This paper describes a method of optimizing the production economy when excavating an old landfill in order to both minimize its environmental impact and obtain a profit. The analysis employs the equality principle and the 'Efficient Use of Resources for Optimal Production Economy' (EUROPE) model introduced by the first-named author for assigning industrial costs to waste. When using this model, waste has the same economic status as any normal industrial product in line with the inherent meaning of the equality principle. Application of the method to landfill mining then creates novel economic incentives for the improvement of the environment and profitability and the technology used when exploiting older landfills. An introduced key factor enables management to immediately obtain an overall comprehension of the economic, technological and environmental performance of their landfill that continuously can be monitored and evaluated. The results of a Norwegian example imply that impure, and hence unwanted, waste fractions have a certain negative impact on the outcome. This is because of the related internal shadow prices for unwanted wastes and wastes of commercial interest created through use of the equality principle. It is beneficial when landfill mining companies act in accordance with the equality principle to promote sustainable development.