Does the phrase 'at least' in a notification set a floor or a ceiling on the obligation?

Environment (Protection) Act, 1986 — free fly ash supply to National Highway projects — Notification dated 14.09.1999 as amended — obligation surviving beyond ten years — legitimate expectation — promissory estoppel against NHAI — writ maintainability despite arbitration clause — unjust enrichment — moulded relief. Held, allowing the appeals in part, that the obligation cast by the Notification dated 14.09.1999 to supply fly ash free of cost and free of transportation did not stand confined to ten years from 1999. The phrase "at least 10 years" set a floor and not a ceiling, and the very clause containing that figure was deleted by the amendment dated 03.11.2009 and replaced with an obligation of unlimited duration, later strengthened by the 2016 amendment adding free transportation. Though the regime was formally superseded by the Notification dated 31.12.2021, it stood saved for all projects whose bid due date fell between 25.01.2016 and 31.12.2021, both under the terms of the Office Memoranda dated 26.06.2023 and 13.07.2023 and as a matter of legitimate expectation flowing from the consistent representations of the Ministries concerned. Both the Pollachi and the Bangalore-Chennai Expressway projects were held to fall within this saved class, on the strength of the Central Government's own records. Held, further, that NHAI, having itself asserted on oath before the Punjab and Haryana High Court and the Supreme Court that Thermal Power Plants are obliged to supply free fly ash with free transportation for projects with bid dates in this window, could not disclaim that position before this Court; an admission does not require to have matured into a decree before it may be relied upon against its maker, and a body meant to speak with one voice across the country cannot affirm on oath in one forum what it disclaims in another. Non-execution of a Memorandum of Understanding between NHAI and the Thermal Power Plants in Tamil Nadu was held not to extinguish, or operate as a condition precedent to, the statutory obligation. Held, also, that the existence of an arbitration clause in the Concession Agreement, and the pendency of Dispute Resolution Board proceedings, did not bar the writ petitions to the extent the reliefs sought were a declaration as to the correct interpretation of the statutory notifications and a mandamus against the Thermal Power Plant, a stranger to both the Concession Agreement and the arbitration clause; the decision in State of U.P. v. Bridge & Roof Co. (India) Ltd applies only to disputes that are, in substance, contractual, and does not go to the root of maintainability of a claim founded on a statutory, public-law obligation. The plea of delay and laches was rejected, since a party cannot be faulted for delay in asserting a right that was itself kept from it by the very authorities resisting the claim. Held, finally, that reimbursement calculated by reference to the actual, demonstrable additional cost of procuring borrow earth in lieu of free fly ash does not amount to unjust enrichment or double payment, since the contractual price for embankment work and the statutory entitlement to free fly ash are distinct. As regards the Thermal Power Plant which had demonstrated ash-utilisation exceeding statutory minimums through competitive e-auction, the obligation of free supply was held not to arise unconditionally; NHAI, as the nodal authority, was directed to take up the matter afresh with that Thermal Power Plant under the Notification dated 31.12.2021 before the obligation of free supply would crystallise, this calibrated relief being intended to avoid doing violence either to the appellants' established statutory entitlement or to the Thermal Power Plant's demonstrated record of ash utilisation.