Acadian Pontchartrain (ACAD) Groundwater Studies

NAWQA Ground-Water Study Design

Types of Studies:

Land-Use Studies (LUS)

Intermediate scale spatially and directed toward the effects of human activities on ground-water quality

Sub-Unit Surveys (SUS)

Large spatial scale and broadly characterizes ground-water quality across the Study Unit

Flow-Path Study (optional)

Local scale, tracing of water movement

General Objectives

Land-use Studies:

to examine natural and human factors that affect the quality of shallow ground water that underlies key types of land use.

Sub-Unit Surveys:

to supplement existing data in providing a broad overview of ground-water quality in each Study Unit

Well Selection Strategies

• Selected by using a grid-based random sampling approach
• Located in recharge areas underlying or immediately downgradient from the selected land use
• Ideally, they are observation wells installed by the Study Unit
• Wells should have short (<3 m in length) open intervals located near the top of unconfined aquifers

• Selected by using a grid-based random sampling approach
• Sub-Unit Survey - Use existing wells (ideally low capacity wells, such as domestic)
• Ideally, wells should be screened near the top of the appropriate aquifer

ACAD NAWQA Ground-Water Studies

• Rice - SW Louisiana [FY 1998-2000]
• Urban - Lafayette [FY2000-2001]

• Chicot Aquifer (Sole Source) - SW Louisiana [FY-2000]
• Chicot-equivalent Aquifer (Sole Source) - SE Louisiana [FY 2001]

Rice Land-use Study - Purpose

Rice Land-use Study - Design

1. Randomly select 30 well sites in the rice growing areas
2. Drill and install 30 monitor wells according to State Regulations and NAWQA guidelines
3. Sample these 30 monitor wells for the constituents listed in USGS Circular 1112, (typically sampled only once)

Rice Land-use Study - Status

• 28 of 30 proposed shallow monitor wells have been drilled (depths range from 13-95 ft. below LSD)
• 2 wells to be redrilled
• 2 reference wells to be drilled (Kisatchie area?)
• 26 of 30 wells have been sampled

Sub-Unit Surveys: Chicot Aquifer and Chicot-equivalent Aquifer - Purpose

Sub-Unit Survey Aquifer Selection Approach

• Shallow Chicot in SW LA
• Shallow Chicot-equivalent in SE LA

Ground-water withdrawals in the Study Unit area

Sub-Unit Survey - Design

1. Select 30 well locations in each aquifer (60 total) using Jon Scott's grid-based random selection program
2. Sample existing wells (domestic), typically sampled only once
3. Contact well owners for permission to sample these wells
4. 5 wells sampled to date

Groundwater well drilling:

Typical monitor well installation:

Typical Groundwater Well construction:

Landuse/Landcover survey for the ACAD groundwater studies

1. Obtain black and white aerial photo's and topographic map for each well location.
2. Draw 50 and 500 meter radius circle around well.
3. Describe landuse within these circles.
4. Send data to Central Processing Group in Mississippi to be digitized and compiled.

Summary

• General NAWQA GW study design focuses on assessing the water-quality conditions of major aquifers with emphasis on the quality of recently recharged ground water associated with present and recent human activities
• ACAD GW Studies
  • 2 Land-use studies (Rice and Urban)
  • 2 sub-unit surveys (Chicot and Chicot-equivalent)
• Conduct landuse surveys for all studies

Special Thanks to:

• Rice farmers and landowners
• County Agriculture Agents
• LSU Rice Research Station
• LSU Cooperative Extension