BOTSFORD, J.

On August 7, 2009, the Energy Facilities Siting Board (board), acting pursuant to G. L. c. 164, § 69J¼ (§ 69J¼), approved the petition of Brockton Power Company LLC (Brockton Power or company), to build and operate a 350-megawatt combined-cycle energy generating facility (facility or project) powered by natural gas and ultra-low sulfur distillate (ULSD) in the city of Brockton (city). As approved by the board, the facility would use wastewater from the city's advanced wastewater reclamation facility (AWRF) for its cooling tower. In a consolidated appeal by three of the interveners, we affirmed the board's decision. See Brockton v. Energy Facilities Siting Bd. (No. 1), ante 196 (2014) (Brockton [No. 1]), decided today.

On April 9, 2010, while the consolidated appeal was pending, Brockton Power submitted a project change filing (PCF) to the board, seeking approval of three changes to its project. In the PCF, Brockton Power sought to: (1) change the source of the facility's cooling tower water from the AWRF to the Brockton municipal water supply (BMWS); (2) eliminate the use of ULSD as an alternative fuel and rely solely on natural gas as the facility's fuel; and (3) make certain changes in the design of the facility. After additional public comment, extensive discovery, testimony, and six days of evidentiary hearings that the board considered as a "continuation of the [o]riginal [p]roceeding," the board issued its PCF decision, denying Brockton Power's proposal to use BMWS but approving the two other project changes.4 Brockton Power appealed from the board's denial of the PCF with respect to the facility's water source,5 and the city appealed from the board's approval of the design and fuel changes. A single justice of this court reserved and reported the appeals to the full court. We affirm the board's final decision with respect to both appeals.

The scope of our review of the board's PCF decision is the same as in Brockton (No. 1), supra, and is set forth in G. L. c. 164, § 69P.6 The board's evidentiary rulings are entitled to deference, and the appellants bear the burden of showing that the board's decision is invalid. Alliance to Protect Nantucket Sound, Inc. v. Energy Facilities Siting Bd., 448 Mass. 45, 51 (2006) (Alliance I).

1. Board's authority to consider PCF as part of original proceeding. In its August 7, 2009, final decision, the board required Brockton Power to notify it of "any changes other than minor variations to the proposal so that the [board] may decide whether to inquire further into a particular issue." In addition to this general requirement, noting "the uncertainty ... around the availability of the Brockton AWRF water supply," the board directed Brockton Power to "work with the [city] regarding use of [the city's] AWRF water, and to provide a report to the [board] with respect to the outcome of such efforts." In the event that Brockton Power determined not to use the AWRF water and instead "to use potable [municipal] water for the majority of the water requirements of its proposed facility," the board directed the company to "provide a project change filing to the [board], together with a detailed analysis focused on those issues that are germane to the use of potable water, including opportunities for water conservation."

Consistent with this directive, on April 9, 2010, Brockton Power submitted its PCF to the board seeking approval of a change in the source of the facility's water supply for the cooling tower, approval of the nonuse of ULSD as an alternate fuel, and approval of building design changes. Over the objection of interveners, who argued that the PCF should be treated as a new petition, the board, as previously described, held evidentiary hearings on the PCF and issued a decision rejecting the proposed change in source of water supply for the cooling tower, but approving the two other changes.

Under § 69J¼, fifth and sixth pars., the board may approve, reject in whole or in part, or conditionally approve a petition for an electrical generating facility.7 The statute provides that "[i]n the event of rejection or conditional approval, the applicant may, within 180 days, submit an amended petition. Public and evidentiary hearings on the amended petition shall be held on the same terms and conditions applicable to the original petition." G. L. c. 164, § 69J¼, sixth par. See note 7, supra. The city contends that Brockton Power's PCF was an "amended petition" within the meaning of § 69J¼, sixth par., and because it was submitted on April 9, 2010, 245 days after the board issued its original decision, the board did not have the authority to consider it as part of the original proceeding — the window for filing an amended petition had already closed. According to the city, the board should have reviewed the PCF as a new petition, which would have required readjudication of the full range of issues the board considered in its original decision issued on August 7, 2009. The city's argument fails.

"We accord substantial discretion to an agency to interpret the statute it is charged with enforcing...." Alliance to Protect Nantucket Sound, Inc. v. Energy Facilities Siting Bd., 457 Mass. 663, 681 (2010). Moreover, "administrative agencies have broad discretion over procedural matters before them." Zachs v. Department of Pub. Utils., 406 Mass. 217, 227 (1989) (Zachs). We defer to an agency's procedural rulings and review them for "error of law or abuse of discretion." Id. This is so in particular when the ruling concerns whether to reopen a proceeding or an administrative record. See Alliance to Protect Nantucket Sound, Inc. v. Department of Pub. Utils. (No. 2), 461 Mass. 190, 193-194 & n.7 (2011); Box Pond Ass'n v. Energy Facilities Siting Bd., 435 Mass. 408, 420 (2001) (Box Pond).

The board determined that Brockton Power's PCF was not an "amended petition" within the meaning of § 69J¼, sixth par. As interpreted by the board, the "amended petition" provision is limited to an amended filing submitted by a project proponent within six months after the board has issued a final decision rejecting the original petition or imposing conditions from which the proponent seeks relief. The board contends that its power under § 69J¼, fifth and sixth pars., to approve a petition with conditions, combined with its ability to "issue orders with respect to any matter over which it has jurisdiction," see G. L. c. 164, § 69H, provides it with more than sufficient authority to include in a final decision an order requiring the project proponent to bring back to the board for potential review any proposed changes to the project that may affect the basis on which it was originally approved.

The board's interpretation of its "statutory mandate will be disturbed only if the interpretation is patently wrong, unreasonable, arbitrary, whimsical, or capricious." Box Pond, 435 Mass. at 416, quoting TBI, Inc. v. Board of Health of N. Andover, 431 Mass. 9, 17 (2000). Where, as here, the relevant statutes are silent on the means of enforcing compliance with its orders, the board has broad discretion to establish appropriate procedures. See Zachs, 406 Mass. at 227-228. An administrative agency may, as here, "adopt policies through adjudication as well as through rulemaking." Alliance I, 448 Mass. at 51, quoting Arthurs v. Board of Registration in Med., 383 Mass. 299, 312-313 (1981). The board's interpretation of § 69J¼, fifth and sixth pars., is a reasonable one to which we accord deference, and the procedure the board adopted to review potentially material changes to Brockton Power's project does not constitute an abuse of its discretion.8

2. Water source. The board in its original final decision approved Brockton Power's proposed use of water from the city's AWRF for the facility's cooling tower. Because the city refused to supply recycled wastewater from the AWRF for the facility, Brockton Power submitted a PCF based on the use of water from BMWS, which supplies potable water to the city. The board concluded that the environmental impacts associated with the Brockton Power's use of BMWS water failed to "minimize the environmental impacts consistent with the minimization of costs associated with the mitigation, control, and reduction of the environmental impacts of the proposed generating facility." G. L. c. 164, § 69J¼, fifth par.

Brockton Power argues that the board's analysis of environmental impacts intruded on the authority of the Department of Environmental Protection (DEP) was unsupported by substantial evidence. We disagree, and conclude that Brockton Power has not met its burden of showing that the board's decision is invalid. See Alliance I, 448 Mass. at 51.

The record reflects the following facts. The city draws its water supply from the Silver Lake system, the Brockton Reservoir, the Hubbard Avenue well and, beginning in 2008, a desalination plant owned and operated by Aquaria, LLC (Aquaria), in Dighton.9 The city's permits issued under the Water Management Act (WMA), G. L. c. 21G, authorize withdrawals of 11.94 million gallons per day (mgd) from the Silver Lake system and Brockton Reservoir.10 In addition, the city is authorized to purchase up to 4.07 mgd from Aquaria, which draws water from the Taunton River.11

In 1986, subsequent to a prolonged drought, the predecessor agency of the DEP issued an administrative order and emergency declaration that, among other requirements, directed the city to control water demand and withdrawals, and to develop new water sources. Thereafter, in 1995, an administrative consent order (ACO) replaced the emergency declaration. Pursuant to the ACO, the city reestablished its water commission and, among other measures, prepared a comprehensive water management plan concerning its water supply. In 1997, a modification to the ACO also established a "safe yield" of 10.33 mgd for the city from its then existing sources, which did not yet include the Aquaria plant. The ACO provides that in the event the city's water withdrawals exceed 11.3 mgd or 110 per cent of the "safe yield,"12 whichever is larger, the excess withdrawal will "constitute a request for the imposition of a [d]eclaration of [w]ater [e]mergency."13 From 1996 to 2010, the city's average annual water use was relatively constant, at approximately 10 mgd. In 2014, the city is estimated to require between 10.15 and 11.44 mgd of water from all sources. The ACO, and the safe yield limits, remain in effect.14

As proposed to be modified by the PCF, the facility's cooling tower will require 1.75 mgd of water at full capacity on a typical day, or 1.1 mgd on an average annual basis.15,16 During the summer electrical peak period, when the Silver Lake system is the most stressed, the facility is expected to use water at the rate of 2.1 mgd, roughly twice its estimated annual average rate.17

Brockton Power contends that BMWS readily can supply the volume of potable water necessary for the facility's cooling tower, essentially because, in Brockton Power's view, "most (if not all) of the incremental water needed to supply [the facility] will come from Aquaria rather than the city's historic system." The board disagreed, noting that the city had never had to manage the supply demand of a water customer the size of the Brockton Power facility, that the facility would account for more than ten per cent of the city's current water demand, and that despite greater flexibility in water withdrawal allocations due to Aquaria, "some, and possibly even a significant portion, of the [facility's] municipal water could come from Silver Lake." Noting that the city's water supply problems have resulted in significant environmental impacts to the Silver Lake system over the years and that Brockton Power had not provided evidence concerning the additional environmental impacts on that system that might result from Brockton Power's increased consumption for the project, the board concluded that Brockton Power had not met its burden to show that the environmental impacts of the proposed change would be minimized consistent with the minimization of related costs, as required by § 69J¼, fifth par.

On appeal, Brockton Power contends that the board impermissibly intruded into the DEP's statutory and regulatory authority as expressed in the ACO's threshold for triggering a declaration of water emergency for the city. Brockton Power argues that the DEP's "determination of safe yield as the basis for the 1995 ACO limit of 11.3 [mgd] specifically included minimization and balancing of environmental protection factors" to which the board was obligated to defer in conducting its review of the PCF. We disagree.

In evaluating a claim that the board's determination is arbitrary, capricious, or unsupported by substantial evidence, we "give[] great deference to the board's expertise and experience." Alliance I, 448 Mass. at 51. "In determining whether an agency decision is supported by substantial evidence, we must consider the record as a whole and reverse the agency's decision if `the cumulative weight of the evidence tends substantially toward opposite inferences.'" Boston Gas Co. v. Department of Telecomm. & Energy, 436 Mass. 233, 237 (2002), quoting Cobble v. Commissioner of the Dep't of Social Servs., 430 Mass. 385, 391 (1999). Here, Brockton Power has not met its burden of showing that board's decision was erroneous.

Pursuant to § 69J¼, fifth par., the board is the agency charged with determining whether a project proponent's petition is an accurate and complete description of the environmental impacts of the proposed facility, and also minimizes environmental impacts consistent with the minimization of costs associated with mitigation, control, and reduction of environmental impacts. "A permit issued by the board is only the first of many permits and licenses that will be required of a developer of a generating facility, and no other State agency may issue a construction permit for a generating facility until it has first been approved by the board." Andover v. Energy Facilities Siting Bd., 435 Mass. 377, 380 (2001) (Andover). The Legislature has provided for complementary but independent roles for the board and the DEP. Just as the board does not delegate or abdicate its statutory responsibility by recognizing the authority and expertise of the DEP over water management issues, see id. at 381, the board's independent exercise of its statutory authority does not intrude upon DEP's authority over issues relating to municipal water supplies under the WMA, G. L. c. 21G, §§ 3, 7.

In short, the board's and the DEP's mandates are not identical although they touch on many of the same environmental concerns; "sensible administrative coordination" between the two agencies is necessary.18 See Andover, 435 Mass. at 382. The board's approval of a petition to construct an energy facility will not necessarily satisfy the DEP's requirements for a permit for that facility under the WMA. Cf. id. at 380-381 (discussing different roles of board and DEP in relation to review of air emissions). Likewise, a DEP permit issued to a municipality under the WMA is not equivalent to a determination that a proposed facility would minimize environmental impacts as required by § 69J¼, nor does the existence of such a permit compel the board to grant a petition under that statute. Far from intruding on the DEP's authority, the board would have abdicated its statutory duties if it had based its decision on the proposed water source change wholly on the DEP's municipal water withdrawal determinations under the WMA.19

Moreover, the board's determination was supported by substantial evidence. In its PCF, Brockton Power contended that because the city was already withdrawing close to the limit of its ACO threshold from its traditional sources, the incremental water volume required by the facility would primarily come from the Aquaria plant, which provided a significant new source of potable water for the city. Consequently, Brockton Power urged, despite the city's historical water supply challenges, the facility would not have a negative effect on the environment of the Silver Lake system. As the board recognized, however, the city's water conservation efforts and stable population forecast made it likely that the city's withdrawals would remain under the ACO threshold. Moreover, Brockton Power had no control over the origins of the municipal water required by the facility, and given the city's view of the Aquaria plant as a supplemental source of its water needs, the volume required by the PCF might come entirely or at least in part from the Silver Lake system. Given the evidence that the city's municipal water withdrawals continue to have a significant environmental impact on the Silver Lake system, the board concluded that Brockton Power had not met its burden of proving that the environmental impacts of the incremental potable water usage from BMWS had been minimized consistent the requirements of § 69J¼, fifth par.

Brockton Power complains that the board did not analyze sufficiently the environmental impacts of the additional withdrawals anticipated by the PCF on the Silver Lake system, but this appears to have been the result of the position the company itself took before the board: the PCF filing proceeded on the assumption that most or all of the increased water required by the facility would come from the Aquaria plant.20 Nevertheless, it is apparent that the board did analyze and consider the effect of the proposed water use on the city's traditional water sources, including two studies and expert testimony indicating that the city's withdrawals have a continued impact on the environment of the Silver Lake system by degrading freshwater mussel habitat and increasing environmental stress on the Jones River, the major tributary of Silver Lake. Moreover, contrary to Brockton Power's assertion, the board considered the city's water conservation progress in light of continuing environmental challenges to the Silver Lake system and the facility's projected water needs.21

Although the board's denial of the PCF with respect to BMWS appears to preclude construction of the facility as currently proposed, we briefly review the city's appeal of the board's approval of the two other proposed changes.22

3. Elimination of ULSD capacity. As initially approved by the board, the facility would use ULSD as an alternative fuel for up to sixty days per year. In its PCF filing, Brockton Power proposed to construct the facility with natural gas-only generators, eliminating the facility's capacity to use ULSD.23 According to Brockton Power, a gas-only plant would reduce air emissions, visual impacts, most ULSD deliveries, and the facility's water requirements, while the expansion of gas supplies in the Northeast would guarantee the reliability of the facility's energy supply. The board found that a gas-only plant would "reduce the environmental impacts, consistent with the minimization of costs associated with the mitigation, control, and reduction of the environmental impacts" of the facility, as required by § 69J¼, fifth par.

On appeal, the city primarily asserts deficiencies with respect to the air emission findings in the board's original final decision.24 As stated previously, in reviewing a PCF, the board need not consider issues that have already been decided in the original decision. The board's PCF decision analyzed the PCF for accuracy and completeness and "compared the environmental impacts of the facility as originally approved with the environmental impacts of the project as changed." This approach is reasonable and consistent with the board's statutory mandate. See Zachs, 406 Mass. at 227 ("administrative agencies have broad discretion over procedural aspects of matters before them"). Our review of the city's appeal is limited to new issues raised by the PCF. See Box Pond, 435 Mass. at 419-420 (rejecting attempt to relitigate issues already decided in underlying proceeding). With respect to the elimination of ULSD fuel, we conclude that Brockton Power's PCF was accurate and complete, and "minimize[d] the environmental impacts consistent with the minimization of costs associated with the mitigation, control, and reduction of the environmental impacts." G. L. c. 164, § 69J¼, fifth par.

The record indicates that with the elimination of ULSD, the emissions of all criteria pollutants will be reduced from the level estimated in the original petition, which the board has already approved (and we have upheld).25 Accordingly, there is no basis upon which the board could have concluded that the PCF would not minimize environmental impacts, as required by G. L. c. 164, § 69J¼, fifth par.26 The city has not met its burden of showing that the board's decision is invalid, unsupported by substantial evidence, or an abuse of discretion. See Alliance I, 448 Mass. at 51.

The city also argues that the board erred by underestimating the carbon monoxide (CO) emissions from the facility by basing its analysis on Brockton Power's allegedly inaccurate estimates of plant "start-up and shut-down" events.27 In its PCF decision, the board noted that the city and Brockton Power disagreed about the modeling of the CO emissions. Without analyzing the dispute, the board noted Brockton Power's lower figures and stated that the facility would be subject to "enforceable annual and hourly limits ... set out in [the DEP's] Conditional Air Plan Approval." Brockton Power's CO emissions estimate, 98.5 tpy, represents 8.6 per cent of the NAAQS threshold for one-hour CO, and 18.9 per cent of the NAAQS threshold for eight-hour CO. Although the city's estimate of 138.8 tpy is higher than Brockton Power's, it is still well below the NAAQS limit for this pollutant. The board is entitled to rely on the NAAQS thresholds to determine whether a project proposal has minimized the environmental impacts pursuant to its review. See Brockton (No. 1), supra at 207-208. The board did not err by concluding that the CO emissions from a gas-only plant satisfied the standards of § 69J¼, fifth par.

4. Structural design changes. In the original final decision, the board declined to grant Brockton Power's requested zoning exemption under G. L. c. 40A, § 3, which would have excused the facility from the Brockton zoning ordinance. Brockton Power did not appeal this aspect of the board's original decision. In its PCF, however, Brockton Power proposed three changes to the facility as approved in the underlying decision, which, in its view, would make the facility compliant with the city's zoning ordinance.28 Although the board took no position on whether the modifications would meet the city's zoning ordinance, it analyzed the changes with respect to noise and visual impacts, and concluded that the changes minimized the facility's environmental impacts as required by G. L. c. 164, § 69J¼, fifth par.29

On appeal, the city argues that the board erred by approving a project that does not comply with a local zoning ordinance. This argument is without merit. In contrast to the minimization of visual and noise impacts, compliance with local zoning is not a precondition for the approval of a siting petition under § 69J¼. The board's determination that zoning issues were "outside the scope" of its § 69J¼ review is reasonable.

5. Conclusion. We affirm the board's PCF decision in all respects.

So ordered.