A mine needs to build an evaporation pond to ensure that runoff from the mine site does not enter the surrounding environment i.e. all the runoff from the site is to be evaporated. The volume of runoff entering the pond each month is listed in the table below. The mine is located near Orange in NSW. 

Your task is to design the pond by determining the required surface area and depth so there is no runoff from the pond in any month of the year and that by the end of the year all the runoff from the site has been evaporated. Runoff can be stored for more than one month if necessary although the pond must be empty at the end of the year. You should model each month of the year to prove that there are no overflows and that at the end of the year the pond is empty. The pond should have as small a surface area as possible whilst meeting the above criteria. The maximum depth is limited to 300 mm, but the pond should be shallower if possible. 

Assume that the runoff enters the pond at the start of each month. It is up to you to obtain appropriate evaporation rates to be used for design; this may be either observed or modelled estimates of evaporation. You can assume that the base of the pond is completely sealed so there are no infiltration losses into the ground. Show your working and the data you have used to justify your answer. 

Your answer should include appropriate plots to illustrate your results. Discuss the uncertainties that are likely in your answer. There are many possible correct answers to this problem - the important point is to make reasonable assumptions, justify your answer and show how you have minimized the pond surface area whilst meeting the constraints.

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Month Mean Runoff (m³) Month Mean Runoff (m) Jan 42 Jul 45 Feb 38 Aug Sep Oct 48 Mar 32 40 Apr May Jun 26 41 34 Nov 38 36 Dec 40 Month Mean Runoff (m³) Month Mean Runoff (m) Jan 42 Jul 45 Feb 38 Aug Sep Oct 48 Mar 32 40 Apr May Jun 26 41 34 Nov 38 36 Dec 40