water, part 3 – public water systems in or near NC gas-rich formations

The predominant concern related to hydraulic fracturing is keeping our water supply safe. In keeping the focus on North Carolina, and particularly in the Sanford sub-basin of the Triassic Basin, I did a quick GIS analysis with NCGS data and NC DENR Public Water Supply System data to identify what public water supply system intakes (wells and surface water sources) lay within or near the Cumnock formation.

Click on the image for a closer look. The map actually displays the Cumnock, Sanford, and Pekin Formations to better illustrate the extent of the organic-rich Cumnock Formation. Then I selected the public water supply intakes that lie within 5 miles of these formations to find there are:

  • 81 Public water supply system utilities lie in this area. Note, many of these systems may serve just a church, camp, or a truck stop, but they include municipal or county systems. And there are…
  • 125 intakes for those 81 systems (many utilities have multiple intakes, or sources). Of these intakes,
  • 8 are surface water sources, and
  • 117 are groundwater sources that range in depth from 40 feet to 900 feet.

I do not have the figures on the total number of customers (households) that rely on these public water systems, and I definitely do not have the number of private wells in the area. The largest utility in this target area is the City of Sanford with a population of 43,650, and their main water source is the Deep River.

As I have stated in earlier posts, the question of whether hydraulic fracturing can occur without compromising water quality remains unanswered. The energy industry says that it can occur safely. Studies showing increased methane content in water wells relative to its proximity to drilling wells cause concern. Larry Murdoch demonstrated how methane from the gas-rich formation can migrate along conduits formed in cracked casing, and shared studies that show casing fails over time. Remember, these casings will be under high pressure, making them much more susceptible to cracking. Methane will eventually get into the aquifer this way. Another possible avenue for methane to migrate into the aquifer from the gas-rich layer is simply through natural fissures in the substrate, which the fracturing process may exacerbate.

It is my impression as an amateur geologist that the bedrock in the Triassic Basins is highly fractured. I would be very curious to see a hydrogeologist’s assessment of how confined the aquifers are in this section of the Sanford Formation sub-group of the Triassic Basin; the geology in and of itself here may present very real challenges to extracting minerals safely. And that is only one piece of the puzzle to getting it right if it should happen.

{Note: all data in the map was downloaded from NC One Map}

-BT

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