Contamination, preliminary hazard

CERCLA was passed in 1980 to provide a federally supervised system for the mitigation of chronic environmental damage, particularly the cleanup of sites contaminated with hazardous waste. In 1986, CERCLA was amended by the Superfund Amendments and Reauthorization Act (SARA). Each Superfund site has been assessed, characterized, and prioritized based on risk. Potential sites are first screened using a preliminary assessment (PA) sites deemed a significant threat are then evaluated using a hazard ranking system (HRS) to measure the risk of the site relative to that of other potential sites. The most hazardous sites are then placed on the NPL in the order of their potential risk. 

The high-high probe is completely independent of the other probes and is hardwired to shut down the system completely, independent of the computer. (In the preliminary safety review, the hazards associated with HF overfeed were identified as important thus the independent high-high shutdown probe system was installed.) All systems are designed to fail into safe conditions. The HF control valves are air operated and of a design that makes it impossible for HF to contaminate the air supply. 

Preliminary assessments have been conducted at more than 31,000 sites reported as possible sources of contamination. In 1990 there were over 1100 sites (presenting the greatest health risk and hence eligible for Superfund reimbursement) on the NPL.8-9 The NCP has outlined the level of cleanup necessary at Superfund sites and established the basic procedures that have to be followed for the discovery, notification, response, and remediation of the hazardous waste sites.10... 

Determination of the presence of contaminant plumes and their flow direction and movement rate is commonly required at hazardous waste sites. The first determination is whether leakage from the hazardous waste site is occurring. If the existence of a plume is confirmed, its direction and extent should be established and identified. A preliminary geophysical survey can aid in better defining the contaminant plume, leading to more effective monitoring with a smaller number of monitoring wells. 

A large, deep cavern (formed from a salt dome) located north of Houston, Texas, has been proposed as an ultimate disposal site for both solid hazardous and municipal wastes. Preliminary geological studies indicate that there is little chance that the wastes and any corresponding leachates will penetrate the cavern walls and contaminate adjacent soil and aquifers. A risk assessment analysis was also conducted during the preliminary study and the results indicate that there was a greater than 99% probability that no hazardous and/or toxic material would meander beyond the cavern walls during the next 25 years. 

A preliminary site characterization analysis and hazard assignment before entering a site known to be contaminated... 

New information gathered from additional desk studies and any site investigation is then collated and used to provide more complete descriptions of the candidate source-pathway-receptor pollutant linkages identified in the Phase la report. Each linkage is considered separately and estimates are made of the extent and strength of the contaminant source, its connectivity to the receptor and the level of hazard that is presented to the receptor. Finally, a preliminary assessment is made of the potential harm that hazards may pose to the receptors. From this analysis it is likely that one or more pollutant linkages will be recognised as the... 

The principal direction of the published photochemical research to date has been to elucidate pathways which might be responsible for the degradation of these refractory substances in nature. This basic research has not been extensively applied either to on-or off site treatment of hazardous substances. In this chapter we extend the existing PCB photochemistry literature by considering this potential. The development and fabrication of a prototype surface photoreactor, and its preliminary evaluation at a PCB-contaminated site are described. Photochemical treatments may be applicable to many other classes of hazardous chemicals as well including the polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF) about which this monograph is chiefly concerned. 

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