•Geo-Cleanse uses a mildly acidic (pH 4) solution to eliminate scavenging carbonates and to maintain iron in solution, which improves oxidation of the target contaminants.
•Carbonates, existing in solution primarily as bicarbonate ion (HCO₃^-), act as a scavenger for hydroxyl free radicals (OH•), thus lowering oxidation efficiency with respect to contaminants.

Bicarbonate is destroyed by reaction with acid: HCO₃^- + H+ = H₂O + CO₂

Reaction of bicarbonate with OH•: HCO₃^- + OH• = CO₃^- + H₂O; Rate constant (kHCO₃) = 8.5 x 10⁶ M^-1s-1 (Buxton et al., 1988)

Compare to rate constant for TCE (kTCE) with OH• = 4.2 x 10⁹ M-1s-1 (Buxton et al., 1988)

Although the rate constant for TCE is much higher (indicating faster reaction) than for bicarbonate, the bicarbonate is typically present at much higher concentrations than the TCE. The relative likelihood of a hydroxyl radical to attack a molecule of TCE versus that of bicarbonate is proportional to the product of the concentration and rate constant for each reaction.

For example, assume [TCE] = 500 ug/L and alkalinity (taken as equivalent to [HCO₃^-]) = 250,000 ug/L (or 250 mg/L). Then:

The proportion is equal to unity, i.e., the hydroxyl radical is equally likely to react with bicarbonate as it is to react with TCE. The implications of competition kinetics are that the most efficient treatment occurs only in the absence of (or at very low concentrations of) bicarbonate, which can generally only occur at mildly acidic pH (<6).

Use of chelated iron does not eliminate bicarbonate scavenging and interference.