the site. Engineers consider plans to inject inert nitrogen gas into the containment buildings of units 1, 2 and 3 to expel atmospheric oxygen and to dilute accumulated hydrogen, which combine explosively. Tuesday, 5 April It is determined that the leak into the cable storage pit from unit 2 was likely due to a faulty joint where the pit meets a duct. The pit leads to a gravel layer beneath, resulting in highly radioactive water pouring directly into the sea. Levels of radioactive iodine-131 in seawater near the facility are found to be 7.5 million times the legal limit. TEPCO drills a hole into the pit near reactor 2, from which highly radioactive water is leaking, and injects water glass (sodium silicate) into the pit to prevent further leaking. Wednesday, 6 April TEPCO announces that an injection of of polymer coagulant into the pit mitigated the leaking; however, the IAEA and others credit additional factors. Sodium silicate ("water glass") and additives are injected into the ground in order to stop the leakage of radioactive water. The residual heat carried by the water used for cooling the damaged reactors accelerates the setting of the injected mixture. Despite protests from the South Korean government, Russian scientists, and Japanese fishermen, Japan authorizes the release of of less radioactive water into the ocean to make room to store the more highly contaminated water. Iodine-131 levels reach 7.5 million times the legal limit in a seawater sample taken near the facility. TEPCO announces that the leak of highly radioactive water from the utility pit near reactor 2 has stopped. According to U.S. Representative Ed Markey, the Nuclear Regulatory Commission says that the core of unit 2 has become so hot that part of it has melted through the reactor pressure vessel; however, a NRC spokesperson says, "That's not clear to us, nor is it clear to us that the reactor has penetrated the vessel." TEPCO begins injection of nitrogen into unit 1 to lower the possibility of hydrogen explosions. Thursday, 7 April Nitrogen injection into the pressure containment vessel of unit 1 commences at 01:31. Workers are evacuated following a magnitude 7.1 aftershock off the north-eastern coast of Japan, 118 kilometers from the plant. TEPCO reports communications and power were not affected and no additional damage was observed as a result. A tsunami warning is also issued, but is lifted after 90 minutes. Most of