South Indian Bend Wash
South Indian Bend Wash (SIBW) site represents the southern portion of the Indian Bend Wash (IBW) Superfund site. The site study area boundary encompasses approximately four-square miles in Tempe, Arizona. The site is bounded by Apache Boulevard on the south, Rural/Scottsdale Road on the west, Price Road on the east, and proximate to Curry Road (Salt River) on the north. The plume boundary varies and may extend beyond the site study area boundary but remains part of the Superfund site in its entirety.
The U.S. Environmental Protection Agency (EPA) negotiated settlement agreements with the remaining potentially responsible parties (PRPs) associated with the central and eastern groundwater contamination plumes in SIBW in 2007. The entire site is a Superfund lead site with a monitored natural attenuation remedy.
ADEQ received the enhanced attenuation study report early to mid 2015 and is currently reviewing the effectiveness of In Situ Chemical Oxidation (ISCO) as a clean-up remedy.
A community information group (CIG) has been formed and EPA has hosted numerous CIG meetings over the years. The most recent fact sheet for the site can be viewed at the Arizona Department Environmental Quality (ADEQ) website.
1981 - 1983: SIBW was initially part of the IBW Superfund site that was placed on EPA’s NPL on September 8, 1983 after the City of Phoenix detected volatile organic compounds (VOCs) in municipal wells in the Scottsdale/Tempe area in1981.
1987 - 1993: The EPA began a remedial investigation (RI) of the IBW site in 1983, and at the end of 1987, informally split the IBW into two study areas: the North IBW and SIBW.
1993: In September, the EPA issued a Record of Decision (ROD) for the cleanup of VOCs in soil at eight industrial facilities. This ROD required a "plug-in" presumptive remedy involving the use of soil vapor extraction (SVE) systems. Each sub-site collected soil vapor data and followed the ROD's guidelines to determine if an SVE system was necessary.The EPA and ADEQ completed technical reviews of the focused RI plug-in assessments and determined that the following six sub-sites (Cerprobe Corp., former Service and Sales, former Eldon Drapery, former Desert Sportswear, former Circuit Express and former Allstate) do not meet or exceed the plug-in criteria as described in the ROD.
1998: In September, the EPA signed a ROD for the cleanup of VOCs in the groundwater operable unit at this site. The selected remedy required MNA for the central and eastern portions of the plume, and a groundwater extraction and treatment system for the western portion of the plume.
1999 - 2000: The EPA entered into negotiations with six PRPs in 1999 and executed an Administrative Order on Consent (AOC) with only one of the PRPs (IMC Magnetics) on September 27, 2000. This AOC required IMC Magnetics to design the MNA remedy for the central and eastern plumes. This work involved the installation of groundwater monitor wells and long-term monitoring of plume behavior and VOC degradation.
The western plume remedy is being addressed by EPA as a fund-lead action. The DCE Circuits site and the APS Ocotillo Generating Station are thought to be contributors to the SIBW western groundwater contaminant plume. EPA and ADEQ completed technical reviews of the focused RI plug-in assessments, and determined that the following six sub-sites (Cerprobe Corp., former Service and Sales, Former Eldon Drapery, former Desert Sportswear, former Circuit Express and former Allstate) do not meet or exceed the plug-in criteria as described in the 1993 ROD.
2003: During February, EPA and ADEQ agreed that the former landfills along the banks of the Salt River do not pose a threat significant enough to continue to be listed as part of the site. As a result, EPA published a notice of intent to delete (NOID) the landfills from the NPL for public comment. The final Notice of Deletion (NOD) was sent by the EPA for filing in the federal register in May.
An Amended Record of Decision (AROD) was completed which changed the remedy associated with the groundwater cleanup of the Western Plume on October 16.. The remedy was originally prescribed as groundwater pump and treat. The AROD now prescribes MNA as the remedy. This AROD now makes the remedy for all three groundwater plumes in the SIBW area MNA.
2004: In December, EPA conducted a removal action at DCE Circuits. A drywell which received hazardous waste in the 1980s, was removed by soil boring. Several truck roll-off bins of soils were disposed as solid waste and several drums of waste were disposed as hazardous waste.
2005: Subsequent to the removal action at DCE Circuits, soil vapor samples were collected. The samples indicated levels of soil vapor which required remediation. A mobile SVE system was installed and operated, and samples were collected. The analyses of these samples will indicate if further remediation is necessary. EPA conducted a “plug-in” determination for soils at the Unitog sub-site in September. EPA determined the Unitog soils do not meet the plug-in determination criteria and therefore can be considered for a close out.
2006: On December 6, EPA announced that all physical construction of cleanup systems was completed. Soil cleanup was expected to be complete in the next five years and groundwater cleanup an additional 30 years.
2007: In December settlements were announced with eight PRPs: Circuit Express, Inc.; IMC Magnetics; Prestige Cleaners, Inc.; Unitog Rental Services, Inc.; Janstar Development, Inc.; K and S Interconnect, Inc.; Service and Sales, Inc.; and Sherman Leibovitz.
2008 - 2009: MNA continued and the wells were sampled on a quarterly basis by EPA.
2010: An additional monitoring well was installed at the southeast boundary of the Central plume during the summer. The FYR process began for this site with site inspections and interviews of community members and stakeholders.
2011 - 2012: The first FYR was completed in September. The FYR determined the remedies at the IBW sites are currently protective of human health and the environment, and exposure pathways that could result in unacceptable risks are being controlled. Specifically for SIBW, identified source areas have been remediated and the MNA remedy has almost met the remedial action objective to restore groundwater to beneficial use. At the DCE Circuits sub-site, indoor air monitoring conducted since 2007 is ongoing to ensure concentrations remain within EPA’s acceptable levels. MNA continued and the wells were sampled on a semi-annual basis by EPA. The SIBW monitoring wells are sampled semi-annually by EPA and ADEQ. The groundwater remedy is resulting in contaminant concentrations which are mainly below the MCL of 5.0 ppb, with four wells indicating contaminant concentrations nominally above the MCL (highest concentration of 8.9 ppb for TCE in March 2011).
2013: EPA began an Enhanced Attenuation Study by performing ISCO at select monitoring wells which involves introducing a chemical oxidation agent (sodium permanganate) into the selected monitoring wells (5) to make contact with the contaminants and break them down into nonhazardous or less toxic compounds that are more stable, less mobile, or inert. The objective of the study is to assess the ability of this technology to restore the aquifer to the clean-up goal (2 parts per billion (ppb)) and to compare its cost effectiveness to Monitored Natural Attenuation (MNA) in both time and money. 25 monitoring wells were abandoned, most of the wells were either non-detect or below the MCL when initially installed and have continued to be below the past 20+ years. MNA sampling continues on a quarterly basis.
2014: 45 groundwater monitoring wells were abandoned with 21 wells remaining in the study area. They will continue to be monitored through annual sampling events. The enhanced attenuation study has been completed and is currently being evaluated.
2015: In early to mid 2015, the enhanced attenuation study was submitted to ADEQ by the EPA to review the effectiveness of performance of ISCO.
The current contaminants of concern in groundwater include VOCs. The current contaminants of concern in soil include VOCs, cyanides, acids, and heavy metals (chromium and lead). Contaminants of concern at the site may change as new data becomes available.
All drinking water supply wells within the site boundaries are inactive. Groundwater in the area is used for industrial purposes only. Drinking water is served by the City of Tempe municipal service from wells outside of the site boundaries.
At SIBW, groundwater occurs in three aquifer units: upper, middle, and lower alluvial units. The materials are primarily a thick, basin-fill sequence of alluvial sediments derived from surrounding mountains. Igneous rocks intrude in places, and crystalline bedrock exists in juxtaposition to the alluvial units as a result of block faulting.
The upper alluvial unit (UAU) is distributed across the entire SIBW study area, and generally has a uniform thickness. The UAU typically is found near or at the ground surface and extends to approximately 110 to 170 feet below ground surface (bgs). The estimated transmissivity values varied widely from a low of 1,900 square feet per day (ft2/day) to a high of 73,000 ft2/day. Groundwater flow directions in the UAU are south to southwest during non-river flow conditions in the Salt River. These flow directions shift to south and southeast during river flow conditions in the Salt River when recharge influences groundwater flow directions. Groundwater flow through the UAU originates mainly from Salt River recharge (during flow events) and lateral inflow moves vertically downward, eventually entering the MAU.
The MAU lies below the UAU and located approximately 170 to 200 feet bgs, and consists primarily of clay and sandy silt with significant interbedded layers of sand and gravel mixtures. These coarser-grained interbedded layers generally represent the zones with higher hydraulic conductivity in the MAU. Weak to strong calcium carbonate cementation is also present in the MAU. The groundwater flow direction in MAU sub-unit B is generally west to east, but insufficient data exist to fully characterize the flow direction. The groundwater flow direction in MAU sub-unit C varies from due north to east, with northeast appearing to be the predominant flow direction.
The lower alluvial unit (LAU) underlies the MAU and usually encountered at 500 feet bgs. Observations of the LAU indicate that the composition of the LAU is a conglomerate, dominated by weakly cemented gravel, sand, silt, and rock fragments. Limited data exist to estimate groundwater flow directions in the LAU. The general flow direction is to the east or northeast, similar to the MAU.
*In Arizona, but outside the Phoenix area, call toll-free at (800) 234-5677.
Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment.
The complete official site file can be reviewed at the EPA Region IX, Records Center, Mail Stop SFD-7C, 95 Hawthorne Street, Room 403, San Francisco, CA 94105, (415) 536-2000.