tailieunhanh - Remediation of Organic Chemicals in the Vadose Zone

The list of pharmaceutical products in the Pharmaceutical Appendix (Appendix) to the Harmonized Tariff Schedule of the United States (HTS) has grown substantially since 1995. As a result of the first update, 496 items were added to the Appendix. The second update introduced an additional 642 items. The third update added 1,298 items. The current update includes 381 drugs identified by their international nonproprietary names (INNs), 17 prefixes and suffixes to identify derivatives of the INNs, and 354 chemical intermediates. When the current update is completed, the Appendix will include more than 10,000 products. The USTR compiled this list. | 7 Remediation of Organic Chemicals in the Vadose Zone Larry Murdoch Contributors . Girke J. Rossabi J. Reed D. Conley J. Phelan . Falta W. Heath . Hazen . Siegrist . West . Urynowicz . Slack P. Bishop V. Hebatpuria . Erickson Davis and . Kulakow INTRODUCTION The remediation of organic chemicals in the vadose zone has been blessed by remarkable success but it has also been cursed by challenges to even our most advanced capabilities. This spectrum of outcomes to the remedial process is a result of the diversity of conditions encountered at contaminated sites. Organic chemicals are rarely stored or intentionally placed beneath the water table so the source of most organic contamination is at the ground surface or in the shallow vadose zone. As a result nearly all sites containing organic contaminants have at least some problems in the vadose zone and commonly the greatest concentrations of contaminants occur in the vadose zone near the source. The large number of sites requiring vadose zone remediation presents a broad range of conditions and circumstances including factors related to geologic conditions properties of the contaminants and the ability to access the subsurface. All are critical to the performance of the remedial technique and currently no single technique addresses all the factors found at contaminated sites. Instead an array of techniques has been developed some to target widespread problems and others to address the more difficult niches. 949 950 Vadose Zone Science and Technology Solutions The development of soil vapor extraction SVE in the mid-to-late 1980s provided a method that can significantly reduce the mass of volatile compounds at sites underlain by relatively dry sandy sediments in areas readily accessed by conventional drilling. A significant number of sites meet those criteria and SVE has been used to close many of them. SVE is widely available and along with several companion techniques it forms the backbone