The Sulige gas field is located in the Maowusu Desert of the Ordos Basin in China, partly located in the Uxin Banner of Inner Mongolia, where natural gases and coal resources abound.  The Sulige gas field was discovered in 2000 and developed by China National Petroleum Corporation (CNPC)’s PetroChina Changqing Oilfield Company (Changqing Oilfield). It has a total proven reserve of around 1,680 billion cubic meters, making it China’s largest gas field and the world’s largest un-compartmentalized gas field. The production at Sulige gas field began in 2006, with an output of around 22.7 billion cubic meters/year as of 2016. The Sulige gas field is also at a strategic location at the junction of the main gas pipelines in China. The gas produced at Sulige is transmitted to major cities in China including Beijing.
On 20 June 2012, a heavy rain destroyed the drainage system of the Su 5-15-27AH gas well of Sulige Gasfield. A large amount of viscous black-color liquid flowed to a local lake (额日克淖尔湖) and the pasture nearby at Saru’nutu Gacha, Galutu Town, Uxin Banner (乌审旗嘎鲁图镇萨如努图嘎查). Since then, local residents had reported death cases of their livestock, which amounted to more than 500 by mid-2013. Some local residents also mentioned that they started to feel sick when an environmental scientist was conducting on-site investigation in 2013. A herdsman mentioned to the journalist that they were afraid to drink the water from the wells at home and had to buy bottled mineral water.
On 26 August 2012, local herdsmen reported the death of their livestock to the government of Galutu Township. The local government initiated an investigation along with the environmental protection bureau and other departments of Uxin Banner and also sent a sample sheep for examination at the Department of Veterinary Medicine at Inner Mongolia Agricultural University. The Galutu Township government issued an official remark with follow-up procedures in response to the herdsmen’s report (name in Chinese “关于对内蒙古乌审旗嘎鲁图镇萨如努图嘎查牧民反映湖水污染致牲畜死亡有关情况的说明”) after the investigation of the water quality and the cause of the livestock death. 
The official remark entails three main aspects. Firstly, a fine of CNY 50,000 (USD 7,141) was issued to the company responsible for the drilling of the gas field, namely the Chuanqing Drilling Engineering Company Safety and Environmental Protection Quality Supervision and Inspection Research Institute (中石油川庆钻探公司安全环保质量监督检验研究院). This fine was due to the fact that the drilling waste treatment facility, although in place, was not properly utilized in the drilling process. Secondly, according to the official remark, the water quality test indicated that the chemical oxygen demand (COD) level is twice the standard level while other indicators were normal, which led to the conclusion that the exceeded COD level was not caused by the overflow of liquid waste from drilling into the lake. (However, this information is different from what was disclosed from the report provided by the Uxin Banner environmental inspection station.) Thirdly, the investigation result of the dead sheep indicated that the death was a result of a parasitic worm infection caused by the common liver fluke (also known as fascioliasis,羊肝片吸虫病), instead of caused by water pollution. Later on, a volunteer lawyer commented that the Inner Mongolia Agricultural University does not have the qualifications for testing and thus the test results do not have legal effect.
It was reported that the herdsmen were not satisfied with the official remark by the local government, the examination result of the dead sheep, and the fact that the inspection result by Uxin Banner environmental inspection station was not factually reflected in the official remark. This led the herdsmen to interrupt the gas field drilling activities. After negotiation, the company responsible for the gas well construction, CNPC’s Chuanqing Drilling Engineering Company, was willing to compensate the 15 herdsmen near the lake with a total of CNY 580,000 (USD 82,840) in the name of “poverty alleviation”. The local government also agreed to conduct a detoxication treatment of the dead livestock, which were left unburied, as the herdsmen were concerned about the lack of evidence if they had buried them. An additional compensation was provided at the rate of CNY 1,000 (about 140 USD per sheep that was dead.
However, there was no official response from CNPC regarding the pollution of the lake and pasture, while the local government was coordinating the follow-up. The local herdsmen did not trust the investigation result, and continued to request for compensation and elimination of the hidden root cause. Some herdsmen also indicated that they had seen the staff from CNPC extended a pipe into the lake, after which the lake that used to be clear gradually became dark and smelly. In March 2013, the 15 herdsmen requested an independent investigation of the chemicals in the lake by SGS-CSTC Standards Technical Services Co. Ltd., an internationally recognized testing, inspection and certification service provider. The test result by SGS provided different results from the investigation report provided by Uxin Banner Environmental Inspection Station (乌审旗环境监测站), as it showed that a total of 11 types of heavy metal along with a number of other chemicals exceeded the standard level of content in the lake. These include iron (exceeding standard level by 599 times), manganese (97 times), arsenic (36 times) and copper (15 times).  While there was no indication of organic matter or petroleum hydrocarbon pollutant, a researcher from the Chinese Research Academy of Environmental Sciences, Zhao Zhangyuan, indicated that this does not mean that the gas well did not pollute the lake. “It is possible that the heavy metal content came from the additive when drilling the well. Besides, it is evident that the gas well is likely the only pollutant source after we investigated the surrounding area”, said Zhao.
In view of the gap between the investigation reports between SGS and the Southern China Institute of Environmental Sciences that was entrusted by the Uxin Banner Environmental Protection Bureau, the herdsmen decided to seek for external expert support in Beijing. In May 2013, the herdsmen reached out to the civil society organization Nature University under the Green Beagle Environment Institute (达尔问环境研究所自然大学) and also a public interest litigation lawyer. The lawyer then reached out to researcher Zhao Zhangyuan, who then decided to travel to Uxin Banner for an on-site investigation. However, his investigation was later on followed by the local government officials “to ensure security” and a media outlet that was traveling together with Zhao was also called back. As a result, the investigation did not achieve much further result. In June 2013, the herdsmen decided to host an expert seminar at their own cost in order to seek for the truth of the death case of their livestock, which was not supported by the municipality of Galutu Township. The herdsmen were not surprised by the attitude of the Galutu Township government officials, as they only received part of the compensation paid by CNPC and their guess was that the Galutu Township government kept the rest of the money (amount unknown). The seminar was held on 18 June 2013 with the participation of a number of environmental protection experts and media representatives. During the meeting, the head of the Galutu Township answered some questions and claimed to protect the safety and freedom of the herdsmen. 
In July 2013, the Uxin Banner Environmental Protection Bureau entrusted the Southern China Institute of Environmental Sciences to retest the lake water. The result indicated that the level of pH, and the amount of nitrogen, phosphorus, chloride, fluoride, COD and arsenic exceeded the standard for surface water mainly for agricultural use (Category V based on water use category in the Surface Water Environmental Quality Standard GB3838-2002), while the level of iron and manganese exceeded the target limit value for surface water used for centralized drinking function. Despite these results, the conclusion of the investigation report suggested that the indicators of the investigated lake is on a similar level with the reference lake and that there was no signs of drilling waste discharge at the site any more. However, researcher Zhao Zhangyuan commented that the mud, or drilling liquid, produced as a result of the drilling activities, contains a lot of heavy metals, alkalis and compounds, and is highly polluting. According to Zhao, it was clear that there was misconduct in the management of pollutant and waste discharge at the drilling company, which led to the pollution of local water systems. 
There was no clear evidence of follow-up by the herdsmen or local government after 2013, and it is unclear whether the situation of the livestock and water quality has changed over the years. As commented by a volunteer lawyer, Xia Jun from Zhongzi Law Office, the challenge for the herdsmen to establish effective forensic evidence and prove the causal relationship between the company’s drilling/polluting activities and the death of the sheep, and the forensic process can cost thousands to millions of CNY (which would be unaffordable for the herdsmen). Li Tao from the environmental NGO that supported the seminar in Beijing, namely the Nature University under the Green Beagle Environment Institute, considered that it is really difficult for the vulnerable groups to obtain sufficient causal evidence in a short period of time, and that the threshold for filing environmental lawsuits is too high for such cases.
On the other hand, it was reported that the Changqing Oilfield enhanced its investment in environmental protection over the years, mainly as a result of strengthened environmental protection law in China that became effective at the beginning of 2015 and the anti-corruption measures against the oil and gas industry taken by the central and local government in China. Before the new regulation took place, Changqing Oilfield faced multiple charges and issuance of fines by local governments regarding its lack of environmental protection procedures. Since early 2015, Changqing Oilfield has invested in new technologies to comply with the local regulations regarding drilling liquid treatment (namely “泥浆不落地” in Chinese) to make sure that the discharged drilling liquid is not in direct contact with the local water system.