(concurring in part and dissenting in part). I agree with the majority that the phrase "sudden and accidental” contained in the exception to the pollution exclusion clause is unambiguous. I also agree that the word "sudden” includes a temporal element. I write separately because the grant of summary disposition in this case was inappropriate and because I am not convinced that this leak could not possibly, as a matter of law, have been sudden. Whether the underground leak occurred gradually or "suddenly” upon the first day’s influx of by-product is a question of fact, and the case should be remanded to allow the lower court to apply the definition developed by this Court.
The lead opinion declares that the release "could not possibly be considered 'sudden’ because the release of by-product from tank fa-129 was not *218unexpected by Upjohn.” Ante, p 209 (emphasis added). This conclusion is based on Upjohn’s process of monitoring tank levels. The lead opinion describes the monitoring process as follows:
Each weekday of the year, an Upjohn employee measured the level of by-product in the tank. The employee recorded the measurement on a tank farm inventory sheet and turned the sheet over to his supervisor. Each day’s sheet was reviewed, and compared with previous days’ sheets which were kept on file at the umc facility. [Id., p 202.]
According to defendant Upjohn, however, the recordings were kept on separate sheets and were not "compared with previous days’ sheets,” until the monthly audit was performed. Since Upjohn disputes the daily comparison, there is a genuine issue of material fact, and it is inappropriate for this Court to decide which version of the facts it prefers.
Furthermore, having defined "sudden” to have a temporal element, it would seem prudent to determine the quickness with which this leak occurred. If the holes in the tank developed simultaneously upon the first day’s influx of by-product, it could be declared a "sudden” occurrence. In fact, the majority opinion confirms my belief that the leak could have been sudden:
Prior to August 16, 1982, the tank-level measurements remained constant at ten inches or 475 gallons. However, on August 16, 1982, the same day that Upjohn had pumped its first batch of approximately seventeen hundred gallons of the by-product into tank fa-129, the tank-level measurement read three inches or eighty gallons. [Id.]
This lends credence to the theory that the leak occurred "suddenly.” The by-product apparently *219ran out of the tank as rapidly as it was put in. Even if it were proper for this Court to make this factual determination, since the tank had maintained its structural integrity over the year since its last use, I cannot at this stage accept the factual conclusion that Upjohn expected this leak.
While Upjohn may have been negligent in its monitoring, the possibility of negligence is the very reason for purchasing comprehensive, general liability insurance. The lapse of time between the beginning of the leak and the discovery of the leak is not determinative of the question whether the leak was sudden or accidental. In Wagner v Milwaukee Mutual Ins Co, 145 Wis 2d 609; 427 NW2d 854 (1988), rev’d on other grounds 155 Wis 2d 737; 456 NW2d 570 (1990),1 a leak in a gas pipe which continued over a three-year period was held to have been sudden. The pipe had been damaged in 1981 when cement footings were poured around it, but the leak was not discovered until 1984. The court reasoned that "reliance on the period of time that elapsed between the event that damaged the pipe and the discovery of the leak is misplaced. . . . The length of time that elapsed before the leak was discovered is irrelevant as to the suddenness of the discharge.” 145 Wis 2d 616. This analysis applies here; there should be a determination whether the holes in the tank all gave way at once, producing a "sudden” discharge, rather than focusing on the length of time which elapsed before Upjohn discovered the leak.
I would remand for a factual determination regarding the "sudden and accidental” nature of this leak.
*220Brickley, J., concurred with Cavanagh, C.J.The Wisconsin Supreme Court modified the appellate court’s definition of "sudden and accidental” to mean "unexpected and unintended.” This definition permits recovery for unexpected damage even if it occurs over time and removes any need for a determination how "quickly” the discharge occurred. 155 Wis 2d 746.