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PUBLIC HEALTH ASSESSMENT

CLARKE ROAD MUNICIPAL SOLID WASTE LANDFILL
WAYNESBORO, BURKE COUNTY, GEORGIA


TABLES

TABLE 1. MAXIMUM CONTAMINANT CONCENTRATIONS DETECTED IN RESIDENTIAL PRIVATE WELL

Contaminant (ppb) MCL MDL ATSDR CV PW-R
Methylene Chloride 5 2 5 (CREG) 7.5
Dichlorodifluoromethane - 2 2000 (RMEG) 9
Trichlorofluoromethane - 2 3000 (RMEG) 5
cis-1,2-Dichloroethene 70 2 3000 (EMEG) 3
Tetrachloroethene 5 2 0.7 (CREG) 7
Trichloroethene 5 2 3 (CREG) 3

MCL : Maximum Contaminant Level
ATSDR CV: Comparison Value
CREG: Cancer Risk Evaluation Guide for 1x10-6 excess cancer risk
MDL: Method Detection Limit
PW-R: Residential Private Well
RMEG: Reference Dose Media Evaluation Guide


TABLE 2 - COMPLETED ENVIRONMENTAL EXPOSURE PATHWAYS

Pathway Name: Source Medium Exposure
Point
Exposure Route Receptor Population Time of Exposure Exposure Activities Estimated Number Exposed Chemicals
Clark Road MSWL Drinking Water MSWL or other GW Single private well Ingestion Residents of home with contaminated water Past, Present Ingestion of well water 4 methylene chloride, tetrachloroethene
* The approximate number of exposed individuals is the estimate of persons who reside in the home that sampling indicates water may have been contaminated.


TABLE 3 - POTENTIAL ENVIRONMENTAL EXPOSURE PATHWAYS

Pathway Name: Source Medium Exposure
Point
Exposure Route Receptor Population Time of Exposure Exposure Activities Estimated Number Exposed Chemicals
Clark Road MSWL Drinking Water MSWL or other GW Private wells Ingestion Residents of homes with contaminated water Future Ingestion of well water Unknown methylene chloride, tetrachloroethene
* Assuming that all of the residences will be impacted by contaminated groundwater in the future, there would be approximately 21 residents exposed.


TABLE 4. EXPOSURE AND DEMOGRAPHIC STRUCTURE FILE
Total Population Estimates Table
DOCUMENT NAME__Clark Road MSWL Waynesboro, Burke County, Georgia_____
SEGMENT NAME (If applicable)____________________
DOCUMENT DATE_07/01/98_

Pathway Name Unknown Estimated Pop. in Pathway Range Minimum Range Maximum
a. Pot. Pathways On-site   0    
b. Pot.
Pathways Off-site
exact number and source 21 15 28
c. Total Pot. On and Off-site   21 15 28
d. Compl. Pathways On-site   0    
e. Compl. Pathways Off-site   4 2 4
f. Total Compl. On and Off-site   4 2 4
g. Pot. and Compl. Pathways On-site   0    
h. Pot. and Compl. Pathways Off-site   25 17 32
I. Total Pot. and Compl. On and Off-site   25 17 32

These population estimates were determined by a resident head count among the seven residences along the southern border of the site.


TABLE 5 - CALCULATION OF EXPOSURE DOSE FROM INGESTION OF CONTAMINATED GROUNDWATER

Maximum Contaminant Level Level in parts per million (ppm) Estimated Adult Exposure Doses in mg/kg/day* Estimated Child Exposure Doses in mg/kg/day* Health Guideline (MRL) in mg/kg/day* Source of Guideline Cancer Risk
methylene chloride 0.0075 0.000214 0.00075 0.2 MRL2 4 in 10,000,000
tetrachloroethene 0.007 0.0002 0.0007 0.05 MRL 3 in 1,000,000
* See Appendix A for cancer risk and MRL explanation.


APPENDIX

Appendix A - Calculation of Cancer Risk and MRL

Calculation of Risk of Carcinogenic Effects

Carcinogenic risks from the ingestion of groundwater were calculated using the following procedure. The adult exposure doses for ingestion of groundwater was calculated and multiplied by the EPA's Cancer Slope Factor (CSF) for that chemical (8). This result was then modified because it was assumed that maximum exposure length was 70 years. (Table 5).

The actual risk of cancer is probably lower than the calculated number. The method used to calculate EPA's Cancer Slope Factor assumes that high dose animal data can be used to estimate the risk for low dose exposures in humans (9). The method also assumes that there is no safe level for exposure (10). There is little experimental evidence to confirm or refute those two assumptions. Lastly, the method computes the 95% upper bound for the risk, rather than the average risk, which results in there being a very good chance that the risk is actually lower, perhaps several orders of magnitude (11). One order of magnitude is 10 times greater or lower than the original number, while two orders of magnitude are 100 times, and three orders 1,000 times.

Calculation of MRL (Health Guidelines)

Where sufficient toxicologic information is available, ATSDR has derived minimal risk levels (MRLs) (12) for inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic). An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure. MRLs are based on noncancer health effects only and are not based on a consideration of cancer effects. These MRLs are not meant to support regulatory action: but to acquaint health professionals with exposure levels at which adverse health effects are not expected to occur in humans. They should help physicians and public health officials determine the safety of a community living near a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. MRLs are based largely on toxicological studies in animals and on reports of human occupational exposure.



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