[
  {
    "year": "2001",
    "underground": 40.7,
    "surface": 33.6
  },
  {
    "year": "2002",
    "underground": 39.3,
    "surface": 35.1
  },
  {
    "year": "2003",
    "underground": 36.4,
    "surface": 33.6
  },
  {
    "year": "2004",
    "underground": 36.1,
    "surface": 34.5
  },
  {
    "year": "2005",
    "underground": 38.4,
    "surface": 35.5
  },
  {
    "year": "2006",
    "underground": 40.5,
    "surface": 37.5
  },
  {
    "year": "2007",
    "underground": 39.6,
    "surface": 37.5
  },
  {
    "year": "2008",
    "underground": 42,
    "surface": 39.2
  },
  {
    "year": "2009",
    "underground": 42.7,
    "surface": 38.8
  },
  {
    "year": "2010",
    "underground": 43.5,
    "surface": 37.2
  },
  {
    "year": "2011",
    "underground": 46.9,
    "surface": 40.3
  },
  {
    "year": "2012",
    "underground": 46,
    "surface": 38.6
  },
  {
    "year": "2013",
    "underground": 42.6,
    "surface": 35.4
  },
  {
    "year": "2014",
    "underground": 39.9,
    "surface": 33.3
  },
  {
    "year": "2015",
    "underground": 33.9,
    "surface": 30.2
  },
  {
    "year": "2016",
    "underground": 25.7,
    "surface": 25
  },
  {
    "year": "2017",
    "underground": 26.5,
    "surface": 24.9
  },
  {
    "year": "2018",
    "underground": 26.9,
    "surface": 24.7
  },
  {
    "year": "2019",
    "underground": 27,
    "surface": 23.4
  },
  {
    "year": "2020",
    "underground": 22.1,
    "surface": 17.8
  },
  {
    "year": "2021",
    "underground": 20.4,
    "surface": 17.1
  },
  {
    "year": "2022",
    "underground": 21.5,
    "surface": 19.4
  },
  {
    "year": "2023",
    "underground": 23.2,
    "surface": 19.3
  },
  {
    "year": "2024",
    "underground": 23.6,
    "surface": 18.6
  },
  {
    "year": "2025",
    "underground": 22.1,
    "surface": 17.8
  },
  {
    "year": "2026",
    "underground": 21.1,
    "surface": 17.5
  }
]