SEDIMENT RESUSPENSION AND COMPLIANCE MONITORING FOR THE NYPA/VELCO PV-20 SUBMARINE CABLE REPLACEMENT PROJECT

In fall 2017, water quality was monitored during the installation of new power cables within the sediment of Lake Champlain between Grand Isle, VT and Cumberland Head, NY to address concerns with sediment resuspension and potential water quality impacts during cable burial activities. The monitoring was conducted in accordance with plans developed to address the specific requirements of two state entities with jurisdiction over the project activities: NY State Department of Environmental Conservation (NYSDEC) and VTDEC. The NYSDEC monitoring plan was established based on precedent for similar projects permitted in NY and involved real-time sampling for total suspended solids and metals to monitor water quality impacts. The VTDEC monitoring plan focused on monitoring and preventing potential impacts to a water supply intake that withdraws water from Lake Champlain to provide public drinking water and fresh water to a fish hatchery. Here, turbidity was the main concern due to drinking water standards and water clarity requirements for the hatchery. Although the intake is located a significant distance from the project corridor (2,900 ft) and preliminary modeling indicated sediment would settle within 200 ft of the point of sediment disturbance, bore currents created by seiche events are known to impact water clarity at the depth of the intake (180 ft below the surface). Intake operators remained concerned that any additional sediment load during a seiche event could overload the hatchery’s filtration system capacity, which could result in irreparable damage to the operations. Therefore, the need for real-time, continuous data to alert the Project Team of potential turbidity issues associated with Project activities was recognized, and the Project Team developed an innovative plan to use data buoys with turbidity sensors and current meters to monitor conditions between the Project corridor and intake, which relayed continuous, real-time data to a webcenter for remote monitoring.

This paper provides a summary of the pre-project planning and studies, project work completed, sampling methods, results of the 2017 monitoring compared to model predictions, and also provides an overview of the regulatory processes and mechanisms in place to maintain water quality within Lake Champlain from an industry perspective.