Table 2. Latitude and longitude of sampling sites in Dagang Oilfield.

Zones	Sampling number	Sampling sites	Latitude	Longitude
Oil-producing zone	S1	Chuangxin Road	38°41′17.92″	117°28′22.24″
	S2	Lesser zone	38°42′12.80″	117°29′21.14″
	S3	Middle zone	38°42′12.69″	117°29′21.52″
	S4	Higher zone	38°42′12.39″	117°29′22.39″
	S5	Test field zone	38°42′12.53″	117°29′23.10″
Residential zone	S6	Chuangxin Road-canal	38°42′8.06″	117°31′54.31″
	S7	Xingfu Road-pool	38°42′7.77″	117°26′42.61″
	S8	Chuangye Road-oil tank	38°44′28.13″	117°32′41.30″
	S9	Chuangxin Road	38°40′16.79″	117°26′24.37″
Oil-refinery and transportation zone	S10	Maxi Road	38°39′47.43″	117°20′1.47″
	S11	Chuangxin Road-living zones	38°41′54.77″	117°30′17.01″
	S12	Xingfu Road1	38°42′41.63″	117°27′34.44″
	S13	Xingfu Road2	38°40′56.46″	117°24′32.47″
	S14	Yard 2 bridge	38°44′42.37″	117°30′16.16″