Police and Environment Agency officers swooped on an illegal scrap metal trader near Shepton Mallet.
High voltage power cable and catalytic converters were among items seized in the raids last Thursday there and at a Glastonbury site.
Both properties were trading as scrap dealers and waste sites and were unregistered and unlicensed.
Three people – two men and a woman – were arrested for suspected environmental offences and on suspicion of theft.
Undercover officers and a police helicopter were used in months of investigations.
All suspects arrested have been bailed until February.
A spokesman for the SW Regional Environmental Crime Team said: "The Environment Agency is working closely with the police to help combat metal thefts and waste crime that have a big impact on the community.
"We will continue to use our powers under the waste legislation to target illegal sites and prosecute offenders."
Officers also carried out stop checks on commercial vehicles and vans in an effort to identify stolen metal and disrupt possible criminal activity.
Some vehicles were seized and others issued with Fixed Penalty Notices.
Officers visited scrap yards to make compliance checks as part of the on-going Operation Tornado.
Legitimate scrap metal yards are working with the police by asking anyone selling metal to provide ID supported by a utility bill to make it easier to trace sellers of stolen metal.
Superintendent Mark Saunders, from Avon and Somerset Police, said: "The majority of scrap yards across this part of the area are legitimate and compliant businesses who are working with us to identify thieves and make it extremely difficult to sell on stolen property.
"Since we launched the regional Metal Theft Coordination Team six months ago, we have seen a significant drop in metal thefts in the South West, in some places by nearly 50 per cent. This is extremely encouraging but we won't be complacent.
"We will continue to work with our police colleagues, partner agencies and commercial industries to take an intrusive approach in dealing with the thieves and handlers who make money at a cost to each and every tax payer.
Changes to the law will soon outlaw all cash transactions at metal recycling yards and see increased fines for dealers who fail to abide by the rules.
Police urge anyone taking metal to yards to sell to ensure they take the necessary documents and proof of ID to avoid being turned away and to contact police if they are not asked to provide appropriate identification.
If you have information about illegal activities in your area, contact police on 101 or call Crimestoppers on 0800 555111.