What is undermining our oak tree?
We notice some wood decay fungi on the trunk and possible carpenter ant shavings on the ground, possible borers, etc. The fungi causes wood to decay and decline and you may have to consider removal in the future. Here is more on our website http://extension.umd.edu/hgic/topics/wood-rots-and-decay-trees-and-shrubs
If there is dead wood and/or compromised wet wood in the trunk area, it is possible carpenter ants may be nesting there. Carpenter ants can nest in dead wood but do not eat the wood like termites. They are not causing the decline.
You did not mention the health of the tree. Does the canopy look healthy, is there branch dieback, girdling roots, poor site conditions, poor drainage, etc.
At this point, we recommend that you contact a certified arborist for an onsite evaluation of the health of the tree and the best way to proceed. http://www.treesaregood.org/
Here is our page on When to Remove a Declining Tree https://extension.umd.edu/hgic/topics/how-do-you-decide-when-remove-tree
Thank you! The drainage is good but you're right that this tree no longer has a full / typical canopy and it (actually like many other oaks on the property) is dropping kinda light / foam-feeling branch pieces that have lichen or something on them.
The tree does not look healthy. Contact a certified arborist regarding the health of the tree and make sure it is not a hazard.
Also, the arborist should check the health of the other tree near your deck. It looks like it may have a double leader or trunk. These trees have a weak juncture and the crotch is a common place for rot.