This paper proposes a deterioration model which considers two mechanisms of system deterioration: wear and shock, both affected by environmental conditions. The deterioration is modeled by the sum of wear and cumulative shocks, where the wear damage is modeled by a non-stationary Gamma process and the random shock damage is modeled by a generalized Pareto distribution satisfying Poisson arrivals. The effect of the environment on the mean deterioration rate is modeled by covariates via the Cox proportional hazards model. Both preventive and corrective replacement will be considered according to the results of system-state inspections. Based on partial inspection information, the so-called wear-oriented and shock-oriented maintenance policies are proposed specially for the different deterioration sources. The performance of these maintenance policies are studied through numerical implementations and compared with the policies which use complete inspection information. The optimal maintenance policy leading to the minimal cost criterion is obtained and limitation of the use of these policies is discussed