American Water Works AssnMS/AL Section

Groundwater Workshop Jackson, MSAugust 2015

Presented By:

Mr. Bill Oakley, RPGConsulting Hydrologist

&Mr. G. Mark Teague, RPG

Consulting Geologist

Major Topics• MS & AL Aquifer Systems

• Pump Tests

• Geophysical Well Logging

Gulf Coastal Regional Aquifers

MS & AL Outcrop Systems Showing Recharge Areas by Geologic Formations:

• Oldest Paleozoic Rock• Youngest Pleistocene Citronelle

sands & gravel

MS Aquifer Recharge Areas

• Line of X-section NE to SW• 15 Major Aquifers• Oldest Located in NE

Mississippi (Paleozoic)• Youngest Located in SW

Mississippi (Miocene)• Variable Base of Fresh

Water

X-Section NE (Amory) Through Starkville SW to (Sturgis)

Base of Fresh Water in MS

Ranges from 300’ in NE Mississippi to Greater Than 3000’ in Hancock County

The MS Salt Dome Basin Contains 53

DomesFacts:

- Dome Size Ranges from ½ mile to 3 mile Diameter

- 30 Domes are Less than 4000’ below land surface

- Richton is the shallowest at 700’ below surface

Structural Influences Related to Salt

Diapirs2 Types:

PiercementNon-Piercement

- Salts and some shales Behave in a Plastic Manner and create Dome as

the Salt is more Buoyant

- Given the Plastic Nature of the material(s) the structural influences continues to migrate to the surface

until equilibrium is met

- Presently there are 5 gas storage facilities inside salt domes in MS

MS Salt Dome Structural Features

- Is the Jackson Dome a Salt Dome?

The Jackson Dome

Water Supply Problems with 1 or More Aquifers

in MS-Water Level Declines in MS:

DeltaJackson Metro Area

NE MississippiAlong MS Gulf Coast

-High Dissolved Solids Washington & Jackson Counties

- Near Base of Upper Cretaceous Aquifers in NE MS

-Little or No Fresh Groundwater in Kemper, Noxubee Counties near AL State Line

Surface Subsidence as a Result of Over Pumping

of Aquifers

1925 Land Surface- Top1955 Land Surface-Middle

1977 Land Surface – Man Standing at Base of Telephone Pole

San Joaquin Valley California at USGS Benchmark #S661

THE PUMPING TEST

• The single most important contribution the water engineer can make to his Client is the development and use of groundwater resources is the specification and achievement of more efficient water-supply wells.

THE PUMPING TEST• For the water engineer the 1st step is to

recognize great room for improvement(s) to efficiency & that many inefficient wells exist.

• An inefficient well is one in which the amount of water level drawdown required to sustain a given rate of discharge is substantially greater than it should be for the aquifer involved.

2 Types of Pumping Tests

2 Types of Pumping Tests

Circular Orifice Weir

Specs generally require 70 - 80 % efficient; less than 50% =

NO PAY!

Friction LossLack of DevelopmentCasing SizeScreen Size/Length/SlotImproper Gravel Pack for AquiferFailure of Screen & Infilling

Unconfined / Confined Aquifers

Geophysical Logging & Groundwater Studies Uses:

• Help determine in-situ water quality

• Help determine base of fresh water zone based upon TDS values

• Draw inferences about aquifer production

• Help resolve issues of well spacing

• Verify drilling depths of contractor

Basic Geophysical Log InterpretationProvide a graphical depiction of

geological formations vertically at 5”=100’

ALWAYS look at scales before attempting to interpret data from

logsScales are located in the title bars at

the top & bottom of e-logs

Using Borehole GL to ID Water-Bearing Strata for Optimum Screen Setting

• Critical when well yield or (max GPM) is required

• Dependent on local and regional geology

• Should be considered when:–Client’s desire is as much water as possible–Geology of the site is not known

SPR= Black Curve at far right margin is not affected by geometry and is best indicator of

bed boundaries.

R8, R16, R32, R64 = Colored curves at right margin are affected by the geometry of the

tool spacing and is best illustrated in the 620’ – 640’ interval to the left.

Gamma Ray = Black Curve far left margin is a tool that measures the natural radioactive

minerals in terms of counts per second with a good clean beach sand reading in a range of

(7.5-15 CPS) and the scale increases in counts as clays can be higher than 250 CPS!

SP= Blue Curve left margin; essentially compares the fluids used to drill hole to that

fluid within the formations and provides indication of fresh water zones verses salt.

Cur= Red curve left margin; is a manipulation of Ohm’s law and is inverse function of the SPR curve. Also, provides ground for the other

electrical operations of electrodes while completing the circuit.

Scales are not shown here as they are based to Client preferences when services are rendered. Unless otherwise specified by stakeholders, technicians will adhere to log scales based on

professional experience in the region(s).

Commonly Used Geophysical Tools• Natural Gamma• Spontaneous Potential• Full Waveform Sonic

– CBL after emplacement

• Resistivity (8,16,32,64)– Formation– Fluid– Resistivity borehole logs

should be borehole corrected, based on measured resistivity, borehole diameter, fluid resistivity, mud resistivity, & temperature

Radioactive Source Tools

• Gamma-Gamma• Neutron Density

Not commonly used due to:

-Regulatory Issues-Liability issues-$$$$$$

Geophysical Logs & GW Data Helps Quantify

• Aquifer Testing Data– K(hydraulic conductivity), S (storativity),

T(transmissivity)• Potentiometric Surface Maps– Water Levels

• Water Quality (Lab)– TDS

• Specific Yield (Sy-dimensionless value)– Always a bit less than Porosity due to water retention during

production– Estimate based upon porosity logs & derived permeability

• Hydraulic Conductivity (K) – determined using a resistivity logs & surface conductivity– Derivative of Sonic Porosity and R ratios

• Apparent Aquifer Thickness (b)– Easily determined from Natural Gamma & Single Point Resistance Logs

• Transmissivity (T) – Once we have the aquifer thickness (b) and (K) we have (T)!

Derive TDS from Resistivity Logs for Example

• TDS (R8/R64) ) [56280/Rmf,T (Tmf + 7)]• Rmf= Resistivity Mud-Filtrate• Tmf= Temperature Mud-Filtrate

• TDS units are in PPM • Values selected from E-Log Curves • In this example. R8 = 62, R64=45, Rmf,t=2.1,

T=77

Elog from Fresh GW Sand in MS

TDS plot Derived from Previous Slides

Spontaneous Potential (SP)

Responses- Establish Clay base of Log

-Evaluate response relative to clay base

- In this instance the Departure is to Right of Clay Base

- Fresh Water Response

SP Departure from Clay Base is

Negligible and Overall Resistivity Decreases Which

Indicates an Increase in Salinity

SP Departure to LEFT of Clay Base = Increase in TDS

Oh“Mudballs”