The following description of the Advanced Drainage Systems, Inc. Retirement and Stock Ownership Plan (the “Plan”) is provided for general information purposes only. Participants should refer to the Plan document and the Plan’s Summary Plan Description for a complete description of the Plan’s provisions.

General - The Plan is a tax-qualified defined contribution retirement plan that benefits substantially all employees of Advanced Drainage Systems, Inc. (the “Company” or “ADS”) and its participating subsidiaries. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”). The Company is the Plan’s sponsor and administrator under ERISA. The day-to-day operation of the Plan is handled by a three member KSOP Committee appointed by the Board of Directors of the Company, and its delegates. Prior to April 1, 2022, the Company sponsored two separate tax-qualified defined contribution retirement plans (i) the Advanced Drainage Systems, Inc. Employee Stock Ownership Plan (the “ESOP”), and (ii) the Advanced Drainage Systems Retirement Plan, formerly named the Advanced Drainage Systems, Inc. Profit Sharing Retirement Plan (the “401(k) Plan”). Effective April 1, 2022, pursuant to resolutions of the Company’s Board of Directors, the ESOP was merged into and with the 401(k) Plan, with the Plan thereafter having two separate components namely, an ESOP component (that qualifies as an “employee stock ownership plan” as defined in Internal Revenue Code (“Code”) Section 4975(e)(7)), and a 401(k) component (that complies with the cash or deferred arrangement requirements of Code Section 401(k)).

Contributions - The Plan provides for pre-tax deferral contributions by the participants through payroll deductions subject to certain limitations of Section 401(k) of the Code. Participants may also make after-tax Roth elective deferral contributions. Participants who have attained age 50 before the end of the Plan year are eligible to make catch-up contributions. Participants may also make rollover contribution amounts representing eligible rollover distributions from other employers’ tax-qualified retirement plans.

The Plan includes an auto-enrollment provision whereby all newly eligible employees are automatically enrolled in the Plan unless they affirmatively elect not to participate in the Plan. All newly eligible employees are automatically enrolled at a pre-tax deferral contribution rate of 3% of eligible compensation (which automatically increases one percent per year up to a maximum of seven percent), unless the employee elects otherwise. All auto-enrollment employee contributions are invested in a designated target date fund based on the participant’s age until changed by the participant.

The Plan also provides for an annual discretionary contribution by the Company in its discretion. Participants direct the investment of their contributions into the various investment options offered by the Plan. The Plan currently offers various mutual funds, a common collective trust fund and an employer common stock fund as investment options for participants.

Eligibility - Eligible employees of the Company and its participating subsidiaries (i.e., not a union employee, leased employee, Puerto Rico employee, or an independent contractor) are eligible to participate in the 401(k) component of the Plan on the first day of the month which coincides with or next follows the date the Plan’s entry requirements are satisfied. The entry requirements for eligible employees are (i) the employee must be at least 18 years old, (ii) must be credited with 30 days of service, and (iii) must be employed on the entry date.

Participant Accounts - Each participant's account is credited with the participant's contributions and Company matching contributions, as well as allocations of the Company's profit sharing contribution, if any, and Plan earnings. Participant accounts are charged with an allocation of administrative expenses that are paid by the Plan. Allocations are based on participant earnings, account balances, or specific participant transactions, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant's vested account.

Cash dividends on shares of Company Common Stock allocated to participants’ Plan accounts under the ESOP portion of the Plan are passed through to such participants. Participants provide voting directions with respect to the investment funds in which their Plan accounts are invested including, without limitation, voting directions with respect to shares of Company Common Stock allocated to their Plan accounts under the Plan’s ESOP portion’s employer stock fund.

Distribution of Plan Accounts - Participants receive the amount credited to their vested Plan accounts upon retirement, disability, death or termination of employment. Participants are also eligible to receive hardship distributions of a portion of their vested Plan accounts, and participants who have attained age 59 ½ may receive all or a portion of his or her account based on the vesting schedule. Distributions are paid to participants or their beneficiaries in a lump sum.

Forfeited Accounts - Forfeitures of participants’ unvested accounts are used to pay plan expenses and to offset Company contributions (with any amount in excess thereof allocated to participants’ accounts). At March 31, 2026 and 2025, forfeited non-vested accounts totaled approximately $0.4 million and less than $0.1 million, respectively. During 2026 and 2025, forfeitures of approximately $1.6 million and $2.5 million, respectively, were used to offset Company contributions and approximately $0.2 million and $0.1 million, respectively were used to pay administrative expenses.

Secure 2.0 Act of 2022 - On December 29, 2022, the SECURE 2.0 Act of 2022 (“SECURE 2.0”) was enacted as part of the Consolidated Appropriations Act, 2023. SECURE 2.0 includes numerous changes affecting qualified retirement plans, including 401(k) plans, such as expanded eligibility rules for long-term part-time employees, new distribution options, changes to required minimum distributions, and optional Roth treatment for certain contributions. The Plan is evaluating these provisions and intends to adopt required amendments by the applicable deadline (generally the last day of the first plan year beginning on or after January 1, 2026 for calendar-year plans), while operating the Plan in good-faith compliance with applicable effective dates in the interim.