Characterizing Storm Water Runoff from Natural Gas Well Sites in North-Central Texas Paul F. Hudak and David J. Wachal Department of Geography University of North Texas

Introduction *Annually, 30,000+ natural gas wells drilled in U.S. *Potentially adverse to surface water quality (sediment, hydrocarbons, metals) *However, few studies have been conducted

Introduction (continued) *The objective of this proposal is to characterize storm water runoff from natural gas well sites in north-central Texas

Background *Adverse effects of “typical” construction activity well known - Regulated by National Pollutant Discharge Elimination System (NPDES), requiring erosion control, storm water pollution prevention plans, site monitoring

Background (continued) *Adverse effects of gas well construction not well known - Oil and gas field operations exempt from federal NPDES permitting requirements

Methods *Collect storm water runoff from 3 natural gas well sites, 2 undisturbed reference sites in southwest Denton County - Grand Prairie, montmorillonitic clays - Average annual rainfall 99 cm, thunderstorms common *ISCO flow-interval samplers: Up to 18 discrete 1000 ml samples *40 runoff events (total) at gas well sites, 10 at reference sites, over a two-year period

Methods (continued) *Collect during rain events *Metals, petroleum hydrocarbons, sediment - Nonparametric statistics to compare differences between gas well, reference sites - Estimate annual sediment yields

ParameterMethodDetection Limit AlkalinitySM 2320 B1.0 mg l -1 CalciumEPA mg l -1 ChlorideSM 4500 Cl (D) a mg l -1 ConductivitySWQMP b 10 µS m -1 HardnessSM 2340 C1.0 mg l -1 pHSWQMP b NA TDSSWQMP b 10.0 mg l -1 TSSSM 2540 D4.0 mg l -1 TurbiditySWQMP b NA Arsenic (As)EPA mg l -1 Cadmium (Cd)EPA mg l -1 Chromium (Cr)EPA mg l -1 Copper (Cu)EPA mg l -1 Iron (Fe)EPA mg l -1 Lead (Pb)EPA mg l -1 Manganese (Mn)EPA mg l -1 Nickel (Ni)EPA mg l -1 Zinc (Zn)EPA mg l -1 TPHTCEQ mg l -1 BTEXEPA 2081 B1.0 µg l -1c ; 2.0 µg l -1d a based on turbidity of sample; b Surface Water Quality Monitoring Procedures Manual (TCEQ, 1997) using Hydrolab, Y.S.I., or other similar meter; c for each Benzene, Toluene, Ethylbenzene, o-Xylene; d for each m-Xylene, p-Xylene Methods (continued) Analytical Methods and Detection Limits

Parameter a n b /n c p-valueRatio d Alkalinity40/10< Chloride40/ Conductivity40/10< Hardness40/10< pH40/10< TDS40/ TSS39/8< Turbidity37/9< Calcium36/8< Iron36/8< Manganese36/8< Nickel36/ a Parameters containing more than 50% of storm event EMCs below detection limit (As, Cd, Cr, Cu, Pb) were not analyzed; b no. of gas well site samples; c no. of reference site samples; d ratio of median EMCs for reference and gas well sites. Example Statistical Procedure (Preliminary Results): Wilcoxon Rank-Sum and Ratio of Median EMCs

Methods (continued) *Also compare observations to drinking water standards and aquatic life criteria (the level of a pollutant or other measurable parameter that allows for protection of aquatic life)

Conclusion and Expected Benefits *Study will show which pollutants are higher at gas drilling sites compared to other construction sites *Helps inform monitoring strategies *Is beneficial to academic community, drillers, and regulatory agencies

Conclusion and Expected Benefits (continued) *If pollutant levels are similar to, or higher than, other construction sites, this may signal a need for also regulating gas well sites *Future work could focus on best management practices for reducing pollutants from gas well sites similar to construction sites (regulated under NPDES)