Dan Kaplan and Gary Iversen
Westinghouse Savannah River Company
Aiken, SC 29808

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

This report has been reproduced directly from the best available copy.

Available for sale to the public, in paper, from:  U.S. Department of Commerce, National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161,  phone: (800) 553-6847,  fax: (703) 605-6900,  email:  orders@ntis.fedworld.gov   online ordering:  http://www.ntis.gov/support/ordering.htm

Available electronically at  http://www.osti.gov/bridge/

Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy, Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, TN 37831-0062,  phone: (865 ) 576-8401,  fax: (865) 576-5728,  email:  reports@adonis.osti.gov

Laboratory tests were conducted for the Environmental Restoration Division (ERD) to evaluate whether filtercake waste generated from the F-Area Ground Water Treatment Unit (GWTU) would satisfy the free moisture Waste Acceptance Criteria, WAC, (<1 vol-% free moisture after transport) of the Nevada Test Site (NTS) (DOE 2000). The vibration test used in this study is an operationally defined parameter that is not expected to simulate precisely the conditions during filtercake transport between the Savannah River Site (SRS) and the NTS. However, the laboratory tests are expected to provide information about trends related to free moisture release. The objectives of this study were to determine: 1) the influence of total moisture content on the amount of free moisture released from the filtercake waste, 2) whether resin material used downstream of the treatment process had mixed into the filtercake, 3) ¹²⁹I-K_d values for the filtercake, and 4) ¹²⁹I concentrations in the filtercake.

The key findings from this study follow.

• The average total moisture content of 12 filtercake samples were nearly identical, 75.1 ± 1.7 wt-% total liquid, irrespective of the manner in which they were dried.
• Attempts were made to measure the free moisture content of filtercake material with an adjusted moisture content of 47.2, 65.6, 69.4, 74.5 ("as received"), 78.3 and 80.9 wt-%. There was no free moisture in the lowest three total moisture content samples.
• For the 74.5 ("as received"), 78.3 and 80.9 wt-% moisture samples, a great deal of small-grained solids moved along with the free moisture. The presence of these solids in the free moisture collection pan precluded measuring the free moisture released by the standard method. However, estimates of the free moisture content were made by measuring the total moisture contents in the filtercake sample before and after the shake test. These conservative estimates indicated that the "as received" sample released 2.5 wt-% (approximately 1.60 vol-%) (To convert wt-% to vol-% the following was assumed: the density of the liquid was 1.0 g/cm³, the bulk density of the filtercake was 0.638 g/cm³ (1341.7 lbs waste/B-12 package [an average weight of 138 B-12 packages filled with filtercake, personnel communications with John Adams, WSRC]), filtercake waste accounted for 75% of the B-12 box volume, and the total B-12 box volume was 45 ft³. ) free moisture.
• The critical total moisture content above which free moisture was released from the filtercake was 71.6 wt-%. Above this critical total moisture content, 0.8 wt-% free moisture was released for each percent of total moisture in the filtercake. So for a filtercake sample with 72.6 wt-% total moisture content, the predicted free moisture would be 0.8 wt-%.
• The average ¹²⁹I concentration of the two samples tested was 3.17 ± 0.25 pCi/g wet wt (8.33 ± 0.89 pCi/g dry wt).
• No resins were detected in the filtercake after systematically examining 11 samples with a 15x magnifying glass.
• The average ¹²⁹I-K_d value in a simulated cementitious environment was 13.9 ± 1.5 mL/g dry wt (5.2 ± 0.6 mL/g wet wt). The average ¹²⁹I-K_d in an acid rain environment was 56.7 ± 9.2 mL/g dry wt (21.2 ± 3.4 mL/g wet wt). These K_d values are appreciably higher than the value of 2 mL/g used in previous performance assessment calculations for generic waste forms.

In conclusion, the potential for fine-grained filtercake material to be released along with free moisture during transit introduces a complication that was not anticipated. Furthermore, based on the calculated free moisture contents, the conditions under which these filtercake samples were dried were not adequate to meet the 1 vol-% WAC requirement. Should further drying of the filtercake prove to be an unacceptable option, then it may still be possible to meet the free moisture WAC criteria by including a sufficient amount of a water absorbent (such as the SP-400 Absorbent) with each shipment.

Key Words: Vibration Tests, F-Area GWTU Filtercake, Iodine Distribution Coefficient

Environmental Restoration Division is presently evaluating whether to dispose of filtercake generated from the F-Area Ground Water Treatment Units (GWTU) at the Nevada Test Site (NTS). One of the criteria for the waste to be accepted at the NTS is that the waste must not contain more than 1 vol-% free moisture (DOE 2000). This criterion controls the amount of liquid, a primary vector for subsurface contaminant migration (along with colloids), introduced into the repository. This criterion also serves to reduce the chance of an accidental spill during transport of the waste to the NTS. On December 15, 1997, a shipment from Fernald to the NTS leaked some liquid waste onto a highway in Kingman Arizona, resulting in a Type B Accident Investigation (Bradburne 1998a, 1998b). The direct cause of the leak was attributed to broken welds related to the use of substandard containers.

The objectives of this study were to determine:

1. the influence of total moisture content on the amount of free moisture released from the filtercake waste,
2. whether resin material used downstream of the treatment process had mixed into the filtercake,
3. ¹²⁹I-K_d values for the filtercake, and
4. ¹²⁹I concentrations in the filtercake.

Personnel from Environmental Restoration Division (ERD) submitted the filtercake samples to Analytical Development Section (ADS) of the Savannah River Technology Center (SRTC). Waste Processing Technology (WPT; also part of SRTC) personnel then retrieved these samples from ADS. WPT personnel conducted all tests described in this report, except for ¹²⁹I concentration analyses, which was conducted by ADS. The 12 filtercake samples are described in Table 1. None of the 12-filtercake samples contained standing water.

Table 1. Filtercake Sample Description.

The total moisture contents of the "as received" samples were determined by the standard EPA method (EPA 1989) in which filtercake was placed in a 105°C oven until no weight change was measured, typically three days. Total moisture content was determined using Equation 1:

(1)

where M_i and M_f are the initial and final mass of the filtercake sample subjected to 105°C drying.

It was originally planned to conduct vibration tests on a series of filtercake materials in which the total moisture content had been adjusted to between 40 and 85%. The moisture contents of the "as received" samples were to be adjusted by first drying at 105°C until no weight change was detected and then adding back the appropriate amount of water. However, the moisture contents could not be adjusted in this manner because when the filtercake was completely dried, it turned into a hard brick that could not be rehydrated. This drying process is similar to how a ceramic clay, after it has been baked, can not be rehydrated to the consistency it had prior to baking. This physical behavior is not entirely surprising in light of the fact that the filtercake consists primarily of various Fe-oxide mineral phases, a primary constituent of bricks used in building construction. Given these limitations, we elected to obtain a range of moisture contents by incompletely drying or by adding moisture to the "as received" filtercake. The total moisture content of the samples tested for free moisture were 47.2, 65.6, 69.4, 74.5 ("as received"), 78.3, and 80.9 wt-%.

Vibration tests were conducted on the "as received" and five moisture amended filtercake samples on a Fritsch vibratory shaker (Idar-Oberstein, Germany) at 60-Hz at an amplitude of 2-mm for 10-min (ASTM D999-96, ASTM D4253-93). There are two parameters that can be changed in the vibratory shaker: amplitude of the shaking and the duration that the sample is shaken. The standard method (ASTM D999-96) for the vibration test does not specify either of these parameters. The procedure leaves it to the discretion of the operator to select the appropriate levels of these two parameters to reflect the scenario of interest. The amplitude of the vibratory shaker can be set between 0 and 3-mm. Based in part on the guidance from the standard method and in part on professional judgement, we believed an amplitude of 1.5-mm would be appropriate, but selected an amplitude of 2-mm to provide a more conservative test. The vibration tests were continued until no change in free moisture was detected.

As will be discussed in more detail in the Section 4.2, fine-grained solids were observed in the free-liquid collection pan during the vibration tests. It was not possible to correct for the presence of the solids in a meaningful manner. Consequently, free moisture content for the "as received" (74.5 wt-% moisture), 78.3 wt-% and the 80.9 wt-% samples could not be determined through the standard method. Instead it was estimated by measuring the change in total moisture content in the sample placed on the vibratory shaker before and after shaking. The conservative nature of this calculation will also be discussed in Section 4.2.

Filtercake samples #1 through #11 (Table 1) were closely inspected with a 15x magnifying glass for the presence of resins. The filtercake was spread out in a baking dish and systematically inspected for the presence of resins.

3.5 Desorption Batch K_d Tests

¹²⁹I-K_d values were determined by standard batch techniques (ASTM D 4319-83). These techniques are identical to those used previously by Kaplan et al. (1999) and Kaplan and Serkiz (2000) for determining ¹²⁹I-K_d values for other waste materials. The tests were conducted in duplicate using the same composited samples used in the vibration tests. The desorption K_d tests were conducted with two solutions, an acid rain simulant and a cement leachate simulant. The acid rain simulant was intended to provide a measure of leaching conditions when the waste is disposed directly in the ground. The cement leachate simulant was intended to provide a measure of leaching conditions when the filtercake waste is disposed in a cement vault. The acid rain simulant (50-L) was prepared by adding drops of a 60/40 wt-% mixture of sulfuric acid/nitric acid to deionized water until a pH of 3.0 (EPA Method 1320, EPA 1986) was achieved (approximately 120 drops/50-L). The cement leachate simulant (50-L) was prepared by the following the recipe of Serne et al. (1987): CaCO₃ (13.70 g), CaOH₂ (10.55 g), KOH (69.30 g), NaOH (173.57 g). Following a 2-hr mixing period, the solution was filtered to remove any precipitated or undissolved materials.

Approximately 20-g (moist weight) of filtercake material and 475-mL leaching solution were placed into 500-mL plastic bottles. Batch leaching experiments were allowed to equilibrate for 7-days, during which time the sample bottles were gently mixed once per day for 30-sec. Following the 7-day equilibration period, leaching solutions were filtered (0.45-m m) and submitted to ADS for ¹²⁹I analyses.

K_d values were calculated using Equation 2,

(2)

where I_solid(final) and I_aq(final) are the ¹²⁹I concentrations in the solid and aqueous phases, respectively, at the end of the equilibration period. K_d values were reported on a dry weight basis.

Approximately 5-g of solid and 450-mL of liquid sample were used by ADS for ¹²⁹I determinations. The filtercake was digested and then subjected to a silver iodide precipitation method to separate any iodide in the matrix from other A blank deionized water sample was analyzed along with the experimental samples as a negative control. This control provided information about background ¹²⁹I contamination resulting from laboratory activities. After the gamma analysis, the precipitate was analyzed by neutron activation analysis (NAA) to determine the levels of stable iodine carrier in the precipitate. The recovery of the iodine carrier was used to correct the gamma spectroscopy results for the ¹²⁹I recovery. Results were reported on a dry-weight basis. The standard QA practices described in the WSRC QA Manual 1Q were followed throughout this study.radionuclides. The precipitate was then analyzed for as long as 2-days using a LOAX HPGe gamma spectroscopy detector.

The moisture contents of the 12-filtercake samples described in Table 1 are presented in Table 2. The raw data used to calculate these moisture percentages is presented in Appendix A (Section 8.0). The average moisture content in the 12 samples were 75.1 ± 1.7 wt-%. The small standard deviation suggests that the various drying treatments had little effect on the final moisture content.

Table 2. Total Moisture Content of "As Received" Filtercake Samples.

The vibration test of the filtercake at the "as received" moisture content was conducted on a sample that was a combination of samples #1 and #7 (Table 1). Unlike previous vibration tests conducted with resin materials (Kaplan and Iversen 2001), fine-grained solids were observed in the free-liquid collection pan after only 30-min of shaking. With continued shaking, large globs of filtercake were observed in the collection pan. The "free liquid" samples collected after 30-min of shaking had increasing amounts of solids in them, with the last sample, collected after 140-min, having a consistency of putty. Consequently, free moisture content for the "as received" (74.5 wt-% moisture) sample could not be determined through the standard method.( In an effort to salvage the data to generate a free-moisture release curve (free moisture versus vibration duration), attempts were made to account for the presence of solids that fell into the free water collection vessel by drying the collected mud samples at 105°C. The idea was to assign the weight change after drying the sample to the free moisture released from the sample. These solids-corrected free-moisture values proved not to be helpful insofar that they grossly overestimated the true free-moisture content. This overestimation resulted because all the moisture associated with the filtercake that fell into the collection pan was not in fact all free-moisture, instead it also included moisture that was strongly bound to the sludge. The raw data from this test and these calculations are presented in Appendix B, Section 9.0.) Instead it was estimated by measuring the change in total moisture content in the sample placed on the vibratory shaker before and after shaking for 140-min (Table 3). Based on this method, the free moisture content was 2.5 wt-%. This may be a slightly larger value than would be measured using the standard technique because a small amount of evaporation of water from the sample invariably occurs during the vibration test, even though efforts were made to minimize evaporation. This weight-difference calculation does not distinguish between evaporated and true free moisture. A non-conservative method to estimate the free moisture in the sample would be to base it on the moisture released during the first 30-min of data, i.e., the free moisture weight without solids in the collection pan. Using this method, which likely underestimates the true value, the percent free moisture was 0.08 wt-% (Appendix B, Section 9.0).

The filtercake samples containing 47.2, 65.6, and 69.4 wt-% moisture did not release any free moisture during the vibration tests. In all three-vibration tests, dry powder, but no moisture, was detected in the collection pans.

Additional vibration tests were conducted with filtercake sample #12 (total moisture content of 76.3 wt-%; Table 1) in which 2.0 and 4.6 wt-% moisture was added (Table 3). As was the case with the "as received" moisture content test, filtercake solids entered the collection pan during the test, nullifying the results. Based on the weight-difference estimate discussed above, the free moisture content in the sample with 78.3 wt-% total moisture was 4.9 wt-% and in the sample with 80.9 wt-% total moisture was 7.7 wt-% (Table 3).

Table 3. Calculations of Free Moisture Content Based on Changes in
Moisture Content in the Sample before and after Shaking on the Vibratory Shaker.

A summary of the influence of total moisture content on free moisture content is presented in Figure 1. The critical moisture content above which free moisture is released from the sample is an important value and its value, based on Figure 1, is between 69.4 and 74.5 wt-% total moisture. To pinpoint this value, an estimate was calculated based on regression analysis of the data in which free moisture was detected, i.e., the 74.5, 78.3, and the 80.9 wt-% total moisture content data. The calculated regression line is presented in Figure 1. The calculated critical total moisture content based on this regression line is 71.6 wt-%. The slope of the regression line was 0.799. In an ideal system, void of particulates in the free liquid and void of matric (capillary) potential, the slope would be expected to be one.

Figure 1. Free moisture content versus total filtercake moisture content.
Regression analysis was conducted to estimate the critical total moisture content,
above which free moisture is released from the filtercake. This critical value was
set equal to the point where the free moisture = 0 wt-%, i.e., the y intercept.

4.3 Inspection of Filtercake Samples for Resins

Filtercake samples #1 through #11 (Table 1) were closely inspected with a 15x magnifying glass for the presence of resins. The filtercake was spread out in a baking dish and systematically inspected for the presence of resins. No resins were detected in any of the samples.

Desorption ¹²⁹I-K_d values were measured by combining ~20 g (wet wt) of "as received" filtercake with 475-mL of either an acid rain simulant or a cementitious leachate simulant. The acid rain simulant was designed to approximate a trench disposal scenario, whereas the cementitious leachate simulant was design to approximate a vault disposal scenario. The ¹²⁹I-K_d values in the acid rain simulant was 56.7 ± 9.2 mL/g dry wt (21.2 ± 3.4 mL/g wet wt) and in the cementitious leachate simulant was 13.9 ± 1.5 mL/g dry wt (5.2 ± 0.6 mL/g wet wt) (Table 4). The larger K_d values in the acid rain than in the cementitious environment is consistent with the results reported for other SRS waste (Kaplan et al. 1999, Kaplan and Serkiz 2000).

The total ¹²⁹I concentrations in two "as received" samples were 3.35 and 2.99 pCi/g wet wt, for an average of 3.17 ± 0.25 pCi/g wet wt. On a dry weight basis, these concentrations become 8.96 and 7.70 pCi/g dry wt, for an average of 8.33 ± 0.89 pCi/g dry wt.

Table 4. Desorption ¹²⁹I-K_d Values.

The average ¹²⁹I-K_d value in a simulated cementitious environment was 13.9 ± 1.5 mL/g dry wt (5.2 ± 0.6 mL/g wet wt). The average ¹²⁹I-K_d in an acid rain environment was 56.7 ± 9.2 mL/g dry wt (21.2 ± 3.4 mL/g wet wt). The larger K_d values in the acid rain than in the cementitious environment is consistent with previous reports. Both K_d values are appreciably greater than the value of 2 mL/g used in previous performance assessment (McDowell-Boyer et al. 2000) for generic waste forms..

The potential for fine-grained filtercake material to be released along with free moisture during transit introduces a complication that was not anticipated. Based on the calculated free moisture contents, the conditions under which these filtercake samples were dried were not adequate to meet the 1 vol-% WAC requirement (see Footnote ). Should further drying of the filtercake prove to be an unacceptable option, then it may still be possible to meet the free moisture WAC criteria by including a sufficient amount of water absorbent (such as the SP-400 Absorbent) with each shipment.

Carl Black helped with the vibration testing of the F-Area filtercake. Cathy Coffey conducted the K_d tests. John Adams, Tom Butcher, Sandy Carroll, Jim Cook, and Carlos Lucha (all with WSRC) provided useful comments to a draft of this report.

ASTM Method D 4319-83, 1984. Standard Test Method for Distribution Ratios by the Short-Term Batch. Annual Book of ASTM Standards.

ASTM Method E 203 – 96, 1996. Standard Test Method for Water Using Volumetric Karl Fisher Titration. Annual Book of ASTM Standards.

ASTM Method D 999-96. 1996. Standard Methods for Vibration Testing of Shipping Containers. Annual Book of ASTM Standards.

ASTM Method D 4253-93. 1993. Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table. Annual Book of ASTM Standards.

Bradburne, J. 1998a. "FDR Corrective Action Plan," C:00TP:98, Rev. 2, Transmission to Jack Craig on March 18, 1998, Fluor Daniel Fernald, Fernald, OH.

Bradburne, J. 1998b "Leaky White, Corrective Action Report, C:00TP:98.0115, Transmission to Jack Craig on January 19, 1998, Fluor Daniel Fernald, Fernald, OH.

DOE. 2000. Nevada Test Site Waste Acceptance Criteria. DOE/NV-325-Rev. 3, U.S. DOE-NV, Las Vegas, NV.

EPA Method 9096, Liquid Release Test (LRT) Procedure, (1994).

EPA, Stabilization/Solidification of CERCLA and RCRA Wastes. 1989. Physical Tests, Chemical Testing Procedures, Technology Screening, and Field Activities, EPA/625/6-89/022, Center for Environmental Research Information and Risk Reduction Engineering Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH 45268.

Kaplan, D. I., and G. Iversen. 2001. Evaluation of Free Moisture in Resins Used at the F- and H-area Groundwater Treatment Units. WSRC-TR-2000-00532, Rev. 0. Westinghouse Savannah River Company, Aiken, SC.

Kaplan, D. I., S. M. Serkiz, and N. C. Bell. 1999. I-129 Desorption from SRS Water Treatment Media from the Effluent Treatment Facility and the F-Area Groundwater Treatment Facility. WSRC-TR-99-00270. Westinghouse Savannah River Company, Aiken, SC.

Kaplan, D. I., and S. M. Serkiz. 2000. Iodine-129 Desorption from Resin, Activated Carbon, and Filtercake Waste Generated from the F- and J-Area Water Treatment Units. WSRC-TR-2000-00308, Rev. 0, Westinghouse Savannah River Company, Aiken, SC.

McDowell-Boyer, L., A. D. Yu, F. R. Cook, D. C. Kocher, E. L. Wilhite, J. Homes-Burens, and K. E. Young. 2000. Radiological Performance Assessment for the E-Area Low-Level Waste Facility. WSRC-RP-94-218 Rev.1, Westinghouse Savannah River Company, Aiken, SC.

8.0 Appendix A: Total Moisture Content of "As Received" Samples