More than 630 open-pit coal mines have been left behind by mining companies in East Kalimantan. These holes have claimed the lives of at least 27 people, mostly childrenIndonesian law requires companies to fill in their mining pits, and prohibits mining within 500 meters of houses. However, these regulations are frequently violated.Mongabay-Indonesia spent months investigating the true scope of the problem, and the individuals responsible for these violations. Hundreds of abandoned open-pit coal mines pockmark the landscape of East Kalimantan Province in Indonesian Borneo. Indonesian law requires mining companies to fill in pits that are no longer in use, and to re-vegetate and restore mining sites. However, these regulations are routinely flouted, with deadly effects. The deep pits left behind by coal mining, which fill up with acidic water, have claimed dozens of lives. Who is ultimately responsible for these violations? Working together with Tempo, Tempo Institute and Free Press Unlimited, Mongabay-Indonesia launched a months-long investigation into this question. Details about the ownership of mining companies in Indonesia remains highly secretive. Groups like the Mining Advocacy Network (JATAM) have been struggling for years for to force the public release of information about mining licenses. Recently, Mongabay-Indonesia learned company registration documents could be purchased from the government, allowing the team to uncover previously unpublished details about the ownership structure of coal mining companies. This analysis was combined with weeks of interviews, field reporting and laboratory tests to reveal new information about the true number abandoned mine pits in East Kalimantan,the dangerous levels of pollution in these water-filled pits, and the companies and individuals responsible for this menace to public health. This lake has formed in a former coal mine pit, left unreclaimed by the company who excavated it. There are no warning signs or barriers around the lake, which is used by locals for fishing, aquaculture and as a source of clean water. Photo by Tommy Apriando for Mongabay-Indonesia. A vast pool of dark green water, about the size of a football field, sits roughly 25 meters from Elementary School 033 in the Loh Iput Darat district in Kutai Kartanegara, East Kalimantan. The only barrier between the school and this pond is a rusty wire fence, broken in several places. “Pit 2 belongs to PT MHU,” proclaims a red-painted sign board, indicating this pool has formed in a hole excavated and then left behind by the coal-mining company PT Multi Harapan Utama. There are no other warnings posted, let alone a guard, despite its proximity to a settlement and a school full of young children. Indonesia’s environmental regulations clearly state that mines should not be excavated within 500 meters of houses. Investigations in mining areas in East Kalimantan found multiple pits in clear violation of this law. A case from the same district sharply illustrates the dangers of having abandoned mines and children in close proximity. In December 2015, a schoolboy named Mulyadi drowned in a similar pit, also owned by PT MHU. On the day Mulyadi died, this pit was left without any guard on duty. Although the pit is only about 300 meters from the nearest house, there was no barrier and no sign banning entry. The company only installed a sign and a fence the day after East Kalimantan Governor Awang Faroek Ishak issued a December 18, 2015 decree freezing the operations of 11 coal mining companies, including PT MHU. In his decree. Ishak stated 11 companies violated rules by, among other things, not “reclaiming” and “revegetating” their mining sites— technical terms for refilling pits and reforesting the land. The companies were also considered neglectful for not supervising the pits they left behind. Suspending permits did not stop mine pits from claiming more victims. The National Commission on Human Rights found that mine pits left behind by 17 companies in East Kalimantan killed 27 people between 2011 and 2016, mostly children or teenagers.