Fig. 8. Co-occurrence of (a) tertiary amide sulfonic acid (ethanesulfonic acid, ESA) soil degradate residues and (b) tertiary amide oxanilic acid (OXA) soil degradate residues. Values reflect the number of program wells with observed residues. No ESA soil degradate residues were observed in 49 of the 182 wells and no OXA soil degradate residues were observed in 110 of the 182 wells.