LNAPL baildown methods and data analysis procedures are relatively new, although they are derived from traditional aquifer testing. Included here are two protocols, each authored by experienced practitioners: “A Methodology for Estimating LNAPL Conductivity and Transmissivity from LNAPL Baildown Tests: The Lundy andZimmerman Approach” by Don Lundy (Environmental Systems and Technologies, a Division of Groundwater and Environmental Services, Inc.) “A Protocol for Performing Field Tasks and Follow-up Analytical Evaluation for LNAPL Transmissivity Using Well Baildown Procedures” by G. D. Beckett (Aqui-Ver, Inc.) and M.A. Lyverse (ChevronTexaco Energy Research and Technology Company). The protocols overlap insome areas, and each emphasize certain analytical data analysis approaches over others. The reader is encouraged to study each protocol and its references carefully before conducting LNAPL baildown tests. Regardless of the chosen analysis method, the importance of careful field data collection cannot be over-emphasized. This means: 1) having reliable information about the subsurface stratigraphyaround the test wells, 2) conducting tests only in thoroughly developed wells, 3) having adequate equipment and personnel on hand to record numerous LNAPL recovery measurements in the wells over the duration of the test, 4) using of procedures that minimize water recovery, and 5) following health and safety plans when handling hazardous materials.
A Methodology for Estimating LNAPL Conductivityand Transmissivity from LNAPL Baildown Tests
The Lundy and Zimmerman Approach
Don Lundy Environmental Systems and Technologies A Division of Groundwater and Environmental Services
1. FREE PRODUCT -WATER SLUG WITHDRAWAL AND BAILDOWN TEST THEORY
A modified version of the popular Bouwer and Rice slug test method can be used to estimate the oil conductivity of the free product zone at atest well. This document reviews the original Bouwer and Rice derivation for groundwater and then provides a derivation of the free oil conductivity solution. Guidance for interpreting filter pack drainage in the test data and recommend actions for when a baildown test composed of multiple slug withdrawals is most applicable to site conditions are also provided in this section. 1.1 REVIEW OF BOUWERAND RICE METHOD FOR GROUNDWATER Figure 1 shows a sketch of the test well and pertinent well and aquifer measurements needed for the Bouwer and Rice (1976) slug test analysis. After a slug of water has been withdrawn, the rate of rise in the water level in the well, dy/dt, is equal to (Bouwer and Rice, 1976):
dy Q =− 2 , dt πrc
where Q is the rate of inflow and rc is the radius of thewell casing or screen in which the water level is recovering. The steady radial flow of groundwater to a well from which water is being pumped is expressed with the following equation (Thiem, 1906):
Figure 1. Well and aquifer dimension variables for a groundwater slug test analysis. Page 1 of 21
Q = 2πKLe
y ln( Re / rw )
where K is the average hydraulic conductivity ofthe aquifer, Le is the screened thickness of aquifer (Figure 1), y is the drawdown in the water level in the well, Re is the effective radius of the cone of depression in the water table around the well, and rw is the effective well radius (Figure 1). In the Bouwer and Rice derivation, Equation 1 is rearranged and expressed in terms of Q so that it can be set equal to the right side of Equation 2.The resulting expression is integrated and rearranged in terms of K to obtain the following: K= rc2 ln( Re / rw ) 1 y i ln , 2 Le t yt (3)
where K is the hydraulic conductivity, rc2 is the well casing radius squared, Re is the effective radius over which head changes (y) are dissipated, rw is the radius of the well screen plus filter pack, Le is the effective length of well screen across which...