11 P.3d 726 (2000) 142 Wash.2d 68

John POSTEMA, and Wallace L. Jorgensen, Appellants,
v.
POLLUTION CONTROL HEARINGS BOARD; James A. Tupper, Jr., Robert V. Jensen, and Richard C. Kelley, each in their official capacities as members of the Pollution Control Hearings Board; Department of Ecology; Tom Fitzsimmons, in his official Capacity as director of the Department of Ecology; and Tulalip Tribes of Washington, Respondents.

No. 67549-0.

Supreme Court of Washington, En Banc.

Argued March 1, 2000. Decided October 19, 2000.

*731 Jonson & Jonson, Richard Jonson, Seattle, Charles Lean, Olympia, Kameron Cayce, Renton, Richard Stephens, Charles Klinge, Bellevue, for Appellants.

Christine Gregoire, Atty. Gen., Jean Wilkinson, Deborah Mull, Asst. Atty. Gens., Olympia, John Arum, Mason Morisset, Robert Caldwell, Russell Busch, Gregory Hicks, Seattle, Karen Allston, Auburn, for Respondents. *727 *728 *729

*730 MADSEN, J.

These two consolidated cases, one of which involves four consolidated cases, present numerous issues arising from the Department of Ecology's denial of applications for groundwater appropriation permits on the basis that the groundwater sources are in hydraulic continuity with surface water sources and further appropriations are foreclosed under the criteria of RCW 90.03.290. In the five individual cases before this court, the Pollution Control Hearings Board upheld Ecology's denial of the groundwater applications.

We conclude that hydraulic continuity between groundwater and a surface water source with unmet minimum flows or which is closed to further appropriation is not, in and of itself, a basis on which to deny an application to withdraw groundwater. However, despite the Board's erroneous legal determination that hydraulic continuity equates to impairment as a matter of law, the Board's findings in two of the cases before us nevertheless support the Board's ultimate decision that denial was proper.

These cases have proceeded, in both the administrative appeals and superior court review, in two parts. First, the Board addressed statewide threshold issues common to these and other appeals. Then, individual hearings were held in each case. The superior courts similarly addressed the threshold issues and the individual issues raised in each case. We affirm the decisions of the King County Superior Court and the Snohomish County Superior Court on the threshold issues, and affirm the courts' orders in Jorgensen v. Washington State Dep't. of Ecology, No. 97-2-17943-2 (King County Super. Ct. Sept. 14, 1998); Black River Quarry, Inc. v. Washington State Dep't of Ecology, No. 96-2-20613-0 (King County Super. Ct. Sept. 14, 1998); and Postema v. Washington State Dep't of Ecology, No. 97-2-00979-9 (Snohomish County Super. Ct. August 18, 1998). Our affirmance in Postema results in remand of that case to the Board. We reverse the orders in Covington Water Dist. v. Washington State Dep't of Ecology, No. 97-2-17946-7 (King County Super. Ct. Sept. 14, 1998) and Herzl Mem'l Park v. Washington State Dep't of Ecology, No. 97-2-17932-7 (King County Super. Ct. Sept. 14, 1998) and remand these cases to the Board.

We first address the threshold issues common to these cases, and then turn to each of the individual cases.

*732 THRESHOLD ISSUES

Facts

In late 1995 and early 1996, the Department of Ecology (Ecology) issued approximately 600 water right decisions on applications to appropriate water in 12 watersheds, using batch processing. A little over half of these decisions were denials. Over 130 of the decisions were appealed to the Pollution Control Hearings Board (Board), which consolidated most of the appeals by Watershed Resource Inventory Area (WRIA). Many of these appeals involved denials of applications for groundwater appropriation permits on the basis that the groundwater is in hydraulic continuity with surface water sources which has minimum flows which are not met a substantial part of the time. In addition, Ecology denied applications for appropriation from groundwater in hydraulic continuity with surface water sources which are closed to further appropriation. Importantly, in the five cases here on appeal, Ecology gave several reasons for denial of applications, but its decision in each case was ultimately premised on hydraulic continuity.

A number of the applicants who appealed to the Board, the Coordinated Appellate Group (CAG), moved for and were granted a special hearing on threshold issues of statewide importance. In addition to CAG, Ecology, and intervenors Center for Environmental Law and Policy, the Muckleshoot Indian Tribe, and the Tulalip Tribes of Washington participated in the briefing and argument. The tribes' treaty rights are not directly at issue in these cases, but their treaty rights form the basis for their interest in these cases. The Board conducted the hearing, addressing 11 threshold issues of law, and on July 16, 1996, issued an order on motions for summary judgment and partial summary judgment. Thereafter, the Board held evidentiary hearings in the individual cases and issued orders in each case. A number of the applicants appealed the Board's decisions, and a number of the appeals were assigned to King County Superior Court Judge Alsdorf. Included in this group of appellants are all of the appellants in one of the two consolidated cases before the court, Jorgensen v. Pollution Control Hr'gs Bd., No. 67786-7 (which itself involves four cases consolidated by the Court of Appeals before transfer to this court). Appellant John Postema, the appellant in the second of the consolidated cases, Postema v. Pollution Control Hr'gs Bd., No. 67549-0, appealed to Snohomish County Superior Court. The superior courts affirmed the Board in most respects on the threshold issues. In the individual orders, the denials of groundwater appropriation permits in the four Jorgensen consolidated cases were upheld, while Postema prevailed on appeal and his case was remanded to the Board for a new hearing.

No attempt is made here to fully explain hydrogeological cycles and the science relating to impact of groundwater withdrawals. In general, water can move from groundwater to surface water, as well as from surface water to groundwater. How groundwater moves and where it moves to depend on several factors, including gravity, saturation of the ground materials, the hydraulic gradient, the level of the groundwater, and the type of material through which it moves. An aquifer is a geologic formation having materials with a higher rate of conductivity. An aquitard is composed of materials with lower conductivity. While at one time it was thought that aquitards could be impermeable, it is now known that an aquitard is never truly impermeable. Pumping well water can affect groundwater movement by lowering pressure and heads, by reducing groundwater storage, and by changing rates of groundwater recharge and discharge. The interrelationship can be quite complex and effects are sometimes difficult or impossible to measure in the field. Also, pumping groundwater may not have a discernable effect on surface water until considerable time has passed, depending upon the conditions.

Ecology's understanding of hydraulic continuity has altered over time, as has its use of methods to determine hydraulic continuity and the effect of groundwater withdrawals on surface waters. In 1996, the United States Geologic Services published a report by Morgan and Jones regarding three-dimensional computer modeling for the complex geologic and hydrogeologic basins of Puget Sound. The report concluded that the effects of *733 pumping always reaches some of the surface water boundaries, and can do so over many square miles. Prior to issuance of this report, there was no such model. Ecology maintains that in a complex hydrologic system, use of a three-dimensional computer model is the best method for determining the effects groundwater withdrawals will have on surface water flow and senior surface water right holders. Ecology concluded that the Morgan and Jones model could be used in decisions on the Jorgensen appellants' applications because the climate, topography, and geology in the Green-Duwamish, Snohomish, and Cedar-Sammamish watersheds were similar.

Although there has been a factual dispute regarding the extent of the impact of groundwater withdrawals on surface waters in western Washington in general, especially given the rates of recharge resulting from precipitation, the arguments on the statewide threshold orders concern issues of law.

Analysis

The Board and the superior courts decided the statewide threshold issues as matters of law on summary judgment. Summary judgment is proper where there are no genuine issues of material fact and the moving party is entitled to judgment as a matter of law. CR 56(c).

The Administrative Procedure Act, RCW 34.05, governs proceedings before the Pollution Control Hearings Board. Department of Ecology v. Theodoratus, 135 Wash.2d 582, 589, 957 P.2d 1241 (1998). This court sits in the same position as the superior court and reviews the Board's decision by applying the standards of review in RCW 34.05.570 directly to the agency record. Id. Agency action may be reversed where the agency has erroneously interpreted or applied the law, the agency's order is not supported by substantial evidence, or the agency's decision is arbitrary and capricious. RCW 34.05.570(3); Okanogan Wilderness League, Inc. v. Town of Twisp, 133 Wash.2d 769, 776, 947 P.2d 732 (1997).

Where construction of statutes is concerned, the error of law standard applies. Id.; RCW 34.05.570(3)(d). Under this standard, this court may substitute its interpretation of the law for the agency's. R.D. Merrill v. Pollution Control Hr'gs Bd., 137 Wash.2d 118, 142-43, 969 P.2d 458 (1999). Where a statute is within the agency's special expertise, the agency's interpretation is accorded great weight, provided that the statute is ambiguous. Theodoratus, 135 Wash.2d at 589, 957 P.2d 1241; Pasco Police Officers' Ass'n v. City of Pasco, 132 Wash.2d 450, 458, 938 P.2d 827 (1997); Waste Mgmt. of Seattle, Inc. v. Utilities & Transp. Comm'n, 123 Wash.2d 621, 627-28, 869 P.2d 1034 (1994). However, an agency's view of the statute will not be accorded deference if it conflicts with the statute. Id. at 628, 869 P.2d 1034. Ultimately, it is for the court to determine the meaning and purpose of a statute. City of Redmond v. Central Puget Sound Growth Mgt. Hr'gs Bd., 136 Wash.2d 38, 46, 959 P.2d 1091 (1998).

The burden of establishing invalidity of agency action is on the party asserting invalidity. RCW 34.05.570(1)(a); City of Redmond, 136 Wash.2d at 45, 959 P.2d 1091.

I. Hydraulic continuity with surface water source having minimum flow requirements.

The primary issues common to these appeals concern the impact of groundwater withdrawals on surface waters having minimum flow requirements set by rule which are unmet a substantial part of the year, and on surface waters closed to further appropriation. The parties do not disagree that groundwater and surface water may be interconnected and that withdrawals from aquifers may affect surface water flows or levels. They disagree, however, on the nature of minimum flow rights and on what constitutes legally significant hydraulic continuity,^[1] as well as on whether hydraulic continuity requires denial of a groundwater application on the basis that a proposed withdrawal will *734 impair existing rights, including minimum flow rights, or will be detrimental to the public welfare. Appellant Postema contends that there must be a significant measurable effect on surface waters before a groundwater application may be denied even though hydraulic continuity between the ground and surface waters is established. In general, the appellants in the Jorgensen cases argue that minimum flows are limited rights, and that Ecology's regulations require a direct and measurable effect of groundwater withdrawal on surface waters using standard stream measuring equipment, which has effective limits of about five percent of stream flow, before hydraulic continuity has any legal significance vis-a-vis minimum flow rights. If, using these methods, no effect is measurable, these appellants reason, Ecology has no authority to deny a groundwater application because of any affect on or relationship to surface waters.

Both the Board and the superior courts ruled against appellants, reasoning that Ecology's regulations do not require nor foreclose use of current scientific tools to determine hydraulic continuity and impact of groundwater withdrawal. The Board held that once hydraulic continuity between a groundwater source and surface water having unmet minimum flows is established, any ground withdrawals will impair existing rights and thus permit applications must be denied as a matter of law. The superior courts rejected the Board's holding, reasoning instead that hydraulic continuity is a factual determination which does not, in and of itself, establish impairment. Rather, water applicants must have the opportunity to present their factual cases on the question of impairment or any of the other criteria justifying denial of a water application. If Ecology wants to avoid a factual hearing on impairment in each case, it must engage in rule-making. Ecology has not cross-appealed the superior courts' holdings that hydraulic continuity alone does not equate to impairment.

To place the issues in context, we begin with general water law principles. The doctrine of prior appropriation applies when an applicant seeks to obtain a water right in this state. RCW 90.03.010; Neubert v. Yakima-Tieton Irrigation Dist., 117 Wash.2d 232, 240-41, 814 P.2d 199 (1991). Under this doctrine, a water right may be acquired where available public water is appropriated for a beneficial use, subject to existing rights. RCW 90.03.010. The same principles apply to groundwater: "Subject to existing rights, all natural groundwaters of the state ... are hereby declared to be public groundwaters and to belong to the public and to be subject to appropriation for beneficial use under the terms of this chapter and not otherwise." RCW 90.44.040; see Hillis v. Department of Ecology, 131 Wash.2d 373, 383, 932 P.2d 139 (1997). When a private party seeks to appropriate groundwater, Ecology must investigate pursuant to RCW 90.03.290. See RCW 90.44.060 (providing that groundwater applications shall be made as provided for in RCW 90.03.250 through .340). RCW 90.03.290 requires that before a permit to appropriate may be issued, Ecology must affirmatively find (1) that water is available, (2) for a beneficial use, and that (3) an appropriation will not impair existing rights, or (4) be detrimental to the public welfare. A basic principle of water rights acquired by appropriation is the principle of first in time, first in right. "[T]he first appropriator is entitled to the quantity of water appropriated by him, to the exclusion of subsequent claimants".... Longmire v. Smith, 26 Wash. 439, 447, 67 P. 246 (1901); see RCW 90.03.010 (codifying first in time, first in right principle); Neubert, 117 Wash.2d at 240, 814 P.2d 199.^[2] A decision whether to grant a permit to appropriate water is within Ecology's exercise of discretion. Hillis, 131 Wash.2d at 384, 932 P.2d 139; Jensen v. Department of Ecology, 102 Wash.2d 109, 113, 685 P.2d 1068 (1984).

*735 The groundwater code recognizes that surface waters and groundwater may be in hydraulic continuity:

The rights to appropriate the surface waters of the state and the rights acquired by the appropriation and use of surface waters shall not be affected or impaired by any of the provisions of this supplementary chapter and, to the extent that any undergroundwater is part of or tributary to the source of any surface stream or lake, or that the withdrawal of groundwater may affect the flow of any spring, water course, lake, or other body of surface water, the right of an appropriator and owner of surface water shall be superior to any subsequent right hereby authorized to be acquired in or to groundwater.

RCW 90.44.030. This statute "emphasizes the potential connections between groundwater and surface water, and makes evident the Legislature's intent that groundwater rights be considered a part of the overall water appropriation scheme, subject to the paramount rule of `first in time, first in right.'" Rettkowski v. Department of Ecology, 122 Wash.2d 219, 226 n. 1, 858 P.2d 232 (1993). Hydraulic continuity between ground and surface waters is also recognized in the Water Resources Act of 1971: "Full recognition shall be given in the administration of water allocation and use programs to the natural interrelationships of surface and groundwaters." RCW 90.54.020(9).

Accordingly, when Ecology determines whether to issue a permit for appropriation of public groundwater, Ecology must consider the interrelationship of the groundwater with surface waters, and must determine whether surface water rights would be impaired or affected by groundwater withdrawals.

RCW 90.22.010 and .020, enacted in 1969, Laws of 1969, 1st Ex.Sess., ch. 284, §§ 3, 4, authorize Ecology to establish, by rule, minimum instream flows or levels to protect fish, game, birds, other wildlife resources, and recreational and aesthetic values. Then, in 1971, as part of the Water Resources Act, establishment of base flows in rivers and streams was mandated by RCW 90.54.020(3)(a), which provides in part: "The quality of the natural environment shall be protected and, where possible, enhanced^[3] as follows: ... Perennial rivers and streams of the state shall be retained with base flows necessary to provide for preservation of wildlife, fish, scenic, aesthetic and other environmental values, and navigational values." RCW 90.54.040 authorizes Ecology to establish by rule a comprehensive state water resources program for making future water allocation and use decisions. Pursuant to this authorization, Ecology adopted rules establishing the WRIAs and minimum flows at issue in these cases.

Once established, a minimum flow constitutes an appropriation with a priority date as of the effective date of the rule establishing the minimum flow. RCW 90.03.345. Thus, a minimum flow set by rule is an existing right which may not be impaired by subsequent groundwater withdrawals. RCW 90.03.345; RCW 90.44.030. The narrow exception to this rule is found in RCW 90.54.020(3)(a), which provides that withdrawals of water which would conflict with the base flows "shall be authorized only in those situations where it is clear that overriding considerations of the public interest will be served."

Appellants in the Jorgensen case contend that before a groundwater application may be denied because of impairment of surface water rights, there must be a direct and measurable effect on surface waters using standard stream measuring equipment. The limits of this equipment are about five percent of the stream flow. Appellants reason that when adopting rules setting minimum flows Ecology was required to balance instream and out-of-stream uses, and, in particular, to give consideration to economic factors. According to appellants, when Ecology adopted the WRIA regulations it was required to and did in fact weigh competing interests in future water use and defined *736 limited minimum flow water rights, containing a "direct, and measurable impact" standard in order to account for, among other things, economic factors. Key to appellants' argument is the belief that the rules setting the minimum flows do not alone define the minimum flow rights; instead, all the regulations pertaining to the water basin in question define the minimum flow rights.

We disagree. First, and most importantly, the statutes simply do not support appellants' view. The statutes plainly provide that minimum flows, once established by rule, are appropriations which cannot be impaired by subsequent withdrawals of groundwater in hydraulic continuity with the surface waters subject to the minimum flows. RCW 90.03.345; RCW 90.44.030. A minimum flow is an appropriation subject to the same protection from subsequent appropriators as other water rights, and RCW 90.03.290 mandates denial of an application where existing rights would be impaired.

Second, these appellants cite no statute which requires any further weighing of interests once minimum flows have been established, and none requiring that economic considerations influence permitting decisions once minimum flows are set. Several statutes recognize that water is essential to the state's growing population and economy as well as necessary to preserve instream resources and values. RCW 90.54.010(1)(a); RCW 90.03.005 (describing policy of water use yielding maximum net benefits from both diversionary use of waters and retention of water instream to protect natural values and rights); RCW 90.54.020(2) (generally same); see also RCW 90.82.010; RCW 43.21C.030(2)(b) (State Environmental Policy Act of 1971); RCW 43.21H.010 (state economic policy act). However, none of these statutes indicate that they are meant to override minimum flow rights once established by rule, none conflict with the statutes authorizing or mandating rules setting minimum flows, and none conflict with the specific statutes respecting priority of minimum rights.

Third, even if the WRIA regulations could be read as establishing a limited minimum flow right (which, as explained below, they do not do), they would be inconsistent with the statutes and invalid. See Winans v. W.A.S., Inc., 112 Wash.2d 529, 540, 772 P.2d 1001 (1989) (regulations must be consistent with statutes under which they are promulgated); Baker v. Morris, 84 Wash.2d 804, 809-10, 529 P.2d 1091 (1974) (agency exceeds its rulemaking authority to the extent it modifies or amends precise requirements of statute).

Finally, the relevant rules do not establish the standard for which the Jorgensen appellants argue. WAC 173-500 of the Washington Administrative Code sets out the general guidelines for administering the water resources management program required under the Water Resources Act of 1971. See WAC 173-500-010. Appellants first point to WAC 173-500-060(5)(a), a general provision which states:

(5) Base flow provisions for water rights.

(a) Surface water and/or groundwater appropriation permits, issued subsequent to the effective dates of chapters 173-501 through 173-599 WAC, that will allow either direct diversion from or have a measurable effect on streams where base flow limitations of this chapter [sic], and any such permits or certificates shall be appropriately conditioned to assure maintenance of said base flows.

Contrary to appellants' arguments, this rule, which is obviously missing some language, does not limit the scope of instream flow regulation, nor does it dictate that permits must be issued, albeit conditioned. The rule simply does not address whether a permit may or may not be issued, and plainly could not modify the statutory requirements of RCW 90.03.290. If the statute's requirements are not satisfied, a permit cannot be issued and the rule never comes into play. The rule provides that if a permit is issued for a surface water source for which minimum flows have been set, the permit may have to be conditioned to assure maintenance of the base flows. Such a situation could arise, for example, where a stream which has unmet minimum flows part of the year nevertheless has sufficient water during high flow periods of the year to allow for issuance of a *737 conditioned permit allowing appropriation of water at a time or in a manner which will not impair existing rights.

The Jorgensen appellants also rely on rules concerning specific WRIAs. The chapters addressing the different WRIAs usually follow a general format where, among other things, they list streams with minimum flows and describe the minimum flow requirements, and also list stream closures. Following these listings are several provisions, including a provision concerning groundwater. Appellants urge that the groundwater regulations for all basins where minimum flows have been set should be interpreted the same, and point to language in the regulation respecting the Puyallup River Basin, WAC 173-510-050, as a specific rule expressly providing the correct interpretation. Postema makes a similar argument. Ecology also argues that there is a consistent interpretation of all the rules which should be followed, but advances a different interpretation, i.e., one which reflects language in the regulation pertaining to the Okanogan River Basin, WAC 173-549-060.

The parties' arguments concerning the groundwater regulations largely overlook the relevant statutory scheme. Also, the parties have for the most part read meanings into the regulations which are simply not supported by the language contained in them. They also have selectively chosen rules which most closely reflect their respective positions. Ultimately, we are unconvinced by the parties' arguments urging their respective versions of a consistent interpretation applying to all WRIAs.

The Jorgensen appellants reason that because Ecology agrees that it intended the same meaning be given the groundwater regulations for all basins where minimum flows have been set, it is legitimate to use similar, but more precise language from an unrelated basin as an aid in interpretation. Of course, the language which they rely on as "more precise" is language that comes closer to supporting their position than the regulations applying to the WRIAs actually involved here. These appellants quote WAC 173-507-040, applicable to the Snohomish River Basin, WRIA 7, as a general statement, and WAC 173-510-050, applicable to the Puyallup River Basin, WRIA 10, as "a more precise guide to interpretation." Br. of Appellant (Jorgensen) at 32.

WAC 173-507-040, the Snohomish rule, states that "[i]n future permitting actions relating to groundwater withdrawals, the natural interrelationship of surface and groundwaters shall be fully considered in water allocation decisions to assure compliance with the meaning and intent of this regulation." As appellants concede, this regulation does no more than repeat the mandate of RCW 90.54.020(9). Thus, it does not advance their arguments.

The Puyallup rule, WAC 173-510-050, however, states that Ecology will determine whether the proposed withdrawal will have a "direct, and measurable" impact on flows in streams with minimum flows and those closed to further appropriation, and then states that, if so, the provisions setting the minimum flows and stream closures will apply. Although more in accord with appellants' argument, this rule does not tie measurable impact to standard stream measuring devices.

Postema also refers to the Puyallup rule, as well as to those of other basins in arguing a consistent interpretation of the rules contrary to Ecology's position. He does not argue, as the Jorgensen appellants do, that standard stream measuring devices with limits of five percent must establish a direct and measurable effect on stream flow before groundwater applications must be denied under RCW 90.03.290. Instead, he contends that the rules require a significant measurable or otherwise detectable effect on surface waters,^[4] relying upon WAC 173-500-060. Further, he urges that the mere existence of instream flows and hydraulic continuity is not enough to warrant denial of a groundwater application under the regulations in effect, nor is a de minimis impact sufficient to *738 deny a groundwater right application. As noted, WAC 173-500-060 does not support his position.

Ecology claims that it has uniformly applied its rules to require only "significant hydraulic continuity." While it is true that interpretation of regulations is purely a question of law, St. Francis Extended Health Care v. Department of Soc. & Health Servs., 115 Wash.2d 690, 695, 801 P.2d 212 (1990), and that deference to the agency's interpretation is particularly appropriate where its own regulations are concerned, Hayes v. Yount, 87 Wash.2d 280, 289, 552 P.2d 1038 (1976), the rules do not contain a general significant hydraulic continuity standard applying to all basins any more than they contain a direct, and measurable impact standard. Like the direct, and measurable impact language relied upon by appellants which appears in a rule for the Puyallup River basin, WAC 173-510-050, the "significant hydraulic continuity" language appears in a rule, WAC 173-549-060, for a basin not involved in these appeals, i.e., the Okanogan River Basin, WRIA 49. The language of that rule was at issue in Hubbard v. Department of Ecology, 86 Wash.App. 119, 936 P.2d 27 (1997), and the court held that the term referred to the continuity between the groundwater aquifer and the surface water, not to the degree of impact on the surface water, and upheld a conditional permit subject to maintenance of minimum flows.

Both the King County and Snohomish County Superior Courts applied the rules specific to the basins in which appropriations were sought, rejecting all parties' arguments of a consistent interpretation across all basins. While there is some appeal to the idea that all of the rules should mean the same thing therefor, we too decline to search for a uniform meaning to rules that simply are not the same.

Appellants urge, however, that at the least the rules respecting WRIAs and groundwater withdrawals are ambiguous as to Ecology's intent about the nature of the right embodied in the minimum flows, and urge that the ambiguity may be resolved by resort to evidence of Ecology's intent when promulgating the rules. They chiefly rely on the declaration of Eugene Wallace, former Assistant Director of Ecology, who maintained that Ecology's intent in adopting WAC 173-500-060(5)(a) was that the surface water restrictions adopted in the regulations would have no effect on future groundwater withdrawals unless there was a measurable effect on minimum flows. Mr. Wallace said that Ecology expected that the effect of groundwater withdrawals would be confined to nearby withdrawals from shallower aquifers. Appellants then rely on the statement of a witness for Ecology, Mr. Wildrick, for the proposition that "measurement" refers to standard measuring equipment with limits of about five percent. Decl. of Linton Wildrick, Pollution Control Hr'gs Bd., Ecology's Br. in Resp. to Mot. for Summ. J. re: Statewide Issues at 236. Appellants urge that this evidence, viewed in the light most favorable to them, supports the conclusion that Ecology intended the direct and measurable impact standard with limits of five percent.

The first difficulty with this argument is that appellants are not entitled to the benefit of any inferences from the evidence in this context. The statewide issues decided by the Board and the courts on summary judgment involve pure questions of law involving the meaning of statutes and rules. The second difficulty with the argument is that appellants misrepresent Mr. Wildrick's testimony. He said that

[u]nless the well captures approximately five percent (5%) of the stream flow, the effect cannot be accurately detected with standard measuring equipment. Five percent of the flow of many streams exceeds the pumping rates of all but the largest wells.... For this reason, hydrologists usually estimate hydraulic properties based on standard aquifer testing and then calculate or model stream flow effects based on those properties. Extensive experimentation has proven that ground-water pumping affects stream flows even if the effects are not detectable due to the limitations of standard measuring equipment. These calculations of effects are considered to be accurate and have become standard professional practice. Hydrologists routinely measure or ascertain effects *739 on surface water sources caused by wells in this manner.

Id. at 236-37, 936 P.2d 27.

Third, the argument would effectively freeze Ecology's ability to implement the statutes, requiring it to rely on scientific knowledge which is now outdated. Ecology concedes that when adopting minimum flow rules it did not believe that withdrawals from deep confined aquifers would have any impact on stream flows because of the presence of an aquitard. New studies by the United States Geologic Services have established that significant leakage occurs across aquifers, and thus withdrawals from deep aquifers will impact surface waters more than was thought appellants do not dispute this. Nor can there be any serious thought that Ecology intended groundwater withdrawals be allowed to deplete surface streams; Ecology's aim has been to protect instream flows as required by statute. For example, as Ecology points out, the final environmental impact statement for the instream flow program states in part: "Adoption of an instream flow for a stream would mean that new public water demands would not be allowed to deplete that stream below the specified flow." T 1142.^[5]

As the King County Superior Court observed, "[i]t is true that all parties to this case originally expected that only nearby and shallow groundwater withdrawals would affect surface waters. However, expectation is not intent. While the undisputed facts show a change from the original manifestation of Ecology's intent, Ecology's intent was and is to prevent interference with instream flows." Id. at 14. We agree with this reasoning. Moreover, it makes no sense to uniformly interpret the rules to require that standard instream gauges with five percent limits show a direct and measurable effect before an application to withdraw from groundwater in hydraulic continuity may be denied. It would not take many such withdrawals before a stream could be depleted a result at odds with Ecology's intent, and, more importantly, at odds with the relevant statutes and the obvious legislative intent manifested in them. As respondent Center for Environmental Law and Policy urges, an instream flow right subject to piecemeal impairment would not preserve flows necessary to protect fish, wildlife and other environmental resources. Not only would minimum flows be subject to depletion, all senior rights in a stream could be impaired by incremental impacts of groundwater withdrawals, none of which alone was "direct and measurable" under appellants' proposed standard.

Postema contends, though, that there is both statutory and regulatory support for his claim that a de minimis impact is not a valid ground for denying a groundwater permit application. As he points out, RCW 90.44.050 allows domestic and stock watering uses of up to 5,000 gallons without a permit, and WAC 173-508-080(2) (Green-Duwamish River Basin, WRIA 8, rule), exempts domestic use of water for a single family dwelling even where withdrawal is from a stream closed to further appropriation. Postema reasons that the statute and the rule are inconsistent with a conclusion that no impairment means any impairment at all, including a de minimis impairment.

RCW 90.03.290 does not, however, differentiate between impairment of existing rights based on whether the impairment is de minimis or significant. If withdrawal would impair existing rights, the statute provides the application must be denied. As to RCW 90.44.050, legislative exemptions from the permitting system do not determine what impairment means. As to Ecology's rule, Ecology says that it has determined that the single family dwelling exempted domestic use is pursuant to RCW 90.54.020(3)(a), which *740 provides that groundwater withdrawals which would conflict with the base flows "shall be authorized only in those situations where it is clear that overriding considerations of the public interest will be served."

The Jorgensen appellants contend that the Pollution Control Hearings Board has already determined that minimum flow rights are not rights like other water rights, citing the Board's decision in Wenatchee-Chiwawa Irr. Dist. v. Department of Ecology, PCHB No. 85-215 (Apr. 7, 1986). Initially, a Board decision does not bind this court. See R.D. Merrill Co. v. Pollution Control Hr'g Bd., 137 Wash.2d 118, 142 n. 9, 969 P.2d 458 (1999). Second, while the Board's decision in Wenatchee Chiwawa appears to treat a minimum flow right differently than "traditional" water rights, the decision specifically concerned priorities under a 1985 statute re-opening the registration period for water rights for a one-month period and was expressly limited to that situation. When the Board was later faced with a question of priorities in general, it reasoned that "a minimum flow regime established by rule functions as an appropriation senior to all permits approved after it was established," and thus where minimum flows were in effect for a river before a junior appropriator's permits were approved, the junior appropriator had to cease diverting water when the river flow fell below the minimum flow set by rule. Williams v. Department of Ecology, PCHB No. 86-63 (Oct. 20, 1986).

The appellants also argue that it is normal for water rights to contain conditions and limitations. While that is the case, it does not support the proposition that minimum flow rights are limited rights subject to impairment.

The appellants' arguments that there must be measurable effects on stream flows raise the question of how impairment must be determined. There seems to be no dispute that Ecology has revised its view of the interconnection of groundwater and surface water in hydraulic continuity as new information has become available. There is also no dispute that Ecology has altered the methods by which it determines the impact of groundwater withdrawal on surface waters. Ecology points to PCHB decisions upholding use of qualitative analysis, such a hydrological studies and conceptual modeling, and quantitative modeling, such as analytical equations or numeric models, Richert v. Department of Ecology, PCHB No. 90-158 (Sept. 11, 1991), and mathematical equations, Richert (citing Anders v. Department of Ecology, PCHB No. 78-38 (1978)).

Ecology may use new methods to determine impairment as they are developed. See American Trucking Ass'n v. Atchison, T. & S.F. Ry. Co., 387 U.S. 397, 416,