Laboratory research has been conducted to evaluate the chemical, physical, and toxicological characteristics of treated and untreated water pumped from the flooded modified in situ retort at lease tract C-a. This wastewater had a total dissolved solids (TDS) content of about 5450 mg/L and a total organic carbon content of about 16 mg/L. Wet chemical analyses, metals analyses, particle-size analyses, and MICROTOX assays were performed on the wastewater before and after treatment by lime-soda softening and reverse osmosis. The reverse osmosis membrane used in this research was a Filmtec model SW30-2521 spiral-wound polyamide unit. In a short duration test at a TDS of 21,800 mg/L, the reverse osmosis system successfully removed dissolved solids and organics from the wastewater. The water was also much less toxic to the MICROTOX organism after treatment by reverse osmosis. Membrane fouling was observed when water with a TDS of 54,500 mg/L was treated. Treatment of the reverse osmosis residual brine was attempted by subcritical wet-air oxidation. The brine remaining after the 170-hour test on the water with a TDS of 5450 mg/L was subjected to temperatures ranging from 204/sup 0/C (400/sup 0/F) to 315/sup 0/C (600/sup 0/F) and pressures from 500 to 1600 psig for approximately 30 minutes. The waste treated by the higher temperatures and pressures showed good removals of organics, nitrogen compounds, and some metals. The sample treated at 302/sup 0/C (575/sup 0/F) and 1300 psi was assayed for MICROTOX response and no toxicity was measured. The reverse osmosis brine was significantly toxic to the MICROTOX organism before treatment by subcritical wet-air oxidation. 14 refs., 8 figs., 14 tabs.