Assessing Impacts

The second major use case for the SAWGraph project supports identifying who and where is impacted by PFAs contamination. It looks at the following types of questions:

  • Where and who is impacted? (Prevalence, risk/vulnerability mapping)
  • Which towns or counties have multiple test results with PFOS levels above 20ppt with no known contamination source nearby?
  • Which chemicals show the highest average readings in samples from a particular region?
  • Which towns/counties are most vulnerable based on their proximity to known or potential PFAS sources?

User Persona - Analytical Anna

State Environmental Toxicologist with a focus on understanding the extent and sources of environmental contamination with PFAS
Likely from a state that has already done some testing

Goals

  • UUnderstand where contamination is likely or known to be most prevalent
  • Understand where PFAS is coming from
  • Communicate contamination and exposure risk to state stakeholders (e.g. legislators, farmers, well owners)

Responsibilities

  • Identify and map PFAS contamination in the state
  • Identify significant sources of contamination in the state
  • Design contamination management and remediation plans

What is the maximum measured PFAs contamination in private well water in each county in Maine?

One first step in assessing impacts is to aggregate sampling data into administrative regions such as Counties or County Subdivisions. Vulnerability information is also aggregated to administrative regions, and regional analysis is also convenient for comparing total features (for example all private water wells) to sampled features (sampled private water wells from a specific dataset without matching identifiers).

This example uses county aggregation to determine what percentage of wells have been tested in each county, what the maximum concentration in private well water was for each county, and what percentage of tested wells were over some specified concentration limit. In this example the limit was set to the current effective public drinking water limit for the state of Maine, which is 20 ppt.

County Total Wells Tested Wells Max Concentration OverLimit Wells OverLimit Samples Percent Tested Percent OverLimit
0 Sagadahoc County, Maine 3425 53 218.310 7 25 1.55 13.21
1 Aroostook County, Maine 3231 87 2290.000 17 39 2.69 19.54
2 Cumberland County, Maine 11779 146 285.000 22 34 1.24 15.07
3 York County, Maine 10917 172 644.000 26 48 1.58 15.12
4 Hancock County, Maine 7295 49 106.000 13 19 0.67 26.53
5 Knox County, Maine 3312 15 265.000 5 7 0.45 33.33
6 Androscoggin County, Maine 5952 99 382.000 7 29 1.66 7.07
7 Penobscot County, Maine 6005 130 3650.000 55 254 2.16 42.31
8 Kennebec County, Maine 5880 296 36000.000 106 720 5.03 35.81
9 Washington County, Maine 4577 43 1674.873 29 167 0.94 67.44
10 Somerset County, Maine 2539 506 54100.000 224 2288 19.93 44.27
11 Oxford County, Maine 4985 23 2560.000 3 13 0.46 13.04
12 Waldo County, Maine 3554 297 23900.000 108 368 8.36 36.36
13 Lincoln County, Maine 5213 74 339.000 22 34 1.42 29.73
14 Franklin County, Maine 2955 8 83.300 1 1 0.27 12.50

This information can also be visualized on a map to highlight the spatial patterns in the percent of wells tested and the percent of tested wells that were over the 20 ppt limit. This limit is a variable built into the query that can be easily modified based on changing regulations or risk levels in different contexts.

Percent of Water Supply Wells Tested for PFAS

Percent of Tested Water Supply Wells Above 20ppt

This code is available here