South Indian Bend Wash Area

Investigation and Cleanup Activities

This site is being addressed in two long-term remedial phases. For the most part, the work has been divided into the following management units: (1) soil; and (2) groundwater. The EPA is addressing SIBW as a separate area of study from NIBW because the contaminants come from different sources and the groundwater plumes are not contiguous.

Site Studies

The Remedial Investigation (RI) for SIBW was conducted over a period of many years and characterized both soil and groundwater conditions. Interim RI Reports were completed in 1991 and 1993. The final RI and the Groundwater Feasibility Study (Groundwater FS) were completed in 1997.

Remedy Selected

On September 27, 1993, EPA issued a Record of Decision for the Soil Operable Unit entitled, “VOCs in the Vadose Zone” (1993 Soils ROD). This ROD selected Soil Vapor Extraction (SVE) as the cleanup technology for VOCs in soils at SIBW.

Within the SIBW study area there are many facilities at separate locations which are known as subsites. These subsites have the same VOC contamination and very similar types of soils. Traditionally, EPA would investigate and then evaluate cleanup alternatives for each facility or subsite. However, due to the similarities among the SIBW subsites it was likely that the same cleanup would have been selected in each case. Rather than select the same remedy repeatedly for many facilities, EPA selected a remedy in the 1993 Soils ROD that utilized the “Plug-in Approach” in order to save time and resources.

Using this approach, EPA selected a cleanup technology (SVE) that would apply whenever a certain set of conditions existed. This set of conditions was defined in the 1993 Soils ROD. First, investigations are required to be conducted at each subsite. These investigations are known as “Focused Remedial Investigations” or FRIs. After the FRIs have been conducted at each facility, EPA compares the results with the standard criteria. If the facility meets the specified conditions, then soil cleanup is required at that facility.

Once EPA has made a decision regarding whether or not a particular subsite meets the criteria, EPA then issues a “Plug-in Determination Document” and makes the FRI Report available for the public to review. To date, EPA has issued two Plug-in Determinations. The first was in February 1994 for the DCE Circuits Subsite. Soil cleanup was required at DCE Circuits and this cleanup is currently nearing completion. The second Plug-in Determination was issued in January 2002 for the following seven subsites: Circuit Express, Allstate Mine Supply, Desert Sportswear, Cerprobe, Service and Sales, and the City of Tempe Right-of-Way. None of these seven subsites plugged-in to the 1993 Soils ROD and, therefore, soil cleanup was not required.

Remedy Selected

On September 30, 1998, EPA issued a Record of Decision for VOCs in groundwater (1998 Groundwater ROD). The 1998 Groundwater ROD addressed all three groundwater plumes at the SIBW Site: the western plume, the central plume and the eastern plume. The remedy selected for the western plume was extraction and treatment and the remedy selected for the central and eastern plumes was monitored natural attenuation (MNA).

Cleanup Ongoing

Currently, work on the central and eastern plumes is being conducted by a potentially responsible party (PRP) under EPA and State oversight. This work includes installation of monitoring wells, groundwater sampling, groundwater modeling and production of a report regarding the status of the MNA remedy. All monitoring wells have been installed. Sampling began in April 2002 and was complete in July 2003. The Remedial Design Report for this work is expected to be submitted in December 2003. Based on current information, the MNA remedy appears to be effectively cleaning up the central and eastern plumes.

Cleanup of the western plume is considered to be a fund-lead action. In other words, EPA is conducting the cleanup and paying for it out of the federal “Superfund”. Following issuance of the 1998 Groundwater ROD, some data gaps needed to be filled before EPA could proceed with design and construction of the extraction and treatment remedy for the western plume. First, additional groundwater data was needed. EPA has continued to collect groundwater monitoring data from the western plume on a quarterly basis to gather this needed information. Also, in order to determine the southernmost boundaries of the western plume three additional monitoring wells were installed early in 2001. EPA is continuing to evaluate this groundwater data.