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.

Abstract. On-site land application of waste water containing very low levels of site-derived contaminants is a commonly used method of disposal. However, the residual soil contamination resulting from such practices may complicate and increase the costs of site remediation if constituent soil concentrations exceed regulatory clean-up standards. The long-term potential human health impacts of land application of waste water containing elevated levels of naturally occurring radionuclides for a hypothetical in-situ uranium facility were investigated using the U. S. Department of Energy RESRAD Computer Code for assessment of dose and risk. The post-reclamation radiation doses in excess of background, attributable to land application of waste water containing uranium and its decay products thorium and radium, were calculated for several different conditions assuming rural-residential use of the land. For contaminated land areas of 10 acres or more, the estimated doses were directly proportional to the soil radionuclide concentration when the thickness · of the contaminated soil and hydrological parameters were held constant. The maximum annual radiation dose to a rural resident on land with surface soil concentration equal to 205 pCi/g natural uranium was estimated to be 34 mrem. In contrast, the maximum annual radiation dose to this hypothetical individual from 22 6Ra at the residual concentration allowed under the regulations for uranium mill tailings, i.e., 5 pCi/g, varied from 135 mrem to 283 mrem depending on the thickness of the contaminated layer.Additional