One hundred fifty-two compounds and compositions of matter were screened as potential evaporation retardants. The homologous straight-chain fatty alkanols are considered the best materials for retardants.
Several methods of application of the alkanols to the reservoir surface were investigated. Although wick-type drippers for the application of liquids and cage rafts for the application of solids appear to be the most promising methods from an economic standpoint, both methods have serious disadvantages. Considerable study was given to reducing biochemical oxidation of the evaporation retardants. Copper in several forms was found adequate as a bacteriostatic agent but posed a potential hazard because of its toxicity. Many other bactericides that were tested were also toxic.
Two sets of large-scale field tests have been completed and several others are still in progress. On the larger reservoirs, the reduction of evaporation was not more than 20 percent under the prevailing conditions and the application procedure used.
Three major practical problems remain; namely, the effects and action of wind on the monofilm, the effects of biochemical oxidation, and the most effective method of application. Fundamental problems remaining include the effects of various impurities, and the composition of the best evaporation retardant; the long-range effects of monofilms on the limnology of a reservoir, including the transfer of oxygen and carbon dioxide; toxicological aspects of all components of any evaporation-retardant composition, plus toxicology of any composition chosen for large-scale use; and further studies of the calorimetry and thermodynamics involved in the mechanism of evaporation and its reduction by a monofilm.