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I have reviewed the f o l l o w i n g documents describing the analysis ofnedial a l t rBio-Ecology S i t e I n v e s t i g a t i o n , Wbodward & C l y d e C o n s u l t a n t s ,A p r i l 1983.

. _ , _ _ - — — ~w«AV«*i«^ vjwv-uneiiua aescxriDing une ana*co s t - e f f e c t iv ene s s of remedial al t ernat ive s for the Bio-Ecology

- Bio-Ecology Remedial A l t e r n a t i v e s A n a l y s i s , Woodward 6 Cl>t3e C o n s u l t a n t sJ u l y 1963. —- S t a f f sorroaries and reconmendations.

Descript ion of Elected f t emedy- Raise the e l evat ion of the s i te above the 100-year f l o o d p l a i n .- Construct an on-site di sposal cell with synthetic l iner and aleachate col lec t ion system.- Construct a f i n a l cover and liner and leachate co l l e c t ion and removal

system in accordance wi th s tandards promulgated under 40 CFR Part 264and a p p l i c a b l e guidance.- S t a b i l i z e the waste and place in on-site c e l l .- Construct a fence with warning signs.- I n s t a l l a ground water monitoring system in accordance with s tandardspronulga t ed under 40 CFR Part 264.

D E C L A R A T I O N

Consistent with the Comprehensive Environmental Response, Compensation,and L i a b i l i t y Act of 1980 (CERCIA), and the N a t i o n a l Contingency Plan (40 CFRPart 3 0 0 ) , I have determined that containment of wastes in an on-site l a n d f i l lin compliance with a p p l i c a b l e technical regulat ions of RCRA is a c o s t - e f f e c t i v eremedy and provide s adequate protect ion of p u b l i c h ea l th , w e l f a r e , and theenvironment. The S t a t e of Texas has been consulted and agrees with the approvedrenedy.I nave also determined that the action being taken is appropriate whenbalanced against the a v a i l a b i l i t y of Trust fund monies for use at otlier sites.

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I an also approving a ground water monitoring program to determine theexistence of any present ground water contamination outside the containmenthouever the decision to proceed with this cleanup does not encompassremedial action with respect to any ground water contamination that may bediacovered. If such ground water contamination is f o u n d , appropriate remedialresponse will be evaluated, and I will make a fu ture determination regardingthe compliance of th i s response with RCRA requirements. If no ex i s t ingcontamination is f o u n d , the monitoring program wil l ensure the continuede f f e c t i v e n e s s of the selected containment remedy. In accordance with section1 0 4 ( e ) ( 3 ) » the S t a t e is required to ensure the continued operation andmaintenance of the selected remedy.

Lee M. ThomasAssistant AdministratorO f f i c e of S o l i d Waste and Emergency ResponseV

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Remedial I m p l e m e n t a t i o n A l t e r n a t i v e S e l e c t i o nBio-Ecology S y s t e m s , I n c . , S i t eGrand i ' r a i r i e , T e x a sS e p t e r r j D e r , 1983

S i t e Loca t i on and D e s c r i p t i o nThe Bio-Ecology s i t e is an 11.2 acre tract located at 4100 Last J e f f e r s o nAvenue in Grand P r a i r i e , Texa s snown in F i g u r e 1, Hie actual waste d i s p o s a lf a c i l i t y occupied a por t i on of the 11.2 acres owned by Bio-Ecology. Thesite is bounced in all d irec t ions by pr iva t e p r o p e r t y and also on the eastand south by the t r i b u t a r i e s o£ old M o u n t a i n Creek. Mountain Creek Lakeand the T r i n i t y River are located a p p r o x i m a t e l y 0.75 mi l e s southwest and2.5 mi l e s nortn of the s i t e , r e s p e c t i v e l y . The s i t e is located in thef l c o d p l a i n o f M o u n t a i n Creek ( T r i n i t y River B a s i n ) and has been e x t e n s i v e l yf l o o d e d on at least two past occasions d u r i n g o p e r a t i o n s ( J u n e 1973 and

J u n e 1 9 7 4 ) .2 and 3.S i t e H i s t o r y

A s i t e d i a g r a m of the Bio-Ecology F a c i l i t y i s shown in F i g u r e s

The Bio-Ecology waste d i s p o s a l s i t e was a C l a s s I i n d u s t r i a l s o l i dwaste management f a c i l i t y , o r i g i n a l l y au thor i z ed by a permit issued by theT e x a s W a t e r Q u a l i t y Board o n A p r i l 2 4 , 1972. P e r m i t t e d a c t i v i t i e s i n c l u d e d :t l j i n c i n e r a t i o n o f c ombus t i b l e l i q u i d s , s l u r r i e s , a n d s l u d g e s ( s u b j e c t t oT e x a s A i r Control Boara s tandards f o r odors a n d e m i s s i o n s ) ; ( 2 ) cnemicaltreatment of a c i d s , c a u s t i c s , and other waste chemical s o l u t i o n s , i n c l u d i n gthose c on ta in ing heavy m e t a l s ; ( 3 ) D i o l o g i c a l o x i d a t i o n o f waste watersr e s u l t i n g f r o m s e p a r a t i o n of mud-water and o i l -water m i x t u r e s and f r o mcnenical tr ea tment o f other was t e s ; a n d ( 4 ) a m o d i f i e d l a n d t i l l o f s o l i d sr e s u l t i n g f r o m the other treatment processes . The s i t e was a c t i v e l y operat edf r o n t J u n e 1972 through J u n e 1978.

Operat ions at the s i t e were characterized by frequent l i t i g a t i o nf i l e d by the T e x a s Department cf W a t e r Resources and its predecessor agency( T e x a s W a t e r Q u a l i t y B o a r d ) . Both agencies had a t t e m p t e d to force thecompany to comply w i t h permit s t a n d a r d s and all the a p p l i c a b l e F e d e r a l andS t a t e laws ana r egu la t i on s . During the 6-year o p e r a t i o n of the f a c i l i t y ,Bio-Ecology w a s c i t ed f o r a number o f m a j o r v i o l s t i o n s i n c l u d i n g : ( 1 )cons truc t ion o£ new t a c i l i t i e s ( i . e . - r e ta i l ing b a s i n s ) without p r o p e ra u t h o r i z a t i o n , ( 2 ) d i s charge o f wastewater into Mounta in Creek, ( 3 1 a l l o w i n gl i q u i d l e v e l s in h o l d i n g basins to reach the Drink w i thou t any f r e e o o a r d ,(4) storage o f drunks, several times beyond the permit maximum ( 2 0 0 d r u m s * ,a n d ( 5 ) several i n c i d e n t s o f o i l s p i l l s .

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From Jane 3 through J u n e 4, 1973, approx ima t e ly 5 inches of rain f e l lon the s i t e dur ing a 24-hour p e r i o d . A p p r o x i m a t e l y 90 percent of theBio-Ecology f a c i l i t y ( 1 1 . 2 acres) was inundated . S t a t e in spec t i ons o f thesite observed f l o o d i n g in several storage basins and wastewater r u n o f f intoMounta in Creek. The s i t e was to have been de s igned to adequat e ly protectagain s t a 24-hour, 25-year r a i n t a l l ; "lowever, the r a i n f a l l dur ing J u n e 3through J u n e 4 was of l e s s thau a 25-year f r equency . J u d c ^ n e n t s were ^assedby the T e x a s courts or. J u l y 6, 1973, and March 24, 19 "H, requiring Bio-Ecology to canply wi th its permit and remedy the above mentioned v i o l a t i o n s .On J u n e H, 1978, Bio-Ecology f i l e d f or bankruptcy under the provis ions o fXI of the Bankruptcy A c t .payment o f a l l p r i o r i t y c r e d i t o r s , th e T e x a s Department o f W a t e rResources was able to r -cover $28,870.50 f r o m Bio-Ecology for c l eanupa c t i v i t i e s . In Decatoer 1979, a contract was made to p a r t i a l l y close thes i t e . Under t h e contrac t , (1) a l l open receiving basins and p i t s wered r a i n e d , (2: a i i c on ta iner iz ed wastes were buried onsi-e and covered w i t i

a p e l l e t i z e d lirne b l a n k e t , a n d ( 3 ) s l u d g e s i n various lagoons a n d l a n d f i l l swere moved to c o n s o l i d a t e tnem e n s i l e . Due to c o n s t r a i n t s in f and i n g , anumber of rrtetal tanks c on ta in ing o i l s , s o l v e n t s , and p a i n t s l u d g e s remaineda t t n e s i t e . A p p r o x i m t e l y 334,000 ( i n c l u d i n g 328,870.50 o b t a i n e d f r o mBio-Ecology b a n k r u p t c y } was expended d u r i n g the per iod f r o m December 12,1 9 7 9 , through F e b r u a r y 1 5 , 1980, f o r t n e p a r t i a l s i t e c l e a n u p .

I n November 1 9 8 1 , t h e a p p l i c a t i o n f o r a C o o p e r a t i v e Agreement f o rrenewal i n v e s t i g a t i o n s and t e a s i D i l i t y s t u d i e s at the Bio-Eco logy s i t ewas f i l e d . The C o o p e r a t i v e Agreement between EPA and the S t a t e ot T e x a swas approved on A p r i l 12, 1982. An award of S 3 2 8 ,000 was au thor iz ed toconduct a remedial i n v e s t i g a t i o n a r d f e a s i b i l i t y s t u d y I R I / F S ) a t t h eBio-Ecology s i t e . I n November 1982 , W o o d w a r d - C l y o e C o n s u l t a n t s o t H o u s t o n ,T e x a s , was s e l e c t ed t o conduct the RI/FS. The s i t e worx f or the inves.: nat ionwas c o m p l e t e d in J a n u a r y of 1983 and the f i n a l report was approved inA p r i l o f 1993. The F e a s i b i l i t y S t u d y wi s s tarted in F ^ o r j a r y o f 1983 anawas co%leted in J u l y o f 1983. The m a j o r f i n d i n g s o f the i n v e s t i g a t i o nand f e a s i b i l i t y reports are di scus sed in the section t i t l e d "Current S i t eS t a t u s " .

In a d d i t i o n t o t h e above work an T n r t i a l Remedial Measure (IBM) wasconcluded at the Bio-Ecology s i t e in S e p t e m b e r of 1983. The IfcM c l eanupa c t i v i t i e s inc luded t h e f o l l o w i n g :1. Remove and d i s p o s e of a p p r o x i m a t e l y 80,000 g a l l o n s of hazardous

l i q u i d ' s a n d s l u d g e s , ( O r g a n i c s , P C B ' s , H e a v y M e t a l s )2. Decontaminate and remove tne 15 storage tanks and other s u r f a c e

structures .

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3. Remove and d i s p o s e of about 35 cubic yards of c o n t a m i n a t e d - s o i l .

-3-4. S u r f a c e c l eanup, (miscel laneous debris, s i te g r a d i n g , e t c . )T h i s ac t ion was deened necessary according to the N a t i o n a l Cont ingencyP l a n (NCP) section 300. fR w i t h regard t o hazardous substances in drums,barre l s , t a n k s , or other bu lk storage containers above s u r f a c e po s ing athreat to p u b l i c h e a l t h or the environment and contaminated soils l a r g e l yat or near the s u r f a c e p o s i n g a threat to p u b l i c h e a l t h or the environment.

C L W F N T 5 I T EThe Bio-Ecology remedial i n v e s t i g a t i o n that was per formed included ah y d r o l o g i c a n a l y s i s , a s t r a t i g r a p h y a n a l y s i s , a h y d r o g e o l o g i c a l a n a l y s i sand a geochtsnical analys i s . The f o l l o w i n g is a summary on the r e su l t s oft h i s i n v e s t i g a t i o n .The h y d r o l o g i c a n a l y s i s showed the s i t e to be poor ly dra ined and sub-j e c t to s u r f a c e r u n - o f f , erosion and f l o o d i n g . A p p r o x i m a t e l y 75 percentof the s i t e i s w i t h i n the 100-year f l o o d p l a i n .T h e s t r a t . i g r a p h i c a n a l y s i s i d e n t i f i e d f o u r s u b s u r f a c e s t r a t a w i t n i nthe u p p e r 60 f e e t at the s i t e . The upperro s t s t r a t u m f r c r c the s u r f a c e toacout 2<"> f e e t in d e p t h consists of modern a l l u v i a l d e p o s i t s f r o m the meanderd e p o s i t i o n of Old M o u n t a i n Creek on the n o r t h , east and south of the s i t e .T h e s e modern a l l u v i a l d e p o s i t s are pervious d e p o s i t s capab l e o f t ransmi t-t i n g water v e r t i c a l l y and l a t e r a l l y and are thus s u b j e c t t o i n f i l t r a t i o nby r a i n f a l l and h i g h f l o o d waters o f Old M o u n t a i n Creek. U n d e r l y i n g t h emodern a l l u v i a l d e p o s i t s a r e e l d e r a l l u v i a l d e p o s i t s f r o m f l o o d b a s i n d e p o s i -

t i o n o f t h e M o u n t a i n Creek v a l l e y . The s e d e p o s i t s ar e p r i m a r i l y h i g hp l a s t i c i t y c l a y s w i t h occasional beds o f l o w p l a s t i c i t y c l a y s . T h e o l d e rf l o o d d a s i n s o i l s contain f i s s u r e s and cracks caused by cyc l i c shr inkageand s w e l l i n g . The o l d e r a l l u v i a l d e p o s i t s t h e r e f o r e *c t as a l e a k y a q u i t a r dc a p a b l e o f t r a n s m i t t i n g f l u i d s v e r t i c a l l y . T h e s e d e p o s i t s vary i r L t h i c k n e s sf r o m 25 to about 40 f e e t across the s i t e . Below t h i s s t ra tum is about a5 - f t layer o f remnant quaternary gravel d e p o s i t s which i s t h e f i r s t s i g n i f -icant a q u i f e r encountered. Beneath the gravel d e p o s i t s i s about a 2 0 0 - f tsect ion o f t h e E a g l e F o r d s h a l e . T h i s s h a l e i s f o r a i l p r a c t i c a l purpose siirpervious and over l i e s the Woodb ine a q u i f e r . The Woodb ine A q u i f e r i sused as a d r i n k i n g water s u p p l y f or the C i t y o f Grand Prair i e ( S e e F i g u r e4 for a t y p i c a l cross sec t ion.

The ground water f l o w , at the time of i n v e s t i g a t i o n , was g e n e r a l l yf r o m northwest to southeast across the s i t e in the remnant gravel a q u i f e r .Ground water encountered was al so under an ar t e s ian head of about 15 f e e t(measured f r o m t h e o l d e r a l l u v i a l d e p o s i t s ) . T h i s a q u i f e r i s s l i g h t l ycontaminated in the v i c i n i t y of the s i t e and is s u b j e c t to c on taninat i onf r c m wastes at the s i t e m i g r a t i n g through the secondary s truc ture of o l d e ra l l u v i a l d e p o s i t s . Ground water i s present in the u p p e r a l l u v i a l d e p o s i t sat water l ev e l s below the level of s u r f a c e water in t£ie a d j a c e n t streamchannel and nearby pond northwest of the s i t e . These s u r f a c e waters arerecharging the a l luv ium at the s i t e .

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The geochisnical a n a l y s i s showed that s u r f a c e contaminat ion at thes i t e is p r i m a r i l y restricted to on-site locations and to o r f - s i t e drainageareas. On-site s ur fa c e contamination is extensive for rae ta l s , cyamcJe andorgarucs. C c m p o s i t e f r c sn the s i t e ind i ca t e h i g h ooncentrat ions otlead a- 100 r n g A g ) , arsenic ( 2 1 0 m g A g ! , and cyanide ( 1 , 0 3 0 r r q A a ) . An* l y s i sa l so ind i ca t e^ tne presence ot many o r g a n i c contaminant s i n c l u d i n g t o l u e r i e( 1 9 , 0 3 0 p p £ » , t n c h l o r o e t h y i e n e ( 1 , 0 0 0 , 0 0 0 p p b ) , benzene ( 1 , 5 0 0 p p b ) ,m e t h y l e n e cnlonde ( 3 7 p p b ; , a n a n a p h t h a l e n e (20,300 p p o ) . O t t - s i t econtaminat ion did not appear to be ssvere a:. the t i j n e of tto f i e l dinve s t i ga t i on . L i K e w i s e , subsurtace contamination appears to be p r i m a r i l yres tr ic ted to waste d e p o s i t s and their v i c in i ty*There are a p p r o x i m a t e l y 40,000 cuoic yards of wastes ana h i g h l ycontaminated soil^ a t th e s i '_e .The conclusions ot tne r emedia l i n v e s t i g a t i o n are the t o l l o w i r x ; :0 S i g n i f i c a n t waste q u a n t i t i e s c o n t a i n i n g h i g h concentrations o fm e t a l s , cyanide s and arana^i.c - j r g a n i c s arc present at the Bio-Lcolo^ys i t e ;0 S e v e n t y - f i v e percent of the s i t e is located w i t f u n the 100-yearf l o o d p l a i n and is s u s c e p t i b l e to sew re f l o o d i n g ;0 M i g r a t i o n , p a t h w a y s and m i g r a t i o n mechanisns are present at the s i t efor p o t e n t i a l s i g n i f i c a n t l*ng-t snn waste m i g r a t i o n t* s u r f a c e anosub sur fa c e waters and a d j a c e n t areas;0 Evidence of s u r f a c e c on tamina t i on in • f f - s i t e dra inage d i t c h e s andtraces ot s u b s u r f a c e c o n t a m i n a t i o n in the quaternary gravel a ^ - j i f e roeneath the s i t e were f o u n d ;0 W a s t e m i g r a t i o n to date has been p r i m a r i l y r e s tr i c t ed to on-sitelocat ions w i t h t h e e x c e p t i o n o f past s u r f a c e o f f - s i t e m i g r a t i o ncaused by t l o o d i n g ;0 T a r g e t receptors c u r r e n t l y impacted are ad ja c en t land areas ( d e a aand d y i n g v e g e t a t i o n ) and s u r f a c e w a t e r s ;0 Remedial ac t ions should be under taken to prevent f u t u r e s u r f a c e ands u b s u r f a c e m i g r a t i o n of wastes tc s u r f a c e water, ground waters anda d j a c e n t p r o p e r t y ; and** A search of d r i n k i n g water well records was conducted d u r i n g thei n v e s t i g a t i o n and did not reveal anyone us ing the s h a l l o w a q u i f e r .

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-s-f e a s i b i l i t y s tudy conpl e t ed by Woodward & C l y d e C o n s u l t a n t s inJ u l y 1983 deve loped the f c l i o w i n g o b j e c t i v e s based on the r e s u l t s o f tr.eremedial i n v e s t i g a t i o n :

* Remove above ground s t r u c t u r e s , d i s p o s e of c o n t e n t s , arx! treat thea s soc ia ted norther" o f f - s i t e c o n t a m i n a t e d s o i l area;* Raise s i t e above 100-year f l c o d p l s i n ;0 provide adequate s i t e d r a i n a g e ?* Treat s p e c ia l wastes ( P C B s in T^nk T2; buried drms and c on ta iner si n c l u d i n g medical v i a l s and laboratory chemica l s ; areas of h i g harsenic concentrat ions: and areas of c y a n i d e - - - ) ? ande Contro l o f F - s i t e m i g r a t i o n c f waste s by suri>ce and s u b s u r f a c em i g r a t i o n p a t h w a y s to s u r f a c e and s u b s u r f a c e waters and a d j a c e n tland areas in order to m i t i g a t e f u t u r e impac t s on these t a r g e t

receptors. ( N o s i g n i f i c a n t a i r m i g r a t i o n prob l ems were de t e c t edd u r i n g t h e s i t e i n v e s t i g a t i o n . )The f e a s i b i l i t y s tudy d e v e l o p e d nine a l t e r n a t i v e s based on theseo b j e c t i v e s . A no-action a l t e r n a t i v e was a l so c on s ider ed for v.he Bio--co logys i t e , but was e l i m i n a t e d p r i o r to i n i t i a l screening based on it s inacerjacyfor nee t ing response o b j e c t i v e s to n i t i g a t e the s i t e - s p e c i f i c problems and

t h e f a c t t ha t pa thways ex i s t f o r s i g n i f i c a n t p o t e n t i a l m i g r a t i o n o f s u r f a c eand s u b s u r f a c e c o n t a m i n a t i o n .The r.ine a l t e r n a t i v e s were screened for p e r f o r m a n c e , cost andenvironmental f a c t o r s . T h e F e a s i b i l i t y S t u d y i n c l u d e s a d e t a ; l e d s creening

procedure and the r e s u l t s are sumranzed here. Three a l t e r n a t i v e s werer e j e c t e d based upon p e r f o r m a n c e and the low r e l i a b i l i t y of a d e q u a t e l yc o n t r o l l i n g t h e source o f c o n t a m i n a t i o n . Ore c l t e r n a t i v e ( o f f - s i t e t r a n s p o r tand d i s p o s a l ) was r e j e c t e d based on cost since its cost was about threetimes more than the next most c o s t l y a l t e r n a t i v e and did not provides u b s t a n t i a l l y greater p u b l i c h e a l t h o r environmental b e n e f i t .

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-6-r e m a i n i n g f i v e a l t e r n a t i v e s were -3eveloped and f u l l y e v a l u a t e d ,More accurate cost e s t imate s were prepared for each. They are:

A I t e r r . a t i v e4 - S t a b i l i z e wastes in-place and i n s t a l ls l u r r y trench througn modern a l l u v i o n( 3 0 - f t !5 - S t a b i l i z e and conso l ida t e wasteand i n s t a l l slarry trenchtnrough modem a l l u v i u m ( 3 0 - f t )6 - S t a b i l i z e wastes i n - p l a c e and i n s t a l ls l u r r y trench througn quaternary sand/jrave l l a y e r ( 6 0 - f t . !7 - S t a o i l i z e anc c o n s o l i d a t e wastes inc l a y l ined c e l l ( w i t h leac*-.ate c o l l e c t i o ns y s t e m )8 - S t a b i l i z e and c o n s o l i d a t e waste s ins y n t h e t i c / c l a y lin^d ceil ( w / l e a c n a t e

c o l l e c t i o n s y s t e m ) ( R C F A approved f a c i l i t y

Est imated Q p s t sD e s i g n C o n s t r u c t i o n

5136 ,300 S I ,604,200

156,700

i 7 d , a o oI " 7 ? , 2 0 0

1,844,800

2,104,000

2,085,200

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215,000 2,497,400Ail the abovy a l t e r n a t i o n s i n c l u d e a c l a y cap , a ground water no i i t or ings y s t e m , and r a i s i n g tne s i t e e l e v a t i o n abo-ve the 100-year f l o o d p l a i n . Thecos t s noted above i n c l u d e c a p i t a l costs. In a d d i t i o n to the costs mentionecabove, post closure m o n i t o r i n g costs are e s t imated to be about 320,000 tnef i r s t year and then aoout $1,000 per year for 30 years and O&M costs foreacr. a l t e m t i v e are e s t imat ed to be $1000 to $2000 per year tor 30 years,A c o s t - e f f e c t i v e n e s s e v a l u a t i o n was p er f ormed by p r o f e s s i o n a l engineerson tne Woodward C i y d e s tar t on the above a l t e rna t iv e s . T h i s e v a l u a t i o nprocess used a we igh t ed r a t i n g system to q u a n t i t a t i v e l y rank the e f f e c t i v e n e s sof tne a l t e r n a t i v e s . F o u r categories are l i s t ed below along wi th thea v a i l a b l e number o f p o i n t s f or each:Category

( 1 ) Human H e a l t h I m p a c t s( 2 ) F e a s i b i l i t y a n d PertormanoR( 3 ) Environmental I m p a c t s( 4 ) T i m e l i n e s s

A v a i l a b l e P o i n t s303010

5-. 750

The f o l l o w i n g is an e x p l a n a t i o n cf the e l ement s considered in each ofthe f i v e evaluat ion categories:( 1 ) t t j n a n H e a l t h I m p a c t s ( 3 0 p o i n t s ) ; I m p a c t s o n human h e a l t h werej udged on a n t i c i p a t e d impacts of eacn a l t e r n a t i v e on a i r , Boil and water inth e r e g i o n , that could p o t e n t i a l l y a f f e c t t h e h e a l t h o f humans. H u n a ncontact w i t h a f f e c t e d ground water , r u n - o f f and run-or water, air in thes i t e area, and s i t e s o i l s were considered d u r i n g both the remedial a c t i v i t i e sand a f t e r c l e a n u p of th<* s i t e . One-half of the category weight was a l l o t e df or impact s d u r i n g construct ion, and one-half f or a f t e r construction.A l t e r n a t i v e s a n t i c i p a t e d to have small adverse e f f e c t s on human h ea l threceived h i c h p o i n t s . A l t e r n a t i v e s a n t i c i p a t e d to have large adversee f f e c t s on human h e a l t h received low po in t s .( 2 ) F e a s i b l i t y a n d Performance ( 3 0 p o i n t s ) : F e a s i b i l i t y o f eacha l t e r n a t i v e was j u d g e d based on the a p p l i c a b i l i t y and degree of s o p h i s t i c a t i o nof the a l t e r n a t i v e . Performance of each a l t e r n a t i v e was rated on itsp o t e n t i a l t o a c c o m p l i s h f o u r main o b j e c t i v e s : ( 1 ) raise s i t e above 100-yo3rf l o o d p l a i n , ( 2 v ide adequate s i t e d r a i t a g e , ( 3 ) treat s p e c i a l was t e s .a n d ? 4 ) c on t ro l o f f - s i t e n i g r a t i i o r . o f c o n t a m i n a n t s . A l t e r n a t i v e s j u d g e dto be the most f e a s i b l e and most e f f e c t i v e in a c c o m p l i s h i n g the o b j e c t i v e swere g i v e n the most p o i n t s . A l t e r n a t i v e s j u d g e d to be less f e a s i b l e ande f f e c t i v e were given lower p o i n t s .

( 3 ) Environmental I m p a c t s ( 1 C p o i n t s ) : Each a l t e r n a t i v e w a s evalu-ated u s i n g t w o main c r i t e r i a : C D impac t s d u r i n g construct ion (shortterr.) a n d ( 2 ) impac t s under normal c o n d i t i o n s ( l o n g t e r m ) . These evalua-t i on c r i t e r i a i n c l u d e environnental impac t s on a i r , water and s o i l . F a c t o r ss p e c i f i c to the s i t e considered were: degree of contaminant h a z a r d , a v a i l -a b i l i t y o f p a t h w a y s f o r contaminant movement, a n d s e n s i t i v i t y o f p o t e n t i a lreceptors. The above items were considered in j u d g i n g each a l t e r n a t i v e ' simpact on a i r , water and s o i l . A l t h o u g h enviroranental impact s are a l l o c a t e donly I ' 1 " * p o i n t s i n t h e e v a l u a t i o n , p er formance { 3 0 p o i n t s ) a n d human h e a l t himpact s ( 3 0 p o i n t s ) a r e d i r e c t l y r e la t ed t o a l t e r n a t i v e e f f e c t i v e n e s s i nn i t i g a t i n g s i t e s p e c i f i c environmental problems. T h e eva lua t i on o f environ-mental i m p a c t s was t h e r e f o r e l im i t ed tc the immediate ( d i r e c t ) and longterm inpact o f i m p l e m e n t i n g the a l t e r n a t i v e . H i g h p o i n t s were given toa l t e r n a t i v e s that were j u d g e d to have lew environmental impac t s and lowp o i n t s were given to a l t e r n a t i v e s j u d g e d to have h i g h environmental i m p a c t s .^ 4 * "^imeliness ( p o t e n t i a l f o r p h a s i n g ) ( 5 p o i n t s ) : Each a l t e r n a t i v ewas reviewed to determine which a c t i v i t i e s may be conducted i n d e p e n d e n t l y

and which a c t i v i t i e s must be conducted concurrent ly. A l t e r n a t i v e s whichwere j u d g e d to have the greate s t f l e x i b i l i t y ( a c t i v i t i e s which may beconducted i n d e p e n d e n t l y ) were awarded h i g h p o i n t s . A l t e r n a t i v e s whosea c t i v i t i e s could not be i s o la t ed f r o n on** another were awarded low p o i n t s .

CM00CMo

-8-The e f f e c t i v e n e s s of each a l t e r n a t i v e was evaluated on a basis of750 po s s iDle total p o i n t s , and juoged in each ot the f o u r categories onan absolute scale f r o n 1 to 10 (10 considered e x c e l l e n t , 1 consideredpoor* . Environmental I i n p a c t s were d i v i d e d into t« groups —— short termand I o n ; term. I m p a c t s curing cons truc t i on (short t e r m ) were a l l o t t e d 30%and i-i^acts a f t e r construction ( l o n g t e r m ) were a l l o t t e d "?Q% of the environmenta limpact category ra t ing . The l to 10 ratings for each category were m u l t i p l i e dby the respective to ta l p o s s i b l e p o i n t s for each category to ob ta in atotal we ighted a^rage e v a l u a t i o n score tor each a l t e rna t iv e .The cost of i n s t a l l i n g or i m p l e m e n t i n g each a l t e rna t iv e was e s t j j n a t e oto be compared against their e f f e c t i v e n e s s . A l i s t of i n d i v i d u a l costitems es t imated tor each a l t ernat ive is presented below:

engineer ing Des ignM o t x l i z a t i o nInsurance and BonesTemporary I n s t a l l a t i o n sTransport at ionwater TreatmentContaminant T r e a t m e n t

0 S i t e C l e a n u p0 S e c u r i t y0 Land I j e a s e0 R e p o r t i n g0 Disposal0 Equipment CleanupO&M CostsT h e f o l l o w i n g t a r l e i l l u s t r a t e s t h e r e s u l t s o f t J i e e v a l u a t i o n :

E V A L U A T I O N R E S U L T SM A X I M U M

E V A L U A T I O N C A T E G O R Y P O S S I B L ESCX)RE

A l t e r n a t i v e N o .

E j F F E C T r V E N E S S F A C T O R SHunan H e a l t h 300

I m p a c t sF e a s i b i l i t y and 300PerformanceEnvironmental 100

I i n p a c t sT i m e l i n e s s 50E f f e c t i v e n e s s Scores 750COSTCost Es t imate ( S K ;

200 18$ 235 192.5 240

175 192.5 23~>.5 230 250

63.5 70.7 76 71.3 76

35 36.7 37.5 20 18.3474 485 583 514 534

31,604.2 1,344.8 2,104 2,085.2 2 , 4 9 7 / 4

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-9-3ased on t h i s e v a l u a t i o n , a l t e r n a t i v e s 6 and 8 are more e f f e c t i v e thanthe other a l t e r n a t i v e s , but roughly comparable to each other. A l t e r n a t i v e 8is s l i g h t l y more p r o t e - t i v e of human h ea l th and is also expected to p e r f o r mbe t t er over an extended period of time. A l t e r n a t i v e 6 can De implementedsooner and it costs le s s . O v e r a l l , A l t e r n a t i v e 8 is more e f f e c t i v e thanA l t e r n a t i v e 6 in that i t prov id e s the h i g h e s t l eve l o f p u b l i c h e a l t h p r o t e c t i o nand tne best long-term r e l i a b i l i t y .

C o n m u n l t y Rela t i on sDocuments made a v a i l a b l e for p u b l i c content inc luded the RemedialI n v e s t i g a t i o n and F e a s i b i l i t y S t u d y r epor t s , two addenda t o t h e F e a s i b i l i t yreport , the d r a f t Record of Deci s ion (ROD)* and a copy of tne press releaseannouncing the ccmraent per iod. The p u b l i c concent perico for the s e l ec teda l t e r a t i v e was held December 2 through Decenoer 23, 1983. A press re leasewas issued announcing th i s on November 23, 1983. A p u b l i c mee t ing was h e l dat tne Grand P r a i r i e C o r a r u n i t y C e n t e r on Decefnber 15, 1983. Two represen-

t a t i v e s f r c r r TWR and two f r o m EPA were p r e s e n t . W i l l i a i r , B. H a t h a w a y( E P A , Regicn V I ) gave a general p r e s e n t a t i o n o n b u p e r f y n c a n d t h e k e ya l t e r n a t i v e s a n d C h a r l e s F a u l d s ( T D W R ) presented t h e t e chn i ca l d a t a f r o nthe s t u d y . Cont en t s received at the m e e t i n g were ail f a v o r a b l e , e x p r e s s i n gc o n f i d e n c e in and thanks to EPA for th e i r t i m e l y res^jonse to the problemat tne Bio-Ecology s i t e . W r i t t e n corrents were received try three of the

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p o t e n t i a l r e s p o n s i b l e p a r t i e s . Response sRespons ivene s s SurmBry a t t a c h e d . these ccnrents are in the

Recormended A l t e r n a t i v eS e c t i o n 300.68 ( j ) o f t h e N C P s t a t e s t ha t "The a p p r o p r i a t e ex tent o fremedy s h a l l be de termined by the lead a g e n c y ' s s e l e c t i o n of the r emedia la l t e r n a t i v e wh i ch t h e agency ' d e t e r m n e s i s c o s t - e f f e c t i v e ( i . e . t h e lowestcost a l t e r a t i v e that i s t e c h n o l o g i c a l l y f e a s i b l e and r e l i a b l e and whiche f f e c t i v e l y m i t i g a t e s and minimizes damage to ana p r o v i d e s adequate p r o t e c t i o nof p u b l i c h e a l t h , w e l f a r e , or the e n v i r o n m e n t ) . " It i s EPA p o l i c y to considerthe degree to wh*ch a remedy under CEHCLA is consistent wi th other environmentallaws and r egu la t i on s in d e t e rmin ing w h e t l i e r that remedy provide s f u l l yadequate p r o t e c t i o n to human h e a l t h , w e l f a r e , and the environment.A l t e r n a t i v e 8 c o m p l i e s w i t h RCRA requirements for a hazardous wastel a n d f i l l and also would inc lude ground water m o n i t o r i n g to de termine i fthere i s contamination that ha s a l r eady migrated f r o m th e s i t e . If groundwater c on tamina t i on is d e t e c t ed beyond the waste management boundaries ofLne l a n d f i l l , RCRA would al so require i m p l e m e n t a t i o n of a corrective a c t i onprogram. The l ined l a n d f i l l w i t h a l ea cha t e c o l l e c t i o n and cap system wouldhave a h i g h degree of r e l i a b i l i t y for c on ta in ing the wastes p l a c e d in thel a n d f i l l ,The f e a s i b i l i t y s tudy also evaluated another source control remedy( A l t e r n a t i v e 6 ) which provided a degree o f p r o t e c t i o n somewhat l e s s ' t h a nthat of the f u l l y pro t e c t i v e /RCRA consistent remedy but at s l i g h t l y lesscost.

-11ive 6 inc lude s the i n s t a l l a t i o n of a 60-foot s l urry trench aroundthe p e r ime t e r of the s i t e , r a i s i n g the s i t e above the 100-year f l o o d p l a i n ,s t a c : l : : i n g the w a s t e s , cons truct ion cf a c l a y c a p , and construction of afence. The cap and s lurry w a l l , keyed in t o an uipenwable stratum, areexpected to be e f f e c t i v e for an extended period in pr ev en t ing migrat ion ofw a s t e s beyond the s i t* boundary. H o w e v e r , A l t e r n a t i v e 6 does not treatg r o u r j water c o n t a - T i n a - i i o n w i t h i n th e s i t e boundary, a s would a f u l l RCRAremecy. In a d d i t i o n , the s l u r r y wail i s s u s c e p t i b l e to leakage over tirodue to p o s s i b l e long-term increase in p e r m e a b i l i t y . In contra s t , s y n t h e t i cl i n e r sy s t ems , corrfcined w i t h l ea cha t e c o l l e c t i o n , are expected to be e f f e c t i v ei n d e f i n i t e l y given the nature of the wastes present at the Bio-Ecology s i t e .Long-term ground wat er moni tor ing o u t s i d e of the containrent c e l l shou ld bes u f f i c i e n t t o detect any l eakage . If necessary, i m p l e m e n t a t i o n o t a correctivemeas j r e addr e s s ing the leakage would oe p e r f o r m e d .

The remainder of the a l t e r n a t i v e s eva lua t ed were c l e a r l y not as e f f e c t i v eor r e l i a b l e as e i t h e r A l t e r n a t i v e s 8 or 6. A l t e r n a t i v e s 4 and 5, a l t h o u g hle s s c o s i l y , are rot as r e l i a b l e as A l t e r n a t i v e b. T h o s e a l t e r n a t i v e s propo s ea 5 h a i i » s l u r r y trencr cons true t ea i n t o t n e a l l u v i a l sys t en. T h e a l l u v i a ld e p o s i t s are act a goco t i e- in s t r a t u m ;ar a s l u r r y wal l because of thepresence o* secondary s t ruc ture s of s l a c k e n s id e s and f i s s u r e s . T h i s woulda l l o w grrund water to f l o w into and through the containment area. T h e r e f o r e ,a l t e r n a t i v e s 4 and 5 pose1 a h i g h e r ri sk for waste m i g r a t i o n . A l t e r n a t i v e 7,a l thoug" less c o s t l y thar. a l t e r n a t i v e 3, is less r e l i a b l e due to long-termincreases in p e r m e a b i l i t y s i m i l a r t o the prob l e tr s described for A l t e r n a t i v e 6 ,The p o t e n t i a l r e s p o n s i b l e p a r t i e s al so proposed a remedy which would capth e s i t e t x j t d i d no t inc lude waste s t a b i l i z a t i o n o r f i x a t i o n . T h e i r p l a n doesnot propo s e e i t h e r a d e e p s l u r r y w a l l or a s y n t h e t i c l i n e r system. T h i sremedy .".as poor r e l i a b i l i t y and does not a d e q u a t e l y c on ta in the wastes.A l t e r n a t i v e s 4, 5, 6 ar,d 7 dc not c o t p l y w i t h RCRA te chni ca l requirements.K i z a r d o - s wastes in each a l t e r n a t i v e are removed, s t a b i l i z e d a n d / o r f i x e d ancp lac ed mtr new or expanded trenches. T h e s e a l t e r n a t i v e s do not c o m p l y w i t hPart 2 6 4 . 2 5 1 ( a } and 2 6 4 . 3 0 1 ( a ) of RCRA technical requirements ( d e s i g n ando p e r a t i n g requirements f o r waste p i l e s a n d l a n d f i l l s ) . T h e a l t e r n a t i v eproposes 5y the p o t e n t i a l r e s pon s i b l e par t i e s is not cons i s t ent w i t h theseRCRA tec-meal r e g u l a t i o n s .Based on t h i s analys i s . A l t e r n a t i v e 8 is the least cost o p t i o n thata d e q u a t e l y p r o t e c t s p u b l i c h e a l t h , w e l f a r e , and the environment and i scons i s t ent: w i t h other environmental acts. T h e r e f o r e , A l t e r n a t i v e 8 i s theE-ecortiTier:ded c o s t - e f f e c t i v e remedy. D e t a i l s of the reccnraended a l t e r n a t i v eare show^ in F i g u r e s 6 and 7. The recorroended remedy inc lude s ground watermon i t o r ing . If e x i s t i n g ground water contamination i s f o u n d beyond th eboundaries of the containment c e l l , EPA w i l l make a separate eva luat ion todetermine whether a corrective action program is consistent wi th the NCP.P r e s e n t l y , a v a i l a b l e i n f o r m a t i o n i s i n s u f f i c i e n t to determine the need f o r ,and cost of, such a program.

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-11-S i n c e the s i t e is located ir. the 100-year f l o o d p l a i n , theof Execu t ive Order No. 11988 covering F l o o d p l a i n Management

A F . a o d p . a i n Management Asses sment wa s prepared ( A d d e n d u m 1) f or th eramecy. T h i s assessment concludes that the proposed remedy w i l l notcreate a s u b s t a n t i a l r i s k to p u b l i c h e a l t h or the environment due to a100-year f i o o d i f c e r t a i n measures a r e f o l l o w e d . T h e r e s p o n s i b l e governmentagencies -nl h* contacted dunr.; the d e s i gn s tage to ensure that tne 'reccmendations are u r p l e m e n t e d ." T e n t a t i v e S c h e d u l e

C o r p l e t e Enfor c ement N e g o t i a t i o n sS i g n RODI s s u e A d m i n i s t r a t i v e OrderCocpera t iv e Agreement Amendment(to f und and to incorporate tne d e s i g nS t a r t DesignC c r p l e t e Des igrS t a r t C l e a n u pC c n p i e t e

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COST SUMMARY - ALTERNATIVE 8S T A B I L I Z E A M D C O N S O L I D A T E W A S T E S I N S Y N T H E T I C / C L A Y L I N E S CELL A N D C A P

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1 . T e m p o r a r y S i t e P e r i a e t t r D i f c e / D i t c h2 . E x c a v a t i o n o f S p e c i a l W a s t e s3 . T r e a t m e n t o f S p e c i a l W a s t e s4 . B a c * f i l l S p e c i a l H a s t e s5 . E x c a v a t i o n o f S l u d g e W a s t e s6 . S t a b i l i z a t i o n o f S l u d g e w a s t e s? . B a c k f i l l o f S l j d g e wa s t e s8. E x c a v a t i o n o f C o n t a m i n a t e d S o i l9 . B a c k f i l l o f C o n t a m i n a t e d S o i l10. Excavat ion of Lined C e l l1 1 . S y n t h e t i c / C l a y L i n e r ( W / L e a c h a t e

C o l l e c t i o n1 2 . B a c x f i l l o f HOP. C o n t a m i n a t e d S o i l1 3 . S y n t h e t i c / C l a y C o v e r / C a p1 4 . T e a p o r a r y S t o r a g e A r e a D i k e

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A D D P C T K 1Bio-Ecology S y s t e m s , I n c . , S i t eGranc P r a i r i e , T e x a s

Remedial A l t e r n a t i v e s A n a l y s i s ( 1 )FLOOD P L A I N M A N A G E M E N T A S S E S S M E N T

I . PurposeThe purpose of t h i s addend jm i s t i:1. Review Exe cu t iv e -Order Nc. ; 1 9 3 3 , May 24, 1977, 42 F. R. 26951e n t i t l e d F l o o d ^ l a i n Management .2. Review a p p l i c a b l e s t a t u t e s r e f e r r e d to in the Execu t ive Orderas required.3. Review tne B i o - E c c i ' . > g y ? . t e F . t f l t e c i a l A l t e r n a t i v e s A n a l y s i s inareas d i s c u s s i n g f l o o d p : a i ^ nanagement.4. S u n m a r i z e the review an-:: de s cr ib , a d d i t i o n a l technical requirementst o c c t n p l y w i t h a p p l i c a b l e r equirrment s .

I I . I n t r o d u c t i o nT h e S i t e I n v e s t i g a t i o n repor- ( 2 i d ev e l op ed a h y d r o l o g i c a l d e s c r i p t i o nand a n a l y s i s of the B i o - E j o l o n y s i t e a^ j is presented in part in t h i saddendum as f o l l o w s :The Bio-Ecology s i t e i s .oca~.ec :r tne W e s t F o r k of the T r i n i t yP.iver water shed. S o e c i : i c a i l y , - ie s i t e is located at the mouthof the M o u n t a i n Creek w a t e r s h e d , oownstream of the M o u n t a i n CreekLake and Dam, A s m a l l t r i b u t a r y of Old M o u n t a i n Creek f l o w salong the north, east and sou thern boundaries of the s i t e . TwoU . S . G e o l o g i c a l Survey G a u g i n g S t a t i o n s N o . 08050C50 a n d OMBOiuuare located up s t r eam and downstream of the s i t e , r e s p e c t i v e l y .S t a t i o n No. 08050100, M o u n t a i n Cree* a t Grand P r a i r i e , T e x a s , ha sbeen in o p e r a t i o n since 1960. The U.S. G e o l o g i c a l Survey m a i n t a i n sthe s t a t i o n which is l o ca t ed on the north s ide of J e f f e r s o n Boulevard( S t a t e H i g h w a y 8 0 ) . For the period o f record noted above, themaximum d i s charge recorded in M o u n t a i n Creek was 38,100 f t . 3 / s e cwhich occurred on A p r i l 19 , 1976 (gauge n e igh t 24.21 f t) . However ,the maximum water level recorded at th ;.s s i t e was 24.62 f e e twhich occurred on May 7, 1969.

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-2-Drainage in M o u n t a i n Creek is a f f e c t e d by- the volume of releasesj»ede at the M o u n t a i n Creek Dam and tne fcacV wat er e f f e c t s of theWes t F o r k o f the T r i n i t y River. A p p r o x i m a t * ly 36 square mi l e sof watershed are drained ups tream f r o m the s i t e . The U . S . AmyC o r p s o f Engineer s h a s e s t i m a t e d t r y f o l l o w i n g water s u r f a c ee l e v a t i o n s a t the J e f f e r s o n B o u l e v a r d cro s s ing c f the creek:

25-year frequency50-year frequency100-year frequencyE l e v a t i o n 433.0E l e v a t i o n 434.5Eleva t i on 436.0

Based on these e l e v a t i o n s , it is e s t imated the 100 year frequencye l e v a t i o n in the v i c i n i t y of the s i t e w i l l be a p p r o x i m a t e l y 437.00f e e t above mean sea l eve l . U s i n g t h i s e l eva t i on , a p p r o x i m a t e l y 75percent o f the s i t e i s located w i t h i n the 100-year f l o o d p l a i nas shown in F i g u r e 23.The s i t e is also located in a h i g h hazard zone (as d e f i n e d by theU . S . Army C o r p s c f E n g i n e e r s ; w i t h respect t o t h e M o u n t a i n CreekDam. In the event a f a i l u r e were to occur in the dam, it isl i k e l y that the f l o w v e l o c i t y and d i s charge s in the v i c i n i t y o fthe s i t e would be h igh . The T e x a s Department of W a t e r Resources,Dam S a f e t y G r o u p , has conducted a Phase I Dan S a f e t y A n a l y s i s ofthe s t ruc ture . T h e s e d a t a w i l l be considered in d e v e l o p i n g remedia lp l a n s f o r t h e s i t e .On a local l e v e l , the Bio-Ecology s i t e dra in s r a d i a l l y in alld i r e c t i o n s ( S e e 1 f t contours o f F i g . 2 3 ) . F r o m T e c h n i c a lP a p e r 4 0 " R a i n f a l l Frequency A t l a s o f t h e U n i t e d S t a t e s " , U . S .Department of Commerce, the 100-year 24 hour r a i n f a l l in thev i c i n i t y of the s i t e is e s t imat ed to be 10.50 inches. Basedon the s i t e t o p o g r a p h y , the s u r f a c e r u n o f f rate d e p e n d i n g onunit r a i n f a l l and type of cover w i l l range f r o m 0.75 to 1.75f e e t per second. T h i s rate o t r u n o f f has been s u f f i c i e n t tocause s u r f a c e erosion and hence s u r f a c e m i g r a t i o n of contami-nants d u r i n g p e r i o d s o f intense r a i n f a l l . T h e s u r f a c e migra-t ion of c on taminat i on has been t e m p o r a r i l y reduced by thep a r t i a l soi l covering p la c ed d u r i n g th e s i t e closure cpera t i onsin 1979.

I l l . Proposed S i t e Remedial A c t i o nThe proposed remedial action at the s i t e involve s the s t a b i l i z a t i o n ofon-site wastes , treatment and s t a b i l i z a t i o n of s p e c i a l wastes , and construc-t ion of a l a n d f i l l w i t h l i n e r , l eachate c o l l e c t i o n system, and clay cap.The f o l l o w i n g proposed cons truct ion and treatment a c t i v i t i e s are a n t i c i p a t e d

on the s i t e:

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1. A per imeter d i k e w i th a s h a l l o w interior drainage d i t c h w i l l t>eb u i l t around the s i t e o u t s i d e of the areas of known contamination. Thed i X e arid d i t c h w i l l c on ta in , d i v e r t , and store s u r f a c e water w i t h i n thes i te f or treatment a n d / o r d i s p o s a l . All waste mater ia l s t a b i l i z a t i o n andr « f i k s C - a l a c t i on a c t i v i t i e s w i l l b e p e r f o r m e d w i t h i n the diked area. Thetop c f the d i k e w i l l b e o f s u f f i c i e n t e l e v a t i o n to hold 100-year f l o o d w a t e r saway f r o m the work area.

The d i k e w i l l be removed a f t e r the remedial action is c o m p l e t e d .2. The spec ia l wastes ( c y a n i d e and ar s en i c) which have been i d e n t i f i e d

on-si te w i l l b e c h e m i c a l l y t r e a t e d , n e u t r a l i z e d , and d i spo s ed o f ( b u r i e d )in the on-site l a n d f i l l .

3. The waste s l u d g e s w i l l be excavated, s t a b i l i z e d , and r e p l a c e d int h e on-site l a n d f i l l .

4. • 1 1 Krten t i r e s i t e w i l l b e 00-year f o o d p l a i n .uo x5. A l a n d f i l l w i t h l i n e r and l ea cha t e c o l l e c t i o n sy s t em w i l l prevent

l a t e r a l m i g r a t i o n of c on taminant s f r o m the s i t e tnrough the ground water .6. A c lay cap w i l l be p l a c e d over the l a n d t i l l to m i n i m i z e s u r f a c e

i n f i l t r a t i o n . F e r t i l i z e d t o p s o i l w i l l be p l a c e d over t.ne cap and see<3ecito p r o v i d e a grass ccvsr.

7. Post closure m o n i t o r i n g of the s i t e w i l l be p e r f o rmed a f t e r theremedial a c t i on s are c o n p l e t e d .I V . ____

I n accordance wi tr . E x e c j t i v e Order 11988, F l o o d p i a i r . Manageraer.c ( 3 ) ,an a p p l i c a b l e e x e c u t i v e agency sha l l prov ide l e a d e r s h i p and s h a l l takeac t i on to recl.:e -ihe risk of f l o o d l o s s , to minimize the irrpact of f l o o d son human s a f e t y , h e a l t h and w e l f a r e , and to restore and preserve trie raturaand b e n e f i c i a l va lu e s served by f l o o d p l a i n s . In a d d i t i o n , an agency r\asthe r e s p o n s i b i l i t y to eva lua t e the p o t e n t i a l e f f e c t s o f any act ion thatmay be taken in a f l o o d p l a i n and to ensure that the d e s igr of the actionm i n i m i z e s p o t e n t i a l harm to or w i t h i n the f l o o d p l a i n .

As a part of the p r e p a r a t i o n of t h i s addendum, the f o l l o w i n g agencieshave beer, i d e n t i f i e d a s having f l o o d p l a i n nanagetnent. r e s p o n s i b i l i t i e s :

U . S . Environmental Prot e c t i on AgencyU . S , Arniy Corps o f EngineersT e x a s Department of W a t e r ResourcesC i t y of Grand Prair i e , Texa sF e d e r a l Emergency Management Agency

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— 4 —S p e c i f i c a l l y for Bio-Ecology s i t e remedial act ions, the proposed re-

med ia l act ion w i l l be d e s i g n e d , cons truc ted, o p e r a t e d , and maintained topresent the washout of any hazardous m a t e r i a l s by a 100-year f l o o d .

The l i s t e d agencies w i l l be provided w i t h the d e s ign and constructionsequence of any remedial actions to ensure that the actions meet the aboverequirement. The submi t t ed d e s i g n w i l l inc lude the construction of anytemporary f a c i l i t i e s d u r i n g the p er f ormance of the remedial ac t ion.

The EPA has de termined that s i t i n g and construction of the remedialaction w i t h i n the f l o o d p l a i n i s the only p r a t i c a b l e a l t e rna t iv e consistentwi th law. The only a l t e r n a t i v e s evaluated which would not require construc-tion of a permanent cap on the s i t e were the no-action a l t e rna t iv e andt o t a l excavat ion and removal of all contaminated soil and ground water.The no-action a l t e r n a t i v e i s incons i s t ent w i t h the NCP because i t f a i l s toaddre s s the threat o f f u r t h e r migra t i on o f wastes f r o m t h i s s i t e ; c o m p l e t eremoval and o f f - s i t e d i s p o s a l of all contaminated mat er ia l was not cost-e f f e c t i v e .V . F l o o d H a z a r d Assessment

Two m a j o r f l o o d hazaras exi s t at the Bio-Ecology s i t e . The s e hazardsare:

1. The 100-year f l o o d event2. The f a i l u r e of the M o u n t a i n Creek DamThe proposed remedia l ac t ion, at the s i t e involves the cons truc t ion

of a t emporary d i k e to prev^rt 100-year f l o o c w a t e r s f r a r t e n t e r i n g thes i t e , F l o o d w a t e r s could p o t e n t i a l l y wash away hazardous m a t e r i a l s f r c mthe s i t e w h i l e these m a t e r i a l s are b e ing treated and s t a b i l i z e d d u r i n g theremedial act ion.

The proposed remedial a c t i on a l so in c lude s ra i s ing the entire s i t eabove the 100-year f l o o d p l a i n to prevent the scouring of any m a t e r i a l saway f r c t t i the s i te . R a i s i n g the s i t e e l eva t ion w i l l not have an adverseimpact on the surround ing environment d u r i n g f l o o d i n g because the areabe ing raised is smal l when compared to a d j a c e n t areas in the f^od p l a i n *

Hie d e s i g n d e t a i l s of both the temporary d i k e and the impermeable capw i l l i n c l u d e prov i s i on s to prevent the erosion of the s ides of the t emporarydike and the s i t e cap dur ing f l o o d s less than or equal to the 100-yearf l o o d . Erosion p r o t e c t i o n a l t e r n a t i v e s i n c l u d e : { 1 } f l e x i b l e p ro t e c t i onsuch as rock r i p r a p or soil f a b r i c s ; (2) s o l id ( r i g i d ) pro t e c t i on such asconcrete r e t a i n i n g w a l l s o r gabions; ( 3 ) a n d vege tat ion pro t e c t ion.

The hazard c l a s s i f i c a t i o n of the Mounta in Creek Darn is considered h ighbecause of the deve lopment and hab i ta t i on on the M o u n t a i n Creek f l o o d p l a i ndownstream of the dam. Dams in the h i g h hazard category are those locatedwhere dam f a i l u r e may cause the loss of six or more human lives and exces-sive economic loss. However, an inspection of the dam did not f i n d any

hazardous condi t i on s at the dam.

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HO i iwEdiat e lY hazardous conditions exist at the Mountain Creek Damand Reservoir. The Am is in good condi t ion, and there are no seepagewater along the downstream toe. The downstream s lopes ,i twl s l i d e area, are in good condi t ion. The spr inkl er« . d i" * fl"" "*' of 9™f °" "* d C W nS^Mn?ors^illwav structure is sound and shows l i t t l e or no sign of cracking orsetting. Sf £t« and hoist ^chanisn* appeared to be in good condition.

In sumnary, the p r o j e c t is j u d g e d to be in good c ond i t i on .It i s , t h e r e f o r e , reasonable to conclude that the proposedactions at the Bio-Ecology s i t e w i l l not exh ib i t a sub s tant ia l risk to theenvir^nt or hunan health due to f l o o d i n g up to the 100-year f l o o d if

the f o l l o w i n g concerns are addre s s ed^1. The de s ign of the radial act ion is s u f f i c i e n t to prevent erosion

o f t h e ' t e n p o r a r y d i k e and s i t e cap d u r i n g f l o o d i n g .2 The M o u n t a i n Creek dam is operated and m a i n t a i n e d to ensure that

hazardous c o n d i t i o n s at the dam and reservoir do not d e v e l o p .3 The r a i s i n g of the s i t e above the 100-year f l o o d p l a i n does not

a d v e r s e l y tnpact .he current extent of the 100-year zone.T h e s e -oncerns w i l l be addre s s ed through the r e spon s i b l e agencies(See Son ™ d^nnc the d e s i g n ?hase of the re^dial ac t ions to ensure

the f l o o d h a z a r d s are m i t i g a t e d .

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Bio-Ecology Systems S i t eGrand Pra ir i e , Itexa sRemedial A l t e r n a t i v e s A n a l y s i s ( 1 )

BIO-ECOLOGY G R O U N D W A T E R M O N I T O R I N G P R O G R A M

I . PurposeItie purpose of t h i s addendum is to:1. Review the Bio-Ecology S i t e Remedial A l t e r n a t i v e s A n a l y s i s inareas d i s c u s s i n g a post closure ground water moni tor ing p lan.2. Describe in more d e t a i l a post c losure ground water p l a n . *

I I . I n t r o d u c t i o nT h e S i t e I n v e s t i g a t i o n report ? 2 ) p r e s e n t e d a d e s c r i p t i o n a n d a n a l y s i sof the Bio-Ecclogy s i t e h y d r o g e o l o g y and is presented in part in thisaddendum as f o l l o w s :The p r i n c i p a l a c j i f e r s c f L a l l a s County are sands o f th e T w i nM o u n t a i n F o r m a t i o n , the P a l u x y F o r m a t i o n , and the W o o d b i n eG r o u p . The P a l u x y and T w i n M o u n t a i n F o r m a t i o n s are presentDeneath the s i t s at about an e l e v a t i o n of -600 f e e t and -1450f e e t , r e s p e c t i v e l y . The W o o d b i n e is present £t about eleva-t ion *18C f e e t , or about 250 f e e t below e x i s t i n g ground sur fac e .The W o o d b i n e G r o u p i s the s h a l l o w e s t m a j o r a q u i f e r beneath theSio~Ecoiogy s i t e . The Woodb ine is a water table a q u i f e r whereit crops cut west of the s i t e ( T a r r a n t County and »ast D a l l a sC o u n t y ) , but beneath most of D a l l a s County it is artesian. Theprimary source of recharge for the Woodbine is r a i n f a l l on theoutcrop, with other sources cons i s t ing of s u r f a c e water seepagef r c m lakes and streams. Sand development is l imi t ed in the jWnodbine section in the s i t e area; consequently, th i s sectionwould not be considered a m a j o r section of the a q u i f e r in theregion.the Eagle Ford Group overlies the woodbine and is considered anaqui tard. The f a c t that the Woodbine a q u i f e r is ar t e s ian in thearea demons trate s th i s r e l a t i o n s h i p . The Eagle Ford is composeddcminant ly of shale. When sandy horizons are present* they are

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they are u s u a l l y d e n s e , rather I m p e r v i o u s , and do not c o n s t i t u t ec o n s i s t e n t l y porous water h o r i z o n s . E a r l y i n v e s t i g a t o r s character-ized th e E a g l e F o r d a s h i g h l y i n d u r a t e d , o f l a m i n a t e d character ,a n d i n t e r m i x e d w i t h s e l e n i t e g y p s u m i n m i n u t e l e n t i c u l a r c r y s t a l s .H a t e r f l o w i n g t h r o u g h t h i s f o r m a t i o n i s g e n e r a l l y b i t t e r a n d d i s -a g r e e a b l e to the ta s t e .I I I . P r o p o s e d S i t e R e m e d i a l A c t i o n

T h e p r o p o s e d r emed ia l a c t i on a t t h e s i t e I n v o l v e s t h e s t a b i l i z a t i o nof onsite was t e s , treatment and s t a b i l i z a t i o n of s p e c i a l wa s t e s , andc o n s t r u c t i o n o f a d e e p s l u r r y trench and c l a y cap around the s t a b i l i z e dand c o n t a m i n a t e d areas o f th e s i t e . The f o l l o w i n g p r o p o s e d con-s t r u c t i o n and t r ea tmen t a c t i v i t i e s are a n t i c i p a t e d on the s i t e :1 . A p e r i m e t e r d i k e w i t h a s h a l l o w i n t e r i o r d r a i n a g e d i t c h w i l lb e b u i l t around the s i t e o u t s i d e o f the ar ea s o f known c o n t a m i n a -t i o n . T h e d i k e a n d d i t c h w i l l c o n t a i n , d i v e r t , a n d store s u r f a c ewater w i t h i n t h e s i t e f o r t r e a t m e n t a n d / o r d i s p o s a l . A l l wastemater ia l s t a b i l i z a t i o n a n d r emed ia l a c t i o n a c t i v i t i e s w i l l b ep e r f o r m e d w i t h i n t h e d i k e d area. T h e t o p o f t h e d i k e w i l l b e o fs u f f i c i e n t e l e v a t i o n t o h o l d 100-year f l o o d w a t e r s away f r o n t t h ework area. T h e d i k e w i l l b e removed a f t e r t h e r e m e d i a l a c t i o ni s c o m p l e t e d .2 . T h e s p e c i a l w a s t e s ( c y a n i d e a n d a r s e n i c ) w h i c h have beeni d e n t i f i e d o n s i t e w i l l b e c h e m i c a l l y t r e a t e d , n e u t r a l i z e d ,a n d d i s p o s e d o f ( b u r i e d ) o n s i t e .3 . T h e was t e s l u d g e s w i l l b e e x c a v a t e d , s t a b i l i z e d , a n d r e p l a c e din the e x c a v a t e d areas o f the s i t e .4 . H a s t e s w i l l b e p l a c e d i n a n o n s i t e d i s p o s a l c e l l w i t h s y n t h e t i cl i n e r a n d l e a c h a t e c o l l e c t i o n sys t em a n d c a p p e d i n a c c ordanc ew i t h R C R A r e g u l a t i o n s ( 4 0 C F R p a r t 2 6 4 ) .5 . T h e e n t i r e s i t e w i l l b e ra i s ed above t h e 100-year f l o o d p l a i n .6 . P o s t c l o s u r e m o n i t o r i n g o f t h e s i t e w i l l b e p e r f o r m e d a f t e r t h er e m e d i a l a c t i o n s a r e c o m p l e t e d ,

I V . P r o p o s e d P o s t C l o s u r e G r o u n d w a t e r M o n i t o r i n g P l a nA g r o o n d w a t e r m o n i t o r i n g p l a n i s i n t e n d e d t o d e t e c t any m i g r a t i o n o fc o n t a m i n a t e d g r o u n d w a t e r f r o m t h e t r e a t e d a n d s t a b i l i z e d was t e s w i t h i nt h e c o n t a i n m e n t s l u r r y trench. T h e p r o p o s e d p l a n w i l l i n c l u d e t h e

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f o l l o w i n g i t ems:1 . I n s t a l l g r o u n d w a t e r m o n i t o r i n g w e l l s o f s u f f i c i e n t number a n dat th e a p p r o p r i a t e l o c a t i o n s and d e p t h s t o y i e l d groundwat ers a m p l e s f r o m t h e qua t ernary a q u i f e r . T h i s p l a n i n c l u d e s s i xt o e i g h t w e l l s around t h e d i s p o s a l c e l l c o m p l e t e d i n t h equa t ernary a q u i f e r . T h e exact l o c a t i o n s a n d d e p t h s , i n c l u d i n gw e l l screen l e n g t h s , w i l l b e d e t e r m i n e d i n t h e d e t a i l e d d e s i g nof the p > a n .2.

3.

A groundwat e r s a m p l i n g a n d a n a l y s i s p l a n w i l l b e d e v e l o p e d t oI n c l u d e t h e p r o c e d u r e s a n d t e c h n i q u e s f o r t h e f o l l o w i n g a c t i v i t i e s :a ) S a m p l e c o l l e c t i o n .b ) S a m p l e p r e s e r v a t i o n a n d s h i p m e n t .c ) A n a l y t i c a l p r o c e d u r e s i n c l u d i n g q u a l i t y contro lp r o c e d u r e s .d ) C h a i n o f c u s t o d y c on t ro l .P r i o r t o s a m p l i n g a g r o u n d w a t e r m o n i t o r i n g w e l l , t h e g r o u n d w a t e rs u r f a c e e l e v a t i o n s h o u l d b e mea sured .G r o u n d w a t e r s a m p l i n g a n d a n a l y s e s w i l l b e c o n d u c t e d q u a r t e r l yf o r t h e f i r s t year a f t e r t h e c o m p l e t i o n o f t h e r e m e d i a l a c t i o nt o e s t a b l i s h b a c k g r o u n d p a r a m e t e r c o n c e n t r a t i o n s i n t h e g r o u n d w a t e rA f t e r t h e f i r s t year, g r o u n d w e t e r s a m p l i n g a n d a n a l y s i s w i l l b ec o n d u c t e d s e m i - a n n u a l l y t o d e t e r m i n e whethe- there i s a s t a t i s t i -c a l l y s i g n i f i c a n t in cr ea s e over b a : * g r o u n d c o n c e n t r a t i o n s i n t h eg r o j n d w a t e r . I f a s t a t i s t i c a l l y s i g n i f i c a n t i n c r e a s e occursover background c o n c e n t r a t i o n s , EPA ard the T e x a s D e p a r t m e n t o fW a t e r R e s o u r c e s w i l l j o i n t l y e v a l u a t e t h e r e l e a s e t o d e t e r m i n e i fa d d i t i o n a l r e m e d i a l a c t i o n s a r e neces sary.T h e g r o u n d w a t e r a n a l y s e s s h o u l d d e t e r m i n e , a t a m i n i m u m , t h ef o l l o w i n g p a r a m e t e r s :

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A r s e n i cBariumC a d m i u mC h r o m i u mL e a dM e r c u r yS e l e n i u m

S i l v e rC y a n i d ePHS p e c i f i c C o n d u c t a n c eT o t a l O r g a n i c C a r b o nT o t a l O r g a n i c H a l o g e n

I n a d d i t i o n t o t h e above p a r a m e t e r s , o n e s a m p l e f r o m a down-g r a d i e n t w e l l a n d o n e s a m p l e f r o m a n u p g r a d i e n t w e l l w i l l b ea n a l y z e d f o r p r i o r i t y p o l l u t a n t s .5 . G r o u n d w a t e r m o n i t o r i n g w i l l c o n t i n u e f or a t l e a s t 30 yearsa f t e r t h e r emed ia l a c t i o n . A f t e r 3 0 years , t h e s i t e w i l lb e r e e v a l u a t e d t o d e t e rmine I f a d d i t i o n a l m o n i t o r i n g i sr equired.

R E F E R E N C E S

1. Remedial A l t e r n a t i v e s A n a l y s i s , Bio-Ecology S i t e , Grand Prair i e , T e x a s ,lexas Department of W a t e r Resources, J u l y 1983, Contract No. 14-300247.2 . S i t e I n v e s t i g a t i o n , Bio-Ecology S i t e , Grand P r a i r i e , T e x a s , T e x a s

Department o f W a t e r Resources, A p r i l 1963, Contract No. 14-30027.3. Executive Order 11988, 42 F.R. 2 6 9 5 1 , May 24, 1977 F l o o d p l a i n Management.

ff

4. Phase 1 I n s p e c t i o n Repor t , N a t i o n a l Dam S a f e t y Program, Mounta in CreekD a m , D a l l a s C o u n t y , T e x a s , Inventory N o . T X O Q 8 2 7 , U . S . Corps o f Engi-neers and T e x a s Department of W a t e r Resources, January 1978. CMCOOJo

ADDENDUM 3Bio-Eco\ogy Responsiveness Suronary

f o l l c w i n g responsiveness summary contains responses to Garmentsd u r i n g th e p u b l i c cement per iod . The f e a s i b i l i t y s t u d y reportand d r a f t RecorO of Decision T r a d e p u b l i c at that time ind i ca t ed a p r e f e r e n c ef^r A l t e r n a t i v e € (on-s i t e containment with a cap and s lurry w a l l ) . EPAhas determined that A l t e r n a t i v e 8 (on-si te containment in a l a n d f i l l w i t hl iner and leachate c o l l e c t i o n sy s t em) should be implemented because it isconsistent w i t h the a p p l i c a b l e RCRA technical regulat ions and providesgreater long-term r e l i a b i l i t y and there fore re sul t s in a level of protec t ionof p u b l i c h e a l t h , w e l f a r e , and the environment considered adequate t^> EPA. Of^i00CMO

Response ToThompson & K n i g h t Le t t e rCements on the Proposed Remedial A l t e r n a t i v eFor th e Bio-Ecology S i t eGrand Prair i e , TexasConsent - The EPA proposal, is not c o s t - e f f e c t i v e and containstechnical d e f i c i e n c i e sResponse

rat ionale for the s e l e c t i on of A l t e r n a t i v e 8 is set f o r t h in t h i sdocument in the section e n t i t l e d "Remedial I m p l e m e n t a t i o n A l t e r n a t i v eS e l e c t i o n . " The response to each, cemwsnt concerning a l l e g e d technicald e f i c i e n c y i s d e t a i l e d below.The f o l l o w i n g s t a t e sn en t s respond to the 8 p o i n t s mentioned on page s 2and 3 of the T h o m p s o n and K n i g h t l e t t e r d a t e d December 23 , 1983.

1. The cost of o b t a i n i n g permiss ion f r o m various landowners to constructa t emporary o f f - s i t e berm around the s i t e was not in c lud ed becauset h i s cost is expected to be n e g l i g i b l e . Permis s ion f r c m only twoa d j a c e n t landowners w i l l be required. In previous d i s cu s s i on s wi ththese landowner s , a w i l l i n g n e s s to cooperate was expres sed on t h e i rp a r t . One landowner has s p e c i f i c a l l y s t a t e d that t emporary i n s t a l l a t i o n son his p r o p e r t y were a c c e p t a b l e . Both par t i e s have expres sed a desireto "clean th i s mess up." It is t h e r e f o r e reasonable to assume thatl i t t l e more than s i m p l e a d m i n i s t r a t i v e expenses w i l l b e incurred. Itshould b e noted that th e f e a s i b i l i t y report (p . 64) i n c l u d e dconsideration of land lease costs. The omission of these minorcharges a s a l i n e i tem does n o t a f f e c t t h e v a l i d i t y o f - E P A ' s s e l e c t i o nof the a p p r o p r i a t e remedial o p t i o n ,2. The proposed s t a b i l i z a t i o n method w i l l not increase the p o s s i b i l i t yof excessive l eacha t e f r o m the s i te. A l t e r n a t i v e 8 o f f e r s thegreatest degree of pro t e c t ion against l eachate e s cap ing f r o m thss i t e; otherwise, only the "pick it up and haul it o f f " a l t ernat ivewould s i g n i f i c a n t l y decrease the p o s s i b i l i t y o f l eachate e s capingf r o m the s i te.3. Damage to the proposed cap f r o m erosion, d e s s i c a t i o n , and rootp e n e t r a t i o n w i l l be prevented or m i t i g a t e d by a regular opera t i ona la n d maintenance ( Q & M ) schedule.4. S t a b i l i z a t i o n a c t i v i t i e s w i l l be conducted w i th in a d iked area suchthat there w i l l be no increased s u r f a c e water release d u r i n g theremedial action. S i m i l a r to the proposed s t a b i l i z a t i o n a c t i v i t i e s ,

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*.

-2-backnoe excavations conducted during the site inve s t i ga t i on and airmoni tor ing curing this sane tin»e did not reveal any air release impactbeyond the immediate excavation area ins ide the site fence. H e a l t htnreats to employees engaged in remedial action are minimized throughth*» e x t en s iv e s a f e t y requirements mandated by EPA. All employees•engaged in raneoial act ion do so only under controlled conditions.T h i s one~tiiw5 risk under monitored and c o n t r o l l e d c ond i t i on s isprqposed in order to a l l e v i a t e the long-term risk to the p u b l i c of anuncontrol led site.

5. The environmental impl i ca t i on s of moving truckloads of soil to thes i t e are i n s i g n i f i c a n t w i th in the context of the environmentalapprovement a f f o r d e d by tne remedial ac t ion, the e x i s t i n g a d j a c e n tland uses, and the e x i s t i n g local t r a f f i c which induces -.overrent oft r u c k l o a d s of soil.6. P o n d i n g , other than t emporary s t o rage , w i l l not re sul t iron thecor..-*.ruction of the d i k e s ; th^s , there w i l l be no increased i n f i l t r a t i o n ,Dike s w i l l r e ta in storm water r j n c f f f r c t h e s i t e f o r t r e a t m e n t , i tnecessary, arid subsequent d i s p o s a l to the local munic ipal was tewatertreatment sy&wan*7. S t a b l i z a t i o n is necessary to prov ide load bearing c a p a c i t y fore q u i p m e n t used to empiace the c a p , ror the cap i t s e l f , and for f u t u r eopera t ions and maintenance a c t i v i t i e s . T e s t i n g has demonstrated thatfor the extreme worst case, l eachate q u a l i t y w i l l not be s i g n i f i c a n t l yimpacted by waste s t a b i l i z a t i o n ,8. R a i s i n g the s i t e above the 100-year f l c o d p l a i n is the most cost-e t f e c t i v e method for mee t ing the o b j e c t i v e o f p r e v e n t i n g m i g r a t i o n orwashout of wastes f r o m the s i t e dur ing a 100-year f l o o d . T h u s , r a i s i n gthe s i t e is not inconsis tent w i t h the N a t i o n a l Cont ingency Plan.

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I I . C O f f n e n t___^_ j £ A ' _ s _ a n a l y s e _ s o f a p p r o p r i a t e reamedies f a i l to i d e n t i f y andq u a n t i f y any danger to the~puklic h e a l t h , w e l f a r e , and~the environment.f t e spon s e

According to Sec t i on 3 0 0 . 6 8 ( e ) ( 2 ) of the NCP (source c o n t r o l ) , remedialactions may be a p p r o p r i a t e if a s u b s t a n t i a l concentration of hazardoussubstances remain at or near the area where the^ **ere o r i g i n a l l y locatedand inadequate barriers exist to retard migrat ion of substances in theenvironment. T h i s is e xac t ly the c ond i t i on at the B i o - E c o J o g y s i t e .The I n v e s t i g a t i o n Report documents the f o l l o w i n g condi t ions:

1 ) S i g n i f i c a n t waste quant i t i e s containing h i g h concentrationsof m e t a l s , cyanide:; , ard arcmatic organics are present at theBio*Ecology site,2) saventy-Cive p^reent of th* »ite is located within the 100-year f l o o d p l a i r and s u s c e p t i b l e to severe f l o o d i n g .

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1.

3 )

4 )

-3-M i g r a t i o n pathways and migra t i on Mechani s e s are present atthe s i t e for po t en t ia l s i g n i f i c a n t long-tern waste migrat ionto s u r f a c e and sub sur fa c e waters and a d j a c e n t areas.S u r f a ' j e c o n t a m i n a t i o n i n o f f - s i t e dra inage d i t c h e s f indtraces of subsurface contaminat ion in the quaternarygravel a q u i f e r beneath the site.

5) W a s t e migra t i on to date has been p r i m a r i l y restricted toon-site l o ca t ions wi th the e x c ep t i on o f past sur face o f f s i t em igra t i on caused by f l o o d i n g .ft) T a r g e t receptors currently impacted ar e a d j a c e n t land areas(dead and d y i n g v e g e t a t i o n ) and s u r f a c e waters.

The NCP f u r t h e r s t a t e s that i f source control remedial act ions arede t ermined to be needed, these act ions may i n c l u d e a l t e r n a t i v e s tocontain the hazardous substances where they are located or to e l i m i n a t ep o t e n t i a l contaminat ion by t r a n s p o r t i n g the hazardous substances to anew loca t ion. It was determined by TDWR and EPA, based on the f i n d i n g sof the I n v e s t i g a t i o n P e p o r t , that on-site source control remedial act ionis needed to a d e q u a t e l y protect p u b l i c h ea l th and the environment.T t i e c r i t e r i a d eve l oped in sect ion 3 0 0 . 6 8 ( e ) ( 2 ) ( i ) were assessed in theI n v e s t i g a t i o n / F e a s i b i l i t y Report. They are the f o l l o w i n g :The extent to which subs tances pose a danger to p u b l i c h e a l t h , w e l f a r e ,or the environment i n c l u d e the f o l l o w i n g f a c t o r s : -A. the p o p u l a t i o n at r i sk was d i s cu s s ed in general terms throughoutthe report and is de l ineated below:

1. A d j a c e n t ccmnercial auto salvage workers.2. Dcwnstream comnercial sur face water users.3- R e s i d e n t s of a nearby mob i l e home p-ark.4. Plane s and an imal s ,5. F u t u r e s h a l l o w groundwater users.

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B. Amount and f o r m of the substance pre s ent:cubic yards of s l u d g e s w i t h : A p p r o x i m a t e l y 40,000

1. Conta iner i z ed waste s , seme of unknown d e s c r i p t i o n .2. Perched water in and around the wastes.3. Large quan t i t i e s of j e l l y - l i k e waste of a. f l o w i n g consistency4. Contaminated soi l .

C. H a z a r d o u s p r o p e r t i e s of the substances inc lude:1. Poison* - OJ, A r s e n i c , and various metals .2. Carcinogens - PCB, chrome, ch l or ina t ed Benzene.3. Corrosiv«es - containerized acids.4. React ives - CN, Red pho sporou s , p i c r i c ac id .5. P r i o r i t y p o l l u t a n t s .

D. H y d r o g e o l o g i c a l f a c t o r s are discussed e x t e n s i v e l y in theI n v e s t i g a t i o n and F e a s i b i l i t y Report, The a l l u v i a l d e p o s i t s havea secondary structure of cracks and f i s s u r e s capable of t r a n s m i t t i n gcontaminants.

E. C l i m a t i c f a c t o r s of concern are:1.2.

R a i n f a l l c a u s i n g f l o o d i n gR a i n f a l l c a u s i n g f l o o d i n g .Dry p e r i o d s cau s ing d e s s i c a t i o n of s o i l s and a l l u v i u m .2. Contaminant m i g r a t i o n at the present time is r e s t r i c t e d to the v i c i n i t yof the s i te . The only adequate barrier p r o v i d i n g contaiment at thes i te is a natural geo log i ca l f o r m a t i o n , the E a g l e F o r d shale.3. EPA and TDWR experience s and approache s used in s i m i l a r s i t u a t i o n sare l i m i t e d , bu t g e n e r a l l y tend toward e f f e c t i v e c onta inment .4. Envirormental e f f e c t s arrf w e l f a r e concerns were discussed in thecontaminant m i g r a t i o n and targe t receptors sections of the I n v e s t i g a t i o n

Report .The NCP has no s p e c i f i c requirement to d e f i n i t i v e l y addre s s the extent orl i k e l i h o o d t o which i d e n t i f i e d substances could m i g r a t e f r c n the ircurrent l o ca t i on , p a r t i c u l a r l y w i t h i n the context of how q u i c k l y theywould nove, and in what concentrations they would be f o u n d , if they didnove. The d e v e l o j y f t s n t of an accurate and c a l i b r a t e d contaminant m i g r a t i o nis unnecessary for a source control s i tua t i on .The overr id ing o b j e c t i v e or per formance standard is to "control o f f s i t em igra t i on of wastes by s u r f a c e and sub sur fac e pathways". T h i s o b j e c t i v ealong w i t h others s tated in the F e a s i b i l i t y S t u d y a l l ow the de t erminat ionof A l t e r n a t i v e 8 as the a p p r o p r i a t e remedy for the site.

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I I I . - EPA was required to prepare an Environmental Impact statementF t e s p o n s e

is not require to prepare an Environmental i T i p a c t S t a t a n e n t foractions taken at S u p e r f u n d s i t e s . However, the remedial i n v e s t i g a t i o n /f e a s i b i l i t y s t u d y prepared a t t h i s s i t e addressed t h e hunan h e a l t hand environmental impac t s o f various response o p t i o n s , t h e i r f e a s i b i l i t yand r e l i a b i l i t y , and the costs of each a l t e r n a t i v e . In a d d i t i o n , EP4,has provided an o p p o r t u n i t y for p u b l i c review and cownent on E P V seva lua t i on of the s i t e and of the range of ren»dial opt ions considered.LA

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Response to E B H - S o u t h w e s t , I n c .Comments on theProposed f c a n e d i a l A l t e r n a t i v ef o r t h e Bio-Ecology S i t eGrand Pra ir i e , T e x a sI . Response to M a j o r Conments ( f r o m ERM report summary

1.

2.

3.

The data demonstrate that the gravel a q u i f e r is sub j e c tto contamination f r om wastes at the s i t e m i g r a t i n g through thesecondary structure of a l l u v i a l d e p o s i t s * The secondarystructure has been reported in geotechnical observations int h e T e x a s Department o f W a t e r Resources ( I t W R ) Bio-Ecology f i l e39009 ( N a t i o n a l S o i l Serv i c e , 1 9 7 8 ) and by Woodward & C l y d e Con-s u l t a n t s ( W C C ) S i t e I n v e s t i g a t i o n a n d Remedia l Report s f o r t h eBio-Ecology s i t e * T t i e ex i s t ence of secondary s t r u c t u r e i sf u r t h e r suppor t ed by sub sur fac e contaminant d i s t r i b u t i o n ins u b s u r f a c e s o i l s and groundwaters . Geo t e chn i ca l labora tory dataf u r t h e r s u p p l e m e n t the data.C o n s i s t e n t wi th a permanent remedy, s t a b i l i z a t i o n of the was te si s required in order to p r o v i d e load bearing c a p a c i t y . T h i s loadb ear ing s t a b i l i t y is required for equipment used to e m p l a c e a cap,for the cap i t s e l f , and for f u t u r e op era t i on and nvaintenance con-s id era t i on s . During the temporary closure, the i n v e s t i g a t i o n phaseof the p r o j e c t conducted by the TDWR, and the I n i t i a l RemedialMeasure conducted f c y t h e Environmental P r o t e c t i o n Agency ( E P A ) ,problems were encountered regarding i n s u f f i c i e n t load bearingc a p a c i t y for equipment at the s i t e .

As a secondary f u n c t i o n , waste s t a D i l i z a t i o n is expec t ed top r o v i d e scm? control o f laachate generation. In the F e a s i b i l i t yS t u d y , leachate t e s t i n g was conducted using h igh snear mix ingwhich re."ul';€d in the worst case l ea cha t e concentrations to beexpec ted under the f i e l d condi t ions .

The e f f e c t o f Joe Poole Reservoir being constructed upstreamf r o m the s i t e was not taken into account when d e t e rmin ingf l o o d p l a i n e levat ion at the site. It is the under s tand ing ofTDWR and EPA that when comple t ed in 1985 or 1986, the reservoirshould result in a lower 100-year f l o o d p l a i n e l evat ion. Thede s ign of the remedial a l t e r n a t i v e w i l l take this e f f e c t intocons iderat ion and w i l l be designed accordingly.

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4.

5.

-2-The F e a s i b i l i t y s tudy objec t ive "Prevent migration of wastesduring a 100-year f l o o d " is indeed prccedural ly correctand should replace the o b j e c t i v e , "Raise the s i t e above the: 00-year f l o o o ^ l a i n e levation." However, this w i l l not havea s i g n i f i c a n t inpact on the f i n a l remedial alternative,,Erosion consideration* w i l l be examined in d e t a i l during thedes ign of the remedial al ternative. The need to raise the s i t eabove the 100-year f l o o d p l a i n f o l l o w s only as a c o s t - e f f e c t i v ecomponent of a remedial a l t e rna t iv e which meets the ob j e c t iveof prevent ing migrat ion of wastes during a 100-year f l o o d .

6.

7.

acknowledges that cost savings may f o l l o w f r om consideringthe waste management practices for the northeast corner of thes i t e as proposed by E R M - S o u t h w e s t , Inc. T h e s e waste managementprac t i c e s w i l l be considered dur ing the de s ign phase of thep r o j e c t .The r emed ia l measure proposed by E R M - S o u t h w e s t , Inc. is nota c c e p t a b l e as e x p l a i n e d below. The ERM propo sa l does notaddress:

T r e a t m e n t o f s p e c i a l w a s t e s ;S t a b i l i z a t i o n o f waste s l u d g e s tor load bearing c a p a c i t yand e l i m i n a t i o n of perched water;Control of s u b s u r f a c e contaminant m i g r a t i o n through thesecondary s truc ture of the o l d e r a l l u v i a l d e p o s i t s ; andManagement of r a i n f a l l rurion and r u n o f f d u r i n g s i t econstruction.

I I . Response t o Comments ( E S M report section t w o )1. Deep S l u r r y Trench

The secondary s tructure of the o ld er a l l u v i a l d e p o s i t s issupported by data and references in both VCC projec t reports.T h i s support induce s f i v e separate bu t correlated f e a t u r e swhich enccropass geotechnical observations, contaminant dis-t r i b u t i o n in soi l s and groundwaters, and geotechnical labora-tory da ta .a. The boring logs in A p p e n d i x A of the S i t e I n v e s t i g a t i o nReport contain references to secondary s t r u c t u r i n g in theo lder a l luv ium. T h i s is a geotechnical observation by* ageo logi s t on the p r o f e s s i o n a l s t a f f of WCC. (ERM does notd i s p u t e these observations.)

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-3-Another geotechnical observation is made in reference tothe ver t i ca l transmissive paths of water through f i s s ur e sand s l i c k e n s ides of trie s t ra tum on pages 29 and 42 of theI n v e s t i g a t i o n Report, T h i s in reference to a report( N o . 4-78016-1) undertaken b y N F S / N a t i o n a l S o i l s Services ,Inc. , e n t i t l e d "Phase I Geotechnical I n v e s t i g a t i o n Indus-t r i a l W a s t e L a n d f i l l Bio-Ecology S y s t e m s , I n c . , Grand P r a i r i e ,Texas." It should be noted that this report was undertakenin A p r i l 1978 and has teen a part of the p u b l i c record ofTOW* f i l e No. 39009 for Bio-Ecology since at least February 201980. Tlie report is an i n v e s t i g a t i o n o£ subsurface con-d i t i o n s at the proposed indu s t r ia l waste l a n d f i l l s i te to thewest of the s i t e which was never constructed.The s i g n i f i c a n t statement of the report wi th regard tosecondary structure resul ted f r o n a dramatic and unusuald r i l l i n g phenomenon encountered in a l l s i x f i e l d boringsundertaken.

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d r i l l i n g method used was a rotary wash technique and thephenomenon is repeated below in its ent irety f r cm page 5or the NFS report,"There was no d r i l l water return* below d e p t h s of 8.0 f e e tin borinys 5-3, B-4 , B - S , and b-6, below 10.0 f e e t inboring B-l, and below 21.0 f e e t in boring 8-2. Allwater d i sappear ed in to cracks and f r a c t u r e s in theunderground f o r m a t i o n s , previous experience with thetype of c lays encountered has shown that during p e r i o d sof r a i n f a l l and higr. ground moi s tur e , the undergroundf r a c t u r e s and j o i n t s remain closed and impermeable.However , if tne c lay s are p e r m i t t e d to lose moi s ture ,or if the water tab l e is e x t r en i e ly deep as it is inthi s area, large cracks develop and the clays exhibitsub s tan t ia l p e r m e a b i l i t y . * The cracks may extendlarge d i s tance s in botn horizontal and vertical d irec t-ions, and can be either continuous or discontinuous.""The major problem wnich w i l l occur during the develop-ment of the s i t e as a l a n c J f . i . 1 1 is to e l i m i n a t e thenumerous large cracks and f i s sure s which are general lypresent below an approximate d e p t h of 8.0 f e e t asevidenced by the large water losses experiencec 'uringthe d r i l l i n g opera t i on s . Only because of the cracks,tne u n d e r l y i n g c lays are not pre s en t ly inpervious" .

-4-c. Contain nant d i s t r i o u t i o n in the s u J D s u r f a c e soils is dis-cussed on page 32 of the i n v e s t i g a t i o n report. WCC s ta te son page 33 tnat "the e l evated test r e su l t s shownin T a b l e 8 at d e p t h may be ind i ca t i v e of the l ead ing edgeof waste migration". T h i s is the type of contaminantd i s t r i b u t i o n expected f r o n contaminant m i g r a t i o n in asecondary s tructure.d. Contaminant d i s t r i b u t i o n in the groundwaters is discussedon page 33 of the i n v e s t i g a t i o n Report. The data r e su l t sof T a b l e 6 are discussed and the f o l l o w i n g pa t t ern isrevealed. "Data for on-site wells show higher l ev e l s ofn i c k e l , T C K , a n d T O C tnan f o r o f f - s i t e w e l l s , with leadand nickel exceeding EPA standards". T h i s is coupled wi tht h e s tatement that "Groundwater d a t a f o r w e l l s o f f - s i t ei n d i c a t e lead anci nickel exceed EPA s t a n d a r d s , wh i l e cadmiuml e v e l s a r e j u s t s l i g h t l y e l e v a t a j " . F r c m t h i s , W C C f u r t h e rs ta t e s that " S h a l l c w groundwater f l o w in the modem a l l u v i a ld e p o s i t s is expec t ed to be a d j a c e n t s tream beds and low areas,p l u s a por t i on of the f l o w v e r t i c a l l y downward toward thegravel layer".e. F u r t h e r evidence of secondary s tructure f o l l o w s f r c m anana ly s i s of the g eo t e chni ca l d a t a i t s e l f . Page 22 of thei n v e s t i g a t i o n report di s cus sed geo t e chni ca l t e s t i n g ands t a t e s that the d a t a were used to d e v e l o p the s h a l l o ws t r a t i g r a p h y . The g e o l og i ca l s e t t i n g i s also describedon page s 3-7 of the i n v e s t i g a t i o n report. WCC considersthese f a c t o r s in c o n c l u d i n g on page 42 of the I n v e s t i g a t i o nReport t h a t :

The o l d e r a l l u v i a l d e p o s i t s that u n d e r l i e the moderns ediments were d e p o s i t e d in a f l o o d b a s i n environmentand are carr^osed of low to h igh p l a s t i c i t y c lays . Asecondary soil s tructure c on s i s t ing of s l i cken s idesand f i s s u r e s due to cyclic shr inkage and s w e l l i n gdur ing seasonal changes is present in the s tratum.It i s ccntnon k n o w l e d g e among soil s c i e n t i s t s , civilengineers, and others that moisture loss in c lays causesshrinkage. At the s ur fa c e , this is evidenced by d i s t i n c t i v ev i s i b l e cracks in the soil. T h e s e were po in t ed out toERM personnel in a s i t e vi s i t on August 25, 1983. The s ecracks result f r c m f i e l d soil moisture which i s s i g n i f i -cant ly lower than at some point in the pa s t .

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. _ — — — , _ r . - „ . „ - . | . .. ._, ,.,. r.---^————,-——.

"The s i t e is s i t ua t ed w i th in the modern f l o c d p l a i n ofM o u n t a i n CreeK." "The s u r f i c i a l sediments at tne s i t e arerecent a l l u v i a l d e p o s i t s of Old Mountain Credc and wered e p o s i t e d in a f l o o d p i a i n meander." The s e s tatements conef r o n pages 3 and 5, r e s p e c t i v e l y , of the I n v e s t i g a t i o n Re-port. T h u s , at the time of d e p o s i t i o n in a f l o o d p i a i nenvironment, it is s a f e to assume that the a l l u v i a l d e p o s i t shad a s i g n i f i c a n t moisture content.Now consider the geotechnical test re sul t s of A p p e n d i x Cof the inve s t iga t iv e Report. The two determinations ofinterest are the f i e l d percent moisture and the p l a s t i cl i m i t of tne A t t e r b e r g L i m i t s series, these data are l i s t edin A p p e n d i x C and are g r a p h i c a l l y d i s p l a y e d on the boringl og s o f A p p e n d i x A f o r easier v i s u a l i z a t i o n . T h e f i e l dmoisture is the actual percent mois ture of undi s turbedsanpie s secured arc! sealed in the f i e l d for t e s t i n g in thelaboratory. The p l a s t i c l i m i t measures the iro i s ture con-tent of the soil at whicn the sarr^le crumbles when r o l l e dinto 3/8-inch threads ,

of the p l a s t i c l i m i t arc moisture content forthe a l l u v i a l d e p o s i t s at the s i t e reveal a s i g n i f i c a n tf e a t u r e . The bu lk of the d a t a reveals a mo i s t ur e contentwhich is near or belcw the p l a s t i c l i m i t . A total of 23d a t a pa ir s al low for the comparison. Out of the 23 pair sfor the a l l uv ia l c l a y s , 19 reveal a mois ture content w i t h i ntne rarye of concern. If the s u r f a c e pairs are d i s r e g a r d e d ,and the a l l u v i a l c l a y s are examined, only one s a m p l e p a i rshews a moi s ture content whicn is s i g n i f i c a n t l y hignerthan the p l a s t i c l i m i t .T h u s , the a l l u v i a l mater ial s were d epo s i t ed in a f l o o d p i a i nmanner which would give them a higher moisture content. Asthe d e p o s i t s were de s s i ca t ed to a lower f i e l d mois ture, themoisture change caused shrinkage. The shr inkage was mani-f e s t e d as secondary structure and is documented by thegeotechnical data.

T a k e n together as a whole, these f i v e po in t s conc lu s ive ly supportthe VCC I n v e s t i g a t i o n Report Conc lu s i on that secondary s truc tureis present and that m i g r a t i o n pathways and m i g r a t i o n mechanisms arepresent at the s i t e for p o t e n t i a l s i g n i f i c a n t long-term wastemigrat ion to subsurface.On page 2-2 of its report , ERM s tate s its c on fu s i on as to how weeconcluded the existence of s l i g h t contamination of groundwater on-pages 33 and 34 of the I n v e s t i g a t i o n Report. T h e s e data in T a b l e6 of the I n v e s t i g a t i o n Report c l ear ly show H?A standards as beingexceeded for lead and nickel.

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-6-confuse s the WCC di s cus s ion of sub sur face soil contaminationwhich sunrarizes the soil me ta l s data in T a b l e 2-1 and concludeson page 2-3 that "the heavy metal s content of the downgradientborings are e s s e n t i a l l y the same as the upgrad i en t boring." ERMs i r - p l y r e f e r s to soil v a r i a b i l i t y and ignores a d i s t i n c t i v e trend.S o i l s me ta l s downgradient increase in all but one case. For thedata present in ERM T a b l e 2-1, s o i l s me ta l s ::.crease downgradi entR6 percent of the time (fi o f 7) w i t h an average increase of82.7 percent. If the da ta were var iab l e , there should be no trend.

Other so i l s m e t a l s trends noted by WCC are d i smi s s ed by ERM as"probably" a natural geologic phenomenon without an exp lanat i on oreven a s u p p o s i t i o n and wi th no s u p p o r t i n g d a t a .FRM d i s c u s s i o n o f quaternary gravel water q u a l i t y d i f f e r s f ronWCC b a s i c a l l y in the i n t e r p r e t a t i o n of contaminat ion source. EflMa p p a r e n t l y considers u p g r a d i e n t and downgradi en t sonewhat f i x e dand does rot recognize the p o s s i b i l i t y of groundwater c o n t a m i n a t i o nf r c n the hazardous waste s i t e i t s e l f . VCC (on page 42 of theF e a s i b i l i t y R e p o r t ) recognizes that "groundwater f l o w i s s u b j e c t t ochange d e p e n d i n g on s i te conditions." T h u s , the h i s t or i ca l down-grad i en t w e l l , ow-6, is not nece s sar i ly downgradi ent at all times.WCC al so recogni2Ps (on page 33 of the I n v e s t i g a t i o n Report* that" s h a l l o w groundwat er f l o w in the modern a l l u v i a l d e p o s i t s i s ex-pec t ed to b e f r o m onsite ( w i t h i n f enc ed a r e a ) to o f f s i t e (out-s ide of f enced a r e a ) to a d j a c e n t stream beds and low j r e a s , p l u sa port ion of the f l o w v e r t i c a l l y downward toward the remnantgravel layer.** Th-s contaminant m i g r a t i o n could e a s i l y be extendedin the modern a l l u v i a l d e p o s i t s to a po int u p d i p ( n o r t h ) of theu p g r a d i e n t wel l OW-1. T h u s , the ERM conclus ion on page 2-7 that"*-.his s h a l l o w a q u i f e r is not s u i t a b l e use for hviran consunptioneven if the Bio-Ecology s i t e did not e x i s t , " is not f u l l ys u p p o r t e d .EPM p r o p e r l y noted that the Bio-West monitor well was screened foralmost its entire l e n g t h and that it should be p l u g g e d as a part ofthe r«nedial p l a n ,A l t h o u g h the WCC report s tates that the r e s i d en t ia l developmentis u n l i k e l y w i t h i n certain d i s t a n c e s of the s i t e , the TDWR and theEPA have no control over land deve lopment . If certain improvementswere made, the land could be d eve l oped .The reference in the I n v e s t i g a t i o n Report ( p a g e 46) regarding lowy i e l d is w i t h i n the context of central n t u n i c i p a l s u p p l i e s , t f r i e con-t a m i n a t i o n re ferenced is l i k e l y to be f r o m bacterial or othernon-hazardous contamination as the reference ( M o r g a n , 1 9 6 5 ) r e f e r sto the d r i l l i n g to under lying artesian sands in the 1880*s timeframe. It in no way i m p l i e s that the groundwater cannot be usedby i n d i v i d u a l s .

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Public desire to contain the contamination at the s i t e wasexpressed ^t the p u b l i c meet ing regarding the s i t e conductedon December 15, 1993, in Grand Prair i e . A d d i t i o n a l l y , ana d j a c e n t auto yard owner/operator expressed an interest to uses h a l l o w groundwater. One sha l l ow well has been docimented inthe area. T h u s , w i t h i n the context of a permanent s o l u t i on ,pro t e c t i on of the sha l l ow a q u i f e r i s c l e a r l y a p p r o p r i a t e .2. S t a b i l i z a t i o n of Was t e

The remedial a l t e r n a t i v e selected by EPA includes wastes t a b i l i z a t i o n in order to provide load bearing capacity.T h i s load bearing s t a b i l i t y is required for equipment used toenqplace a cap, for the cap i t s e l f , and for f u t u r e operat ionand maintenance considerations.Leachat e t e s t i n g in the f e a s i b i l i t y report was undertaken asa "worst-case" t e s t . T h i s was to ensure that s t a b i l i z a t i o ndid not s i g n i f i c a n t l y impair l ea cha t e q u a l i t y . The test usedh i g h shear m i x i n g in order to a p p r o x i m a t e the h i g h e s t l e a c h a t econcentrations to be e x p e c t e d under f i e l d c ondi t i ons . ( F e a s i -b i l i t y Report pages 22, 2 3 ) . ERM has p r o p e r l y noted that sta-b i l i z a t i o n "could" increase the rcle of contaminant migra t i onf r c m the waste , Hcwever , t h i s p o s s i b i l i t y is very small be-cause the "worst-case" t e s t i n g does not s i g n i f i c a n t l yincrease l eachat e concentrations.The waste s t a b i l i z a t i o n was undertaken to "determine the optnnunratio of cement f l u e dus t necessary to s o l i d i f y the s l u d g e , "( F e a s i b i l i t y report page 2 0 ) . The waste s a m p l i n g por t i on o f th eWCC i n v e s t i g a t i o n report ( p a g e s 13-17g) i s r e p l e t e withre f erence s regarding the s t u c t u r a l p r o p e r t i e s of the waste.Page14

15

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17b

CerementTt»e ( c h r o n e ) pit was under s t and ing water duringthe s i t e i n v e s t i g a t i o n and was of the consi s tencyof j e l l y . T h e r e f o r e , s a m p l i n g was l imi t ed to thenorthern h a l f of the chrotie p i t .It was found that the proposed grease t r a p con-tained 14 f e e t of j e l l y - l i k e s l u d g e at Pit 5 / 6 .The a d j a c e n t southern lagoons were f i l l e d wi thwater and were of low load bearing strength.Excavations were made next to the lagoons.i- t s l iowing a determination of adequate support forthe backhoe. Pit 17c was dug.Pit 4A: M i l k y perched water.Pit 4Bs Pit caved in.Pit I&A: Much perahed water, dn s t t s , trash,yel low f l u i d s , chemicals

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17c

1 7 f

Pit 17C: Drums, perched water at 2 f e e tPit 17D: Perched water( V a r i o u s drums in several p i t s )Pit 21C: Caved in :

Pit 2&: Perched waterPit 2RA: Rubble over trees and v ege ta t i onPit 4 3 A < 5GA, SOB (water under timber m a t )

The i n a b i l i t y of the wastes to support a cap has been demonstratedon at least three occasions. F i r s t , d u r i n g the temporary s i t e c lo sure ,the contractor ( H a n c o c k ) experienced problems e m p l a c i n g a coverover s l u d g e s . The s l u d g e s "erupted" into the area o f tanks T2, T3,and T4. ( T h i s was mentioned to EPM personnel d u r i n g a s i t e v i s i ton A u g u s t 2Z. l ^ e j ) . Other s l udge s s lumped and were unable to main-t a i n a crowned s l o p e . S e c o n d , d u r i n g the waste s a m p l i n g under-taken by R o l l i n s , the TDWR o n s i t e i n v e s t i g a t o r noted the backhoes i n k i n g in t o s l u d g e at least once to the p o i n t that t r a c k i n gs l i p p e d and the bucket had to be used to " p u l l " the backhoe outo f a s i n k i n g s i t u a t i o n . T h i r d , d u r i n g th e i n i t i a l remedialmeasure, E P A ' s contractor ( C o a s t a l Environmental C o r p . ) experi-enced s i m i l a r prob l ems w i t h c er ta in areas being unable to supportremedia l equ ipnen t . T J M J S , : h e need f o r waste s t a b i l i z a t i o n h a sbeen a d e q u a t e l y denions trated.The degree to which the waste is s t a b i l i z e d w i l l b£ f u r t h e r speci-f i e d i n t h e d e s i g n pha s e , T h e f e a s i b i l i t y t e s t i n g d i s cu s s ed i nthe f e a s i b i l i t y report f or waste s t a b i l i z a t i o n i s r o u t i n e l y usedby the hazardous waste management p r o f e s s i o n a l s at R o l l i n s .A c c e p t a b l e test r e s u l t s were reccrtr*ended based upon th e i r broadexper i ence base in d e a l i n g w i t h s i m i l a r hazardous wastes. T h e i rt e s t i n g goal is s ta t ed on page 21 as one which is " s u f f i c i e n tto impart load bearing s t a b i l i t y to the mass."A c t u a l numerical d e s i gn s t andard s to meet t h i s per formancec r i t e r i a have not been p r o m u l g a t e d . T t i e f e a s i b i l i t y s t a b i l i t yt e s t i n g has demonstrated the f e a s i b i l i t y o f s t a b i l i s i n g theBio-Ecclogy waste up to the 500 I b s / i n 2 range. The proposedEW load bearing capac i ty of 450 I t t s / f t * is much les s and isbased c n l y upon the weight of a c lay cap and does not considerthe w e i g h t of veh i c l e s used to f i m p l a c e the cap. ERM has in-c luded no f a c t o r of s a f e t y for t e s t i n g v a r i a b i l i t y or construct-ion error. Yet it proposes to cover the undis turbed wastewithout p r o v i d i n g a technical basis to demonstrate that itsmethod is e i t h e r f e a s i b l e or r e l i a b l e . No assurances of long-term per formance of the EI5M c a p p i n g approach have been prov ided .T h u s , c ons i s t en t w i t h a permanent renedy ( N C P 3 0 0 . 6 8 a ) , t h e lackof waste s t a b i l i z a t i o n is not ac c ep tab l e . A l t h o u g h the degreeof s t a b i l i z a t i o n need not be as h igh as 500 I b s / i n 2 , s t a b i l ' n a t i o nfor load bearing support is required and w i l l IDS f ur th er r e f i n e d

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in the d e s i g n phase once the methods of construction andtype s of equipment are s p e c i f i e d . F a i l u r e to deal w i t h thes i g n i f i c a n t amounts of perched water at the site is anotherunac c ep tab l e f e a t u r e o f the EHM p r o p o s a l ,has provided cements on several f a c t o r s regarding the WCCdi scus s ion of waste p e r m e a b i l i t y and l eacha t e quanti ty. Thesecomments are d u l y noted. However* the WCC po s i t i on is notwithout merit and as a secondary f u n c t i o n , waste s t a b i l i z a t i o nis expec t ed to provide improved control of l eachate generat ion,p a r t i c u l a r l y in l i g h t of the current saturated c ond i t i on s of thewaste due to extensive perched water.

3. E f f e c t of New Dam on F l o o d p l a i nooCMoThe EW cements r egard ing the new Joe Poole reservoir and itsp o t e n t i a l t o s i g n i f i c a n t l y reduce t h e downstream f l o o d i n ge f f e c t s a l o n g M o u n t a i n Creek a r e d u l y no t ed , ' t h e revisedi n f o r m a t i o n w i l l be used in all d e s ign a spe c t s r egard ing thesite.

F l o o d p l a i n O b j e c t i v ehas p r o p e r l y noted that the f l o o d p l a i n o b j e c t i v e shouldhave been to prevent waste m i g r a t i o n d u r i n g the nG~year f l o o d s .However, it is not l i k e l y that a l e s s c o s t ly remedial p l a ncould have been d ev e l op ed . Even under current 100-year f l o o dc o n d i t i o n s , and w i t h a d d i t i o n a l t o p s o i l as reccrrmended byEW, the WCC cap meets the revised o b j e c t i v e for a 19P4 e s tL-nat edcons truc t ion cost of 5313,430. The FRM proposed cap must havea g e o f a b r i c to be emplaced according to E P M , and since it w i l lbe below the f l o o d l e v e l , it must have a syn th e t i c membraneand cover m a t e r i a l s to prevent u p l i f t of wastes. Once thesecons iderat ions are made, the EfcM cap d e s i g n , i f f e a s i b l e ,would meet the de s ign o b j e c t i v e but at an e s t imated cost of

$349,000.E f f e c t of 100- Y e a r F l o e d on the Cap

comments r egard ing the e f f e c t of the 100-year f l o o d on thecap are d u l y noted. These Garments w i l l oe considered indur ing the f i n a l d e s i g n of the cap. Furthermore, because thearea being raised is small when conpared to a d j a c e n t areas inthe f l o o d p l a i n , ra i s ing the s i t e to the 100-year f l o o d p l a i n isnot expected to have an adverse impact on the surroundingenvircment.

-10-Cost for S n a l l e r "L" Shaped Cap Versus larger RectangularShaped Cap

EPM comments regarding an "L" shaped cap are du ly noted andw i l l be considered in the d e s i g n phase of the p r o j e c t .7. C r i t i q u e of the Proposed No. 6 Cap Des ign

EPM comments regarding inadequacy of th« proposed cap underA l t e r n a t i v e 6 g enera l ly ignore the provis ion for routineoperational and maintenance (0 & H) a c t i v i t i e s . H3WR, as ac o n d i t i o n of i t s Coopera t ive Agreements w i t h EPA, has assuredf u t u r e 0 & M.As a r e su l t , damage to the prcr-nsed cap or the cap to beimplemented f o r t h e chosen a l t e r n a t i v e ( N o . 8 } f r o m erosion,d e s s i c a t i c n , and root p e n e t r a t i o n w i l l be prevented or m i t i g a t e sby a regular 0 & M schedule . Erosion damage w i l l be r e p a i r e d .D e s s i c a t i o n w i l l be minimized by w a t e r i n g as necessary. Rootp e n e t r a t i o n w i l l be minimized ty a l l o w i n g only grasses togrow on the s i t e . A regu lar mowing s c h e d u l e w i l l prevent thedeve lopment of trees on the s i te. In concert with the proposedremedial a c t i on , these O & M measures w i l l prevent the releaseof e n c a p s u l a t e d m a t e r i a l s , EPM comments r egard ing the t h i nsoil layer of the WCC proposed cap are not wi thout m e r i t ,however, and miner changes of thi s aspect may be consideredd u r i n g the d e s i gn phase of the p r o j e c t .Any d e s i g n which i n c l u d e s extension cf the cap onto a d j a c e n tproper ty is not acceptable because of the easanents required.EPA and TDWR have no control over a d j a c e n t land uses and as aresult cannot reccmmend any a l t e r n a t i v e which impinge s upona d j a c e n t land. W i t h a lower d e s i g n e l e v a t i o n , due to the JoePoole reservoir, s lope s and subsequent erosion w i l l be minimized.

I I I . Response t o E R H Reconriended A l t e r n a t i v e ( N o . . 1 0 )1. F e a t u r e s

A l t h o u g h the EBM proposed a l t ernat ive shows an innovativeapproach and presents seme i n t e r e s t i n g de s ign f e a t u r e s , it isnot an ac c ep tab l e s u b s t i t u t e for e i ther WCC A l t e r n a t i v e No. 6or No. 8. It f a i l s to meet o b j e c t i v e s for the s i t e which havenot been questioned by e i ther EWl or Thompson and K n i g h t . Italso f a i l s to ccnply wi th RCRA technical regulat ions for on-sited i s p o s a l of hazardous wastes.a. An "L" shaped s lurry trench is acceptable but must beex tended to a 60 f e e t d e p t h ( p r e v i o u s l y d i s c u s s e d } .b. the proposed ERM cap is not r e l iab l e due to poor loadsupport capaci ty (prev iou s ly d i s c u s s e d ) .

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-11-c. S u r f a c e s hap ing and f i l l as proposed by ERM is po s s i b lyac c ep tab l e , but once again, is probab ly not f e a s i b l e dueto poor load support capac i ty . A d d i t i o n a l l y , no provi s ionis made to control stormwater dur ing construction.d. Four groundwater monitoring w e l l s may not be s u f f i c i e n tto detect all contaminated groundwater p l u m e s , and wouldrequire f u r t h e r consideration.

The E»1 a l t e r n a t i v e has no provis ion to treat the special wastes asout l ined in all WCC a l t ernat ive s . Ei ther EBM nor Thomson and K n i g h thave pro t e s t ed this provi s ion contained in the s i t e s p e c i f i c responseo b j e c t i v e s , but th i s element of work is emitted f r o m tne EW4 p l a n ,2. F u n c t i o n

S i n c e the EW report does not demons tra t e or e s t a b l i s h thatf e a s i b l e and r e l i a b l e p r a c t i c e s are being e m p l o y e d , i t i si j r p o s s i b l e t o e s t a b l i s h that th e ERM a l t e r n a t i v e e f f e c t i v e l yb l o ck s p o l l u t a n t migrat ion pathways. Furthermore , the ERMa l t e r n a t i v e f a i l s to meet several c r i t e r i a of the N a t i o n a lContingency P l a n ( N C P ) .S e c t i o n 3 0 0 . 6 3 { a ? of the NCP c a l l s for remedial ac t ions to beconsi s tent w i t h permanent renedy to prevent or m i t i g a t e them i g r a t i o n of hazardous substances into the environrant. TheERM proposal is d e f i c i e n t in thi s aspect because it does notaddres s:

a. Trea tmen t of spec ial waste s ( c y a n i d e and a r s e n i c ) :u n l i k e the se lec ted remedy, the ERM a l t e r n a t i v edoes not provide for s t a b i l i z a t i o n and n e u t r a l i z a t i o n .b. S t a b i l i z a t i o n of waste s ludge s for load bearing capac i tyarid e l m i n a t i o n of perched water;c. Control of sub surface contaminant m i g r a t i o n throughthe secondary structure of the o lder a l l u v i a l d e p o s i t s :the s h a l l o w s lurry wall proposed by ERM does notextend to an a p p r o p r i a t e s t ra tum, and thus mighta l l o w ground water migrat ion into and through thes i te .d. Management of r a i n f a l l runon and r u n o f f during s i t econstruction.

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3. CostA l t h o u g h the ERM proposal is less c o s t ly , it has not beendemonstrated to be as f e a s i b l e and r e l i a b l e and it doss notas e f f e c t i v e l y m i t i g a t e the problems as well as the cost-e f f e c t i v e or the selected remedy.

-12-4. Discussion

As p o i n t e d out by Thompson and K n i g h t , the NCP presentscr i t er ia for assessment in f o r m u l a t i n g source controlremedial actions in Sec t i on 3 0 0 . 6 8 ( e ) ( 2 ) . None of these• c r i t e r i a were adequate ly considered by ERM in the deve lop-ment o f the ir p r o p o s a l . For e x a m p l e , S u b h e a d i n g I l . l . b . o ft h i s re f erence c a l l s for an assessment of the extent to whichsubstances have migrated or are contained by natural barriers.The only adequate natural barrier at the s i t e i& the Eagl e Fordf o r m a t i o n .the ERM proposal recognizes the need for a sha l l ow s lurrywall but even in l i g h t of the secondary structure of the o ldera l l u v i u m , they f a i l to recognize the need to e l i m i n a t e p o t e n t i a lm i g r a t i o n by e i ther the use of a l a n d f i l l to conta.in wastes or ofa deep s lurry wal l keyed into the E a g l e F o r d . The incrementalcost of t h i s a c t i v i t y is worth the incremental b e n e f i t of e l imina t-ing u n c e r t a i n t y and is consistent wi th a permanent remedy forthe site.W C C ' s method o f d e a l i n g w i t h s tonnwater d u r i n g cons truc t ion i sa c c e p t a b l e waste management p r a c t i c e which is c r i t i z e d by ERM.S i n c e EPM f a i l s t o manage s tormwater d u r i n g cons truc t ion, i ti s reasonable t o expec t s i g n i f i c a n t adverse e f f e c t s d u r i n gi m p l e m e n t a t i o n whi ch i s incons i s t en t w i t h S e c t i o n 3 0 Q . 6 6 ( h ) ( 2 )of the NCP.

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Response toAir Force Comments on theProposed Remedial A l t e r n a t i v efor theBio-Ecology Sys t em, I n c . , S i t eGrand P r a i r i e , Texas1. Garment

T t i e r e p o r t ' s reccmended al ternative (Number 6 ) appears t o providea good balance between e n v i r o n m e n t a l / h e a l t h considerations and costof remedial action. However, the e l i m i n a t i o n of cheaper a l t ernat ive sshould be e x p l a i n e d in de ta i l rather than to e l iminate thm "basedon performance". We say t h i s because all e igh t opt ions pose muchthe same risks to the environment a f t e r c ompl e t i on of the remedialaction.ResponseP r o v i d i n g a good balance between e n v i r o n m e n t a l / h e a l t h c on s id era t i on sand cost of remedial act ion is c e r t a i n l y the goal in s e l e c t i n g aremedial a l t e rna t iv e . A l t e r n a t i v e Six minimize s risk to theenvironment and thus , based upon p e r f o r m a n c e , A l t e r n a t i v e Sixwas recomiended o r i g i n a l l y . The less expensive a l t e r n a t i v e s weree l i m i n a t e d because they did not prov ide r i sk m i n i m i ? * t i o n for theQuaternary S a n d s . The deeper s lurry w a l l provides more r e l i a b i l i t yover less c o s t l y a l t e r n a t i v e s as i t provide s for risk m i n i m i z a t i o nfor the Quaternary S a n d s , therety assuring be t t er p e r f o r m a n c e .However , the s lurry wal l is s u s c e p t i b l e to l eakage over time due top o s s i b l e long-term increase in p e r m e a b i l i t y . In contra s t , s y n t h e t i cl i n e r systems, conbined wi th l eachate c o l l e c t i o n are expec t ed to bee f f e c t i v e i n d e f i n i t e l y g iven the nature of wastes presented at tnes i t e .

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2. GarmentThe de s ign l i f e used for the comparison of a l t e r n a t i v e s was nots t a t ed . T h i s is an important f a c t since the d e s i r a b i l i t y of thevarious a l t e r n a t i v e s w i l l s h i f t by varying the de s ign l i f e . Wenote that RCRA f a c i l i t i e s have a 30 year design l i f e .ResponseA de s i gn l i f e of 30 years was used in the report (pp. 4, 42, 55).T h i s d e s i gn l i f e i s analogous to RCRA f a c i l i t i e s .

3. CommentRemoval of sll contaminants f rom the s i t e is an al t ernat ive that doesnot appear in th i s f i n a l cut. If the de s ign l i f e of the reeownsiideda l t e r n a t i v e s was 100 years, would the a l t e rna t iv e to remove allcontaminants f r om the s i t e be pract i cal? At what point wouldfron the s i t e be prac t i ca l?

-2-ResponseIf the de s ign l i f e of the reccnmended a l t e r n a t i v e s were 100 years,the a l t e rna t iv e to renove all contaminants f r c ro the site s t i l lw o j l d not be economical ly p r a c t i c a l . T h i s is because the presentworth of the annual 0 & M costs ( a p p r o x i m a t e l y 5100,000} would s t i l lrepresent a r e l a t i v e l y small port ion of the to tal cost of the pro-posed remedial act ion ( a p p r o x i m a t e l y $2 ,700 ,000). T h i s ccrapareswith a cost of $4,470,000 to rwnove all contaminants f r o n the s i te.The point at which removal of contaminants f r on the s i t e would beeconomically prac t i ca l is uncertain. It is more than 100 yearsand thus not w i t h i n the p l a n n i n g range of the T e x a s Department ofW a t e r Resources ( T D W R J .

4. CommentO & M costs are only extended for 30 years. What w i l l be Air Forceo b l i g a t i o n s d u r i n g and a f t e r the O 6 M per i od .ResponseIt is the intent of the TEWR to recover 0 & M f u n d s f r c m re spons ib l ep a r t i e s , e i t h e r in a lump sum or a c o n t i n u i n g payment s basis. TheT e x a s W a t e r Development Board has ins truc t ed the Exe cu t iv e Director torecommend s t a t e l e g i s l a t i o n concerning thi s s u b j e c t . T h i s e f f o r tis b e ing d eve l op ed at the current time.

5. GarmentThe cost of the s l u r r y w a l l is in general agreement w i t h the a t tachedP o l l u t i o n Equipment a r t i c l e f o r a 6 0 ' wa l l wi th f a i r soil c ond i t i on s ,ResponseYcur comment on the a p p r o p r i a t e n e s s of slurry wall costs is herebyacknowledged .

6. GarmentPage 5 of the "Remedial I m p l e m e n t a t i o n Alt erna t iv e Selec t ion" indicatest h e S t a t e ' s p a r t i a l s i te closure included burying containerized wasteon s i t e . T h e s e containerized wastes were presumably 55 g a l l o n drums.If the burying o f these wastes on-site s i g n i f i c a n t l y increased thecost of the u l t i m a t e clean-up, then the State's share of the c leanupshould be increased.ResponseThe burying of containerized waste onsite during the part ial s i teclosure is not expected to s i g n i f i c a n t l y increase the u l t i m a t ec l e a n u p costs. The containerized wastes were already present at

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-3-the s i t e and would have to be remedied 5n any event. During thewaste s a m p l i n g phase 01 the f i e l d i n v e s t i g a t i o n , buried drums wereencountered in a randcn f a s h i o n throughout all l a n d f i l l e d areas ofthe s i t e . It should be noted that the p a r t i a l s i t e closure hass i g n i f i c a n t l y minimized the risk of release during the interimperiod pre c ed ing implementat ion of a f i n a l remedial a l t e rna t iv e .

7. CommentThe " ini t ia l remedial measure" (Page 50) includes the removal andd i s p o s a l of a p p r o x i m a t e l y 80,000 g a l l o n s of hazardous l i q u i d s ands l u d g e s . If th i s has not yet occurred, it would be p r e f e r a b l e toi n c i n e r a t e the m a t e r i a l , rather than moving i t to another l a n d f i l l ,only to run the r i sk of having the problem reoccur in the f u t u r e .ResponseThe i n i t i a l remedial measure has a l r e a d y been c c rop l e t ed . Some ofthe l i q u i d s removed contained a s i g n i f i c a n t perc entage of water andwere not in c inerab l e . It is the u n d e r s t a n d i n g ot TDWR that wherep o s s i b l e , PCB l i q u i d s removed f r o n the s i t e have been or w i l l beinc inera t ed .

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GarmentThere d o e s n ' t appear t o b e a n y t h i n g i n c l u d e d in th e a l t e r n a t i v e s f orremoval of s i g n i f i c a n t amounts of o f f - s i t e soil in the stream bedshould con taminat i on {heavy m e t a l s , most p r o b a b l y ) be d e t e c t e d . Arewe t r u l y f i n i s h e d w i t h Bio-Ecology once the waste is s tab i l i z edand the s i t e c a p p e d , or are these costs j u s t the beginning?ResponseThe removal of o f f s i t e so i l s f r on the streambed was not included inthe a l t e r n a t i v e s because s i g n i f i c a n t contamination was not detec tedin these so i l s . The a l t e rna t iv e s focused ma in ly on source controlremedial measure since the hazardous substances located at the s i tehave not migra t ed s i g n i f i c a n t l y beyond the immediate s i t e area.W i t h the exception of routine 0 t M, once the remedial al ternativeis implemented the closure of the s i t e should be cot?>lete,OcmnentThe "Evaluation Results" ( p a g e 11} show a "degree of s i g n i f i c a n c e "far in excess of what is a c t u a l l y the case for a r e l a t i v e l y subjec t-ive process. One s i m p l y cannot q u a n t i f y "po t ent ia l hunsn heal thimpacts" to f o u r s i g n i f i c a n t f i g u r e s . Oily cost is a so l id number,and even then, it is a sub j e c t ive decision that 350 points out of1,000 arc for economics. Furthermore, it is not clear why the

-4-Icwest coat al ternative, Number 4, didn't receive the maxiaunnunber of po in t s , rather than 175 of 250. If there are a d d i t i o n a l ,f e a s i b l e a l t ernat ive s , they should be discussed. The table would befar more credible with two s i g n i f i c a n t f i g u r e s for each category.

Evaluation Results ( T a b l e 13 of the F e a s i b i l i t y R e p o r t ) showseveral s i g n i f i c a n t f i g u r e s due to the development of soores andthe averaging of these scores. Scoring began by considering eachof the categories on an absolute scale f r om 1 to 10, whiche s s e n t i a l l y represents only one s i g n i f i c a n t f i g u r e . A l l o c a t i o n ofshort-term and long-term e f f e c t s , consideration of the total point sfor each category, and averaging six total scores yie ld several sig-n i f i c a n t f i g u r e s . The scoring process is described on page 64 ofthe F e a s i b i l i t y Report and eva lua t i on sheets are included inA p p e n d i x D. The lowest cost a l t e r n a t i v e . Number 4, received themost p o i n t s of any a l t e r n a t i v e in the cost category, TDWR andEPA acknowledge that the process, like many others, is subject toa certain amount of sub jec t ivenes s . Woodward & C l y d e Consul tant s (WCC)deve loped the process and have rou t ine ly used it s u c c e s s f u l l y intheir work with other c l ients . TDWR and EPA do not endorse theprocedure as a f a i l - s a f e s e l e c t ion process, but b e l iv e that theselected remedy is consis tent wi th the NCP and necessary to protecthuman h e a l t h and the environment.

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10. CommentI n regard t o t h e suggested Ground W a t e r M o n i t o r i n g Program, ( 1 ) f o u rmoni tor ing w e l l s may not be s u f f i c i e n t to p i c k up all contaminatedground water p lume s and (2) M o n i t o r i n g for only 13 contaminantsappears inadequate considering that organics and PCB's were alsodisposed of at the s ite. It would be prudent to p e r i o d i c a l l ymonitor for s p e c i f i c v o l a t i l e and purgeable organics in up s lopeand s i te monitoring we l l s .ResponseThe ground water monitoring program is described on pages 42 and43 of the WCC Report and in the EPA Mdendum 2. The 13 parametersl i s t e d in the A d d e n d u m are mini jnimum t e s t i n g requirements requiredin a d d i t i o n to p r i o r i t y p o l l u t a n t analys i s for upgradient anddowngradient wel l s . As stated in the Addendum, the program wil linclude the i n s t a l l a t i o n of groundwater monitoring we l l s of s u f f i c i e n tnumber and at the a p p r o p r i a t e locations and depths to yie ld repre-sentative groundwater samples f r om the quaternary aqui f er . Theexact parameters w i l l be determined in the d e t a i l e d des ign for thep lan.

11. GarmentThere is no e xp lana t i on for the we igh t ing a p p l i e d to the rubricalfaccors which makes it d i f f i c u l t to determine if the d i f f e r e n c e s inthe values obtained for the various opt ions (Page 11) is s i g n i f i c a n t .The cost variances are s i g n i f i c a n t , and an explanation of the ratingsystem would aid in the evaluation of the alternatives.ResponseAn exp lanat ion of the we igh t ing a p p l i e d to the numerical factorsis included on pages 52-53 and 61-64 of the WCC Report.

12. CementThe selected o p t i o n appears redundant. The waste is f i x e d in placeand then a clay cap is a p p l i e d . Both of these techniques are usedto control the downward m i g r a t i o n of contaminants. If the clay capis correctly a p p l i e d , f i x a t i o n should not be required. The converseis a l s o true. The s lurry w a l l , intended to prevent migration ofcontaminants down the groundwater hydraul i c grad i en t , appears to beoverdes igned. The only b e r j c f i t to be gained f r o n the downstreamport ion of the slurry wall is contairurfc>nt of water which hasintruded f r o m the s u r f a c e of the s i te* If the clay cap has beencorrectly i n s t a l l e d , there shoulo be no such intrusion. A slurrywall i n s t a l l e d arour>d the upgradiene ha l f of the s i te would appearto be an e f f e c t i v e approach. Please exp la in.ResponseThe recownended opt ion considers several integrated fac tors inachieving a long-term re l iab l e remedial alternative. A clay capat the s i t e wi l l provide the coverage of waste required to preventdirect contact of wastes by intruders, surface migration of wastesby weathering, and w i l l provide sane degree of control over thedownward migrat ion of contaminants. S t a b i l i z a t i o n of wastes isrequired in order to provide loadbearing capacity for equipmentused to e j f p l a e e the cap, for the cap i t s e l f , and for fu tureoperation and maintenance consideratiorjs . As a secondary f u n c t i o n ,waste s t a b i l i s a t i o n is expected to provide some inproved controlof l e s c f . a t e f c?nerat ion. Due to the secondary structure in thea l l u v i a l d e p o s i t s , a slurry wall would serve to ensure control oversubsurface migrat ion of contaminants. A partial slurry wall wouldnot be as c - f f active an approach as it would not provide containmentof contaminants. The option selected by EPA essentially replacesthe slurry wall with a liner and leachate collection system to.i "-itain wastes on-site. EPA f e e l s that the selected option,< lough s l i g h t l y more expensive than the opt ion recommended; ; ous ly , is more reliable over the long term.

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