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Figure 1
Figure 1. Site Location Map

Figure 2
Figure 2. Local Map

Figure 3
Figure 3. Site Map

Figure 4
Figure 4. Sampling Locations

Figure 5
Figure 5. Location of Two Ground Water Plumes

Figure 6
Figure 6. Soil Gas VOC Isoconcentration Map with Select VOC Soil Sample Results


ATSDR released a draft of this public health assessment for public comment on May 22, 1995. Thepublic comment period ended on June 30, 1995. ATSDR received comments on the draft publichealth assessment from Sherwood Medical Company, in a letter dated June 29, 1995, and from theNebraska Department of Environmental Quality, in a letter dated June 28, 1995. The commentsreceived and ATSDR's responses are detailed below.

Comments from Sherwood Medical Co.
General Comments
1a-1."The Assessment of Potential Health Implications for Park Mobile Home Court Should UseOnly Properly Controlled Data from Before the Installation of the Alternative Water Supply Although the Draft Assessment notes that EPA installed a carbon water treatment systemthere by February 1988,...the Draft Assessment uses sampling data from the PMHC wellsfrom after February 1988 to calculate potential health implications...the use of post-February1988 sampling results misleadingly exaggerates the health implications, if any, from thatexposure pathway. Consequently, Table 10a. and the calculation of potential healthimplications should be revised to include only the sampling data from February 1988, beforeEPA installed the carbon treatment system at PMHC."

Response: ATSDR agrees that some sampling data from the PMHC wells after February 1988 donot represent the actual contaminant levels to which PMHC residents were exposed since some ofthe data do not take into account contaminant removal by the EPA temporary carbon treatmentsystem. Therefore, ATSDR has modified Table 10a to include only the following sampling data: 1)pre-February 1988 data from samples collected from the PMHC wells themselves (i.e., untreatedwater samples), and 2) post-February 1988 data from samples collected after treatment by thecarbon treatment system. These sampling data are more representative of the levels of contaminantsto which PMHC residents were exposed via their drinking water.

1a-2."...[T]he Nebraska Department of Health (NDOH) sampling data from the PMHC wells inOctober and November 1987 should not be used in Table 10a. and the potential healthimplications analysis because they were not obtained pursuant to level III to V QualityAssurance/Quality Control (QA/QC) protocols for health assessments as required by theATSDR guidance 'Environmental Data Needed for Public Health Assessments,'...Similarlythe [ATSDR Public Health Assessment Guidance] Manual explains that only level III to Vdata may be used for risk assessment,...and states that '[d]ata evaluated and used to makehealth assessment determinations for hazardous waste sites must meet QA/QC criteria.' TheFebruary 1988 analyses from the PMHC wells are the only Level III data available for theperiod prior to the installation of EPA's carbon treatment system, and thus, they are the onlydata that should be used to calculate whether there were any health implications..."

Response: ATSDR believes that the 1987 NDOH sampling data are appropriate for inclusion inTable 10a and in the analysis of potential public health implications. First, ATSDR disagrees thatthe NDOH data were not obtained according to level III to V QA/QC criteria. ATSDR believes thatthe NDOH data were at least analytical level III which include non-CLP analyses performed in anoff-site laboratory. Second, even if the NDOH data are below level III, that is, level I or II, the datacould still be included in the public health assessment. Although the ATSDR Public HealthAssessment Guidance Manual (the manual) indicates that data used in the public health assessmentshould meet QA/QC criteria, it does not dictate the specific QA/QC criteria and does not require thatthe data be of level III or higher. In addition, the manual allows for the use of data which may notmeet appropriate QA/QC criteria as long as the limitations associated with using such data areindicated in the public health assessment. Furthermore, both ATSDR's health assessment guidanceand EPA's risk assessment guidance support the use of historical data, such as the 1987 NDOHsampling data, to supplement more current data, such as the EPA RI data. In fact, p. 28 of the EPAdocument "Guidance for Data Useability for Risk Assessment (Part A)," April 1992, states"...historical data of lower quality may be used if the concentrations are confirmed by subsequent RIanalyses." In the case of the PMHC wells, the VOC concentrations reported by NDOH in 1987 wereconfirmed by later EPA RI samples. For these reasons, ATSDR believes that the 1987 NDOH dataare appropriate for use in evaluating potential public health implications associated with exposure toVOCs in the PMHC wells.

1b."The Draft Assessment Overestimates the Time of Exposure at the PMHC The DraftAssessment estimates that contaminants reached the PMHC wells in 1966, and thatconsequently, there could have been a maximum exposure to contaminants there of 23 years. First, it appears that it is based on an inaccurate estimate of the transport rate of contaminantsof 450 feet per year...The RI calculated that the retardation factor for PCE was 9...The RIcalculated the average groundwater flow rate at 900 feet per year, so the average transportrate for PCE would be 100 feet per year...Similar calculations should be performed in thefinal Assessment to accurately calculate the potential maximum time of exposure at thePMHC wells. Page 36 of the Draft Assessment and the public health implications analysisshould be revised to take into account the shorter period for exposure.

In addition, the 23-year estimate was based on exposure continuing until Sherwood providedthe alternate water supply in September, 1989...The time period for drinking water exposureshould continue only until November 1987, when EPA started supplying bottled water to thePMHC. In addition, EPA installed its carbon treatment system at the PMHC in February1988..."

Response: ATSDR has reevaluated the maximum exposure period for the PMHC wells based oninformation in the Final RI Report (May 1993). According to the Final RI, the average horizontalgroundwater flow velocity at the site is about 800 feet per year and the retardation factor for PCE insite groundwater is about 1.5. Using these two values results in a PCE transport velocity of 533 feetper year, which translates to a travel time of 2.7 years for PCE to reach the PMHC wells. Assumingthat VOCs were released at the Sherwood Medical UST area as early as 1963, they could havemigrated to the mobile home park wells by late 1965 or early 1966. This means that residents of thePMHC could have been exposed to site-related VOCs from late 1966, when the mobile home parkwas first occupied, until early 1988, when EPA installed a temporary carbon treatment system on thePMHC wells. As such, the maximum exposure period for VOCs in the PMHC wells is about 21years, which is fairly close to the estimate of 23 years in the draft public health assessment. ATSDRhas revised the maximum exposure period in the final health assessment and has factored the revisedexposure period into the public health implications evaluation.

Note: ATSDR does not agree that the exposure period ended in November 1988 when EPA begansupplying bottled drinking water to the PMHC residents. Although most drinking water exposuresto VOCs likely ended at that time, exposure via inhalation of VOCs evaporating from the PMHCwell water during indoor water uses (such as bathing and showering) probably continued untilFebruary 1988 when the EPA carbon treatment system was installed.

1c."The Conclusion that Past Exposure at PMHC Posed a Public Health Hazard is Inaccurate The Draft Assessment's conclusion that past exposure to PMHC water posed a public healthhazard is inaccurate...First,..the Draft Assessment's estimate of past risk at PMHC isoverstated...due to the use of sampling data from the period after EPA installed the carbontreatment system at PMHC, the use of inadequately QA/QC'd data, and the overestimate ofthe maximum time of exposure. Second, the chloromethane and chloroform detected in thePMHC well water are not associated with the release at Sherwood,...and thus, should not beincluded in the conclusions regarding"

Response: ATSDR has reevaluated the public health implications of past exposures to VOCs in thePMHC wells in the final public health assessment to account for the revised contaminantconcentrations (resulting from exclusion of post-February 1988 untreated well water data) and theshorter calculated exposure period (21 vs. 23 years). The new evaluation shows, as did the originalevaluation of the draft assessment, that exposure to VOCs in the PMHC wells represented a pastpublic health hazard for PMHC residents.

ATSDR disagrees that the data used in the public health assessment were inappropriate because ofQA/QC inadequacies (see response to Comment 1a-2). ATSDR also disagrees that sampling datafor chloroform and chloromethane from the PMHC drinking water should not be used because thosetwo contaminants are not associated with the release from the Sherwood Medical plant.

It is ATSDR's policy to consider all contaminants present at levels of concern in evaluating a humanexposure pathway, even if such contaminants are unrelated to the site. This approach is consistentwith ATSDR's mission "to prevent exposure and adverse health effects...associated with exposure tohazardous substances..." ATSDR acknowledges that the presence of chloroform and chloromethanein samples of PMHC drinking water may have resulted from the PMHC's chlorination system (asSherwood Medical claims) because these two substances are common by-products of chlorination. However, because chloroform was found in solid and liquid wastes from the UST/septic tank and in3 site monitoring wells, and chloromethane was detected in at least one the plant's supply wells, it ispossible that their presence in the PMHC water samples was site-related. In either case, ATSDRbelieves that including the data for both chloroform and chloromethane in its analysis of the PMHCdrinking water exposure pathway was appropriate.

2a."The Sherwood Wells Should Be Eliminated as a Potential Exposure Pathway. ...Sherwoodhas always used carbon filtration, either at the wellhead, at the tap, or at the centralizedtreatment system, to treat its water. In addition, with the exception of one sample...samplesof that treated water have not detected contaminants...Consequently, the 'Worker DrinkingWater' pathway should be eliminated because exposure to contaminants via that pathway, ifany, was 'extremely unlikely'...In addition, the reference to Sherwood plant drinking wateras a potential source of exposure should be deleted from the Conclusions...for the reasonsexplained above."

Response: High levels of VOCs, such as 1,1-DCE, PCE, and 1,1,1-TCA, were detected inSherwood Medical industrial supply well #5 which, before September 1989, was used as a source ofdrinking water for plant employees. Although the water from the plant's supply wells was carbontreated at the wellhead or at the drinking water fountain, it is likely that some VOCs in the plant'swell water were not entirely removed by the plant's treatment units. Therefore, it is possible thatplant employees were exposed to some level of VOCs in their drinking water before September1989 when the plant quit using the most contaminated supply wells and installed a modern, high-capacity centralized carbon treatment system. Therefore, ATSDR believes that it is appropriate toinclude ingestion of in-plant drinking water as a past potential exposure pathway, even if the actuallevels of contaminants to which employees may have been exposed are not known. Bycharacterizing the drinking water pathway as a potential exposure pathway (rather than as acompleted pathway), ATSDR is indicating that such exposures could have occurred, not that theyabsolutely did occur. In addition, ATSDR does not believe that one negative sample from the plant'sdrinking water supply over a period of more than 20 years is sufficient evidence that VOCs werenever present in the plant's drinking water. For these reasons, ATSDR has retained in-plantdrinking water as a past potential human exposure pathway in the final public health assessment.

2b."Sherwood Lake Should Be Eliminated as a Potential Exposure Pathway...SherwoodLake...should be eliminated as a pathway for two reasons. First,...Sherwood has posted itsproperty, and no trespassers have ever been found in or around Sherwood Lake. Accordingto the manual, a point of exposure is present only where 'evidence exists that persons had orstill have access to the contaminated medium.'...Here, the evidence is that there has not beenany exposure to children or trespassers at Sherwood it should be eliminated as anexposure pathway.

In addition, a pathway should be eliminated when exposure is 'extremely unlikely.'...That isprecisely the case with Sherwood Lake, because of all the samples taken there, only thosefrom 1988 detected low levels of 1,1,1-TCA (31 UG/L and 1,1-DCA (8 UG/L)...Subsequenttesting did not detect volatile organic compounds in Sherwood Lake...Given that very lowconcentrations were detected only one time, Sherwood Lake should be eliminated as apotential pathway of exposure.

For both of these reasons, the Conclusion that Sherwood Lake is a potential exposurepathway should be deleted....In addition, the Recommendation regarding restricting access tothe Sherwood property...should reflect that Sherwood has restricted, and will continue torestrict, such access."

Response: ATSDR agrees that human exposure to VOCs in Sherwood Lake is "extremely unlikely"since 1) the site is posted, 2) no trespassers have ever been observed on or near the lake, and 3)VOCs are unlikely to be present in the lake's water or sediments. Therefore, ATSDR has changedthe designation of Sherwood Lake from a potential to an eliminated exposure pathway in the finalpublic health assessment. In addition, ATSDR has revised the recommendation regarding restrictingaccess to Sherwood Lake to reflect that the company has posted its property.

2c-1."In-Plant Areas Should be Eliminated as a Potential Exposure Pathway The DraftAssessment identifies 'in-plant areas where solvents are used and handled' as a potentialpathway...This should be eliminated as a potential pathway for two reasons. First, the scopeof an ATSDR health assessment is limited to releases of hazardous substances in theenvironment...Workplace exposures not related to an environmental release are not withinthe proper ambit of an ATSDR health assessment. Second, the Sherwood plant in Norfolkstopped using 1,1,1,-TCA in 1992, and has not used any chlorinated solvents since that time. For both of these reasons, the conclusion that Sherwood workers who handle chlorinatedsolvents are subject to exposure should be deleted."

Response: The purpose of ATSDR's public health assessments is " assist in determiningwhether actions...should be taken to reduce human exposure to hazardous substances from a facilityand whether additional information on human exposure and associated health risks is needed andshould be acquired.." (42 U.S.C. 9604(i)(6)(G)) and " assess any current or future impact onpublic health,...and identify...actions needed to evaluate and mitigate or prevent human healtheffects" (42 C.F.R. 90.2 definition of 'health assessment'). Therefore, ATSDR believes that it mustconsider all human exposures to hazardous substances at a site which may result in adverse healtheffects, including exposures by employees or site workers. This is consistent with ATSDR'smission "to prevent exposure and adverse human health effects...associated with exposure tohazardous substances..." ATSDR does not believe that it is precluded by the definitions of 'healthassessment' in 42 U.S.C. 9604(i)(6)(G) and 42 C.F.R. 90.2 from evaluating employee exposuresassociated with hazardous substances present in their workplace. This is especially true when siteworkers or employees are subject to similar substances from multiple exposure pathways. Byignoring workplace exposures, ATSDR could significantly underestimate a person's total exposureto one or more substances and the potential health risks pose by such exposure. In addition, ATSDRmust consider workplace exposures to hazardous substances to determine if actions are needed toreduce such exposures to protect public health.

At the Sherwood Medical site, some workers who used chlorinated solvents in their on-the-jobactivities were likely exposed to VOCs. This is supported by reports from a former plant employeewho described adverse short-term health effects from exposure to chlorinated solvent fumes whileworking with such solvents. For these reasons, and the reasons discussed previously, ATSDRbelieves that it is appropriate to include workplace exposure to VOCs as a potential exposurepathway in the public health assessment. However, ATSDR has noted in the pathway discussionthat chlorinated solvents are no longer used at the plant, and, therefore, employee exposures toVOCs are no longer occurring. In addition, ATSDR has changed the exposure pathway time-framefrom "past/present/future" to "past" only in the final public health assessment.

Note: Since the health concerns raised by the former plant worker involved on-the-job exposuresand since chlorinated solvents were still being used by the plant at the time, ATSDR concluded thatthe worker's health concerns should be referred to the state agencies responsible for safeguardingworker health and safety.

2c-2."[A]n analysis of potential physical hazards unrelated to the release of hazardous substancesis beyond the scope of a Health Assessment. Consequently, the reference to 'potentialphysical hazards such as Sherwood Lake and broken glass near the solid waste disposalbins,'...should be eliminated from the Assessment. Moreover, since Sherwood has posted itsproperty and trespassers have not been detected at Sherwood Lake, it is inaccurate tocharacterize Sherwood Lake or the disposal bins as a potential physical hazard."

Response: ATSDR disagrees that its public health assessments cannot include analysis of a site'sphysical hazards. As stated in Sec. 3.1.1 of the ATSDR Public Health Assessment GuidanceManual, "[a]ll aspects of a site's health implications are covered in a health assessment," and"[p]hysical hazards at a site may constitute a public health concern." In addition, as indicated in Sec.9.4.4 of the manual, "[i]n some instances, hazards other than those posed by chemical contaminationmay be present, including physical hazards (e.g., holes, lagoons, open steel tanks, abandonedmaterials, and equipment), special hazards such as the threat of fire or explosion, or hazards endemicto the site area." Therefore, the health assessment "should contain a brief description of suchhazards and the potential health threat they represent." Furthermore, the following language from42 U.S.C., Sec. 9604(i)(6)(F) implies that public health assessment may consider health threatsposed by a site's physical hazards: "[T]he term 'health assessments' shall include preliminaryassessments of the potential risk to human health posed by individual sites and facilities..."

ATSDR believes that Sherwood Lake and broken glass near the plant's solid waste disposal bins dorepresent minor physical hazards for children who live in houses or mobile homes near the plant. However, in accordance with the company's comments, ATSDR has added language to the Physicaland Other Hazards section of the public health assessment indicating that the plant property is postedand that no children have ever been observed trespassing on the site property.

3."The downgradient industrial/commercial wells are identified as a completed past, present,and future exposure pathway...The Madison County Weed Control Shop, the MadisonCounty Maintenance Building, the Civil Defense Building, and the Medelmans and Ohlrichproperties are being provided with alternate water supplies. Accordingly, these wells shouldbe eliminated as a completed present and future exposure pathway."

Response: ATSDR agrees that the five downgradient industrial/commercial wells in question nolonger represent a current or future pathway because these wells are no longer used as a drinkingwater source. Therefore, the pathway exposure time-frame has been changed from"past/present/future" to "past" only in the final public health assessment.

Technical Comments

1."...Bottled drinking water has been provided to two of the commercial/industrial well owners(Medelman and Ohlrich) since 1993 and to the remaining three commercial/industrial wellsowners (County Weed, County Maintenance, and Emergency Management) since early1995. Therefore, the downgradient commercial/industrial well owners and employees are nolonger exposed to drinking water with low concentrations of VOCs...Attached is a revisedversion Table 10b with supporting DQO Level III analytical data on downgradientcommercial well water quality..."

Response: ATSDR has revised the public health assessment to reflect this information and haschanged the exposure pathway time-frame to "past" only (see response to General Comment 3.) Inaddition, Table 10b has been revised to include the most recent (i.e., 12/94) sampling data submitted by the company.

2."Sherwood Medical has historically carbon treated its well water either at the well head,drinking fountain point of use, or at a centralized facility treatment system. Prior to 1979,well. Prior to 1979, well water was treated by several 3,000-pound carbon units on eachwell. Beginning in 1979, well water was treated with individual canisters on each of thefacility's drinking water fountains...In September 1989, two, 10,000-pound carbon unitswere installed to centrally process all of the facility's well water prior to distribution withinthe plant and to the PMHC residents.

The Nebraska Department of Health collected a sample on December 1, 1987 from theSherwood Medical water distribution system for DQO Level II VOC analysis. Only oneVOC (1,1,1-TCA) was detected at a trace concentration of 1 ug/l in this sample. Theseresults help substantiate the fact that Sherwood's well water was carbon treated prior to theinstallation of the centralized large carbon treatment system in 1989..."

Response: ATSDR has revised the public health assessment to reflect this information.

3."Sherwood Lake surface water does not constitute a current or future potential exposurepathway...Prior to September 1989, Sherwood utilized untreated well water, which containedVOCs, for non-contact cooling water purposes. These non-contact cooling waters containinglow concentrations of VOCs were discharged to Sherwood Lake following use.

With the shutdown of Sherwood wells 4 and 5 in September 1989..., water discharged toSherwood Lake contains virtually no VOCs...Furthermore, Sherwood discontinued all use ofchlorinated solvents at the facility in December 1992. Seven Sherwood Lake 1991 RI watersamples contained no detectable concentrations of VOCs.

Additionally, there has never been any reported incident where non-plant related personnelhave come into contact with Sherwood Lake waters. Therefore, Sherwood Lake should notbe considered a current or future potential exposure pathway since two of the exposurepathway elements (contamination and receptors) are not documented to be present.

In consideration of the pre-September 1989 use of Sherwood well 5 for non-contact coolingwater and its past effect on Sherwood Lake water quality, Table 5 should be split into twotables (5a and 5b)."

Response: ATSDR has 1) revised the public health assessment to reflect the information regardingthe plant's discontinued use of VOC-contaminated cooling water and the resulting decrease in VOClevels in Sherwood Lake; 2) separated out the pre- and post-September 1989 sampling data in Table5 of the health assessment; and 3) eliminated Sherwood Lake as a potential human exposurepathway (see response to General Comment 2b).

4."Sherwood has never used trichloroethylene at their Norfolk facility...As a result, TCE wasnot detected in either the UST waste liquids, UST solids, or in site soil samples...Therefore,none of Sherwood's employees have been exposed on the job to TCE since TCE has notbeen used at the facility."

Response: ATSDR has revised the health assessment to reflect the fact that the plant never usedTCE and to indicate that the former plant employee who expressed health concerns about on-the-jobexposure to TCE may have actually been referring to 1,1,1-trichloroethane (TCA) (which was usedat the plant until 1992).

5."...Prior to September 1989, wastewater discharged to Sherwood Lake contained lowconcentrations of VOCs. Four wastewater discharges to Sherwood Lake were sampled in1988. The wastewater discharge with the highest concentration of VOCs only contained fourdetectable VOCs at low concentrations...

Following the September 1989 discontinued use of Sherwood well 5, wastewater dischargedto Sherwood Lake has contained trace to no detectable concentrations of VOCs. Fourwastewater discharges to Sherwood Lake were sampled in 1991. Two of the samples had nodetected VOCs, while the other two samples had a trace concentration (1 ug/l)...

As with Sherwood Lake water quality Table 5, the Table 1c for wastewater discharges toSherwood Lake should be split into two tables (1c and 1d)..."

Response: ATSDR has revised the public health assessment to reflect the information regarding theplant's discontinued use of VOC-contaminated cooling water and the resulting decrease in VOClevels in the plant's wastewater discharges to Sherwood Lake, and has separated out the pre- andpost-September 1989 sampling data in Table 1c of the health assessment.

6."Carbon tetrachloride has not been documented to be present in the site's groundwatercontaminant plume. The one carbon tetrachloride value cited in this table [Table 3a] isassociated with a water sample which failed QA/QC validation. A duplicate samplecollected from the same monitoring well on the same date which passed QA/QC validationhad no detected concentration of carbon tetrachloride."

Response: Carbon tetrachloride was detected in Sherwood Medical supply well #3 in 1990, in thePMHC main well in 1987, and in monitoring well #8a in 1991. This suggests that carbontetrachloride is present, at least to some extent, in site groundwater. The 1991 sample result wasassigned an "E" qualifier indicating that the concentration exceeded the calibration range of theGC/MS instrument for that analysis. The "E" qualifier does not mean that the data point is invalid,only that the value may be semi-quantitative. For these reasons, ATSDR is retaining theconcentration value for carbon tetrachloride in Table 3a of the health assessment.

7."Prior to September 1989, Sherwood Medical rotated operation of facility wells 3, 4, and 5 toprovide the facility's water needs. In September of 1989, Sherwood Medical discontinueduse of facility wells 4 and 5. Sherwood well 3 with well 6 as a backup has provided all ofthe facility's and PMHC water needs since September 1989.

Only one of the plant's four industrial supply wells, Sherwood well 5, has been impacted by"high levels" of VOC contamination. DQO Level III water quality information is availablefor each of Sherwood's facility wells. Some of the information contained in the Draft PublicHealth Assessment's Table 4 reflect samples which do not meet DQO Level III standards.

The best source of water quality information for Sherwood well 5 are seven water samplesthat were collected during a 72-hour RI pump test. The highest concentration of the threeprincipal VOC constituents detected during the pump test was 870 ug/l of 1,1,1-TCA, 600ug/l of 1,1-DCE, and 2,300 ug/l of PCE.

Attached is a new Table 4b with supporting DQO Level II analytical data on facilitygroundwater supply well water quality. In accordance with ATSDR Public HealthAssessment Guidance Manual dated March 1992, the revised Table 4b only incorporatesDQO Level III data."

Response: ATSDR has revised the health assessment to reflect the information regarding thehistorical use of the plant's water supply wells. In addition, ATSDR has modified Table 4b of thehealth assessment to include the sampling data submitted by the company for the plant's industrialsupply wells. However, ATSDR disagrees that only the data submitted by the company should beused in Table 4a. Rather, ATSDR believes that all data presented in Table 4b are valid and suitablefor use in this public health assessment. (See response to General Comment 1-c.)

8."...The PMHC well water was chlorinated at the pump house prior to distribution to PMHCresidents. The well's chlorination system had historical operational problems. The presenceof two trihalomethane compounds, chloroform and chlorodibromomethane, in PMHC wellwater is solely attributable to the PMHC's chlorination system and is not reflective of thewell's groundwater quality.

One DQO Level III water sample is available for the period of use of untreated PMHC wellwater. The key DQO Level III sample was collected on February 2, 1988. The analyticalresults for only this sample should be used for public health evaluation purposes..."

Response: ATSDR public health assessments consider all contaminants that may pose a threat topublic health, regardless of whether they are site-related. Since both chloroform andchlorodibromomethane were present above ATSDR's comparison values in the PMHC well water,they were properly identified as contaminants of concern. ATSDR acknowledges that the presenceof chloroform and chlorodibromomethane in the PMHC well water may have been due to thePMHC's chlorination system rather than the site's groundwater contamination and has revised thepublic health assessment to reflect this information.

ATSDR disagrees that only the February 2, 1988, sampling data should be used in Table 10a of thepublic health assessment. As discussed in response to General Comment 1a-2, ATSDR believes thatall data used in the public health assessment are valid and that the quality of the data is adequate forevaluating the site's public health implications. Furthermore, any QA/QC limitations associatedwith specific analytical data are indicated by appropriate data qualifiers in the health assessmentcontaminant tables. For these reasons, ATSDR has retained the sampling data obtained prior toFebruary 2, 1988, in Table 10a of the final public health assessment.

9."Industrial/commercial wells should not be considered as a completed pathway for thepresent or future."

Response: ATSDR agrees. See response to General Comment 3 and Technical Comment 1.

10a."Worker drinking water should be removed as a past potential exposure pathway."

Response: ATSDR disagrees. See response to General Comment 2a.

10b."Surface water should be removed as a present and future exposure pathway."

Response: See response to General Comment 2b and Technical Comment 3.

10c."Other private wells should be removed as a future exposure pathway."

Response: ATSDR disagrees. Five private wells downgradient of the plant are currently affected bysite contamination and are part of a completed human exposure pathway. However, several otherprivate water supply wells are near the plant, both upgradient and downgradient, which couldpotentially be affected by groundwater contaminants in the future. If any of these wells do becomecontaminated, human exposure to VOCs could occur. Therefore, ATSDR believes that "otherprivate wells" should be included as a potential future exposure pathway in the public healthassessment.

11."Plant employees of Sherwood Medical should not be considered as 'exposed' populations."

Response: Plant employees are identified as a potentially exposed population in the healthassessment since they were potentially exposed to site contamination.

12a."The average linear groundwater flow velocity determined during the RI was approximately900 feet per year (October 1991 Subsurface Exploration Memo, Page 4-9). The RI alsodetermined that the site conditions effectively yielded a contaminant retardation factor of 9for PCE due to such factors as adsorption and dispersion (October 1991 SubsurfaceExploration Memo, Page 7-8). Accordingly, the average linear PCE contaminant transportvelocity calculated for the site is approximately 100 feet per year."

Response: ATSDR disagrees with the PCE transport velocity calculated by Sherwood Medical. Seeresponse to General Comment 1b.

12b."Provision of bottled water to PMHC residents in November 1987 constitutes the end ofdrinking water exposure to untreated PMHC well water."

Response: See "Note" in response to General Comment 1b.

13."Employees who worked at the Madison County Weed Control and the Madison CountyMaintenance Building were exposed to low concentrations of PCE which slightly exceed theEPA MCL drinking water standard in their work place drinking water for a period of lessthan three years. PCE was not present above the laboratory detection limit of 1 ug/l whenthese wells were sampled and tested in December 1991. Both wells were resampled inDecember 1994 and were found to contain 7.1 and 8.5 ug/l of PCE. The MCL for PCE is 5ug/l. Bottled drinking water was provided to these two facilities in early 1995. These twowells have only recently been impacted by the Site's groundwater contaminant plume as itcontinues to migrate in a northeasterly, downgradient direction."

Response: ATSDR acknowledges that the exposure period for employees who used the MadisonCounty Weed Control and Madison County Maintenance Building wells may have been as short as 2to 3 years. However, since historical sampling data for these wells is limited, the actual exposureperiod cannot be determined with a high degree of certainty. In any case, since ATSDR's evaluation indicates that exposure to VOCs at the levels found in those two wells did notpose a health threat, the uncertainty associated with the length of the exposure period is not crucial.

14a."The total historic time of the PMHC residents should be reduced for the reasons set forth in Comment 14."

Response: See response to General Comment 1b and Technical Comment 12.

14b."Chloroform and chloromethane should not be considered as part of the public healthassessment since these trihalomethanes are the product of the PMHC well's past poorchlorination practices and are not related to the site's release of VOC groundwatercontaminants."

Response: See response to General Comment 1c and Technical Comment 8.

14c."Carbon tetrachloride, vinyl chloride, 1,1,2,2-PCA, and 1,2-DCA should not be consideredas part of the public health assessment since these VOC constituents were not detected in anyDQO Level III water samples that were collected while untreated well water was still in use."

Response: Carbon tetrachloride, vinyl chloride, and 1,2-DCA were detected in the PMHC wellsbefore the temporary carbon treatment system was installed in February 1988 by EPA to treat thewell water. The sampling data for these contaminants are valid and suitable for use in the publichealth assessment. ATSDR could not verify, however, that 1,1,2,2-PCA was detected in the PMHCwells before the carbon treatment system was in use, and, therefore, has deleted 1,1,2,2-PCA from Table 10a of the final public health assessment.

14d."Corrected concentration values of the remaining VOCs (1,1-DCE, PCE, TCE, 1,1,1-TCA,and 1,1-DCA) should be used for public health assessment purposes."

Response: As discussed in response to General Comment 1a-1, ATSDR has revised Table 10a of thepublic health assessment to include only those VOC sampling data that represent potential drinkingwater exposures for PMHC residents. The resulting "corrected" VOC concentrations are presentedin Table 10a of the final public health assessment.

15."The total noncancer and cancer effects of past exposure to untreated PMHC well water needto be re-evaluated on the sole basis of DQO Level III data."

Response: ATSDR has reevaluated the public health implications of past exposure to VOCs in thePMHC's drinking water based on the revised contaminant concentrations from Table 10a of the final public health assessment. (See response to General Comment 1c.)

16."The list of VOCs present in PMHC well water should correspond to DQO Level III data."

Response: See response to General Comment 1a-2 and Technical Comments 8 and 14d.

Comments from the Nebraska Department of Environmental Quality

General Comment

1."The document states ATSDR's Health Activities Recommendation Panel has evaluated thedata and information in the assessment and determined no other follow-up health activitiesare indicated at this time for three reasons. One of the reasons was many persons who wereexposed to site contaminants over the years, primarily residents of Park Mobil Home Court,have likely moved away, and therefore cannot be located or contacted.

We suggest this is not a viable reason for the panel's determination. We believe many of thepersons who were exposed that have moved away could be located or contacted. Also, webelieve there may be a number of persons who were exposed to site contaminants over theyears and have not moved away and may be contacted."

Response: Since exposure of PMHC residents to VOCs from the PMHC wells ended more than 9years ago, and since turnover at the PMHC in the past was fairly high, it is likely that many of theresidents who were exposed are no longer living in the PMHC. In addition, many of the currentPMHC residents probably did not live at the PMHC during the 1970s and 1980s when the exposuresto VOCS in the PMHC drinking water supply occurred. Therefore, ATSDR believes it would bedifficult to conduct follow-up health activities with the majority of persons who were significantlyexposed to VOCs from the PMHC wells. More importantly, few persons have expressed any healthconcerns related to the site, and ATSDR is not aware of any adverse health effects that have resultedfrom past exposure to site contaminants. In light of these factors, especially the last two, ATSDR'sHealth Activities Recommendation Panel (HARP) determined that no follow-up health activitieswere warranted for the site at the present time. However, as indicated in the health assessment,ATSDR will reevaluate the need for any follow-up health activities at the site if informationbecomes available indicating that human exposure to site contaminants is occurring at levels ofhealth concern or that past exposure to site contaminants is causing adverse health effects.

Specific Comments

1."This document states that the Sherwood Medical Company is located approximately 1.5miles south of Norfolk, Nebraska. It is more accurate to say that the facility is one milesouth of Norfolk because the city limits south end at the Elkhorn River which is less than onemile north of the Sherwood facility."

Response: ATSDR has revised the health assessment to reflect this information.

2."Page 8, Para. 2, Sentence 3: The document states that the 'river intercepts groundwaterflow but is not considered by EPA to be a hydraulic barrier.' Please indicate if the river isconsidered a hydraulic barrier for the health assessment."

Response: ATSDR has revised the health assessment to more accurately indicate that it is notcertain whether or not the Elkhorn River is a hydraulic barrier to groundwater movement.

3."Page 14, Last Para., Last Sentence: The last sentence discusses contamination of surfacesoils and appears to introduce circular reasoning into the discussion. This sentence needsclarification."

Response: ATSDR has clarified the paragraph in question.

4."Page 16, Para. 1, Last Sentence: Include a brief description of why only unfiltered data will be used in the health assessment."

Response: ATSDR has revised the sentence in question to explain why only data from unfilteredsamples were used in the health assessment.

5."Page 23, Last Para., Last Sentence: Explain your rationale for this statement. How areresidual VOCs trapped under the parking lot going to be detected by soil gas analysis asVOCs in the north leach field area?"

Response: The statement in question indicates that VOC-contaminated soil gas found near thenorthern leach area could have migrated there from contaminated soil underneath the plant's parkinglot. This statement is reasonable because the impervious parking lot would tend to prevent theVOCs from being released into the atmosphere and, therefore, force them to travel horizontallythrough the soil.

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