CRMC keeping an eye on cable depth

At the Town Beach
Fri, 02/09/2018 - 9:15am

There is concern about the shallow burial depth of National Grid’s sea2shore transmission cable about 200 feet off Block Island’s Town Beach. The utility’s 20-mile long sea2shore cable links Block Island to the mainland, and transmits the flow of electrons to and from the Island.

The concern with the shallow burial depth is cable protection, as it could incur damage from contacting hard seabed. 

Ted Kresse, spokesman for National Grid, said, “There has not been any damage to the cable, and there is no threat to the public or boaters. It is armored and sheathed. We would simply be looking to add additional protection to a small area that could be subject to periodic erosion issues.”

In June of 2016, when the sea2shore cable was installed by National Grid, the utility encountered hard, impassable seabed about 200 feet from shore, making the requisite burial depth of six feet unattainable for an 80-foot stretch. As a result, that section of the cable was buried to a depth of about two to three feet, presenting a concern to the Rhode Island Coastal Resources Management Council and the Department of Environmental Management.

Laura Dwyer, spokesperson for the CRMC, told The Block Island Times that, “There is a concern that the burial depth on which the permit was based was quite different from the as-built condition, but we and the other parties have been working to address that since it was discovered.” Dwyer said Deepwater Wind’s export cable, which links the Island to the Block Island Wind Farm, has better burial depth than the sea2shore cable, “so we are not concerned with that one.”

“There’s no concern for swimmers, we are taking extra precautions for boaters,” said Dwyer. 

In the spring of 2017, National Grid installed a protective sleeve over a section of the sea2shore cable that was not buried at proper depth. National Grid officials told The Times at the time that the cable would need future monitoring, as harsh weather conditions and shifting sediment could lead to further shallowing.

“Erosion and hard bottom in the area do impact burial depth,” said Kresse. “We are continuing to evaluate the issue and exploring potential options to address it.”

Dwyer said, “The CRMC and National Grid are currently working on possible plans of action. One possible action might be to dredge material from Old Harbor, and use it to further bury the cable in the offshore area in question. We are studying the movement of sediment in that area.”

“We are also working on a situational, conditional set of parameters, which would require action from National Grid,” said Dwyer, who noted that any work on the cable would not be conducted during the summer. “For example, if the cable were exposed for a certain number of days, it would prompt action.”

‘No hazard’ from EMFs 

Results of the Electromagnetic Fields survey conducted on sea2shore cable by University of Rhode Island Oceanography Prof. John King on Dec. 18 indicate EMF levels are low, averaging a maximum of 3.1 milliGauss, similar to his Feb. 28, 2017 survey, which also noted a higher reading where the cable is buried at a 2.3-foot depth. King issued two reports to the CRMC on Jan. 21: one for offshore readings of the sea2shore cable, and the other for a section of cable near the Town Beach.

“The readings do not present a hazard,” said Kresse of National Grid. “The Dec. 2017 measurements are consistent with previous measurements. Overall, the December survey concluded that the EMF levels in general for the cable are lower than predicted when the project was being permitted.” 

An EMF is a charged electro-magnetic field generated by an electrical source flowing through a live cable. In order to glean EMF readings, King and his URI crew employed a device called a SEMLA, which stands for Swedish Electromagnetic Low-noise Apparatus. There was no indication in King’s report that wind speeds of about 10 miles an hour on Dec. 18 impacted the power output of the Block Island Wind Farm, or readings for the survey.

“The wind speed at the time of the surveys did not have an impact on our ability to take the readings,” Kresse told The Times. “The report includes potential EMF levels scaled to full power based on the data we collected that day. The magnetic field data and the cable’s electric load were taken the day of the survey. They were then scaled using established engineering principles to magnetic fields that would occur if the wind farm were putting out maximum generation.”

In his report, King wrote that, “Employing the magnetic field scaling demonstrated by measurements in the shallow depth area (of the cable) obtained during Dec. 18, the observed maximum magnetic field strength at full power is estimated to be 38 mG for a minimum burial depth of 2.3 feet.” He noted that “the magnetic field at the start of the measurement was 13 mG, and 2.2 mG at the end.”

Kresse said, “Household items, such as hair dryers, vacuum cleaners, electric mixers, and can openers produce magnetic fields. For example, six inches from a hair dryer the median magnetic field reported by National Institute of Environmental Health Science is 300 mG. After more than 35 years of research, the consensus of the international scientific community is that the science has not established a causal link between exposure to EMF and risks to public health.”

Dwyer said, “The overall assessment is that all of the readings, from both surveys, show the EMF readings all within the permitted levels. The EMF readings are all within the parameters of the permit, which was based on model assumptions that were quantified as safe to humans and ocean life. We are, however, working to improve the burial of the cable landing at the beach on Block Island.”