Cal Iaq

About cal-iaq 


Asthma triggers

Environmental Tobacco Smoke (ETS)

Indoor Ozone

Mold Information


Chemicals (VOCs)

Healthy Homes

Healthy Schools


Cal- IAQ Homepage


Radon in California Homes: 

Current State of Knowledge in California


Radon Survey
Statewide study of residential radon concentrations was carried out by the California Department of Health Services (CDHS) in -89.  The survey was a statewide effort to determine the extent of indoor radon exposure in representative California homes and to identify areas of the State where residences may have elevated radon concentrations.


In this study, radon monitors were placed in 310 residences.  Measurements were carried out for a full year to obtain an accurate estimate of exposure unbiased by short-term fluctuations in radon levels because of weather conditions or changes in ventilation.  The survey determined the proportion of homes exceeding the action level of 4 picocuries per liter (pCi/L) of air recommended by the U. S. EPA.  Homes with long-term concentrations measured at or above the action level are recommended for radon reduction.  The U.S. EPA action level is largely based on current mitigation technologies. It is recognized that radon exposures below 4 pCi/L still contribute to the risk of lung cancer.


The statewide survey showed that about 0.8% (approximately 100,000) of California homes are expected to have annual average radon levels exceeding the U.S. EPA action level.  These results confirmed the magnitude of high radon homes found in earlier limited studies and another statewide radon survey by CDHS and U.S.EPA using short-term monitors.  The geometric mean (GM) for long-term radon concentrations in the state was 0.85 pCi/L.  


Selected Regions
The results also were analyzed by dividing the state into six geographic regions.  The highest level was measured in the Sierra Nevada region (from Placer south to Mariposa, as well as Alpine, Mono, Inyo counties), which was significantly higher than other areas (GM=2.2 pCi/L).  The limited data for this region in the statewide survey indicated 11-45% of homes are above the U.S. EPA action level.  The Fresno-Ventura region (Madera, Fresno, Kings, Tulare, Kern, Santa Barbara, Ventura counties) had the next highest level (GM=1.3 pCi/L).
In, a focused survey of residential radon levels was carried out in 862 residences of Ventura and northwestern Los Angeles.  It determined 1-14% of homes in this region had long-term radon exposure above the U.S. EPA action level.  Currently, CDHS is conducting a survey of residential radon levels in 1,000 homes in the Sierra Nevada region, with preliminary results expected in early.


Related Publications
Journal Articles: 

  • The Distribution of Lifetime Cumulative Exposures to Radon for California Residents,
    Liu KS, Chang YL, Hayward SB, Gadgil AJ and Nero AJ,,
    Journal of Exposure Analysis and Environmental Epidemiology. 3:165-179.

  • Annual Average Radon Concentrations in California Residences,
    Liu KS, Hayward SB, Girman JR, Moed BA and Huang FY,,
    J. Air and Waste Mgmt. Assoc. 41:1207-1212.

Survey of Indoor Radon Concentrations in California Elementary Schools,
report by Zhou J, Liu KS, and Waldman J, May

Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.
Survey of Residential Radon Levels in Ventura County and Northwestern Los Angeles County,
Liu K-S, Chang Y-L, Hayward SB, .

Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.
Survey of Residential Indoor and Outdoor Radon Concentrations in California,
Liu K-S, Hayward SB, Girman JR, et al.,.

Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.

General Information

  • Indoor Air Quality - U.S. EPA Radon Publications

  • California Radon Risk Map

  • California Radon Programs - 1 -800 - 745-7236

Health Effects

  • Health Effects of Exposure to Radon: BEIR VI - Executive Summary

  • RADON: A Physician's Guide - The Health Threat with a Simple Solution


Radon Risk and Risk Reduction

  • Consumer's Guide to Radon Reduction

  • Radon Mititgation Standards

  • Model Standards and Techniques for Control of Radon in New Residential Buildings

Radon Research Projects

  • Lawrence Berkeley National Lab (LBNL)-High Radon Project

  • Columbia University -- Radon Project

Radon in Drinking Water

  • Proposed Drinking Water Standards for Radon

  • Radon in Drinking Water - Multimedia Mitigation Program

  • Drinking Water Priority Rulemaking: Radon

  • Office of Ground Water and Drinking Water

  • NAS Report on Radon in Drinking Water



© Copyright. . Cal Iaq. All Rights Reserved. Terms | Site Map