China has built a massive experimental radio antenna capable of communicating with submarines in deep water, but some are raising concerns about potential health risks, reports the South China Morning Post.

Though its exact location remains unclear, the Wireless Electromagnetic Method project was built on a site nearly five times the size of New York City and is now ready to emit extremely low frequency radio waves, the paper reports. The project’s official use is for earthquake and mineral detection, but it could reportedly also play a crucial role in military communications by allowing deep-sea submarines to pick up the transmissions without needing to surface.

The paper reports China first completed a military-grade low frequency station in 2009, and the following year a Chinese nuclear submarine successfully communicated with the station from deep water. But the Chinese government has reportedly downplayed the importance of the latest facility, which took 13 years to build and occupies about 1,400 square miles of land, in information released to the public.

Concerns over the potential negative health effects of the extremely low frequency (or ELF) waves have been documented by the World Health Organization. The organization found short-term exposure to ELF magnetic fields at high levels can cause nerve and muscle stimulation and changes in the central nervous system and recommended the development of international exposure guidelines. WHO also reviewed studies over possible links to childhood leukemia arising from long-term exposure to ELF magnetic fields. While it found no clear link, it recommended further study and suggested governments and industries should explore low-cost ways of reducing exposure when developing new facilities and equipment.

According to the South China Morning Post, a calculation by the Chinese Navy found a person standing on the emission site would be subject to radiation no greater than 10 watts, enough to power several LED light bulbs. The researcher with the navy’s Ship Communication Research Institute in Wuhan reportedly found those levels to be far too low to pose a risk. However, the paper cites an unnamed Beijing-based researcher who said the the Ministry of Ecology and Environment asked for a comprehensive review of the project’s environmental impact, but the request was denied.

A researcher with the Institute of Earthquake Forecasting, who was informed of the project but wasn’t directly involved with it, told the paper authorities had recently conducted final checks on the emission site and found it was ready for operation.