Saturday, August 3, 2013

The source of elevated constituents is speculative, but... - Part 7

The UT Arlington webpage describing the study titled "An evaluation of water quality in private drinking water wells near natural gas extraction sites in the Barnett Shale Formation" states this:
Researchers gathered samples from private water wells of varying depth within a 13 county area in or near the Barnett Shale in North Texas over four months in the summer and fall of 2011. Ninety-one samples were drawn from what they termed “active extraction areas,” or areas that had one or more gas wells within a five kilometer radius.
They compared the samples to historical data on water wells in these counties from the Texas Water Development Board groundwater database for 1989-1999, prior to the proliferation of natural gas drilling.
The website states this as one of the results of the study:
Arsenic occurs naturally in the region’s water and was detected in 99 of the 100 samples. But, the concentrations of arsenic were significantly higher in the active extraction areas compared to non-extraction areas and historical data.
The paper states this:
The United States Geological Survey (USGS) sampled arsenic as well as pesticides, nitrates, and volatile organic compounds (VOCs) in drinking water wells, including wells from aquifers overlying the Barnett Shale formation. Using these data and other data from the Texas Water Development Board, Reedy et al. characterized groundwater in the Trinity and Woodbine aquifers as generally good quality with very few exceedances for constituents such as arsenic, selenium, strontium, and barium.
So we have good groundwater to start with.  The paper states that they collected samples and performed analytical tests for certain chemicals of concern.  Then they write:
These data were compared to a historical dataset from the same aquifers prior to the expansion of natural gas extraction activities
And now we have a before and after to make some type of inference.
While our data indicate elevated levels of potentially harmful compounds in private water wells located near natural gas wells, it is important to recognize that there were also a number of private water wells in close proximity to natural gas wells that showed no elevated constituents.
This indicates that natural gas extraction activities do not result in systematic contamination of groundwater.
If it did, we would expect to see contaminants in all the wells.  Fair enough.  I concur (for whatever that's worth). So, what's going on?
We suggest that episodic contamination of private water wells could be due to a variety of natural and anthropogenic factors such as the mobilization of naturally occurring constituents into private wells through mechanical disturbances caused by intense drilling activity, reduction of the water table from drought or groundwater withdrawals, and faulty drilling equipment and well casings.
There's that "sandwich effect" I talked about in Part 2.  But wait, there's more...
The geographic locations of elevated constituent levels in our study are consistent with the notion that mechanical disturbance of private water wells and industrial accidents (e.g. equipment failure, faulty well casings, fluid spills,) are more frequent in areas where natural gas extraction is active.
Here is my takeaway when I read this report.
  1. The water was low in arsenic and other CoCs before the year 2000
  2. Arsenic, in particular, is higher in wells closer to active gas wells.
  3. That level of arsenic, in almost a third of the wells sampled, is over the MCL
  4. The above MCL level of arsenic now found in the wells happened after the year 1999
  5. Mechanical disturbance of private water wells and industrial accidents (e.g. equipment failure, faulty well casings, fluid spills,) are the most probable cause as they were not present before the year 2000.
I think that's a reasonable conclusion that the majority of readers of the report would come away with.  Now let me add this to the mix.  If the level of arsenic detected in the pre-2000 year historical samples did not change after the year 1999, would that impact the "powerful argument" that natural gas drilling and extraction is the culprit?

Let's look at line 389:
...we chose to evaluate the geographic occurrence and absolute concentration changes for these constituents over time by comparing this study’s data against previous characterizations of groundwater in this region from the scientific literature and a large historical dataset from the same region.
The "plausible scenarios to explain our data" is based on a comparison of the historical dataset up to 1999 with what they found in wells from the same area.  Line 393:
This comparison shows a significant increase in the mean concentration, maximum detected concentration, and MCL exceedances for As, Se, and Sr in our study area when compared to historical data and previous characterizations of these aquifers.
So the historical samples showed "x" amount, and their samples showed "x" plus "y" amount, does this lend credibility to the notion that natural gas drilling and extraction plays a part in this?  If that notion is plausible, because there is more "x" now then in 1999, that notion would be void, if the amount of "x" after the year 1999 has not changed.  At least that's where my thinking goes.

The paper tells me that their historical data was derived from the Texas Water Development Board Groundwater Database Website. So I went there.  And like the good little cynical nerd I am, I downloaded the "Entire Groundwater Database" which is an Access Database.

And being the nerdy-type, I know how to use Access.  So I did this:

Nerdy Query I Put Together from the Texas Water Development Board Groundwater Database

Here is what I got from the query.  Please note that I am sorting by "const_val" (I removed descending from the state_well_number).  What you see in the graphic of the results below is the highest value of arsenic reported in the same wells the historical data they used in the report were collected from.  All the other values, including the ones you do not see, are lower than that.

Report from running the nerdy-query.
I limited the query to just the four counties the Railroad Commission calls "Core Counties."  This is where the bulk of the drilling takes place and where the proximity of a gas well to the groundwater well would be closest.

Notice that this query only shows two wells with levels of arsenic above 2 ppb?  All we need to know is how many samples we have post 1999 and how that would compare to the same query pre 2000.

Time to get nerdy.

Next post: Part 8.


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