Groundwater Workshop Jackson, MS August 2015 Presented By: Mr. Bill Oakley, RPG Consulting 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

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

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

The Jackson Dome

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.

For the water engineer the 1 st 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

Circular Orifice Weir

Specs generally require % efficient; less than 50% = NO PAY! Friction Loss Lack of Development Casing Size Screen Size/Length/Slot Improper Gravel Pack for Aquifer Failure 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

Provide a graphical depiction of geological formations vertically at 5”=100’ ALWAYS look at scales before attempting to interpret data from logs Scales 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 ( 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  (R 8 /R 64) ) [56280/R mf,T (T mf + 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”