Hi, 

Yes this is wooly adelgid and it looks like a heavy population that should be treated. It could be the original infestation if it was never treated. 

Treatment for the Hemlock can be expensive and needs to be administered by a certified arborist or pesticide applicator. You can visit our informational page on the wooly adelgids for reference. https://extension.umd.edu/resource/hemlock-woolly-adelgid-trees You can also search for an arborist at https://www.treesaregood.org/findanarborist

Usually treatments last for a few years before the need for reapplying so consulting with an arborist about a management plan would be best. If you both determine that the population is too high for treatment, or cost is not warranted, they could provide you a quote for removal. Cornell Botanical Gardens has an informative fact page about woolly adelgids that may be helpful as well. You may determine that it is still beneficial to leave the tree for now while it can still provide winter coverage for birds and biodiversity in your landscape.

You could always leave it for now until it declines enough to remove but consulting with the arborist to determine that would be best. 

Let us know if you have further questions.

Emily