Effects of changes in pumping on regional groundwater-flow paths, 2005 and 2010, and areas contributing recharge to discharging wells, 1990–2010, in the vicinity of North Penn Area 7 Superfund site, Montgomery County, Pennsylvania

Senior, Lisa A.; Goode, Daniel J.

doi:10.3133/sir20175014

Cited by 2 publications

(1 citation statement)

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“…Assuming that flow through the unsaturated zone is vertical, a well is vulnerable to contaminants on the overlying land surface. Steady‐state models have typically been used to identify CAs and associated travel times to wells in fractured rocks (e.g., Knochenmus and Robinson 1996; Podgorney and Ritzi 1997; Barton et al 2003; Lipfert et al 2004; Guha 2008; Senior and Goode 2013, 2017). In these models, recharge and pumping are simulated using average annual rates.…”

Section: Introductionmentioning

confidence: 99%

Contributing Areas to Domestic Wells in Dipping Sedimentary Rocks under Extreme Recharge Events

Tiedeman

Shapiro

2022

Groundwater

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We use particle tracking to determine contributing areas (CAs) to wells for transient flow models that simulate cyclic domestic pumping and extreme recharge events in a small synthetic watershed underlain by dipping sedimentary rocks. The CAs consist of strike-oriented bands at locations where the water table intersects high-hydraulic conductivity beds, and from which groundwater flows to the pumping well. Factors that affect the size and location of the CAs include topographic flow directions, rock dip direction, cross-bed fracture density, and position of the well relative to streams. For an effective fracture porosity (n e ) of 10 −4 , the fastest advective travel times from CAs to wells are only a few hours. These results indicate that wells in this type of geologic setting can be highly vulnerable to contaminants or pathogens flushed into the subsurface during extreme recharge events. Increasing n e to 10 −3 results in modestly smaller CAs and delayed well vulnerability due to slower travel times. CAs determined for steady-state models of the same setting, but with long-term average recharge and pumping rates, are smaller than CAs in the models with extreme recharge. Also, the earliest-arriving particles arrive at the wells later in the steady-state models than in the extreme-recharge models. The results highlight the importance of characterizing geologic structure, simulating plausible effective porosities, and simulating pumping and recharge transience when determining CAs in fractured rock aquifers to assess well vulnerability under extreme precipitation events.

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