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They are intended to help expedite the identification and evaluation of potential environmental concerns at contaminated sites. ESLs address a range of media (soil, groundwater, soil gas, and indoor air) and a range of concerns (e.g., impacts to drinking water, vapor intrusion, and impacts to aquatic habitat).

The Department of Toxic Substances Control (DTSC) established a regional background arsenic concentration in soil that can be used as a screening tool for sites throughout southern California. The term "background" collectively refers to both naturally occurring and anthropogenic concentrations in shallow soil.

Screening levels are also used when a potential site is initially investigated to determine if potentially significant levels of contamination are present to warrant further investigation such as an RI/FS.

The DTSC residential use soil screening level for arsenic in soil is 0.11 mg/kg (DTSC 2019) resulting in a residential cancer risk estimate of 1E-04 for the upper-bound arsenic background screening concentration of 12 mg/kg and a residential cancer risk of 2E-05 for the 95% UCL arsenic concentration of 2.4 mg/kg.

The DTSC-modified screening levels based on noncancer effects were calculated to be 16 mg/kg and 230 mg/kg for residential and industrial land use, respectively.

Consistent with federal and state guidance, the Toxicity Criteria Rule defines risk-based screening levels to be 1×10-6 (one in a million) excess lifetime cancer risk from exposure and a hazard index of “1” for a noncancer effect for each contaminant.

They are intended to help expedite the identification and evaluation of potential environmental concerns at contaminated sites. ESLs address a range of media (soil, groundwater, soil gas, and indoor air) and a range of concerns (e.g., impacts to drinking water, vapor intrusion, and impacts to aquatic habitat).

Screening level risk assessment (SLRA) The SLRA process involves an assessment of exposure pathways and receptors. Contaminated sites that have acceptable risk under SLRA are considered to satisfy Contaminated Sites Regulation (CSR) risk-based standards.