Offices


SeattleGeolocation: 47.8005, -122.3181

 Terracon (formerly Zipper Zeman Associates, Inc.) has been serving clients in the greater Seattle area since 1998.

Terracon (formerly Zipper Zeman Associates, Inc.) has been serving clients in the greater Seattle area since 1998.

The Seattle office provides multiple related service lines to clients at local, regional, and national levels. In the Northwest, Terracon specializes in geotechnical engineering, environmental consulting, and construction materials engineering and testing services. Terracon's basic strength is our commitment to our local clients; we are proud of our commitment to the Northwest region. The senior engineering staff of Terracon's Washington offices offers more than 250 years of local experience.


After operating in the greater Seattle area and Portland, Ore., since 1998, Zipper Zeman Associates, Inc. joined Terracon in 2005. These local offices officially became Terracon in 2009. RGA Environmental joined Terracon in 2014, and in 2015 the Seattle location joined Terracon's Mountlake Terrace office, further expanding services from this location.

Key Projects


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Kent/Auburn Conveyance System ImprovementsGeolocation: 47.548, -121.9836
This project consists of approximately 12,500 linear feet of gravity trunk sewer and 10,000 linear feet of sewer force main, and includes five railroad and highway trenchless crossings. Terracon completed pre-design geotechnical and environmental evaluations for several alignment alternatives. Following these evaluations we were asking to perform design phase geotechnical and environmental evaluations for the four preferred alignments that were selected during the pre-design phase.

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North Twin BridgeGeolocation: 47.4018, -122.3243
Terracon was contracted to provide geotechnical services to assess site conditions at the North Twin Bridge in Des Moines, Wash. The bridge was built in 1950 and is about 230 feet long, spanning a steep sided ravine above McSorley Creek. During initial observations of the site, a void was discovered below the foundation of Bent 1. Terracon evaluated the existing foundation support conditions at Bent 1 and provided recommendations for methods for emergency foundation repair. Additionally, Terracon also provided options for seismic retrofit intended to upgrade the bridge to a performance based…

 PropertyDamageClaims
Property Insurance Damage ClaimsGeolocation: 47.4235, -120.3103
RGA Environmental, A Terracon Company, conducted industrial hygiene consulting for smoke damage insurance claims following wildfires in Wenatchee, Wash. The project involved soot and char residue assessments at 30 private residences in the impacted area. The Seattle laboratory analyzed more than 300 samples for microscopic smoke related particulate deposition.

 SohomishCountyPublicUtilityComplex
Snohomish County Public Utility District ComplexGeolocation: 47.8081, -122.3193
RGA Environmental, A Terracon Company, provided environmental consulting services related to the demolition of an existing 33,000 sq. ft. building to prepare the site for construction of a new $7.8M public utility district (PUD) complex. The complex will house the utility’s operational center and customer service office. Snohomish County PUD is the second-largest publicly owned utility in the state of Washington.

 South Shore School
South Shore SchoolGeolocation: 0, 0
Located in Southwest Seattle, the South Shore School is a new $40-million structure replacing the existing South Shore building. Though designed to meet the growing program needs, the structure still maintains its communal roots by remaining attached to the Rainier Beach Community Center and sharing a larger educational and community-use campus. Designed to symbolize community and inclusiveness, the new facility will provide a unique space for connection and unification of students while emphasizing personalized learning. Throughout the construction, Terracon had a full-time, multi-certified…

 USNavyAHERAtraining
U.S. Navy (AHERA) TrainingGeolocation: 48.2517, -122.6737
RGA Environmental, A Terracon Company, is an Asbestos Hazard Emergency Response Act (AHERA) training provider for the U.S. Navy. Over a three-month period, instructors developed and delivered custom 24-hour initial AHERA Building Inspector and 40-hour initial asbestos supervisor training for U.S. Navy personnel at Navy facilities in Whidbey, Bangor, and Everett, Wash.