ch 9 groundwater and land use

8/3/2019 Ch 9 Groundwater and Land Use

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Water & Land Use:Groundwater


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Groundwater and Land Use


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Primary,Secondary, andTertiary Aquifers


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Piezometric Surface and the Cone of Depression


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Flow inunconsolidatedaquifer


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Flow inconsolidatedAquifer withrestrictive layer


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Flow infractured aquifer


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Flow insolutioned(karst) aquifer


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Groundwater/surface waterinteraction in karst terrain


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Major Sources of Groundwater ContaminationSeptic systems can be a problem when located too close to wellsin soils having very high permeability or structural avenues forrapid wastewater movement.

Leaking underground storage tanks containing petroleumproducts have caused considerable contamination and

abandonment of wells.

Contamination from landfills and lagoons has led to stricterstandards and controls, including dual liners and groundwatermonitoring.

Surface runofffrom agricultural, urban, mining, and industriallands have all contributed to contamination. Nitrogen fertilizersand pesticides on agricultural lands have created human health-related problems.


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Managing Groundwater

1. Understanding the groundwater system:

a. Hydrogeologic investigations

b. DRASTIC studies

c. Wellhead protection area (WHPA) delineation2. Inventorying and assessing threats and potential sources of

contamination

3. Monitoring groundwater

4. Developing a groundwater management programa. Prevention

Regulatory measures

Non-regulatory measures

b. Remediation


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DRASTIC:Susceptibility to Groundwater Contamination


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DRASTIC Factors and Weights


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DRASTIC Weights(1 to 5 scale)

Factor Basic Weight Agric. WeightD 5 5R 4 4A 3 3S 2 5T 1 3I 5 4

C 3 2


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Hydrogeological Regions

Example of a Hydrogeologic Setting


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Example of a Hydrogeologic Setting


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DRASTIC Assumptions1. The contaminant is introduced at the ground level.2. The contaminant is flushed into the groundwater by

precipitation.3. The contaminant has the mobility of water.4. The area evaluated using DRASTIC is 100 acres or

larger.


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SDWA Source Water ProtectionStates are required to conduct source water assessment for each

public water system (PWS).PWS is one serving at least 25 people at least 60 days of the year or a systemwith at least 15 service connections.

Over 80% of PWS rely on groundwater as their primary source; 93% serve lessthan 10,000 people.

The source water assessment includes:delineation of the source water protection area (the watershed or groundwaterrecharge area that may contribute pollution),

contamination source inventory, which identifies potential sources of

pollution,susceptibility determination, which indicates potential for contamination, and

dissemination of source water assessment results to the public.


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Protection Areas for Source Waters

(Texas)


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Delineation Methods for Protection Zones


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Delineation Methods for Protection Zones

Around Wells

There are six methods, in order of increasing technicalsophistication.

1. Arbitrary fixed radius

2. Calculated fixed radius3. Modified calculated fixed radius

4. Analytical methods

5. Hydrogeologic mapping6. Numerical flow/transport models

These methods range from simple and nexpensive to highlycomplex and costly.


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Difference between aquifer protection area


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q pand Wellhead protection area


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Regulatory and Non-Regulatory Measures for

Wellhead Protection Areas

Regulatory ToolsLand Use Controls:

Zoning ordinances, Subdivision controls, Cluster and PlannedUnit development

Prohibitions or conditional permitting of Potentially Contaminating

Uses: Gas stations, landfills, industries handling hazardouschemicals

Public Health regulations:

Septic system controls

Non-Regulatory Measures

Public education

Land purchase, conservation easements

Ground water monitoring


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Overlay Zoning for Wellhead and Watershed Protection


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ch 9 groundwater and land use

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