January 25, 2009 Follow-up questions to issues first raised in EPA's May 21, 2009 letter, 

comment 1-23-6 

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 

NdOHCO3(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 predicted 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 fairly good reproducibility of results 

from undersaturation (dissolution of NdOHCO3) and oversaturation (precipitation) 

experiments. There appears to have been limited to no characterization of the postexperiment solid phases. Although precisely what was done to characterize the solids 

after the experiments was unclear to me after reading the test plan and Borkowski et al. 

2008 report, Marion Borkowski stated in our conference call this week that there were 

insufficient amounts of solids to characterize after the oversaturation (precipitation) 

experiments. As a result, the identity of the solid phases at the end of the experiments is 

not certain. The data in Figure 4-8 and the interpretation by Borkowski et al 2008 seem to 

indicate that the stable phase was NdOHCO3. Consequently, FMT calculations predict 

that Am(III) solubility for WIPP PA is controlled by Am(OH)3(s) but the experiments 

seem to indicate the solubility-controlling phase will be AmOHCO3. This raises the 

question of whether the FMT modeling is accurately predicting the concentrations of 

Am(III) (and by analogy Pu(III)) in the WIPP brines for PA. 

2. The observed differences in the concentrations at similar 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 increase 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 concentration by a factor 

of2.5 would increase the Nd(III) concentration by approximately the same factor. 

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 function 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 ifhydrolysis species such as Nd(OH)3(aq) became more important at high pcH, these 

concentrations would be present in addition to the Nd-borate species concentrations. It is 

unclear whether a different solid might be controlling the Nd(III) solubilities in the highpcH region. An understanding of the solubility in this pcH region is important because 

in ERDA-6 the maximum concentration is observed at approximately the repository pcH 

predicted by FMT calculations (9.6-9.7). [Note: Clarification on this issue was requested 
in a phone call with LANL staff, but it was not resolved.] 

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 for 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 solubility 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 approaches 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, because 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 undersaturation in this pcH region. Consequently, the 

concentration of Nd(III) in pcH 9.4 GWB could be higher than 10-6 M. 

5. When discussing possible effects of increased +III actinide solubilities on PA during 

our call, a LANL staff member said that he thought the increased ligands concentrations 

predicted for the CRA-2009 PABC FMT calculations might have increased the +III 

actinide solubilities to the extent that americium was inventory limited. Although he did 

not think Pu would be inventory-limited, he suggested that high EDTA concentrations 

might result in sufficient EDTA complexation 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 concentration of Am(III) was predicted to be 1.51 x 10-

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 effects of borate complexation described bythe 

results of Borkowski et al. 2008 can be neglected. 

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 concentrations measured in 

experiments approached from undersaturation are higher by approximately an order of 

magnitude than the concentrations measured in experiments approached 

fromoversaturation. Does DOE have an explanation for this? 

7. DOE's response to 1-23-6c dated November 25, 2009 statement that "For the III 

actinides, the complexation of borate effectively substitutes for the calculated effect of 

carbonate presently in the WIPP model." Is inconsistent 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 complexes constituted negligible proportions 
of the total americium in solution 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" between 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. 

8. DOE should perform FMT calculations to predict the concentrations of Nd(III) under 

the conditions of the Nd(III) solubility experiments in the NaCl, GWB, and ERDA-6 

brines. These calculations would provide direct evidence of the extent of the differences 

between the experimental results and the FMT calculated solubilities, which will be 

useful even though experimental data are unavailable at higher pcH in GWB. For the 

carbonate experiments, it may be useful to perform calculations using Am(OH)3(s) as the 

solubility-controlling solid as well as calculations using AmOHCO3(s) as the solubilty 

controlling solid, to indicate potential solution composition changes that might be caused 

by a change in the stable phase or mixed solid phase formation. 

9. Another question is related to the carbonate concentrations in the experiments that they 

conducted. I understand that they spiked an initial carbonate concentration 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 CO2? It is my understanding that all of the experiments 

were performed in a CO2-free glove box, so gain of CO2 should not have occurred. Do 

they assume that the amounts of NdOHCO3 precipitated in their experiments were so 

small that it did not affect the total carbonate in the solutions?