## 1 Introduction  
The North Railroad Avenue Plume (NRAP) Site was discovered in 1989. The 23.5 hectares (58 acres) of groundwater were contaminated with tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene (DCE) isomers (1,2-cis DCE and 1,2-trans DCE), and vinyl chloride (VC) from a release at a former dry cleaner and laundromat business. The three known groundwater units underlying the site are defined by differences in water pressures and geology. All three units contain chlorinated solvent impacts from the NRAP source zone. The contaminated groundwater aquifers are the sole source drinking water aquifers for the City of Espanola, Santa Clara Pueblo, and individual water supply wells near the site. Figure 1 shows the site area with groundwater plume. In 1999, the site was added to the National Priority List (NPL) and recognized as a superfund site. A study to determine a remediation plan was conducted from 1999 through 2001 [1;2]. Based on the findings, the original field test plan (FTP) was prepared in 2003 proposing bioremediation, specifically enhanced reductive dechlorination (ERD) with surfactant flushing for the source zone [3;4]. Figure 1: North Railroad Avenue Plume Superfund Site. Approximate groundwater plumes prior to remediation and the groundwater flow directions in the shallow aquifer (red plume with red arrow) and deep aquifer (blue plume and blue arrow) are shown. The location of the source of contamination, a former dry cleaner/laundromat business, is also shown. Approximately 100 wells (injection/extraction/monitoring) were installed during the summer and fall of 2005. Intensive soil/sediment and groundwater sampling, screening, and analyses were conducted during the well installation operations. Results improved the understanding of the contamination distribution and provided an enhanced picture of the lithology, especially concerning the shallow aquifer and aquitard. Based on the findings stemming from the well installation and soil/groundwater sampling and analysis campaigns, surfactant flushing was eliminated, and the 2003 FTP was revised. The primary changes to the 2003 FTP included new amendment selection, new test cell well pairs, and additional test cell to evaluate source area remediation. Construction of the remediation system was completed in 2006, and pilot test treatment was initiated in 2007 through 2008. This article presents the result of the Revised FTP. Remedial action at the site was divided into four treatment areas: the source zone, a hotspot, and downregulation treatment areas located in the shallow groundwater aquifer and the deep zone area. Based on high-concentration dissolved-phase PCE detected in the source zone area, ganglia-phase dense non-aqueous phase liquid (DNAPL) contamination may have been present. Alternatively, the high-concentration dissolved-phase PCE may have been the result of increased solubility due to surfactants from the laundry wastewater discharge that mixed with the dry-cleaner chemicals at the release site, an inline lint trap. The hotspot area emanates downregulation from source zone in the shallow aquifer. Pilot testing was conducted in the source zone and hotspot areas. Although pilot test activities were not conducted at the downgradient or deep-zone areas, the results were used to inform remedial action approach for these areas. Shifts in microbial consortia diversity, including changes in microbes that harbor the key enzyme-producing genes involved in the biodegradation of chlorinated hydrocarbons, were monitored during the pilot test by analyses of the microbiome, using molecular microbiological methods (MMMs). Changes in biomass measured by microscopic examination of concentrated consortia samples [5] was employed to assess the overall response of the microbiome to changing aquifer conditions.