Abstract: The Dawu Well Field is one of the largest karst-fractured groundwater sources in the east of zibo City, Shandong Province and It is the most important resource for the urban water supply in Zibo City. However, data from 35～ 56 monitoring wells in the Well Field indicated that groundwater was seriously polluted by petroleum products. Maximum concentration of organic contaminants up to 77.34 mg/1 was detected in the water supply wells located at the Liuhang-Hougao zone in the went part of Dawu Well Filed. A series of environmental investigations during the recent years showed that serious leaking of petroleum contaminant occurred in the subsurface of petrochemical factory areas in the upriver of Dawn Wel1 Field forming a major source of groundwater contamination by petroleum hydrocarbons. Since the Hougao and Liuhang zones are seriously polluted, hydrochemical environment has changed greatly in the past ten years (1987 to 1996). Concentrations of nitrate and sulfate in the groundwater oontaminated by pe trochemicals were reduced from 29.04 to <0.4mg/l and 113.59 to 51.23 mg/l respectively. On the other hand, concentrations of bicarbonate and ammoniumion, were increased from 298.79 to 426.84 mg/l and < 0.04 to 0.43 mg/1. Dissolved oxygen was almost not detected. Comparing with the zones seriously polluted, concentrations of nitrate and sulfate in the ground water of Xixia wells located in the east of Dawa Wel1 Field were increased from 15.75 to 21.71mg/1, and 38.90 to 55.23mg/l in the past ten years. And concentration of bicarbonate changed from 237.97 to 215.81 mg/l. These changes of hydrochemical characteristics suggested that some microbial processes have graded organic materials in the groundwater leading to a decrease in the concentrations of electric acceptors and an increase in concentration of bicarbonate near the zones seriously polluted. These microbial processes included biodegradations with oxygen, nitrate and sulfate ere. However, the hydrogeochemical conditions of the Hougao and Liuhong aquifers are characterized by absences of nitrate and dissolved oxygen and the low concentration of sulfate. The subsurface environmental conditions would reduce the rate of biodegradation beeaL1se of the absence of the electric acceptors. Therefore, the results of this research have demonstrated that： 1. The microbial processes could be evaluated through the hydrochemical data of groundwater. 2. Biorestoration method to renovate aquifers contaminated with petroleum productions in Zibo city is feasible. 3. To enhance the activities of micro-organisms in the subsurface water, increasing the concentrations of electric acceptors, such as nitrate, probably is a effective biorestoration method.