United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S9-89/057 Dec. 1989 Project Summary Proceedings of the Radon Diagnostics Workshop, April 13-14, 1987 David T. Harrje and Lynn M. Hubbard Diagnostic approaches offer im- proved evaluations of radon-related Indoor air quality problems. An in- formed solution Involves knowledge of the building, the building site, and the interaction of radon sources with the living space. The diagnostics are applicable in four phases of the miti- gation process: 1) diagnostics that assess the radon problem; 2) pre- mltlgatlon diagnostics, from which a suitable mitigation approach must be chosen; 3) diagnostics that check the performance of the radon mitigation solution; and 4) diagnostics that de- termine If the radon problem has been solved and that guideline radon concentrations have not been ex- ceeded over the different seasonal conditions experienced. A consensus of current knowledge on important radon diagnostic tech- niques and how they may be best applied are the result of the 2-day workshop at Princeton University, April 13-14, 1987. That knowledge is summarized, placing the various radon diagnostic techniques In perspective. This Project Summary was devel- oped by EPA's Air and Energy Engineering Research Laboratory, Re- search Triangle Park, NC, to announce key findings of the research project that Is fully documented In a separate report of the same title (see Project Report ordering Information at back). Introduction The scope and objectives of the work- shop were to gain an improved perspective and develop guidelines on the usefulness and range of applicability of different diagnostic techniques. To categorize state-of-the-art diagnostic techniques and to treat questions that diagnostic techniques seek to answer regarding radon emanation, transport, entry, and indoor distribution, four phases of radon diagnostics were highlighted: 1. Radon Problem Assessment Diag- nostics: radon source strength, loca- tion, house characteristics, and house occupancy characteristics. 2. Premitigation Diagnostics: selecting the best mitigation system for the building, taking into account radon source strength and location, partic- ularly involving the substructure. 3. Mitigation Installation Diagnostics: used during installation of mitigation systems to ensure proper operation. 4. Post-Mitigation Diagnostics: assur- ance that the radon guidelines have been met and that the mitigation system is adjusted properly. The backgrounds of the attendees were varied, but much of their experience with radon had been a direct result of the U.S. Environmental Protection Agency, U.S. Department of Energy, and state programs to understand and mitigate radon problems, primarily in residential buildings. Examples of that experience come from numerous areas in the U.S. and Canada. Questions that were applied to the diagnostic methods included: 1. How good is the rationale for the diagnostic measurement? 2. How easy is the diagnostic pro- cedure? ------- 3. What resources and expenses are required to implement the diagnostic? 4. What information can be obtained from using the diagnostic? The workshop included formal presen- tations summarizing the four phases of diagnostics as well as discussion ses- sions emphasizing the individual diag- nostic procedures. The emphasis on diagnostics in radon- troubled homes is a quest for knowledge of the nature and severity of the problem, the mitigation approach that may be used to solve the problem, and evaluation of the performance of each solution. It was clear from the workshop discussions that such diagnostics are absolutely necessary in certain homes, but many of the procedures are not cost effective in the homes that are simple to mitigate. For example, anticipating possible radon problems during the house design phase and incorporating mitigation possibilities in the design is likely to prove more cost effective than extensive soil probing to quantify the radon problem potential for the individual building lot. Measurements to determine radon levels for most homes are generally rec- ommended. In areas of high incidence of homes with radon levels greater than the EPA guidelines and/or regions where very high house radon levels have been observed, every homeowner should check for radon concentration levels. Where radon problems exist, it is im- portant to evaluate exactly what should be done. In homes with concrete basement floor slabs, the diagnostic approach receiving wide acceptance is to check for com- munication under the slab. Subslab de- pressurization is commonly used to remove the radon gas using a fan and piping that exhausts to the outdoors; but diagnostics are necessary to ensure that the suction, and thus airflow, extends over the entire subslab area. The total openings through the slab or basement walls need be only a few square centi- meters for significant radon entry to take place. Just sealing the basement or crawlspace may not be enough, since sealing techniques rarely cover every possible floor or wall radon leakage site. Diagnostics, after mitigation devices are in place, are necessary to ensure that the job has been done correctly. An informed homeowner or private testing agency is recommended for these checks, to avoid the conflict of interest of a mitigator being asked to evaluate his own work. The workshop treated these radon diagnostic subjects in depth, look- ing at the pros and cons of diagnosing the radon troubled house before, during, and after mitigation. The techniques described here are evolving rapidly in a field where discoveries are being made daily. However, many of the diagnostic approaches may already be viewed as "standard," while many others are in the process of being developed. Radon Problem Assessment Diagnostics Gamma scans may provide the initial phase of the radon diagnostics. In the U.S., the National Uranium Resource Evaluation (NURE) uses an overflight approach to document broad land expanses. Because of local geological differences and local hotspots, low gam- ma readings should not be viewed as nonproblem areas; rather, the high level locations should be viewed as the first places to check. Such scans needn't be from aircraft but may use vans or on-foot surveys. Vans are limited to access roads and on-foot surveys may be limited by time constraints. Surveys may be very detailed using miniature gamma sensors which can supply very local readings. Soil gas measurements are another approach to assessing the probability of local indoor radon problems. High radon levels in the soil gas (thousands of pCi/L), combined with soil information, can indicate the potential for elevated indoor levels. However, the number of measurements necessary to identify the radon problem potential for a particular construction lot could cost more than designing radon prevention into a house. Hotspots may be missed in the survey, even with a large number of samples. The best correlation between soil and indoor radon levels is provided by a homogeneous soil such as that found in sandy soils, for example in Florida. In npnuniform soils, 100- to 1000-fold differences in radon concentrations in the soil gas within a few meters may be observed. Rock fractures and direct soil gas conduits are one extreme in permeability and impermeable clay soils are the other; moisture and the mix of clay and sand can greatly influence radon passage. Soil gas measurements would appear to be useful in the general identification on a regional or "housing development" scale, but would require excessive testing for detailed, single building lot prediction. The preferred methods for soil gas measurement are grab samples for single point meas- urements or the charcoal canister method for time-averaged measurements. Sam- pling from at least 1 m depths is recom- mended to avoid atmospheric dilution. Problem house identification depends on indoor screening/measurement sur- veys. The way the house is operated, the tightness of the below grade construction, and the surrounding soil influence the resulting radon concentration in the house. It is essential that "closed house" measurements be made and that "fan out" approaches be considered carefully when the first high radon levels are measured in problem houses. Thus, the radon screening should be based on: 1) sampling during winter "closed house" seasons, 2) testing areas where houses have indicated very elevated indoor radon levels, and 3) increased sampling in areas where a high percentage of the homes exceed the 4 pCi/L EPA guideline. Screening questionnaires are impor- tant to radon problem assessment diag- nostics. Not only are such questionnaires useful in research house selection but they are important to the radon mitigator in evaluating whether confirmation meas- urements have been performed to sub- stantiate the indoor radon levels. Basic questions concerning house construction, operation, possible major entry routes, etc., are also part of the questionnaire. Questions can guide the homeowner on the need for professional assistance. Visual inspection and use of a ques- tionnaire can prove to be the diag- nostician's most useful tool. Photographs of house construction and blueprints may prove very valuable and serve to check the accuracy of the occupant's answers to the questionnaire. Identification of prin- cipal radon entry routes, using the questionnaire, may preempt the need for other diagnostics. Research needs are evident in radon problem assessment diagnostics. Al- though certain housing types are rela- tively well understood, slab-on-grade and basements with exposed soil and other complicating factors are not well charac- terized and need a larger data base. Basic research on radon availability, transport, and entry into buildings is needed to better understand the phe- nomenon being dealt with and develop better mitigation and prevention tech- niques. Modeling radon entry, to correlate geological factors and indoor radon levels, is an area in which little research has been carried out. Premltlgatlon Diagnostics Promulgation diagnostics concentrated on specific features of the home, the radon transport involved, and diagnostic ------- techniques to choose the appropriate mitigation approach. Between the researcher and mitigator, premitigation diagnostics moves from detailed time consuming techniques aimed at im- proved understanding to measurements sufficient to guide the mitigator to successful solutions. Mitigators at the workshop explained the approaches currently in use. The simplest diagnostics included only visual inspection. The more complex diagnostic procedures added grab samples of local radon concentrations, differential pres- sure measurements to document "radon driving potential," and subslab and wall airflow communications testing. In one instance, the mitigator quantified the airflows through test openings in the floor to better understand the nature of the below-slab airflow and thereby determine the size of the mitigation system needed. Recent construction offers the best chance for success, where sufficient aggregate under the slab tends to ensure good airflow communication. Visual inspection is a natural diagnostic tool if the type housing is well understood and the mitigation method has proven to be effective. For example, the experienced mitigator using subslab depressurization in housing where there is good communication via the subslab aggregate will use visual inspection to locate the subslab penetrations, exhausts, and fans. Without diagnostic measurements, one will not know whether too little or too much air is being exhausted. Nor will the mitigation system yield a best mode of operation, especially if more than one floor/wall de- pressurization point is being used. Even with these factors in mind, many mitiga- tors are using no premitigation diagnos- tics, rather they are installing mitigation systems and using post-mitigation radon concentrations to motivate any necessary system alternations. Communication testing has proved very useful. Subslab depressurization ap- proaches to radon mitigation have prompted this type of diagnostic meas- urement. Typically a vacuum cleaner is used to pull air through a test hole drilled through the slab. At other slab penetrations, airflow and direction are monitored with smoke tracers, sensitive flow measurement methods, etc. The dif- ferential pressure change between the basement and subslab is also a direct indication that flow is present and communication exists under the slab. An electronic digital manometer has proven to be an effective differential pressure measurement device. Several test holes are drilled to test various locations under the slab. Adding wall holes allows wall/floor communication to be checked. In each case measurable flows indicate that the final subslab ventilation system will be effective. Major airflow "short circuits" (e.g., an easy flow path to sumps or perimeter drains) make it difficult to achieve sufficient airflow across the subslab area. It also should be recognized when measuring differential pressures that heating, ventilating, and air conditioning systems that are not well balanced will often exert as much as a 5 Pa negative pressure when the air handler is on. Thus, it is necessary to achieve at least that magnitude of dif- ferential pressure to ensure that the miti- gation system is immune to such interactions. Grab samples using Lucas cells through the same test holes (prior to communication testing) indicates the radon source strength and variability. These samples may also be taken at crack sites or other points of possible radon entry, including hollow block walls. The purpose is to better locate the prin- cipal radon sources and from that deter- mine the mitigation approach. The same grab sampling technique may be used in the soil surrounding the house. From these 1 m deep locations, soil perme- ability can also be measured. The prob- lem is that correlation between what the soil reveals and the radon problems in the house is yet to be established. Cases of high inside radon concentrations on the sides of the houses that indicated lower soil readings are not uncommon; hence this diagnostic procedure has not proven very useful. (How readily the radon can be transported, and very local variability in soil properties and source strength help determine the severity of a particular radon problem.) Blower door tests are used for a variety of purposes in premitigation diag- nostics. Regular blower door tests, which relate the amount of air flow into (or out of) a house under a specific amount of pressurization (or depressurization), are used to determine the effective leakage area; i.e., the "leakiness" associated with a particular house. If the test is applied only to the basement area, it is possible to determine the amount of air flow necessary to maintain a basement pres- surization of between 5 and 10 Pa. This is the amount of "counter-pressure" which should be sufficient to prevent con- vective entry of radon gas. If the air flow determined from the blower door test is less than about 600 m3/hr (ideally below 350 m3/hr), basement pressurization may be a viable mitigation strategy if subslab depressurization is not suitable. Another use of a blower door test is to determine how much air exchange is needed in the basement or crawlspace for a heat recovery ventilator to effectively remediate a radon problem using dilution. A depressurization of the substructure to -10 Pa by the blower door can be used in the summer to simulate winter stack effect, although there is some question of the reality of this simulation. In this -10 Pa depressurized mode, grab samples, pressure differentials, and air velocities through the substructure test holes can be recorded and used to deter- mine radon source strengths at specific points (in the depressurized mode). Tracer gas measurements can be used in premitigation diagnostics to augment communication testing. Also, leaks through the exterior of the substructure can be located using tracer gas tech- niques (and sealed if a tighter basement is necessary for success of a basement pressurization system). One example is that tracer gases can be used to find a footing drain. Mitigation Installation Diagnostics Four radon mitigation approaches were discussed in the workshop, along with re- lated diagnostic procedures. Sealing was the first mitigation method mentioned, where Canadian studies in- dicate that a total area equal to 1 cm2 opening in the basement slab or walls is all that can be allowed if the sealing approach is to be successful. Quality control is thus extremely important, as well as the choice of materials. Epoxies often don't bond well with themselves; they require special surface preparation, and bonding to the surroundings is vital. Sealing, properly done, is viewed as expensive and difficult but not impos- sible. The best success would be antic- ipated in new construction where an experienced team is required, using com- mon sense in the choice of sealing meth- ods. A specific recommendation was the use of a sealant such as solvent-harden- ing, rubberized asphalt. Tracer gas meth- ods are also recommended in assessing radon leakage paths and determining the success of sealing. Dilution was the second general meth- od discussed for radon mitigation. Pre- cautions with this approach include ensuring that the air intake isn't near radon sources or near the ground, and avoiding short circuiting (air exiting prior to complete mixing). Diagnostics for dilu- tion methods include the use of the ------- blower door to evaluate the envelope leakage rate of the house as well as to catalog bypass leakage areas which allow radon to move within the building. For example, unless appropriate tightness levels are present it may make no sense to use heat recovery ventilation. The blower door tests can also be used to evaluate communication between zones. Pressure measurements can be used to ensure that indoor pressures are slightly positive (by a few pascals) rather than negative, to avoid drawing radon into a living area. Airflow measurements may make use of pilot tubes, heated-wire anemometers, vane-type anemometers, etc., in ducts or pipes. A grid-type measurement, such as a pitot tube grid, is a superior approach to averaging flow profiles. Tracer gas measurements are also very useful in flow measurement and air movement, as well as detecting leaks in the system. Use of a continuous radon monitor as a diagnostic tool allows exhaust air radon concentrations to be evaluated, and to ensure that exhaust flow isn't being reintroduced to the house by the supply air. Because of shorter air residence times, dilution may result in reduction of working levels greater than the radon levels themselves. Radon pro- files (as a result of multilocation testing) may be used to check for hotspots. One approach is to flush out the radon with high initial ventilation and then observe the ingrowth of radon. This diagnostic method may be used to evaluate the amount of ventilation required to meet the 4 pCi/L EPA guideline (this is an annual average concentration). Pressurization of the basement was the third category discussed. Separation of the basement/crawlspace from the up- stairs is an initial requirement. If upstairs air is used to pressurize the basement, care must be taken with the venting of upstairs combustion devices. Use of the blower door is recommended to check for air leaks between zones, crack leakage to the outdoors, and back-drafting of appliances. Flow of approximately 850 m3/hr, and pressure differences of at least 3 Pa are representative numbers for judging airflow requirements for pres- surization. Turning on all venting appli- ances is one way to check if a mitigation system maintains proper pressurization. Subslab depressurization was the fourth approach discussed. Using the slab as the separation between house space and soil gas, depressurization of the subslab must be sufficient to overcome stack effects (buoyant airflow in the house that depressurizes the basement) and venting appliance opera- tion since the resulting basement depres- surization can move soil gas through the slab and walls to the living space. Sensitive pressure measurement tech- niques (such as electronic digital manometers) may be used to evaluate the pressure differences, and smoke tracers can determine the direction of air movement. The lowest pressure drop locations across the slab are the critical zones and should not be located near any radon hotspots. Since the exhaust from the subslab depressurization contains high radon concentrations, avoiding reentrainment is essential; tracer gas techniques work well in this check. The exhaust also often contains high levels of moisture, making it essential to design piping to avoid water ac- cumulation and eliminate pipe blockage or fan damage. Again back-drafting of the combustion appliance can be influenced by the operation of the radon mitigation system since air is being removed from the house substructure. Indication of spilling of exhaust products into the space may be documented by a small temperature-sensitive "tab" at the flue entry. Spillage tends to be worst at the start of combustion appliance operation. Use of blower door techniques can also supply information on the required air leakage necessary to supply combustion devices. Dedicated makeup air to the appliance is highly desirable. Post-mitigation Diagnostics Radon monitoring is the principal post- mitigation diagnostic test commonly utilized by commercial mitigators. The first question is: Should the emphasis be on measurement of radon or progeny? Currently most people measure radon gas. One reason is that it is simpler to measure radon gas, with charcoal canis- ters and alpha-track detectors. Radon measurements might provide a less ambiguous indication of mitigation perfor- mance. Radon might even provide a better indication of health risk (given that only a relatively inexpensive measure- ment can be made, and that the working level (WL)-versus-particle size measure- ments needed for dosage/risk models are thus impractical for routine use); the radon is tracked by reading the value for Polonium-218, which—as the daughter with the greatest fraction unattached -- probably represents the largest co- ntribution to the health risk. There is a need for technical clarification of the EPA guideline of 4 pCi/L or 0.02 WL because the equilibrium value between radon and radon progeny is variable (sometimes as much difference as 50%). However, because the EPA guideline is expressed as 4 pCi/L or 0.02 WL, with no reference to a specific equilibrium relationship, it is sufficient guidance from a policy perspective. Who makes the measurement is an- other question in post-mitigation radon monitoring. A mitigator faced with the question of liability needs direct knowl- edge of how the mitigation system is functioning. Also, information on the success of the mitigation method aids the mitigator in selecting mitigation ap- proaches for other homes. The home- owner wonders if the problem has really been solved and might want an inde- pendent measurement, made by some- one other than the mitigator. Federal or state government representatives may be most interested in how well the mitigators are performing from a public health standpoint, and therefore may desire an independent evaluation of radon levels. These results may dictate which mitiga- tors are placed on a "recommended list," where local or state government main- tains such a list. Wow long to test is the next question. Short-term monitoring is essential, im- mediately after radon mitigation system installation, to confirm that the system is functioning properly. In addition to this immediate measurement, an integrated measurement over 2 to 3 months (alpha track) in the winter is a recommended minimum evaluation. The need to de- velop 2-week monitors as an intermediate measure was also discussed. Arriving at an annual average radon exposure is a point that needs further clarification; if the 4 pCi/L guideline is interpreted as the annual average that a homeowner should try to achieve, then measurements might cover a full year. Multi-year monitoring could be valuable in evaluating changes in mitigation system efficiency and/or variations in the radon source strength over time. Annual and multi-year measurements would probably not be conducted by the mitigator, but would be the responsibility of the homeowner, or might be carried out by researchers or state agencies. Inexpensive monitoring devices may be heading to the marketplace to help solve some of these radon monitoring problems. Where do you monitor is the next logical question. Measurements are nor- mally taken in more than one location: in the living area, both upstairs and downstairs, in the basement/crawlspace, and in other locations cited by the home- owner as important. Protocols must spec- ify monitoring location. By surveying the radon levels throughout the house (radon ------- profile), one is less likely to miss a high radon area, and also these data can be the basis for estimating total occupant radon exposure. The basement (or per- haps crawlspace) area normally registers the highest radon levels and thus is most sensitive in revealing if any radon prob- lem still exists after mitigation. Which monitoring technique is another question. Charcoal canisters and alpha- track detectors are popular because of ease of use and relatively low cost. For immediate information on radon concen- trations, grab and continuous radon sam- pling are popular. There remain several uncertainties associated with the vari- ability in indoor radon levels (which are evident from continuous radon data). In view of all the uncertainties, there would appear to be a need for a standardized procedure that could be routinely applied in the post-mitigation period. Other diagnostics should also be considered. Diagnostics other than checking radon concentrations are usually not done routinely by commercial mitigators. Testing of the final pressure field under the slab after installation of a subslab ventilation system was empha- sized by several workshop participants as important to consider as a post-mitigation diagnostic measurement. Assurance that combustion devices are not back-drafting is also an important post-mitigation measurement. Measurement of flows and pressures in piping associated with the mitigation system can be important in the post-pressure-mitigation diagnostics as well as during system installation. Mounting a pressure gauge (or pressure switch) on the piping to indicate proper system function is being used and is a form of a post-mitigation diagnostics that assures the homeowner that the system is functioning satisfactorily. Acknowledgments The authors wish to acknowledge the contributions of Michael Mardis, Michael Osborne, and Bruce Henschel who served as session chairmen for the work- shop and provided guidance in sum- marizing the diagnostic methods dis- cussed in this summary. The authors also wish to acknowledge the sponsorship of the U.S. Environmental Protection Agency for the workshop under EPA Co- operative Agreement CR814014-01-0. #U.S. GOVERNMENT PRINTING OFFICE 1989/748-012/07187 ------- |