delivered the Opinion of the Court.
The People urge this court to reinstate Respondents' convictions for unpermitted disposal of hazardous waste in violation of section 25-15-3810, 8 CRS. (2002). The court of appeals reversed the convictions af*1190ter concluding that the prosecution of the Respondents was barred by the applicable statute of limitations. We affirm the judgment of the court of appeals.
We hold that the plain language of the statute, the apparent legislative policies underlying the statute, and the various federal interpretations of the term "disposal," do not provide a clear answer to the question presented herein, namely, whether the legislature intended the passive migration of waste to constitute the crime of unpermitted "disposal" of hazardous waste. We therefore conclude that the Respondents did not have adequate notice of the conduct the statute was intended to prohibit; specifically, the Respondents did not have notice that their failure to remediate contaminated soil and prevent the passive migration of previously spilled waste would constitute a continuing crime such that they would be subject to the possibility of criminal charges twelve years after the last affirmative act of disposal. Based on the rule of lenity, we accordingly construe this ambiguity in favor of the Respondents and hold that their prosecution is barred by the statute of limitations.
I. FACTS
Thoro Products Company, Inc. and its CEO, Richard E. Newman, were accused of various crimes in connection with the unper-mitted storage and disposal of hazardous waste.
Thoro, a manufacturer of spot remover and other cleaning products, was founded in 1902 by Newman's grandfather. After World War II, Newman's father became president of the company and the business was moved to its current location, an industrial area served by a railroad spur in Arvada.
Respondent, Richard E. Newman, began working for Thoro in 1974. He worked in several different roles in the business and soon rose to a supervisory position. Following his father's retirement in 1987, Newman became the president and CEO of the company.
This case arose as a result of Thoro's twenty-year business relationship with Dow Chemical Company. In 1964, as part of a plan to diversify its operations, Thoro became a bulk distribution facility for Dow. Dow shipped various chemicals to Thoro where they were pumped from rail cars into several above-ground storage tanks. Thoro would later pump the chemicals from the storage tanks into trucks for shipment to Dow's customers. Among the Dow chemicals shipped to Thoro were four types of chlorinated solvents later identified by the EPA to be potentially hazardous wastes1 These four solvents led to the plume of contamination at issue here.
While the solvents were handled at the Thoro facility, it was not uncommon for there to be a significant amount of spillage. Former employees of Thoro testified that spills occurred as a result of over-filled tank cars, leaky pumps and hoses, or accidents. Newman recounted three major spills-estimated to have discharged up to several hundred gallons of solvents-during the 1970s. Although the storage tanks were placed upon small concrete pads, the areas between the tanks and the rail tracks and between the tanks and the truck loading area were unpaved. It was therefore almost certain that a substantial amount of the solvents seeped into the soil.
The contract with Dow came to an end and Thoro stopped handling solvents at some point during 1984 or 1985, several years before Newman became CEO of the company.2 *1191Eventually, the company's fortunes declined and by 1997, Thoro was officially dissolved as a Colorado eorporation.
In the spring of 1995, high concentrations of chlorinated solvents were discovered in a water well at the Twins Inn bar and restaurant, located approximately one mile from the Thoro facility. The EPA began an investigation to determine the source of the groundwater contamination and eventually removed soil samples from the Thoro property. Based upon the nature and extent of the contamination found around the storage tanks, the EPA concluded that Thoro was responsible for the mile-long plume of contaminated groundwater.
In November 1996, the EPA, along with local law enforcement agents, executed a search warrant at the Thoro property and seized a variety of documents and records relating to Thoro's business relationship with Dow. Authorities also discovered several 55-gallon drums which, later analysis revealed, contained a mixture of various hazardous solvents.
Thoro Products Company, Inc. and Richard E. Newman were each indicted on three charges: (1) Unpermitted disposal of hazardous waste in violation of section 25-15-310, 8 C.R.S. (2002); (2) Unpermitted storage of hazardous waste in violation of section 25-15-310, 8 C.RS. (2002); and (8) Criminal mischief, a class three felony in violation of section 18-4-501, 6 C.R.S. (2002).
After a two-week trial, Thoro was convicted of all three charges. The company was sentenced to probation for ten years and assessed a fine of $750,000 for criminal mischief, $100,000 for unpermitted disposal, and $100,000 for unpermitted storage.
Newman was convicted of two charges, unpermitted disposal and unpermitted storage of hazardous waste. During sentencing, the trial court found extraordinary aggravating cireumstances and sentenced Newman to consecutive terms of incarceration of eight years for unpermitted disposal and six years for unpermitted storage.
The court of appeals reversed both Respondents' convictions for unpermitted disposal, concluding that they were barred by the statute of limitations.3 People v. Thoro Products Co., Inc., 45 P.3d 787 (Colo.App.2001). The statute of limitations, section 25-15-308(4)(a), provides that criminal charges must be brought within two years after discovery of the violation or within five years after the date on which the alleged violation occurred, whichever date occurred earlier. Respondents argued that the last act of disposal occurred no later than 1985, and that therefore the prosecution was barred. The People countered that the definition of "disposal" in the statute is broad enough to encompass the passive migration of waste in the soil or groundwater. Although Thoro's handling of the solvents had ceased, they were still "disposing" of hazardous waste because the waste continued to seep through the soil on their property. The court of appeals agreed with the Respondents and reversed their convictions.
We granted certiorari on the question of whether the passive migration of previously leaked or spilled hazardous solvents constitutes "disposal" under section 25-15-8310, 8 C.R.S. (2002).
II. ANALYSIS
Respondents were convicted of unpermit-ted disposal of hazardous waste in violation of section 25-15-310(1)(b), 8 C.R.S. (2002). That section provides: >
On or after [November 2, 1984], no person shall ... [tJreat, store, or dispose of any hazardous waste identified or listed pursuant to this article ... without having obtained a permit as required by this article....
An act of disposal is defined to include:
... the discharge, deposit, injection, dumping, spilling, leaking, or placing of any *1192hazardous waste into or on any land or water so that such hazardous waste or any constituent thereof may enter the environment or be emitted into the air or discharged into any waters, including ground waters.
§ 25-15-101(8), 8 C.R.S. (2002).
Criminal charges under this statute must be brought "within two years after the date upon which the department [of public health and environment] discovers an alleged violation ... or within five years after the date upon which the alleged violation occurred, whichever date occurs earkier ..." § 25-15 808(4)(a), 8 C.R.S. (2002) (emphasis added). Because it would be the first to run in this case, only the five-year limitation period is relevant here.
We hold, after considering various tools of statutory construction, that the General Assembly did not manifestly indicate its intent to include passive migration of waste within the meaning of "disposal." Relying on the rule of lenity, we conclude that Respondents' failure to remediate the contaminated soil and prevent the passive migration of previously spilled waste did not constitute a continuing crime such that Respondents remain subject to the possibility of criminal charges twelve years after the last affirmative act of disposal.
First, we discuss the doctrine of continuing offenses and note that the General Assembly did not explicitly declare that un-permitted disposal of hazardous waste should be construed as a continuing offense. Nonetheless, a crime may be a continuing offense if the nature of the offense indicates that the legislature "must assuredly have intended" it be treated as one. Toussie v. United States, 397 U.S. 112, 90 S.Ct. 858, 25 L.Ed.2d 156 (1970).
Next, we consider the meaning of "disposal" to determine whether the legislature intended unpermitted disposal to constitute a continuing offense. We conclude that the plain language of the statute does not answer the question.
We then consider the underlying purposes of the statute as a whole, and more specifically, the purpose of the applicable statute of limitations. We conclude that an examination of the competing policy interests reflected in the statute does not answer the question of whether the legislature intended that unpermitted disposal be deemed a continuing offense.
We further review the interpretation of "disposal" provided by various federal courts but ultimately conclude that since none of them consider the meaning of "disposal" in the context of a criminal statute of limitations, their analysis is unhelpful.
Finally, because we are unable to determine whether the General Assembly intended the passive migration of waste to constitute the crime of unpermitted disposal, we conclude, under the rule of lenity, that the Respondents did not have adequate notice that their failure to remediate previously spilled waste would result in the possibility of criminal charges.
A. The Statute of Limitations and the Doctrine of Continuing Crimes
To decide the applicability of the statute of limitations, we must determine when the alleged violation-unpermitted disposal of hazardous waste-occurred. Normally, a statute of limitations begins to run when the crime is complete; when all its substantive elements have been satisfied. See Wayne R. LaFave, et al. 4 Criminal Procedure § 18.5(a) (2d ed.1999). In this case, all the elements of the crime were satisfied at the moment Thoro's employees knowingly allowed solvents to spill into the soil without first obtaining a permit.
However, in certain cireumstances, a crime continues beyond the first moment when all its substantive elements are satisfied. See Toussie v. United States, 397 U.S. 112, 115, 90 S.Ct. 858, 25 L.Ed.2d 156 (1970); United States v. De La Mata, 266 F.3d 1275, 1288 (11th Cir.2001) ("A continuing offense is one which is not complete upon the first act, but instead continues to be perpetrated over time."); 21 Am.Jur.2d Criminal Law § 518 (1998) ("[A] continuing offense is a continuous, unlawful act or series of acts set in motion by a single impulse and operated by an unintermittent foree...."). In such a *1193continuing offense, the crime continues (and the statute of limitations does not begin to run) so long as the illegal conduct continues. See § 16-5-401(4), 6 C.R.S. (2002) ("When an offense or delinquent act is based on a series of acts performed at different times, the period of limitation prescribed by this code starts at the time when the last act in the series of acts is committed.")4 We have found no relevant case in which the doctrine of continuing offenses has been applied to impose eriminal penalties for the unpermit-ted disposal of hazardous waste.5
Because there is "tension between the purpose of a statute of limitations and the continuing offense doctrine," the Supreme Court has cautioned that "the doctrine of continuing offenses should be applied in only limited cireumstances." Toussie, 397 U.S. at 115, 90 S.Ct. 858 (holding the failure to register for the draft was not a continuing offense and the five-year statute of limitations began to run five days after defendant's eighteenth birthday). The Court further advised that, because the limitation of actions is a matter of legislative policy, it would not find a continuing offense unless "the explicit language of the substantive criminal statute compels such a conclusion, or the nature of the crime involved is such that Congress must assuredly have intended that it be treated as a continuing one." Id. Although we need not follow the Supreme Court's analysis in Tous-sie, we are persuaded that it provides an appropriate framework for analyzing the doe-trine of continuing offenses. See State v. Legg, 9 S.W.3d 111 (Tenn.1999) (adopting the Toussie analysis for continuing offenses in Tennessee).
Using Towusste as a backdrop. for our analysis, we first note that Colorado's statute contains no explicit language which compels us to conclude that the unpermitted disposal of hazardous waste is a continuing offense. This absence of explicit language is notable. For example, when the General Assembly defined the crime of conspiracy, it specifically declared that the crime was a "continuing course of conduct" which ends only upon completion of the erime or the abandonment of the agreement. § 18-2-204(1), 6 C.R.S. (2002). If the General Assembly intended to create a continuing offense in this case, it knew the sort of language it could include to unmistakably communicate this intent.
Nonetheless, as noted in Toussie, a crime may be deemed a continuing offense if the "nature of the erime" is such that the General Assembly "must assuredly have intended" it be treated as such. See Toussig, 397 U.S. at 115, 90 S.Ct. 858. Therefore, the outcome of this case depends on whether the General Assembly intended the crime of un-permitted "disposal" to include the passive *1194migration of previously spilled hazardous solvents.6
B. The Meaning of "Disposal"
In the People's view, the definition of "disposal" includes the passive migration of solvents through the groundwater. Although the Respondents have not placed any solvents into the ground since 1985, the People assert that the Respondents are continuing to "dispose" of the chemicals because the spilled solvents are still seeping through the soil.
On the other hand, Respondents contend that "disposal" includes only an affirmative act of disposal. Thus, they argue the initial spilling of solvents onto the soil was "disposal," but any subsequent seeping of the chemicals was not.
1. Plain Language
The first step in any statutory interpretation is an examination of the plain language of the statute itself. People v. Nor-tor, 63 P.3d 389 (Colo.20083). The statute defines disposal broadly:
"Disposal" means the discharge, deposit, injection, dumping, spilling, leaking, or placing of any hazardous waste into or on any land or water so that such hazardous waste or any constituent thereof may enter the environment or be emitted into the air or discharged into any waters, including ground waters.
§ 25-15-101(8), 8 C.R.S. (2002). The People embrace the word "leaking" as evidence that the legislature "must assuredly have intended" that unpermitted "disposal" includes passive migration and therefore constitutes a continuing offense. Towussie, 397 U.S. at 115, 90 S.Ct. 858. We disagree.
First, the plain meaning of "leaking" does not support the People's interpretation. We have frequently looked to the dictionary to ascertain the meaning of undefined words in a statute. See People v. Forgey, TIO P.2d 781, 788 (Colo.1989). The most common definition of "leak" is "to enter or escape through a hole, crevice, or other opening." Websters Third New International Dictionary 1285 (1986). This definition connotes the movement of the substance out of its containment through some opening. Here, the waste is not contained.
If the General Assembly intended to insert a word into the definition of disposal to describe the passive migration of underground waste, we can think of many more likely candidates than "leaking." For example, words such as "oozing," "percolating," "migrating," or "seeping," would all provide a more exact description of that event. See Carson Harbor Village, Litd. v. Unocal Corp., 270 F.3d 863 (9th Cir.2001). None of these were included in the definition.
The more likely reason for the inclusion of "leaking" in the definition is to address a situation in which waste was allowed to accidentally or negligently escape from its containment, such as a barrel or drum, or, as was the case here, from defective hoses or pumps. See United States v. Waste Industries, 556 F.Supp. 18301, 1306 (D.N.C.1982).
Next, an examination of the other descriptive words in the same statute belies a passive migration interpretation of the term *1195"leaking." The meaning of an undefined word in a statute may be determined by reference to the meaning of words associated with it. See State v. Hartsough, 790 P.2d 836, 888 (Colo.1990). Six of the seven words in the statute, "discharge," "deposit," "injection," "dumping," "spilling," and "placing," all describe an affirmative act by one or more individuals. That is, someone must discharge, deposit, inject, dump, spill, or place waste into or on any land or water. That leaves "leaking" as the only word which could arguably be subject to a passive interpretation. However, "leaking" may just as easily be subject to an active interpretation; it may be used to describe a way in which an individual could introduce waste into the environment. For example, the accidental or negligent release of solvents from defective hoses and pumps may be described as "leaking." While the word does not necessarily describe intentional conduct, it nonetheless describes an affirmative act of disposal. The fact that six of the seven words in the statute are subject only to an active interpretation lends support to the argument that "leaking" should also be given a similarly active interpretation.
We conclude that the plain language of the statute does not answer the question of whether the legislature intended that unper-mitted disposal be deemed a continuing offense. Therefore, we next consider the legislative purpose and policies underlying the statute.
2, Legislative Purpose
Initially we note that traditional sources of legislative history have proven unhelpful in this case. The parties do not cite, and our own research has not uncovered, any relevant piece of legislative history on the meaning of "disposal" under the Colorado statute. In addition, the federal statutes which form the foundation of Colorado's hazardous waste management system are similarly uncooperative in yielding useful legislative history on the meaning of "disposal." Therefore, the parties attempt to decipher the intent of the legislature by reference to their view of the purpose. and policy underlying the statute's various provisions.
The People argue that a passive migration interpretation of disposal is consistent with the legislative intent of ensuring the protection of the environment from the adverse effects of illegally disposed hazardous waste. On the other hand, Respondents argue that a passive migration interpretation of disposal thwarts the General Assembly's intent to limit the use of criminal punishment to {only recent violators of the act.
The hazardous waste management system in Colorado was created to "ensure protection of public health and safety and the environment." Part 260, Statement of Basis and Purpose, 6 C.C.R. 1007-8 (1995). The criminal penalties contained in the statute play a role in this scheme by deterring and punishing the unpermitted transportation, storage, and disposal of hazardous waste.
We acknowledge that an interpretation of disposal which excludes passive migration may indeed make it more difficult to bring criminal charges under the disposal portion of section 25-15-8310. Because of the slow movement of waste in the groundwater, the crime may not be discovered until many years after the last affirmative act of disposal. Violators are given an incentive, therefore, to remain silent regardlng their crimes and avoid prosecution.
The People, however, overstate the magnitude of this problem. First, an offender who intentionally conceals his unlawful disposal will still be subject to prosecution. See § 25-15-308(4)(a), 8 C.R.S. (2002) (providing that the statute of limitations is tolled for, any period during which a violator, intentionally conceals his misconduct). In addition, even if the potential for civil fines or criminal Hability is barred, the department of public health and environment still has the authority to issue an order requiring remediation of the site, so long as the order is issued within two years after discovery of the violation. See § 25-15-308(4)(b), 8 C.R.S. (2002).
While there is a risk that an offender will conceal his misdeeds in the hopes of avoiding prosecution, this is no less a risk here than it would be in every criminal case in which a statute of limitations exists. Nonetheless, the General Assembly saw fit to *1196include a statute of limitations for this crime. This reflects a policy choice made by the legislature to which we must defer. The purpose of a statute of limitation is to protect individuals from defending themselves against stale criminal charges, to prevent punishment for acts committed in the remote past, and to "insure that the accused will be informed of the decision to prosecute and the general nature of the charge with sufficient promptness to allow him to prepare his defense before evidence of his innocence becomes weakened with age." Higgins v. People, 868 P.2d 871, 378 (Colo.1994) (quoting Wayne R. LaFave & Jerold H. Israel, 2 Criminal Procedure § 18.5(a) (1984)). Thus, the statute provides predictability "by specifying a limit beyond which there is an irre-buttable presumption that a defendant's right to a fair trial would be prejudiced." United States v. Marion, 404 U.S. 307, 322, 92 S.Ct. 455, 30 L.Ed.2d 468 (1971). For these reasons, criminal statutes of limitations generally should be construed liberally in favor of the defendant. People v. Midgley, 714 P.2d 902, 904 (Colo.1986); Toussie v. United States, 397 U.S. 112, 90 S.Ct. 858, 25 L.Ed.2d 156 (1970).
By extending into perpetuity the period of time during which criminal charges may be brought, the People eviscerate the purpose of the statute of limitations. Under the People's interpretation of "disposal," the five-year statute of limitations will not begin to run until one of two events occurs: 1) a permit is obtained in accordance with the regulations, or 2) the waste is no longer "leaking"-éither because it has been cleaned up, or because there exists a natural barrier to its movement. In practice, an offender would be forced to admit his wrongdoing to a government agency (in order 'to obtain a permit), or hope that the geological composition of the land is such that passive migration of the waste is precluded. This could not have been the scheme the legislature intended when it created a statute of limitations for the unpermitted disposal of hazardous waste.
In summary, this case presents two competing policy interests. On the one hand, a passive migration interpretation of disposal would seem to more fully implement the legislative intent of ensuring protection of the environment. However, that interpretation thwarts the General Assembly's intent to limit the time during which criminal charges may be brought. Thus, we conclude that an analysis of the statute's purposes does not answer the question of whether the legislature intended that unpermitted disposal be deemed a continuing offense.
3. Federal Interpretation
Next, the parties urge us to look to the federal courts for assistance in discerning the meaning of "disposal." However, our review of federal law in this area reveals only that the interpretation of "disposal" adopted by federal courts tends to be quite fact and context specific. Because none of the cases cited by the parties consider the meaning of "disposal" in the context of a eriminal statute of limitations, we do not assign significant weight to their analysis.
a RCRA
The People rely primarily on federal cases interpreting "disposal" under the Resource Conservation and Recovery Act of 1976 (RCRA). 42 U.S.C. § 6901 to 6992k (1995). The state statute at issue here was derived in large part from RCRA and was intended to create a hazardous waste management program in Colorado which is similar to its federal counterpart. However, there is one notable difference between the two statutes. The Colorado statute contains a specific statute of limitations while RCRA contains no comparable provision. Instead, actions under RCRA are limited only by the more general five-year federal statutes of limitations. See 18 U.S.C. § 3282 (federal criminal offenses); 28 U.S.C. § 2462 (civil actions). While it is true that most RCRA cases have interpreted "disposal" to include passive migration, none have done so in the context of a criminal statute of limitations.
Most of the RCRA cases have arisen in one of two contexts. The first type of case involves a "citizen suit" under section 7002 of RCRA. 42 U.S.C. § 6972. That section authorizes "any person" to bring a civil action against "any person ... who is alleged to be in violation" of a RCRA permit, regulation or *1197standard. 42 U.S.C. § 6972(a)(1)(A) (1995). In order to bring a suit under section 7002, plaintiffs must first show that there is a "continuous or intermittent violation" of the statute. See Gwaltney of Smithfield, Ltd. v. Chesapeake Bay Found., Inc., 484 U.S. 49, 58-59, 108 S.Ct. 376, 98 L.Ed.2d 806 (1987) (holding that the "to be in violation" language in the Clean Water Act requires a showing of an ongoing or intermittent violation); Acme Printing Ink Co. v. Menard, Inc., 812 F.Supp. 1498, 1511 (E.D.Wis.1992) (noting that "every court that has analyzed [RCRA] section 7002 in the wake of Gwaltney has concluded that an allegation of either a continuous or intermittent violation is required").
Several courts have been asked to decide whether the passive migration of previously dumped waste constitutes an ongoing violation of the statute in these citizen suit cases. Most conclude that it does. See Fallowfield Dev. Corp. v. Strunk, 1990 WL 52745, at *10 (E.D.Pa.1990) (The prior disposal of waste is an ongoing violation "until the proper disposal procedures are put into effect or the hazardous waste is cleaned up."); City of Toledo v. Beazer Materials and Servs., Inc., 883 F.Supp. 646, 656 (N.D.Ohio 1993) (same); Acme Printing Ink Co., 812 F.Supp. at 1512 ("leaking of hazardous substances may constitute a continuous or intermittent violation"); but see Connecticut Coastal Fishermen's Ass'n v. Remington Arms Co., Inc., 989 F.2d 1305 (2d Cir.1998) (no present violation under RCRA section 7002 for the "mere decomposition of pollutants").
The second situation in which RCRA cases typically address "disposal" is in the context of a remediation action brought by the EPA under RCRA section 7003. This section grants broad equitable powers to the EPA to seek injunctive relief restraining further violation of the Act where there is an "imminent and substantial endangerment to health or the environment." 42 U.S.C. § 6978(a). Several courts have been asked to determine whether an inactive disposal site, where no affirmative acts of disposal are occurring, may constitute an "imminent and substantial endangerment." Once again, most courts accept a passive definition of "disposal" in this context. See United States v. Price, 528 F.Supp. 1055, 1071 (D.N.J.1981), aff'd United States v. Price, 688 F.2d 204 (3rd Cir.1982) (holding that section 7003 authorizes relief restraining further "leaking" of waste from a landfill but noting that section 7008 does not authorize a general cleanup of dormant waste sites); United States v. Waste Indus., 734 F.2d 159 (4th Cir.1984) (noting that section 7008 restrains more than just ongoing human conduct); United States v. Diamond Shamrock Corp., No. C80-1857, 12 Envtl. L. Rep. 20819, 20821, 1981 WL 187997 (N.D.Ohio May 29, 1981) (noting that "a disposal clearly requires no active human conduct"); United States v. Conservation Chemical Co., 619 F.Supp. 162, 200 (D.Mo.1985) (" 'disposal' occurs ... when [wastes] migrate from their initial location"); but see United States v. Wade, 546 F.Supp. 785 (E.D.Pa.1982) (noting in dicta that leaking of previously dumped waste does not constitute "disposal").
In addition, one notable case, relied on by the People, was not brought under either section 7002 or 7008. See United States v. Power Eng'g Co., 10 F.Supp.2d 1145 (D.Colo.1998), affd 191 F.3d 1224 (10th Cir.1999). In Power Engineering, the issue was whether the EPA could, under section 3008 of RCRA, enjoin a defendant, the operator of a metal refinishing plant, to. enforce state regulations. See 42 U.S.C. § 6928. Specifically, the EPA sought compliance with state regulations requiring financial assurances from owners and operators of hazardous waste facilities requiring them to document that they have sufficient resources to close their facilities and pay third-party claims that may arise. Defendants argued that since they were not currently disposing of waste, they were operating in compliance with state regulations and exempt from financial assurance requirements. The court disagreed. It held that the use of the word "leaking" in the definition of "disposal" indicated that the leaching of hazardous waste into the groundwater constitutes continuing disposal of hazardous waste. Id. at 1159-60. In so holding, the court was particularly concerned that allowing the defendant to be exempt from the financial assurance requirements would encourage others to evade or ignore the permit requirgments of RCRA. Id. at 1162.
*1198b. CERCLA
The definition of "disposal" has been interpreted much differently under another piece of federal legislation, the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) 42 U.S.C. §§ 9601 to 9675 (1995). The definition of "disposal" under CERCLA is identical to the 'definition of the term under RCRA. 42 U.S.C. § 9601(29). However, CERCLA, unlike RCRA, was created as a solution to the problem of old and abandoned waste sites. Its focus is, by its very nature, remedial. - The statute provides for potential liability for any person "who at the time of disposal of any hazardous substance owned or operated any facility at which such hazardous substances were disposed of" 42 U.S.C. § 9607(a)(2). Many courts have been confronted with the question of whether the owner of a property on which the passive migration of waste is occurring is an owner "at the time of disposal." Most courts to consider this issue have concluded that disposal does not include the passive migration of waste. Prime Tech., Inc., 120 F.3d 351 (2d Cir.1997) (prior owners are not liable under CERCLA for passive migration); Umited States v. CDMG Realty Co., 96 F.3d 706 (3rd Cir.1996) (citing the plain language of the definition of disposal in concluding that disposal does not include passive migration); United States v. 150 Acres of Land, 204 F.3d 698 (6th Cir.2000) (noting that "spilling" and "leaking" in the definition of disposal should be interpreted actively); Carson Harbor Vill Ltd. v. Unocal Corp., 270 F.3d 868, 879 n. 7 (9th Cir.2001) (noting that "[nlothing in the context of [CERCLA] or the term 'disposal suggests that Congress meant to include chemical or geological processes or passive migration"); United States v. Petersen Sand and Gravel, Inc., 806 F.Supp. 1846 (N.D.Ill.1992) (meaning of "disposal" determined in conjunction with the meaning of the statutory term "release" indicates that disposal does not include passive migration); Redwing Carriers, Inc. v. Saraland Apartments, Ltd., 875 F.Supp. 1545 (S.D.Ala.1995) (same); but see Nurad, Inc. v. William E. Hooper & Sons Co., 966 F.2d 837 (4th Cir.1992) (passive See ABB Indus. Sys., Inc. leaking of waste from tanks may constitute disposal under CERCLA).
While it is difficult to derive significant insight from this brief overview of federal law, one fact becomes apparent: the meaning affixed to "disposal" under RCRA and CERCLA depends less on the precise language of the definition and more on the specific facts and equities of each particular case and the context of the statute under which the term was interpreted.
None of the cases cited by the People or the Respondents involve the situation we confront here: the application of a statute of limitations on potential criminal prosecution. Therefore, we do not assign significant weight to the interpretation of "disposal" provided by the federal courts.
C. The Rule of Lenity
It is axiomatic that criminal law must be sufficiently clear such that a citizen will know what the law forbids. See People v. Heckard, 164 Colo. 19, 431 P.2d 1014 (1967). For this reason, ambiguity in the meaning of a criminal statute must be interpreted in favor of the defendant under the rule of lenity. People v. Lowe, 660 P.2d 1261 (Colo.1983).
The rule of lenity should not be applied to defeat the evident intent of the General Assembly. Terry v. People, 977 P.2d 145 (Colo.1999). However, if after utilizing the various aids of statutory construction, the General Assembly's intent remains obscured, the rule of lenity should be applied to resolve the ambiguity. See Muscarello v. United States, 524 U.S. 125, 138, 118 S.Ct. 1911, 141 L.Ed.2d 111 (1998) ("[the rule of lenity applies only if, after seizing everything from which aid can be derived, ... we can make no more than a guess as to what Congress intended") (internal quotations omitted); United States v. Wilson, 10 F.3d 734, 736 (10th Cir.1993) ("The rule of lenity is a rule of last resort, to be invoked only after traditional means of interpreting the statute have been exhausted.").
On numerous occasions, this court has found a genuine ambiguity in a criminal statute and adopted the interpretation which fa*1199vors the accused. See, e.g., Fields v. Suthers, 984 P.2d 1167 (Colo.1999) (holding that even if statutory term was subject to alternative interpretations, the rule of lenity requires that pre-sentence confinement credit be taken into account to determine when twenty year period for parole eligibility acerued); People v. Glover, 898 P.2d 1811 (Colo.1995) (because statutes were ambiguous, application of the rule of lenity requires that a defendant may not be convicted of felony murder and murder after deliberation where there was only a single victim); Faulkner v. Dist. Court, 826 P.2d 1277 (Colo.1992) (where statutory language lent itself to alternate constructions, application of the rule of lenity requires that a defendant who received a jail term as a condition of probation would still be eligible for good time eredit).
In this case, the plain language of the statute, the apparent legislative policies underlying the statute, and the various federal interpretations of the term "disposal," do not provide a clear answer to the question presented herein, namely, whether the legislature intended the passive migration of waste to constitute the crime of unpermitted "disposal" of hazardous waste. We therefore conclude that the Respondents did not have adequate notice of the conduct the statute was intended to prohibit; specifically, the Respondents did not have notice that their failure to remediate contaminated soil and prevent the passive migration of previously spilled waste would constitute a continuing crime such that they would be subject to the possibility of criminal charges twelve years after the last affirmative act of disposal. Based on the rule of lenity, we accordingly construe this ambiguity in favor of the Respondents and hold that their prosecution is barred by the statute of limitations.7
IH. CONCLUSION
For the foregoing reasons, we cannot conclude that the legislature intended "disposal" to include the passive migration of previously leaked or spilled waste for the purposes of the criminal statute of limitations provision contained in section 25~15-308(d)(a). Because the last affirmative act of disposal occurred more than five years before Respondents' indictment, we hold that their prosecution was barred by the statute of limitations. The judgment of the court of appeals is affirmed.
Justice HOBBS concurs. Justice BENDER dissents, Chief Justice MULLARKEY and Justice MARTINEZ join in the dissent.. The four solvents were Tetrachloroethene (PCE), Trichloroethene (TCE), 1,1,1, Trichloro-ethane (1,1,1-TCA), and Methylene Chloride.
. Respondents vigorously argued, both at trial and on appeal, that they stopped handling solvents in October 1984, prior to the effective date (November 2, 1984) of the Colorado hazardous waste management statute. See § 25-15-102(3), 8 C.RS. (2002). Therefore, Respondents contend that their prosecution violated the ex post facto clause of both the state and federal constitutions. U.S. Const. art. I, § 9, cl. 3; Colo. Const. art. II, § 11. The People, however, presented evidence that the handling of the Dow solvents continued through at least 1985. The jury made no specific finding with regard to this issue and the court of appeals, because of its holding on the statute of limitations question, did not address Respondents' ex post facto argument. For the purpose of this opinion, we will assume that *1191Thoro did, in fact, handle Dow solvents through at least 1985.
. The court of appeals also concluded that the trial court erred in sentencing Mr. Newman above the authorized statutory range for his conviction for unpermitted storage of hazardous waste. The court reversed the sentence and remanded for re-sentencing. 45 P.3d at 747-49. This part of the court's ruling is not before us.
. The most frequently cited example of a continuing offense is conspiracy. See United States v. Jaynes, 75 F.3d 1493, 1505 (10th Cir.1996) ("Conspiracy ... is the prototypical continuing offense."). In addition to conspiracy, various other offenses have been categorized as continuing offenses. See, eg., United States v. Bailey, 444 U.S. 394, 100 S.Ct. 624, 62 L.Ed.2d 575 (1980) (escape); United States v. Denny-Shaffer, 2 F.3d 999 (10th Cir.1993) (kidnapping under the federal statute); United States v. Martinez, 890 F.2d 1088 (10th Cir.1989) (failure to appear); People v. Martinez, 37 Colo.App. 71, 543 P.2d 1290 (1975) (larceny is a continuing crime and every asportation constitutes a new taking).
. The cases cited by the People are inapplicable. First, in United States v. White, 766 F.Supp. 873 (E.D.Wash.1991) the defendant was charged with unpermitted storage of hazardous waste, rather than unpermitted disposal. As the court in White concluded, there can be "little doubt" that the crime of unpermitted storage is a continuing offense. Id. at 887. The nature of the offense-storage-is such that any other interpretation would be illogical.
Second, in State v. Brothers, No. 2001-Ohio-8725, 2001 WL 1602692 (Ohio Ct.App. Dec. 14, 2001), the defendant allegedly buried drums of hazardous waste on his property from 1991 to 1997. Indicted in 1999, defendant argued that the crime of illegal disposal of waste was barred by the five-year statute of limitations. Id. at *1. The court disagreed, specifically noting that the drums were continuously leaking through 1997. Id. at *2. It was this leaking from the drums into the soil which was the "continuous" disposal for which defendants were charged. The court made no reference to any underground passive migration as is the case here.
In fact, the only criminal case we have found which considered this precise issue agreed with the analysis of the court of appeals. See L.B. Foster Co. v. State, Nos. 01-01-00299-CR & 01-01-00300-CR, 106 S.W.3d 194, 2003 WL 1563989 (Tex.Ct.App. Mar. 27, 2003).
. The People contend that Respondents' failure to obtain a permit, rather than the act of disposal, was the ongoing criminal conduct. In their view, the Thoro plant was a "disposal facility," which is defined in the regulations to include any "facility ... at which hazardous waste is intentionally placed into or on any land or water...." Rule 260.10, 6 C.C.R. 1007-3 (2001). The owners and operators of such facilities "must have permits during the active life (including the closure period) of the unit." Rule 100.10, 6 C.C.R. 1007-3 (1999). This permit requirement continues throughout the active life of the disposal facility until the department of public health and environment receives certification of final closure. Rule 260.10, 6 C.C.R. 1007-3 (1999) (defining "active life" of a facility).
The People's reliance on the permit requirements in the regulations begs the question. It is clear that Respondents did not obtain the necessary permits. However, this failure does not automatically trigger criminal liability. The crime of unpermitted disposal of hazardous waste has essentially three elements. To be convicted, a defendant must 1) knowingly 2) dispose of hazardous waste 3) without a permit. The failure to obtain a permit is merely one element. The People must still show that Respondents-within the five years prior to their indictment-were "disposing" of hazardous waste. Therefore, the outcome of this case depends on the meaning of the term, "disposal."
. Our decision is based on the rule of lenity, a doctrine which is inapplicable to civil proceed-, ings. We therefore express no opinion on the meaning of the term "disposal" in any context other than a criminal prosecution.