Evidence for Increasing Indoor Sources of 1,2‐Dichloroethane Since 2004 at Two Colorado Residential Vapor Intrusion Sites

Abstract

Groundwater contamination associated with two former industrial facilities in Denver, Colorado, has led to concerns about vapor intrusion into residences adjacent to the facilities. 1,1,1‐Trichloroethane (1,1,1‐TCA), 1,1‐dichloroethene (1,1‐DCE), and trichloroethene (TCE) are the main contaminants of concern in groundwater, with trace levels of 1,2‐dichloroethane (1,2‐DCA) present at one of the sites. Indoor air monitoring programs have been ongoing at these two sites since 1998 and recent results have suggested that background, indoor source, 1,2‐DCA has been increasing in the frequency of detection, and median and maximum concentration over the past several years. A lines of evidence evaluation was undertaken for both sites in order to document the predominance of indoor sources of 1,2‐DCA. Evidence utilized included spatial evaluation of 1,2‐DCA in indoor air; comparison of 1,2‐DCA concentrations in mitigated and unmitigated homes; a phone survey to evaluate the potential for smoking to contribute to indoor air 1,2‐DCA levels; evaluation of mitigation system effluent data; and an evaluation of volatile organic compound (VOC) ratios in groundwater and indoor air. The results of this evaluation indicated that smoking had no demonstrable influence on measured indoor air concentrations. In addition, it appears that consumer products have had a markedly increased influence on indoor air concentrations since 2005. Data from one of the industrial facilities at one of the sites also indicated that polyvinyl chloride (PVC) and vinyl composite floor adhesive used in a building remodel in 2005 apparently generated elevated levels of indoor 1,2‐DCA and vinyl chloride, which have been sustained up to the present time.

Vapor Intrusion Investigations and Decision-Making: A Critical Review

“…Studies have explored the typical range and variation trends of indoor background VOC concentrations in different countries/areas including North America, ,− China, − Europe, − and others. ,− The background concentration of the same VOC varied considerably among different areas/countries. ,, This can be attributed to differences in the geographic settings, climatic conditions, building structures and materials, indoor air exchange rates, living habit, household products, and outdoor air concentrations. Compilations of North American data reveal several interesting phenomena: , (1) typical indoor background concentrations are log-normally distributed; (2) the variations between the 25th to the 95th percentile values of most VOCs are >10-fold (typical sampling period are between 12 and 24 h; longer sampling period would result in lower variations); (3) for a number of common VOCs such as benzene, carbon tetrachloride, chloroform, and PCE, the upper end of the observed range for background indoor air concentrations typically exceeds USEPA’s regional screening levels .…”

“…Compilations of North American data reveal several interesting phenomena: , (1) typical indoor background concentrations are log-normally distributed; (2) the variations between the 25th to the 95th percentile values of most VOCs are >10-fold (typical sampling period are between 12 and 24 h; longer sampling period would result in lower variations); (3) for a number of common VOCs such as benzene, carbon tetrachloride, chloroform, and PCE, the upper end of the observed range for background indoor air concentrations typically exceeds USEPA’s regional screening levels . For many individual VOCs, the observed range of indoor air concentrations has generally declined in recent years likely due to concerns regarding the toxicity of individual VOCs resulting in the general move toward the development of consumer products containing lower total VOC concentrations. , However, indoor air concentrations of at least one individual chlorinated VOC (1,2-dichloroethane) has been observed to increase over time apparently due to changes in the manufacturing of molded plastics. , …”

“…In other cases, removal of indoor sources is not practical . In several cases where background sources were not properly identified or considered during initial testing, VOC detections in indoor air were initially attributed to VI; indoor sources were identified only through subsequent testing. ,,, If the background concentration is mistakenly attributed to VI, it may result in unnecessary and ineffective site investigation and mitigation. Therefore, it is necessary to assess the contribution of background sources to indoor air contamination.…”

“…241,257 However, indoor air concentrations of at least one individual chlorinated VOC (1,2-dichloroethane) has been observed to increase over time apparently due to changes in the manufacturing of molded plastics. 238,243 To reduce the impact of indoor sources, regulatory guidance typically recommends identifying possible indoor sources by occupant questionnaires and indoor surveys and removing them prior to testing of indoor air for the evaluation of vapor intrusion. 4 However, in many cases, it is not possible to identify all sources though visual inspection.…”

Indoor Air Contamination from Hazardous Waste Sites: Improving the Evidence Base for Decision-Making

“…Indoor air sampling for vapor intrusion is further complicated by the potential for confounding indoor or other non-vapor intrusion sources, as highlighted extensively in the EPA guidance [ 17 , 18 , 19 , 20 ]. Consumer products can off-gas the same chemicals of concern, introducing a different indoor source.…”