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Environmental Matters
 9 Months Ended
Sep. 30, 2023
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
September 30,December 31,September 30,December 31,
In thousands202320222022202320222022
Portland Harbor site:
Gasco/Siltronic Sediments$18,679 $5,556 $9,744 $41,392 $40,740 $42,120 
Other Portland Harbor3,524 2,430 2,634 9,580 8,135 11,270 
Gasco/Siltronic Upland site8,908 8,367 16,067 32,512 33,354 35,457 
Front Street site812 201 457 939 868 879 
Oregon Steel Mills— — — 179 179 179 
Total$31,923 $16,554 $28,902 $84,602 $83,276 $89,905 
Environmental Regulatory Table
The following table presents information regarding the total regulatory asset deferred:
September 30,December 31,
In thousands202320222022
Deferred costs and interest (1)
$49,899 $47,011 $47,666 
Accrued site liabilities (2)
116,469 99,795 118,763 
Insurance proceeds and interest(50,380)(54,678)(54,784)
Total regulatory asset deferral(1)
$115,988 $92,128 $111,645 
Current regulatory assets(3)
7,047 9,461 7,392 
Long-term regulatory assets(3)
108,941 82,667 104,253 
(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 $57 thousand at September 30, 2023, $34 thousand at September 30, 2022, and $43 thousand at December 31, 2022.
(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.