Por: Alfredo Gallardo Ríos, especialista en procesos de gestión ambiental, manejo y tratamiento de aguas y cierre de minas.AbstractIn recent years, Compañía de Minas Buenaventura has been promoting important projects related to the closure plan for the La Zanja mining unit of its subsidiary Minera La Zanja, located in Cajamarca. Reconciling the strictly regulatory aspects and achieving an environmental balance are not two separate objectives; on the contrary, they are necessarily indivisible.Water treatment during the mining operation already posed us great challenges back in 2013, when we decided to start a process of searching for alternatives and options for closing components focused on reducing the amount of acidic water and improving its quality.Another problem that La Zanja faces with respect to closure is the limited availability of low-permeability material (clays) from sources close to the mine. One of the sources used for the construction of mining components is located approximately 100 km from the unit, making freight costs more expensive, as well as gravel material for the drainage filters that are part of the cover designs included in the closure engineering commissioned by La Zanja. To this we could add the poor chemical condition of the organic soil and its difficult storage conditions in the unit.With these limitations, we built and adapted an area to perform tests and cover trials, where we included the use of improved soils, artificial soils, constructed soils or commonly called technosoils. A technology developed in Canada and Spain for the remediation of areas degraded by mining, which consists of "designing" and "building" soils with the necessary characteristics to help correct the factors that cause or generate the degradation of a specific environment or ecosystem.The then Fund for Innovation in Science and Technology (FINCyT), now Innóvate Perú, an agency attached to the Ministry of Production (Produce), approved a project presented by La Zanja called: "Formulation of soil cover with mining waste that allows impermeability, physical, biological and geochemical stability, to be used in the closure of components that generate acid mine drainage in Minera La Zanja, Pulan, Cajamarca", by means of agreement No. 363-INNOVATEPERU-PITEI-2016, which allowed not only to finance part of the project, but mainly to be declared by this organization as of national interest.Thus, Buenaventura bet on the development of a research that allows adapting this technology to the Peruvian reality and innovating in the use of soils and the approach of closing a mine in operation. For this purpose, an old waste and sludge deposit called Turmalina (6 ha) was chosen, located in a sector of Tajo San Pedro.To date, Buenaventura has invested additional funds to implement the pilot Turmalina deposit, conduct studies and have a group of researchers collaborating with the University of Lisbon (Portugal) and Santiago de Compostela (Spain), measuring and monitoring the results of this pilot, whose first indicators have exceeded expectations.