Impacts of natural gas development compared with silviculture on surface water quality at the Alto Experimental Watersheds

In the spring of 2008 two natural gas wells were drilled at the Alto Experimental Watersheds. At the first site (F-1), the well pad was constructed directly in the channel of an intermittent headwater stream and had a total watershed area of 13.7 ha with the area disturbed by the well pad comprising 1.4 ha. At the second site (F-2), the pad was constructed 15 m from the creek channel, with a total watershed area of 4.5 ha and an area disturbed by well pad construction of 1.1 ha. Downstream from each respective well pad, a v-notch weir was installed to measure discharge. Sediment collected in the drop box section of the weir was weighed after each runoff event. Water samples from these runoff events were collected at the mouth of the weir for water quality analysis. Data obtained from the storm water runoff were then compared to the results of previous studies at the Alto Watersheds contrasting the difference in the impacts of silviculture to natural gas development. In addition to observed field data, the ArcAPEX (Agricultural Policy/Environmental Extender) Model was used to estimate land use effects. ArcAPEX was used to estimate residual impacts and to test different precipitation regimes and evaluate the resulting variation.;In spite of persistent drought conditions throughout the duration of the study, notable differences were observed between the two sites. Overall sediment losses were six and a half times greater at F-1 than F-2. Sediment accumulation was so great that it compromised the flow measuring equipment installed in the weirs. Consequently, flow data were estimated using ArcAPEX. Sediment losses at both sites were considerably greater in terms of losses per unit area of disturbance than any of the values observed in the silviculture studies. Losses per unit area were 26094 kg ha-1 at the site where the pad was constructed in stream and 4100 kg ha -1 where the pad was offset from the stream with a riparian buffer. In the silviculture studies losses per unit area were 2409 kg ha-1 in the treatments where no Best Management Practices (BMPs) were used, and 208 kg ha-1 in the treatments that used BMPs. Nutrient yields were also consistently greater at F-1, further emphasizing the importance of well pad placement in proximity to nearby streams. Analysis of these data illustrated the considerable difference in impacts placed on surface water quality compared to standard silvicultural practices, further emphasizing the need for (BMPs) for natural gas development.