IntroductionNothing is as difficult to deal with as the shattering of a closely held belief. In Health Physics, especially among the fission product crowd, natural radioactivity, including radon to some extent, had been a parenthetical issue. Results were expressed as (twice background), or air particulate analyses were delayed (to allow for decay of short lived radon daughters). Radon was a nuisance. The management of fission product and by product problems consumed a large fraction of the nuclear talent in the nation. For some, however, things were about to change.
At mid-day December 19, 1984 during the Christmas lunch in the Department of Environmental Resources, Bureau of Radiation Protection, the Senior Health Physicist at Limerick Generating Station called with a message which shook old beliefs. He indicated that a contractor engineer at the site had been tripping the recently installed portal monitor on his way to meeting outside and at the end of shift. The facility had not yet achieved criticality. The contamination was radon daughters. The administrative burden to the station and the inconvenience to the engineer were noticeable. Earlier that week the engineer decided to use the portal monitor on the way to work. His surface contamination set off all the detectors (large, thin window gas flow proportional counters) in the array. He asked the utility to sample his house, since that had to be the problem. It was. Utility consultants found in excess of 10 Working Levels (WL) radon progeny activity in the air of the engineerís home. Based on our limited knowledge at the time, that sounded like a lot.
Since the problem was obviously not of nuclear power origins, the utility was interested in handing it off to the appropriate state agency, and rightfully so. A one dayís grace was begged to allow us to become somewhat conversant in the issue. That night NCRP Report No. 77 and No. 78 were speed read. Using risk estimates and does estimation factors in those documents, the maximum annual dose equivalent to lung epithelium was estimated to be to the order of 10,000 Rem with a lifetime risk of lung cancer over 10% per year of exposure.
The next day we contacted the engineer employed at Limerick to discuss the matter. He asked whether he should get his family out of the house. We could not argue against it. We arranged to visit the house on December 26. The family stayed with relatives in a neighboring state over the holiday.
On December 26 alpha track radon gas detectors were posted in the house, along with thermoluminescence dosimeters (TLD) for measuring gamma exposure. High volume air samples were collected on charcoal to establish the presence, if any, of thoron. (None was found.) Micro-R meter readings in the basement were in the range of 100 µR/hr. The gamma exposure rate was a combination of shine through the floor plus immersion in airborne gamma emitting radon progeny.
The passive detectors were retrieved on January 2, 1985. The radon gas concentrations ranged from 100 pCi/l (0.5 WL) in the garage, to 2700 pCi/l (13.5 WL) in the basement. An alpha track detector posted in the stand pipe of the septic system was in agreement with basement data. This tended to suggest that the problem indeed arose from the ground rather than building materials. TLD results from the basement extrapolated to over 900 mrad/year.
Soil samples were collected, along with a tap water sample. Soil radium concentrations ranged to 15 pCi/g. Water radon concentration was about 15,000 pCi/l. Radium was found in a sample of basement wall efflorescence.
On January 5, a letter was hand delivered to the family, strongly recommending their vacating the house. They did.
Meanwhile, officials of Colebrookdale Township was contacted to advise them of the situation, and to ask their cooperation in arranging home visits. With their help, we took measurements in the homes of immediate neighbors and several other homes in the township. Although several homes had moderate to high radon concentrations, none were nearly as severe as the index house.
For those who believe that random sampling is adequate to assess indoor radon problems, note should be taken that one immediate neighboring house had a radon concentration of less than 2 pCi/l. This compared to 2700 pCi/l in the index house.
By now it is rather common knowledge that the region of concern is a physiographic province known as the Reading Prong. The province underlies parts of Pennsylvania, New Jersey, New York and Connecticut. In Pennsylvania the Prong begins in the hill just east of Reading and runs east-north easterly just south of Allentown, Bethlehem and Easton to the Delaware River. Outlying pieces of Prong are also located north of the Lehigh River in Allentown and Bethlehem, and north of Easton. It includes parts of Berks, Bucks, Lehigh and Northampton Counties. The areal extent is about 300 square miles with an estimated housing stock of 22,000 homes.
The Reading Prong had long been known to have enhanced abundance of uranium and thorium. In the mid-to-late 1970ís, the Pennsylvania Geologic Survey (PGS) had done a carbone gamma survey in the Prong in an effort to locate uranium anomalies. This effort was a supplement to USDOE aerial surveys to locate uranium and estimate national reserves at a time of higher demand.
An informal plan to examine radiation hazards in the Prong was scheduled for the spring/summer of 1979. The concerns at the time were basically ambient gamma and ingestion pathways. Radon was alien. Events elsewhere overshadowed 1979 and several years thereafter.
By mid-January 1985, the Department of Environmental Resources went public on the issue by offering radon surveys at no cost to interested householders in Colebrookdale Township, Berks County.
In the interim, the U.S. Environmental Protection Agency (EPA) and U.S. Department of Energy (DOE) were contacted to request technical assistance. EPA teams took measurements in several hundred homes. The Agency also provided laboratory support for well water analysis. DOE provided a helicopter survey for terrestrial gamma emitters for the immediate vicinity and van-borne gamma analyzer for surface land characterization.
At the outset of the project, the situation suffered from the lack of a widely accepted criterion for radon/radon progeny concentration in domestic air. Discussions with the Pennsylvania Department of Health, the Centers for Disease Control, and EPA led to the selection of 0.02 WL radon progeny concentration which corresponds to 4 pCi/l radon gas concentration.
During the first phase of the project, which continued into the Fall of 1985, the survey effort consisted of taking a grab air sample in the basement for analysis using the modified Kusnetz method, the posting of alpha track detectors for one to three months, the collection of tap well water samples for radon if requested, and a micro-R survey. Results of the Kusnetz samples were telephoned back to the homeowner as soon as the results were available. Kusnetz, alpha track, and water results were provided in writing after receipt of alpha track data.
Homes with basement Kusnetz results over 0.1 WL underwent integrated radon progeny measurement for several days in normal living space. The instrument used was the EPA radon progeny integrated sampling unit (RPISU). This measurement estimated real exposure.
The house surveys also included gathering of information on house construction characteristics, and demographic information such as number and age of occupants, smoking history, length of occupancy, and identity of previous owners.
By February 1985, a fact sheet was published. A table for estimating risk, and a tiered recommended schedule for lowering radon progeny exposure were produced. It was clear from the onset that remediation of homes would be the responsibility of the homeowner. Since we were aware of only two forms in North America with any experience in radon remediation, some creativity was in order. Radon remediation, then and now, was not something widely understood in the general contractor community.
The Department contracted with one of the available firms to characterize 25 selected houses for routes of radon entry, and to develop remedial designs for those houses. From this they developed a booklet of passive remedial designs. The designs for the individual houses were sent to the homeowners. The booklet was available for general distribution by early May 1985.
Beginning in January 1985, all school buildings in the Reading Prong in each Township were screened for radon as the project progressed. By late summer the program focused on all school buildings in the Prong, then, to all school buildings in the eligible area for mail order detectors. Eventually all school buildings (131) of any school district having any buildings in the Prong were surveyed. A total of 40 buildings had rooms over 0.02 WL.
To assist school districts where elevated radon concentrations were found, the Department contracted to have the problem building diagnosed and a menu of remedial options developed. The report of the diagnostics and remedial designs are provided to the subject school boards for their use.
Starting in the summer of 1985 the Department contracted with the Berks County Votech School to provide training to homeowners, contractors and building inspectors in the use of these remediation options.
In early 1985 the Department learned of EPA plans to demonstrate low cost semi-passive remedial designs. We requested their including homes in our project area: Eighteen homes were selected. Work began in the summer of 1985.
In April 1985 Philadelphia Electric Company took on the project of attempting to remediate the index house. This research project was multiphased. The first phase consisted of excavating the exterior basement walls to the footing and installing a radon-opaque membrane and new drain tile. The excavated volume was replaced in large part with washed gravel.
The second phase consisted of application of epoxy paint on an interior basement stub wall which had shown a high radon flux rate. The top of the stub wall was fitted with an accumulator to attempt to draw radon out of the concrete masonry unit cavities.
The third phase consisted of dressing floor cracks and the basement floor slab perimeter french drain, and filling with flowable silicone sealant.
These three phases combined brought the basement concentration down from over 10 WL to about 2 WL.
The fourth phase consisted of the removal of the slab on two levels, and the installation of a subslab ventilation system. Since the slab had no aggregate beneath it, at least a foot of bedrock had to be hammered out to make space for the diabase aggregate gas lines, the slotted drain tile network imbedded therein, a sand cushion, radon opaque membranes and the new four inch slab.
Diabase was used in place of regular ground due to a perceived need to provide shielding from insitu uranium in the native rock. Samples of bedrock from beneath the floor contained 50 ppm uranium. The locally produced diabase contained 15% iron oxide, a condition which raises the shielding effectiveness of the fill due to an increase in the atomic number fill material. The drain tiles were connected to two vertical stacks extending up through the house to the roof. Wind turbines provide a slight negative pressure to the drain tile and aggregate gas lens to draw radon bearing soil gas.
To avoid future controversy regarding disposal of the old slab, excavated dirt and rock, all these materials were retained on the property, covered with topsoil and regraded.
The family returned to the house on July 3, 1985. Basement radon progeny concentrations stabilized at about 0.02 WL. The ambient gamma in the basement is at or below 20 Micro-R/hr.
As the survey project proceeded to the various townships, it began to emerge that the practice of individual house visits would require years to cover the entire Reading Prong. In addition, the participation rate was much less than one would expect, given the health risks involved. Participation rates ran from 12% to 33% of eligible homes. In an effort to increase coverage fast, a mail order campaign was organized for distribution of alpha track detectors in the Reading Prong.
Since the Prong completely ignored political boundaries and other cultural features, the Department had to expand the area eligible for mail order detectors to meet some recognizable boundary. A full page paid advertisement was placed in each of 5 regional newspapers in the Sunday edition of October 13, 1985 and again the following Wednesday. The ad was preceded by pair radio spot announcements during drive time at the end of the preceding week. The response was literally overwhelming with over 10,000 requests received the first week, of which 75% were really eligible. Several requests were received from New Jersey residents! To date about 23,000 detectors have been sent out for screening purposes.
Those homes where basement screening results ranged from 0.02 - 0.10 WL (4-20 pCi/l) were sent a second detector for finding annual exposure in normal living space. Homes where screening results exceeded 20 pCi/l are visited by a field team for further verification measurements, and information gathering.
In early October Governor Thornburgh announced the development of a 3,000.000 low interest loan program for home radon remediation. Administrative elements were developed and the program went public in late Spring 1986 with the mailing of over 8,000 loan information packages to all homes known to exceed 0.02 WL.
As 1985 came into its final days, the Department was advised of a house at 10 WL in the Prong north of Easton. A separate mailing was made to homes in that area to advise them of the local problem and to invite them to ask for detectors. A similar follow-up is underway for other neighborhoods where significantly elevated houses have been identified.
To date (September 15, 1986) data have been collected from over 17,000 homes (table 1). The criterion of 0.02 WL was exceeded in about 59% of the homes. One Working Level was equalled or exceeded in 101 homes.
|Alpha-track Radon Monitor Reading||No. of Homes Surveyed||Percent||Cumulative Percent|
|All greater than 0.020 WL||Above 1.0 WL||101||0.6||59.1%|
|0 500 to 0.999 WL||163||1.0|
|0.100 to 0.499 WL||1851||10.8|
|0.050 to 0.099 WL||2655||15.6|
|0.021 to 0.049 WL||5312||31.1|
|All less than or equal to 0.020 WL||0.010 to 0.020 WL||4223||24.7||40.9%|
|0.000 to 0.009 WL||2758||16.2|
|Total Number of Homes Surveyed = 17,063|
For 1986, the "big thing" appears to be remediation. EPA developed a three day course in structure diagnosis, remedial techniques, and supporting measurements for training government and private sector. The course has been presented several times in Pennsylvania and other Prong states.
In June 1986 Act 62 was passed by the General Assembly and signed by Governor Thornburgh. The legislation provided $1,000,000 for the Department to use to research and demonstrate remedial actions.
In addition EPA will be diagnosing 80 more houses and recommending remediation methods to the homeowners. Most if not all of these homes will be remediated using Act 62 money. The Act 62 money is expected to treat a total of 100 to 200 homes. The Department is contracting with an architect/engineering firm to manage the actual construction work.
By late 1987, the radon community may have a much better understanding of remedial techniques.
Coming events in the Pennsylvania radon effort include surveys in homes in other areas suspected of harboring uranium anomalies. The Pennsylvania Geologic Survey is doing carbone gamma surveys in other areas underlain by precambrian granitic gneisses and dark marine shales.
Several epidemiological studies are under consideration or underway. One, which was conceived before the index house was found, is a case matched retrospective study of lung cancer in nonsmoking females in the eastern 40% of Pennsylvania. The study is being conducted by Argonne National Laboratory using DOE money. The expected time to completion is five to seven years.
The general area of epidemiology of lung cancer due to domestic radon exposure needs work. The only epidemiological basis is the uranium miners and related occupations. Uncertainties exist as to the applicability of their risks to population-at-large. Perhaps the one way to address that issue is by establishing a registry for individuals with a high exposure history. Attempts to correlate incidence of disease for various areas using vital statistics data are usually flawed since the published data reflects municipality where the diagnosis or death occurred. This is not frequently the place where the risk accrued, given our current mobile society. Also given the comparatively large "background" of lung cancer due to smoking and other agents, it is difficult to detect a difference in rate of incidence.
Nevertheless, given our current understanding of radon progeny exposure risks from NCRP Report No. 77, one rapidly comes to the conclusion that domestic exposure may be the largest radiation related source of mortality we have. Consider that continuous exposure to 0.02 WL for 40-45 years yields a 1% risk of lung cancer. If the lifetime risk accrued per year of exposure is 2 x 10-4 at 0.02 WL, one can do all sorts of estimates. Assume 10,000 homes, each within 3 occupants, with a concentration of 0.02 WL for only 10 years, with a 50% occupation factor. This yields 30 fatalities, total. Assume 100 houses at 1.0 WL, with all other variables held constant, with the foregoing, and the yield is 15 cases total.Some conversions are offered for the readers use and abuse (Source: NCRP Report No. 77):
Suppose a family of 4 spends one-third of its time in a room with a concentration of 80 pCi/l (0.4 WL) for 20 years. The individual lifetime risk from that exposure is 2.6%. The combined family risk is 10.6% that someone is committed to lung cancer. The individual total exposure is 132 WL - months. The individual absorbed dose is 92.4 Rad, and, dose equivalent is 1294 Rem to lung epithelium.
After about two years of total immersion in the radon issue, a few lessons should have been learned. Several are offered below:
The net effect to the Bureau of Radiation Protection has been profound. During the first 6 months of 1985 the radon project was handled by existing staff and a contracted community relations consultant. A field office was opened in January 1985 in Gilbertsville. Extra costs in that period were $1 million. For fiscal years 85/86 and 86/87 the budget each year has been $1.3 million. A total of 21 new positions were added in fiscal 85/86. Act 62 provided another $1 million for remedial research and demonstration.