Water and the Hydrogeology of Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 108

Pumped well

Land surface

Water table

Fresh groundwater

Saline groundwater

FIGURE 3.51
Saltwater intrusion by pumping groundwater.

minimum of three monitoring wells is usually not sufficient. The flow patterns of ground-
water in urban areas vary considerably due to anthropogenic influence, especially if the
water table is shallow (less than 6 m or 20 ft beneath the surface), so using more than three
monitoring wells is necessary. Although no precise number of monitoring wells necessary
to adequately characterize the groundwater flow pattern beneath a specific location has
been established, the authors recommend installing a monitoring well network of six or
more monitoring wells to begin the process.
The following considerations can help with the evaluation:

• Size and shape of a site: large or irregularly shaped sites require more monitoring
wells to evaluate groundwater flow patterns.
• Surface water features: if a stream is located along the boundary or dissects the
site.
• Potential presence of multiple aquifers or perched aquifers. The presence of mul-
tiple aquifers may indicate different groundwater flow directions.
• Seasonal fluctuations in surface water discharge and precipitation patterns.
• Anthropogenic influences including the following:
• Utility corridors or sewers. Utility corridors or sewers potentially influence
groundwater flow in two basic ways: (1) leaking water supplies act to recharge
groundwater and (2) storm sewers and other utilities corridors act as preferential
groundwater flow pathways when the water table intersects the utility corridor.
• Extraction or pumping wells.
• Deep building foundations.
• Land disturbance.
• Artificial recharge areas.
• Pipelines.
• Wastewater discharge points.