Are there documents for dissolved oxygen stabilization range
You referenced a Dissolved Oxygen (DO) stabilization criteria range of +/- 0.2 mg/L. I have not been able to find any documentation identifying DO stabilization as a range. Presently we use +/- 10% as prescribed by EPA. Could you please direct me to documents that provide this DO stabilization range information.
Indicator parameter stabilization criteria do vary widely in both regulatory guidance documents and in published research on the topic. The USEPA 1996 Groundwater Issue guidance does state pH as a range of units (i.e., +/- 0.1 pH units). This makes sense, as pH is measured on a log scale, so the percentage difference as you move away from 7.0 would be greater at either end of the scale than toward the middle. The ASTM Standard D6771 on low-flow purging and sampling states stabilization criteria for pH in units (i.e., +/- 0.2 pH units) and DO as a combination of a percentage of the reading value as well as units (i.e., +/- 10% or 0.2 mg/L, whichever is greater). The reason for the latter is that most commercially available DO sensors cannot read DO accurately below 0.2 mg/L, so when the DO value drops below 0.2 mg/L, the units should be used in lieu of the percentage.
Indicator parameter stabilization criteria do vary widely in both regulatory guidance documents and in published research on the topic. The USEPA 1996 Groundwater Issue guidance does state pH as a range of units (i.e., +/- 0.1 pH units). This makes sense, as pH is measured on a log scale, so the percentage difference as you move away from 7.0 would be greater at either end of the scale than toward the middle. The ASTM Standard D6771 on low-flow purging and sampling states stabilization criteria for pH in units (i.e., +/- 0.2 pH units) and DO as a combination of a percentage of the reading value as well as units (i.e., +/- 10% or 0.2 mg/L, whichever is greater). The reason for the latter is that most commercially available DO sensors cannot read DO accurately below 0.2 mg/L, so when the DO value drops below 0.2 mg/L, the units should be used in lieu of the percentage.