Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Human Health Risk Assessments Quick Reference Guide

A Human Health Risk Assessment (HHRA) is a process to determine if contaminants detected at a site are of concern to human health and the environment. The HHRA falls under the evaluation step of the voluntary agreement process, and involves using environmental data to estimate the nature, magnitude, and probability of adverse health effects on people who may be exposed to the contaminated environmental media (e.g., soil, soil gas, groundwater, surface water), now and in the future. Voluntary agreement projects use the HHRA to make decisions about allowable use or reuse of the property, and to facilitate an effective assessment and cleanup strategy to ensure safe end use. DTSC’s Human and Ecological Risk Office (HERO) should be involved in the scoping meeting for new voluntary agreements in order to provide feedback and guidance on the HHRA process.

Human Health Risk Assessment Process Flowchart: 1. Hazard Identification: a) Gather and analyze relevant data; and b) Identify potential chemical of concern. 2-a. Toxicity Assessment: a) Collect qualitative and quantitative toxicity information; and b) Determine toxicity values. 2-b. Exposure Assessment: a) Analyze containment releases; b) Identify potential exposure pathways; c) Estimate exposure concentration for pathways; and d) Estimate containment intakes for pathways. 3. Risk Characterization: a) Characterize potential for adverse health effects to occur; b) Estimate cancer risks; c) Estimate non-cancer risks; d) Evaluate uncertainty; and e) Summarize risk information.

Source: Risk Assessment Guidance for Superfund (RAGS)

There are four steps to the HHRA process:

  1. Hazard Identification: Data collected at a site are used to determine what chemicals are present and whether they can cause effects (both cancerous and non-cancerous) harmful to people who may come in contact with the contaminated media.
  2. Exposure Assessment: This step identifies current and potential future populations who may come in contact with the site’s contaminants; the various media that may have been affected by the contamination; pathways of exposures for potentially exposed populations (through ingestion, inhalation, or absorption through the skin); and estimated contaminant concentrations (intake rates) that may be taken up via the various exposure pathways.
  3. Toxicity Assessment: This step incorporates toxicity information about the chemicals into the HHRA. This information is typically available on the U.S. Environmental Protection Agency and/or the California Environmental Protection Agency websites, including DTSC’s HHRA Note 3.
  4. Risk Characterization: This step combines information from the previous steps to evaluate cumulative cancer risks and non-cancer hazards the site poses to potentially exposed human populations. This information is used to determine whether the site is safe or contaminants are present at levels posing unacceptable risks to people and the environment, requiring remediation of contaminated media. Risk management decisions are developed based on the results of cumulative cancer risk and non-cancer hazard estimates for the site.

An Uncertainty Analysis is included as part of the risk assessment process to discuss: (a) the sources and degrees of uncertainty associated with the data collected at the site; (b) exposure assumption and toxicity information used to estimate cancer risks and non-cancer hazards to populations; (c) and assumptions and input variables associated with the models employed in the assessments. This information should also be used by the risk managers and incorporated into the risk management decisions for the site, such as the need for remediation and/or operation and maintenance.

Please visit DTSC’s HERO website for details on risk assessment guidance and documents, including:

DTSC’s Preliminary Endangerment Assessment Guidance Manual for the Human Health Screening Evaluation, as well as DTSC’s perspective on data collection, analysis, and reporting

DTSC HHRA Note 1: Recommended DTSC Default Exposure Factors for Use in Risk Assessment at California Hazardous Waste Sites and Permitted Facilities

DTSC HHRA Note 2: Soil Remedial Goals for Dioxins and Dioxin-like Compounds for Consideration at California Hazardous Waste Sites

DTSC HHRA Note 3: DTSC-modified Screening Levels (DTSC-SLs)

DTSC HHRA Note 4: Screening Level Human Health Risk Assessments

DTSC HHRA Note 5: Health-based Indoor Air Screening Criteria for Trichloroethylene (TCE)

DTSC HHRA Note 6: Recommended Methodology for Evaluating Site-Specific Arsenic Bioavailability in California Soils

DTSC HHRA Note 8: Recommendations for Evaluating Polychlorinated Biphenyls (PCBs) at Contaminated Sites in California and DTSC’s PCB Evaluation Quick Reference Guide

Ecological Risk Assessment section on the HERO website for details on the Ecological Risk Assessment process

For more information, contact:

Shukla Roy-Semmen, Senior Toxicologist
HERO Southern California Unit Chief
(714) 484-5448

Download a collection of all DTSC Voluntary Agreements Quick Reference Guides

DTSC’s Voluntary Agreements – Assessment and Cleanup Process: 1) Agreement: a) Standard Voluntary Agreement b) California Land Reuse and Revitalization Act Agreement c) Reimbursement Agreement d) Prospective Purchaser Agreement e) Local Agency Oversight Agreement 2) Scoping Meetings a) During negotiation or shortly after agreement execution b) Establishes strong working relationship between DTSC, the Proponent, and the environmental consultant c) Also may be held prior to submitting any documents to DTSC for review 3) Evaluation a) Preliminary Endangerment Assessment (PEA) b) Supplemental Site Investigation c) Remedial Investigation d) Report of Findings Possible End Point 4) Remedy Selection a) Feasibility Study b) Removal Action Work Plan c) Remedial Action Plan d) Response Plan 5) Implementation a) Removal Action Implementation b) Remedial Design c) Remedial Action Implementation d) Response Plan Implementation 6) Certification & Stewardship a) No Further Action b) Certificate of Completion c) Land Use Restriction d) Operation and Maintenance e) Five-Year Review Possible End Point During Remedy Selection, there is a Public Comment Period and California Environmental Quality Act (CEQA). During this entire process, Public Participation Activities and Tribal Consulation is included, as needed. Possible End Points: 1) Based on site evaluation, projects may conclude without need for any further action; 2) Based on site evaluation, projects may conclude with the need for a Land Use Covenant, in which case a public notice process will be implemented through a Preliminary Endangerment Assessment, Report of Findings, or equivalent documents; and 3) Cleanups may either be conducted to unrestricted land use levels, or may require long term stewardships.

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This document is intended to be guidance only and it does not supersede or implement laws or regulations. The information in this advisory is intended solely as guidance and as educational reference material and should not be considered enforceable or regulatory in nature.