CLEAN HARBORS INC

The changes in goodwill for the years ended December 31, 2023 and 2022 were as follows (in thousands):

The Company assesses goodwill for impairment on an annual basis as of December 31 or at an interim date when it is more likely than not that events or changes in the business environment (“triggering events”) would reduce the fair value of a reporting unit below its carrying value. The Company did not identify any triggering events in the years presented.

During the fourth quarter of 2023, the Company changed reporting units, separating the historical Environmental Sales and Service reporting unit into two reporting units, Environmental Sales and Service and Industrial Services. This change required goodwill in the Environmental Sales and Services reporting unit to be allocated to the new reporting units based on relative fair value. The Company tested goodwill of the new reporting units for impairment both before and following the change in reporting unit structure, and no impairment was identified.

The Company conducted its annual impairment test of goodwill as of December 31, 2023 and determined that no adjustment to the carrying value of goodwill for any reporting unit was then necessary because the fair values of the reporting units exceeded their respective carrying values. The fair value of all reporting units was determined using an income approach based upon estimates of future discounted cash flows. The resulting estimates of fair value were validated through the consideration of other factors such as the fair value of comparable companies to the reporting units and a reconciliation of the sum of all estimated fair values of the reporting units to the Company’s overall market capitalization. In all cases, the estimated fair values of the reporting units significantly exceeded the respective carrying values.

Significant judgments and unobservable inputs, categorized as Level 3 in the fair value hierarchy, are inherent in the impairment tests performed and include assumptions about the amount and timing of expected future cash flows, growth rates, and the determination of appropriate discount rates. Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The Company believes that the assumptions used in its impairment tests are reasonable, but variations in any of the assumptions may result in different measurements of fair values.

The impacts of any adverse business and market conditions which may impact the overall performance of the Company's reporting units will continue to be monitored. If the Company's reporting units do not achieve the financial performance that the Company expects, or if there is a significant prolonged change in demand for the Company's products and services, it is possible that goodwill impairment charges may result. Therefore, there can be no assurance that future events will not result in an impairment of goodwill.

As of December 31, 2023 and 2022, the Company's intangible assets consisted of the following (in thousands):

During the periods presented, there were no events or changes in circumstances which would indicate that the carrying values of the Company's asset groups would not be recoverable and thus no impairment charges were recorded. If expectations of future cash flows were to decrease in the future as a result of worse than expected or prolonged periods of depressed activity, future impairments may become evident.

Amortization expense of permits, customer and supplier relationships and other intangible assets for the years ended December 31, 2023, 2022 and 2021 were $50.3 million, $50.2 million and $34.7 million, respectively.

The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2023 was as follows (in thousands):