Free Additional Attachments to Main Document - District Court of Arizona - Arizona

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The above comment applies to this table as well.
RESPONSE Table 8-6 has been revised.
20. CHAPTER 9. TABLE 9-10

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How were flow rates derived for Alternatives 3 and 4 for contamination greater than background?
RESPONSE

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There are no flow rates presented for Alternatives 3 and 4 for contamination greater than background. Alternatives 3 and 4 are developed for the contamination above ARARs target area only.
21. CHAPTER 10, PAGE 10-12. PARAGRAPH 5
What is EBCT?

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EBCT refers to Empty Bed Contact Time which is a design parameter for liquid phase activated carb vessels.
22. CHAPTER 10. TABLE 10-11 AND TABLE 10-12

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These tables appear to be incomplete. Often no comments appear for Alternatives 4, 5, 6.
RESPONSE

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The tables will be revised to include comments for the other alternatives.
23. APPENDIX J. PAGE J-3. FIRST EQUATION

The term should be 2S-X

not 25-x.

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RESPONSE The term has been revised.

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24. APPENDIX R. PAGE R-44« PARAGRAPH 3 ·

Figure R-3 does not show TCE or chromium concentrations as referenced.
RESPONSE

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The figure has been revised to show the areas.
25. APPENDIX S. PAGE S-29, PARAGRAPH 2

Where are Figures 9 and 10?
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Figures 9 and 10 are included on pages 24 and 25 of Appendix S.
26. APPENDIX S. PAGE S-68

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Upon examination of Figure 43, it appears that carbon capacity at a TCE concentration of 920 ug/1 and a temperature of 185 degrees Fahrenheit is greater than 10 percent by mass.

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While the graph is subject to interpolation error, it appears that the 8 percent by mass capacity referred to in the text on page 68 is approximately correct.
27. APPENDIX S. SUB-APPENDICES B & C

The Summary of Pressure and Flow Measurements and the Summary of Concentration Measurements are not labeled with page numbers. This makes reference to the tables and data difficult.
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Page numbers will be added to the appendixes in the final RI/FS.

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COMMENTS FROM E. A. WOOTON

If carbon absorption is used to clean the fouled water placed in and around Goodyear, then:

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What is to be done with the polluted carbon material?
Where is it to be stored to eventually corrupt that area?

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What is the "life" of this pollutant before nature neutralizes it?

It would appear that the Soil Vapor Extraction will pollute the surrounding air of this valley. o What amount of pollution will this method add to the problems we already have in this area?

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As one who has asthma and is already concerned about pollution, it seems to me that every effort should be made to protect the citizens as completely as possible.
Cost should not be the first concern.

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RESPONSE

This comment appears to address two concerns. The first has to do with the fate of any activated carbon that may be used onsite. The second has to do with the disposition of the vapor from the SVE system, whether it is treated, and any possible health effects resulting from the discharge.

If activated carbon is used onsite, there are three possible options for disposal of the spent material. The first is landfilling. In this case, the spent carbon would be properly packaged and shipped to an approved disposal site which is in conformance with all current restrictions on the disposal of hazardous waste. Generally, this is only economical if small amounts of carbon are used. The carbon would also be subject to EPA's land ban restrictions issued under RCRA which may make this option unfeasible if the concentrations of contaminants exceed the limits imposed under the regulations.

The second option is regeneration of the spent carbon.
This option entails removing the contamination from the

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carbon so that the carbon can be reused. The contamination that is removed is either recovered for reuse or destroyed through incineration. This option could be implemented onsite or offsite depending on economics and other factors. The third option is incineration of the spent carbon. This means the carbon and contamination are both destroyed in an incinerator.
The alternative chosen will be protective of human health and the environment and will depend on the quantity of carbon used, the concentrations of contaminant on the carbon, and the relative costs of the options. An analysis to determine the final disposition of the carbon would be done as part of the design of the remedial action.

Soil vapor extraction as proposed in the RI/FS includes installation of activated carbon to reduce emissions to the atmosphere. The concentrations of contaminants at the outlet of the two bed carbon units proposed will normally be nondetectable. Thus, the health risk posed in the ambient air by the soil vapor extraction unit will be negligible.

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RESPONSES TO GOODYEAR TIRE AND RUBBER COMPANY*S LETTER DATED JULY 6. 1989

(Letter attached at back of this appendix)
RESPONSE TO PAGE 2, 3RD PARAGRAPH

The June 7, 1989, Public Comment Draft ADWR's model as Volume IX, Appendix V. Goodyear states they received the model will exercise their right to comment on its receipt. The 3 weeks expired prior

RI/FS did contain Nonetheless, in late May and they it within 3 weeks of to the date of their

letter.
RESPONSE TO SECTION ON "TCE RESIDUALS IN SOIL"

Goodyear states that the mass estimate for TCE in the vadose zone is wrong for several reasons. It is agreed that the method used to estimate the VOC mass in the soil is subject to much uncertainty. Due to soil and contamination heterogeneities, the dynamic nature of transport phenomena in the
vadose zone, and the difficulty in defining the necessary parameters, among other things, the calculation of mass in the vadose zone will always be merely an estimate. However, the Goodyear assertion that the mass is only 20,000 to 30,000 pounds is not accompanied by any calculations, so we cannot assess its validity. The fact remains, based on soil gas and soil data, that significant contamination continues to reside in the vadose zone.

Goodyear asserts that contaminant equilibrium is not attained in the soil at the site but offers no reasons supporting this conclusion. While the vadose zone conditions will constantly change with varying recharge, barometric pressure changes, temperature fluctuations, etc., the system is likely to attain a rough equilibrium. The method used in the RI/FS is the best estimate obtainable of those conditions, and to our knowledge there is no reason to believe that they significantly vary from equilibrium.
Goodyear asserts that the organic carbon fraction (foe) in the soils and therefore the partition coefficient Kd should both be 0.0 since apparently ADWR used this value in its model. The foe used in the mass estimate is based on the average organic fraction actually measured in soil samples from the site. These data are shown in Table B-l of Appendix S of the RI/FS. The value is not 0.0 but approximately 500 mg/kg. It should also be noted that while use of this value increased the total mass in the vadose zone to

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some degree, it also reduces the effect of recharge by estimating contaminant retardation.
It is agreed that the best approach to vadose zone remediation is to formulate a plan for evaluating the field conditions as they are encountered. The problems that this approach creates relate to the residual level of contamination that is acceptable (how clean is clean?) and how do you measure them. This decision will also relate to the target areas chosen for remediation. The decision tree offered by Goodyear is a good start but leaves several questions unanswered relating to prediction of the threat of residual contamination and the measurement technique used to determine compliance. Goodyear also states that drawing containination up from the groundwater is an undesired result from the SVE system. Since removing contamination from the PGA site is the desired result and the SVE system will accomplish this, it is difficult to see why drawing contamination from the groundwater into the SVE system is undesired.
RESPONSE TO SECTION ON "GROUNDWATER"

Goodyear inaccurately restates the groundwater pumping alternatives. Page 8-13 of the Public Comment Draft RI/FS includes a description of the pumping alternatives evaluated. None of the alternatives include pumping of existing wells at an accelerated rate. Pumping rates for existing wells are based on annual average pumping rates obtained from ADWR records. As presented in Chapter 8 of the RI/FS, the alternative that considers pumping at an average rate from only existing wells is ineffective at meeting the remedial response obj ectives. The Subunit A remedy will not eliminate contamination in Subunits B and C.
The fact that the ADWR model was not used to evaluate the groundwater alternatives does not mean that the evaluation is "flawed." See the responses to technical comments Numbers 12 and 14 for further discussion on this issue. The techniques used for determining the hydraulic head in the aquifer for various alternatives are based on valid and

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accepted hydrogeologic formulas.

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Reinjection is not the only end use considered. An entire chapter o£ the RI/FS deals with alternative end uses for treated groundwater.

Goodyear also presents data in support of installing air stripping without vapor phase carbon treatment on the overhead air stream. While these data will be factored into the decision regarding treatment of the air effluent, they are not the only data that must be considered. Other factors include SARAs mandate on reducing contaminant toxicity, mobility, and volume, other public comments regarding the site, and the air quality in the Phoenix area, which is currently a non-attainment area for ozone precursors such as those emitted by the proposed air strippers.

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ATTACHMENT A TO GOODYEAR TIRE AND RUBBER COMPANY'S LETTER DATED JULY 6, 1 8 9 9 TECHNICAL COMMENTS

1.

PAGE 2-37 The discussion of metals in soil encompasses all metal data generated regardless of the probable source of the metal or background levels in the area of the PGA. This discussion is particularly misleading with respect to arsenic since natural arsenic levels are sufficiently high to generate risk levels of concern and there is no record of use of arsenic onsite. The failure to segregate site-related contaminants from naturally occurring ones results in soil ingestion risks being driven by arsenic which cannot be remedied since it is ubiquitous in the native soil. A few statements to this effect would prevent the reader from being misled about site-related risks. RESPONSE

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It seems appropriate to include all data generated during the RI in the RI/FS report. Pages 2-40 through 254 include discussions of site-related contaminants and background concentrations for contaminants. These pages should eliminate any confusion about site-related risks.
2. PAGE 2-40

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No attempt has been made to differentiate Cr(III) from Cr(VI) or leachable chromium from fixed or insoluble chromium. As a consequence, total chromium values are reported and used for the purposes of estimating public health impacts even though availability and valence state greatly affect the nature and magnitude of risks.
RESPONSE

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Appendix G contains results of some sequential extraction tests done on samples containing chromium in excess of background levels.

As stated in the endangerment assessment, risks were calculated conservatively by assuming that all of the

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chromium was Chromium VI. However, in areas outside
the former sludge beds (which are the areas of concern

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in this FS), even this conservative approach yielded no significant health risks. The areas in and around the former sludge beds are being handled by Goodyear under an Administrative Order on Consent and were not included in this RI/FS. Calculating risks for the soils considered in this FS based on Chromium VI values (which will not exceed total chromium values) will only shown a smaller risk, but the risk has already been shown to be insignificant.
3. PAGE 2-54

An estimate of the inventory of TCE in soil of 450 Ibs was made from existing soil boring data. When an amount equal to this was removed during pilot soil evacuation work, a second estimate was attempted using soil vapor data. The latter estimate came to as much as 115,000 Ibs depending on the assumptions made with respect to vertical distribution of TCE residuals. The algorithm used to calculate total soil TCE mass from soil vapor data relies on an assumed equilibrium condition between soil-sorbed TCE, water-bound TCE, and soil vapors.

For simplification, a single partition value was used to calculate soil/water ratios. This value was also used in conjunction with the Henry's law constant to predict soil/vapor ratios. The partition value selected was based on a prescribed soil organic level.
Use of any value other than 0.0 contradicts the assumptions made by the Arizona Department of Water Resources (ADWR) in preparing the groundwater model for the site. While the ADWR assumption is probably overly conservative, an assumed constant value throughout a 60-foot depth is also misleading. It is highly likely that deep sands and gravels will have little or no affinity for the TCE. Hence, use of the algorithm will overpredict soil-bound TCE from the existing TCE vapor data.

The likelihood of overprediction is illustrated by analysis of the existing data. The highest soil vapor values were found in the area of the soccer field. Borings in that same area revealed no measurable TCE in subsoils. Hence, the algorithm is assigning TCE at significant concentrations to soils that have no evidence of contamination. Similarly, soil vapor readings from the area of the Phillips well were as high as 1.7 ug/1 even through this property is 3 miles from the

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site. These vapor levels are either derived from other sources or reflect the groundwater plume at that point. There is no evidence that they are associated with soil contamination.
RESPONSE
As stated previously, there are shortcomings to the method used to predict the total TCE mass. Actual soil data confirm that the organic content fraction in the soil is lower than the assumed average at depth but also that it is higher than average at the surface. The assertion that this makes the prediction less accurate is not clear.

It also is true as alluded to in the comment that soil gas readings can be an indicator of a groundwater plume as well as an indicator of a soil contamination source area. However, any presence of contaminants in soil gas is an indication of environmental degradation however small. It should also be noted that sampling and measurement of soils for the presence of
contaminants is subject to error through excessive handling and volatilization. Only upon reviewing the data in total can a determination be made of source and nonsource areas and a prediction made of the effectiveness of remedial action. PAGE 2-61

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Calculations are made to estimate the total volume of soil in excess of Arizona Department of Health Services (ADHS) soil action levels. These volumes are meant for use in determining the cost of remedial action. The volumes are misleading, however, since they encompass all soils and subsoils with VOC concentrations in excess of the action level. The action level was devised for surface soils, not deep subsoils. Most TCE residuals lie 20 to 30 feet below the surface. Alternate action levels are needed for these soils on the basis of their ability to affect groundwater quality.
RESPONSE

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To our knowledge, the ADEQ action levels are healthbased but apply to all soils and are not restricted as to the depth over which they apply. While a determination of which soils are a threat to

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groundwater is a good way of defining target areas, this is difficult in practice. The target areas in the RI/FS were chosen as a means of defining order-ofmagnitude costs. At this time, target areas for soils remediation are under discussion and are likely to change from those in the RI/FS prior to issuance of the ROD. 5. PAGE 2-61 Vadose zone calculations are made suggesting that 16,000 Ibs of TCE will move to the groundwater in 20 years. These calculations are based on an assumed recharge that is without documentation. They also appear to take no recognition of unsaturated zone transport times. Using EPA time-of-travel algorithms, recharge at 0.32 in/yr would take 117 years to move 20 feet downwind under current conditions. If the TCE has a partition coefficient of 0.49 I/kg, its travel time

would be retarded by a factor of 2.6 and hence would be
304 years. RESPONSE Recharge is estimated based on our knowledge of annual precipitation, ambient temperatures, estimated evapotranspiration, and runoff. The fact that contaminants have in fact traveled through the vadose zone to the groundwater is evidence that some recharge occurs at the site. 0.32 in/yr was chosen as a reasonable estimate but it is only an estimate. Currently, the leaching of contaminants to the groundwater table is being recalculated and the time over which recharge occurs will likely be revised. 6. PAGE 3-46

The risk calculations are based on current TCE concentrations at various wells around the PGA site.
No attempt was made to use the ADWR model to see how those concentrations will change over time. Since cancer risks are based on 70 years of exposure, the assumption is tantamount to saying that the groundwater at any one well will not see any appreciable change in TCE concentrations over a 70-year period. That is unrealistic. Simple application of plume size and the estimated velocities in the affected aquifer suggest that concentrations will drop an order-of-magnitude in 7 years. If that does occur, the actual risk at the

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site will be one tenth that predicted in the RI/FS. The analysis also fails to consider the effects of the Operable Unit 16 remedy which is currently under construction.
RESPONSE
Pages R-139 and R-140 in Appendix R discuss the risks for various scenarios under the no action alternative. Future concentrations under the no action alternative were estimated by ADWR with their model. The Section 16 OU remedy was included.

7.

PAGE 3-46

Well logs from construction of extraction and injection wells for the Operable Unit 16 remedy suggest that the boundaries between Subunits A, B, and C are not always distinct and then in some areas, the units may be indistinguishable. Previous descriptions imply rather clear cut interfaces which is misleading.
RESPONSE

CH2M HILL is willing to assist Goodyear in interpreting well logs and serve as a resource of hydrogeologic data which has been compiled over the last 5 years.

8.

PAGE 4-1 Risk estimates for suspended particulate are based on current emission rates being sustained over a 70-year period. A simple calculation shows that in a period of 7 years, the finer suspendable particles will be depleted to a depth of 1.5 cm. This in effect will leave the larger, nonsuspendable particles to armor the surface and minimize further resuspension. As a consequence, risks will actually be an order of magnitude less than predicted. The bulk of the risk from suspended particles is attributable to arsenic in the soil. Since arsenic is naturally present and not a site-related contaminant, the risk calculations provide a misleading picture of incremental risk and risks that can be addressed by a site remedy. All soils in the area pose the same level of arsenic driven risk.

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RESPONSE

The risks were estimated using the most conservative scenario. No backup is given for the calculation showing a depletion of finer particles in 7 years, but data from soil samples show silt contents of 60 to 70 percent in surface soils.
The bottom line is servative approach considered in this servative approach that risks calculated using the conare not significant for the soils RI/FS; therefore, using a less conwill not change the conclusions.

9.

PAGE 5-41
The ultraviolet-ozone oxidation process is dismissed prematurely. Recent studies show this process to be very effective in removing organic contaminants from water. In areas where air stripper emissions must be treated with carbon, the UV-ozone process can be cost competitive.

RESPONSE

To our knowledge UV-ozone type treatment has not been proven commercially for treating halocarbons such as those found at the site. In addition, the relatively high TDS levels may make this option unattractive. In the presence of a proven low cost alternative such as air stripping, use of a new technology is unwarranted without further study.
10. PAGE 6-13

Target Area 1 is inappropriate. ADHS action levels were designed to address surface soils, not subsoils 20 to 30 feet beneath the surface. If a target area is to be defined using ADHS action levels, it should be based solely on TCE concentrations in surface soils.

Target Area 3 is not based on any defensible rationale. No attempt is made to relate soil vapor concentrations to site risk values. Since soil vapor results do not correspond with subsoil concentrations of TCE, the use of soil vapor to delineate a target area is illogical. At a minimum soil vapor values should be converted to equivalent soil concentrations and the target area defined on the basis of the latter.

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RESPONSE

The ARAR analysis identified a lack of cleanup criteria or standards to be applied to the contaminated soils in the vadose zone. In the absence of ARARs or other criteria, EPA is to select a cost-effective remedial action that meets the remedial response objectives, unless meeting the objectives is not feasible. To allow the selection of a cost-effective action, a range

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of action levels was evaluated and the costs and benefits of each were identified. Target Area 1 was developed based on the ADHS action levels and is considered the area containing the most significant amounts of
contamination at the site. Target Area 3 is considered to be the area encompassing all contamination in the vadose zone as a result of site-related activities. 11. PAGE 6-21
The discussion of the capping alternative appears to contradict other portions of the RI/FS. The implication of this discussion is that recharge is insignificant with respect to TCE movement. And yet, the calculations of vadose zone movement and soil residual effects on groundwater quality are based on a prescribed recharge rate of 0.32 in/year. Either recharge is driving TCE downward and capping will minimize or prevent this migration, or recharge is insignificant and subsoil contamination can be left in place without remedy.

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RESPONSE The implication of this discussion is that the existing paved areas are not adequate caps. A properly designed cap will minimize infiltration and leaching of cont aminant s. 12. PAGE 8-2 9
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A very simplistic analysis is employed to calculate aquifer flushing times. This is difficult to explain since a great deal of money has been spent developing a sophisticated groundwater model to predict flushing times and plume movement. The RI/FS should rely on model results for flow and transport predictions.

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RESPONSE

In our opinion, the analysis performed in the FS is appropriate for the task of developing and evaluating conceptual alternatives for the project. The goal of the analysis is not to predict the actual times for flushing the aquifer of contaminants but rather to evaluate the relative difference in flushing times between the several alternatives. Evaluation using the solute transport model developed by ADWR would cost considerably more than the method used but would not provide any additional accuracy in prediction of the rate of flushing. This is because the model does not account for the slow rate of flushing from the aquifer. Rather, the model assumes that contaminants move in piston flow. This assumption results in the inaccurate conclusion that the aquifer is flushed after only one pore volume is extracted.
13. FIGURE 8-3

The contaminant plumes have been depicted as large areas joining points wherever VOCs were detected in groundwater without regard to the relative concentrations at adjoining wells. Geostatistical analysis should be used to prepare these plots. The relatively high values at the Phillips well and lower concentrations at points between Phillips and the site open the possibility of multiple sources or a more concentrated transient plume that is passing by Phillips to be followed by water of better quality. Since risk was estimated on the basis of continued exposure to current levels, a better characterization of the actual plume could have a big impact on conclusions concerning risk and the nature of required remedies.
RESPONSE

The target areas for remediation are based on the available data on the actual distribution of contamination in the aquifer. For the purpose of developing and evaluating alternative remedial actions, it was conservatively assumed that the target areas should encompass the entire area that is bounded by observed contamination in groundwater. It may be that the actual distribution of groundwater contamination differs from the target area. However, without actual field data showing that an area is clean, we believe that it is appropriate to assume that it should be

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included in the target. Geostatistical analysis of the data is not reliable enough to reduce the size of the target areas for remediating. After additional monitoring and extraction wells are drilled, modifications to the target area for remediation can be developed.
14. PAGE 8-30

Simple equations are applied to estimate groundwater travel times. The ADWR model was developed to provide much more accurate predictions of travel times and

should be employed for that purpose.
RESPONSE -

See response to Comment 12.
15. PAGE 8-36

A simplified approach is taken to calculate the time required to achieve cleanup. Once again, the ADWR model should be employed for this purpose. Furthermore, the estimates do not consider implementation of the Operable Unit 16 remedy or continued inputs from the vadose zone. This static evaluation of aquifer cleansing is unrealistic.
RESPONSE

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Additional evaluation of the impact of the vadose zone in prolonging the cleanup is currently in progress. These calculations suggest that if the vadose zone is not flushed of contaminants, then the cleanup times could extend for hundreds of years. In the evaluation of the alternative in the FS, it was assumed that the vadose zone would not be a continuing source of contamination. Likewise, in the evaluation, it was assumed that contaminants from Subunit A would no longer be moving to Subunit C. This assumption implicitly includes to the Section 16 Operable Unit.
16. PAGE 9-7

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The analysis of end use options for the treated groundwater does not give ample consideration to problems associated with water rights. A brief discussion is given of water rights after discharge. However, it is not clear if the water is currently owned by a party who can subsequently dictate where the

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treated water should go. If some similar entity owns the allow it to be delivered for other entities. A much more ownership is required before be considered. RESPONSE

the City of Phoenix or groundwater, they may not private or public use by thorough evaluation of discharge alternatives can

The thorough evaluation of ownership and water rights can be evaluated during remedial design. Presently, the preferred alternative is to provide the water to the current users of the existing wells. Additional water from new extraction wells may be provided to the City of Goodyear for municipal use.
17. PAGE 10-1

The options for design of the groundwater extraction system should be evaluated using the available models of the local groundwater. A simple water balance approach fails to consider the Operable Unit 16 remedy and the complexities of the aquifer. With sophisticated tools readily available to support the analysis, reliance on simple approaches is
indefensible.
RESPONSE

See responses to Comments 12 through 15.

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COMMENTS EXPRESSED AT JUNE 21. 1989, PUBLIC MEETING IN GOODYEAR. ARIZONA, AND RESPONSES
PAMELA SWIFT

I'm still very concerned about the health problems here and of the employees that used to work here. So once again, this is the fourth time they have been here and the fourth time I've requested for health surveys. I do not want to see air stripping because of our air quality laws. And even if we didn't have that, when these chemicals are mixed with other chemicals that are being emitted mostly at night from our industries here, I think it's very dangerous. We do have inversion here, so that's going to be very harmful if there's any of the air stripping. Also, since it appears that Goodyear and EPA has their mind made up to go ahead with the air stripping, because it is cost-effective, it's not health-effective, but it's costeffective -- I would hope that they would put scrubbers on, which I doubt if they will because scrubbers are very expensive. But I do not want to see air stripping, and I think it's going to be very dangerous for us to do that. Thank you. RESPONSE

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Health surveys are typically conducted by agencies other than EPA such as the Agency for Toxic Substance and Disease Registry (ATSDR). Please contact Ms. Gwen Eng at ATSDR for more information.
The air-stripping alternative for treatment of VOCs will be well below all applicable air quality standards for emissions. The current estimates are that approximately one pound per day or less of VOCs will be emitted from the air strippers. These low emission rates will be insignificant to the ambient air quality, and no additional threat to public health will be incurred.

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If "scrubbers" or vapor phase emission controls are added to the stripping towers, the treatment cost will be doubled or tripled and an additional hazardous waste will have to be dealt with. The activated carbon used to remove VOCs from the airstream will require disposal or destruction through incineration. Given the disadvantages of a significant
increase in cost and the required handling of a generated waste, it is not feasible to add emission controls to the

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air strippers which are already deemed protective of human

health.
MIKE BOONE

I'm for cleaning up the environment. I've lived in Arizona all my life, and I'm very concerned about the environment. I love the outdoors. And I think that we need to do all we can to clean it up and for the future and for the present.
But I would be opposed to any type of emissions put into our air unless you're certain that it won't affect the people in the town of Goodyear and Avondale. Other than that, I think it's a good plan, and I support it.
RESPONSE

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See response to Pamela Swift.
DENNIS MYERS

F.A.A. will respond with written correspondence during the allotted time.
COMMENTS FROM FEDERAL AVIATION ADMINISTRATION AND RESPONSES

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1.

During transportation of the contaminated soil, ensure that the contractor(s) wet or cover the soil in the vehicles to prevent wind blqwing contaminated dust toward the air traffic control tower (ATCT).
RESPONSE

If contaminated soil is transported, Department of Transportation regulations will be followed to cover the soil and mitigate dust.

2.

Provide dust control for vehicle traffic south and west of the ATCT on the unpaved roads and dirt areas.
RESPONSE

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The surface soils are not contaminated except those near the former GAG sludge drying beds which do not receive vehicle traffic.
3. Brief Air Traffic Manager on any emergency procedures and contingency plans concerning site cleanup.

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RESPONSE

This can be done at the beginning of remedial activities. Goodyear Tire and Rubber should perform this task for the Section 16 remedial action.
4. We are concerned as to the locations of the air strippers in relation to the ATCT, as we have an average of

seven employees on duty during a typical day shift, working 75 feet above grade at the cab level and may be exposed to high concentrations of VOCs. According to your statement at the June 21 meeting in Goodyear, you thought the air stripper towers would reach a height of 40 feet. Our employees would be 30 feet above that.
RESPONSE

Goodyear Tire and Rubber should address this concern for the Section 16 remedial action. To determine the exposure of employees in the tower from the air stripping conducted during the final remedy, several factors must be considered: treatment plant location, emission rates from the stripping towers, and the source of the air supply into the air traffic control tower. More precise information concerning these factors will be gathered during the remedial design phase and a more accurate assessment can be made at that time.

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August 3, 1989

ARIZONA DEPARTMENT OF WATER RESOURCES

Rose Mofford, Governor

N. W, Plummer
Director

Mr. Jeff Rosenbloom PGA Project Manager US Environmental Protection Agency Mail Code T-4-2

15 South 15th A^e-,e Phoenix. Arizona 95-07

215 Freemont Street San Francisco, California 94105
Dear Jeff:

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I I I I f I I I

Here is the responsiveness summary for the Three-Dimensional Contaminant Transport Modeling Report otherwise known as Appendix V, Volume IX of the PGA RI/FS report. I have received and addressed comments from the Arizona Department of Water Resources and CH2MHILL. These are the only comments that I have received at this time. The responsiveness summary follows the same format as the responsiveness summary included in the Public Comment Draft of the RI/FS report.

You will be receiving several quarterly reports to the present quarter by the end of the month. If there are any other administrative tasks that need to be taken care of for this site please let me know.
If you have any questions or need additional information, regarding the responsiveness summary, please do not hesitate to call me at (602)542-1586.
Thank you.

With Best Regards,

Greg L. Bushner Hydrologist
GB/rb

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1 1 1 1 1 1
1 1 1 1 1 1 I 1 1 1 1 1 1

RESPONSE TO WRITTEN COMMENTS RECEIVED ON JUNE 1 8 PUBLIC COMMENT DRAFT 99 REMEDIAL INVESTIGATION/FEASIBILITY STUDY PHOENIX-GOODYEAR AIRPORT

Written comments on the public comment draft Volume IX were received from the following parties:
o Arizona Department of Environmental Quality

o CH 2 M-Hill (Peter Mock)
Because of the wide variety of numbering styles used on comments submitted and for ease in future references, the comments have been numbered consecutively, from Comment No. 1 through Comment No. 80. All comments received which relate to Appendix V - Three-Dimensional Contaminant Transport Model prepared by the Arizona Department of Water Resources have been included in their entirety.
COMMENT 1 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Volume IX- ADWR 3-D Contaminant Transport Model Overall, the report is thorough and well documented, however, the figures are difficult to use. The maps showing locations of the facilities and wells are not at the same scale as the maps showing the results of the various computer runs. The addition of some reference points consistently used throughout the figures would aid in orientation and interpretation of the results.
RESPONSE 1:

Comment noted.
COMMENT 2 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Page 44, Paragraph 2
The MFU and LCU probably do not significantly impact groundwater flow and can be ignored in the water budget, however, the MFU is probably not a hydraulic barrier to flow between units.
RESPONSE 2:

Due to the fact that the MFU within the study area is primarily fine-grained, the vertical hydraulic conductivity within that unit is probably very low, thereby, providing somewhat of a hydraulic barrier to groundwater flow in to the MFU and LCU.
COMMENT 3 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Page 87, Last Two Points
Detectable concentrations of TCE have been reported for wells which produce from the MFU

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RESPONSE 3;

For the purposes of the contaminant transport modeling the simplifying assumption that the MFU is not significantly contaminated was necessary.
COMMENT 4 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Page 90, Last Paragraph

--

The last point is missing the verb "is" before the word "based".
Table 9 indicates that model input values for field parameters were varied over a broader range during the sensitivity analysis than indicated here.
RESPONSE 4: -

Comment noted.
Model input parameters were varied from one-tenth to 1370 times the model input value rather than from one-half to 1370 times model input values as reported in the text. The values changed are as reported in Table 9.
COMMENT 5 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

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Page 97-99

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Throughout this report, Unidynamics is ciscussed along with the airport and GAC as a potential source of groundwater contamination at the PGA site. The contaminant transport modeling does not address the plume beneath the Unidynamics facility. An explanation as to why the model does not include the Unidynamics plume may be appropriate here. -

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RESPONSE 5:

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There are several reasons that the contaminant transport model does not address the plume beneath the Unidynamics site. They are as follows: 1. The total extent of contamination in this area was not known at the time the model was discretized. The framework for the contaminant transport model was discussed in a memorandum to the PGA Modeling Sub-Committee dated July 16, 1987.

_ V " · ·

2. Unidynamics is responsible for the entire RI/FS for their site. The ADWR modeling study supports the EPA, who is the technical lead responsible for the FS for sub-unit C of the UAU beneath the Airport site. 3. Boundary conditions at the NE of the model domain were set too close to accu to accurately simulate the entire extent of the plume in this area.
Although the plume beneath the Unidynamics site was not modeled, the data

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that ADWR developed as a result of the modeling process was given to Dames and Moore (groundwater consultants for Unidynamics) to assist them

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in development of their own model. All of the data collected by ADWR benefited all parties involved at the PGA Site.
COMMENT 6 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Page 101. Table 11
Predicted TCE concentrations remaining adjacent to COG #11 well after 21 years under Base Case 3 are higher for Alternatives 4, 5, and 6 than for the NoAction Alternative (Alternative 1). How can this be? This does not seem to agree with the figures of the model-predicted TCE concentrations for these alternatives. In the figures, the model results are presented separately for Subunit A and Subunit B/C. Are the TCE concentrations in this table the sum of concentrations from these Subunits?
RESPONSE 6;

The predicted concentrations for the City of Goodyear Well No. 11 for Base Case 3 range from 1.1 ppb (No Action Alternative) to 5.8 ppb for (Alternative 5). The relatively small rise in contaminant concentration in Well No. 11 could be due to several variables including the proposed FS wells, downgradient of the City's wells. These additional wells could be pulling contamination further towards Well No. 11.
TCE concentrations reported in Table 11 are taken representative of the screened interval of the well.
COMMENT 7 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

from

layers

Page 106, Paragraph 2

Do the proposed COG wells withdraw groundwater from Subunit A? Due to ambient inorganic water quality, it is anticipated that the wells would produce from Subunit B/C. Therefore, would the wells be expected to dewater Subunit A?
RESPONSE 7:

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The proposed City of Goodyear wells are assumed to withdraw water from sub-units B/C. The problem of the model dewatering near the western model domain is a combination 1 of (1) a groundwater flux out of the model domain, (2) City of Goodyear s projected pumpage for 21 years, and (3) the relatively small saturated thickness of the UAU in this area. However, the proposed City of Goodyear wells would create a typical cone of depression as normally seen from other production wells in this area. Therefore some dewatering from these wells would probably occur.
COMMENT 8 (ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY)

Page 174, Paragraph 2
Table 16 indicates the best reduction of contamination results from Alternative 4. Is this statement regarding Alternatives 5 and 6 accurate?

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RESPONSE 8:

Comment noted, this statement is incorrect as Alternative 4 achieves the best reduction of contamination than any of the alternatives including 5 and 6.
COMMENT 9 (CH2M-HILL) _

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General Comment (1)

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The ground water flow model calibration did not benefit from the use of all of the data, specifically the numerous water-level times series available for the area.
RESPONSE 9: _

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The water level data has not changed significantly during the past two years. However, hydrographs will be incorporated in future model studies of this area.
COMMENT 10 (CH2M-HILL) _

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General Comment (2)

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Data on water levels are very sparse in an areal sense for the large modeled area. This results in our not knowing which way the water flows in the required detail over much of the modeled area. If we don't know, the model surely can't. This makes the accuracy of calculated flow vectors and concentration changes with time very suspect.
RESPONSE 10: _

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To the west of the airport, there is an area of contamination that we felt necessary to include within the model domain. The problem dealing with this contamination remains, regardless of the tool used to evaluate it. The model predicts the groundwater flow direction reasonably well given the current data available in this area of the site.

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In an attempt to address the data deficiences that have been recognized at the PGA site, AOWR proposed to collect additional hydrologic data towards the western site boundary by installing additional monitoring wells. This was proposed in the PGA committee meeting of December 18, 1986. This proposal was not acted upon. Until further hydrologic information is gathered, a lack of adequate data will hinder modeling efforts at this site.
COMMENT 11 (CH2M-HILL) _

B B
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General Comment (3)

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The report presents geologic and hydraulic interpretations different from those we made in the RI/FS report. Some of these are large enough to make a significant difference. ·

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RESPONSE 11;

Comment noted; comments regarding geologic and hydraulic interpretations will be addressed under Ch^MHILL's specific comments that follow.
COMMENT 12 (CH2M-HILL)

General Comment (4)
Sensitivity analyses can give us a feel for the potential effects of uncertainty on the predicted flow vectors and concentrations. Unfortunately, the ADWR work didn't analyze the key parameters sufficiently (some not at all) and didn't measure their results in such a way that we could benefit from what work they did do.
RESPONSE 12;

Comment noted; comments regarding the sensitivity analysis will be addressed under CH2MHILL's specific comments that follow.
COMMENT 13 (CH2M-HILL)

General Comment (5)

The predicted percent removals should not be treated as accurate engineering estimates. Their use of the model for this purpose can not be supported on the basis of the report or from what I remember them presenting to the Committee.
RESPONSE 13;

I agree that the percent removals should not be treated as engineering estimates, however they can be used to compare how effective the various alternatives are relative to one another using different future scenarios. I think it is fairly clear in the text that the percent removals should be used as a guide and not as a definitive answer. This was just one of the uses of the model, and as an investigative tool the model can be supported by the report and by what has been presented to the Committee as documented in the meeting minutes.
COMMENT 14 (CH2M-HILL)

I i I

P. 1, Par. 2
The ground water investigations (monitoring well installation, water quality and water-level monitoring, aquifer testing, geophysical logging) were conducted to support the development and evaluation of remedial action alternatives.
RESPONSE 14;

In the context of this report a detailed groundwater investigation meant that geologic and hydrologic data was collected and analyzed from all sources for support of the modeling investigation. This was done for the

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EPA in support of the Investigation/Feasibility Study.
COMMENT 15 (CH2H-HILL)

Phoenix-Goodyear

Airport
_

Remedial

P. 1. Par. 2

--

Sufficient information is not provided to evaluate the statement that a reasonable match was achieved.
RESPONSE 15:

I disagree, sufficient information is provided in the report to evaluate whether a reasonable match between simulated and observed parameters was achieved.
COMMENT 16 (CH2M-HILL) _

P. 1, Par. 2

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The sensitivity analysis as reported in this document did not explore the full range of each parameter's potential value and impact on calculated heads, local velocity vectors, and concentrations. Uncertainty was not quantified.
RESPONSE 16: Z

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The sensitivity analysis did explore the the full range of reasonable values for the reported parameters and the impact that ^changing these parameters had on the calculated heads and local velocity vectors. The uncertainty was qualified.
COMMENT 17 (CH2M-HILL) _

m m £
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P. 1, Par. 2

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There is an inconsistency between the statement that order of magnitude changes in horizontal hydraulic conductivity had little or no effect and the statement that parameters such as horizontal hydraulic conductivity significantly affected the flow model results. ~
RESPONSE 17: I

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The last sentence of this paragraph should be revised to read: 'Also brought out . . . model results (i.e., horizontal hydraulic conductivity of sub-unit C)' ....
COMMENT 18 (CH2M-HILL) _

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P. 1, Par. 2

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The qualitative evaluations of parameter certainty based on field data can not substitute for a more rigorous analysis of model sensitivity.
RESPONSE 18: . -

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A more rigorous sensitivity analysis will be applied' to the next phase of numerical modeling at this site.
COMMENT 19 (CH2M-HILL)

P. 2, Par. 2

The implied accuracy of the predicted percentage removals of contamination is not supported by the apparent problems encountered in applying the TARGET model to contamination evaluations at this site.
RESPONSE 19;

Although percent removals of contamination are presented throughout the report, they are intended to provide a comparative analysis of the base cases and respective alternatives. As presented in the general comments, they were never intended to serve as exact estimates of TCE removal given the number of unquantifiable and unknown variables at this site.
COMMENT 20 (CH2M-HILL)

P. 6, Par. 2

The blanket statement "The disposal of waste products at these facilities occurred from the late 1940's until the 1970's" is questionable and probably not something ADWR wants to say in its model study report.
RESPONSE 20:

This statement is supported by the Source Verification/Field Investigation Report by Ecology and Environment, 1986. Specifically Tables 2-1 (Waste Disposal Summary: Litchfield Naval Air Facility), 2-2 (Waste Disposal Summary: Goodyear Aerospace Corporation), and 2-4 (Waste Disposal Summary: Unidynamics/Phoenix, Inc.), list the waste types, quantities, dates, and reported disposal practices. The statement is true with the exception that disposal of solvents at. the Unidynamics facility occurred between the late 1960's through the late 1970's.
COMMENT 21 (CH2M-HILL)

P. 6, Par. 2 Data are not available to say that contamination does not affect the Middle Fine-Grained Unit or Lower Conglomerate Units.
RESPONSE 21: Comment noted. Information to date indicates that the significant contamination has not yet affected the MFU.

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COMMENT 22 (CH2M-HILL)

P. 8, Bul.

5

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This bullet indicates that the model study was to simulate the~future response of contaminants. Based on this, it would seem that the model study would include predicting movement, not comparing percentage removal or clean-up efficiency.
RESPONSE 22;

I
is correct as stated; Figures have been provided in the Study that show the predicted flow fields that illustrate movement, and figures of plumes that illustrate the predicted movement.
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The bullet Feasibility groundwater contaminant

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COMMENT 23 (CH2M-HILL)

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P. 10, Par. 2

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The statement that GAC retains liability for contaminated sorils and ground water at the site may be stronger than GAC has actually stated. This statement may not be appropriate for ADWR to make in a model study report.
RESPONSE 23:

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The intent of the statement was to indicate that the Loral Corporation is not a Responsible Party at this site even though it owns the property and that the Goodyear Aerospace Corporation is one of the Responsible Parties at this site. It was not intended to offend or make _a judgement of liability at this site which is clearly outside of the purview of ADWR and this study.
COMMENT 24 (CH2M-HILL)

jj g · .

P. 11. Par. 1

Eberly and Stanley (1978) defined two units - Unit I and Unit II, not the UAU, MFU and LCU. Also, work by the USGS and others indicates that the upper portions of what has been called the MFU and the entire UAU may be Quaternary

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in age.
RESPONSE 24: ~

Comment noted.
COMMENT 25 (CH2M-HILL) I -|

P. 11. Par. 2

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Laney and Hahn (1986) address only the East Salt River Valley.^ The parallel work of Brown and Pool (1989) for the West Salt River Valley is too recent to be included in this model study. At any rate, the Laney and __Hahn reference should be explained as pertaining to another sub-basin.

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RESPONSE 25;
Comment noted.
COMMENT 26 (CH2M-HILL)

P. 11, Par. 2

The origin of the statements regarding the UAU's thickness, character, and transition to the MFU is not explained. For example, refer to illustrative cross-sections, isopachous, or percent-coarse mapping in this or other documents to which the reader can go to verify these statements.
RESPONSE 26:

The point is taken that the reader should have been informed of these illustrations when they were first discussed. This section of the report is intended as an introduction to the UAU. The reader is referred to the rest of the section, which presents geologic cross-sections, isopach, and structure maps.
COMMENT 27 (CH2M-HILL)

P. 11, Par. 2

I believe that this hydraulic conductivity estimate is an ensemble average of
estimates derived from the ADWR Drillers Log Program. Since use of this program is relatively unique, it needs to be discussed when first referenced and its accuracy compared to the more standard aquifer testing methods.

RESPONSE 27:

The hydraulic conductivity value of 750 gpd/ft2 was derived from an analysis of driller's logs using the Driller's Log Program and specific capacity data. This information has been provided to the PGA Modeling Sub-Committee in a memorandum dated March 11, 1987. The Driller's Log Program was developed by ADWR personnel to generate aquifer parameter data for areas that aquifer tests or specific capacity data were not available. This program is used to calculate computer-generated values for specific yield, hydraulic conductivity, and transmissivity. The results obtained when using this program give a relative distribution of the aquifer characteristics. The accuracy of the results are limited by the quality, quantity, and distribution of the driller's logs within the study area. This program has been used in several of the Department's model studies including but not limited to the Salt River Valley Cooperative Study Modeling Effort (Long et. a!., 1982), and Groundwater Modeling Study of the Upper Santa Cruz Basin and Avra Valley in Pima, Pinal and Santa Cruz Counties, Southeastern Arizona (Travers and Mock, 1984). This program is a first cut at determining the aquifer parameters in an area. It should not replace information derived from long term aquifer tests. For the PGA site all available driller's logs were used to evaluate the aquifer characteristics as reported in the above mentioned memorandum to the committee. However, during the course of the RI new aquifer parameter information was gathered and is used in

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conjunction with that derived by the driller's log program. Please refer to Table 6, page 62 for the values used in the model.
COMMENT 28 (CH2M-HILL)

P. 11. Par. 2

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The reference to Bouwer (1978) here and elsewhere in the te*t incorrectly implies that a recognized authority supports a very narrow potential range of vertical anisotropy for this particular site. The general nature of Bouwer's suggested guidelines should be discussed when first referenced "along with how you applied those guidelines for this site. "
RESPONSE 28: --

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Comment noted.
COMMENT 29 (CH2H-HILL)

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P. 11, Par. 2

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I disagree with the statement that the UAU is the water table aquifer in the PGA area. My interpretation for the vicinity of PGA is that the UAU contains one water table aquifer (Subunit A), at least one confined aquifer (Subunit C) and at least one leaky aquitard (Subunit B). In fact, therelis some field evidence which indicates that Subunit A is confined in some areas. In summary, the UAU is geologic unit defined on the basis of stratigraphy which contains a system of aquifers and aquitards. RESPONSE 29: _

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Agreed, the UAU is a geologic unit defined on the basis of stratigraphy which contains a system of aquifers. This description holds true for both the East and West Salt River Valleys. The UAU however, does contain the water table aquifer within Sub-unit A.
COMMENT 30 (CH2M-HILL) _

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P. 12, Par. 2

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The statement that Subunit A thickens at the basin margin should be tempered by the recognition that the general driller's descriptions may not allow precise distinction between the coarse materials of the UAU and LCU which may be in contact at the basin margin. Also the presence of the Gila River indicates that substantial reworking of LCU, MFU and UAU sediments would blur the distinctions in this area adjacent to the Sierra Estrella.
RESPONSE 30;

Comment noted.

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