July will mark the 55th anniversary of the partial nuclear meltdown at the Santa Susana Field Laboratory in the hills near Simi Valley.

That event occurred from July 12 to July 26, 1959, which some have described as the longest nuclear accident in history.

Now, the debate over how to clean up the extensively polluted field lab land, groundwater and buildings — the site is laced with chemical and radiological contamination from nuclear reactors, rocket-engine tests and other research activities over four decades — seems to be stretching into one of the longest delays in history.

The gabfest continues even though, seven years ago, the state of California laid down the law regarding the cleanup that’s required. In 2007, the state Legislature passed, and Gov. Arnold Schwarzenegger signed into law, Senate Bill 990, which requires the land to become open space once it has been cleaned to the highest environmental standard.

Boeing Co., owner of most of the field lab property, successfully challenged SB 990 in court. The state’s appeal is pending.

SB 990 — whose author, Sen. Sheila Kuehl, D-Santa Monica, had pushed the legislation doggedly for six years — set a 2017 deadline for soil cleanup. Groundwater cleanup will take many decades, officials predict.

At the rate of action so far, critics and other observers are right to be concerned about how long the entire process will take and how effective it might be.

The 2,850-acre site, formerly known as the Rocketdyne nuclear and rocket-engine test facility, is mostly owned by Boeing, but about 451 acres are federal land administered by NASA.

In May, NASA announced it plans to demolish its field lab structures but will postpone decisions on cleanup of the soil and groundwater pending further field work, surveys and studies. Translation: more delays.

This month, an advocacy group called Consumer Watchdog issued a report that accused Boeing of derailing progress toward a cleanup. The report also charged that regulators in the state Department of Toxic Substances Control failed to push Boeing aggressively and were outmaneuvered by the company and its hired representatives.

Boeing and the state agency say they’ve done nothing wrong and are working toward a complete cleanup. But as these arguments stretch out, the bottom line increasingly looks like more delays.

It’s estimated that 500,000 people live within 10 miles of the field lab. The public has justifiable concern about substances that are known carcinogens migrating off the property through the air, groundwater and other dynamic factors. A complete and effective cleanup of the property is a priority for protection of public health and safety.

Who will it take, and what will it take, to light a fire under those responsible for cleaning this up? Private stakeholders and local, state and federal authorities must reassert their commitment to a complete cleanup at an accelerated pace — without delay.