2020 Excellence in Environmental Engineering and Science™ Awards Competition Winner

Honor Award - Design

Middlefield-Ellis-Whisman Superfund Study Area

Entrant: Geosyntec Consultants, Inc.
Engineer in Charge: Eric Suchomel, Ph.D., P.E.
Location: Mountain View, California
Media Contact: Eric Suchomel, Ph.D., P.E.

Entrant Profile

Geosyntec Consultants, Inc. works with cities, counties, and public and private entities promoting sustainable economic redevelopment benefitting all parties on sites that may be complicated by actual or perceived environmental contamination of soil or groundwater.

As a multi‐disciplinary, full‐service environmental and engineering firm, Geosyntec has over 1,400 practitioners in 80 offices on three continents. We offer an extensive set of tools for site cleanup and reuse and can bring together the necessary expertise to provide solutions for the array of environmental issues at each step of the way – evaluation, design, and construction.

From former commercial properties to industrial complexes to manufactured gas plants, our practical experience and innovative remedial designs have enabled our clients to make economically sound, regulatory‐compliant, and risk‐based management decisions for remediating and redeveloping contaminated properties.

The Geosyntec team for the Middlefield‐Ellis‐Whisman Superfund Study Area in Mountain View, California is comprised of over 20 Geosyntec professionals from five offices. However, the success of the project is also attributable to our close collaboration with our client, other legal and environmental consultants working for our client at the Study Area, regulatory agencies, and public and private stakeholders working to remediate the Study Area. Some of these entities are acknowledged below.

Owner: Schlumberger Technology Corporation
Regulatory Agency: United States Environmental Protection Agency
Legal Consultants:
- Hunton Andrews Kurth, LLP
- Farella Braun & Martel, LLP
Environmental Consultants:
- Weiss Associates
- Haley & Aldrich

Project Description

Project Objective

The Middlefield‐Ellis‐Whisman (MEW) Superfund Study Area (Study Area) in Mountain View, California includes multiple sites at former semiconductor manufacturing facilities and the former Naval Air Station Moffett Field. The footprint of the Study Area is approximately one square mile and consists of areas of facility‐specific and regional responsibility. Eight parties are performing activities within the Study Area to address United States Environmental Protection Agency (USEPA) Region 9 enforcement instruments. Geosyntec was retained in 2008 to provide services for the Regional Groundwater Remediation Program (RGRP) and certain facility‐specific areas.

Of primary concern within the Study Area are impacts to groundwater and indoor air from trichloroethylene (TCE) and related chlorinated volatile organic compounds (VOCs). To address the impacted environmental media at this highly complex site, pump and treat and containment via slurry walls for the impacted groundwater and vapor intrusion (VI) assessment and control measures are required by the USEPA enforcement instruments.

Geosyntec's Scope of Services

Geosyntec is the primary strategic and program management consultant working to meet the technical and reporting requirements while facilitating land use improvements. In this role, Geosyntec has worked closely with USEPA and other stakeholders to update and optimize the groundwater monitoring and treatment program, develop a proactive approach to assess and address the potential for VI into existing or planned residential and commercial buildings, and modified existing treatment system components to facilitate development.

Vapor Intrusion Pathway Assessment and Remedial Design

Geosyntec has worked with a team of technical and legal consultants and the USEPA to develop a first of its kind risk‐based VI pathway‐specific management strategy that facilitates residential and commercial development within the Study Area while being protective of inhalation exposure via the VI pathway to current and future building occupants. This includes using a multiple lines of evidence approach to assess the potential for VI to impact the indoor air quality of existing and future structures overlying contaminated shallow groundwater within the Study Area. A comprehensive, integrated approach that considers all environmental media (air, water, soil, and soil vapor) is used to develop an appropriate strategy for each parcel that facilitates social and economic advancement via development. Geosyntec works with developers, property owners, the responding parties, legal and technical consultants, architects, the City of Mountain View permitting departments, the USEPA and the Bay Area Air Quality Management District to collect and assess the necessary environmental data to design and construct VI mitigation measures, if any, needed for each building while meeting permitting requirements. These measures have included heating, ventilation and air conditioning modification; soil vapor extraction systems; active sub‐slab venting systems; and passive sub‐slab venting systems using innovative, green, and sustainable technologies such as aerated floors and wind turbines.

Working closely with the stakeholders, from initial notice of intent to development, Geosyntec has successfully assessed and designed USEPA‐approved vapor intrusion mitigation measures within two months thereby working within the developer's schedule.

Groundwater Remedy Design Optimization

Geosyntec performed a comprehensive optimization study of the existing pump and treat remedy that provided a design basis for integrating operation of multiple treatment systems, increasing mass removal by modifying the existing remedy, or implementing alternative technologies. Development of this design basis included:

Design and implement pilot studies to evaluate enhanced in situ chemical oxidation. This included a novel method to utilize manganese dioxide (MnO₂) from the reduction of permanganate (MnO₄) to subsequently activate persulfate. This method is advantageous compared to other approaches as it requires less permanganate mass for treatment and persulfate has a longer period of activity in the subsurface. Full‐ scale design and implementation resulted in:
- Short‐term post‐injection concentration reductions of up to 98%; long‐term concentration reductions in some areas exceeded 90%.
- The mass of VOCs destroyed after the injection was equivalent to the estimated mass removal by operating the groundwater extraction system over 30 years.
Design and implement pilot studies to evaluate the feasibility of increasing mass removal by increasing extraction by the existing remedy where in situ remedies are infeasible due to access constraints. A solute transport model for TCE in groundwater was created and used to evaluate multiple extraction scenarios. Model results guided a five‐year assessment of optimized extraction. The assessment validated key aspects of the conceptual site model (CSM), specifically that the time to achieve remedial objectives within the Study Area is limited by the presence of TCE mass in non‐transmissive lithological units.
Design and construct the integration of three existing groundwater extraction and treatment systems. As part of this effort, new pipelines were constructed to consolidate groundwater flow to a single location within the Study Area, an existing system was expanded and reconfigured to address current and future project needs, and system electricals and controls were modified for remote operation. Given the expected lifetime of the extraction and treatment systems (many decades) and ongoing development at the Study Area, this integration is an example of "evergreen" system engineering and operation, with the objective of allowing continued and new beneficial uses within the Study Area and minimizing the responding parties' operational footprint.
Education of project stakeholders, including the regulatory community, on how a key aspect of the project CSM, matrix diffusion, or the presence of TCE in non‐transmissive units, impacts remedy selection, remedy performance, and projected remedial timeframes. This has increased trust between the responding parties and key stakeholders and led to community support and acceptance of the current remedial approaches and continued redevelopment of the area.

Geosyntec's Value

Geosyntec works with technical and legal consultants, local and federal agencies, and the responding parties to effectively remediate legacy contamination and to facilitate redevelopment of this highly complex area. As a result of our efforts since 2008, the Study Area has continued to grow and develop into a mixed‐use area supporting single family homes, multi‐family residential units, commercial, industrial, and educational facilities. USEPA considers this Study Area a model of beneficial reuse of Superfund Sites; the Study Area was a case study on encouraging private investment to support redevelopment in their recent Superfund Task Force report.

Click images to enlarge in separate window.