Tokyo Electric Power Co., a company struggling with water problems, even messed up its rain forecast.

The latest spillage of radioactive rainwater over barriers surrounding storage tanks during the downpour on Oct. 20 is yet another sign that TEPCO is far from in control of the growing volume of contaminated water at the Fukushima No. 1 nuclear power plant.

Equipment is inadequate, human error is a continuing problem, and Mother Nature refuses to cooperate in efforts to remove the radioactive water at the site. Even the storage tanks holding highly contaminated water have leaked.

“The water transfer operations are complicated,” Noriyuki Imaizumi, acting general director of TEPCO’s Nuclear Power & Plant Siting Division, told a news conference on Oct. 21. “Water could not be pumped out fast enough during the precipitous rainfall.”

TEPCO had forecast between 30 and 40 millimeters of rain over the entire day of Oct. 20. The company’s prediction was way off.

More than 120 mm poured down on the Fukushima No. 1 plant site that day, filling the enclosures around the tanks and forcing water with radioactive content exceeding safety standards to breach the barriers.

The barriers were already filled with a previous accumulation of rainwater, but the available pumping capacity was too poor to quickly remove the liquid.

TEPCO faces another immediate challenge; Typhoon No. 27 is expected to hit the Japanese islands next weekend.

The company said it will install additional pumps so that as much water as possible can be transferred from the barriers to storage tanks and elsewhere before the storm hits.

But Imaizumi said he expected a “tough situation” if the rainfall from the typhoon is similar in scale to the Oct. 20 downpour.

TEPCO said the storage tank areas have a total of 67 pumps, but they have relatively modest pumping capacity–7.2 tons per hour for 35 of the devices, 12 tons per hour for 31, and 36 tons per hour for the remaining one.

The utility said it will install 19 more pumps, each with a capacity of 60 tons per hour, starting on Oct. 22, and hopes to eventually equip the plant with 11 additional pumps.

TEPCO also plans to build 60- to 130-cm-tall concrete walls outside the existing 30-cm-high barriers to surround the tank areas, but they will only be completed by the end of this year.

In the latest incident, TEPCO said rainwater overflowed the barriers in 11 locations. The water seeped into surrounding soil, and part of it likely ran along a drainage ditch and reached the ocean.

In six of the 11 storage tank areas, the rainwater contained radioactive substances exceeding provisional safety standards for drainage. The highest strontium-90 reading was 710 becquerels per liter, about 70 times the safety standards.

Contaminated water that had escaped the storage tanks, as well as radioactive fallout from the hydrogen explosions in March 2011, likely mixed with the rainwater.

According to TEPCO’s operational protocol, water accumulating within a barrier should be transferred to temporary storage for testing. The water can only be discharged after its radioactivity level is confirmed below the safety standards.

Water exceeding the safety standards should be collected and stored in designated areas, including a 4,000-ton storage tank, the protocol says.

But the water within the barrier walls rose too fast during the heavy rainfall from Typhoon No. 26 on Oct. 16, leaving workers no time to transfer the water into temporary storage. The workers instead tested the water directly behind the barriers and let it flow out if it showed levels below the safety standards.

But during the downpour on Oct. 20, rainwater exceeding the safety standards overflowed the barrier walls before the workers could test it.

TEPCO at that time was working to remove water within the barriers following Typhoon No. 26, with a priority on areas where high levels of radioactive substances had been detected in the past.

With poor pumping capacity, however, the utility could only lower the water levels by several centimeters a day.

Large pools of water from Typhoon No. 26 remained in seven of the 11 overflow areas. When the rainfall intensified at 3 p.m. on Oct. 20, the water was more than 20 cm high and on the verge of flowing over the 30-cm-high barriers that surround five of the storage tank areas.

Until August, rainwater accumulating within the barriers was allowed to run freely outside. After the discovery that month of 300 tons of highly radioactive water that escaped a storage tank, protocols were modified to keep drainage valves on the barriers shut to prevent water from running outside.

It then became mandatory to test and process rainwater every time it rained.