J. D. Quaranta

First-Exposure Performance of the Bentonite Component of a GCL in a Low-pH, Calcium-Enriched Environment

Testing was conducted on the bentonite portion of a Geosynthetic Clay Liner (GCL) for application to an environment characterized as having high concentrations of dissolved calcium ions. This environment presents conditions that might affect the long-term hydraulic function of the GCL as a component in a barrier system. Experiments were conducted to investigate first-exposure compatibility of a sodium bentonite GCL subject to the affects of acidic groundwater and second from the combined affects of acidic groundwater enriched with calcium. Relationships between the ionic exchange of sodium, potassium, magnesium and calcium species in the bentonite, and changes in hydraulic conductivity and electrical conductance are reported and discussed.

Characteristics and Performance of Prefabricated Vertical Drains for Enhanced Soil Flushing

The use of prefabricated vertical drains (PVDs) under vacuum conditions for soil flushing was investigated with soils consisting of 100 percent sand or a combination of 80 percent sand and 20 percent kaolinite. Tests of the 100 percent sand specimens indicated that the areal extent of the PVD zone of influence remained approximately 16 to 21 times the PVD-equivalent diameter (PVD circumference/π) as the extraction vacuum increased from 2.5 to 20 kPa. Tests of the sand kaolinite specimens (80/20 soil) indicated that the areal extent of the PVD zone of influence remained approximately 5 to 8 times the PVD equivalent diameter as the extraction vacuum increased from 2.5 to 20 kPa. The effective zone of influence in the 80/20 soil did not show a corresponding increase in areal extent as the vacuum pressure was increased beyond the PVD embedment depth. Pilot-scale tracer flushing tests demonstrated the feasibility of using PVDs for flushing 100 percent sand soil. The tracer testing demonstrated that longer flushing times were necessary to achieve 80 percent cleanup levels as the dry unit weights of soil increased from 1.57 to 1.67 g/cm3. The ratio of final to initial concentration reached 0.2 after flushing of the 1.57 g/cm3 soil for approximately 40 minutes. A similar ratio was reached after flushing of the 1.67 g/cm3 soil for 50 minutes.

Multiphase Extraction of Light Non-aqueous Phase Liquid (LNAPL) Using Prefabricated Vertical Wells

Work in this paper describes the results of a field and modeling study conducted to investigate the extraction of LNAPL (jet propellant 4, i.e., JP-4, jet fuel) using Prefabricated Vertical Wells (PVWs) at a former air force base. Field testing consisted of 185 operating hours on 25 rows, each consisting of 7 or 8 PVWs. A total of 133 L of free-phase liquid is removed from the subsurface in addition to 467 kg of organics in the vapor phase as a result of volatilization due to the application of vacuum heads exceeding the JP-4 vapor pressure. Monitored field data are used to calibrate a numerical model for investigating the effect of irreducible water content, LNAPL, and gas contents on system performance. Analysis results show that increasing the irreducible water content from 5 % to 20 % decreases the free-LNAPL specific volume from 0.08 m to 0.067 m, which led to reduction in removal efficiency. Under a continuous saturation condition, more wetting fluid (water), traps the nonwetting fluid (LNAPL) in the soil pores, and reduces its mobility, which eventually impedes the LNAPL recovery. Given the model parameters that simulate field conditions, the PVWs show best removal rates in the gas phase. The model results indicated that 292 L of JP-4 can be recovered in 19.5 days (based on 8 h of operation per day) with an effective rate of 1.87 L/h. At the end of 4.25 years of system operation, the maximum benzene concentration is 0.002 ppm. At a gas extraction rate of 10,273 L/min, a maximum concentration of 0.38 ppm in the vapor phase is achieved after 2.5 years of vapor extraction.