WISCONSIN AVENUE SCHOOL CHEMICAL VAPORS
MILWAUKEE, MILWAUKEE COUNTY, WISCONSIN
This consultation provides an evaluation of petroleum vapors entering the indoor air of theWisconsin Avenue Elementary School in Milwaukee. This school is located at 2708 WestWisconsin Avenue in the City of Milwaukee. School district staff identified chemical odors at theschool. Followup investigations conducted by district staff and contractors for the adjacent businessidentified petroleum contamination entering the basement foundation through vapor intrusion. Theresults of the investigations based on current conditions did not identify a health hazard. However,some mitigation work is clearly needed to prevent long-term exposures of health concern. Thecontaminant source should be better characterized and removed. Information about currentconditions and planned cleanup activities should be discussed with staff at the school.
After a recent rainfall event, Milwaukee Public Schools (MPS) building management staff werecontacted about gasoline odors coming from a small utility room in the basement of the WisconsinAvenue School. Gasoline odors had not been noticed previously in this building. A former gasstation on an adjacent property has been identified as the likely source of the gasoline vapors/odors entering the building. Soil contamination possibly related to existing utilities outside the buildingfoundation seems to be the source of the most significant impact to indoor air.
MPS staff informed the Wisconsin Bureau of Environmental Health (BEH) that a high photoionization detector (PID) reading of 50 instrument units was recorded in the small utility room, nearthe opening in the wall where odors were strongest. This reading is roughly 50 parts per million fortotal petroleum related VOCs. That level is roughly 300 times below the lower explosive limit forgasoline, making a fire and explosion hazard unlikely.
The odors outside the utility room were no longer evident after a few days. Inside the utility roomthe odors lasted only a day or two longer and, since February 23, 2001, are no longer noticeable. MPS staff also indicated that when the building ventilation system is operating there appears to be apositive air pressure created inside the building effectively preventing the vapors from entering. Because the building ventilation system has recently been "balanced", a positive pressure would be expected.
SUMMA Canister Samples
MPS staff have provided BEH with the results of four air samples collected on February 16th and 17th, 2001. These samples were collected in SUMMA canisters and analyzed for VOCs using EPA method TO-14. A summary of these results is included in Table 1. The first sample was collected on Friday (2/16) afternoon from the utility room when the ventilation system was shut down and odors were present. The results of that sample show the highest chemical concentrations by far. The remaining samples were taken the following day from classrooms and hallways in parts of the building used daily by children and staff. Prior to collecting these samples the ventilation system was operated overnight and allowed to run during sampling. After collecting these samples (about noon) the ventilation system was turned off. The VOCs detected are all representative of gasoline contamination.
|Parameter||Basement Utility Room 2/16/01||Basement Class/Hall 2/17/01||1st Floor Room 13 (0205) 2/17/01||First Floor Room 13 (0005) 2/17/01||Comparison Value|
|Benzene||34||3.0||0.8 J||0.9 J||0.03 CREG|
|Toluene||790 D||7.0||3.0||3.0||1,000 EMEG|
|Ethyl benzene||350 D||1.0||0.9 J||0.9 J||300 EMEG|
|Xylenes (total)||1570 D||6.0||4.0||4.0 J||100 EMEG|
|Methyl t-butyl ether||1 J||ND||ND||ND||700 EMEG|
|Octane||170 D||0.6 J||ND||ND||NA|
|Total C4-C10 Hydrocarbons||6.0 ppmv J||<3.0 ppmv||ND||ND||NA|
|Methane||13 ppmv||6.8 ppmv J||5.4 ppm J||6.5 J||NA|
D - Sample diluted at the lab
J - Compound detected lab's limit of quantitation - concentration estimated
ND - Compound Not Detected
ppmv - Parts Per Million by Volume
CREG - Cancer Risk Evaluation Guide. Levels above this threshold do not necessarily represent a health concern. However, exposures to lower concentrations are very unlikely to pose an increased cancer risk. This level is base on a lifetime of continuous exposure which is not reflective of exposures in this situation.
EMEG - Environmental Media Evaluation Guide. Exposure to concentrations below this threshold are very unlikely to cause non cancer health effects. Based on ATSDR Minimal Risk Level.
NA - Comparison Value not available for this compound.
Charcoal Tube Samples
On Sunday February 18th, with the ventilation system still turned off, thirteen charcoal tube samples were collected from various locations in the building. Four samples were collected in various parts of the building's basement. These samples were analyzed for the primary indicators of gasoline vapor contamination (benzene, ethylbenzene, toluene, xylenes and total VOCs as gasoline). As with previous observations and sampling, the sample from the utility room contained the highest concentrations of gasoline related chemicals. The samples from the first, second, and third floors contained generally lower levels than those from the basement. Two samples collected from a boiler room located in a sub-basement did not show significant impacts. Two outdoor samples were collected at the same time. A sample from near the air intake vent on the roof and one from ground level outside the principal's office contained low and no detectable gasoline related VOCs respectively.(1) Table 2 contains a summary of the results from the charcoal tube samples.
|Parameter||Basement||Basement Closet||Basement||Basement||1st Floor||1st Floor||1st Floor||Boiler Room||Boiler Room||2nd Floor||3rd Floor||Roof Air Intake||Principal's||Comparison Value|
|Ethyl benzene||9.0||3.0J||ND||ND||ND||ND||ND||ND||ND||ND||ND||ND||ND||300 EMEG|
|Xylenes (total)||54||12||3.0||ND||2.0J||ND||ND||ND||ND||ND||2.0J||ND||ND||100 EMEG|
|Total VOCs as Gasoline*||1200||400||244||31||72||16||ND||14J||16||32||42||4.0J||ND||NA|
Because the charcoal tube method involves a very different sampling and analysis process than thatof the SUMMA canister, the results from the two sampling events should only be comparedqualitatively. The limit of detection for benzene in the charcoal tubes (2.0 ppbv) is also not as sensitive as that of the SUMMA canisters.
Gasoline is a complex mixture of thousands of chemicals. MPS staff noted that odors have onlybeen faint and infrequent in areas commonly occupied by staff. These areas were not used after theodors were noted. Because the odor thresholds for toluene and xylenes are so low, faint andinfrequent odors are an indication of exposure to relatively low levels of gasoline vapors. Short-term exposures during the brief period (<two weeks) when odors were noted are below levels of health concern.
Because it is a known human carcinogen, benzene is the primary gasoline related contaminant ofconcern for evaluating long-term exposures. Long term exposure to benzene in gasoline vaporbelow the odor threshold, can contribute to an increase in overall cancer risk (2). For less than severalyears of exposure, at the levels measured shortly after the problem was found, the risks would bequite low. However, even these low risks are unnecessary and should be avoided. The threesamples collected in and near classroom areas found benzene levels at 0.8, 0.9, and 3.0 ppbv.(3) Thehighest of those concentrations was detected in a sample taken in a basement-level classroom areacloser to the utility room. The vapor concentrations in the utility room were above the odorthreshold when that first sample was collected on Friday. The level of benzene in that sample was34 parts per billion by volume (ppbv), though it is not representative of likely exposureconcentrations.(4)
There are no chemical specific indoor air quality standards for schools. Most sampling andanalytical methods currently available cannot consistently detect benzene below levels of possiblehealth concern. For this reason, BEH recommends that benzene levels in residential indoor air bebelow levels of detection using the lowest detection limits practically achievable (generally 0.1 to1.0 ppbv). (5) The period of exposure is considerably less in a school than in a residence, but a similarrecommendation is appropriate because children are among the most sensitive individuals tochemical exposures. The Agency for Toxic Substances and Disease Registry (ATSDR) has an acuteminimal risk level (MRL) of 50 ppbv for benzene. Short-term exposures (less than two weeks) tothis level and below are not expected to cause health effects. The cancer risk based comparisonvalue of 0.03 ppbv was developed based on lifetime residential exposures assumptions, andsignificantly over states the risk to a school employee or student.
Unfortunately, in Milwaukee and every other community in the country, benzene is often detectablein ambient air. Past studies of urban air quality in Wisconsin (including Milwaukee) found averagebenzene levels to be between 0.28 ppbv and 0.38 ppbv. (6) Sampling conducted in July of 2000 atanother Milwaukee public school found benzene levels between 0.28 and 1.2 ppbv in indoor air,while outdoor levels were between 0.8 and 1.4 ppbv.(7) A sample of outdoor air quality at theWisconsin Avenue School was not collected during the indoor air sample collection. If additionalsampling will be conducted in the future, a concurrent outdoor sample would be useful for thisreason.
Wind speed, temperature, barometric pressure, rainfall and other weather factors can have adramatic effect on indoor air quality related to vapor intrusion into buildings. Other factors such asopening doors, and heating/cooling and ventilation system operation are also variable and have asignificant effect. For this reason, analytical sample results of indoor air quality cannot be used asquantitatively as we would like. Qualitative indicators such as odor, are often more useful to us inevaluating air quality related to contaminants such as gasoline with low odor thresholds.
The odors related to gasoline vapors are very important as an indicator of the degree of the problem. Therefore, it is very important that air fresheners and other cover scents not be used. Thesechemicals merely mask existing odors and provide additional unnecessary chemical exposures. Similarly, projects (other than standard school work and art projects) that involve painting or woodfinishing should be postponed (if practical) until we are confident that an interim solution is in place. It currently appears that the vapor intrusion is caused by rainwater infiltration influencing themigration of an existing contamination problem. This factor would make the problem moresporadic rather than continuous. Special effort should be made to check for odors in the utility roomduring and immediately after rainfall or other significant weather events.
Because operating the ventilation system may reduce and possibly prevent the intrusion of gasolinevapors, this system can be an important part of the short-term solution to the problem. A simplesmoke test while the system is operating and while it is not can tell you if it is having the desiredimpact. This type of test should be done at a few different locations of the basement foundation incase the pressure isn't evenly balanced within the building. Other options to consider would involvecreating a negative pressure on the outside of the basement foundation. This would also effectivelyprevent vapor intrusion similar to a radon mitigation system. Ultimately the source ofcontamination outside the building should be cleaned up to provide the most complete and effective results.
The SUMMA canister results also identified low but measurable levels of methane. Methane is not generally related to gasoline related contamination. In indoor air it is most commonly related to sewer gas. At the trace concentrations that were detected a significant problem is not expected. BEH still recommends periodically checking to see that floor drain traps are full of water and wastewater pipes are properly vented away from the air intakes for the ventilation system.
This case involves the air quality of an elementary school. Children can be more sensitive to theeffects of chemical exposures than adults. At concentrations in the range of the odor threshold andabove for petroleum contaminants, children with preexisting respiratory problems may be the mostsensitive to the short term irritation effects of exposure. Because children may attend this schoolover several years, chronic health effects could also be of concern if vapor intrusion recurs and is not addressed effectively and permanently.
- Indoor air at the school has been impacted by gasoline vapors. Those impacts have beenprimarily limited to a small utility room in the basement. Samples in other parts of the buildingseem to indicate some possibly related but low-level impacts. These levels have not remained consistently since the initial problem was identified.
- Indoor air impacts have not created a health hazard to date and we classify exposures as posingno apparent public health hazard. However, the current understanding of the problem does not allow BEH to rule out a hazard developing in the future.
- The operation of the building's ventilation system appears to reduce soil vapor intrusion by creating a greater pressure inside the building.
- The source of contamination outside the building should be remediated to prevent on-going contribution of soil vapors to indoor air. MPS staff and the cleanup contractor have agreed that this is the primary cleanup goal.
- At least a portion of that remediation should be conducted this spring or early summer to addressthe exposure pathway that has been identified. This work began as initially requested andshould effectively reduce vapor intrusion until the cleanup is completed.
- Until that remediation can be conducted, additional sampling of soils adjacent to the foundationand around utility lines entering the building should be conducted to better understand the nature of the contamination and vapor intrusion problem.
- If future indoor air quality sampling is considered, samples should also be collected concurrently from outside air.
- School staff should report any gasoline odors outside the utility room. Special attention shouldbe paid to check for odors in the utility room during and immediately after rainfall or other significant weather events.
- The information in this evaluation and BEH contact information should be provided to school staff or others who have concerns about the health significance of this problem.
The cooperative participation of all parties in this case indicates that these recommendations can andwill be followed and that all health issues will be effectively addressed.
MPS has provided instructions to staff in the school on how to respond if an indication of vaporintrusion comes up in the future.
DHFS will continue to work with MPS staff and the contractor conducting the investigation andcleanup work to ensure that health questions are addressed as they arise. DHFS has provided thisconsultation to staff at the school and MPS will contact DHFS if any health concerns are raised in the future.
Wisconsin Department of Health and Family Services
This Wisconsin Avenue School Chemical Vapors public health consultation was prepared by theWisconsin Department of Health and Family Services under a cooperative agreement with theAgency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approvedmethodology and procedures existing at the time the public health consultation was begun.
Technical Project Officer, SPS, SSAB, DHAC
The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health consultation and concurs with the findings.
Lisa C. Hayes
for Chief, SPS, SSAB, DHAC, ATSDR
- IH Solutions. Results of air monitoring performed at the Wisconsin Avenue School on 2/18/01. February 21, 2001.
- ATSDR. "Toxicological Profile for Benzene". September 1997.
- Lancaster Laboratories. "Volatile Organics In Air SUMMA Canister Sample Analysis Data Sheet - Sample Numbers AQ3554239-41". February 19, 2001.
- Lancaster Laboratories. "Volatile Organics In Air SUMMA Canister Sample Analysis Data Sheet - Sample Number AQ3554011". February 19, 2001.
- DHFS. "Information on Toxic Chemicals - Benzene". POH# 4341. Revised December, 2000.
- DNR. "Wisconsin Urban Air Toxics Monitoring - A Summary Report for the Period. July 1997 - June 1998
- ATSDR. "Health Consultation for the Lincoln Creek Groundwater Plume (a/k/a Daniel Webster Middle School". Milwaukee, Wisconsin. August 16, 2000.