Toxins exceeded safety limits after the developer skipped required soil surveys, forcing site-wide containment measures before construction can resume.
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Construction of large-scale solar power plants (mega-solar) around Kushiro Shitsugen National Park in Hokkaido, August 12, 2025. (Video courtesy of Keisuke Saito, Institute for Raptor Biomedicine Japan)

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The Hokkaido prefectural government announced on July 13 that it will designate the construction site of a large-scale solar power plant (megasolar) near Kushiroshitsugen National Park as an area requiring contamination-containment measures, under the Soil Contamination Countermeasures Act. 

The prefecture judged the developer's soil survey inadequate and deemed the entire site contaminated with hazardous substances.

The designation takes effect on July 14 and covers the full site, which spans more than four hectares. Construction had been suspended since last year after it emerged that the developer, Nihon Ecology Group, had begun work without filing the required notifications under the law. 

According to the prefectural government, resuming construction under the new designation will require containment measures such as enclosing the entire site with metal sheeting. It said it "will provide the necessary guidance and respond appropriately."

Survey Found Arsenic Among Contaminants

Soil testing detected three hazardous substances, including arsenic, exceeding standard limits. In March this year, the prefecture ordered the company to conduct a detailed investigation under the law. The company submitted its report on July 7, but part of the on-site survey had been omitted.

Under the law's enforcement regulations, a site is deemed non-compliant and contaminated if the on-site survey is omitted. The company reportedly cited the project's uncertain future prospects as its reason for the omission.

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Author: Takahiro Sakamoto, The Sankei Shimbun

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