Estimation of methane concentrations and loads in groundwater discharge to Sugar Run, Lycoming County, Pennsylvania
Estimation of methane concentrations and loads in groundwater discharge to Sugar Run, Lycoming County, Pennsylvania
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宾夕法尼亚州莱康明县 Sugar Run 地下水排放中的甲烷浓度和负荷估算
DOI：
10.3133/ofr20141126
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发表时间：
2014
影响因子：
2.4
通讯作者：
S. Hynek
中科院分区：
文献类型：
--
作者：
V. Heilweil;D. Risser;Randall W. Conger;P. Grieve;S. Hynek
在宾夕法尼亚州东北部一个活跃的页岩气开发区，进行了一项河流取样研究，以估计地下水排放到一条小溪中的甲烷浓度和负荷。从宾夕法尼亚州布拉德福德县、莱康明县、萨斯奎汉纳县和泰奥加县的15条溪流中采集样本，在2013年5月和6月的一次普查中，溶解的甲烷浓度从低于最低报告限值（1.0）到68.5微克/升（μg/L）不等。采用河段质量平衡法估算地下水排放中甲烷的浓度和负荷，并将其应用于莱康明县Sugar Run 4 km河段，该河段是甲烷浓度大于或等于5 μg/L的4条河流之一。在2013年5月、6月和11月的基流期间，对河流流量和甲烷浓度进行了三次天气调查。河流下游的流量分别约为0.10、0.04和0.02立方米/秒，河流甲烷峰值浓度约为20、67和29 μg/L。为了精确估计地下水排放量和地下水甲烷排放到河流的位置，在连续的研究中，研究河段的下部被更精确地定位，5月、6月和11月的河流采样点之间的近似间距分别为800米、400米和200米。从浅层压力计和在溪流中测量的甲烷浓度峰值附近的一个渗漏处收集的样本，地下水甲烷浓度为2，300至4，600微克/升。这些现场数据，结合一维河流甲烷传输模型，表明地下水甲烷负荷分别为1.8 ±0.8，0.7 ±0.3和0.7 ±0.2千克/天，排放到糖运行。根据迁移模型，估计地下水甲烷浓度在100至3，200微克/升之间。虽然总的甲烷负荷和计算负荷的不确定性都降低了较低的径流条件和更精细的分辨率采样在6月和11月，较高的负荷在5月可能表明基流的季节性变化。这与流量计测量结果一致，表明6月和11月期间在较低流量条件下发生的流入量较少。
A stream-sampling study was conducted to estimate methane concentrations and loads in groundwater discharge to a small stream in an active shale-gas development area of northeastern Pennsylvania. Grab samples collected from 15 streams in Bradford, Lycoming, Susquehanna, and Tioga Counties, Pa., during a reconnaissance survey in May and June 2013 contained dissolved methane concentrations ranging from less than the minimum reporting limit (1.0) to 68.5 micrograms per liter (μg/L). The stream-reach mass-balance method of estimating concentrations and loads of methane in groundwater discharge was applied to a 4-kilometer (km) reach of Sugar Run in Lycoming County, one of the four streams with methane concentrations greater than or equal to 5 μg/L. Three synoptic surveys of stream discharge and methane concentrations were conducted during base-flow periods in May, June, and November 2013. Stream discharge at the lower end of the reach was about 0.10, 0.04, and 0.02 cubic meters per second, respectively, and peak stream methane concentrations were about 20, 67, and 29 μg/L. In order to refine estimated amounts of groundwater discharge and locations where groundwater with methane discharges to the stream, the lower part of the study reach was targeted more precisely during the successive studies, with approximate spacing between stream sampling sites of 800 meters (m), 400 m, and 200 m, in May, June, and November, respectively. Samples collected from shallow piezometers and a seep near the location of the peak methane concentration measured in streamwater had groundwater methane concentrations of 2,300 to 4,600 μg/L. These field data, combined with one-dimensional streammethane transport modeling, indicate groundwater methane loads of 1.8 ±0.8, 0.7 ±0.3, and 0.7 ±0.2 kilograms per day, respectively, discharging to Sugar Run. Estimated groundwater methane concentrations, based on the transport modeling, ranged from 100 to 3,200 μg/L. Although total methane load and the uncertainty in calculated loads both decreased with lower streamflow conditions and finer-resolution sampling in June and November, the higher loads during May could indicate seasonal variability in base flow. This is consistent with flowmeter measurements indicating that there was less inflow occurring at lower streamflow conditions during June and November.