What is an Environmental Screening Level (ESL)?
“I keep reading about how contamination levels are above the ESL, but all I really care about is closure. Instead, more samples and more talk about the ESL. I don’t know what this ESL is, but apparently I won’t get case closure until it is reached,” she said. “I’ve ignored it long enough - what is an ESL?”
“Good question,” I said. This prospective client came prepared with a tough question.
“ESL stands for Environmental Screening Level, '' I told her. “It’s the level of a chemical that signals there is a potential for harm to humans, water life, and animal life.” In the lull that followed, I added, “I know that’s a lot, so let’s start with where ESLs come from.”
Risk-Based Screening Levels (RBSLs) and Environmental Screening Levels (ESLs)
ESLs began as RBSLs
Risk-based screening levels (RBSLs) were first published by the San Francisco Bay Regional Water Quality Control Board (Board) in 2000 as a way to speed up human health and environmental risk assessments for contaminated sites.
Assessments were made easier by using a set of site conditions to estimate chemical levels (risk-based levels) that pose no harm and using them for comparison with levels at a contaminated site. If contaminant levels in soil, groundwater, or soil vapor were found to be below the RBSLs, then the site was considered low risk, otherwise, contamination levels were judged to be a potential risk.
The scope of the RBSLs expanded, and in 2003 the Board changed the name to Environmental Screening Levels (ELSs). Since then there have been several updates with the last in 2019.
The Board states that ESLs are not cleanup goals, however, the Board also states that for many sites ESLs are selected as cleanup goals. At a minimum, the Board accepts ESLs as preliminary cleanup goals.
“Okay,” my prospective client said. “What does low-threat mean?”
What is a Low-Threat Environmental Screening Level (ESL)?
In the context of ESLs, low-threat typically refers to chemical concentrations in soil, groundwater, or air that do not increase the chance of developing cancer or increase harm to humans.
For chemicals that cause cancer (carcinogen), low-threat means concentrations that result in less than one chance in a million (1 in 1,000,000) of developing cancer from lifetime exposure. For non-cancer-causing chemicals, a hazard quotient is used to gauge the potential for bodily harm. The hazard quotient is a ratio that compares the estimated exposure to a chemical to the reference level of that chemical at which no harmful health effects are expected. A hazard index of 1 or more indicates the potential for harmful non-cancer health effects.
“Well, thank you,” my caller said. “ If I understand you correctly, an ESL is an okay amount of contamination that is not a threat to human health and animals. I can appreciate that.” With that, we set up a time to talk about her site and ended our phone call.
Environmental Screening Levels and Cleanup Goals
We took a look at environmental screening levels, or ESLs, published by the San Francisco Bay Regional Water Quality Control Board. We noted that while ESLs are not specifically contamination cleanup goals, they can be used as cleanup goals and oftentimes are. Do you have a question about environmental investigation and cleanup? We have over 30 years of experience providing environmental services. Give us a call at 831-475-8141 or click the button below for a free consultation.