No issue with EMFs and undersea cable
National Grid recently conducted an underwater, electromagnetic post-installation marine survey of its 20-mile long sea2shore AC power transmission cable that connects Block Island to the mainland. According to the utility company, the work is a requirement of its approval process, and the survey was performed to determine if the cable’s EMF levels are permissible.
“This survey, as required by permit, was to collect electric and magnetic field levels readings along the entire length of the submarine cable,” said Michael Masseur, a spokesman for National Grid. “Upon agency review, we anticipate that this survey will be a one-time occurrence.” The work began on May 30 and was completed on June 11.
An electromagnetic field is generated when charged electrons, or electricity, are put into motion, delivered through a source such as a power cable. National Grid has said that the goal of the EMF survey is to ensure that the cable is operating properly, is protected, and does not pose a hazard to the public.
“The survey was completed, as expected and without issue,” said Masseur. “We are now in the process of analyzing the data, which will be shared with the appropriate state agencies once the analysis is complete.”
National Grid used a unique device mounted on a sled called the Swedish Electromagnetic Low-noise Apparatus, or SEMLA, that was created by Swedish engineer Peter Sigray to record the data. The device has sensors on it that take readings of electromagnetic fields from the seafloor while being towed by a boat.
“The sled was towed in a path perpendicular to the cable at approximately 1-kilometer intervals,” said Masseur, noting that a “research vessel” was utilized to conduct the survey. “The work was performed during daylight hours, and weather dependent.”
Masseur said, “The on-going survey is similar to the nearshore survey completed off Crescent Beach using the same survey instrument. The difference now is that the survey was completed in deeper waters and thus the sled was being towed by a vessel, as opposed to being manipulated by hand in shallow waters.”
Engineers from National Grid, along with Sigray and Professor John King from the University of Rhode Island’s Oceanography department, conducted a similar test in late February and early March on Block Island. That was when National Grid took a survey of the length of cable that was buried at a shallow depth 200-feet off the Town Beach. As a remedy to the shallow burial depth, National Grid installed a protective plastic sleeve around the cable to protect it from abrasion by the seafloor.
National Grid’s EMF readings taken at the beach were approved by the Department of Environmental Management in March. Laura Dwyer, spokesperson for the Coastal Resources Management Council, said, “We are evaluating all of the data (from the beach survey) to determine the next course of action.” She furnished The Times with National Grid’s EMF report from its beach survey, which denotes that “the magnetic field levels were all quite low.”