An aerated lagoon (a sewage treatment pond that is mixed with air) is being proposed for a small lake community in northern Wisconsin. The lagoon must be designed for the summer population but will operate year-round. The winter population is about half of the summer population. Based on these design assumptions, the volume of the proposed lagoon is 3420 m3. The daily volume of sewage in the winter is estimated to be 300 m3. In January, the temperature of the lagoon drops to 0 C, but it is not yet frozen.

If the temperature of the waste water following into the lagoon is 15 C, estimate the temperature of the lagoon in the end of the day.