Locations
| Name | Sites | Samples |
|---|---|---|
| Abbeville County | 2 | 5 |
| Adams County | 7 | 17 |
| Adams County | 1 | 1 |
| Addison County | 23 | 77 |
| Aiken County | 16 | 79 |
| Aitkin County | 6 | 11 |
| Alachua County | 6 | 71 |
| Alamance County | 5 | 7 |
| Albania | 4 | 5 |
| Albany County | 2 | 2 |
| Albemarle County | 2 | 21 |
| Alberta | 4 | 7 |
| Alcorn County | 1 | 2 |
| Alger County | 8 | 13 |
| Algeria | 0 | 0 |
| Allegany County | 1 | 1 |
| Alleghany County | 1 | 1 |
| Alleghany County | 1 | 1 |
| Allen County | 1 | 1 |
| Allendale County | 5 | 45 |
| Amherst County | 1 | 9 |
| Amite County | 2 | 9 |
| Anderson County | 2 | 11 |
| Anderson County | 1 | 3 |
| Anderson County | 9 | 35 |
| Andrew County | 1 | 2 |
| Andrews County | 2 | 4 |
| Anoka County | 3 | 9 |
| Anson County | 1 | 15 |
| Aransas County | 3 | 11 |