Since 1983, M&A has played a critical role in characterizing and remediating groundwater contamination at Arizona’s largest Superfund site.
Clients: North Indian Bend Wash Participating Companies; Motorola, Inc.- Time frame: 1983–present
- Location: Scottsdale, Arizona
Located in the Salt River and Paradise Valley groundwater basins, NIBW was selected by the EPA for inclusion on its Superfund list in the early 1980s after groundwater from several municipal supply wells was found to be contaminated with volatile organic compounds (VOCs). Soil and groundwater characterization efforts uncovered a regional plume caused by multiple historical industrial facilities. The NIBW site is not only the largest currently active groundwater cleanup in Arizona but also one of the largest such efforts in the country. Working initially on behalf of Motorola and later representing the entire group of participating companies, M&A has been integrally involved in strategic management of the project since its inception. We have played a key role in developing, gaining regulatory approval for, and implementing all aspects of the remedial actions.
M&A designed and implemented a comprehensive field program to gather data for characterizing the site’s hydrogeology and the extent of VOC contamination in soils and groundwater. We supervised the installation of numerous soil borings and monitoring wells. We also led field efforts and analyzed data from depth-specific groundwater sampling and from geophysical, hydrophysical, and spinner logging. This data was needed to characterize the lithologic properties, hydraulic properties, and contamination profile at individual source areas and within the regional plume.
M&A designed and tested three large-diameter extraction wells completed to depths exceeding 1,200 feet as part of the pump-and-treat remedy. To select favorable drilling sites for these wells, we evaluated hydrogeologic, water quality, and land ownership data and negotiated property access.
M&A developed models and participated in modeling efforts to achieve various remedial design objectives, including the selection of a final remedy for the site.
| Target Zone | Model Type | Objective |
|---|---|---|
| Groundwater | Flow | Evaluate groundwater movement within and between aquifers |
| Flow / particle tracking | Assess plume capture and containment under a range of extraction regimes | |
| Flow / solute transport | Compare the effectiveness of remedial alternatives for remedy selection | |
| Vadose zone | Assess the potential threat to groundwater from VOCs in the vadose zone and identify areas requiring soil vapor extraction |
During the characterization and subsequent remedy-development process, M&A constructed and tested an extensive monitoring network at the site. We then designed a comprehensive monitoring program to track the occurrence and migration of VOCs and to continuously verify containment projections. Ongoing monitoring and reporting ensures that the remedial action objectives are met and that groundwater containing VOCs does not impact nearby wells.
M&A provided technical support for an alternate dispute-resolution process to allocate costs for operating the remediation program over the long term. We also developed cost-sharing approaches for ongoing treatment activities and provided expert testimony related to an alleged loss of value for property overlying the zone of contamination.
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