To date, six cooling tower tests have been conducted to evaluate the wastewater treatment and reuse process utilized by the Great Plains Gasification Plant (GPGP) facility near Beulah, North Dakota. The first three tests, Phases I, II, and III, were performed using extracted, steam-stripped gas liquor (SGL) produced in the UNDERC pilot-scale slagging fixed-bed gasifier as makeup. The last three tests, Phases IV-A, IV-B and V, were conducted using GPGP produced SGL as makeup. The final test, Phase V, is the subject of this report. Prior to its use as Phase V cooling tower makeup, the GPGP SGL was solvent extracted using the Phenosolvan process to reduce the phenolics level, followed by treatment by the Phosam-W process to reduce ammonia concentrations. Additional pretreatment of the Phase V makeup stream included activated sludge treatment to reduce the organic loading, filtering through diatomaceous earth to remove solids, the use of the Calgon Corporation pHreeGUARD dispersant/corrosion inhibitor system to reduce corrosion and fouling, and the use of Calgon H-510 biocide to control microbial populations within the system. All steps in the pretreatment scheme proved to be effective. Corrosion of carbon steel in the system was held to 2 mils per year (mpy) or less, as measured by weight loss coupons. There was no apparent loss of heat transfer capability or increase in pressure drops in the heat transfer equipment. Fouling was minimal in the Phase V system, although at the end of the testing there was a small amount of biomass present on the cooling tower packing as well as some inorganic fouling in the tower basin. The results of this test indicated that a pretreatment program exists that will allow the successful reuse of SGL as cooling tower makeup. 11 refs., 22 figs., 10 tabs.