This information last updated on January 26, 2021. Additional information for GRYN water resources data sets. All results are reported in mg/L. Reporting limit (RL) is the threshold value that many analytical labs consider to be the lowest reportable value for an individual analyte. This value may be higher than the maximum detection limit (MDL). Resources: https://www.nps.gov/im/gryn/water-resources.htm https://www.nps.gov/yell/learn/nature/water.htm