You are to present a local environmental issue or problem, a solution or solutions to the problem, an analysis of the associated COSTS and BENEFITS of the solution(s), and a determination of the best solution(s), based on your analysis of the costs and benefits.
Be sure to not make your topic too broad. It should cover a specific town or area, not the entire world or a country. Please stay away from global warming issues. This is an extremely difficult area to narrow down locally and present reasonable solutions. It is simply much too broad for this type of presentation.
As an example, runoff from a coalmine may be contaminating the groundwater of a nearby town. A solution to abating the contaminated groundwater could be to shut down the coalmine, but at the cost of everyone losing their jobs. A benefit to this solution could be clean drinking water for the community.
There are a host of other costs and benefits associated with the solution to the above example. There are also many alternatives for solutions, none of which would make everyone happy. It is your job to find these costs and benefits for whatever solution(s) you choose and defend your solution(s) to the problem - most likely by choosing the solutions where the benefits outweigh the costs. Remember when considering costs, they go far beyond monetary costs (e.g. loss of jobs, land use, recreation, convenience, etc.)
Include a slide with the title of your presentation, then an introduction slide(s) describing the environmental problem and then naming the solution(s), the main body of the presentation should describe the solution and the costs and benefits to the proposed solution (probably 1 or 2 cost slides for each solution and 1 or 2 benefit slides for each solution), then a slide(s) with recommendations based on your cost/benefit analysis, and finally, a slide with your references.
A PowerPoint presentation is really just an outline (with topics, subtopics, and bulleted statements), so it only contains the main points (just like you make an outline when writing a research paper). If you have never used PowerPoint, there are many tutorials on the Net, such as https://www.actden.com/pp/, that explain how to create a presentation.
It is better to have a short well-organized and well-written presentation, than a lengthy one that rambles off topic.