Recent advances in compression and storage technologies have opened the door to a new possibility: pumping atmospheric gasses into reservoirs, compression them, and storing them underground. It's labor-intensive and inelegant, but it works.
| Level | Pressure | Cost | Time |
|---|---|---|---|
| I | -4 | 250,000c | 30m |
| II | -6 | 125,000c | 3m 45s |
| III | -8 | 250,000c | 7m 30s |
| IV | -10 | 375,000c | 11m 15s |
| V | -12 | 500,000c | 15m |
| VI | -14 | 625,000c | 18m 45s |
| VII | -16 | 750,000c | 22m 30s |
| VIII | -18 | 875,000c | 26m 15s |
| IX | -20 | 1,000,000c | 30m |
| X | -22 | 1,125,000c | 33m 45s |