¶1 In 2003, our legislature made substantial amendments to this state’s water law. In 2010, we found those amendments facially constitutional. Today, Scott Cornelius, Palouse Water Conservation Network, and Sierra Club Palouse Group (collectively Cornelius) bring an as-applied constitutional claim (among other claims) against Washington State University (WSU), the Department of Ecology, and the Pollution Control Hearings Board (PCHB). We find the amendments were applied constitutionally and find the other claims unavailing. We affirm.
FACTS
¶2 Cornelius and WSU both draw water from the Grande Ronde Aquifer underlying the Palouse Basin. The aquifer is declining from overpumping. WSU has seven groundwater rights that serve its Pullman campus with priority dates ranging from 1934 to 1987. These rights are documented by claims, permits, or certificates depending on when the rights were perfected. Two certificates are primarily at issue in this case: 5070-A and 5072-A. Although the documents for some of WSU’s rights state that their purpose was “municipal,” the documents for Certificate Nos. 5070-A and *5835072-A state their purpose as “domestic.” 4 Admin. Record (AR) Doc. 85, at 5 (Order on Summ. J.). The holders of “municipal” water rights are now entitled to added protections under the law. See RCW 90.14.140(2)(d). There was no added protection for “municipal” water rights when Ecology-issued Certificate Nos. 5070-A and 5072-A.
¶3 Ecology issued Certificate No. 5070-A in 1962 and Certificate No. 5072-A in 1963. When Ecology granted those certificates, it did so on the basis of system capacity rather than beneficial use. Those two certificates, as well as the document representing WSU’s other water rights, assigned the water rights to particular wells. However, over the years, WSU has integrated and consolidated its water system, shifting almost all of its groundwater pumping from older wells to two newer wells drawing from the same aquifer. WSU admits Ecology did not previously authorize that integration, and no court has previously adjudicated WSU’s water rights. However, after the legislature enacted the municipal water law (MWL) in 2003, Laws of 2003, 1st Spec. Sess., ch. 5, WSU applied to Ecology to amend its water right permits and certificates to conform to its actual usage. WSU wanted to legitimize its integrated system, and it sought to amend its certificates to explicitly authorize it to withdraw the aggregate quantity of water represented by all its relevant water rights from the two wells it uses today. Notice of WSU’s application appeared in the Moscow-Pullman Daily News as required by statute, and Cornelius timely protested. RCW 90.03.280.
¶4 Processing WSU’s applications required Ecology to apply a number of common law principles and statutes such as the common law of abandonment, the water code, and the State Environmental Policy Act (SEPA), chapter 43.21C RCW. Ecology also applied the MWL. Ultimately, Ecology approved all but one of WSU’s applications.1 Cornelius appealed Ecology’s decision approving the other applica*584tions to the PCHB, an independent agency authorized to hear certain environmental appeals under RCW 43.21B-.110, on various grounds. The PCHB ruled in favor of WSU and Ecology on all issues, some on summary judgment and some after a hearing. Cornelius appealed to the Whitman County Superior Court, which affirmed the PCHB, and to the Court of Appeals, which certified the case to us. We accepted certification.
ISSUES
¶5 1. Is the MWL unconstitutional as applied to Cornelius?
¶6 2. Did the PCHB err by allowing Ecology to use a streamlined process for evaluating WSU’s application?
¶7 3. Does RCW 90.44.100 authorize WSU to amend its certificates and add well locations?
¶8 4. Did the PCHB correctly apply SEPA?
¶9 5. Did the PCHB’s summary judgment order improperly preclude Cornelius from presenting evidence about impairment and the public welfare?
¶10 6. Did RCW 90.44.130 require Ecology to determine if WSU’s proposal would maintain a “safe sustaining yield” of groundwater?
¶11 7. Did WSU exercise reasonable diligence in putting its water rights to beneficial use?
¶12 8. Did WSU abandon Claim No. 98523?
¶13 9. Did the PCHB err in granting WSU’s summary judgment motion regarding beneficial use and reasonable efficiency?
¶14 10. Did the water quantities authorized under Permit No. G3-28278P need to be reduced?
¶15 11. Is Cornelius entitled to attorney fees?
STANDARD OF REVIEW
¶16 The Washington Administrative Procedure Act (APA), chapter 34.05 RCW, governs our review of PCHB *585orders. See RCW 34.05.570(1). We sit in the same position as the superior court and apply the APA to the administrative record. Postema v. Pollution Control Hr’gs Bd., 142 Wn.2d 68, 77, 11 P.3d 726 (2000). We will grant relief from an order if we determine that it is based on an unconstitutional statute, an erroneous interpretation or application of the law, or insufficient evidence, among other things. RCW 34.05.570(3)(a), (d), (e). “The burden of demonstrating the invalidity of agency action is on the party asserting invalidity” — Cornelius in this case. RCW 34.05.570(l)(a). We review questions of law and an agency’s application of the law to the facts de novo, but we give the agency’s interpretation of the law great weight where the statute is within the agency’s special expertise. Port of Seattle v. Pollution Control Hr’gs Bd., 151 Wn.2d 568, 593, 90 P.3d 659 (2004). We will overturn an agency’s factual findings only if they are clearly erroneous. Id. at 594. Finally, many of the PCHB’s rulings were made on summary judgment, which we review de novo, making the same inquiry as the PCHB. See Owen v. Burlington N. Santa Fe R.R. Co., 153 Wn.2d 780, 787, 108 P.3d 1220 (2005).
ANALYSIS
1. Constitutional Claims
. ¶17 Cornelius argues that the MWL cannot be applied in this case without violating his due process rights and the separation of powers doctrine. He argues both of these doctrines were violated when Ecology applied the MWL to WSU and approved WSU’s groundwater amendment application. Cornelius claims those constitutional doctrines were violated when Ecology and the PCHB “reviv[ed]” WSU’s allegedly relinquished groundwater rights. Appellants’ Opening Br. at 20.
¶18 Before we address Cornelius’s as-applied constitutional claims, it is helpful to review Washington’s water laws and our recent decision in Lummi Indian Nation v. *586State, 170 Wn.2d 247, 241 P.3d 1220 (2010), which dealt with the facial constitutional challenge to the MWL underlying the conflict here.
A. Washington Water Law and Lummi Indian Nation
¶19 Washington, like other western territories in the late 1800s, followed a water law system called “prior appropriation.” Ellis v. Pomeroy Improvement Co., 1 Wash. 572, 578, 21 P. 27 (1889). Prior appropriation is a system of “first in time . . . first in right,” and our legislature formally recognized that system in 1917. Laws of 1917, ch. 117, § 1 (currently codified as RCW 90.03.010). Prior appropriation focuses on the beneficial use of water and generally provides that a person’s right to the beneficial use of water is superior to others if he or she first appropriated the water for beneficial use. Id.
¶20 Washington still follows the general prior appropriation system but has a regulatory permit scheme to balance and prioritize competing beneficial uses of the state’s waters. Put simply and very generally, would-be users submit applications to Ecology and Ecology determines what water is available and to what beneficial use it can be applied before issuing permits. Lummi Indian Nation, 170 Wn.2d at 252-53; RCW 90.03.290(1). Permits represent inchoate water rights, which are not choate (i.e., vested) until perfected. Lummi Indian Nation, 170 Wn.2d at 253; RCW 90.03.330. Before the right is perfected, the applicant still has an incomplete appropriative right in good standing, but he or she must act with reasonable diligence to perfect the right by developing the water system. RCW 90.03.320; Lummi Indian Nation, 170 Wn.2d at 253. Ecology can cancel the permit if the permit’s terms are violated. RCW 90.03.320. Once the water right is perfected, Ecology issues a certificate. RCW 90.03.330. Importantly, the perfected right evidenced by the certificate relates back to the date the applicant filed the original application with Ecology. RCW 90.03.340. Thus, the date a water right vests is often determined by the date the application was filed.
*587¶21 Ecology and its predecessor have applied the perfection doctrine inconsistently over the years. Lummi Indian Nation, 170 Wn.2d at 254-55. Initially, water users needed to both appropriate water and put it to beneficial use before they could perfect their right. See, e.g., Ortel v. Stone, 119 Wash. 500, 503, 205 P. 1055 (1922). However, in the 1950s, Ecology and its predecessor issued both permits and certificates based on a user’s need and capacity rather than on its actual beneficial use; this different approach was aptly named “ ‘pumps and pipes.’ ” Dep’t of Ecology v. Theodo-ratus, 135 Wn.2d 582, 587, 957 P.2d 1241 (1998). Tension arose because of this inconsistency, and it led to our decision in Theodoratus.
¶22 George Theodoratus had a water right application approved by Ecology for a development he planned to build. Id. Ecology’s “Report of Examination” approving his application had language purporting to create a vested water right based on his development’s capacity for water so long as it was built by a particular date. Id. Under the original report, Theodoratus would have been entitled to a certificate and his rights would have thus vested once he completed his water supply system and it was capable of delivering water — regardless of actual beneficial use. Id. Theodoratus was delayed in completing the development, and Ecology granted him several permit extensions, the last of which placed conditions on his water rights vesting. Id. at 587-88. The conditions provided, among other things, that his vested water right would be determined based on actual application of water to beneficial use, not on system capacity. Id. at 588. Theodoratus appealed Ecology’s condition, and we eventually held that the relevant statutes and our common law left no doubt that Theodoratus’s vested water rights must be based on beneficial use — not system capacity. Id. at 590. We noted, however, that our decision did not involve “municipal water suppliers,” which are treated differently under our “statutory scheme.” Id. at 594.
¶23 Specifically, since 1967, our statutory scheme has treated water rights claimed for municipal water sup*588ply purposes as immune from statutory relinquishment, while nonmunicipal water rights may be relinquished through nonuse. Laws of 1967, ch. 233, § 18 (codified as RCW 90.14.180); cf. Laws of 1967, ch. 233, § 14 (codified as RCW 90.14.140(2)(d)). Generally, a nonmunicipal water right holder relinquishes all or part of its right if it fails to beneficially use the water right for five successive years without sufficient cause. RCW 90.14.180; see RCW 90.14-.140(2)(d). However, despite this favorable treatment, until recently, our laws did not define “municipal water supplier” or “municipal water supply purposes.”
¶24 This ambiguity in the water code, combined with our Theodoratus decision, caused water users concern about the validity of their water rights based on system capacity and whether their water rights were subject to relinquishment. In response, our legislature amended the water law act. Lummi Indian Nation, 170 Wn.2d at 256; Laws of 2003, 1st Spec. Sess., ch. 5; Second Engrossed Second Substitute H.B. 1338, 58th Leg., 1st Spec. Sess. (Wash. 2003) (2E2SHB 1338). In addition to defining “municipal water supplier” and “municipal water supply purposes” for the first time, the law declared that water right certificates issued prior to September 9, 2003, for municipal water supply purposes based on system capacity were in good standing. Lummi Indian Nation, 170 Wn.2d at 256-57 (citing Laws of 2003, 1st Spec. Sess., ch. 5; 2E2SHB 1338; H.B. Rep. on 2E2SHB 1338, at 1-2). It further provided that after September 9, 2003, Ecology must issue certificates based on the actual beneficial use of water. Id. at 257 (quoting RCW 90.03-.330(4)). As we' stated in Lummi Indian Nation, “The legislation essentially put the legislature’s imprimatur on our holding in Theodoratus prospectively while confirming the good standing of water certificates issued under the former system.” Id.
¶25 The amendments garnered opposition from various groups and ultimately led to our Lummi Indian Nation decision. In that case, two groups of challengers (including *589Cornelius) brought facial constitutional challenges, arguing that the amendments, specifically RCW 90.03.015(3) and (4) and RCW 90.03.330(3), violated separation of powers and due process. Id. at 259, 265. The challengers argued the amendments violated separation of powers by changing the requirements we noted in Theodoratus for private water rights to vest and thereby unsettling our decision. Id. at 259-60. As discussed further below, we found no separation of powers violation because the legislature did not “apply the law to an existing set of facts, affect the rights of parties to the court’s judgment, . . . interfere with any judicial function,” or adjudicate facts. Id. at 263. The challengers argued that the amendments violated due process by potentially depriving junior water users of vested rights by “ ‘resurrecting’ ” the relinquished water rights of potentially senior rights holders. Id. at 268-69. Again, as discussed further below, we found that the amendments by themselves did not resurrect any relinquished rights and did not deprive junior water rights holders of vested property rights. Id. We left “for another day consideration of any as-applied challenges.” Id. at 263. Today is that day.
B. Separation of Powers
¶26 The doctrine of separation of powers “ ‘preserves the constitutional division between the three branches of government’ ” and ensures that the activities of one branch do not “ ‘threaten or invade the prerogatives of another.’ ” In re Estate of Hambleton, 181 Wn.2d 802, 817, 335 P.3d 398 (2014) (quoting State v. Elmore, 154 Wn. App. 885, 905, 228 P.3d 760 (2010)); Zylstra v. Piva, 85 Wn.2d 743, 750, 539 P.2d 823 (1975). The legislature violates separation of powers when it applies “the law to an existing set of facts, affect[s] the rights of parties to the court’s judgment, . . . interfere [s] with any judicial function,” or adjudicates facts. Lummi Indian Nation, 170 Wn.2d at 263. The legislature is occasionally disappointed with our interpretation of a statute, and it may amend statutes within its *590sphere of authority and may sometimes apply the amended statute retroactively; however, the legislature may not retroactively reverse decisions of this court or interfere with any judicial functions. Hale v. Wellpinit Sch. Dist. No. 49, 165 Wn.2d 494, 509-10, 198 P.3d 1021 (2009). “[W]hen the legislature passes a statute premised on finding an adjudicative fact” or if it interferes with someone’s previously litigated vested rights, “it may violate separation of powers.” Lummi Indian Nation, 170 Wn.2d at 264-65.
¶27 Cornelius first claims that by adjudicating facts, the PCHB interpreted the MWL in the manner we stated in Lummi Indian Nation would violate the separation of powers doctrine. In that case, we were careful not to prejudge whether water rights holders could bring a successful as-applied challenge if their previously adjudicated water rights were sufficiently affected by the MWL. See id. at 265. But Cornelius’s as-applied challenge is a thinly veiled facial challenge, and it fails.
¶28 Cornelius argues that when the PCHB applied the MWL in this case, it changed the past status of WSU’s water rights — rights that had already been relinquished by operation of law though not yet memorialized by Ecology or in a court opinion. He claims that because WSU’s two certificates were not issued specifically for “municipal water supply purposes,” WSU’s failure to use the water for more than five years prior to 2003 relinquished WSU’s water rights. Appellants’ Opening Br. at 22-24. And because, he contends, WSU’s rights were relinquished through nonuse, the PCHB ran afoul of the separation of powers doctrine by applying the MWL and “chang [ing] that legal conclusion.” Id. at 19-20.
¶29 We disagree. Retroactive application of a statute does not necessarily violate separation of powers— there must be some interference either with vested rights or with the prerogatives of another branch of government. Hale, 165 Wn.2d at 507-10; Lummi Indian Nation, 170 Wn.2d at 262. In Lummi Indian Nation, we already held *591that retroactively applying the MWL does not violate the constitution — including RCW 90.03.560, the amendment that allows for water rights to be relabeled using the new definition of “municipal water supply purposes.” 170 Wn.2d at 260-63, 272. We found that allowing this statute to apply retroactively is a legislative policy decision — confirming existing rights — not a factual adjudication. Id. at 264-65. Although we stated that retroactive application of this statute could unconstitutionally disturb previously litigated adjudicative facts, we must be faced with previously litigated adjudicative facts in order to find an as-applied constitutional violation.
¶30 Here, there are no previously litigated adjudicative facts regarding WSU’s past water rights. Accordingly, there is no way that the PCHB violated the separation of powers doctrine by applying the MWL to WSU’s certificates — there were no “adjudicative facts” the PCHB could have upset. Id. at 265. The PCHB merely applied the MWL definition to WSU in the current adjudication. That is the precise general application of the MWL we found constitutional in Lummi Indian Nation. Id. at 260-63, 272.
¶31 Cornelius would have us overrule Lummi Indian Nation in all but name. Cornelius would have us rule that the purpose of use stated on water right certificates must control — that only certificates stating a “municipal” purpose can be treated as municipal. That holding would invalidate RCW 90.03.560 on its face and overrule Lummi Indian Nation, where we held that the new definition of “municipal water supply purposes” applies retroactively, even to rights that were not originally labeled “municipal.” Id. at 268-69.
¶32 RCW 90.03.560 demonstrates that the legislature foresaw that too much weight might be placed on the characterizations of water rights holders and water rights use on certificates issued before “municipal” was defined. The legislature created a mechanism to fix this problem. The statute states in relevant part:
*592When requested, by a municipal water supplier or when processing a change or amendment to the right, the department shall amend the water right documents and related records to ensure that water rights that are for municipal water supply purposes, as defined in RCW 90.03.015, are correctly identified as being for municipal water supply purposes. This section authorizes a water right or portion of a water right held or acquired by a municipal water supplier that is for municipal water supply purposes as defined in RCW 90.03.015 to be identified as being a water right for municipal water supply purposes.
RCW 90.03.560 (emphasis added). Thus, the legislature recognized that some water rights had been issued for municipal purposes under nonmunicipal labels and provided a simple mechanism to fix that problem. And as we held in Lummi Indian Nation, allowing this statute to apply retroactively is a legislative policy decision — confirming existing rights — not a factual adjudication. 170 Wn.2d at 264-65.
¶33 This case exemplifies the labeling problem the legislature sought to resolve in passing RCW 90.03.560. When the relevant certificates were issued in 1962 and 1963, Ecology did not have a reason to be precise about distinguishing “municipal” and domestic uses because “municipal water supply purposes” was undefined and the legislature did not give municipal suppliers an exemption from relinquishment until 1967. See id. at 255-56; Laws or 1967, ch. 233, § 14 (currently codified as RCW 90.14.140). Thus, Ecology could have issued domestic supply certificates to entities that were functionally municipal and vice versa.
¶34 That is clearly the case here. WSU is a major public university that provides on-campus housing for thousands of residents. The relevant certificates give WSU the right to pump over 971 million gallons of water per year to service its large population, and Ecology’s report prepared in 1962 in response to WSU’s permit application for Certificate No. 5070-A specifically states that the recommended quantity *593is based on “the anticipated amount required for 15,000 students.” Ex. A-ll, at 2. Moreover, it is undisputed that WSU’s water system far exceeds the necessary number of residential service connections to qualify as a municipal water supplier under the current definition of “municipal water supply purposes.” It makes no sense to say that in 1962 and 1963, Ecology issued WSU the right to pump over 971 million gallons of water per year but never intended WSU to use that water for municipal purposes. We refuse to elevate form over substance and overrule Lummi Indian Nation. The PCHB correctly confirmed WSU’s existing water rights by applying RCW 90.03.560. Under that statute, WSU is deemed to have always been a municipal supplier, and that determination does not violate separation of powers because it upsets no adjudicative facts.
C. Due Process
¶35 Cornelius next claims that the PCHB violated his due process rights as a junior water user when it “revive [d]” WSU’s relinquished senior water rights. Appellants’ Opening Br. at 20. He argues the revival moved him “further down the line” of water rights. Id. Again, Cornelius’s as-applied challenge is a thinly veiled facial challenge and fails.2
¶36 Cornelius again cites to Lummi Indian Nation to support his argument. He claims we held in that case that the MWL did not resurrect rights already lost and that when water right applicants apply to amend their certificates, Ecology is required to determine which water rights *594have been relinquished pursuant to RCW 90.03.330(2) and RCW 90.44.100. Thus, he argues that here, Ecology unconstitutionally applied the MWL to WSU’s water rights because it resurrected a relinquished water right.
¶37 We disposed of this argument in Lummi Indian Nation. We held in Lummi Indian Nation that merely relabeling a previously granted water right as “municipal” does not violate due process, provided the water user falls under the new municipal definition. See 170 Wn.2d at 265-67. We stated,
[T]hese amendments confirm what the department has already declared (that certain water rights are rights in good standing) and statutorily define something that had previously been statutorily undefined (the meaning of municipal water supplier). RCW 90.03.015, .260, .330, .386, .560. Of themselves, these changes to the law do not violate due process.
Id. at 266-67. Here, Ecology merely applied RCW 90.03.560 and RCW 90.03.015 retroactively to WSU to determine that WSU’s water rights were valid and met the definition of “municipal water supply purposes.” 4 AR Doc. 85, at 14-15 (Order on Summ. J.). This is precisely the kind of action we found constitutional in Lummi Indian Nation. If we ruled for Cornelius, Ecology would regularly violate a junior water right holder’s due process rights when it applied RCW 90.03.560 to amend a senior municipal holder’s water right, the precise argument we rejected in Lummi Indian Nation.
¶38 While there may be an unconstitutional application of the MWL, we find none in this case.3 Cornelius’s water rights are junior to WSU’s. As observed in Lummi Indian Nation, “Junior rights holders always take their water rights subject to the risk that there may be no water to *595fulfill those rights.” 170 Wn.2d at 267 (emphasis added). We do not mean to minimize Cornelius’s need for water and realize that Washington’s prior appropriation water law system can lead to unpleasant outcomes. However, it is the legislature’s prerogative to categorize water uses and decide which categories will be relinquished by nonuse. It has done so with the MWL, and under the MWL, Cornelius’s claim fails.
2. Ecology’s Streamlined Process
¶39 Cornelius next argues that the PCHB erred in approving Ecology’s streamlined process for evaluating WSU’s application. Specifically, he claims that the streamlined process conflicts with the MWL’s requirement that when a person applies to amend his or her water right, Ecology must conduct a tentative determination of the extent and validity of the water right. He concludes from that requirement that the streamlined process is ultra vires because it contradicts our water laws. His claim suffers from the same erroneous characterization of the MWL we outlined above and fails.
¶40 An agency’s policy is ultra vires if it exceeds its statutory authority. S. Tacoma Way, LLC v. State, 169 Wn.2d 118, 122-23, 233 P.3d 871 (2010). The parties agree that when someone applies to amend their certificates or change the manner or place of use of the water, Ecology must conduct a tentative determination of the extent and validity of the applicant’s water rights pursuant to RCW 90.44.100. We accept their agreement for the limited purposes of deciding the issue presented. Tentative determinations generally include Ecology staff examining an applicant’s historical water use, often looking at year-to-year use, to determine if the applicant relinquished rights. However, Ecology has a streamlined policy for making “simplified” tentative determinations when relinquishment is not an issue. 2 AR Doc. 23, Ex. 2, at 3 (Decl. of Patrick Kevin Brown in Supp. of WSU’s Mot. for Partial Summ. J.). Under this *596streamlined policy, Ecology’s staff does not generally require applicants to demonstrate their year-to-year water use because relinquishment is not an issue. Intuitively, instances where Ecology permits the streamlined policy would include when the water right is for a municipal water supply under RCW 90.03.330(3), since those rights are immune from relinquishment. RCW 90.14.140(2)(d).
¶41 Here, Ecology made a simplified tentative determination of some of WSU’s water rights, which Cornelius challenges, arguing that the MWL still required Ecology to look at WSU’s historical nonuse of its water rights and revoke any relinquished rights.
¶42 Accepting Cornelius’s argument would require us to ignore RCW 90.03.560 and our holding in Lummi Indian Nation. Here, Ecology appropriately applied RCW 90.03-.560 and RCW 90.03.015 retroactively to WSU to determine that WSU’s water rights were valid and met the definition of “municipal water supply purposes.” 4 AR Doc. 85, at 14-15 (Order on Summ. J.). Ecology applying the streamlined policy to WSU is consistent with the MWL because WSU’s water rights were for municipal water supply purposes and immune from relinquishment. Accordingly, Ecology’s action was not ultra vires and Cornelius’s claim fails.
3. Amending Certificates To Add Well Locations
¶43 Cornelius next challenges the PCHB’s summary judgment order allowing WSU to amend its certificates to add well locations under RCW 90.44.100. He argues that under our decision in R.D. Merrill Co. v. Pollution Control Hearings Board, 137 Wn.2d 118, 969 P.2d 458 (1999), in order to amend a certificate, the water right documented by the certificate must be completely perfected. And, because three of WSU’s certificates involve water rights that WSU never fully perfected, the certificates could not be amended. Cornelius’s argument is based on a misunderstanding of the MWL and fails.
*597¶44 RCW 90.44.100 authorizes individuals to apply to amend their permits or certificates to add well locations. RCW 90.44.100(1). In R.D. Merrill, we said that because RCW 90.44.100 includes the word “permit,” it expressly does not require applicants to perfect their water rights through beneficial use before they can amend a groundwater permit. 137 Wn.2d at 130. That case did not involve certificates or water rights for municipal supply purposes. See id.
¶45 The plain language of RCW 90.44.100 and the logic of our decision in R.D. Merrill, combined with the operation of the MWL, allows water users who possess unperfected water rights documented by certificates to amend them to add well locations, at least where the certificates were originally based on system capacity and were for municipal supply purposes. RCW 90.44.100 itself does not require certificate holders to perfect any unperfected rights before amending them to add well locations. In R.D. Merrill, we allowed permit holders to amend their unperfected rights specifically because the statute mentioned “permit” and thus contemplated that permit holders need not have beneficially used water. 137 Wn.2d at 130. Although we hinted that in the certificate-holder context, water would likely need to be put to beneficial use before it could be amended under RCW 90.44.100, it was because certificates issue only once water has been put to beneficial use — not because RCW 90.44.100 requires it. Id. at 133. In other words, in many cases, certificate holders would need to put their water rights to beneficial use because if they failed to do so, Ecology could find those rights relinquished under RCW 90.44.100 once the applicant applied to amend. See id. at 133 n.7. But, in scenarios involving system capacity certificates for municipal supply purposes, relinquishment is simply not an issue. System capacity certificates for municipal supply purposes represent rights “in good standing,” i.e., the water rights are deemed perfected, even if the rights were not actually put to beneficial use. RCW 90.03.330(3).
*598¶46 As discussed above, WSU’s water rights are represented by system capacity certificates for municipal supply purposes. Thus, WSU did not need to take any action to fully perfect its rights before amending them under RCW 90.44-.100 because they are deemed perfected. Accordingly, Cornelius’s claim fails.
4. SEPA
¶47 Cornelius next argues that Ecology failed to comply with SEPA when it processed WSU’s applications. The PCHB granted Ecology’s summary judgment motion on this issue, and Cornelius appeals, arguing that Ecology should have supplemented its SEPA review. His claim fails.
¶48 SEPA is a procedural law that ensures state agencies, among others, consider environmental impacts and alternatives before taking certain actions. Save Our Rural Env’t v. Snohomish County, 99 Wn.2d 363, 371, 662 P.2d 816 (1983). If no categorical exemption from SEPA exists, the relevant agency or actor proposing a development must meet certain environmental review and documentation requirements. WAC 197-11-310. First, applicants must prepare an “environmental checklist” to describe basic information about a proposal’s environmental impacts. WAC 197-11-960. The responsible agency4 reviews the checklist to determine if an environmental impact statement (EIS) is required. WAC 197-11-330. An EIS is required if the responsible agency reasonably believes that a proposal may have a significant adverse impact on the environment. WAC 197-11-330(4). If the agency determines that the action will not significantly impact the environment, the agency issues a determination of nonsignificance (DNS), which ends the environmental review. WAC 197-11-340; 24 Timothy Butler *599& Matthew King, Washington Practice: Environmental Law and Practice § 17.3, at 195 (2d ed. 2007). Even if the agency issues a DNS, though, it must create a supplemental EIS or prepare a new “determination” if “[n]ew information” indicates the proposed action may significantly affect environmental quality. WAC 197-11-600(3)(b)(ii). “New in form a - tion” includes discovering misrepresentation or the lack of material disclosure. Id. The agency’s determination is entitled to “substantial weight.” RCW 43.21C.090. We apply the “clearly erroneous” standard of review to an agency’s DNS. Nor. Hill Pres. & Prot. Ass’n v. King County Council, 87 Wn.2d 267, 275-76, 552 P.2d 674 (1976).
¶49 Here, WSU was the lead agency, and it prepared an environmental checklist and issued a DNS. The checklist and DNS did not address whether WSU, by integrating its water system, would increase groundwater withdrawals and exacerbate the declining water level in the aquifer. When Ecology processed WSU’s application, it relied on WSU’s DNS without adding a supplemental EIS or preparing a new determination. Cornelius argues that when Ecology allowed WSU to amend and integrate its water system, it expanded WSU’s water rights, allowing it to pump more groundwater than legally allowed. He claims Ecology was thus obligated under SEPA to supplement WSU’s DNS based on the “ ‘new information’ ” of WSU’s increased pumping capacity and its impact on the aquifer. Appellants’ Opening Br. at 33.
¶50 Cornelius’s argument is unpersuasive. As we stated above, Ecology and the PCHB did not expand WSU’s water rights in approving WSU’s application; rather, they confirmed WSU’s rights by applying RCW 90.03.560. The PCHB correctly noted that the amendment does not allow WSU to pump any more water than it currently has a vested right to pump — it merely allows WSU to more cost effectively utilize its existing rights. Thus, Ecology did not need to supplement WSU’s DNS because there was no “new *600information.” Accordingly, we affirm the PCHB’s summary judgment order on this issue.
5. Impairment and Public Welfare
¶51 Cornelius next argues that through its “unconstitutional interpretation of the MWL,” the PCHB improperly limited the evidence and argument that would, he contends, have shown that amending WSU’s water rights certificates would impair existing rights and be detrimental to the public welfare. Id. at 34. Cornelius’s claim is meritless because it is predicated on the same flawed argument that WSU’s water rights are being expanded under the MWL that we rejected above. Properly understood, the PCHB did not expand or revive relinquished water rights; rather, it confirmed WSU’s existing water rights. Accordingly, Cornelius’s claim fails.
6. Safe Sustaining Yield
¶52 Cornelius next argues that when WSU applied to amend its water rights certificates, RCW 90.44.130 required Ecology to determine if WSU’s proposal would maintain a safe sustaining yield of groundwater. Id. at 35. Cornelius’s claim again fails.
¶53 Generally, RCW 90.44.130 protects “prior appropriator[s],” i.e., senior water users, from subsequent appropriators overdrafting public groundwater. The statute protects senior users by giving Ecology the power to limit subsequent appropriators’ withdrawals to an amount that will “maintain and provide a safe sustaining yield in the amount of the prior appropriation.” RCW 90.44.130.
¶54 Here, Ecology did not apply the safe sustaining yield provision to WSU and interpreted the statute to mean that the safe sustaining yield requirement applies only to new applications for water rights, not to applications to amend existing water rights certificates. The PCHB agreed with Ecology’s interpretation. Cornelius argues Ecology’s interpretation was erroneous for two reasons. First, he contends *601Ecology’s erroneous interpretation stems from its unconstitutional interpretation of the MWL expanding WSU’s rights. For the reasons above, we reject this argument. Second, he contends that whenever an existing water user seeks to amend his or her water rights, RCW 90.44.130 broadly mandates that Ecology limit the user’s groundwater to maintain a safe sustaining yield for other users — the statute does not apply only when Ecology evaluates new permits. We disagree.
¶55 Although RCW 90.44.130 clearly protects senior water users against overdrafting by subsequent users, it is unclear whether the senior users’ enjoyment of a “safe sustaining yield” applies only to new users who wish to appropriate water or if it applies to existing users who seek to amend. However, here, that is an academic question. WSU is the senior water user, not Cornelius. Thus, Ecology and the PCHB did not err by not applying the safe sustaining yield provision to WSU.
7. Reasonable Diligence
¶56 Cornelius again challenges the formally inchoate portions of several of WSU’s water rights, this time arguing that they are invalid because they were not put to beneficial use with “reasonable diligence.” Appellants’ Opening Br. at 37. Cornelius’s claim again fails.
¶57 When individuals apply to amend their water rights certificates under RCW 90.44.100, rights represented by system capacity certificates for municipal supply purposes are rights “in good standing,” i.e., the rights are deemed perfected, even if they were not actually put to beneficial use. RCW 90.03.330(3). However, although the water need not actually have been put to beneficial use for the rights to remain in good standing, the water rights must still be “prosecuted with reasonable diligence” to remain valid. RCW 90.03.460. What constitutes reasonable diligence depends on the circumstances, including the magnitude of the project, the engineering and physical features to *602be encountered, and public interests. RCW 90.03.320. Another circumstance relevant in the municipal supply purposes context is “delays that may result from planned and existing conservation and water use efficiency measures.” Id. One of the purposes of the reasonable diligence requirement is to avoid a party speculating in water rights (i.e., acquiring water rights for future profit rather than specifically intending to apply them to a beneficial use). See R.D. Merrill, 137 Wn.2d at 130-31.
¶58 Here, four of WSU’s water rights are at issue, represented by Certificate Nos. 5070-A, 5072-A, and G3-22065C, and Permit No. G3-28278P. WSU has not historically used the quantity of water listed on those certificates and the one permit since the priority dates of those water rights — 1962,1963,1973, and 1987 respectively. Thus, WSU has not put to beneficial use the full extent of those water rights for several decades. There is no evidence that WSU is speculating its water rights for profit; WSU exclusively exercises its rights to serve its Pullman campus. Over those decades, WSU has developed as an institution, increasing its enrollment and developing additional facilities. Even with this growth, in recent years WSU’s water use has actually declined because it has taken water conservation measures.
¶59 Here, we find WSU has exercised reasonable diligence. Although in other circumstances failing to use the full extent of one’s water rights for decades might not meet the reasonable diligence requirement, here WSU meets the requirement because of its unique situation and development throughout the decades. WSU is a large public institution that has developed new facilities and increased enrollment over the years. It is in the unusual position of being unable to predict or plan its own growth because its budget and enrollment targets are largely controlled by the legislature. Additionally, WSU is not speculating its water rights, and it has not exercised the full extent of its rights at least in part because of water conservation measures. *603Considering these circumstances, taking away WSU’s water rights for lack of reasonable diligence would hinder WSU’s ability to educate students, and it would essentially punish WSU for taking water conservation measures. Accordingly, WSU exercised reasonable diligence and Cornelius’s claim fails.
8. Abandonment of Claim No. 98523
¶60 Cornelius next argues that WSU abandoned its water right represented by Claim No. 98523. His claim fails.
¶61 “Abandonment is the intentional relinquishment of a water right.” Okanogan Wilderness League, Inc. v. Town of Twisp, 133 Wn.2d 769, 781, 947 P.2d 732 (1997). Abandonment requires a two-part showing: nonuse plus an intent to abandon the water right. See id. The party alleging abandonment has the burden of proof. Id. However, “long periods of nonuse raise a rebuttable presumption of intent to abandon” a water right, and the burden shifts to the water right holder to give reasons justifying the nonuse. Id.
|62 Here, WSU filed Claim No. 98523 in 1974, and the claim identifies WSU’s Well No. 2 as the source or point of withdrawal. The water right represented by this claim has a priority date of 1938, which is also the year Well No. 2 was drilled. WSU stopped using Well No. 2 as a water source in 1978 because of a misaligned hole and low water level, and WSU decommissioned the well in 1995, using it as a monitoring well instead. WSU’s 2002 Water System Plan formally denoted Well No. 2 as being abandoned. However, WSU’s 2002 Water System Plan also identified Claim No. 98523 as an existing water right, listing quantities of water for its current and forecasted water right tables. When WSU prepared its applications to amend its water rights, the responsible employee corresponded with Ecology, and the employee assumed that WSU’s abandonment of Well No. 2 meant that WSU had abandoned the water right itself. Ecology informed the employee that when a person abandons a well, he or she does not necessarily abandon the associated water right.
*604¶63 Cornelius argues he demonstrated a long period of nonuse because WSU ceased using Well No. 2 in the late 1970s, and he says that unauthorized pumping from other wells cannot make up for WSU not using Well No. 2. He argues WSU cannot rebut the presumption of an intent to abandon Claim No. 98523 because WSU listed Well No. 2 as abandoned and WSU (through its agent employee) assumed Claim No. 98523 was abandoned.
¶64 Assuming without deciding that Cornelius demonstrated a long period of nonuse, WSU demonstrated that it did not intend to abandon Claim No. 98523. Cornelius’s argument heavily relies on Okanogan Wilderness League. In that case, the town of Twisp had a water right dating back to 1912 to divert water from the Twisp River. Id. at 772. At least since 1948, Twisp stopped diverting from the river and instead drew water from wells in the town. Id. When Twisp belatedly applied for groundwater certificates for the wells in 1967 and 1971, “it did not mention the 1912 water right even though the application forms asked whether there were any other water rights appurtenant to the lands served by the groundwater withdrawals.” Id. at 783. In the 1990s, Twisp applied to Ecology for a new water right and an Ecology employee discovered a certificate for the 1912 right. Id. at 773. Twisp then sought to use the discovered 1912 right to withdraw water from two new wells. Id. The only evidence Twisp had that it did not abandon the 1912 water right was Twisp’s continuing existence and need for a water supply. Id. at 784. We found Twisp’s showing inadequate and held that Twisp abandoned the 1912 right. Id. at 786.
¶65 Here, WSU shows it did not intend to abandon Claim No. 98523. Unlike Twisp in Okanogan Wilderness League, where Twisp apparently forgot it had the 1912 right and failed to list the right on subsequent applications, here WSU never forgot about Claim No. 98523. Although WSU listed the claim’s associated well as abandoned in 2002, it also stated that the water right represented by the claim *605existed, listing quantities of water for its current and forecasted water right status tables. The record indicates WSU’s employee’s mistake about Claim No. 98523 being abandoned was a theoretical concern he had while preparing WSU’s applications to amend its water rights, not a demonstration of an intent to abandon the claim. Accordingly, WSU did not abandon Claim No. 98523 and Cornelius’s claim fails.
9. Beneficial Use and Reasonable Efficiency
¶66 Cornelius next argues that the PCHB erred in granting WSU’s summary judgment motion on whether WSU’s irrigation of its golf course complied with beneficial use requirements. We disagree.
¶67 In water law, “beneficial use” encompasses two principles. In re Rights of Surface & Ground Waters of Marshall Lake & Marshall Creek Drainage Basin, 121 Wn.2d 459, 468, 852 P.2d 1044 (1993). First, “beneficial use” refers to the types of activities for which water may be used (e.g., irrigation or agriculture). Id. Second, “beneficial use” determines the measure of a person’s water right (i.e., a person is entitled to the amount of water he or she has traditionally put to beneficial use). Id. Closely related to the idea of beneficial use is an appropriator’s duty to avoid waste — when someone appropriates water to beneficial use, that appropriation must be reasonably (not absolutely) efficient. Id. at 472. Whether a beneficial use is reasonably efficient turns on a variety of factors, such as local custom, the relative efficiency of irrigation systems in common use, and the costs and benefits of improvements to irrigation systems. Id. at 475.
¶68 Here, Cornelius originally alleged that WSU’s irrigation of its golf course did not meet the reasonable efficiency requirement for beneficial use. WSU moved for summary judgment, and to defeat WSU’s summary judgment motion, Scott Cornelius submitted a declaration describing personal observations he made of WSU’s golf *606course while driving or bicycling past it, including photographs and temperature data. In his declaration, Scott Cornelius says he saw, among other things, sprinklers operating during the day when local temperatures were in the 90s and water runoff on hillsides adjacent to the golf course. The PCHB granted WSU’s summary judgment motion, saying that Scott Cornelius’s personal observations could not meet his burden of showing a triable issue of fact regarding reasonable efficiency according to the relevant legal factors in Rights of Surface & Ground Waters. Additionally, the PCHB stated that Scott Cornelius’s “allegations may be more properly evaluated in the context of an enforcement action.” 4 AR Doc. 85, at 28 (Order on Summ. J.). Cornelius now argues that the PCHB erred by (1) applying the wrong summary judgment standard by ruling that expert testimony was required to defeat summary judgment and (2) ruling that Ecology lacks the authority to evaluate reasonable efficiency when it reviews groundwater amendment applications (i.e., that reasonable efficiency can be reviewed only in an enforcement action).
¶69 Cornelius’s arguments fail. First, the PCHB did not rule that expert testimony was required to defeat summary judgment. Rather, it said that “the observations of Scott Cornelius, who is admittedly not an expert in this area, along with the photographs and temperature data, fail to establish a genuine dispute about the reasonable efficiency of WSU’s water use.” Id. The PCHB properly found Scott Cornelius’s observations insufficient to show triable questions of fact regarding reasonable efficiency according to the relevant legal factors in Rights of Surface & Ground Waters. Scott Cornelius’s personal observations about the sprinklers tell us nothing about local custom, the relative efficiency of commonly used irrigation systems, or costs and benefits associated with improvements to irrigation systems — the relevant legal inquiries under Rights of Surface & Ground Waters. At best, Scott Cornelius’s evidence establishes that WSU’s sprinkler system is not absolutely effi*607cient, which is not required for reasonable efficiency. Accordingly, his challenge fails.
¶70 Second, the PCHB did not rule that Ecology lacked the authority to evaluate reasonable efficiency when it reviews groundwater amendment applications. The PCHB merely stated that it thought Scott Cornelius’s “allegations may be more properly evaluated in the context of an enforcement action,” not that Ecology lacked the authority to evaluate reasonable efficiency. Id. Thus, Cornelius’s second argument is based on a misunderstanding of the PCHB’s summary judgment order. Accordingly, Cornelius’s claims fail.
10. Permit No. G3-28278P
f 71 Cornelius next argues that the PCHB erred when it ruled after a hearing that Ecology was not required to reduce the water quantity authorized under Permit No. G3-28278P. Cornelius claims that because Permit No. G3--28278P is supplemental to Claim No. 098524 (which Ecology found invalid), Ecology should have subtracted the water quantity associated with Claim No. 098524 from Permit No. G3-28278P. We disagree.
¶72 The groundwater code contains a prohibition on enlargement of rights. See RCW 90.44.100(2)(c). It prohibits Ecology from authorizing additional wells as points of withdrawal if the combined total withdrawal from the original and additional well enlarges the rights conveyed by the original permit or certificate. Id. We will grant relief from an agency order resulting from an adjudicative proceeding if the order is not supported by substantial evidence. RCW 34.05.570(3)(e). “[Substantial evidence is ‘a sufficient quantity of evidence to persuade a fair-minded person of the truth or correctness of the order.’ ” King County v. Cent. Puget Sound Growth Mgmt. Hr’gs Bd., 142 Wn.2d 543, 553, 14 P.3d 133 (2000) (quoting Callecod v. Wash. State Patrol, 84 Wn. App. 663, 673, 929 P.2d 510 (1997)).
*608¶73 Here, Ecology issued a report of examination (ROE) regarding Permit No. G3-28278P, informing WSU that the permit is “for supplemental water only” and that the “waters to be appropriated from Well No. 7 will serve to replace, as necessary, those waters originally authorized or claimed for appropriation from Wells No. 1, 3 and 4.” Ex. A-26, at 3. In other words, Ecology granted the permit to supplement the water WSU was already authorized to appropriate under its primary water rights. The permit itself contains the following language:
The quantities granted under this permit are issued less those amounts appropriated under Ground Water Certificate No. 5070-A and Ground Water Claims No. 098522 and No. 098524. The total combined withdrawal under this permit and Ground Water Certificate No. 5070-A shall not exceed 2500 gallons per minute, 2260 acre feet per year.
Ex. A-25, at 2. The PCHB conducted a hearing to determine whether Ecology meant “supplemental” to mean that the water right represented by Permit No. G3-28278P was valid only to the extent that the primary (older) water rights were valid, or whether “supplemental” meant that the permit was an alternate way for WSU to appropriate its previously authorized rights. 4 AR Doc. 89, at 30-31 (Findings of Fact, Conclusions of Law & Order). After examining the language in the permit and the ROE, the PCHB determined that Permit No. G3-28278P was intended as an alternate source of water for WSU and that the amount of water authorized under the permit was not legally dependent on WSU’s existing water claims. Thus, the PCHB did not require WSU to subtract the amount of water authorized in invalid Claim No. 098524 from Permit No. G3--28278P because the permit merely represented an alternate source of water for WSU. Cornelius claims the PCHB erred, arguing that the permit’s validity depends on the preexisting water rights’ validity.
¶74 Cornelius contends that the permit’s language and its status as “supplemental” necessarily means that the *609permit’s validity depends on the preexisting water rights’ validity. We find that the evidence the PCHB relied on — the language of the permit itself — is sufficient to persuade a fair-minded person of the truth or correctness of the finding. Accordingly, the PCHB’s finding is supported by substantial evidence and Cornelius’s claim fails.
11. Attorney Fees
¶75 Cornelius requests attorney fees pursuant to RCW 4.84.350. That statute allows for attorney fees when a qualified party prevails in judicial review of an agency action. Here, Cornelius does not prevail. Thus, we deny the request for attorney fees.
CONCLUSION
¶76 The legislature substantially amended this state’s water law in 2003, categorizing water uses and deciding which categories would be relinquished through nonuse. In Lummi Indian Nation, we found those amendments facially constitutional. We find the amendments were constitutionally applied in this case and reject Cornelius’s remaining claims. We affirm.
C. Johnson, Fairhurst, Stephens, and González, JJ., and J.M. Johnson, J. Pro Tem., concur.WSU has not challenged Ecology’s denial, and thus it is not before us.
Cornelius argues a separate procedural due process violation, asserting that “[t]he PCHB’s limitation on Cornelius’ impairment evidence prejudiced his ability to protect his rights in violation of procedural due process.” Appellants’ Opening Br. at 20. He fails to cite to the record or provide details about how the PCHB limited his evidence, and he merely cites Motley-Motley, Inc. v. Pollution Control Hearings Board, 127 Wn. App. 62, 110 P.3d 812 (2005), for the broad principle that parties must be prejudiced regarding preparation to establish due process violations in administrative proceedings. Id. We will not reach arguments unsupported by adequate argument and authority. Saunders v. Lloyd’s of London, 113 Wn.2d 330, 345, 779 P.2d 249 (1989).
If Ecology applied the MWL in a way that invalidated an individual’s vested water right, it might well violate due process. See Lummi Indian Nation, 170 Wn.2d at 268-69. But junior rights holders always take their rights subject to the possibility that senior rights holders’ use will limit, possibly severely, the amount of water available. That is a consequence of scarcity, not a due process violation.
Meaning the agency that seeks to develop or the agency that is presented with a proposal for development. See WAC 197-11-050. If more than one agency is involved, a lead agency must be designated. WAC 197-11-050. The lead agency is the one with the main responsibility for complying with SEPA’s procedural requirements, and it is also responsible for preparing environmental impact statements. WAC 197-11-050(2).