Development of a leaching procedure to assess the risk of uranium leaching due to construction and demolition waste disposal

Naturally-occurring uranium can be found at elevated concentrations in groundwater throughout the world, with the potential to cause kidney damage in chronically exposed individuals. Empirical evidence shows that uranium mobilization can be enhanced in the presence of ions that are associated with leachate from construction and demolition (C&D) disposal sites. There is need for a simple and effective procedure to evaluate soil and rock formations for uranium mobility prior to the permitting of waste disposal facilities which could alter groundwater chemistry. A series of leachate extractions were performed to represent the impact of C&D leachate on uranium-bearing rocks, focusing on the impact of calcium, sodium, chloride, sulphate, and bicarbonate concentrations on uranium mobilization. Based on these observations a uranium leaching procedure (ULP) was developed and compared to the synthetic precipitation leaching procedure (SPLP). The ULP was capable of mobilizing an order of magnitude more uranium than the SPLP from six rock samples and shows promise as a tool for assessing the risk of groundwater contamination by C&D waste through uranium mobilization.

Understanding the translation of scientific knowledge about arsenic risk exposure among private well water users in Nova Scotia

Arsenic is a class I human carcinogen that has been identified as the second most important global health concern in groundwater supplies after contamination by pathogenic organisms. Hydrogeological assessments have shown naturally occurring arsenic to be widespread in groundwater across the northeastern United States and eastern Canada. Knowledge of arsenic risk exposure among private well users in these arsenic endemic areas has not yet been fully explored but research on water quality perceptions indicates a consistent misalignment between public and scientific assessments of environmental risk. This paper evaluates knowledge of arsenic risk exposure among a demographic cross-section of well users residing in 5 areas of Nova Scotia assessed to be at variable risk (high-low) of arsenic occurrence in groundwater based on water sample analysis. An integrated knowledge-to-action (KTA) methodological approach is utilized to comprehensively assess the personal, social and local factors shaping perception of well water contaminant risks and the translation of knowledge into routine water testing behaviors. Analysis of well user survey data (n=420) reveals a high level of confidence in well water quality that is unrelated to the relative risk of arsenic exposure or homeowner adherence to government testing recommendations. Further analysis from the survey and in-depth well user interviews (n=32) finds that well users' assessments of risk are influenced by personal experience, local knowledge, social networks and convenience of infrastructure rather than by formal information channels, which are largely failing to reach their target audiences. Insights from interviews with stakeholders representing government health and environment agencies (n=15) are used to reflect on the institutional barriers that mediate the translation of scientific knowledge into public awareness and stewardship behaviors. The utilization of local knowledge brokers, community-based networks and regulatory incentives to improve risk knowledge and support routine testing among private well users is discussed.

Arsenic in private drinking water wells: an assessment of jurisdictional regulations and guidelines for risk remediation in North America

Arsenic is a known carcinogen found globally in groundwater supplies due to natural geological occurrence. Levels exceeding the internationally recognized safe drinking water standard of 10 μg/L have been found in private drinking water supplies in many parts of Canada and the United States. Emerging epidemiological evidence confirms groundwater arsenic to be a significant health concern, even at the low to moderate levels typically found in this region. These findings, coupled with survey data reporting limited public adherence to testing and treatment guidelines, have prompted calls for improved protective measures for private well users. The purpose of this review is to assess current jurisdictional provisions for private well water protection in areas where arsenic is known to naturally occur in groundwater at elevated levels. Significant limitations in risk management approaches are identified, including inconsistent and uncoordinated risk communication approaches, lack of support mechanisms for routine water testing and limited government resources to check that testing and treatment guidelines are followed. Key action areas are discussed that can help to build regulatory, community and individual capacity for improved protection of private well water supplies and enhancement of public health.

Nanoporous Silica For Low K Dielectrics

As integrated circuit sizes decrease below 0.25 microns, device performance will no longer improve at the same rate as for past generations because of RC interconnect delay which becomes significant as compared to the intrinsic gate delay. Parallel approaches to address this are to use a lower resistance metal (i.e., copper instead of aluminum) and to use a dielectric material with a dielectric constant significantly below that of dense silica (∼4). Recently, considerable progress has been made in development of thin films of nanoporous silica for these applications. Advantages include high thermal stability, small pore size, similarity to conventional spin-on deposition processes and spin-on glass precursors and final material (silica). The dielectric constant of nanoporous silica can be tailored between ∼1 and 3 which allows its’ implementation at multiple technology nodes in integrated circuit manufacture.

Recent development efforts have been focused on; 1) simpler and more reproducible deposition processes, 2) a more complete understanding of processing-property relationships for this material, 3) scale-up of manufacturing to yield a range of precursor products with stability for at least six months and very high purity, and 4) working with customers to integrate this material into both aluminum/gapfill and copper/damascene process flows. This paper targets several specific issues related to nanoporous silica use including water adsorption, pore size distribution control, processing at commercially viable throughputs, and obtaining thickness and dielectric uniformity across 200 mm wafers and wafer to wafer.