Formatted Title
Vapor Intrusion Investigation of Two Sources of TCE in Residential Homes: Lessons Learned and Applied
Background/Objectives
At two sites, one in Texas and one in New Mexico, TCE was present in indoor air but absent in sub-slab soil gas. Identification of the source of the TCE required detailed analysis of potential indoor sources at the Texas Site. Lessons learned from the Texas Site were used to quickly evaluate and find the source of indoor air at the New Mexico Site.
The Texas Site is a TCE groundwater plume within a bedrock aquifer present at 70 feet below ground surface. This release resulted in a groundwater plume that is more than 1 mile long by ½ mile wide that has affected numerous private water wells and two municipal wells. The New Mexico Site is a release of PCE from a dry cleaner that contaminated an alluvial aquifer present at 30 feet below ground surface. The New Mexico Site groundwater plume has PCE and its daughter products TCE resulting in a 1,600-foot-long plume.
Approach/Activities
At the Texas Site vapor intrusion (VI) evaluations were completed in 2011 and again in 2018. The VI evaluations conducted in 2011 indicated the VI pathway was not complete. In 2018 several residences were reassessed, and one had TCE above the EPA residential screening levels (SLs) for indoor air. Multiple sampling events occurred at the residence consisting of indoor air, sub-slab soil gas, and tap water from March through July 2018 to determine if the contamination was site-related and to identify the source of contamination. Sampling indicated that there was a probable indoor air source for the TCE, since the sub-slab soil gas results were below the EPA residential SLs.
Tap samples collected from multiple faucets in the residence identified the water from an auxiliary kitchen tap and an outside tap were connected to a separate water line supplied by contaminated well water. The water line from the well was located and disconnected from the home. Indoor air grab samples were recollected to determine if the disconnection of well water reduced the indoor air concentrations. The sample results showed the concentrations of TCE remained above exceedance levels.
Finally, a portable gas chromatograph/mass spectrometer referred to as a HAPSITE® was used to locate the indoor air contamination source.
At the New Mexico Site VI evaluations were completed in 2020 with several residential properties being assessed. One residential property had a TCE indoor air concentration above EPA residential SLs for indoor air and a sub-slab soil gas sample that below EPA residential SLs. This indicated that there was an indoor air source for the TCE. After an initial reevaluation to confirm results, the HAPSITE® was used to locate the indoor air contamination source.
Results/Lessons Learned
At the Texas Site, the HAPSITE® readings in the master bedroom indicated the highest concentrations of TCE were coming from a dresser and nightstand of similar design from the same manufacturer. It was determined the source of TCE was varnish and glue used in the manufacture of the furniture. At the New Mexico Site the source of the TCE was gun cleaner.