concurring in part and dissenting in part.
I write for a majority of this Court in stating we could not agree more with Justice Pleicones’s conclusion in Part I of *205his concurring and dissenting opinion that DHEC acted on the Certification requested for the SHEP.3 However, we do not agree with Part II of his opinion. We take the analysis one step further and find that because the Board acted in contravention of section 54-6-10 of the South Carolina Code when it negotiated the Agreement with the Corps and the GPA before issuing the Certification requested for the SHEP, no deference is owed the DHEC Board’s decision. Because the Board’s decision incorporated the statutorily prohibited Agreement, we further hold that the staff denial of the Certification is now the final agency decision for purposes of contested case review. Consequently, the Certification is denied, and the contested case hearing pending in the ALC is moot. Moving forward, any activity, including any settlement negotiations, concerning the Certification must properly be directed to the Commission.
When undertaking contested case review, the ALC is the ultimate fact finder, and is not restricted by the findings of the administrative agency. Risher v. S.C. Dep’t of Health and Envtl. Control, 393 S.C. 198, 207-08, 712 S.E.2d 428, 433 (2011); see also Brown v. S.C. Dep’t of Health and Envtl. Control, 348 S.C. 507, 512, 560 S.E.2d 410, 413 (2002) (finding the ALC sits de novo in a contested case hearing).
However, as a general rule, “agencies charged with enforcing statutes ... receive deference from the courts as to their interpretation of those laws.” State v. Sweat, 379 S.C. 367, 385, 665 S.E.2d 645, 655 (Ct.App.2008) (citation omitted). Thus, the reviewing tribunal will defer to the relevant administrative agency’s decision unless there is a compelling reason to differ. S.C. Coastal Conservation League v. S.C. Dep’t of Health & Envtl. Control, 363 S.C. 67, 75, 610 S.E.2d 482, 486 (2005) (holding the circuit court should have deferred to the Panel’s decision because “there was no compelling reason to *206overrule the Panel’s decision that the [regulation] governed”). An agency’s interpretation of a statute or regulation that is erroneous or controlled by an error of law presents a compelling reason not to defer to the agency’s interpretation. See Brown v. Bi-Lo, Inc., 354 S.C. 436, 440-41, 581 S.E.2d 836, 838-39 (2003) (reversing the circuit court because the agency’s conclusions in the case were affected by an error of law); Sweat, 379 S.C. at 385, 665 S.E.2d at 655 (finding the State was “not entitled to any deference in its interpretation because the plain language of [the statute at issue] refute[d] the State’s position” and holding the Court was “free to read the statute based on its plain language without deference to the State’s position”). Thus, where the plain language of the statute is contrary to the agency’s interpretation, the agency’s interpretation should be rejected. Brown, 354 S.C. at 440, 581 S.E.2d at 838. In this case, DHEC has not followed the relevant law in issuing its final decision, as the Board erroneously believed it had the authority to enter into the Agreement with the Corps and the GPA prior to issuing its final decision. Therefore, compelling reasons obviate any deference to the Board’s decision in this case. DHEC usurped the Commission’s authority in settling with the Corps and the GPA before the final review conference in contravention of the express requirements of section 54-6-10. See S.C.Code Ann. § 54-6-10(A) (endowing the Commission with the exclusive power “to negotiate on behalf of the State of South Carolina and enter into agreements with the State of Georgia, the United States Corps of Engineers, and other involved parties.”).
Thus, we find the conditional staff denial of the Certification, which the Commission actively participated in formulating, is now the final agency decision for purposes of contested case review. See S.C.Code Ann. § 44-l-60(F) (Supp.2011) (“If a final review conference is not conducted within sixty days, the department decision becomes the final agency decision, and an applicant ... may request a contested case hearing before the [ALC].”).
For these reasons, Appellants’ request for a contested case hearing currently pending in the ALC is moot, as the relief Appellants ultimately seek is the conditional denial of the Certification. See Mathis v. S.C. State Highway Dep’t, 260 S.C. 344, 346, 195 S.E.2d 713, 715 (1973) (“A case becomes *207moot when judgment, if rendered, will have no practical legal effect upon [the] existing controversy. This is true when some event occurs making it impossible for [the] reviewing Court to grant effectual relief.”).
Therefore, we hold that the Certification is denied, and any future activity, including any negotiations concerning the Certification, must be directed to the Commission. See S.C.Code Ann. § 54-6-10(A).
BEATTY and HEARN, JJ., concur.. Under the federal Clean Water Act, any entity commencing a project that will create a discharge into waters of the United States must apply for a state certification that the project will comply with that state's water quality standards. 33 U.S.C. § 1341(a)(1). However, if a state “fails or refuses to act on a request for certification, within a reasonable period of time (which shall not exceed one year)” the state certification requirement is waived. Id. It is undisputed that DHEC “acted" for purposes of the state certification requirement.