How can you graph the effect of investing in repairs for a company for a given timespand?

Basically I was given a "job" in my chemistry cl for an expirement were I hold the job title, "consultant" and I had to investigate weither it was managable, given a certain maximum amount of money to spend, to repair a mine that was polluting the towns water supply. The way to solve the mine's problem is buying limestone and placing it in leakage areas to neutralizethe pH of the acid being drilled up. After researching the price for both shipping and purchasing and calculating the amount of CaCo3 needed I have a price that the company would have to spend monthly to import new limestone every month. In addition the company would have to follow EPA regulations and have the mine looked at one a month costing a great deal of money too. Copared to the amount of money they make I just need to know how to show on a graph where the benifit of repairs would stop and the negative effectsstart so that I can tell the company how long of a time period they could give advanced notice to workers