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August 19, 1992 Mr. Russell Killebrew Woodward-Clyde consultants P.O. BOX 66317 Baton Rouge, Louisiana 70896 Dear Mr. Killebrew: Enclosed are the comments of the Environmental Protection Agency (EPA) Region 6 on the draft Remedial Investigation (RI) and Risk Assessment for the Dutchtown Oil Treatment site in Dutchtown, Louisiana. Overall, the RI and Risk Assessment were well written and in accordance with EPA guidance. If you have any questions on the enclosed EPA comments, please do not hesitate to contact me* Also enclosed is the EPA Region 6 clarification concerning the difference between Central Tendency and the Reasonable Maximum Exposure Parameters. If you wish to discuss the comments in person, I will be in Baton Rouge on September 2, 1992, for another meeting and will be available to meet with you on the Dutchtown RI and Risk Assessment on the morning of September 3, 1992. Dr. Jon Rauscher is also available for a September 3, 1992, meeting, if needed. Sincerely yours, o 00 o o (LA- Cathy D. Gilmore Remedial Project Manager AR/LA Section (6H-EA) Enclosures cc: Ms. Barbara Anderson Black and Veatch Waste Science and Technology Mr. Tom Stafford Louisiana Department of Environmental Quality Mr. Frank Craig Garder© and Wynne Mr. Bob Holden Liskow and Lewis Mr* Rick Addison Parnell, Rain, and Harrell 6 Bbnd 6H-EA sGilmoi-a:tgT8/17/92:DutchtOWn - At \RILTR.WC fherx 008477

(LA-y D. Gilmore · the drums and tanks during the ERA. A summary of the ERA results should be presented in the RI RreporI datat becaus. e the results serve as additional support

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August 19, 1992Mr. Russell K i l l e b r e wW o o d w a r d - C l y d e c onsu l tant sP.O. BOX 66317Baton Rouge, Louisiana 70896Dear Mr. K i l l e b r e w :Enclosed are the comments of the Environmental Pro t e c t i on Agency(EPA) Region 6 on the d r a f t Remedial I n v e s t i g a t i o n (RI) and RiskAssessment for the Dutchtown Oil Treatment site in Dutchtown,Louis iana. O v e r a l l , the RI and Risk Asse s sment were wel l wri t t enand in accordance with EPA guidance .If you have any questions on the enclosed EPA comments, p l e a s e donot h e s i ta t e to contact me* A l s o enclosed is the EPA Region 6c l a r i f i c a t i o n concerning the d i f f e r e n c e between Central Tendencyand the Reasonabl e Maximum Exposure Parameter s .If you wish to discuss the comments in person, I wi l l be in BatonRouge on S e p t e m b e r 2, 1 9 9 2 , for another meet ing and w i l l bea v a i l a b l e to meet with you on the Dutchtown RI and Risk Asse s smenton the morning of S e p t e m b e r 3, 1992. Dr. Jon Rauscher is al soa v a i l a b l e f or a S e p t e m b e r 3 , 1 9 9 2 , m e e t i n g , i f needed.S i n c e r e l y yours,

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(LA-Cathy D. G i l m o r eRemedia l P r o j e c t M a n a g e rA R / L A S e c t i o n ( 6 H - E A )Enclo sure scc: Ms. Barbara AndersonBlack and V e a t c h W a s t e S c i e n c e and T e c h n o l o g y

M r . T o m S t a f f o r dL o u i s i a n a Department o f Environmenta l Q u a l i t yMr. F r a n k CraigGarder© and W y n n eMr. Bob H o l d e nLiskow and Lewi sMr* Rick A d d i s o nP a r n e l l , Rain, and H a r r e l l

6Bbnd6 H - E A

s G i l m o i - a : t g T 8 / 1 7 / 9 2 : D u t c h t O W n - A t \ R I L T R . W Cf h e rx

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R E V I E W C O M M E N T SD U T C H T O R S O I L T R E A T M E N T S I T E

D 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 REPORTG E N E R A L C O M M E N T S1. The presence of inorganics in the s u r f a c e and s u b s u r f a c e soilneeds to eva luat ed more t h o r o u g h l y . The presence ofinorganics in the background s a m p l e s is to be e xp e c t ed .However, the background concentrations should be d e f i n e d andused when eva lua t ing the presence of inorganics at the site.T h i s w i l l a l l o w f o r d e t e r m i n i n g i f e l evated l ev e l s o finorganic s are present and if the e l evated l e v e l s can bein t e rpr e t ed a s e f f e c t s f r o m t h e f a c i l i t y o p e r a t i o n s .2 . The r e su l t s o f the e x p e d i t e d re sponse action (ERA) conductedat the site need to be incorporat ed into the R e m e d i a J .I n v e s t i g a t i o n ( R I ) report i n greater d e t a i l . T h e remedialac t ions c o m p l e t e d d u r i n g the ERA r e s u l t i n g in the removal ofsource areas have a great dea l of i n f l u e n c e on the e x i s t i n gnature and extent of c on taminat i on at the s i t e , and thep o t e n t i a l f o r m i g r a t i o n o f contaminant s f r o m th e s i te.S P E C I F I C C O M M E N T S1. section 1.2.1, S i t e H i s t o r y , E x p e d i t e d Response A c t i o n

The q u a n t i t i e s of wastewater r epor t ed to have been treatedons i t e and d i s c h a r g e d , as s ta t ed in th i s s e c t ion, contradi c tthe volumes that were r epor t ed in the "Dutchtown ERA F i n a lS i t e P r o d u c t i o n R e p o r t , N o v e m b e r 15, 1990 - October 4, 1991".P l e a s e amend the RI or e x p l a i n the reason for th i s d i f f e r e n c ein r e p o r t e d volumes of was tewater t r e a t e d .A l s o , p l e a s e p r o v i d e a b r i e f d e s c r i p t i o n o f th e soil treatmentproce s s e s used d u r i n g the ERA in th i s section.As a l l u d e d to in Sec t i on 1.1 of the RI repor t , p l ea s esummarize t h e b e n e f i t s o f p e r f o r m i n g t h e R I / F S concurrent lywith the ERA in th i s s ec t ion.T h i s s e c t ion on page 5 should a l s o s t a t e that v i s i b l ycontaminated ground water was observed s e e p i n g into theh o l d i n g pond d u r i n g axcavat ion and v e r i f i c a t i o n s a m p l i n g .T h i s section shou ld also ind i ca t e that the ERA work p l a n wasm o d i f i e d to inc lude the i n s t a l l a t i o n of a f r e n c h drain toserve a« an interim measure a d d r e s s i n g th© contaminated groundw a f c & r observed to b& s e ep ing into the waste p i t *

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S e c t i o n 1.2.3, S i t e De s c r ip t i onThe f i r s t p a r a g r a p h o f th i s section should a l s o r e f er enceF i g u r e 2. In a d d i t i o n , the text should note, e x p l a i n , or becorrected such that the 0*07 acre smal l waste pit is the sameas the "oil pit" i d e n t i f i e d on F i g u r e 2. Using both names isc o n f u s i n g .A d d i t i o n a l i n f o r m a t i o n concerning the p e r m e a b i l i t y o f th e c l a ycap should be in c luded . The text should s p e c i f y whether thep e r m e a b i l i t y of the cap was v e r i f i e d a f t e r construct ion orwhether the p e r m e a b i l i t y is only a d e s i g n cri teria based upongeotechnical laboratory tests.S e c t i o n 2.1, F i e l d I n v e s t i g a t i o n sThe text a l s o needs to s ta t e that the s u b s u r f a c e i n v e s t i g a t i o nwas a l so conducted to de t ermine the hor i zon ta l extent ofc on tamina t i on at the s i te.T h e R I / F S work p l a n s ta t e s that t h e s i te c h a r a c t e r i z a t i o n taskal so i n c l u d e s i d e n t i f y i n g t h e contaminant s o f concern. T h i sshould be added to the d e s c r i p t i o n of the s i techarac t e r i za t i on task.The term ground water monitoring in the s ix th b u l l e t under theseries of i n v e s t i g a t i o n s should be changed to ground waters a m p l i n g because s a m p l e s were not c o l l e c t e d at e s t a b l i s h e din t erva l s f r o m the new or e x i s t i n g m o n i t o r i n g w e l l s at thes i te .S e c t i o n 2.1.1, T o p o g r a p h i c SurveyP l e a s e i n c l u d e the year that the t o p o g r a p h i c survey wasconducted at the site.The text should s ta t e in the las t sentence of p a r a g r a p h 2 thatthe s i te f e a t u r e s m a p p e d dur ing the t o p o g r a p h i c survey areindicat ive of the site b e f o r e any of the e x p e d i t e d responseact ion was i m p l e m e n t e d .s e c t ion 2 , 1 . 2 , Contaminant Sourc e I n v e s t i g a t i o nThe p a r a g r a p h on the waste oil pit i n d i c a t e s that the wasteoil pit is l o ca t ed a l o n g the northwes t ern edge of the s i t e ,H o w e v a r , ac cording to the f i g u r e s in the RX and the f i e l dover s igh t , the pit is a c t u a l l y l o ca t ed at the west central0dg© of the site. T h i s p a r a g r a p h should ba m o d i f i e dac cord ing ly .The d i s cu s s i on of the wasta pit should inc lude a more thoroughe x p l a n a t i o n of the visual contamination present in the waste

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oi l p i t during the ERA. The text should s p e c i f i c a l l y inc ludethat visual contaminat ion was present in the pit to 9 f e e tbelow ground s u r f a c e and that ground x^ater was observeds e e p i n g into the pit on several occasions.Under tankage , p l e a s e s ta te what was done with the contents ofthe drums and tanks during the ERA.A summary of the ERA re su l t s should be pre s ent ed in the RIreport because the r e su l t s serve as a d d i t i o n a l s uppor t of theRI data .

6. S e c t i o n 2.1.3, M e t e o r o l o g i c a l I n v e s t i g a t i o nP l e a s e s ta t e the year that the me t e oro l og i ca1 survey wasc o m p l e t e d .

7. S e c t i o n 2.1.4, s u r f a c e W a t e r / S e d i m e n t i n v e s t i g a t i o n sP l e a s e s p e c i f y the parameter s r e f e r r e d to as "conventionals".The text i n d i c a t e s that a d r a i n a g e d i t c h e x i s t s west of thep r o p e r t y p a r a l l e l to I n t e r s t a t e 10, and that another d i t chruns a l o n g the eastern edge of the s i te a d j a c e n t to the W a t t sp r o p e r t y . H o w e v e r , the I n t e r s t a t e i s l o ca t ed east of the siteand the W a t t s p r o p e r t y i s l o ca t ed west of the site. T h i sp a r a g r a p h should be changed a c c o r d i n g l y .The r e p o r t i n g l i m i t for lead was pre s en t ed as 2.5 u g . l .should b e pre s ent ed a s J . 5 u g / 1 . I t

Because many t y p e s of soil s a m p l e s are pr e s en t ed on F i g u r e 3,p l e a s e s ta t e how these s a m p l e s can be d i s t i n g u i s h e d on thef i g u r e . The d i s c u s s i o n should a l s o s t a t e th e number o fs a m p l e s c o l l e c t e d and whether these s a m p l e s were c o l l e c t e db e f o r e or a f t e r the c l a y cap was i n s t a l l e d .8. S e c t i o n 2 . 1 , 6 , S o i l ana V a d o s e Zone I n v e s t i g a t i o n s

The text should e x p l a i n the reason why the s u b s u r f a c e boringsB-113, B-120, and B-121 were t erminated b e f o r e encounteringthe water t ab l e .The t«xt shou ld s tate the average d e p t h o f the s h a l l o wboringe.The BPA f i e l d oversight contractor recorded that the boringthrough the h o l d i n g pond was terminated at 28 f e e t becausevi s ib l e contaminat ion was s t i l l present in the ho l e at thatd e p t h and it was f ear ed that advancing the boring f u r t h e rwould cause th© contaminat ion t o spread. F l e a s © e x p l a i n f u l l ythe r a t i o n a l e for th© dec i s ion to tarminata the boring through

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the h o l d i n g pond at 28 f e e t .

9. S e c t i o n 2.1.7.2, W e l l I n s t a l l a t i o nP l e a s e i d e n t i f y the l o c a t i o n s o f the three e x p l o r a t o r y boringsassociated with each de ep we l l i n s t a l l e d at the site*The text should s tate that the p i e z ome t e r s were i n s t a l l e d toa p p r o x i m a t e l y the same d e p t h as the s h a l l o w w e l l s at the site.

10. E l e c t i o n 2.1.7.3^ Ground W a t e r S a m p l i n gThe text should s ta t e that the d e v e l o p m e n t water was capturedand c on ta iner i z ed .

11 S e c t i o n 2.1.8 and 2.1.E c o l o g i c a l I n v e s t i g a t i o n s Human P o p u l a t i o n surveys and

The textconduc t ed . should s ta t e when these i n v e s t i g a t i o n s were.

12. S e c t i o n 2.3, F i e l d Documentat ionThe las t p a r a g r a p h s ta t e s that the do cumenta t i on i s pre s en t edin the a p p e n d i c e s . For the ease of the reader, it would beh e l p f u l to s ta t e where the r e f e r e n c e d i n f o r m a t i o n can bef o u n d .

13. sec t ion 3.4.1.2, Y o u n g e r D e l t a i c D e p o s i t sP l e a s e d i s cu s s the da ta that i n d i c a t e that the younger d e l t a i cd e p o s i t s are not pre sent in the Dutchtovn s i t e v i c in i ty .

1 4 . s ec t ion 3 , S . I . 2 * Ground W a t e r tig©The text does not s ta t e that in the immed ia t e v i c i n i t y of thes i t e that the s urround ing p o p u l a t i o n e x c l u s i v e l y uses p r i v a t eground water w e l l s f or r e s i d e n t i a l use.

1 5 . S e c t i o n 3 , 5 . 2 , S i t e H y d r o g e o l o g yBecause the terms p e r m e a b i l i t y and h y d r a u l i c c o n d u c t i v i t y aresynonymous as used in th i s r e p o r t , the uni t s for both shouldbe c ons i s t en t . In the t e x t , p e r m e a b i l i t y has a unit ofe & n t i m e t a r s per second wh i l e h y d r a u l i c c o n d u c t i v i t y has a unitot f ® e t per minute.The text shou ld describe th© u p p e r and lowsr permeabl e uni t saa b e l o n g i n g to the point bar s ed iment s a q u i f e r system whichwas d i s cu s s ed in S e c t i o n 3.5.1.

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A d i s cu s s i on de s cr i b ing th e p o s s i b l e e f f e c t s o f t o p o g r a p h i ccontrol s on p r e c i p i t a t i o n i n f i l t r a t i o n needs to be included inthe eva lua t i on of ground water f l o w in the upper p ermeab l eunit which is di scus sed in p a r a g r a p h 3.The third sentence in the third p a r a g r a p h s ta t e s that groundwater f l o w in the u p p e r p ermeab l e unit is rad ia l f r o m tht>h o l d i n g pond* T h i s d e s c r i p t i o n a p p e a r s to be correct for pre»ERA condi t ions . P l e a s e s tate thi s in the text .The units for h y d r a u l i c gradient should al so be inc luded inthe t ex t .The text s tate s that the vertical gradient i s uncertain. T h i sconclusion should be q u a l i f i e d as based on p r e s e n t l y a v a i l a b l eda ta .P a r a g r a p h 2 on p a g e 37 s ta t e s that the p e r m e a b l e uni t s whichare monitored ons i t e do not b e l o n g to any of the regionalg e o l o g i c or h y d r o g e o l o g i c unit s . Based on i n f o r m a t i o npre s ent ed in the r e p o r t , it a p p e a r s that the p e rmeab l e unit si m m e d i a t e l y u n d e r l y i n g the Dutchtown s i te are po int barsediment o f the younger d e l t a i c d e p o s i t s . E x p l a i n the.r a t i o n a l e for d e t e r m i n i n g that the p ermeab l e units do notb e l ong to any of the regional g e o l o g i c or h y d r o g e o l o g i c units .

16. S e c t i o n 4.5, AirThe f i r s t sentence s ta te s that "since the sources f r o m thesite have been removed, ,*.". T h i s wording is too conclusivef o r a Remedial I n v e s t i g a t i o n ( R I ) repor t . T h e c lause could b etrue and the RI report s hou ld be used to s u p p o r t thes ta tement .

17* S e c t i o n 5.3.1, Eva lua t i on Parame t er sT h i s section should in c lud e a d i s cu s s i on d e s c r i b i n g why theparameter s benzene, e t h y l b e n z e n e , and styrene were s e l e c t edf o r m o d e l i n g .

18. S e c t i o n 5 . 3 . 2 , M o d e l i n g T e c h n i q u e s and R e s u l t sThe s tatement in the text that the model p r e s e n t s aconservative view is not e n t i r e l y correct for the f o l l o w i n greasons:* The vertical p e r m e a b i l i t i e s were estimated f r o ml a b o r a t o r y teats which have been shown in some casas tobe one to two orders of magni tude lower than actual f i e l dp s o i a a b i l i t i a s . Laboratory p e rmeab i l i t i e s do not r e f l e c tin-situ p e r m e a b i l i t i e s because the values do notnecmssar i ly in c lud e an adj ustment f or f l o w a long

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f r a c t u r e s which o f t e n d e v e l o p in c lays .* The p o r o s i t y used in the s e epage ve loc i ty c a l c u l a t i o n sshould be e f f e c t i v e , no t actual poro s i ty . The a f f e c t i v ep o r o s i t y of a clay is g e n e r a l l y much less than the actualp o r o s i t y .* The l o n g i t u d i n a l d i s p e r s i v i t y values used in the modela p p e a r quite low. The s e n s i t i v i t y o f th i s parametershould be ta s t ed by using a larger value, such as 10f e a t .* The h a l f - l i f e values used in the model have an ex tr eme lylarge i n f l u e n c e on the model r e su l t s . However , thesenumbers a l so have a great deal of uncer ta inty as sociatedw i t h them. Severa l model runs should be c o m p l e t e d us ingd i f f e r e n t h a l f - l i f e value s t o d emons tra t e t h e s e n s i t i v i t yof t h e model t o th i s p a r a m e t e r , I n c r e a s i n g th e h a l f - l i f eof the compounds by an order of magni tud e , which isp o s s i b l e given the uncer ta in ty of e s t i m a t i n g thi sparameter , may have a large i n f l u e n c e on th© r e su l t s .Because an a n a l y t i c a l model is being used for the s i m u l a t i o n s ,it is not a time consuming proces s to run a d d i t i o n a lscenarios. P l e a s e run the m o d e l s to i n c l u d e a s e n s i t i v i t ya n a l y s i s to d emons t ra t e the s e n s i t i v i t y of the mode l to thevarious parameter s ©numerated above. A range of values shouldbe pre s en t ed in the conc lus ion sec t ion, i n c l u d i n g a d i s cu s s i onof the uncer ta in ty of each parame t er . M o d e l i n g at any l e v e l ,e s p e c i a l l y a n a l y t i c a l m o d e l i n g , has a large degree o fu n c e r t a i n t y as sociated with it that s h o u l d be q u a n t i f i e d tothe gr ea t e s t extent p o s s i b l e .

19 . S e c t i o n 7.2.1, Data L i m i t a t i o n s and Recommendat ions f or F u t u r eW o r kP r o d u c t i o n h i s t o r y and a n a l y t i c a l r e su l t s f o r th e f r e n c h d r a i nshould be a v a i l a b l e f or the f i n a l Rl report . T h i s i n f o r m a t i o nand how it may a f f e c t the pre sent i n t e r p r e t a t i o n s ofcontaminant extent near the waste pit should be i n c l u d e d inthe f i n a l RI repor t .

2 0 . S e c t i o n 7 . 2 , 2 , Recommended Remed ia l A c t i o n O b j e c t i v e sC o n t a m i n a n t s i d e n t i f i e d onsite ar@ s t i l l consideredcontaminants of concern even though the concentrations arewith in a c c e p t a b l e h e a l t h - r i s k l ev e l s . Furthermore , M C L s f o rs thylbenzena and benzene (0 .7 and 0.005 m g / 1 , r e s p e c t i v e l y )were excaaded in well M W - 1 4 . The d i s cu s s ion on thecontaminants of concern needs to b© revised to r e f l e c t thesepoints.

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21. T a b l e 4*7S p e c i f i c c onduc t iv i ty , pH, and t emperature o f th e ground waters a m p l e s should be added to T a b l e 4-7.

2 2 * F i g u r e I SThe e thylb enzene concentration in the soil s a m p l e c o l l e c t e d atboring B-13Q was 1200 u g / g . T h e r e f o r e , an i soconcentrat ioncontour of 1000 u g / g needs to be inc luded on the f i g u r e .Due to the l im i t ed s u b s u r f a c e soil s a m p l i n g in the area of theh o l d i n g p o n d , the e x t r a p o l a t i o n of the l e v e l s o f contaminantconcentrations in th i s area needs to i l l u s t r a t e d on F i g u r e 15.Because of l im i t ed data r e s u l t s , the concentrat ion ofcontaminants in thi s area may be greater than 100 x i g / g .

23. F i g u r e 17It i s not c lear whether " T o t a l Organic C o n s t i t u e n t s " i n c l u d e sthe s e m i v o l a t i l e r e su l t s . The f i g u r e should be reconstructedusing both s e m i v o l a t i l e and v o l a t i l e r e s u l t s , or i f the f i g u r ehas a l r e a d y been constructed based on both v o l a t i l e ands a m i v o l a t i l e r e s u l t s , the f i g u r e should be r e t i t l e d .

24. A p p e n d i x BThe d e p t h s at which water was encountered are not i n c l u d e d onthe l o g s for borings B-122, B-123, B-126, B-127, and B-128.If a v a i l a b l e , inc lude thi s i n f o r m a t i o n on the boring log s orgive an e x p l a n a t i o n as to why it does not ex i s t .E x p l a i n why bor ings B-113, B-120, and B-121 were t e rminat edb e f o r e encountering the water t a b l e .For c l a r i t y , the l o g s for borings B - E X P L - 3 , B - E X P L - 2 , and B~E X P L - 1 need to i n d i c a t e that the borings were a l s o for M W - 1 8 ,M W - 1 9 , a n d M W - 2 0 , r e s p e c t i v e l y .

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R E V I E W C O M M E N T SD t J T C H T O W N O I L T R E A T M E N T S I T S

D R A F T R I S K A S S E S S M E N TGeneral comments1. Ground W a t e r P a t h w a y : The exposure pathway f r o m ground waterto human re c ep tor s is l i s t e d as i n c o m p l e t e ( F i g u r e 18, S i t eConceptual M o d e l ) * However, thi s exposure pathway i saddressed quanti tat ive ly through the ground water mode l ing.The risk assessment should either use the ground waterm o d e l i n g data to characterize risk f r o m ground water exposure( i n g e s t i o n and i n h a l a t i o n ) or prov ide more d e t a i l s on why theground water pa thway is i n c o m p l e t e as described in C h a p t e r 5.0Contaminant F a t e and T r a n s p o r t .2. Environmental Evaluat ion: The Environmental Eva lua t i on shouldprovide a d i s cu s s i on of cap maintenance to prevent v eg e ta t i on( e . g . , tree r o o t s ) and b u r r o w i n g / d i g g i n g animal s f r o md i s r u p t i n g the i n t e g r i t y o f the c lay cap. The cap i n t e g r i t yassures that the environmental pa thways are i n c o m p l e t e . Theground water to s u r f a c e water pa thway should be d i s cu s s ed . Ina d d i t i o n , the Environmental Eva lua t i on should p r o v i d e a S i t eC o n c e p t u a l M o d e l s im i lar to F i g u r e 18 (or by m o d i f y i n g F i g u r e18) .S p e c i f i c Comments1. S e c t i o n s 6*1 and 6 .2 , I n t r o d u c t i o n and scope and O b j e c t i v e s

In a d d i t i o n to current use and no act ion c o n d i t i o n s , theba s e l ine risk assessment should cons ider f u t u r e land usec o n d i t i o n s . Discu s s ions of f u t u r e c o n d i t i o n s should be morec l e a r l y d e f i n e d .2. S e c t i o n 6 * 4 * 1 , Source s of Chemical Data

The e l i m i n a t i o n of ch emica l s that do not exceed backgroundconcentrat ions has been a source of c o n f l i c t at several s i te s( e . g . , G u l f C o a s t , D . L . M u d ) . T h e "treatment" o f backgroundchemical s i s ambiguous in the RAGS guidanc e . The ra t ional fore l i m i n a t i n g ch emica l s should be s tated on a chemical s p e c i f i cbasis.3. S e c t i o n 6 .5 .2 .2 , P o t e n t i a l Recep tor P o p u l a t i o n s

^feis p a r a g r a p h s ta t e s that the f u t u r e land use is lUc^ ly to befor indu s t r ia l purpose s . T h i s stat@ment is inconsistent withSec t i on 3,6 (Demography and tand U s m ) which s tates that thesite is surrounded by r e s i d en t ia l and commercial land withsome pa s ture and S e c t i o n 6.5.1 ( S i t e D e s c r i p t i o n ) which

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mentions the prox imi ty of the r e s id en t ia l area,c l a r i f y . Please

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Sect ion 6 * 5 . 2 . 5 , integration of Exposure Pathway Components:The S i t e Conceptual Exposure ModelThe site conceptual exposure model is shown in F i g u r e 18instead of F i g u r e 17. T h i s paragraph notes that the twoprimary sources of contaminants are the sha l l ow ground waterand the sur face and subsurface soils* However, F i g u r e 18( S i t e Conceptual M o d e l ) indicates that the exposure pathwayf r o m ground water to human receptors is l i s t ed as incomplete.T h i s exposure pathway is addressed quant i ta t ive ly through theground water mode l ing . A discussion on the p r a c t i c a l i t y ofusing the shal low aqu i f e r s as a drinking water source shouldbe included ( e . g . , the i n s u f f i c i e n t y i e l d ) .S e c t i o n 6 . 5 * 3 , Exposure Point Concentrat ionsThe last sentence of the last ^ p a r a g r a p h should read that theuse of the .upper, c o n f i d e n c e l imit of the arithmetic mean asrecommended by the guidance document is a conservativeapproach ( U S E P A 1 9 9 2 a ) .S e c t i o n 6.5.4.1, Q u a n t i f y i n g Average and Reasonable MaximumExposure sThe average exposure should be e s t imat ed using the 95% u p p e rc o n f i d e n c e l i m i t on the a r i t h m e t i c mean of the measuredchemical concentrations. The average and reasonable maximumexposure (RME) should use the same concentration term (US EPA1 9 9 2 a ) .Sect ion 6*5 .4 .3 ,A s s u m p t i o n s Exposure A s s u m p t i o n s , S p e c i f i c Exposure

What is th& j u s t i f i c a t i o n or basis for the assumption that aperson is exposed 8 h o u r s / d a y and 275 d a y s / y e a r in the averagecase and 16 h o u r s / d a y and 350 d a y s / y e a r in the RME case? Areasonable as sumption would be to assume 24 h o u r s / d a y and 350d a y s / y e a r for both cases*The average and RME soil i n g & s t i o n rates for ch i ldren shouldbe 200 m g / d a y (US EPA 1989a). A soil inge s t ion rate forch i ldren of 200 m g / d a y r epre s en t s an average case. An u p p e rbound soil inge s t i on rate for ch i ldr en would be Suo m g / d a y (USEPA 1989b) . Tha average and RME soil inge s t ion rates fora d u l t s should be 100 m g / d a y (US EPA 1 9 8 9 a ) . P l e a s t e reviseaccordingly.

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What is the basis for the assumption that th© f r a c t i o n of soilcontaminated is 10% and 20% for the average and RME eases,

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r e sp e c t i v e ly? A reasonable a s s u m p t i o n would be to assume thef r a c t i o n of soil contaminated to be 100% for both cases.What is the basis for the a s sumpt i on that 10% and 20% of thebody surface would be exposed for the average and RME cases,r e s p e c t i v e l y ? P l e a s e c l a r i f y *The toxic i ty values (reference doses and oral s l o p e f a c t o r s )used in risk assessment are based upon admini s t e r ed dose.T h e r e f o r e , "matrix e f f e c t " for oral inge s t i on should not beaccounted s e p a r a t e l y in the risk c a l c u l a t i o n s . The riskc a l c u l a t i o n s should be p e r f o r m e d using 100% b i o a v a i l a b i l i t y .The soil l o a d i n g on skin (adherence f a c t o r ) should be 0.2rag/ cm 2 and 1 m g / c m 2 for the average and RME cases, r e s p e c t i v e l y( U S E P A I 9 9 2 b ) , P l e a s e revise a c c o r d i n g l y *T o x i c i t y values (re f e r enc e concentrations and inha la t i on s l o p ef a c t o r s ) used in risk assessment u s u a l l y are based uponi n h a l a t i o n s t u d i e s a n d a d j u s t e d f o r do s ime try ( U S E P A 1 9 9 0 ) .Clearance should not be accounted for s e p a r a t e l y in the riskc a l c u l a t i o n s . T h e correction f o r lung d e p o s i t i o n a n d c i l i a r yclearance should be e l i m i n a t e d .S e c t i o n 6 .6 .3 , T o x i c i t y A s s e s s m e n t f o r C o m p o u n d s withCarc inogen i c E f f e c t sPleas e d e l e t e last sentence of the last p a r a g r a p h in thissection.S e c t i o n 6.6.4, Lead T o x i c i t y , R e s u l t sPage 89 , T h i r d P a r a g r a p h : P l e a s e p r o v i d e a d e p i c t i o n o f th ed i s t r i b u t i o n o f c h i l d r e n ' s b lood lead a n d p r o p o r t i o n o f t h ep o p u l a t i o n which exceeds a blood lead concentrat ion of 10/ i g / d l .S e c t i o n 6 . 6 . 4 , Lead T o x i c i t y , P r e d i c t e d Average Blood L e v e l sThe mean b lood lead l e v e l s mentioned in the text are f r o m 1975to 1980. A more recent re ference on mean blood lead l eve l s isd e s i r a b l e due to the reduction of lead sources since the l a t e1 9 7 0 ' s .

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R e f e r e n c e s :U S E P A . 1989a. I n t e r i m F i n a l G u i d a n c e f o r S o i l I n g e s t i o n H a t e s .OSWER Directive 9850.4.U S E P A . 1 9 f l 9 b , Exposure F a c t o r s H a n d b o o k , E P A / 6 0 0 / 8 - 8 9 / 0 4 3 .

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US E P A . 1990. I n t e r i m methods for d eve l opment o f inha la t i onr e f e r enc e concentrations. B P A / 6 0 0 / 8 - 9 0 / 0 6 6 A .US E P A . 1992a. S u p p l e m e n t a l Guidance t o RAGS: C a l c u l a t i n g th eConcentra t ion Term. P u b l i c a t i o n 9285 ,7-081 .US E P A . 1992b. Dermal Expo sure A s s e s s m e n t : P r i n c i p l e s andA p p l i c a t i o n s , E P A / 6 0 0 / 8 - 9 1 / 0 1 1 B .

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