HAS WATER DEMAND ASSOCIATED WITH HAYNESVILLE HYDROFRACTURING ACTIVITY IMPACTED WILCOX AQUIFER WATER QUALITY

In October 2007 through June 2008 study, 140 water wells which are screened in the Wilcox Formation aquifer in southern Caddo Parish, Louisiana, were sampled for water quality as related to in-situ lignite. A current study (starting in August, 2010) of water wells in Caddo, Bossier, and De Soto Parishes are for generation of a baseline of water chemistry while development of the Haynesville natural gas play is in an early stage. Approximately 320 domestic water wells have been sampled to date, 57 of which were sampled in the ’07-’08 study, and analyzed for water quality parameters and ion concentrations. The lab results were examined for changes in Wilcox water chemistry with particular attention to possible impact of Haynesville gas development activity since 2007.

Water well samples were collected after the system was purged for 20 minutes. Sample aliquots included 250 ml (non-preserved) for anions and total dissolved solids (TDS) and 100 ml (preserved with nitric acid) for cations. The samples were cooled to 4^o C in the field and transferred to permanent refrigerated storage in the lab. Concentrations of F^-, Cl^-, Br^-, NO₂^-, NO₃^-, SO₄^2-, and PO₄^3- in the non-preserved samples were measured using a Dionex ICS-1000 Ion Chromatography System; TDS were determined by weighing evaporation residue. The preserved samples were analyzed for a number of metals, including Al, As, Ca, Cd, Fe, and Pb, using a Varian (ICP-OES model MPX) Inductively Coupled Plasma-Optical Emission Spectrometer.

Ionic concentrations, TDS, and water quality parameters were compared with analyses from the earlier (’07-’08) study, accounting for the individual Wilcox aquifer sands that were tapped by the wells. Despite some inconsistencies in trends the results indicate significant changes in water chemistry at the sampled wells over the three year period, apparently due to downward movement of ground-water from upper to lower sand within the aquifer. Rig wells that supply water for Haynesville gas development usually tap the upper sand in the Wilcox. Downward movement of water and ions is likely caused by withdrawal from deeper domestic and municipal wells in Wilcox that tap the lower sand.