Methods of Obtaining Aquifer Data for Groundwater Remediation System Design

GARVEY, TIMOTHY P., JAMES M. EVENSEN, JR.,* and ROBERT J. MENZIE, JR., Groundwater Technology, Inc., Ventura, CA

Characterization of unconfined aquifer parameters prior to design of a groundwater pumping and treatment remediation system is essential for proper system engineering and yields long-term cost savings. An approach for stepwise characterization includes (1) physical property definition of sediments within the saturated zone to initially estimate aquifer parameters, and (2) proper selection, design, and execution of aquifer tests using appropriate data analyses methods.

During a soil/groundwater investigation, soil samples are obtained from the saturated zone. These samples provide information on the geometry of subsurface lithosomes and are used in a series of laboratory analyses to determine the porosity, permeability, pore-fluid saturation, grain density, grain-size distribution, and saturated hydraulic conductivity of the aquifer at the sample points within the saturated zone. The analytical results are used to calculate average hydraulic conductivity (K), transmissivity (T), and specific yield for the aquifer. These data permit the appropriate aquifer test to be engineered.

Three end member field tests to acquire data from unconfined aquifers exist. These are (1) slug/recovery, (2) step-drawdown, and (3) constant rate. Results of slug/recovery tests are used to determine T and K when these values cannot be accurately estimated from sedimentologic properties, or when the aquifer can be defined as being low yield (K < 10-7 cm/sec). Results of step-drawdown tests are used to quantify reduction in specific capacity with increasing well yield and to define optimum pumping rates. Pumping rates and step durations are based on estimations of aquifer parameters using sediment properties and/or results of slug/recovery tests. Results of constant-rate tests (single or multiple well) are used to verify aquifer response and equilibrium conditions at a designed, op imum pumping rate and to model interference between pumping wells.

Results from aquifer tests are used to refine original estimates of aquifer parameters, and to accurately quantify to down- and lateral-gradient capture zones from pumping wells at select pumping rates. This provides information needed for groundwater treatment system design.

Cost analyses of various pumping and treatment remediation systems indicate that expenditures associated with thorough aquifer characterization represent less than 5% of the total remedial project cost. These expenditures represent a savings through the life of a project due to greater efficiency of a properly designed remediation system.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)