Testing Indoor Air for Vapor Intrusion
Study finds no solvent vapor in most Algona homes tested - Update, January 21, 2014
Vapor intrusion occurs when chemicals in the shallowest groundwater (the water table) evaporate and move through the soil as a gas. These vapors can make their way indoors, affecting air quality in buildings above the ground.
Vapor intrusion is investigated by focusing on buildings in an area near contaminated groundwater. Investigators can determine what effects, if any, vapor intrusion is having on indoor air quality by inspecting buildings and collecting indoor air samples. Some buildings are more susceptible to vapor intrusion due to their foundation types and construction.
Contamination at Boeing Fabrication in Auburn
Groundwater is water that flows through sub-surface spaces between soil, sand, and gravel particles or through fractures in rock. The groundwater flowing away from the Boeing Auburn property is contaminated with a class of chemicals called “volatile organic compounds” (VOCs), which give off vapors. Some of the contaminated groundwater flows north and northwest from the Boeing property, into portions of the cities of Algona and Auburn.
Testing for Vapor Intrusion in Algona
The buildings were selected based on their nearness to shallow groundwater contamination where trichloroethene (TCE) and/or vinyl chloride are above the preliminary concern levels (PCLs). PCLs are the levels of pollution in groundwater that indicate the need for initial testing. The PCL for indoor air quality in the Algona neighborhood is one part per billion for TCE and 0.23 parts per billion for vinyl chloride.
The levels of TCE and vinyl chloride in Algona’s groundwater are not likely to lead to unhealthy concentrations in indoor air. Still, Ecology wants to make sure vapor intrusion is not affecting indoor air quality. Buildings located outside the area of the contaminated water table are not likely to have vapor intrusion. So there are no current plans to test indoor air beyond where samples from the shallow groundwater show negligible contamination.
For more information about the vapor intrusion testing process in Algona, read Vapor Intrusion Investigation in Algona, Washington, Ecology publication 13-09-175.
A second phase of testing will be offered to homes in the study area. Should action become necessary based on future sampling, a plan has been approved by Ecology and Boeing to take immediate action.Department of Health’s fact sheet City of Algona – Residential Indoor Air Results for more information.
Testing for Vapor Intrusion in Auburn
The Sample Collection Process
At homes with a crawlspace, a sample of crawlspace air is susually be collected as well. At some homes where there is a basement or the building is constructed slab-on-grade, samples of soil gas is collected.
Most air samples are collected over a 24-hour period. At homes where trichloroethene (TCE) has been detected in nearby shallow groundwater, three-week samples are collected in addition to the day-long samples. This shows one-day average indoor TCE levels as well as three-week average levels.
Step-by-Step Review and Results Reporting to Homeowners
STEP 1. Boeing provides sampling data to Ecology.
Note: If residents whose homes are being sampled want to see their home’s data before getting it in the assessment report (STEP 3), Ecology will provide the data. Please notify the site manager with your request by phone: 425-649-7232 or by email Robin Harrover at firstname.lastname@example.org.
The lab can usually analyze the concentration data for the 24-hour samples within a week. Boeing’s environmental consultant provides that data to Ecology. Ecology then shares the data with the Department of Health and the environmental consultant for the City of Algona.
The concentration data, just by itself, is not enough to properly assess vapor intrusion. Ecology and its partners must combine that data with other information about each home before it is possible to make a report.
STEP 2. Boeing prepares preliminary vapor intrusion assessment.
Boeing prepares a preliminary vapor intrusion assessment for each home within about a week of getting data from the laboratory. Boeing submits these preliminary assessments to Ecology, and Ecology then shares the data with the state Department of Health, Public Health – Seattle & King County, and the City of Algona’s environmental consultant.
With assistance from these partners, Ecology reviews the data to see whether immediate follow-up actions are needed. Ecology’s response to each building-specific assessment will be sent to Boeing within about a week of receiving the preliminary assessment.
STEP 3. Boeing sends final vapor intrusion assessment report to residents.
Boeing prepares a vapor intrusion assessment report for each home within about one week from receiving Ecology’s comments. The report addresses Ecology’s comments, modifying the preliminary assessment as needed. Boeing notifies the residents and the property owner (if not the same person) and delivers a copy of the report to them and to Ecology. A cover letter in plain language summarizes the assessment.
STEP 4. Report provides recommendations for next steps.
Each vapor intrusion assessment report includes recommendations for that home. Boeing’s report may recommend that air sampling be repeated next winter. Or it might recommend further investigation, and possibly more sampling, right away. If the results suggest there may be health risks, we take action to address the risk. This is called mitigation.
Once the reports are available, Ecology offers to individually discuss the assessment report and the recommendations with each home’s owners and occupants.
Ecology’s goal is to complete these four steps and send assessment reports to each resident within about four weeks of collecting 24-hour samples. The time frame will be different for those homes where three-week samples are also collected.
Ecology understands that public interest in this situation goes beyond those living at the properties we initially chose for sampling. Once the summer sampling and house-by-house assessments are complete and the owners and occupants have received the information, Ecology posts a summary of results and our plans for next steps on this website.
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