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Human and Ecological Risk Office (HERO)

Human Health Risk Assessment

Guidance | Tools | Vapor Intrusion Guidance & Tools

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. The Text of the Final Toxicity Rule Regulation is available at the link below.

Download Text of the Final Toxicity Criteria Rule Approved September 4, 2018

Toxicity Criteria that shall be used in this Final Toxicity Rule Regulation are listed in the Revised Toxicity Criteria Rule Appendix 1 – Tables A and B that is available at the link below.

Download Revised Toxicity Criteria Rule – Appendix I – Tables A and B 2018-08-31 updated

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 Revised 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.   HHRA Note 3 Revised was updated to address lead and cadmium. This update supersedes the June 2020 Update to HHRA Note Number 3.  A new HHRA Note 3 with a complete revision of screening levels is forth coming.

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 Edward.Fendick@dtsc.ca.gov).

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 on evaluating individual polycyclic aromatic hydrocarbons (PAHs) in a screening level risk assessment, a discussion on HHRA Note 12 and characterization and evaluation of sites contaminated with petroleum hydrocarbons, and other chemicals that are often associated with releases of petroleum and petroleum-containing products, and a discussion on the updates to LeadSpread.

Download HHRA Note 4 – March 2022 Revised

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 (HHRA) Note 12 – Guidance for Evaluating Human Health Risk at Sites Contaminated by Petroleum Hydrocarbons and Related Chemicals of Potential Concern (COPC)

This Human Health Risk Assessment (HHRA) note addresses the characterization and evaluation of the potential risks and hazards at sites contaminated with petroleum hydrocarbons, and other chemicals that are often associated with releases of petroleum and petroleum hydrocarbon-containing products.  It is intended to supplement—not replace— other existing DTSC guidance documents, including but not limited to the Preliminary Endangerment Assessment (PEA) Guidance Manual and the Vapor Intrusion Guidance.  It is not intended to limit investigations at sites with a history of other hazardous material uses and does not diminish the need to collect additional samples to address on-site and off-site releases of hazardous substance other than petroleum and petroleum-related chemicals.  It is not intended for certain fuel releases that fall under the Low-Threat Underground Storage Tank Case Closure Policy in 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 Sarah.Berry@dtsc.ca.gov 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

LeadSpread is a tool for evaluating lead exposure and the potential for adverse health effects resulting from lead in the environment. An updated version of LeadSpread has been developed (LeadSpread 9, 2022) to incorporate the recent changes in exposure parameters adopted by DTSC and US EPA. LeadSpread 9 is based on the CalEPA toxicity criterion which is a source-specific benchmark incremental increase in blood lead concentration of 1 μg/dL (OEHHA, 2007). LeadSpread 9 is designed to ensure protection of the most sensitive human receptors, including children and women of child-bearing age, from exposure to lead in soil.

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

Vapor intrusion is the movement of chemical vapors from contaminated soil and groundwater, through the cracks and gaps in building foundations into the air inside buildings. Vapor intrusion can be a concern at sites contaminated with solvents and other vapor-forming chemicals. If uncontrolled, chemical vapors can enter buildings and potentially pose a risk to the health of building occupants. Evaluating vapor intrusion and assessing potential current and future health risks is complex. Sites may be affected by different types and amounts of chemical contamination. A large number of environmental and human-caused conditions also influence vapor behavior and movement.

Vapor Intrusion Fact Sheet

Vapor Intrusion and Your Health Fact Sheet provides a general overview of vapor intrusion:

Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion, February 2023

The Department of Toxic Substances Control (DTSC) and State Water Resources Control Board (State Water Board) developed the Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (Supplemental VI Guidance) for use with existing State guidance in conducting vapor intrusion evaluations in California.

The Supplemental VI Guidance provides a screening process to determine if buildings located near known or suspected subsurface contamination by vapor-forming chemicals are potentially affected by vapor intrusion. The process focuses the investigation and sampling for early assessment of potential vapor intrusion health risks for building occupants.  The Supplemental VI Guidance is meant to promote Statewide consistency in site investigation and cleanup at sites where contaminants in soil gas and groundwater pose an unacceptable risk to current and future building occupants. For more information see the DTSC Vapor Intrusion webpage.

When conducting a human health risk assessment for vapor intrusion, DTSC recommends consulting Human Health Risk Assessment (HHRA) Note 3 for the DTSC recommended indoor air screening levels and HHRA Note 4 when conducting a screening level human health risk assessment.

August 2022 – Vapor Intrusion Update, DTSC Vapor Intrusion Advisory

The August 2022 Vapor Intrusion Update, DTSC Vapor Intrusion Advisory Vapor Intrusion has been superseded by the February 2023 Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion. The DTSC 2011 Final Guidance for the Evaluation & Mitigation of Subsurface Vapor Intrusion to Indoor Air provides information on evaluating the extent of contamination.

2015 Flow Diagram of DTSC Vapor Intrusion Documents

Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air – Final

(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.

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.

Vapor Intrusion Modeling Spreadsheets

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 from DTSC Vapor Intrusion and HERO webpages because they were outdated.  DTSC is modifying the USEPA’s September 2017 Version 6.0 of the JEM for use in evaluating vapor intrusion at chemical release sites in California, and releasing a DRAFT “beta test” version of DTSC JEM spreadsheet to seek feedback from practitioners working on sites in California.  The JEM may be used as one line of evidence when supported by other lines of evidence in the conceptual site model.

The DTSC DRAFT JEM spreadsheet is a beta version, and as such will not be accepted as a line of evidence for projects under DTSC oversight.  See the DTSC Vapor Intrusion webpage for more information on the Johnson and Ettinger Vapor Intrusion Model.

Vapor Intrusion Public Participation Advisory 

(March 2012)
DTSC developed an Advisory to determine and implement appropriate public participation coordination and activities at sites where a potential vapor intrusion risk was identified. The Advisory is a companion document to DTSC’s Vapor Intrusion Guidance and Vapor Intrusion Mitigation Advisory. In addition, the Advisory supplements DTSC’s Public Participation and Procedures Manual. The Advisory is currently under review and will be available mid-2023.

Vapor Intrusion Mitigation Advisory, Revision 1 (October 2011)

The VI Mitigation Advisory provides a framework that guides the reader through the decision process for:

  • determining if mitigation is appropriate for the project site,
  • selecting a mitigation system that is protective of human health, and
  • ensuring that implementation is sustainable for the duration of mitigation.

The VI Mitigation Advisory emphasizes public participation and implementation considerations. The Advisory also identifies likely technologies for vapor intrusion mitigation, but does not identify proven technologies.

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