Human Health Risk (HERO)



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.

Evaluating Human Health Risks from Total Petroleum Hydrocarbons (TPH) - Interim Guidance

This guidance document is no longer active. Future approaches to petroleum hydrocarbon contamination will be part of the revised Preliminary Endangerment Assessment Guidance Manual.

Arsenic Strategies: Determination of Arsenic Remediation - Development of Arsenic Cleanup Goals for Proposed and Existing School Sites 

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.

Supplemental Guidance for Human Health Multimedia Risk Assessments of Hazardous Waste Sites and Permitted Facilities

This guidance document has been rescinded and will be replaced by a revised document following departmental review and comment.

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
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-TEQ (Interim)
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 Recommended Methodology for Use of U.S. EPA Regional Screening Levels (RSLs) in Human Health Risk Assessment Process at Hazardous Waste Sites and Permitted Facilities.

The Office of Human and Ecological Risk Assessment has, in the past, used the U.S. EPA Region 9 Preliminary Remediation Goals (PRGs), which included 'Cal-modified' PRGs, to facilitate Screening Level Human Health Risk Assessments. The EPA Region 9 PRG values have now been harmonized with risk-based PRGs from other EPA Regional Headquarters, and are called Regional Screening Levels (RSL) which no longer contain the more protective 'Cal-modified' PRGs. This version of HHRA Note Number 3 outlines the most recent HERO review of the soil, air and tapwater RSLs released in May, 2013 and presents recommended screening values for constituents in which the RSL is not as health protective as the 2004 PRGs, 2004 'Cal-modified' PRGs, or HERO-calculated risk-based screening levels. A separate link is also provided for download of the associated Table 1 with a listing of alternate soil and tapwater screening values currently recommended in lieu of November 2012 RSLs. New to this iteration of HHRA Note 3 is the incorporation of Phase II HERO recommendations for residential and industrial air screening levels for a selected subset of VOCs frequently detected at California hazardous waste sites and permitted facilities. For all constituents other than those addressed in Note 3, the DTSC site toxicologist should be consulted prior to using the air RSLs.

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

In a memorandum dated October 28, 1994, the Office of Human and Ecological Risk Assessment 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 formerly available from several U.S. EPA Regional offices. 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. 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.

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

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. 




CalTOX is a spreadsheet model that relates the concentration of a chemical in soil to the risk of an adverse health effect for a person living or working on or near the contaminated soil. CalTOX computes site-specific health-based soil clean-up concentrations given target risk levels or human health risks given soil concentrations at the site.


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.



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.  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.

U.S. EPA Johnson & Ettinger Models Modified to Include California Chemical Toxicity Criteria

The Johnson and Ettinger (J&E) model (1991) predicts indoor air concentrations resulting from subsurface vapor migration into indoor air.  The model produces an attenuation factor "alpha" that represents the ratio of the indoor air concentration to the subsurface concentration.  In 1998, the United States Environmental Protection Agency (USEPA) programmed the J&E model into Microsoft EXCEL® and added a health risk component that calculates human health risks and/or hazards associated with inhalation of a specific contaminant at the estimated indoor air concentration.  The USEPA periodically revised the model to incorporate different assumptions about soil parameters and chemical properties, including new human health toxicity criteria developed by USEPA.  The USEPA model (last revised in 2004), a fact sheet, and User's Guide are available at:

The DTSC Human and Ecological Risk Office has modified the USEPA screening models for estimating indoor air concentrations from subsurface soil gas or groundwater data and incorporated human health toxicity criteria developed by the Cal/EPA Office of Environmental Health Hazard Assessment (OEHHA).  The toxicity criteria will be periodically updated as new California and USEPA criteria values are released: however it is the responsibility of the user to verify that all criteria in the models are current.  The models were revised in March 2014 to reflect recommendations in the Final DTSC Vapor Intrusion Guidance (2011), provide additional receptor scenarios and incorporate exposure time as a receptor exposure parameter, update toxicity criteria, and add features for user convenience.  The models were updated in December 2014 to incorporate USEPA and DTSC revisions in residential receptor exposure duration and noncancer averaging time.

The user can download these EXCEL® files and use the default input for screening and/or insert site-specific data to calculate indoor air concentrations and risk estimates for a specific site.  Microsoft EXCEL® or the Microsoft EXCEL® Viewer is required to view these files.  If the user does not have Microsoft EXCEL®, the EXCEL® Viewer is available at:

Johnson, P. and Ettinger, R., 1991.  Heuristic Model for Predicting the Intrusion Rate of Contaminant Vapors into Buildings.  Environmental Science and Technology, 25:1445-1452.

USEPA, 2004.  User's Guide for Evaluating Subsurface Vapor Intrusion into Buildings.  United States Environmental Protection Agency, Office of Emergency and Remedial Response.  February 22, 2004.