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Superfund Site | 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.

Contaminants of Concern

The current contaminants of concern in groundwater include volatile organic compounds (VOCs), cyanides, acids and heavy metals (chromium and lead). Contaminants of concern at the site may change as new data becomes available.

Public Health Impact

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.

Site Hydrogeology

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 middle alluvial unit (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.

Action Taken

In 2016, the Army Corps of Engineers, on behalf of the U.S. EPA, completed the second Five Year Review (FYR). The FYR concluded that while the remedies are still protective of groundwater, indoor air near where soil was contaminated will need to be re-evaluated.

In April 2017, the U.S. EPA released a fact sheet explaining what vapor intrusion is, how it is determined if vapor intrusion is a concern, and the areas to be re-evaluated.


Vapor intrusion work is currently underway at the SIBW Superfund Site, lead by the U.S. EPA. For more information on vapor intrusion, please contact the U.S. EPA.

An amended FYR will be released after the vapor intrusion work has been completed and evaluated.