Chapter 15: Land Use and Groundwater

Questions
Exercises
Links

Summary
Groundwater is an important source of drinking water. Although most of population in the United States uses surface water supplies, about 80 percent of public water systems and nearly all individual systems depend on groundwater sources. Most individual groundwater sources are used without treatment.
Groundwater is closely related to the land since nearly all of it comes from infiltration recharge from the land surface. Impervious cover on the land surface inhibits infiltration and recharge. Unconfined shallow aquifers are closely connected to surface waters. Groundwater contributes baseflows to gaining streams and is recharged by losing streams. In fractured or karst geology, there are direct conduits between surface waters and groundwaters. Because of its close connection to the land surface, groundwater is susceptible to contamination from surface sources, including underground storage tanks of petroleum and other chemical products, landfills and other waste areas, polluted stormwater, septic systems and wastewater lagoons, among others.
As a result, management of groundwater requires planning and management of the land. It is important to understand groundwater flow and recharge as well as susceptibility to contamination. In recharge areas, impervious surfaces should be minimized, and potential sources of contamination should be restricted. DRASTIC and other hydrogeological studies can help understand surface-groundwater relationships and guide land use decisions.
Special care should be taken to manage land use in the vicinity of wellheads of public water supplies. Overlay zoning and other land regulations are appropriate to restrict land uses to protect public health.

Chapter 15 Discussion questions:

1. Both DRASTIC and Wellhead Protection are methods to protect groundwater.
a. What is the basic difference between the two?
b. Using a diagram and a few words, explain the difference between the zone of influence and the zone of contribution.
1. "Karst areas pose a dual environmental concern for land development." Briefly explain.

2. Explain the difference between the following: aquaclude, aquatard, aquafuge, confined aquifer, unconfined aquifer, perched and aquifer.

3. Explain how a well’s cone of depression can:
a. Create conflicts among groundwater users
b. Exacerbate saltwater intrusion
c. Change a gaining stream into a losing stream

Chapter 15 Exercises

4. As a county planner outside a city which depends on groundwater for water supply, you are concerned about the potential for ground water contamination. Both city and county residents have requested that you apply the DRASTIC method to evaluate groundwater pollution potential in an agricultural area bounded by the city. The area shown on the posted map, contains four different hydrogeological settings having the characteristics given in the attachment (add graphics). While the DRASTIC scores have been computed for these settings, given the land use, the agricultural or pesticide assigned weights should be used. In addition, more specific information has been gathered for four locations (B,C,D,E) within the area. This is given in the table.
1. Using the DRASTIC procedure, compute scores for each subarea and compare them in terms of potential for land-use induced groundwater contamination. Using the attached map (or an enlarged copy), prepare a small DRASTIC map, distinguishing the relative potential for groundwater contamination by color or shading. (Use the designated DRASTIC score ranges, but don't worry about making overlays or using the designated DRASTIC colors).
B C D E
Area (acres) 300 400 450 53
Depth to
Water Table (ft.) 60 40 25 10
Net Recharge (inches) 1 3 8 6

Aquifer Media bedded Karst gravelly
shale limestone limestone sand
Soil Media clay loam sandy aggreg.
loam loam clay
Topography (% Slope) 3 5 3 3
Impact of shale limestone Karst sand and
Vadose Zone Media limestone gravel
Hydraulic Conductivity 220 350 800 1200
(GPD/Ft2)
b. Comment on the procedure and the usefulness of the results.
c. What additional steps would you suggest that the county take to protect groundwater?