I 1 1 1 I 1 I I 1
COMMENT 31 (CH2M-HILL)
P. 12, Par.
2
If the horizontal and vertical hydraulic conductivities are not equal then the statement should not be made that the average hydraul ic conductivity is isotropic.
RESPONSE 31:
It is stated that the average horizontal hydraul ic conductivity is assumed to be isotropic throughout the study area.
COMMENT 32 (CH2M-HILL)
P. 12, Par.
2
The use of the Drillers Log Program for estimating horizontal hydraulic conductivity should be thoroughly explained and compared to aquifer testing results.
RESPONSE 32:
Please refer to Response 27 above for an explanation of the Driller's Loa Program.
COMMENT 33 (CH2M-HILL)
P. '12,
Par.
2
The use of Bouwer (1978) as referenced here is again questioned for supporting such a narrow potential range in anisotropy.
RESPONSE 33:
i i t i
i i
Comment noted.
COMMENT 34 (CH2M-HILL)
P. 12, Par.
2
A reference or method for estimating specific yield should be provided.
RESPONSE 34:
Specific yield values were derived using the Driller's Log Program and from results of the aquifer testing completed on the site during the RI. Please refer to the memorandum and attached maps sent to the PGA Modeling Sub-Committee dated March 11, 1987 for further information. Also, refer to Response 27 for further information reqardina the Driller's Log Program.
11
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 1 of 37
COMMENT 35 (CH2M-HILL)
Figs. 3a-3c
--
| 9 · · ·
, ^
The local cross-sections developed by CH2M-HILL in the Phase II Well Installation Memo and the regional cross-sections developed by CH2M-HILL in the RI Report were available to ADWR prior to the release of this report. The subunit contact interpretations made by ADWR are different fronf those shown in the RI/FS report. What alternate interpretations did ADWR make that led to the development of additional cross-sections?
RESPONSE 35:
Many cross-sections were developed by ADWR during the RI (please refer to the work products that were delivered to the Modeling Sub-Committee in November 1984, and March 1985). The cross-sections included in the modeling report are a combination of drillers logs (data from the previous ADWR cross-sections) and geophysical logs from wells installed as part of the RI. There can be many interpretations of the stratigraphy in this area that are valid, which is why the logs are included in Figures 3a through 3c, The cross-sections that CH2MHILT derived were based on a simple percent fine and percent coarse material. ADWR based their interpretations on descriptive drillers logs and the geophysical information gathered during the RI. The information gathered by ADWR has always been available to the committee, especially the drillers logs for this area. The cross-section information, also has been available to the committee for inspection. COMMENT 36 (CH2M-HILL) --
ft m tt J| » ·
ft m
I
Figs. 4a-4g
.
--
-
These maps are quite different from figures found in Chapter 3 of the RI/FS Report which present the same titles. ADWR has interpreted different elevations for the contacts between subunits and thicknesses of units than CH2MHILL has. Since the figures from the RI report were available"to ADWR prior to the writing of their report, what alternate interpretations did ADWR make that led to the development of different structural contact and isopachous maps?
RESPONSE 36:
· JB » M
Alternative interpretations are fairly clear throughout the_ report (refer to Figs. 2 through 4, and Table 2 for the interpreted picks from the available information). Each interpretation of the stratigraphy in this report is adequate and serves the purpose for which it was developed.
COMMENT 37 (CH2M-HILL) _
·
·
P. 25. Par. 1
--
|
The use of the Drillers Log Program for estimating horizontal hydraulic
M
conductivity and Freeze and Cherry (1979) for estimating vertical hydraulic
conductivity should be better explained and evaluated. How uncertain are these methods and how do they compare to aquifer testing results?
12
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 2 of 37
·
,,
I
I I I
I
RESPONSE 37;
Please refer to response 27 above for an explanation of the Driller's Log Program. In the absence of field data, the values of vertical hydraulic conductivity for the various aquifers and aquitards within the study were derived from a literature review or were assumed as stated in the report.
COMMENT 38 (CH2M-HILL)
I I 1 I I
P. 25. Par. 2
What methods were used to estimate specific yield and storage coefficient and what accuracy bounds are appropriate?
RESPONSE 38;
Please refer to Response 34.
COMMENT 39 (CH2M-HILL)
P. 25, Par. 2
I 1 I
The discussions of Subunit C aquifer parameter estimates are questioned as they were for Subunits A and B above. In addition, is the potential range in value given for horizontal hydraulic conductivity based on the available data or is it some other type of estimate?
RESPONSE 39:
Please refer to Response 27; aquifer parameter estimates are based on the available data as stated in the text and on Table 6, page 62.
COMMENT 40 (CH2M-HILL)
I I I I I 1 I
P. 25, Par. 2
The interpretations of subunit contacts and thicknesses described here are different from those presented by CH2M-HILL in the RI/FS report.
RESPONSE 40;
Please refer to Response 35
COMMENT 41 (CH2M-HILL)
P. 26. Par. 2 Cross-sections or other presentations in this or another report should be referenced to allow the reader to verify the interpretations of the MFU's extent and character.
13
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 3 of 37
RESPONSE 41:
Comment noted. Please refer to Response 35.
COMMENT 42 (CH2M-HILL)
P. 26, Par. 2
Are Montgomery and Associates estimates for horizontal hydraulic conductivity locally derived? Would you expect them to represent the MFU as a whole or would the hydraulic conductivity of aquifers in the stringers mentioned be different?
RESPONSE 42:
The reference of horizontal hydraulic conductivity is locally derived, as noted in the referenced document. The value as reported in the Montgomery and Associates report provides an idea of the aquifer properties of the MFU near the study area. I would expect the hydraulic conductivity estimates to vary through out the MFU.
COMMENT 43 (CH2M-HILL) _
B ·
g| £
^
P. 26, Par. 2
--
*
The referenced value of vertical hydraulic conductivity from one test of a 6 foot section of a stratigraphic unit in another sub-basin should be viewed with caution. What data do you have for the MFU in the PGA area that leads you to believe that the estimates from the 6 foot interval in Scottsdale is also representative here? The potential range in value for this parameter in any one location at PGA or Scottsdale is several orders of magnitude, not a factor of 2 as implied here.
RESPONSE 43: -
tt · m fj M
"
The reported value for vertical hydraulic conductivity was presented as an estimate based actual field data from tests conducted in the East Valley. The text is correct as stated in that the vertical conductivities are not known with certainty and that the data reported is from the East Valley.
COMMENT 44 (CH2M-HILL)
· ''·
g
P. 27, Par. 1
I
I I I
References to presentations of data in this or other reports are needed to allow the reader to verify these statements on the extent and character of the LCU. Also, the entire sequence of alluvial fill (UAU, MFU, and LCU) may be 10,000 feet in the basin center, but I doubt that the LCU itself is that thick. I suggest you provide an authoritative reference for that.
14
Case 2:03-cv-02226-ROS
Document 81-11
Filed 06/27/2006
Page 4 of 37
I I 1 I
I I I
RESPONSE 44:
Please refer to Response 35. For further information the reader is referred to the Central Arizona Project Geology and Groundwater Resources Report Maricopa and Pinal Counties, Arizona, published in 1976 by the U.S. Department of the Interior Bureau of Reclamation Lower Colorado River Region.
COMMENT 45 (CH2M-HILL)
I
P. 27, Par. 1 What potential effects could the pumping in the LCU have on the MFU and UAU? Based on this you coul'd explain why it is reasonable to disregard it in your analyses.
RESPONSE 45:
I I I I I I I I
Within the study area the majority of wells are perforated and with draw water from the UAU. There are relatively few wells that withdraw water from the MFU and fewer yet that withdraw water from the LCU. Since the MFU is at least as thick as the UAU throughout most of the study area and acts as a confining unit, the UAU would be buffered from much of the MFU and LCU pumpage. Therefore it is reasonable to disregard the pumpage from these lower layers.
COMMENT 46 (CH2M-HILL)
P. 27, Par. 2
The reference to Laney and Hahn (1986) should be explained as their report is for another sub-basin. The existence and character of a unit that correlates with the Red Unit of Laney and Hahn in the PGA area is presently unknown.
RESPONSE 46:
Comment noted. It should be stated that this reference is for a similar sub-basin in the Salt River Valley.
COMMENT 47 (CH2M-HILL)
P. 28, Par. 1
I i i
I disagree that the three stratigraphic units can be characterized as three distinct aquifers. It is my interpretation that each of the units described in the PGA area contains systems of multiple aquifers and aquitards. I suggest you should revise the wording in this section which describes the UAU, MFU or LCU as "aquifers". The USBR which developed the UAU-MFU-LCU nomenclature used gross stratigraphy to define them. Therefore, they are stratigraphic units, not hydrographic units.
15
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 5 of 37
RESPONSE 47:
--
Although it is true that each of the stratigraphic units in the study area can contain systems of multiple aquifers and aquitards, for the sake of discussion and simplification of interpretation these aquifers and aquitards are discussed based on the three main stratigraphic units (UAU, MFU, and LCU) found within the study area.
COMMENT 48 (CH2M-HILLMOCK)
· B
--
P. 28, Par. 3
_
1
Aquifers in Subunits B and C are under confined conditions as their upper boundaries are below the head measurements made in them. This is based on the definitions for confined aquifers given in Freeze and Cherry (1979). Bear's (1979) definition would classify them as leaky confined aquifers.
RESPONSE 48: -
fi m
m
Comment noted.
COMMENT 49 (CH2M-HILL)
B
Figs. 5a-6b
--
If
The point values are very hard to read on these figures.
RESPONSE 49: -
m
Comment noted.
COMMENT 50 (CH2H-HILL) _
B
P. 33. Par. 1
'
--
I
Heads in subunit B are commonly higher than in subunit C. The presentation of figures 7a, 7b, and 7c together is misleading because only figure 7b includes a well perforated only in subunit B. It is important to note that well GMW-2 in figure 7a and well UMW-5 in figure 7c are perforated in the top half of subunit C, not in subunit B. Hydrographs from other well clusters with subunit B wells provide a better demonstration of the head differences between subunits B and C.
RESPONSE 50: . -
m £
_ · "'
I
Comment noted.
COMMENT 51 (CH2M-HILL) _
£t
'
P. 33 Par. 2
·=-
.
·
Hydrographs from different key locations in the area are needed to support the discussion of UAU history. I disagree that the UAU was "largely dewatered". I could accept the observation that subunit C was depressurized 40 to 50 feet
16
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 6 of 37
I
I
I
1 i i i i i i i
between 1945 and 1965. Even with a 40 to 50 foot drop in subunit C waterlevels, the difference in storage coefficients between subunits C and A would likely result in a drop in the water table of less than ten feet which certainly isn't largely dewatered. This water-level fall and subsequent rise would have important consequences for contaminant movement. Such a discussion would be appropriate here in the report.
RESPONSE 51;
The point is well taken that the UAU was probably not largely dewatered. Unfortunately, the lack of high-quality data has prohibited us from knowing exactly how the hydrologic system was behaving historically. The information we do have as presented in figures 8a through 8e gives us snap shots of the hydrologic system during specific time periods from which inferences are made.
COMMENT 52 (CH2M-HILL)
Figs. 8a-8e
What can be inferred from the historical water levels and the presently observed extent of contamination? This could be an aid to understanding the long term ground water flow system and the movement of contaminants.
RESPONSE 52:
There is probably insufficient historic water level and water use information to draw any type of conclusions regarding historical
i i
_ · ·
contaminant migration. For this reason the model simulation begins in 1978, when more data are available.
COMMENT 53 (CH2M-HILL)
P. 43 Par. 2
How do water levels in the waterlogged Gila River compare to UAU water levels in the PGA area? Do they indicate if the Gila River gains or loses water in this reach? What quantities of water could be gained or lost?
RESPONSE 53:
I I I I 1 1
During the RI investigation and the preliminary groundwater flow modeling by ADWR at this site many estimates were made of river recharge that range from 0 to 46,500 af/yr as illustrated in Appendix A. Based on current water level data it is very difficult to infer whether the Gila River in this reach is a gaining or losing stream. More information is needed to determine the interconnection between the Gila River and the aquifer in this area.
Case 2:03-cv-02226-ROS
Document 81-11
Filed 06/27/2006
Page 7 of 37
I
COMMENT 54 (CH2M-HILL)
P. 44 Par. 1
_
-- I
The data given in this section indicate that the vertical gradients across the MFU maybe 5 to 15 feet per 300 feet of MFU thickness compared to horizontal gradients of 15 feet per 5000 feet. This indicates that vertical gradients are roughly ten times the horizontal gradients in the MFU. Near LCU pumping centers, they could be even higher. The assumption of the MFU being a no-flow boundary should address this observation.
RESPONSE 54: --
· m · ·
The vertical gradient in the MFU may be greater than the horizontal gradient however, the vertical conductivity values are much lower, therefore the net flux is less. The MFU was assumed to be a no-flow boundary for modeling purposes, that is simplification purposes.
COMMENT 55 (CH2M-HILL) --
I
·
P. 45 T. 3
1
a * · 0
Does BIC concur with the estimated loss of over 6000 af/yr in this stretch of their canal? Also, is there a variation in recharge over time that could account for some of the observed water-level changes over a typical year? How do you resolve the difference between the estimated and calculated changes in storage? Do the indicated ranges in value include uncertainty in all of the parameters used to calculate them?
RESPONSE 55:
i
^ · TM
The estimate of 6000 af/yr of water lost from the BIC canal was provided by BIC personnel. There definitely could be much variation in recharge over time that could account for some of the observed water-level changes a within typical year. There could be & lot of variation in agricultural recharge for example, however there is very little information from which to base or revise estimates on. The difference between the water budget change in storage and the calculated change in storage is probably within the range of error of all of the data listed in Table 3. The residual is within 25 percent of the overall inflows and outflows which is reasonable given the data limitations for this area.
COMMENT 56 (CH2M-HILL) -
· ·
m
ft
Figs, lib, c
Where are the interpreted aquifer-aquitard or stratigraphic subunits located on this grid? More importantly, is the grid fine enough to include observed gradients of head and concentration?.
RESPONSE 56: --
| ·(
«
'
Unfortunately, reponse time did not allow any revisions to the text, otherwise the first comment would have been incorporated. A 200 x 200
· *
18
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 8 of 37
i
I i I I
I I
foot grid in the horizontal plane and 30 foot in the vertical plane is sufficiently fine to include observed gradients and concentrations.
COMMENT 57 (CH2M-HILL)
P. 56 Par. 1 The use of the assumed dispersivity to calculate the grid sizes may not be adequate. The assumed dispersivity is quite large and recent work at the
University of Waterloo indicates that excessively large longitudinal dispersivities are commonly assumed for model studies. Instead, testing of the grid for simplified conditions will indicate if it is of a size and orientation necessary to simulate the observed gradients of head and concentration. No such testing is indicated in the report.
RESPONSE 57;
I i I
f
Usually the dispersivity values are determined as part of the calibration process. This is accomplished by historically reproducing the contamination with the model to arrive at the current plume configuration and concentration. However, this was not possible given the data limitations at this site. This has been clearly stated in the report. The reported dispersivity estimates that were used provided reasonable results as borne out from the transport calculations and there was no justification for reducing these values.
COMMENT 58 (CH2M-HILL)
I
P. 56 Par. 2
I
The derivation of the specified flux boundaries is not discussed. Were they varied with time? How were they distributed around the model domain? How does the orientation of the rectangular boundaries with respect to flow affect the distribution of fluxes?
RESPONSE 58:
I I 1
I I
I
The flux boundaries used in the transport model were based on previous three-dimensional modeling by ADWR at the PGA site. The results from this previous effort indicated that the flux boundaries did vary with time and that they were distributed proportionally around the model domain. The specified flux boundaries are admittedly not the best condition for a groundwater flow and contaminant transport model. At the time the target model was developed it was thought that rather than expanding the model domain for several miles to include a hard rock boundary, it would be more appropriate to use a flow net analysis to determine the boundary conditions. This information is included in the PGA files in the modeling section at ADWR and is available to interested parties for review. The orientation of the rectangular boundaries would have little impact on the distribution of fluxes. In other words, even if the grid was oriented north-south east-west the specified fluxes would have been determined and distributed in the same manner.
19
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 9 of 37
COMMENT 59 (CH2M-HILL)
P. 56 Par. 4
How well does the present model structure and boundaries match that of the flow net and previous model? What is the uncertainty in the calculated fluxes and their positions?
RESPONSE 59; --
The present model structure is almost exactly identical to the three-dimensional groundwater flow model. The main difference between the two groundwater flow models is the use of the USGS MODFLOW code and that of the Dames & Moore TARGET code. These two models handle boundary conditions much differently and it was difficult to transpose the flux values from one model to the other.
There is a large uncertainty in the calculated fluxes and their exact positions along the model boundary. However this uncertainty is mitigated by the fact that the model reproduced water levels that compare with the observed field data.
COMMENT 60 (CH2M-HILL) --
· jg
jjjj
P. 58 Par. 1 ---------------- If these recharge sources are so significant, how large is the uncertainty in these estimates and how does it affect the calculated heads and more importantly, the local velocity vectors?
RESPONSE 60:
It is difficult to quantify the recharge estimates with precision, however a potential range in values has been given in Table 3, page 45 in the text, and Table 2 in Appendix A. Future modeling studies will try to better address the uncertainty in these parameters. The heads will rise or fall commensurate with an increase or decrease in recharge. Recharge is assumed to be negligible at the airport property. Recharge due to agriculture is fairly evenly distributed and would therefore not have a great impact on the local velocity vectors. Much of the uncertainty in these values is mitigated by the fact that the model reproduced water levels that compare with the observed field data.
COMMENT 61 (CH2M-HILL) -
1 m
|j
·
' · H
· || w 1 -
P. 58 Par. 2
What is the accuracy of the pumpage data? Are all significant wells included?
RESPONSE 61: -
I
|j
Pumpage data were either reported by the user or estimated by use of power divider records. All significant wells within the contaminant transport model domain were included (please refer to Table 5).
20
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 10 of 37
m ·
*
I I
COMMENT 62 (CH2M-HILL)
I I I I i
M m t
P. 58 Par. 1-2
The distribution of pumpage and recharge to individual grid cells is not discussed. How does this affect local velocity vectors?
RESPONSE 62:
Pumpage and recharge estimates were distributed within the model domain by overlaying the grid on the area of interest and determining the cell in which the pumpage or recharge occurs. The distribution of these parameters follow the real system as closely as the grid size allows.
COMMENT 63 (CH2M-HILL)
P. 62 T. 6
What methods were used to calculate these parameters? What are their potential ranges in value? What is the need for: specific yield of confined units, TCE specific gravity, TCE viscosity - is this used in the model formulation? If so, how? Wouldn't dispersivity vary with lithology? Given the scale dependent nature of dispersivity, does the given value represent an intermediate for projected growth of the plume or is it an initial value? Finally, how do these values compare to the final model input values?
RESPONSE 63:
1 I I I I I I 1 I
The sources of the data are clearly stated in the table. The sources of these data are contained in ADWR files, complete with analyses.
Potential ranges in values were discussed in the text. The model requires all of the input parameters listed except for transverse vertical dispersivity which was erroneously included. Please refer to the TARGET model documentation for a thorough explanation of these values.
Dispersivity does vary with lithology, however it is beyond the scope of the available data to determine how dispersivity varies within the study area. The value of dispersivity appears to give sensible results.
These are the final model input values.
COMMENT 64 (CH2M-HILL)
P. 65 Par. 1
If the water levels are rising, the Gila River would become a gaining stream. This may explain the southwestern flow direction in Subunit A. Since the river surface elevations are known, the model can allow flow into the river when calculated ground water levels are above river levels. This could provide local velocity vectors which are consistent with the real system.
21
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 11 of 37
RESPONSE 64:
Comment noted. The model reproduces velocity vectors consistent with the real system and may replicate discharge to the Gila in future years.
COMMENT 65 (CH2M-HILL)
P. 65 Par. 2
--
Why weren't the results of spinner-flowmeter surveys in eight productions wells at PGA used to guide the vertical distribution of pumpage? Information gathered from this program is considered more representative than estimates based on drillers calls.
RESPONSE 65:
The information provided from the results of the spinner-flowmeter survey does not correlate from well to well and therefore can only be used to distribute pumpage in the well that the testing was done. Future modeling at tfps site may include the results of the spinner-flowmeter surveys.
COMMENT 66 (CH2M-HILL.^ --
P. 66 Par. 3
--
-
I
· ·
This logic would preclude the use of Agua Fria River recharge (Page 48, Table 4).
RESPONSE 66:
I
· £
m -
Agreed which is why Agua Fria River recharge is not included in the model. The rate given in page 48, Table 4 was done so for completeness and information.
COMMENT 67 (CH2M-HILL)
P. 68 Par. 2
^
*
Estimates of field scale dispersivity vary widely. The modeling should account for this. Recent work suggest that large values are probably not representative. What relation does dispersivity have to soil types?
RESPONSE 67: -
· *
1
The estimates for dispersivity values are based on a literature source as stated in the text. Unfortunately there are no measured values for this parameter at this site. Therefore, it was necessary and appropriate to make this assumption. In addition, since calibrating the model to an area and concentration of contaminant was not possible due to the lack of historical source information, this assumption was the most appropriate to make. It would not help to make up a variability in the dispersivity estimates as suggested due to the uncertainty involved in the parameter itself. The reference for dispersivity values is for alluvial sediments.
22
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 12 of 37
gi ·
_ · ·
· ft
1
I
I I
COMMENT 68 (CH2M-HILL)
P. 69 Par. 3
The observed variations in concentration with depth could be used to guide the distribution used in the model. It is possible that the assumption of full vertical mixing of observed values is not conservative. The potential uncertainty in the field data should be discussed because it relates strongly to
I 1
the usefulness of the model's output.
RESPONSE 68:
I 1 1
The observed variations in concentration with depth were used to guide the distribution of the contamination in the model. I think the approach taken was conservative based on the available data.
COMMENT 69 (CH2M-HILL)
P. 71 Par. 2
I I I
I
Because the simulation is transient and the area! distribution of head data is sparse, comparison of model-simulated to the abundant measured hydrographs in the area should have been the key criteria for flow model calibration.
RESPONSE 69:
Comment noted. Future modeling by ADWR at this site will include calibrating to some type time-series analysis. However, it should be noted that the abundant measured hydrographs are for very specific areas near the RP facilities.
COMMENT 70 (CH2M-HILL)
P. 71 Par. 4
Were fine enough time steps used to benefit from the six-month breakdown in pumpage?
RESPONSE 70:
I I I
Initial tests of time step sensitivity indicated that the time steps used were fine enough to benefit from the six-month breakdown in pumpage.
COMMENT 71 (CH2M-HILL)
I I I
I
P. 73 Par. 1 Although the simulated gradients are said to be close to measured gradients, inspection of figure 14a indicates that interpolation between data points yields gradients near the Airport which are more than twice those simulated. Large areas are present for which the local velocity vectors can not be determined by visual inspection. Are the stated velocities for the center of mass or the edge of the contamination? There is no clear demonstration that the model matches historical data.
23
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 13 of 37
RESPONSE 71;
The stated velocities are representative of the flux in the areas of contamination and are as noted in Table 8 on page 84. The model matches the observed data as presented on Figures 14a through 15e and as stated in the text. It is important to note that this model is the best tool available to analyze the groundwater flow system in this area. Though there are many data deficiencies within the study area these have been recognized by the EPA, ADWR, and CH2MHILL since 1985. ADWR has suggested that additional information be gathered in areas other than the RP's however this has not been acted on. Therefore until more information is collected the model is the best tool available.
COMMENT 72 (CH2M-HILL)
P. 84 Par. 1
=
The comparison of heads does not indicate if the local velocity vectors are correct. What may seem like a close head match could result in local flow directions which are 90 degrees or more in the wrong direction. This point is critical to evaluation of the model estimates. The discussion in this paragraph of the paucity of data for determining the goodness of fit only indicates that we do not have enough information to determine if our model is simulating the real system,
RESPONSE 72:
1 1
_ · TM
ft |
The equipotential lines as illustrated on figures 14a_through 15e indicate that the predicted flow directions near the RP facilities and further due west of the facilities are consistent with historic and present flow directions. There is no indication that the flow directions are 90 degrees or more in direction opposite of what the simulated heads represent. In simulating the RA's the model did a good job in predicting local velocity vectors, (please refer to the figures in the Groundwater Modeling Feasibility Study section of this report). It is true that there is not enough information to the west of the RPs to determine if the model simulates the real system.
COMMENT 73 (CH2M-HILL)
I
^ · TM · m m I
P. 85
-
I
·
|[
_
See previous comment.
RESPONSE 73: Please refer to Response 72.
COMMENT 74 (CH2M-HILL - PETER MOCK)
_
P. 86 Par. 2
I m
·
Inspection of figures 14a through 14e indicates that the ground water model flow calibration to the available head data is incomplete. Data are not
I
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 14 of 37
I I I I I I I I I I I I I I I I I I I
available within enough of the modeled area to indicate what gradients and local velocity vectors are present in the real system. Addition calibration to the abundant measured head hydrographs in the area could be used to improve the confidence in the ground water flow model calibration. We do not believe that confidence can be placed in the model's prediction of gradients and local ground water velocities.
RESPONSE 74:
Comment noted. Most of the abundant measured hydrographs referred to are represented in Figures 14a through 15e. This data is localized in the area of the RPs. Within the rest of the model domain, there is very little information available to indicate what gradients and local velocity vectors are present in the real system. ADWR recommended in 1986 that additional monitor wells be installed to gather more regional data within the study area. Additional data collection is necessary to achieve the local accuracy referred to above. However, since this was not done we have to live with a degree of confidence based on the available data. The model is a useful comparative tool, but is based on limited available data.
COMMENT 75 (CH2M-HILL)
Figs. 16a. b
What is the uncertainty in these distributions?
RESPONSE 75:
There is much uncertainty in these distributions, however, this is the best information we have. The text on page 97, paragraph 1 lists the source of information for both the sub-unit A and B/C plumes.
COMMENT 76 (CH2M-HILL)
Table 9 The sensitivity analysis is incomplete because it does not run the model with the full potential range in each parameters value. For example, hydraulic conductivity could easily vary over several orders of magnitude. The rationale for the selected variations used for analysis is not clear. Given that the use of this model would be for contaminant transport, the variations in the velocity field caused by uncertain parameters are of most critical concern. It is not clear why the effect of variations was only observed on calculated heads (especially porosity which probably is not included in head calculations). The percentage change in head during the simulation period per percentage change in the selected parameter provides a much stronger indication of sensitivity. The sensitivity analysis time period should be as long as the expected projection time period for its results to be useful. An expanded sensitivity analysis which includes variations in all uncertain inputs including recharge and boundary conditions would be required to fully evaluate this model's usefulness for projections.
25
Case 2:03-cv-02226-ROS Document 81-11 Filed 06/27/2006 Page 15 of 37
RESPONSE 76:
Comment noted. This will be taken into consideration in future modeling at this site.
COMMENT 77 (CH2M-HILL)
P. 96 Par. 1
The parameters critical to transport were not analyzed. If aljarameter such as dispersivity or porosity, is not measured or if it is poorlyjknown, then it is even more critical that its potential effect on model results be evaluated. Sensitivity analysis is far from an academic exercise if its importance is understood.
RESPONSE 77:
Please refer to Responses 67 and 74.
COMMENT 78 (CH2M-HILL)
_
P. 172
^
An evaluation of the model's projections was curtailed because^ of the large uncertainties discovered in the ground water flow modeling and transport sensitivity analysis. The accuracy of the model's calculated velocity field · and resulting contaminant concentration can not be even roughly guessed at with the available information. The predicted reductions in concentration must therefore be viewed as one set of potential outcomes whose accuracy is « unknown. A cursory examination of the projection runs indicates excessive I drawdowns near model boundaries and extensive movement of contamination that has not occurred to date. These observations call into question the ability of the model to simulate the ground water flow system at PGA. I
RESPONSE 78: --
Comment noted. Please refer to Response 74.
COMMENT 79 (CH2M-HILL)
P. 172 Par. 2
I
I ·
We disagree with the statement that the results of the sensitivity analysis indicate that acceptable confidence can be put into the ground water flow model calibration results.
RESPONSE 79:
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^ _
Comment noted. Please refer to Response 74.
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COMMENT 80 (CH2M-HILU
P. 174 Par. 3
While the model does provide a relative evaluation of the various ground water remediation alternatives, the accuracy of that evaluation can not be estimated with the information provided. Considerable sensitivity analyses on the model with respect to uncertain transport parameters, numerical stability and the model grid orientation and size would be required to develop some understanding of the model's performance and accuracy.
RESPONSE 80:
Comment noted. Please refer to Response 74.
rb
27
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1
'
TELEPHONE -(60S) 9324100 TELEX -t«M*« TWX -- 910-9S8-08S3 FAX - 60293249*9
CR/(N E
·
UNIDYNAMICS/PHOENIX
UNIDYNAMICS/PHOENIX
· POST OFFICE BOX 46100 · PHOENIX, ARIZONA 85063^100
1 1 1 1
I Mr. Jeff Rosenbloom, Chief Enforcement Programs Section
12 September 1989
rtMGEHEjj]) .
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SEp
1 8 1389
-
CHaM HIUU
oirorMMG
T^ 1^. 1, , * · . ' - -
1
·
·
United States Environmental Protection Agency Region IX 215 Fremont Street
Dear Jeff:
Enclosed is the response to comments you requested which were prepared by our consultant, Dames & Moore.
Please call me if you have any questions.
1 1
· "
WCD/dl
Very truly yours,
W. C. Donahue Director Human Resources Enclosure
£.ctys*K*£v-<^
1
1 1 1 1
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Responses to Corps of Engineers Page 1
COMMENTS BY TED STRECKFUSS, ENVIRONMENTAL ENGINEER
Page 5-8
Response:
Include documentation substantiating the selection of a 100 ppb level for * removal concentration in Subunit A*
See our responses to ADEQ RI Comment #3 dated July 7, 1989, EPA
FS Comment $30 dated June 9, 1989 and Technical Comments dated July 17, 1989. Page 5-9 Response: Document the selection of the 10,000 cfn gas flowrate to be used in the air stripper. This flow rate appears to be excessive* See our response to CH2M Hill Comment 024 dated March 23, 1989*
COMMENTS BY JOHN £. SARTORE
General Comments; The preferred remedial alternatives proposed for site remediation (Alternatives A-l and A-2) are not supported by the analytical data presented in this draft. Additional assays are needed especially at Waste Facility #1 and building 19 areas. Conclusion* reached throughout the draft are often based on speculation. Response: The comment does not provide support for its conclusion and is not specific enough about the areas of disagreement to allow for specific rebuttal.
Pag* 2-11, 2«3»2.6 Building 19, Paragraph 2.
1. The groundwater beneath Building 19 contains more than 100,000 ppb. of Trichloroethene (TCE). Considering the Density of TCE and the solubility of TCE in water, there is probably a layer of TCE present in the lower part of the Aquifer (Subunit A). Response: Comment noted, conclusion reached is not substantiated. 2* There is insufficient data to support the statement that "Building 10 does not appear to be a source of VOC's to groundwater based on the data collected*
Response: See our response to EPA RI comment #8 dated June 9, 1989.
Page 2-11, 2.3.2.7 Drum Storage Area
The open area to the north of Building 19 used to store empty solvent drum* is now bare which indicates that solvents could be present in sufficient quantities to suppress the growth of gras* in that area*
Responses The entire UPI facility is controlled to be purposely grass-free with the exception of the front lawn near the reception area.
The no-grass areas are intentional and have been since 1963*
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R«*ponte* to Corps of Engineers Page 2
Page 2-16, Sentence #4
Th« conclusion that Waste Facility #1 is the primary source contributor of TCB to groundwater is not supported by this analytic*! data presented. Response: See our response to ADEQ RX comment £2 dated July 7, 1989.
Page 2-13, Paragraph 3
The analytical results on toil sampling indicate that the high Bariuo and Aluminum concentrations found need to b« further investigated. Although Aluminum was not reported as being used at the facility, the pond assay r**ult* ( 0 0 0 rag/kg) cannot b* 8,0 ignored. Response; Comment noted*
Page 2-16, Sentence #4
The conclusion that the Waste Facility #1 is the primary source contributor of TC2 to groundwater is not supported by the analytical data presented.
Response: See our response to comment regarding 2-16, Sentence #4.
COMMENTS BY DAVE BECKIR
Rl, Page 2-10
Low levels at various facilities do not necessarily suggest that the facilities are not source* - look at low levels at sone areas at the GAG/Airport areas* Response: See our response to E?A Rl comment* #7 and #8 dated June 9, 1989.
Rl, Table 2.1
Were any analyses done for explosives and volatile propellant at building 12? Responses Building 12 i* designated as Waste Facility #8* Table 2.3 and 2.4 of the Rl reports that this facility was tested for total metal* within the sedimentation tank and for VOC concentration and total metals within the soil surrounding the sedimentation tank. No other testing was performed.
RZ, Page 3-28, last paragraph
MW-14 i* not really directly downgradient - more crossgradient thi* may impact the definition of contamination in "C".
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Responses CO Corps of Engineers Page 3 Response:
See our response to CH2M Hill comment #8 dated March 23, 1989. RX, Page 3-19, cop paragraph
Can veil SF4A be a cross-contamination source? replaced with a well not open to "A"? Should ic be
Response:
See our response to ADEQ Rl comment #38 dated July 7, 1989 RI, Page 3-20, 3rd to last line
Describing "B" as a barrier is too strong - it's a leaky
barrier.
Response:
See our response to EPA Rl comment #13 dated June 9, 1989.
FS, Page 1-2, see 1.2.1
The RI did not characterize ground vater over 6 sq. miles. Response: The text states that the Unidynamics study area is approximately six square miles. Separately, the text states that the RI characterized groundwater and soil quality* To interpret and combine these two sentence* in the manner which this comment does is incorrect.
FS, Page 2-14, 3rd paragraph
Dilution will reduce VOC levels but increase volumes over ARARs
- may be foolish to wait!
Response:
See our legal comments dated August 1, 1989.
FS, Page 2-15, 2nd paragraph
Remember 2 possible sources of TCE - TCE in vadose zone and DNAPL in saturated zone H M Nothing is said about addressing possible pure TCE at "A"/ B interface. Either way, dilution would take a very long time considering levels at UPI.
Response:
Dilution and point-of-use treatment options address the possibility that pure TCE may be present at the Subunic A/Subunit B interface. FS, Page 2-16, 1st full paragraph
Reference in 4th line of paragraph to current point of us* is misleading - the point is that you don't know where "points of use" will be in future.
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Re*pon$e» Co Corps of Engineers Pag* 4
Response i
Comment noted*
FS, Page 2-20, 3rd paragraph
Though no estimates of ri*k were made - level of risk will undoubtedly increase. Responce:
The comment does not provide support for the conclusion that the l«v«l of ri*fc will undoubtedly increase*
FS, Page 2-20, see 2*7*3.3
This section downplays risk too much.
Response;
The purpose of this section is to report th« potential risks arising from exposure to on-*ite groundwater* This is done in an objective manner using quantitative results. It cannot be intimated from any part of this section that the risks are "downplayed".
FS, P*g* 3-7, l*t full paragraph I disagree that "A" is a III aquifer - try lib.
Response:
o See our legal comments dated August 1, 1989. o See "Guidelines for Groundwater Classification under the EPA Groundwater Protection Strategy", December, 1986. FS, Page 3-9, last line Exposure pathways does not lead to risk levels greater than 10"^ now - but may if points of exposure change in future.
Response:
Comment noted*
FS, Page 3-10, see 3*3.1.5
Exposure to toil is not the impact of concern.- TCS in the soil can continue to impact groundwater.
Response: The primary concern associated with TCB contamination within the soil is indeed its potential impact on groundwater. However, since the possibility that exposure to TCE in the soil could occur, a complete investigation of this possibility and its ramifications was performed*
FS, Page 3-13, last sentence
Disagree that the technological and permitting makes aquifer
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recharge less desirable.
Response: Comment noted.
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Response* to Corps of Engineers Page 5
FS, Page 3-18, 2nd paragraph
Disagree vith conclusions here.
Response:
See our legal comments dated August 1, 1989. FS, Page 4-3
1st bullet - ... process in handling...What?
Response:
This statement is referring to the ability of tha process to reduce toxicity, mobility or volume of the contaminants.
FS, page 4-6 last bullet - SVE should be option without capping*
Response:
The comment provides no support for its conclusion and cannot be addressed*
FS, Page 5-6, last paragraph
Time for treatment will be very long especially if pure product is present*
Response;
Comment noted.
FS, Page 5-8
Treatment to 100 ppb TCE is probably not acceptable - how was 100 ppb chosen? I wouldn't think that assuming dilution with B
and C i* acceptable way to meet ARAR*
Response; See our responses to EPA FS comment #30 dated June 9, 1989; ADEQ RI comment #3 dated July 7, 1989, and legal comments dated August 1, 1989.
FS, Page 5-9, 2nd to last paragraph
Will the State let you pump wells for waste-? -That's what you'd be doing in going to sewer.
Response:
There are serious and unanswered questions regarding the implementability of this option. These are discussed in Chapter 5, pages 5-21 to 5-22 of the FS.
FS, Page 5-19, 1st full paragraph
GW-1 should be GW-3 (Also on page 5-21).
Response!
A typographical error occurred in the preparation of the text. GW-1 should be GW-3 as. pointed out.
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Responses to Corps of Engineers Page 6 FS, Page 5-21 Mention need to limit and discharge of VOCs to 40 lb/d*y as part of iapleaentability. Response: We recognize that air emission limitations may be needed.
FS, Page 6-9, last sentence of top paragraph
The logic here (not treating all water, only water used) is poor when dealing with the levels you have in Subunit A. Response: o The comment does not provide support for its conclusion. o See our technical comments to EPA dated July i7, 1989.
FS, Page 7-3, 2nd paragraph
Uncertainties in contaminant fate could be reduced if you dealt with the problem now.
Response: Comment noted.
FS, Page 7-4
I disagree with technical logic behind recommended alternatives. Response: This comment is not specific enough about the areas of disagreement to allow for a response.
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Response from City P*g« 1
70LUME 8. CHAPTER 1 .- RI COMMENTS
Pag* 2-3
Paragraph four. The conclusion presented regarding waste facility 4 it not supported by th« evidence given. "Iff" and "probablys" ar« insufficient to establish a firm conclusion*
Response: See our response to EPA Comments dated June 9, 1989. Page 2-11 Last paragraph* second sentence*
"Some liquid*" .. Should .. describe then or Identify if possible.
Response : The identity of the liquids is not known.
Page 2-16 Last four bullets require more evidence than presented in this chapter in order to make these conclusions*
Response: o Third bullet: 7, 1989
See our response to ADEQ comments dated July
o Fourth bullet: See our response to EPA comments daced June 9, 1989
o Fifth bullet: Comment noted o Sixth bullet: See our response to ADEQ comments dated July 7, 1989 Chapter 3 Page 3-9 First paragraph* Be more specific in gram size rather than use of terms like "fine grained", etc. It i* important here because of the controversy regarding possible groundvater movement
between subunits. The gram size data is surely available from sieving of the drill samples.
Response: o
Drill samples were not sieved as per EPA - approved drilling program.
o A more thorough and detailed description of the UAU subunits and MFU characteristics, including composition can be found in Chapter 3, Vol. I (Public Comments Draft) of the RI/FS.
Pa
Page 3-19 Third paragraph, last sentence* Data from the City of file* for the years 1983-1988 would be better than Veatch, 1985* Average groundvater production for the 1983-1988 was 920 af/yr (City of Goodyear Water Use 18) 99.
Goodyear Black & city of Reports,
.
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Response to G. Stephenson Comments froa City of Ooodyear oa RI/FS Page 2
Response: Comment noted*
Pag* 3-19 Last paragraph. The City currently u*«* a total of 8 wells, not 6* Need co be more thorough about the location of Well #10. The so-called "warehouse" currently employee* 237 people and is expanding* They expect to employ 30 more over the next two years. Well #10 is a sole source, sole supply for this facility* City Well No*. 2 and 3 are both screened la Subunit C, and both have recorded TCE concentrations as high as 6.8 ug/1 and 16.0 ug/1 respectively* This should be recognized here.
Response: o The text states that the City currently has a total of 8 wells that supply the water distribution system.
o Cosaaent noted regarding the warehouse. o The text recognizes that City Well Nos* Z and 3 have detectable TCE concentrations. o See our response to the comment regarding pages 2-4, fourth bullet, last sentence.
Page 3-20 First paragraph* Well No. 10 is perforated in the upper part of the Middle Fine Grained Unit ( 8 ' 5 8 } as determined by a TV 31-7' scan by Gilbert Pump Coapany in August, 1984 (City of Goodyear files).
Response: This information is already included in the text.
FS COMMENTS - CHAPTER 2
Page 2-2
Paragraph two* The site encompasses 35 square miles, not 25* Litchfield Park is not in the site boundary. Except for the Loral facility, and the Phoenix-Goodyear airport, and about 4 square miles of Avondale along the southeast part, the remainder of the site lies within the City of Goodyear.
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Response: Comment noted.
Page 2-3
Paragraph two* Is Subunit B also a "water-bearing zone"? See page 2-11, third paragraph, where it is referred to as such*
Response: Although it is not explicitly stated at this poinc in the text, Subunit B is a water-bearing zone* Page 2-4
First bullet, "hydraulic isolation" seeos to ba inappropriate usage here* Simply because of a local change in gradient does not mean that regionally the area* are not part of the same system*
Response: The text doe* not imply that the two subareas arc not part of the same regional system. - However, the text does point out that a divide within this system has caused groundwater to flow in two distinct directions leading to a hydraulic isolation of the groundwater contamination within the two subareas*.
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«t«*pwiu»e co u« stepnenson Comment* from City of Goodyear on RI/F8
Page 3 ''
Third ballet* last sentence* Not »are whet thi» means, buc it c*n be Interpreted a* spying the evidence !· disputable* Would
two negatives Bake it positive?
Response: While previous investigations have yielded insights into the degree of Interconnection between Subunits B and C, the exact extent of this interconnection has not been established* Hence, the statement "no indisputable" evidence refers to the uncertainty regarding the evidence*
Fourth bullet, last sentence* This statement is wrong! City Veil No. 2 recorded 8 ug/1 TCE on 4/14/87 and No* 3 recorded 16 ug/1 TCE on 10/9/87* Both are well within the vicinity of DPI. ,, Response: o According to Chapter 3, Table 3 4 Vol. I (Public Comments Draft) of the RI/FS, the highest detected concentration recorded in City Well Nos. 2 and 3 is 6.8 ug/1.
o The implication of this comment seems to be that sinew COG Well Nos. 2 and 3 lie within the general vicinity of UPI, the facility is responsible for causing the elevated TCE concentrations. However, 'generally known features, of. chls facility do not support this conclusion* First, regular water measurements have not shown groundwater flow towards City Wells #2 and #3. Furthermore, these wells are located cross-gradient to and outside of the known TCE contaminant plume and would not be affected by UPI activity.
Page 2-6
Paragraph three*
Use of the words "most solvents" implies that
there are solvents not stored* How about those that ore not? What is done with them? Use of "most" and "oome" leaves the impression that 49Z could be elsewhere* Need to be more exact in your statement* The data support it.
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Response to 6. Stephenson Comments froa City of Goodyear on RI/FS Page 4
Response: Solvents not stored are chose solvents not regulated by SPA or ADEQ. These are solvent* which are not listed under RCBA. Page 2-8 Second paragraph. concentrations were* Unclear as to what the background
Response: Background concentrations for aluminum, barium, arsenic, mercury, lead, chromium and zinc are listed in Chapter 2, Table 2.10 of the RI. Page 2-12 First paragraph* Absolutely no supporting evidence to say that uncertainty exists regarding connection between Subunits B and C. The fact that TCE is present in Subunit C ia evidence enough to verify connection* The method of connection, either hydraulic or via poorly constructed veils or both, may be uncertain.
Response: The text states that there is uncertainty regarding the degree of interconnection between Subunits B and C. It does not state that there is uncertainty regarding connection between Subunits B and C.
Page 2-13 Last paragraph* Use mean concentrations instead of average to be consistent with Table ' - . Table 2-1 has 179,000 not 180,000* 21
Response: Comment noted*
Table 2-1
Put note foe units at top of Table. Caanot tell from thee Table which unite are A and which are C unless the reader knows acre detail about the wells. A note stating 5, 6 and 10 are Subunit C
wells would help*
Responses The subunie in which a particular well is located can be determined froo the heading "Aquifer" which plainly states this Information. Page 2-14 First paragraph. Be consistent when using average and mean.'
Response: Comment noted.
Last paragraph end top of page 2-15* If contaminated groundwater in Subunit C has not aoved off-site, how do you account for contamination in Subunit C off-site City Wells No», 2 and 3?
Response: See response to comaent concerning Page 2-4, Fourth bullet.
Page 2-16 Second paragraph, last sentence. The City i* not willing to gamble any longer on th* fact that their, "supply wells are not likely to be affected, if at all, for several years." Soae are already affected.
Response: Proposed rcoedial *ctioji would provide for well-head treatment of
city wells, if needed. part.
There would be no "gamble" on city's
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Response co G. Stephenson Comaents from City of Goodyear on Rl/FS Page 5
Page 2-18 First paragraph* There Is too much conjecture in this entire paragraph, which is not supported by evidence. Certainly, conditions may change but projections must continue to be made. The projections for growth have been made based on sound planning* Granted, they are not absolute, but they are predicated on a clean, adequate groundwater supply.
Response: Comment noted.
Pag* 3-7
First paragraph, last sentence. Remember that S C MA is .. screened froa 1 0 to 685'; that is from mid Subunit B well into 4' the MFU, and has recorded TCE concentrations as high as 22 ug/1. This would certainly indicate that the MFU is affected adversely by the release of TCE at this site.
Response: No veils have been screened exclusively in the MFU. Therefore, it is not possible to claim with any degree of certainty that the MFU is adversely affected by the release of TCE at this site* The high level is most probably attributable to TCE contamination present in subunit A*
... Page 3-17 Second paragraph, under Section 3 4 1 Nothing given to support this. In fact, see above comment.
Response: The comment is net specific enough regarding disagreement with the text.
the area of
Page 3-18 First paragraph, last sentence. Bow is this so when TCE is recorded in Subunit C as you have noted previously. Response: The comment is not specific enough regarding the area of disagreement with the text*
Page 6-5 Response:
First paragraph* The MCL for Subunit C has been exceeded. See our response to the comment concerning Page 2-4, fourth bullet, last sentence. - --
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Response to ADWR Comment* Page 1
GENERAL CONCERNS
The preferred remedial alternative for the ttnidynamic* sice allov* for continued degradation of the drinking water aquifer*. The uncertainty whether trichloroethene and other solvent* trill migrate to the Subunit C aquifer i* ittelf a reason to take a
conservative approach and implement remedial action* to prevent contamination from migrating to the Subunit C aquifer, which will include treatment of Subunit A.
Response: Comment noted* Not enough information is available to discount contamination in the MFU at this tine in the Superfund area*
Respon*e:
Nor is enough information available to speculate that the MFU is adversely affected.
7oluae
For each organic compound listed on the page, the minimum and maximum concentrations should be stated along with their frequency of detection*
Response
A listing of minimum and maximum concentrations for each detected organic compound i* more meaningful when it is presented with the location at which this minimum/maximum occurs* This information is presented in Chapter 2, Table 2.7 and 2»8 of the RI*
Page 3-2, First Full Paragraph and Table 3*1: The monitor well completion data for Mtf-1 through MW-4 is missing from Table 3.1. Thi* information needs to be included*
Re*ponse
See our response to ADEQ RI comment #30 dated July7 ?, 1989.-
Page 3-16, Second Paragraph: The Environmental Quality Act affirm* that all aquifers in the state are classified for drinking water purposes*
Response:
See our legal comments dated August 1, 1989. e Page 3-20, Second Paragraph; Reference: Map of Well Locations for Abandoned and De*troyed Wells (USGS aad ADWR Records; Prepared by CB2M-HZLL; U»t Update, May 1983)i Several abandoned well* exist within the plume of organic contaminant* migrating from the tfaidynaaic* facility. The report fails to recognize that these veils say be acting as a vertical conduit for contaminants to migrate from subunit A to the lover aquifer*.
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Response to ADWR Comment* P*g« 2 Response: Comment noted* Pag* 3-21, Second Paragraph:
Th* reported hydraulic conductivity values in this paragraph do not agree with the reported values for transmissivities on page
I I I I I I I I I I I I I I I I I
3-13 when using the reported saturated thicknesses as found in section 3*2.1.2 on pages 3-6 through 3-8*
Response: Comment noted.
FS/Pag* 2-11, Second and Fifth Paragraphs:
The reported hydraulic conductivity values are not consistent with what is reported in the Remedial Investigation Section of this report* Response: Hydraulic conductivities are reported in the text at three different locations: Chapter 3, page 3-21 of he RI; Chapter 3, Table 3.3 of the RI; Chapter 2, pages 2-10 to 2-11 of the FS. These values (in gpd/ft*) are summarized below: Page 3-21 ( I R)
Subunit A Subunit B Subunit C 100-200 <30 600-1400
Table 3.5 (RI)
50-120 798-1430
Pages 2-10 to 2-11 ( S F) 120-220 14-100 280-340
Clearly, the above table shows chat Subunit A and Subunit 5 hydraulic conductivity values are consistently reported. There is a discrepancy between the reported RI values and the FS value for Subunit C. The correct values for Subunit C are those presented in the RI.
Page 2-12, First Paragraph:
Although the interconnection between subunits A and C has not been very well established at th* UPI site, the assumption that no contaminants will migrate due to * lack of information is not appropriate. It is apparent that additional information is needed to determine vertical hydraulic conductivities and th* extent of the interconnection between subunits A and C*
Response t
The text states that the degree of interconnection between the subunits is uncertain. Because of this uncertainty, the rate of migration of the contaminants, and consequently, the long-term impact of TCE contamination on Subunit C, is unknown. The text does not »ay that this uncertainty is reason to conclude that no migration will occur*
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Response to ADWR Comments
Page 3
Page 2-12, Second Paragraph:
The direction of groundwater flow in subunit A at the airport is to the west-southwest? it is DOC strictly to the southwest a* stated in ch« report*
Response:
Comment noted* Page 2-14, Top of the Page: The concentrations of trichloroethene in MW-3 and MW-6 should be the basis for concern as they are close to the MCL of 5*0 parts per billion.
Response:
Comment noted, also see our legal comments dated August 1, 1989 relative to MCL's. Page 2-14, Second Paragraph; The assumption that adsorption of TC2 and other VOC's onto aquifer aaterial removes them from the groundwater, reduces their concentration, and retards their movement may or nay not
be appropriate at this site. At the Motorola 52nd Street site
tests conducted on similar materials indicated that adsorption was not important in restricting the movement of contaminant*.
Response: Comment noted, we do not agree geologically "similar" however. chat the two sites are
Page 2-14, Third Paragraph The assumption that the plume will eventually be diluted and
reach some sort of steady state condition may be theoretically true, however this is by no means a practical solution to the
problem* It will take a very long tise for this to occur and a large volume of clean water* Sven if the source of- the
contamination is removed the area of contamination will become
larger as the plume disperses*
Response: See our response to ADEQ FS comment 96 dated July 13, 1 8 . 99 Page 3-2, Second Paragraph:
The Environmental Quality Act and the Groundwater Management Ace should be recognized in thi* section*
Response: See our legal comments dated August 1, 1 8 . 99
Page 3-S» Waivers froa ARARs; The relevance of the -exceptions has not been supported* exceptions that are deemed relevant should be stated. Those
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Response to ADWR Comment;* Page 4
Response: See our legal commence dated August 1, 1989. Page 3-7, Flr*t Paragraph: Please refer to comment 3* Response: See our legal comment* dated August I, 1989.
Page 3-9, Top of the Page;
The MCL, ARAR, is five microgram* per liter for ICE in aquifers designated as drinking water aquifers by the State of Arizona* The Environmental Quality Act designates all aquifer* in the *tate a* drinking water aquifers*
Response: See our legal comments dated August 1, 1989* Also see "Guidelines for Groundwater Classification under the SPA Groundwater Protection Strategy", December, 1986.
Page 3-11, Ground-Water Withdrawali The right to withdraw groundwater would need to be obtained from the Arizona Department .of Water Re*ources.
Response: Under CERCLA, substantive compliance is required.
Page 3-11, Ground-Water Withdrawal, Paragraph I:
ADWR does not have authority to prevent the installation of all wells, nor does it have ultimate authority in limiting the use of water in any area.
Response: ADWR doe* have authority to regulate well construction standards which could be used to eliminate groundwater us* from specific zones.
Page 3-11, Fifth Paragraph:
Withdrawal of groundwater at the Unidynamics facility will require a groundwater withdrawal right. ADWR considers a PQGWP a* a right to withdraw water and will require a PQGWP to be obtained.
Response: It is our understanding that substantive compliance for a PQGWWP is all that is required under the provisions of CERCLA.
Page 3-13, Surface Water Ditcharget
The Phoenix Active Management Area will not permit this type of end use a* it i* not con*istent with the Groundwater Management
Act.
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Response to ADWR Comments S
Response: Comment: noted.
Page 3-18, Second Paragraph:
Th« ARAR or TBC conclusions of this paragraph have not bees supported nor approved by the agencies.
Response:
See our legal comments dated August 1, 1989. Page 5-12, First Paragraph:
The statement chat the "No Action" or monitoring alternative would be sufficient to protect public health it not appropriate due to the uncertainties that exist in the current data regarding the extent of subunit C contamination and vertical permeability estimate*. These data deficiencies should be determined before any remedial alternative is chosen.
Response; The text recognizes that there are several factors which will impact the long term effectiveness of this option* Specifically, Chapter 5, Page 5-13, Section 5.3.11 of the FS lists these factors as:
o The extent of TCS migration into Subunit; C
o Effects of development of additional groundwater supplies and its impact on fate and transport of ICE in the groundwater system
o Whether future wells will produce water from
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