¶1 — During the winter of 1998-99, the Doumas pumped dairy waste into an unlined trench on land they leased from the State. Pursuant to RCW 90-.48.144, the Department of Ecology (Ecology) assessed a $53,000 penalty against the Doumas for discharging pollutants into Washington State waters. The Doumas appealed to the Pollution Control Hearings Board (PCHB), which reduced and partially suspended the penalty. Both Ecology and the Doumas petitioned for review in Thurston County Superior Court, which affirmed the PCHB’s decision in its entirety. The Doumas argue that (1) the PCHB’s decision was based on an error of law and (2) the PCHB’s decision regarding the penalty was arbitrary and capricious. Ecology argues that (1) the PCHB erred in suspending a portion of the penalty’s gravity component and (2) the PCHB erred in reducing the penalty’s economic benefit component. The PCHB is a named party to this appeal but does not advocate on the merits of the action. We affirm the PCHB’s conclusion that a violation occurred and its suspension of a portion of the gravity component of the penalty but remand for further findings regarding its reduction of the economic benefit portion of the penalty.
FACTS
¶2 The Doumas operate a dairy and beef cattle ranch in Whatcom County, Washington. Waste from dairy cows is collected and stored in manure lagoons until the Doumas apply it to field crops during the growing season. During the end of 1998 and the beginning of 1999, the area surrounding the Doumas’ dairy received higher than normal levels of precipitation. This caused the Doumas’ manure lagoons to fill more quickly than normal.1 The Doumas felt that the *147manure lagoons might overflow, causing dairy waste to enter nearby surface waters.2
¶3 On February 25, 1999, the Doumas hired an excavation company to construct an unlined trench on wooded land adjacent to the Doumas’ dairy,3 which the Washington State Department of Natural Resources (DNR) managed and leased to the Doumas.4 The Doumas’ lease with DNR did not authorize use of the wooded parcel. Furthermore, the lease both prohibited the storage of harmful substances on the wooded parcel and required immediate notification to the State of any spill or release of a harmful substance that affected the leased land. The Doumas’ excavation contractor constructed a rectangular trench approximately 550 feet long. The trench varied in width between 5 and 10 feet wide, and was 3 to 6 feet deep. After constructing the trench, the Doumas pumped approximately 500,000 gallons of dairy waste from the manure lagoons into the trench, a volume roughly equal to 10 days of dairy waste production at the Doumas’ dairy. The Doumas did not contact Ecology before or after constructing and filling the trench.
¶4 In late April 1999, an anonymous third party informed DNR of the manure trench and DNR initiated an inspection. On May 3, 1999, DNR contacted Ecology. Ecology inspectors Mark Kaufman and Andrew Craig inspected the site on May 5, 1999. With his boot, Craig dug a hole approximately 6 to 12 inches deep near the trench; the hole *148gradually filled with water. Based on this, Craig concluded that the water table was at the level of the dairy waste in the trench, and that the dairy waste came in contact with groundwater. Consistent with orders from Ecology, the Doumas had the dairy waste pumped out of the trench and applied to nearby fields on May 7 and 8, 1999.
¶5 On May 21, 1999, Ecology issued a notice of violation to the Doumas. On June 21, the Doumas’ attorney responded in a letter explaining the circumstances of the incident. On August 20, 1999, Ecology issued a notice of penalty for $53,000 for discharging pollutants into State waters without a discharge permit.5 On September 9,1999, the Doumas submitted an application for relief from the penalty. Ecology affirmed the $53,000 penalty in a notice of disposition dated November 29, 1999.
¶6 The Doumas appealed to the PCHB.6 The PCHB initially dismissed the appeal as untimely. The Doumas then appealed the dismissal to Whatcom County Superior Court, arguing that Ecology violated their procedural due process rights when it failed to serve their attorney with a copy of the decision on their application for relief from the penalty. The Whatcom County Superior Court reversed the dismissal and remanded the matter to the PCHB for a hearing on the merits.
¶7 On December 20, 2004, the PCHB held a hearing on the merits and on March 30, 2005, it issued its findings of fact, conclusions of law, and order. In its decision, the PCHB stated:
*149There is no dispute that some amount of dairy waste seeped into groundwater from the trench, and that groundwater more likely than not entered the trench. Therefore, the actions at the Doumas’ dairy constituted a discharge of pollutants into waters of the state under Chapter 90.48 RCW.
Clerk’s Papers (CP) at 174-75. The $53,000 penalty Ecology assessed had two components. The gravity portion of the penalty totaled $40,000. The economic benefit portion of the penalty totaled $13,000.7 Based on testimony regarding the costs of having the dairy waste pumped and removed from the Doumas’ dairy, the PCHB concluded that the $13,000 economic benefit calculation was approximately twice as high as it should have been, and it reduced the economic benefit component of the penalty to $6,500. The PCHB also suspended $10,000 of the $40,000 gravity component of the penalty on condition that the Doumas obtain technical assistance to review their dairy nutrient management practices and implement any recommendations and abstain from committing any water quality violations for a two-year period from the order date.
¶8 Ecology petitioned for review in Thurston County Superior Court. The Doumas petitioned for review in What-com County Superior Court. The two petitions were consolidated in Thurston County Superior Court. The superior court affirmed the PCHB’s decision in its entirety. This appeal follows.
ANALYSIS
¶9 Our state legislature has acted to prevent water pollution: “It is declared to be the public policy of the state of Washington to maintain the highest possible standards to insure the purity of all waters of the state ... to prevent and control the pollution of the waters of the state of Washington . . . .” RCW 90.48.010. To support this public *150policy, the legislature has outlawed the discharge of pollution into State waters:
It shall be unlawful for any person to throw, drain, run, or otherwise discharge into any of the waters of this state, or to cause, permit or suffer to be thrown, run, drained, allowed to seep or otherwise discharged into such waters any organic or inorganic matter that shall cause or tend to cause pollution of such waters according to the determination of the department, as provided for in this chapter.
RCW 90.48.080. This case involves the application of this public policy of preventing water pollution to the actions of the Doumas as dairy farmers.
¶10 The legislature has also determined:
[T]here is a need to establish a clear and understandable process that provides for the proper and effective management of dairy nutrients that affect the quality of surface or ground waters in the state of Washington. The legislature finds that there is a need for a program that will provide a stable and predictable business climate upon which dairy farms may base future investment decisions.
RCW 90.64.005. In fact, an entire RCW chapter is devoted to the treatment of dairy farm nutrients: chapter 90.64 RCW. We must determine whether chapters 90.64 and 90.48 RCW have been correctly applied to the Doumas’ actions.
¶11 RCW 90.48.080 prohibits the discharge of pollutants into State waters. A dairy that is determined to be a significant contributor of pollution based on actual water quality tests, photographs, or other pertinent information is subject to the provisions of chapters 90.64 and 90.48 RCW, including civil penalties issued under RCW 90-.48.144. See RCW 90.64.030(6). Therefore, a dairy may be subject to the general enforcement provisions of RCW 90.48.080 if it is determined to be a significant contributor of pollution under chapter 90.64 RCW. Thus, our task is to carefully review the law, the record, and the parties’ arguments to determine if the record supports the finding *151that the Doumas discharged pollutants into State waters and whether the conditions that allow a chapter 90.48 RCW enforcement action to proceed against a dairy were established.
I. Standard and Scope of Review
¶12 “In reviewing an administrative action, [this] court sits in the same position as the superior court, applying the standards of the WAPA [Washington Administrative Procedure Act, chapter 34.05 RCW] directly to the record before the agency.” Tapper v. Employment Sec. Dep’t, 122 Wn.2d 397, 402, 858 P.2d 494 (1993). The WAPA allows a reviewing court to reverse an administrative decision when: (1) the administrative decision is based on an error of law, (2) the decision is not based on substantial evidence, or (3) the decision is arbitrary and capricious. RCW 34.05.570(3). “ ‘Arbitrary and capricious action has been defined as willful and unreasoning action, without consideration and in disregard of facts and circumstances. Where there is room for two opinions, action is not arbitrary and capricious even though one may believe an erroneous conclusion has been reached.’ ” Heinmiller v. Dep’t of Health, 127 Wn.2d 595, 609, 903 P.2d 433 (1995) (quoting Pierce County Sheriff v. Civil Serv. Comm’n, 98 Wn.2d 690, 695, 658 P.2d 648 (1983)).
¶13 We review questions of law de novo but accord substantial weight to the agency’s interpretation of the statutes it administers. Superior Asphalt & Concrete Co. v. Dep’t of Labor & Indus., 112 Wn. App. 291, 296, 49 P.3d 135 (2002) (citing Everett Concrete Prods., Inc. v. Dep’t of Labor & Indus., 109 Wn.2d 819, 823, 748 P.2d 1112 (1988)). We review the PCHB’s findings of fact for substantial evidence in light of the whole record. RCW 34.05.570(3)(e). Substantial evidence is evidence that is sufficient to persuade a fair-minded person of the truth or correctness of the matter. King County v. Cent. Puget Sound Growth Mgmt. Hearings Bd., 142 Wn.2d 543, 553, 14 P.3d 133 (2000). On mixed questions of law and fact, we independently determine the *152law, then apply it to the facts as found by the agency. Hamel v. Employment Sec. Dep’t, 93 Wn. App. 140, 145, 966 P.2d 1282 (1998).
¶14 The Doumas argue that the PCHB’s decision erroneously applied and interpreted the law, was not supported by substantial evidence, and was arbitrary and capricious. Ecology argues that we should defer to its interpretation of chapter 90.48 RCW8 and that the PCHB cannot reduce or add new conditions to a penalty Ecology established unless the PCHB concludes that Ecology’s penalty determination is incorrect in a particular respect. Ecology contends that the PCHB’s decision to reduce and suspend portions of the penalty is based on an erroneous interpretation and application of the law and is not based on substantial evidence.
¶15 In assessing these arguments, we apply the WAPA standards directly to the administrative record before the PCHB.
II. Chapter 90.48 RCW Violation
RCW 90.64.030(6)
¶16 The Doumas argue that Ecology bore the burden of proving by a preponderance of the evidence that the violation occurred and the penalty was reasonable under WAC 371-08-485.9 They argue that the PCHB wrongfully concluded that Ecology met its burden of proving that the Doumas violated chapter 90.48 RCW. The Doumas contend that the legislature has determined that dairies shall be treated differently than other entities and that the Doumas cannot be subject to chapter 90.48 RCW enforcement provisions without a finding that it was a “significant contribu*153tor of pollution” under RCW 90.64.030(6). Ecology responds that RCW 90.64.030(6) does not shield the Douinas from enforcement under RCW 90.48.080. Ecology asks us to “deny the Doumas’ invitation to rewrite chapter 90.64 RCW to provide them with an enforcement shield for their deliberate and intentional violations of this state’s environmental laws.” Resp’t/Cross-Appellant’s Br. at 19.10 The law lies between the parties’ positions.
¶17 The PCHB concluded that chapter 90.64 RCW does not establish a process for making a formal determination that a dairy is a “significant contributor of pollution” as a condition precedent to instituting an enforcement action. CP at 176. Rather, it noted, “[T]his phrase is consistent with the statutory purpose of the [dairy nutrient management act] to provide technical and compliance assistance, while retaining enforcement authority when necessary to address serious violations.” CP at 176. Furthermore, the PCHB noted that chapter 90.64 RCW “does include a limitation on what discharges from dairies constitute a violation of [chapter 90.48 RCW].” CP at 176.
¶18 RCW 90.48.080 makes it unlawful for any person to allow any organic or inorganic matter that shall cause or tend to cause pollution11 to seep into State waters. RCW 90.64.030(6) specifically provides that a dairy that is a significant contributor of pollution is subject to the enforcement provisions of chapter 90.48 RCW, including civil penalties levied under RCW 90.48.144.12 Ecology ar*154gues, however, that RCW 90.64.120(1) provides that “nothing in this chapter shall affect the department of ecology’s authority ... to administer . . . the provisions of [c]hapter 90.48 RCW.” Resp’t/Cross-Appellant’s Br. at 11. Although the Doumas fail to respond to this argument, we find that it is misplaced. Ecology misinterprets the RCW 90.64.120(l)’s actual language. The subsection, in its entirety, states:
Nothing in this chapter shall affect the department of ecology’s authority or responsibility to administer or enforce the national pollution discharge elimination system permits for operators of concentrated dairy animal feeding operations, where required by federal regulations or to administer the provisions of chapter 90.48 RCW.
RCW 90.64.120(1) (emphasis added). This statute highlights the interplay between federal and state laws as they relate to national pollution discharge elimination system (NPDES) permits. Under federal law, states are authorized to impose stricter requirements under these permits than federal law required. See Water Quality Act of 1987, Pub. L. No. 100-4, 101 Stat. 7 (1987). Thus, RCW 90.64.120(1) allows Ecology to impose stricter standards under chapter 90.48 RCW when administering one of these permits. This interpretation of RCW 90.64.120(1) is consistent with the placement of the statute’s single comma, which indicates that Ecology’s ability to administer NPDES permits under both federal and state law was not affected by chapter 90.64 RCW. It is clear that the phrase “where required by federal regulations or to administer the provisions of chapter 90.48 RCW” modifies the language that appears before the comma and does not exist independently of this language. RCW 90.64.120(1).
¶19 RCW 90.64.120(1) does not, as Ecology argues, operate to shield chapter 90.48 RCW from the subsequently enacted RCW 90.64.030(6). Chapter 90.64 RCW, which specifically addresses dairies, was intended to balance the need for clean water with the need for dairies. If Ecology *155were permitted to bring an enforcement action against a dairy without first establishing that it was a significant contributor of pollution under RCW 90.64.030(6), then the statute — which establishes a separate standard by which a dairy is assessed for potential water pollution violations— would be rendered meaningless. RCW 90.64.030(6), then, may provide a potential defense for a dairy charged with violating chapter 90.48 RCW In other words, a dairy that is not determined to be a significant contributor of pollution is not subject to chapter 90.48 RCW penalties. In the unpublished part of this opinion, we will examine the evidence to determine if it supports a finding that the Doumas were a significant contributor of pollution in this case.
¶20 A majority of the panel having determined that only the foregoing portion of this opinion will be printed in the Washington Appellate Reports and that the remainder shall be filed for public record pursuant to RCW 2.06.040, it is so ordered.
Houghton and Hunt, JJ., concur.