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Appendix 1 - Figure 1, 2 and 3

List of Figures

Figure 1 - Site Map for the Proposed Potter Company National Priorities List Site, Wesson, Copiah County, Mississippi

Figure 2 - The Estimated Extent of Groundwater Contamination in the Deeper Groundwater Zones at the Proposed Potter Company National Priorities List Site, Wesson, Copiah County, Mississippi

Figure 3 - Location of the Existing Municipal Drinking Water Wells Near the Proposed Potter Company National Priorities List Site, Wesson, Copiah County, Mississippi

Figure 1. Site Map for the Proposed Potter
Company National Priorities List Site

Figure 2. The Estimated Extent of Groundwater Contamination
in the Deeper Groundwater Zones at the Proposed Potter Company
National Priorities List Site

Figure 3. Location of the Existing Municipal Drinking Water
Wells Near the Proposed Potter Company National Priorities
List Site

Appendix 2 - Health Comparison Values

Health comparison values for ATSDR public health assessments are contaminant concentrations that are found in specific media (air, soil, and water) and that are used to select contaminants for further evaluation. The values provide guidelines that are used to estimate a dose at which health effects might be observed. Health comparison values used in the Environmental Contamination and Other Hazards and the Public Health Implications sections of this public health assessment are listed and described below.

Remedial Media Evaluation Guides (RMEGs) are estimated contaminant concentrations in media where there is no chance for noncarcinogenic health effects to occur. The RMEG is derived from U.S. Environmental Protection Agency's (EPA) reference dose.

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10E-6) persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors.

Lifetime Health Advisory for drinking water (LTHA) is developed by the U.S. Environmental Protection Agency. The LTHA is a lifetime exposure level specific for drinking water (assuming 20 percent of an individuals exposure comes from drinking water) at which adverse, noncarcinogenic health effects would not be expected to occur.

Appendix 3 - Calculation of Estimated Exposure Doses

Calculation of Exposure Dose from Ingestion of Drinking Water

The exposure doses for ingestion of drinking water were calculated in the following manner. The maximum concentration for a contaminant was multiplied by the water ingestion rate for adults, 2 liters/day; or children, 1 liter/day. This product was divided by the average weight for an adult, 70 kg (154 pounds) or for a child, 10 kg (22 pounds). A qualitative summary of these results can be found in Table 6 on page 19.

Calculation of Risk of Carcinogenic Effects

Carcinogenic risk from the ingestion of drinking water were calculated through the following. The exposure doses for ingestion of drinking water calculated as described previously, were multiplied by the EPA's Cancer Slope Factor for the contaminants of concern (17). The result represents the maximum risk for cancer after 70 years of exposure to the maximum concentration of the contaminant. Cancer slope factors were available for 1,1-dichloroethylene and trichloroethylene (TCE).

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 (27). The method also assumes that there is no safe level for exposure (28). There is little experimental evidence to confirm or refute those two assumptions. Lastly, the method computes the 95% upper bound for the risk, rather the average risk, which results in there being a very good chance that the risk is actually lower, perhaps several orders of magnitude (29).

Appendix 4 - Response to Public Comments


The Potter Company Public Health Assessment was available for public review and comment from August 31, 1994 through September 29, 1994. The Public Comment Period was announced in the Brookhaven Daily Leader. Copies of the public health assessment were made available for review at the Copiah-Lincoln Community College Library, and the Wesson Town Hall. In addition, the public health assessment was sent to seven persons or organizations. Comments were received from First Environment, the environmental consultant to Potter Company.

Comments and responses are summarized below. The comment letter can be requested from ATSDR through the Freedom of Information Act.

COMMENT: ATSDR estimates that the residents of Wesson and other humans were exposed to trichloroethylene ('TCE") in the Wesson municipal water supply for up to 18 years. Based on the construction and start-up date of the Wesson water supply treatment plant, the maximum potential exposure would have been limited to 15 years. The Wesson water supply treatment plant was installed and operational in 1974. Even though Wesson Well 1 was installed in 1971, no water was pumped from for consumptive use until the water supply treatment plant was constructed in 1974.

First Environment had utilized a United States Environmental Protection Agency (EPA) recognized model (RWH/RWHE [Random Walk}) to estimate the time at which the water supply first showed the presence of TCE. Based on the results of this modelling, we submit that the Health Assessment's discussion of "worst case" exposure duration be revised to reflect an exposure period of 11 to 14 years. The time of exposure listed in Table 4 should be similarly revised.

RESPONSE: Thanks for the information on when use of the Wesson City wells began. The public health assessment has been revised accordingly.

ATSDR does not accept your suggestion that an exposure period of 11 to 14 years be used. Given the inherit uncertainty in the RWH/RWHE model 11 to 15 years of exposure can not be distinguished statistically from 11 to 14 years. Therefore, ATSDR will use 15 years for exposure until we are able to conduct the groundwater flow modelling promised in the public health action plan on page 24.

COMMENT: We suggest that the fourth full paragraph on page 3 of the Health Assessment starting with the phrase "By the end of 1990" be revised to reflect that the groundwater Remediation Action Plan was approved by the Mississippi Bureau of Pollution Control on September 30, 1991. In addition, it should be indicated that, since the State is the site-lead, EPA will not take any further action in connection with the approval of the groundwater remedial plan.

The remediation system should be operational by the first quarter of 1995. The text in item 2 on page 16 of the Health Assessment that discussed groundwater control should be revised to reflect this.

RESPONSE: These two paragraphs have been revised per the information provided.

COMMENT: Appendix 1, Figure 3 depicts the approximate location of the leading edge of the groundwater contamination in relation to the four presently operating potable water supply wells identified as LRW1, LRW2, WW3, and WW4. This figure should be modified to further indicate that the estimated time for the leading edge of the plume to reach each of these wells is 22, 28, 41, and 38 years, respectively.

RESPONSE: Because there are no monitoring or specific geological data for the area around these four water supply wells, ATSDR does not consider it possible to make valid estimates of the travel time of contaminants to these wells.

COMMENT: ATSDR recommends analysis for PCBs in monitoring wells where contaminant levels are the highest. We submit that this action is unnecessary. At the initial stages of the investigation in 1987 and 1988, groundwater samples at locations of highest solvent concentrations were analyzed for PCBs. The results were below the detection limit of 0.05 ppb. Migration of PCBs in groundwater is much slower than solvent movement due to the fact that PCBs strongly adsorb to soil particles. In order for PCBs to contaminate groundwater, PCBs would have had to migrate vertically through a soil column of approximately 50 feet, then across the top of a clay layer located below the Site. The estimated minimal distance of linear travel along the top of the clay layer is 200 feet. It is very unlikely that PCBs in measurable quantities would remain available for dissolution in groundwater after traveling these distances. We submit that the recommendation to analyze PCBs in groundwater is unwarranted and should be removed from the Health Assessment.

RESPONSE: ATSDR stands by its recommendation. It is the prudent public health action. As stated in the public health assessment, the PCBs would likely migrate at a speed approaching that for TCE and other solvents because the PCBs readily dissolve in those solvents. The arguments above assume that the solvents had no influence on the movement of the PCBs. Analysis of the samples from the monitoring wells that will be taken as part of the remediation action for PCBs would be an easy and inexpensive way to demonstrate which hypothesis is correct.

COMMENT: We recommend that the possible health consequences discussion in the Public Health Implications section be modified on page 20 to indicate that there are additional causes of non-carcinogenic health effects to those discussed on pages 18 and 20. Amongst these causes would be other environmental conditions and genetic factors unrelated to TCE. Additional factors would include lifestyle characteristics (diet, alcohol, etc.), and occupational and environmental exposure to chemicals other than TCE.

RESPONSE: Such a discussion is appropriate when discussing whether a particular symptom or health effect can be due to a specific chemical. However, in this part of the public health assessment, the purpose is to identify the possible health consequences from a specific exposure. Including other possible causes for a symptom or health effect would be confusing.

COMMENT: The third paragraph under Site Description and History on page 2 erroneously states that Potter Company was purchased by Varian Associates, Inc. in 1986. In fact, Varian Associates, Inc. sold Potter Company at this time.

RESPONSE: Thanks for bringing this to our attention. The appropriate revision has been made.

COMMENT: The first full sentence on page 3 should be revised to indicate that PCB-contaminated soils were disposed in permitted hazardous and solid waste landfills.

RESPONSE: This requested change has been made.

COMMENT: The Health Assessment states, on page 5 in the introductory paragraph under the Environmental Contamination and Other Hazards discussion, that Appendix 2 contains a list of comparison values used in the Public Health Assessment. The copy of the Health Assessment we received does not contain a list of these values. Moreover, the discussion of the health comparison values is limited and does not provide us sufficient detail to enable us (or the public) to understand how the levels were determined.

RESPONSE: The comparison values used for each contaminant are listed on Tables 1 - 3. The introductory paragraph of the Environmental Contaminants and Other Hazards section has been revised to indicate this. For additional information on how comparison values are derived please see the ATSDR Public Health Assessment Guidance Manual.

COMMENT: On page 14 of the Health Assessment, the exposed population is approximated to be 2,313, consisting of the City of Wesson population of 1,313 and approximately 1,000 students at the Copiah-Lincoln Community College. It is likely that a significant percentage of the Community College students are drawn from the local area, and that there is an overlap between the 1980 U.S. Census and the estimated student body of the Community College. It is therefore likely that the estimated exposed population is less than 2,313. We recommend modification of this discussion to reflect this.

RESPONSE: The estimated exposed population has been changed to 2300 to indicate less precision. However, we disagree with the assertion that Wesson residents make up a significant portion of the student body. The number of college-age individuals in a community of 1,313 can not large enough to be a factor. It is doubtful all of these individuals go to Copiah-Lincoln.

COMMENT: On page 5 of the Health Assessment, ATSDR states that mixtures of PCB and TCA were discharged. This could not have occurred because PCB usage at the Site ended in 1968, prior to the use of TCA commencing in 1975.

RESPONSE: This suggested revision has been made.

COMMENT: Tables 1, 2 and 3 identify contaminants detected above health comparison values. In various instances, values for specific contaminants are listed as less than a numerical value, thereby implying that this contaminant was detected at a specific value. In fact, in many instances, the level of the contaminant was below the detection limit. Thus, it is misleading to use the sign "<" to imply a specific, numeric value was determined and to designate these values as being above specific health comparison values. Moreover, various entries are shaded in these tables. What is the significance of the shading? In addition, what does "RMEG" in the Comparison Value Source columns mean? Finally, various federal drinking water MCLs are higher than the ingestion comparison values listed in the tables. We submit that MCLs should be substituted for lower comparison values used in these tables inasmuch as the basis for establishing drinking water MCLs is protection of human health.

RESPONSE: Nondetect (ND) has been substituted for the < values in Tables 1 - 3. The shading identifies those contaminant levels which were above a comparison value; an explanation of this has been added to Tables 1 - 3. An explanation of RMEG has been added to Appendix 2. It is inappropriate for ATSDR to use MCLs in most circumstances. Many MCLs are adjusted upwards because of limitations in treatment technology. Thus MCLs are usually not health-based. ATSDR believes strongly that health-based guidelines should be used and therefore derives its own values for many chemicals.

COMMENT: In the first line on page 7 under discussion of TCE and TCA, the phrase "dumped unto" should be replaced with the phrase "deposited on the ground".

RESPONSE: This suggested revision has been made.

COMMENT: In the second full paragraph on page 11, a reference to BPC's preliminary assessment of the Site dated December 29, 1987 is listed as the reference for the identification of a residential drinking water well located northwest of the site. We have reviewed BPC's preliminary assessment, and cannot find any reference to this residential well. This should be clarified.

RESPONSE: This residential well is mentioned on page 3 of the Preliminary Assessment. We will send the commenter a copy of this page.

COMMENT: The last full sentence on page 12 should be clarified to indicate that Wesson Wells 1 and 2 are no longer in use.

RESPONSE: This is clearly stated at the end of the paragraph that this sentence is in and thus does not need to be repeated here.

COMMENT: The discussion of worker exposure at the bottom of page 16 should be corrected to state that waste fluids came in contact with the ground; these materials were not dumped unto the groundwater.

RESPONSE: Thanks for catching this. Groundwater was changed to ground.

COMMENT: We have attempted to reproduce the Table 6 exposure doses by using the methodology in Appendix 3, but have been unable to do so. We suggest that this Appendix be expanded to more fully describe the methodology. In addition, the discussion of the drinking water ingestion exposure calculation states that a qualitative summary of the results can be found in the "table above". There is no table in Appendix 3.

RESPONSE: There are no exposure doses listed in Table 6, only health guidelines. The reference to a table in Appendix 3 has been deleted.

COMMENT: The introduction in the Toxicological Evaluation discussion on page 18 references an Appendix 4. This appendix was not included in the Health Assessment we received.

RESPONSE: The reference to Appendix 4 was a typographic error. It should have been Appendix 3. The public health assessment has been revised to correct this.

COMMENT: First Environment, Inc. has been incorrectly referred to as "First Environmental, Inc. in the references for the Health Assessment.

RESPONSE: The public health assessment has been revised accordingly.

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