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CONCENTRATIONS USED <br /> In order to test the probable impact of the current groundwater plume the upper confidence level <br /> (UCL) concentrations were calculated for the Monitor Wells within the plume, from the May 28, <br /> 1998 sampling round. <br /> The values used to determine the soil impacts were the highest values from the June 1997 <br /> conformation borings. <br /> COMPOUND MILLIGRAMS/LITER WELL <br /> Benzene Water 0.044 UCL <br /> Benzene Soil 0.005 Detection limit <br /> Ethylbenzene Water 0.31 UCL <br /> Ethylbenzene Soil 0.18 Highest value SB5-65' <br /> TPHg water represented in 10 UCL <br /> the RSCA by Hexane . <br /> TPHg soil represented in 87 Highest value SB6-50' <br /> the RBCA by Hexane . <br /> MTBE Water 0.081 UCL <br /> MTBE Soil 0.005 Detection limit <br /> Toluene Water 0.49 UCL <br /> Toluene Soil 0.005 Detection limit <br /> Xylenes Water 2.2 UCL <br /> Xylenes Soil 7.7 SB7-50 <br /> At the concentrations currently found at this site, the risk of most importance is the chronic or long- <br /> term risk. Two types of chronic risk have to be assessed: cancer risk and non-cancer chronic <br /> exposure risk. <br /> These two types of risk are treated differently because of the way they effect people. Carcinogens <br /> are modeled as if any amount of the compound will produce some possibility of causing cancer. <br /> Non carcinogens will not cause health effects until they reach a threshold value at which <br /> concentration they may have some adverse effect on the population. Below the threshold value, a <br /> high-risk compound may even have a beneficial effect, e.g., vitamin A and sodium chloride (table <br /> salt). <br /> Because of these different effect models, the risk is calculated differently. The cancer risk is <br /> calculated as a probability of causing cancer using a slope factor (SF). The SF expresses the <br /> probability of cancer from the intake of 1 mg of compound per kg of body weight over a 70-year <br /> lifetime. <br /> The non-cancer risk is calculated by comparing the chance of exceeding the threshold limit of the <br /> compound. In order to insure that no sensitive person will be effected by the chemical, the <br /> Reference Dose (Rfd) that is used to calculate the risk of exposure is given an uncertainty factor of <br /> 10 to 1000 times less than the No-Observed-Adverse-Effect-Level (NOAEL). The NOAEL is the <br /> concentration at which no adverse effect was found in human and/or animal studies. The non-cancer <br /> 13 R603 Update#52/CLOSURE RV 7198 <br />