The geomembrane market for waterproofing ground ponds used to isolate olive mill wastewaters offers a wide choice both in terms of the material used and liner thickness and size. With regard to the physical and mechanical properties of the material forming the geomembrane, this paper proposes a method for the assessment and design of the waterproofing system. This method foresees the calculation and analysis of geomembrane stress caused by the most stressful conditions, also taking into consideration the physical characteristics of the material within the pond, the elastic and elastic-plastic behaviour of the geomembrane and the physical characteristics of the soil. Criteria and graphs for the rapid dimensioning of the waterproofing system are also proposed. In addition to the environmental and climatic characteristics of the site, the results presented also take into consideration the dimensional characteristics of the ponds and the physical properties of the olive mill wastewaters.