Yes, you can amortize the cost of removing storage tanks from Rental Property, or you can claim it as a Rental Expense for 2018.
In the Assets/Depreciation section, you could categorize this as a 'land improvement'.
Depending on the total cost, TurboTax may present you options for depreciation, and several options for claiming it as an expense.
The 'Asset Summary' page will give you depreciation details. Land Improvements have a 15-year depreciation schedule (screenshot).
Here's more info:
https://ttlc.intuit.com/replies/4791833
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