Bridgeport Village Development Site (Durham Quarry) in Tualatin and Tigard, Oregon, for Opus Northwest, LLC and Washington County Facilities Management
GeoDesign recently conducted Phase I and II Environmental Site Assessments, a Remedial Investigation/Feasability Study (RI/FS), and remedial actions for the approximately 28.64-acre development. This site was purchased by Washington County in the early 1950s for use as a gravel quarrying operation (Durham Quarry). Quarrying operations ceased in the late 1970s, and the County hired a contractor to fill the quarry. After filling the quarry, the County sold the reclaimed parcel to Opus Northwest, LLC who is in the process of constructing approximately 466,000 square feet of upscale retail and office space.

During the RI, GeoDesign conducted a four-phase investigation to evaluate methane occurrence within the interior filled portions at the site, in fill near the perimeter of the former quarry, in native gravels surrounding the former quarry, and in near-surface soils. All four phases were followed by a program of methane monitoring. GeoDesign submitted an RI/FS report to Oregon Department of Environmental Quality (DEQ) presenting the results of various investigations conducted for methane and other hazardous substances. The RI activities were completed to gather sufficient information to support an informed risk-management decision regarding the selection of an appropriate remedy for the site and provided the basis for preparing an FS in accordance with applicable DEQ and U.S. Environmental Protection Agency requirements. Based on the RI/FS, the DEQ issued a Record of Decision, including engineering controls, institutional controls, and inspections/monitoring.

The required engineering controls implemented by GeoDesign include an active gas extraction system around portions of the interior/perimeter of the site, a passive sub-slab venting system and low permeability gas membrane beneath each building slab, and low permeability membrane collars or trench plugs for every utility that enters or exits each building or crosses a site boundary. GeoDesign is conducting inspections of the engineering controls and monitoring sub-slab probes and vent risers to verify the effectiveness of the passive sub-slab engineering controls. GeoDesign is also monitoring the operation of interior methane gas sensors installed within unventilated building spaces.