Title: Colloid characterization and quantification in groundwater samples

This report describes the work conducted at Los Alamos National Laboratory for studying the groundwater colloids for the Yucca Mountain Project in conjunction with the Hydrologic Resources Management Program (HRMP) and the Underground Test Area (UGTA) Project. Colloidal particle size distributions and total particle concentration in groundwater samples are quantified and characterized. Colloid materials from cavity waters collected near underground nuclear explosion sites by HRMP field sampling personnel at the Nevada Test Site (NTS) were quantified. Selected colloid samples were further characterized by electron microscope to evaluate the colloid shapes, elemental compositions, and mineral phases. The authors have evaluated the colloid size and concentration in the natural groundwater sample that was collected from the ER-20-5 well and stored in a 50-gallon (about 200-liter) barrel for several months. This groundwater sample was studied because HRMP personnel have identified trace levels of radionuclides in the water sample. Colloid results show that even though the water sample had filtered through a series of Millipore filters, high-colloid concentrations were identified in all unfiltered and filtered samples. They had studied the samples that were diluted with distilled water and found that diluted samples contained more colloids than the undiluted ones. These results imply that colloids are probably not stable during the storage conditions. Furthermore, results demonstrate that undesired colloids have been introduced into the samples during the storage, filtration, and dilution processes. They have evaluated possible sources of colloid contamination associated with sample collection, filtrating, storage, and analyses of natural groundwaters. The effects of container types and sample storage time on colloid size distribution and total concentration were studied to evaluate colloid stability by using J13 groundwater. The data suggests that groundwater samples should be analyzed for colloid size and concentration shortly after they have been collected. A prolonged waiting period after sampling will affect the colloid size distribution as well as colloid concentration resulting from the changes of water chemical properties. The data also shows that sample containers, filter materials, and labware that are used for colloid analyses should be cleaned by specially treated low-colloid-containing water. Water used for sample dilution should be verified for total colloidal particle concentration. They then analyzed freshly collected groundwater from NTS wells ER-20-5{number_sign}1 and {number_sign}3. Results show that these groundwater samples have similar colloid concentrations and particle size distributions. For the particle size range between 50- and 200-nm, about ten trillion (1E10) colloidal particles per liter are present in these water samples. Most of these colloidal particles are less than 100 mm in size. For example, more than 98% of the colloids are smaller than 100 nm in size in the ER-20-5 {number_sign}1 sample. Furthermore, it was found that the smaller the sizes of colloid, the higher the colloid concentration present in the water. For another site at NTS, Cheshire, they had analyzed two zones of groundwater samples. For water samples collected from the lower water zone (near the underground detonation cavity about 3,700 feet of slanted depth from the surface), the colloid concentration was about 5E12 particles per liter. About 20 times less than the lower zone of total colloids was found in water samples collected from the upper aquifer (around 2,511 feet of slanted depth), although colloid size distributions from these two zones appear to be rather similar.