Risk factors groundwater

Groundwater contamination is most likely where stormwater is discharged into soakaways (e.g. pits filled with rubble to speed transfer to groundwater) or infiltration areas, and where the aquifer is vulnerable. However, in many cases, stormwater is collected in the drainage system, which may discharge into sewers. Stormwater or (when sewer capacity is exceeded) a combination of stormwater and diluted raw sewage may be discharged into surface waters, Box 6,3 summarizes the main risk factors associated with urban runoff,... 

The toxicological basis of SSLs are oral cancer slope factors, non-cancer reference doses, inhalation unit risk factors and reference concentrations. Drinking water and health based standards are used to determine screening levels in groundwater.21... 

Risks The general definition of risk is the danger of injury, harm, or loss. With respect to soil and groundwater remediation, this definition can be extended to the danger of failure or the likelihood of an unwanted situation occurring. The probability that one or more of these calamities will actually happen is the risk factor. 

SEPARATION OF WASTE FROM GROUNDWATER Does the estimated depth to the water table imply a high or low risk for contamination or leachate production. Relate to permeability and gradient factors. 

A variety of factors and methods were used to evaluate and rank the twelve options. For example, the study team considered the reduction in relative risk to human health achieved by different options. Generally, an option s effectiveness in reducing health risks was evaluated by calculating its effect on exposure to benzene emissions. The study team selected benzene emissions as an indicator because benzene can be found in all waste media (air, water, groundwater, and surface water) and poses a known threat to human health. 

The development of an ADI is essentially the same in the NAS procedures, the EPA Food Tolerance procedures, and the NACA proposal for groundwater. An ADI is determined by dividing the NOEL in the most sensitive species by a suitable Safety Factor (SF). Safety Factors for subchronic or repeat administration are usually 1,000 for chronic or lifetime studies, 100 is used. Species conversions can be based upon mg/kg, ppm in the food, or body surface area conversion [29]. Currently, non-oncogenic effects are considered on an mg/kg basis without attempts to correct for species differences. Risk assessment procedures for oncogenic risk employed by the EPA are based upon surface area extrapolations in an attempt to relate to man [30]. 

Priority Response Remedial measures must be expedited for high-priority health/environmental concerns (i.e., Class 1 ratings). In some cases, interim stabilization actions (e.g., surface cover, vapour cut-off, etc.) may serve to control the potential exposure and reduce the risk rating, pending implementation of final remedial actions. For sites receiving a high-priority classification due to the absence of critical site data (e.g., no groundwater measurement), the response action may involve an expedited site assessment to confirm the presence or absence of an actual concern. In the absence of near-term health/environmental concerns, time-sensitive secondary risk drivers (i.e., Class 1 community concern) will serve as the principal factor in prioritization of response actions. 

Hazardous Ranking System (HRS) The principal screening tool used by EPA to evaluate risks to public health and environment associated with abandoned or uncontrolled hazardous waste sites. The HRS calculates a score based on the potential for hazardous substances spreading from the site through the air, surface water, or groundwater and on other factors such as nearby population. This score is the primary factor in deciding if the site should be on the National Priorities List and, if so, what ranking it should have there. 

In this portion of a risk assessment, all the ways that chemicals could move in the environment, as well as all types of people that might be located in areas where the chemicals could be present, need to be considered. Even though the leak has occurred in soil below the ground, exposure could occur off-site because chemicals could be in groundwater, which moves over time. This is illustrated in figure 8.2 for the gas station example introduced in the Data Evaluation section. It is beyond the scope of this book to discuss the mechanisms by which chemicals can move in the environment. However, it is important to know that there are predictable factors that can be used to identify the likely ways by which people could come into contact with chemicals from a site. 

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