This action was brought by respondent developers, Dujardin Development Company, Conner Development Company, and Henderson Homes, Inc., for a refund of money paid to the City of Bothell (Bothell) as park impact mitigation fees imposed as a condition of Bothell's approval of preliminary plats for three separate subdivisions proposed by the three developers. They allege that Bothell's assessment and expenditure of the park impact mitigation fees violated RCW 82.02.020.
Bothell contended below, inter alia, that the action was barred by the 30-day statute of limitations period established by RCW 58.17.180 for review of a municipal action approving or disapproving plats. The trial court ruled that the 30-day statute of limitations period did not apply to this action and that both Bothell's assessment and its expenditure of the park impact mitigation fees violated RCW 82.02.020. It concluded that Bothell did not have any ascertainable standards for evaluating the impact of proposed developments on the park system, that Bothell had failed to specifically identify any direct impact of respondents' developments on its park system, that the fee agreements were not executed vohmtarily, and that the funds were not *199properly expended as required by RCW 82.02.020. The trial court accordingly awarded judgment against Bothell in the amount of $106,000 plus prejudgment interest. We reverse.
In the course of negotiating with Bothell for preliminary plat approval, each of the developers1 executed a mitigation agreement stating that the proposed developments would have a direct impact on the existing park system and agreeing to pay fees of $400 per dwelling unit at the time of final plat approval to mitigate that impact. The agreement recited that the fee was in lieu of dedicating land within the subdivision for the same purpose. Public hearings were held on each of the proposed developments before the planning commission and the city council. Bothell approved each of the preliminary plats conditioned on payment of the park impact mitigation fee.2 The fees were paid, final plat approval was granted, building permits were issued, and the homes were constructed and sold.
I
Estoppel
Bothell affirmatively asserts the defense of estoppel, the elements of which are: (1) an admission, statement or act inconsistent with a claim afterward asserted; (2) action by another in reliance upon that act; and (3) that the relying party would suffer injury if the party to be estopped were allowed to repudiate the earlier admission, statement or act. PUD 1 v. Walbrook Ins. Co., 115 Wn.2d 339, 347, 797 P.2d 504 (1990).
*200The developers first reply that Bothell failed to timely raise the defense, asserting it was raised for the first time in a motion to reconsider the trial court's judgment. We disagree. Bothell raised the defense in its answer to the complaint. Evidence presented at trial supports the estoppel theory. Thus, it was timely raised and may be considered here.
In reviewing Bothell's estoppel defense, we must consider the substantial economic benefit these developers received by approval of their plats and the construction and sale of the homes thereon. The fact that these developments have been completed and sold prevents Bothell from negotiating any solution to the park fee imposition issue other than refund. We cannot countenance allowing a developer to challenge plat approval conditions when the challenge is raised for the first time only after reaping the economic benefits secured by silent acceptance of those same conditions. See Trimen Dev. Co. v. King Cy., 65 Wn. App. 692, 702, 829 P.2d 226 (1992). A developer may not enter into an agreement under RCW 82.02.020, obtain the benefit of it without any challenge to the municipality's right to condition plat approval on such agreement, and then assert its invalidity. These facts evoke estoppel in its most classic form.
The developers assert that Bothell may not rely on estoppel since it has "unclean hands". They point out that the trial court concluded the agreements were not executed voluntarily and the imposition of park fees was contrary to RCW 82.02.020.
We find no support in the record for the developers' charge that Bothell lacked clean hands in somehow forcing these fee-in-lieu agreements. The developers could have chosen instead to dedicate land, for example.
Furthermore, though the agreements may not comply with the requirement of RCW 82.02.020 that direct impacts of a particular development be identified, Bothell did have the fundamental authority under RCW 58.17.110 to require of these developers dedications of land or, under RCW 82.02-*201.020, fees in lieu thereof. Thus, these were not wholly void assessments. See Ivy Club Invs. Ltd. Partnership v. Kennewick, 40 Wn. App. 524, 530-31, 699 P.2d 782 (taxing authority under RCW 82.02.020 concerns dedications of land or fees in lieu thereof under RCW 58.17.110), review denied, 104 Wn.2d 1006 (1985). Indeed, in many instances developers may prefer to sign agreements of this type rather than face the alternatives of either enduring the costs and delays inherent in an in-depth analysis of direct impacts or risking modifications to or rejection of plat applications due to unmitigated impacts. We do not imply that a developer may not elect to stand on its statutory rights and demand such an analysis. There is simply no violation of RCW 82.02.020 when both parties agree to forgo such a procedure in favor of agreeing on a less specific method of fee exaction and expenditure.
The developers herein signed agreements based on city ordinances, resolutions and staff reports stating that their proposed developments would have a direct impact on Both-ell's park system and that the fees necessary to mitigate that impact were imposed in lieu of a dedication of land. Bothell relied upon these agreements in approving the preliminary plats, permitting the homes to be constructed, and planning the expenditure of the funds on park-related improvements. Bothell should not now be expected to refund those fees which have already been expended or allocated for improvements to its park system. We thus conclude that the developers' claims both as to fee imposition and expenditure are barred by estoppel.
II
Statute of Limitations
We next address whether the 30-day limitation provided in RCW 58.17.180 for actions challenging the approval or disapproval of proposed plats applies to this action for recoupment of park mitigation fees imposed as a condition of plat approval. The answer to that question turns on the interplay *202between RCW 58.17.110, RCW 58.17.180, and RCW 82.02-.020.
RCW 58.17.110 requires a municipality to inquire into the public use and interest that will be served by a proposed subdivision and to determine if appropriate provisions are made for, among other things, open spaces and parks. If the proposed plat does not make appropriate provisions, the municipality may deny the plat or require dedication of land to a public body as a condition of subdivision approval. RCW 58.17.180 provides for judicial review of decisions concerning plat approval:
Any decision approving or disapproving any plat shall be reviewable for unlawful, arbitrary, capricious or corrupt action or nonaction by writ of review before the superior court of the county in which such matter is pending. . . .
Application for a writ of review shall be made to the court within thirty days from any decision so to be reviewed.[3]
See Northwest Land & Inv., Inc. v. Bellingham, 31 Wn. App. 742, 644 P.2d 740 (1982).
RCW 82.02.020 preempts local taxation in certain areas and specifically provides that no city "shall impose any tax, fee, or charge, either direct or indirect, ... on the development [or] subdivision ... of land." The version of the statute in effect at the time these agreements were negotiated specifically exempts dedications of land pursuant to RCW 58.17-.110 from this overall state tax preemption statute.4 RCW 82.02.020 further provides for voluntary agreements to allow payments in lieu of dedicating land or to mitigate a direct impact identified as a consequence of a proposed development, subdivision, or plat. RCW 82.02.020 itself makes no provision for review or appeal of these agreements.
*203Respondent developers assert that the 3-year statute of limitations applicable to actions on unwritten contracts, RCW 4.16.080(3),5 should apply to this action. They argue that the suit should be characterized as an action to recover void taxes on a theory of unjust enrichment, not as a challenge to approval of the plats or to the conditions of plat approval. The developers rely on Hillis Homes, Inc. v. Snohomish Cy., 97 Wn.2d 804, 650 P.2d 193 (1982) and Hart v. Clark Cy., 52 Wn. App. 113, 116, 758 P.2d 515 (1988) for this proposition.6
Hillis Homes considered the validity of park impact mitigation fees imposed before the 1982 amendments to RCW 82.02.020 which permitted agreements to pay fees in lieu of dedications of land. The court's analysis focused on whether the primary purpose of the fees was to regulate the use of land or to raise revenue. Hillis Homes, 97 Wn.2d at 809. Because no express grant of legislative authority to impose park fees existed at the time the fees were imposed, the court held that the park impact mitigation fees were an impermissible tax on development. Hillis Homes, 97 Wn.2d at 810.
Hart involved an action by developers seeking a refund of park impact mitigation fees paid under an ordinance invalidated by the holding in Hillis Homes. Because the action was filed more than 3 years after the fees were paid, the developers argued that the 6-year statute of limitations for actions on written contracts should apply. The County argued that the 3-year statute of limitations for unwritten contracts should apply. Hart, 52 Wn. App. at 114-15. The court's analy*204sis of this issue focused on whether the agreement was written or unwritten. Because it concluded that the agreement was unwritten, the court held that the 3-year statute of limitations applied. Hart, 52 Wn. App. at 115-16. The court expressly refused, however, to consider whether RCW 58.17-.180's 30-day statute of limitations applied because the question was not properly before it. Hart, 52 Wn. App. at 119. Hart thus does not resolve the question before us in this case.
Neither does the respondent developers' citation to the recent case of Robinson v. Seattle, 119 Wn.2d 34, 830 P.2d 318 (1992) assist them in their attempts to establish a 3-year statute of limitations. Relying on Hart, that case similarly held that a 3-year statute was applicable to refund actions for invalid taxes. However, the fees at issue have not been held to be an invalid tax. As we have held above, Bothell had fundamental authority to require land dedications or fees in lieu thereof. Thus, Robinson is not applicable here.
Respondent developers next suggest that it is significant to our analysis that RCW 58.17.180 does not incorporate RCW 82.02.020 "by its terms". However, RCW 58.17.180 predated RCW 82.02.020 by a number of years. We cannot place any significance on the Legislature's failure to amend the older statute when it enacted a new one. See State v. Roth, 78 Wn.2d 711, 715, 479 P.2d 55 (1971) (in enacting new statutes, the Legislature is presumed to have considered previous enactments). As noted in Ivy Club Investors Ltd. Partnership v. Kennewick, 40 Wn. App. at 530, the authority to charge a fee under RCW 82.02.020 is explicitly conditioned on the applicability of the plat statute, i.e., RCW 58.17.110. It is the plat statute which provides the authority to require dedication of land for parks and open space in the first place. That authority is a condition precedent to RCW- 82.02.020's provision permitting agreements to pay a fee in lieu of the dedication.
Where a statute provides no express mechanism for appeal but instead supplements existing authority, we have held that claims based on the supplemental statute are to *205be brought in accordance with the statutory procedures for challenging the underlying governmental action. South Hollywood Hills Citizens Ass'n v. King Cy., 33 Wn. App. 169, 173, 653 P.2d 1324 (1982) (challenge to a plat based on the State Environmental Policy Act of 1971 (SEPA), RCW 43.21C, must be brought within the 30-day appeal period of RCW 58.17.180), rev'd on other grounds, 101 Wn.2d 68, 78, 677 P.2d 114 (1984); see also cases cited therein. In Hollywood Hills, 33 Wn. App. at 173-74, we held:
Here, RCW 58.17.180 and [the county code] provide specific mechanisms for review of the . . . preliminary plat decisions. Consequently, we hold that these enactments control the time within which all claims, including SEPA causes of action, must be brought.
Although Hollywood Hills did not address the interplay between RCW 82.02.020 and RCW 58.17.180, we believe that a similar analysis is appropriate here because RCW 82.02.020, like RCW 43.21C, supplements existing plat approval authority. When, as here, the condition being challenged is an integral part of the underlying governmental decision, law and logic dictate that it be challenged at the same time and on the same terms as the underlying action.7
The language of RCW 58.17.180 is not ambiguous: it states simply that "[a]ny decision approving or disapproving any plat shall be reviewable for unlawful, arbitrary, capricious or corrupt action or nonaction . . . within thirty days from any decision so to be reviewed." (Italics ours.) The language of Bothell Municipal Code 16.36.020, which parallels the language of RCW 58.17.180, is equally clear. Where a statute or ordinance is unambiguous, courts will give effect to the plain meaning of its language. DiGiovanni v. Tukwila, 54 Wn. App. 627, 630, 774 P.2d 1244 (1989), review denied, 114 Wn.2d 1001 (1990). Because the municipal action challenged here concerns a fee imposed as a condition of plat *206approval, we are required to give effect to the plain meaning of the language of the applicable statute and ordinance requiring that an appeal from that, or any, plat condition be brought within 30 days.
Further, the 30-day limitation period is the only logical period to apply to any condition of plat approval. The fee requirement here is indistinguishable from plat conditions requiring drainage or roads, which depend on statutes and ordinances existing independent of the plat statute itself for authority to impose the condition. No logical reason exists to apply different limitation periods to different conditions. The result would be chaotic at best.
Substituting a 3-year limitation period for the 30-day period provided by RCW 58.17.180 would also prevent the rational, orderly planning of parks and other municipal services for which fee payments can lawfully be charged. New municipalities could risk spending the funds received during the first 3 years of the 5-year statutory period within which they must be expended under RCW 82.02.020, unless they were prepared to refund those fees if a court later determined that the statute was violated. As a practical matter, 2 years is simply not enough time in which to plan for and construct municipal park improvements.
Finally, applying a 3-year limitation period to conditions of plat approval would directly contravene the policy favoring finality in land use decisions. Deschenes v. King Cy., 83 Wn.2d 714, 717, 521 P.2d 1181 (1974). The statute of limitations at issue here exists for the benefit of all parties to land use decisions.
The purpose of the 30-day limitation period of RCW 58.17.180 is to give finality to actions on zoning matters. If there is no finality to the actions on zoning matters, no landowner would ever be safe in proceeding with the development of his property.
(Citation omitted.) Veradale Vly. Citizens' Planning Comm. v. Board of Cy. Comm'rs, 22 Wn. App. 229, 239, 588 P.2d 750 (1978).
For all of these reasons, we hold under RCW 58.17.180 that claims alleging that park impact mitigation fees *207are illegally imposed are barred unless challenged by writ of certiorari within 30 days of final plat approval in the same manner that all other conditions of plat approval must be challenged.
Furthermore, in this case a challenge to the manner of expending these funds should also have been raised within the 30-day limitation period. Here, the manner and purposes of expenditure of the funds was clearly set forth in the agreements entered into during the preliminary plat approval process. For example, each agreement stated that the fees collected would be used "for capital expenditures only which include, but are not limited to the acquisition of new park sites, improvement to these sites, or additions or improvements to existing facilities." The agreements further stated, pursuant to a city ordinance, that a certain percentage of the funds would be devoted to parks in the neighborhood of the development, in a neighborhood park within one-half mile of the project, or in the nearest community park; and that the remainder of the funds would be spent on the community park system serving the community at large.
The respondent developers do not argue that Bothell misled them or is expending the subject funds other than as agreed. Rather, they challenge Bothell's expenditures made in compliance with the agreements. Precisely the same challenges could and should have been raised within 30 days of prehminary plat approval.
If the method of expenditure called for in the agreements were being disregarded by Bothell, then Bothell would be in breach of those agreements, and a different statute of limitations would apply, although any such claims might still be subject to defenses such as equitable estoppel, waiver, or laches. Alternatively, if the agreements were silent as to the manner of expenditure, and a developer believed the expenditure method violated RCW 82.02.020, then Bothell might be subject to a claim brought within 3 years of the discovery of the alleged violation of RCW 82.02.020. Neither of these allegations is raised here, however.
*208We therefore conclude that the respondents' actions are barred by the doctrine of equitable estoppel and by the 30-day limitation period set forth in RCW 58.17.180. Reversed.
Forrest, J., concurs.
Dujardin Development Company and Henderson Homes, Inc., are successors in interest to Goldsmith & Associates, Inc., and Crown Capital Corp., respectively, the entities that initially entered into agreements with Bothell to obtain preliminary plat approval for their subdivisions. For simplicity's sake, the name of the successor will be used to include its predecessor.
No evidence was presented that any of the developers challenged the park impact mitigation fee condition of approval before the planning commission or the city council. Dujardin Development Company, however, later paid the fee under protest. Preliminary plat approval was granted on the following dates: March 17, 1986 (Dujardin); January 16, 1984 (Conner); and May 11, 1987 (Henderson).
Section 16.36.020 of the Bothell Municipal Code parallels the language of RCW 58.17.180 and incorporates the 30-day appeal period.
RCW 82.02.020 was amended in 1990 to delete the reference to RCW 58.17-.110. Laws of 1990, 1st Ex. Sess., ch. 17, § 42.
RCW 4.16.080(3) provides:
"The following actions shall he commenced within three years:
"(3)... an action upon a contract or liability, express or implied, which is not in writing, and does not arise out of any written instrumentL]"
The trial court also relied on Hart in concluding that the 30-day limit under RCW 58.17.180 did not apply to the action before it.
This policy has been specifically adopted by the Legislature in the context of SEPA appeals, RCW 43.210.075(1), (2), (5), as this court previously stated in Waterford Place Condominium. Ass’n v. Seattle, 58 Wn. App. 39,46, 791 P.2d 908, review denied, 115 Wn.2d 1019 (1990).