Contaminated sites undergoing remediation are managed with cleanup goals that are driven by guidelines and regulations published by regulatory agencies. Many regulators now require the collection of environmental data which may not be published in guidelines to assess closure.
Closure plans are prepared to supplement work plans for contaminated sites when a property owner is interested in obtaining No Further Action letters from the lead regulatory agency. Closure plans provide a description of administrative and technical requirements and factors supporting closure, including cleanup goals based on indoor vapor intrusion pathways and groundwater intrusion pathways. Communicating closure strategy is effective for early regulatory approval. Although regulatory input does not guarantee a change in the regulators requirements, it allows early review and approval of data and models.
Site closure requires that a site meets a criteria which may include substantial removal of contaminant mass impacting; demonstrating that cost effective remediation has been performed; calculating cleanup goals in accordance with all applicable regulations; comparing site conditions to cleanup goals; and assessing risks to the environment and human health risks, including direct contact and indirect pathways such as indoor vapor intrusion.
The closure approach requires outlining the following site-specific factors:
- Site-Specific Regulations for Cleanup – Developing Closure Plans requires a review of local regulations governing site cleanups. These include regulations associated with water, groundwater, air, health risk, and environmental protection published by regulatory agencies mandated to protect the environment.
- Site Development Plans and Land Use – Current property uses and potential site development are used to evaluate the type of site closure. For unrestricted land use, the cleanup requirements may be protective of all types of development, including residential standards. Identifying the potential of future development or land use at a site and the impact on property value should be considered by the property owner and the regulator when applying for site closure.
- Regional Groundwater Conditions – The presence of impacted regional groundwater and the source of groundwater impacts are evaluated. The plans may include a specialized assessment of site-specific conditions such as plume capture, breakdown of chemicals and the formation of byproducts, monitoring, upstream contaminant sources, and estimates of chemical mass present at the site.
- Impact of Breakdown Products – Identify the impact of breakdown products at a site. Priorities in remediation and operations that may be driven by the breakdown of chemicals in the environment and the production of byproducts that may affect the performance of the remediation process, increase long term costs, or increase the potential of vapor intrusion pathways. Examples include soil vapor monitoring in Perchloroethyene (PCE) and Trichloroethylene (TCE), contaminated sites to assess if biological activity degrades chemicals into vinyl chloride, or if (Methyl-ter-Butlyl-Ether) MTBE breaks down in groundwater into products such as Ter-Butyl-Alcohol (TBA).
- Cleanup Goals Based on Vapor Intrusion Pathway – Health risks associated with potential vapor intrusion have been estimated using Johnson & Ettinger model. The model is used to calculate cleanup goals in shallow soils. Vapor intrusion pathway is an issue of increasing regulatory concern, and many regulators require modeling to determine if the property is acceptable for industrial/commercial or residential land use. Soil vapor surveys are designed to collect the necessary data and to identify potential indoor air health risks.
- Groundwater Impact Pathway – Some cleanup models published by regulatory agencies intended to calculate cleanup goals can be conservative. Other highly accepted computer models are available to estimate the impacts to groundwater. VLEACH models (among others) have been used to estimate the impacts to groundwater.
- Specific Action in Managing Site Remediation Systems – Closure Plans may incorporate additional monitoring and environmental data collection requirements at the remediation processes to optimize the process effectiveness. At the end of the remediation period, optimization data demonstrates that cost effective remediation has been performed. If performance data collection requirements for remediation are identified, the operation and maintenance procedures and instrumentation are modified.
Closure plans enhance communication with the regulators who seek early approval into remediation objectives and assist in providing the regulator with a comfort factor. This in turn allows the client to proactive, which allows time for planning, scheduling, and cost effective project execution.
Assessing Indoor Vapor Intrusion Pathways and Groundwater Intrusion Pathways
Models for indoor vapor intrusion pathways and groundwater intrusion pathways are prepared by specialists with many years of experience. Previous Closure Plans and reports have been approved without modification by the regulatory agencies, including the California Regional Water Board (CRWQCB) and the Office of Environmental Health Hazard Assessment (OEHHA).
Assessment of vapor intrusion pathways includes calculation of cleanup levels in shallow soil, design of soil vapor surveys, installation of soil vapor monitoring wells, baseline assessments, and ongoing sampling of soil vapor (performed at the end of the remediation process). For VOC-impacted sites, vapor surveys are integrated with the remediation process to determine if VOC concentrations are rebounding in soil vapor.
Closure Plans have been successfully developed and implemented for high profile sites. Due to the increased level of oversight at many sites and a regulatory requirements, these plans can be used for underground storage tanks and other contaminated sites as an effective tool to identify if unrestricted land use closure is feasible, if deed covenants are required, and to facilitate site closure with the lead regulatory agency.