6 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #1

There seems to be a disconnect between the previous (CRA-2004 PABC) FMT modeling results and the experimental investigation of Nd (III) solubilities. Borkowski et al. (2008) assumed that the stable Nd(III) phase in the carbonate system would be NdOHCO 3 (s). In the CRA-2004 PABC modeling results, the stable +III phase was predicted to be Am(OH) 3 (s). I have looked at a few of the CRA-2009 PABC FMT output files that you sent to me, and it appears that the stable +III phase predicte d by the FMT model continues to Am(OH) 3 (s). In Figure 4-8 of Borkowski et al (GWB brine with carbonates), it appears that they were able to get fair ly good reproducibility of results from undersaturation (dissolution of NdOHCO 3 ) and oversaturation (precipitation) experiments. There appears to have been lim ited to no characterization of the postexperiment solid phases. Although precisely what was done to characterize the solids after the experiments was uncle ar to me after reading the test plan and Borkowski et al. 2008 report, Marion Borkowski stated in our co nference call this week that there were insufficient amounts of solids to characteri ze after the oversaturation (precipitation) experiments. As a result, the id entity of the solid phases at the end of the experiments is not certain. The data in Figure 4-8 and the in terpretation by Borkowski et al 2008 seem to indicate that the stable phase was NdOHCO 3 . Consequently, FMT calculations predict that Am(III) solubility for WI PP PA is controlled by Am(OH) 3 (s) but the experiments seem to indicate the solubili ty-controlling phase will be AmOHCO 3 . This raises the question of whether the FMT modeling is accu rately predicting the concentrations of Am(III) (and by analogy Pu(III)) in the WIPP brines for PA.

EPA Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
DOE Response The DOE believes that the current Nd(III) expe rimental investigati ons agree with WIPP FMT modeling results. The results summarized in the Nd(III) report, in fact, support the modeling position that one phase is controlling th e solubility of neodymium in these brine experiments (Borkowski et al., 2008). These data are part of an on-going experimental program that has not been comp leted. Based on the experimental results to date, the DOE does not believe the solubil ity controlling phase used in the FMT modeling should be changed (see Sec tion 4.4.2 of Borkowski et al., 2008).
The perception of a disconnect likely exists because there is not a full recognition of the differences between the experimental goals of a long-term solubility study (such as Borkowski et al., 2008) and the shor t term studies that are repo rted in the l iterature. In

1 March 30, 20106 th Response Submittal to the EPA Enclosure 1

short-term studies, the goal is to design the experiment to measure the solubility of a specific and well defined phase th at is carefully prepared a nd added to the experiment. Here, equilibrium is rapidly established and a case is made that the solubility measured is directly linked to the characterized phase added to the experiment.
In long term studies, the expectation is that the solubility controlling phase will be established as a response to the brine chemistry (pH, ionic strength, anion/cation concentrations, and E h ). In this experimental appro ach, given enough time, the solubility controlling phase will appro ach the same phase or group of phases and the measured solubility will be somewhat independent of th e initial phase present. Results reported for the WIPP-relevant Nd(III) undersaturation experiments (Borkowski et al., 2008) are shown in Table 1.

Table 1. Solubility of neodymium in the GWB undersaturation experiments

Initial Nd Phase Brine and pC H+ Measured Solubility (M) Nd(OH) 3 GWB / 8.6 6.9 x 10 -7 (avg. of two)

1 NdOHCO 3 GWB / 8.4 3.8 x 10 -7 (avg. of two)

2 NdOHCO 3 GWB / 8.4 5.8 x 10 -7

3 FMT model prediction Reacted GWB / 9.7 2.25 x 10 -7

1 data taken from experiments with a total carbonate value of 0.1 mM
2 data taken from experiments with a total carbonate value of 1 mM
3 FMT calculations based on Brush et al., 2009 (in the absence of organics)
The agreement in the neodymium solubilities measured for the two solids in GWB brine are a factor of 1.7 to 3.1 higher but are at a pC H+ that is almost a pH unit lower than the FMT calculations. The CRA-2009 PABC calcu lations (Brush et al., 2009) specifically indicate that Am(OH) 3 is the solubility controlling phase at carbon dioxide fugacities established by the brucite-hydromagnesite bu ffer (WIPP reference case) but carbonate phases can be formed at the higher fugaci ties established by the brucite-nesquehonite buffer. Overall, the modeling and experiment al results are well within the “order of magnitude” agreement typical of solubility studies in complex groundwater systems and support the existence of a single solubility-c ontrolling phase or group of phases. The DOE believes this agreement is consistent with the Nd(OH) 3 phase in the Nd experiments performed at WIPP-relevant carbonate levels (see Table 1). In Borkowski et al. 2008, there were no firm conclusions about the nature of the solubility-c ontrolling solid phase present in these experiments other than to note that the solubility results presented are consistent with the current WIPP PA position that it is the Am(OH) 3 phase (and by analogy the Nd(OH) 3 phase in the neodymium experiments performed).

2 March 30, 20106 th Response Submittal to the EPA Enclosure 1

DOE References
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. Brush, L.H., Y.-L. Xiong, and J.J. Long. 2009. “Results of the Calculations of Actinide Solubilities for the CRA-2009 PABC.” Anal ysis Report, October 7, 2009. Carlsbad, NM: Sandia National Labor atories. ERMS 552201

3 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #2
The observed differences in th e concentrations at simila r pcH in GWB and ERDA-6 brine are attributed to borate complexation. GWB has approximately 2.5 times the borate concentration of ERDA-6. The neodymium concentrations measured at pcH 8.7 in ERDA-6 brine (no carbonate) is approximately 5 x 10 -8 M (Figure 4-10). In GWB brine at pcH 8.7 (Figure 4-9) is approximately 5 x10 -7 M. What is the neodymium-borate speciation that would explain a ten-fold incr ease in neodymium concentrations with a 2.5-fold increase in borate concentration? If it is a one-to-one complex such as NdB(OH) 4 ++ , then one would expect that increasing the borate concentra tion by a factor of 2.5 would increase the Nd(III) concentr ation by approximately the same factor.

EPA Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
DOE Response
The DOE agrees with the hypothetical argum ent presented by the EPA on the potential effects of borate complexation on the solubility of th e III actinides but does not agree that the differences noted in the GWB and ERDA-6 neodymium solubility experiments should be attributed to borate complexation alone (Borkowski et al., 2008). The results summarized in this report ar e part of a long-term experimental program and the full effects of borate complexation will not be understood until research to establish appropriate Pitzer parameters for this speci es and the subsequent modeling of the full brine system is performed. There are, how ever, significant differences in the neodymium solubilities measured in these brine systems and differences are also predicted by current WIPP FMT modeling of the III actinides without organics present for the GWB (2.25 x 10 -7 M) and ERDA-6 (8.6 x 10 -8 M) reacted brine systems (Brush et al., 2009). These are best explained by the many differences that exist between these tw o brines, (e.g., ionic strength, pH, sulfate/borate /chloride concentrations, a nd cation concentrations) and should not be attributed solely to differences in the concen tration of borate. There are statements in the Borkowski et al. 2008 repor t that speculate on the relative importance of borate – but this should be viewed as pr eliminary in nature and not yet the accepted position of the WIPP project.

DOE References Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.

4 March 30, 20106 th Response Submittal to the EPA Enclosure 1

Brush, L.H., Y.-L. Xiong, and J.J. Long. 2009. “Results of the Calculations of Actinide Solubilities for the CRA-2009 PABC.” Anal ysis Report, October 7, 2009. Carlsbad, NM: Sandia National Labor atories. ERMS 552201

5 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #3

The "shoulder" in the Nd concentration in ERDA-6 brine as a function of increasing pcH was attributed by Borkowski et al. 2008 to borate complexation. However, the reason for the decreasing Nd complexation as a func tion of pcH above about 9.75 was not clear. There is no reason that I know of for borate complexation to cease at higher pcH, and if hydrolysis species such as Nd(OH) 3 (aq) became more important at high pcH, these concentrations would be presen t in addition to the Nd-borate species concentrations. It is unclear whether a different solid might be c ontrolling the Nd(III) solubilities in the highpcH region. An understanding of th e solubility in this pcH region is important because in ERDA-6 the maximum concentration is obs erved at approximately the repository pcH predicted by FMT calculations (9.6-9.7). [Not e: Clarification on this issue was requested in a phone call with LANL staff, but it was not resolved.]
DOE Response
The DOE believes that the concentration of complexes in solution, once formed, can decrease. The concentration of any neodymiu m (or III actinide) complex in solution is defined by the formation constant and the conc entration of each contributing species. This is illustrated for a mononuclear comp lex of neodymium in the following:


## ( ) n

n K XNd nXNd − − + ⎯→

←+ 3 3

[complex] = 

## ( ) 

# [ ] [ ] [ ] n n

n XNdkXNd −+ − = 3 3

In this context, the solution concentra tion of the complex will decrease when the concentration of the complexant is decreas ed or the concentration of the cation is decreased. For a fixed concentration of the complexant X - , the complex will decrease when the concentration of the cation decreases (e.g., when its solubility decreases). For the Nd 3+ solubility experiments reported, it re mains the position of the DOE that the Nd 3+ (aq) concentration decreases with increasing pH (above pC H+ = 9) due to the formation of hydroxide phases which corre spondingly decrease th e concentration of borate complexes in solution (as well as othe r complexes). An ove rall decrease in the solubility of the II I actinides with increasing pH (a bove 9.75) is supported by the WIPPspecific and literature data (see Section 3) reported in Borkowski et al. (2008).

6 March 30, 20106 th Response Submittal to the EPA Enclosure 1

DOE Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.

7 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #4
If the trend in Nd concentrations in GWB (Figure 4-8) is simply extrapolated up to pcH 9.4 (the pcH predicted by FMT modeling fo r GWB brine in the repository), the Nd concentration could be as high as 4 x 10 -5 M, which is much higher than the concentrations predicted for the CRA- 2004 PABC (GWB no ligands) of 2 x 10 -7 M. In our discussion, LANL staff said that the so lubility at the pcH of 9.4 would be best represented by the solubility of Nd(III) in ERDA-6, because as pcH is increased, Mg precipitates and the composition of GWB appr oaches that of ERDA-6. However, if one compares the predicted Mg concentration of GWB at pcH 9.4 based on FMT modeling for the CRA-2004 PABC to the composition of ERDA-6, the Mg concentration in the higher-pcH GWB is still 0.55 M, which is 29 times the Mg concentration in ERDA-6. Even if one accepts that the solubility in ERDA-6 is a perfect way to estimate the concentration of Nd in pcH 9.4 GWB (1 x 10 -6 M or higher), then the concentration is still, at a minimum, 5 times what was predicted by FMT (2 x 10 -7 M). There is a lot of uncertainty in such a prediction, becaus e the higher-pcH GWB is not the same composition as ERDA-6 and the results with carbonate in ERDA-6 (Figure 4-11) were only approached from unde rsaturation in this pcH region. Consequently, the concentration of Nd(III) in pcH 9.4 GWB could be higher than 10 -6 M.

EPA Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
DOE Response
The DOE continues to maintain that the extrapolation of the Nd 3+ solubility data in GWB brine (as described in the EPA comment a bove) does not properly reflect what is understood about the high pH chemistry of the I II actinides in these brines. It is also important to note that the ch emistry of these brine systems is complex and depends on many factors (see DOE answers to 1-23-6 fo llow-up comments #2 and #3) that are not properly captured by linear extrapolations.
At high pH, hydroxide complexation and pr ecipitation overwhelms the carbonate and borate complexes formed to lower the overall so lubility of the III act inides (see Section 3 in Borkowski et al., 2008). In the Nd 3+ experiments this was best captured by the ERDA6 data which covered the current WIPP repository pC H+ . Although no solubility data was collected for Nd 3+ beyond the GWB “cloud point”, this was however done for the U(VI) experiments performed in carbonate-free GWB brine (Lucchini et al., 2009). Although U(VI) is not an analog for the III actinides, qu alitatively similar solubility trends should

8 March 30, 20106 th Response Submittal to the EPA Enclosure 1

be present in the GWB brine system. These data are shown in Figure 1 along with the corresponding neodymium data and illustrate th e expected dependence of the III actinide solubility on pH.

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4

Nd oversaturated U(VI) oversaturation Nd undersaturatedMetal Concentration, M

pC H+ 

### GWB

Figure 1

. Plot of the uranium(VI) over-satu ration data (upper curve) and neodymium over and undersaturation data (lower curve) in GWB brine. The pC H+ ~ 9.2 data point for uranium already shows a decrease in solubility due to hydrolysis and is beyond the cloud point of GWB brine meaning that some magnesium precipitation has occurred.

DOE Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
Lucchini, J.-F., H. Khaing, M. Borkowski, M.K. Richmann, and D.T. Reed. 2009. “Actinide (VI) Solubility in Carbonat e-free WIPP Brine: Data Summary and Recommendations.” LCO-AC P-10, LANL\ACRSP Report. Ca rlsbad NM: Los Alamos National Laboratory.

9 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #5

When discussing possible effects of increased +III actinide solubiliti es on PA during our call, a LANL staff member said that he thought the increased ligands concentrations predicted for the CRA-2009 PABC FMT calc ulations might have increased the +III actinide solubilities to the ext ent that americium was invento ry limited. Although he did not think Pu would be inventory-limited, he suggested that high EDTA concentrations might result in sufficient EDTA complexa tion that the effects of borate would be relatively unimportant. I have only looked at what I believe are the ERDA-6 results for the CRA-2009 PABC calculations. This output file (FMT_PABC09_E6_HMAG_ORGS_013.OUT) is for ERDA-6 brine, with organics, and was run on July 8 2009. The total concentra tion of Am(III) was predicted to be 1.51 x10 -6 M at pcH 9.7. This concentration does not dwarf the concentration observed in Figure 4- 11 (about 1 x 10 -6 M), so it does not appear that EDTA complexation of the +III actinides will be so high that the potential ef fects of borate compl exation described by the results of Borkowski et al . 2008 can be neglected.

EPA Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
DOE Response
The initial results of the ongoi ng neodymium experiments rema in inconclusive about the overall effect of borate complexation on the III actinides under WIPP -relevant conditions. The most important reason for this, as di scussed in 1-23-6 EPA follow-up comment # 2, is that the issue of borate complexation has not been fully addressed by the WIPP project and continues to be the subject of ongoing res earch. The full quantification of the true impact of borate complexation cannot be esta blished until all the ne eded Pitzer data and species information are obtaine d by the project and calculations can be done that reflect all the key solution parameters at WIPP -relevant ionic strengths and conditions.
It is also important to note, as stated in 1-23-6 EPA follow-up comme nt # 2, that there are potentially other factors besides borate that account for the small differences between the modeling and experimental results (e.g., pH, brine component concentrations) and it remains the DOE position that a factor of 10 or less agreement between modeling and experimental results is excellent agreement for complex groundwater systems such as the WIPP-relevant brines used in Borkowski et al . (2008). In this context, differences of factors of 2 or 3 are not c onsidered significant. The DOE ’s position is that the FMT model calculations for An(III) we re confirmed by the data in Borkowski et al. (2008).

10 March 30, 20106 th Response Submittal to the EPA Enclosure 1

Addressing the influence of organic ligands (i.e. EDTA), comparisons of the FMT calculations with and without organics show an increase in americium solubility from 2.25 x 10 -7 M to 1.51 x 10 -6 M, about a factor of seven (Brush et al., 2009). The final concentration of the actinides is a function of several uncertainties and is calculated as a function of time (Garner, 2010). For exam ple, after including the effects of the uncertainties, this leads to a range of total potential mobilized americium in the Castile brine used in PA of 3 x 10 -8 M to 2 x 10 -3 M (Garner, 2010). The DOE believes that this range is sufficient to account for any possibl e borate effects or ot her uncertainties.

DOE References
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
Brush, L.H., Y.-L. Xiong, and J.J. Long. 2009. “Results of the Calculations of Actinide Solubilities for the CRA-2009 PABC.” Anal ysis Report, October 7, 2009. Carlsbad, NM: Sandia National Labor atories. ERMS 552201.
Garner, J. 2010. “Analysis Package for PANEL: CRA-2009 Performance Assessment Baseline Calculation.” Carlsbad, NM: Sandia National Laboratories. ERMS 553032.
U. S. Department of Energy (DOE) 2009

. CRA-2009 Appendix SOTERM. Carlsbad NM: Carlsbad Area Field Office.
Xiong, Y.L., L.H. Brush, A.E. Ismail, and J. J. Long. 2009. “Uncertainty Analysis of Actinide Solubilities for the WIPP CRA-2009 PABC.” Analysis report, December 1, 2009. Carlsbad, NM: Sandia National Laboratories. ERMS 552500.

11 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #6
Figure 4-9 presents Nd(III) solubility data in GWB as a function of pcH in the absence of carbonate. At pcH values of approximately 7.3 and 8.0, the concentr ations measured in experiments approached from undersaturati on are higher by approx imately an order of magnitude than the concentrations measuredin experiments approached from oversaturation. Does DOE have an explanation for this?

EPA Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
DOE Response
The EPA has correctly noted that there is of ten disequilibrium in experiments that start from undersaturation. This is commonly obser ved in many solubility studies in complex media that start with a specific solid. The explanation for this is that it takes time for the solubility-controlling phases to form and define the observed solubility. In this context, the initially-observed solution concentrations are defined by the relative rates of the dissolution of the “unstable” phase added to the experime nt and the precipitation/ formation of the solubility controlling phases – rather than simply the solubility of the solubility-controlling phases.
In time, the undersaturation experiments and oversaturation experime nts are expected to approach the same value because, at least in the time frame of the experiments, equilibrium has been reached. This is what is generally observe d in the III actinide experiments reported (Borkowski et al., 2008). The figure noted in the EPA response is shown in Figure 1 (Figure 4-9, Borkowsk i et al., 2008) and corresponds to the neodymium concentrations measured after a pproximately 9.2 months. The same data taken at 13.0 months (~ 4 months later), wh ich was after the CRA- 2009 data cut-off, are shown in Figure 2. As can be seen, alt hough some discrepancy remains, the over- and under saturation results are reachi ng better agreement (a factor of ~3 rather than ~10).

DOE Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.

12 March 30, 20106 th Response Submittal to the EPA Enclosure 1

6.0 6.5 7.0 7.5 8.0 8.5 9.0 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4Nd Concentration, M

pC H+ - oversaturation - undersaturation - carbonate trend 

## GWB
over- and under-saturation carbonate free

Figure 1. Solubility of neodymium in GWB brine at 9.2 months (this is Figure 4-9 in Borkowski et al., 2008).

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4

- oversaturation - undersaurationNd Concentration, M

pC H+ GWB carbonate free

Figure 2. Neodymium solubility in GWB brin e at 13 months. This compares to the data presented in Figure 1 and shows increased agreement between the undersaturation and oversaturation data.

13 March 30, 20106 th Response Submittal to the EPA Enclosure 1

1-23-6 EPA Follow-up Comment #7
DOE's response to 1-23-6c dated November 25, 2009 statement that "For the III actinides, the complexation of borate effectivel y substitutes for the calculated effect of carbonate presently in the WIPP model." Is in consistent with the modeling results from the CRA-2004 PABC. These results, both with and without ligands present in the brine, showed that aqueous americium-carbonate co mplexes constituted negligible proportions of the total americium in so lution in all four solution compositions (GWB and ERDA-6 with and without ligands). In addition, because there is an assumed excess of Am(OH) 3 (s) in the WIPP repository, "competition" betw een borate and carbonate for americium in the system will not occur. Americium-borate aqueous complexes, if formed, will form in addition to americium-carbonate complexes. However, under WIPP conditions, current FMT modeling does not predict significant carbonate complexation of the +III actinides.
DOE Response
The DOE agrees with the EPA that carbonate complexation does not significantly impact the solubility of the III actinides in the WI PP. The effects of borate complexation have not yet been fully evaluated (see responses to 1-23-6 EPA follow-up comments #2, #3 and #5). The intention of the 1-23-6c DOE response was to make a general point that borate and carbonate complexa tion behave in a similar way in the brine systems investigated. The reasons for this are 1) th ey have a similar pKa: 9.0 for borate vs. 9.6 for carbonate; and 2) the effec tive complexation strength (K f [concentration]) value is very similar (K eff = ~320 for carbonate, 370 for borat e in GWB and 150 for borate in ERDA-6). Therefore, even though the forma tion constant for borate is smaller than carbonate, both anions have similar complexation strengths.

14 March 30, 20106 th Response Submittal to the EPA Enclosure 1

15 March 30, 2010 1-23-6 EPA Follow-up Comment #9
Another question is related to the carbonate concentrations in the experiments that they conducted. I understand that they spiked an initial carbonate c oncentration into the solutions and used "gas-tight polypropylene bottles" for the experiments. Did they measure carbonate concentrations in solution at the end of any of the experiments to confirm that there was no loss of CO 2 ? It is my understanding th at all of the experiments were performed in a CO 2 -free glove box, so gain of CO 2 should not have occurred. Do they assume that the amounts of NdOHCO 3 precipitated in their experiments were so small that it did not affect the total carbonate in the solutions?
DOE Response

Carbonate levels were measured in the experiments reported. After three years, which is well beyond the duration of the experiments reported (Borkowski et al., 2008), there is satisfactory agreement between the measured carbonate concentratio ns and the initial concentrations added to the br ine (typically 80% or greate r). It was not stated in Borkowski et al., 2008 that car bonate phases were formed in the experiments reported. The DOE position continues to be that the so lubility controlling phase is the hydroxide phase since there is good agreement be tween FMT model predictions and the experimental results (good agreement in this co ntext is less than an or der of magnitude).

DOE Reference
Borkowski, M., J.-F. Lucchini, M.K. Ri chmann, and D.T. Reed. 2008. “Actinide (III) Solubility in WIPP Brine: Data Su mmary and Recommendations.” LCO-ACP-08, LANL\ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.