Remediation

In general, there are two ways in which to reduce indoor radon concentrations: either by preventing the radon from entering the building or by diluting the indoor high radon air with radon free or low radon air. The following are some common remediation methods used to reduce radon concentrations:

• Ventilation: As we saw in Chapter 3, the outside radon concentration is generally substantially lower (details are available from national or local authorities) than the indoor concentration, so by continuously replacing indoor air with outdoor air then radon dilution should occur [105]. Modern building regulations lay out mandates to provide adequate ventilation to ensure that harmful pollutants and moisture do

Figure 5.1: Passive ventilation (images courtesy of the EPA).

not build up inside buildings. There are different methods of ventilation which can be used to reduce the radon concentration indoors:

– Passive ventilation: Wall ventilation or window trickle ventilation can be installed to set up an air exchange (figure 5.1). Wall vents can be easily installed in existing buildings but they may not be a solution for larger buildings where some rooms have no outer wall. Passive ventilation is low cost and low maintenance and because of this, it is often used for slightly raised radon concentration or in combination with other remediation methods for higher radon concentrations.

– Underfloor ventilation: In buildings where the ground floor is suspended (timber or concrete floors) the use of airbricks or vents on outer, below floor level walls can set up an adequate underfloor ventilation, in order to prevent radon from entering the building and vent it directly to the outdoors instead (figure 5.2).

– Positive ventilation: The principle of this type of ventilation is to set up a positive pressure inside a building, thereby reversing the normal flow of radon into the building from the soil below. An intake of air from the outdoors would be drawn in to the attic space by a temperature (and hence pressure)

(a) Passive underfloor ventilation.

(b) Active underfloor ventilation.

difference; in colder seasons this would be assisted by adding heating to the space. A fan in the attic is installed to create an airflow in to the rooms below via ceiling ducts and force the air to exit out of the building via gaps or openings in the doors, windows and service pipes.

– Balanced ventilation: This system of ventilation creates an air supply and an air extraction which when in equilibrium would prohibit radon being drawn up from the ground below. In warm climates, it can be achieved by opening two windows/doors in opposite sides of the building but in cold climates this is not practical so it can be achieved though mechanical systems with heating. Finnieet al.reported that, though this method of ventilation was less effective than other methods and some users reported condensation problems in colder climates, it was durable over several years [141].

• Sub-floor de-pressurisation (sump): A warm environment inside a house creates a pressure difference between it and the colder ground below; this draws radon from the soil/rocks in to the building. As the temperature difference is generally larger in winter, the pressure difference is larger, creating a higher radon concentration indoors. To counteract this pressure difference and alleviate the flow of radon to the indoors, a cavity can be created inside the foundation wall and linked to a mechanical (figure 5.3c and 5.3d) or passive extractor fan (figure 5.3b) on the outer wall through piping. The radon soil gas is vented to the outdoors and quickly dissipates. Where the radon is vented at ground level, the vent will need to be positioned away from windows and doors so as to avoid it re-entering the house. This method of remediation is called sub-floor de-pressurisation or a sump. In Ireland, building regulations specify that dwellings built since 1998 must be fitted with a standby sump (figure5.3a) which can be later activated in the event that elevated radon concentrations are found inside the dwelling [142].

• Sealing: During the construction of new buildings it is favourable to lay a radon proof membrane which will prevent radon rising up through the foundations and into the building. In some countries, as is the case in Ireland, laying a radon membrane has been incorporated into the building regulations particularly in

(a) Standby sump. (b) Passive sump.

(c) Active sump (high vent). (d) Active sump (low vent).

high radon areas [142]. Other ways to seal a building are to fill cracks in the floors and walls or around entry points such as service conduits. Sealing is usually done in combination with another mitigation method as it can be difficult, almost impossible, to seal all entry routes.

Several publications detail the types and effectiveness of remediation methods [141,143– 147]. Hodgsonet al.in particular give a very comprehensive report on the different types of remediation, their effectiveness when implemented alone and in combination, the effect of different house characteristics on remediation success, the cost of the remediation types and dose reduction calculations following remediation, for a dataset of approximately 2,400 dwellings [145]. Both this study and Finnieet al.examined the radon reduction for the different types of remediation methods [141]. They found sub-floor de-pressurisation to be the most effective, and sealing and passive ventilation to be the least effective.

Fewer publications look at how the remediation methods perform after several years [141, 148]. Finnieet al.looked at the radon concentration 7 - 10 years later in 224 homes and found the radon reduction was 50 - 80% following remediation, but 7 - 10 years later the methods were not as effective and the reduction was 30 - 80%. Rydock et al.

conducted their study in a smaller sample of 12 homes and found that only 3 out of the 12 homes remained below the 200 Bq/m3 reference level after 10 years.

Building upgrades and insulating improvements can have an impact on radon remedies. A UK modelling study predicted an increase in the radon concentration by up to 57% if the air tightness of the dwelling was increased [149]. An experimental and comprehensive Swiss study showed an average increase of 26% in 163 dwellings which were measured before and after thermal retrofitting, with a 35% increase in radon concentrations seen due to replacing of windows alone [150]. A study completed in Ireland also found that the type of retrofitting dictated whether the radon concentrations would increase. Wall cavity and loft insulation showed no impact on the radon concentration but replacing or sealing doors and windows had a greater effect [151].

The type of remediation implemented will depend on the radon concentration, the structure and the type of building. Often a radon adviser is contracted to determine which method is most suitable, and it is also common that a combination of methods is

installed. When remediation has been implemented, a re-test should be performed to confirm that it has been successful. Following this, the building occupier will need to maintain the radon system and, though not specifically recommended in Ireland, complete intermittent retests, the frequency of which will depend on the remediation. Passive ventilation or sumps need little maintenance but mechanical methods need a regular service programme because if there is a fan failure then the radon concentration will increase again. The lifetime of the mechanical unit would be stated by the manufacturer and this would dictate the need for servicing or replacement. The EPA recommend checking active sumps every 5 years: Rydock et al.also recommend this time frame [148].

This chapter describes a project which re-visits schools that have been remediated 10 - 17 years previously to determine the durability of the remediation method implemented and consequently looks at the value of structured follow-up programmes. The study also hopes to ascertain the level of radon awareness in Irish schools and to ascertain the effects of subsequent retrofitting on the radon concentrations.