Risk-based tiered residential methamphetamine remediation limits

U.S. states that regulate methamphetamine (meth) contamination in residences require remediation to reduce meth surface concentrations to below a concentration limit. Existing limits vary widely, by 30-fold. States that have regulatory limits usually have a single limit that does not account for the extent of human contact with contaminated surfaces in different parts of residences (e.g., bedroom vs. attic). Actual exposure in low contact areas does not contribute to total occupant dose as much as that in high contact areas, yet contributes similarly to remediation costs under the single limit paradigm. Heating, ventilation, and air-conditioning (HVAC) systems are also usually subject to the same limits despite low contact and without a basis in risk analysis. Methods for averaging test results into a compliance metric also affect remediation cost. This study analyzes the changes in total occupant meth dose and the concomitant reduction in remediation cost for various alternative concentration limits relative to these four issues. Residences were subdivided into normal occupancy areas (NOAs), low occupancy areas (LOAs) such as attics, moderate occupancy areas (MOAs) such as exterior hallways, and HVAC systems. Dose calculations were based on existing risk assessment methodologies, and cost reductions were based on contractor survey data and random residence sampling data. Raising only the conservative remediation limits adopted by some states to the California single limit would reduce the average cost to remediate a contaminated house from $21,000 to $10,000. Further raising limits to concentrations that remain below risk assessment boundaries is estimated to save an additional $5,000 on LOA and $2,000 on HVAC per remedial project. If all recommended alternate concentration limits are implemented, an estimated 50% cost reduction is possible with tiered limits based on contact time. These alternate limits still allow the occupant dose to fall below the recommended dose levels, which implies that these LOAs, MOAs, and HVAC systems are being over-remediated when they are required to be remediated to the same limit as NOAs.