Abstract: Taking an informal landfill in Zhejiang province as an example, the landfill gas content, leachate concentration, organic matter content and biodegradability of waste was investigated, to analysis the pollution status, stabilization level and environmental risk of the landfill. The results showed that the CH4 volume fraction in landfill gas ranged from 2.41% to 44.94%, with an average of 25.64%. While 87% of drilling sites CH4 volume fraction exceeded the gas limit value (5%) above the landfill in GB 16889—2024 Standard for Pollution Control on the Landfill Site of Municipal Solid Waste. 12 indexes such as color scale, SS, COD, BOD5, Hg and Cr in landfill leachate exceeded the standard value in GB 16889—2024, and the exceeding standard rate were all more than 30%. The contents of organic matter and biodegradability in the waste pile were both high, ranging from 30.50% to 70.70% and 7.10% to 19.40%, respectively, so the degree of waste decay was low. In short, although the landfill had been closed for a long time, it had high methane production, organic matter content, biodegradability and leachate concentration, which was still in an unstable state. In addition, the pollution risk index of the stock garbage was 90.93 points, which belongs to the high level pollution risk, indicating that the informal landfill has great environmental risks and security risks due to its large scale and pollution-free prevention and control measures.

Key words: informal landfill, environmental pollution, stabilization level, environmental risk assessment