Just to clarify, a formula cannot give two results. However, it would be possible to have two results in a cell if you Concatenate two separate formulas to combine the results in a cell. In addition, you could add text into the resulting string if desired. Here is an example using your two criteria groups in separate formulas concatenated along with some text.
="Settle Plate: "&IFERROR(IF(G16+H16<50,"Complies",IF(G16+H16<=75,"Alert",IF(G16+H16>75,"Action"))),"N/A")&" / Air Sampling: "&IFERROR(IF(I16+J16<140,"Complies",IF(16+J16<200,"Alert",IF(16+J16>=200,"Action"))),"NA")
EDIT;
Just noticed that in your formula there seems to be an error in two of the cell references in the second part. The Alert and Action conditions refer to I6+J16. I believe from the pattern that those should both be I16 +J16.