Question that I asked:

Is there a relationship between the distance between wells, their communication status based on a pumping interference test, and whether or not they are separated by a fault?

Name of the tool or approach used:

Polyline creation and classification in ArcGIS Pro, boxplot creation and two-sided t-tests in R.

Method:

29 wells in my study area were evaluated by the Oregon Water Resources Department during pumping interference tests in 2018 and 2019. This test involves pumping one well, and seeing whether the water levels in nearby wells drop in response. I received a verbal account of the wells that did and did not communicate, sketched it on a map, and then transferred that information to ArcIS Pro. I drew polylines using the well locations as snapped endpoints. Then, I created and populated fields containing the well communication type (“communicate” for wells that respond to pumping at a nearby well, and “does not communicate” for wells that do not) and whether or not the path between two wells crosses a fault. Shape_Length in feet was automatically calculated when I created the polylines, on account of the projection I used for the shapefile.

I exported that data table to a csv and imported it in R, where I subset it into three categories: all paths, paths between wells that communicate, and paths between wells that do not communicate. I then created box plots and ran t-tests to see differences between means and distributions of path length based on communication type or fault length.

Results:

Comparing the path length and the communication type of all 29 wells involved in the communication test, there is not significant evidence of a difference in mean path length between wells that do and do not communicate because the p-value of a two-sided t-test was 0.152. While the mean distance between wells that do not communicate is larger than the mean distance between wells that do communicate, the overlapping interquartile ranges in both categories make this difference less significant. There is not clear evidence that distance plays a role in well communication.

There is some evidence for a difference in mean path lengths between wells that do and do not cross faults, based on a p-value of 0.047 in a two-sided t-test. The mean path length that crosses a fault is 5,139 ft, while the mean path length that does not cross a fault is 3,608 ft. Wells that are closer together are less likely to be separated by a fault.

For wells that do communicate, there is evidence of a difference between the mean path lengths that cross faults and the mean path lengths that do not cross faults. The p-value for a two-sided t-test was 0.024. Wells that communicate but are not separated by a fault are more likely to be closer together than wells that are separated by a fault.

For wells that do not communicate, there is no evidence of a difference in mean path lengths between paths that do and do not cross faults, given a p-value of 0.98 in a two-sided t-test. Wells that do not communicate are likely to be separated by the same mean distance whether or not they are separated by faults, although there is a larger range of path length values for wells separated by a fault that do not communicate.

 

Summary of results:

Wells that communicate in pumping tests do not have a significantly different mean distance between them than wells that do not communicate (p = 0.152)

Wells that are closer together are less likely to be separated by a fault. (p = 0.047)

Wells that communicate but are not separated by a fault are more likely to be closer together than communicating wells that are separated by a fault. (p = 0.024)

Wells that do not communicate are likely to be separated by the same mean distance whether or not they are separated by faults, although there is a larger range of path length values for non-communicating wells separated by a fault. (p = 0.98)

Critique: I wish I had more sample points and paths to work with, so I could use a more interesting analysis such as ANOVA.