The town of Hull (town) appeals from a judgment affirming a decision of the Massachusetts Commission Against Discrimination (commission). The commission found that the town discriminated against defendant Donald Gillis on the basis of age and handicap in violation of G. L. c. 151B, § 4, when it failed to reinstate him as a firefighter upon his return from disability retirement. The commission awarded Gillis $63,106.47 in damages for lost wages, $50,000 in damages for emotional distress, and $61,212.28 in attorney’s fees and costs, and further ordered the town to pay $94,760.02 to the Hull Retirement Board (board), in repayment of the retirement benefits the board had paid to Gillis after the town’s discriminatory act.

The town claims that the commission’s decision is based on errors of law and is not supported by substantial evidence. See G. L. c. 30A, § 14(7)(c), (e). For reasons we explain below, we affirm the lost income and emotional distress damage awards and accompanying attorney’s fees, but conclude that the commission erred in ordering reimbursement of disability income benefits paid by the board.

Background. Gillis began work as a firefighter for the town in November, 1965. In 1985, he fell from a fire truck and was injured. Gillis was found disabled from returning to work and was put on disability retirement by the board.

In late 1994, when Gillis was approximately fifty-eight years *527old, the board required Gillis to undergo a medical examination. See G. L. c. 32, § 8(1), as in effect prior to its amendment by St. 1996, c. 306, § 16 (the “1996 amendment”). The appointed physician reported that Gillis’s injury had resolved and that he now could perform firefighter duties. The board, in turn, requested the approval of the chief of Hull’s fire department for Gillis’s reinstatement, which was then required under G. L. c. 32, § 8(2). See Milton v. Personnel Administrator of the Dept. of Personnel Admn., 406 Mass. 818, 825-826 (1990). In a letter to the board, the fire chief refused his approval.

A hearing before the board followed in March, 1995, where Gillis asked the fire chief why he had refused to approve Gillis’s reinstatement. The chief responded, “I like you, Don, but I have to think of the town. I’ll get more bang for the buck by hiring a younger guy.” During this period, the commission’s hearing officer found, there were two vacant firefighter positions available, which the town filled with two men aged thirty-two and thirty.

Discussion. Many of the town’s arguments on appeal challenge determinations by the hearing officer that the fire chief’s testimony before the hearing officer was not credible. The hearing officer is the sole judge of the credibility of the witnesses appearing before her, and thus these arguments must fail. See School Comm. of Brockton v. Massachusetts Commn. Against Discrimination, 423 Mass. 7, 15 (1996). We address each of the town’s more substantial arguments in turn.

1. The commission’s authority to delegate public hearings to hearing officers. The town argues that the commission unlawfully delegated the public hearing in this case to a hearing officer, where the governing statute requires either the full commission or a single commissioner to conduct all public hearings. The town acknowledges that a regulation promulgated by the commission permits qualified hearing officers to conduct public hearings for the commission, see 804 Code Mass. Regs. § 1.21(1) (1998),2 but claims that this regulation exceeds the *528commission’s statutory authority.3

General Laws c. 151B, § 3(6), inserted by St. 1971, c. 923, provides that “[t]he commission through its chairman may appoint a single commissioner to hold public hearings, as hereinafter provided, and to otherwise act on its behalf in connection therewith; provided, however, that a person aggrieved by the decision of said single commissioner may, within ten days of said decision, file an appeal for rehearing or review by the commission.” General Laws c. 6, § 56, as appearing in St. 1990, c. 150, § 194, provides that “[e]ach commissioner shall hold such hearings as are needed in the respective region, but each commissioner may also hold hearings in other regions.”

These provisions do not explicitly require that public hearings be conducted by only the full commission or a single commissioner. General Laws c. 151B, § 3(6), can be read as authorizing a single commissioner to hold public hearings, as contrasted with the entire commission. Likewise, G. L. c. 6, § 56, can be read as merely clarifying that commissioners are not restricted to their designated regions for purposes of holding public hearings. Neither provision expressly prohibits the commission from delegating public hearings to officials other than commissioners.

“An administrative agency has the authority to promulgate regulations giving effect to legislative mandates.” Massachusetts Fedn. of Teachers, AFT, AFL-CIO v. Board of Educ., 436 Mass. 763, 773 (2002). See id. at 773-774, and cases cited. “[T]he validity of a regulation . . . will be sustained so long as it is ‘reasonably related to the purposes of the enabling legislation.’ ” Consolidated Cigar Corp. v. Department of Pub. Health, *529372 Mass. 844, 855 (1977), quoting from Mourning v. Family Publications Serv., Inc., 411 U.S. 356, 369 (1973).

Under its enabling statutes, the commission may “appoint such attorneys, clerks, and other employees and agents as it may deem necessary, . . . and prescribe their duties.” G. L. c. 151B, § 3(3), inserted by St. 1946, c. 368, § 4. Further, the Legislature has granted the commission the power to “adopt, promulgate, amend, and rescind rules and regulations suitable to carry out the provisions of [c. 151B], and the policies and practice of the commission in connection therewith.” G. L. c. 151B, § 3(5), inserted by St. 1946, c. 368, § 4.

The commission has only three commissioners. See G. L. c. 6, § 56. According to the commission’s brief, in the year 2000 (the year of the hearing officer’s decision in Gillis’s case), 4,000 cases were filed with the commission. The commission’s delegation to hearing officers of its duty to hold public hearings, subject to later review by the commission, effectuates the commission’s legislative mandate. The regulation is reasonably related to the purpose of c. 151B, which requires the holding of public hearings and the making of findings of fact in a large number of discrimination claims in pursuit of its purpose to implement the right to equal treatment guaranteed to all citizens. See Katz v. Massachusetts Commn. Against Discrimination, 365 Mass. 357, 366 (1974).

Both this court and the Supreme Judicial Court have routinely considered and affirmed many decisions of the commission where a hearing officer conducted the public hearing.4 Those cases illustrate that the practice of assigning hearing officers to conduct public hearings has been accepted without question over many years. Given the long acceptance of the practice and the deference we accord to the interpretation of its constituent law by the agency the Legislature authorized to execute the statutory policy, see Haines’s Case, 71 Mass. App. Ct. 845, 846 *530(2008), we would be reluctant at this late date, and in the absence of explicit statutory language requiring us to do so, to find a jurisdictional defect in the way the commission has been conducting its business for many years.

For all of these reasons, we conclude that the commission did not exceed its statutory authority in promulgating 804 Code Mass. Regs. § 1.21(1) (1998), or in delegating the public hearing in Gillis’s case to a hearing officer.

2. Regional medical panel requirement. The town argues that the commission committed an error of law by finding that Gillis was qualified for reinstatement to a firefighter position. Under the version of G. L. c. 32, § 8(2), in effect at the time, the statute had three prerequisites for reinstatement: (1) a determination by a regional medical panel that the retiree is qualified to perform the duties of the position; (2) a vacancy in the retiree’s former department; and (3) the approval of the department head.5 See Milton v. Personnel Administrator of the Dept. of Personnel Admn., 406 Mass, at 825. The town claims that, because Gillis had been cleared by only a single physician and not a regional medical panel, Gillis was not eligible for reinstatement, irrespective of the fire chief’s approval; thus, the fire chief’s refusal to approve Gillis’s reinstatement, whether or not discriminatory as alleged, was not the operative factor causing Gillis to be precluded from reinstatement, as Gillis did not otherwise meet the statutory requirements for reinstatement.

The hearing officer’s determination that the fire chief prevented Gillis’s reinstatement was a finding of fact supported by substantial evidence. The hearing officer found that, had the fire chief approved Gillis’s reinstatement, the board would have initiated the process for a regional medical panel to examine Gillis and that the panel would have cleared Gillis for reinstatement.6 The fire chief’s refusal to approve Gillis’s reinstatement, in other words, caused the reinstatement to grind to a *531halt, simply because there was no point in conducting the examination if the chief would not accept Gillis back in any event. See G. L. c. 151B, § 4(1C), (16).

The town argues that the commission’s decision, notwithstanding its support in the evidence, is in conflict with our unpublished decision in Gillis v. Hull, 53 Mass. App. Ct. 1108 (2001), which held that Gillis’s demand for reinstatement following the 1996 amendment was properly denied by the board because Gillis had not met the remaining prerequisite for reinstatement, namely, clearance by the regional medical panel.7 The argument is unavailing to efface the effect of the town’s discrimination in 1995. Our decision spoke to a later time when the department head’s approval was no longer required for reinstatement under G. L. c. 32, § 8(2). Our decision at that time is res judicata only for the proposition that Gillis was not eligible for reinstatement as of August 31, 1999, because he had not at that time been cleared by the regional medical panel. It had nothing to do with the question whether the fire chief’s refusal in 1994-1995 was discriminatory (or whether his refusal was the reason for Gillis’s remaining on disability retirement).

Following approval by the regional medical panel in 2000, Gillis was theoretically eligible for reinstatement as a firefighter, provided there was then a vacancy in the fire department, see G. L. c. 32, § 8(2)(a), second par., as appearing in St. 1998, c. 252, § 2, and provided that he successfully completed a retraining program required by G. L. c. 31, § 39, for public employees returning to active service from disability retirement after more than five years’ separation from the job. *532See Sullivan v. Brookline, 435 Mass. 353, 359-363 (2001). The record does not disclose whether there was then a vacancy; moreover, it does not disclose that Gillis ever began or successfully completed the required retraining. In any event, by sometime in 2001, Gillis would reach the mandatory retirement age for firefighters (see note 11, infra). It is possible that time simply ran out. Notwithstanding the 1996 amendment (implemented in November of that year), the record does not disclose that the effect of the fire chief’s discrimination came to a definitive end anytime before Gillis aged out of the possibility of restoration to active service. The record, therefore, supported the commission’s award of lost income damages for the entire period.8

3. Other issues, a. Reimbursement for payment of disability pension benefits. The part of the commission’s order directing the town to reimburse the board for $94,760.02 in disability pension benefits disbursed for the same period (August 1, 1995, through March 31, 2000) must be struck from the commission’s award, because the board, although originally a party to the proceedings before the commission, had withdrawn at an early stage, with the agreement of all parties. The commission could not make an award in favor of a nonparty for the reasons stated in D’Errico v. Assessors of Woburn, 384 Mass. 301, 305 (1981), and Demoulas v. Demoulas, 428 Mass. 555, 591 (1998). Compare Brothers Bldg. Co. of Nantucket, Inc. v. Yankow, 56 Mass. App. Ct. 688, 693-694 (2002) (arbitration award). Moreover, no basis has been shown in these proceedings for the board or the State Retirement System to be reimbursed for all or any part of its disability pension payments during the subject period.9

b. Emotional distress damages. We have considered the town’s *533arguments with respect to the excessiveness of the award ($50,000) for emotional distress. The argument is predicated on Stonehill College v. Massachusetts Commn. Against Discrimination, 441 Mass. 549, 576, cert, denied sub nom. Wilfert Bros. Realty Co. v. Massachusetts Commn. Against Discrimination, 543 U.S. 979 (2004). After the Stonehill decision came down, the Superior Court remanded the present case to the commission for reconsideration of the damages for emotional distress in light of Stonehill. The hearing officer buttressed her earlier award with more detailed findings, and the commission then confirmed that portion of its award, with a further award of attorney’s fees ($23,204) for the work involved in the remand. We have no basis for concluding that the evidence did not support the findings of the hearing officer and the commission on the appropriate measure of compensation to Gillis for emotional distress. See Smith v. Bell Atl., 63 Mass. App. Ct. 702, 723-724 (2005); School Comm. of Norton v. Massachusetts Commn. Against Discrimination, 63 Mass. App. Ct. 839, 849 (2005).

c. Other issues. No issue is made in this appeal on the size of the attorney’s fee award, either as part of the commission’s original order, or as part of the order on remand. As the issue is not argued, we do not consider it.10

Conclusion. The second paragraph of the judgment of the *534Superior Court is modified to require that paragraphs number 4 (relating to reimbursing the town retirement board) and 5 (reinstatement of Gillis* 11 to the position of firefighter) of the commission’s order dated March 18, 2003, be struck, and to affirm the decision of the commission in all other respects. As so modified, the judgment of the Superior Court is affirmed.

Gillis’s request for appellate attorney’s fees is allowed. He may submit a petition therefor, together with supporting materials, within fourteen days of the date of the rescript of this opinion. The town shall have fourteen days thereafter to respond. See Fabre v. Walton, 441 Mass. 9, 10-11 (2004).

So ordered.