Hudson High Voltage Direct Current (HVDC) Converter Station

Challenge

GZA was asked to provide geotechnical services and environmental studies for Siemens Energy, Inc. for its proposed Hudson High Voltage Direct Current (HVDC) Converter Station in the New Jersey Meadowlands, part of a transmission project intended to convert the power between New Jersey’s Public Service Electrical & Gas (PSEG) 230 kV grid and New York’s Con Edison 345 kV grid. The site includes active trucking and warehouse operations as well as wetlands.

Solution

Geotechnical: GZA performed a geotechnical subsurface exploration program and provided geotechnical and foundation recommendations for the project. The major structures for the proposed station include four transformer pads, one spare transformer pad, two valve halls, a control building, six AC filter banks consisting of a total of 18 foundation pads, and various other necessary support facilities including valve hall cooling fans, smoothing reactors, fire protection water storages and pump house, and a heavy transport access road.

GZA’s subsurface exploration consisted of eight soil borings, three observation wells, and five cone penetration soundings (CPT). Geotechnical laboratory testing was performed on soil samples and field “slug” tests to determine in-situ permeability. GZA determined that the site, located within the Hackensack Meadowlands, was underlain by man-made fill over a layer of organic peat, over glacially deposited silt, sand, and clay, over glacial till and bedrock. Groundwater was approximately five feet below ground surface.

To optimize foundation designs, GZA provided recommendations for four different types and sizes of deep foundations for the most heavily loaded structures, and recommendations for shallow foundations for lighter and less settlement-sensitive structures. A small amount of general filling of the site was required which posed the potential for additional settlement. Another portion of the site required the filling of virgin wetlands; slope stability and settlement of that area were addressed.

Environmental: GZA’s environmental studies included a Phase I Environmental Site Assessment (ESA), a Phase II Site Investigation, and additional site investigations as warranted. The Phase I ESA provided an opinion on the presence of Recognized Environmental conditions which may result in hazardous substances or petroleum products in the soil and groundwater at the site.

GZA’s Phase II Site Investigation evaluated soil and groundwater conditions at potential Areas of Concern (AOCs) identified in previous environmental reports completed by others and made available to GZA, as well as AOCs identified during GZA’s Phase I ESA. Potential AOCs on the site include former locations of underground storage tanks, an on-site septic system, transformers, a railroad spur, building floor drains and sumps, and portions of the site downgradient of off-site groundwater plumes. An additional site investigation was completed to further delineate impacted areas of soil and groundwater contamination confirmed in the initial Phase II Site Investigation.

Hazardous Materials: A pre-demolition Hazardous Materials Survey of the site building included testing and assessments for asbestos-containing materials (ACM) and a visual survey for residual solid and hazardous wastes, universal wastes, and potential poly-chlorinated bi-phenyl (PCB)-containing components. Given the age of the facility and strong likelihood that detectable levels of lead are present in the paint, lead safe work practices will be required during demolition. Construction Management: GZA completed a Construction Contaminant Management Plan to present the extent and magnitude of contaminated soils and groundwater, in light of proposed construction activities that may encounter these contaminated media. In addition, the plan evaluated the impact of regulatory requirements on planned construction and development plans. Ecological: GZA also evaluated a Wetlands Mitigation Plan for the site prepared by others. GZA’s evaluation included a cost estimate to implement the plan.

Benefit

This project successfully harnessed the breadth of GZA’s in-house, multidisciplinary services, facilitating a fast-tracked project schedule that met the client’s needs.