At issue in this case is whether the Court of Appeals properly concluded that the Washington Department of Labor and Industries (the Department) had violated a statutory duty to promulgate a rule requiring mandatory blood testing for agricultural pesticide handlers. Although the Court of Appeals acknowledged that differing standards of review applied to the Department’s rule-*487making in 1993 and its denial of rulemaking in 1997, it did not review the two challenges separately. We agree with the Department that the plaintiffs failed to show that the 1993 rule was arbitrary and capricious. However, we have determined that the Department’s denial of the plaintiffs’ 1997 request was arbitrary in light of the Department’s post-1993 investigation, and we therefore conclude that the Department’s failure to act was contrary to the requirements of the Washington Industrial Safety and Health Act of 1973 (WISHA), chapter 49.17 RCW.
The Court of Appeals decision is therefore affirmed in part and reversed in part. We remand this matter to the Department with our order to initiate rulemaking.
FACTS
The plaintiffs in this class action lawsuit are agricultural pesticide handlers, farm workers directly engaged in mixing, loading, and applying pesticides. Because exposure to pesticides containing organophosphate and carbamate compounds is known to inhibit levels of cholinesterase, a blood enzyme essential to the proper functioning of the nervous system,1 the pesticide handlers asked the Department in 1986 and again in 1991 to adopt a mandatory blood testing program to monitor their cholinesterase levels. The Department initiated rulemaking and, in March 1993, adopted WAC 296-307-14520 (originally codified as WAC 296-306--40011 (1993)),2 which recommends but does not require a *488blood testing program for monitoring cholinesterase levels. Stephen M. Cant, the Department’s “industrial hygiene program manager,” “made the initial decision not to require mandatory cholinesterase monitoring, and the Assistant Director for WISHA and the Director for the Department accepted that recommendation.” Clerk’s Papers (CP) at 508, 516.
The pesticide handlers informed the Department that they intended to seek judicial review. In response, the Department set up a Technical Advisory Group (TAG) “to assist the Department... in determining an appropriate response” and “to identify the essential components of a successful monitoring program in Washington State.” CP at 273. The TAG, comprised of three health care professionals from the University of Washington, along with two representatives from the Department, completed a 20-page report in August 1995. See CP at 271-91. Although the heading to section II of the TAG report termed *489cholinesterase monitoring “the most well developed and feasible method among available worker monitoring approaches for cholinesterase-inhibitor exposure,” the TAG “recommend [ed] the following” in its September 1995 cover letter to the report: “Cholinesterase monitoring on a voluntary basis for those working in occupations involved with handling cholinesterase-inhibiting pesticides within the specific trigger levels described in this document.” CP at 274, 202. The TAG explained that, “[g]iven the current limitations of various resources vital for the implementation of some of the recommendations described in this document, we are not advising mandatory cholinesterase monitoring programs.” CP at 202.
In letters dated June 19 and July 18, 1997, the pesticide handlers’ counsel asked the Department to “state its intent to adopt a mandatory medical monitoring rule for pesticide handlers.” CP at 492. Michael Silverstein, the Department’s Assistant Director for industrial safety and health, responded by letter of August 29, 1997. Silverstein explained that “[t]he primary rationale for not making ChE [(cholinesterase)] monitoring mandatory at this time grows out of the technical limitations involved with ChE testing,” CP at 215, but he also discussed the constraints placed on the Department by competing priorities and limited resources. While Silverstein concluded that the Department had correctly decided in 1993 to recommend nonmandatory cholinesterase monitoring and had properly adhered to the voluntary recommendations in light of the 1995 TAG report, he nevertheless recognized “that additional review of technical issues related to cholinesterase monitoring was warranted both in light of the Technical Advisory Group advice to this effect, and also in light of the Governor’s Executive Order on Regulatory Improvement (EO 97-02).” CP at 493. Consequently, the Department included “the voluntary monitoring recommendations in the Rule Review Plan . . . submitted to the Governor in August 1997.” Id.
The pesticide handlers filed the present declaratory judgment action in October 1997 in Thurston County Superior *490Court. CP at 5-15. They stated causes of action for the Department’s alleged violation of WISHA, RCW 49.17-.050(4) and 49.17.240(2); the Washington Administrative Procedure Act (APA), RCW 34.05.570(4)(b) and 34.05-.570(2)(c); the Washington Law Against Discrimination, RCW 49.60.030; article I, section 12 of the Washington State Constitution; and Title VI of the federal Civil Rights Act of 1964, 42 U.S.C. § 2000d. In January 1998, the case was certified as a class action on behalf of “all persons who are or will be employed as pesticide handlers in the agriculture industry in Washington State.” CP at 21. At a bench trial in June 1998, the trial court issued an oral ruling based on the oral argument of counsel, the testimony from witnesses, and “the rule-making file required by RCW 34.05.370, as well as all pleadings, briefs and evidence which were called to the Court’s attention.” CP at 2221. The trial court ruled against the pesticide handlers on all causes of action.
This court denied the pesticide handlers’ request for discretionary review and transferred the matter to the Court of Appeals. Division Two reversed, and we granted the Department’s petition for review.
ISSUE
When the Department decided not to include mandatory cholinesterase monitoring in the agricultural pesticide regulations promulgated in 1993, and then rejected in 1997 the pesticide handlers’ renewed request for rulemaking on such a program, did the Department violate its statutory duty under WISHA or otherwise act arbitrarily or capriciously?
ANALYSIS
Standard of Review. The pesticide handlers have challenged the validity of the 1993 rule,3 as well as the *491Department’s subsequent failure to initiate rule making in 1997. The two challenges are based on distinct provisions in the APA.
The APA provides that “[t]he validity of any rule may be determined upon petition for a declaratory judgment addressed to the superior court of Thurston county, when it appears that the rule, or its threatened application, interferes with or impairs or immediately threatens to interfere with or impair the legal rights or privileges of the petitioner.” RCW 34.05.570(2)(b) (emphasis added). The APA places “[t]he burden of demonstrating the invalidity of agency action... on the party asserting invalidity” and further provides that “[t]he validity of agency action shall be determined in accordance with the standards of review provided in this section, as applied to the agency action at the time it was taken.” RCW 34.05.570(l)(a), (b). The following standard of review is applicable to the pesticide handlers’ challenge to the Department’s 1993 rule:
(c) In a proceeding involving review of a rule, the court shall declare the rule invalid only if it finds that: The rule violates constitutional provisions; the rule exceeds the statutory authority of the agency; the rule was adopted without compliance with statutory rule-making procedures; or the rule is arbitrary and capricious.
RCW 34.05.570(2)(c) (emphasis added).
Whereas the pesticide handlers’ challenge of the 1993 rule falls under RCW 34.05.570(2), their challenge to the Department’s 1997 denial of their rulemaking request comes under RCW 34.05.570(4), the subsection governing actions other than rules or orders: “A person whose rights are violated by an agency’s failure to perform a duty that is *492required by law to be performed may file a petition for review pursuant to RCW 34.05.514, seeking an order pursuant to this subsection requiring performance.” RCW 34.05.570(4)(b) (emphasis added). As with the challenge to the 1993 rule, the pesticide handlers bear the burden of demonstrating their entitlement to relief, and judicial review must be based on the standard prescribed in the APA. Here, the standard applicable to the Department’s alleged “failure to perform” in 1997 is very similar to the standard of review governing the challenge to the 1993 rule:
(c) Relief for persons aggrieved by the performance of an agency action, including the exercise of discretion, or an action under (b) of this subsection [subsection (4)] can be granted only if the court determines that the action is:
(i) Unconstitutional;
(ii) Outside the statutory authority of the agency or the authority conferred by a provision of law;
(iii) Arbitrary or capricious; or
(iv) Taken by persons who were not properly constituted as agency officials lawfully entitled to take such action.
RCW 34.05.570(4)(c) (emphasis added).
Thus, in broadest terms, the APA’s standards of judicial review require that we make two inquiries: first, whether the pesticide handlers met their burden of demonstrating that the 1993 rule was unconstitutional, exceeded the Department’s statutory authority, was adopted without compliance with rulemaking procedures, or was arbitrary and capricious; and, second, whether the pesticide handlers met their burden of demonstrating that the Department’s 1997 decision to forgo rulemaking was unconstitutional, outside the Department’s statutory authority, arbitrary or capricious, or made by unauthorized persons.
Not all of the statutory standards apply to our review of the 1993 rule and the 1997 denial of rulemaking. Although the pesticide handlers claimed that the Department’s 1993 rule violated state and federal constitutional provisions, exceeded the Department’s statutory authority, and was *493arbitrary and capricious, the Court of Appeals declined to address the pesticide handlers’ inadequately developed constitutional argument and focused exclusively on whether the 1993 rule was “invalid for failure to comply with WISHA requirements.” Rios v. Dep’t of Labor & Indus., 103 Wn. App. 126, 136, 5 P.3d 19 (2000). We conclude that we may declare the omission in the 1993 rule invalid only upon the pesticide handlers’ demonstration that the omission of a mandatory requirement violated the Department’s duty under WISHA or was otherwise arbitrary and capricious.
Regarding the Department’s 1997 refusal to initiate the requested rulemaking, the pesticide handlers’ complaint made no specific reference to the grounds for review set forth in RCW 34.05.570(4)(c)(i)-(iv). Focusing solely on option (ii), the Court of Appeals analyzed only whether the Department had failed to perform a duty required under WISHA. As with our review of the 1993 rule, we conclude that the pesticide handlers will be entitled to relief only if they demonstrate that the Department’s failure to initiate rulemaking in 1997 violated a duty under WISHA or was otherwise arbitrary or capricious.
The Department’s Duty under WISHA. Given the applicable standards of review, our threshold task in reviewing both the 1993 rule and the 1997 refusal to initiate rulemaking is to define the nature of the Department’s statutory duty under WISHA. Exercising its police power and respecting “the mandates of Article II, section 35 of the state Constitution,” the Washington legislature enacted WISHA in 1973 “to create, maintain, continue, and enhance the industrial safety and health program of the state.”4 The statute provides that the “program shall equal or exceed the standards prescribed by the Occupational Safety and *494Health Act of 1970,” (OSHA), 29 U.S.C. § 651. RCW 49-.17.010 (emphasis added).
Pivotal in this case is the WISHA provision regarding safety and health standards for exposure to toxic agents:
[T]he director shall:
(4) Provide for the promulgation of health and safety standards and the control of conditions in all work places concerning gases, vapors, dust, or other airborne particles, toxic materials, or harmful physical agents which shall set a standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life; any such standards shall require where appropriate the use of protective devices or equipment and for monitoring or measuring any such gases, vapors, dust, or other airborne particles, toxic materials, or harmful physical agents [.][5]
The statute is not well drafted. In skeletal form, it states that “the director shall. . . [pjrovide for the promulgation of. . . standards and the control of conditions . . . which shall set a standard which most adequately assures . . . that no employee will suffer material impairment of health.” It is anybody’s guess what the relative pronoun “which” refers to in the clause “which shall set a standard”—“promulgation,” “standards,” or “control of conditions.” In contrast to the WISHA provision, the first sentence in the seminal OSHA provision virtually sings with clarity: “The Secretary, in promulgating standards dealing *495with toxic materials or harmful physical agents under this subsection, shall set the standard which most adequately assures, . . . that no employee will suffer material impairment of health!.]* 29 U.S.C. § 655(b)(5).
As a preliminary step in our analysis of RCW 49.17.050(4), we must correct a distinction between the state and federal provisions that the pesticide handlers urged and that the Court of Appeals adopted. The pesticide handlers maintained that OSHA says “may” where WISHA says “shall” and that, consequently, the state provision curtails the director’s discretion. But this position is based on a misleading distinction. The federal statute actually uses the permissive “may” in an introductory statement lacking in WISHA. Because OSHA gives the secretary a series of optional means for developing safety and health standards, Congress necessarily used “may” to introduce the eight subsections delineating those options: “The Secretary may by rule promulgate, modify, or revoke any occupational safety or health standard in the following manner.” 29 U.S.C. § 655(b) (emphasis added). From those eight subsections (the first of which, for example, permits the secretary to appoint an advisory committee), Washington adopted only subsections (5) and (7), which pertain to the requirements of the standards that are promulgated. See RCW 49.17.050(4), .240(2). We simply do not find the permissive “may” in the overarching OSHA framework pertinent to our analysis of RCW 49.17.050(4), which we have previously described as “mirroring” 29 U.S.C. § 655(b)(5). Aviation W. Corp. v. Dep’t of Labor & Indus., 138 Wn.2d 413, 431, 980 P.2d 701 (1999).
In fact, other than the greater coherence in the federal provision, we can see no significant difference between RCW 49.17.050(4), which states that “the director shall. . . \p\rovide for the promulgation o/health and safety standards . . . which shall set a standard,” and 29 U.S.C. § 655(b)(5), which states that “[t]he Secretary, in promulgating standards . . ., shall set the standard.” (Emphasis added.) While it may not be entirely clear what our legislature intended when it said “shall provide for the promul*496gation of” rather than “shall promulgate,” the chosen language makes the director’s duty not a duty to promulgate, but a duty to make promulgation possible, a duty to create an opportunity for such rulemaking. In sum, we decline to conclude that the director’s rulemaking discretion under WISHA is more circumscribed than that of the Secretary under OSHA. And, in any case, the issue presented is not whether the Department breached the statutory command that the director “provide for the promulgation of” rules, but whether the Department, having committed its energies to regulating the exposure of agricultural workers to pesticides, met the statutory requirements for such regulation. What this case thus demands is our close consideration of the specific requirements set forth in RCW 49.17.050(4).
We must determine whether the pesticide handlers have shown that the Department, in failing to require mandatory cholinesterase monitoring, failed to “set a standard [that] most adequately assure [d], to the extent feasible, on the basis of the best available evidence, that no employee [would] suffer material impairment of health.”6 The essence of the pesticide handlers’ challenges to the 1993 rule and the 1997 denial of rulemaking is that the Department linderregulated the significant risk of pesticide exposure— more specifically, that the Department did not set the standard that regulated the risk “to the extent feasible.” The definition of “feasible” in an underregulation challenge is an issue of first impression in this state.
*497In our relatively recent decision in Aviation West, we confronted an owerregulation challenge under RCW 49.17.050(4). In that case, cigarette manufacturers and other affected companies contended that the Department’s regulation of smoking in private workplaces had gone beyond the Department’s statutory authority. Our primary focus in that overregulation case was RCW 49.17.020(7), the general definition of “safety and health standard”: “The term ‘safety and health standard’ means a standard which requires the adoption or use of one or more practices, means, methods, operations, or processes reasonably necessary or appropriate to provide safe or healthful employment and places of employment.”7
To better understand not only the distinction between our review of overregulation and underregulation challenges but also the interplay between the general definition of a safety and health standard and the more specific requirements of a toxic exposure standard, we may find guidance in federal cases interpreting the mirror image OSHA provisions, although plainly we are not bound by such cases. Adkins v. Aluminum Co. of Am., 110 Wn.2d 128, 147, 750 P.2d 1257 (1988); Aviation W. Corp., 138 Wn.2d at 424.
Federal cases have focused on the phrase “to the extent feasible” in 29 U.S.C. § 655(b)(5), the OSHA precursor to RCW 49.17.050(4). In construing “feasible,” the United States Supreme Court took as its starting point the dictionary definition “ ‘capable of being done, executed, or effected.’ ” Am. Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490, 508-09, 101 S. Ct. 2478, 69 L. Ed. 2d 185 (1981) [hereinafter ATMI\ (quoting Webster’s Third New International Dictionary of the English Language 831 (1976)); see also Aviation W. Corp., 138 Wn.2d at 433 n.ll (quoting Indus. Union Dep’t v. Am. Petroleum Inst., 448 U.S. 607, *498719, 100 S. Ct. 2844, 65 L. Ed. 2d 1010 (1980) (Marshall, J., dissenting)). Although the ATMI court refused to make the feasibility assessment of § 655(b)(5) dependent upon a compulsory cost-benefit analysis, the court acknowledged that the legislative history of OSHA indicated that a “feasible” standard must nevertheless be one “capable of economic and technological accomplishment”: “Congress was concerned that the Act might be thought to require achievement of absolute safety, an impossible standard, and therefore insisted that health and safety goals be capable of economic and technological accomplishment.” ATMI, 452 U.S. at 514 (emphasis added); see also AFL-CIO v. OSHA, 965 F.2d 962, 980 (11th Cir. 1992) (stating that “[t]he Supreme Court has defined ‘feasibility’ as ‘ “capable of being done, executed, or effected,” ’. . . both technologically and economically”). While the ATMI court cautioned that the general definition of a safety and health standard in § 652(8), which suggests a cost-benefit analysis, should not nullify the feasibility requirement, the court recognized that the “reasonably necessary or appropriate” language in the general definition nevertheless “might. . . impose additional restraints” on the feasibility analysis:
[I]f the use of one respirator would achieve the same reduction in health risk as the use of five, the use of five respirators was “technologically and economically feasible,” and OSHA thus insisted on the use of five, then the “reasonably necessary or appropriate” limitation might come into play as an additional restriction on OSHA to choose the one-respirator standard.
ATMI, 452 U.S. at 514 n.32. The ATMI court also recognized that “any standard that was not economically or technologically feasible would a fortiori not be ‘reasonably necessary or appropriate’under the Act.” Id. at 513 n.31 (citing Indus. Union Dep’t v. Hodgson, 499 F.2d 467, 478 (1974) (“Congress does not appear to have intended to protect employees by putting their employers out of business .. . .”)).
In sum, in light of the guidance provided in ATMI, we conclude that the phrase “to the extent feasible” in RCW 49.17.050(4) means “to the extent the standard is capable of *499being economically and technologically accomplished.” Two points regarding economic feasibility warrant emphasis. First, in determining economic feasibility under WISHA, the director must consider the degree to which a standard will affect the regulated industry’s “ ‘competitive stability.’ ” ATMI, 452 U.S. at 530 n.55 (quoting United Steelworkers of Am. v. Marshall, 647 F.2d 1189, 1265 (D.C. Cir. 1980)). This analysis of economic feasibility under RCW 49.17.050(4) must not be confused with the Department’s exercise of discretion in prioritizing among the many areas that could potentially benefit from rulemaking. In other words, the economic feasibility analysis must focus on the effect of the particular toxic agent standard on the regulated industry, not on the inadequacy of the Department’s fiscal resources for rulemaking.8
Second, the Department’s analysis of economic feasibility cannot be limited by the distinction in the federal cases between cost-benefit analysis and cost effectiveness,9 for our state’s APA expressly requires a cost-benefit analysis.10 We likewise embrace the principle of cost effectiveness and acknowledge here that the critical language in the general *500definition of safety and health standard—“reasonably necessary or appropriate”—works in tandem with the economic feasibility analysis to set a limit on the adoption of feasible methods. RCW 49.17.020(7). Applying the respirator hypothetical from ATMI, we conclude that the director has a duty under RCW 49.17.050(4) to continue adding “respirators” so long as the additions are feasible, but only up to the point where additional ones are no longer necessary to protect against the worker’s “material impairment of health.” See ATMI, 452 U.S. at 513 n.32; Bldg. & Constr. Trades Dep’t v. Brock, 838 F.2d 1258, 1269 (D.C. Cir. 1988) (concluding that “it is [the Secretary’s] duty to keep adding measures so long as they afford benefit and are feasible”). In effect, to outstrip what is “reasonably necessary” is to go beyond “the extent feasible.” Clearly, whether the Department has fulfilled its mandatory duty under WISHA will depend upon whether the Department has properly exercised its discretion in making the feasibility analysis.
Returning to the discussion of our previous decision in Aviation West, we note that our analysis in that overregulation challenge naturally focused on whether the regulation had been “reasonably necessary or appropriate,” for there, the appellants had maintained that the Department engaged in overkill, promulgating, in effect, a “five-respirator” standard, one that exaggerated the statutorily defined risk to worker health. In contrast to the overregulation challenge, the pesticide handlers do not say that what was done was not “reasonably necessary or appropriate”; rather, they focus on RCW 49.17.050(4) and contend that the Department underestimated—again, in our hypothetical terms—the number of “respirators” necessary to protect against the “material impairment of health.” In the pesticide handlers’ view, even with the enactment of the other agricultural pesticide regulations, a risk of “material impairment of health” remained. They contend that the addition of a monitoring program was feasible—that is, capable of economic and technological accomplishment—and that the addition was necessary to achieve the statutorily mandated level of worker protection.
*501Review of the Department’s 1993 Rule. We must decide whether the Department violated its statutory duty under WISHA or otherwise acted arbitrarily and capriciously when it decided not to include mandatory cholinesterase monitoring in the agricultural pesticide regulations promulgated in 1993. As is evident from our analysis of WISHA, the narrower question here is whether the Department in its 1993 rulemaking added measures “to the extent feasible” to protect against the pesticide handlers’ “material impairment of health.” RCW 49.17.050(4).
Applicable to the Department’s feasibility analysis is but one standard of review—whether its feasibility decision was “arbitrary and capricious.”11 We have explained that “[algency action is arbitrary and capricious if it is willful and unreasoning and taken without regard to the attending facts or circumstances.” Hillis v. Dep’t of Ecology, 131 Wn.2d 373, 383, 932 P.2d 139 (1997). More specifically, “[w]here there is room for two opinions, an action taken after due consideration is not arbitrary and capricious even though a reviewing court may believe it to be erroneous.” Id. When reviewing in Aviation West whether the Department’s WISHA regulation had been “reasonably necessary or appropriate,” we defined our inquiry as “a question for the fact finder [i.e., the agency] to determine on a case-by-case basis, subject to only limited review by this court,” and we repeated that “the standard is that £[t]he court must scrutinize the record to determine if the result was reached through a process of reason, not whether the result was itself reasonable in the judgment of the court.’ ”12 Further, in scrutinizing the record, we ask whether the decision “was *502rational at the time it was made.” Aviation W. Corp., 138 Wn.2d at 427 (emphasis added).
In 1993, Stephen M. Cant, the Department’s industrial hygiene program manager, determined that a mandatory monitoring program “was not justified” in light of the Department’s adoption of “extensive other mandatory requirements to protect pesticide workers.” CP at 516. Those requirements included “personal protective clothing, respiratory protection, gloves, training, posting, first aid, emergency facilities, washing facilities, eye-wash requirements, and other provisions designed to protect workers.” CP at 515. It was Cant’s belief that, if the 1993 standards were “correctly followed, pesticide workers [would] be protected” and the necessity for cholinesterase monitoring would be “obviate[d].” Id. Cant also considered “technical and practical problems associated with the test” that “had not been resolved” and could be only with “an additional expenditure of resources.”13 In sum, Cant concluded that the 1993 package of regulations protected agricultural pesticide workers “to the extent [economically and technologically] feasible” and that “to layer a burdensome blood test on top of the comprehensive worker protection requirements in place” would have produced a standard that was not cost *503effective and thus not “reasonably necessary or appropriate.” RCW 49.17.050(4); CP at 518; RCW 49.17.020(7).
The primary evidence on which Cant relied was from the Environmental Protection Agency (the EPA). The EPA, rather than OSHA, has responsibility for setting the standards for pesticide protection. In fact, the Department’s 1993 package of pesticide regulations was “adapted from the final draft of EPA’s then proposed pesticide work protection standards.” CP at 513. While initially endorsing cholinesterase monitoring, the EPA ultimately concluded that too many implementation difficulties remained to permit inclusion of the requirement in its final rule. Cant considered the EPA’s decision not to require cholinesterase monitoring and “read their comments on this issue in the Federal Register before deciding this issue.” CP at 516. Cant likewise noted his reliance on “data from the Pesticide Incident Review and Tracking Panel created by the Legislature to compile data on pesticide exposures.” CP at 518.
The pesticide handlers assert that the Department neglected the evidence derived from California’s mandatory monitoring program. The only such program in the country, California’s program was adopted in 1974 through its Department of Agriculture. A 1989 study of the California program, based on a 1985 worker survey, showed that “23 percent of the 542 handlers in the study had cholinesterase levels indicating overexposure.” CP at 2125; see also CP at 277 (citing Richard G. Ames et al., Cholinesterase Depression Among Pesticide Applicators: Results from the 1985 California Medical Monitoring Program, 15 Am. J. Indus. Med. 143-50 (1989)). Cant acknowledged his familiarity with the California program prior to his 1993 decision, but he maintained that the existence of the California program did not ipso facto make such a program necessary in Washington: “[T]here is no justification in Washington State to support the notion that, because California did something, that somehow, whatever the ‘something’ was should be adopted here.” CP at 514. In his view, because states are different, there will be “variation in approaches *504to problem solving.” CP at 514. Indeed, no other state labor department has a mandatory program, nor does an OSHA standard even exist, given the EPA’s jurisdiction over such pesticide regulations. Moreover, while the results in the 1989 study were significant, what the pesticide handlers did not show was that a comparable exposure rate would occur in Washington after its implementation of the 1993 protective regulations.14
As we demonstrated in Aviation West, neither the existence of contradictory evidence nor the possibility of deriving conflicting conclusions from the evidence renders an agency decision arbitrary and capricious. Aviation W. Corp., 138 Wn.2d at 429 (citing ATMI, 452 U.S. at 523 (quoting Consolo v. Fed. Mar. Comm’n, 383 U.S. 607, 620, 86 S. Ct. 1018, 16 L. Ed. 2d 131 (1966))). In Aviation West, we concluded that the Department’s fundamental reliance on the EPA report on environmental tobacco smoke met the “best available evidence” requirement of RCW 49.17.050(4). Aviation W. Corp., 138 Wn.2d at 427-29. Just as we could not declare the Department’s action unreasoning in Aviation West, we cannot in the present case conclude that the Department’s 1993 rulemaking decision was not “rational at the time it was made.” Aviation W. Corp., 138 Wn.2d at 427. The Department based its determination that a mandatory cholinesterase program was unnecessary on the EPA’s decision not to include such a program among its federal pesticide protections. In sum, the pesticide handlers have not met their burden of showing that the absence of a mandatory program in the 1993 pesticide regulations ren*505dered the 1993 rule “arbitrary and capricious” under RCW 34.05.570(2)(c).
Review of the Department’s 1997Decision Not to Act. We review the Department’s 1997 denial of the pesticide handlers’ request under the standards set forth in RCW 34.05.570(4)(c). The pesticide handlers have the burden of showing that Silverstein’s August 1997 decision was “[arbitrary or capricious” in light of the record at that time.15
The critical post-1993 evidence in the record is the August 1995 TAG report. The basic tenets of the report are that cholinesterase-inhibiting pesticides can materially harm workers, that medical monitoring by means of a simple blood test is “the most well developed and feasible method” for monitoring such exposure, and that the California program and the Washington nonmandatory guidelines provide a substantial model for a mandatory Washington rule. CP at 274.
The TAG report relies on significant post-1993 research. The report cites two 1995 articles supporting its straightforward observation that “[t]he surveillance system in California has succeeded in reducing the number of work-related pesticide illnesses.” CP at 272, 287; see also CP at 2088-89. According to the report, the TAG contacted the medical coordinator of the California program, a medical supervisor involved in the program, and “other organizations and individuals representing workers in California.” CP at 281-82. The report addressed “[t]he difficulties” prompting the EPA to reverse its original decision to initiate a mandatory nationwide requirement, CP at 275, and the TAG also reviewed information from the World Health Organization and the National Institute on Safety and Health, as well as the annual reports from Washington’s Pesticide Incident Reporting and Tracking panel *506(PIRT). See CP at 2091. The 1991-97 PIRT data showed that, of 279 reported pesticide incidents for which cholinesterase testing had been done, 43 workers (15 percent) had depressed cholinesterase levels. CP at 498. Also available to the TAG was a 1995 Washington study showing that 10 percent of workers who were tested had cholinesterase levels low enough to meet the California trigger levels. CP at 278.
The tenor of the TAG report is proactive. The TAG outlined the essential requirements of a mandatory monitoring program, the “resources required, and technical issues that must be addressed to ensure that these primary goals are accomplished and maintained.” CP at 280-81; see also CP at 283-84. The TAG identified the ways in which the California model would have to be modified to meet the TAG’s goals. Consistent with the report’s description of its recommended monitoring program as “the most well developed and feasible method,” the report does not conclude that the suggested modifications are not technologically or economically capable of accomplishment.
The Department can do little to parry the thrust of the TAG report. In explaining his 1997 decision not to go forward with the requested rulemaking, Michael Silverstein, the Department’s Assistant Director for the WISHA Services Division, did not claim that a mandatory rule was not technologically or economically feasible. Rather, he admitted that “it might be possible to demonstrate feasibility for a cholinesterase monitoring program,” but simply cautioned that it “[would] be a challenging and complex undertaking.” CP at 502. Silverstein focused primarily on the Department’s limited resources, noting in particular the budget and staff constraints in the rule-making section of his division, and he stressed the importance of setting priorities for the allocation of scarce resources. In his view, “any substantial new rulemaking project would require new budget or the displacement of other agency activities,” and he speculated that, because “regulation in the agricultural sector has been controversial *507and contentious,” the Department “would need to prepare for this by securing additional technical and legal resources to develop and evaluate a voluminous record, and to prepare for likely litigation.” CP at 494, 502. Surmising that it was “unlikely” that the Department would “have any capacity to do rulemaking for medical surveillance in the foreseeable future,” Silverstein went on to observe that, should the Department “nevertheless . . . choose a specific chemical exposure or group of workers for medical surveillance rulemaking, [the Department] would consider cholinesterase monitoring for farm workers as one of many possibilities.” CP at 497. He emphasized that cholinesterase had no special claim by noting that “[t]here are literally hundreds of such chemicals to which millions of workers are exposed.” Id.
Ordinarily, an agency is accorded wide discretion in deciding to forgo rulemaking in an area, and fiscal constraints may reasonably determine whether an agency takes action (and, if so, how). But an agency’s allusion to fiscal considerations and prioritizing cannot be regarded as an unbeatable trump in the agency’s hand; on review, a plaintiff has the opportunity to show that the agency’s failure to act was “[arbitrary or capricious.” RCW 34.05-.570(4)(c)(iii); see Hillis, 131 Wn.2d at 390-91. This case presents an extraordinary circumstance: even though we recognize the Department’s wide discretion in choosing and scheduling its rulemaking efforts, we conclude that the Department’s denial of the pesticide handlers’ 1997 request was arbitrary. At the time of their request in 1997, the pesticide handlers were not asking the Department to embark on a new enterprise—they had not simply pulled from a hat the name of one dangerous workplace chemical among the hundreds. In fact, the Department had already made cholinesterase monitoring enough of a priority to draft the nonmandatory guidelines and to convene a team of experts “to identify the essential components of a successful monitoring program.” CP at 273. And that report announced in its introductory summary that “[t]he TAG *508recommends cholinesterase monitoring for all occupations handling Class I or II organophosphate or carbamate pesticides.”16 Because the Department had already invested its resources in studying cholinesterase-inhibiting pesticides and because the report of its own team of technical experts had, in light of the most current research, deemed a monitoring program both necessary and doable, the Department’s 1997 denial of the pesticide handlers’ request was “unreasoning and taken without regard to the attending facts or circumstances.” Hillis, 131 Wn.2d at 383. Consequently, in failing to act on the request for rulemaking, the Department violated RCW 49.17.050(4), the requirement that the Department “set a standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health.”
CONCLUSION
Under RCW 34.05.574, a court reviewing agency action has an array of options: “the court may (a) affirm the agency action or (b) order an agency to take action required by law, order an agency to exercise discretion required by law, set aside agency action, enjoin or stay the agency action, remand the matter for further proceedings, or enter a declaratory judgment order.” While we affirm the validity of the Department’s 1993 rule, we conclude that the pesticide handlers met their burden of showing that the Department’s 1997 denial of the pesticide handlers’ request for rulemaking was unreasonable. We therefore order the Department to initiate rulemaking on a mandatory cholinesterase monitoring program for agricultural pesticide handlers.
*509We affirm in part, reverse in part, and remand to the Department for further proceedings consistent with this opinion.
Smith, Johnson, Ireland, Bridge, and Chambers, JJ., concur.
The pesticides’ interference with cholinesterase causes an accumulation of the chemical acetylcholine in the synapses between nerves and muscles, glands, and other nerves; the acetylcholine thus “continues to stimulate or overstimulate the effector organs, and we get the manifestations of toxicity.” Clerk’s Papers (CP) at 2114-15. Overexposure to such pesticides can be fatal. The common symptoms of overexposure include headaches, sweating, weakness, diarrhea, vomiting, increased salivation, respiratory distress, repetitive muscle contractions, blurred vision, cognitive difficulties, seizures, and loss of consciousness. Long-term effects may include “delayed peripheral neuropathy,... a dying back of the nerves in the body as a result of the toxicity of the pesticide,” as well as impairment of “relatively basic neurological function.” Id. at 2115, 2119.
“(1) We recommend that you implement a screening program for cholinesterase monitoring for employees handling organophosphate and carbamate pesticides. *488“(2) Red blood cell and plasma cholinesterase testing of employees who handle toxicity class 1 or 2 carbamate or organophosphate pesticides is an acceptable bioassay method for determining the extent and effects of exposure to these types of pesticides. The schedule of testing should include a preexposure baseline level, followed by periodic monitoring during the period of exposure.
“(3) You should provide baseline cholinesterase tests for all employees handling carbamate or organophosphate pesticides for 30 hours or more in any 30-day period.
“(4) Employees should be given baseline tests before actual exposure, at the beginning of the growing season, or upon first hire. These baseline tests should be repeated every two years.
“(5) Periodic tests should be conducted every 30 days after the initial baseline for the next three months, and every 60 days thereafter until organophosphate or carbamate pesticide exposure ceases.
“(6) You should not allow a monitored employee to be further exposed to carbamate or organophosphate pesticides if any cholinesterase test in comparison to the baseline is less than 70% of red blood cell baseline levels or 60% of plasma baseline levels. These employees should not be further exposed to organophosphate pesticides until their cholinesterase levels return to 80% or more of their baseline levels.
“(7) Employees should be monitored for plasma or red blood cell cholinesterase levels.
“(8) Monitoring programs should include appropriate follow-up and referrals to health care providers as needed, and should include a mechanism for recordkeeping and report tracking.” WAC 296-307-14520.
We agree with the conclusion of the Court of Appeals that, because the Department’s decision to make cholinesterase monitoring nonmandatory was *491closely related to the rules promulgated in 1993, the decision not to include a mandatory cholinesterase program is reviewable as a deficiency in the rules. Rios v. Dep’t of Labor & Indus., 103 Wn. App. 126, 132-33, 5 P.3d 19 (2000) (citing Consumers Union of U.S., Inc. v. F.T.C., 801 F.2d 417, 422 (D.C. Cir. 1986)). Thus, by “the 1993 rule” under review, we mean the 1993 pesticide regulations, chapter 296-307 WAC, Parts I-J, which did not include a mandatory cholinesterase program. Rios, 103 Wn. App. at 133.
RCW 49.17.010. Article II, section 35, of the Washington State Constitution provides that “[t]he legislature shall pass necessary laws for the protection of persons working in mines, factories and other employments dangerous to life or deleterious to health.”
RCW 49.17.050(4). Cf. 29 U.S.C. § 655(b)(5), (7): "The Secretary, in promulgating standards dealing with toxic materials or harmful physical agents under this subsection, shall set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life.. .. Where appropriate, such standard shall also prescribe suitable protective equipment, and control or technological procedures to be used in connection with such hazards and shall provide for monitoring or measuring employee exposure at such locations and intervals, and in such manner as may be necessary for the protection of employees.” (Emphasis added.)
RCW 49.17.050(4). WISHA further mandates that, “[w]here appropriate, such [safety and health standards] ... shall provide for monitoring or measuring employee exposure at such locations and intervals, and in such manner as may be reasonably necessary for the protection of employees,” and that, “[i]n addition, where appropriate, any such rule shall prescribe the type and frequency of medical examinations or other tests which shall be made available, by the employer or at his cost, to employees exposed to such hazards in order to most effectively determine whether the health of such employees is adversely affected by such exposure.” RCW 49.17.240(2) (emphasis added). Cf. 29 U.S.C. § 655(b)(7): “Where appropriate, such standard. .. shall provide for monitoring or measuring employee exposure at such locations and intervals, and in such manner as may be necessary for the protection of employees. In addition, where appropriate, any such standard shall prescribe the type and frequency of medical examinations or other tests which shall be made available, by the employer or at his cost, to employees exposed to such hazards in order to most effectively determine whether the health of such employees is adversely affected by such exposure.” (Emphasis added.)
RCW 49.17.020(7) (emphasis added). Cf. 29 U.S.C § 652(8): “The term ‘occupational safety and health standard’ means a standard which requires conditions, or the adoption or use of one or more practices, means, methods, operations, or processes, reasonably necessary or appropriate to provide safe or healthful employment and places of employment.” (Emphasis added.)
This distinction—between weighing the economic feasibility of a proposed standard and prioritizing rulemaking due to budgetary constraints—-is perhaps somewhat clearer under OSHA because the federal statute includes a specific provision acknowledging that the secretary will necessarily have to set priorities. See 29 U.S.C. § 655(g) (“Priority for establishment of standards”). Although § 655(g) was not included among the WISHA provisions, the indisputable reality is that the Department’s finite fiscal resources require the director to exercise discretion in prioritizing among potential rulemaking initiatives.
“Although the practical effect of the [ATMI] decision was the elimination of cost-benefit analysis as a tool of judicial review, the doctrine of cost effectiveness was not abolished. Cost-benefit analysis determines whether the social benefits of the regulation outweigh the costs to the industry of imposing it and, therefore, whether standards ought to be imposed at all. On the other hand, cost effectiveness merely compels the choice of a less costly alternative in the case where there are multiple methods of effectively reducing the significant risk.” David R. Cherrington, Comment, The Race to the Courthouse: Conflicting Views Toward the Judicial Review of OSHA Standards, 1994 B.Y.U. L. Rev. 95, 111 (1994) (footnote omitted).
“Before adopting a rule ..., an agency shall... [d]etermine that the probable benefits of the rule are greater than its probable costs, taking into account both the qualitative and quantitative benefits and costs and the specific directives of the statute being implemented.” RCW 34.05.328(l)(c).
RCW 34.05.570(2)(c). Where the Department assesses the feasibility of a toxic agent standard arbitrarily and capriciously, it thereby violates the mandatory language of RCW 49.17.050(4) (“shall set a standard which most adequately assures, to the extent feasible”). The resulting rule would arguably meet another basis for judicial review (“exeeed[ing] the statutory authority of the agency”). RCW 34.05.570(2)(c).
Aviation W. Corp., 138 Wn.2d at 432 (quoting and adding emphasis to Neah Bay Chamber of Commerce v. Dep’t of Fisheries, 119 Wn.2d 464, 474, 832 P.2d 1310 (1992)). Prior to the 1995 amendment to RCW 34.05.570(2)(c), a reviewing court *502could invalidate a rule upon finding that the rule “could not conceivably have been the product of a rational decision-maker.” Laws or 1995, ch. 403, § 802(2)(c). The Neah Bay court observed that this standard “involve [d] an inquiry into the reasonableness of regulations analogous to the application of the arbitrary and capricious standard.” 119 Wn.2d at 473; see also William R. Andersen, The 1988 Washington Administrative Procedure Act—An Introduction, 64 Wash. L. Rev. 781, 835 (1989) (expressing doubt “that a judge can distinguish [the rational decision-maker standard] from the arbitrary and capricious standard”). Indeed, the 1995 amendment substituted the arbitrary and capricious standard. That standard is consistent with the APA provision that, “[i]n reviewing matters within agency discretion, the court shall limit its function to assuring that the agency has exercised its discretion in accordance with law, and shall not itself undertake to exercise the discretion that the legislature has placed in the agency.” RCW 34.05.574(1). And we have registered agreement with Professor Andersen’s opinion that “substantial judicial deference” should be accorded “when an agency determination is based heavily on factual matters, especially factual matters which are complex, technical, and close to the heart of the agency’s expertise.” Andersen, supra, at 832, cited in Hillis, 131 Wn.2d at 396.
CP at 516. Whether Cant was referring to additional costs to the employers, a permissible consideration in the feasibility analysis, or to the Department’s resources is unclear.
It appears that California did not have in place in 1985 a package of protections comparable to Washington’s 1993 regulations. Although California had “closed systems for mixing and loading Category I pesticides,” CP at 2180, “Workers handling cholinesterase-inhibiting chemicals in closed mixing and loading systems exclusively [were] not subject to routine cholinesterase monitoring, and the time spent using only closed mixing and loading apparatus [was] excluded from the hours which trigger routine cholinesterase monitoring.” Richard G. Ames et al., Protecting Agricultural Applicators from Over-Exposure to Cholinesterase-Inhibiting Pesticides: Perspectives from the California Programme, 39 J. Soc. Occup. Med. 85,88 (1989). Thus, the 1985 Ames study apparently did not measure the benefits of the closed system, California’s most important protective measure.
RCW 34.05.570(4)(c)(iii). If our review reveals that the Department’s 1997 decision was “arbitrary or capricious,” then the Department’s denial of the pesticide handlers’ request will have contravened the mandatory language of WISHA and will have provided another basis for relief under the APA’s judicial review statute as an action “[ojutside the statutory authority of the agency or the authority conferred by a provision of law.” RCW 34.05.570(4)(c)(ii).
CP at 272. That the TAG recommended in its September 1995 cover letter a nonmandatory program rather than a mandatory one requires some qualification. The TAG deferred to the Department’s financial straits and attributed the group’s endorsement of a nonmandatory program to “the current limitations of various resources vital for the implementation of some of the recommendations described in this document.” CP at 202.