Repository for Oil and Gas Energy Research (ROGER)

Abstract:
The widespread use of unconventional drilling involving hydraulic fracturing (“fracking”) has allowed for increased oil-and-gas extraction, produced water generation, and subsequent spills of produced water in Colorado and elsewhere. Produced water contains BTEX (benzene, toluene, ethylbenzene, xylene) and naphthalene, all of which are known to induce varying levels of toxicity upon exposure. When spilled, these contaminants can migrate through the soil and contaminant groundwater. This research modeled the solute transport of BTEX and naphthalene for a range of spill sizes on contrasting soils overlying groundwater at different depths. The results showed that benzene and toluene were expected to reach human health relevant concentration in groundwater because of their high concentrations in produced water, relatively low solid/liquid partition coefficient and low EPA drinking water limits for these contaminants. Peak groundwater concentrations were higher and were reached more rapidly in coarser textured soil. Risk categories of “low,” “medium,” and “high” were established by dividing the EPA drinking water limit for each contaminant into sequential thirds and modeled scenarios were classified into such categories. A quick reference guide was created that allows the user to input specific variables about an area of interest to evaluate that site’s risk of groundwater contamination in the event of a produced water spill. A large fraction of produced water spills occur at hydraulic-fracturing well pads; thus, the results of this research suggest that the surface area selected for a hydraulic-fracturing site should exclude or require extra precaution when considering areas with shallow aquifers and coarsely textured soils.

Abstract:
Approximately 81% of the nation's energy demands are supported by hydrocarbons, largely in part to the relatively recent exploration of oil and gas from unconventional shale energy reserves. The extraction of shale energy requires technological ingenuity, such as hydraulic fracturing and horizontal drilling, and significant freshwater resources to successfully recover the previously sequestered hydrocarbons from low porosity formations. As unconventional oil and gas development continues to expand to meet the growing energy demands, it becomes increasingly more important to understand the potential environmental implications and to practice proper environmental stewardship. For example, concerns over water usage and the related consequences have dramatically increased due to the demand for water used in hydraulic fracturing, the increased volumes of wastewater being produced, and the need to dispose of or reuse the wastewater without compromising the surface and subsurface environments. As such, this chapter will cover the life cycle of water in oil and gas development (conventional and unconventional), including water use and waste production in the drilling, stimulation, and production phases; the current waste management strategies and challenges within the various treatment modalities; and the widespread implications of the varying forms of waste management.

Abstract:
A holistic risk assessment of surface water (SW) contamination due to lead-210 (Pb-210) in oil produced water (PW) from the Bakken Shale in North Dakota (ND) was conducted. Pb-210 is a relatively long-lived radionuclide and very mobile in water. Because of limited data on Pb-210, a simulation model was developed to determine its concentration based on its parent radium-226 and historical total dissolved solids levels in PW. Scenarios where PW spills could reach SW were analyzed by applying the four steps of the risk assessment process. These scenarios are: (1) storage tank overflow, (2) leakage in equipment, and (3) spills related to trucks used to transport PW. Furthermore, a survey was conducted in ND to quantify the risk perception of PW from different stakeholders. Findings from the study include a low probability of a PW spill reaching SW and simulated concentration of Pb-210 in drinking water higher than the recommended value established by the World Health Organization. Also, after including the results from the risk perception survey, the assessment indicates that the risk of contamination of the three scenarios evaluated is between medium-high to high.

Abstract:
A dramatic increase in unconventional drilling that utilizes hydraulic fracturing to extract oil/gas over the past decade has led to concern over handling and management of produced/ flowback water (PFW; hydraulic-fracturing wastewater) because the potential exists for its accidental release into the environment. This PFW contains high amounts of total dissolved solids acquired from interaction with the reservoir formation. Development and testing of geochemical methods, such as strontium (Sr) isotope ratio (87Sr/86Sr) analysis, to determine the origin of dissolved solids in an environment would be valuable. Samples acquired from different sources in Texas overlying and within the Barnett Shale, such as surface/ground water and PFW, contain unique Sr concentrations and 87Sr/86Sr values, with the potential to be used as a geochemical fingerprint. This study shows that because of the very high concentration of Sr in PFW and its high 87Sr/86Sr value, when as little as 1% of a sample is PFW, the sample experiences a measurable change in 87Sr/86Sr. To determine which phase within the reservoir rock imparts its 87Sr/86Sr to the PFW, sequential extractions were performed on powdered Barnett Shale core samples. Results of the extractions show varying geochemical affinities and distinct 87Sr/86Sr values by leaching solution. However, a direct link to the PFW sample was not conclusive, likely because of the unknown location of the PFW sample and the spatially variable 87Sr/86Sr of the Barnett Shale. Future work requires further cooperation with industry or federal agencies that could provide a more complete set of samples.

Abstract:
The large volume of wastewater produced during unconventional oil and gas (UOG) extraction is a significant challenge for the energy industry and of environmental concern, as the risks due to leaks, spills, and migration of these fluids into natural waters are unknown. UOG wastewater is often hypersaline, and contains myriad organic and inorganic substances added for production purposes and derived from the source rock or formation water. In this study, we examined the organic composition and toxicology of water and sediments in a stream adjacent to an underground injection disposal facility that handles UOG wastewaters. We sampled water and streambed sediments from an unnamed tributary of Wolf Creek upstream from the disposal facility, near the injection well, and downstream. Two sites downstream from the disposal facility contained organic compounds in both water and sediments that were consistent with a source from UOG wastewater. These compounds included: 2-(2-butoxyethoxy)-ethanol, tris(1-chloro-2-propyl)phosphate, α, α-dimethyl-benzenemethanol, 3-ethyl-4-methyl-1H-pyrrole-2,5-dione, and tetrahydro-thiophene-1,1-dioxide in water, diesel fuel hydrocarbons (e.g. pentacosane, Z-14-nonacosane), and halogenated hydrocarbons (e.g., 1-iodo-octadecane, octatriacontyl trifluoroacetate, dotriacontyl pentafluoropropionate) in sediments. Concentrations of UOG-derived organic compounds at these sites were generally low, typically 4 to <1 μg/L in the water, and <70 μg/g (dry wt.) in the sediment. In addition, water and sediment at a site immediately downstream from the facility contained many chromatographically unresolved and unidentified hydrocarbons. In contrast, sites upstream from the facility or in nearby watersheds not influenced by the disposal well facility contained primarily natural (biologically produced) organic substances from the local environment. Toxicological assays of human cell line exposures to water and sediment showed minimal effects. Results indicate that UOG wastewater has entered the stream and that UOG-derived organic substances are present. The contamination level, however, is low and appears to be restricted to sites immediately downstream from the disposal facility at this time.

Abstract:
The development of unconventional oil and gas (UOG) resources has rapidly increased in recent years; however, the environmental impacts and risks are poorly understood. A single well can generate millions of liters of wastewater, representing a mixture of formation brine and injected hydraulic fracturing fluids. One of the most common methods for wastewater disposal is underground injection; we are assessing potential risks of this method through an intensive, interdisciplinary study at an injection disposal facility in West Virginia. In June 2014, waters collected downstream from the site had elevated specific conductance (416 µS/cm) and Na, Cl, Ba, Br, Sr and Li concentrations, compared to upstream, background waters (conductivity, 74 µS/cm). Elevated TDS, a marker of UOG wastewater, provided an early indication of impacts in the stream. Wastewater inputs are also evident by changes in 87Sr/86Sr in stream water adjacent to the disposal facility. Sediments downstream from the facility were enriched in Ra and had high bioavailable Fe(III) concentrations relative to upstream sediments. Microbial communities in downstream sediments had lower diversity and shifts in composition. Although the hydrologic pathways were not able to be assessed, these data provide evidence demonstrating that activities at the disposal facility are impacting a nearby stream and altering the biogeochemistry of nearby ecosystems.

Abstract:
In 2010, a dramatic increase in the levels of total trihalomethane (THM) and the relative proportion of brominated species was observed in finished water at several Pennsylvania water utilities (PDW) using the Allegheny River as their raw water supply. An increase in bromide (Br−) concentrations in the Allegheny River was implicated to be the cause of the elevated water disinfection byproducts. This study focused on quantifying the contribution of Br− from a commercial wastewater treatment facility (CWTF) that solely treats wastes from oil and gas producers and discharges into the upper reaches of the Allegheny River, and impacts on two downstream PDWs. In 2012, automated daily integrated samples were collected on the Allegheny River at six sites during three seasonal two-week sampling campaigns to characterize Br− concentrations and river dispersion characteristics during periods of high and low river discharges. The CWTF discharges resulted in significant increases in Br− compared to upstream baseline values in PDW raw drinking water intakes during periods of low river discharge. During high river discharge, the assimilative dilution capacity of the river resulted in lower absolute halide concentrations, but significant elevations Br− concentrations were still observed at the nearest downstream PDW intake over baseline river levels. On days with active CWTF effluent discharge the magnitude of bromide impact increased by 39 ppb (53%) and 7 ppb (22%) for low and high river discharge campaigns, respectively. Despite a declining trend in Allegheny River Br− (2009–2014), significant impacts from CWTF and coal-fired power plant discharges to Br− concentrations during the low river discharge regime at downstream PDW intakes was observed, resulting in small modeled increases in total THM (3%), and estimated positive shifts (41–47%) to more toxic brominated THM analogs. The lack of available coincident measurements of THM, precursors, and physical parameters limited the interpretation of historical trends.

Abstract:
Real and potential environmental effects of drill cuttings deposition in open-mining pit were studied. An analysis of selected parameters of deposited drilling waste, groundwater taken from piezometers and eluates obtained during batch leaching tests of drill cuttings was the basis for the estimation. The high concentrations of barium, lead, and zinc in drilling waste (maximum measured values equal to 54; 152; and 438 mg/kg dry weight, respectively) do not allow to classify the examined materials as inert waste from the extractive industries. The groundwater taken from the piezometers located around the drilling waste landfill contained high concentrations of total organic carbon (up to 21.9 mgC/L) boron, calcium, magnesium, manganese, aluminum, and potassium (up to 2.12; 455; 148; 1.75; 5.11; and 25 mg/L, respectively). In contrast to this observation, concentrations of barium and chlorides were the most exceeded in the batch leaching tests. It suggests that pollution of groundwater was not caused by drilling waste deposition.

Abstract:
Unconventional oil and gas (UOG) production produces large quantities of wastewater with complex geochemistry and largely uncharacterized impacts on surface waters. In this study, we assessed shifts in microbial community structure and function in sediments and waters upstream and downstream from a UOG wastewater disposal facility. To do this, quantitative PCR for 16S rRNA and antibiotic resistance genes along with metagenomic sequencing were performed. Elevated conductivity and markers of UOG wastewater characterized sites sampled downstream from the disposal facility compared to background sites. Shifts in overall high level functions and microbial community structure were observed between background sites and downstream sediments. Increases in Deltaproteobacteria and Methanomicrobia and decreases in Thaumarchaeota were observed at downstream sites. Genes related to dormancy and sporulation and methanogenic respiration were 18–86 times higher at downstream, impacted sites. The potential for these sediments to serve as reservoirs of antimicrobial resistance was investigated given frequent reports of the use of biocides to control the growth of nuisance bacteria in UOG operations. A shift in resistance profiles downstream of the UOG facility was observed including increases in acrB and mexB genes encoding for multidrug efflux pumps, but not overall abundance of resistance genes. The observed shifts in microbial community structure and potential function indicate changes in respiration, nutrient cycling, and markers of stress in a stream impacted by UOG waste disposal operations.

Abstract:
Oil and gas extraction and coal-fired electrical power generating stations produce wastewaters that are treated and discharged to rivers in Western Pennsylvania with public drinking water system (PDWS) intakes. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to quantify inorganic species in wastewater and river samples using a method based on EPA Method 200.7 rev4.4. A total of 53 emission lines from 30 elements (Al, As, B, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sn, Sr, Ti, Tl, V, and Zn) were investigated. Samples were prepared by microwave-assisted acid digestion using a mixture of 2% HNO3 and 0.5% HCl. Lower interferences and better detection characteristics resulted in selection of alternative wavelengths for Al, As, Sb, Mg, Mo, and Na. Radial view measurements offered accurate determinations of Al, Ba, K, Li, Na, and Sr in high-brine samples. Spike recovery studies and analyses of reference materials showed 80–105% recoveries for most analytes. This method was used to quantify species in samples with high to low brine concentrations with method detection limits a factor of 2 below the maximum contaminant limit concentrations of national drinking water standards. Elements B, Ca, K, Li, Mg, Na, and Sr were identified as potential tracers for the sources impacting PDWS intakes. Usability of the ICP-OES derived data for factor analytic model applications was also demonstrated.

Abstract:
The ecologically sensitive Susquehanna River Basin (SRB) is an important recharge area and drinking water source for a large population in the northeastern United States. Seasonal road salt application, the presence of regional brines at shallow depths, and produced waters associated with active and legacy conventional Upper Devonian oil and gas wells could increase total dissolved solids (TDS) in groundwater and streams. This study focused on SRB watersheds along the New York/Pennsylvania border, in order to assess current water quality and to establish baseline geochemistry for ground and surface water in a region with potential for increased development of the Marcellus Shale and other unconventional shale gas units. Geochemical composition was determined for 300 stream samples collected from ten sites in four watersheds over variable seasonal flow conditions, and for groundwater from over 500 drinking water wells in this region. Results indicate that many streams and groundwater wells in the study area have elevated TDS levels that indicate pre-existing contributions from saline sources. Dilution of these inputs with fresh water, and the lack of low-level trace element concentrations and isotopic composition in many water quality analyses, highlight the need for alternate robust and sensitive chemical signatures. Comparison with Cl/Br anion ratios and 87Sr/86Sr isotope ratios indicate that the (Ba + Sr)/Mg ratio can be used to discriminate between road salt and regional brine in these cases, and mixing models show that even small additions (0.1–0.01%) of these contaminants can be detected with this cation ratio. The (Ba + Sr)/Mg ratio may be even more sensitive (by an order of magnitude) to incursions of Marcellus Shale produced water, depending on the composition of Marcellus produced waters in this region. This study highlights the need for baseline sampling of freshwater reservoirs and the characterization of potential high TDS sources at a local and regional scale.

Abstract:
Due to the rapid expansion in hydraulic fracturing (fracking), there is a need for robust, portable and specific water analysis techniques. Early detection of contamination is crucial for the prevention of lasting environmental damage. Bromide can potentially function as an early indicator of water contamination by fracking waste, because there is a high concentration of bromide ions in fracking wastewaters. To facilitate this, a microfluidic paper-based analytical device (μPAD) has been developed and optimized for the quantitative colorimetric detection of bromide in water using a smartphone. A paper microfluidic platform offers the advantages of inexpensive fabrication, elimination of unstable wet reagents, portability and high adaptability for widespread distribution. These features make this assay an attractive option for a new field test for on-site determination of bromide.

Abstract:
Northeastern Pennsylvania has rapidly changed over the past 5 years from an area with no unconventional natural gas drilling, to the most productive shale gas region within the Marcellus shale play, causing concerns about environmental safety. One issue that has caught the attention of homeowners and media is the possibility that flow-back fluids from drilling and fracturing processes have contaminated private water wells. Major and trace ion water chemistry was analyzed from 21 groundwater wells suspected by homeowners to be contaminated by flow-back fluids. These data, collected in 2012-2013, were compared to historical groundwater data, Marcellus flow-back fluid, and other sources of common groundwater contamination in rural areas (agricultural waste, septic waste, and road salt). Results from graphical and statistical tests indicate that flow-back fluids have not impacted these wells. However, some of the 2012-2013 wells do plot graphically within zones identified as waters that have been influenced by animal waste, septic, or road salt. The remaining 2012-2013 wells are geochemically similar to historical groundwater wells. These findings suggest that the major and trace element geochemistry of local groundwater in the northeastern Pennsylvania study area has not been detectably influenced by flow-back fluid spills.

Abstract:
The disposal and leaks of hydraulic fracturing wastewater (HFW) to the environment pose human health risks. Since HFW is typically characterized by elevated salinity, concerns have been raised whether the high bromide and iodide in HFW may promote the formation of disinfection byproducts (DBPs) and alter their speciation to more toxic brominated and iodinated analogues. This study evaluated the minimum volume percentage of two Marcellus Shale and one Fayetteville Shale HFWs diluted by fresh water collected from the Ohio and Allegheny Rivers that would generate and/or alter the formation and speciation of DBPs following chlorination, chloramination and ozonation treatments of the blended solutions. During chlorination, dilutions as low as 0.01% HFW altered the speciation towards formation of brominated and iodinated trihalomethanes (THMs) and brominated haloacetonitriles (HANs), and dilutions as low as 0.03% increased the overall formation of both compound classes. The increase in bromide concentration associated with 0.01%-0.03% contribution of Marcellus HFW (a range of 70 to 200 g/L for HFW with bromide = 600 mg/L) mimics the increased bromide levels observed in western Pennsylvanian surface waters following the Marcellus Shale gas production boom. Chloramination reduced HAN and regulated THM formation; however iodinated trihalomethane formation was observed at lower pH. For municipal wastewater-impacted river water, the presence of 0.1% HFW increased the formation of N-nitrosodimethylamine (NDMA) during chloramination, particularly for the high iodide (54 ppm) Fayetteville Shale HFW. Finally, ozonation of 0.01%-0.03% HFW-impacted river water resulted in significant increases in bromate formation. The results suggest that total elimination of HFW discharge and/or installation of halide-specific removal techniques in centralized brine treatment facilities may be a better strategy to mitigate impacts on downstream drinking water treatment plants than altering disinfection strategies. The potential formation of multiple DBPs in drinking water utilities in areas of shale gas development requires comprehensive monitoring plans beyond the common regulated DBPs.

Abstract:
Hydraulic fracturing is expanding rapidly in the US to meet increasing energy demand and requires high volumes of hydrofracking fluid to displace natural gas from shale. Accidental spills and deliberate land application of hydrofracking fluids, which return to the surface during hydrofracking, are common causes of environmental contamination. Since the chemistry of hydrofracking fluids favors transport of colloids and mineral particles through rock cracks, it may also facilitate transport of in-situ colloids and associated pollutants in unsaturated soils. We investigated this by subsequently injecting deionized water and flowback fluid at increasing flow rates into unsaturated sand columns containing colloids. Colloid retention and mobilization was measured in the column effluent and visualized in-situ with bright field microscopy. While <5% of initial colloids were released by flushing with deionized water, 32-36% were released by flushing with flowback fluid in two distinct breakthrough peaks. These peaks resulted from 1) surface tension reduction and steric repulsion, and 2) slow kinetic disaggregation of colloid flocs. Increasing the flow rate of the flowback fluid mobilized an additional 36% of colloids, due to the expansion of water filled pore space. This study suggests that hydrofracking fluid may also indirectly contaminate groundwater by remobilizing existing colloidal pollutants.

Abstract:
Waters co-produced with hydrocarbons in the Appalachian Basin are of notably poor quality (concentrations of total dissolved solids (TDS) and total radium up to and exceeding 300,000 mg/L and 10,000 pCi/L, respectively). Since 2008, a rapid increase in Marcellus Shale gas production has led to a commensurate rise in associated wastewater while generation of produced water from conventional oil and gas activities has continued. In this study, we assess whether disposal practices from treatment of produced waters from both shale gas and conventional operations in Pennsylvania could result in the accumulation of associated alkali earth elements. The results from our 5 study sites indicate that there was no increase in concentrations of total Ra (Ra-226) and extractable Ba, Ca, Na, or Sr in fluvial sediments downstream of the discharge outfalls (p > 0.05) of publicly owned treatment works (POTWs) and centralized waste treatment facilities (CWTs). However, the use of road spreading of brines from conventional oil and gas wells for deicing resulted in accumulation of Ra-226 (1.2 ×), and extractable Sr (3.0 ×), Ca (5.3 ×), and Na (6.2 ×) in soil and sediment proximal to roads (p < 0.05). Although this study is an important initial assessment of the impacts of these disposal practices, more work is needed to consider the environmental consequences of produced waters management.

Abstract:
Fluids co-produced with oil and gas production (produced waters) are often brines that contain elevated concentrations of bromide. Bromide is an important precursor of several toxic disinfection by-products (DBPs) and the treatment of produced water may lead to more brominated DBPs. To determine if wastewater treatment plants that accept produced waters discharge greater amounts of brominated DBPs, water samples were collected in Pennsylvania from four sites along a large river including an upstream site, a site below a publicly owned wastewater treatment plant (POTW) outfall (does not accept produced water), a site below an oil and gas commercial wastewater treatment plant (CWT) outfall, and downstream of the POTW and CWT. Of 29 DBPs analyzed, the site at the POTW outfall had the highest number detected (six) ranging in concentration from 0.01 to 0.09 μg L− 1 with a similar mixture of DBPs that have been detected at POTW outfalls elsewhere in the United States. The DBP profile at the CWT outfall was much different, although only two DBPs, dibromochloronitromethane (DBCNM) and chloroform, were detected, DBCNM was found at relatively high concentrations (up to 8.5 μg L− 1). The water at the CWT outfall also had a mixture of inorganic and organic precursors including elevated concentrations of bromide (75 mg L− 1) and other organic DBP precursors (phenol at 15 μg L− 1). To corroborate these DBP results, samples were collected in Pennsylvania from additional POTW and CWT outfalls that accept produced waters. The additional CWT also had high concentrations of DBCNM (3.1 μg L− 1) while the POTWs that accept produced waters had elevated numbers (up to 15) and concentrations of DBPs, especially brominated and iodinated THMs (up to 12 μg L− 1 total THM concentration). Therefore, produced water brines that have been disinfected are potential sources of DBPs along with DBP precursors to streams wherever these wastewaters are discharged.

Abstract:
The safe disposal of liquid wastes associated with oil and gas production in the United States is a major challenge given their large volumes and typically high levels of contaminants. In Pennsylvania, oil and gas wastewater is sometimes treated at brine treatment facilities and discharged to local streams. This study examined the water quality and isotopic compositions of discharged effluents, surface waters, and stream sediments associated with a treatment facility site in western Pennsylvania. The elevated levels of chloride and bromide, combined with the strontium, radium, oxygen, and hydrogen isotopic compositions of the effluents reflect the composition of Marcellus Shale produced waters. The discharge of the effluent from the treatment facility increased downstream concentrations of chloride and bromide above background levels. Barium and radium were substantially (>90%) reduced in the treated effluents compared to concentrations in Marcellus Shale produced waters. Nonetheless, 226Ra levels in stream sediments (544?8759 Bq/kg) at the point of discharge were ?200 times greater than upstream and background sediments (22?44 Bq/kg) and above radioactive waste disposal threshold regulations, posing potential environmental risks of radium bioaccumulation in localized areas of shale gas wastewater disposal.

Abstract:

Abstract:
Unconventional natural gas development in Pennsylvania has created a new wastewater stream. In an effort to stop the discharge of Marcellus Shale unconventional natural gas development wastewaters into surface waters, on May 19, 2011 the Pennsylvania Department of Environmental Protection (PADEP) requested drilling companies stop disposing their wastewater through wastewater treatment plants (WWTPs). This research includes a chemical analysis of effluents discharged from three WWTPs before and after the aforementioned request. The WWTPs sampled included two municipal, publicly owned treatment works and a commercially operated industrial wastewater treatment plant. Analyte concentrations were quanitified and then compared to water quality criteria, including U.S. Environmental Protection Agency MCLs and "human health criteria." Certain analytes including barium, strontium, bromides, chlorides, total dissolved solids, and benzene were measured in the effluent at concentrations above criteria. Analyte concentrations measured in effluent samples before and after the PADEP's request were compared for each facility. Analyte concentrations in the effluents decreased in the majority of samples after the PADEP's request (p < .05). This research provides preliminary evidence that these and similar WWTPs may not be able to provide sufficient treatment for this wastewater stream, and more thorough monitoring is recommended.

Abstract:
Concern has been raised in the scientific literature about the environmental implications of extracting natural gas from deep shale formations, and published studies suggest that shale gas development may affect local groundwater quality. The potential for surface water quality degradation has been discussed in prior work, although no empirical analysis of this issue has been published. The potential for large-scale surface water quality degradation has affected regulatory approaches to shale gas development in some US states, despite the dearth of evidence. This paper conducts a large-scale examination of the extent to which shale gas development activities affect surface water quality. Focusing on the Marcellus Shale in Pennsylvania, we estimate the effect of shale gas wells and the release of treated shale gas waste by permitted treatment facilities on observed downstream concentrations of chloride (Cl(-)) and total suspended solids (TSS), controlling for other factors. Results suggest that (i) the treatment of shale gas waste by treatment plants in a watershed raises downstream Cl(-) concentrations but not TSS concentrations, and (ii) the presence of shale gas wells in a watershed raises downstream TSS concentrations but not Cl(-) concentrations. These results can inform future voluntary measures taken by shale gas operators and policy approaches taken by regulators to protect surface water quality as the scale of this economically important activity increases.