Document Type

Honors Thesis

Publication Date

Spring 5-8-2026

Abstract

Residential radon exposure is a leading cause of lung cancer worldwide, yet home testing and mitigation remain infrequent. Active mitigation systems can be costly, and existing passive radon-resistant construction techniques, while cost-effective, are not always sufficient to reduce indoor radon to below the recommended EPA threshold of 4.0 pCi/L (148 Bq/m3). This initial work examines the potential for a superficial biochar layer placed beneath a house foundation during construction to reduce soil radon exhalation and subsequent indoor radon concentration. Biochar is also being explored as an admixture to concrete, and this study investigates radon transmission through concrete with varying biochar content. Radon adsorption capacity in biochar depends on characteristics resulting from feedstock and production methods. To contextualize soil radon exhalation results, the biochar used in this experiment was characterized using a Nova BET Surface Area Analyzer following the Density Functional Theory (DFT) method, elemental analysis following the CHN in coal method, and qualitative surface morphology analysis using scanning electron microscopy (SEM) imaging. A field experiment was performed at two test sites to compare the soil radon exhalation rates of control, biochar, vapor barrier, and combined biochar/vapor barrier plots, and to compare radon transmission through concrete pavers with 0, 5, 10, and 15 percent biochar replacement. Field measurements were taken using a Durridge RAD8 continuous radon monitor with a soil surface emission chamber using a closed-loop method (CLM). Results showed a 63% reduction at Site 1 (0.38 vs 1.04 Bq/m²/min, p< 0.001) and an 82% reduction at Site 2 (0.21 vs 1.15 Bq/m²/min, p< 0.001) in mean soil radon exhalation in the biochar test plots versus control. Consistent with prior research, the vapor barrier and combination test plots showed near-zero radon exhalation, supporting the reliability of the methodology and measurements in this study. A preliminary evaluation of concrete pavers with varying biochar admixture percentages did not yield meaningful results with the methodology employed. Alternative methodology is proposed to assess radon transmission through concrete with biochar admixture. Some favorable radon adsorption characteristics were noted in the biochar used, including a high surface area (440.43 m²/g) and a mode pore width (0.48 nm) that falls within optimal range for radon capture (0.42-0.6 nm), though higher radon adsorption capacity is likely possible with a purpose-produced biochar. The significant reductions in soil radon exhalation demonstrated in this study show that a superficial layer of biochar holds promise as a passive method for residential radon mitigation. Further research is warranted to investigate system longevity, the influence of particle size class and thickness in the biochar layer on adsorptive capacity, and optimal biochars for radon adsorption. Keywords:

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