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Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America (U.S. GAAP) requires management to make estimates and assumptions that affect reported amounts in the consolidated financial statements and accompanying notes. Actual amounts could differ from those estimates, and changes would most likely be reported in future periods. Management believes the estimates and assumptions used are reasonable.

Industry Regulation

NW Holdings' principal business is to operate as a holding company for NW Natural and its other subsidiaries. NW Natural's principal business is the distribution of natural gas, which is regulated by the OPUC and WUTC. NW Natural also has natural gas storage services, which are regulated by the FERC, and to a certain extent by the OPUC and WUTC. Additionally, certain of NW Holdings' subsidiaries own water businesses, which are regulated by the public utility commission in the state in which the water utility is located, which is currently Oregon, Washington, Idaho, Texas and Arizona. Wastewater businesses, to the extent they are regulated, are generally regulated by the public utility commissions in the state in which the wastewater utility is located, which is currently Texas and Arizona. Accounting records and practices of the regulated businesses conform to the requirements and uniform system of accounts prescribed by these regulatory authorities in accordance with U.S. GAAP. The businesses in which customer rates are regulated by the OPUC, WUTC, IPUC, PUTC, ACC and FERC have approved cost-based rates which are intended to allow such businesses to earn a reasonable return on invested capital.

In applying regulatory accounting principles, NW Holdings and NW Natural capitalize or defer certain costs and revenues as regulatory assets and liabilities pursuant to orders of the applicable state public utility commission, which provide for the recovery of revenues or expenses from, or refunds to, utility customers in future periods, including a return or a carrying charge in certain cases.

Amounts NW Natural deferred as regulatory assets and liabilities were as follows:


	Regulatory Assets
In thousands	2022		2021
NW Natural:
Current:
Unrealized loss on derivatives(1)	$	28,728	$	10,402
Gas costs	61,223		35,641
Environmental costs(2)	7,392		6,694
Decoupling(3)	—		969
Pension balancing(4)	7,131		7,131
Income taxes	2,208		2,568

Other(5)	10,809		8,986
Total current	$	117,491	$	72,391
Non-current:
Unrealized loss on derivatives(1)	$	20,838	$	412
Pension balancing(4)	32,997		38,302
Income taxes	10,943		12,609
Pension and other postretirement benefit liabilities	101,413		116,440
Environmental costs(2)	104,253		94,636
Gas costs	22,355		15,477

Other(5)	47,608		36,663
Total non-current	$	340,407	$	314,539
Other (NW Holdings)	25		40
Total non-current -NW Holdings	$	340,432	$	314,579


	Regulatory Liabilities
In thousands	2022		2021
NW Natural:
Current:
Gas costs	$	4,121	$	70
Unrealized gain on derivatives(1)	194,236		48,130
Decoupling(3)	14,026		4,475
Income taxes(6)	7,166		8,192
Asset optimization revenue sharing	26,368		45,124
Other(5)	2,636		6,290
Total current - NW Natural	$	248,553	$	112,281


Other (NW Holdings)	29		—
Total current - NW Holdings	$	248,582	$	112,281
Non-current:
Gas costs	$	12,644	$	250
Unrealized gain on derivatives(1)	5,045		10,730
Decoupling(3)	3,814		3,412
Income taxes(6)	174,212		181,404
Accrued asset removal costs(7)	467,742		445,952
Asset optimization revenue sharing	8,401		1,810
Other(5)	16,741		13,792
Total non-current - NW Natural	$	688,599	$	657,350
Other (NW Holdings)	979		982
Total non-current -NW Holdings	$	689,578	$	658,332

(1)Unrealized gains or losses on derivatives are non-cash items and, therefore, do not earn a rate of return or a carrying charge. These amounts are recoverable through natural gas distribution rates as part of the annual Purchased Gas Adjustment (PGA) mechanism when realized at settlement.

(2)Refer to the Environmental Cost Deferral and Recovery table in Note 17 for a description of environmental costs.

(3)This deferral represents the margin adjustment resulting from differences between actual and expected volumes.

(4)Refer to Note 10 for information regarding the deferral of pension expenses.

(5)Balances consist of deferrals and amortizations under approved regulatory mechanisms and typically earn a rate of return or carrying charge.

(6)This balance represents estimated amounts associated with the Tax Cuts and Jobs Act. See Note 11.

(7)Estimated costs of removal on certain regulated properties are collected through rates. See "Accounting Policies—Plant, Property, and Accrued Asset Removal Costs" below.

The amortization period for NW Natural's regulatory assets and liabilities ranges from less than one year to an indeterminable period. Regulatory deferrals for gas costs payable are generally amortized over 12 months beginning each November 1 following the gas contract year during which the deferred gas costs are recorded. Similarly, most other regulatory deferred accounts are amortized over 12 months. However, certain regulatory account balances, such as income taxes, environmental costs, pension liabilities, and accrued asset removal costs, are large and tend to be amortized over longer periods once NW Natural has agreed upon an amortization period with the respective regulatory agency.

We believe all costs incurred and deferred at December 31, 2022 are prudent. All regulatory assets are reviewed annually for recoverability, or more often if circumstances warrant. If we should determine that all or a portion of these regulatory assets no longer meet the criteria for continued application of regulatory accounting, then NW Natural would be required to write-off the net unrecoverable balances in the period such determination is made.

Regulatory interest income of $7.0 million and $6.1 million and regulatory interest expense of $2.0 million and $1.3 million was recognized within other income (expense), net for the years ended December 31, 2022 and 2021, respectively.

Environmental Regulatory Accounting

See Note 17 for information about the SRRM and OPUC orders regarding implementation.

New Accounting Standards

NW Natural and NW Holdings consider the applicability and impact of all accounting standards updates (ASUs) issued by the Financial Accounting Standards Board (FASB). ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on consolidated financial position or results of operations.

Recently Adopted Accounting Pronouncements

REFERENCE RATE REFORM. In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." The purpose of the amendment is to provide optional expedients and exceptions for applying generally accepted accounting principles (GAAP) to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments in this ASU apply only to contracts, hedging relationships, and other transactions that reference London Inter-Bank Offered Rate (LIBOR) or another reference rate expected to be discontinued because of reference rate reform.

In January 2021, the FASB issued ASU 2021-01, "Reference Rate Reform (Topic 848): Scope." The purpose of the amendment is to clarify guidance on reference rate reform activities, specifically related to accounting for derivative contracts and certain hedging relationships affected by changes in the interest rates used for discounting, margining, and contract price alignment (the "discounting transition"). The amendments in ASUs 2020-04 and 2021-01 are effective for all entities as of March 12, 2020 through December 31, 2022.

In December 2022, the FASB issued ASU 2022-06, "Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848." The purpose of the amendment is to defer the sunset date of Topic 848 from December 31, 2022, to December 31, 2024, after which entities will no longer be permitted to apply the relief in Topic 848. The objective of the guidance in Topic 848 is to provide temporary relief during the transition period. The Board included a sunset provision within Topic 848 based on expectations of when the London Interbank Offered Rate (LIBOR) would cease being published. We do not expect the ASUs to materially affect the financial statements and disclosures of NW Holdings or NW Natural.

LEASES. In July 2021, the FASB issued ASU 2021-05, "Leases (Topic 842), Lessors - Certain Leases with Variable Lease Payments." The purpose of the amendment is to require lessors to account for certain lease transactions that contain variable lease payments as operating leases. The amendments in this ASU are intended to eliminate the recognition of any day-one loss

associated with certain sales-type and direct-financing lease transactions. The changes do not impact lessee accounting. The new guidance was effective on January 1, 2022 and adopted using a prospective approach. The adoption did not materially affect the financial statements and disclosures of NW Holdings or NW Natural.

Property, Plant and Accrued Asset Removal Costs

Plant, Property, and Accrued Asset Removal Costs

Plant and property are stated at cost, including capitalized labor, materials, and overhead. In accordance with regulatory accounting standards, the cost of acquiring and constructing long-lived plant and property generally includes an allowance for funds used during construction (AFUDC) or capitalized interest. AFUDC represents the regulatory financing cost incurred when debt and equity funds are used for construction (see “AFUDC” below). When constructed assets are subject to market-based rates rather than cost-based rates, the financing costs incurred during construction are included in capitalized interest in accordance with U.S. GAAP, not as regulatory financing costs under AFUDC.

In accordance with long-standing regulatory treatment, our depreciation rates consist of three components: one based on the average service life of the asset, a second based on the estimated salvage value of the asset, and a third based on the asset’s estimated cost of removal. We collect, through rates, the estimated cost of removal on certain regulated properties through depreciation expense, with a corresponding offset to accumulated depreciation. These removal costs are non-legal obligations as defined by regulatory accounting guidance. Therefore, we have included these costs as non-current regulatory liabilities rather than as accumulated depreciation on our consolidated balance sheets. In the rate setting process, the liability for removal costs is treated as a reduction to the net rate base on which the NGD business has the opportunity to earn its allowed rate of return.

The costs of NGD plant retired or otherwise disposed of are removed from NGD plant and charged to accumulated depreciation for recovery or refund through future rates. Gains from the sale of regulated assets are generally deferred and refunded to customers. For assets not related to NGD, we record a gain or loss upon the disposal of the property, and the gain or loss is recorded in operating income or loss in the consolidated statements of comprehensive income.

The provision for depreciation of NGD property, plant, and equipment is recorded under the group method on a straight-line basis with rates computed in accordance with depreciation studies approved by regulatory authorities. The weighted-average depreciation rate for NGD assets in service was approximately 3.0% for 2022, 2021 and 2020, reflecting the approximate weighted-average economic life of the property. This includes 2022 weighted-average depreciation rates for the following asset categories: 2.5% for transmission and distribution plant, 2.1% for gas storage facilities, 6.1% for general plant, and 6.7% for intangible and other fixed assets.

AFUDC. Certain additions to NGD plant include AFUDC, which represents the net cost of debt and equity funds used during construction. AFUDC is calculated using actual interest rates for debt and authorized rates for ROE, if applicable. If short-term debt balances are less than the total balance of construction work in progress, then a composite AFUDC rate is used to represent interest on all debt funds, shown as a reduction to interest charges, and on ROE funds, shown as other income. While cash is not immediately recognized from recording AFUDC, it is realized in future years through rate recovery resulting from the higher NGD cost of service. Our composite AFUDC rate was 2.8% in 2022, 0.7% in 2021, and 1.9% in 2020.

IMPAIRMENT OF LONG-LIVED ASSETS. We review the carrying value of long-lived assets whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. Factors that would necessitate an impairment assessment of long-lived assets include a significant adverse change in the extent or manner in which the asset is used, a significant adverse change in legal factors or business climate that could affect the value of the asset, or a significant decline in the observable market value or expected future cash flows of the asset, among others.

When such factors are present, we assess the recoverability by determining whether the carrying value of the asset will be recovered through expected future cash flows. An asset is determined to be impaired when the carrying value of the asset exceeds the expected undiscounted future cash flows from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss for the difference between the carrying value and the fair value of the long-lived assets. Fair value is estimated using appropriate valuation methodologies, which may include an estimate of discounted cash flows.

Cash and Cash Equivalents

For purposes of reporting cash flows, cash and cash equivalents include cash on hand plus highly liquid investment accounts with original maturity dates of three months or less. At December 31, 2022, NW Holdings had outstanding checks of $5.8 million, substantially all of which is recorded at NW Natural, and at December 31, 2021, NW Holdings had no outstanding checks. These balances are included in accounts payable in the NW Holdings and NW Natural balance sheets.

Restricted cash is primarily comprised of funds from public purpose charges for programs that assist low-income customers with bill payments or energy efficiency. These balances are included in other current assets in the NW Holdings and NW Natural balance sheets. There were no transfers between restricted cash and cash and cash equivalents during the years ended December 31, 2022 and 2021. Prior period amounts have been reclassified to conform prior period information to the current presentation.

The following table provides a reconciliation of the cash, cash equivalents and restricted cash balances at NW Holdings as of December 31, 2022 and 2021:


	December 31,
In thousands	2022		2021
Cash and cash equivalents	$	29,270	$	18,559
Restricted cash included in other current assets	11,694		8,561
Cash, cash equivalents and restricted cash	$	40,964	$	27,120

The following table provides a reconciliation of the cash, cash equivalents and restricted cash balances at NW Natural as of December 31, 2022 and 2021:


	December 31,
In thousands	2022		2021
Cash and cash equivalents	$	12,977	$	12,271
Restricted cash included in other current assets	11,694		8,561
Cash, cash equivalents and restricted cash	$	24,671	$	20,832

Revenue Recognition and Accrued Unbilled Revenue

Revenues, derived primarily from the sale and transportation of natural gas, are recognized upon delivery of gas or water, or service to customers. Revenues include accruals for gas or water delivered but not yet billed to customers based on estimates of deliveries from meter reading dates to month end (accrued unbilled revenue). Accrued unbilled revenue is dependent upon a number of factors that require management’s judgment, including total natural gas receipts and deliveries, customer use of natural gas or water by billing cycle, and weather factors. Accrued unbilled revenue is reversed the following month when actual billings occur. NW Holdings' accrued unbilled revenue at December 31, 2022 and 2021 was $89.0 million and $82.2 million, respectively, substantially all of which is accrued unbilled revenue at NW Natural.

Revenues not related to NGD are derived primarily from Interstate Storage Services, asset management activities at the Mist gas storage facility, and other investments and business activities. At the Mist underground storage facility, revenues are primarily firm service revenues in the form of fixed monthly reservation charges. In addition, we also have asset management service revenue from an independent energy marketing company that optimizes commodity, storage, and pipeline capacity release transactions. Under this agreement, guaranteed asset management revenue is recognized using a straight-line, pro-rata methodology over the term of each contract. Revenues earned above the guaranteed amount are recognized as they are earned.

Revenue Taxes

Revenue Taxes Revenue-based taxes are primarily franchise taxes, which are collected from customers and remitted to taxing authorities. Revenue taxes are included in operating expenses in the statements of comprehensive income for NW Holdings and NW Natural. Revenue taxes at NW Holdings were $41.8 million, $34.7 million, and $30.3 million for 2022, 2021, and 2020, respectively.

Accounts Receivable and Allowance for Uncollectible Accounts

Accounts receivable consist primarily of amounts due for natural gas sales and transportation services to NGD customers, plus amounts due for gas storage services. NW Holdings and NW Natural establish allowances for uncollectible accounts (allowance) for trade receivables, including accrued unbilled revenue, based on the aging of receivables, collection experience of past due account balances including payment plans, and historical trends of write-offs as a percent of revenues. A specific allowance is established and recorded for large individual customer receivables when amounts are identified as unlikely to be partially or fully recovered. Inactive accounts are written-off against the allowance after they are 120 days past due or when deemed uncollectible. Differences between the estimated allowance and actual write-offs will occur based on a number of factors, including changes in economic conditions, customer creditworthiness, and natural gas prices. The allowance for uncollectible accounts is adjusted quarterly, as necessary, based on information currently available.

ALLOWANCE FOR TRADE RECEIVABLES. The payment term of our NGD receivables is generally 15 days. For these short-term receivables, it is not expected that forecasted economic conditions would significantly affect the loss estimates under stable economic conditions. For extreme situations like a financial crisis, natural disaster, and the economic slowdown caused by the COVID-19 pandemic, we enhanced our review and analysis.

For the 2022 residential and commercial uncollectible provision, we primarily followed our standard methodology, which includes assessing historical write-off trends and current information on delinquent accounts. Beginning October 1, 2022, new collection rules from the OPUC applied to residential and commercial customers. This included enhanced protections for low-income customers, a return to pre-pandemic time payment arrangements terms, revised disconnection rules during the heating season, and other items. As a result of these Oregon rule changes and our recent collection process experience, we augmented our

provision review in the third and fourth quarter for Oregon accounts in the following categories: closed or inactive accounts aged less than 120 days, accounts on payment plans, and all other open accounts not on payment plans. For industrial accounts, we continue to assess the provision on an account-by-account basis with specific reserves taken as necessary. NW Natural will continue to closely monitor and evaluate our accounts receivable and the provision for uncollectible accounts.

The following table presents the activity related to the NW Holdings provision for uncollectible accounts by pool, substantially all of which is related to NW Natural's accounts receivable:


	As of December 31, 2021						As of December 31, 2022
			Year ended December 31, 2022
In thousands	Beginning Balance		Provision recorded, net of adjustments		Write-offs recognized, net of recoveries		Ending Balance
Allowance for uncollectible accounts:
Residential	$	1,460	$	1,974	$	(1,062)	$	2,372
Commercial	178		546		(324)		400
Industrial	67		186		(65)		188
Accrued unbilled and other	313		185		(162)		336
Total	$	2,018	$	2,891	$	(1,613)	$	3,296

ALLOWANCE FOR NET INVESTMENTS IN SALES-TYPE LEASES. NW Natural currently holds two net investments in sales-type leases, with substantially all of the net investment balance related to the North Mist natural gas storage agreement with Portland General Electric (PGE) which is billed under an OPUC-approved rate schedule. See Note 7 for more information on the North Mist lease. Due to the nature of this service, PGE may recover the costs of the lease through general rate cases. Therefore, we expect the risk of loss due to the credit of this lessee to be remote. As such, no allowance for uncollectibility was recorded for our sales-type lease receivables. NW Natural will continue monitoring the credit health of the lessees and the overall economic environment, including the economic factors closely tied to the financial health of our current and future lessees.

Inventories

NGD gas inventories, which consist of natural gas in storage for NGD customers, are stated at the lower of weighted-average cost or net realizable value. The regulatory treatment of these inventories provides for cost recovery in customer rates. NGD gas inventories injected into storage are priced in inventory based on actual purchase costs, and those withdrawn from storage are charged to cost of gas during the period they are withdrawn at the weighted-average inventory cost.

Gas storage inventories mainly consist of natural gas received as fuel-in-kind from storage customers. Gas storage inventories are valued at the lower of average cost or net realizable value. Cushion gas is not included in inventory balances, is recorded at original cost, and is classified as a long-term plant asset.

Materials and supplies inventories consist of inventories both related to and unrelated to NGD and are stated at the lower of average cost or net realizable value.

NW Natural's NGD and gas storage inventories totaled $61.9 million and $37.4 million at December 31, 2022 and 2021, respectively. At December 31, 2022 and 2021, NW Holdings' materials and supplies inventories, which are comprised primarily of NW Natural's materials and supplies, totaled $23.5 million and $19.9 million, respectively.

During 2022 and 2021, NW Natural entered into certain agreements to purchase renewable thermal certificates (RTCs). RTCs are initially recorded at cost and subsequently assessed for impairment based on the lower-of-cost or market model. NW Natural's RTCs inventory totaled $1.7 million at December 31, 2022, and all RTCs purchased during 2021 were retired or used on customers behalf prior to December 31, 2021.

Gas Reserves

Gas reserves are payments to acquire and produce natural gas reserves. Gas reserves are stated at cost, adjusted for regulatory amortization, with the associated deferred tax benefits recorded as liabilities on the balance sheet. The current portion is calculated based on expected gas deliveries within the next fiscal year. NW Natural recognizes regulatory amortization of this asset on a volumetric basis calculated using the estimated gas reserves and the estimated therms extracted and sold each month. The amortization of gas reserves is recorded to cost of gas along with gas production revenues and production costs. See Note 13.

Derivatives

NW Natural's derivatives are measured at fair value and recognized as either assets or liabilities on the balance sheet. Changes in the fair value of the derivatives are recognized in earnings unless specific regulatory or hedge accounting criteria are met. Accounting for derivatives and hedges provides an exception for contracts intended for normal purchases and normal sales for which physical delivery is probable. In addition, certain derivative contracts are approved by regulatory authorities for recovery or refund through customer rates. Accordingly, the changes in fair value of these approved contracts are deferred as regulatory

assets or liabilities pursuant to regulatory accounting principles. NW Natural's financial derivatives generally qualify for deferral under regulatory accounting. NW Natural's index-priced physical derivative contracts also qualify for regulatory deferral accounting treatment.

Derivative contracts entered into for NGD requirements after the annual PGA rate has been set and maturing during the PGA year are subject to the PGA incentive sharing mechanism. In Oregon, NW Natural participates in a PGA sharing mechanism under which it is required to select either an 80% or 90% deferral of higher or lower gas costs such that the impact on current earnings from the gas cost sharing is either 20% or 10% of gas cost differences compared to PGA prices, respectively. For each of the PGA years in Oregon beginning November 1, 2022, 2021, and 2020, NW Natural selected the 90% deferral of gas cost differences. In Washington, 100% of the differences between the PGA prices and actual gas costs are deferred. See Note 15.

NW Holdings and NW Natural have financial derivative policies that set forth guidelines for using selected derivative products to support prudent risk management strategies within designated parameters. NW Natural's objective for using derivatives is to decrease the volatility of gas prices and cash flows without speculative risk. The use of derivatives is permitted only after the risk exposures have been identified, are determined to exceed acceptable tolerance levels, and are determined necessary to support normal business activities. NW Natural does not enter into derivative instruments for trading purposes. All commodity and foreign exchange derivatives are currently held at NW Natural, and interest rate swaps are held at NW Holdings and NWN Water.

Fair Value

In accordance with fair value accounting, we use the following fair value hierarchy for determining inputs for our debt, pension plan assets, and derivative fair value measurements:

•Level 1: Valuation is based on quoted prices for identical instruments traded in active markets;

•Level 2: Valuation is based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market; and

•Level 3: Valuation is generated from model-based techniques that use significant assumptions not observable in the market. These unobservable assumptions reflect our own estimates of assumptions market participants would use in valuing the asset or liability.

In addition, the fair value for certain pension trust investments is determined using Net Asset Value per share (NAV) as a practical expedient, and therefore they are not classified within the fair value hierarchy. These investments primarily consist of institutional investment products.

When developing fair value measurements, it is our policy to use quoted market prices whenever available or to maximize the use of observable inputs and minimize the use of unobservable inputs when quoted market prices are not available. Fair values are primarily developed using industry-standard models that consider various inputs including: (a) quoted future prices for commodities; (b) forward currency prices; (c) time value; (d) volatility factors; (e) current market and contractual prices for underlying instruments; (f) market interest rates and yield curves; (g) credit spreads; and (h) other relevant economic measures. NW Natural considers liquid points for natural gas hedging to be those points for which there are regularly published prices in a nationally recognized publication or where the instruments are traded on an exchange.

Goodwill

Goodwill and Business Combinations

NW Holdings, through its wholly-owned subsidiary NWN Water and NWN Water's wholly-owned subsidiaries, has completed various acquisitions that resulted in the recognition of goodwill. Goodwill is measured as the excess of the acquisition-date fair value of the consideration transferred over the acquisition-date fair value of the net identifiable assets assumed. Adjustments are recorded during the measurement period to finalize the allocation of the purchase price. The carrying value of goodwill is reviewed annually during the fourth quarter, or whenever events or changes in circumstance indicate that such carrying values may not be recoverable. The goodwill assessment policy begins with a qualitative analysis in which events and circumstances are evaluated, including macroeconomic conditions, industry and market conditions, regulatory environments, and overall financial performance of the reporting unit. If the qualitative assessment indicates that the carrying value may be at risk of recoverability, a quantitative evaluation is performed to measure the carrying value of the goodwill against the fair value of the reporting unit. The reporting unit is determined primarily based on current operating segments and the level of review provided by the Chief Operating Decision Maker (CODM) and/or segment management on the operating segment's financial results. Reporting units are evaluated periodically for changes in the corporate environment.

As of December 31, 2022 and 2021, NW Holdings had goodwill of $149.3 million and $70.6 million, respectively. All of NW Holdings' goodwill was acquired through the business combinations completed by NWN Water and its wholly-owned subsidiaries. No impairment charges were recorded as a result of the fourth quarter goodwill impairment assessment.

Income Taxes

We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the enactment date period unless, for NW Natural, a regulatory order specifies deferral of the effect of the change in tax rates over a longer period of time.

For NW Natural, deferred income tax assets and liabilities are also recognized for temporary differences where the deferred income tax benefits or expenses have previously been flowed through in the ratemaking process of the NGD business. Regulatory tax assets and liabilities are recorded on these deferred tax assets and liabilities to the extent it is believed they will be recoverable from or refunded to customers in future rates.

Investment tax credits associated with rate regulated plant additions are deferred for financial statement purposes and amortized over the estimated useful lives of the related plant.

NW Holdings files consolidated or combined income tax returns that include NW Natural. Income tax expense is allocated on a separate company basis incorporating certain consolidated return considerations. Subsidiary income taxes payable or receivable are generally settled with NW Holdings, the common agent for income tax matters.

Interest and penalties related to unrecognized tax benefits, if any, are recognized within income tax expense and accrued interest and penalties are recognized within the related tax liability line in the consolidated balance sheets. No accrued interest or penalties for uncertain tax benefits have been recorded. See Note 11.

Environmental Contingencies

Loss contingencies are recorded as liabilities when it is probable a liability has been incurred and the amount of the loss is reasonably estimable in accordance with accounting standards for contingencies. Estimating probable losses requires an analysis of uncertainties that often depend upon judgments about potential actions by third parties. Accruals for loss contingencies are recorded based on an analysis of potential results.

With respect to environmental liabilities and related costs, estimates are developed based on a review of information available from numerous sources, including completed studies and site specific negotiations. NW Natural's policy is to accrue the full amount of such liability when information is sufficient to reasonably estimate the amount of probable liability. When information is not available to reasonably estimate the probable liability, or when only the range of probable liabilities can be estimated and no amount within the range is more likely than another, it is our policy to accrue at the low end of the range. Accordingly, due to numerous uncertainties surrounding the course of environmental remediation and the preliminary nature of several site investigations, in some cases, it may not be possible to reasonably estimate the high end of the range of possible loss. In those cases, the nature of the potential loss and the fact that the high end of the range cannot be reasonably estimated is disclosed. See Note 17.

Subsequent Events

We monitor significant events occurring after the balance sheet date and prior to the issuance of the financial statements to determine the impacts, if any, of events on the financial statements to be issued.