Use of Site Screening Levels at Contaminated Properties

So just how clean is your property? Are you concerned if known contaminant levels in soil or groundwater warrant additional assessment or cleanup of impacted areas? These are questions that are posed to many property owners and stakeholders of sites where contamination has been discovered. Screening levels for soil, soil vapor, indoor air, and groundwater are commonly used to determine the severity of contaminants and to evaluate if a site needs a risk-based assessment, a conventional subsurface assessment, or remediation. Screening levels are particularly helpful where low levels of contaminants are detected. ​

Screening levels for chemicals of potential concern (COPCs) are used for each medium (soil, air, water) and for different land-use scenarios (residential or industrial/commercial). In general, for soil and ambient (indoor) air, the preferred screening levels to use are the Department of Toxic Substances Control (DTSC) Human and Ecological Risk Office (HERO) Note #3 (January 2018) screening levels. If a COPC of interest is not included in the HERO Note #3 tables, then we use the most recent (May 2018) US EPA Regional Screening Levels (RSLs). The air screening levels for VOCs could also be used to screen for soil vapor concentrations when used in conjunction with an appropriate attenuation factor as described in DTSC’s 2011 Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air.

In addition, Environmental Screening Levels (ESLs) prepared by the San Francisco Bay Regional Water Quality Board (SFRWQCB) provide conservative screening levels at sites with soil and groundwater contamination. ESLs address a range of media (soil, soil vapor, indoor air, and groundwater) and a range of concerns (e.g., impacts to drinking water, vapor intrusion, and impacts to aquatic life). Even though they were prepared by SFRWQCB staff, the ESLs are commonly used at impacted sites throughout California.

For groundwater, the preferred screening levels to use are still the California Maximum Contaminant Levels (MCLs). These are regulated, performance-based levels used to determine cleanup goals in aquifers or wells. MCLs include a wide variety of COPCs, including VOCs, semi-volatile organic compounds, and metals. 

There are also the screening levels in the State Water Resources Control Board’s Low Threat Closure Policy for soil, soil vapor, and groundwater. These are specific to petroleum underground storage tank cases and are dependent on site and media-specific criteria. 

In addition, for VOCs in soil, the Los Angeles Regional Water Quality Control Board (LARWQCB) uses the Attenuation Factor method to calculate screening levels that are based on soil type and the vertical distance above groundwater. These soil screening levels are protective of groundwater and apply primarily to VOC sites regulated by the LARWQCB-Site Cleanup Program.

As you can see the use of site screening levels is extremely varied and are site and regulatory-specific. Which screening levels to use depends on site-specific conditions and regulatory preference. 

For questions, please contact Steve Ridenour (steve.ridenour@altaenviron.com) or Mike Cassidy (mike.cassidy@altaenviron.com). We can also be reached by phone at 562-495-5777.

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