| Date | Value |
|---|---|
| May 25, 2015 10:46 | 29 ppb |
| May 19, 2015 18:37 | 65 ppb |
| May 9, 2015 14:25 | 4 ppb |
| Apr 25, 2015 12:24 | 1 ppb |
| Apr 5, 2015 16:40 | 12 ppb |
| Mar 28, 2015 11:15 | 0 ppb |
| Mar 21, 2015 11:25 | 14 ppb |
| Mar 15, 2015 09:46 | 0 ppb |
| Mar 8, 2015 13:31 | 5 ppb |
| Feb 28, 2015 15:56 | 1 ppb |
| Feb 21, 2015 15:01 | 1 ppb |