Comments on draft baseline risk assessment533 lbs (0.25 tons) * Although more factual than the data...

^ 1 5 i ^ CONESTOGA-ROVERS & ASSOCIATES LIMITED % ^ l « i F ^ 651 Colby Drive, Consulting Engineers ^FUND RECORDS CTR Waterloo, Ontario, CanacJa N " " " - "

88015011 (519)884-0510 SFUND RECORDS CTR

0222-00449

March 8,1991 Reference No. 2141

Mr. Tom Dunkelman (H-7-2) Remedial Project Manager United States Envirotimental Protection Agency 75 Hawthorne Street San Francisco, California 94105

Dear Mr. Dunkelman:

Re: Comments - Draft Baseline Risk Assessment Hassayampa Landfill. Maricopa County, Ari2ona

Enclosed are comments prepared on behalf of the Hassayampa Steering Committee (HSC) on the above captioned report. The comments have been prepared by Errol L. Montgomery and Associates (M&A) and CRA with the review of the HSC Technical Subcommittee.

These comments are submitted to the EPA pursuant to the provisions of the approved Remedial Investigation/Feasibility Study Work Plan. Draft responses from the EPA are due within 30 days of the receipt of the comments.

These comments represent the joint concems of the Hassayampa Steering Committee, M&A and CRA. It is their conclusion that this Risk Assessment is fundamentally flawed because: (i) iiisuffident data is provided to adequately document and justify the modeling approach; (ii) the model used is not calibrated to site data; (iii) Remedial Investigation data and historical data are not used; (iv) present and future Site risks are grossly overestimated; and (v) appropriate EPA guidance documents are not followed. Numerous significant revisions are, in our joint opinion, required in the Risk Assessment for it to be technically accurate and legally adequate.

Based on the foregoing, it is the opinion of the Hassayampa Steering Committee that a revised draft Risk Assessment should be prepared and reissued. In the event

March 8,1991 2 Reference No. 2141

that the EPA does not intend for the Risk Assessment to be wholly revised and reissued, the Hassayampa Steering Committee strongly requests a meeting with the EPA at the earliest possible opportunity pursuant to Administrative Consent Order 88-08.

Yours truly,

CONESTOGA-ROVERS & ASSOCIATES

pO> Stephen M. Quigley, P. Eng.

SMQ/cz/7 End.

TABLE OF CONTENTS

Page

1. EXECUTIVE SUMMARY ES-1

SPECinC COMMENTS.

LIST OF TABLES

TABLE 1 EVALUATION - DATA USED FOR ASSESSMENT OF MIXTURES

TABLE 2 EVALUATION - DATA USED FOR QUANTITATIVE ASSESSMENT

TABLE 3 EVALUATION - DATA USED FOR QUALITATIVE ASSESSMENT

TABLE 4 COMPARISON OF MODELED DATA TO GROUNDWATER DATA

TABLE 5 COMPARISON OF CALCULATED EMISSION RATES TO MANIFESTED QUANTITIES

Following Page

16

16

26

29

LIST OF ATTACHMENTS

ATTACHMENT A

ATTACHMENT B

ATTACHMENT C

ATTACHMENT D

CHRONOLOGICAL DESCRIPTION -DEVELOPMENT OF RI/FS SCOPE OF WORK

ASSESSMENT - TOTAL DISPOSAL QUANTITIES

ASSESSMENT - MONTHLY DISPOSAL QUANTITIES

MARCH 7,1991 LETTER FROM THE OFFICE OF THE MARICOPA COUNTY ATTORNEY TO MONTGOMERY AND ASSOCIATES

COMMENTS - DRAFT BASELINE RISK ASSESSMENT HASSAYAMPA LANDFILL

MARICOPA COUNTY, ARIZONA

SECTION I - EXECUTIVE SUMMARY

1. The Risk Assessment methodology is inconsistent with established EPA guidance.

The Risk Assessment report utilizes methods for calculating exposure point concentrations that do not conform to EPA guidance (see Risk Assessment Guidance for Superfund (RAGS), EPA, 1989, the Superfund Public Health Evaluation Manual, EPA, 1986 and the Superfund Exposure Assessment Manual, EPA, 1988) and accepted approaches.

Specific examples of this are as follows:

• The draft Risk Assessment assumes vinyl chloride to be present even though it was never detected in groundwater. RAGS requires that a compound be demonstrated to be present before it can be included in a Risk Assessment.

• A qualitative risk assessment is included as a separate Section in the draft Risk Assessment when RAGS does not recognize the use of a qualitative assessment separate from the quantitative assessment. This qualitative assessment contains subjective statements that are apparently intended to provide support for the overconservative assumptions used in the unrelated quantitative assessment.

• The SUTRA groundwater model is not calibrated to Remedial Investigation Report (RI) (M&A and CRA, 1991) data. The Superfund Public Health Evaluation Manual requires models to be calibrated and the Superfund Exposure Assessment Manual.

• The RI monitoring data are considered in the Risk Assessment to be inadequate for use in estimating risks. RAGS requires that RI monitoring data be used.

• Degradation of chlorinated compounds to 1,1-dichloroethene is assumed. RAGS does not support such an assumption.

These inconsistencies between the Risk Assessment and EPA guidance as well as significant errors in reporting RI data are indicative of a lack of quality control in the development of the Risk Assessment report. This lack of

ES-1

quality control contributes substantially to the unsupportable conclusions of the Risk Assessment.

The draft Risk Assessment inappropriately considers the RI Report to be inadequate in spite of ongoing participation, review and approval of the EPA.

The RI report was prepared pursuant to Work Plans that were reviewed and approved by the EPA. Further, the RI Report conforms to EPA guidance that requires the RI to characterize the Site adequately for the Feasibility Study (FS) and Risk Assessment.

Criticisms of the scope of the RI are without basis, and at this late hour, unacceptable. The Risk Assessment should be rewritten and based on the Final RI.

3. The Draft Risk Assessment ignores much of the pertinent data from the Remedial Investigation Report and severely misstates and misrepresents important results from the RI.

The draft report as presented fails to accurately represent existing Site conditions. The existing Site conditions and past disposal practices are documented in the RI and the Liquid Waste Evaluation Report (LWE) (CRA and M&A, 1991). The estimation of future risks is thus flawed because it is not substantiated by measured data and because it relies on incorrect exposure point concentration calculations. The report suffers from numerous, highly significant errors that must be corrected in order for the report to be technically adequate and representative of potential risks at the Site.

The criticisms contained in the Risk Assessment that relate to the scope of the RI/FS are unwarranted. Clearly, the authors did not realize that the RI/FS scope of work and Work Plans were developed in consultation with and ultimately approved by the EPA. Attachment A to these comments provides a partial chronology of the process that led to development and EPA approval of the RI/FS Work Plan.

The EPA-approved RI Work Plan was designed to provide the essential data necessary for the FS and the Risk Assessment. In accordance with comments on the draft RI Report, although EPA did not previously require such a section in the Consent Order, the final RI Report contains a section on contaminant transport and fate.

The RI obtained all the data required by EPA in the Work Plans and some additional data not required. The accepted approach for the development of an investigative database, which was reviewed and approved by EPA and was

ES-2

completed for the RI, includes analyses via scans for a large number of the substances induding EPA Target Compound List, Target Analyte List and EP Toxicity parameters. All sampling plans were approved by EPA prior to Site activities being conducted.

The Risk Assessment implies that the RI Report did not contain all necessary data and that some of the data presented was inconsistent or suspect. In order for a meaningful response to be provided, this statement needs to be expanded to show: 1) how any potential shortcomings in the RI data are critical for conduct of the FS or the Risk Assessment; and 2) how these potential shortcomings are inconsistent with the plarmed approach given in the RI Work Plans reviewed and approved by EPA.

Significant overestimates and errors in the disposal quantities are reported in the Risk Assessment. Comparative manifest and Risk Assessment values are summarized below.

Compound Designated for Disposal

hydrocarbons copper

lead (solid) wastes lead (liquid) wastes 1,2-dichloropropane formaldehyde trichloroethane butyl acetate butyl cellosolve diethanolamine

Quantity Reported in Draft Risk Assessment

45,000 gals «2,000,000 gals

3,420 lbs 2,229 gals 1,350 gals 534 tons 7340 gals

50,000 gals 1,000 gals 286 tons

Manifested Quantity*

3,845 gals + 6.8 lbs =45,000 gals

(indudes hydroxides) 113 lbs

7,685 gals Ogals

4,465 lbs (2.2 tons) + 8 gals 2,400 gals 24,000 gals

Ogals 533 lbs (0.25 tons)

* Although more factual than the data assumed in the draft Risk Assessment, these manifested quantities are not considered to be sufficiently accurate or precise to be used in contaminant transport and fate modeling.

The Risk Assessment report states that the "risk assessment at the Site is based on measured RI data supplemented by contaminant fate and transport modeling."

This statement misrepresents the Risk Assessment which is, in fact, substantially based on fate and transport modeling which, in turn, utilizes an array of assumptions which are inconsistent with and unsupported by RI data.

RI analytical data do not demonstrate widespread contamination at the Site or the presence of contaminants above or remotely approaching saturation and,

ES-3

thus, support the conclusions of the LWE which indicate that a substantial proportion of the wastes which were approved for disposal at the Site either evaporated or were adsorbed on the subsurface soils.

If the manifest information is used for groundwater modeling, a complete review of the manifests themselves should be completed to ensure the reasonable accuracy of the data. For example, much of the disposed copper was in the form of copper hydroxide, and this was disposed of in Pit #3 (metallic and alkaline sludges). Under these conditions, the copper would be essentially insoluble in water.

The Risk Assessment was submitted for review prior to finalization of the RI Report. The EPA approved Work Plans clearly provided for submission of a Risk Assessment based on data presented in the Final RI. [The offidal schedule provided for 14 weeks for completion of the draft Risk Assessment following submission of the Final RI. In this case, the Risk Assessment was submitted prior to the finalization of the draft RI.] The Risk Assessment should be modified to reflect the Final RI and supporting documents to avoid the gross errors summarized in the Comments.

4. The presentation given in the Risk Assessment Report for modeling results is incomplete.

Modeling results typically and necessarily indude many details not given in the Risk Assessment Report. Because the Risk Assessment places an inordinate degree of importance on the modeling results versus the measured RI results for the projection of impact and risks, the detailed information on the model must be reviewed and evaluated. The additional data necessary for review were requested in letters to EPA dated February 12 and February 25,1991.

Although the SUTRA model was not calibrated as required by EPA guidance documents, it was used to predict groundwater chemical migration through the saturated and tmsaturated zones at the Site. To do so, the following specific parameters have to be defined: •

• the location of the source; • rate of release; and • concentrations of contaminant source.

The Risk Assessment report does not include all assumptions and equations necessary to specify how the modeled data were derived nor were the data input files submitted with the report. The discussion on the estimation of groimdwater exposure point concentrations using SUTRA is insuffident, resulting in the reviewer's inability to comprehend how the groundwater modeling data were derived.

ES-4

The Risk Assessment modeled assimiptions, not data, and such assimiptions are unrelated to measured RI data. In addition, the model was not calibrated to RI data and overstates measured concentrations by factors up to 1800.

The modeled assumptions used in the evaluation of chronic daily intakes (CDIs) for groundwater exposures are significantly higher than the maximum measured RI data. The ratios of modeling results to measured RI data range from 0.1 to 1,800. A range of ratios of 0.25 to 4 is considered to be acceptable (Schmidtke, K.D., University of Waterloo, 1985). Table ES-1 illustrates the significant differences between the modeled Risk Assessment assumption results and the maximum measured RI value. The use of these modeled assumption results, therefore, does not reflect Site conditions and, thereby grossly exaggerates exposure intakes and estimated cancer risks.

Calibration is essential for obtaining proper results and for evaluating such results from a numerical solute transport model such as SUTRA. In discussions on February 22,1991, PRC personnel responsible for the SUTRA modeling effort indicated that the model was not calibrated to Site conditions. Therefore, the reference to calibration given in the Risk Assessment should be removed. The lack of calibration casts severe doubt on the validity of using the model results to estimate risk at the Site. The model will be reviewed further when data requested from EPA are received. However, our preliminary evaluation indicates that the SUTRA model results should be removed from the Risk Assessment.

The results of the Risk Assessment indicate that the compound 1,1-dichloroethene (1,1-DCE) presents a significant cancer risk and the elements Copper and Lead present a non-cardnogenic hazard. The assumptions used to calculate the exposure point concentrations of these species are largely suspect because:

• The assumption that 100% of 1,1-IX!E present in the groundwater was all due to biodegradation of TCE is unrealistic. Competition of reaction processes such as volatilization, adsorption and most importantly, the bacterial/microbial population present in the groundwater are ignored by this assumption.

• Modeled data for Copper overestimate measured on-Site concentrations by 1,800 times. Further, the disposal volumes assumed for Copper are unsupportable. The Risk Assessment reported a disposal volume of "...nearly 2 million gallons..." yet the artual manifest records suggest a volume closer to 45,000 gallons.

ES-5

TABLE ES-1

COMPARISON OF MODELLED DATA TO THE RI GROUNDWATER DATA RISK ASSESSMENT COMMENTS HASSAYAMPA LANDFILL SITE

Compound

tetrachloroethene chloroethane 1,1,1-trichloroethane trichloroethene total xylenes dichloromethane 1,2-dichloropropane phenol Freon 113 MEK formaldehyde Copper Lead 1,2-dichloroethene (4) vinyl chloride (4) 1,1 -dichloroethene(4)

Modeled Concentration

(Ug/L)

27 357 98 182 10 36 199 455 49 626

303,000 42,000

201 31 0.5

290(5)

Maximum Concentration

Detected in Groundwater Samples

(tig/L)

2.1 ND(2)

25 5

ND(2) 47(1) 0.2 18

359 57

NA 23 13 10

ND (0.2) 547

Measured On-Site Unit A

RlWell

MW-6UA Not Detected

MW-IUA MW-6UA

Not Detected MW-IUA MW-6UA MW-IUA MW-6UA MW-2UA

MW-5UA MW-6UA MW-5UA

Not Detected MW-IUA

Frequency of Detection

4/93 0/93 16/93 10/93 0/93

38/93 1/93 1/46 11/93 13/39 - / -7/60 16/61 4/93 0/93 19/93

RaHo Modeled to

Measured Concentration

12.8 357 (3)

3.9 36.4

10(3) 0.8 995 25.3 0.1 11 —

1826 15.5 3.1

5(3) 0.53

Notes:

ND - not detected, the detection limil is in brackets. NA - not analyzed (1) no single sample of dichloromethane was reported which was not qualified by blank contamination (2) calculated basied on approximate detection limit (3) calculated based on 1/2 times the detection limit (4) Based on the Risk Assessment's calculation for the noted fractions of degradation products present. (5) The Risk Assessment indicates a time weighted average concentration of 341.1 ̂ g/L. We are unable to

reproduce this and several other time weighted averages in Table 3-13. ugl/L - micrograms per litre

• Modeled data for Lead overestimate measured on-Site concentrations by 15.5 times.

An assessment of the data and risk calculations for each of these three species indicates that the modeling results used to calculate the risk or hazard under any scenario are not supportable or relative in any way to the RI data.

The EPA requires the RI to develop an adequate knowledge of Site conditions for use in both the Feasibility Study and Risk Assessment. The Work Plans were approved by the EPA with this understanding and the RI successfully obtained the data required by the Work Plans. Because this Risk Assessment ignores RI data and is inconsistent with EPA Guidance, it therefore uses an unacceptable approach.

The gross imprecision and inaccuracy of the SUTRA model probably results from the lack of calibration, incorrect input to the model, and the unsupportable assumption that one-third of the wastes disposed entered the groundwater. This assumption is not supported by RI quantitative data, RI qualitative data and the LWE.

This assumption and the resultant modeled data, therefore, overestimate exposure and, consequently, exaggerate the current and potentiai problems at the Site. The lack of any effort to calibrate the model to RI data is inconsistent with EPA guidance and thus, produces results that are unsupportable and overestimate the risk.

The groundwater modeling presented in the Risk Assessment is wholly unreliable and, therefore, should not be used for estimating risk under any scenario.

The assumptions used in the Risk Assessment conceming the degradation of products of chlorinated solvents are incorrect.

Indusion of suspected contaminants based on the invalid assumption that Site-related chemicals degrade or will generate toxic by-produrts in the future is erroneous and is not supported by RI data. This is exemplified by the evaluation of vinyl chloride in the risk assessment with an exposure point concentration assumed equal to one-half of the sample quantitation limit even though vinyl chloride was never deterted in any groundwater sample.

The assumption is unrealistic that 1,2-dichloroethene (1,2-DCE) undergoes microbial degradation at a sufficient rate to be of concem. This is evident since vinyl chloride was not detected in any groundwater sample taken during the RI. Biodegradation of 1,2-DCE is influenced most importantly by the type of barterial/microbial population in the ground that would be able to

ES-6

degrade the compound. The EPA Risk Assessment Guidelines (RAGS, December 1989 page 5-20) outline the aiteria for the development of chemicals of potential concem. According to the criteria stated in RAGS, transformation products should be considered as a chemical of potential concem only if they are demonstrated to be present. Vinyl chloride should not, therefore, be treated in the Risk Assessment as a chemical of potential concem since it was not deterted in any groundwater sample.

The Risk Assessment assumption that 100 percent of parent compounds, (PCE, TCE and TCA) degrade to 1,1-DCE is erroneous. This unrealistic assumption ignores Site conditions as well as competition among reartion processes that influences chemical degradation. In the absence of data from the RI which supports this assumption, the Risk Assessment should assume no such degradation. An assumption of this degradation is inconsistent with EPA guidance (see RAGS page 6-11).

Estimated risks are based on misrepresented contaminant concentrations and, as such, are flawed and unsupportable.

The estimated Site risks indicate that "exposure under three of the four conditions evaluated in this risk assessment (off-site, near-site, and on-site residential) may pose unacceptable cancer risks" (Section 5.4).

The excess cancer risks given in the Risk Assessment are almost exdusively assodated with modeled results and assumptions which are inconsistent with measured RI results and assumptions and which overestimate the concentrations of contaminants in the various matrices. The resultant overestimated risks are applied to exposure calculations based on implausible scenarios, such as an on-Site residential setting. Hence, the estimated risks are unreasonable and unsupportable based on measured data and documentation presented in the RI Report.

The conceptual approach used for the Risk Assessment is excessively and unjustifiably conservative, leading to condusions regarding remedial objectives that are not consistent with Site conditions nor with analytical data and interpretations given in the RI. The conceptual approach in the Risk Assessment, therefore, requires substantial revision.

ES-7

SECTION II - SFEgPIC COMMENTS

Section 1.1, Paragraph 2, Sentence 3 and Last Clause of Last Sentence - Page 1

In 1987, the only monitor wells at the Hassayampa Landfill were Arizona Department of Health Services (ADHS) wells HS-1, HS-2, and HS-3. Well HS-1 is within the 10-acre hazardous waste area (the Site) while wells HS-2 and HS-3 are located distant from the hazardous waste area, but within the 47-acre area of the Hassayampa Landfill. The inconsistent use of the terms off-site" and on-site" in the draft Risk Assessment is confusing and should be clarified.

The detection of several volatile organic compounds (VOCs) at wells HS-2 and HS-3 in 1987 has not been confirmed during all of the sampling condurted from 1982 to the present and, thus "contaminant transport off-site" has not been confirmed.

Sentence 3 should be removed. If the clause in the last sentence means that Site contaminants have migrated off the Hassayampa Landfill, it should be deleted because data from the RI does not support the conclusion that Site contaminants have migrated off the Landfill.

Section 1.2, Paragraph 2 of Section, Last 2 Sentences - Page 2

Wind velocity data measured by the Goodyear Airport (approximately 22 miles east from the Site) are for the airport, not the Site. These sentences should be more spedfic.

Section 1.2, Paragraph 3 - Page 2

Depths given in this peiragraph should be referred to as average depths. As stated on page 53 of the RI Report, the average depth to the base of the basaltic lava-flow unit and top of Unit A is 73 feet at the Site, not 72 feet.

The definition for Unit B is wrong. As stated on page 52 of the RI Report, Unit B is bounded by Unit A on the top and by the Middle Alluvium unit on the bottom.

4. Figure 1-2 - Page 4

The dirertion of groundwater movement shown on this Figure is exaggerated to the southwest and is not consistent with the direction of groundwater

movement shown on Figure 16 of the RI Report. Although well MW-8UA is shown on Figure 1-2 as having "positive" contamination detertion, this detertion has not been confirmed.

The RI Report indicates that well (C-l-5)10aaa is an unused well, not an unused "domestic" well. The dashed Une indicating the location of a "cross sertion of the landfill (Fig. 3-1)" is not a line of section for any sertion given in the draft Risk Assessment Report, and Figure 3-1 contains no section. It would be helpful to use standard scales for Figures in the Risk Assessment. Finally, according to the windrose shown on this Figure, windspeed is nine miles per hour; however, this speed is not given in the text.

Section 1.2, Paragraph 2, Last 2 Sentences - Page 5

Neither the RI Report nor the available data indicate that Pit B contains substances similar to Pit 4. Pit 4 was designated for the disposal of pestiddes and alkaline sludges, whereas Pit B reportedly received hydrate wastes and no pesticides. This text should be changed further to indicate that Pits A and B were not part of the manifest program and were not designated to receive any of the wastes reported to be generated by the Respondents.

The Risk Assessment states that there was "a history of illegal dumping" at the Site. The report should document any information regarding the nature, source and significance of illegal dumping so that it may be evaluated. If verified documentation of the alleged illegal dumping is not available, the references should be removed and RI data should be used.

Section 1.2, Paragraph 3, Sentences 2,3, and 6 - Page 5

The Risk Assessment should also state that, as reported by Schmidt and Scott (1977), the type of waste disposed from 1961 to 1977 consisted chiefly of garbage, rubbish, tree trimmings, and other plant refuse. The last sentence should be changed to indicate that the waste was approved for disposal, but the volumes disposed were less (see page 36 of final RI Report).

7. Section 1.2, Ninth Paragraph of Section, Third Sentence - Page 5

The report states that "high" levels of contamination have been detected in the unsaturated zone. This is urmecessarily subjective and should be substantiated or deleted.

8. Section 1.2, Paragraph 1, Next to Last Sentence - Page 6

The RI Report Table 30 indicates that concentrations of volatile organic compounds in monitor wells MW-IUA and HS-1 inaeased and decreased during the RI; therefore, no temporal pattem is evident. Such increases during the first several sampling rounds are not uncommon for monitor wells completed in sediments having low permeability, and are indicative of slow recovery of such wells from the disturbance of drilling operations. This type of increase would appear to be occurring at recently constructed well MW-6UA. Additional sampling rounds would be required to investigate any potential temporal patterns for monitor wells MW-5UA and MW-6UA.

The reference to "off-site" contamination needs to be clarified and made consistent throughout the draft Risk Assessment. Contaminants have been detected and confirmed in groundwater samples obtained from wells MW-IUA (located on the border of the former hazardous waste area) and MW-5UA (located adjacent to the former hazardous waste area). Contaminants have not been confirmed in groundwater samples obtained from well MW-8UA, which is located on the southem boundary of the Hassayampa Landfill property and distant from the former hazardous waste area. A concentration of 0.7 M-g/L of 1,1,1-trichloroethane (TCA) was detected in one sample from well MW-8UA, but not in the duplicate sample and not in any other samples obtained from the well. Please also see Specific Comment #1.

It is incorrect to imply that evidence exists for contaminant transport south of the Hassayampa Landfill property without confirmation of contamination at the property boundary wells. The sentence subject to this comment should be removed from the Risk Assessment.

9. Section 1.3, Paragraph 2 of Section - Page 6

The report is critical of the RI as follows:

i) the RI presents a static picture of contamination at the Site; ii) the RI did not analyze samples for many potential contaminants and

did not consider all exposure pathways; iii) the RI did not indude the collection of samples from particular areas of

concem; and iv) no evidence has been provided to show that contaminated soil in and

beneath the pits will not continue to art as a source of groundwater contamination.

Responses to these criticisms are as follows:

i) The design of the RI is consistent with EPA Guidance (Guidelines for Conduction Remedial Investigations and Feasibility Studies under CERCLA, 1988, Chapter 2)

The EPA-approved RI Work Plan did not indude groundwater modeling and was designed to provide the essential data necessary for the FS and the Risk Assessment. In accordance with comments on the draft RI Report, although EPA did not previously require such a sertion in the Consent Order, the final RI Report contains a sertion on contaminant transport and fate. The RI obtained all the data required by EPA in the Work Plans and some additional data not required. It is not common and not necessary to analyze for all potential contaminants at a hazardous waste disposal site that received a wide range of substances; the accepted approach, which was reviewed and approved by EPA and was completed for the RI, includes analyses via scans for a large number of the substances. All sampling plans were approved by EPA prior to conducting Site artivities.

The criticisms contained in the Risk Assessment that relate to the scope of the RI/FS are unwarranted. Clearly, the authors did not realize that the RI/FS scope of work and Work Plans were developed in consultation with and ultimately approved by the EPA. Attachment A to these comments provides a partial chronology of the process that led to the development and EPA approved of the RI/FS Work Plan.

ii) All exposure pathways are considered in the RI Report and assessed in the sertion on Contaminant Transport and Fate.

iii) Without further explanation, this criticism is so vague that it is meaningless and, thus, prevents adequate response. The Risk Assessment should identify specifically what the particular areas of concem are so that responses to this critidsm can be prepared.

iv) The RI and LWE contain substantial evidence that contaminated soil will not continue to act as a source of groundwater contamination.

The RI Report states that "Soil borings have been drilled and sampled at the Site, and the soils encountered were neither saturated nor near saturation. Potential present sources to provide liquid for gravity drainage were not deterted during the RI. It is possible that potential residual contamination in the lower part of the vadose zone could be a continuing source of groundwater contamination if groundwater levels were to rise in the soils. However, data shown on Figure 23

indicate that groundwater levels in Unit A monitor wells have declined during the period of record."

The Risk Assessment report states that the "risk assessment at the Site is based on measured RI data supplemented by contaminant fate and transport modeling".

This statement misrepresents the Risk Assessment which is intact, substantially based on fate and transport modeling which in turn, utilizes an array of assumptions which are inconsistent with and unsupported by RI data.

Analytical data from the RI which do not demonstrate widespread contamination at the Site or the presence of contaminants above or remotely approaching saturation support the conclusions of the LWE which indicate that a substantial proportion of the wastes which were approved for disposal at the Site either evaporated or are adsorbed on the subsurface soils.

10. Section 1.3, Paragraph 3 of Section - Page 6

Based on our spedfic comment #9 above, the reference to "limitations" in this paragraph should be deleted. The Risk Assessment modeling modeling suffers from serious deficiencies as explained in subsequent comments.


It is not possible to discern from this Figure which media are indicated by "positive contaminant detection"; the information on the Figure should be clarified so that it can be evaluated. A line on Figure 1-3 is shown to indicate the location of a "cross sertion of the landfill for Figure 3-1"; however, no cross section is shown on Figure 3-1. Also, it would be helpful to use standard scales for Figures in the Risk Assessment.

12. Sertion 13, Last Paragraph of Section - Page 8

The final risk estimates neglect important monitoring data obtained during the RI and rely on modeling efforts that are questionable. Considering the previous comments, use of the terms "data gaps" and "data limitations" need to be explained and supported so that they can be evaluated, or they should be deleted.

13. Section 2.1, First Paragraph of Sertion, Sentence 2 - Page 10

The source for the statement regarding suitability of disposal is Schmidt and Scott (1977), not the citation given in the Risk Assessment.

14. Sertion 2.1 - Pages 11-14

The Risk Assessment states that the volumes disposed range "from less than one-tenth of a gallon of barium, cadmium and cyanide to approximately 2 million gallons of copper wastes".

This accounting is apparently derived from Appendix A to the Risk Assessment which is derived from the ADHS Compilation of Waste Types and (Quantities (ADHS, 1985). However, the accounting is grossly in error and does not reflect the artual waste disposal history at the Site.

Attachment B to these comments presents a review of key compounds in Appendix A to the Risk Assessment.

Table 1 provides an assessment of the accuracy of estimates of disposal quantities presented in the text for mixtures of chemicals. As the table demonstrates, the estimated quantities are largely incorrect.

This attachment and Table 1 demonstrate clearly that the contaminant transport and fate modeling utilized in the Risk Assessment does not in any way reflect actual past disposal practices at the Site and significantly overstates contaminant concentrations in groundwater and soil.

15. Section 2.1.1 - Page 11

Appendix B to the Risk Assessment presents a summary of monthly waste disposal in each pit which may have formed the source terms for groundwater modeling. Attachment C to these comments presents a review of Appendix B.

Attachment C indicates that, in general, the monthly summaries of waste disposal are inconsistent with the manifest database developed by M&A and CRA. This manifest database is stated to be the source of Appendix B.

The Risk Assessment states on page 11 that Appendix B formed the source terms for groundwater modeling. However, later in the Report, it is indicated that Appendix A formed the source terms for groundwater modeling. In any event, both the Appendices contain substantial errors.

TABLE 1

EVALUATION DATA USED FOR ASSESSMENT OF MIXTURES RISK ASSESSMENT REVIEW

HASSAYAMPA LANDFILL

1. page 12, Antifreeze Solution:

2. page 12, Chlorinated Hydrocarbon Solvents:

3. page 12, Miscellaneous Solvents:

400 gallons in Pit #1 reported. This is incorrect. No antifreeze solution was reported disposed of in Pit #1.

7,950 gallons in Pit #1 reported. This is incorrert. 9,475 gallons of TCA, TCE, PCE and methylene chloride were reported disposed of in Pit #1.

"Over 9,000 gallons identified....". This value is incorrect. The LWE (Appendix B) identifies approximately 17,000 gallons of "solvents".

4. page 13, Petroleum Distillates:

5. page 14, Hydrocarbons:

(a) 113,315 gallons in Pit #1 reported. This is incorrect. 71,414 gallons of "unspecified petroleum distillates" were reported disposed of in Pit #1.

Qo) 21,366 gallons in Pit #3 reported. This is incorrert. 14,822 gallons of "unspecified petroleum distillates" were reported disposed of in Pit #3.

(c) "Over 9,000 gallons of...J-100...disposed of in the Special Pits". This statement is an exaggeration. Approximately 8,790 gallons of J-100 were reported disposed of in the Spedal Pits.

45,000 gallons of "Hydrocarbons" in Pit #1 reported. This in incorrert. 3,845 gallons and 6.8 pounds of "Hydrocarbons" were reported disposed of in Pit #1.

Note: The totals reported disposed above reflert the potential disposal volumes recorded on the manifests and approved by ADHS. The Manifest Database developed in the LWE was intended to be used in the LWE and was not subject to appropriate review for use in the Risk Assessment.

The substantial errors described in this comment, the Attachments and the comments that follow are evidence of a complete disregard for Quality assurance and Quality Control in the development of the Risk Assessment.

16. Section 2.1, First Paragraph - Page 11

The wrong citation is given for the source of the statement regarding where wastes were generated; the proper dtation is Bureau of Waste Control (1980), which is given in Appendix B of the RI Report.

17. Sertion 2.1.2, Chlorinated Hydrocarbon Solvents Section - Page 12

An explanation should be given to justify the condusion regarding the "most likely" identity of the solvents so that the condusion can be evaluated.

18. Sertion 2.1.2, Miscellaneous Solvents Sertion - Page 12

An explanation should be given to justify the speculated identity of miscellaneous solvents so that the conclusion can be evaluated.

19. Section 2.1.2, Petiroleum Distillates Sertion - Page 13

An explanation should be given to justify the conclusion regarding the "most likely" identity of the waste so that the condusion can be evaluated.

20. Section 2.1.2, Sertions (1) and (2) - Page 14

The Risk Assessment should state that no evidence of floating free produrt was found during the RI. Neither gasoline nor oil were observed on the surface of groundwater during video surveys in the Unit A wells and these substances were not observed in the drilling fluids during monitor well construction.

21. Section 2.2, Paragraphs 1 and 2 - Page 15

Results from the RI do not indicate that surface sediment or surface soil are contaminated by artivities at the Site, and do not indicate the presence of eroded, contaminated surface soil. These statements should be removed.

22. Section 2.2.1, Paragraph 1 - Page 15

To our knowledge, ADHS did not obtain any samples at the Landfill during or after the RI. All references to "contaminant transport off-site" should be removed. Use of the terms "off-site" and "on-site" is not consistent in the draft Risk Assessment and should be clarified. See Comment No.l.


The use of comparability of data as a justification to neglert certain data from the Risk Assessment needs to be justified in this paragraph. The Risk Assessment arbitrarily accepts certain data that fail an acceptance criterion and to rejert similar data that meet the same criterion. For example, in subsequent sertions of the Risk Assessment, analytical data for groundwater samples obtained during well development are rejerted summarily as being nonrepresentative and yet are accepted where chemical compounds were deterted in such samples. Where small concentrations of a compound are detected in a development sample and not in any subsequent samples, the development sample is used as a basis for Risk Assessment. This procedure is inappropriate.

24. Section 2.2.2, Paragraphs 2 and 3 of Sertion - Page 16

M&A conducted comprehensive reviews of all laboratory chemical results for soil, groundwater, and waste samples obtained for the RI. These reviews included data quality and usability, and those elements required by the QAPP. Where data were not useable or data quality was problematic, notations were made in the data validations, which are summarized in Appendix M of the RI Report. The RI documentation is replete with data reviews to support quality and usability of the RI data. Therefore, statements in the Risk Assessment regarding limitation of the data review are unsubstantiated and, thus, should be removed.


The assumption that 1,2-dichloroethene (1,2-EXZE) undergoes microbial degradation at a suffident rate to be of concem is unrealistic. This is evident since vinyl chloride was not detected in any groundwater sample taken during the RI. Biodegradation of 1,2-DCE is influenced most importantly by the type of barterial/microbial population in the ground that would be able to degrade the compound. The EPA Risk Assessment Guidelines (RAGS, December 1989 page 5-20) outiine the aiteria for the development of chemicals of potential concem. According to the criteria stated in RAGS,

8

transformation products should be considered as a chemical of potential concem only if it is demonstrated to be present. As stated previously, vinyl chloride is not detected in the groundwater and consequently, vinyl chloride should not be treated in the Risk Assessment as a chemical of potential concern.

26. Sertion 2.2.2, Eleventh Paragraph, Sentences 5 and 6 - Page 19

The compounds diethanolamine, dihydrazine sulfate, formaldehyde, propylene oxide, thiourea and organophosphate amd cairbamate pesticides are referred to as being disposed of in large quantities and were not induded as analytes in the RI.

Attachment B presents a disposal summary for each of the above items. As shown, the materials were not disposed of in large quantities with respect to the total disposal and were correctly not induded as analytes in the RI.

This error in the Risk Assessment is of particular concern with respect to formaldehyde which is significantiy over-stated in the report as being a compound of concem but was not disposed of in significant quantities. Formaldehyde is modeled later in the Risk Assessment as if it is present in the groundwater in concentrations of hundreds of milligrams per liter (mg/L) based on these enormous errors in unsupported assumed disposal quantities.


The analytical methods and sampling plans were reviewed and approved by EPA. Methods 608 and 8080 are appropriate scans for those pestiddes that are most persistent in the environment after disposal or application.

28. Section 2.2J:, Paragraphs 2 and 3 of Sertion - Page 19

The nearest upgradient water well is too distant from the Site to be considered a representative background sampling point, and such wells outside the Landfill property do not yield groundwater from the same aquifer zones as monitor wells at the Landfill. Therefore, use of these wells for background data is not appropriate. Justification for not constructing upgradient monitor wells is given in the Work Plan and was approved by EPA. It was assumed in the Work Plan that essentially no upgradient sources of potential groundwater contaminants attributable to the Site exist. Therefore, if a volatile organic compound is detected and confirmed, upgradient sources need not be considered. It was assumed that there are no background

s

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concentrations of volatile organic compounds. These farts should be acknowledged in this section of the Risk Assessment.

29. Section 2.2.2.1, Paragraph 1 of Sertion - Page 20

Justification is needed for the statement regarding "the general assumption" in the first sentence; no such assumption was made for the RI. The Stage I soil sampling plan was designed to consider the entire hazardous waste area as a potential source; therefore, it was neither necessary nor safe to drill soil borings directiy into spedfic pits. Soil samples were obtained from as deep as 64.8 feet, not 60 feet, during Stage I. The condusion that Stage I soil data are not representative for the Site is unjustified and should be removed. An explanation is needed to understand and evaluate the comparison given in this paragraph for Stage I and Stage n soil analytical data.


The pits selerted for the Stage II soil program were the prindpal pits (Pits 1 through 4) cited in the manifests. In addition to the pits identified in this paragraph, soil borings were also drilled and sampled at Pits 3b, 4b, and 4c. Because the Spedal Pits were small individual pits designated for isolation and burial of low-volume wastes, it was not considered cost effective for the RI to attempt to locate and sample soils beneath individual Special Pits, and such an attempt would risk dirertly penetrating the residue from a former pit.


Justification is needed for selection of soil boring SB-5 as a background location for the Risk Assessment so that the condusion can be evaluated. Any of the Stage I borings could be selected because they all show the "absence of chemicals of potential concem."

32. Section 2.2.2.1, Paragraph 5 of Section - Pages 20-21

Justification is needed for selection of only the analytical results for Pit 1 and rejection of all other results so that the selertion can be evaluated.

33. Section 2.2.2.1, Paragraph 6 of Section - Page 21

Results for soil boring SB-14 are reported in the RI Report. As indicated on Table 8 of the RI Report, soil samples obtained from soil boring SB-14 were

10

e analyzed for total organic carbon, vertical hydraulic conductivity, and moisture content. Data for total organic carbon are given on page 77 of the final RI Report; data for vertical hydraulic conductivity, moisture content, and lithology are given in Appendix F. Therefore, references to "incompleteness" made in this paragraph are unjustified and, thus, should be removed.

34. Section 2.2.2.1, Seventh Paragraph, Sentence 2 - Page 21

The text indicates the "presence of oil and hydrocarbons, that, even at low concentrations, may interfere with the extraction or concentration process and the detection of other halogenated compounds in gas chromatograph/mass spectometer (GC/MS) analyses."

This statement and the one that follows are not supported in any way by the Quality Assurance/Quality Control data assembled and reported during the RI. Hence, the statements should be deleted.

35. Section 2.2.2.2, Paragraph 1 of Sertion, Last Sentence - Page 21

Refer to Comment No. 8. The text states again that levels of contamination appear to inaease with time. This statement is not supported by the RI. Speculation about concentrations inaeasing with time are unjustified and, thus, should be removed.


The concentration for 1,2-dichlorobenzene shown for the Pit 3a area should be ND, not 59. The six non-volatile compounds for the Spedal Pit soil boring (SB-16) were not analyzed; therefore, the ND should be changed to NA (not analyzed). As described in the RI Report, soil boring SB-16 was not part of the plaimed Stage n soil boring program. Soil boring SB-16 was intended to be the surface borehole for monitor well MW-7UA; however, well MW-7UA was relocated because wastes attributed to nearby Spedal Pits were encountered in the surface borehole. A sample of the soil fill material in this boring was obtained from the auger flights for analysis of volatile organic compounds. The boring was subsequently designated SB-16. The total depth of the boring was 16 feet.

The reference to angle boring AB-10 in the legend on this Figure should be removed because such a boring does not exist.

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37. Table 2-1 - Page 23

Pit waste analytical data were comprised of one sample and a duplicate. The duplicate sample was induded in the frequency of detertion calculation. This should be clarified in this Table.

The duplicate data is appropriate for use in the Report, but the duplicates should be averaged and the average value should be included in the calculations and detection frequency.

In accordance with the Work Plan, soil samples obtained from soil boring SB-5 were not analyzed for semi-volatile organic compounds. Therefore, the background concentrations shown for semi-volatile organic compounds in this table should not be given as ND. Also, ND should be defined in this Table.

38. Section 2.2.2.2, Paragraph 1 - Page 24

The Stage II groundwater investigation included continued monitoring of all monitor wells at the Landfill; the description for scope of Stage II given in the first sentence of this paragraph should indude the entire Stage n monitoring program. The seconci sentence is incorrert; EPA method 624 was also used during Stage n for certain analyses for volatile organic compounds (see Table 30 of RI Report).

The text indicates that "positive results of groundwater samples" were detected at well MW-8UA, implying that there were detections of compounds of concem at well MW-8UA. Although contaminants were deterted, they were not confirmed in well MW-8UA due to the fact that the detections were not reproduced in a duplicate sample.

(See Comment No. 8)


As indicated in the RI Report, the basaltic lava-flow unit is believed to be substantially fractured. Vadose zone contamination that may occur in the basaltic lava-flow unit would be expected to occur chiefly in fractures and in weathered zones. Although it is possible that the basaltic lava-flow unit may have influenced movement of liquids in the vadose zone at the Site, it is likely that the unit is sufficiently fractured to not have been a substantial influence. Saturated zones were not deterted in the basaltic lava-flow unit during drilling operations for the RI. Also, "pooled" liquids were not detected in the vadose zone penetrated by any of the soil borings or monitor wells drilled. Migration fronts are not believed to be expanding; however.

12

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efforts to provide data to support this assumption, to analyze in detail potential migration through fractures, and to estimate the rates and magnitude of past contaminant migration through the unit were not considered to be necessary for the scope of the RI and were not induded in the Work Plans. EPA reviewed and approved the scope of work and did not find it necessary to require such efforts considering the "macro" approach of the RI. The Risk Assessment must, therefore take these facts into account to properly estimate potential imparts.

Contaminants have not been deterted in samples from monitor wells located in the potential pathways of contaminant migration from Pit 1 to well MW-IUA; therefore. Pit 1 is not considered to be a source for contaminants detected for well MW-IUA. Certain Spedal Pit areas are potential sources for contamination detected for well MW-IUA.

During the RI, essentially the entire thickness of Unit A was saturated; the overlying unit is the basaltic lava-flow unit. In the vadose zone, the subsurface soils nearest to Unit A occur in the fine-grained part of the upper alluvial deposits unit. Numerous soil borings were drilled and sampled in the fine-grained part of the upper alluvial deposits unit, and provided suffident chararterization for the purposes of the RI. Therefore, the data gap referred to in this paragraph does not exist and the paragraph should be revised.

40. Section 2.2.2.2, Paragraph 3 , Sentence 2- Page 24

An assumption made for the Work Plan was that the source for any contamination by organic compounds deterted at the Site would be disposal pits at the Site. Hence, no reliance was placed on the collection of background data for the RI.


As stated elsewhere in these comments, contamination has not been detected and confirmed in samples from well MW-8UA. Further, even though water samples obtained during well development operations may not be representative for groundwater conditions, such data are used and presented in Figure 2-2 of the Risk Assessment. The toluene concentration of 0.7 given for well MW-8UA was deterted in a development sample. Based on the data given in Table 30 of the RI, toluene was a laboratory contaminant wherever deterted in water samples; therefore, toluene should be removed from Figure 2-2.

13


The selection of only those groundwater samples analyzed by method 601/602 to be representative for aquifer conditions is flawed because analytical data for these compounds provided through comparable methods would provide a more complete database for the development of the exposure assessment. Table 2-2 therefore requires revision.


This Figure should be revised as follows:

a. All references to units in the tabulated data should be changed from milligrams per liter to miaograms per liter.

b. For well MW-IUA: minimum concentration for 1,1-DCA should be ND; minimum concentration for 1,1-DCE should be 11; and minimum concentration for TCA should be 0.9.

c. For well MW-6UA: all minimum values shown for ranges of concentrations should be ND.

d. For well MW-8UA: see Specific Comment #41 regarding toluene.

e. Pit 1 should not be shown as a "positive contaminant detection" for this map of groundwater results. No groundwater samples have been obtained at Pit 1.

In addition, it has been noted in these comments that contamination has not been detected and confirmed for wells MW-8UA and HS-2.

44. Table 2-2 - Page 26

The units under the heading "Average Concentration" are incorrectly stated as mg/kg. This should be correrted to |Xg/L. Abbreviations in this table are confusing and should be defined in the footnotes (i.e., DL).

45. Section 2J.2.2, Table 2-2-Page 26

Average concentrations calculated from detected values were determined incorrectly. In calculating the arithmetic mean of all analytical results for a particular chemical, duplicate samples should be averaged first prior to determining the average of all deterted values. As it is presented in the Risk

14

Assessment text, duplicate samples are given the same weight as all data points.

46. Sertion 2.2.2.2, Seventh Paragraph, Sentence 1 - Page 27

The text states that the "possibility of false negatives in sampling could increase because there were not enough wells at various locations to identify the contaminant plume, thereby affecting the representativeness of the data".

EPA Region IX approved the monitoring well network. The network is comprised of an adequate number of wells in strategically located positions so that migration of Site contaminants in the groundwater on-Site and in the Landfill should be deterted by the network.

The statement in the text is subjective, unsupportable and, incorrert and therefore, should be removed. It also ignores the historic involvement of EPA in considering and approving all Site work before it was undertaken.

47. Section 2.2.2.2, Eighth Paragraph, Sentence 2 - Page 27

The text again refers to interferences with analyses by oil, hydrocarbons, phthalates and non-pesticide chlorinated compounds, yet no quantitative evidence is provided to support this claim for the Site. The statement should be removed.

48. Section 2.2.2.3 - Pages 27-30

The text states that analytical results for laboratory spike sample AMP-D and the field duplicate of AMP-A were not reported. This is incorrect. These data were reported in Appendix I to the RI.

Further, incorrect data are reported in Table 2-3 of the Risk Assessment: carbon disulfide, AMP-J should be 3.200U; chloromethane, AMP-J should be non detert; 1,1-dichloroethane, AMP-A should be 2.380 J; and trichlorotrifluoromethane, AMP-A should be 3.600.


The analytical methods and sampling plans were reviewed and approved by EPA. Methods 608 and 8080 are appropriate scans for those pestiddes that are most persistent in the environment after disposal or application.

15

50. Sertion 2.5.1 - Pages 33-39

The Risk Assessment summarizes the selection of chemicals of concern for use in the quantitative evaluation of the Risk Assessment. The rationale presented for the selection of some compounds is unsupportable.

Table 2 summarizes the Risk Assessment's rationale for the selection of compounds for the Quantitative Evaluation and the data from the RI that contradicts the selection. The Risk Assessment should utilize RI data to select compounds of concern.

Table 2 demonstrates that the Risk Assessment's accounting of the waste disposal history for the development of a groundwater modeling database is largely inconsistent with the ADHS manifests.

51. Section 2.5.2 - Pages 39-44

The qualitative evaluation, like the quantitative evaluation, contains significant errors in the quantities of many cited contaminants which were approved for disposal. Further, the desaiption of the significance of the disposals is highly subjective.

Table 3 presents a summary of the significant disaepancies between the data presented in the Risk Assessment and the data from the LWE manifest database. The subjertive qualitative assessment is inaccurate and should be deleted.

Rags refers to the use of qualitative analyses or approaches:

1) in consideration for the initial scoping of the RI/FS, 2) where quantitative data are unnecessary because of the simple nature

of the Site, and 3) to describe the likelihood of potential exposures.

There is no basis for a separate qualitative Risk Assessment when quantitative data are available for evaluation, thus this dubious assessment is inconsistent with EPA guidance (See RAGS, pages 1-4 to 1-6). The qualitative evaluation of the Risk Assessment was of limited value in terms of the Risk Assessment conclusion.

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TABLE 2

EVALUATION-DATA USED FOR QUANTITATIVE ASSESSMENT RISK ASSESSMENT REVIEW

HASSAYAMPA LANDFILL

1. pages 12 Coatings: -13

2. page 19, Pesticides:

3. page 19, Full Paragraph #2:

4. page 33, Acetone:

5. page 33, Carbon Disulfide:

13,000 gallons in Pit #1 reported. This is incorrect. The approximate breakdown of "coatings"in Pit #1 is as follows:

hiks 3,400 gallons Lacquer 0 Photo Resistant 750 Thinners 6.100

10,250 gallons

"Assuming that coatings are 50% solvent...." (page 13, Risk Assessment) Total Volume of Solvents Associated with coatings

= 10250 * 0.5 = 5013 gaUons

(a) Approximately 140 gallons were reported disposed of at the Site. Also reported disposed of were 1800 pestidde drums, and 3750 pounds of fjesticide cans.

(b) The text should either quantify the term "large quantity" or it should be removed.

14,740 gallons of Freon 113 were reported disposed of at the Site. The text should either quantify the term "large quantity" or it should be removed.

(a) 60 gallons in Pit #1 reported. This is incorrect. 20 gallons of acetone were reported disposed of in P i t# l .

(b) Third line: "Detected in the Methanol Blank" should read "Detected in the Method Blank".

(c) 138 gallons in Special Pits reported. This is incorrect. No acetone was reported disposed of in Special Pits.

(d) Data indicated 320 mg/kg below Pit #1. This data should be qualified as non-detect (Qualifier U) based on the method blank data. The acetone was detected in the air in one sampling location, and this quantity was estimated due to field contamination. The statement that miscellaneous disposals were expected to occur is unsupportable.

Carbon disulfide was not detected in groundwater or in air. The data should be qualified as non-detect (U).

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I TABLE 2 EVALUATION - DATA USED FOR QUANTITATIVE ASSESSMENT

RISK ASSESSMENT REVIEW HASSAYAMPA LANDFILL

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6. page 35, Carbon Tetrachloride:

7. page 35, Chloromethane:

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8. page 35, Chloroethane:

9. page 35, Chromium:

10. page 35, Copper

11. page 35, Dichlorobenzene:

12. page 36, Dichloropropane (1,2-):

13. page 36, Ethylene Glycol in Antifreeze Solution:

The quantities that were detected in the air are estimated. The statement that carbon tetrachloride is believed to have tieen disposed is not supported by the approved manifest.

The text assumes a disposal quantity. Disposal does not have to be assumed. 3,900 gallons of methyl chloride (chloromethane) were reported disfX)sed of in Pit #1 and 1,500 gallons were repxjrted disposed of in Pit #3.

"Over" 18,000 gallons in Pit #1 reported. This statement is an exaggeration. 16,866 gallons of chloroethane were reported disposed of in Pit #1.

2,900 gallons in Pit #3 and 1,300 gallons in Pit #2 were reported. These values are incorrect. It is assumed that other sources of chromium (such as chrome, chromic acid, chromium dioxide and trivalent chromium) were not incorporated into these totals. Including the above mentioned compounds, the volumes reported disposed of are:

5,263 gallons in Pit #2 13,506 gallons in Pit #3

"Nearly 2 million gallons of copper containing wastes were disposed of in Pit #3". This is incorrect. Including copper chloride and copper hydroxide, approximately 42,400 gallons of copper-containing wastes were reported disposed of in Pit #3.

Insignificant trace levels to 7.1 mg/kg were detected in soil beneath Pit #1.

1,350 gallons in Pit #1 reported. This is incorrect. No 1,2-dichloropropane was reported disposed of in Pit #1. This compound was detected in one sample in air at 0.47 Ug/m3.

(a)

(b)

400 gallons of antifreeze solution in Pit #1 reported. This is incorrect. No antifreeze was reported disposed of in Pit #1. 1,000 gallons in Special Pits reported; actual reported dispx)sal volume is 983 gallons.

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TABLE 2

EVALUATION - DATA USED FOR QUANTTTATTVE ASSESSMENT RISK ASSESSMENT REVIEW

HASSAYAMPA LANDHLL

I 14. page 36, Formaldehyde:

15. page 37, FieonllS:

16. page 37, Lead:

17. page 37, Methyl Ethyl Ketone (MEK):

I 18. page 37, Methyl Phenol:

19. page 37, Methylene Chloride:

I 20. page 38. Nickel:

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534 tons reported disposed in Special Pits. This is incorrect. 4,465 pounds (2.2 tons) of solid formaldehyde and 8 gallons of liquid formaldehyde were reported disposed of in the Special Pits.

16,217 gallons in Pit #1 reported. This is incorrect. 14,645 gallons were reported disposed of in Pit #1.

(a) 600 gallons of lead containing compounds in Pit #2 reported. This is incorrect. 406 gallons of lead containing compounds were disposed in Pit #2.

(b) 3,420 pounds and 2,229 gallons of lead containing comix)unds were reported as being disposed in Pit #3. This is incorrect. 113 pounds and 7,685 gallons of lead containing compounds were reported disposed of in Pit #3.

205 gallons in Pit #1 reported. This is incorrect. 122 gallons of MEK were reported dispxjsed of in Pit #1. "Potential detection could be obscured by laboratory contamination" is subjective and unsupportable. This compound was shown in the RI Report to be a laboratory contaminant wherever detected in groundwater samples.

150 gallons in Pit #3 reported. This is incorrect. There was no methyl phenol reported disposed of anywhere on the Site. This com|x>und was not detected in soils at Pit 2; it was detected in waste from Pit 1 (see Table 16 of RI Report).

5,437 gallons in Pit #1 and 9385 gallons in Pit #3 were reported. These cU"e incorrect. The volumes reported disposed of at the Site are:

3,000 gallons in Pit #1 1,420 gallons in Pit #3

380 pounds in Pit #2 and 604 gallons of nickel containing wastes in Pit #3 were reported. These are incorrect. Approximately 4 pounds of nickel containing wastes were reported disposed of in Pit #2, and 15,271 gallons of nickel containing wastes were reported disposed of in Pit #3.

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TABLE 2

EVALUATION - DATA USED FOR QUANTITATIVE ASSESSMENT RISK ASSESSMENT REVIEW

HASSAYAMPA LANDHLL

21. page 38, Phenol:

22. page 38, Tetrachloroethene:

The Risk Assessment reported the following amount of phenol-related wastes:

Special Pits: 318 gallons, 260 tons Pit#l: 760 gallons Pit #3: 807 gallons

These are incorrect. The following are correct values:

Special Pits: 561 gallons, 3,082 pounds Pit #1: 850 gallons Pit #3: 792 gallons

It should be noted that phenol was only detected in the well development sample from well MW-IUA, which as the Risk Assessment selectively notes is not a representative for groundwater conditions.

219 gallons in Pit #1 reported. This is incorrect. This should read "175 gallons of PCE were reported disposed of in Pit # r .

23. page 38, Toluene:

24. page 38, Trichloroethane:

40 gallons in Pit #1 reported. This is incorrect. This should read "20 gallons were identified".

The Risk Assessment reported that 5,534 gallons and 225 gallons of TCA were disposed of in Pit 1 and the Special Pits, respectively. These are incorrect. The values should be:

Pit#l: 6,257 gallons Special Pits: 5,423 gallons

Air data is mostly qualified as non-detect. Groundwater contamination has not been detected and confirmed in well MW-8UA.

25. page 38, Trichloroethene: The Risk Assessment reported that 7,840 gallons and 101 gallons of TCE were disposed of in the Special Pits and Pit 1, resjjectively. These are incorrect. The values should be:

Special Pits: 2,400 gallons Pit#l: 44 gallons

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TABLE 2

EVALUATION-DATA USED FOR QUANTTTATrVE ASSESSMENT RISK ASSESSMENT REVIEW

HASSAYAMPA LANDFILL

26. page 39, Xylene: The Risk Assessment reported that 42,223 gallorw and 3,220 gallons of xylene were disposed of in the Special Pits and Pit 1, respectively. These are incorrect. The values should be:

Special Pits: 66,800 gallons Pit#l: 3,090 gallons

Note: The totals reported disposed above reflect the potential disposed volumes recorded on the manifests and approveid by ADHS. The Manifest Datal)ase developed in the LWE was intended to be used in the LWE and was not subject to appropriate review for use in the Risk Assessment.

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TABLE 3

EVALUATION-DATA USED FOR QUALITATIVE ASSESSMENT RISK ASSESSMENT REVIEW

HASSAYAMPA LANDFILL

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1. page 40, Second Paragraph:

2. page 40, Petroleum Distillates:

3. page 41, Miscellaneous Solvents:

4. page 41, Chlorinated Hydrocarbon Solvents:

5. page 42, Alcohols:

6. page 42 Organic Acids:

7. page 42, Butyl Acetate:

8. page 42, Butyl Cellosolve:

9. page 43, Diethanolamine:

10. page 43, Diisocyanates:

11. page 43, Napthalene:

The estimate of 100 gallons for the total volume of pestiddes manifested for disposed needs to be documented and supported.

The Risk Assessment reported that 100,000 gallons were reported disposed. The correct total is 103,000 gallons.

See Table 1

See Table 1

The Risk Assessment reported 8,000 gaUons of methanol disposed of in the Spedal Pits. This is incorrect. No methanol was reported disposed of in the Special Pits: 715 gallons reported disposed in Pit #1; 200 gallons reported disposed of in Pit #2

The Risk Assessment reported 400 gaUons of organic acids disp>osed of in Pit #1. Approximately 250 gallons (not 400) were reported disposed of in Pit #1, and 100 gaUons were reported disposed of in Pit #3.

"Over 50,000 gallons" reported. Approximately 24,000 gallons were manifested. AU (100%) of this amount was reported disposed of in the Special Pits, not 98%. There was none reported disposed of in Pit #1; 2% is incorrect.

The reported value of 1,000 gcillons is incorrect. No Butyl Cellosolve was disposed of in Pit #3 or at the Site.

286 tons were indicated as having been disposed of in the Spedal Pits. 533 pounds were manifested for disposal in the Spedal Pits.

100 gallons were reported disposed of in Pit #1 No diisocyanates were manifested for disposal in Pit #1. The value for the Special Pits is correct.

100 gaUons were reported disposed in Pit #3. No napthalene was manifested for disposal in Pit #3. The value for Pit #1 is correct.

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I TABLE 3 EVALUATION - DATA USED FOR QUALITATIVE ASSESSMENT

RISK ASSESSMENT REVIEW HASSAYAMPA LANDFILL

12. page 43, Propylene Oxide: The method of reporting Propylene Oxide disposal amounts is misleading.

13. page 43, Thiourea: The Risk Assessment reported that 460 gallons and 44,780 gallons of Thiourea were disposed of in Pits 2 and 3, respectively. These are incorrect. No Thiourea was reported disposed of in Pit #2. 448 gallons were reported disfxjsed of in Pit #3.

Note: The totals reported disposed above reflect the potential disposed volumes recorded on the manifests and approved by ADHS. The Manifest Database developed in the LWE was intended to be used in the LWE and was not subject to appropriate review for use in the Risk Assessment.

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52. Section 2.5.2, First Paragraph, Last Sentence - Page 40

A vertical soil boring was drilled and sampled in the narrow (four or five feet) space between the large cells of Pits 4b and 4c. Therefore, for all prartical purposes, these soil samples may be considered to have been obtained beneath these cells of Pit 4. The subject sentence should be modified to reflect this fart.

53. Section 2.5.2, Last Paragraph, Last Sentence - Page 41

These compounds were deterted below the limit of quantitation in one sample, but not in the duplicate sample; this sentence should be revised to reflect this.

54. Section 2.6.1, Second Paragraph, Sentence 3 - Page 44

The report indicates that "the amounts reported may be overestimated because they represent the truck load rather than the actual volume of disposed wastes. On the other hand, these numbers may be underestimated due to a large number of missing manifests identified in the Liquid Waste Evaluation Report."

It is irrefutable that tank trucks would regularly be filled to a volume less than their rated capadty (to prevent spillage, overweight vehicles, expansion of liquids, etc.). However, it has not been established that missing manifests are necessarily related to unknown disposals. It is more probable that manifests were issued and never used, or the manifest numbers were never used by the ADHS. The Risk Assessment should be modified to include further discussion of this issue.


All sampling plans were reviewed and approved by EPA. The RI chararterized the extent of contamination suffidentiy for the FS. The assumption of lateral migration stated in the Risk Assessment for the RI is incorrect and has no basis. All exposure pathways were evaluated by the RI. This section needs to be substantially revised to reflect this and previous comments.

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56. Sertion 2.6.2 - Pages 44,45

The Risk Assessment is critical of an RI program which was completed according to EPA approved Work Plans. The unsupported, undocumented, and subjective critidsm, such as the lack of sampling all affected media and areas of concem, interference by hydrocarbons with analyses (in the absence of defensible QA/C^C data to support tiie aitidsm), should, therefore, be removed. All chemical analyses conducted during the RI were completed in accordance with EPA approved (Quality Assurance Projert Plans. In addition, the EPA completed a separate, independent QA/QC review and found the RI data to be acceptable.

57. Section 3.1.1, Paragraph 2 of Section on Geology, Last Sentence - Page 47

The RI Report does not indicate that the presence of caliche is limited to the fine-grained sediments. This sentence should be revised.

58. Section 3.1.1, Paragraph 3 of Section on Geology, Last Sentence - Page 47

Average thickness of the basaltic lava flow unit reported in the RI Report is 17 feet, not 24 feet. This sentence should be revised.

59. Section 3.1.1, Paragraph 4 of Section on Geology, Sentence 2 - Page 48

Unit A was only penetrated by monitor wells and is not exposed in outaops at land surface near the Site; therefore, no reference is made in the RI Report to alluvial structures in Unit A. No references should be made in the Risk Assessment about sedimentary structures in the unit where such structures caimot be inspected, and no such statements should be attributed to the RI Report.

60. Sertion 3.1.1, Paragraph 5 of Section on Geology - Page 48

No reference is made in the RI Report to alluvial structures in Unit B. Unit B was only penetrated by monitor wells and is not exposed at land surface; therefore, comments should not be made regarding sedimentary structures in the unit where such strurtures cannot be insperted. Unit B and the Middle Alluvium unit are characterized more than sufficiently by the RI Report. No assumption is made in the RI Report that the Middle Alluvium unit is "impermeable" or that this unit is a "barrier to downward contaminant transport". The Palo Verde clay is chararterized in the RI Report as comprising a"basal confining unit for Unit B". Incorrect statements and

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misrepresentation of the information provided in the RI Report should be removed from the Risk Assessment.

61. Section 3.1.1, Paragraph 1 of Section on Meteorology - Page 48

Altitude of land surface at the Landfill does not range from 910 to 915 feet, but altitude of land surface at the Site does. This sentence should be revised.

62. Sertion 3.1.1, Paragraph 1 of Sertion on Grotmdwater Hydrology - Page 50

Soil borings in the vadose zone were not and should not be used to chararterize groundwater movement in the saturated zone. Groundwater movement is characterized in the RI Report by results of pumping tests at monitor wells, measurement of groundwater levels in monitor wells, and estimation of selected parameters, such as effective porosity. Long-term pumping tests and tracer tests were deemed unnecessary for the RI on the basis that groundwater movement can be characterized sufficiently without them. Further, they were not required by the Work Plans which were reviewed and approved by EPA.

63. Section 3.1.1, Paragraph 2 of Section on Groundwater Hydrology - Page 50

Laboratory analyses for hydraulic conductivity of the basaltic lava-flow imit and Unit B were not necessary for tiie RI and were not required by the EPA approved Work Plans. Moderate to high hydraulic conductivity may occur in the basaltic lava-flow unit where open frartures are abundant, and may occur in Unit B where sand and gravel layers are relatively free of silt and clay. However, low hydraulic conductivity would be experted in the basaltic lava-flow unit where fractures are filled or few, and in the fine-grained parts of Unit B. The Risk Assessment should be revised to reflect this comment.

64. Section 3.1.1, Paragraph 4 of Sertion on Groundwater Hydrology - Page 51

Operative hydraulic conductivity given in the RI Report for Unit B is 140, not 40. This paragraph should be correrted.

65. Section 3.1.1, Paragraph 5 of Section on Groundwater Hydrology - Page 51

The methods used to calculate aquifer parameters in the RI Report are widely accepted for such lithologic units and provide reliable values for use in groundwater hydrology. Assumptions for ideal conditions commonly made

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for dassical equations in hydrology are not experted to be identical to field conditions, but such assumptions are accepted and do not hinder the usefulness of the methods. Field measurements for water level drawdown and recovery commonly match solutions calculated by methods used in the RI Report. Therefore, the uncertainty desaibed in this statement is excessively overemphasized and the statement should be removed from the Risk Assessment.

66. Table 3-1 - Page 52

In accordance with data given in the RI Report, the value 2.01 x 10'^ should be changed to 2.58 x 10"^, tiie value 3.812 x 108 should be changed to 3.82 x IQ-^, and tiie value 1.99 x 106 should be changed to 1.99 x lO'^.

67. Sertion 3.1.2, Paragraph 2 of Section on Population Characteristics - Page 54

The "surrounding area" referred to in the first sentence should be defined.

68. Section 3.1.2, Site Spedfic Land Uses - Pages 56-59

The Risk Assessment argues that the uncertain future of the landfill coupled with apparent future expected population growth is justification for assuming a future residential land use.

This assumption is developed from personal communications with Mr. Clark Bullock (Maricopa County Landfill Department, Planner II) who is reported to have stated that the entire landfill could close in 3 to 4 years and be converted to a reaeational park in 1 to 3 years, thereby making future reaeational exposure a reasonable scenario.

Residential exposure is assumed in the Risk Assessment to be "plausible" after a decade or two.

This assumption is not based on a reliable assessment of the potential future land uses in the area (such as the suitability of the location of the Site, the availability of other sites and the need for the development of a park) and available reasonable estimates of potential growth.

The assumptions for future land use are inappropriate as follows:

• future residential use does not seem plausible because the Site is owned by the County, because much of the adjacent land is owned by the Federal

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Government and predirted population growth in the remote area of the Site is speculative;

• movement of the off-site population closer to the Site does not seem likely given the ownership of adjacent lands;

• groundwater use for any potential residential development is inconsistent with the goals of the Arizona Groundwater Management Act; and

• the exposure point identified in the Risk Assessment as being 300 meters downgradient from the Site is in the middle of a large active sanitary landfill cell on the landfill property and therefore cannot plausibly be considered to be an appropriate exposure point.

The office of the Maricopa County Attomey has reviewed the above concems regarding the assumptions in the Risk Assessment related to future land use. M&A has received a letter from the County which indicates that the current plans for the Hassayampa Landfill are not consistent with the assumptions utilized in the Risk Assessment. The correspondence to M&A is presented in Attachment D.

69. Section 3.2.2, Release Mechanisms, Second Paragraph, Sentence 1 - Page 60

The text states that soil beneath the pits is "heavily" contaminated. This subjective statement should be deleted.

No evidence or substantiation is provided for the claim that the cited compounds are moving in any significant way through soils. The Risk Assessment should provide such evidence or this claim should be deleted.

70. Section 3.2.2, Paragraph 1 of Section on Groundwater - Page 61

The characterization of concentrations of containinants deterted and confirmed for monitor wells as "high" is questionable, and is certainly improper for well MW-5UA. In addition, the Risk Assessment incorrectiy states that monitoring wells HS-2 and MW-8UA have confirmed detections of VOCs, thus incorrectiy conduding that contaminants have migrated off Site. Groundwater from off-site domestic wells has been sampled and analyzed by ADHS.

71. Section 3.2.4, Exposiure Points - Pages 62,63, Table 3-5

Subjective statements such as "high concentrations" should be removed from this section.

See Comment No. 68.

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72. Sertion 3.3, Sentence 3 - Page 63

Comparison of results from the modeling with results from the RI suggest that data obtained from the RI were not properly used to calibrate the groundwater model. This sentence is the only reference in the Risk Assessment to calibration of the groundwater model.

Calibration is essential for obtaining proper results and for evaluating such results from a numerical solute transport model such as SUTRA. In discussions on Febmary 22, 1991, PRC personnel responsible for the SUTRA modeling effort indicated that the model was not calibrated to Site conditions. Therefore, the reference to calibration given in the Risk Assessment should be removed. The lack of calibration casts severe doubt on the validity of using the model results to estimate risk at the Site. The model will be reviewed further when data requested from EPA are received. However, our preliminary evaluation indicates that the SUTRA model results should be removed from the Risk Assessment and should not be basis for assessment of risks.


Again, the use of the term "site" in the Risk Assessment is inconsistent and should be clarified.

74. Section 3.2.4 - Table 3-4, Page 65

The use of the term "actual risk" implies that the potentially exposed population will develop cancer. These are not actual risks but are hypothetical risk estimates to assist in evaluating which chemicals are probably responsible for the major risk, which media and exposure present the greatest problems, what remediation, if necessary, is needed, and how effective the remediation will be in deaeasing the estimated risk. Therefore, the use of the term "actual risk" should be deleted from Table 3-4.


As stated in the Work Plans and other RI documents, the conceptual approach used for the RI was to assume the entire Site was a potential source of groundwater contamination. This approach is conservative because it addresses uncertainties in the disposal manifests by treating each of the hazardous waste disposal pits equally. The Contaminant Transport And Fate

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section of the RI Report addresses routes of contaminant migration and potential imparts. It is true that the RI data set, as with all data sets, is not unlimited; howeyer, the quantity of data is more than sufficient for purposes of the RI/FS and the Risk Assessment and was obtained using Work Plans which were reviewed and approved by EPA and which are consistent with EPA guidance.

The conceptual approach used for the Risk Assessment is excessively and unjustifiably conservative, leading to condusions regarding remedial objectives that are not consistent with Site conditions nor with analytical data and interpretations given in the RI. The conceptual approach in the Risk Assessment, therefore, requires substantial revision.


The last sentence in this paragraph is true; however, the information required for such a review is not included in the draft Risk Assessment Report. The Risk Assessment Report should be revised to include the input data to the groundwater model so that it can be evaluated. It has been necessary to submit letters dated February 12,1991 and February 25,1991, from M&A to EPA to request additional data necessary to evaluate the use, documentation, and results of the groundwater modeling operations. This letter is included herewith at the end of Attachment A.

Without this additional data, it is not possible to prepare complete comments on modeling methods used and conclusions reached in the Risk Assessment based on that modeling.


Neither Figure 3-2 nor 3-3 illustrates the information given in this paragraph. A new Figure of this information would be more helpful and should be induded in the Risk Assessment.


Accurate locations for potential source terms should be shown on the appropriate Figures. In addition, the basis for the acceptance criteria for the projection distances from the pits should be given in the Risk Assessment so that the criteria can be evaluated.

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The appropriateness of the nodal grid used for the model can not be evaluated without the additional data requested in the February 12 and February 25,1991 letters to EPA.


Specific source (reference and pages) of the pit dimensions and locations used to projert pits onto this geologic section should be given in the Risk Assessment Report. The map location for this geologic section is not provided. The purpose of this Figure should be given in the text. The generalized lithologic desaiptions shown do not correspond to data given in the RI Report: for the fine-grained part of the upper alluvial deposits unit, the lithologic desaiption shown should be replaced with "sandy silt to silty clay"; for Unit A, the lithologic desaiption shown should be replaced with "dayey silt and silty clay"; and for Unit B, the lithologic description shown should be replaced with "dayey silt and silty day interbedded with sand and gravel". At the scale shown on this Figure, the depth shown for the top of the Palo Verde day is incorrert and should be changed to 268 feet (see page 53 of RI Report).


As requested in the February 12 and Febmary 25,1991 letters to EPA, a more detailed grid is required for proper evaluation of the model.


The groundwater flow and solute transport parameters discussed for each nodal element should be given in the Risk Assessment and are requested in tiie February 12 and Febmary 25,1991 letters to tiie EPA.

The second sentence of this paragraph should state that the RI Report does provide characterization of the lateral extent of the lithologic units, but not beyond the Landfill boundary. A discussion should therefore be provided in the Risk Assessment on the potential impact that the "regular and horizontal" assumption has on accuracy and comparability of model results.

The source and justification for the parameters listed in Table 3-6 should be given in the Risk Assessment and were requested in the letters to the EPA dated Febmary 12 and February 25,1991.

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The Risk Assessment implies that the RI Report did not contain all necessary data and some of the data presented was inconsistent or suspert. In order for a meaningful response to be provided, this statement needs to be expanded to show: 1) how any potential shortcomings of the RI data are critical for conduct of the FS or the Risk Assessment; and 2) how these potential shortcomings are inconsistent with the planned approach given in the RI Work Plans reviewed and approved by EPA. In addition, any assumptions used in place of RI data shoiild be described and justified. For a partial response to these concems to the extent that they can be currentiy understood, see responses to comments on draft RI report, dated February 7,1991 previously submitted to EPA.


An explanation should be provided in the Risk Assessment for use of a simulation period ending in the year 2070.

84. Section 3.3.1.3 - Pages 73-90

The Risk Assessment dismisses the modeling of liquid waste transport presented in the LWE and arbitrarily and unsupportably assumes that one third of the wastes evaporated, one third of the wastes were adsorbed into the vadose zone and fully one third "infiltrated" into the vadose zone and presumably ended up in the groundwater. There is no scientific basis for this assumption.

The statement, "therefore, in the absence of defensible data, it is assumed that for organic contaminants, each of the three processes is equally successful at competing for contaminant mass" assumes that volatilization, infiltration into groundwater and adsorption occurs at the same rate simultaneously. The probable behavior, environmental fate and the rate at which the reartion processes occurs is a function of the chemical-spedfic physical properties and chemical properties; site conditions; presence of miaoorganisms, water chemistry, pH and redox potential.

Comments on draft baseline risk assessment533 lbs (0.25 tons) * Although more factual than the data...

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