T-<ir?

Hercules Incorporate?MERCULES _____ Hercules Plaza '"̂1313 North Market S«SSt

T n^ innc Wilmington, DE 1989^)001January 24, 1995 (302) 594-5000

VIA FAX: No of pages-24Originals Hand Carried - January 25, 1995

Mr. M. S. RameshSuperfund Enforcement Branch (6H-EA)U.S. EPA Region VI1445 Ross AvenueDallas, Texas 75202-2733

Mr. M. ArjmandiArkansas Department of Pollution Control and EcologyHazardous Waste DivisionP.O. Box 9583Little Rock, Arkansas 72219

SUBJECT: Vertac Site Surface Soil Cleanup Criteria

Gentlemen:

Hercules had previously submitted two reports prepared by ENVIRONCorporation regarding risk assessments for potential future exposure to Vertacsite soil. They are "Risk^Agsessment.o^Prospective Cleanup Levels for 2,3,7.8-TCDD in Surface Soils at the Vertac Chenniffll Corporation Site. Jacksonville.Arkansas" (revised report), April 11, 1994, and "EPA RME Scenarios for theVertac Chemical Site, Jacksonville, Arkansas" letter report dated June 28, 1994.Hercules and ENVIRON Corporation welcome the opportunity to provide theattached additional information on this subject in response to questions raised byEPA and ADPC&E.

The risk analyses performed by ENVIRON indicate that use of a 5.2 ppbaverage 2,3,7,8-TCDD concentration in combination with a 50 ppb not-to-exceed(NTE) standard would meet EPA's acceptable risk criteria for trespassers andprotected workers when the 95th percentile exposure is used to define the RMEcondition. ENVIRON's reports and the additional information enclosed with thisletter describe the basis for our belief that the risks posed by a 50 ppb NTEcleanup goal have been conservatively estimated. Examples of conservatism arethat the calculated potential risk is based on 95% UCL concentrations instead ofaverage concentrations and some of the clean areas of the site were excluded whencalculating the average residual concentrations. Additional protection can beprovided by establishing cleanup goals based on the Toxicity Equivalent (TEQ)concentrations instead of the concentration of 2,3,7,8-TCDD alone.

Messrs. Ramesh and ArjmandiJanuary 24, 1995Page 2

The additional information provided with this letter and other questionswhich might arise can be discussed at the meeting scheduled for 12:00 noon onJanuary 25.1995.

Sincerely,

^-Douglas J-KeilmanDirector, Environmental Affairs

DJK/Iarwp/i: mtgschdJtr

cc: R. Kapuscinski - ENVIRON CorporationF. Kinoshita - Hercules Incorporated

?/•?Review of the Risk Assessment of Prospective Cleanup Levels -. -.•',

for 2,3,7,8 TCDD in Surface Soil 0at the Vertac Chemical Corporation Site °

RESPONSE TO AGENCY COMMENTS

General FftmiH t̂a and Responses

1. Risk assessment was based on 2,3,7,8-TCDD concentrations. Evaluatecumulative risk from exposure to dioxin/furans at the site based on toxicityequivalents (TEQs) to 2,3,7,8-TCDD instead.

Response: Although 2,3,7,8-TCDD has been recognized as theprimary contaminant of concern related to the Vertac site, Herculeshas recently developed data to show that other dioxin/furancongeners may represent between 0% and 30% of the potential healthrisk-at the site. That data was provided to EPA and ADPC&E onDecember 28,1994 (Attachment 1). The risk assessments contained inthe ENVIRON reports are based on the average residual 2,3,7,8-TCDDconcentration after remediation. The agency can achieve the desiredrisk reduction by specifying that the remediation reduce the averageresidual TEQ to the average 2,3,7,8-TCDD concentration used in therisk assessment. As an example, a "not to exceed" (NTE) cleanupstandard of 50 ppb 2,3,7,8,-TCDD for the gridded areas within the sitefence win result in an average residual concentration of 6.2 ppb2,3,7,8-TCDD. The residual risk calculated by ENVIRON can beachieved if the cleanup standard Is specified as that required toachieve an average residual concentration of 6.2 ppb TEQ. ^ENVIRONS reports describe the basis for our belief that the risksposed by an average residual concentration of 6.2 ppb have beenconservatively estimated. Because many scientists question thevalidity of the additivity assumption that is implicit in the TEQapproach, adopting an average residual concentration of 6.2 ppb TEQshould provide an additional margin of safety.

2. Representative samples from remediated areas should be collected to verify theassumption that the residual TCDD concentrations (again report values asTEQs not TCDD) do not exceed 0.3 ng/g.

R^sppnse; Several areas within the fenced southern portion ofVertac site were remediated under EPA and ADPC&E oversight usingclean soil imported from an off-site area. EPA is correct, however,that the current contamination level should be verified. Whencurrent levels are determined, they should be included in the

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calculation to demonstrate that the required average residualconcentration has been achieved. This subject is addressed ingreater detail in response to "Specific Comments" numbers 1 and 2below.

3. The hazard quotient calculated in this risk assessment was based on an RfD^ developed by ENVIRON. The reassessment of dioxin document recommended

^ '/ V against developing an RfD toxicity value for dioxin. The document reports^ (̂ if that the body burdens of the general population of the United States from^ t ^ ' background exposures are at the levels where non-cancer adverse effects could

01 oe observed. As such, RfD values should not be developed.y'^y EPA recommends determining the incremental increase in intake of dioxin.

That is, calculate the proportion of intake from the site relative to backgroundintake. This is done to determine if a significant increase over backgroundintake is expected from the site.

Response; There is substantial disagreement within the scientificcommunity about the magnitude of background intakes of dioxinsand furans and about the chronic dose levels that would be necessaryto cause non-cancer health effects in humans. Hence, it is not certainthat non-cancer effects will be observed at dose levels several timeshigher than the background intake, which EPA estimates at 119 -——pg/day in its August 1994 exposure assessment report/

As requested by the comment, however, ENVIRON has translated thelifetime excess cancer risk estimates for various NTE cleanup goalsinto daily intakes to facilitate risk management decision-making.The resulting values are shown in Table 1. Comparing the intakevalues for a not-to-exceed cleanup goal of 60 ppb f̂o tihue EPA •estimated "background" intake of approximately 119pg/day leads tothe following conclusions: '<_/-"

o The projected daily intake is approximately 16% ofbackground for a 95th percentile adult trespasser and

1 For comparison, the subchronic ADI developed by ENVIRON (6.5 pg/kg-day),based upon the most sensitive endpoint in experimental animals, corresponds to anacceptable intake of 455 pg/day for a 70-kg adult.

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approximately 1% of background for a typical (50thpercentile) adult trespasser.

o The projected daily intake is approximately 2% ofbackground for a 95th percentile teenage trespasser andapproximately 0.3% of background for a typical (50thpercentile) teenage trespasser.

o The projected daily intake is approximately 16% ofbackground for a 95th percentile protected worker andapproximately 2% of background for a typical (50thpercentile) protected worker.

o The projected daily intake is approximately 60% ofbackground for a 95th percentile unprotected worker andapproximately 5% of background for a typical (50thpercentile) unprotected worker.

Only for the unprotected worker with a "high end" exposure is theestimated daily intake greater than the EPA's current estimate ofbackground intake. The "high end" estimates for workers assumethat 250 work days per year for each of 25 years will be spent in thecontaminated (gridded) portions of the fenced area of the site. Thisand other conservative factors undoubtedly lead to a substantialoverstatement of the actual exposure that site maintenance workerscould reasonably experience, because there will be no need for theseworkers to visit the contaminated portions of the site so frequently.Furthermore, it is not certain that any non-cancer effects will beobserved at dose levels even several times higher than thebackground intake.

4. Cleanup guidance requires the use of reasonable maximum exposure (RME)scenario for the site to be protective of human health and the environment on along term basis. RME is determined by using a combination of average and95% UCL values. Average body weights and average skin surface area couldbe used.

Response: We concur the RME is determined using a combination ofaverage and "high end" values of exposure factors. We also concurthat cleanup guidance requires the use of an RME scenario. U.S.EPA guidance indicates, however, that the 90th percentile or 95thpercentile values are acceptable for establishing RME conditions for

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risb. management decision-making. The ENVIRON report, therefore,presents risk measures for the 96th and 90th percentile exposures inevaluating alternative NTE cleanup levels at the Yertac site. Asnoted below, we believe probabilistic simulations are an appropriatemeans of developing these KME values.

ENVIRON'8 calculations indicate the point estimates of exposure andrisk obtained using U.S. EPA Region VTs recommended exposurefactors greatly exceed the 95th percentile; hence, we believe they aremore conservative than what was intended for an RME condition.This finding is consistent with those of other investigators who haveevaluated the problem of "compounding conservatisms" (see RiskA«nlv«a l3(2): 131-134 and Reyulatorv Toxicology and Plinrmannlnfv14: 107-117, copies of which are attached).

5. Monte Carlo simulations and analysis could be used as supplementalquantitative evaluation of the uncertainties in the risk assessments for cleanuplevels but not in place of the recommended EPA Reasonable MaximumExposure approach for calculating cleanup levels for the site.

Response; We submit that exposures and risk measures developedusing probabilistic simulations, in addition to being useful inevaluating uncertainties in risk assessments, are an appropriatebasis for combining average and "high end" values and, thereby,identifying multiple potential RME conditions (each with its ownprobability of exceedance). Several U.S. EPA scientists and riskmanagers, including Roy Smith of Region m (see H"̂ AnfllYfliff 14(4):433-439) a copy of which is attached), concur that Monte Carlosimulations can be useful in implementing U.S. EPA guidance fordeveloping "multiple descriptors of risk", as contrasted to a singleconservative point estimate of risk.

The ENVIRON report, which is based upon probabilistic riskcalculations, is supplemented by ENVIRON's June 1994 letter report,which provides point estimates of exposure and risk for a NTEcleanup goal of 50 ng/g. Hence, risk measures using both approacheshave been developed and submitted to U.S. EPA Region VI.

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Specific rnmrnantq and Responses

(Page 2, 3rd paragraph)

1. It was reported that "Because approximately 40% of the area proposed forfencing was not gridded and is believed not to have TCDD in surface soil...."Statements made based on belief rather than actual surface soil samplesshould be avoided. Recommend deleting the whole paragraph or provide thedata to support the statement.

(Page 2, last paragraph)

2. The 50 ppb NTE cleanup goal was calculated using the assumption that theresidual TCDD concentration would be 0.3 ng/g. Report cleanup levels andresidual concentrations as TEQs and not TCDDs. Actual cleanup levelsshould not rely on assumptions made for concentrations of TEQs in clean soilcover. Samples should be collected to verify the concentrations ofdioxin / furans TEQs in clean soil.

Raaponsei Specific comments 1 and 2 are being addressed togetherbecause they deal with related aspects of the issue of averageresidual surface contaminant concentration following remediation.(The response to the TEQ vs. 2,3,7,8-TCDD issue was provided in"General Response" (above) and is not repeated here.) ENVIRON didnot include the ungridded areas of the south fenced portion of thesite when average residual dioxin/furan congener concentration andresidual risk were calculated. ENVIRON did, however, point out itsexistance to the risk manager. Hercules disagrees that "statementsmade based on belief rather than actual surface soil samples shouldbe avoided" when offered for the risk manager's qualitativeconsideration. This is especially true when the "beliefs" are based onthe fact that the areas in question were remediated under EPA andADPC&E oversight using off-site soil that had been analyzed as clean.

We agree that the beliefs should be verified if relied on by the riskmanager. Verification should occur during the remedial design orremedial action phase of ROD implement? tion. Hercules anticipatesthat the ROD will include both a "Not to Exceed" criteria and an"Average Residual Concentration" criteria for 2,3,7,8-TCDD or TEQ insoil for all areas included in the fenced portion of the site.

3. It was reported that EPA recommended values include upper-bound values for

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seueral of the exposure factors. Each factor mentioned is discussed here:

(a) It was reported that the oral absorption factor of 0.4 may substantiallyoverestimate the bioavailability of TCDD in surface soil at the Vertac site.The study conducted by Gallo and Meeker (1993) suggests that TCDD insurface soils at the site is not as bioavailable as was TCDD in the soilsamples from other sites that formed the basis for EPA's generic defaultvalues. A sensitivity analysis was performed by ENVIRON and EPA onoral absorption factor. The sensitivity analysis did not show anysignificant change in risk due to a change in the absorption factor. AlsoEPA reviewed the study done by Gallo and Meeker (1993) and hadreservations on using the data. This was relayed to the PRPs in writingand in a meeting with Gallo and John Doull.

Rg^ponw EPA Risk Assessment Guidance for Superfund Sitesencourages the use of the site-specific exposure information overgeneric default assumptions. Despite the fact that ENVIRON'8sensitivity analysis for changes in oral absorption factor showedthere is not a significant change in risk due to a change in the factorHercules believes that the site-specific data should be considered bythe risk manager.

In the case of the oral absorption factor, the derivation of a value(i.e., upper bound of 10%) based upon the studies by Gallo andMeeker, which used Vertac soil samples, is scientifically preferable tousing a default value (40%) that is derived from a study in which ratsreceived 2,3,7,8-TCDD dissolved in corn oil that was mixed with "ratchow."

In response to EPA's concerns, expressed at the meeting with Dr.Michael Gallo and Dr. John Doull, it was agreed that a follow-upstudy to support the bioavailability study was desirable. Therefore, astudy was conducted to determine whether the extractability of2,3,7,8-TCDD from contaminated soil taken from the Vertac sitediffered for some unknown reason from the extractability of 2,3,7,8-TCDD in contaminated soils from Times Beach, Missouri andNewark, New Jersey. The report on the follow-up study wassubmitted to EPA Region VI and Arkansas Department of PollutionControl & Ecology (ADPC&E) on November 1,1994. Use of an enzymeassay demonstrated that the 2,3,7,8-TCDD in the tested soil remainedbound to the soil, confirming the results of the rat bioavailabilitystudy.

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3. (a) continuedFor dermal absorption factor, EPA guidance on dermal exposure (1992)pages 6-19 recommends using 0.1 % for soil with high organic contentand 3% for soil with low organic carbon content Since the organiccontent of soil at Vertac is not known, EPA recommends using the high-end value of 3% to err on the conservative side of the range.

Rasponaa' A chemical substance on soil that is adhered to skin mustfirst desorb from the soil before it can contact and permeate skin.Consequently, the data obtained by Gallo and Meeker regarding theextractability of 2,3,7,8-TCDD from Vertac soil samples is relevant toan assessment of dermal absorption also.

As noted above, the follow-up study conducted by Gallo and Meekerdetermined that 2,3,7,8-TCDD in the tested Vertac soil remainedbound to the soil when mixed with a buffer solution and agitated for24 hours. When present on skin-adhering soil, 2,3,7,8-TCDD isexpected to desorb at an even slower rate and, to a smaller extent,because test conditions in the laboratory are intended to acceleratedesorption and mass transfer into the solution. On this basis, thedermal absorption factor for 2,3,7,8-TCDD in Vertac soil is expectedto be very low.

Animal testing data used to derive the default value of 3% for dermalabsorption employed dense coatings of contaminated soil on skin.According to EPA's dermal exposure assessment guidance manual,such dense coatings exceed the amount of soil adherence that wouldbe expected to occur naturally and enhance dermal permeation rates.

Given the above, Hercules and ENVIRON believe the default value of3% for dermal absorption should not be used exclusively for theVertac risk assessment. The risk analysis performed by ENVIRONrecognizes the possibility that the dermal absorption factor could beas high as 3%. It includes other possibilities also, in part because ofthe recent findings of Gallo and Meeker.

(b) It is reported by ENVIRON the soil adherence factor of 1.0 mg/cm2 is atthe maximum plausible value, as identified by EPA in its dermalguidance. The dermal guidance gives a range of 0.2 to 1.5 mg/cm2 andidentifies 1.0 mg/cm2 as a reasonable upper value.

Response: Hercules and ENVIRON agree with the comment.

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(c) It was reported that me values for exposure frequency and duration for atrespasser is 60 times a year for each of ten years and for a worker 250days per year for each of 25 years. EPA recognizes the lack ofinformation on trespasser exposure frequency and duration. Unless thereare trespassing site-specific scientific studies done for the site, theassumption made for a trespasser scenario by EPA Region 6 is consideredadequate for the site. The default values used for a worker scenario is thesame values as recommended by EPA guidance on standard defaultexposure values for calculating cleanup levels for Super fund sites.

Response; The risk analysis performed by ENVIRON recognizesthere is a possibility an individual will trespass on the Vertac site ata frequency suggested by EPA, i.e., 60 times per year. In the absenceof the site specific data ENVIRON used a trespass probabilitydistribution that ranged from. 0 to 365 trespasses per year and had anaverage frequency of 17.6 per year. This distribution assumes that3.3% of the trespassing population visits the fenced area of the sitebetween 60 and 365 days per year. Although Hercules site personnelobservations indicated only about ten incidents of trespass in aboutsix years, no data existed for those periods when site personnel wereabsent, e.g., nights and weekends.

Hercules installed additional security fencing at the site during thesummer of 1994. Pinkerton Security Services were hired on July 26,1994, to provide site security and information on trespass andattempted trespass frequency. During the period July 26, 1994, andJanuary 9, 1995, (see Attachment 2) they have only one "accesswithout being detected"; that being an authorized EPA employee.Hercules believes this site specific trespass data should be consideredby the EPA risk manager when establishing site cleanuprequirements. Specifically, we believe the risks to trespassers for a50 ppb not-to-exceed cleanup goal are overstated in the ENVIRONreports due to the conservative assumption regarding trespassfrequency. Such conservatism provides an additional margin ofsafety for trespassers.

(d) It was reported that the skin surface area for adults is based upon the95th percentile values for men and women.

Although the total surface skin area was used, it was not mentioned thata fraction of the skin surface exposed was also applied. A fraction of 0.16was used for unprotected worker and 0.037 for a protected worker

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(corresponding to the face only). Note that the average value for the totalskin surface area should be used instead of the 95th percentile value,especially when the average body weight is used.

Response: As suggested by EPA, the average value for the total skinarea was used instead of the 96th percentile value to recalculate theconservative point estimates for teenage (12 • 18 years of age) andchild (7 • 18 years of age) trespassers. Average total skin areas andan as«(umed exposed fraction of 0.317 (31.7%) which corresponds tothe average portion of the head, hands, forearms, and lower legs wasalso used. The resulting estimates of excess lifetime cancer risk(LCR) for these two groups of trespassers for a NTE concentration of50 ng/g are shown in Figure 1 as the "high-end base case" estimates.The high-end base case estimates are compared to the respective95th, 90th, and 50th percentile values, as determined by probabilisticrisk assessment calculations. The following conclusions can bederived from. these calculations.

o For both child and teenage trespassers the 50th percentile valuesof LCR are approximately 1 per million (10"8) and, so, are wellwithin the risk range typically deemed acceptable by U.S. EPA.

o For both child and teenage trespassers the 95th and 90thpercentile values of LCR are within the risk range typicallydeemed acceptable by U.S. EPA. U.S. EPA guidance indicates the90th percentile or 95th percentile values are acceptable forestablishing reasonable mmrimmn exposure (RME) conditions forrisk management decision making.

o The conservative point (high-end base case) estimates aresubstantially higher than their respective 95th percentile values.For both teenage and child trespassers, the high-end base caseestimates are at the maximum values obtained with theprobabilistic simulations, indicating they are associated with anexposure that is highly unlikely to occur.

o The conservative point (high-end base case) estimate of LCR fora child (7-18 years old) trespasser is 1.1 x 10"4 (110 per million),which is slightly above the risk range typically deemedacceptable by U.S. EPA.

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o Hie conservative point (high-end base case) estimate of LCR fora teenage (12 • 18 year old) trespasser is 6 z 10'" (60 per million),which is within the risk range typically deemed acceptable byU.S. EPA.

Although all types of potential populations should be discouragedfrom trespassing as a result of site security measures, includingfencing, a child trespasser seems a much less plausible scenario thana teenage trespasser.

(page 4, last paragraph)

4. It was reported that the 95th percentile values of LCR (Figure 1) aresubstantially lower than the EPA recommended RME approach.

Figure 1 shows the incremental cancer risk calculated for the unprotectedworker using the 95th percentile of the curve derived by Monte Carlosimulation was 1.55 x 10'4 compared to a cancer risk of 6.1 x 10'4 using EPAapproach. The same for the protected worker, the incremental cancer risk was0.42 x 10~* compared to 1.8 x Iff* using EPA approach. In both calculations(protected and unprotected workers) the difference between the two methodswas a factor of four. A factor of four does not seem to be a substantialdifference.

Response: Hercules recognizes the risk manager must decide if afactor of four is significant as part of an overall decision.

5. Conclusions: Dioxin ffurans were found nationally at background levels wheretoxic effects were or could be observed. There, it is recommended to evaluatethe percent increase of daily intake of dioxin due to site exposure over thatfrom background levels.

Unprotected Worker:Cancer Risk = Intake (mg/kg/day) * Slope Factor1.550-04 = Intake (mg/kg/day} * Slope FactorIntake = [2.56E+5 I L55E-4^J'= [1006451613*nmgfkg bwfday)

orIntake = 1 (pglkg bw/day)

The national background intake value of TCDDs was reported in thereassessment of dioxin document to be between 0.3 to 0.6 pg TCDD I kgbw/day.

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I/'we compare the daily intake ofdioxin/furans from the site to the dailyintake due to national background levels, we find the site will contribute about300% to 600% increase over that of background intake. If we consider TEQsinstead of TCDDs, the increase in intake over background might even be more.

Response: The response to this specific comment was included in theresponse to General Comment #3.

6. Therefore, I am recommending that a cleanup level of not-to-exceed value of 50ppb for Vertac site using a worker scenario be re-evaluated. Note that thereassessment ofdioxin document reported an intake value of 0.01 pg TEQs/kgbw/day that is associated with a 1 x 10^ cancer risk.

R«»aponflpii Hercules believes a 50 ppb 2,3,7,8-TCDD cleanup standardis appropriate for the southern half of the Vertac site. That belief isbased on two factors. The first is that this portion of the Vertac sitewhich contains waste burial areas will require groundwatermonitoring, collection, and treatment for the foreseeable future.These areas and appropriate buffer zones will be fenced and securefrom public access. Such secure areas represent lower potential riskthan areas where commercial activities occur without restriction.Therefore, less restrictive cleanup standards can be used to achieveequivalent health protection. _

Second, the risk assessments show that a high percentage ofpotentially exposed individuals will experience risks that are withinthe normally acceptable range, Le., less than 1 in 10,000.

One category of potentially exposed individuals is that of trespasserson the site. Ongoing experience has shown that trespassing isinfrequent despite the existence of many "attractive nuances" suchas equipment and buildings. Passive security measures can be takenin the unlikely event that trespass becomes more frequent.

Another category of potentially exposed individuals is that of siteemployee. All employees are, and will be, subject to work practicesthat will limit their potential exposure to well below that assumed inthe risk assessments.

For these reasons Hercules believes a 50 ppb 2,3,7,8-TCDD NTEcleanup standard is appropriate for the southern fenced position ofthe Vertac site.