title: Domestic radon remediation of UK dwellings by Sub-Slab Depressurisation: evidence for a baseline contribution from constructional materials.
abstract: To quantify the effectiveness of Sub-Slab Depressurisation, widely used in the United Kingdom (U.K.) to mitigate indoor radon gas levels in residential properties, a study was made of radon concentration data collected from a set of 170 homes situated in Radon Affected Areas in Northamptonshire and neighbouring counties, remediated using conventional sump/pump technology. A high incidence of satisfactory remediation outcomes was achieved, with 100% of the houses remediated demonstrating post-remediation radon concentrations below the U.K. domestic Action Level of 200 Bq m(-3), while more than 75% of the sample exhibited radon mitigation factors (defined as the ratio of radon concentrations following and prior to remediation) <0.2. Two systematic trends are identified. Firstly, absolute radon concentration reduction following remediation is directly proportional to initial radon concentration, with a mean reduction factor of 0.96 and a residual component of around 75 Bq m(-3). Secondly, houses with lower initial radon concentrations demonstrate poorer (higher) mitigation factors. These observations support a model in which the total indoor radon concentration within a dwelling can be represented by two principal components, one susceptible to mitigation by sub-slab depressurisation, the other remaining essentially unaffected. The first component can be identified with radon emanating from the subsoil and bedrock geologies, percolating through the foundations of the dwelling as a component of the soil-gas, and potentially capable of being attenuated by sub-slab depressurisation or radon-barrier remediation technologies. The second contribution can be identified with radon emanating from materials used in the construction of the dwelling with a further contribution from the natural background level, and is essentially unaffected by ground-level remediation strategies. Modelling of a multi-component radon dependency using ground-radon attenuation factors derived from the experimental data, in conjunction with typical background and structural-radon levels, yields behaviour in good agreement with the observed dependence of mitigation factor on initial radon concentration.
authors.affiliation: Medical Physics Department, Northampton General Hospital, Cliftonville, Northampton NN1 5BD, UK. chris.groves-kirkby@ngh.nhs.uk <chris.groves-kirkby@ngh.nhs.uk>
authors.forename: C J
authors.initials: CJ
authors.lastname: Groves-Kirkby
authors.forename: A R
authors.initials: AR
authors.lastname: Denman
authors.forename: P S
authors.initials: PS
authors.lastname: Phillips
authors.forename: R
authors.initials: R
authors.lastname: Tornberg
authors.forename: A C
authors.initials: AC
authors.lastname: Woolridge
authors.forename: R G M
authors.initials: RG
authors.lastname: Crockett
mesh_terms: D016902:Air Pollution, Indoor; D000398:Air Pollution, Radioactive; D003252:Construction Materials; D052918:Environmental Restoration and Remediation / Q000379:methods*; D006874:Hydrostatic Pressure; D011886:Radon / Q000032:analysis*; D006113:United Kingdom
chemical_list: D011886:Radon