It's generally understood now that using the earth for transmitting electrical current is a bad idea... It causes more corrosion in building foundations even hundreds of kilometers away, and soil microbes that navigate with electric fields die.
Therefore, most new DC transmission systems have a balanced pair of cables, and only use earth return for emergencies
The article says that the intertie has one +500Kv line and one -500Kv line. So why does current need to travel via earth? I would think the DC current flows in a loop via the two conductor lines.
Therefore, most new DC transmission systems have a balanced pair of cables, and only use earth return for emergencies