FEASIBILITY OF USING CONDUCTANCE AND REMOTE SAMPLING FOR MONITORING STREAMS FOR HYDROFRACTURING FLOWBACK WATER: HAS THE HORSE ALREADY LEFT THE BARN?

Production of natural gas from the Marcellus Formation produces large volumes of very saline Na/Ca/Cl dominated “flowback” water. We examine the feasibility of using specific conductance (SC) and remote sampling for flowrate and chemistry for monitoring potential receiving streams. Such monitoring would be most valuable if “red flags” were noticeable in real-time.

Chloride-selective electrodes will not serve because they do not maintain sufficient calibration for remote deployment. SC electrodes maintain reasonably good calibration, but SC by itself is inadequate for monitoring because 1) it cannot distinguish between high-Cl, low-SO4 flowback water, low-Cl, high-SO₄ mine drainage, and high-Cl, low-SO₄ road salt runoff, and 2) poor mixing in some streams could give false negative signals if sensors are poorly located and miss a high conductivity event. Combining SC with continuous flowrate or stage monitoring can also give both false positives and false negatives due to hysteresis in flowrate/SC response.

SC electrodes can be used to activate remote water samplers during unusual SC spikes, allowing for collection of water samples for later chemical analysis. Such analyses could be used forensically to determine the likely cause of an anomalous SC event. However, the SC event will likely be long over by the time lab analyses are interpreted, and thus the time for remedial action will have been missed, leaving open only the possibility of punitive action. Mixing modeling suggests that such combined remote detection and sampling would be most effective in small watersheds, but not in large watersheds.

Preliminary feasibility of deployment of SC electrodes with remote water samplers was examined. In order to estimate a reasonable number of deployments, we mapped Marcellus wells, small watersheds, and streams with Strahler order < 5. 1200 small watersheds had a least one Marcellus well. Targeting watersheds with high well density gave 350 watersheds with > 1 well per km^2. Assuming installation (without maintenance) of $15000 per deployment requires a $5 million capital outlay. Vandalism and equipment failure could also be a significant problem for the reliability of remote monitoring stations.