The Wampanoag water testing lab has a clean bill of health this week after a visit from the state Department of Public Health. The lab has been under scrutiny after test results for beaches in Edgartown and Oak Bluffs last week showed levels of the bacteria enterococcus at levels high enough to close South Beach in Edgartown and Inkwell Beach in Oak Bluffs, results that were not duplicated by water testing facilities in Tisbury and Chatham.

Following a rash of beach closures earlier this month, on July 18 the state coordinated a “split sampling” of Vineyard beaches, asking board of health officials to submit samples of seawater from various town beaches to the Wampanoag lab in Aquinnah as well as testing facilities in Tisbury and Chatham. All Island towns use the Wampanoag lab for its water testing except Tisbury, which tests at its wastewater treatment facility.

Test results for State Beach and Inkwell Beach on July 18 from the Wampanoag lab indicated levels of enterococcus that would have resulted in the closure of those beaches but the state allowed the towns to use lower, acceptable results from the Tisbury and Chatham labs, and keep the beaches open. State officials said the disparity between the labs was within a statistically acceptable margin.

“When conducting split samples for bacteria in surface water we don’t expect laboratories to report the same results from individual samples,” department of public health spokesman Julia Hurley wrote in an e-mail on Thursday. “The relative per cent difference between all three lab results were well within the margins required.”

A state audit Tuesday at the Wampanoag laboratory found no faults. “MDPH did not find any issues with Wampanoag Laboratory’s procedures for analyzation as a result of our laboratory audit,” Ms. Hurley wrote.