ADVANCED DRAINAGE SYSTEMS INC

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the shareholders and the Board of Directors of Advanced Drainage Systems Inc.,

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Advanced Drainage Systems, Inc., and subsidiaries (the “Company”) as of March 31, 2024 and 2023, the related consolidated statements of operations, comprehensive income, stockholder's equity and mezzanine equity, and cash flows, for each of the three years in the period ended March 31, 2024, and the related notes and the financial statement schedule listed in the Index at Item 15 (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of March 31, 2024 and 2023, and the results of its operations and its cash flows for each of the three years in the period ended March 31, 2024, in conformity with accounting principles generally accepted in the United States of America.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of March 31, 2024, based on criteria established in Internal Control — Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission and our report dated May 16, 2024, expressed an unqualified opinion on the Company's internal control over financial reporting.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company's financial statements based on our audits. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current-period audit of the financial statements that was communicated or required to be communicated to the audit committee and that (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of critical audit matters does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Goodwill, Infiltrator Water Technologies Reporting Unit — Refer to Note 8 to the financial statements

Critical Audit Matter Description

The Company’s evaluation of goodwill for impairment involves comparing the carrying value of each reporting unit to the estimated fair value of the reporting unit. For the year ended March 31, 2024, the Company performed its evaluation of goodwill for impairment using a qualitative assessment or “Step Zero” impairment test to determine whether it is more likely than not that impairment has occurred. If the Company determines that it is more likely than not that the carrying amount of its’ reporting units exceeds their fair value, the Company would perform a quantitative assessment or “Step One” impairment test and calculate the estimated fair value of the respective reporting unit. Changes in the assumptions utilized could have a significant impact on fair value. The Company’s consolidated goodwill balance was $617.2 million as of March 31, 2024, of which $495.8 million was allocated to the Infiltrator Water Technologies (“Infiltrator”) reporting unit.

We identified the evaluation of goodwill for impairment for the Infiltrator reporting unit as a critical audit matter due to significant judgments made by management to determine whether it is more likely than not that impairment of the underlying reporting unit has occurred, including management’s judgment as it relates to their evaluation of macroeconomic conditions, industry and market considerations, internal cost factors, and the Company’s overall financial and share price performance, among other factors. This required a high degree of auditor judgment and an increased effort, including the need to involve our fair value specialists.

How the Critical Audit Matter Was Addressed in the Audit

We, along with the assistance from our fair value specialists, evaluated the reasonableness of management’s Step Zero impairment test by performing the following procedures:

•Tested the design and operating effectiveness of management's internal controls over their goodwill impairment evaluation, including those over the significant assumptions used in management's qualitative Step Zero test.

•Evaluated the Company’s qualitative Step Zero test, including consideration of macroeconomic factors, industry and market considerations, internal cost factors, and overall financial and share price performance, among other factors that could change discount and growth rates, and key performance indicators, such as projected revenue and EBITDA, and performed sensitivity analysis on the key assumptions.

•Performed a retrospective review of current year results compared to the projections used in the most recent quantitative impairment test.

•Evaluated historical data used in developing the assumptions to assess whether the data is comparable and consistent with data of the period under audit.

•Assessed the cushion between the most recent fair value estimate performed as of March 31, 2023 and the carrying value of the reporting unit.

•Inquired with management, the board of directors, and the legal department regarding any changes in management strategy or operations during the year that could potentially affect the drivers of the fair value for the reporting unit.

/s/ Deloitte & Touche LLP

Columbus, Ohio

May 16, 2024

We have served as the Company's auditor since 2002.

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the stockholders and the Board of Directors of Advanced Drainage Systems, Inc.,

Opinion on Internal Control over Financial Reporting

We have audited the internal control over financial reporting of Advanced Drainage Systems, Inc., and subsidiaries (the “Company”) as of March 31, 2024, based on criteria established in Internal Control — Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission (COSO). In our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of March 31, 2024, based on criteria established in Internal Control — Integrated Framework (2013) issued by COSO.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the consolidated financial statements as of and for the year ended March 31, 2024, of the Company and our report dated May 16, 2024, expressed an unqualified opinion on those financial statements.

Basis for Opinion

The Company’s management is responsible for maintaining effective internal control over financial reporting and for its assessment of the effectiveness of internal control over financial reporting, included in the accompanying Management’s Report on Internal Control Over Financial Reporting. Our responsibility is to express an opinion on the Company’s internal control over financial reporting based on our audit. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether effective internal control over financial reporting was maintained in all material respects. Our audit included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, testing and evaluating the design and operating effectiveness of internal control based on the assessed risk, and performing such other procedures as we considered necessary in the circumstances. We believe that our audit provides a reasonable basis for our opinion.

Definition and Limitations of Internal Control over Financial Reporting

A company’s internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company’s internal control over financial reporting includes those policies and procedures that (1) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use, or disposition of the company’s assets that could have a material effect on the financial statements.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

/s/ Deloitte & Touche LLP

Columbus, Ohio

May 16, 2024