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## PICK-UPDATE : 3/15/200 7 BO X O F 

# W Ste p 2 : FO R ASR C INTERNA L US E ONL Y (PAR TB o f B )



## EP ADOCKE T ID : 102RQ-R N
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## 2 ) 102RQ-RN-5-1 7 4 ) 102RQ-RN-5-1 9 6 ) 102RQ-RN-5-2 1 8 ) 102RQ-RN-5-2 3 10 ) (502RQ-RN-5-25T ) 12 ) 102RQ-RN-5-2 7 14 ) 102RQ-RN-5-2 9 16 ) 102RQ-RN-5-3 2 18 ) 102RQ-RN-6- 2 20 ) 102RQ-RN-6- 4 22 ) 102RQ-RN-6- 6 24 ) 102RQ-RN-6- 8 26 ) 102RQ-RN-6-1 0 28 ) 102RQ-RN-6-1 2 30 ) 102RQ-RN-6-1 4 32 ) 102RQ-RN-6-1 6 34 ) 102RQ-RN-6-1 8 36 ) 102RQ-RN-6-2 0 38 ) 102RQ-RN-6-2 2 40 ) 102RQ-RN-6-2 4

Ste p 1 : FO R ASR

C INTERNA L US E ONL Y Ar e ther e more document s fo r thi s Docke t i n anothe r box ? *YE S //$ 0 *Fil l ou t Continuatio n Shee t an d go t o Ste p 2
Interna l SFUN D Bo

x Numbe r _3 6 O F _28 3
Initials/Date : LDS__/_3-15 - 2007

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# T P. 2

Unite d »«
. / D ^ ^ ~f^-J^^-S Environmenta l Protectio n Agency 

# &EP A OFFIC E O F SOLI D WAST E JANUAR Y 198 5 

# DRAF TREPORT

LINE R LOCATIO N RIS K AN D COST ANALYSI S MODE L

M

# f y . . .

• LINE RLOCATIO N RIS K | AND COS T ANALYSI S MODE L
-"- DRAF T REPOR T

I • : !
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/

_-
; SUBMITTE D T O TH E 1
. . - | • - " " . - OFFIC E Q E SOLI D WAST E ECONOMI C ANALYSI S BRANC H U.S . ENVIRONMENTA L PROTECTIO N AGENC Y

(Under"Contrac t No . 68-01-6621 )
EPA Projec t Office r Clif f Rothenstei n

JANUARY198 5

/

i .

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- P. 3

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-P. 4

EXECUTIV E SUMMARY

Th e Line r Locatio nRis k an dCos t Analysi s Mode l estimate s th e chroni c ris k t o humanhealt hfro

m land.disposa l o f hazardou s waste s unde r differen t technology , location , an dwast e stream

scenarios . I t als o estimate s th e cos t o f differen t design s an dsize s o f landfill s an dsurfac e impoundments . Together , thi s cos t an dris k informatio nenable s EPA t o investigat e th e cost/ris k andcost-effectivenes s implication s o f variou s technology , waste , an d"location-standards . -
Thi s repor t document s th e firs t phas e of.th e model's~.development . I t describe s th e basi c mode l and v thre e polic y application s p f th e model . Th e EPA projec t team

i s currentl y

revisin g severa l component s o f th e mode l and expect s t o mak e additiona l revision s i nrespons e t o review s o f thi s report . Th e tea m wil l .als o perform

additiona l policy , analyses. - Thus , th e conclusion s presente dhere - ar e preliminar y and " exploratory . Furthermore, ! whil e th e repor t andit s appendice s provid e a soundfundamenta l explanatio n o f th e methodolog y

andstructur e o f th e model,

_the y ar e no t entirel y

upt o dat e onall-points, , sinc e th e mode l i s currentl y bein g improved . EPA expect s t o prepar e a secon drepor t explainin g improvement s inth e mode l and th e result s o f additiona l applications .
Thi s summar y

provide s a genera l descriptio nof.th e model , it s structure , inputs , andoutputs ; a brie f discussio no f th e thre e applications ; an dou r plan s fo r th e futur e o f thi s project .
1 . TH E LINE RLOCATIO N RIS KAND COS T ANALYSI S MODE L COUPLE S

- A RIS KAN D A

COS T MODE L

Th e Line r Locatio nRis k andCost . Analysi s Model-link s a ris k and- a cos t model . Th e ris k mode l simulate s th e chroni c ris k t o huma nhealt hfro m land disposa l facilitie s (landfill s andsurfac e impoundments ) wit hdifferen t desig ntechnology , location , an dwast e stream

combinations . I t integrate s a serie s o f submodel s andalgorithm s tha t trac e constituen t release s fro m 1P. 5

landfill s andsurfac e impoundment s t o thei r movemen t throug hth e ai r and ground , the nt o resultin g huma nexposures , an dfinall y

t o th e resultan t huma nrisk . T o d o so , mode l component s predict :

• Release s t o groundwate r an dsubsurfac e transport . A failur e "an

d releas e submode l estimate s facilit y failur e andth e quantit y o f leachat e released ; anunsaturate dzon e algorith m calculate s th e time require dfo r th e leachat e t o reac hanunderlyin g aquifer ; anda saturate dzon e submode l calculate s th e time and concentration s o f constituent s reachin g a down-gradien t well .

• Release s t o ai r an datmospheri c transport . A volatilization : algorith m calculate s th e quantit y o f constituent s tha t volatiliz e ove r time ; anatmospheri c transpor t algorith m calculate s th e concentration s o f thes e constituent s a t th e exposur e points .

• v Huma nexposure y

A nexposur e algorith

m calculate s th e exposur e
• - ' . " fro m drinkin g wate r an

dfro m .breathin g constituents " i nair .

• Healt hrisks . A hazar destimationsubmode l calculate s expecte d cance r andnoncance r risk s fro m th e exposures . .
Th e mode l calculate s ris k ove r a 400-yea r time horizon . Indoin g so , i t embodie s man y

assumptions : facilitie s operat e fo r 2 0 year s wit ha 30-yea r post-closur e period ; contaminatio ngoe s undetecte danduncorrected; " multipl e contaminant s d o no t interact ; an dfew constituent s degrad e ove r time , wit hdegradatio nbeginnin g onl y afte r facility-failure . Th e model " als o assume s tha t aquifer s ar e homogeneou s andisotropic . In.general , w e believ e tha t th e mode l overestimate s risk .
Th e companio ncos t mode l estimate s th e cost s o f landdisposa l facilitie s wit hdifferin g technologie s an dsizes . Th e result s o f th e ris k mode l combine dwit hcos t dat a fro m th e cos t mode l provid e EP A wit hth e capabilit y t o perform

cost/ris k andcost-effectivenes s analysis .P. 6

1. 1 Ris k Mode l

Th e failur e andreleas e submode l estimate s th e probabilit y andtime o f failur e andth e quantit y o f subsequen t leachat e releas e throug hth e us e o f
a Mont e Carl o simulatio nmodel . Th e mode l use s a "faul t tree " structure; . tha t is , i t trace s eac hpossibl e failur e even t (leakag e fro m the.facility ) fro m al l possibl e Combination s o f mor e elementar y event s whic hcoul d combin e t o caus e failure : infiltratio no f liquid , line r failure , etc . Th e mode l assume s tha t eac ho f thes e elementar y event s occur s a t random , followin g specifie dprobability.distributions . Th e failur e probabilitie s
ove r time ar e th e averag e o f probabilitie s fo r a-larg e numbe r o f facilities . Usin g thi s faul t tre e analysis , th e model " predict s th e yea r o f failur e andth e releas e rate s fo r te ndifferen t landfil l andsurfac e impoundmen t design s i nfiv e differen t climates . Line r ari dcove r typ e and materia l defin e facilit y designs , whil e averag e ne t infiltratio no f moistur e pe r yea r an ddept ht o groun dwate r correspon dt o Climat e type .

Inth e releas e componen t o f th e submodel , w e assum e that-ch'ssolutioni n- f leachat e release s wast e constituent s t o groun d wate r andtha t - • : . '" - volatilizatio nrelease s constituent s t o air . Althoug hthe-failur e submode l i s stochasti c andprovide s a probabilit y distributio nfo r line r failure , th e "downstream " exposur e modelin g component s ar e al l deterministic , and thu s produc e ris k estimate s fo r a give nreleas e rat e startin g a t a specifi c time i nth e simulatio nperiod . T o lin k th e failur e component-o f th e .mode l wit hth e subsequen t exposur e submodel , w e use dth e convention-tha t release - . t o th e unsaturate dzon e begin s t o occu r whe nth e probabilit y o f .failur e "exceed s 0701 . Preliminar y sensitivit y

analysi s show s tha t ove r th e 400-yea r simulatio nperiod , risk s ar e no t ver y "sensitiv e t o th e probabil-it y o f failur e selecte dt o trigge r releases .

Th e submode l perform s a yearl y mas s balanc e t o simulat e th e releas e o f constituents . Th e annua l potentia l releas e mas s t o groundwate r "i s equal : t o th e leachat e volum e multiplie db y th e aqueou s solubility . Potentia l releas e mas s t o ai r i s calculate dusin g empirica l formula s fo r

..,!»«—

- J" ^P. 7

volatilizatio nrate . Afte r failure , releas e o f constituen t occur s unti l al l o f th e mas s ha s bee nleache d o r volatilize d fro m th e facility . Althoug hth e failur e an d releas e submode l predict s differen t probabilitie s of.failur e an

d average-releas e volume s fo r differen t designs , th e submode l doe s no t remov e a . correspondin g amoun t o f constituen t mas s fro m facilitie s wit hintac t leachat e collectio nan d removal.-systems. . Becaus e single-line d lan d disposa l facilitie s generall y fai l soone r tha ndouble-line d facilities , th e submode l ma y understat e th e contributio no f delayin g line r failur e to-reducin g risk .

Th e exposur e modelin g fo r th e groundwate r rout e examine s bot hth e unsaturated.zone.an d th e saturate d zones . I t use s th e McWhorter-Nelso n wettin g fron t equatio nt o calculat e th e dela y fro m th e time liner s fai l t o th e time that - th e leachat e come s i ncontac t wit hanunderlyin g aquifer . Th e mas s breakin g throug hth e unsaturate d zon e the ndisperse s throug han d dilutes_i ngroundwater . Usin g a nadaptatio no f Prickett' s Random-Wal k Particl e Trackin g Model , w e mode l groundwate r concentration s ove r a 400-yea r time'horizo na t distance s corresponding-t o location s o f wells. " W e calculat e .thes e concentration s fo r nin e differen t groundwate r flow scenario s tha t involv e variation s i naquife r configuratio nand velocity ; al l scenario s appl y onl y t o homogeneous , isotropi c aquifers .

Th e rat e o f flow

o f th e groundwate r and retardatio ncause d b y adsorptio nt o organi c carbo ni nth e eart hmaterial s gover nth e transpor t o f constituent s "throug hth e unsaturate d an d saturate d zones . Retardatio ncalculation s us e th e Freundlic hisotherm algorithm , whic hassume s direc t proportionalit y between^constituen t velocit y (relativ e t o th e groundwate r front ) and th e water : organi c carbo npartitio ncoefficient .

T o estimat e th e transpor t o f volatil e constituents , w e use d th e OT S "Atmospheri c Transpor t Mode l (ATM-SECPOP) . W e calculate d annua l averag e groun d leve l concentration s a t te nsampl e scenario s tha t represen t meteorologica l condition s a t location s i nth e U.S . t o determin e whethe r site-specifi c difference s inmeteorolog y resul t i nsignifican t difference s



# LP. 8

inestimate dconcentrations . The y di d not ; th e site-to-sit e variatio ni n concentration s wa s smal l an d concentratio nwa s linearl y proportiona l t o emission s rate . We thu s calculate da linea r scalin g facto r t o translat e volatilizatio nrat e int o concentration s a t variou s distance s fro m th e source , an

d the nuse dthes e factor s t o estimat e annua l averag e ambien t ai r concentration s fo r population s expose dt o emission s o f volatil e constituents .
Th e groundwate r concentration s caus e exposur e dose s a s a resul t o f th e assumptio ntha t al l receptor s drin k tw o liter s o f wate r pe r day . Ai r : . concentration s caus e exposur e dose s a s a resul t o f th e assumptio ntha t - receptor s have , anai r intak e o f 2 2 cubi c meter s pe r day . Inbot hcase s w e assume th e averag e weigh t o f receptor s i s 7 0 kg , and i nmos t case s w e assum e equa l absorptio nthroug hal l exposur e routes . Th e lifetim e dos e i s th e runnin g 70-yea r averag e dose .
To.produc e a ris k estimate ; w e multipl y dos e b y a dose-respons e factor. : Th e hazar dsubmode l use s th e sam e ris k estimatio nformul a a s th e OS W Risk/Cos t Analysi s Model . Th e Liner'Locatio nRis k an d Cos t Analysi s Mode l use s continuou s function s t o mode l potenc y fo r thes e threshol dpollutants ; thes e functions.predic t les s ris k below no-effec t level s thanmor e traditiona l method s suc ha s acceptabl e dail y intake s (ADIs ) woul dpredict . Thus , whil e w e trea t ris k fro

m carcinogeni c contaminant s ina manne r consisten t wit h traditiona l EPA

methods , ou r approac ht o contaminant s whic hpos e threshol d risk s differ s fro

m th e traditiona l approach .
Th e hazar dsubmodel , reports-risk"estimate s a s averag e ris k (i.e. , th e time-weighte dlifetime ris k ove r th e 400-yea r period ) an d maximum

ris k (i.e. , th e ris k fo r the-70-yea r perio dwit hth e highes t runnin g averag e exposure) . By

usin g populatio ndata , th e submode l ca nals o calculat e th e additiona l numbe r o f case s o f advers e healt heffect s ove r th e 400--year simulatio nperiod . Finally , a singl e compute r mode l link s al l th e algorithm s and submodel s describe dabove .

iwrwuw n w ' '«g>°y-ay>-

- w ~ > •-nqpiinn iP. 9

1. 2 Cos t Mode l

T o calculat e costs fo r landfill s andsurfac e impoundment s we :

- t Specifie ddesign s an dsizes ; - • y

• Estimate dth e engineerin g costs fo r thos e design s and sizes ; and t Discounte dth e engineerin g costs , t o produc e comparabl e economi c

• measures .

W e use dEPA's .Facilitie s Desig nCompute r Cos t Mode l t o estimat e const-ructionand closur e cost s fo r landfill s an dsurfac e impoundment s o f differen t line r configurations " andvaryin g sizes . Inimplementin g th e model , w e estimate dinitia l capita l cost s (land , constructin g th e firs t year' s cel l fo r landfill s o r excavating"an d installin g liner s fo r surfac e impoundments , buildin g th e infrastructure , etc) , annua l capita l cost s (buildin g th e nex t year' s cel l andclosing.th e las t year' s cel l fo r landfills) , closur e costs , (coverin g th e fina l cel l fo r landfill s or " ~ coverin g th e surfac e impoundment , .decontaminatin g equipment , monitoring , andcertifyin g closure) , and"O&M.cost s associate dwit hth e technica l aspect s o f operatin g th e facility . .Fo r surfac e impoundments , w e als o estimate dth e frequenc y andcos t o f dredging . Sinc e ou r cost s wer e developed"t o compar e relativ e technolog y costs , w e di dno t includ e O& M costs fo r recordkeeping , reporting , financia l responsibility , o r any othe r cost s tha t d o no t chang e a s th e stringenc y o f line r regulation s changes . Thus , fo r a particular-line r designyou r cost s underestimat e th e tota l cos t
o f disposin g o f hazardou s waste . ""••- • . • ~

Importan t assumption s underli e thes e engineerin g cos t estimates . First , w e assume dtha t facilitie s ar e abl e t o us e on-site , recompacte d cla y i nal l design s whic hrequir e clay . I f the y ar e unabl e t o d o so , engineerin g cost s will-b e from

1 2 t o 53_percen t greate r tha nou r calculation s indicate , dependin g o nfacilit y desig nandsize . We assum e tha t al l surfac e impoundment s an dsmalle r landfill s ar e on-sit e andwil l no t requir e fence s
andgates , offic e buildings , scales , andequipmen t tha t th e large r off-sit e facilitie s wil l require . 

# LP.1 0 

## r

T o conver t engineerin g cost s t o economi c measure s w e calculate dtota l

presen t value s fo r eac hfacilit y desig nan

dsiz e b

y discountin g th e engineerin g cost s i neac hyea r o f th e facility' s lif e andsummin g th e discounte dcost s ove r al l years . We use da thre e percen t rea l discoun t rat e t o calculat e presen t values .

OSW' s standar dassumption s fo r economi c analysi s pertainin g t o facilit y lif e andoperatin g procedure s applie dt o th e cos t model : surfac e impoundment s andlandfill s bot hoperat e fo r 2 0 years ; operator s ope nth e firs t cel l i na landfil l a t th e beginnin g o f yea r on e andcove r i t a t th e beginnin g o f yea r two , andcove r th e las t "cel l a t th e beginnin g o f yea r 21 ; andoperator s lin e surfac e impoundment s a t th e beginnin g o f yea r on e andcove r them

a t th e beginnin g o f yea r 21 .
Afte r calculatin g th e presen t values , w e als o annualize dthem . Cost s ar e ofte nunevenl y

distribute dthroug htime ; annualizin g spread s them evenl y ove r th e ltfe'o f th e facility . We annualize db y multiplyin g th e presen t valu e a f each^facilit y siz e an

ddesig nb

y a capita l recover y

factor . Wit h
a thre e percen t rea l rat e o f retur nanda "20-yea r facilit y life , th e capita l recover y

facto r i s 0.0672 . Finally , w e calculate dth e annualize dpresent-valu e oha per.uni t basi s b y dividin g th e annualize dcos t fo r eac hfacilit y siz e anddesig nb

y it s capacity . Thi s result s i nannualize dcost s pe r tonfo r landfills , and annualize dcost s pe r acr e an dpe r gallo nfo r surfac e impoundments .
2 . APPLICATION S FO

RTH E MODE L EVALUAT E TH E COST/RIS KIMPLICATION S O F TECHNOLOG YSTANDARD S AN D COMPARE RISK S O F DIFFEREN T ENVIRONMENTA L SETTING S AND DIFFEREN T WASTE S

We hav e applie dth e Line r Locatio nRis k andCos t Analysi s Mode l onsevera l occasions , bot ht o tes t anddebu g i t and.t o us e i t fo r polic y analysis . Give nth e complexit y

o f th e mode l andrestrictiv e time schedules , w e ofte n performe dth e polic y

analysi s closel y

followin g andsometime s concurren t wit htestin g anddebuggin g th e model . Also , thos e instance s wher e w e knowP.1 1

th e distribution s aroun dinpu t values , w e hav e no t carrie dthi s informatio n throug ht o fina l estimate s bu t hav e onl y determine dpoin t estimates . In othe r instances , w e d o no t currentl y hav e estimate s o f th e distributio no f values , andhav e no t performe dsensitivit y analyse s t o determin e how changin g value s woul dchang e ou r ris k estimates . Therefore, ' w e hav e no t ye t calculate derro r band s o r confidenc e interval s fo r th e ris k an dcos t estimates. " We therefore , vie w th e result s o f th e firs t thre e set s o f application s a s tentativ e an dexplorator y

rathe r tha nconclusive .

I nth e firs t application , w e evaluate dnationa l technolog y standard s fro

m a . cost/ris k perspective ; inth e secon dwe compared - th e ris k o f environmenta l settings , holdin g technolog y and"wast e stream s constant ; an dinth e third , we compare dth e ris k o f differen t wast e .streams , holdin g technology-an d environmenta l settin g constant . In-general , w e found:-that-risk s o f land disposa l var y

widel y dependin g o

nwastes , environments , andtechnologies . W e als o foun dtha t risk s ar e mor e sensitiv e t o waste s an denvironment s tha n the y ar e t o technology . J -..-" - 1

2. 1 Evaluatin g National-Technolog y Standard s - . - •

I nthi s applicatio no f th e Line r Locatio nRis k andCos t Analysi s Model , w e use dtwo differen t set s o f input-data . Th e firs t se t represent s a cros s sectio no f 1 7 landfill s and3 1 surfac e impoundment s usin g actua l dat a fo r th e facilitie s whereve r possible . Whil e w e fhirvk-thes e s.ite s compris e a reasonabl y

representativ e sampl e o f landfill s andsurface"impoundments , the y ar e no t a statisticall y vali drandom

samp-le . ... - : .... . - . -

Amon g th e "actua l sites, " onl y tw o o f th e landfill s andfiv e o f th e surfac e impoundments.hav e nearby population s usin g groun dwate r a s thei r sourc e o f drinkin g water . O f these , onl y on e landfil l andthre e impoundment s show an y risk , eve nfo r th e unline ddesign . Moreover , mor e stringen t line r design s (single , double , andtripl e liners ) provide dlittl e incrementa l ris k abatemen t a t thes e facilities . Consequently , requirin g liner s a t al l
o f thes e facilitie s woul dresul t i na ^ery hig hcos t pe r cas e avoided .



### 8Becaus e thes e estimate drisk s ar e largel y drive nb

y th e numbe r o f receptors , w e repeate dth e analysi s usin g 4 4 additiona l landfil l site s and assumin g tha t receptor s exis t a t al l sites . (Figure s showin g thes e result s ar e labele d"Augmente dSites." )

Amon g th e site s augmente dwit hhypothetica l populations , risk s ar e substantiall y

larger . "Almos t two-third s o f th e unline dfacilitie s whic h
wer e modele dshowe dsome leve l o f risk , althoug hmos t o f thi s ris k wa s concentrate da t a smal l numbe r o f site s andslightl y mor e tha none-thir do f thes e unline dfacilitie s hadno risk . Further , th e result s indicat e tha t line r technolog y

i s no t particularl y

effectiv e inabatin g thes e risk s a t al l modele dsites . Eve nso , combinin g technolog y cos t informatio nwit hth e ris k information , suggest s tha t th e cost/ris k ratio s o f requirin g liner s a t al l modele dsites.i s favorable . However , tailorin g th e requirement s t o site-specifi c factor s tha t increas e ris k rathe r tha nrequirin g th e same standard s fo r al l facilitie s coul dprovid e eve nbette r cost/ris k ratios .
2. 2 -Comparin g th e Ris k o f Environmenta l Setting s

Inthi s applicatio nw e examine dth e effec t tha t environmenta l settin g ha s onrisk . Holdin g technolog y constan t (doubl e syntheti c liners ) w e examine d th e distributio no f ris k t o expose dpopulation s unde r varyin g climate , hydrogeologi c setting , andwel l distanc e scenarios . Thus , fo r thre e wast e constituent s (chromium , carbo ntetrachloride , andparathion ) w e examine d ris k t o individual s unde r 13 5 possibl e combination s o f environmenta l settin g (fiv e climates , nin e hydrogeologi c settings , andthre e wel l

_- distances) . We performe dth e simulation s fo r landfill s andfor . surface impoundments .
The . result s indicat e tha t difference s inenvironmenta l setting s lea dt o larg e difference s i nrisk s t o expose dindividual s fro m disposin g o f a wast e stream "wit ha give nmanagement"practic e andtechnology . Approximatel y one-thir do f th e scenario s fo r chromiu m i nsurfac e impoundment s produc e risk s o f 10 " (on e i nten ) t o expose dindividual s whil e abou t one-thir do fP.1 3

th e scenario s produc e no risks . Fo r landfills , almos t 4 0 percen t o f th e scenario s produc e ris k < produc e no ris k a t all . scenario s produc e ris k o f 10 " , bu t abou t 2 5 percen t o f th e scenario s

Th e result s fo r carbo ntetrachlorid e show a simila r patter no f bot hhig h
an dlo w risk . However , th e overal l risk s ar e lowe r (nearl y three-quarter s o f th e scenario s produce dn o risk ) becaus e carbo ntetrachlorid e i s les s mobil e tha nchromiu

m an dexposure s occu r i nfewe r scenarios .

Non e o f th e parathio nscenario s resul t i nany exposures ; du e t o it s lo w mobilit y an dhighrateo f degregation , n o significan t concentratio nbreak s throug hth e unsaturate dzon e durin g th e simulatio nperiod .

I nadditio nt o showin g tha t environmenta l settin g cause s larg e difference s i nrisks , thi s applicatio nals o begin s t o sugges t ho w th e thre e environmenta l factor s w e varie dar e importan t i ndeterminin g risk . First,

_ drie r climate s "produc e les s ris k becaus e ther e i s les s leachat e "an d therefor e release s afte r failur e ar e smaller" . Next , th e result s illustrat e th e effec t o f distanc e o nris k a s zer o ris k scenario s ar e fa r mor e likel y
• at " longe r distance s fro m wells . Finally , i ncomparin g scenario s with , y . slow-movin g aquifer s t o scenario s wit hfaste r ones , w e observ e tha t fo r - persisten t constituent s i nth e fas t aquifers , th e peak,an daverag e constituen t concentration s ar e lower , th e perio do f exposur e i s shorter , an dth e averag e ris k range s fro m two t o a s muc ha s fiv e order s o f magnitud e lower . Fo r degradabl e constituents , th e perio do f exposur e i s shorte r i n-'- • fas t aquifer s bu t th e peak"an daverag e concentration s ma y b e highe r and consequently , risk s ma y als o b e higher . -; - - . '••:

_-.-

Insummary , thi s applicatio nshow s tha t risk s ar e extremel y sensitiv e t o environmenta l setting . Juxtapose dwit hth e evaluatio no f nationa l technolog y

standards , i t show s ris k i s fa r more"dependen t onenvironmenta l ; settin g tha no nline r technology .



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# r

2. 3 Comparin g th e Ris k o f Differen t Waste s

T o compar e th e risk s o f differen t wastes , w e simulate drisk s fo r 1 5 wast e Stream s i nlandfill s an d 3 0 wast e stream s i nsurfac e impoundments , holdin g design, " line r technology , and environmenta l settin g constant . W e selecte d wast e stream s b

y examinin g response s t o OSW' s mai l survey . W e modele dth e ris k fo r a wast e stream eithe r i nlandfills , surfac e impoundments , o r bot h i f (1 ) i t appeare di nlandfills, , surfac e impoundments , wast e piles , injectio nwells , o r landtreatmen t a s on e o f any facility' s te nlarges t wast e streams ; (2. ) i t ca nb e manage dinlandfill s o r surfac e impoundments ; an d(3 ) w e coul dcharacteriz e it s constituent s an d fin dth e physicochemica i properties.necessar y

t o simulat e it s risks .

Ou r re.sult s showe dtha t ther e i s wid e variabilit y i nris k fo r differen t wast e stream s holdin g al l othe r factor s constant . Inlandfills , eigh t o f 1 5 waste s w e modele dshowe daverag e risk s o f les s tha n1 0 (on e i na ; biTlion)- , ye t al l bu t on e o f th e remainin g seve nwast e stream s showe drisk s

- - -"- 4 / • " ' ~- o f 1 0 - (on e i nte nthousand ) o r greater . Insurfac e impoundments , nine " o f

- _

g

- 3 0 wast e stream s showe drisk s o f les s tha n1 0 , whil e 1 7 showe drisk s o f

_ 4 •'•'•
. - "1 0 o r more. - - .
Thi s applicatio njuxtapose dwit hth e evaluatio no f nationa l technolog y standard s indicate s tha t ris k i s fa r mor e sensitiv e t o change s i nwast e strea m compositio ntha nt o change s intechnology .

..'-'."

_' i. -PLAN S FORTH E PROJECT'CAL L FO RIMPROVINGTH E MODEL , : : .VALIDATIN GIT , AN D ISSUINGA PHAS E II . REPOR T

We hav e no t currentl y complete dal l th e sensitivit y analyses , no r hav e w e examine dal l th e assumption s and limit s t o determin e th e constraint s the y impos e onfutur e us e o f th e mode l fo r polic y purposes . A s th e task s ar e completed , EP A

wil l issu e a secon dreport .



### 1 13. 1 Improvin g and Validatin g th e Mode l

I n buildin g and applyin g th e mode l w e hav e notice d severa l area s tha t w e ca n improve ; basi c area s o f effor t includ e th e failur e an d releas e submodel , th e subsurfac e transpor t submodel , th e exposur e submodel , th e hazar d model , and th e cos t model
.

I n th e failur e an d releas e submodel , w e wil l (1 ) perfor msensitivit y analyse s t o determin e ho wimportan t th e underlying , probabilit y distribution s ar e i n determinin g failure s an d releases ; ("2 ) modif yth e assumptio n tha t leachat e collectio n system s remov e water , bu t no t hazardou s wast e from.facilities ; ahd (3. ) chang e th e basi c structur e o f th e submode l
s o w e ca n repor t statistic s associate d wit h th e estimate s o f failur e percentage s an d leachat e volum e releases
.

W e are-also-workin g o n way s t o mode l constituen t degradatio n prio r t o releas e fro mth e sit e a s wel l a s othe r modification s t o th e estimates~of_:- ' wast e mas s availabl e t o ente r th e unsaturate d zone .
Th e subsurfac e transpor t submode l wil l b e expande d t o consider-attenuatio n . i n th e unsaturate d zone , dispersio n int o a thir d dimension , dilutio n o f contaminant s a t th e wel l site , an d transpor t throug h fractured , no t homogeneou s and isotropic , aquifers

.

W e "wil l als o rela x ou r worst-cas e assumption s abou t exposure : first , tha t peopledrin k contaminate d water , eve n i f contaminant s excee d thei r odor , taste , an d physica l appearanc e thresholds ; and second , tha t groundwate r " monitorin g i s no t i n place
.

I n th e hazar d submode l w e wil l furthe r evaluat e som e o f th e basi c assumption s underlyin g th e ris k estimatio n algorithmfo r noncarcinogens , compar e ou r ris k estimate s wit h thos e derive d b yothe r methods , an d ermin e th e sensitivit yo f result s t o change s i n inpu t values
.

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I nth e cos t model , w e wil l includ e th e cos t o f treatin g leachat e fro m th e facility , whethe r ono r off-site , th e cos t an deffectivenes s o f takin g correctiv e o r remedia l action s a s wel l a s the cos t o f repairin g o r replacin g cover s andothe r facilit y components .

Becaus e o f th e difficult y inmeasurin g som

e o f the comple xprocesse s w e model , i t i s no t possibl e to.verif y directl y

the performanc e o f th e model , bu t w e ca ninfe r th e accurac y o f severa l key

element s b

y reviewin g some type s o f empirica l data . A s on e example , w e pla nt o revie w result s o f ongoin g ai r monitorin g a t landfill s andsurfac e impoundment s i norde r t o verif y that-pu r approximation s o f ai r emission s ar e realisti c Some o f th e othe r materia l we.wi1 1 revie w include s dat a oneffectivenes s o f groundwate r monitorin g an

dcontaminant-concentratio ningroundwate r a t CERCL A sites .
3. 2 Phas e I I Repor t

Whe nw e complet e th e wor k describe dabove,-EP A wil l issu e andcirculat e fo r peer - revie w

th e final-Line r Locatio nRis k an dCos t Analysi s Mode l Report . Thi s wil l presen t th e model , modifie dt o incorporat e th e improvement s

- discusse dpreviousl y an dcomment s fro

m thi s firs t roundo f review .



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