6

--------------------------------------------------------------- EXAMS-> ZERO LOAD All allochthonous loads removed. EXAMS-> SHOW LOAD Name of environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Total number of segments (KOUNT) = 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 2 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: 1) Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Mean of year 2000: allochthonous chemical loads (kg/hr).

--------------------------------------------------------------- Load data-- Seg Streams Rainfall Seeps NPS Loads Drift
--- --------- --------- --------- --------- --------- 1 2 3 4 5 6

--------------------------------------------------------------- EXAMS-> SET ICHEM(1)=1 Command processing complete; ready for input. EXAMS-> SET ISEG(1)=1 Command processing complete; ready for input. EXAMS-> SET IMASS(1)=.1 Command processing complete; ready for input.Introduction to EXA MS . ................................... Page 102

EXAMS-> SHO PU Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 2 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: 1) Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Table 3. Chemical input data: pulse loadings.*

--------------------------------------------------------------- Load Entry-- ICHEM-ADB# 1 ISEGment 1 IMASS (kg) 0.100 Event Number 1

--------------------------------------------------------------- * N.B.: Input data only; may be revised during simulation. EXAMS-> SET TEND=14 Command processing complete; ready for input. EXAMS-> RUN Simulation beginning for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] RUN command completed. EXAMS-> PL KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 6 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0Introduction to EXA MS . ................................... Page 103

System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 0.100 I* I I * I I * 6.667E-02 I I * I * I * I * 3.333E-02 I * I * I * * * I + + + + + + + + + I + + + + 0.00 I+ + +----+----+----+----+----+----+----+----+----+----+ 0.00 2.80 5.60 8.40 11.2 14.0 1.40 4.20 7.00 9.80 12.6 Time, Days EXAMS-> CONTINUE Initial time for integration will be 14 Days Enter ending time of integration, Help, or Quit-> 28 Simulation continuing for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] CONTINUE command completed. EXAMS-> CONTINUE Initial time for integration will be 28.0 Days Enter ending time of integration, Help, or Quit-> 60 Simulation continuing for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] CONTINUE command completed. EXAMS-> PL KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg)Introduction to EXA MS . ................................... Page 104

Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 6 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0

System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 0.112 I * * I I* * * I * I * * 7.467E-02 I * I * * I * * * I * * * I * * * 3.733E-02 I * * * I ** * ** I * +++++ ++++++++++++++ I +++* ++++ ++ *** ++++++++++ I ++++++ ++ ******* +++ 0.00 I++ ******** +----+----+----+----+----+----+----+----+----+----+ 0.00 12.0 24.0 36.0 48.0 60.0 6.00 18.0 30.0 42.0 54.0 Time, Days EXAMS-> PL KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space: No tice ho w the pu lse is rep eate d on e ach “c onti nue” if it is not e xpli citly rem oved.Introduction to EXA MS . ................................... Page 105

1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 6 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 2.395E-02 I ***** I * ** I * ** I ****** * *** I * ** ** 1.597E-02 I * ** I * ** I * ** I ******* *** I ** *** 7.983E-03 I * I * I * I * I 0.00 I* +----+----+----+----+----+----+----+----+----+----+ 0.00 12.0 24.0 36.0 48.0 60.0 6.00 18.0 30.0 42.0 54.0 Time, DaysIntroduction to EXA MS . ................................... Page 106 

### 3. 4. 3 L ab. 1 , E

xerci se 3 : E X A MS

### in Mo de3 M ode 3 i s use d f

or expos ur e ove r a mi ni m um per i od of one ye ar , w i t h m ont hl y updat es of t he pr oper t i es of

t he e nvi r onm ent
. I t ca n be use d w i t h PR ZM t o exa m i ne t he e xposur e pa t t er n ar i si ng f r om us e of

a pe st i ci de ove r m any ye ar s. I n t hi s exer ci se t he l oad i s ent er ed m anual l y t o i l l ust r at e t he s t r uct ur e of t he da t a.

EXAMS-> REC CHEM 11 Selected compound is Methyl Parathion [CAS# 298-00-0] EXAMS-> SET MODE=3 Command processing complete; ready for input. EXAMS-> REC ENV 2 Selected environment is "Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136)" EXAMS-> SET OUTFIL(1)=Y Command processing complete; ready for input. EXAMS-> SET OUTFIL(2)=Y Command processing complete; ready for input. EXAMS-> SET ICHEM(1)=1 Command processing complete; ready for input. EXAMS-> SET ISEG(1)=1 Command processing complete; ready for input. EXAMS-> SET IMASS(1)=.1 Command processing complete; ready for input. EXAMS-> SET IMON(1)=5 Command processing complete; ready for input. EXAMS-> SET IDAY(1)=15 Command processing complete; ready for input. EXAMS-> SET ICHEM(2)=1 Command processing complete; ready for input. EXAMS-> SET ICHEM(3)=1 Command processing complete; ready for input. EXAMS-> SET ISEG(2)=1 Command processing complete; ready for input. EXAMS-> SET ISEG(3)=1 Command processing complete; ready for input. EXAMS-> SET IMASS(2)=.1 Command processing complete; ready for input. EXAMS-> SET IMASS(3)=.1 Command processing complete; ready for input. EXAMS-> SET IMON(2)=6Introduction to EXA MS . ................................... Page 107

Command processing complete; ready for input. EXAMS-> SET IMON(3)= 6 Command processing complete; ready for input. EXAMS-> SET IDAY(2)=1 Command processing complete; ready for input. EXAMS-> SET IDAY(3)=15 Command processing complete; ready for input. EXAMS-> SHO PU LO Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 3 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: 1) Methyl Parathion [CAS# 298-00-0]

--------------------------------------------------------------- Table 3. Chemical input data: pulse loadings.*

--------------------------------------------------------------- Load Entry-- IMONth 5 6 6 IDAY 15 1 15 ICHEM-ADB# 1 1 1 ISEGment 1 1 1 IMASS (kg) 0.100 0.100 0.100 Event Number 1 2 3

--------------------------------------------------------------- * N.B.: Input data only; may be revised during simulation. EXAMS-> RUN Simulation beginning for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] RUN command completed. EXAMS-> PL KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed.Introduction to EXA MS . ................................... Page 108

Parameter-> 3 Parameter-> 6 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 0.111 I * I * * I * I * * I * 7.384E-02 I * * I * * I * * I * * * I * * * 3.692E-02 I * * * I ** * * I * *+++ I *+++*++ I +++ * *++++ 0.00 I++++++++++++++++++++ ****+++++++++++++++++++++ +----+----+----+----+----+----+----+----+----+----+ 0.00 73.2 146. 220. 293. 366. 36.6 110. 183. 256. 329. Time, Days EXAMS-> PL KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space: 1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line;Introduction to EXA MS . ................................... Page 109

enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 0.111 I * I * * I * I * * I * 7.384E-02 I * * I * * I * * I * * * I * * * 3.692E-02 I * * * I ** * * I * * * I * **** I ** * ** 0.00 I******************* ************************* +----+----+----+----+----+----+----+----+----+----+ 0.00 73.2 146. 220. 293. 366. 36.6 110. 183. 256. 329. Time, Days EXAMS-> CONTINUE CONTinuing integration through 31 December 2001. Simulation continuing for: Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical 1: Methyl Parathion [CAS# 298-00-0] CONTINUE command completed. EXAMS-> PLOT KI PL Chemical: Methyl Parathion [CAS# 298-00-0] Environment: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Simulation units: Days Number of segments: 6 Segment Number: 1 2 3 4 5 6 Segment "TYPE": L B L B L B The following parameters are available for time-trace plotting of values averaged over the ecosystem space:Introduction to EXA MS . ................................... Page 110

1 - Water Column: average dissolved (mg/L) 2 - average sorbed (mg/kg) 3 - total mass (kg) 4 - Benthic: average dissolved (mg/L) 5 average sorbed (mg/kg) 6 total mass (kg) Enter parameters, one per line; enter "0" to end data entry and proceed. Parameter-> 3 Parameter-> 0 The following parameters are available for each segment: 1 - Total concentration (Water Column, mg/L; benthic, mg/kg) 2 - Dissolved (mg/liter of fluid volume) 3 - Sorbed (mg/kg of sediment) 4 - Biosorbed (ug/g) 5 - Mass (grams/square meter of AREA) Enter segment-parameter number pair, one number per line; enter 0 when data entry is complete; or Quit to cancel. Enter segment number---> 0 System: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] 0.111 I * * I ** ** I * * I ** ** I * * 7.384E-02 I * * ** I ** ** I * * * * I *** * ** I *** *** 3.692E-02 I *** *** I *** *** I *** *** I *** *** I   ** ** 0.00 I********** ********************** ************* +----+----+----+----+----+----+----+----+----+----+ 0.00 146. 292. 439. 585. 731. 73.1 219. 366. 512. 658. Time, Days

EXAMS-> LIST 20Introduction to EXA MS . ................................... Page 111

Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 3 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] Table 20.01. Exposure analysis summary: Maximum Events of 2000.

----------------------------------------------------------------------------- Event Duration 96-hour 21-day 60-day 90-day 2000 ==============----==== --------- --------- --------- --------- --------- ***** Ecotoxicological Direct Exposure Concentrations ****** Water Column Min. 2.781E-03 5.128E-04 7.040E-05 7.664E-06 0.00 dissolved mg/L Mean 3.995E-03 2.423E-03 1.487E-03 9.994E-04 2.581E-04 Peak 5.505E-03 5.505E-03 5.505E-03 5.505E-03 5.505E-03 Benthic Sediment Min. 1.617E-03 1.165E-03 5.834E-04 1.578E-04 0.00 mg/L dissolved Mean 1.640E-03 1.446E-03 1.108E-03 8.522E-04 7.716E-05 in pore water Peak 1.650E-03 1.650E-03 1.650E-03 1.650E-03 1.650E-03 ***** Ecotoxicological Trophic Exposure Concentrations ***** Water Column Min. 1.03 0.191 2.615E-02 2.847E-03 0.00 ug/g dry weight Mean 1.48 0.900 0.552 0.371 9.588E-02 of plankton Peak 2.04 2.04 2.04 2.04 2.04 Benthic Sediment Min. 0.601 0.433 0.217 5.864E-02 0.00 ug/g dry weight Mean 0.609 0.537 0.411 0.317 2.867E-02 of benthos Peak 0.613 0.613 0.613 0.613 0.613 ***** Total Media Concentrations *************************** Water Column Min. 2.785E-03 5.137E-04 7.051E-05 7.677E-06 0.00 total mg/L Mean 4.002E-03 2.427E-03 1.489E-03 1.001E-03 2.585E-04 Peak 5.514E-03 5.514E-03 5.514E-03 5.514E-03 5.514E-03 Benthic Sediment Min. 8.145E-02 5.867E-02 2.938E-02 7.951E-03 0.00 total mg/kg Mean 8.262E-02 7.284E-02 5.579E-02 4.293E-02 3.887E-03 dry weight Peak 8.313E-02 8.313E-02 8.313E-02 8.313E-02 8.313E-02 More? (Yes/No/Quit)-> Y Exposure Analysis Modeling System -- EXAMS Version <ver>, Mode 3 Ecosystem: Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136) Chemical: Methyl Parathion [CAS# 298-00-0] Table 20.01. Exposure analysis summary: Maximum Events of 2001.

----------------------------------------------------------------------------- Event Duration 96-hour 21-day 60-day 90-day 2001 ==============----==== --------- --------- --------- --------- --------- ***** Ecotoxicological Direct Exposure Concentrations ****** Water Column Min. 2.781E-03 5.128E-04 7.040E-05 7.664E-06 2.018E-12 dissolved mg/L Mean 3.995E-03 2.423E-03 1.487E-03 9.994E-04 2.588E-04 Peak 5.505E-03 5.505E-03 5.505E-03 5.505E-03 5.505E-03 Benthic Sediment Min. 1.617E-03 1.165E-03 5.834E-04 1.578E-04 9.304E-12 mg/L dissolved Mean 1.640E-03 1.446E-03 1.108E-03 8.522E-04 7.737E-05 in pore water Peak 1.650E-03 1.650E-03 1.650E-03 1.650E-03 1.650E-03 ***** Ecotoxicological Trophic Exposure Concentrations ***** Water Column Min. 1.03 0.191 2.615E-02 2.847E-03 7.499E-10 ug/g dry weight Mean 1.48 0.900 0.552 0.371 9.613E-02 of plankton Peak 2.04 2.04 2.04 2.04 2.04 Benthic Sediment Min. 0.601 0.433 0.217 5.864E-02 3.456E-09 ug/g dry weight Mean 0.609 0.537 0.411 0.317 2.874E-02 of benthos Peak 0.613 0.613 0.613 0.613 0.613 ***** Total Media Concentrations *************************** Water Column Min. 2.785E-03 5.137E-04 7.051E-05 7.677E-06 2.022E-12 total mg/L Mean 4.002E-03 2.427E-03 1.489E-03 1.001E-03 2.592E-04 Peak 5.514E-03 5.514E-03 5.514E-03 5.514E-03 5.514E-03 EXAMS-> QUITE X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 112 

### 3. 5 T ut or ial2: C he mic al & En vir on men talDa ta E nt ry T h i s tutori al ex am p l e il l u str ates t h e e n t ry o f EX A M S chemi cal and e nvi r onm ent al dat a a nd t he e xpl or at i on of al t er nat i ve pr oces s m odel s and pa r am et er s. The E X A M S s es si on dupl i cat es th e p ro b le m a n a ly sis in th e tex t b e g in n in g o n p a g e 3 9 ; i t shoul d be e xecut ed us i ng t hat t ext as a gui de. N ot e t hat t he envi r onm ent al dat a a r e nota c om pl et e c har act er i zat i on of Lake Zuri ch; t hey i ncl ude onl y a s i m pl e ge om et r y pl us t he par am et er s neede d t o cons t r uct a vol at i l i zat i on m odel f or E X A M S . T he d at a entr y sequ enc e con t ai ns som e err ors; t hese are i nt end ed as i l l ust r at i on s of er r or r eco very m et ho ds.



### 3. 5. 1 E xerci se 4 : p- DC B i n L ake Z urich

! Commands for Lake Zurich analysis of p-DCB
1 REC CHEM 1 2 SET MODE=1 3 CHEM NAME IS 1,4-Dichlorobenzene 4 set mwt(1)=147.0 5 change sol(1,1) to 73.8 6 set kow(1)=2340 7 set henry(1)=2.66e-3 8 cat chem 9 stor chem 20 10 rec env 1 11 env name is Lake Zurich - central basin (Untersee) 12 set elev=431 13 set airty(*)=r 14 set lat=47.48 15 set lon=8.53 16 SET KO2(1,13)=2.5 17 SET WIND(13)=1.38 18 HELP WIND 19 SET WIND(1,13)=1.38 20 SHOW KOUNT 21 SET KOUNT=3 22 SET TYPE(1)=E 23 SET TYPE(2)=H 24 SET TYPE(3)=B 25 SET DEPTH(1)=10 26 SET VOL(1)=6.8E8 27 SET DEPTH(2)=40 28 SET VOL(2)=2.72E9E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 113 29 SET DEPTH(3)=0.02 30 SET VOL(3)=1.36E6 31 SET AREA(*)=6.8E7 32 SET TCEL(1,13)=11 33 SET TCEL(2,13)=5.6 34 SET TCEL(3,13)=5.6 35 SET DSP(1,13)=0.2 36 SET DSP(2,13)=1.E-4 37 SET XST(*)=6.8E7 38 SET JTUR(1)=1 39 SET ITUR(1) TO 2 40 CHA JTUR(2)=2 41 SET ITUR(2)=3 42 SHO DISP 43 HELP CHARL 44 SET CHARL(1)=25 45 SET CHARL(2)=20.01 46 SHO DISP 47 SET SUSED(*,13)=5 48 SET BULKD(3,13)=1.5 49 SET PCTWA(3,13)=150 50 SET FROC(*,13)=.02 51 SET STRFL(1,13)=3.E5 52 HELP STFL 53 SET STF(1,13)=3.E5 54 SET STSED(1,13)=1500 55 SET STRLD(1,1,13)=0.01 56 SET OUTFIL(1)=Y 57 Show Ad 58 RUN 59 LI 15 60 list 18 61 list 20 62 CAT ENV 63 STOR ENV 5 64 SET DRFL(2,1,13)=1.5E-3 65 SET STRL(1,1,13)=8.5E-3 66 ENV NAME IS Lake Zurich with partial load to hypolimnion 67 run 68 li 15 69 list 18E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 114 70 li 20 71 zero load 72 cat chem 73 rec chem 20 74 rec env 5 75 env name is Lake Zurich with oceanic wind and reaeration 76 show ko2(1,13) 77 set ko2(1,13)=20 78 sho wind(1,13) 79 set wind(1,13)=2.6245 80 set strl(1,1,13)=0.01 81 run 82 list 15 83 list 18 84 era chem 20 85 quitE X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 115 

### 3. 5. 2 E xerci se 4 (L ake Z urich ) with ill us tra tive E

X AMS 

### Re sp on ses

Welcome to EXAMS Release <current release number> Exposure Analysis Modeling System Technical Contact: Lawrence A. Burns, Ph.D. U.S. Environmental Protection Agency 960 College Station Road Athens, GA 30605-2700 USA Phone: (706) 355-8119 (Fax) 355-8104 Internet: burns.lawrence@epa.gov Latest Maintenance <date of latest maintenance> Type HELP and press the RETURN key for command names, HELP USER for a summary of command functions, HELP PAGES for a list of information pages, or HELP EXAMS for introductory information. Please stand by while EXAMS checks the computational precision of this computer and initializes the Activity Data Base.

EXAMS-> REC CHEM 1 Selected compound is "Chemical Data Entry Template" EXAMS-> SET MODE=1 Command processing complete; ready for input. EXAMS-> CHEM NAME IS 1,4-Dichlorobenzene EXAMS-> set mwt(1)=147.0 EXAMS-> change sol(1,1) to 73.8 EXAMS-> set kow(1)=2340 EXAMS-> set henry(1)=2.66e-3 EXAMS-> cat chem UDB # Name of Chemistry Dataset ===== ================================================== 1 Chemical Data Entry Template 2 p-Cresol [CAS# 106-44-5] 3 Benz[a]anthracene [CAS# 56-55-3] 4 Benzo[a]pyrene [CAS# 50-32-8] 5 Quinoline [CAS# 91-22-5] 6 Benzo[f]quinoline [CAS# 85-02-9] 7 9H-Carbazole [CAS# 86-74-8] 8 7H-Dibenzo[c,g]carbazole [CAS# 194-59-2] 9 Benzo[b]thiophene [CAS# 95-15-8] 10 Dibenzothiophene [CAS# 132-65-0] 11 Methyl Parathion [CAS# 298-00-0] 12 Mirex [CAS# 2385-85-5] 13 Heptachlor [CAS# 76-44-8]

EXAMS-> store chem 20 Chemical stored: "1,4-Dichlorobenzene" EXAMS-> rec env 1 Selected environment is "Environmental Data Entry Template"E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 116

EXAMS-> env name is Lake Zurich - central basin (Untersee) EXAMS-> set elev=431 EXAMS-> set airty(*)=r EXAMS-> set lat=47.48 EXAMS-> set lon=8.53 EXAMS-> SET KO2(1,13)=2.5 EXAMS-> SET WIND(13)=1.38 Invalid number of subscripts. EXAMS-> HELP WIND WIND is a Real Matrix with 100 rows and 13 columns. WINDspeed (segment,month) Units: meters/second Average wind velocity at a reference height of ten centimeters above the water surface. Parameter is used to compute a piston velocity for water vapor (Liss 1973, Deep-Sea Research 20:221) in the 2-resistance treatment of volatilization losses.

EXAMS-> SET WIND(1,13)=1.38 EXAMS-> SHOW KOUNT KOUNT is 1 EXAMS-> SET KOUNT=3 EXAMS-> SET TYPE(1)=E EXAMS-> SET TYPE(2)=H EXAMS-> SET TYPE(3)=B EXAMS-> SET DEPTH(1)=10 EXAMS-> SET VOL(1)=6.8E8 EXAMS-> SET DEPTH(2)=40 EXAMS-> SET VOL(2)=2.72E9 EXAMS-> SET DEPTH(3)=0.02 EXAMS-> SET VOL(3)=1.36E6 EXAMS-> SET AREA(*)=6.8E7 EXAMS-> SET TCEL(1,13)=11 EXAMS-> SET TCEL(2,13)=5.6 EXAMS-> SET TCEL(3,13)=5.6 EXAMS-> SET DSP(1,13)=0.2 EXAMS-> SET DSP(2,13)=1.E-4 EXAMS-> SET XST(*)=6.8E7 EXAMS-> SET JTUR(1)=1 EXAMS-> SET ITUR(1) TO 2 EXAMS-> CHA JTUR(2)=2 EXAMS-> SET ITUR(2)=3 EXAMS-> SHO DISPE X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 117

Name of environment: Lake Zurich - central basin (Untersee) Total number of segments (KOUNT) = 3 Segment Number: 1 2 3 Segment "TYPE": E H B

--------------------------------------------------------------- Table 10.13. Mean dispersive transport field.

--------------------------------------------------------------- J TURB 1 2 I TURB 2 3 XS TUR m2 6.800E+07 6.800E+07 CHARL m 1.00 0.000 DSP m2/h* 0.200 1.000E-04 Path No.: 1 2

--------------------------------------------------------------- * Average of 12 monthly mean values. EXAMS-> HELP CHARL CHARL is a real vector with 600 elements. CHARacteristic_Length or mixing length (path) Units: meters Average of segment dimensions normal to the exchange interface linking segment numbers JTURB(p) and ITURB(p). The matching ("p" subscript) members of JTURB, ITURB, CHARL, DSP, and XSTUR define define a dispersive transport pathway. N.B.: A given segment may have different mixing lengths at different interfaces. CHARL can also be calculated from the distance along a path that connects the centers of segments JTURB(p) and ITURB(p), passing through the interface whose area is XSTURG(p). See also: DSP, ITURB, JTURB, XSTUR EXAMS-> SET CHARL(1)=25 EXAMS-> SET CHARL(2)=20.01 EXAMS-> SHO DISP Name of environment: Lake Zurich - central basin (Untersee) Total number of segments (KOUNT) = 3 Segment Number: 1 2 3 Segment "TYPE": E H B

--------------------------------------------------------------- Table 10.13. Mean dispersive transport field.

--------------------------------------------------------------- J TURB 1 2 I TURB 2 3 XS TUR m2 6.800E+07 6.800E+07 CHARL m 25.0 20.0 DSP m2/h* 0.200 1.000E-04 Path No.: 1 2

--------------------------------------------------------------- * Average of 12 monthly mean values. EXAMS-> SET SUSED(*,13)=5 EXAMS-> SET BULKD(3,13)=1.5 EXAMS-> SET PCTWA(3,13)=150 EXAMS-> SET FROC(*,13)=.02 EXAMS-> SET STRFL(1,13)=3.E5 Option not identified. EXAMS-> HELP STFLE X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 118

STFLO is a real matrix with 100 rows and 13 columns. STream_FLOws (segment,month) Units: cubic meters/hour Flow into head reach of river or estuary; segment tributaries and creeks or other streamflows entering a lake or pond. Note that STFLO represents stream flow entering system segments from external sources ONLY. EXAMS itself computes hydrologic flows among segments that are part of the waterbody being studied, via the specified advective and dispersive flow patterns (see JFRAD, JTURB, etc.). Therefore, DO NOT compute net water balances for each segment and enter these into the database--enter ONLY those flows entering the system across external boundaries! EXAMS-> SET STF(1,13)=3.E5 EXAMS-> SET STSED(1,13)=1500 EXAMS-> SET STRLD(1,1,13)=0.01 EXAMS-> SET OUTFIL(1)=Y EXAMS-> Show ad Name of environment: Lake Zurich - central basin (Untersee) Total number of segments (KOUNT) = 3 Segment Number: 1 2 3 Segment "TYPE": E H B

--------------------------------------------------------------- Table 9. Input specifications -- advective transport field.

--------------------------------------------------------------- J FR AD 1 I TO AD 0 ADV PR 1.00 Path No.: 1

--------------------------------------------------------------- EXAMS-> RUN Simulation beginning for: Environment: Lake Zurich - central basin (Untersee) Chemical 1: 1,4-Dichlorobenzene RUN command completed. EXAMS-> LI 15E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 119

Ecosystem: Lake Zurich - central basin (Untersee) Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.

--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 7.3 20.00 1.074E-05 1.074E-05 1.759E-04 0.00 2 29. 80.00 1.074E-05 1.074E-05 1.759E-04 0.00 ======== ====== 37. 99.33 and in the Benthic Sediments: 3 0.24 100.00 1.798E-04 1.065E-05 1.745E-04 0.00 ======== ====== 0.24 0.67 Total Mass (kilograms) = 36.76

--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics.

EXAMS-> list 18 Ecosystem: Lake Zurich - central basin (Untersee) Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 18.01. Analysis of steady-state fate of organic chemical.

--------------------------------------------------------------- Steady-state Values Mass Flux % of Load Half-Life* by Process Kg/ day days
--------------------- ---------- --------- ---------- Hydrolysis Reduction Radical oxidation Direct photolysis Singlet oxygen oxidation Bacterioplankton Benthic Bacteria Surface Water-borne Export 7.7323E-02 32.22 329.5 Seepage export Volatilization 0.1627 67.78 156.6

--------------------------------------------------------------- Chemical Mass Balance: Sum of fluxes = 0.2400 Sum of loadings = 0.2400 Allochthonous load: 100.0 Autochthonous load: 0.0 Residual Accumulation = 6.82E-09 0.0

--------------------------------------------------------------- * Pseudo-first-order estimates based on flux/resident mass.

EXAMS-> list 20E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 120

Ecosystem: Lake Zurich - central basin (Untersee) Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 20.01. Exposure analysis summary.

--------------------------------------------------------------- Exposure (maximum steady-state concentrations): Water column: 1.074E-05 mg/L dissolved; total = 1.074E-05 mg/L Benthic sediments: 1.065E-05 mg/L dissolved in pore water; maximum total concentration = 1.798E-04 mg/kg (dry weight). Biota (ug/g dry weight): Plankton: Benthos: Fate: Total steady-state accumulation: 36.8 kg, with 99.33% in the water column and 0.67% in the benthic sediments. Total chemical load: 0.24 kg/ day. Disposition: 0.00% chemically transformed, 0.00% biotransformed, 67.78% volatilized, and 32.22% exported via other pathways. Persistence: After 216. days of recovery time, the water column had lost 50.52% of its initial chemical burden; the benthic zone had lost 19.55%; system-wide total loss of chemical = 50.3%. Five half-lives (>95% cleanup) thus require ca. 35. months. EXAMS-> CAT ENV UDB # Name of Environmental Dataset ===== ================================================== 1 Environmental Data Entry Template 2 Georgia Piedmont Farm Pond (WBAN 13873, MLRA P136)

EXAMS-> STORE ENV 5 Environment stored: "Lake Zurich - central basin (Untersee)" EXAMS-> SET DRFL(2,1,13)=1.5E-3 EXAMS-> SET STRL(1,1,13)=8.5E-3 EXAMS-> ENV NAME IS Lake Zurich with partial load to hypolimnion EXAMS-> run Simulation beginning for: Environment: Lake Zurich with partial load to hypolimnion Chemical 1: 1,4-Dichlorobenzene RUN command completed. EXAMS-> li 15E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 121

Ecosystem: Lake Zurich with partial load to hypolimnion Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.

--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 7.3 16.59 1.074E-05 1.074E-05 1.759E-04 0.00 2 37. 83.41 1.350E-05 1.349E-05 2.210E-04 0.00 ======== ====== 44. 99.31 and in the Benthic Sediments: 3 0.31 100.00 2.260E-04 1.339E-05 2.193E-04 0.00 ======== ====== 0.31 0.69 Total Mass (kilograms) = 44.32

--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics.

EXAMS-> list 18 Ecosystem: Lake Zurich with partial load to hypolimnion Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 18.01. Analysis of steady-state fate of organic chemical.

--------------------------------------------------------------- Steady-state Values Mass Flux % of Load Half-Life* by Process Kg/ day days
--------------------- ---------- --------- ---------- Hydrolysis Reduction Radical oxidation Direct photolysis Singlet oxygen oxidation Bacterioplankton Benthic Bacteria Surface Water-borne Export 7.7323E-02 32.22 397.3 Seepage export Volatilization 0.1627 67.78 188.8

--------------------------------------------------------------- Chemical Mass Balance: Sum of fluxes = 0.2400 Sum of loadings = 0.2400 Allochthonous load: 100.0 Autochthonous load: 0.0 Residual Accumulation = 6.82E-09 0.0

--------------------------------------------------------------- * Pseudo-first-order estimates based on flux/resident mass. EXAMS-> li 20E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 122

Ecosystem: Lake Zurich with partial load to hypolimnion Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 20.01. Exposure analysis summary.

--------------------------------------------------------------- Exposure (maximum steady-state concentrations): Water column: 1.349E-05 mg/L dissolved; total = 1.350E-05 mg/L Benthic sediments: 1.339E-05 mg/L dissolved in pore water; maximum total concentration = 2.260E-04 mg/kg (dry weight). Biota (ug/g dry weight): Plankton: Benthos: Fate: Total steady-state accumulation: 44.3 kg, with 99.31% in the water column and 0.69% in the benthic sediments. Total chemical load: 0.24 kg/ day. Disposition: 0.00% chemically transformed, 0.00% biotransformed, 67.78% volatilized, and 32.22% exported via other pathways. Persistence: After 252. days of recovery time, the water column had lost 54.37% of its initial chemical burden; the benthic zone had lost 25.71%; system-wide total loss of chemical = 54.2%. Five half-lives (>95% cleanup) thus require ca. 37. months. EXAMS-> zero load All allochthonous loads removed. EXAMS-> cat chem UDB # Name of Chemistry Dataset ===== ================================================== 1 Chemical Data Entry Template 2 p-Cresol [CAS# 106-44-5] 3 Benz[a]anthracene [CAS# 56-55-3] 4 Benzo[a]pyrene [CAS# 50-32-8] 5 Quinoline [CAS# 91-22-5] 6 Benzo[f]quinoline [CAS# 85-02-9] 7 9H-Carbazole [CAS# 86-74-8] 8 7H-Dibenzo[c,g]carbazole [CAS# 194-59-2] 9 Benzo[b]thiophene [CAS# 95-15-8] 10 Dibenzothiophene [CAS# 132-65-0] 11 Methyl Parathion [CAS# 298-00-0] 12 Mirex [CAS# 2385-85-5] 13 Heptachlor [CAS# 76-44-8] 20 1,4-Dichlorobenzene EXAMS-> rec chem 20 Selected compound is "1,4-Dichlorobenzene" EXAMS-> rec env 5 Selected environment is "Lake Zurich - central basin (Untersee)" EXAMS-> env name is Lake Zurich with oceanic wind and reaeration EXAMS-> show ko2(1,13) KO2(1,13) is 2.500 EXAMS-> set ko2(1,13)=20 EXAMS-> sho wind(1,13) WIND(1,13) is 1.380

w In this st u d y , w e w i sh t o set V t o 30 0 0 cm / h
. U se E q . (2-8 2 ) ( O n pa g e 3 7 ) t o ca l cu l ate the req u i red va l u e fo r W I ND . EXAMS-> set wind(1,13)=2.6245 EXAMS-> set strl(1,1,13)=0.01 EXAMS-> run Simulation beginning on <date> at <time> for:E X A M S L a k e Z u r i c h D a t a E n t r y L a b o r a t o r y . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Page 123

Environment: Lake Zurich with oceanic wind and reaeration Chemical 1: 1,4-Dichlorobenzene RUN command completed. EXAMS-> list 15 Ecosystem: Lake Zurich with oceanic wind and reaeration Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 15.01. Distribution of chemical at steady state.

--------------------------------------------------------------- Seg Resident Mass ******** Chemical Concentrations ********* # Total Dissolved Sediments Biota Kilos % mg/* mg/L ** mg/kg ug/g
--- -------- ------ --------- --------- --------- --------- In the Water Column: 1 1.3 20.00 1.953E-06 1.952E-06 3.198E-05 0.00 2 5.3 80.00 1.953E-06 1.952E-06 3.198E-05 0.00 ======== ====== 6.6 99.33 and in the Benthic Sediments: 3 4.45E-02 100.00 3.270E-05 1.937E-06 3.172E-05 0.00 ======== ====== 4.45E-02 0.67 Total Mass (kilograms) = 6.684

--------------------------------------------------------------- * Units: mg/L in Water Column; mg/kg in Benthic Zone. ** Excludes complexes with "dissolved" organics. EXAMS-> list 18 Ecosystem: Lake Zurich with oceanic wind and reaeration Chemical: 1,4-Dichlorobenzene

--------------------------------------------------------------- Table 18.01. Analysis of steady-state fate of organic chemical.

--------------------------------------------------------------- Steady-state Values Mass Flux % of Load Half-Life* by Process Kg/ day days
--------------------- ---------- --------- ---------- Hydrolysis Reduction Radical oxidation Direct photolysis Singlet oxygen oxidation Bacterioplankton Benthic Bacteria Surface Water-borne Export 1.4060E-02 5.86 329.5 Seepage export Volatilization 0.2259 94.14 20.50

--------------------------------------------------------------- Chemical Mass Balance: Sum of fluxes = 0.2400 Sum of loadings = 0.2400 Allochthonous load: 100.0 Autochthonous load: 0.0 Residual Accumulation = 8.33E-09 0.0

--------------------------------------------------------------- * Pseudo-first-order estimates based on flux/resident mass. EXAMS-> quit124



## 4. 0 E XA MS 

## C om m and Lang uag e I nt e r f ac e ( C LI ) U s e r ’ s G ui de

Int roduct i on Thi s C hapt er des cr i bes t he E X A M S com m and l ang uag e, i ncludi ng usage and r efer enc e i nfor m at i on . Th e fi r st p a rt p ro v id e s a n o v e rv ie w o f th e c o m m a n d la n g u a g e a n d it s gr am m ar . The sec ond par t cont ai ns det ai l ed de sc r i pt i ons of ea ch co m m an d
. T h e c o m m an d s are l i sted i n alph ab eti ca l ord er. 

### 4. 1 C on ve nt ion s U sedin th is C ha pt er C onvent i on M eani ng
CT RL / x The phr as e CTRL / x i ndi cat es t hat you must pr ess

t he key l abel ed CT RL w h i l e sim u l t an eo u sly p re ss in g a n o th e r k e y , fo r e x a m p le , CT RL / Q .

- > LI ST 7 V er t i cal s er i es of per i ods, or el l i psi s, m ean t hat

. not al l t he da t a E X A M S w o u ld

. d isp la y in re sp o n se to

. t he pa r t i cul ar comm and i s show n,

. o r th a t n o t all

. th e d a ta a u se r w o u ld e n te r is

. show n. k e y w o r d , . . . H or i zon t al el l i psi s i nd i cat es t hat addi t i onal

key- w or ds, comm and par am et er s, or dat a c an be e n te re d in a c o m m a n d se q u e n c e , o r th a t E X A M S d isp la y s a d d iti o n a l d a ta a s p a rt o f t h e sa m p le out put l i ne. [k e y w o rd ] S q u a re b ra c k e ts in d ic a te th a t t h e it e m e n c lo se d is

opt i onal , t hat i s, t he e nt i t y ca n be omi t t ed f r om t he co m m an d l i n e a l t o g eth er.
< op t i on > A ng l e brackets i nd i cat e t hat a com m and r equ i r es a

cho i ce am on g t w o or m ore opt i on s. 

### 4. 2 Ov erview The E X A M S c om m and l anguage pr ovi des a s et of comm ands f

or
! Ent er i ng, s t or i ng, and mani pul at i ng dat a de sc r i bi ng t he r eac t i on c he mi st r y of s ynt het i c c om pounds, t he envi r onm ent al pa r am et er s gover ni ng t hei r t r ans port and t r ans f or m at i on i n a quat i c sys t em s, pat t er ns of al l ocht honous l oadi ngs, and pr oduct che m i st r y.
! St udyi ng t he r es ul t s of an a nal ysi s by l i st i ng t abul ar output on a t er m i nal , pl ot t i ng t he c oncent r at i on dat a ( “Expect ed Envi r onm ent al C oncent r at i ons” orEE C s) comput ed dur i ng si m ul at i ons, and pr i nt i ng pape r copy. ! C hoosi ng among anal yt i cal f r am ew or ks f

or i nves t i gat i ng e x p o su re to c h e m ic a ls in a p a rticu la r c a se stu d y . E X A M S i n clu d es t h ree op era t i o n al m o d ali t i es or “ M ODE s”
M ODE A nal yt i cal M et hodol ogy 1 Long-t er m cons equenc es of cont i nued r el eas es of che m i cal s; st ead y-st at e ana l ysi s. 2 D et ai l ed e xam i nat i on of i m m edi at e c onse quence s of che m i cal r el eases; i ni t i al

- value probl em s. 3 I nt er m edi at e- sc al e r es ol ut i on of eve nt s overs ever al year s, i ncl udi ng eff

ect s of s eas onal envi r onm ent al var i abi l i t y; ana l ysi s of

t i m e- se r i es dat a. 

### 4.3 Entering Commands E X A M S comm ands ar e c om pose d of Engl i sh- l anguage w or ds (m o stly v e rb s) th a t d e sc rib e w h a t y o u w a n t E X A M S t o d o . S o me com m ands r equi r e qua l i f i er s and pa r am et er s. These gi ve E X A M S m or e i nf or mat i on on ho w t o e xe cu t e t he c ommand
. Com mand par am et er s des cr i be t he obj ectt o be a ct ed upon by t he c om m and. I n som e ca se s, t he obj ecti s a ke yw or d ( as i n t he HELP com m and) ; i n ot her s, i t i s an E X A M S d a ta e le m e n t ( SE T c o m m a n d ) o r a se c tion o f a fil e o f in p u t d a ta or a n a ly sis re su lts t o m ani pul at e ( S T ORE and LI ST co m m an d s). T h ro u g h o u t t h is C h a p te r, E X A M S co m m a n d s a re prin te d in u p p e rc a se lette rs fo r th e sa k e o f c la rity. H o w e v e r, E X A M S w ill ac ce p t co m m an d s en t ere d i n up p erc as e, l o w erc as e, or a m i x t u re o f u p p e rc a se a n d lo w e rc a se le tters . M o st E X A M S comm ands and k eyw ords can be abb r eviat ed t o t he l east num ber of characters neede d t o uni quel y di st i ngui sh t hem f r om ot her opt i ons avai l abl e. For exam pl e, t o end E X A M S yo u ca n en t er “ Q U IT ”,
“ QUI ”, “ QU ”, or “ Q ”. T h e le as t nu m b er o f r eq u i red ch ara cters depends on t he c ont ext , how ever , but i s neverm or e t han t hr ee. For exa m pl e, t he S HOW comm and i ncl udes among i t s opt i ons bot h < QU ALI TY > and < Q U IT >; i n t hi s cas e you must ent er t hr ee ch ara cters for E X A M S t o di st i ngui sh bet w een t hem
. I n E X A M S ’ “he l p f i el ds” and pr om pt s, ca pi t al i zat i on i s use d t o s how you ho w m any charact ers ar e r equ i r ed for uniquen ess. The f ol l ow i ng exampl e show s an A U D IT comm and a nd E X A M S ’ re sp o n se , as th e y w o u ld a p p e a r o n a term in a l.
E X A M S - > AUD I T ON A ll in p u t w ill n o w b e c o p ie d in to th e fil e nam ed “ AUD OUT ” o n F o rt ran U n i t N u m b er 4
E X A M S - > ! Thi s C om m and Fi l e s houl d be r enamed f i l e. E XA125

E X A M S ->
E X A M S analyzes t he p art s of t he ab ov e exa m pl e as f ol l ow s.
E X A M S -> The E X A M S sy ste m p ro m p t f o r c o m m a n d in p u t; a g re a te r-th a n (-> ) m e a n s th a t E X A M S ’ comm and i nt erpr et er i s r eady f

or a c om m and t o be e nt er ed.
A U D IT T h e c o m m a n d n a m e , req u e stin g th a t E X A M S

en ab l e/d i sa b l e the U se r N o t ep ad / C o m m an d F i le C r eat i on f

aci l i t y.
ON A n opt i on of

t he A U D IT c ommand , r eq ue s t i ng t ha t t he N ot epad/ C r eat e f

aci l i t y be e nabl ed. A ll in p u t w ill n o w b e c o p ie d in to th e fil e nam ed “ AUD OUT ” on Fort ran U ni t N um ber 4 A m es sa ge f

r om t he A U D IT comm and, i ndi cat i ng t hat t he c om m and c om pl et ed s ucce ss f ul l y. The comm and i n t erp reter u se d t h e v alu e o f AUD OUT ( 4) t o est abli sh com m uni cat i on w i t h an e xt er nal f i l e.
E X A M S -> The next s yst em comm and pr om pt , c on f i r mi ng t hat t he com m and has com pl et ed i t s operat i on s ( A U D IT h a s o p e n e d c o m m u n ic a tion s w ith a n e x te rn a l fi le and s t ar t ed r ecor di ng t er m i nal i nput s) , and E X A M S is re a d y fo r a d d iti o n a l i n p u t. ! T h i s C o mm a n d F i l e s h o u l d b e r e n a me d f i l e . E XA A com m ent enter ed b y t he u se r . C om m ent l i nes m ust b eg i n w i t h an ex clam ati o n po i n t (! ) or an asterisk (*). Y o u c a n u se c o m m e n ts, a s n e e d e d , t o d o c u m e n t E X A M S ana l ysi s sessi on s or com m and procedu r es.
E X A M S -> T h e n e x t E X A M S s y ste m c o m m a n d p ro m p t,

c o n firm in g th a t t h e c o m m e n t h a s b e e n re c o rd e d in t he N ot epad/ C om m and f i l e a nd E X A M S is rea d y to acc ept anot her comm and. 

### 4.4 Command Prompting W hen you e nt er a c om m and a tt he t er m i nal , you nee d not ent er t he e nt i r e c om m and on a si ngl e l i ne. I f you ent er a c om m and t hat r equi r es t hat you s peci f y i t s r ange or t he obj ectof t he r eques t ed a c tion , an d y o u d o n o t i n c lu d e th e n e e d e d in fo rm a tion , E X A M S ’ com m and i nt erpr et er pr om pt s you f or al l m i ss i ng i nf

or m at i on. For exa m pl e:
E X A M S - > A U D IT The f ol l ow i ng A U D IT o p tion s a re a v a ilab le O N - - begi ns a ne w A udi t f i l e, O FF - - end s A ud i t r eco r di ng of i np ut com m and s, H el p - - t hi s m es sa ge, Q ui t - - r et ur n t o t he E X A M S p ro m p t. A U D IT -> ON A l l i nput w i l l now be c opi ed i nt o t he f i l e na m ed “ AUD OUT ” o n F o rt ran un i t nu m b er 4

I n t hi s exampl e, no A U D IT opt i on w as ent er ed, s o E X A M S p ro m p ts f or a mor e c om pl et e s peci f i cat i on of

t he i nt ended act i on. The l i ne e n d in g w ith a -> in d ic a te s th a t E X A M S i s w ai t i ng f or t he a d d iti o n a l i n p u t. In m a n y c a se s, E X A M S ’ p ro m p ts d o n o t i n c lu d e a n a u to m a tic des cr i pt i on of

t he f ul l r ange of

pos si bl e r es ponse opt i ons. O f t en, how ever , ent er i ng HELP i n r es ponse t o t he pr om pt w i l l di spl ay a l i stof ava i l abl e c hoi ces , as i n t he f ol l ow i ng exa m pl e.

E X A M S - > LI ST A t t he pr om pt , e nt er a Tabl e num ber , “ Q ui t , ” or“ H el p” t o s ee a cat al og of t he o ut pu t t ables. En t e r Ta b l e Numb e r - > HELP 1 C h e m ic a l i n p u ts: FATE D a ta 2 C h e m ic a l i n p u ts: P RODUCT C h em i str y 3 PU LSE C hem i cal Loadi ngs

.

.

. 20 E xp osure A nalysi s S UM M ARY ALL E n t i re R ep o rt A t t h e p ro m p t, e n te r a T a b le n u m b e r, “Q u it, ” or “ H el p” t o see a catal og of t he o ut pu t t ables. Ent er Tabl e N um ber - > 18 Ecosystem: Name of Water body Chemical: Name of chemical

------------------------------------------ Table 18.01. Analysis of steady-state fate

-----------------------------------------

.

. (body of table)

.

------------------------------------------ In th e e x a m p le a b o v e , LI ST i s ent er ed w i t hout t he num ber of t he out put t abl e t o be di spl ayed. E X A M S pr om pt s f or t he mi ss i ng i nf or m at i on; t ypi ng HELP i n r es ponse t o t he LI ST pr om pt di spl ays a c atalog of E X A M S output t ables. 

### 4 . 5 E XA MS 

### Mes sa ge s W h e n a c o m m a n d is e n te re d in c o rre c tly, E X A M S di spl ays a des cr i pt i ve e r r or m es sa ge i ndi cat i ng w ha ti s w r on g. For exa m pl e,126

i f a da t a s ubsc r i pt l ar ger t hat t he maxi m um ava i l abl e i s ent er ed, E X A M S w i l l r es pond Sub sc ri pt out - of

- range. Y ou ca n t hen r et ype t he c om m and c or r ect l y. O t her er r or m es sa ges m ay be pr oduced duri ng t he e xecut i on of a c om m and, or dur i ng a s i m ul at i on or dat a di spl ay s equence. T h e se m e ss a g e s in d ic a te s u c h th in g s a s in c o m p le te e n v iro n m e n ta l d a ta , ch a ra c te r d a ta e n te re d w h e re n u m e ric d a ta are r equ i r ed, or t yp og rap h i c err ors du r i ng ent r y of com m and s. E X A M S w i l l r es pond t o t ypogr aphi c e r r or s i n comm and e nt r i es by di spl ayi ng: C om m and not recogni ze d. T ype HELP f or c om m and i nf or m at i on. B e c a u se th e m e ss a g e s a re d e sc rip tive , i t is u s u a lly p o ss ib le to det er m i ne w hat cor r ect i ve a ct i on i s r equi r ed i n or der t o pr ocee d. W h e n t h is is n o t t h e c a se , E X A M S ’ HELP f aci l i t y cont ai ns a l ar ge b o d y o f a d d iti o n a l an d su p p le m e n ta ry in fo rm a tion a v a ilab le t hr ough t he HELP , DES CRI BE , and S HOW com m and s. 

### 4. 6 T he HELP 

### Command C onsul t i ng a pr i nt ed gui de i s not t he most conve ni ent w ay t o get a s um m ar y of

t he s ynt ax of

a c om m and or a de f

i ni t i on of

an i n p u t d a t u m. E X A M S ’ HELP c ommand pr ov i de s t hi s i nf or mat i on i n E X A M S ’ i nt er ac t i ve e nv i r on ment
. Fo r e xa mpl e, yo u c an t ype t he c om m and:
E X A M S -> H ELP LI ST
E X A M S r es ponds by di spl ayi ng a de sc r i pt i on of t he LI ST com m and, i t s synt ax, and t he opt i ons neede d t o s peci f y t he r ange of t he c om m and. The HELP facil i t y also p rov i d es on -l i n e a ssistan ce for E X A M S ’ in p u t d a ta , e.g ., E X A M S -> H ELP QY I EL D

w i l l di spl ay t he subs cr i pt r anges , t hei r meani ngs, t he p hysi cal d i m en sion s, an d the E n g l i sh de fi n i t i o n of E X A M S che m i cal i nput d a t u m “ QY I EL D ” . T h is in fo rm a tio n is a v a ilab le o n line fo r a ll E X A M S ’ i nput dat a a nd cont r ol par am et er s. The names of al l of E X A M S ’ i n p u t va ri ab l es w ere selec t ed as m n em o n i cs for t h e ir E n g l i s h

- l a n g u a g e n a m e s . ( F o r e x a m p l e , QY I EL D i s t he p h o to c h e m ic a l q u a n tu m y ie ld .) T h e se m n e m o n ic s a re u se d in E X A M S ’ o u tp u t t a b le s; d e fin iti o n s a re g iv e n in th e D a ta D i ct i onar y ( pages 180 f f
. ) as w el l as i n t he on- l i ne HELP . E X A M S ’ HELP f

aci l i t y s uppl i es l i st s of i ndi vi dual t opi cs and subt opi cs . The HELP c ommand i s de s cr i be d i n mor e de t ai l l at er in th is C h a p te r, an d a tu to ria l ex p la n a tion o f th e c o m m a n d is avai l abl e onl i ne by e nt er i ng E X A M S -> HE L P T UT OR 

### 4. 7 C omm an d P ro ced ur es A co m m and pr ocedur e i s a f i l e t hat cont ai ns a s equenc e of E X A M S comm ands , opt i onal l y i nt er spe r se d w i t h descr i pt i ve c o m m e n ts (lin e s w ith “!” or “* ” i n c o lu m n o n e ). B y p la c in g se ts of f r equent l y- use d comm ands and/ or r es ponse opt i ons i n a com m and pr ocedur e, al l t he c om m ands i n i t ca n be exe cut ed a s a g ro u p u sin g a sin g le c o m m a n d . F o r e x a m p le , su p p o se a fil e ca l l ed S T ART . E XA w er e t o cont ai n t hes e c om m and l i nes and com m ents:
S E T M ODE T O 3 S E T KC HE M T O 4 S E T NYE AR T O 5 RE CA L L L OAD 7 ! L oad i ng s UDB Sect or 7 i s t he s pr ay dr i f t s t udy
The f our comm ands i n t hi s f i l e can be exec ut ed by ent er i ng t he com m and
E X A M S -> DO S T ART
or E X A M S -> @ S T ART Y o u do no t ha v e t o spe cify t h e fi l e t y p e o f a co m m an d pro ce d u re w h e n y o u u se th e @ c o m m a n d , so lo n g a s th e fil e ty p e is “.E X A ”--t h e d efa u l t fi l e typ e fo r E X A M S ’ @ comm and. Y ou ca n u s e a n o t h e r f

i l e s u f f i x , i f y o u s o i n f

o r m E X A M S w hen you e nt er t he c om m and r eques t
. For exa m pl e, t o execut e c om m ands i n a f i l e na m ed S T ART . UP
E X A M S -> @ S T ART . UP 

### 4. 8 W ildCa rdCh ar ac ter s Som e E X A M S c ommand s a cc ep t a “ w i l d ca r d” c ha r ac t er i n t he i n p u t co m m an d spe cifi ca t i o n s. T h e as t erisk (*) i s t h e o n ly symbol ha vi ng t hi s f

unct i on i n E X A M S . W i l d ca rd c h ara cters a re use d t o r ef

er t o a r ange of

dat a s ubsc r i pt s, or ot her ent i t i es , by a gener al name, r at her t han ha vi ng t o ent er a s peci f i c na m e f

or e a c h m e m b e r o f th e g ro u p . P a rticu la r u se s o f w ild c a rd s in E X A M S var y w i t h t he i ndi vi dual comm ands
. The comm and d es cripti o n s lat er i n t h i s C h ap t er i n d i ca t e w h ere w i l d c a rd s are al l ow ed an d de scr i be t heiref f ect s. 

### 4.9 Truncating Command Names and Keywords A l l keyw or ds and na m es of i nput dat a t hat ar e ent er ed a s c o m m an d i n p u t can be ab b rev i ated
. O n l y en o u g h ch ara cters to u n iq u e ly d istin g u ish a k e y w o rd o r d a tu m fro m o th e rs w ith sim i l ar n am es ne ed be en t ere d (oft en on l y on e).127 

### 4. 10 Su mma ryDe scr ip tio n o f E XA MS 

### ’ Syst em Commands

E X A M S C om m and Sum m ar y D es cr i pt i on
A U D IT St ar t / St op us er not epad f or r ecor di ng pr ocedur es CA T AL OG L i st t he co nt ents of U ser D at aba ses ( UDB s) CH ANG E / SE T E n te r/re se t i n p u t d a ta a n d p ro g ra m c o n tro ls CO NT I NUE R es um e i nt egr at i on ( M odes 2 and 3 onl y) DES CRI BE R epor t di m ens i ons and da t a t ype of par am et er DO or @ E x ec u t e fi l e o f E X A M S c o m m a n d s ( f i l e . E XA) E CH O C ont r ol comm and e choi ng ER A SE C l ears ect i on of s t or ed da t abas e ( UDB ) HELP D es cr i bes ac ces s t o E X A M S on- l i ne HELP fa c ili ty LI ST Show t abul ar r es ul t s on t he s cr een N A M E Speci f

y t he name of

a UDB , e.g ., C H E M N A M E IS ... P L OT Pl ot r es ul t s on t he s cr een P RI NT Q ueue t abul ar r es ul t s f or har dcopy pr i nt i ng Q U IT A bor t comm and, or End i nt er act i ve s es si on RE AD U pl oad da t a f r om non- E X A M S A S C II d isk fil e RECALL A ct i vat e da t a f r om s t or ed da t abas e ( UDB ) RU N B egi n s i m ul at i on r un S HOW D i spl ay c ur r ent dat a va l ues or cont r ol s et t i ngs S T ORE D ow nl oad c ur r ent dat a i nt o s t or ed da t abas e ( UDB ) W RI TE D ow nl oad da t a t o A S C II d isk fil e Z E RO C le a r c h e m ic a l l o a d in g s, p u lse s, o r re sid u a ls128 

## 5. 0 Sy s t e m C om m and De s c r i pt i ons

A U D I T C r eat es a c opy of

us er i nput comm ands and r es ponse s i n an e xt er nal f i l e. R el at ed: C on t r ol vari ables: AUD OUT

C om m and s: DO Synt ax: A U D IT <opt i on>

O pt i ons O N O F f Pr om pt : The f

ol l ow i ng A U D IT o p tion s a re a v a ilab le

O N - - begi ns a ne w A udi t f i l e, O F f - - end s A ud i t r eco r di ng of i np ut com m and s, H el p - - t hi s m es sa ge, Q ui t - - r et ur n t o t he E X A M S p ro m p t.
A U D IT ->
O pt i on s: O F f

E n d s co p y i n g of E X A M S comm ands t o t he e xt er nal f i l e. O N B eg i n s co p y i n g of E X A M S comm ands t o an e xt er nal f i l e. D es cr i pt i on: The A U D IT comm and s t ar t s copyi ng i nput s t yped at t he t er m i nal , i nt o an e xt er nal f i l e. These i nput s i ncl ude E X A M S com m and s, and us er r es ponse s t o E X A M S pr om pt s and opt i on s el ect i ons. The out put t er m i nus f or t he copy i s a f

i l e na m ed “ AUD OUT . ” The r es ul t i ng ou t pu t fi l e ca n be us ed t o r ecor d an a nal ysi s pr ocedur e, or as a ge ner al not epad. The out put f i l e c an be r enamed “f i l e. EX A ” a nd us ed a s an E X A M S comm and ( DO ) f i l e.
E xam pl es: 1
. E X A M S -> A U D IT The f ol l ow i ng A U D IT opt i ons ar e a vai l abl e:

O N - - begi ns a ne w A udi t f i l e, O F f - - end s A ud i t r eco r di ng of i np ut com m and s, H el p - - t hi s m es sa ge, Q ui t - - r et ur n t o t he E X A M S p ro m p t. A U D IT -> ON A l l i nput w i l l now be c opi ed i nt o f i l e “ AUD OUT . X M S”. Thi s com m and be gi ns r ecor di ng of i nput f r om t he t er m i nal i nt o an e xt er nal f i l e. The o ut pu t w i l l go t o a di sk f i l e na m ed
“ AUD OUT . X M S”. A f

t er l eavi ng E X A M S , t hi s f i l e can be pri nt ed t o give a perm ane nt r eco r d of t he an al ysi s.129

2
. E X A M S -> A U D I T O FF The A U D IT opt i on has bee n t er m i nat ed. T h i s co m m an d en d s co p y i n g of E X A M S co m m an d s an d resp o n se s to t h e e x t ern al m ed i u m (usu all y a d i sk fi l e).

3
. E X A M S -> AUD I T ON A l l i nput w i l l now be c opi ed i nt o t he f i l e na m ed “ AUD OUT ” o n F o rt ran U n i t N u m b er 4
E X A M S -> RE CA L L E NV 2 Sel ect ed e nvi r onm ent i s: Phant om I nl et
E X A M S -> R E C A L L C H E M 2 S e le c te d c o m p o u n d is: D ic h lo ro e x a m p le
E X A M S -> R E C A L L C H E M 4 A S 2 S e le c te d c o m p o u n d is: T e tra b ro m o e x a m p le
E X A M S -> A U D I T O FF These com m ands bui l d a f i l e ( AUD OUT ) t hat ca n l at er be us ed a s a c om m and f i l e upon e nt er i ng t he E X A M S s yst em . I n t hi s i nst ance , th e fil e w o u ld b e re n a m e d (e .g ., M YC OMAND . E XA ) an d us ed t o ex ec u t e the ab o v e se ri es of co m m an d s as a u n i t
--
E X A M S -> DO MYC OMAND130 C A T A L O G Li st s, by ac ces si on num ber , t he t i t l e of al l cur r ent ent r i es i n t he s peci f i ed U se r D at abas e ( UDB ). R el at ed: C ont r ol var i abl es : none

C om m and s: ER A SE , N A M E , RECALL , S T ORE Synt ax: CA T AL OG <opt i on> O p tion s: CH E M I CA L , E NVI RO NME NT , L OAD , P RODUCT P rom p t : E n t er E n v i ron m en t , C h em i ca l , L o ad , P rod u ct, H elp , o r Q u i t -> O pt i on s: CH E M I CA L L ists th e ti tles , b y a c c e ss n u m b e r, o f c h e m ic a l d a ta b a se s c u rre n tly in th e U se r D a ta b a se . E a c h e n try c o rr e s p o n d s to a sin g le che m i cal , and con t ai ns t he l abo r at ory dat a descri bi ng i on i zat i on and ( species- specif i c) part i t i on i ng and r eacti on ki neti cs.
E NVI RO NME NT L ist th e ti tles , b y a c c e ss n u m b e r, o f e n v iro n m e n ta l d a ta b a se s c u rre n tly in th e U se r D a ta b a se . E a c h e n try c o n ta in s a “c a n o n ic a l” p h y sica l an d ch em i ca l m o d el of an aq u ati c sy stem , i n clu d i n g t h e e n v i ron m en t al da t a n ee d ed t o co m p u t e rea cti v i t y an d t ran sp o rt o f s y n t h e t i c c h e mi c a l s i n t h e s y s t e m.
L OAD Li st s t he t i t l es , by acc es s num ber , of a l l ocht honous chemi cal l oadi ng pa t t er ns st or ed i n t he U se r D at abas e. Thes e dat a i ncl ude m ont hl y val ues ( kg/ hour ) f or s t r eam- l oads , non- poi nt
- sour ce l oa ds , gr ou nd w at ers ee pa ge l oads , pr eci pi t at i on l oads , and dr i f t l oads of che m i cal s ent er i ng t he aquat i c envi r onm ent , pl us s peci f i cat i on of

pul se l oadi ngs. T he pul se l oad dat a i ncl ude t he magni t ude ( k g ) , t a r g e t e n v i r o n me n t a l s e g me n t , a n d s c h e d u l i n g ( mo n t h a n d d a y ) o f p u l s e s o f

s y n t h e t i c c h e mi c a l s e n t e r i n g t h e s y s t e m.
P RODUCT L ists th e ti tles , b y a c c e ss n u m b e r, o f re a c tion o r tran sf o rm a tion p ro d u c t ch e m is trie s sto re d in th e U se r D a ta b a se . T h e se d a ta i ncl ude t he A ct i vi t y D at abas e number s of che m i cal par ent and pr oduct compounds, t he number of t he pr oces s r es ponsi bl e f or t he t r ans f or m at i on, and t he yi el d ef f i ci ency ( m ol e/ m ol e) as an ( opt i onal ) f unct i on of

t em per at ur e. D es cr i pt i on: The CA T AL OG c ommand i nv en t or i es t he c on t en t s of t he s pe ci f

i ed U s erD at ab as e ( UDB ) and l i st s t he t i t l es of ac t i ve e nt r i es o n t h e term i n al scre en . F o u r t y p es of UDB s ar e a vai l abl e, co r r espondi ng t o t he f our opt i ons avai l abl e t o t he CA T AL OG com m and. The t i t l es ar e l i st ed by a cce ss i on num ber ; t hi s num ber i s use d t o S T ORE , RECALL , o r ER A SE dat aba se ent r i es.
E xam pl es: 1
. E X A M S -> CA TALOG HELP The CA T AL OG co m m an d req u i res tha t yo u sp ec i fy e i t h er: 1 . E n v iro n m e n t, 2 . C h e m ic a l, 3. Load, 4 . P ro d u c t, 5. H el p ( t hi s opt i on) , or 6 . Q u it.

En t e r En v i r o n me n t , Che mi c a l , Lo a d , P r o d u c t , Hel p , o r Qui t
- > CH E M I CA L C atalog of CH E M I CA L p a ra m e te r se ts UDB No
. Na me o f E n t r y Vo l u me131 1 C h e m ic a l D a ta E n try T e m p la te 2 p- C r es ol 3 B enz[ a] ant hr ace ne

.

.

. E X A M S -> Thi s exampl e us e of

t he CA T AL OG comm and l i st s t he c ont ent s of t he c ur r ent U se r D at abas e f or che m i cal dat a. A ny of t hes e da t as et s can be l oaded i nt o t he A ct i vi t y D at abas e ( ADB ) f or s t udy, us i ng t he RECALL co m m an d an d t h e a p p rop ri ate a cc e ss n u m b e r. T h e fi rst en t ry ( “Chem i cal D at a Ent r y Tem pl at e”) i s a bl ank da t a a r ea r es er ved f or ent er i ng new che m i cal dat a.
2
. E X A M S -> CA T AL OG E NVI RO N C atalog of E NVI RO NME NT a l m o d e ls UDB No
. Na me o f E n t r y Vo l u me 1 E n v iro n m e n ta l D a ta E n try T e m p la te 2 P o n d -- co d e tes t d a ta 3 C o n n ec t i cu t R i v er es t u ary

.

. Thi s exampl e CA T AL OG comm and ge ner at es a l i st i ng of t he e nvi r onm ent al dat as et s presenti n t he U se r D at abas e. A ny of t hes e c an be r et r i eved f

or s t udy us i ng a RECALL com m and and t he ac cessi on num ber. T he fi r st ent r y (“ E nv i r on m ental D at a E nt r y T em pl at e”) i s a te m p la te fo r e n te rin g a n e w e n v iro n m e n ta l m o d e l.132 C H A N G E U se t o ent er dat a i nt o t he a ct i vi t y dat abas e ( synonymous w i t h SE T ).

R el at ed: C om m and s: DES CRI BE , HELP , SE T Synt ax: CH ANG E <nam e of var i abl e> TO <new val ue> o r SE T <nam e of var i abl e> = <new val ue>

P rom p t : E n t er n am e= v alu e c o m m an d ->
V ariab l e: T h e d ata e n t ry o r va ri ab l e to b e e n t ere d ca n be spe cifi ed ei t h er as a sing l e d atu m or, using w i l d ca rds (*), as a n en t i re v ec t o r,

r ow / col um n of

a mat r i x, et c.
D es cr i pt i on: U se t he CH ANG E comm and t o s peci f y t he va l ues of

dat a i n t he a ct i vi t y dat abas e. “ V al ue” can be a ny num er i cal quant i t y or l i t era l ch ara cters, as a p p rop ri ate. “V ariab l e” s p e c ifies a n ind i v i d u al elem en t of inp u t da t a o r a pro g ram co n t rol pa ram eter. E n t i re v ec t o rs, row s/co l u m n s o f m atri ce s, etc. ca n be set t o a sing l e u n i form va l u e u sing w i l d ca rds (*).

E xam pl es: 1. E X A M S -> CH ANG E VOL ( 153) T O 7 E 5 Subscr i pt out
- of

- r ange.
E X A M S -> DE S CR I BE VOL
VOL i s a R eal V ect or w i t h 10 0 el em ents.
E X A M S > CH ANG E VOL ( 2) T O E Inv ali d nu m eric qu an t i t y aft er TO o r=.
E X A M S -> CH ANG E VOL ( 2) T O 7 E 5
Thi s com m and s et s t he e nvi r onm ent al vol um e of s egm ent 2 t o 7. 0E+ 05 c ubi c m et er s. The i ni t i al a t t em pt t o s et t he vol um e of s egm ent 153 w as r ej ect ed by E X A M S be caus e t he ver si on i n us e w as s et up f or e nvi r onm ent al model s of 100 s egm ent s at m ost
. The DES CRI BE comm and w as us ed t o c heck t he number of s ubsc r i pt s and t he di m ens i onal s i ze of t he va r i abl e “ VOL ”. T he acc i dent al ent r y of an al phabet i c c har act er ( “E”) f or t he vol um e w as t r apped by t he CH ANG E c o m m a n d ; VOL ( 2) w as not al t er ed.

2. E X A M S -> HELP TCEL
TCEL i s a R eal M at r i x w i t h 10 0 row s and 1 3 co l um ns. Te mp e r a t u r e - CE Ls i u s ( s e g me n t , mo n t h ) Un i t s : d e g r e e s C. A ver age t em per at ur e of ec osys t em s egm ent s. U sed (as enabl ed by i nput dat a) t o comput e e f f ect s of t em per at ur e on t r ans f

or m at i on r at es and ot her pr op ert i es of che m i cal s.
E X A M S -> CH AN GE TCEL ( 2, 7) T O 24133

T hi s com m and change s t he J ul y t em per at ur e i n s egm ent 2 t o 24 E C
. T he H E L P co m m and w as used to check subscri pt di m ensions, m axi m um val ues , t he meani ng of t he s ubsc r i pt s ( subs cr i pt #1 denot es t he s egm ent , s ubsc r i pt #2, t he m ont h) , a nd t he pr oper uni t s f or t he i n p u t da t u m (de g ree s C elsius).

3. E X A M S -> HE L P P OH
P OH i s a R eal M at r i x w i t h 10 0 row s and 1 3 co l um ns. p O H (se g m e n t, m o n th ) U n its: p O H u n its T h e n e g a t i v e v a l u e o f

t h e p o we r t o wh i c h 1 0 i s r a i s e d i n o r d e r t o o b t a i n t h e t e m p o r a l l y a v e r a g e d c o n c e n t r a t i o n o f h y d r o x i d e [ OH ] - i o n s in g ram -eq u i v alen t s p er l i t er.
E X A M S -> CH ANG E P OH ( *, 13) T O 6 .2
Thi s com m and s et s t he a ver age pO H ( se ct or 13) of e ver y s egm ent t o 6. 2. N ot e use of w i l d c ar d “ *” t o s peci f y t hat al l s egm ent s ar e t o be c h a n g e d . A s in th e p re v io u s e x a m p le , HELP w a s u se d to c h e c k su b sc rip t d im e n sio n s, u n its, etc . T h is s te p , o f c o u rs e , i s o p tion a l.134 C O N T I N U E The CO NT I NUE com m and r esum es E X A M S ’ s i mu l a t i o n a n a l y s i s o f c h e mi c a l d y n a mi c s b e g i n n i n g f r o m t h e c u r r e n t s t a t e o f t h e s y s t e m.
R el at ed: C on t r ol vari ables: CI NT , T IN IT , T E ND , T CO DE , NYE AR

C om m and s: RU N , S HOW

_ T I M E

_ F R A M E Synt ax: CO NT I NUE P ro m p t: (In M o d e 2 o n ly :)

In iti a l t im e fo r in te g ra tion w ill b e (n n .n ) u n its E n t er en d i n g t i m e o f i n t eg rati o n , H elp , o r Q u i t -> O p t i o n s: N o n e. R ep l y t o pro m p t w i t h a v alu e g rea t er t h an (nn .n). D es cr i pt i on: The CO NT I NUE com m and r esum es E X A M S ’ s i m ul at i on ana l ysi s of chemi cal dynam i cs , begi nni ng f r om t he c ur r ent s t at e of t he sys t em . Chem i cal l oadi ngs and ot her i nput da t a can be a l t er ed ( CH ANG E d or SE T ) b e tw e e n sim u la tion ti m e se g m e n ts; E X A M S w ill re -e v a lu a te e q u a tion p a ra m e te rs a s n e e d e d to in c o rp o ra te th e c h a n g e d c o n d iti o n s in to th e a n a ly sis
. CO NT I NUE cannot be i nvo ked fr om M od e 1 , w her e i t i s not appr opr i at e. The S H O W T I M E F R A M E ( abbr evi at e t o SH T F ) c o m m a n d c a n b e u se d to exami ne t he cur r ent st at e of t he i nt egr at or t i m er cont r ol s. I n M ode 2, t he C om m un i cat i on s I NT e rv a l CI NT can be use d t o va ry th e te m p o ra l re so lu tion in d iffe re n t se g m e n ts o f th e a n a ly sis (se e E x a m p le 1 ). In M o d e 3 , NYE AR , t he num ber of ye ar s i n a si m ul at i on t i m e s egm ent , ca n s i m i l ar l y be a l t er ed. E xam pl es: 1
. E X A M S -> S E T M ODE =2
E X A M S -> S H O W T I M E F R A M E A RU N w i l l i n t eg rate fr o m 0
. t o 2 4
. H o u rs w i t h ou t p u t at i n t erv als o f 2 .00 H o u rs
E X A M S - > S E T T CO DE =2
E X A M S - > S E T T E ND =10
E X A M S - > S E T CI NT =1
E X A M S - > S H T I F A RU N w i l l i nt egr at e f

r om 0 t o 10 D ays w i t h output ati nt er val s of 1 D ays
E X A M S - > RU N S i m u l ati o n be g i n n i n g for: E n v iro n m e n t: P o n d -- co d e tes t d a ta C h e m ic a l 1 : D ic h lo ro e x a m p le R u n c o m p le te
E X A M S -> PLO T K I N PL ( 3, 0, 0 -

- s ee P L OT comm and)

System: Pond -- code test data135 Chemical: Dichloroexample 2.00 I** *** I * ****   I ** **   ** * I * ****   **  I ** *** 1.33 I I I I I 0.667 I I I I I 0.000 I +----+----+----+----+----+----+----+----+----+----+ 0.000 2.00 4.00 6.00 8.00 10.0 1.00 3.00 5.00 7.00 9.00 Time, Days

E X A M S - > CO NT I NUE I ni t i al t i m e for i nt egr at i on w i l l be 10. 0 D ays Ent er endi ng t i m e of

i nt egr at i on, H el p, or Q ui t
- > 30 S i m u l ati o n be g i n n i n g for: E n v iro n m e n t: P o n d -- co d e tes t d a ta C h e m ic a l 1 : D ic h lo ro e x a m p le R un com pl et e.
E X A M S - > S E T CI NT =10 E X A M S - > Z E RO P UL S E L OAD E X A M S - > CO NT I NUE I ni t i al t i m e for i nt egr at i on w i l l be 30. 0 D ays Ent er endi ng t i m e of

i nt egr at i on, H el p, or Q ui t
- > 90 S i m u l ati o n be g i n n i n g for: E n v iro n m e n t: P o n d -- co d e tes t d a ta C h e m ic a l 1 : D ic h lo ro e x a m p le R un com pl et e.
E X A M S -> P L OT KI NE T I C P L OT ( 3, 0, 0)136 System: Pond -- code test data Chemical: Dichloroexample 3.49 I * I ** I ** I * I ** 2.33 I ** I* ** I*** *** I *** I ** * 1.16 I * I * I * * * I I 0.000 I +----+----+----+----+----+----+----+----+----+----+ 0.000 18.0 36.0 54.0 72.0 90.0 9.00 27.0 45.0 63.0 81.0 Time, Days

These com m ands show t he use of t he CO NT I NUE c om m and i n M ode 2. The obj ect i ve of t he anal ysi s w as t o i nt r oduce t w o pul se s of chem i cal sepa r at ed by 10 days and t o fol l ow exposur e over 90 days. N ot e t he phas ed i ncr eas e i n t he C om m un i cat i on s I NT er val CI NT f r om 1 t o 10 days
. N ot e t he us e of t he Z E RO com m and t o cl ear t he pul se l oad ADB befor e t he s i m ul at i on of di ss i m i l at i on f

r om d a y 3 0 th ro u g h d a y 9 0 . If t h is w e re n o t d o n e , E X A M S w oul d i nt r oduce an a ddi t i onal pul se on day 30.

2
. E X A M S - > S E T M ODE =3
E X A M S - > SH O TI FR A RU N w i l l i nt egr at e f

r om 1 J anuar y 1989 t hr ough 31 D ece m ber 1989. ( YE AR 1 = 1989, and NYE AR = 1.)
E X A M S - > RU N S i m u l ati o n be g i n n i n g for: E n v iro n m e n t: P o n d -- co d e tes t d a ta C h e m ic a l 1 : D ic h lo ro e x a m p le R un com pl et e.
E X A M S - > SH O TI FR A RU N w i l l i nt egr at e f

r om 1 J anuar y 1989 t hr ough 31 D ece m ber 1989. ( YE AR 1 = 1989, and NYE AR = 1.)
CO NT i nuat i on w i l l pr ocee d t hr ough 31 D ece m ber 1990 ( NYE AR = 1 .)
E X A M S - > S E T NYE AR =3 E X A M S - > S H T I F137

A RU N w i l l i nt egr at e f

r om 1 J anuar y 1989 t hr ough 31 D ece m ber 1991. ( YE AR 1 = 1989, and NYE AR = 3.)
CO NT i nuat i on w i l l pr ocee d t hr ough 31 D ece m ber 1992 ( NYE AR = 3 .)
E X A M S - > CO NT I NUE
CO NT i nui ng i nt egr at i on t hr ough 31 D ece m ber 1992. S i m u l ati o n be g i n n i n g for: E n v iro n m e n t: P o n d -- co d e tes t d a ta C h e m ic a l 1 : D ic h lo ro e x a m p le R un com pl et e.
E X A M S -> These com m ands i l l ust r at e the us e of t he CO NT I NUE c o m m a n d in M o d e 3 . “ S H O W T I M E F R A M E ” i s use d t o c hec k t he s t at e of t he i nt egrat or t i m er con t r ol s.138 D E S C R I B E R epo r t s t he d at a t yp e, di m ensional i t y, and m axim um U D B st orage si ze of par am et ers .
R el at ed: C on t r ol vari ables:

C om m and s: HELP Synt ax: DES CRI BE < p ara m eter>

Pa r am et ers : A n y “ sy ste m p a ra m e te r” --a n y c h e m ic a l o r e n v iro n m e n ta l i n p u t d a tu m , co n tro l p a ra m e te r (e .g ., M ODE , CI NT ) , et c.
P rom p t : E n t er n am e o f i n p u t pa ram eter->
O pt i ons: A ny par am et er ac ces si bl e t o t he CH ANG E and SE T com m and s.
D es cr i pt i on: The DES CRI BE c o m m a n d re tu rn s in fo rm a tion a b o u t E X A M S ’ i nput dat a a nd cont r ol par am et er s. A l l var i ables w hose val ues

can be al t er ed us i ng t he CH ANG E and SE T com m ands ca n be i nspe ct ed by t he DES CRI BE com m and. The i nfor m at i on r et ur ned by DES CRI BE in c lu d e s th e d a ta ty p e (r e a l, in te g e r, ch a ra c te r), d im e n sio n a lit y (sc a la r, v e c to r, m a trix (2 -d im e n sio n a l), t a b le ( 3- di m ens i onal m at r i x) ) and t he m axi m um s i ze t hat ca n be STO R Ed i n t he U D B ( fi l e “ EX A M S. D A F”) of t he ve r si on of E X A M S i n us e. W hen a SE T or CH ANG E com m and fai l s, t he DES CRI BE com m and c an he l p di agnos e t he pr obl em by i ndi cat i ng t he s t r uct ur e a nd di m ens i onal i t y of t he va r i abl e.
E xam pl es: 1
. E X A M S - > DE S R MODE C om m and notr ecogni zed. Type HELP for com m and i nfor m at i on.
E X A M S - > DES CR En t e r n a m e o f

i n p u t p a r a m e t e r - > M ODE
M ODE i s an Integ er S ca l ar. T h e se c o m m a n d s e sta b lish th a t “ M ODE ” is an i n t eg er sc alar. N o t e tha t t h e init i al t y p i n g error ( D ESR ) r es ul t ed i n a “notr ecogni zed” er r or m es sa ge fol l ow ed by r et ur n t o t he E X A M S p ro m p t.
2
. E X A M S -> CH ANG E VOL ( 133) T O 7 E 5 Subscr i pt out
- of

- r ange.
E X A M S -> DE S CR I BE VOL
VOL i s a R eal V ect or w i t h 10 0 el em ents. T h is c o m m a n d re p o rts th a t VOL i s a r eal vari able, a vector of 10 0 el em ents. I n t hi s exa m pl e, t he n um ber of segm ents ( N PX ) of

an aquat i c s yst em m odel t o be S T ORE d i n t he UDB of the ve rsi o n of E X A M S cur r ent l y i n us e i s se t for 100 atm ost . T he num ber of com put at i onal el em ent s of t he c ur r ent m odel i n t he ADB i s co n t roll ed by t h e u se r’ s se t t i n g of “ KOU NT . ” A ny ( i nt ent i onal or139

acc i dent al ) at t em pt t o ent er a va l ue for t he VOL u m e o f a seg m en t > t h e c u rr en t va l u e o f KOU NT (e .g ., VOL ( 13 3)) w i l l fai l , as i l l ust r at ed a bove. Si m i l ar l y, an a t t em pt t o S T ORE an e nvi r onm ent w i t h >100 segm ent s w i l l be r ej ect ed, w i t h t he s ugges t i on t hat t he W RI TE c o m m a n d b e u se d to sto re th e d a ta in a se p a ra te fil e . D E S CRI BE ca n be us ed t o ch eck t he r eas on for a fai l ur e of t he S T ORE com m and w hen a pr obl em w i t h di m ens i on s i zes i s sus pect ed.
3
. E X A M S -> DESCRI BE QY I EL D Q Y I EL D i s a R eal Tabl e w i t h di m ens i ons ( 3, 7, 5)
E X A M S -> H ELP QY I EL D Q Y I EL D i s a R eal Tabl e w i t h di m ens i ons ( 3, 7, 5) Q uant um _Y I EL D ( form , i on , chem i cal ) U ni t s: di m ensionl ess R e a c tion q u a n tu m y ie ld fo r d ire c t p h o to ly sis o f c h e m ic a ls--fra c tion o f th e to ta l l ig h t q u a n ta a b so rb e d b y a c h e m ic a l t h a t res u lts i n t r ans for m at i ons. Separ at e va l ues ( 3×7= 21) for ea ch pot ent i al m ol ecul ar t ype of ea ch chem i cal a l l ow t he e ffect s of s peci at i on and s or pt i on on r eac t i vi t y t o be s peci fi ed i n det ai l
. M at r i x of 21 val ues s peci fi es quant um yi el ds for t he ( 3) phys i cal for m s: ( 1) d i sso l v ed , (2) sed i m en t -so rbe d , an d (3) DOC - com pl exed; of e ach of ( 7) pos si bl e c hem i cal s peci es : neut r al m ol ecul es ( 1) , ca t i ons ( 2

- 4 ) , a n d a n i o n s ( 5

- 7 )
. ( QY I EL D is a n e ffic ie n c y , h e n c e d im e n sio n le ss .) These com m ands r epor t t he da t a t ype a nd UDB st o rag e ca p ac i t y of E X A M S ’ i n p u t “ QY I EL D ” (resu l t of “ DESCRI BE QY I EL D ”) and t h en rep o rtt h e m ea n i n g of the dim en sion s an d t h e p h y sica l un i t s o f t h e v ariab l e (resu l t of “ HELP QY I EL D ”)
. The l ocal i m p l em en t ati o n of E X A M S us ed i n t hi s exam pl e ha s t he c apac i t y t o s t or e l oad pa t t er ns and pr oduct che m i st r i es of no m or e t han fiv e c h e m ic a ls s im u ltan e o u sly . T h u s, QY I EL D w as DES CRI BE d a s co n sist i n g of a se t of fi v e m atri ce s, eac h of (f i x ed ) si ze (3,7). N o t e, ho w e v e r, tha t E X A M S c a n a c c o m m o d a te a n u n lim ited n u m b e r o f c h e m ic a ls in a n y g iv e n stu d y (e .g ., 25 se p a ra te or ganophos phor us pes t i ci des , a s ui t e of 12 P C B congener s, et c. ) by SE T t i n g t h e v alu e o f KC HEM . Loadi ng pat t er ns or pr oduct chem i st r i es of

di m ens i onal i t i es >5 c annot be s t or ed i n t he UDB , how ever , but m ustbe w r i t t en t o ext er nal f i l es ( se e doc um ent at i on for t he W RI TE co m m an d ).140 D O

E x e c u te s a c o m m a n d p ro c e d u re ; req u e sts th a t E X A M S r ead subs equenti nput f r om a s peci fi c f

i l e. R el at ed: C on t r ol vari ables:

C om m and s: A U D IT Synt ax: DO <nam e of com m and f

i l e> P rom p t : E n t er n am e o f f i l e (n o m o re t h an nn ch ara cters), H elp , o r Q u i t -> P a ra m e te rs : n a m e o f fil e

S p ec i fi es t h e fi l e from w h i ch t o read a se ri es of E X A M S co m m an d s. If yo u do no t spe cify a f i l e t y p e s u ffix , E X A M S u se s a d efa u l t fi l e typ e o f E XA ( e. g. , “f i l enam e. E XA ”)
. W i l d ca r ds ar e notal l ow ed i n t he f i l e s peci fi cat i on. D es cr i pt i on: U se c om m and pr ocedur es t o ca t al og f r equent l y us ed s equenc es of com m ands
. A n E X A M S c o m m a n d p ro c e d u re c a n c o n ta in
! A ny val i d E X A M S com m and. The com m and l i ne c an i ncl ud e all t he nec es sa r y opt i ons and da t a t o bui l d a c om pl et e c om m and (ex ce p t i o n : kin eti c p l o t s).
! Pa r am et ers or r espo nse o pt i on s for a spec i fi c co m m and
. W hen t he cu r r entl y ex ecu t i ng com m and r equ i r es add i t i on al param et ers , th e n e x t l in e o f th e c o m m a n d fil e is se a rc h e d fo r a p p ro p ria te in p u t.
! D a ta . W h e n t h e cu rr en t l y ex ec u t i n g co m m an d r eq u i res nu m erical or ch ara cter da t a en t ry, t h e n ex t l i n e o f t h e co m m an d fil e is se a rc h e d fo r in p u t.
! C om m ent l i nes . A ny l i ne t hat cont ai ns an e xcl am at i on poi nt ( ! ) or as t er i sk (*) i n c ol um n one i s i gnor ed by E X A M S ’ com m and i nt er pr et er . These l i nes ca n be us ed a s neede d t o docum ent t he c om m and pr ocedur e. C om m and pr ocedur es m ustnot cont ai n a r eques t t o exe cut e an ot her com m and pr ocedur e. ( I n ot her w or ds, a DO f i l e m ustnot cont ai n a DO (@ ) c o m m a n d ; E X A M S ’ DO com m ands ca nnot be ne st ed. ) C om m and pr ocedur es ca n be c onst r uct ed as e xt er nal f i l es usi ng yourfavor i t e edi t or , ort hey can be cons t r uct ed i nt er act i vel y t hr ough t he E X A M S sys t em com m and pr oces sor , as i l l ust r at ed below
. T he d efaul t f

i l e t yp e i s “ E XA ”, but f

i l es of a ny t ype ( suf

fi x) c an be use d i f

t he ent i r e fi l e nam e i s spe ci fi ed w hen e nt er i ng t he D O com m and. E x a m p le s: 1
. E X A M S - > AUD I T ON

A l l i nput w i l l now be c opi ed i nt o t he fi l e na m ed “ AUD OUT ” o n F o rt ran U n i t N u m b er 4
E X A M S - > RECALL En t e r En v i r o n m e n t , Che m i c a l , Lo a d , P r o d u c t , Hel p o r Qui t
- > E NV E n te r e n v iro n m e n t UDB c a t a l o g n u m b e r , Hel p , o r Qui t
- > 2 Sel ect ed e nvi r onm ent i s: Phant om I nl et
E X A M S - > R E C A L L C H E M 2 S e le c te d c o m p o u n d is: D ic h lo ro e x a m p le
E X A M S - > RE CA L L L OAD 2 S elec t ed l o ad i s: A ed es co n t rol spra y drif t141 E X A M S - > ! Load 2 i s t he Phant om I nl et s al t m ar sh st udy E X A M S - > S E T KC HE M T O 2 E X A M S - > R E C A L L C H E M 4 A S 2 S e le c te d c o m p o u n d is: T e tra b ro m o e x a m p le
E X A M S - > A U D I T O FF These com m ands bui l d a f i l e ( AUD OUT .D AT ) t hat ca n l at er be us ed a s a c om m and f i l e upon e nt er i ng t he E X A M S sy ste m . In th is in sta n c e , t h e fil e c o u ld b e re n a m e d (e .g ., S E T UP .E XA ) a n d u se d to e x e c u te th e a b o v e se rie s o f c o m m a n d s a s a u n it:
E X A M S - > DO S E T UP o r, E X A M S - > @ S E T UP T h e c o mp l e t e d c o mma n d f i l e a p p e a r s a s fo l l o ws RECALL E N V 2 R E C A L L C H E M 2 RE CA L L L OAD 2 ! Load 2 i s t he Phant om I nl et s al t m ar sh st udy S E T KC HE M T O 2 R E C A L L C H E M 4 A S 2 A U D I T O FF N ot e t hat com m and fi l es t hat a r e cons t r uct ed i nt er act i vel y w i l l i ncl ude “ A U D I T O FF ” a s t he f i nal i nst r uct i on. Thi s can, of cour se , be r em oved by e di t i ng t he f i l e i f i t i s undes i r abl e. 2
. E X A M S - > DO En t e r n a m e o f

f i l e ( n o m o r e t h a n n n c h a r a c t e r s ) , Hel p , o r Qui t
- > HELP The “ DO ” or “ @ ” com m and pr ovi des a m eans of exe cut i ng s t or ed E X A M S c o mma n d s . I n r e s p o n s e t o t h e p r o mp t , e n t e r t h e n a me o f t h e fi l e tha t co n t ain s the stored co m m an d s. A t h ree -ch ara cter fi l en am e e x t en sion of “ E XA ” i s adde d t o t he nam e i f no per i od i s pr es ent i n t he na m e a s ent er ed. The m axi m um l engt h for f i l e na m es i s nn cha r act er s; t hi s l i m i t i ncl udes t he . E XA s uffi x. En t e r n a m e o f

f i l e ( n o m o r e t h a n n n c h a r a c t e r s ) , Hel p , o r Qui t
- > AUD OUT
E X A M S / DO - > ! A u d i t t r a i l o f i n p u t s e q u e n c e f

r o m E X A M S . E X A M S / DO -> RECALL E n t er E n v i ron m en t , C h em i ca l , L o ad , P rod u ct, H elp , o r Q u i t -> E X A M S / DO -> E NV E n te r e n v iro n m e n t UDB ca t alo g nu m b er, H elp , o r Q u i t -> E X A M S / DO -> 2 Sel ect ed e nvi r onm ent i s: Phant om I nl et E X A M S / DO -> R E C A L L C H E M 2 S e le c te d c o m p o u n d is: D ic h lo ro e x a m p le E X A M S / DO -> RE CA L L L OAD 2 S elec t ed l o ad i s: A ed es co n t rol spra y drif t E X A M S / DO - > ! Load 2 i s t he Phant om I nl et s al t m ar sh st udy E X A M S / DO -> S E T KC HE M T O 2142 E X A M S / DO -> R E C A L L C H E M 4 A S 2 S e le c te d c o m p o u n d is: T e tra b ro m o e x a m p le E X A M S / DO -> A U D I T O FF The A U D IT opt i on has bee n t er m i nat ed. Thi s com m and r eques t s exec ut i on of t he c om m and pr ocedur e cons t r uct ed i n E xam pl e 1 above
. The defaul t nam e ( AUD OUT ) w as not al t er ed, s o t he c om pl et e f i l e s peci fi cat i on w as gi ven t o t he DO com m and a s t he e nt r y par am et er . The DO fi l e t r a n s fe r s a s e t o f t wo chem i cal s, an e nvi r onm ent al m odel , and a l oad pa t t er n f r om t he s t or ed UDB t o t he ADB for s t ud y an d an al ysi s.143 E C H O
The E CH O co m m an d t u rns ec h o i n g of co m m an d i n p u t s o n an d off.

R el at ed: C ont r ol var i abl es : N one

C om m ands : N one Synt ax: E CH O O N / O FF P ro m p t: T h e fo llow in g E c h o o p tion s a re a v a ilab le

O N – begi ns com m and e cho, O ff – t urns off

echo of i np ut com m and s, H el p – t hi s m es sa ge Q ui t – r et ur n t o t he E X A M S pr om pt O pt i on s : O FF

End echoi ng of

com m ands O N B egi ns echoi ng of

com m ands

D es cripti o n : If E CH O i s ent er ed f r om t he E X A M S pro m p t co m m a n d lev e l, E X A M S s to p s e c h o in g c o m m a n d s o n th e in te ra c tive term in a l. T h is feat ure i s pr i m ari l y useful for bat ch p r oce ssi ng , i n w hi ch ca se i t ser ves t o l i m i t t he si ze of r esult i ng output f i l es. E xam pl es: 1
. E X A M S -> E CH O O FF T h i s co m m an d t erm i n ates ec h o i n g of E X A M S com m ands att he t er m i nal or i n t he l og f i l e.
2
. E X A M S -> E CH O ON T h i s co m m an d resu m es ec h o i n g of E X A M S com m ands att he t er m i nal or i n t he l og f i l e.144 E R A S E

D el et es , by ac ces si on nu m ber, t he da t a s t or ed a t a s i ngl e s ect or of a U se r D at abas e ( UDB ) l i brar y (chem i cal , env i r on m ental , l oad i ng s, p rod u ct ch em i str y ).

R el at ed: C on t r ol vari ables:

C om m and s: CA T AL OG , RECALL , S T ORE Synt ax: ER A SE < o p t i o n > < ac ce ssion nu m b er> O pt i ons
CH E M I CA L E NVI RO NME NT L OAD P RODUCT

P rom p t : E n t er E n v i ron m en t , C h em i ca l , L o ad , P rod u ct, H elp , o r Q u i t ->
O pt i on s: CH E M I CA L D e le te s th e c o n te n ts, b y e n try a c c e ss n u m b e r, o f c h e m ic a l d a ta b a se s c u rre n tly in th e U se r D a ta b a se . E a c h e n try c o rre sp o n d s to a si ng l e che m i cal , and co nt ai ns t he l abo r at ory dat a descri bi ng i on i zat i on and ( species- specif i c) part i t i on i ng and r eacti on ki neti cs.
E NVI RO NME NT D el et es t he co nt ents, by en t r y a ccess nu m ber, of env i r on m ental dat aba ses curr entl y i n t he U ser D at aba se. E ach ent r y co nt ai ns a c a n o n ic a l p h y sic a l an d c h e m ic a l m o d e l o f a n a q u a tic sy ste m , in c lu d in g t h e en v iro n m e n ta l d a ta n e e d e d to c o m p u te th e re a c tivity a n d t r a n s p o r t o f

s y n t h e t i c c h e mi c a l s i n t h e s y s t e m.
L OAD D el et es t he c ont ent s, by entr y ac ces s num ber , of che m i cal l oadi ng pat t er ns st or ed i n t he U se r D at abas e. These dat a i ncl ude m o n t h l y va l u es (kg / h o u r) for st rea m l o ad s, n o n -po i n t -so u rce l o ad s, g rou n d w ater see p ag e l o ad i n g s, p rec i p i t ati o n l o ad s, an d drif t lo a d s o f c h e m ic a ls e n te rin g th e a q u a tic e n v iro n m e n t, p lu s th e m a g n itud e (k g ), ta rg e t e n v iro n m e n ta l se c to r, an d sc h e d u ling (m o n th and day ) of che m i cal pulse l oad s.
P RODUCT D el et es t he c ont ent s, by entr y ac ces s num ber , of che m i cal pr oduct dat a s t or ed i n t he U se r D at abas e ( UDB )
. Thes e dat a i ncl ude t he A ct i vi t y D at abas e num ber s of r eac t ant s and pr oduct s, t he num ber c ode of t he chem i cal pr oces s, a nd yi el d ef fi ci enci es ( m ol e/ m ol e) as an ( opt i onal ) f

unct i on of

t em per at ur e.
D es cr i pt i on: ER A SE del et es t he c ont ent s of a s i ngl e s ect or of

t he spe ci fi ed U se r D at abas e ( UDB ) l i brar y (chem i cal , env i r on m ental , l oad s, or pr oduct che m i st r y)
. The dat a t o be de l et ed ar e se l ect ed by c hoosi ng t he a ppr opr i at e a cce ss i on num ber
. ( I f you w or k i n a m u lti -u se r e n v iro n m e n t, b e su re to a v o id e ra sin g o th e rs ’ d a ta .)

E xam pl es: 1
. E X A M S -> E RA S E E NV 20 Envi r onm ent 20 er as ed.145

T h is c o m m a n d e ra se s th e d a ta sto re d a t E n v iro n m e n ta l UDB s ect or num ber t w ent y. T he spa ce i s now ava i l abl e for s t or i ng anot her d a ta se t.
2
. E X A M S -> ER A SE En t e r En v i r o n m e n t , Che m i c a l , Lo a d , P r o d u c t , Hel p , o r Qui t
- > HELP
The ER A SE co m m an d req u i res tha t yo u sp ec i fy e i t h er: 1 . E n v iro n m e n t, 2 . C h e m ic a l, 3. Load, 4 . P ro d u c t, 5. H el p ( t hi s opt i on) , or 6 . Q u it. En t e r En v i r o n m e n t , Che m i c a l , Lo a d , P r o d u c t , Hel p , o r Qui t
- > L OAD Ent er al l ocht honous l oadi ng UDB ca t al og num ber , H el p, or Q ui t
- > 10 Load 10 er as ed. T hi s com m and er ases t he d at a st ored at L oad i ng s UDB se c to r n u m b e r ten . T h e sp a c e is n o w a v a ilab le fo r a n o th e r d a ta se t.146 E X I T

E X IT ca n be us ed as a sy n o n y m for Q U IT t o end a n i nt er act i ve s es si on.
R el at ed: C on t r ol vari ables:

C om m and s: Q U IT i s used t o ab ortcom m and s i n progress. Synt ax: E X IT
Pr om pt : N one
O pt i ons: N one
D es cripti o n : If E X IT i s ent er ed f r om t he E X A M S p ro m p t co m m a n d lev e l, E X A M S s t o p s a n d r e t u r n s c o n t r o l t o t h e c o mp u t e r o p e r a t i n g s y s t e m.
E xam pl es: 1
. E X A M S -> E X IT Thi s com m and t er m i nat es an i nt er act i ve E X A M S s es si on.147 H E L P D i spl ays , on t he t er m i nal , i nfor m at i on ava i l abl e i n E X A M S ’ h e lp fil e s. E X A M S pr ovi des des cr i pt i ons of i t s com m ands , i nput dat a, cont r ol param et ers , and gen eral con cep t s and an al ysi s pr oce du r es.
R el at ed: C on t r ol vari ables:

C om m and s: DES CRI BE Synt ax: HELP [ keyw or d]

Pr om pt : N one
K ey w o rd: S p ec i fi es a k ey w o rd (a top i c o r an elem en t of E X A M S i np ut dat a) t hat t el l s E X A M S w hat i nfor m at i on t o di spl ay.

! N o n e--i f HELP is ty p e d w ith n o k e y w o rd , E X A M S l i st s t he ke yw or ds t hat ca n be s peci fi ed t o obt ai n i nfor m at i on aboutot her t op i cs.
! Topi c- nam e- - des cr i bes e i t her a ba si c E X A M S c o m m an d , an info rm ati o n p ag e, o r a “ sy stem p ara m eter.” S y stem pa ram eters in c lu d e c h e m ic a l an d e n v iron m en t al i n p u tda ta , sy ste m c o n tro l p a ra m e te rs (e .g ., CI NT ) , and pa r am et er s t hat cont r ol t he c ur r ent a n a ly sis (e .g ., I M A SS ).

A m bi guous abbr evi at i ons r es ul t i n a fai l ur e t o ac hi eve a m at ch on t he ke yw or d, and a n er r or m es sa ge i s di spl ayed.

D es cr i pt i on: The HELP com m and pr ovi des ac ces s t o E X A M S ’ col l ect i on of on- l i ne us er ai ds and i nfor m at i on t ext s. Thi s m at er i al i ncl udes
! B ri ef d i sc u ssion s o f t h e sy n t ax an d fun cti o n of ea ch of E X A M S ’ com m and w ords ( RECALL , RU N , etc .)
! D efinit i o n s, p h y sica l dim en sion s, an d m ea n i n g s of sub sc ri p t s fo r E X A M S ’ che m i cal and e nvi r onm ent al i nput dat a a nd cont r ol param et ers . ! A s er i es of

i nfor m at i on pa ges pr ovi di ng or i ent at i on t o t he c oncept s i m pl em ent ed i n t he E X A M S pr ogr am , t he r ange of ca pabi l i t i es and analyses t hat can be ex ecu t ed w i t h t he p r og r am , and bri ef exp osi t i on s on da t a st r uctur es and program con t r ol opti on s. E xam pl es: 1
. E X A M S - > HELP
E X A M S i ncludes t hese system com m and s:

.

. HELP m es sa ge t ext and l i stof com m and a nd

. i nfor m at i on t opi cs
I ss ui ng t he HELP com m and w i t hout any ke yw or ds pr oduces a l i stof t he HELP t opi cs i n E X A M S m ai n c om m and l i brar y. W hen re sp o n d in g to o n e o f th e to p ic s o n th e li st, E X A M S di spl ays a HELP m es sa g e o n t h at t o p i c, an d a li st of sub t o p i cs (i f an y ).

2
. E X A M S -> H E L P Q U O IT N o in fo rm a tion a v a ilab le fo r th is re q u e st.148 E X A M S -> W h e n y o u re q u e st in fo rm a tion fo r a to p ic n o t o n fil e , E X A M S di spl ays a m es sa ge t o t hat ef fectand r et ur ns you t o t he E X A M S -> p ro m p t.
3
. E X A M S - > H ELP QY I EL D Q Y I EL D i s a R eal Tabl e w i t h di m ens i ons( 3, 7, 4) Q uant um _Y I EL D ( form , i on , chem i cal ) U ni t s: di m ensionl ess R e a c tion q u a n tu m yie ld for d ire c t p h o to ly sis of c h e m ic a ls--fra c tion of th e t o ta l ligh t q u a n ta ab so rb e d by a c h e m ic a l t h a t res u lts i n tr ans for m at i ons. Sepa r at e val ues ( 3×7= 21) for ea ch pot ent i al m ol ecul ar t ype of ea ch c hem i cal al l ow t he e ffect s of s peci at i on and s or pt i on on r eac t i vi t y t o be s peci fi ed i n de t ai l
. M at r i x of 21 val ues s peci fi es qua nt um yi el ds for t he ( 3) phys i cal for m s: ( 1) d i sso l v ed , (2) sed i m en t -so rbe d , an d (3) DOC - com pl exed; of e ach of ( 7) pos si bl e chem i cal s peci es : ne ut r al m ol ecul es ( 1) , ca t i ons ( 2

- 4 ) , a n d a n i o n s ( 5

- 7 )
. ( QY I EL D is a n e ffic ie n c y .) Y o u c a n re q u e st in fo rm a tion a b o u t an y in p u t d a tu m (c h e m ic a l, e n v iro n m e n ta l, c o n tro l p a ra m e te rs , an a ly sis p a ra m e te rs ) a c c e ss ib le t o t he CH ANG E and SE T com m and s. E X A M S t hen di spl ays on t he s cr een t he c har act er i st i cs of t he va r i abl e ( equi val ent t o t he r es ul t s of DES CRI BE ), foll o w ed by a d i sc u ssion of the va ri ab l e tha t ec h o es t h e e n t ry in the D ata D i cti o n ary (pa g e 1 8 0 ).149 L I S T

D i spl ays an E X A M S out put t abl e on t he t er m i nal s cr een.
R el at ed: C on t r ol vari ables: F IX F IL

C om m and s: P L OT , P RI NT Synt ax: LI ST <opt i on>

O pt i ons t ab l e-# ALL HELP
Pr om pt : Ent er Tabl e N um ber - > opt i on

O pt i ons: t abl e- # spe ci fi es t he num ber of an E X A M S out put t abl e t o be di spl ayed.
ALL Se qu enti al di spl ay o f al l curr ent ou t pu t t ables.
HELP D i sp l ay s a li st of t i t l es of E X A M S outpu t t ables.

D es cr i pt i on: The LI ST com m and di spl ays E X A M S ’ out pu t t ables at t he t er m i nal
. To t em por ar i l y hal t t he out put and r es um e i t att he l i ne

w her e i t w as i nt er r upt ed, us e CT RL / S fol l ow ed by CT RL / Q . W h en yo u req u es t a p ri m ary tab l e n u m b er (t h at is, a n integ er from 1 to 2 0 ) E X A M S di spl ays t he f i r stt abl e of

t hat num ber pr es ent in th e a n a ly sis fil e . If ad d iti o n a l t a b le s o f t h a t ty p e are pre se n t i n th e fil e , E X A M S w i l l disp l ay t h e fi rst , an d t h en sea rch for m o re t a b l e s o f t h a t t y p e a n d , i f

a n y a r e fo u n d , a s k i f

y o u w a n t t o s e e t h e m. E xam pl es: 1
. E X A M S - > LI ST A P RI NT , LI ST , o r P L OT com m and w as i ss ued be for e e xecut i ng a RU N . I f r es ul t s exi stf

r om a pr evi ous si m ul at i on, t hes e c an be a c c e ss e d a fte r iss u in g th e c o m m a n d : S E T F I XF I L T O 1
E X A M S -> S E T F I XF I L T O 1
E X A M S - > LI ST En t e r Ta b l e Numbe r - > HELP 1 C h e m ic a l i n p u ts: FATE D a ta 2 C h e m ic a l i n p u ts: P RODUCT C h em i str y 3 PU LSE C hem i cal Loadi ngs

.

.

.150

1 8 S e n sitiv ity A n a ly sis o f C h e m ic a l FATE 19 Sum m ar y T I M E - T RACE of C hem i cal C oncent r at i ons 20 E xp osure A nalysi s S UM M ARY A L L E n t i re R ep o rt Tabl e- > 18 Ecosystem: Name of Water body Chemical: Name of chemical

---------------------------------------------------------- TABLE 18.01. Analysis of steady-state fate ...

----------------------------------------------------------

. . (body of table)

.

----------------------------------------------------------
The LI ST c om m and r eques t s t hat out put Tabl e 18 f r om an E X A M S resul t s fi l e b e d i spl aye d o n the t erm i nal. F or i l l ust r at i ve p urposes, it w a s a ss u m e d th a t t h e u se r h a d left E X A M S and t hen r et ur ned t o i nspe ct Tabl e 18 ge ner at ed i n t he pr evi ous se ss i on.

2
. E X A M S - > LI ST 20 Ecosystem: Name of Water body Chemical: Name of FIR ST chemical

---------------------------------------------------------- TABLE 20.01. Exposure analysis summary: 1983--1985.

----------------------------------------------------------

. . (body of table)

. M o r e ? ( Y e s / N o / Q u i t )

- > Y Ecosystem: Name of Water body Chemical: Name of SEC OND chemical

---------------------------------------------------------- TABLE 20.02. Exposure analysis summary: 1983--1985.

----------------------------------------------------------

. . (body of table)

.
In th is e x a m p le , E X A M S w as us ed t o i nves t i gat e t he be havi or of t w o che m i cal s ov er a peri od of s ever al yea r s, us i ng M ode 3 si m ul at i ons. The anal ysi s began w i t h ye ar 1983, and NYE AR w as sett o 3 t o pr oduce an a nal ysi s of t he pe r i od 1983 t hr ough 1985. The LI ST com m and r eques t s t hat al l ver si ons of T abl e 20 i n t he anal ysi s f i l e be di spl ayed, w i t h a pause bet w een ea ch for i nspe ct i on of t he r e s u l t s . I n t h e e x a mp l e , t h e a n a l y s t c h o s e t o e x a mi n e t h e o u t p u t fo r b o t h c h e mi c a l s . I f t h e a n a l y s i s i s n o w CO NT I NUE d, t he c ur r ent s et of t abl es w i l l be r epl ace d w i t h ne w r es ul t s. The P RI NT com m and shoul d be used t o m ake copi es of al l i nt er m edi at e r es ul t s you w ant t o s ave.
T h e su b -t ab l e n u m b ers o f E X A M S ’ out put t abl es i dent i f y t he ADB num ber of

t he c hem i cal , t he i ndexes of any i ons ( se e SP FL G i n t he D at a D i ct i on ary on pa ge 1 80 ) , and t he m on t h of t he y ear, as fol l ow s.
Tabl e Sub- t abl es Exam pl es Sub- t abl e M eani ng151

1 1. cc. i 1. 01. 1 Tabl e. chem i cal
. i on 4 -6 , 8 , N N .m m 4 .0 1 T a b le .m o n th 10, 11, 13 10. 13 ( 13 = annual m ean) 1 2 1 2 .c c .m m 1 2 .0 1 .1 2 T a b le .c h e m ic a l.m o n th 14 ( M ode 1⁄2 ) 14. cc 14. 01 Tabl e. chem i cal 1 4 (M o d e 3 ) 1 4 .c c .m m 1 4 .0 1 .1 2 T a b le .c h e m ic a l.m o n th 15- 18, 20 N N
. cc 18. 01 Tabl e. chem i cal 20. 01152 N A M E U se t he N A M E com m and t o at t ach unique n am es t o da t aset s.
R el at ed: C on t r ol V ari ables: M CH EM

C om m and s: CA T AL OG , ER A SE , S T ORE , RECALL Sy n t a x : <d a t a t y p e > N A M E IS a[ aa. . . ] ( up t o 50 cha r act er s) , w her e <dat at ype> can be CH E m ic a l, EN v iro n m e n t, LO ad , o r P RO duct Pr om pt : O pt i ons avai l abl e a r e:

H el p - t hi s m es sa ge. Q ui t
- r et ur n t o E X A M S com m and m ode. < c a rria g e re tu rn > = H e lp <any ot her r es ponse > - ac cept ed a s t he ne w nam e. E n t er n ew na m e-> <d a t a t y p e >: E X A M S uses t hese four ki nd s of dat aset s: 1
. CH E M I CA L r eac t i vi t y and pa r t i t i oni ng, 2
. E NVI RO NME NT al phy si co/chem i cal param et ers , 3 . allo c h th o n o u s c h e m ic a l L OAD i ngs, and 4
. PR ODUCT c h e m istry fo r g e n e ra ting in te rc o n v e rs io n s a m o n g m u lti p le c h e m ic a ls in a n a n a ly sis

D es cr i pt i on: The N A M E com m and i s use d t o as soc i at e uni que na m es w i t h dat as et s i n t he UDB . These nam es ca n be S T ORE d i n t he

CA T AL OG s; t h ey are p ri n t ed i n t h e h ea d ers o f E X A M S ’ out put t abl es . W hen na m i ng CH E M I CA L dat as et s, t he ADB num ber of t he c hem i cal t o be na m ed i s gi ven by M CH EM ; us e “ SE T M CH EM TO n” be for e na m i ng dat as et “n”
. E xam pl es: 1
. E X A M S - > C H E M N A M E IS T e tra c h lo ro e x a m p le The N A M E com m and a ss oci at es t he nam e “Tet r achl or o. . . ” w i t h t he chem i cal dat a i n t he se ct or of t he a ct i vi t y dat abas e ( ADB ) gi ven b y the c u rr en t v alu e o f M CH EM . T h is n a m e w ill be prin te d on all su b se q u e n t a p p ro p ria te ou tp u t ta b le s, a n d i t w ill be u se d a s a ti tle for t he da t abas e i f

t he S T ORE com m and i s use d t o dow nl oad t he da t a i nt o t he U se r D at abas e ( UDB ).

2
. E X A M S -> SE T M CH EM = 2
E X A M S -> C H E M N A M E IS D ic h lo ro e x a m p le The chem i cal nam e c om m and a l w ays addr es se s t he M CH EM se c to r ofth e c h e m ic a l ADB , t hus, t hi s exam pl e na m es che m i cal num ber 2 t o “D i chl or o. . . ”.
3
. E X A M S -> E N V IR N A M E IS Pogue Sound T h is c o m m a n d n a m e s th e c u rre n t en v iro n m e n ta l d a ta se t “P o g u e S o u n d ” . T h e n a m e w ill n o w a p p e a r o n o u tp u t t a b le s, a n d re m a in w i t h t he da t as et i f

i t i s dow nl oaded t o t he UDB perm ane nt f i l es.153 P L O T Us e d t o p l o t c h a r a c t e r g r a p h i c s fo r t h e c h e mi c a l s t a t e o f t h e e c o s y s t e m.
R el at ed: C on t r ol V ari ables: M CH EM

C om m and s: LI ST , P RI NT Synt ax: P L OT <O pt i on1, O pt i on2, O pt i on3> O pt i ons
P OI NT PROFI LE K IN E T IC
Pr om pt : The fol l ow i ng opt i ons ar e a vai l abl e: P O in t - V e rtica l co n c e n tra tion p ro file P R o file - L o n g itud in a l co n c e n tra tion p ro file K in e tic - L ist o r p lo t k in e tic o u tp u ts H el p - Thi s m es sa ge Q ui t
- R et ur n t o t he E X A M S pr ogr am pr om pt O p t i o n ->
Plot opti on s: P OI NT

“ P OI NT ” pl ot s ar e ge ner al i zed pr ofi l es of che m i cal conc ent r at i ons. T hes e al so r equi r e se l ect i on of a var i abl e t o be di spl ayed ( t ot al co n ce n t rati o n , d i sso l v ed co n ce n t rati o n , etc.) an d a “ stati sti ca l ” c l as s (av era g e v alu es , m i n i m a, or m ax i m a).

PROFI LE

“ PROFI LE ” pl ot s ar e l ongi t udi nal pr ofi l es of che m i cal conc ent r at i ons. These r equi r e sel ect i on of a c oncent r at i on var i abl e ( t ot al conce nt r at i on, di ss ol ved c oncent r at i on, et c. ) a nd a n envi r onm ent al s ect or ( w at er col um n or bent hi c s edi m ent s)
. The abs ci ss a of t he r esul t i ng plot i s se t up by i ncr eas i ng s egm ent num ber , w hi ch i n m ostca se s shoul d r epr es ent an ups t r eam - dow nst r eam pr ogr es si on. W hen t he a quat i c m odel i ncl udes bot h l ongi t udi nal and ver t i cal segm ent at i on, each s ect i on of t he pl ot begi ns at t he air- w ater or w ater/be n t h i c interfac e a n d pro ce ed s v erti ca l l y do w n w ard (t h e b ars a re p rese n t ed alon g t h e a b sc i ssa ).
K IN E T IC

“ K IN E T IC ” pl ot s di spl ay t he resul t s of i nt egrat i on of t he g ov erni ng equ at i on s over t he t i m e span s sel ect ed for si m ul at i on . T hese p l o t s a l s o r e q u i r e s e l e c t i o n o f c o n c e n t r a t i o n v a r i a b l e s a n d e i t h e r p a r t i c u l a r s e g me n t s , o r s u mma r y “ s t a t i s t i c s , ” fo r d i s p l a y . T i me i s use d as t he abs ci ss a for t he pl ot . The “ LI ST ” opt i on pr oduces num er i cal output w hi ch, w hen r e- di r ect ed t o an e xt er nal f i l e, ca n be u sed as a data s ou r ce for any graphi cs pack age t hat can assi m i l at e A SC I I f i l es.
D es cr i pt i on: U se t he P L OT com m and t o di spl ay r es ul t s of t he cur r ent ana l ysi s. Thr ee ki nds of cha r act er gr aphi c P L OT s ar e a vai l abl e on- l i ne f r o m E X A M S : P OI NT , PROFI LE , and K IN E T IC . Each P L OT r equi r es t he spe ci fi cat i on of seve r al opt i ons; t hes e c an e i t her be e nt er ed on t he s yst em com m and l i ne or ent er ed i n r es ponse t o E X A M S pro m p t s. T h e a v ail ab l e se co n d - an d t h i rd-lev el op t i o n s are i l l ust r at ed i n t he e xam pl es bel ow . The r es ul t s avai l abl e t o P OI NT and PROFI LE pl ot s depend on t he M ode use d i n t he si m ul at i on. I n M ode 1, t he out put s ar e st eady- st at e conce nt r at i ons. I n M ode 2, t he r es ul t s ar e a s nap- shotof conc ent r at i ons154 as of t he e nd of

t he cur r ent t em por al s i m ul at i on s egm ent . I n M ode 3, t he r es ul t s ar e t i m e- aver aged conce nt r at i ons over t he m ostr ece nt t em por al s i m ul at i on s egm ent of l engt h NYE AR . E xam pl es: 1
. E X A M S -> P L OT P OI NT The fol l ow i ng conc ent r at i on opt i ons ar e a vai l abl e: T o t a l

- mg / L i n W a t e r C o l u mn

- m g /k g in B e n th ic S e d im e n ts D i s s o l v e d

- “ D i s s o l v e d ” ( m g / L)

( aqu eou s + co m pl exe s w i t h “d i ssol ved ” organics) P a rticu la te
- S e d im e n t-so rb e d (m g /k g d ry w e ig h t) B io ta
- B io so rb e d (u g /g d ry w e ig h t) M a s s - Che m i c a l m a s s a s g r a m s / s q u a r e m e t e r AR EA H el p - Thi s m es sa ge Q ui t
- R et ur n t o t he E X A M S pr om pt O p t i o n - > DI SS OLVED The fol l ow i ng s t at i st i cal opt i ons ar e a vai l abl e: M AX - M axi m um conc ent r at i on M IN - M i ni m um conc ent r at i on AVE - A ver age conce nt r at i on H el p - Thi s m es sa ge Q ui t - R et ur n t o t he E X A M S pr om pt O p t i o n - > AVE RA GE 9.00E-04 -I I I AAAAAAAAAAA I A|||||||||A C I A|||||||||A O 8.00E-04 -I A|||||||||A N I A||||D||||A D A C I A||||I||||A I V E I A||||S||||A S E N I A||||S||||A S R T 7.00E-04 -I A||||O||||A O A R I A||||L||||A L G A I A||||V||||A V E T I A||||E||||A E I I A||||D||||A D O 6.00E-04 -I A|||| ||||A N I A||||M||||A M I A||||G||||A AAAAAGAAAAA I A||||/||||A A||||/||||A I A||||L||||A A||||L||||A 5.00E-04 -+_AAAAAAAAAAA_AAAAAAAAAAA Water Col Benthic

EX AMS 

### -> SETMCHEM 

### =2
EX AMS 

### -> PL PO DIAV155 4.00E-04 -I I I I C I O 3.50E-03 -I N I D D A C I I I V E I S S E N I S AAAAASAAAAA R T 3.00E-03 -I O A||||O||||A A R I L A||||L||||A G A I AAAAAVAAAAA A||||V||||A E T I A||||E||||A A||||E||||A I I A||||D||||A A||||D||||A O 2.50E-03 -I A|||| ||||A A|||| ||||A N I A||||M||||A A||||M||||A I A||||G||||A A||||G||||A I A||||/||||A A||||/||||A I A||||L||||A A||||L||||A 2.00E-03 -+_AAAAAAAAAAA_AAAAAAAAAAA Water Col Benthic T hi s exam pl e i l l ust r at es E X A M S ’ i n t ern al p rom p t in g fo r P OI NT pl ot s. N ot e t hat t he a nal ysi s i ncl uded t w o che m i cal s; t he pl ot for c h e m ic a l n u m b e r t w o w a s o b ta in e d b y first SE T t i ng M CH EM =2. The se cond pl ot w as r eques t ed vi a a s i ngl e c om m and l i ne, t hus bypas si ng t he P L OT prom pt s. 2
. E X A M S -> P L OT P RO F The fol l ow i ng conc ent r at i on opt i ons ar e a vai l abl e: T o t a l

- mg / L i n W a t e r C o l u mn

- m g /k g in B e n th ic S e d im e n ts D i s s o l v e d

- “ D i s s o l v e d ” ( m g / L)

( aqu eou s + co m pl exe s w i t h “d i ssol ved ” organics) P a rticu la te
- S e d im e n t-so rb e d (m g /k g d ry w e ig h t) B io ta
- B io so rb e d (u g /g d ry w e ig h t) M as s - C h em i ca l m as s as gra m s/squ are m eter AR EA H el p - Thi s m es sa ge Q ui t
- R et ur n t o t he E X A M S pr om pt O p t i o n - > T OT AL The fol l ow i ng opt i ons ar e a vai l abl e:
W ATER - W at er C ol um n conc ent r at i ons SE DI M ENTS - B ent hi c Sedi m ent conc ent r at i ons H el p - Thi s m es sa ge Q ui t
- R et ur n t o t he E X A M S pr om pt O p t i o n - > W A TER156 8.00E-01 -I I I I C I T O 6.00E-01 -I O N I T C I 015 A E I H|H L N I 014 H|H T 4.00E-01 -I H|H H|H M R I H|H H|H G A I 013 H|H H|H / T I E|E H|H H|H L I I 012 E|E H|H H|H O 2.00E-01 -I 010 011 E|E E|E H|H H|H N I 009 E|E E|E E|E E|E H|H H|H I 008 E|E E|E E|E E|E E|E H|H H|H I 005 006 007 E|E E|E E|E E|E E|E E|E H|H H|H I 002 003 004 E|E E|E E|E E|E E|E E|E E|E E|E E|E H|H H|H 0.00E+00 -+_001_EEE_EEE_EEE_EEE_EEE_EEE_EEE_EEE_EEE_EEE_EEE_EEE_HHH_HHH WATER COLUMN T he ab ov e exa m pl e i l l ust r at es E X A M S ’ i nt er nal pr om pt s for a PROFI LE pl ot . A s w i t h t he P OI NT opt i on, t hi s ent i r e c om m and c oul d be ent er ed on a s i ngl e l i ne:
E X A M S -> P L OT P RO F T OT W AT
3
. E X A M S -> P L O T K IN
The fol l ow i ng K IN E T IC opt i ons ar e a vai l abl e: Li st- l i st s se l ect ed K IN E T IC ou t p u t pa ram eters Pl ot - pl ot s se l ect ed K IN E T IC ou t p u t pa ram eters H el p - t hi s m es sa ge Q ui t - r et ur n t o t he E X A M S pr om pt O p t i o n - > P L OT C hem i cal : M et hyl Par at hi on E n v iro n m e n t: P o n d -- co d e tes t d a ta Si m ul at i on uni t s: D ays N um ber of

segm ents: 2 1 2 T y p e o f se g m e n t ( TY PE ) : L B The fol l ow i ng par am et er s ar e a vai l abl e for t i m e- t r ace pl ot t i ng of val ues ave r aged over t he e cos yst em s pace : (“ D iss o lv e d ” = a q u e o u s + c o m p le x e s w ith “ d iss o lv e d ” o rg a n ic s.) 1

- W a t e r Col u m n : a v e r a g e “ d i s s o l v e d ” ( m g / L) 2

- aver age sor bed ( m g/ kg) 3

- t ot al m as s ( kg) 4

- Ben t h i c : a v e r a g e “ d i s s o l v e d ” ( m g / L) 5 aver age sor bed ( m g/ kg)157

6 t ot al m as s ( kg) Ent er par am et er s, one pe r l i ne; ent er 0 t o end da t a e nt r y and pr ocee d. Pa r a m e t e r - > 3 Pa r a m e t e r - > 6 Pa r a m e t e r - > 0

T h e fo llow in g p a ra m e te rs a re a v a ilab le fo r e a c h se g m e n t: 1

- Tot al conc ent r at i on ( W at er C ol um n, m g/ L; bent hi c, m g/ kg) 2

- “D i ss ol ved” ( m g/ l i t er of f l ui d vol um e) 3 - S o rb e d (m g /k g o f se d im e n t) 4

- B i osor bed ( ug/ g) 5

- M as s (gram s/squ are m eter of AR EA ) Ent er s egm ent
- par am et er num ber pai r , one num ber per l i ne; e n te r 0 w h e n d a ta e n try is c o m p le te ; Q u it to a b o rt. En t e r s e g m e n t n u m b e r - - - > 0
System: Monthly pond -- code test data Chemical: Methyl Parathion
0.160 I ** I * I ** * I * I * * 0.106 I * * I * * I * * I * +++ I * ++* +++ 5.322E-02 I * ++ * +++ I ** * + ** +++ I * ++ * ++++ I * * *+ ** +++++ I *+++++++ **** ++++++++++ 0.000 I++++++++++++++++****** *****************+ +----+----+----+----+----+----+----+----+----+----+ 0.000 73.0 146. 219. 292. 365 Time, Days

T hi s exam pl e i l l ust r at es E X A M S ’ pr om pt i ng i n K IN E T IC pl ot s. T he n um eri cal opti on s cann ot be en t ered on t he co m m and l i ne, but m ust be en t ered i n response to t he p r om pt s.158 P R I N T U se t he P RI NT c o m m a n d to e x p o rt an o u tp u t t a b le to a fil e fo r h a rd c o p y p rin ting o r in c o rp o ra tion in to a d o c u m e n t.

R el at ed: C on t r ol vari ables: F IX F IL

C om m and s: LI ST Synt ax: P RI NT <opt i on> O pt i on s: t ab l e-# ALL H e lp Q u it P rom p t : E n t er T ab l e N u m b er->
O pt i ons: t abl e- # spe ci fi es t he num ber of an E X A M S out put t abl e t o be di spl ayed.
ALL Se qu enti al pri nt i ng of al l curr ent ou t pu t t ables.
HELP D i sp l ay s a li st of t i t l es of E X A M S output t ables.

D es cr i pt i on: The P RI NT com m and t r ansfer s E X A M S r es ul t s t abl es t o an output f i l e for s ubse quent pr i nt i ng. The com m and f unct i ons m uch l i ke t he LI ST com m and, exc ept t hat out put i s sa ved for l at er har dcopy pr i nt i ng or i ncor por at i on i nt o a r epor t , r at her t han be i ng r out ed t o your i nt er act i ve t er m i nal
. Shoul d t he P RI NT c o m m a n d re su lt in o u tp u t at y o u r term in a l, y o u m a y n e e d to c o n su lt w i t h s i t e ADP per sonne l t o pr oper l y di r ectt he pr i nt s t r eam t o a f i l e.

Exam pl es : See t he doc um ent at i on for t he LI ST com m and.159 Q U I T

U se Q U IT t o abor t a c om m and i n pr ogr es s or t o end a n i nt er act i ve E X A M S s es si on.
R el at ed: C on t r ol vari ables:

C om m and s: E X IT Synt ax: Q U IT
Pr om pt : N one
O pt i ons: N one
D es cr i pt i on: Ent er i ng Q U IT att he E X A M S pro m p t co m m an d l ev el w i l l t erm i n ate a n i n t era cti v e se ssion , return i n g co n t rol t o t h e c o m p u t er’s

o p e ra ting sy ste m . Q U IT i s i ncl uded a s an opt i on of m any E X A M S com m ands t o al l ow t he c om m and t o be a bor t ed.

E xam pl es: 1
. E X A M S -> A U D IT The fol l ow i ng A U D IT o p tion s a re a v a ilab le O N

- - begi ns a ne w audi t f i l e, O Ff

– end s A ud i t r eco r di ng of i np ut com m and s, H el p - - t hi s m es sa ge, Q ui t
- - r et ur n t o t he E X A M S p ro m p t.
A U D IT -> Q U IT
E X A M S -> Thi s com m and t er m i nat es pr oces si ng of t he A U D IT com m and and r et ur ns cont r ol t o t he E X A M S pr om pt com m and l evel
. The cur r ent status o f A U D IT i s not al t er ed.

2
. E X A M S -> Q U IT Thi s com m and t er m i nat es an i nt er act i ve E X A M S s es si on.160 R E A D U se t he RE AD com m and t o t r ans fer dat a f r om a pr oper l y or gani zed non- E X A M S f i l e i nt o t he A ct i vi t y D at a B as e ( ADB ). R el at ed: C on t r ol vari ables: M ODE , M CH EM , PRBEN

C om m and s: W RI TE Synt ax: RE AD <dat at ype> <nam e of f i l e> P ro m p t: E n te r E n v iro n m e n t, C h e m ic a l, PRZ M , M eteo rolog y , H elp , o r Q u i t -> D es cr i pt i on: The RE AD com m and pr ovi des a faci l i t y for up- l oadi ng E X A M S d a ta se ts fro m e x te rn a l A S C II s equent i al fi l es . These non- E X A M S

fi l es can be st or ed ent i r el y sepa r at el y f r om t he m ai n E X A M S U se r D at a B as e ( UDB ), w h ic h i s c o n ta in e d i n a d ire c t a c c e ss fil e nam ed “ E X A M S . DAF ”. D at a a r e t r ans fer r ed di r ect l y t o t he A ct i vi t y D at a B as e ( for egr ound m em or y ADB ) r at her t han t o t he U se r D at a B as e ( UDB ) f i l e a r ea, s o t he S T ORE com m and m ustbe us ed t o t r ans fer dat a t o t he UDB f r om t he ADB af

t er i nvoki ng RE AD o r t h e y w i l l b e d i s c a r d e d w h e n y o u e x i t f r o m E X A M S . U nder t he E NVI RO NME NT op t i o n of RE AD , t he e nt i r e ADB d a ta se t (“m o n th s” 1 th ro u g h 1 3 ) w ill b e u p lo a d e d fro m th e e x te rn a l fi le c a l l e d <n a m e o f

f i l e >. U nder t he CH E M I CA L op t i o n of RE AD , t he chem i cal dat as et t o be upl oaded f r om <nam e of

f i l e> i s put i nt o t he M CH EM s ect or of t he A ct i vi t y D at a B as e ( ADB ). I n t he PRZ M opt i on of

t he RE AD c o m m a n d , E X A M S ac qui r es a s et of e xt er nal l oadi ngs gener at ed by t he Pes t i ci de R oot Zone M odel ( PRZ M )
. Thi s faci l i t y tr ans fer s chem i cal s expor t ed f r om t he l and s ur face i nt o an a dj ace nt aqua t i c s yst em . The PRZ M tra n sfe r fil e i s a M ODE 3 cons t r uct , i n w hi ch t he fi r sts et of l oadi ngs cont ai ns t he a ppl i cat i on r at e of t he pe st i ci de, and t he s ucce edi ng l oadi ngs co n t ain run o ff

e v en t s g en era t i n g w ater-bo rne a n d se d i m en t -bo rne ch em i ca l t ran sfers to the aq u ati c sy stem . T h e p ara m eter PRBEN ( c. f
. ) con t r ol s E X A M S ’ t r eat m ent of s edi m ent
- bor ne m at er i al s. W hen PRBEN i s zer o, al l s edi m ent
- bor ne m at er i al s ar e e qui l i br at ed w i t h the w at er col um n upon entr y i nt o t he s yst em . W hen PRBEN i s 1
. 0, a l l s ed i m en t
- bo r ne m at er i al s a r e r ou t ed d i r ec t l y t o t he b e n th ic z o n e . PRBEN h a s a d e fa u lt v a lu e o f 0 .5 , b a se d o n th e o b se rv a tion th a t, in g e n e ra l, a b o u t 5 0 % of s o rb e d c h e m ic a l i s u su a lly l a b i l e , a n d a b o u t5 0 % r e c a l c i t r a n t , t o r a p i d r e - e q u i l i b r a t i o n i n w a t e r . R u n o ff f r o m PRZ M i s t r anslat ed i nt o m on t hl y no n- poi nt
- sour ce w a te r a n d se d im e n t i n p u t. The M E T E OR OL OGY opti on r ead s a PRZ M m et eor ol ogy f i l e. These fi l es co nt ai n dai l y val ues of pr eci pi t at i on, pan e vapor at i on, t em p era t u re, an d w i n d sp ee d . I f ( a n do n ly if ) an E X A M S envi r onm ent has bee n s el ect ed, t he pe r i od- of

- r ecor d m ont hl y ave r ages ar e t r ans fer r ed t o t he c or r es pondi ng E X A M S var i abl es . I n addi t i on, a di ges t of m ont hl y m ean val ues i s pr epar ed for ea ch ye ar of dat a i n t he f

i l e; w hen a PRZ M t r ans fer f i l e i s r ead, t he w eat her dat a for t hat yea r i s l oaded i nt o E X A M S .161

E xam pl es: 1. Tr ans fer an e nvi r onm ent al dat as et f r om a f i l e c al l ed “ I NLET .D AT ” on t he de faul t di r ect or y; t he da t as et ca n t hen be t hen S T ORE d in E X A M S ’ di r ect access UDB f i l e.
E X A M S -> RE AD En t e r En v i r o n m e n t , Che m i c a l , Lo a d , Hel p , o r Qui t
- > EN En t e r n a m e o f

f i l e , Hel p , o r Qui t
- > I NLET .D AT 2. R ead pr eci pi t at i on, pan e vapor at i on, t em per at ur e, and w i nd s peed f r om a m et eorol og y fi l e. N ot e t hat a di r ect or y ot her t han t he defaul tca n be s peci fi ed a s par t of t he RE AD com m and <nam e of f i l e> opt i on; t he de faul t s uffi x for m et eor ol ogy f i l es i s “. m et ”.
E X A M S -> S E T M ODE =3
E X A M S -> RE AD M ET C :\ E X A M S \ PROJ ECTX \ W 13873 3. To r ead a PRZ M tran sfe r fil e , first se t M ODE t o 3, an d t h en read t h e d atas et. N o t e the co n v en t i o n fo r n am i n g of PRZ M t r ans fer f i l es - - t he base nam e i s al w ays “ PRZ M 2 E XA ” o r “P 2 E -C n ” an d the su ff i x ind i ca t es the y ea r- -i n this ca se da t a from 19 8 9 (“ D 89")
. B eca use E X A M S w i l l ac ceptany f

i l e na m e for ac qui si t i on by t he RE AD com m and, t hes e fi l es can be r enam ed t o any conveni ent fi l e nam e for ar chi vi ng o r to p re v e n t su b se q u e n t PRZ M r u n s f r o m o v e r - wr i t i n g t h e m.
E X A M S -> READ PRZ M PRZ M 2 E XA . D 89162 R E C A L L

U se RECALL t o upl oad da t a f r om t he pe r m anentdat abas e ( UDB ) i nt o cur r ent for egr ound m em or y ( ADB ).

R el at ed: C on t r ol V ari ables: M CH EM

C om m and s: CA T AL OG , ER A SE , N A M E , S T ORE Synt ax: RECALL <d a t a t y p e > < UDB #> [ AS ADB #] P rom p t : E n t er E n v i ron m en t , C h em i ca l , L o ad , P rod u ct, H elp , o r Q u i t ->
C om m and param et ers : <dat at ype> can be C hem i cal , Envi r onm ent , Load, or Pr oduct ( E X A M S u se s th e se fo u r k in d s o f d a ta se ts.)
AS ADB # i s an op t i o n al ex p l i cit sp ec i fi ca t i o n of M CH EM (see E x am p l e 1 ).
UDB # s peci fi es t he a cce ss i on num ber or l ocat i on i n t he U se r D at abas e for t he s our ce dat a for t r ans fer t o t he ADB (E x am p l e 2 ). D es cr i pt i on: RECALL t r ans fer s dat a f r om per m anents t or age ( UDB ) t o acti vi t y da t aba ses ( ADB s)
. The dat a i n ac t i ve us e by E X A M S a re h e ld i n a fore g rou n d m em o ry b an k (A cti v i t y D ataB as e o r ADB ) w i t h four s ect or s, one for ea ch da t at ype r equi r ed by E X A M S -- <C >hem i cal r eac t i vi t y and pa r t i t i oni ng,
< E > nv i r on m ental phy si cal and chem i cal param et ers , al l ocht honous chem i cal <L >oadi ngs, and
< P> r od uct che m i st r y forgen erat i ng i nt erconv ers i on s am on g m ul t i pl e che m i cal s i n an analysi s. W hen E X A M S i s st ar t ed, t he ADB i s em pt y. U se t he RECALL com m and t o t r ansfer dat a f r om t he p erm ane nt U ser D at aba ses ( UDB s) t o for egr ound m em or y ( ADB )
. W hen an anal ysi s se ss i on i s ended ( Q U IT or E X IT ), ADB s ar e di sc ar ded. U se t he S T ORE com m and t o t r ans fer new dat a f

r om t he ADB t o t he UDB s ect or of t he s am e da t at ype for per m anentr et ent i on of t he da t a. E xam pl es: 1. B eca use E X A M S ca n pr oces s se ver al che m i cal s i n a s i ngl e a nal ysi s, t he t ar get s ect or of t he c hem i cal ac t i vi t y dat abase s houl d be spe ci fi ed w hen us i ng t he RECALL com m and t o ac t i vat e CH E M I CA L d a ta . (T h is s e c tion o f th e c o m m a n d s h o u ld b e o m itt e d fo r o th e r d a ta t ypes . ) W hen t he ADB # (an i nt eger bet w een 1 and KC HEM ) is o m itt e d , t h e c h e m ic a l d a ta a re tran sfe rre d to th e se c to r o f th e a c tivity d atab as e g i v en by t h e c u rr en t va l u e o f M CH EM . F o r ex a m p le , to a c tiva te d a ta fro m th e c h e m ic a l UDB , put t i ng UDB da t as et nu m b er 9 i nt o ADB s ect or 1, and UDB #14 i nt o s ect or 2: E i t h er:
E X A M S -> S E T M CH E M T O 1
E X A M S -> RECALL CH EM I CA L 9
E X A M S -> S E T M CH E M T O 2163 E X A M S -> RECALL CH EM I CA L 14

or , equi val ent l y:
E X A M S -> RECALL CH EM I CA L 9 A S 1
E X A M S -> RECALL CH EM I CA L 14 A S 2
2. Long- t er m r et ent i on of dat a r equi r ed by E X A M S i s pr ovi ded by s t or age i n t he “ U se r D at abas e” ( UDB , gene r al l y r es i dent on a physi cal devi ce- - e. g. , a ha r d di sk) for Chem i cal s, Envi r onm ent s, Loads, or Pr oduct s. W i t hi n ea ch UDB s e c to r, e a c h d a ta se t is c a ta lo g u e d v ia a u n i q u e a cc es sion nu m b er ( UDB # ). W h en t ran sferri n g da t a to fo reg rou n d m em o ry (t h e a cti v i t y da t ab as e o r ADB ) f r om a UDB , t he sour ce l ocat i on m ustbe s peci fi ed by t he na m e of t he UDB s ect or and t he a cce ss i on num ber w i t hi n t he s ect or . For exa m pl e, t o RECALL a n e n v iro n m e n ta l d a ta se t:
E X A M S -> RE CAL L E NVI R 2 Sel ect ed e nvi r onm ent i s: Phant om I nl et , B ogue Sound
E X A M S ->164 R U N The RU N com m and beg i ns a si m ul at i on analysi s.
R el at ed: C on t r ol V ari ables: M ODE

C om m and s: CO NT I NUE Synt ax: RU N
Pr om pt : N one
D es cr i pt i on: The RU N com m and e xecut es an a nal ysi s and c r eat es t he out putf i l es ac ces se d by t he LI ST and P L OT c o m m a n d s. T h e a c tivity dat abas e ( ADB ) m ustbe l oaded, ei t her vi a e nt r y of new dat a or by RECALL f r om t he UDB , befor e a RU N ca n be s t ar t ed.

E xam pl es: 1
. E X A M S -> RECALL CH EM I CA L 22 S e le c te d c o m p o u n d is: D ib ro m o e x a m p le
E X A M S -> RE CA L L E NVI RO N 17 Sel ect ed e nvi r onm ent i s: A l bem ar l e Sound-

- B ogue B ank
E X A M S -> S E T S T RL ( 1, 1, 13) =. 01
E X A M S -> RU N S i m u l ati o n be g i n n i n g for: Envi r onm ent : A l bem ar l e Sound-

- B ogue B ank C h e m ic a l 1 : D ib ro m o e x a m p le R un com pl et e.
E X A M S -> I n t hi s exam pl e, a s t eady- st at e ( M ODE =1) ana l ysi s i s conduct ed by s el ect i ng a c hem i cal and a n envi r onm ent , i m posi ng a l oadi ng o f c h e m ic a l 1 o n se g m e n t 1 u n d e r a v e ra g e c o n d iti o n s (i.e ., da ta se c to r 1 3 , E X A M S i ni t i al de f ault val ue) and i nvoki ng E X A M S ’ si m ul at i on al gor i t hm s w i t h t he RU N com m and.165 S E T

U se SE T t o s peci f

y t he va l ues of

dat a i n t he a ct i vi t y dat abas e.
R el at ed: C om m and s: CH ANG E (sy n o n y m ), DES CRI BE , HELP Synt ax: SE T <n a m e o f v a r i a b l e > TO <new val ue> o r SE T <nam e of

var i abl e> = <new val ue> P rom p t : E n t er n am e= v alu e c o m m an d ->
V ari a bl e: The dat a e nt r y or var i abl e t o be SE T can b e specif i ed eit her as a s i ng l e datum or, usi ng w i l d cards ( *), as an enti r e v ec t o r, r ow / col um n of

a m at r i x, et c.
D es cr i pt i on: U se t he SE T c o m m a n d t o sp e c ify t h e va lu e s o f da ta i n t h e ac tivity da ta b a se . “ V a lu e ” ca n b e a n y n u m e ric a l q u a n tit y o r li te ra l,

as app r op r i at e. “V ari able” speci fi es an i nd i vi du al el em en t o f i n pu t dat a or a pr og r am con t r ol param et er. E nt i r e vec t ors, row s/co l u m n s o f m atri ce s, etc. ca n be set t o sing l e v alu es us i n g w i l d ca rds (*).

E xam pl es: 1
. E X A M S -> S E T VOL ( 167) T O 7 E 5 Subscr i pt out
- of

- r ange.
E X A M S -> DE S CR I BE VOL
VOL i s a R eal V ect or w i t h 10 0 el em ents.
E X A M S > S E T VOL ( 2) T O E Inv ali d nu m eric qu an t i t y aft er TO . E X A M S -> S E T VOL ( 2) T O 7 E 5

Thi s com m and s et s t he e nvi r onm ent al vol um e of s egm ent 2 t o 7. 0E+ 05 cubi c m et er s. The i ni t i al at t em pt t o s et t he vol um e of s egm ent 67 w as r ej ect ed by E X A M S becaus e t he ver si on i n use w as setup for envi r onm ent al m odel s of 100 s egm ent s at m ost . The DES CRI BE com m and w as us ed t o check t he nu m ber of subs cr i pt s and t he di m ens i onal s i ze of t he va r i abl e “ VOL ”. The er r oneous ent r y of an al phabet i c for t he vol um e w as t r apped by t he SE T co m m an d ; t h e init i al va l u e o f VOL ( 2) w as not al t er ed.

2
. E X A M S -> HELP TCEL
TCEL i s a R eal M at r i x w i t h 10 0 row s and 1 3 co l um ns. Te mp e r a t u r e - CE Ls i u s ( s e g me n t , mo n t h ) Un i t s : d e g r e e s C. A ver age t em per at ur e of ec osys t em s egm ent s. U se d ( as ena bl ed by i nput dat a) t o com put e e ffect s of t em per at ur e on tr ans for m at i on r at es and ot her pr op ert i es of che m i cal s.
E X A M S -> SE T T CEL ( 2, 7) =24166

Thi s com m and c hange s t he Jul y t em per at ur e i n s egm ent 2 t o 24 E C
. The HELP com m and w as used to check subscri pt di m ensions, m axi m um val ues , t he m eani ng of t he subs cr i pt s ( subs cr i pt #1 denot es t he s egm ent ; s ubsc r i pt #2, t he m ont h) , and t he pr oper uni t s for t h e inp u t da t u m (de g ree s C elsius).
3
. E X A M S -> HE L P P OH PO H i s a R eal M at r i x w i t h 10 0 row s and 1 3 co l um ns. p O H (se g m e n t, m o n th ) U n its: p O H u n its T h e n e g a t i v e v a l u e o f

t h e p o we r t o wh i c h 1 0 i s r a i s e d i n o r d e r t o o b t a i n t h e t e mp o r a l l y a v e r a g e d c o n c e n t r a t i o n o f h y d r o x i d e [ OH ] - i o n s in g ram -m o l ec u l es pe r l i t er.
E X A M S -> S E T P OH ( *, 13) T O 6 .2

T h i s co m m an d sets t h e av era g e p O H ( se cto r 13 ) of ev ery seg m en t t o 6.2
. N o t e u se of w i l d ca rd “ * ” to sp ec i fy tha t all seg m en t s are to b e c h a n g e d . A s in th e p re v io u s e x a m p le , HELP w a s u se d to c h e c k su b sc rip t d im e n sio n s, u n its, etc . T h is s te p , o f c o u rs e , i s o p tion a l.167 S H O W

U se S HOW t o displ ay cu r r ent data val ues or contr ol set t i ng s.
R el at ed: C on t r ol V ari ables: M CH EM , M ON TH

C om m and s: CH ANG E , SE T Synt ax: S HOW <opt i on> [ r ange] Pr om pt : The fol l ow i ng opt i ons ar e a vai l abl e: A dvect i on, C hem i st r y, D i spe r si on, G Eom etr y, G L ob al s, L oad s, PL ot , PU l se L oad s, PR od ucts, Q U A l i t y, T i m e Fram e, V ari ables, H elp , o r Q U It ->
C om m and param et ers : R ange: Som e opt i ons of t he S HOW com m and acc ept t he s peci fi cat i on of a r ange of

val ues t o def

i ne t he s cope of

t he da t a t o be di spl ayed ( se e Exam pl e 1)
. U se M CH EM t o de l i m i t t h e ran g e o f S HOW C hem i st r y, and M ON TH fo r G E o m e try , QUA l i t y, et c. O pt i on s:
ADV E CT I ON
S HOW ADV E CT I ON gi ves t he advect i ve hydr ol ogi c f l ow s t r uct ur e of

t he c ur r ent aqua t i c s yst em . A s i ngl e e l em ent i n a da t as et m i ght t ypi cal l y l ook l i ke t he fol l ow i ng exa m pl e.
J F R A D 1 J FR om A D vect i on: Sour ce Segm ent I T O AD 3 I TO A D vect i on: Ter m i nus A D V PR 1. 00 A D V ect i on Pr opor t i on: Per cent o f to ta l J F RA D flo w o n p a th P a th N o .: 1 V e c to r in d e x fo r S E T ting d a ta N o m or e t han NC ON hy d rolog i c p ath w ay s ca n be spe cifi ed
. If m o re are ne ed ed , sp ec i al ve rsi o n s o f E X A M S ca n be pro d u ce d
. S p ec i fy e x p o r t p a t h wa y s b y e n t e r i n g a z e r o ( 0 ) fo r t h e n u mb e r o f t h e s e g me n t t o r e c e i v e t h e fl o w ( I T OAD )
. D o not s peci f y a hydr ol ogi c s our ce t er m by ent er i ng ze r o i n t he J F RA D vec t or ; i nst ead use s t r eam fl ow s, non- poi nt
- sour ce fl ow s, et c.

DI S P E RS I ON
S HOW DI S P E RS I ON di spl ays t he i nput da t a des cr i bi ng t r ans por t i n t he a ct i ve ( l oaded i n t he ADB ) Envi r onm ent al dat as et . The i ndex vec t ors ( J T URB , I T URB ) defi ne t he exi st ence of i nt er - se gm ent di spe r si ve t r ans por t pat hs. A ze r o i n ei t her vec t or , w hen pa i r ed w i t h a non- z er o va l ue at t he cor r es pondi ng pos i t i on i n t he ot her i ndex vect or , i s t aken as a bounda r y condi t i on w i t h an unc ont am i nat ed body of w at er . A s i ngl e e l em ent i n a da t as et m i ght t ypi cal l y be di spl ayed l i ke t he fol l ow i ng exa m pl e.
J T URB 1 Segm ent num ber for di spe r si on I T URB 2 Segm ent num ber for di spe r si on XS T UR m 5 .0 0 0 E + 0 4 C ro ss -s e c tion a l are a o f p a th

2 CHARL m 2. 53 CH AR act er i st i c_ L e n g th o f p a th D SP m / h 4. 676E-05 Eddy D i SPer si on coe ffi ci ent

2 Pa t h N o .: 1 V ec t o r i n d ex for da t a e n t ry168

N o m or e t han NC ON hydr ol ogi c pa t hw ays c an be spe ci fi ed. I f m or e ar e neede d, t hi s num ber ca n be i ncr eas ed a nd E X A M S r ecom pi l ed.

CHE M I S T RY
S HOW CHE M I S T RY di spl ays t he c hem i cal out put dat a c ur r ent l y i n t he ADB ( for egr ound m em or y bank)
. The se ct or of t he ADB denot ed b y t h e cu rr en t va l u e o f M CH EM i s di spl ayed. W i t hi n each se ct or of t he ADB (th a t i s, fo r e a c h c h e m ic a l u n d e r a c tive re v ie w ), the d a ta for each i on i c species are pr esented separat el y, and pho t och em i cal dat a are present ed o n sepa r at e scr een s.
GEOMET RY
S HOW GEOMET RY r et ur ns a segm ent- by

- segm ent des cr i pt i on of t he ge om et r y ( vol um es , ar eas , et c. ) of t he c ur r ent ec osys t em . The se gm ent num ber r epor t ed w i t h ea ch bl ock of dat a i s t he f

i r sts ubsc r i pt for m odi f yi ng t he da t um us i ng CH ANG E or SE T . T h e m o n th to b e d i sp l ay ed i s se t by t h e c u rr en t va l u e o f M ON TH ( expl i ci t m ean val ues ar e de not ed by M ON TH num ber 13) : t he m ont h i s t he s econd subsc r i pt of such dat a as W I ND , ST FL O , et c.

GLOB ALS
SHOW GLOB ALS d i s p l a y s t h e i n p u t d a t a t h a t a r e “ g l o b a l ” i n e x t e n t , t h a t i s , “ g l o b a l ” d a t a a p p l y t o a l l s e g me n t s o f t h e c u r r e n t e c o s y s t e m.

L OAD S
S HOW L OAD S di spl ays t he cur r ent s t at e of a l l ocht honous chem i cal l oadi ngs. The for m of t he di spl ay de pends on t he c ur r ent oper at i onal M ODE : init i al v alu es a re ign o red i n M o d e 1 as the y ha v e n o effec t on t h e a n aly sis r es u l t s. T h e v alu e o f PRSW a l so affect s t he di spl ay: w hen PRSW is 0 , S HOW L OAD S r et ur ns a s um m ar y of annual l oadi ngs; w hen PRSW = 1 , a m o n th -b y -m o n th t a b u la tion i s d isp la y e d a s w e ll. Thi s di spl ay m ay not r epr es ent t he f i nal val ues us ed i n t he a nal ysi s, bec aus e E X A M S w i l l m odi f y l oads t hat r es ul t i n vi ol at i on of t he l i near i zi ng as sum pt i ons use d t o cons t r uct t he pr ogr am . A f t er a RU N h a s b e e n e x e c u te d , h o w e v e r, S HOW L OAD S w i l l di spl ay t he corr ect ed v al ues.

PRODU CTS
SHOW PRODU CTS di spl ays t he s peci fi cat i ons for pr oduct che m i st r y cur r ent l y i n t he ADB . Each ent r y i s i dent i fi ed a nd l oaded acc or di ng t o a un i qu e “pa t hw ay n um ber. ” A si ng l e el em ent of a dat aset m i gh tl oo k l i ke t hi s:
CH P AR 1 ADB nu m b er o f CH e m ic a l P AR ent T P RO D 2 ADB num ber of Tr ans for m at i on P RO D uct N P RO C 7 N um ber of t r ans for m i ng P RO C ess R F ORM 29 R eac t i ve F ORM (d iss o lv e d , etc .) YI E L D M / M 0. 100 M ol e/ M ol e YI EL D of pr oduct EAYLD K cal 0. 000 Ent hal py of yi el d ( i f appr opr i at e) Pat hw ay: 1 N um ber of t he pa t hw ay M o re d etail a s to t h e n u m b ering of NP RO C and RF ORM i s gi ven i n t he D at a D i ct i onar y ( page 180) , w hi ch c an a l so be a cce ss ed on- l i ne usi ng t he HELP com m and. N o m or e t han NT RA N tr ans for m at i on pa t hw ays c an be s peci fi ed. I f m or e a r e ne eded, a s peci al ver si on of E X A M S ca n be c r eat ed.

P L OT
S HOW P L OT exa m i nes t he c ont ent s of t he c oncent r at i on t i m e- se r i es and s t eady- st at e f i l es , a nd r epor t s t he nam es of t he c hem i cal s and eco syst em used in t he an al ysi s.169

P UL S E L OAD S
S H O W P U L S E L OAD S dis pl ays t he s peci fi cat i ons for al l ocht honous pul se s of che m i cal s ent er i ng t he s yst em . Thi s di spl ay m ay not r epr es ent t he fi nal va l ues us ed i n t he a nal ysi s, bec aus e E X A M S w i l l m odi f y l oads t hat r es ul t i n vi ol at i on of t he l i near i zi ng as sum pt i ons u se d to c o n stru c t t h e p ro g ra m . A ltho u g h fa u lty p u lse lo a d s a re d isc a rd e d , E X A M S doe s not corr ect t he i np ut pulse l oad dat a, beca use t he occur r ence of

l oad c onst r ai nt vi ol at i ons depends on t he c ont ext ( i
. e. , t he s i ze of cur r ent s t r eam l oadi ngs, et c. )
. Thus, unl i ke S HOW L OAD S , t he SH O W PU LSE di spl ay fol l ow i ng exe cut i on of a RU N does not di spl ay c or r ect ed da t a. The pul se s act ual l y us ed dur i ng an anal ysi s ar e i nst ead ent er ed i nt o E X A M S ’ out put t abl es , w her e t hey c an be exa m i ned us i ng t he LI ST and P RI NT com m and s. QU ALI TY
SHOW QU ALI TY re tu rn s a se g m e n t-b y -s e g m e n t d isp la y o f th e c a n o n ic a l w a te r-q u a lit y d a ta in c lu d e d in th e c u rre n t E n v iro n m e n ta l ADB d atas et. T h e m o n t h to b e d i sp l ay ed i s se t by t h e c u rr en t va l u e o f M ON TH ( expl i ci t m ean val ues a r e denot ed by M ON TH num ber 13)
. The m ont h i s t he s econd subs cr i pt of s uch da t a a s pH , pO H , et c. The f i r sts ubsc r i pt i s t he s egm ent num ber ; t hus t hes e da t a a r e e nt er ed ( CH ANG E / SE T ) as “da t um ( se gm ent , m ont h) ”.

T I M E F R A M E
S H O W T I M E F R A M E di spl ays t he c ur r ent s t at us of t he pa r am et er s neede d t o cont r ol t he t em por al as pect s of a M ode 2 orM ode 3 si m ul at i on.

VA RI AB LE S
SHOW VA RI AB LE S disp l ay s a li st of t h e n am es of E X A M S i nput dat a a nd cont r ol pa r am et er s. Thes e nam es m ustbe us ed t o SE T / CH ANG E , S HOW v a lu e s, HELP / DES CRI BE , et c.
D es cr i pt i on: U se t he S HOW com m and t o exa m i ne t he c ur r ent cont ent s of t he ADB , t hat i s, t he for egr ound dat aset s used for t he c ur r ent anal ysi s. The S HOW c o m m a n d c a n b e u se d to e x a m in e c lu ste rs o f sim ilar d a ta , t h e v a lu e s o f i n d iv id u a l p a ra m e te rs , o r th e d a ta cont ai ned i n ent i r e ve ct or s. Typi ng S HOW w i t ho ut an op t i on w i l l di spl ay a l i st of t he av ai l able opt i on s.
Exam pl es : 1. The S HOW com m and can be use d t o exam i ne t he val ue of s i ngl e par am et er s. For exam pl e, t he pH of s egm ent 7 of t he c ur r ent ec osys t em dur i ng Sept em ber coul d be i nspe ct ed by e nt er i ng: E X A M S - > SH O W PH ( 7, 9) U si ng w i l d car ds ( *) , t he S HOW com m and c an a l so be us ed t o di spl ay the da t a i n an e nt i r e ve ct or or r ow / col um n of a da t a m at r i x. For exa m pl e, t he pH i n eve r y s egm ent of t he c ur r ent ec osys t em dur i ng Sept em ber coul d be di spl ayed by ent er i ng: E X A M S - > SH O W PH ( *, 9) and t he pH of

s egm ent 7 t hr ough t he ye ar coul d be di spl ayed by:

E X A M S -> SH O W PH ( 7, *)170 S T O R E

U se S T ORE to d o w n lo a d c u rre n t ( ADB ) dat a i nt o t he pe r m anentdat abas e ( UDB ).

R el at ed: C on t r ol V ari ables: M CH EM

C om m and s: CA T AL OG , ER A SE , N A M E , RECALL Synt ax: S T ORE <d a t a t y p e > [ ADB # IN ] < UDB #> P rom p t : E n t er E n v i ron m en t , C h em i ca l , L o ad , P rod u ct, H elp , o r Q u i t -> C om m and param et ers : <dat at ype> can be C hem i cal , Envi r onm ent , Load, or Pr oduct ( E X A M S u se s th e se fo u r k in d s o f d a ta se ts.)
ADB # IN i s an op t i o n al ex p l i cit sp ec i fi ca t i o n of M CH EM (see E x am p l e 1 ).
UDB # sp e c ifies th e a c c e ss io n n u m b e r o r lo c a tion in th e U se r D a ta b a se fo r sto ra g e o f th e c u rre n t ADB sec t o r ( E x am p l e 2 ). D es cr i pt i on: S T ORE dow nl oad s dat a f r om act i vi t y da t aba ses ( ADB s) i nt o t he p erm ane nt U ser D at aB ases ( UDB s)
. The dat a i n ac t i ve us e by E X A M S are h eld in a fore g rou n d m em o ry b an k (A cti v i t y D ataB as e o r ADB ) w i t h four s ect or s, one for ea ch da t at ype r equi r ed by E X A M S : CH E M I CA L r eac t i vi t y and pa r t i t i oni ng,
E NVI RO NME NT al phy si cal and chem i cal param et ers ,
a lloc h th o n o u s c h e m ic a l L OAD i ngs, and
P RODUCT chem i st r y for gen erat i ng i nt erconv ers i on s am on g m ul t i pl e che m i cal s i n an analysi s. W hen an anal ysi s se ss i on i s ended ( Q U IT or E X IT ) , t hes e da t a a r e di sc ar ded. U se t he S T ORE com m and t o t r ans fer dat a f r om t he ADB t o t he UDB s ect or of

t he s am e da t at ype for per m anentr et ent i on of t he da t a. Exam pl es : 1. B eca use E X A M S c a n p ro c e ss se v e ra l c h e m ic a ls in a sin g le an a ly sis , th e so u rc e se c to r of th e c h e m ic a l ac tivity dat abas e s houl d be s peci fi ed w hen us i ng t he S T ORE com m and t o dow nl oad CH E M I CA L dat a. ( Thi s se ct i on of t he com m and s houl d be om i t t ed for ot her dat a t ypes . ) W hen t he ADB # ( an i nt eger f r om 1 t o KC HEM ) i s om i t t ed, t he c h e m ic al da t a a re t ak en fr o m t h e se cto r of t h e a cti v i t y da t ab as e g i v en by t h e c u rr en t va l u e o f M CH EM . For exam pl e, t o S T ORE dat a i n t he UDB , put t i ng ADB se c to r 1 in to th e c h e m ic a l UDB under ca t al og/ acc es si on 9 and ADB s ect or 2 i nt o UDB s ect or 14: E i t h er: E X A M S -> S E T M CH E M T O 1
E X A M S -> ST OR E CHEM I CA L 9
E X A M S -> S E T M CH E M T O 2
E X A M S -> ST OR E CHEM I CA L 14

or , equi val ent l y:
E X A M S -> ST OR E CHEM I CA L 1 I N 9171 E X A M S -> ST OR E CHEM I CA L 2 I N 14
2. Long-t er m r et ent i on of dat a r equi r ed by E X A M S i s pr ovi ded by s t or age i n t he “ U se r D at abas e” ( UDB , gene r al l y r es i dent on a physi cal devi ce- - e. g. , a har d d i sk) for C hem i cal s, Envi r onm ent s, Loads, or Pr oduct s. W i t hi n ea ch of t hes e UDB s ect or s, ea ch dataseti s CA T AL OG u ed via a un i q u e a cc es sion nu m b er ( UDB # ). W h e n tran sfe rrin g d a ta b e tw e e n fo re g ro u n d m e m o ry (th e a c tivity d atab as e o r ADB ) and a UDB , t he t ar get l ocat i on m ustbe s peci f i ed by t he na m e of

t he UDB se c to r a n d th e a c c e ss io n n u m b e r w ithin t he s ect or . For exa m pl e, t o S T ORE th e c u rre n t en v iro n m e n ta l d a ta se t:
E X A M S -> S T ORE E NVI R 2 E n v iro n m e n t rec o rd 2 is in u se w ith P o n d -- co d e tes t d a ta R epl ace ?- > no N ot hi ng cha nged.
E X A M S -> S T ORE E NVI R 14 E n v iro n m e n t sto re d : P h a n to m In le t-B o g u e S o u n d S tu d y D a ta
E X A M S -> N o te th a t E X A M S p ro v id e s a m e a su re of p ro te c tion ag a in st a c c id e n ta l o v e rw riti n g of e x istin g d a ta se ts, a n im p o rta n t co u rte sy in a m u lti -u se r e n v iro n m e n t.172 W R I T E U se t he W RI TE com m and t o t r ans fer dat a f r om t he A ct i vi t y D at a B as e ( ADB ) t o an e xt er nal ( out si de E X A M S ’ UDB d ire c t ac c e ss fil e E X A M S . DAF ) s equent i al f i l e. R el at ed: C on t r ol vari ables: M ODE , M CH EM

C om m and s: RE AD Synt ax: W RI TE <dat at ype> <nam e of f i l e> P rom p t : E n t er E n v i ron m en t , C h em i ca l , L o ad , H elp , o r Q u i t -> D es cr i pt i on: The W RI TE com m and pr ovi des a faci l i t y for off

- l oadi ng E X A M S d a ta se ts in to e x te rn a l A S C II seq u en t i al f i l es . T h es e fi l es are st or ed s epar at el y f

r om t he m ai n E X A M S U se r D at a B as e ( UDB )
. D at a a r e t r ans fer r ed f r om t he A ct i vi t y D at a B as e ( for egr ound m em or y ADB ) r at her t han di r ect l y f r om t he U se r D at a B as e ( UDB ) f i l e, s o t he RECALL c o m m a n d m u st b e u se d to tran sfe r d a ta f r om t he UDB t o t he ADB pr i or t o i nvoki ng W RI TE , w hen t he i nt ent i on i s t o tr ans fer dat a f r om t he UDB t o an e xt er nal f i l e. The w r i t e c om m and m ustbe us ed t o s t or e pr obl em s cena r i os ( l oad pa t t er ns, pr oduct che m i st r i es ) or da t as et s i n w hi ch t he num ber of envi r onm ent al s egm ent s exce eds 100 or t he num ber of che m i cal s bei ng s t udi ed e xcee ds fi ve. U nder t he CH E M I CA L op t i o n of W RI TE , t he c hem i cal dat as ett o be dow nl oaded t o <nam e of f i l e> i s chos en f

r om t he M CH EM s ect or of t he A ct i vi t y D at a B as e ( ADB ). I n t he L OAD op t i o n of W RI TE , a s et of ext er nal che m i cal l oadi ngs ar e w r i t t en t o an A S C II fi l e. T h e se t t i n g of M ODE af fect s t he am ount of

dat a w r i t t en t o t he f

i l e. I n M ode 1, onl y m ont hl y da t a and m ean val ues ar e w r i t t en f r om t he ADB , p u l se l o ad i n g s are del et ed a s t hey a r e of

no r el evanc e t o a s t eady- st at e anal ysi s. i n M ode 2, i ni t i al condi t i ons ar e a dded, and i n M ode 3 a f ul l s et of m ont hl y l oads and dai l y pul se l oads ar e w r i t t en f r om t he ADB t o t he e xt er nal f i l e. U si ng E X A M S ’ W RI TE faci l i t y t o m anage che m i cal l oadi ng s cena r i os t hus r equi r es som e car e w hen m ovi ng acr oss oper at i onal m odes
. For exa m pl e, a M ODE 3 p u lse lo a d sc e n a rio can be r ead by E X A M S oper at i ng i n M ODE 2, but w hen t he scen ari o i s RU N , t he dai l y va l ues ar e a ccum ul at ed i nt o a s i ngl e s et of in iti a l m a ss lo a d in g s fo r e a c h se g m e n t. I n t he P RODUCT op t i o n of W RI TE , pr oduct chem i st r y s peci fi cat i ons ar e w r i t t en t o an e xt er nal f i l e; t he f i l e c ont ai ns i nt er nal cha r act er fie ld s d o c u m e n ting th e d a ta stru c tu re .
E xam pl es: 1. I n t hi s exam pl e, t he en vi r on m ental dat a i s RECALL ed f r om t he UDB , a n d t h e d a t a a r e d o w n l o a d e d t o a f i l e c a l l e d “ I N LET
. D A T” on t he de faul t di r ect or y.
E X A M S -> RECALL ENVI RO NM ENT 12 Sel ect ed e nvi r onm ent i s: C hi nquot eague I nl et
E X A M S -> W RI TE En t e r En v i r o n m e n t , Che m i c a l , Lo a d , P r o d u c t , Hel p , o r Qui t
- > EN En t e r n a m e o f

f i l e , Hel p , o r Qui t
- > I NLET .D AT 2. To cont i nue t he a bove e xam pl e, an e nt i r e l oadi ngs dat as et coul d be s t or ed i n anot her f i l e by changi ng t he M ODE t o 3. N ot e t hat a di r ect or y ot her t han t he de faul t ca n be s peci fi ed a s par t of t he W RI TE com m and <nam e of f i l e> opt i on.
E X A M S -> S E T M ODE =3 E X A M S -> W RI T E L OA D C :\ E X A M S \ PROJ ECTX \ I NLET . L OD173 Z E R O

U se t he Z E RO c o mma n d t o i n i t i a l i z e ( s e t t o z e r o ) l o a d i n g s d a t a b a s e s o r t h e c o n c e n t r a t i o n o f p o l l u t a n t c h e mi c a l s t h r o u g h o u t t h e e c o s y s t e m.
R el at ed: C on t r ol vari ables: M ODE

C om m and s: CO NT I NUE , RU N Synt ax: Z E RO <opt i on> O pt i on s:
P UL S E L OAD S L OAD S RES I DU ALS
Pr om pt : The fol l ow i ng opt i ons ar e a vai l abl e: Pu l se L oad s - zero al l pulse l oad s, L oad s - zero al l ot her l oad s, R esi du al s - zero al l poll ut ant con cen t r at i on s, H el p - t hi s m es sa ge, or Q ui t
- r et ur n t o com m and m ode w i t h no ac t i on.
Z E RO -> D es cr i pt i on: The Z E RO com m and i ni t i al i zes (set s t o z ero) t he enti r e suit e o f al l och t ho no us che m i cal pulse l oad i ng s ( I M A SS ), l o n g er t erm l o a d i n g s ( s t r e a m l o a d s , d r i f t l o a d s , e t c . ) , o r t h e c u r r e n t v a l u e s o f p o l l u t a n t c h e mi c a l c o n c e n t r a t i o n s t h r o u g h o u t t h e e c o s y s t e m. The Z E RO c o mma n d i s d e s i g n e d p r i ma r i l y fo r u s e d u r i n g t h e c o u r s e o f t e mp o r a l l y s e g me n t e d s i mu l a t i o n s t u d i e s . T h e s a me effectc an be achi eved w i t h m ul t i pl e appl i cat i ons of t he CH ANG E / SE T c o m m a n d ; Z E RO i s a bl ock- m ode i m pl em ent at i on t hat r educe s t he w or k nee ded t o r em ove l oadi ngs dat as et s. ( See Exam pl e 1 i n t he doc um ent at i on of t he CO NT I NUE c o m m a n d .)

E xam pl es: 1
. E X A M S -> S E T M ODE =2
E X A M S -> RECALL CH EM I CA L 22 S e le c te d c o m p o u n d is: D ib ro m o e x a m p le
E X A M S -> RE CA L L E NVI RO N 17 Sel ect ed e nvi r onm ent i s: A l bem ar l e Sound-

- B ogue B ank
E X A M S -> S E T S T RL ( 1, 1, 13) =. 01
E X A M S -> SET I M A SS (1 )= 2 .0
E X A M S -> SE T I SE G ( 1) =14
E X A M S -> SE T I CH EM ( 1 ) =1174 E X A M S -> RU N S i m u l ati o n be g i n n i n g for: Envi r onm ent : A l bem ar l e Sound-

- B ogue B ank C h e m ic a l 1 : D ib ro m o e x a m p le R un com pl et e.

.

.

. E X A M S -> Z E RO P UL S E L OAD S
E X A M S -> CO NT I NUE
I n t hi s exam pl e, an i ni t i al

- val ue ( M ODE =2) anal ysi s i s begun by s el ect i ng a c hem i cal and a n envi r onm ent , i m posi ng an a l l ocht honous lo a d o f c h e m ic a l 1 o n s e g m e n t 1 u n d e r a v e ra g e c o n d iti o n s (i.e ., da ta se c to r 1 3 , E X A M S ’ i ni t i al defaul t val ue) , and s peci f yi ng t he i ni t i al p re se n c e (o r in tro d u c tion a t t im e z e ro ) o f 2 .0 k g o f m a te ria l i n se g m e n t 1 4 . A t t h e e n d o f th e in iti a l RU N se g m e n t, o n e m ig h t w a n t t o exam i ne t he out put t abl es , pl ot t he r es ul t s, et c. Then, befor e CO NT I NU i ng, t he Z E RO com m and i s use d t o r em ove t he pul se l oad sp e c ifica tion s. If th is w e re n o t d o n e , E X A M S w oul d i nt r oduce a s econd 2. 0 kg pul se i nt o s egm ent 14 at t he be gi nni ng of t he c ont i nuat i on se gm ent . A l t er nat i vel y, t he ot her l oadi ngs coul d have bee n r em oved, and t he e ffectof a s er i es of

pul se l oads coul d be s t udi ed by i ssu i n g a se q u en ce of CO NT I NUE com m and s.175 

## 6. 0 E X A MS 

## D ata D i ct i on ary

AB SE R ABS ol ut e ER ror t o l era n ce of integ rators W h en t h e c h ara cterist i cs of the ch em i ca l an d ec o sy stem are suc h as t o r es ul t i n “s t i ff” e quat i ons, num er i cal er r or s m ay l ead t o s m al l ne gat i ve num ber s i n t he t i m e s er i es . I f des i r ed, t h e v alu e o f AB SE R and RELE R ca n be de c re a se d i n o rd e r to ach i eve great er preci si on i n t he si m ul at i on output s.
ADB A ct i vi t y D at aB ase
E X A M S pro v i d es for l o n g -t erm storag e o f CH EM ic a l, E NV i r onm ent al , t r ans for m at i on P RO D uct che m i st r y, and al l och t ho no us L OAD i ngs dat abas es i n a U ser D at aB as e or UDB . The act ual ana l yse s ar e con duct ed on pa r t i cul ar dat as et s dr awn f

r om t hes e f

i l es ( or ent er ed vi a SE T / CH ANG E ). Par t i cul ar c as es a r e l oaded f r om t he UDB i nt o t he for egr ound t r ansient m em ory of yo ur com pu t er i n an A ct i vi t y D at aB ase o r ADB , us i ng t he RECA LL com m and. B eca use E X A M S sim u la te s th e b e h a v io r o f se v e ra l ( M CH EM ) c h e m ic a ls si m ul t aneous l y, t he ADB for chem i cal s has M CH EM se p a ra te se ct or s. These dat a a r e l ostw hen you E X IT f r o m E X A M S , so be s ur e t o S T ORE an y ne w or co rr ec t ed da t as ets b efo re l eavi ng E X A M S . AB S OR AB S OR p tion sp e c tra (w a v e le n g th , i o n , ch e m ic a l) U n i t s : c m ( m o l e / L) ( N. B. : W hen ent er i ng dat a, “w ” i s t he

-1 -1 i n d ex nu m b er for ë , nott he w avel engt h per se . See pa ge 200 for t he m appi ng bet w een AB S OR ent r i es and ë .) M ean deca di c m ol ar l i ghtext i nct i on coe ffi ci ent s i n 46 w a v e le n g th in te rv a ls o v e r 2 8 0 – 8 2 5 n m . F o r w a v e le n g th “w ” a nd che m i cal “c ”:

3 A B S O R ( w, 1 , c ) i s mo l a r a b s o r p t i o n c o e ffi c i e n t of RH ( neut r al m ol ecul e) 4 A B S O R ( w, 2 , c ) i s mo l a r a b s o r p t i o n c o e ffi c i e n t o f RH ( +1 + cat i on) 5 A B S O R ( w, 3 , c ) i s m o l a r a b s o r p t i o n c o e ffi c i e n t o f RH ( +2 2+ cat i on) 6 A B S O R ( w, 4 , c ) i s mo l a r a b s o r p t i o n c o e ffi c i e n t o f RH ( +3 3+ cat i on) 2 A B S O R ( w, 5 , c ) i s mo l a r a b s o r p t i o n c o e ffi c i e n t o f RH (

! 1 ! ani on) A B S O R ( w , 6 , c ) i s mo l a r a b s o r p t i o n c o e ffi c i e n t o f RH (

! 2 2

! ani on) A B S O R ( w , 7,c) i s m ol ar abso r pt i on coeff i ci ent of R (

! 3

3

! ani on) A D V PR ADV ect i on PR opor t i on ( pat h) U n its: n /a R a n g e : > 0 – 1 .0
PR o p o r t i o n o f

fl o w ADV e c te d fro m se g m e n t J F RA D t hat enter s I T OAD . The m at chi ng ( sa m e s ubsc r i pt ) m em ber s of J F RA D , I T OAD , and A D V PR d e fin e a n a d v e c tive h y d ro lo g ic flo w p a th w a y . A ltho u g h u su a lly 1 , A D V PR l et s one e nt er b raide d ch an n els, etc. T h e t o t al of A D V PR s for each se gm ent m u st s u m to e ithe r 0 o r 1 , f a ilin g w h ic h , E X A M S abor t s t he RU N . The fl ow dat a can be i nspe ct ed by t ypi ng S HOW ADV ; p a th n u m b e rs a re g iv e n a b o v e e a c h ac tive da ta se t. E n te r d a ta vi a CH ANG E or SE T com m and s. A d d iti o n a l i n fo rm a tion a v a ilab le : J F RA D , I T OAD
AEC A ni on E xchange C apac i t y ( se gm ent , m ont h) U ni t s: m eq/ 100 g ( dr y) A ni on exchange ca paci t y of s edi m ent phas e of

ea ch se gm ent . U se f

ul i n r el at i ng s edi m ent s or pt i on ( par t i t i oni ng) of ani on s t o a va r i able charact eri st i c of s yst em sedi m ents. A er M et A q u a tic A e ro b ic M e ta b o lism H a lf-L ife (c h e m ic a l) U ni t s: days A quat i c a er obi c met abol i sm hal f

- l i f e of ea ch st udy c h e m ic a l. W h e n b io ly sis ra te c o n sta n ts a re z e ro , A e rM e t i s u se d to cal cul at e bi ol ysi s r at e c onst ant s f or w at er - col um n bac t er i op la n k to n . In m a k in g th is c o m p u ta tion , t h e p la n k to n ic popul at i ons ar e a ver aged f or t he e nt i r e w at er body. I n M ode 1 a n d M o d e 2 , t h e s i n g l e t e mp o r a l v a l u e i n u s e a t RUN t i me i s u se d
. F o r o t h er M o d es , t h e m i d -Su m m er p o p u l ati o n s are use d.
AI RTY A IR m ass TY pe ( m ont h) U ni t s: l et t er code s S e le c t: R u ra l (d e fa u lt), U rb a n , M a riti m e , o r T ro p o sp h e ric A n ae rM A q u a tic A n a e ro b ic M e ta b o lism h a lf-li fe (c h e m ic a l) U ni t s: D ays A qu at i c an ae r ob i c met ab ol i s m ha l f

- l i f e of e ac h s t udy c h e m ic a l. W h e n bio ly sis rate co n sta n ts a re ze ro , A n a e rM is u se d to c a lc u la te b io ly sis ra te c o n sta n ts fo r t h e b e n th ic m i cr obi ot a. Thi s com put at i on us es a popul at i on num ber f or bent hi c ba ct er i a c al cul at ed a s t he a ver age f or al l s ur f

i ci al176

se di m ent s. I n M ode 1 and M ode 2, t he s i ngl e t em por al val ue i n us e at R U N t i m e i s use d. For ot herM odes , t he m i d- Sum m er popul at i ons ar e us ed.
AR EA AR EA (se g m e n t) U n its: m 2 Top pl an a r ea of

ea ch m odel s egm ent of t he w at er body. For E p ili m n io n a n d L itt o ra l se g m e n ts, AR EA i s t he a r ea of t he ai r - w at er i nt erface; for H yp ol i m ni on segm ents AR EA i s t he ar ea o f t he t her m ocl i ne; for B ent hi c s egm ent s i t i s t he sur face ar ea of

t he bot t om . I n t he l at t er ca se AR EA m ay d i ffe r f r o m XS T UR i n a di spe r si ve excha nge pai r bec aus e of r educt i on i n exc hangi ng ar ea due t o r ock out cr ops, et c.
ATUR B A t m osphe r i c T URB i di t y ( m ont h) U ni t s: km E qu i valent aerosol l aye r t hi ckn ess.
BA CPL BA C te rio PL ankt on popul at i on ( se gm ent , m ont h) Un i t s : c f u / mL Popul at i on dens i t y of bac t er i a c apabl e of degr adi ng xenobi ot i cs . The abbr evi at i on “c f u” s t ands for a “ col ony fo rm in g u n it. ”
BN BA C B e N t hi c BA C t er i a ( se gm ent , m ont h) U ni t s: cf u/ 100g dr y s edi m ent Popul at i on dens i t y of bent hi c ba ct er i a t hat degr ade xenobi ot i cs . The abbr evi at i on “c f u” s t ands for a “ col ony fo rm in g u n it. ”
BN M AS B e N th ic b io M AS s ( se gm ent , m ont h) U n its: g (d ry )/m 2 B i om as s of

sm al l bent hos – i nfauna subj ectt o bi osor pt i on.
BU L KD BU L K D ens i t y ( se gm ent , m ont h) U ni t s: g/ cm 3 Fresh w ei gh t per uni t volum e of bent hi c sedi m ents.
CEC C at i on E xchange C apac i t y ( se gm ent , m ont h) U ni t s: m eq/ 100g ( dr y) C at i on exc hange capa ci t y of s edi m ent phas e i n ea ch se gm ent . U se f

ul i n r el at i ng s edi m ent s or pt i on ( par t i t i oni ng) of cat i on s t o a va r i able charact eri st i c of s yst em sedi m ents.
CHARL CH AR act er i st i c L engt h or m i xi ng l engt h ( pat h) U n its: m A ver age of

s egm ent di m ens i ons nor m al t o t he exchange i nt erface l i nk i ng segm ent nu m bers J T URB ( p) and I T URB (p). T h e m atch i n g (s a m e “p ” su b sc ri p t ) m em b ers o f J T URB , I T URB , CHARL , D SP , and XS T UR t oget her def i ne a di spe r si ve t r ans por t pat hw ay. A gi ven s egm ent m ay ha ve di ffer ent m ix in g len g th s a t d iffe re n t i n te rfa c e s. CHARL ca n al so be cal cul at ed f

r om t he di s t an ce a l on g a pa t h t ha t c on ne ct s t he cen t ers of segm ents J T URB ( p) and I T URB ( p) , pa ss i ng t hr ough t he i nt erface w ho se ar ea i s XS T UR (p). S e e a lso : D SP , I T URB , J T URB , XS T UR
CH E M NA CH EM ic a l NA me o f

c o mp o u n d s ( 5 0 c h a r a c t e r s , c h e m) U n its: n /a D o notus e “ CH ANG E ” o r “ SE T ” t o e nt er nam es ! The NA me for a CH EM i cal i s ent er ed i nt o t he dat abas e vi a t he c om m and se quence :
E X A M S -> C H E M IC A L N A M E IS n n n ...
w h e re “n n n ... “ ca n in c lu d e a s m a n y a s 5 0 c h a ra c te rs . T h is n a m e is a ss o c ia te d w ith c h e m ic a l l ib ra ry e n trie s a n d is pr i nt ed i n t he hea der i nfor m at i on of t he a ppr opr i at e out put t ables.
CH L CH L or ophyl l s + pheophyt i ns ( se gm ent , m ont h) U n its: m g /L C on cen t rati o n of ch l o rop h y l l plu s ch l o rop h y l l -l i k e p i gm ents. U se d t o com put e s pect r al l i ght abs or pt i on coe ffi ci ent s due t o pi gm ent s w hi ch abs or b l i ght f r om t he w at er col um n and t hu s com pete w i t h ph ot ol ysi s of synthet i c che m i cal s.
CH P AR CH e m ic a l P AR ent com pound ( pat h) U ni t s: n/ a R ange: 1– KC HEM
CH P AR ( p) gi ve s t he ADB l ocat i on of t he pa r ent s our ce of T P RO D ( p)
. The m at chi ng ( sa m e t r ans for m at i on pat h num ber “p ”) m em b e rs of CH P AR and T P RO D gi ve t he l ocat i on num ber s i n t he a ct i ve da t abas e of t he parentche m i cal and t he t r ans for m at i on pr oduct for pat hw ay “ p”. For exa m pl e, “ S E T CH P AR (p) TO 1" , and T P RO D (p) TO 4, t o s how t hat t he chem i cal i n ADB s ect or 4 i s pr oduced vi a t r ans for m at i on of t he c hem i cal i n ADB s ect or 1, vi a pr oces s dat a de fi ned by t he r em ai ni ng m em ber s of pr oduct che m i st r y s ect or “p”
.177

S e e a lso : EAYLD , NP RO C , RF ORM , T P RO D , YI EL D
CI NT C om m un i cat i on s I NT erval for dyna m i c si m ul at i on s. U ni t s: s ee T CO DE
CI NT i s t he i nt er val bet w een out put cycl es f r om t he in te g ra to rs . In M o d e 2 , CI NT ca n be s et t o pr oduce any des i r ed out put f

r equenc y, so l ong as t he r es ul t i ng r epor t i ng i nt er val i s >1 hour
. W hen CI NT is se t t o 0 , E X A M S ( M ode 2) set s CI NT t o reportat t h e 1 2 eq ual- i ncrem ent peri od s m ost cl os el y m at ch i ng t he d ur at i on s pe ci fi ed by ( T E ND - T IN IT ). CI NT i s und er f

ul l user con t r ol only i n M od e 2; i n M od es 1 and 3 E X A M S i t se lf se t s the va l u e o f CI NT ac cor di ng t o t he nee ds of t he an al ysi s.
CL OUD CL OUD i nes s ( m ont h) U ni t s: di m ens i onl es s Range: 0 – 10 M ea n m o n t h l y op aq u e c l o u d i n es s i n t en t h s o f f u l l sk y co v er.
DEPT H DEPT H (se g m e n t) U n its: m A v e ra g e v e rtica l d e p th o f e a c h se g m e n t.
DF AC D i st r i but i on F AC t or ( se gm ent , m ont h) U n its: d im e n sio n le ss ra tio R at i o of opt i cal pat h l engt h t o ver t i cal dept h, r ange 1. 0 – 2. 0. A ver t i cal l i ght bea m has a DF AC of 1. 0; a f ul l y di ff use d l i ght f i el d has a DF AC of

2. 0. For w hol e da ys, a va l ue of 1. 19 is o fte n a d e q u a te ; E X A M S defaul t s t o t hi s val ue w hen t he en t ry for DF AC i s out si de t he r ange 1. 0 – 2. 0.
D I SO 2 D IS sol ved O 2 ( se gm ent , m ont h) U n its: m g /L

2 C oncent r at i on of

di ss ol ved oxyge n ( O ) i n each s egm ent of e c o s y s t e m.
DOC D i ss ol ved O r gani c C ar bon ( se gm ent , m ont h) U n its: m g /L U se d forc om pu t i ng s pe ctr al l i ght abs or pt i on, s i ngl et oxygen conce nt r at i ons, and com pl exat i on.
DR FL D DR i F t L oa D ( se gm ent , che m i cal , m ont h) U ni t s: kg/ hour D r i f t l oadi ngs: aer i al dr i f

t , di r ectappl i cat i ons, s t ack fal l out (e tc .) o f c h e m ic a l o n e a c h sy ste m e le m e n t.
D SP D i SP er si on coe ffi ci ent ( pat h, m ont h) U ni t s: m / hour

2 Eddy di ff

usi vi t y t o be a ppl i ed t o di spe r si ve e xchange pai r i ng “p”
. The m at chi ng ( sa m e “p” subs cr i pt ) m em ber s of J T URB , I T URB , CHARL , and XS T UR t oget her def i ne a di spe r si ve t r ans por t pat hw ay. I n t he c as e o f hor i zont al m ix in g , D SP i s t he l ongi t udi nal di spe r si on coeff i ci ent ; for ver t i cal m i xi ng i t m ay r epr es ent exch ange ac r oss t he t her m ocl i ne or exc hanges w i t h bot t om s edi m ent s. I n t he l at t er ca se D SP i s a s t at i s t i ca l ki ne t i c c om posi t e i ncor por at i ng di r ects or pt i on t o t he s edi m ent s ur face , m i xi ng of t he sedi m ent s by bent hos ( bi ot ur bat i on) , s t i r r i ng by dem er sa l fi she s, et c. S e e a lso : CHARL , I T URB , J T URB , XS T UR
E AH
a E for A ci d H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol

a A r r he ni us a ct i va t i on e ne r gy E of s pe ci fi c- ac i d- ca t al yzed h y d rolys i s o f ch em i ca l s. M atri x i n d i ce s m atch t h o se of KAH , gi vi ng, for each chem i cal , dat a for 3 for m s ( 1: di ss ol ved, 2: so lids -s o rb e d , 3 : DOC - com pl exed) of 7 i oni c s peci es ( 1: neut r al ; 2, 3, 4: ca t i ons; 5, 6, 7: ani ons)
. W hen E AH is n o n - z e r o , t h e s e c o n d

- o r d e r r a t e c o n s t a n t K ( M h ) is -1 -1 c a l c u l a t e d f

r o m:

EAYLD

A E Y ie LD ( pat h) U ni t s: kca l

a EAYLD ( p) i s act i vat i on ene r gy E t o com put e t r ans for m at i on pr oduct yi el d as a f

unct i on of

envi r onm ent al t em per at ur es ( TCEL )
. W hen EA

_ Y ie LD (p ) is z e ro , YI EL D ( p) gi ves t he di m ens i onl es s m ol ar pr oduct yi el d. A non- zer o EAYLD ( p) i nvokes a r e- eval uat i on i n w hi ch YI EL D ( p) i s i nt er pr et ed a s t he Br i gg s i an l og ar i t hm o f t he p r e- ex po ne nt i al fac t or i n an A r r heni us- t ype f

unct i on, gi vi ng pr oduct yi el d as a f unct i on of t em per at ur e ( var yi ng w i t h pos i t i on and t i m e) ( TCEL (seg m en t , m o n t h )) :

S e e a lso : CH P AR , NP RO C , RF ORM , T P RO D , YI EL D
E BH178

a E for B as e H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol

a A r r heni us act i vat i on ene r gy E of s peci fi c- bas e c at al yzed h y d rolys i s o f ch em i ca l s. M atri x i n d i ce s m atch t h o se of KBH , gi vi ng, for e ach chem i cal , da t a for 3 for m s ( 1: di ss ol ved, 2: so lids -s o rb e d , 3 : DOC - com pl exed) of 7 i oni c s peci es ( 1: ne ut r al , 2, 3, 4: c at i on s , 5, 6, 7: a ni on s )
. W hen E BH is n o n - z e r o , t h e s e c o n d

- o r d e r r a t e c o n s t a n t K ( M h ) is -1 -1 c a l c u l a t e d f

r o m:

EHEN E n t h alp y t erm for HEN ry ’s law (c h e m ic a l) U ni t s: kca l / m ol U se d t o com put e H enr y’ s l aw cons t ant s as a f unct i on of TCEL ( envi r onm ent al t em per at ur e)
. W hen EHEN i s non- zer o, th e H e n ry ’s law c o n sta n t (H ) a ffe c ting v o la til iz a tion a t a p a r t i c u l a r ( s e g me n t , mo n t h ) i s c o mp u t e d f r o m TCEL :

EK 1 O 2

a E K 1 O 2 (sin g le t o x y g e n ) (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol A r r heni us act i vat i on ene r gy for s i ngl et oxygen ph ot o-oxy gen at i on of chem i cal s. M atr i x i ndi ces m at ch those o f K 1 O 2, gi vi ng, for e ach chem i cal , da t a for 3 for m s ( 1: d iss o lv e d , 2 : so lids -s o rb e d , 3 : DOC -c o m p le x e d ) o f 7 io n ic spe ci es ( 1: neut r al , 2, 3, 4: ca t i ons, 5, 6, 7: ani ons)
. W hen EK 1 O 2 i s n o n - z e r o , t h e s e c o n d

- o r d e r r a t e c o n s t a n t K ( M h ) -1 -1 i s cal culat ed as:

EL EV EL EV at i on U ni t s: m et er s above m ean se a l evel G r ound s t at i on el evat i on.
E NH
a E for N e u tra l H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol A r r heni us act i vat i on energy for neut r al hydr ol ysi s of ch em i ca l s. M atri x i n d ice s m atch t h o se of KNH , gi vi ng, for eac h che m i cal , dat a for 3 for m s ( 1: di ss ol ved, 2: so lids -s o rb e d , 3 : DOC - com pl exed) of 7 i oni c s peci es ( 1: neut r al , 2, 3, 4: ca t i ons, 5, 6, 7: ani ons)
. W hen E NH is n o n -z e ro , th e p se u d o -first-o rd e r ra te c o n sta n t (h ) is -1 c a l c u l a t e d f r o m:

E OX
a E OX id a tion (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol A r r hen i us act i vati on energy for oxidat i ve t r ansfor m at i ons of c h em i ca l s. M atri x i n d i ce s m atch t h o se of KOX , gi vi ng, for each chem i cal , dat a for 3 for m s ( 1: di ss ol ved, 2: sol i ds- sor bed, 3: DOC - co m pl ex ed ) of 7 i on i c s pe ci es ( 1: neut r al , 2, 3, 4: ca t i ons, 5, 6, 7: ani ons)
. W hen E OX is n o n - z e r o , t h e s e c o n d

- o r d e r r a t e c o n s t a n t K ( M h ) is -1 -1 c a l c u l a t e d f

r o m:

EPK E n th a lp y term fo r p K (io n , ch e m ic a l) U ni t s: kca l / m ol W hen EPK i s no n- ze r o, pK i s c om pu t ed a s a f un ct i on of t em per at ur e vi a:

T h e v ec t o r i n d i ce s for EPK (“c” de n o t es t h e c h em i ca l ) are

4 3 EPK ( 1 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f RH f r o m RH + 5 4 EPK ( 2 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f RH f r o m RH 2 + + 6 5 EPK ( 3 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f RH f r o m RH 3+ 2+ 2 3 EPK ( 4 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f RH f r o m RH - 2 EPK ( 5 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f RH f r o m RH =

- EPK ( 6 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f R f r o m RH 3- =
ERED
a E RED u c tion (fo rm , i o n , ch e m ic a l) U ni t s: kca l / m ol A r r heni us act i vati on energy for r edu ct i ve t r ansfor m at i ons of ch em i ca l s. M atri x i n d i ce s m atch t h o se of KR ED , gi vi ng, for each chem i cal , dat a for t hr ee for m s ( 1: di ss ol ved, 2: so lids -s o rb e d , 3 : DOC - com pl exed) of s even i oni c spe ci es ( 1: ne ut r al , 2, 3, 4: c at i on s , 5, 6, 7: a ni on s )
. W hen ERED is n o n - z e r o , t h e s e c o n d

- o r d e r r a t e c o n s t a n t K ( M h ) is -1 -1 cal culat ed as:

E S OL E n t h alp y t erm for S OL u b ili ty (io n , ch e m ic a l)179

U ni t s: kca l / m ol
E S OL des cr i bes che m i cal s ol ubi l i t y as a f un ct i on of t em pe r at ur e ( TCEL )
. The m at r i x i ndi ces ( “c” denot es t he chem i cal ) denot e:

3 E S OL ( 1 , c ) i s d a t u m fo r s o l u b i l i t y o f n e u t r a l mo l e c u l e s RH E S OL ( 2, c) i s dat um for sol ubi l i t y of s i ngl y cha r ged c at i ons 4 RH + E S OL ( 3, c) i s dat um for s ol ubi l i t y of doubl y cha r ged c at i ons 5 RH 2 + E S OL ( 4, c) i s dat um fors ol ubi l i t y of t r i pl y cha r ged c at i ons 6 RH 3 + E S OL ( 5, c) i s dat um for s ol ubi l i t y of s i ngl y cha r ged a ni ons 2 RH

- E S OL ( 6, c) i s dat um for s ol ubi l i t y of doubl y cha r ged a ni ons RH = E S OL ( 7,c) i s dat um for s ol ub i l i t y of t r i pl y ch arged an i on s R 3-

E VAP E VAP or at i on ( se gm ent , m ont h) U n its: m m /m o n th ( M ont hl y) eva por at i ve w at er l oss es f r om ec osys t em segm ents.
EV PR M o l ar h E at of V a P o R iz a tion (c h e m ic a l) U ni t s: kca l / m ol Ent hal py t er m for com put i ng vapor pr es sur e as a f unct i on of TCEL ( envi r onm ent al t em per at ur e ( se gm ent , m ont h) )
. W hen EV PR i s n o n - z e r o , v a p o r p r e s s u r e V a i s c o mp u t e d f r o m:

E VE NT D Event D ur at i on ( 5) U ni t s: days Range: 1–364 I n M ode 3, E xam s r epor t s per i od ave r age, m i ni m um , and peak conce nt r at i ons, and t he m i ni m um , ave r age, and pe ak conce nt r at i on of

t he l ar ges t ( as def

i ned by t hei r m ean val ues ) 96- hour , 21- day, 60- day, a nd 90- day event s dur i ng e a c h t i me s e g me n t ( o n e o r mo r e y e a r s ) o f t h e s i mu l a t i o n . Up t o f i ve add i t i on al averagi ng per i od s can be s pec i fi ed; t hese ar e r epor t ed i n an a ddendum t o Tabl e 20.
F IX F IL F IX F IL sign als the ex i sten ce of o u t p u t da t a fo r LI ST s and P L OT s. T o a c c e ss re su lts fro m a p rio r ru n , “ S E T F I XF I L T O 1. ” F IX F IL i s set t o ze r o w hen E X A M S i s i nvoked, s o t hat t he LI ST and P L OT com m and s are prot ect ed f r om at t em pt s t o ac ce ss n o n - e x i s t e n t o u t p u t d a t a f i l e s . W h e n r e s u l t s e x i s t f r o m a p re v io u s s im u la tio n , y o u c a n re se t F IX F IL to 1 in o rd e r to

g a i n a c c e s s t o t h e m.
F RO C FR act i on O r gani c C ar bon ( se gm ent , m ont h) U ni t s: di m ensionl ess O rg a n ic c a rb o n c o n te n t o f so lids a s fra c tio n o f d ry w e ig h t. F RO C i s c ou pl ed t o KOC t o gene r at e t he s edi m ent par t i t i on 3 co effi cien t for n e u tral ch em i ca l s (R -H ) as a fu n cti o n of a p ro p e rty (o rg a n ic c a rb o n c o n te n t) o f th e se d im e n t.
HENR Y HENR Y ’s law c o n sta n t (ch e m ic a l) U n its: atm o sp h e re -m /m o le 3 U se d i n c om pu t at i on of a i r / w at ere xc ha ng e r at es (v o la til iz a tion ). If p a ra m e te r E H E N is n o n -z e ro , HENR Y is u se d as the pre -ex p o n en t i al fac t o r i n co m p u t i n g t h e H en ry’s l aw cons t ant H as a f

unct i on of

envi r onm ent al t em per at ur es ( TCEL ):

I CH EM I CH EM ic a l (ev e n t) U n i t s: n/a R an g e: 1-- KC HEM E v e n t “e” i s a p u l se of ch em i ca l nu m b er I CH EM ( e) i n t he act i ve da t abas e I CH EM id e n tifi e s th e lo c a tion in th e A c tivity D at abas e ( ADB ) o f th e c h e m ic a l e n te rin g th e e c o sy ste m v ia p u l se l o ad ev en t “e ”. W h en , for ex am p l e, ch em i ca l da t a a re l oaded i nt o ADB sec t o r 3 (w h eth er RECALL ed f r om t he U se r D at abas e Li brar y ( UDB ) ( vi a, for exa m pl e, t he c om m and se quence “ R E C A L L C H E M 7 A S 3 ") or en t ere d as n ew da t a), I CH EM ( e) ca n be SE T t o 3 t o cr eat e a pul se l oad e vent of t hat c h e m ic a l. S e e a lso : I DAY , I M A SS , I M ON , I SE G
I DAY I DAY (e v e n t) U ni t s: n/ a R ange: 1–31 Pul se l oad e vent “e ” t akes pl ace on day I DAY (e ) o f m o n th I M ON ( e)
. The pul se l oad dat a ar e or gani zed by ver t i cal eve nt colum ns, t hat i s, t he set of pu l se l oad vari ables ( I M A SS (e), I CH EM (e ), I SE G (e ), I M ON ( e) , and I DAY ( e ) ) w i t h t h e s a me v e c to r su b sc rip t d e s c rib e s a sin g le c h e m ic a l p u lse e v e n t. T h u s a p u ls e o f c h e m ic a l I CH EM ( e) , of m agni t ude IM A S S (e ), is re le a se d in to se g m e n t I SE G ( e) on day I DAY ( e) of m ont h I M ON (e ). D u rin g m o d e 2 sim u la tion s, I DAY and I M ON ar e i noper at i ve. S e e a lso : I CH EM , I M A SS , I M ON , I SE G180

I M A SS I n iti a l M A SS (e v e n t) U ni t s: kg
I M A SS gi ves t he m agni t ude of chem i cal pul se l oad e vent “e ”. I n m ode 2, pu l s es a r e en t er ed a t t i m e 0 ( i
. e. , a s i ni t i al condi t i ons) , and at t he out se t of ea ch CO NT I NU at i on of t he sim u la tion . In m o d e 3 , I M ON and I DAY s peci f y t he dat e of t he l oad e vent s. A n eve nt r ecur s i n each yea r of t he RU N or CO NT I NU ed s i m ul at i on. The pul se l oad dat a ar e or gani zed by ver t i cal eve nt col um ns; t hat i s, t he s er i es of pul se l oad v ariabl es ( I M A SS , I CH EM , I SE G , I M ON , and I DAY ) wi t h t he sa m e v e c to r su b sc rip t d e sc rib e s a sin g le e v e n t. S e e a lso : I CH EM , I DAY , I M ON , I SE G
I M ON I M ON th (e v e n t) U ni t s: n/ a R ange: 1-

- 12 Pul se l oad e vent “e ” t akes pl ace on day I DAY (e ) o f m o n th I M ON ( e)
. The pul se l oad dat a ar e or gani zed by ver t i cal eve nt colum ns; t h at i s, t he set of pu l se l oad vari ables ( I M A SS (e), I CH EM (e ), I SE G (e ), I M ON ( e) , and I DAY ( e ) ) w i t h t h e s a me v e c to r su b sc rip t d e sc rib e s a sin g le c h e m ic a l p u lse e v e n t. T h u s a p u lse o f c h e m ic a l I CH EM ( e) , of m agni t ude I M A SS (e), is re le a se d in to se g m e n t I SE G ( e) on day I DAY (e ) o f m o n th I M ON (e ). D u rin g m o d e 2 sim u la tion s, I DAY and I M ON are i noper at i ve. S e e a lso : I DAY , I CH EM , I M A SS , I SE G
I SE G I SE G m e n t (ev e n t) U n i t s: n/a R an g e: 1-- KOU NT P u lse lo a d e v e n t “ e ” lo a d s c h e m ic a l I CH EM ( e) on s egm ent I SE G ( e)
. A ny segm ent ca n r ece i ve a pul se l oad. Shoul d t he pul se l oads i ncr eas e t he f re e conce nt r at i on of

uni oni zed chem i cal above 10 M ( or hal f i t s aqueous s ol ubi l i t y, -5 w h ic h e v e r is le ss ), th e siz e of th e ev e n t is re d u c e d , to a v o id vi ol at i ng t he l i near i zi ng a ss um pt i ons use d t o cr eat e E X A M S . T he p ul se l oad da t a are organ i zed by v ert i cal even t col um ns; t hat i s, t he pul se l oad va r i abl es hav i ng t he s am e ve ct or su b sc rip t d e fin e a sin g le c h e m ic a l p u lse e v e n t. S e e a lso : I CH EM , I DAY , I M A SS , I M ON
I T OAD I T O AD vect i on ( pat h) U n i t s: n/a R an g e: 0-- KOU NT (0 = e x p o rt) C h e m ic a ls a re ad v e c te d t o se g m e n t I T OAD ( p) f r om s egm ent J F RA D ( p)
. The m at chi ng ( sa m e subs cr i pt ) m em ber s of J F RA D , I T OAD , and A D V PR d e fin e a n a d v e c tive h y d ro lo g ic fl ow pat hw ay c arr yi ng ent r ai ned c hem i cal s and s ol i ds t hr ough t he w at er body. W hen I T OAD ( p) i s 0, t he pa t hw ay advec t s w at er and ent r ai ned s ubst ance s acr oss s yst em b o u n d a rie s, i.e ., I T OAD ( p) = 0 spe ci fi es a n e xpor t pat hw ay. The f l ow da t a can be i nspe ct ed by t ypi ng “ S HOW ADV ” ; p a th n u m b ers are g i v en ab o v e ea ch acti v e d atas et. E n t er d a ta w i t h SE T or CH ANG E com m and s. S e e a lso : J F RA D , A D V PR
I T URB I T URB ul ent di spe r si on ( pat h) U n i t s: n/a R an g e: 0-- KOU NT Segm ent s I T URB ( p) and J T URB ( p) exc hange vi a t ur bul ent di spe r si on. The m at chi ng ( sa m e “p” subs cr i pt ) m em ber s of I T URB , J T URB , CHARL , D SP , and XS T UR t oget her def i ne a d isp e rs iv e tran sp o rt p a th w a y ; I T URB ( p) and J T URB ( p) i n d i ca t e w h i ch seg m en t s are l i n k ed by disp ersive t ran sp o rt pat hw ay “ p”. A “0" i n I T URB pai r ed w i t h a no n -ze ro se gm ent num ber i n J T URB denot es a bounda r y condi t i on w i t h a pur e ( zer o c hem i cal ) w at er - body. The i nput dat a c an be e xam i ned vi a S HOW T URBUL E NCE ; pa t h w ay nu m b ers a re sh o w n w ith e a c h d a ta se t. S e e a lso : CHARL , D SP , J T URB , XS T UR
IU N IT IU N IT cont r ol s t he pr i nt i ng o f di agnos t i cs f

r om t he i nt egrat ors. No r ma l l y z e r o ( o ff) , i t ma y b e t u r n e d o n w h e n p r o b l e ms o cc u r. T o m an u all y se t IU N IT t o gene r at e i nt egr at or d ia g n o stic m e ss a g e s, SE T I UN I T T O 1. The m es sa ge ge ner at or can be di sa bl ed a t any t i m e by SE T t i ng IU N IT t o 0.
J F RA D J FR o m AD vect i on ( pat h) U ni t s: n/ a Range: 1– KOU NT C h e m ic a ls a re a d v e c te d fro m se g m e n t J F RA D ( p) t o s egm ent I T OAD ( p)
. The m at chi ng ( sa m e s ubsc r i pt ) m em ber s of J F RA D , I T OAD , and A D V PR d e fin e a n a d v e c tive h y d ro lo g ic fl ow pat hw ay. E X A M S c o m p u te s th e t o ta l n e t fl o w a v a ilab le fo r a d v e c tion fro m se g m e n t J F RA D ( p)
. O f t he t ot al fl ow , t he f r act i on A D V PR (p ) flo w s fro m se g m e n t J F RA D (p ) in to se g m e n t I T OAD ( p)
. The hydr ol ogi c fl ow c ar r i es an e nt r ai ned m as s of

che m i cal al on g the pat hw ay. The fl ow spe ci fi cat i ons can be i nspe ct ed by t ypi ng S HOW ADV ; pat hw ay num ber s ar e gi ven a bove e ach act i ve da t as et . Ent er dat a w i t h SE T or CH ANG E com m and s. S e e a lso : I T OAD , A D V PR
J T URB J T URB ul ent di spe r si on ( pat h) U n i t s: n/a R an g e: 0-- KOU NT181

Se gm ents J T URB ( p) and I T URB ( p) exc hange vi a t ur bul ent di spe r si on. The m at chi ng ( sa m e “p” s ubsc r i pt ) m em ber s of J T URB , I T URB , CHARL , D SP , and X S T UR t oget her def i ne a d isp e rs iv e tran sp o rt p a th w a y ; J T URB ( p) and I T URB ( p) i n d i ca t e w h i ch seg m en t s are l i n k ed by disp ersive t ran sp o rt pat hw ay “ p”. A “0 " i n J T URB pa i red w i t h a n o n -ze ro s eg m en t nu m be r i n I TURB denot es a bounda r y condi t i on w i t h a pur e ( zer o che m i cal ) w at er - body. T he i nput dat a c an be e xam i ned vi a S HOW T URBUL E NCE ; p ath w ay n u m b ers a re sh o w n w ith e a c h d a ta se t. S e e a lso : CHARL , D SP , I T URB , XS T UR
KAH K A ci d H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: per m ol e [ H ] per hour + Second- or der r at e c onst ant for s peci fi c- aci d- cat al yzed h y d r o l y s i s o f

c h e mi c a l s . W h e n t h e ma t c h i n g ( s a me subs cr i pt s) A r r heni us act i vat i on ene r gy ( E AH ) is z e ro , KAH i s i nt er pr et ed a s t he s econd- or der r at e c onst ant . W hen t he m at chi ng ent r y i n E AH is n o n -z e ro , KAH i s i nt er pr et ed a s t he ( B r i ggsi an) l ogar i t hm of t he f r equenc y fact or i n an A rrh e n iu s e q u a tion , an d th e 2 n d -o rd e r ra te c o n sta n t i s com pu t ed as a funct i on of segm ent t em perat ures TCEL . M at r i x i ndi ces r efer t o t hr ee for m s- - 1: aque ous, 2: so lids -s o rb e d , an d 3 : DOC - com pl exed; by s even i ons- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
KBACS K B AC t er i a be nt ho S (fo rm , i o n , ch e m ic a l) U ni t s: ( cf

u/ m L) hour

-1 -1 Second- or der r at e c onst ant s- - bent hi c s edi m ent bact er i al bi ol ysi s of

chem i cal s norm al i zed by “c ol on y for m i ng unit s” ( c f u ) p e r m L o f

t e s t m e d i u m. Wh e n t h e m a t c h i n g ( s a me 10 su b sc ri p t s) Q ( QT BA S ) i s z e ro , KBACS i s i nt er pr et ed a s t he se c o n d -o rd e r ra te c o n st a n t. W h e n th e m a tc h in g e n try in QT BA S is n o n -z e ro , KBACS i s i nt er pr et ed a s t he num er i cal val ue of t he s econd- or der r at e c onst ant at25 E C , a nd l ocal val ues of

t he r at e co nst ant ar e c om put ed a s a f unct i on of t em per at ur e ( TCEL ) i n eac h ecosyst em s egm ent . I ndi ces r ef er t o f our f or m s- - 1: aque ous, 2: s ol i ds- s or bed, 3: DOC - com pl exed, and 4: bi o- sor bed; by s even i ons- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
KBACW K B AC t er i opl ankt on W a te r (fo rm , i o n , ch e m ic a l) U ni t s: ( cf

u/ m L) hour

-1 -1 Second- or der r at e c onst ant s K for w at er col um n bac t er i al bi ol ysi s of

chem i cal s norm al i zed by “c ol on y for m i ng unit s” ( c f u ) p e r mL o f

t e s t me d i u m. W h e n t h e ma t c h i n g ( s a me 10 su b sc ri p t s) Q ( QT BA W ) is z e ro , KBACW i s i nt er pr et ed a s t he se c o n d -o rd e r ra te c o n sta n t. W h e n th e m a tc h in g e n try in QT BA W is n o n -z e ro , KBACW i s i nt er pr et ed a s t he num er i cal val ue of t he second- or der r at e c onst ant at25 E C , and l ocal val ues of

t he r at e c onst ant ar e c om put ed a s a fun ct i on of t em pe r at ur e ( TCEL ) i n eac h eco syst em s egm ent . I ndi ces r ef er t o f our f or m s- - 1: aq ue ous , 2: s ol i ds- sor bed, 3: DOC -co m p l ex ed , an d 4:b i o -so rbe d ; by sev en i o n s--1: ne u t ral, 2-4: cat i on s, and 5-7: ani on s.
KBH K B as e H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: per m ol e [ O H ] per hour - Second- or der r at e c onst ant for s peci fi c- base- cat al yzed h y d r o l y s i s o f

c h e mi c a l s . Wh e n t h e m a t c h i n g ( s a me subscr i pt s) A r r heni us act i vat i on ene r gy ( E BH ) is z e ro , KBH i s i nt er pr et ed a s t he s econd- or der r at e c onst ant . W hen t he m at chi ng ent r y i n E BH is n o n -z e ro , KBH i s i nt er pr et ed a s t he ( B r i ggsi an) l ogar i t hm of t he f r equenc y fact or i n an A rrh e n iu s e q u a tion , an d th e 2 n d -o rd e r ra te c o n sta n t i s com pu t ed as a funct i on of segm ent t em perat ures TCEL . M at r i x i ndi ces r efer t o t hr ee for m s- - 1: aque ous, 2: so lids -s o rb e d , a n d 3 : DOC - com pl exed; by s even i ons- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
KC HEM N um ber of

che m i cal s under r evi ew i n cur r ent s t udy. U n its: n /a
KDP K D ire c t P h o to ly sis (io n , ch e m ic a l) U ni t s: hour -1 Est i m at ed phot ol ysi s r at es - - us e onl y w hen AB S OR , t he a ct ual l i g h t ab so rpti o n sp ec t ra o f t h e co m p o u n d in p u re w ater, are u n a v a ilab le
. KDP i s an a nnual ave r age pse udo- fi r st
- or der p h o to ly sis ra te c o n s ta n t u n d e r c lo u d le ss c o n d iti o n s a t RF L AT , w h ere
KDP ( 1, c) ar e ps eudo- fi r st
- or der phot ol ysi s r at e c onst ant s of 3 n e u t r a l mo l e c u l e s RH KDP ( 2, c) ar e pse udo- fi r st
- or der phot ol ysi s r at e c onst ant s of 4 s i n g l y c h a r g e d c a t i o n s RH + KDP ( 3, c) a r e pse udo- fi r st
- or der phot ol ysi s r at e cons t ant s of 5 d o u b l y c h a r g e d c a t i o n s RH 2 + KDP ( 4, c) ar e ps eudo- fi r st
- or der phot ol ysi s r at e c onst ant s of 6 t r i p l y c h a r g e d c a t i o n s RH 3 + KDP ( 5, c) ar e pse udo- fi r st
- or der phot ol ysi s r at e c onst ant s of 2 s i n g l y c h a r g e d a n i o n s RH

- KDP ( 6, c) a r e pse udo- fi r st
- or der phot ol ysi s r at e cons t ant s of d o u b l y c h a r g e d a n i o n s RH = KDP ( 7, c) ar e ps eudo- fi r st
- or der phot ol ysi s r at e c onst ant s of t r i pl y ch arged an i on s R 3-

KI EC K p for I on E xchange C a p a c ity (io n , ch e m ic a l) U ni t s: K p ( m eq/ 100g dr y) -1182

C oef f i ci entr el at i ng sedi m ent part i t i on coeff i ci ent K p of i ons to e x c h a n g e c a p a c ity o f se d im e n ts. KI EC t i m es t he c at i on excha nge c apac i t y CEC ( se g, m ont h) ( or ani on exc hange capa ci t y AEC for ani oni c spe ci es ) gi ves t he K p for s or pt i on of i ons w i t h s ol i d phas es . Thi s com put at i on i s over r i dden by e x p li cit (no n -ze ro) va l u es of K PS , i
. e. , a non- zer o val ue of K PS t akes pr ece dence over a K p com put ed by E X A M S us i ng KI EC . KI EC (1 ,c) i s d atu m for r elati n g C E C an d so rpti o n of sin g ly 4 c h a r g e d c a t i o n RH + K I E C (2 ,c ) is d a tu m fo r rela ting C E C a n d so rp tion o f d o u b ly 5 c h a r g e d c a t i o n RH 2 + K I E C (3 ,c ) is d a tu m fo r re la ting C E C a n d so rp tion o f tri p ly 6 c h a r g e d c a t i o n RH 3 + K I E C (4 ,c ) is d a tu m fo r re la ting A E C a n d s o rp tio n o f sin g ly 2 c h a r g e d a n i o n RH

- K I E C (5 ,c ) is d a tu m fo r re la ting A E C a n d so rp tion of d o u b ly c h a r g e d a n i o n RH = K I E C (6 ,c ) is d a tu m fo r re la ting A E C a n d so rp tion o f trip ly char ged a ni on R 3-

KNH K N e u tra l H y d ro ly sis (fo rm , i o n , ch e m ic a l) U ni t s: hour -1 Pseudo- fi r st
- or der r at e c onst ant s for neut r al hydr ol ysi s of chem i cal s. W hen t he m at chi ng ( sa m e s ubsc r i pt s) A r r heni us act i vat i on ene r gy ( E NH ) is z e ro , KNH i s i nt erpr et ed a s t he fi r st
- or der r at e cons t ant . W hen t he m at chi ng ent r y i n E NH is n o n -z e ro , KNH i s i nt er pr et ed as t he ( B r i ggsi an) l ogar i t hm of t he f r equency f act or i n an A r r heni us equat i on, and t he 1st

- or der r at e c onst ant i s com put ed as a f unct i on of

s egm ent t em perat u res TCEL . M at r i x i ndi ces r efer t o t hr ee for m s- - 1: a q u e o u s, 2 : so lids -s o rb e d , an d 3 : DOC - com pl exed; by s even i on s- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
KOC K OC (c h e m ic a l) U ni t s: [ ( m g/ kg) / ( m g/ L)] ( or gani c c ar bon f r act i on) -1
KOC i s par t i t i on coeff

i ci ent ( K p) keye d t o or gani c c ar bon c o n te n t F RO C ( s, m ) of t he sed i m ent sol i d s in ea ch (s) se gm ent , dur i ng ea ch ( m ) m ont h of s i m ul at i on of

che m i cal b eh av i o r i n t h e sy stem . M u l t i p l i ca t i o n of KOC b y th e o rg a n ic car bon f r act i on FR O C ( s) of

t he soli ds i n ea ch s egm ent yi el ds t he pa r t i t i on coe ffi ci ent ( K p) for s or pt i on of un i oni zed ( R

- H 3) s pec i es w i t h t ho se sol i ds: K p (ch em i ca l , se g m en t , m o n t h )= KOC ( c h e m i c a l ) × F RO C ( se gm ent , m ont h)
KOU NT Nu mb e r o f

s e g me n t s u s e d t o d e fi n e c u r r e n t e c o s y s t e m. U n its: n /a K OW O c ta n o l-W a te r p a rtit io n c o e ffic ie n t (ch e m ic a l) U n i t s : ( m g / L) / ( m g / L) K ow i s an exp eri m ental l y de t erm i ned chem i cal descri pt o r. Ko w ( KOW ( c) ) ca n be us ed t o es t i m at e K oc ( c. f
. ) , and t hus r el at e t he K p of

a c hem i cal t o t he or gani c c ar bon cont ent of sedim ents.
KOX K OX id a tion (fo rm , i o n , ch e m ic a l) U ni t s: per m ol e [ OXR AD ] per hour S e c o n d -o rd e r ra te c o n sta n ts fo r fre e -ra d ic a l ( OXR AD ) o x i d a t i o n o f

c h e mi c a l s . W h e n t h e ma t c h i n g ( s a me subs cr i pt s) A r r heni us ac t i vat i on ene r gy ( E OX ) is z e ro , KOX i s i nt er pr et ed a s t he s econd- or der r at e c onst ant . W hen t he m at chi ng ent r y i n E OX is n o n -z e ro , KOX i s i nt er pr et ed a s t he ( B r i ggsi an) l ogar i t hm of t he f r equency fact or i n an A rrh e n iu s e q u a tion , an d th e 2 n d -o rd e r ra te c o n sta n t i s co m pu t ed as a funct i on of segm ent t em perat ures TCEL . M at r i x i ndi ces r efer t o t hr ee for m s- - 1: aque ous, 2: so lids -s o rb e d , a n d 3 : DOC - com pl exed; by s even i ons- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
KO 2 KO 2 ( se gm ent , m ont h) U ni t s: cm / hour O xygen e xchange cons t antor pi st on ve l oci t y at20 degr ees C i n ea ch ec o sy stem seg m en t . W h en ex p l i cit va l u es of KO 2 a re n o t p re se n t as e n v iro n m e n ta l d e sc rip to rs , E X A M S cal culat es KO 2 f

r om w i ndspe ed.
K PB KP for B io m a ss (io n , ch e m ic a l) U n i t s : ( u g / g ) /( m g / L) Par t i t i on coe ffi ci ent (K p) for com put i ng equi l i br i um bi osor pt i on. The “c” s ubsc r i pt denot es t he c hem i cal ; t he “i on” s ubsc r i pt s i dent i f y:

3 K PB ( 1 , c ) d a t u m fo r b i o s o r p t i o n o f n e u t r a l mo l e c u l e s RH K PB ( 2, c) dat um for bi osor pt i on of s i ngl y cha r ged c at i ons 4 RH + K PB ( 3, c) dat um for bi osor pt i on of doubl y cha r ged c at i ons 5 RH 2 + K PB ( 4, c) dat um for bi osor pt i on of t r i pl y cha r ged c at i ons 6 RH 3 + K PB ( 5, c) dat um for bi osor pt i on of s i ngl y char ged a ni ons 2 RH

- K PB ( 6, c) dat um for bi osor pt i on of doubly char ged a ni ons RH = K PB ( 7,c) dat um for bi osorpt i on of t r i pl y charged ani on s R 3-183

KP DOC K P D i ss ol ved O r gani c C a rb o n (io n , ch e m ic a l) U n i t s : ( u g / g ) / ( m g / L) P a rtit io n c o e ffic ie n t (K p ) fo r e q u ilib riu m c o m p le x a tion w ith DOC . The “c” subs cr i pt denot es t he c hem i cal ; t he “ i on” subs cr i pt s i dent i f

y:
KP DO C ( 1, c) dat um for com pl exat i on of neut r al m ol ecul es 3 RH KP DO C ( 2, c) dat um for com pl exat i on of s i ngl y cha r ged 4 c a t i o n s RH + KP DO C ( 3, c) dat um for com pl exat i on of doubl y cha r ged 5 c a t i o n s RH 2 + KP DO C ( 4, c) dat um for com pl exat i on of t r i pl y cha r ged 6 c a t i o n s RH 3 + KP DO C ( 5, c) dat um for com pl exat i on of s i ngl y cha r ged 2 a n i o n s RH

- KP DO C ( 6, c) dat um for com pl exat i on of do ubl y cha r ged a n i o n s RH = KP DO C ( 7, c) da t um for com pl exat i on of t r i pl y cha r ged a ni ons R 3-

K PS KP for S e d im e n t so lids (io n , ch e m ic a l) U n i t s : ( m g /k g ) / ( m g / L) P a rtiti o n c o e ffic ie n ts (K p ) fo r c o m p u ting so rp tion w ith se di m ent s. The “ c” s ub sc r i pt denot es t he c hem i cal ; t he “ i on” subs cr i pt s i dent i f

y:

3 K PS ( 1 , c ) d a t u m fo r s o r p t i o n o f n e u t r a l mo l e c u l e s RH 4 K PS (2 , c ) d a t u m fo r s o r p t i o n o f s i n g l y c h a r g e d c a t i o n s RH + 5 K PS (3 , c ) d a t u m fo r s o r p t i o n o f d o u b l y c h a r g e d c a t i o n s RH 2 + 6 K PS (4 , c ) d a t u m fo r s o r p t i o n o f t r i p l y c h a r g e d c a t i o n s RH 3 + 2 K PS (5 , c ) d a t u m fo r s o r p t i o n o f s i n g l y c h a r g e d a n i o n s RH

- K PS (6 , c ) d a t u m fo r s o r p t i o n o f d o u b l y c h a r g e d a n i o n s RH = K PS ( 7,c) dat um for s orpt i on of t r i pl y ch arged an i on s R 3-

KR ED K R ED u c tion (fo rm , i o n , ch e m ic a l) U ni t s: per m ol e [ RE DAG ] per hour S ec o n d -ord er rate co n stan t s for RED uci ng AG ent che m i cal r e d u c t i o n o f

c o mp o u n d s . W h e n t h e ma t c h i n g ( s a me subsc r i pt s) A r r hen i us ac t i vat i on ene r gy ( ERED ) i s z e ro , KR ED i s i nt er pr et ed a s t he s econd- or der r at e c onst ant . W hen t he m at ch i ng e nt r y i n ERED is n o n -z e ro , KR ED i s i nt er pr et ed a s t he ( B r i ggsi an) l ogar i t hm of t he f r equenc y fact or i n an A rrh e n iu s e q u a tion , an d th e 2 n d -o rd e r ra te c o n s ta n t i s com pu t ed as a funct i on of segm ent t em perat ures TC EL . M at r i x i ndi ces r efer t o t hr ee for m s- - 1: aque ous, 2: so lids -s o rb e d , an d 3 : DOC - com pl exed; by s even i ons- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
K 1 O 2 K 1 O 2 (sin g le t o x y g e n ) (fo rm , i o n , ch e m ic a l) 2 U n i t s: pe r M [ O ] per hour

1 Second- or der r at e c onst ant s for s i ngl et oxygen p h o t o - o x y g e n a t i o n o f

c h e mi c a l s . W h e n t h e ma t c h i n g ( s a me subs cr i pt s) A r r heni us act i vat i on ene r gy ( EK 1 O 2) i s zer o, K 1O 2 i s i nt er pr et ed as t he se cond- or der r at e cons t ant . W hen th e m a tc h in g e n try in E K 1 O 2 is n o n -z e ro , K 1 O 2 is i nt er pr et ed as t he ( B r i ggsi an) l ogar i t hm of t he f r equenc y fa c to r in a n A rr h e n iu s e q u a tion , an d th e 2 n d -o rd e r ra te cons t ant i s com put ed a s a f unct i on of

s egm ent t em per at ur es TCEL . M at r i x i ndi ces ref er t o t hr ee for m s- - 1: aque ous, 2: so lids -s o rb e d , an d 3 : DOC - com pl exed; by s even i on s- - 1: neu t r al , 2-4: cat i on s, and 5-7: ani on s.
L AMAX L AM bda M AX im u m (io n , ch e m ic a l) U n i t s: na n o m eters W a v e le n g th o f m a x im u m ab so rp tion of ligh t b y e a c h io n ic spe ci es , or w avel engt h of m axi m um over l ap of s ol ar sp ec t rum an d ch em i ca l ’s ab so rpti o n spe ctrum ( o f eac h i o n ). I ndi ces m at ch w i t h KDP m a trix. L AMAX s el ect s t he w avel engt hs use d t o com put e l i ght ext i nct i on fact or s for phot ochem i cal t r ans for m at i on, i n t hose ca se s w her e t he abs or pt i on spect r um of t he c om pound i s not ava i l abl e, but t he r es ul t s of

s i m pl e phot ochem i cal expe r i m ent s can be us ed as a c oar se es t i m at e of r at es of

photochem i cal tra n sf o rm a tion s (i.e ., KDP > 0 .0 ). W h e n s e t to z e ro , L AMAX d e fa u l t s t o 3 0 0 n m.
L AT L AT i t ude U ni t s: degr ees and t ent hs ( e. g. , 37. 24) G e o g ra p h ic latitu d e o f th e e c o sy ste m . E X A M S us es l at i t ude and l ongi t ude for r et r i evi ng dat a a nd for ca l cul at i ng cl i m at ol ogi cal par am et er s. W hen e nt er i ng l at i t ude a nd l ongi t ud e of

a s t udy s i t e, ent er s out h l at i t ude a s a ne gat i ve n u m b er; n o rt h l ati t u d e a s a p o sit i v e n u m b er.
L E NG L E NG th (se g m e n t) U n its: m Lengt h of

a r eac h – us ed t o com put e vol um e, ar ea, dept h.
L OAD NM L OAD i ngs dat abas e N a M e ( 50 charact ers ) U n its: n /a D o notus e “ CH ANG E ” o r “ SE T ” t o e n t e r n a m e s ! T h e N a Me for a L OAD i ngs dat abas e i s ent er ed vi a t he c om m and se quence :
E X A M S -> L O A D N A M E IS n n n ...184

w h e re “ n n n ... “ ca n i n c lu d e as m a n y a s 5 0 c h a ra c te rs . T h is n am e i s a sso ciated w i t h c h em i ca l loa d i n g s d atab as e li b rary ent r i es , s o t hat l oad pa t t er ns can be found i n t he c at al og. The I t h cha r act er ca n be cor r ect ed w i t h a CH ANG E or SE T c o m m a n d . F o r e x a m p le , t o re p a ir t h e 7 th c h a ra c te r, “ SE T L OAD NM ( 7) TO ... .”
L ONG L ONG i t ude U ni t s: degr ees and t ent hs ( e. g. , - 83. 2) G e o g ra p h ic lo n g itud e o f th e e c o sy ste m . E X A M S us es l ongi t ude a nd l at i t ude for r et r i evi ng da t a and for ca l cul at i ng cl i m at ol ogi cal par am et er s. W hen ent er i ng l ongi t ude a nd l at i t ude of

a s t udy s i t e, ent er w es t l ong i t ud e as a ne gat i ve n u m b er; ea st l o n g i t u d e a s a p o sit i v e n u m b er.
M CH EM M CH EM i cal U n its: n /a N um ber of

che m i cal i n ac t i vi t y dat a ba se . M ODE M ODE sets t h e o p era t i n g “m o d e” of E X A M S . Thr ee o pe r at i ng m od es a r e av ai l ab l e; t he s e ar e s el ec t ed by SE T t i ng M ODE t o 1, 2, or 3: M ODE O p era t i o n al ch ara cterist i cs of E X A M S 1 L on g-t erm ( st ead y-st at e) ana l ysi s. 2 Pu l se analysi s - - speci fi able i nit i al chem i cal m ass ( I M A SS ) a n d ti m e fra m e , t im e -in v a ria n t en v iro n m e n t. 3 M on t hl y e n vi r on m ental dat a, dai l y pu l se l oad s I M A SS and m on t hl y ch em i cal l oad i ng s of ot her t yp es.
M ON TH M ON TH U n its: n /a S e t M ON TH t o i nspe ct a s peci fi c bl ock of envi r onm ent al data. M on t hs 1-- 12 corr espo nd t o Janu ary- - D ecem ber; m ont h 13 i s aver age dat a.
M P M e lti n g P o in t (ch e m ic a l) U ni t s: degr ees C el si us M el t i ng poi nt of

t he chem i cal – use d for c al cul at i ng l i near r a n g e o f s o r p t i o n i s o t h e r m. M el t i ng Poi nt i s use d i n t he c al cul at i on of t he m axi m um conce nt r at i ons w i t hi n t he r ange of l i near i sot her m s. W hen co m pu t i ng t he cryst al energy t erm for che m i cal s t ha t are sol i ds at t he am bi ent t em p erat ure ( K ari ckh off 198 4, J. H y d ra u lic E n g . 1 1 0 :7 0 7 -7 3 5 ) t h e so lu te e n tro p y o f fu sio n is t aken as 13 eu. M W T Gr a m M o l ec u l ar W ei gh T (c h e m ic a l) U n its: g /m o le M ol ecul ar w ei ght of

t he ne ut r al s peci es of each s t udy ch em i ca l
. C h an g es i n m o l ec u l ar w eig h t du e to ion i za t i o n are negl ect ed.
NP RO C N u m b er o f P RO C es s ( pat h) U n i t s: n/a R an g e: 1--9 Si gnal s t he t ype of

pr oces s t r ans for m i ng CH P AR (p ) in to T P RO D (p ). NP RO C ca n be s et t o t he fol l ow i ng: 1 --> sp e c ific a c id h y d ro ly sis 2 --> n e u tra l h y d ro ly sis 3 --> sp e c ific b a se h y d ro ly sis 4 --> d ire c t p h o to ly sis 5 -

- > si ngl et oxygen r eac t i ons 6 -

- > f r ee r adi cal oxi dat i on 7 --> w a te r c o lu m n b a c te ria l b io ly sis 8 --> b e n th ic se d im e n t b a c te ria l b io ly sis 9 -

- > r educt i ons, e. g. , r educt i ve de chl or i nat i on S e e a lso : CH P AR , EAYLD , RF ORM , T P RO D , YI EL D
NPS ED N on- P oi nt
- Sour ce SE D i m ent ( se gm ent , m ont h) U ni t s: kg/ hour N on- poi nt
- sour ce se di m ent l oads ent er i ng ec osys t em segm ents.
N PSFL N on- P o in t- S our ce FL ow ( se gm ent , m ont h) U ni t s: m / hour

3 N on - po i nt
- source w at er f l ow en t eri ng ecosy st em segm ents.
NPS LD N on- P o in t- S our ce L oa D ( se gm ent , che m i cal , m ont h) U ni t s: kg/ hour C h em i ca l l o ad i n g s en t ering seg m en t s v i a n o n -po i n t so u rces.
NYE AR N u m b er o f YE AR s U n its: n /a
NYE AR i s num ber of

yea r s t o be s i m ul at ed for a m ode 3 r un.
OXR AD OX id a n t RA D i cal s ( m ont h) U n its: m o le s/L185

C oncent r at i on of

en vi r onm ent al oxi dant s i n nea r - sur face w at ers ( e. g., per ox y rad i ca l s). E X A M S com put es se gm ent
- spe ci fi c oxi dant conc ent r at i ons usi ng ul t r a- vi ol et l i g h t e x t i n c t i o n i n t h e s y s t e m.
O U T F IL OUT p u t F IL e c ont r ol s ( 10) Un i t s : “ Y” o r “ N” C ont r ol t he pr oduct i on of out put f i l es . Set t he c or r es pondi ng m e m b e r to “ Y ” to p ro d u c e th e fil e (s ); se t i t t o “ N ” to su p p re ss fil e p ro d u c tion
. 1: st and ard r epo r t f

i l e ( r epo r t . xm s) 2 : sta n d a rd p lo tti n g fil e s (s so u t.p lt, k in o u t.p lt) 3: B A SS dat a t r ansfer f i l e ( bassex p.xm s) 4: FG ET S dat a t r ans fer f i l es ( fget sc m d. xm s and fgetsexp. xm s) 5: H W I R dat a t r ansfer f i l e ( H W I R E xp . xm s) 6 : c o m p a rtm e n t-o rie n te d E c o T o x e x p o su re d a ta fil e ( E coT ox C
. xm s) 7 : c o m p a rtm e n t-o rie n te d e v e n t an a ly sis a n d re p o rt file ( E coR i skC
. xm s) 8 : re a c h -o rie n te d E co T o x e x p o su re d a ta file ( E coT ox R
. xm s) 9 : re a c h -o rie n te d ev e n t a n a ly sis an d rep o rt file ( E coR i skR
. xm s) 10: f ul l Exam s com par t m ent f i l e of t i m e- var yi ng con cen t r at i on s ( Fu l l O ut . xm s)
OZ ONE OZ ONE ( m ont h) U ni t s: centi m et ers NTP Typi cal l y 0. 2-

- 0. 4 cm

3 M ean ( m ont hl y) ozone ( O ) cont ent of at m osphe r e. E X A M S i n c l u d e s a d a t a b a s e ( o z o n e . d a f) o f t o t a l c o l u mn ozone dat a s um m ar i zed f r om t he Tot al O zone M appi ng S p ec t rom eter (T O M S ) t h at fl ew on t h e N i m b u s7 sp ac ec raft f r om 11/ N ov/ 78 t hr ough 06/ M ay/ 93. Fr om t he l at i t ude a nd lo n g itud e o f th e e n v iro n m e n t, E X A M S fi nds i t s pos i t i on i n a 1 d e g re e latitu d e b y 1 .2 5 d e g re e lo n g itud e g rid o f th e E a rth and r et r i eves m ont hl y m ean ozone for t he si t e. I n t hi s gr i d, sout h l at i t ude i s negat i ve, nor t h l at i t ude pos i t i ve; w est l ongi t ude i s negat i ve, ea stl ongi t ude pos i t i ve.
PCP LD P re C i P i t at i on L oa D ( se gm ent , che m i cal , m ont h) U ni t s: kg/ hour C h e m ic a l l o a d in g s e n te rin g e a c h se g m e n t v ia ra in fa ll.
P C T W A P er C en T W A t er ( se gm ent , m ont h) U ni t s: di m ensionl ess Pe r cen t w at er i n bo t t om sedi m en t s of benthi c segm ents. E l e me n t s o f t h e s e v e c t o r s t h a t c o r r e s p o n d t o w a t e r c o l u mn se g m e n ts a re n o t u se d (d u m m y v a lu e s)
. P C T W A s houl d be exp r essed as t he co nv ent i onal s oi l s ci enc e vari able ( t he fr esh w ei ght : dr y w ei ght r at i o t i m es 100) ; a l l va l ues m ust be gr eat er t han or e qual t o 100. A n e nt r y i n P C T W A t hat i s l ess t han 100. 0 for a bent hi c segm ent r ai se s an e r r or condi t i on, and c ont r ol i s r et ur ned t o t he use r for cor r ect i on of t he i nput dat a.
PH pH ( se gm ent , m ont h) U n its: p H u n its T h e n e g a tive v a lu e o f th e p o w e r to w h ic h 1 0 is ra ise d in or der t o obt ai n t he t em por al l y ave r aged conce nt r at i on of 3 h y d ron i u m i o n s [H O ] i n gra m -eq u i v alen t s p er l i t er. +
PK p K (io n , ch e m ic a l) N ega t i ve of

bas e- 10 l ogar i t hm of ac i d/ bas e di ss oci at i on cons t ant s. W hen t he m at chi ng val ue i n t he EPK m atri x is z e ro , PK (I, c) is tak e n a s th e p K v a lu e . ( T o “ m a tc h ” is to have t he sa m e s ubsc r i pt val ues . ) W hen EPK ( I , c) i s non- zer o, PK i s t aken as t he ba se - 10 l ogar i t hm of t he pr e- exponent i al fact or i n t he e quat i on for pK as a f unct i on of

envi r onm ent al t em per at ur e TCEL . T h e v ec t o r i n d i ce s for PK (“c” de n o t es t h e c h em i ca l ) are

4 3 PK (1,c) co n t ain s d atu m for ge n era t i o n of R -H f r o m RH + 5 4 P K (2 ,c) co n t ain s d atu m fo r ge n era t i o n of R -H f r o m RH 2 + + 6 5 P K (3 ,c) co n t ain s da t u m fo r g en era t i o n of R -H f r o m RH 3+ 2+ 2 3 P K (4 ,c) co n t ain s d atu m for ge n era t i o n of R -H f r o m RH -1 2 P K (5 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f R- H f r o m RH =

- PK ( 6 , c ) c o n t a i n s d a t u m fo r g e n e r a t i o n o f R f r o m RH 3- =
P L M AS PL a n k to n ic b io M AS s ( se gm ent , m ont h) U n its: m g (d ry w e ig h t)/L T ot al pl ank t on subjectt o biosorpt i on of s ynt heti c che m i cal s.
P OH pO H ( se gm ent , m ont h) U n its: p O H u n its T h e n e g a tive v a lu e o f th e p o w e r to w h ic h 1 0 is ra ise d in or der t o obt ai n t he t em por al l y ave r aged conce nt r at i on of h y d rox i d e [O H ] i o n s in g ram -eq u i v alen t s p er l i t er. -
PRBEN PR opor t i on of

s or bed c hem i cal del i ver ed t o BEN t hi c z one U ni t l ess The PRZ M m odel gene r at es an out put fi l e t hat can be r ead by186

t he RE AD com m and i n E X A M S . PRZ M rep o rt s, fo r eac h run o ff dat e, cont am i nant di ss ol ved i n t he f l ow , and c ont am i nant sor bed t o ent r ai ned pa r t i cul at e m at t er . U se PRBEN ( SE T t o a val ue be t w een 0. 0 and 1. 0) t o i ndi cat e how m uch of t he sor bed m at er i al i s t o s i nk t hr ough t he w at er col um n and bec om e i ncor por at ed i nt o t he be nt hi c s edi m ent s. B as ed on th e g e n e ra liza tion th a t ab o u t 5 0 % o f so rb e d c o n ta m in a n t i s ty p ic a lly q u ite la b ile, a n d 5 0 % is re fra c to ry , t h e d e fa u lt v alu e o f PRBEN i s se t t o 0. 50.
P RO DNM P RO D uct che m i st r y dat abas e N a M e ( 50 charact ers ) U n its: n /a D o notu s e “ CH ANG E ” o r “ SE T ” t o ent er nam es ! The N a M e for a P RO D uct che m i st r y dat abas e i s ent er ed vi a t he com m and s equenc e:
E X A M S -> P R O D U C T N A M E IS n n n ...
w h e re “ n n n ... “ ca n i n c lu d e as m a n y a s 5 0 c h a ra c te rs . T h is n am e is ass o ciated w i t h pro d u ct ch em i str y da t ab as e li b rary ent r i es , s o t hat dat abas es ca n be found i n t he c at al og. U se a CH ANG E or SE T com m and t o r epai r s i ngl e c har act er s i n t he n am e. F o r ex am p l e, t o rep air ch ara cter se v en , en t er “ SE T P RO DNM ( 7) TO ... .”
PRSW PR in t SW i t ch U n its: n /a
PRSW i s a s w i t ch for cont r ol l i ng pr i nt i ng opt i ons. I n m ode 3, w hen PRSW i s s ett o 0 ( t he d efau l t ) , a ve r ag e va l ues of t he envi r onm ent al par am et er s ar e r ecor ded i n t he r un l og. W hen PRSW i s 1, a s epar at e t abl e i s produced for ea ch ( m ont hl y) d a ta se t, e x c e p t fo r th o se v a lu e s w h ic h a re in v a ria n t ( VOL etc.). QT BA S Q T en BA ct er i a be nt ho S (fo rm , i o n , ch e m ic a l) U ni t s: di m ensionl ess

10 Q val ues for bent hi c ba ct er i al bi ol ysi s ( se e KB ACS ) of

10 c h e m ic a l. “ Q " is th e in c re a se in th e s e c o n d -o rd e r ra te cons t ant due t o a 10 E C i ncr eas e i n t em per at ur e. I ndi ces r efer t o 2 8 m ol ecul ar s pp: 4 for m s- - 1: aqueous , 2: sol i ds- sor bed, 3: DOC -c o m p le x e d , an d 4 : b io -s o rb e d ; b y 7 io n s- -1 :n e u tra l, 2- 4: cat i ons, and 5- 7: ani ons. W hen QT BA S i s non- zer o, t he m at ching ( sam e subscri pt s) r at e con st ant i s com pu t ed as:
KBACS (f ,i ,c)= QT BA S ( f , i , c) × KBACS ( f , i , c) TCEL ( (seg,month)-QTBTS)/10 QT BA W Q T en BA ct er i a W a te r (fo rm , i o n , ch e m ic a l) U ni t s: di m ensionl ess 10 Q val ues for bac t er i opl ankt on b i ol ysi s ( se e KBACW ) of

10 c h e m ic a l. “ Q " is th e in c re a se in th e se c o n d -o rd e r ra te cons t ant due t o a 10 E C i ncr eas e i n t em per at ur e. I ndi ces r efer t o 28 m ol ecul ar s pp: 4 for m s- - 1: aqueous , 2: sol i ds- sor bed, 3: DOC -c o m p le x e d , an d 4 : b io -s o rb e d ; b y 7 io n s- -1 :n e u tra l, 2- 4: cat i ons, and 5- 7: ani ons. W hen QT BA W i s no n- zer o, t he m at ching ( sam e subscri pt s) r at e con st ant i s com pu t ed as:
KBACW (f,i, c)= QT BA W (f,i, c) × KBACW (f,i, c) TCEL ( (s eg, month )- QTB TW / 10 Q TBTW Q

_ T e n

_ B a se

_ T e m p e ra tu re

_ W a te r (fo rm ,io n ,c h e m ic a l) U n its: E C Tem per at ur e of

ae r obi c l i m net i c m et abol i sm s t udy. Q TBTS Q

_ T e n

_ B a se

_ T e m p e ra tu re

_ S e d im e n t (fo rm ,io n ,c h e m ic a l) U n its: E C Tem per at ur e of

ana er obi c be nt hi c m et abol i sm s t udy. QY I EL D Q uant um _Y I EL D (fo rm , i o n , ch e m ic a l) U ni t s: di m ensionl ess R eac t i on quant um yi el d for di r ectphot ol ysi s of chem i cal s- - f

r act i on of

t he t ot al l i ght quant a a bsor bed by a chem i cal t hat resul t s i n t r ans for m at i ons. Separ at e va l ues ( 3×7= 21) for ea ch pot ent i al m ol ecul ar t ype of ea ch c hem i cal a llow th e e ffe c ts o f sp e c ia tion a n d so rp tion o n re a c tivity to be s peci fi ed i n det ai l
. M at r i x of 21 val ues s peci fi es quant um yi el ds for t he ( 3) physi cal for m s: ( 1) di ss ol ved, ( 2) se d i m en t -so rbe d , an d (3) DOC - com pl exed; of ea ch of ( 7) poss i bl e c hem i cal s pec i es : neut r al m ol ecul es ( 1) , ca t i ons ( 2

- 4 ) , a n d a n i o n s ( 5

- 7 )
. ( QY I EL D is a n e ffic ie n c y .)
R A IN R A IN fal l ( m ont h) U n its: m m /m o n th Av e r a g e ( mo n t h l y ) r a i n fa l l i n g e o g r a p h i c a r e a o f s y s t e m.
RE DAG RED uci ng AG ent s ( se gm ent , m ont h) U n its: m o le s/L M ol ar conc ent r at i on of r educi ng age nt s i n ea ch s yst em se g m e n t.
RELE R REL at i ve ER r or t ol erance for i nt egrat ors. W h en t h e c h ara cterist i cs of the ch em i ca l an d ec o sy stem are such a s t o r es ul t i n “s t i ff” e quat i ons, num er i cal er r or s m ay l ead t o s m al l nega t i ve num ber s i n t he t i m e s er i es . I f des i r ed,187

t h e v alu e o f AB SE R and RELE R c a n b e d e c re a se d in o rd e r to ach i eve great er preci si on i n t he si m ul at i on output s.
RF L AT R e F er ence L AT itud e (io n , ch e m ic a l) U ni t s: degr ees ( e. g. , 40. 72) ( RF L AT - L AT ) cor r ect s for N or t h or Sout h di spl ace m ent of t h e e c o s y s t e m L AT i t ude f r om t he l ocat i on ( RF L AT ) of a p h o t o c h e mi c a l s t u d y u s e d t o d e v e l o p a ma t c h e d ( s a me su b sc ri p t ) KDP p se u d o -first-o rd e r ra te c o n sta n t.

3 RF L AT ( 1 , c ) r e fe r t o p h o t o l y s i s o f n e u t r a l mo l e c u l e s RH R F L A T ( 2, c) r efer t o phot ol ysi s of s i ngl y cha r ged c at i ons 4 RH + R F L A T ( 3, c) r efer t o phot ol ysi s of doubl y char ged c at i ons 5 RH 2 + R F L A T ( 4, c) r efer t o p hot ol ysi s of t r i pl y cha r ged c at i ons 6 RH 3 + 2 R F L A T ( 5 , c ) r e fe r t o p h o t o l y s i s o f s i n g l y c h a r g e d a n i o n s RH

- R F L A T ( 6 , c ) r e fe r t o p h o t o l y s i s o f d o u b l y c h a r g e d a n i o n s RH = R F L A T ( 7,c) r efer t o ph ot ol ysi s of t r i pl y ch arged an i on s R 3-

RF ORM R eac t i ve F ORM ( pat h) U ni t s: n/ a R ange: 1-

- 32
RF ORM g iv e s th e re a c tive m o le c u la r fo rm (io n ic sp e c ie s in ea ch of the po ssible so rpti v e states) o f CH P AR (p ) re su lti n g in p ro d u c t T P RO D ( p)
. The fol l ow i ng t able s how s t he va l ue of RF ORM for ea ch m ol ecul ar ent i t y, i ncl udi ng val ues for t ot al d iss o lv e d (2 9 ), so lids -s o rb e d (3 0 ), e tc . S e e a lso : CH P AR , EAYLD , NP RO C , T P RO D , YI EL D
I oni c s peci es N eut r al C at i ons A ni ons Tot al V a le n c e 0 1 + 2 + 3 + 1

- 2

- 3

- (a ll) For m s: D i ss ol ved 1 5 9 13 17 21 25 29

Sol i ds- sor bed 2 6 10 14 18 22 26 30 DOC - com pl exed 3 7 11 15 19 23 27 31 B i osor bed 4 8 12 16 20 24 28 32

RH UM R el at i ve HUM i di t y ( m ont h) U n i t s : %, i
. e . , s a t u r a t i o n = 1 0 0 % R . H. M ean ( m on t hl y) r el at i ve h um i di t y du r i ng day l i gh t hou r s. D a ta ty p ic a l o f d a y ligh t h o u rs a re n e e d e d b e c a u se th e ir pr i m ar y u s e i s t o c ha r ac t er i ze l i gh t t r an s m i s s i on i n t he at m osphe r e.
SE EL D SE E page L oa D ( se gm ent , che m i cal , m ont h) U ni t s: kg/ hour C hem i cal l oadi ngs ent er i ng t he s yst em vi a “ i nt er fl ow s” or s e e p a g e ( a l l s u b

- s u r fa c e w a t e r f l o ws e n t e r i n g t h e s y s t e m, (us u all y ) via a b en t h i c se g m en t ).
SEEPS SE EP age fl ow S ( se gm ent , m ont h) U ni t s: m / hour

3 I nt er fl ow ( subs ur face w at er fl ow , s eepa ge) en t er i ng ea ch se g m e n t. SEEPS u su a lly e n te r v ia a b e n th ic se g m e n t. SEEPS ar e a ss um ed t o l ack an ent r ai ned se di m ent fl ow ; t hat i s, t hey ar e f l ow s of w at er onl y. S OL S OL u b ili ty (io n , ch e m ic a l) U n its: m g /L A q u e o u s s o lu b ili ty o f e a c h sp e c ie s (n e u tra l m o le c u le + a ll i ons)
. W hen t he m at chi ng val ue i n t he E S OL m at r i x i s zer o, S OL ( I , c ) i s t ak e n a s t h e a q u e o u s s o l u b i l i t y i n m g / L. ( To “m at ch” i s t o have t he s am e s ubsc r i pt val ues . ) W hen E S OL (I , c ) is n o n -z e ro , S OL ( I , c ) i s t aken as t he ba se - 10 l ogar i t hm of t he pr e- exponent i al fact or of t he e quat i on des cr i bi ng t he m ol ar sol ubi l i t y of

t he s peci es as a f unct i on of envi r onm ent al t em per at ur e ( TCEL )
. The vect or i ndi ces for SO L ar e gi ven i n t he t ext descri bi ng E SO L
. S ol ub i l i t y m ust be spe ci fi ed, because iti s used as a con st r ai nt on l oad s.
SP FL G SP eci es FL a G s (io n , ch e m ic a l) Takes on val ues of

“1” ( exi st s) or “0” T h is v e c to r of “ fla g s” or “ sw itch e s” sh o w s w h ic h io n s e x ist. Se t t h e fl a g s ( “ SE T SP FL G ( I , c) =1”) w hen ent er i ng che m i cal d a t a i n o r d e r t o s h o w E X A M S t he i oni c s t r uct ur e of t he chem i cal
. W hen E X A M S s t ar t s, onl y SP FL G (1 ,* ) a re se t, i.e., t he de faul t che m i cal s t r uct ur e i s a ne ut r al ( non- i on i zi ng) m o le c u le . A s a d d iti o n a l SP FL G a re s e t, E X A M S di spl ays t he addi t i onal che m i cal dat a t abl es neede d t o di spl ay t he188

propert i es of t he i on i c species.

se t S PF LG (1 ,c )= 1 to sig n a l ex iste n c e o f a n e u tra l m o le c u le

3 RH s e t S PF LG ( 2, c) = 1 to si gnal exi st ence of a s i ngl y cha r ged 4 c a t i o n RH + se t S PF LG ( 3, c) =1 t o s i gnal exi st ence of a doubl y cha r ged 5 c a t i o n RH 2 + se t S PF LG ( 4, c) =1 t o s i gnal exi st ence of a tr i pl y charged 6 c a t i o n RH 3 + se t S PF LG ( 5, c) =1 t o s i gnal exi st ence of a singl y cha r ged 2 a n i o n RH

- se t S PF LG ( 6, c) =1 t o s i gnal exi st enc e of a doubl y cha r ged a n i o n RH = se t S PF LG ( 7, c) =1 t o si gnal exi st ence of a tr i pl y cha r ged ani on R 3-
S P RA Y
S P RA Y d rift fro m a g ric u ltura l ch e m ic a ls U ni t l es s per cent age The PRZ M m odel gene r at es an out put f i l e t hat c an be r ead by t he RE AD com m and i n E X A M S . P RZM 3 r ep or t s , for e ac h ap p l i ca t i o n d ate, the a p p l i ca t i o n rate a n d t h e p erc en t ag e d ri ft t o adj ace nt aqua t i c e cos yst em s. U se S P RA Y t o set a d ri ft p erc en t ag e fo r earli er v ersion s o f PRZ M . E X A M S d e fa u lts S P RAY t o 10 %
. N o t e tha t va l u es of S P RA Y ar e e nt er ed a s percentages r at her t han as f r act i on s.
ST FL O ST r e a m FL O w s ( se gm ent , m ont h) U ni t s: m / hour

3 Fl ow i nt o hea d r eac h of r i ver ore st uar y; s egm ent t r i but ar i es and c r eeks or ot her s t r eam fl ow s ent er i ng a l ake or pond. N o te th a t ST FL O r epr es ent s st r eam f l ow e nt er i ng syst em segm ents f

r om ext er nal s our ces o n ly
. E X A M S i t se l f com put es hydr ol ogi c fl ow s am ong segm ent s t hat ar e par t of t he w at er body bei ng st udi ed, vi a t he s peci fi ed a dvect i ve a nd di spe r si ve fl ow pa t t er ns ( se e J F RA D , J T URB , et c. )
. Ther efor e, do notcom put e ne t w at er bal ance s for ea ch s egm ent and en t er t h es e into the da t ab as e--en t er o n ly t hose fl ow s ent er i ng t he system across exter nal bo un dari es!
ST RLD ST R e a m L oa D ( se gm ent , che m i cal , m ont h) U ni t s: kg/ hour C hem i cal l oadi ngs ent er i ng ec osys t em s egm ent s vi a s t r eam fl o w.
ST SE D ST r eam - bor ne SE D i m ent ( se gm ent , m ont h) U ni t s: kg/ hour Str eam - bo r ne sed i m ent l oad ent eri ng ecosy st em segm ents.
SUS ED SU spe nded SE D i m ent ( se gm ent , m ont h) U n its: m g /L Suspende d par t i cul at e m at t er – appl i cabl e t o t he w at er col um n onl y.
S YS T YP N am e of aqua t i c e co S YS t e m T YP e ( 50 charact ers ) U n its: n /a D o notus e “ CH ANG E ” o r “ SE T ” t o ent er nam es ! The nam e of a w at er body i s ent er ed i nt o t he da t abas e vi a t he c om m and se quence :
E X A M S -> E N V IR O N M E N T N A M E IS n n n ...
w h e re “ n n n ... “ ca n i n c lu d e a s m a n y a s 5 0 c h a ra c te rs . T h is nam e i s assoc i at ed w i t h envi r onm ent al l i br ar y ent r i es ( t he UDB ca t al og) and i s pr i nt ed i n t he he ader i nfor m at i on of t he appr opr i at e out put t abl es . U se SE T and CHANGE t o cor r ect si ngl e c ha r ac t er s i n t he na m e. Fo r e xa m pl e, t o c or r ec t t he se vent h cha r act er i n a na m e,
E X A M S -> CH AN S YS T YP ( 7) TO ... TCEL T em per at ur e i n C EL si us ( se gm ent , m ont h) U ni t s: deg r ees C A ver age t em per at ur e of ec osys t em s egm ent s. U se d ( as enabl ed by i nput dat a) t o com put e effect s of t em per at ur e on t r ansfor m at i on r at es and ot her pr op ert i es of che m i cal s.
T CO DE T he value of T i m e CO DE sets t h e u n i t s o f T IN IT , T E ND , and CI NT . T CO DE c an be SE T t o 1 (h o u rs), 2 (d ay s), 3 (m o n t h s), or 4 (y e a rs ). T CO DE i s u n d er full u se r co n t rol o n l y in M o d e 2
. In m o d e 2 , T CO DE cont r ol s t he t i m e f r am e of t he s t udy. For exam pl e, gi ven T IN IT = 0 ., T E ND =24. , a nd CI NT = 2 .; CH AN gi ng T C O DE f r om 1 t o 3 conve r t s a 0- 24 hour s t udy i nt o 0- 24 m o n th s, w ith b im o n th ly re p o rts. In m o d e 1 , E X A M S se le c ts t he uni t s for r epor t i ng r es ul t s, f r om t he pr obabl e ha l f

- l i fe of t he s t udy chem i cal ( s)
. I n m ode 3, a RU N enc om pas se s one y ea r or l o n g er, an d t h e ti m i n g i s se t t o pro d u ce stan d ard ou t pu t s.
T E ND T i m e E ND fo r a d y n a m ic sim u la tion se g m e n t. U ni t s: s ee T CO DE A s i m ul at i on s egm ent enc om pa s s es t he pe r i od T IN IT t hr ough189

T E ND . A t t h e e n d o f e a c h in te g ra tion , T IN IT i s r es et t o T E ND . The si m ul at i on ca n be e xt ended by i nvoki ng t he
“ CO NT I NUE ” c o m m a n d ; E X A M S w i l l t hen r eques t a ne w v alu e o f T E ND . Pu l se l oad s ( I M A SS ) an d l o n g er-t erm che m i cal l oad s ( ST RLD , NPS LD , et c. ) can be m odi fi ed or delet ed d uri ng t he p ause b et w een si m ul at i on segm ents.
T IN IT T i m e IN IT ia l fo r a d y n a m ic sim u la tion se g m e n t. U ni t s: s ee T CO DE A s i m ul at i on RU N encom passes t he pe r i od T IN IT t hr ough T E ND . A t t h e e n d o f e a c h in te g ra tion , T E ND i s tra n sfe rre d to T IN IT . The s i m ul at i on r es ul t s can be e val uat ed, and t he s t udy cont i nued vi a t he “ CO NT I NUE ” c om m and. E X A M S w ill n o te t h e n ew v alu e o f T IN IT and r equ est a new end po i nt . Pu l se and ot her chem i cal l oadi ngs can be m odi fi ed or del et ed betw een si m ul at i on segm ents.
T P RO D T r ans for m at i on P RO D uct ( pat h) U ni t s: n/ a Range: 1- KC HEM
T P ROD ( p) – ADB l ocat i on of t he t r ans for m at i on pr oduct of CH P AR ( p)
. The m at chi ng ( sa m e t r ans for m at i on pat h num ber “p ”) m em b ers o f CH P AR and T P ROD gi ve t he l ocat i on num ber s i n t he a ct i ve data bas e of t he pa r ent che m i cal and t he t r ansfor m at i on pr oduct for pat hw ay “ p”. For exa m pl e, S E T CH P AR (p) TO 1, and T P RO D ( p) t o 4 , t o s how t hat t he chem i cal i n ADB s ect or 4 i s pr oduced vi a t r ans for m at i on of t he c hem i cal i n ADB s ect or 1, vi a pr oces s dat a de fi ned by t he r em ai ni ng m em ber s of pr oduct che m i st r y s ect or “p”
. S e e a lso : CH P AR , EAYLD , NP RO C , RF ORM , YI EL D
TY PE S e g m e n t TY PE (se g m e n t) U ni t s: l et t er code s Let t er code s desi gnat i ng s egm ent t ypes us ed t o def i ne eco syst em s. A v a ilab le ty p e s: L itt o ra l, E p i l i m n i o n , H ypol i m ni on, and B ent hi c.
UDB U ser D at aB ase Long-t er m r et ent i on of dat a r equi r ed by E X A M S i s pr ovi ded by s t or age i n t he “ U se r D at abas e” ( UDB , gene r al l y r es i dent o n a p h y sica l de v i ce , e.g ., a h ard disk ) fo r C H E MI CA L s, E NVI RO NME NT s, L OAD s, or P RODUCT s. W i t hi n eac h of t hese UDB sect ors, each dat aset i s CAT AL OG ued vi a a uni que ac ce ssion n u m b er ( UDB #)
. W hen t r ans fer r i ng dat a be t w een fo re g rou n d m em o ry (t h e a cti v i t y da t ab as e o r ADB ) and a UDB , t he t ar get l ocat i on m ustbe s peci fi ed by t he na m e of t he UDB s ect or and t he a cce ss i on num ber w i t hi n t he se ct or . For exam pl e, t o S T ORE t he cu r r ent patt ern of chem i cal l oad i ng s: S T OR E L OAD 7. S i m i l arly, t o r etri ev e o r RECALL d a t a f r o m a UDB i nt o t he ADB for us e in a n an aly sis, on e c o u l d en t er: RE CA L L L OAD 7.
V A PR VAP o R p re ss u re (c h e m ic a l) U n i t s: T o rr U se d t o com put e H enr y’ s l aw cons t ant w hen HENR Y dat um is z e ro (0 ) b u t V A PR i s non- zer o:

HENR Y = ( V A PR /7 6 0 ) / ( S OL / M W T ) I f t he a ss oci at ed m ol ar heatof vapor i zat i on ( EV PR ) is n o n -ze ro, V A PR i s t aken as t he ba se - 10 l ogar i t hm of t he pr e- exponent i al f act or i n an expone nt i al f unct i on des cr i bi ng vapor pr es sur e a s a f

unct i on of

t em per at ur e ( TCEL ).
VOL VOL u m e (se g m e n t) U n its: m 3 T ot al env i r on m ental volum e of ecosyst em segm ents.
W I DTH W I DTH (se g m e n t) U n its: m A ver age bank- t o- bank di st ance –for co m pu t i ng vo l um e, ar ea, dept h of l ot i c syste m s des cr i bed vi a l engt h, w i dt h, and cross- sect i on al ar eas.
W I ND W I ND spe ed ( se gm ent , m ont h) U ni t s: m et er s/ se cond A ver age w i nd vel oci t y ata r efer ence hei gh t of t en c e n tim e te rs a b o v e th e w a te r su rfa c e . P a ra m e te r is u se d to com put e a pi st on v el oci t y for w at er vapor ( Li ss 1973, D eep- Sea R es ear ch 20: 221) i n t he 2- r es i st ance t r eat m ent of vo l at i l i zat i on l osses.
X SA C ro ss -s e c tion a l ( XS ) A re a (se g m e n t) U n its: m 2 A r ea of w at er body i n s ect i on al ong adve ct i ve f l ow pat h.
XS T UR X S ec t i o n for T UR bul ent di spe r si on ( pat h) U n its: m 2
XS T UR i s cr oss - se ct i onal ar ea of a di spe r si ve e xchange i nt erface at t he bo un dary bet w een seg m ents J T URB ( p) and I T URB ( p)
. The m at chi ng ( sa m e “ p” s ubsc r i pt ) m em bers of J T URB , I T URB , CHARL , D SP , and XS T UR col l ect i vel y def i ne a d isp e rs iv e tra n sp o rt p a th w a y . T h e e x c h a n g e c o n sta n t E (p ) is190

com pu t ed as: E( p ) ( m / h o u r ) = D SP (p) × XS T UR (p ) / CHARL ( p)

3 S e e a lso : CHARL , D SP , I T URB , J T URB
YE AR 1 YE AR 1 U n its: n /a S t arti n g ye ar for m o d e 3 sim u l ati o n (e.g., 19 8 5 ). YI EL D YI EL D of pr oduct ( pat h) U n its: m o le p e r m o le
YI EL D ( p) i s t he pr oduct yi el d f r om t he t r ans for m at i on pat hw ay “ p” w i t h di m ens i ons m ol e of t r ans for m at i on p ro d u c t T P RO D ( p) pr oduced per m ol e of par ent com pound CH P AR (p) reac t ed (dim en sion l es s). S e e a lso : CH P AR , EAYLD , NP RO C , RF ORM , T P RO D191 

## A p p end i ce s A ppend i x A Par t i t i oni ng t o Nat ur al O rg ani c C ol l oi ds E X A M S u se s th e o c ta n o l:w a te r p a rtit io n c o e ffic ie n t (K o w ) to e stim a te b in d in g c o n sta n ts (K p d o c ) fo r “ d iss o lv e d ” (i.e., co l l o i d al) o rga n i c m att er ( DOC )
. T he ca l culat i on fac t or i s a s i mp l e r a t i o t o Ko w ( Set h et al
. 1999)
. For deve l opi ng t he E X A M S fact or , val ues of

par t i t i oni ng on w at er s am pl es cont ai ni ng com pl et e DOC (o n ly ) w e re tab u la te d , i .e ., stu d ie s o n c h e m ic a lly se par at ed f

r act i ons w er e notut i l i zed. M eas ur em ent m et hods in c lu d e d , in te r a lia , di al ysi s ( C ar t er a nd Suffet 1982) , r ever se dph as e s ep ar at i on (L a n d ru m e t al. 1 9 8 4 ) a n d so lu b ili ty e n h a n c e m e n t ( C hi ou etal
. 1986) ; val ues deve l oped us i ng fl u orescence que nch i ng m et ho ds (G au t h i er et al. 19 8 6 ) w ere excl uded be caus e t hi s m et hod i s subj ectt o i nt er ferences t hat of t en l ead t o over - es t i m at es of K oc ( (L ao r an d R eb h u n 19 9 7 ) , (D a n ie lso n e t al. 1 9 9 5 ) , (T i l l er an d Jo n es 19 9 7 ) ).

C om pound C A S # R efer ence Log K ow (1) l og K pdoc a nd K pdoc/ K ow r at i os

lim n e tic ra tio b e n th ic ra tio 1, 3, 6, 8- TC D D 33423- 92- 6 (Se rvo s an d M u i r 19 8 9 ) 7. 13 5. 50 0. 023 6. 06 0. 085 (2) 1, 3, 6, 8- TC D D 33423- 92- 6 (Se rvo s et al. 19 8 9 ) 7. 13 5. 12 0. 010 (2) H 7C D D 37871- 00- 4 (Se rvo s et al. 19 8 9 ) 8. 20 6. 85 0. 045 (2) O 8C D D 3268- 87- 9 (Se rvo s et al. 19 8 9 ) 8. 60 5. 78 0. 002 (2) p ,p '

- D D T 50- 29- 3 (C arter an d S u ffet 19 8 2 ) 6. 36 4. 84 0. 030 p ,p '

- D D T 50- 29- 3 (L an d rum et al. 19 8 4 ) 6. 36 4. 52 0. 014 p ,p '

- D D T 50- 29- 3 (C h i o u et al. 19 8 7 ) 6. 36 4. 39 0. 011 p ,p '

- D D T 50- 29- 3 (E ad i e e t al. 19 9 0 ) 6. 36 4. 36 0. 010 p ,p '

- D D T 50- 29- 3 (K u l o v aa ra 1 9 9 3 ) 6. 36 3. 81 0. 003 B enzo[ a] pyr ene 50- 32- 8 (L an d rum et al. 19 8 4 ) 5. 97 4. 56 0. 039 B enzo[ a] pyr ene 50- 32- 8 (A l b erts et al. 19 9 4 ) 5. 97 4. 80 0. 068 B enzo[ a] pyr ene 50- 32- 8 (L an d rum et al. 19 8 5 ) 5. 97 5. 56 0. 389 B enzo[ a] pyr ene 50- 32- 8 (M o reh ea d et al. 19 8 6 ) 5. 97 4. 80 0. 068 B enzo[ a] pyr ene 50- 32- 8 (K u k k o n en et al. 19 8 9 ) 5. 97 5. 33 0. 229 B enzo[ a] pyr ene 50- 32- 8 (M cC arthy et al. 19 8 9 ) 5. 97 5. 16 0. 155 B enzo[ a] pyr ene 50- 32- 8 (K u k k o n en et al. 19 9 0 ) 5. 97 5. 18 0. 162 B enzo[ a] pyr ene 50- 32- 8 (E ad i e e t al. 19 9 0 ) 5. 97 4. 57 0. 040 B enzo[ a] pyr ene 50- 32- 8 (K u k k o n en an d O i k ari 1 9 9 1 ) 5. 97 5. 00 0. 107 B enzo[ a] pyr ene 50- 32- 8 (K u l o v aa ra 1 9 9 3 ) 5. 97 4. 36 0. 025 D ehydr oabi et i c a ci d 1740- 19- 8 (K u k k o n en an d O i k ari 1 9 9 1 ) 4. 80 2. 70 0. 008 (3)C om pound C A S # R efer ence Log K ow (1) l og K pdoc a nd K pdoc/ K ow r at i os

lim n e tic ra tio b e n th ic ra tio

192 D i el dr i n 60- 57- 1 (K o sian et al. 19 9 5 ) 5. 25 4. 43 0. 151 (3) Fl uor ant hene 206- 44- 0 (B ran n o n et al. 19 9 5 ) 4. 95 3. 83 0. 076 M i r ex 2385- 85- 5 (Y i n an d H as se t t 19 8 9 ) 6. 89 6. 08 0. 155 (4) N apht hal ene 91- 20- 3 (K u k k o n en et al. 19 9 0 ) 3. 30 3. 00 0. 501 Phenant hr ene 85- 01- 8 (L an d rum et al. 19 8 5 ) 4. 46 4. 18 0. 525 Phenant hr ene 85- 01- 8 (L an d rum et al. 19 8 7 ) 4. 46 4. 04 0. 380 Phenant hr ene 85- 01- 8 (C h i n an d G sc h w en d 19 9 2 ) 4. 46 4. 19 0. 537 4- PC B 2051- 62- 9 (E ad i e e t al. 19 9 0 ) 4. 40 4. 02 0. 417 2, 4, 4'

- PC B 7012- 37- 5 (C h i o u et al. 19 8 7 ) 5. 62 3. 55 0. 009 2, 4, 2' , 4'

- PC B 2437- 79- 8 (L an d rum et al. 19 8 7 ) 6. 29 5. 49 0. 158 2, 4, 2' , 4'

- PC B 2437- 79- 8 (C aro n an d S u ffet 19 8 9 ) 6. 29 5. 21 0. 083 2, 4, 2' , 4'

- PC B 2437- 79- 8 (K u k k o n en et al. 19 9 0 ) 6. 29 4. 30 0. 010 2, 4, 2' , 4'

- PC B 2437- 79- 8 (H u n ch ak -K ariou k an d S u ffet 19 9 4 ) 6. 29 4. 68 0. 025 2, 5, 2' , 5'

- PC B 35693- 99- 3 (L an d rum et al. 19 8 4 ) 6. 09 3. 88 0. 006 2, 5, 2' , 5'

- PC B 35693- 99- 3 (E ad i e e t al. 19 9 0 ) 6. 09 3. 88 0. 006 2, 5, 2' , 5'

- PC B 35693- 99- 3 (K u k k o n en et al. 19 9 0 ) 6. 09 4. 60 0. 032 3, 4, 3' , 4'

- PC B 32598- 13- 3 (K u k k o n en et al. 19 9 0 ) 5. 62 4. 90 0. 191 (5) 3, 4, 3' , 4'

- PC B 32598- 13- 3 (K u k k o n en an d O i k ari 1 9 9 1 ) 5. 62 4. 00 0. 024 2, 4, 5, 2' , 5'

- PC B 37680- 73- 2 (C h i o u et al. 19 8 7 ) 6. 11 4. 05 0. 009 2, 4, 5, 2' , 4, 5'

- PC B 35065- 27- 1 (K u k k o n en et al. 19 9 0 ) 7. 75 5. 54 0. 006 (5) 2, 4, 5, 2' , 4, 5'

- PC B 35065- 27- 1 (E ad i e e t al. 19 9 0 ) 7. 75 4. 42 0. 0005 Pyr ene 129- 00- 0 (L an d rum et al. 19 8 7 ) 5. 18 4. 71 0. 339 Pyr ene 129- 00- 0 (E ad i e e t al. 19 9 0 ) 5. 18 3. 76 0. 038 Pyr ene 129- 00- 0 (C h i n an d G sc h w en d 19 9 2 ) 5. 18 4. 73 0. 355 6 P AH (L ü ers a n d t en H u l sc h er 1 9 9 6 ) 3. 326 37 C om po un ds (O zre t i ch et al. 19 9 5 ) 0. 072 A ver ag es 0. 074 0. 46 1. K ow f r om C hem Fat e da t abas e ( h t t p : // e s c . s y r r e s . c o m/ e fd b
. h t m) exc ept as ot her w i se i ndi cat ed. 2
. (G o v ers a n d K rop 19 9 8 ) 3. K ow ci t ed by a ut hor 4
. (D ev i l l ers e t al. 19 9 6 )193

5
. (R ap ap o rtan d E i se n reich 19 8 4 )

R ef ere nces f

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### Appendix B E X A MS 

### data entry tem plate for chem ical mol ar absorption spectr a (ABSOR)

W aveba nd W aveba nd N o. C ent er

nm B andw id th nm ABS OR

cm M -1 -1 N o. C ent er
nm B andw id th nm ABS OR

cm M -1 -1 1 2 8 0 .0 2 .5 2 4 3 8 0 .0 1 0 .0 2 2 8 2 .5 2 .5 2 5 3 9 0 .0 1 0 .0 3 2 8 5 .0 2 .5 2 6 4 0 0 .0 1 0 .0 4 2 8 7 .5 2 .5 2 7 4 1 0 .0 1 0 .0 5 2 9 0 .0 2 .5 2 8 4 2 0 .0 1 0 .0 6 2 9 2 .5 2 .5 2 9 4 3 0 .0 1 0 .0 7 2 9 5 .0 2 .5 3 0 4 4 0 .0 1 0 .0 8 2 9 7 .5 2 .5 3 1 4 5 0 .0 1 0 .0 9 3 0 0 .0 2 .5 3 2 4 6 0 .0 1 0 .0 1 0 3 0 2 .5 2 .5 3 3 4 7 0 .0 1 0 .0 1 1 3 0 5 .0 2 .5 3 4 4 8 0 .0 1 0 .0 1 2 3 0 7 .5 2 .5 3 5 4 9 0 .0 1 0 .0 1 3 3 1 0 .0 2 .5 3 6 5 0 3 .7 5 1 7 .5 1 4 3 1 2 .5 2 .5 3 7 5 2 5 .0 2 5 .0 1 5 3 1 5 .0 2 .5 3 8 5 5 0 .0 2 5 .0 1 6 3 1 7 .5 2 .5 3 9 5 7 5 .0 2 5 .0 1 7 3 2 0 .0 2 .5 4 0 6 0 0 .0 2 5 .0 1 8 3 2 3 .1 3 .7 5 4 1 6 2 5 .0 2 5 .0 1 9 3 3 0 .0 1 0 .0 4 2 6 5 0 .0 2 5 .0 2 0 3 4 0 .0 1 0 .0 4 3 6 7 5 .0 2 5 .0 2 1 3 5 0 .0 1 0 .0 4 4 7 0 6 .2 5 3 7 .5 2 2 3 6 0 .0 1 0 .0 4 5 7 5 0 .0 5 0 .0 2 3 3 7 0 .0 1 0 .0 4 6 8 0 0 .0 5 0 .0196 

### Appendix C Imp lem en tin g th e mi cro co mp uter run tim e E XA MS Exa ms pro gra m f ile s a re ins tal ledfr om a s elf -un pac kin g a rch iva l c omp res sed for mat (I nst all _EX AMS .ex e). Th e f ile s r equ ire a tot al of abo ut 1.5 Mb of ma ss sto rag e f or tra nsf er to a h arddi sk, pl us an add iti ona l 2 0 m ega byt es for sto rag e o f t he fil es as the y a re ret rie vedfr om the Ar chi ves , p lus ad dit ion al wor kin g s pac e f or the fi les pr odu cedwh ile Ex ams ru ns. The fi les in clu de The fi le for in sta lli ng the EX AMS pr ogr am, in fi le Ins tal l_E XAM S.E XE, wit hin wh ich is co nta ine d: o T he tas k i mag e i n f ile EX AMS .EX E, whi ch all ows sp ace fo r f ive si mul
- t ane ous ch emi cal s ( or one ch emi cal an d t wo deg rad ati on pro duc ts, e tc. ), anden vir onm ent al mod els of up to on e h und redse gme nts . o T he unf orm att ed dir ect ac ces s d ata - a nd hel p-f ile EX AMS .DA F, w ith sp ace fo r 2 5 c hem ica l d ata set s, 10 env iro nme nta l d ata set s, 5 ex ter nal ch emi cal lo ad ser ies , a nd 5 p rod uct ch emi str ies . o Agl oba l d ata bas e o f t ota l c olu mn ozo ne (oz one .da f) fro m t he TOM S (T ota l O zon e M app ing Sp ect rom ete r) flo wn on the Ni mbu s-7 sp ace cra ft. o A n E XAM S c omm andfi le for te sti ng the in sta lla tio n, in TES T.E XA. o T EST OUT .XM S, a s amp le out put fo r c omp ari son wi th the re sul ts of the i nst all ati on tes t r un. Thi s U ser 's Gui de for EX AMS (f ile Ex ams Rev G.p df) is av ail abl e s epa rat elyin A dob e P DF (Po rta ble Do cum ent Fo rma t); it ca n b e r eadan d p rin tedwi th t he Ado be Acr oba t R ead er, av ail abl e g rat is fro m h ttp :// www .ad obe .co m/ EXAMS acc ess es ext end ed mem oryth rou gh Win dow s s erv ice s; und er the W ind ows co nso le all vi rtu al mem oryis av ail abl e t o t he pro gra m. U nde r W ind ows 95 /98 , b est pe rfo rma nce ca n b e a chi eve d b y s ett ing m emo ry pro per tie s o f t he DOS co nso le to "no ne" fo r E xpa nde d ( EMS ) a nd all ot her s t o " Aut o" exc ept DP MI mem ory . S et DPM I m emo ry to 655 35. Fir st, ma ke sur e t hat yo ur IBMPC /AT 38 6/4 86/ Pen tiu m o r " Com pat ibl e" mea sur es up to the fo llo win g m ini mumha rdw are an d s oft war e s pec ifi cat ion s. o 2 0 m ega byt e a vai lab le mas s s tor age (h arddi sk) o 8 0x8 7 m ath co -pr oce sso r o W ind ows 95 /98 /NT /20 00 ope rat ing sy ste m If you r m ach ine do es not co nfo rm to the se min imu m s pec ifi cat ion s, the EXAMS pro gra m W ILL NO T e xec ute pr ope rly .

- mor e -197 The n, to ins tal l t he pro gra m 1. T ran sfe r t he fil e " Ins tal l_E XAM S.E XE" to yo ur har d d isk in so me sui tab le s ubd ire cto ry or par tit ion an d i nst all Ex ams . F roma Win dow s c ons ole :
a . Set th e d efa ult dr ive to th e m ass sto rag e d evi ce (e. g., ha rd dis k " C") : C: b . Cre ate an EX AMS di rec tor y: (BU T, if MK DIREX AMS ins tal lin g a s p art of PI RAN HA, th e PIRANH A\E XAM S d ire cto ry alr ead y e xis ts. Do NOT cr eat e a not her EX AMS di rec tor y)
c . Req ues t v eri fic ati on of cop y r esu lts : VE RIF Y O N d . Cha nge de fau lt dir ect oryto EX AMS , CD \EX AMS or to PIRANH A E XAM S s ubd ire cto ry CD \PI RAN HA\ EXAMS
e . Exe cut e t he fil e I nst all _EX AMS .EX E t o rec ove r f ile s f romth e arc hiv es: In sta ll_ EXAMS andfo llo w t he dir ect ion s p rov ide d. 2. S tar t t he EXAMS pro gra m f romth e E XAM S d ire cto ry.
a . Sta rt the EX AMS pr ogr am: EX AMS b . Whe n y ou rea ch the EX AMS sy ste m pro mpt , s tar t t he tes t c omm andfi le: EX AMS -> DO TES T 3. W hen th e t est ru n f ini she s c omp are th e o utc ome (i n f ile RE POR T.X MS) w ith th e f ile TE STO UT. XMS su ppl iedwi th the pr ogr am:

FC R EPO RT. XMS TE STO UT. XMS Fil es TES TOU T.X MS andTE ST. EXAar e n ot nee dedfo r r out ine op era tio n o f EXAMS andca n b e d ele ted , a s c an fil e I nst all _EX AMS .EX E.