The development of oil and gas resources, especially by hydraulic fracturing, has increased concerns about potential groundwater contamination. Typically, grab sample collection and expensive analytical tests are required to determine whether or not groundwater quality has been compromised. Time-consuming analytical methods may be expensive and difficult to perform. Site operators, stakeholders, regulatory agencies, and the public often need information instantly in order to meet regulatory requirements and to prevent contamination and exposure. Real-time data can keep interested parties informed and able to quickly address potential contamination of groundwater supplies. But real-time monitoring of criteria pollutants such as methane and hydraulic fracturing fluid is not practical with currently available technologies. However, by identifying reliable pollutant indicators or surrogates, operators and regulatory agencies can monitor sites efficiently and respond to groundwater quality changes that may indicate potential breakthrough of contaminants.