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Maps and Figures

Intro Map

Figure 1. Site Features Map

Figure 2. Site Map

Figure 3.

Table 4.

Potential Exposure Pathway - ON SITE
Medium Exposure Route Time of Exposure Exposure Activities Estimated Exposed* Chemicals Public
Total Children (<18 yrs)
Air Inhalation Past, Current, Future Workers, recycling 50 unknown Volatile Organic Compounds Yes

Table 5.

Potential Exposure Pathway - OFF SITE
Medium Exposure Route Time of Exposure Exposure Activities Estimated Number Exposed* Chemicals Public Health Concern
Total Children
(<18 yrs)
Air Inhalation Past, Current, Future Outdoor, Inside 50 unknown Volatile Organic Compounds Yes


Comparison Values

ATSDR comparison values are media-specific concentrations that are considered to be "safe" underdefault conditions of exposure. They are used as screening values in the preliminary identificationof "contaminants of concern" at a site. The latter is, perhaps, an unfortunate term since the word"concern" may be misinterpreted as an implication of "hazard." As ATSDR uses the phrase,however, a "contaminant of concern" is merely a site-specific chemical substance that the healthassessor has selected for further evaluation of potential health effects.

Generally, a chemical is selected as a contaminant of concern because its maximum concentration inair, water, or soil at the site exceeds one of ATSDR's comparison values. However, it cannot beemphasized strongly enough that comparison values are not thresholds of toxicity. Whileconcentrations at or below the relevant comparison value may reasonably be considered safe, it doesnot automatically follow that any environmental concentration that exceeds a comparison valuewould be expected to produce adverse health effects. Indeed, the whole purpose behind highlyconservative, health-based standards and guidelines is to enable health professionals to recognize andresolve potential public health problems before they become actual health hazards. The probabilitythat adverse health outcomes will actually occur as a result of exposure to environmentalcontaminants depends on site specific conditions and individual lifestyle and genetic factors thataffect the route, magnitude, and duration of actual exposure, and not on environmentalconcentrations alone.

Screening values based on noncancer effects are obtained by dividing NOAELs or LOAELsdetermined in animal or (less often) human studies by cumulative safety margins (variously calledsafety factors, uncertainty factors, and modifying factors) that typically range from 10 to 1,000 ormore. By contrast, cancer-based screening values are usually derived by linear extrapolation fromanimal data obtained at high doses, because human cancer incidence data for very low levels ofexposure simply do not exist, and probably never will. In neither case can the resulting screeningvalues (i.e., EMEGs or CREGs) be used to make realistic predictions of health risk associated withlow-level exposures in humans.

Listed and described below are the various comparison values that ATSDR uses to select chemicalsfor further evaluation, along with the abbreviations for the most common units of measure.

CREG =Cancer Risk Evaluation Guide
MRL =Minimal Risk Level
IMRL =Intermediate Risk Level
CMRL=Chronic Risk Level
EMEG=Environmental Media Evaluation Guide
aEMEG=Environmental Media Evaluation Guide based on acute Minimal Risk Level
IEMEG =Intermediate Environmental Media Evaluation Guide
RMEG=Reference Dose Media Evaluation Guide
RfD =Reference Dose
RfC =Reference Dose Concentration
DWEL=Drinking Water Equivalent Level
CLHA=Child Longer-Term Health Advisory
LTHA =Drinking Water Lifetime Health Advisory
MCL =Maximum Contaminant Level
MCLG=Maximum Contaminant Level Goal (µg/L)
MCLA=Maximum Contaminant Level Action
NAAQS=National Ambient Air Quality Standards
PEL =Permissible Exposure Limit (OSHA)
REL =Recommended Exposure Limit (NIOSH)
TLV =Threshold Limit Value (ACGIH)
FDA =Food and Drug Administration
ppm =parts per million, e.g., mg/L or mg/kg
ppb =parts per billion, e.g., µg/L or µg/kg
kg =kilogram (1,000 grams)
mg =milligram (0.001 grams)
µg =microgram (0.000001 grams)
L =liter
m3=cubic meter (used in reference to a volume of air equal to 1,000 liters)

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations in water, soil,or air that would be expected to cause no more than one excess cancer in a million persons exposedover a lifetime. CREGs are calculated from EPA's cancer slope factors.

Minimal Risk Levels (MRLs) are estimates of daily human exposure to a chemical (i.e., dosesexpressed in mg/kg/day) that are unlikely to be associated with any appreciable risk of deleteriousnoncancer effects over a specified duration of exposure. MRLs are derived for acute (< 14 days),intermediate (15-364 days), and chronic (> 365 days) exposures, and are published in ATSDR'sToxicological Profiles for specific chemicals.

Environmental Media Evaluation Guides (EMEGs) are concentrations of a contaminant in water,soil, or air that are unlikely to be associated with any appreciable risk of deleterious noncancereffects over a specified duration of exposure. EMEGs are derived from ATSDR minimal risk levelsby factoring in default body weights and ingestion rates. Separate EMEGS are computed for acute (<14 days), intermediate (15-364 days), and chronic (> 365 days) exposures.

Intermediate Environmental Media Evaluation Guides (IEMEGs) are media-specificconcentrations that correspond to a minimal risk level, factoring in body weight and ingestion ratesfor intermediate exposures (i.e., >14 days and <1 year).

Reference Dose Media Evaluation Guide (RMEG) is the concentration of a contaminant in air,water, or soil that corresponds to EPA's RfD of RfC for that contaminant when default values forbody weight and intake rates are taken into account.

EPA's Reference Dose (RfD) is an estimate of the daily exposure to a contaminant unlikely to causenoncarcinogenic adverse health effects over a lifetime of exposure. Like ATSDR's MRL, EPA'sRfD is a dose expressed in mg/kg/day.

Reference Concentration (RfC) is a concentration in air expected to be associated with nodeleterious health effects over a lifetime of exposure, assuming default body weights and inhalationrates.

Environmental Protection Agency Region III (EPA III) values are similar to ATSDR's EMEGs inthat they are risk-based concentrations derived for carcinogens and noncarcinogens from RfDs andCancer Slope Factors, respectively, assuming default values for body weight, exposure duration andfrequency, etc. Unlike EMEGs, however, they are available for fish, as well as for water, soil, andair.

Drinking Water Equivalent Levels (DWELs) are based on EPA's oral RfD and representcorresponding concentrations of a substance in drinking water that are estimated to have negligibledeleterious effects in humans over a lifetime of exposure, at an intake rate of 2 L/day, and assumingthat drinking water is the sole source of exposure to the contaminant. Similar to ATSDR's RMEGfor drinking water.

Child Longer-Term Health Advisories (CLHAs) are contaminant concentrations in water that theEnvironmental Protection Agency (EPA) deems protective of public health (taking into considerationthe availability and economics of water treatment technology) over a period of about 7 years, using achild's weight (10 Kg) and ingestion rate (1 L/day).

Lifetime Health Advisories (LTHAs) are calculated from the DWEL and represent theconcentration of a substance in drinking water estimated to have negligible deleterious effects inhumans over a lifetime of 70 years, assuming 2 L/day water consumption for a 70-kg adult, andtaking into account other sources of exposure. In the absence of chemical-specific data, the assumedfraction of total intake from drinking water is 20%. Lifetime HAs are not derived for compoundsthat are potentially carcinogenic for humans.

Maximum Contaminant Levels (MCLs) represent contaminant concentrations in drinking waterthat EPA deems protective of public health (considering the availability and economics of watertreatment technology) over a lifetime (70 years) at an exposure rate of 2 liters of water per day.

Maximum Contaminant Level Goals (MCLGs) are drinking water health goals set at levels atwhich no known or anticipated adverse effect on the health of persons occurs, and which allow anadequate margin of safety. Such levels consider the possible impact of synergistic effects, long-termand multi-stage exposures, and the existence of more susceptible groups in the population. Whenthere is no safe threshold for a contaminant, the MCLG should be set at zero.

Maximum Contaminant Level Action (MCLA) are levels set by EPA under Superfund that triggera regulatory response when the contaminant concentration exceeds this value.

National Ambient Air Quality Standards (NAAQS) are established by the EPA, as mandated inthe Clean Air Act, for six criteria pollutants (carbon monoxide, sulfur dioxide, nitrogen dioxide,ozone, particulate, and lead). NAAQS are classified as either primary, which define levels deemedprotective of public health, or secondary, which in some instances establish lower levels to preventadverse effects on vegetation, property, or other elements of the environment.

Permissible Exposure Limits (PELs) are air standards developed by the Occupational Safety andHealth Administration (OSHA) for the workplace. They are time-weighted average concentrationsof contaminants considered safe for healthy workers over the course of an 8-hr workday and a 40-hrworkweek. A PEL may be exceeded for brief periods, but the sum of the exposure levels averagedover 8 hours must be equal to or below the PEL.

Recommended Exposure Limits (RELs) are established by the National Institute for OccupationalSafety and Health (NIOSH) and are similar to OSHA's PELs. They are time-weighted averageconcentrations for the workplace deemed to be safe for up to 10 hours/day, for 40-hours/week.

Threshold Limit Values (TLVs) are established by the American Conference of GovernmentalIndustrial Hygienists (ACGIH). The TLV is the time-weighted average concentrations for a normal8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed,day after day, without adverse effect. Many of ACGIH's TLVs were adopted by OSHA for use asPELs. TLVs and PELs, which were designed to protect healthy workers, are usually much higherthan the health-based values of ATSDR and EPA, which were designed to protect the health of thegeneral population, including the very young and the elderly. Although the ATSDR does not baseany of its community health decisions on TLVs or PELs, it sometimes cites such values in PublicHealth Assessments merely as a means of putting concentrations of site-specific contaminants into ameaningful perspective for the reader.

The Food and Drug Administration (FDA) has recommended concentration levels for certain substances in food, including fish. Levels above the FDA levels mean the food may be unsafe for human consumption.


  1. Agency for Toxic Substances and Disease Registry. Health Assessment Guidance Manual. Atlanta: ATSDR, October 1992.
  2. National Institute for Occupational Safety and Health. Pocket Guide to Chemical Hazards. Washington D.C.: U.S. Department of Health and Human Services, June 1994.
  3. U.S. Environmental Protection Agency. New Interim Region IV Guidance for ToxicityEquivalent Factors Methodology for Carcinogenic PAHs. February 11, 1992.


Review of Air Modeling Procedure

ATSDR was requested in September 1998 to review the procedures provided in the Non-methaneorganic compound (NMOC) emissions and dispersion modeling that was completed for the YaworskiLandfill facility (21). The following conclusions and recommendations were made: The use of aone-time sampling event for the database may underestimate the actual emission values unless asufficient number of samples are collected and an upper confidence limit is established. Leaks in thesumma canisters during air sampling activities, introduce errors in the evaluation of flux emissionsduring the one-time sampling event, and the concentrations obtained for the VOCs needed to beadjusted. In addition, other software is available that may be used to predict optimal samplingperiods for measuring peak emissions. Meteorological conditions may affect the flux rate and adjustthe short term (observed) emission rates. Landfill pressure measurements would be useful indetermining emission flux rates. Also, the conservative estimate within the model (80th percentile)may underestimate the actual emission rates due to the sampling time selected.

Sampling a 75 ft stack would require 275 Pascals of pressure to overcome gravity (21). In addition,a stack negates the buoyancy that is usually obtained by the sun heating the surface of the landfilland may not represent actual emissions. Since the stack diameter is less than 4 inches, variable gasflows may be measured by the anemometer which could result in an edge effect, especially with flowrates near the low end of its calibration range of 3 meters per second. A pito tube may be a moreaccurate instrument for measuring this variable gas flow, and landfill pressure measurements shouldbe collected concurrently. This would also more accurately measure long-term flow rates.

The actual values for the decay rates (k and Lo) used in the model were not clearly identified,although the document stated that default values were used (21). The landfill model determines themass fraction of daughter compounds that are formed by the decay of waste over time by reportingthe time that the waste was put in the landfill cells. Estimating the age the waste was placed in thelandfill, prior to 1987, may impact the reliability of the prediction of the more distal daughtercompounds (ie; tichloroethane, dichloroethane, and vinyl chloride). Therefore, selecting areasonable upper confidence level of decay (a conservative k and Lo) within the model, wouldaccount for the possible errors associated with estimating the age of the waste.

Use of the air dispersion ISCST3 model is sufficient, however, more recent meteorological data areavailable through EPA's Office of Air Quality Pollution Standards (21). Since predicted annualaverage concentrations may vary by a factor of three from one year to another at a given receptor,the inclusion of five years of meteorological data may predict more accurate weather conditions and emission rates.


Public Comments

ATSDR released the Yaworski Landfill Public Health Assessment for public review and commentduring the period from September 29 through November 26, 1999. ATSDR appreciates the writtencomments provided. This section includes the comments received and ATSDR's response to thesecomments. General editorial comments were addressed, where appropriate, within the final document.

Comment 1
The "Note of Explanation" at the beginning of the report sites that this document was previouslyprovided to EPA and the affected state in an initial release for review. By way of clarification EPAwas NOT presented with an initial release version for review prior to this public comment version,and it appears that the various state agencies also did not receive an initial release. Given the natureof the following comments, much of the expected confusion form the public about this reportprobably could have been avoided had EPA been given the opportunity to review an earlier version.

Response 1
In most cases, ATSDR will provide the initial document for other federal and state agencies toreview prior to being released to the public for comment. However, it is not unusual for ATSDR torelease the document to other agencies and the public at the same time in situations where thecommunity expresses concerns with this procedure. Due to controversies regarding the Yaworskisite, ATSDR deem sending the document out for comment to everyone the most appropriate action. ATSDR explained during a site visit and meeting in May, 1999 that the document would be releasedto all interested persons at the same time for review and comment.

Comment 2
In general, the report does not adequately describe and distinguish between the Yaworski LagoonSuperfund Site and the Packer Road (Yaworski) Landfill. While the two sites are located very closeto each other, the Landfill is NOT part of the Yaworski Lagoon Superfund Site, and the Landfillitself is not on the National Priorities List (NPL). The Landfill is currently regulated under Stateauthority only.

Because the differences between the NPL and the non-NPL site is not outlined up front, the public islikely to have significant confusion regarding the appropriate regulatory agency. There are alsorelated sections of the report that need to be addressed.

The foreword states that ATSDR is required to conduct a public health assessment at each of thesites on the EPA National Priorities List, and will also conduct a public health assessment whenpetitioned by concerned individuals. ATSDR should clarify the foreword to explain that thisassessment is for a non-NPL site, and that the Superfund site was not included in this assessment.

Response 2
This document states in several sections that it will address concerns and issues regarding theYaworski Landfill. Please refer to the title of the document, summary, page headers, the purposeand health issues, community concerns, and throughout the rest of the document. The documentdoes not refer to the Landfill as a National Priorities List site, even though it was proposed for theNPL in the past. ATSDR's focus is advisory and does not routinely address regulatory issues. However, for clarification, the non-NPL status of the Yaworski Landfill site has been added to thesummary and the background section.

Comment 3
The background section starting on page 4 should clearly describe the status of the Packer Road(Yaworski) Landfill as a State-regulated site and clearly that it is not a superfund site. This sectionshould include a very brief description of the Yaworski Lagoon Superfund site and note it'sproximity to the Landfill. Because the Purpose and Health Issues section on pages 3-4 also mentionsthe Gallup's Quarry Superfund Site, the Background should also briefly describe that site and itsproximity to the Landfill.

Response 3
Please refer to the response to comment 3, above. In addition, a brief statement regarding theYaworski Lagoon Superfund site and the Gallup's Quarry Superfund site, has been added whereappropriate in the Background Section of the document.

Comment 4
The second paragraph in the Background section also describes the largest section of the YaworskiLandfill site as the "active landfill". This is inaccurate since the Landfill stopped accepting waste in 1995.

Most of the figures in Appendix A have references to the "open" or "active" portions of the landfill. These are inaccurate descriptions as the landfill stopped accepting waste in 1995.

Response 4
The word "active" or "open" has been changed in the document to the former "active" area of thelandfill, when referring to the unclosed section of the landfill that stopped accepting waste in 1995.

Comment 5
Reference No.2 under the Public Health Action Plan-Actions Completed section is incorrect. The1988 ATSDR Public Health Assessment did not evaluate the Yaworski Landfill.

The color "Intro Map" in Appendix A refers only to the Yaworski Lagoon and does not identify theLandfill. As presented, this map only serves to confuse the distinction between the Superfund siteand the State-regulated Landfill.

Response 5
Thank you for your comments, the corrections have been made where appropriate.

Comment 6
On the cover page and throughout the report, the terms "Yaworski Dump." "Yaworski Landfill"and "Packer Road Landfill" are all used somewhat inconsistently. Although EPA has designated thearea as the "Packer Road (Yaworski) Landfill," it is suggested that ATSDR clarify with the State ofConnecticut how best to reference the site.

Response 6
The name "Yaworski Dump" appears on the cover page due to a database error which has beenaddressed. The name "Packer Road Landfill" appears as an alias only in the Summary and Purposeand Health Issues sections of the document. The name, "Yaworski Landfill is used throughout the document and will be identified in the final document as the official site name.

Comment 7
Thank you for the opportunity to review and comment upon the Public Health Assessment-PublicComment Release version of the "Petitioned Public Health Assessment-Public Comment onYaworski Dump" dated September 26, 1999. This health assessment contains the recommendationthat useful ambient air monitoring data be collected. The document further recommends thatperimeter air sampling at the active landfill be conducted for methane and non-methane organiccompounds and that methane should be monitored in the basements of residences adjacent to the landfill.

Toward these ends, this agency recommends that you develop a detailed monitoring plan. In theinterest of obtaining the most relevant and scientifically defensible monitoring information for yourhealth assessment and modeling evaluations, your plan, at a minimum, should include the following:

1. An identification of the exact chemicals to be sampled and analyzed (element and form),

2. Reference methodologies for sampling and analysis, including real time versus longer termambient sampling, indoor air sampling, landfill vent sampling and leachate,

3. Acceptable holding times, handling procedures, chains of custody for samples,

4. Acceptable equipment and media to be used including pre and post sampling parameters to bemeasure and recorded (e.g. canister pressure),

5. Duration of frequency of sampling, including number of field and trip blanks,

6. Number of sampling sites along with site maps including exact locations of monitoring equipment(both on and off site) including collocated samplers for any compounds including methane,

7. Meteorological parameters and location for equipment,

8. Environmental or meteorological conditions under which sampling should occur,

9. Flow rates,

10. Time of day of sampling, including need for correlation with any potential excavation activities,

11. Specific landfill pressure

Response 7
We appreciate your comments to the Yaworski Landfill (Dump) Petitioned Public Health Assessmentreleased for public comment in September, 1999. In your comments, you recommended thatATSDR develop a detailed air monitoring plan. While this activity is not within the purview of thishealth agency, ATSDR would be available to review any proposed air sampling plans. In the past,ATSDR has provided comments to the "Air Impact Scope of Study" for the Yaworski Landfill,develop by Fuss & O'Neill, Inc. for Yaworski, Inc., revised October 24, 1994 (8). These commentsand recommendations were provided to the Connecticut Department of Environmental Protection byATSDR in September 1994. ATSDR reviewed available landfill gas sampling results in April of1996 and provided further comments and recommendations for ambient air sampling including targetchemicals, sampling equipment, locations, and procedures. Additional reviews andrecommendations were provided from 1996 to 1998 including recommendations for air samplingduring excavation activities and air dispersion modeling (10, 11, 12). Additional copies of thesereviews can be provided upon request. EPA's NSPS New Source Air Emissions guideline alsoprovide a model for air sampling procedures at a landfill site. ATSDR will be available to reviewand comment on an updated sampling plan for ambient air emissions at the Yaworski Landfill andwithin residential areas.

Comment 8
Page 5 Review of Air Modeling Proposal The last sentence refers to the model in the future tense,"will be used to ...". Was this the model that was used and referred to in the Discussion section?

Page 5 Evaluation of Ambient Air Sampling Plan While this information appears to be provided togive the reader some historical perspective on ATSDR involvement, it is confusing in that the readerdoes not know if this work was ever done and if not why. Should be stated clearly that this ambientair sampling plan was not carried out and perhaps less information regarding what ATSDRrecommended should be provided.

Response 8
ATSDR was requested by CTDEP to assist in determining air monitoring plans and sampling needsfor the Yaworski landfill. Recommendations were provide by our air specialist to the CTDEP inApril 22, 1996. It was recommended initially that additional sampling be conducted at the landfillvents, gas migration interceptor trench and leachate. EPA priority pollutants should be sampled forto include VOCs, volatile sulfur compounds, ammonia, and amines. Based on these results, it wasfurther recommended that identified contaminants should be sampled for at the perimeter andambient air sampling should be conducted for a representative and/worst case time period orconditions. It was also recommended that residences adjacent to the active landfill be sampled foruntil soil migration is better characterized. Additional air sampling was also recommended duringexcavation activities on site. To ATSDR's knowledge, the recommended air sampling activitieshave not occurred. However, air modeling was proposed using data collected from subsurface soil-gas samples in 1995/96. The model and ATSDR's evaluation is presented in the discussion section of this document.

Comment 9
Page 7 On-Site Air Sampling Title suggests that ambient sampling was done. Perhaps moreappropriate title should indicate soil gas sampling. Clarification is very important since theassumptions that one can draw regarding potential exposure are very different for air sampling dataversus soil gas sampling data.

Response 9
The title on page 7 is a general title but the accompanying paragraph has been modified to clarifythat the data reviewed was from soil gas sampling. No ambient air data were available to review forthis site.

Comment 10
Page 7 Landfill Gas Sampling Data Would help to provide a brief description of how these samplesare collected to provide reader with a better understanding of soil gas, and what this data means.

Response 10
The sampling protocol for samples collected at the Yaworski Landfill during the winter of 1995/96is described in the "Air impact scope of study" (Fuss & O'Neil, 1994).

Comment 11
Page 8 top of page Is it realistic that ambient levels of methane can present an asphyxiant hazard,"replace available oxygen..."? More information should be given to provide a better description ofrealistic methane hazards at this site, where and to whom. There is no discussion here regardingthe potential for methane migration and potential build up in confined spaces, particularly homes. This seems to be one of the more significant public health issues but has not been presented.

Response 11
The migration of methane at the landfill has not been characterized and the potential for pockets ofhigh levels of methane may represent a hazard to workers or people who frequent the recycling areawhich is in a low lying area. "Because of methane's low density it may accumulate in the upperstrata of poorly ventilated areas to produce an asphyxiating atmosphere" (Patty, E. (ed.). inIndustrial Hygiene and Toxicology: Volume II: Toxicology. 2nd ed. New York: IntersciencePublishers, 1963. 1196) peer reviewed. In addition, methane migration was known to be movingtoward the residential areas in the past, potential also exists for accumulation of methane in theconfined areas of basements. Therefore, ATSDR recommends ambient air sampling onsite and inthe basements of residents living near the active landfill.

Comment 12
Page 8 There is discussion about excavation activities. Some additional discussion about what theseexcavation activities entail, the duration of these activities and a description of how these activitiesmay affect exposure potential would be helpful, since the excavation activities are identified as problematic.

Response 12
Air monitoring during excavation activities is recommended to identify the presence of volatilecontaminants and odors released onsite during periods of activity where the landfill cap or soil isdisturbed and to ensure that intermittent releases do not move offsite into residential areas. Actionlevels should be set to implement corrective action if emissions exceed health based levels. Thisinformation is provided on page 9, under the heading of data needs.

Comment 13
Page 8 Why is there extensive discussion about the April, 1996 ATSDR Health Consultation in themiddle of the Discussion Section. To have sub-titles like Perimeter Air Sampling and Air SamplingDuring Excavation Activities suggests that these activities were performed and are in some wayproviding information that was evaluated for this health consultation. It is very confusing and wouldbe more appropriate in the Background section. Recommendations that ATSDR made in 1996 havelittle or no relevance to the current discussion, which tries to use limited data to evaluate the healthimplications of air emissions from the landfill. It might also be more appropriate to restate some ofthese recommendations in the Recommendation Section of this document.

Response 13
The reference to the April 1996 ATSDR Health Consultation is presented in the discussion section toidentify data gaps and recommendations to obtain data to characterize the site further and to identifyair monitoring that is necessary during periods of landfill activity where volatilization ofcontaminants are more likely to occur. The headings may be misleading and that section of thediscussion has been placed under a general "Data Gaps" heading.

Comment 14
Table 1 and 2. It is very inappropriate to cite comparison values in tables of data that have littlerelevance to actual exposure potential. While it is appropriate to use the comparison values toidentify contaminants of concern, to present the comparison values in a table of soil gas or riser pipeconcentrations is misleading and can easily be misinterpreted. Does anyone think someone mayactually be exposed to 8,210 mg/m3 of benzene or 39,603 mg/m3 of methylene chloride? A moregeneral discussion indicating that very high levels of volatile organic compounds were identified anda comparison with soil gas data found at other landfills could better make the case that this landfill isunique and higher concentrations of volatile organic compounds were identified than would beexpected from a municipal waste landfill. This is essentially all you can conclude from this data. IfATSDR leaves the comparison values in they should be checked for accuracy, available CREGswere not cited for some chemicals. It is our understanding that CREGs are to be used first in thehierarchy of selected comparison values. In addition, the odor threshold for hydrogen sulfide is incorrect.

Response 14
The opening paragraph of the discussion section, " ATSDR selects and compares on- and off-siteconcentrations of contaminants with ATSDR comparison values for noncarcinogenic andcarcinogenic effects. Comparison values are concentrations of contaminants in specificenvironmental media (air, soil, drinking water) that are not expected to produce an adverse healtheffect in people who are exposed. These values are used only as screening values, listing acontaminant in a table of "chemicals of concern" does not mean that it will necessarily causeadverse health effects if exposure occurs at that specified concentration. When the concentration ofa contaminant detected on or off the site is above the comparison value it is further evaluated todetermine the potential for adverse health effects", discusses this point. The comparison values wereadded to the tables of contaminants to identify the contaminants that are of concern according toATSDR standards and should be sampled for during any future on-site ambient air sampling or offsite residential air sampling. However to clarify the point, additional text has been added to thediscussion section to make the point that potential exposures exist on-site to workers and peoplerecycling as well as off site emissions are not clearly defined. Therefore ambient air data arenecessary to evaluate these potential exposures to people who frequent the site and residents who live nearby.

The odor threshold range for hydrogen sulfide was obtained from Table 5.1, page 20 in the "OdorThresholds for Chemicals with Established Occupational Health Standards. American IndustrialHygiene Association, 2700 Prosperity Avenue, Suite 250. Fairfax Virginia, 1997". This range isbased on a technical critique of primary odor threshold values present in the literature and is the bestestimate of odor thresholds for chemicals with experimental data available for evaluation using astandard set of criteria.

Comment 15
Page 16. This page is very technical and provides little assistance in interpreting the usefulness ofthe modeling exercise. The document should state the strengths and weaknesses of the model interms that are understandable to the lay public. The modeled data should be provided withcorresponding comparison values and ATSDR should qualitatively describe how they feel about thatinformation given the strengths and weaknesses of the model. The paragraph on Page 17 startingwith, " In conclusion," begins to do this. One of the clearer public health messages in thisdocument "The annual and one-hour average concentrations......were not at levels of healthconcern." is buried in this paragraph. The reader needs to be provided with a clearer discussion ofhow comfortable they should feel with that finding.

Response 15
Specific technical issues addressed in ATSDR's review of the NMOC emissions and dispersion modeling procedure, used to evaluate potential off-site contaminant emissions, are provided in Appendix C.

Comment 16
Page 17 Toxicological Evaluation The discussion regarding "data representing concentrations insidepipes driven several feet into the ground..." should also be stated in the Discussion sections wherethe types of available data are presented.

Response 16
Thank you for the comment, statements clarifying this issue have been added to the Discussion section.

Comment 17
Page 18 The top paragraph provides some perspective for the reader regarding the available data andshould be repeated in the conclusion section. It also provides the foundation for therecommendation regarding the need for more data.

Response 17
Thank you for your comments, please refer to conclusions 6 through 8 in the Conclusion section andrecommendations 1 and 2 in the Recommendation section of the document, which address these issues.

Comment 18
Conclusions Conclusion #2. It would be more appropriate to discuss the soil gas data in qualitativeterms and not refer to comparison values. Conclusion #3 clarify that the highest concentration ofmethane was found in soil gas as opposed to ambient air. This same comment holds for all mentionof landfill air sampling data. This conclusion should mention the potential for migration of methaneinto confined spaces since the second recommendation focuses on the need for monitoring in homesbut there is nothing in the text to support this. Conclusion #9 should provide more specifics on whythis area is being recognized as a potential health hazard. Is it because of the methane, is it becausethe highest soil gas data were collected near this area, What?

Response 18
We appreciate your comments. Additional information has been provided in the sections of the textsuggested above to further clarify this issue.

Comment 19
Recommendations Since ATSDR is recommending air sampling, the limitations of this approachshould be outlined to illuminate the fact that ambient air sampling may not answer citizens' concernsabout exposure in the past and that representative ambient air sampling is difficult to do and isreflective only of conditions of the landfill during the sampling. ATSDR should provide more detailwith respect to an air sampling and monitoring plan that would provide useful data from a public health perspective particularly if ATSDR is going to be interpreting the results.

Response 19
Thank you for your comment, please see the response to Comment 7 above. ATSDR will beavailable to review and comment on any updated sampling plan for measuring ambient air emissionsat the Yaworski Landfill and within residential areas.

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