Colloid Formation at Waste Plume Fronts

Wan, Jiamin; Tokunaga, Tetsu K.; Saiz, Eduardo; Larsen, Joern T.; Zheng, Zuoping; Couture, Rex A.

doi:10.1021/es0492384

Cited by 26 publications

(26 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The high concentrations of sodium in leaked tank waste relative to native pore water cations leads to almost complete saturation of the exchanger phase by waste Na + . The displacement of ion exchangeable Ca 2+ can lead to calcite supersaturation and precipitation at the ion exchange front (Wan et al 2004a(Wan et al , 2004b(Wan et al , 2004c, with an associated decrease in pH within this zone by the reaction shown in Equation (6.11):…”

Section: +mentioning

confidence: 99%

“…Laboratory studies to simulate the reaction process of alkaline tank waste (e.g., pH > 14) with Hanford sediment have identified two primary reaction zones Wan et al 2004a;Wan et al 2004b) that progress hydrologically downgradient from the source of tank waste release. The zone nearest the source is dominated by silica (e.g., quartz) and fine-grained aluminosilicate dissolution reactions that moderate pH (from pH 14 to pH 11-12) by hydroxide consumption.…”

Section: 22mentioning

confidence: 99%

See 1 more Smart Citation

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

Cantrell¹,

Zachara²,

Dresel³

et al. 2007

View full text Add to dashboard Cite

Companion reports that review other subject matter areas relevant to contaminant transport within the vadose zone beneath the SST WMAs, the IDF, and groundwater have been recently published. The specific subject areas include the geology of the SST WMAs iv contaminants released to the vadose zone exhibit a wide range of mobility behaviors. Many tank waste contaminants have been strongly retarded by adsorption and precipitation reactions (e.g., cesium, plutonium, americium, and europium), while others have remained mobile (e.g., technetium, nitrate, and selenium). Still others show variable, waste-specific behaviors (e.g., cesium [where sodium concentrations are very high], strontium, chromium, and uranium) that are closely tied to evolving composition of pore water in the sediments, and for chromium, a change in oxidation state. The temperature of in-ground tank waste has moderated by heat exchange with the subsurface sediment, and high concentrations of base (OH -) have been neutralized through reactions with sediment minerals and secondary mineral precipitation. Major geochemical features that may potentially affect the mobility of key contaminants of interest in the vadose zone include oxidation state, aqueous speciation, solubility, and adsorption reactions.Processes suspected of facilitating the far-field migration of immobile radionuclides, such as formation of stable aqueous complex formation and mobile colloids, were found to be potentially operative, but unlikely to occur in the field. An exception is the enhanced migration of cobalt-60 facilitated by the formation of highly stable aqueous-cyanide complexes. Certain fission-product oxyanions (e. • Adsorption is suppressed by large concentrations of tank waste anions (e.g., NO 3 -, OH -, and CO 3 2-)• Surface charge of clay-size minerals is negative and will therefore tend to repel anions• Unlike chromium, their less-soluble, less-mobile reduced forms are unstable in oxidizing environments.Laboratory studies conducted through PNNL's Vadose Zone Characterization Project and basic-science geochemical studies are expected to continue in partnership to provide information to further refine the conceptual model used for risk assessment modeling. Results of these studies can be used to help ascertain uncertainties associated with the refinement of the conceptual models for contaminant migration in the vadose zone beneath the single-shell tanks. Results can also provide improved parameterization, such as distribution coefficients (K d ), and mathematical constructs used by modelers to predict contaminant mobility under these conditions, and to decrease the degree of conservatism incorporated in these models.For various reasons, risk assessment models typically use various approximations to represent the conceptual model developed for the site. Adsorption is frequently approximated using empirical distribution coefficients (K d s). Although the use of empirical distribution coefficients can potentially lead to erroneous results under certain conditions where the...

show abstract

Section: +mentioning

confidence: 99%

Section: 22mentioning

confidence: 99%

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

Cantrell¹,

Zachara²,

Dresel³

et al. 2007

View full text Add to dashboard Cite

show abstract

“…However, we did not expect to find a significant amount of mobile metals in these samples because they were all collected within a few vertical feet of the contaminant source term. Because mobile metals are not retained by the solid matrix, we only expect to find elevated concentrations along a narrow front farther down gradient from the source (see Wan et al 2004, for an enlightening example). These results agree with previous characterization efforts that revealed a lack of water-extractable mobile tank waste metals in zones exhibiting elevated soil pH values (Serne et al 2002b,c;Brown et al 2006).…”

Section: 8mentioning

confidence: 99%

“…We infer that this is because mobile elements were not retained by the sediment grains as the contaminant front swept through. Presumably, the mobile elements are distributed along a narrow front marked by sharp concentration gradients (Wan et al 2004), and it is perhaps no surprise that the sediments recovered from the direct-push boreholes did not intercept this limited distribution of mobile elements at the front. It is plausible that such a front exists below the depth sampled using the direct-push method.…”

Section: Summary and Observationsmentioning

confidence: 99%

Characterization of Direct-Push Vadose Zone Sediments from the 241-B and 241-BX Tank Farms

Brown¹,

Icenhower²,

Um³

et al. 2007

View full text Add to dashboard Cite

Executive SummaryGeochemical tests provide evidence for the transit of a plume of caustic waste solution through the sediment column at the Hanford 241-B and -BX Tank Farms. Direct-push samples recovered from boreholes surrounding Tanks 241-B-110 and 241-BX-102 and related waste transfer lines and diversion boxes included sediments typical of those previously recovered from other localities on the Hanford Site. The Hanford formation sediments are dominantly quartzo-feldspathic sands containing lithic fragments, displaying a range of particle size distributions and sorting characteristics. Some moderately well-sorted, fine-grained lithologies are interpreted as lenticular bodies irregularly dispersed in coarser-grained, more poorly sorted sediments. Tier I tests conducted on the vadose zone sediments revealed an inverse correlation between moisture content and sediment size fraction (i.e., there is greater moisture content in finergrained sediments). The Tier I tests also showed that the pore water solutions were likely sodium-rich, moderately saline, and possessed higher pH values than background (uncontaminated) sediments. These data are characteristic of sediments that have encountered sodium-rich, saline, caustic waste solution, as documented in other reports at other suspect contamination sites around Hanford. Analyses of solutions from 1:1 water extracts reveal relatively balanced cation and anion concentrations, indicating that most of the geochemical species have been accounted for. The water extract data for affected sediments also indicate unusually high concentrations of aluminum, iron, and phosphorus. The relatively high concentrations of aluminum and iron may be the result of dissolution of secondary amorphous phases that precipitated after a reactive plume partially dissolved aluminum-and iron-bearing phases as it migrated through the sediment column. On the other hand, the presence of elevated concentrations of phosphorous may be the tell-tale signature of wastes derived from the bismuth phosphate separation process. Elements typically mobile in the subsurface, such as technetium-99, are present at either low concentrations or are below the analytical detection limit. However, we expect that the mobile elements would be present mainly along a narrow plume front, and if this front had passed deeper into the sediment profile than depths sampled, the retention of these elements would be minor. Alternatively, uranium-238 was detected in nearly all the direct-push sediments (by acid extract experiments) from around the BX Tank Farm at concentrations above the natural crustal average (0.76 pCi/g), and we also detected the presence of several anthropogenic radioisotopes, such as cobalt-60, cesium-137, europium-154, and europium-155 (by gamma energy analysis). These data confirm contamination of the sediments.We selected a pair of lithologies from a single direct-push hole from near BX-102 that we anticipated would reveal details of the mechanism of radionuclide binding in the sediments and subjected them ...

show abstract

“…Natural or anthropogenic disturbances can promote the formation of colloids as well as the mobilization of pre-existing colloids (Gschwend et al, 1990;Newman, 1990;Ryan, 1992;Ryan and Gschwend, 1990), or introduce colloids from waste sites (Bunn et al, 2002;Seaman andBertsch, 2000, McCarthy andNewman et al, 1993;Seaman et al, 1995;Grolimund et al, 2001;Wan et al, 2004). Once mobilized, colloids can migrate significant distances and appreciably enhance the transport of adsorbed contaminants.…”

Section: Introductionmentioning

confidence: 99%