R E S P O N S E S T O E P A C O M M E N T SD R A F T R E M E D I A L I N V E S T I G A T I O N REPORT

A R K W O O D , I N C . S I T EO M A H A , A R K A N S A S

February 26, 1990

Each EPA comment ir, repeated below in thn order given, f o l l o w e d bythe response.Comment on S e c t i o n j; I n c l u d e a map which shows general s i t ef e a t u r e s .Response i A map showing general s i te f e a t u r e s was ^dded to thereport (note reference to F i g u r e 1-2 at the end of S e c t i o n 1.1.1).Comment s on...Page ii. Para. 4: It is unclear which ash p i l e isbeing re ferred to here. I n c l u d e a discussion of the ash p i l e whichwas pushed over the s l o p e .Response.: P a r a g r a p h 4 was revised to c l a r i f y the r e f e r en c e to theash p i l e and i n c l u d e a d i s cu s s i on of the p o r t i o n s of the ash p i l epushed over the edge of the site.Comments on £age 3_-8. Para. 4: I n c l u d e a d i s cu s s i on of the recents a m p l i n g event,Response: Paragraph 4 was replaced with a discussion of there c ent ly c o m p l e t e d serial s a m p l i n g event.Comment s on Page 3-19. Para. 2: I n c l u d e either a d i s cu s s i on of theash p i l e s a m p l i n g r e s u l t s , or r e f e r enc e where these r e su l t s may bef o u n d .Response: A sentence was added to the end of P a r a g r a p h 2 r e f e r e n c -ing where the a n a l y t i c a l re su l t s are discussed and t a b u l a t e d .Comments on...Page 3-24, Para. 4: U p d a t e the Dye T r a c i n g section tor e f l e c t the mutual dec i s ion of EPA and MMI to d e l a y the t ra c ingunti l c ond i t i on s are more conducive to the s tudy.Response: In view of the f a c t s that the ex t ended drought condi-tions have bsen m o s t l y a l l e v i a t e d by recent rains and that thenormal rainy season is a p p r o a c h i n g , it may be p o s s i b l e to conductthe dye tracing thi s spr ing. The dye tracing section was revisedto r e f l e c t that some work has been c o m p l e t e d . F u r t h e r progre s sd e p e n d s upon water level c ond i t i on s and t en ta t i v e EPA a p p r o v a l ofthe work p l a n as revised by MMI's response to the Agency comments.

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Comments on Page 4 - l , _ S e c t . 4-_l: I n c l u d e a map or d iagram showingthe sice w e l l s and i n d i c a t i n g which f o r m a t i o n they are mon i t o r ing .Respons e: The f i r s t f o u r page s o f S e c t i o n 4 .1 di s cus s the basicsurface and sub surface geo logy of the site. The requested map wasadded to the report ( F i g u r e 4 - l a ) and r e f e r enc ed on p a g e 4-4 nearthe end of thi s g e o l o g y section.Comments on Page 4~5 . S e c t . 4 . 1 . 2 ; Rela t e the r e su l t s of the gp.o-p h y s i c a l l o g g i n g to the site. The current d i s cu s s i on t e l l s very3 i t t l e r egard ing conc lu s ions which may be drawn as a re sul t of thel o g g i n g . What i n f o r m a t i o n has the l o g g i n g provided which may bere la t ed to the RI?Response: One of the o b j e c t i v e s of the RI was to examine the d e e ps t ra ta u n d e r l y i n g t h e Arkwood s i te. The g e o p h y s i c a l wel l l o g g i n gintr ^rotations d i s cu s s ed in the report have achieved thi s o b j e c t -ive. An a d d i t i o n a l d i s c u s s i o n has been added to the end of S e c t i o n4.1.2 which a t t e m p t s to r e l a t e the s h a l l o w s t r a t i g r a p h y and hydro-g e o l o g y t o th e d e e p s t r a t i g r a p h i c i n t e r p r e t a t i o n s .Comments on Page 4*9.., Para. 3: It is not clear if the area s p r i n g sd i s c h a r g e at the top of the S y l a m o r e as has been h y p o t h e s i z e d .C l a r i f y t h e d i s c u s s i o n t o addr e s s t h i s .R e s p o n s e : T e x t was a d d e d to th i s p a r a g r a p h to i n d i c a t e that manyof the area s p r i n g s do d i s c h a r g e at the top of the S y l a m o r eS a n d s t o n e .Comment s .on. Page 4-19_, Para. . _ ! ; T h i s is an e x a m p l e of numerousoccasions where a r e f e r enc e to r e s u l t s , but the t a b l e where thedata m a y b e f o u n d i s n o t noted. T h e Authors should review L ' eentire document and ensure that r e f er ence s are made v . :ea p p r o p r i a t e .Response: In this instance as in other instances where on ly oneor two values are being d i s c u s s e d , the da ta are given in the textrather than in tabu lar f o r m . However , text was added r e f e r e n c i n gthe lab data. The document was reviewed and where a p p r o p r i a t e ,data t a b l e s and f i g u r e s have been r e f e r e n c e d in the t e x t .Comment s o n _ P a g e 8&c t . 4 , 5 * 1 ; Provide a d i s t i n c t i o n between.the ash p i l e s a m p l e s tak^n during the phase 1 and pha s e 2 of theRI. R e f e r e n c e where each set of data may be f o u n d .Response: The las t three p a r a g r a p h s on page 4-21 ware revised toprov ide a d i s t i n c t i o n between Phase I and Phase II ash p i l e s a m p l e sand more c l e a r l y s t a t e where the da ta ia t a b u l a t e d .

Coronents on Perre 4 - 2 3 , _ P a r a . 2: Provide a f i g u r e showing the con-centration of PNAs using one-ha l f d e t e c t i on l i m i t s a s concentra-tions. Provide a d i s cus s ion of how this f i g u r e compares with thePCP concentration maps.Response: The PCP concentration maps are based on actual analy-tical resul t s with only occasional po in t s being represented bynonquanti tat ive data ( o n e - h a l f d e t e c t i on l i m i t s ) . However ,i n s u f f i c i e n t data p o i n t s are a v a i l a b l e with which to contour PNAconcentrat ions and there is no s c i e n t i f i c basis for contouringbased almost e x c l u s i v e l y on nonquant i ta t ive data* In S e c t i o n 2.1of the F e a s i b i l i t y S t u d y a general PCP/PNA corre la t i on has beene s t ab l i s h ed and should be used as a h"*.is for c ompar ing PCP andPNA concentrat ions . I n c l u d i n g a map j . the RI report based s o l e l yon PNA de t e c t i on l i m i t s is unwarranted since it may not ber epr e s en ta t iv e o f soil concentrat ions.Comment s on Page 4^23. Para. 3t Provide a d i s c u s F - . ' o n of ther e l a t i v e l y larg<*. spread of the values of the Toe s a m p l i n g r e su l t s .Respons e: A b r i e f s tatement was added near the end of p a r a g r a p h3 s t a t i n g that the range in TOG values is a t t r i b u t a b l e to naturalvariat ion.Comments on Page. 4-24, _Para. 2: W h a t is the source of the PCPf ound in SED 18? W i l l thi s source need to be addre s s ed in s i teremediat ion?Response i The p r o b a b l e source of the PCP in SED-18 was the rail-road d i t c h area and a note to th i s a f f e c t was added to the t ex t .During heavy r a i n f a l l events, r u n o f f f r o m thi s area f l o w s over thel o ca t ion at which S E D - 1 8 was c o l l e c t e d .The rai lroad d i t c h area is one of the p r i o r i t y areas to be addre s s-ed during s i t e remediat ion.Conanent.s. on page. 4-28. Sec_t._4_._7: Discuss the d i f f e r e n c e betweenthe we l l and s p r i n g waters. Are these d i f f e r e n c e s s u p p o r t i v e ofthe idea that the w e l l s do not come f r o m a q u i f e r s which may bep o t e n t i a l l y contaminated? W h a t data d id the inorganic analyse sprovide which r e la t e to the s i te and the r emedia t i on of the site?Response; As discussed in S e c t i o n 4.7, there are sevoral d i f f e r -ences between the domes t i c wel l and s p r i n g waters. A summary anddi s cu s s i on of some of these d i f f e r e n c e s was added to the end ofSact ion 4.7.9. T h e s e d i f f e r e n c e s s u p p o r t the conclus ion that thes h a l l o w , p o t e n t i a l l y a f f e c t e d water bearing zone does not prov idewater d i r e c t l y to the d e e p domes t i c w e l l s . W a t e r in these w e l l sr e f l e c t s a d i f f u s e , d o l o m i t i c source charac t er i s t i c o f d e e pa q u i f e r s u n a f f e c t e d by near s u r f a c e v a r i a b i l i t y .

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Two of the o b j e c t i v a s of the s tudy were to determine if the areas pr ing s were part of the same h y d r o l o g i c system and if variationsin inorganic water chemistry could be used to pr ed i c t source areasIt is obvious that the s p r i n g s ai.d on-site monitor w e l l s are allpart of the same ground water system. V a r i a t i o n s in water chemis-try between s p r i n g s are best e xp la in ed in g e o l o g i c terms such asd i f f u s e versus conduit f l o w , with some importance ascribed to thenature of the source area. However , nothing was discovered duringthe inorganic water qual i ty etudy that would a l l ow one to predictthat the source for a p a r t i c u l a r s p r i n g might be w i t h i n the vicin-ity of one of the Arkwood site source areas.^A, Para, ?; S t r e n g t h e n the f o u r t h sentence o fp a r a g r a p h to r e f e r e n c e that three subsequent s a m p l i n o eventsshowed no contaminat ion.

A d d i t i o n a l texc was added to P a r a g r a p h 3 to s t r eng thenW a s n f c a f f e c t e d and that the sampl e wast.contaminated either in the f i e l d or in the labora tory.S o a m e n t g gnJEaaa-. fca r . C 9 n P - 21: I n c l u d e the areas around B-25 andB-<:7 as source areas.E f i S f i O n s s : C o n c l u s i o n 23 was revised to r e f l e c t the p o s s i b i l i t ythat s u r f i c i a l s o i l s at B-25 and B-27 may act as source areas.Comments on Paae 6-4, r?n^r 34. E x p l a i n what is meant by theconcentrated hydrocarbons in d e ep e r zones, provide r e f e r enc e s tosupport this conclusion.f r a g p o n s f i : The reference to concentrated hydrocarbons in deeperzones p e r t a i n s to the o i l y hydrocarbon layers f o u n d f l o a t i n g on theground water encountered near the bottom of some of the boreholesin the t r o l l e y / t r e a t m e n t and railroad d i t ch areas (see Page 4-23P a r a g r a p h 3 ; Page 4-27, Paragraph 2 a n d Page 4-28, Paragraph 3 ) 'In s p i t e ( o f these hydrocarbon layers , ind i ca t or compoundconcentrations tended to be much higher in the s h a l l o w s o i l s ands l u d g e s than they were in the deeper soi l s .f l f l m m e n t f t _ o n . _ F i c n i r e 4-49 1 Provide more annotation of this f i g u r eW h a t do tha heavy dashad l inea represent?EaaROngQ: Many of the data p o i n t s are represented by e s t imatedconcant rations or concentrations f r o m interval s a d j a c e n t to thosea c t u a l l y being m a p p e d . Some l o ca t i on s within the contoured areashave no da ta at a l l . The dashad l ine s indi ca t e the uncer ta inty andh y p o t h e t i c a l nature of the contours and a note e x p l a i n i n g thi s wasadded to tha f i g u r e .

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APPENDIX H

Laboratory P~ Aeability Data

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December 26, 1989

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