A group of Coast Guard Academy cadets, studying how fast the hull of the USS Arizona — still submerged at the bottom of Pearl Harbor, Hawaii, where Japanese forces sank it more than 75 years ago — is corroding, say their findings will help develop a model to predict the corrosion rates of other shipwrecks and when they might become an environmental risk.

Last month, the four cadets, seniors Marshall Grant, Ali Re and Terry Jung, and sophomore Cadet Linda Duncan, with the help of the National Park Service, dove to place so-called steel coupons — rectangular pieces of metal — on the battleship to determine how much of it has rusted away. The steel coupons are suspended from racks made of PVC pipe.

The cadets measured the mass of the steel coupons before placing them in the water, and will measure them again after they take them out of the water at different points in time to determine both the short-term and long-term corrosion rate. The coupons will be sent to the academy for the cadets to analyze how water temperature, salinity and currents impact corrosion.

The Arizona is submerged in about 40 feet of murky water. The cadets said a large portion of the ship is underneath mud and is covered in algae and other growth.

The ship has been leaking oil since at least the 1940s, currently at a rate of 2 to 9 quarts per day, according to NPS. Arizona, which held about 1.5 million gallons of oil, burned for two and a half days, so it's unknown exactly how much oil is still on board. The cadets also worked with Chris Reddy, senior scientist at Woods Hole Oceanographic Institute, to collect oil samples. Reddy has been analyzing these oil samples to determine the exact location of the leaking.

A report from the National Oceanic and Atmospheric Administration, presented to the Coast Guard in 2013, found that 36 shipwrecks scattered across the U.S. seafloor "could pose an oil pollution threat to the nation's coastal and marine resources." The report recommended 17 of the vessels for further assessment and potential removal of both fuel oil and oil cargo.

The study the cadets are involved with, which builds on decades of research on the Arizona, including its hull condition and oil leakage, will help explain "why these wrecks are corroding, and how fast they're corroding, so we can predict when we have to act before an environmental catastrophe happens," said Grant, 21, of Acton, Mass.

Jung, 22, of Centreville, Va., added that they will be able to develop "a prediction model to find the most optimal time for a salvage operation."

Duncan, 20, of Angwin, Calif., pointed to the large amount of research and information about the sinking of the Arizona, and said the findings from the study can be applied to other types of metal, and shipwrecks that we don't know as much about. Early analysis of the steel coupons placed on the Arizona shows that, in the beginning, the metal corrodes at a very fast rate, but then starts to slow down, Duncan said.

"Depending on how fast it corrodes in the beginning, it could have a much longer time stamp before things start to leak than we realized," she added.

Of the 1,177 sailors and marines on the Arizona who were killed, more than 900 could not be recovered and are still on board the ship, according to NPS. Capt. Rich Sanders, head of the science department at the academy and the cadets' research advisor, noted the cadets are around the same age the crewmembers were when they died.

The study "ties them back to that history and gives them a chance to understand at a deeper level about the active-duty commission service they're entering," Sanders said.

j.bergman@theday.com