	(in thousands)
December 31,	2022			2021
Land and improvements, net	$	905,598		$	845,772
Buildings and improvements		2,230,672			1,845,937
Machinery and equipment		15,125,653			13,119,177
Proved oil and gas properties		558,486			558,336
Leasehold interest in unproved oil and gas properties		96,000			96,000
Construction in process and equipment deposits		1,815,638			2,039,245
		20,732,047			18,504,467
Less accumulated depreciation		(11,115,127	)		(10,389,649	)
	$	9,616,920		$	8,114,818

The estimated useful lives primarily range from five to 25 years for land improvements, four to 40 years for buildings and improvements and two to 15 years for machinery and equipment. The useful life for proved oil and gas properties is based on the unit-of-production method and varies by well.

In 2020, Nucor recorded non-cash impairment charges totaling $103.2 million related to certain inventory and long-lived assets, which primarily related to our Castrip sheet mill operations. Due to the advancements in the capabilities at our new cold mill and galvanizing line at Nucor Steel Arkansas, we believe the value of the technology and process has diminished for Nucor. As such, the existing Castrip assets are not expected to be materially utilized going forward. These charges are included in losses and impairments of assets in the consolidated statement of earnings for the year ended December 31, 2020.

In 2020, regulatory authorities in Colorado adopted new rules that became effective January 2021. One of these rules increased drilling setback distances. In the fourth quarter of 2020, Nucor determined a triggering event had occurred, and performed an impairment analysis. As a result, Nucor recorded a $27.0 million non-cash impairment charge related to the write-down of our leasehold interest in unproved oil and gas properties. This charge is included in losses and impairments of assets in the consolidated statement of earnings for the year ended December 31, 2020.

In the second quarter of 2021, Nucor decided that it would not develop a portion of its unproved oil and natural gas properties (“Portion A”) within the contractually specified time period related to Portion A. As a result of this decision, the Company will forfeit its leasehold rights for Portion A. The Company recorded a charge of $42.0 million to write off the value of Portion A that is included in losses and impairments of assets in the consolidated statement of earnings for the year ended December 31, 2021. The decision not to develop Portion A was heavily influenced by the approaching deadline to commence development combined with Portion A’s expected near-term profitability not achieving management’s desired returns relative to the cost of development. A significant portion of the Company’s remaining leasehold interest in unproved oil and natural gas properties are held by production. The carrying value of the remaining portions of unproved oil and natural gas properties was $96.0 million at December 31, 2021.

In the fourth quarter of 2022, Nucor decided that it is unlikely to develop the remaining portions of its unproved oil and natural gas properties. As a result of this decision, Nucor recorded a $96.0 million impairment charge for the entire balance of those assets, which are included in the raw materials segment. The impairment charge is included in losses and impairments of assets in the consolidated statement of earnings for the year ended December 31, 2022. We retain ownership of our leasehold interest in unproved oil and natural gas properties. The carrying value of the leasehold interest in unproved oil and gas properties was zero at December 31, 2022.

Nucor received $275.0 million of financial assistance during 2022 from the West Virginia Department of Economic Development in connection with Nucor’s planned construction of Nucor Steel West Virginia (NSWV), a sheet mill in Mason County, West Virginia. Nucor will earn the financial assistance if, by the Completion Date (defined in the agreement as on or before December 31, 2026), Nucor meets certain capital investment, full-time jobs creation and total annual payroll criteria. Nucor believes that it is probable we will meet these conditions. Through December of 2022, Nucor has spent $179.7 million in qualifying expenditures for the construction of NSWV, and that amount is included as a contra-asset in construction in process and equipment deposits that are a part of property, plant and equipment, net on the consolidated balance sheet at December 31, 2022. The remaining $95.3 million is included in deferred credits and other liabilities on the consolidated balance sheet at December 31, 2022. When the NSWV assets are placed into service, the effect of depreciating the assets constructed with the financial assistance will decrease depreciation expense in the statement of earnings.