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Indoor Air Impacts to Residential Property Associated with Groundwater Contamination



The New Hampshire Bureau of Environmental and Occupational Health (BEOH) was askedto evaluate environmental contamination at a private residence in Dover, Strafford County,New Hampshire. The residents are worried the home is not habitable because of chemicalcontamination. The Agency for Toxic Substances and Disease Registry (ATSDR), RegionI, requested technical assistance to determine if past, present or future levels of chemicals inthe indoor air present a health hazard to the residents; BEOH also evaluated levels ofchemicals in the air after Department of Environmental Services (DES) installed a ventilationfan in the basement. BEOH has technical experience in assessing indoor air quality issues,including those situations related to volatile organic chemicals (VOCs).

Chemical releases from the former Ken's Southside Service Station have resulted in plumesof contaminated groundwater that have migrated off-site. VOCs in groundwater have thepotential to infiltrate through building foundations and impact the indoor air of residencesand commercial buildings located above the plume.

In May 2003, there was an increase in levels of VOCs in the basement and first floor of theresidence. As a result, New Hampshire Department of Environmental Services (DES)installed a ventilation fan in the basement in June 2003. Additional air samples were takenafter the installation of the ventilation fan.

Staff from DES and an environmental consulting firm conducted a health hazard assessmentof the property on May 29, 2003. The initial walk-through of the house was conducted toassess living arrangements (i.e., where residents spent their time eating, sleeping etc.),identify existing chemical sources and to determine a sampling strategy and to assess thehome for ambient levels of VOCs. The health hazard assessment of this home consisted ofthe following activities:

  1. A walk-through and visual inspection of the property.
  2. An assessment of sources of household VOCs (e.g., paints, solvents, moth balls).
  3. Collection of air samples.

After the installation of the air fan, another round of air samples were taken. The ventilationfan is a temporary measure of reducing contamination. DES has plans to install contaminant mitigation systems (such as a pump and treat system) at both the service station site and theresidence as a means of reducing the level of contamination in the groundwater (which is theprobable source of indoor air contamination). Following installation of the mitigation system at the residence, additional indoor air samples will be taken at the residence.


Chemicals of Concern and Pathways of Exposure

Inhalation of contaminated indoor air is the exposure pathway of concern for the past, presentand future. There is no drinking water exposure pathway since the residence is connectedto the municipal water supply. Acute (up to 14 days), intermediate (15 to 364 days) andchronic (greater than 365 days) exposure scenarios were considered for the ground floor; thisis where living and sleeping areas are located. The majority of all exposures take place onthis floor. Since the basement is unfinished and has no living or sleeping areas, it is unlikely that a person will reside in this area for a chronic exposure to be considered applicable.

Indoor air samples were collected from the basement and the ground level of the residenceover a two-year period. These values can be seen in Table 1. The maximum levels, as wellas the average levels from both floors, were compared to two types of health-basedguidelines, EPA Risk-Based Concentrations (RBCs), and ATSDR Minimal Risk Levels(MRL).

It is important to note that these comparison values are not an indication of a health hazard,but rather a screening tool used to evaluate environmental data that is relevant to theexposure pathways. Comparison values (CVs) are concentrations of contaminants that areconsidered to be levels of exposure at which health effects are not expected to occur. Thederivation of a comparison value uses conservative (i.e., "worst case") exposure assumptions,resulting in values that are much lower than the actual exposure concentrations observed tocause adverse health effects. Therefore, comparison values are protective of public healthin most exposure situations. That is, if the concentrations in the exposure medium are lessthan the CV, the exposures are not of health concern and no further analysis of the pathwayis required. However, while concentrations below the comparison value are not expected tolead to any observable adverse health effect, a concentration above this level doesn'tautomatically indicate a public health hazard. It simply means there is a need to examine theexposure scenarios more closely. Depending on site-specific environmental exposure factors(for example, duration of exposure) and activities of people that result in exposure (timespent in area of contamination), exposure to levels above the comparison value may or maynot lead to an adverse health effect. Therefore, ATSDR's comparison values and EPA'sRBCs are not used to predict the occurrence of adverse health effects, but rather they are amechanism to determine whether or not to further examine exposure to a chemical througha specific pathway.

Table 1.

Levels of VOCs in the basement (B) and ground floor (G) areas. Concentrations are in micrograms per cubic meter (g/m3). Maximum concentrations are in bold.
Date Benzene Toluene Ethylbenzene Xylenes MtBE
6/26/2001 5.2 NA 26 20 8.9 NA 34.6 4.8 190 5.7
8/1/2002 2.1 2.4 14 40 4.3 3.5 18.8 11.5 130 NA
1/28/2003 NA NA NA 5.5 NA NA 5.8 NA 53 9.6
4/10/2003 2.1 9.5 12 55 5.3 4.1 28.3 25.5 26 45
5/29/2003 3.6 2.1 11 50 39 51 95 64 700 88
7/02/03* NA 1.8 11 7.6 5.6 3.6 19.8 4.5 270 2.2

NA- Not available
* Sample was taken after the installation of a ventilation fan in the basement.

As seen in Table 2, the maximum (and average) levels of ethylbenzene, toluene and totalxylenes were well below both comparison values. Benzene and methyl-tert-butyl-ethyl(MTBE) levels, however, were above at least one of the comparison values; benzeneexceeded both ATSDR's Cancer Risk Evaluation Guide (CREG) and EPA's RBC andMTBE exceeded EPA's RBC.

It should be noted that it is unlikely that an individual would be exposed to the maximumvalues seen in Table 2. Exposures take place over time, and it is more probable that anindividual would be exposed to the average concentration measured over this several monthmonitoring period. Using maximum values is simply a conservative assumption (a "worst-case" scenario) when determining chemicals of concern.

Table 2.

The maximum and average concentrations (for the basement (B) and ground floor (G) areas) of VOCs found in the Dover residence and comparison of these levels to EPA risk-based concentrations and the ATSDR MRLs. Concentrations are in micrograms per cubic meter (g/m3).
Benzene Toluene Ethylbenzene Xylenes MtBE
Maximum Concentration 9.5 55 51 95 700
Average Concentration (B) 3.3 14.8 12.6 33.7 228.2
Average Concentration (G) 4.0 29.7 15.6 22.1 30.1
EPA RBC 0.23 420 1,100 110 1.6
ATSDR MRL 0.1 300 4,342 434 2,524


The health risks associated with exposure to chemicals in the environment depends on manythings, including the dose (how much) and how long you are exposed. Other factors areother chemicals you are exposed to and your age, sex and general health status.


Benzene is widely distributed in the environment. Benzene is released from manmade andnatural sources. Natural sources include crude oil seeps, forest fires, and decaying vegetation.Sources from human activities include automobile exhaust, automobile refueling, cigarettesmoke, and industrial emissions. The most significant source for release of benzene to theenvironment is from combustion of gasoline [ATSDR, 1995].

The levels of benzene in the air samples range from 2.1 g/m3 to 9.5 g/m3 (Table 1). Eightsamples (four from the basement and four from the ground floor) samples were analyzed forbenzene, and the average from these samples is 4.0 g/m3 for the ground floor and 3.3 g/m3for the basement. These averages represent likely levels of exposure.

Although these levels are greater than the CREG (0.1 g/m3), they are lower than ATSDR'sminimal risk levels (MRL) for acute and intermediate exposure, 50 ppb (equivalent to 159.7g/m3) and 4 ppb (equivalent to 12.8 g/m3), respectively [ATSDR, 1995]. This means thatnon-cancer effects are unlikely.

A few human studies indicate that chronic exposure to low levels of benzene may beassociated with leukemia [ACS, 1997]. However, these studies are not conclusive and cannotrule out other exposure factors. Most studies indicate that carcinogenic effects are the resultof exposures to concentrations of benzene greater than 10,000 ppb (equivalent to 31,947g/m3) [ATSDR, 1996]. Levels of benzene on both floors of this residence are several ordersof magnitude lower than benzene levels potentially associated with leukemia. Therefore,cancer effects as a result of chronic exposure are unlikely.

Methyl-t-Butyl-Ether (MTBE)

MTBE is a flammable liquid used as a gasoline additive. It can contaminate water suppliesvia leaking fuel storage tanks. It can be found in indoor air through volatilization (ormigration) from contaminated groundwater through soil and into houses.

The levels of MTBE in the air samples range from 4.5 g/m3 to 700 g/m3. Nine sampleswere analyzed for MTBE, four from the basement and five from the ground floor. Theaverage levels from these samples are 228.2 g/m3 and 30.1 g/m3, for the basement andground floor, respectively. This average represents a likely average level of exposure. Thislevel is well below the ATSDR chronic MRL of 700 ppb (equivalent to 2,524 g/m3). Sincethe average levels in the residence are nearly twenty-one thousand times below the levels inwhich actual non-cancer health effects are observed [ATSDR, 1996], it is unlikely thatresidents would experience noncancer health effects due to inhalation of MTBE.

Very large doses of MTBE over a long period of time have been shown to cause cancer inlaboratory animals. MTBE is considered a "confirmed animal carcinogen" by the AmericanConference of Governmental Industrial Hygienists (ACGIH); this classification is based onvarious long-term animal studies. The U.S. Environmental Protection Agency has not yetclassified MTBE as a carcinogen, pending additional studies. There are no available studieson the cancer-causing potential of MTBE in humans. The most recent animal studies,however, indicate that carcinogenic effects are the result of exposures to concentrations ofMTBE greater than 400,000 ppb (equivalent to 1,442,127 g/m3) [ACGIH, 2002]. Levelsof MTBE in this residence are several orders of magnitude lower than MTBE levelspotentially associated with cancer in animals. Therefore, cancer effects as a result of chronicexposure are unlikely.

The higher levels of VOCs were observed in the basement of the residence. Since thebasement is unfinished and only used for storage and activities such as doing laundry, it isunlikely that a long-term (chronic) exposure could occur in this area. Chronic exposurerequires near-daily exposures for several hours a day, continuously, for a period of timelonger than a year.


To ensure that the health of New Hampshire's children is protected, BEOH followsATSDR's Child Health Considerations requiring that Public Health Assessments and healthconsultations specifically evaluate the potential for children being exposed to site-relatedhazardous waste and whether or not the health of children might be affected.

This health consultation reflects ATSDR's and BEOH's concern about protecting children'shealth from toxic chemicals in the environment. Site-specific children's health impacts wereevaluated and found not to be of concern due to the low contaminant concentrations andactivity patterns that would limit potential exposure.

The comparison values used in this health consultation take children into consideration. Children are often more sensitive to chemical exposures due to differences in height weightand metabolism. These differences are reflected in the establishment of all health-basedcomparison values.


No apparent public health hazard exists for residents exposed to volatile groundwater contaminants in residential indoor air, in the past, present or future. Contaminants in indoorair from both the basement and ground level are below levels of concern for human healthrisk from inhalation. Indoor air in the basement of the residence will be re- sampled asneeded. It is expected that VOC levels will decrease in the future, after remediation (at theservice station site and near the residence) has been completed.

Actions still need to be taken, however, to ensure that VOCs do not pose a health hazard inthe future. DES should continue with its planned actions to reduce the levels ofcontaminated groundwater near the residence. There are many factors that can change thecontaminant concentration or the level of exposure. These include, but are not limited to,seasonal variations, the amount of time spent in the basement area, the amount of rainfall and fluctuations in the water table.


BEOH should discuss with the residents that they should, as a precautionary measure, avoidlong-term activities in the basement until remedial actions have been completed andadditional sampling has been conducted that indicates that contaminant concentrations arebelow a level of concern.


The Public Health Action Plan (PHAC) contains a description of actions that have been orwill be taken by BEOH and other government agencies at the site. The purpose of this planis to ensure that this health consultation not only identifies potential public health hazards, but also provides a plan of action to prevent or minimize the potential for adverse human health effects from exposure to site-related hazardous substances.

    Completed, Current and Ongoing Actions

  • DES has been taking indoor air samples in the basement and ground floor of theresidence since June 2001.

  • In June 2003, DES installed a ventilation fan in the basement of the residence toremove existing levels of contaminants.
  • Actions Planned

  • DES is planning to install contaminant mitigation at both Ken's Southside ServiceStation and at this residence. These systems will act as barriers to preventingcontamination from entering the residence

  • After installation of the mitigation systems, DES will periodically sample air in thefuture to make sure that contaminant levels are not increasing.

  • BEOH will provide the residents of the house with information regarding all sourcesof indoor air quality, including providing a copy of this Health Consultation andexplaining the recommendation.

  • To ensure that future contaminant levels have subsided, BEOH will obtain all futuremonitoring data and evaluate contaminant levels taken at the residence.


Todd C. Hudson, MSPH
Environmental Health Risk Analyst
Bureau of Environmental and Occupational Health
New Hampshire Department of Health and Human Services


Gary Perlman
Regional Representative
ATSDR Region I


Gregory V. Ulirsch
Technical Project Officer/Environmental Health Scientist
Superfund Site Assessment Branch
Division of Health Assessment and Consultation, ATSDR


American Cancer Society (ACS). 1997. Cancer Facts and Figures.

American Conference of Governmental Industrial Hygienists (ACGIH). 2002 ToxicologicalProfile for Methyl-t-Butyl Ether.

ATSDR. 1995. Toxicological Profile for Benzene. Atlanta: U.S. Department of Health andHuman Services, Public Health Service.

ATSDR. 1996. Toxicological Profile for Methyl-t-Butyl Ether. Atlanta: U.S. Departmentof Health and Human Services, Public Health Service.


The Health Consultation for the evaluation of Indoor Air Impacts to Residential Property,Former Ken's Southside Service Station, Dover, New Hampshire was prepared by the NewHampshire Department of Health and Human Services under a cooperative agreement withthe Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance withapproved methodology and procedures existing at the time that the health consultation wasinitiated.

Gregory V. Ulirsch
Technical Project Officer, SPS,SSAB,DHAC

The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed thisHealth Consultation and concurs with its findings.

Gregory V. Ulirsch
for Roberta Erlwein

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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