Simultaneous abatement of 2,4-dichlorophenoxyacetic acid (2,4-D at 70 mu g L-1), Escherichia coll. and Klebsiella pnewnoniae (laboratory and wild strains) cells from real groundwater samples containing natural iron concentrations (similar to 0.3 mg L-1) was studied by addition of H2O2 (10 mg L-1) using a 18-L compound parabolic collector-CPC solar reactor (under natural sunlight irradiation 150,000J m(-2)) equipped with a UV(A + B + Visible) lamp (15 W: UV-B and UV-A intensities were 0.74 and 6.47 W m(-2) respectively) powered by a photovoltaic panel. Viability of E. coli K12 and K. pnewnoniae laboratory strains at high initial concentrations of 10(6) - 10(7) cells mL(-1) (followed by DVC-FISH) dropped 4.69 and 2.18 Logs, respectively after 30 min t(30w) of combined UVA + B-Visible lamps and sunlight irradiation (SL + UV + H2O2). Moreover, the initial 2,4-D concentration underwent a strong reduction reaching concentrations below the detection limit after 5 min t(30w) of SL + UV + H2O2 treatment. Regarding real wild bacteria strains often present in natural well waters, which were at low initial concentrations, total culturability (initial concentration 10(1) CFU mL(-1)) and viability (initial concentration 10(2)-10(3) cells mL(-1)) reductions were reached after 30 min (t(30w)) of combined treatment. Participation of several photochemical and dark events such as photocatalysis (by iron hydro-oxides and other metal oxides naturally present), Fenton and photo-Fenton (by natural dissolved iron), UV-A + B/NO3-, Dissolved organic matter (DOM)/UV + Vis and UV-B photolysis of H2O2 are suggested as responsible of simultaneous 2,4-D abatement and microbial inactivation in natural groundwater samples.