{'fraction_non_alphanumeric': 0.020464601769911505, 'fraction_numerical': 0.007743362831858407, 'mean_word_length': 5.050167224080267, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Correct Delineation of Capture Zones Using Particle Tracking under Transient Conditions

Hydrogeologists commonly use particle tracking to determine groundwater flow paths by tracing the movement of imaginary particles placed in the flow field of a numerical model. Particle tracking codes such as MODPATH (Pollock 2012) calculate the velocity field from the simulated head solution and use it to track the movement of the particles. The method is commonly used to evaluate model boundary conditions, determine the locations of recharge and discharge areas in a modeled aquifer, and approximate the movement of contaminants (Anderson and Woessner 1992). A particularly common use of particle tracking is to delineate the capture zone of a pumping well, which is the aquifer volume that contributes water to it. Capture zone delineation used for wellhead protection studies is often based on a time-of-travel criterion, such as a 1- or 5-year capture zone (U.S. Environmental Protection Agency 1987). Capture zones in steady-state models can be delineated using particles moving in forward or reverse directions. In forward tracking, particles are placed in the model domain and are traced as they move downgradient toward a sink (a well or discharge area). The capture zone is delineated by the pathlines of those particles that arrive at the sink in a specified time. Reverse tracking involves placing particles at a sink and tracking them in the reverse (upgradient) flow direction to their sources. Because all the particles start at a common location, the ensemble of the pathlines defines the capture zone of the sink. Steady-state flow models are often used with particle-tracking codes to delineate capture zones because of simplicity and the desirability of representing long-term average conditions.