What are VOCs?Volatile organic compounds (VOCs)are a class of chemicals that readilyevaporate at room temperature. Gaso-line, drycleaningfluid,degreasingagents(solvents) and paint thinners are sev-eral examples of products that containthese compounds. VOCs may be foundin soil and/or ground water due to spill-age onto the ground, leaks from under-ground storage tanks and other typesof discharges.

How VOCs in soil or groundwater can affect indoor airIf VOCs contaminate soil or groundwater at a site, it is important to evalu-ate nearby buildings for possible im-pacts from vapor intrusion. Vaporintrusion occurs when gases from thecontaminated soil or ground waterseep through cracks and holes in

Fact Sheet

Evaluating IndoorAir near VOCContaminated Sites

New JerseyDepartment of Environmental ProtectionSiteRemediation Program

(609) 984-3081 • Office of CommunityRelations

basementslab

crawl-space

Indoor Air

Organic Vapors

VOCContaminated

Soil

VOC Contaminated Ground Water

Ground Water Table

foundations or slabs of buildings andaccumulate in basements, crawlspaces or living areas, as shown inthe diagram below.

A variety of factors can influencewhether vapor intrusion will occur ata building located near soil or groundwater contaminated with VOCs.These include, but are not limited to,the concentration of the contaminants,the type of soil, the depth to groundwater, the construction of the build-ing, the condition of the foundation orslab and the existence of undergroundutilities that can create pathways forvapors to travel.

Short term exposure to high levels oforganic vapors can cause eye and res-piratory irritation, headache and/ornausea. Breathing low levels of or-ganic vapors over a long period oftime may increase an individual’s risk

for respiratory ailments, cancer andother health problems.

Organic vapors can be present insidea building at potentially harmful lev-els without being detectable by odor.Sub-slab soil gas testing, near-slabsoil gas testing and/or indoor airtesting are usually required to deter-mine whether vapor intrusion is oc-curring at a property.

Testing for vapor intrusionIf your home or building is locatednear VOC-contaminated soil orgr ound water, NJDEP or an envir on-mental contractor may ask permissionto evaluate your property for vaporintrusion. This process typically in-volves first conducting sub-slab soilgas testing to check for vapors be-neath the building, followed by indoorair testing, if necessary. During sub-

(over)

Diagram adapted from USEPA’s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from GroundWater and Soils, November 2002

An evacuated air testing canister. The pres-sure inside the canister is initially set lowerthan the indoor air, causing air to flow intothe canister when the valve is opened.

slab testing, a small hole is boredthrough the basement floor or slaband a sample of the soil gas (the airtrapped between the soil particles) iscollected using an evacuated air test-ing canister (see below). If it is notpossible to collect a soil gas samplefrom beneath the floor or slab, thesample may be collected by placinga probe in the soil directly adjacent tothe building (near-slab testing). Thesoil gas sample is then sent to a cer-tified laboratory to be analyzed forVOCs. If the analysis shows VOCsrelated to the subsurface contamina-tion are present above NJDEP’s SoilGas Screening Levels (SGSL), thenindoor air testing is necessary.During indoor air testing, a canisteris placed in the basement, crawlspace or other part of the building fora period of time (normally 24 hours).If the analysis of the indoor air sampleshows VOCs related to the subsur-face contamination are present aboveNJDEP’s Indoor Air Screening Lev-els (IASL), vapor intrusion is likelyoccurring.Additional evaluation of theproperty may be needed to confirmthis finding.

Background contaminationMany materials and substances com-monly found in commercial and resi-dential settings, such as paints, paintthinners, gasoline-powered machin-ery, certain building materials andcleaning products, dry cleaned cloth-ing and cigarette smoke, containVOCs that may be detected by in-door air testing. Even VOCs frommotor vehicle emissions and other out-door sources can contaminate indoorair. When VOCs from these sourcesare detected during indoor air test-ing, they are referred to as back-ground contamination.

Sometimes it can be difficult to de-termine whether the VOCs detectedinside a building are due to vapor in-trusion, background contamination ora combination of both. Before yourbuilding is evaluated for vapor intru-sion you should receive a copy ofNJDEP’s Instructions for Occu-pants – Indoor Air SamplingEvents. Please follow these instruc-tions to minimizebackground contami-nation and help ensure that the testresults are as definitive as possible.

Addressing vapor intrusionIf testing confirms vapor intrusion iscausing potentially harmful levels ofVOCs to accumulate inside a building,a subsurface depressurization sys-tem may be installed at the property.The system prevents vapors from en-teringthebuildingby continuouslyvent-ing the contaminated air beneath thebasement slab or crawl space to theexterior of thestructure. Subsurfacede-pressurization systems are also usedthroughout the country to reduce levelsof naturally occurring radon gas inbuildings. SeeNJDEP’s fact sheet titledSubsurface Depressurization Sys-tems for more information about howthese systems work.

Instructions for Occupants —Indoor Air Sampling Events, theSubsurface Depressurization Sys-tems fact sheet and general in-formation about vapor intrusioncan be found in NJDEP’s VaporIntrusion Guidance Document,which is available at http://www. s t a t e . nj . us / d e p / s r p /guidance/vaporintrusion

(continued)

Information for Residents and Property Owners

Contact Name

Agency/Company

Phone Number

Email Address

NJDEP Contact &Phone Number(if different than above)

Sampling Date/Time

Notes/Instructions

June 2008