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Environmental Matters
 3 Months Ended
Mar. 31, 2022
Environmental Remediation Obligations [Abstract]  
Schedule of Environmental Loss Contingencies by Site
The following table summarizes information regarding liabilities related to environmental sites, which are recorded in other current liabilities and other noncurrent liabilities in NW Natural's balance sheet:
Current LiabilitiesNon-Current Liabilities
March 31,December 31,March 31,December 31,
In thousands202220212021202220212021
Portland Harbor site:
Gasco/Siltronic Sediments$6,086 $7,026 $7,582 $41,408 $42,374 $42,076 
Other Portland Harbor2,198 2,175 2,592 9,092 6,954 9,570 
Gasco/Siltronic Upland site13,203 13,135 15,711 35,283 39,302 36,215 
Front Street site799 1,258 1,100 868 1,132 811 
Oregon Steel Mills— — — 179 179 179 
Total$22,286 $23,594 $26,985 $86,830 $89,941 $88,851 
Environmental Regulatory Table
The following table presents information regarding the total regulatory asset deferred:
March 31,December 31,
In thousands202220212021
Deferred costs and interest (1)
$45,482 $46,409 $45,122 
Accrued site liabilities (2)
109,061 113,456 115,773 
Insurance proceeds and interest(59,895)(69,492)(59,564)
Total regulatory asset deferral(1)
$94,648 $90,373 $101,331 
Current regulatory assets(3)
7,082 5,396 6,694 
Long-term regulatory assets(3)
87,566 84,977 94,636 
(1)     Includes pre-review and post-review deferred costs, amounts currently in amortization, and interest, net of amounts collected from customers.
(2)    Excludes 3.3% of the Front Street site liability as the OPUC only allows recovery of 96.7% of costs for those sites allocable to Oregon, including those that historically served only Oregon customers. Amounts excluded from regulatory assets were $0.1 million at March 31, 2022, $0.1 million at March 31, 2021, and $0.1 million at December 31, 2021.
(3)    Environmental costs relate to specific sites approved for regulatory deferral by the OPUC and WUTC. In Oregon, NW Natural earns a carrying charge on cash amounts paid, whereas amounts accrued but not yet paid do not earn a carrying charge until expended. It also accrues a carrying charge on insurance proceeds for amounts owed to customers. In Washington, neither the cash paid for insurance proceeds received accrue a carrying charge. Current environmental costs represent remediation costs management expects to collect from customers in the next 12 months. Amounts included in this estimate are still subject to a prudence and earnings test review by the OPUC and do not include the $5.0 million tariff rider. The amounts allocable to Oregon are recoverable through NGD rates, subject to an earnings test.