Litoclean was one of the companies that worked on the drafting of the document and summarizes the main points to be taken into account.
NÚRIA RASÓS, MARC MEDINA, SONIA BALUK
The Waste Agency of Catalonia (ARC) has recently published the Guide to the intrusion of petroleum hydrocarbon vapors in indoor spaces, which includes the guidelines and criteria to be applied in the evaluation of these cases from the point of view of the risk for health. human health described in Royal Decree 9/2005 on contaminated soils.
For the preparation of the guide, the ARC has had the collaboration of three expert companies, including Litoclean, which have worked together to establish an adequate assessment of HCP vapor intrusion.
The document serves as a tool for decision making by developers, owners of potentially soil contaminating activities, consultants and technical personnel of the competent administrations.
What is vapor intrusion?
Before explaining the key points of this guide, it is important to describe what we mean by vapor intrusion.
Vapor intrusion is the migration of volatile organic compounds (VOCs) from the ground into nearby buildings and enclosed spaces. In other words, it is the process by which vapors from the soil or groundwater reach nearby buildings and contaminate the indoor air, endangering the health of those who occupy these spaces.
Generally speaking, the key components in hydrocarbon vapor intrusion (HVI) processes include volatile aromatics or BTEX, non-specific hydrocarbons classified in TPH groups according to type and carbon range (aromatics from C8 to C16 and aliphatics from C6 to C16) and potential volatile additives, such as MTBE and ETBE in the case of gasoline.
The following are the key points of the guide, which cover the first assessment to decide whether a detailed study should be carried out, the methodology and strategies for vapor sampling, the interpretation of the results obtained and the main guidelines for action plans and control programs.
Preliminary Study and Conceptual Site Model (CSM)
The Conceptual Site Model (CSM) is a fundamental part of the vapor intrusion assessment process. It aims to integrate the available information by emphasizing the relationships in space and time between impact sources and potential receptors. The SCM has to be updated with the acquisition of new data throughout the different phases of the investigation.
In the guide we find the minimum aspects to be included in the ECM in order to define if there is a complete pathway for vapor intrusion, i.e., if the receptor can be exposed to vapors from soil contamination.
In the preliminary study, with the MCE it will be necessary to assess whether there may be immediate risks that require emergency actions, define the areas of influence to be considered in the IVH and assess whether the impact of vapors in the subsoil is significant in relation to the risk.
Detailed evaluation (vapor sampling)
The detailed assessment will be based on obtaining direct vapor data. Measurements may include sampling of floor air, under-slab vapors and indoor air. These measurements may be complemented by other survey strategies or techniques, such as passive vapor surveys, vacuum testing, surface emissions, etc.
The guide discusses the different types of sampling, as well as the general criteria and basic guidelines for carrying them out. We also find a table with the number of recommended sampling points depending on the surface of the indoor space that is within the area of influence according to the lateral and vertical separation distances, as well as the number of campaigns according to the Margin of Safety (MS), which is the ratio between the maximum allowable concentration and the maximum estimated or measured concentration in indoor air.
Results interpretation
Before interpreting the results obtained, it is necessary to assess whether the available data are valid, representative and sufficient to evaluate the vapor intrusion process. If so, the interpretation of the data normally follows one of the following guidelines:
- Comparison with generic concentrations or quality levels of the sampled medium (in our country, generic soil vapor levels and concentration limits in soil and groundwater specific to IVH processes have not been published so far).
- Application of a generic attenuation factor on the maximum concentrations detected in the subsurface air to obtain the concentrations in indoor air and then compare them with the maximum allowable concentrations in indoor air.
- Application of a mathematical model to derive indoor air concentrations from results obtained in different media, taking into account more site-specific characteristics.
Action and Follow-up Plan
In the event that the presence of IVH is confirmed and poses an unacceptable risk to human health, action and monitoring measures must be implemented and can be defined following different strategies, such as subsoil remediation actions, mitigation actions or institutional controls. The selection of the action strategy is carried out depending on the site, the objective to be achieved and the type of solutions to be implemented, as detailed in the document.
Once the recovery and IVH control actions have been completed, a monitoring plan must be implemented, the objective of which is to monitor soil quality to ensure that the measures adopted ensure an acceptable level of risk and are permanent over time.
Both the action plan and the monitoring plan must be approved by the Agència de Residus de Catalunya.
