Ecological Impacts of Hog Lagoons

Background & Objectives

Digesters, a technology for extracting methane produced by hog waste lagoons, are an opportunity to minimize the environmental impacts associated with these lagoons. Which lagoons would provide the largest net improvement if fitted with a digester?

Evaluate the aquatic and health impacts associated with existing hog waste lagoons.
Identify a set of lagoons that would benefit most, environmentally, if fitted with lagoons. If possible take into consideration the energy production/greenhouse gas aspects of installing these digesters.

Narrowing in on an actionable project

♦ Define the study area

To make our project more manageable, we'll narrow in on a workable study area. Looking at a single county will be more feasible than looking at all of southeastern NC, and it should be easy to scale up our analyses later on if we should want to.
We will choose Duplin County to start off with. Perhaps we'll find reason to change that later, but we'll select this to start.

♦ Refine the study question and data requirements: aquatic impacts

To evaluate the "aquatic impacts" we need to further define more the aquatic resources that will be affected and how, and we'll also need to establish the metrics used to quantify impacts. Neither of these were explicitly defined by our client, Tanja Vujic, so we'll need to choose meaningful values ourselves.

What aquatic resources will be affected and how?
The primary threat hog lagoons pose to aquatic resources are from spillovers occurring during flooding events whereby highly polluted hog sludge contaminates local waterways. The resources affected then are aquatic species inhabiting contaminated streams and estuaries and possibly drinking water intakes. Thus, we'd want to discern the following:
- Where are sensitive streams and estuaries located relative to hog lagoons?
- Where are drinking water intakes (municipal and well) locations relative to hog lagoons?
- What is the likelihood that hog lagoons will spillover and contaminate these locations?
How will we measure impacts on aquatic resources?
Here we want to get at the likelihood that the above resources will be affected by hog lagoons. First, mere proximity is not necessarily indicative of whether contaminated water will reach it; instead we want to look at some sort of hydrologic distance. And secondly, not all lagoons are likely to flood so we will need to quantify that likelihood.
- How far are each hog lagoons to the resources listed above, hydrologically speaking.
- How much flooding must occur before the banks of a hog lagoon are breached?

♦ Refine the study question and data requirements: health impacts

While it would be ideal to have solid information on how far air currents might carry odors and other potential irritants from hog farms, we're not likely to find that. Instead, we'll rely on papers such as Murray (2009) to guide us in evaluating the demographics affected by our various hog farms. Specifically we'd want to discern

How far away are the airborne impacts of hog lagoons likely felt.
What are demographic characteristics of census tracts/block groups found within this area? Are these demographics substantially different than other areas within the county or region?

♦ Refine the study question and data requirements: energy considerations

Biogas processing will be more cost effective if multiple lagoons can feed into the same pipeline. The cost effectiveness of biogas processing is a factor of how many hogs are producing waste and how far the facility is from an existing pipeline. Thus sometimes two nearby hog smaller farms are better candidates than a single farm. While solving this two-factor problem can be challenging, we can certainly provide relevant information, namely:

How far is each hog farm from the nearest gas pipeline?
What if we were to adjust cost to minimize road crossings and building pipelines over water?
What if we were to truck the biogas to the nearest pumping facility?

♦ Contemplate you analysis and output options

With the main bits out of the way, it's also useful to think about your project more broadly and how it will proceed:

Data analysis
- As mentioned above, you will want to sketch out the logical workflow going from data to results prior to diving in. This will allow you to perhaps foresee any potential flaws in your analysis or data gaps. This is just a sketch, of course, and you can deviate from it later, as needed.
Presentation of results
- You will also want to consider how you will present your results most effectively. Tables? Plots? Maps? Which is the best format to communicate your findings, to answer you initial question, given your intended audience.

♦ What's next?

From the above, you should have a better idea of the tasks at hand. The first step is usually to accumulate the data you need. I find that if you are working in teams, building a shared web map in ArcGIS online can be useful. In fact, I have created on myself, which you are welcome to use: http://arcg.is/1fXaXD

Next, you'll want chip away at your analyses. If you get stuck, seek help from your classmates, TAs, and instructor. Remain focused and keep in mind that time is limited. A well formed and presented simple analysis is better than an incomplete and sloppy complex analysis. You may find it necessary to make some sweeping assumptions which is fine as long as you are transparent and allude to how these assumptions might bias your results.