Site Mitigation & Restoration Program

We protect and maintain California’s land and places
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Human and Ecological Risk Office

Human Health Risk Assessment


Rulemaking Notice

Toxicity Criteria Selection for Risk Assessments, Screening Levels, and Remediation Goals

On September 4, 2018, the Toxicity Criteria for Human Health Risk Assessments, Screening Levels, and Remediation Goals rule was approved by the Office of Administrative Law and became immediately effective. For further information please click on the link below.

NEW – DTSC Toxicity Criteria Rule for Human Health Risk Assessments: Response to Frequently Asked Questions (FAQs).

 DTSC Developed the following brief answers to the most frequently asked questions regarding the Toxicity Criteria Rule.

HERO Quarterly Updates

Quarterly information from HERO with important recent updates on human health risk assessment.

HERO Roles and Responsibilities

As a training tool and to facilitate consistent HERO Toxicologist review of submitted risk assessment and toxicology documents an outline of HERO Roles and Responsibilities was developed.  This document includes: 1) a general outline of both the human health and ecological risk assessment processes with associated HERO guidance documents; 2) the components of a human health and ecological risk assessment the HERO Toxicologists are expected to address in each review; and, 3) identification of some site data report components that may, on occasion, require review by the HERO Toxicologist.  A dispute resolution process is outlined with a proposed timeframe for those technical review documents where the requestor may question the necessity or direction of technical review comments. 

Human Health Risk Assessment Guidance

Preliminary Endangerment Assessment Guidance Manual (PEA Guidance Manual) (January 1994. Revised October 2015).

This manual provides guidance on the basic information needed to determine if a release of hazardous substances to the environment presents a risk to human health or the environment. It explains how a PEA ties into the cleanup process and provides technical recommendations for conducting a PEA site investigation and human health and ecological screening evaluations. The manual also makes recommendations on how a PEA report should be organized and what information should be included in the report.

Use of the Northern and Southern California Polynuclear Aromatic Hydrocarbon (PAH) Studies in the Manufactured Gas Plant Site Cleanup Process (July 1, 2009) The purpose of this advisory is to describe how the ambient conditions for carcinogenic polynuclear aromatic hydrocarbons identified by the Northern or Southern California PAH Study (i.e., the ambient data sets) might be used as a pragmatic tool in various stages of the soil cleanup process at manufactured gas plant (MGP) sites. Additional files available for download include the Northern and Southern California PAH studies and their corresponding ambient PAH datasets.

Arsenic Strategies: Determination of Arsenic Remediation – Development of Arsenic Cleanup Goals January 16, 2009

During the site investigation, arsenic may be identified as a chemical of concern based on comparisons to naturally occurring background concentrations. Once arsenic has been identified as a chemical of concern, a standard approach is needed to determine if remedial action is warranted and, if so, how to develop appropriate cleanup goals.

Ambient Metal Concentrations

This guidance document presents several useful principles for defining the local ambient data set, including pooling all data from all impacted sites and locating ambient conditions in the presence of possible contamination.

Background Metals at Los Angeles Unified School Sites – Arsenic

This guidance is intended to supplement the DTSC PEA Guidance Manual (DTSC1994), and provide a uniform and streamlined approach for evaluating background arsenic at LAUSD school sites.

Human Health Risk Assessment Note 1 – Default Human Health Exposure Factors, April 2019
This note summarizes exposure factors which may be used as default values in human health risk assessments for California hazardous waste sites and permitted facilities.

Human Health Risk Assessment Note 2 – Dioxin, April, 2017
Soil Remedial Goals for Dioxins and Dioxin-like Compounds for consideration at California Hazardous Waste Sites. This note presents a suite of suggested Dioxin-TEQ soil remediation goals that have been developed for consideration at mitigation sites in California for the protection of human health. These goals may be revised in the future, as new scientific information becomes available.


Human Health Risk Assessment Note 3 – DTSC-Modified Screening Levels (DTSC-SLs), June 2020 Update.

HHRA Note Number 3 presents recommended screening levels (derived using DTSC-modified exposure and toxicity factors) for constituents in soil, tap water, and ambient air.  This June 2020 update incorporates the U.S. Environmental Protection Agency’s May and November 2019 releases of their regional screening levels and other changes, and is compliant with the September 2018 Toxicity Criteria Rule (see text).  This update supersedes the April 2019 Update to HHRA Note Number 3.

Links are provided for download of the HHRA Note 3 narrative and screening-level document, and to spreadsheet-based versions of the screening-level tables for users’ convenience.  Supporting documentation of the computations for the DTSC SLs can be provided upon request (contact

Human Health Risk Assessment Note 4 – Screening Level Human Health Risk Assessments

In a memorandum dated October 28, 1994, the Human and Ecological Risk Office recommended guidelines for use of the U.S. EPA Region 9 Preliminary Remediation Goals (PRGs) at military sites. Subsequently, the U.S. EPA released Regional Screening Levels (RSLs) to replace the PRGs. In HHRA Note 3, HERO addressed the recommended methodology for use of U.S. EPA RSLs in the human health risk assessment process at DTSC sites. HHRA Note 4 outlines the current recommended methodology for conducting screening level human health risk assessments, and is an update which replaces our 1994 memorandum and earlier versions of Note 4. This revision incorporates HERO recommendations based on the adoption of the Toxicity Criteria Rule and recommendations for sites with vapor intrusion into indoor air.

Human Health Risk Assessment Note 5 – Indoor Air Action Levels for Trichloroethylene (TCE), August 23, 2014

The U.S. EPA Region 9 released trichloroethylene (TCE) guidance on December 3, 2013 for expanded sample collection in the investigation of the Vapor Intrusion (VI) exposure pathway at specific National Priority List (NPL) sites in the San Francisco, CA South Bay. Accelerated Response Action Levels and Urgent Response Level Action Levels for indoor air concentrations of TCE under residential, commercial/industrial (8-hour workday), and commercial/industrial (10-hour workday) exposure scenarios were presented in this document. Use of these Region 9 Interim Action Levels to sites beyond the NPL South Bay sites in San Francisco, California was provided in the June 30, 2014 U.S. EPA Region 9 Regional Toxicologist’s memorandum, released under a July 9, 2014 transmittal memorandum from Enrique Manzanilla, Director of the Superfund Division, U.S. EPA Region 9.

Human Health Risk Assessment Note 5 describes how HERO recommends implementation of the TCE Action Levels contained in this EPA Region 9 guidance, specifically on the issues of: 1) applicability to all sites where VI is being evaluated; 2) interim measures; and, 3) response actions.

Human Health Risk Assessment Note 6 – Recommended Methodology for Evaluating Site-Specific Arsenic Bioavailability in California Soils

This note introduces the California Arsenic Bioaccessibility (CAB) method. CAB is the recommended in vitro method for site-specific evaluation of arsenic bioavailability where arsenic levels in soil are 1500 mg/kg or less. It can accurately predict in vivo relative bioavailability (RBA) and can be used in place of expensive and time-consuming animal studies. The use of site-specific RBA reduces the uncertainty of the risk assessment thereby improving remedial decision making. Using the CAB method, where appropriate, often leads to a more effective use of the resources available for remediation without compromising the level of health protectiveness. The CAB method is the outcome of a Brownfields Training, Research and Technical Assistance Grant from the US EPA (Brownfields Research Cooperative Agreement TR – 83415101) and was developed in collaboration with Nicholas Basta at The Ohio State University. For more detailed information on how the method was developed and additional work completed under this grant please refer to our Arsenic Relative Bioavailability Study web page.

Human Health Risk Assessment Note 8 – Recommendations for Evaluating Polychlorinated Biphenyls (PCBs) at Contaminated Sites in California

This HHRA Note (updated in June 2020; see “WHAT’S NEW” section) was developed, in part with funding from the DTSC State Response Program (SRP) grant, to be a resource for use by DTSC staff as well as external stakeholders to address key technical issues related to evaluation of exposures and health risks, including regulatory framework, conceptual site model, sample collection and analysis, data evaluation, and human health risk assessment at sites contaminated by leaks or releases of PCBs. The contents of this Note are not regulatory requirements, and do not address site-specific considerations for these topics. It also does not discuss other site characterization and risk management issues such as remediation methods and risk communication. Moreover, the USEPA should be consulted on management and cleanup of products manufactured with PCBs (e.g., transformer oil, fluorescent light ballasts, and caulking) and PCB-contaminated floors/walls that are regulated under the federal Toxic Substances Control Act (TSCA).

Human Health Risk Assessment Note 10 – Toxicity Criteria
On September 4, 2018, the State of California Office of Administrative Law approved the Toxicity Criteria for Human Health Risk Assessments, Screening Levels, and Remediation Goals Rule. The Rule requires human health risk assessments, risk-based screening levels, and remediation goals prepared pursuant to the Hazardous Substances Account Act (Health and Safety Code [HSC] §25300 et seq., “Chapter 6.8”) to be based on a specified hierarchy of toxicity criteria. HHRA Note 10 addresses the specification of required and recommended toxicity criteria under the Rule. For user convenience, a link to a functional workbook version of the HHRA Note 10 tables is provided below.

Human Health Risk Assessment Note 11 – Southern California Ambient Arsenic Screening Level

DTSC assembled a data set of arsenic soil concentrations from five southern California counties (Los Angeles, Orange, Riverside, San Bernardino and San Diego) and developed an upper-bound estimate of the regional ambient arsenic soil concentration that can be used as a screening tool for sites throughout southern California. HHRA Note 11 summarizes the development of this regional, ambient arsenic concentration and provides guidelines on how it should be used in evaluating sites in southern California.

Human Health Risk Assessment Tools

Community Air Monitoring Plan (CAMP) Guidance (January 2020)

This CAMP Guidance describes air monitoring protocols and operational controls to be performed during soil activities when fugitive emissions (i.e., dust and/or vapors) could be released.  It also presents methods to establish site-specific action levels for compounds of concern (COCs) in ambient air to protect the community from fugitive emissions containing these compounds.  A CAMP is required at response sites under DTSC’s oversight whenever remediation or removal activities may release site COCs into the air, so site workers can react quickly to make appropriate changes to emission control measures, as needed, to minimize fugitive emissions during authorized work.

The CAMP Guidance has been prepared by the DTSC Health and Safety Program in collaboration with HERO for the protection of public health and to ensure compliance with applicable regulations.  In compliance with Assembly Bill 434, this document is accessible using the NVDA screen reader. If you find that this document is not accessible with your accessibility software please contact Sarah Berry for further assistance.


OEHHA “Schoolscreen” Spreadsheet

HERO no longer recommends the use of the OEHHA “Schoolscreen” spreadsheet (last updated January 2010) for evaluation of school sites, as the spreadsheet model is outdated and no longer supported by the OEHHA. Please consult with a HERO toxicologist for evaluating health risks in such cases.


LeadSpread is a tool for evaluating exposure and the potential for adverse health effects resulting from exposure to lead in the environment. An updated version of LeadSpread has been developed (LeadSpread 8; 2011) to incorporate the updated CalEPA incremental lead toxicity criterion of 1ug/dL (OEHHA, 2007), as well as ensure that the model is adequately protective of women of child-bearing age.  The link to LeadSpread 7 is maintained for sites outside California being evaluated based on the 10 ug/dL total blood lead criterion.


Cancer Potency Factors and Reference Doses
Cancer Potency Factors and Reference Doses are available from the California Office of Environmental Health Hazard Assessment.

Vapor Intrusion Guidance And Tools

Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion – February 2020

The Department of Toxic Substances Control (DTSC), State Water Resources Control Board, and San Francisco Bay Regional Water Quality Control Board have developed supplemental vapor intrusion guidance for conducting vapor intrusion evaluations in California. The Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion is available for review and public comment until 12:00 noon, April 30, 2020.  See the DTSC Vapor Intrusion webpage for information.

Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor AirFinal (October 2011; also known as the Vapor Intrusion Guidance)
DTSC’s Vapor Intrusion Guidance provides a process for the investigation of subsurface vapor intrusion into indoor air and describes procedures for screening and site-specific evaluation of potential risks associated with this exposure pathway. Indoor air concentrations estimated from soil gas or groundwater concentrations by default vapor attenuation factors, vapor intrusion modeling, and/or measured indoor air concentrations are used in the assessment. Models for estimating indoor air concentrations include the DTSC modification of the U.S. EPA version of the Johnson and Ettinger vapor intrusion model with default and site-specific inputs.

Advisory – Active Soil Gas Investigations (July 2015). This Cal EPA Advisory was jointly revised and updated July 2015 by DTSC, Los Angeles Regional Water Quality Control Board (LARWQCB), and San Francisco Regional Water Quality Control Board. This updated Advisory provides technically consistent approaches and best practices for collecting and analyzing soil gas samples. Data obtained from soil gas investigations can be used to identify the spatial distribution of volatile contamination at a site and assist in the evaluation of vapor intrusion.

The DTSC Screening-Level Model spreadsheets that used the Johnson & Ettinger (J&E) model to predict theoretical indoor air concentrations of contaminants from soil gas and groundwater data have been removed because they were not updated and are not based on the most current J&E model spreadsheet tool from USEPA.

Page last updated September 16, 2020.