Funnel‐and‐Gate Performance in a Moderately Heterogeneous Flow Domain

Abstract

The funnel‐and‐gate ground water remediation technology (Starr and Cherry 1994) has received increased attention and application as an in situ alternative to the typical pump‐and‐treat system. Understanding the effects of heterogeneity on system performance can mean the difference between a successful remediation project and one that fails to meet its cleanup goals. In an attempt to characterize and quantify the effects of heterogeneity on funnel‐and‐gate system performance, a numerical modeling study of 15 simulated heterogeneous flow domains was conducted. Each realization was tested to determine if the predicted capture width met the capture width expected for a homogeneous flow domain with the same hulk properties. This study revealed that the capture width of the funnel‐and‐gate system varied significantly with the level of heterogeneity of the aquifer. Two possible remedies were investigated for bringing systems with less than acceptable capture widths to acceptable levels of performance. First, it was determined that enlarging the funnel and gate via a factor of safety applied to the design capture width could compensate for the capture width variation in the heterogeneous flow domains. In addition, it was shown that the use of a pumping well downstream of the funnel and gate could compensate for the effects of aquifer heterogeneity on the funnel‐and‐gate capture width. However, if a pumping well is placed downstream of the funnel and gate to control the hydraulic gradient through the gate, consideration should be given to the gate residence time in relation to the geochemistry of the contaminant removal or destruction process in the gate.

Moderate Bioclogging Leading to Preferential Flow Paths in Biobarriers

“…The performance of biobarriers is tested by model predictions and the breakthrough of reactive and nonreactive tracers measured at selected observation points downstream of the barrier (e.g., Hyndman et al 2000; Dybas et al 2002). These approaches are certainly limited by the occurrence of flow field heterogeneities caused by the aquifer material at a site (Bilbrey and Shafer 2001). Our experiments show that even in the absence of these initial heterogeneities, the occurrence of bioclogging can lead to a heterogeneous flow pattern.…”

Analytical expressions for the hydraulic design of continuous permeable reactive barriers

“…Conventionally, two PRB configurations are considered: the continuous barrier and the funnel and gate system. Whereas the hydraulics of funnel-and-gate systems have undergone a degree of scrutiny [18,16,17,3,4], the hydraulic behavior of the simpler continuous barrier system has not been extensively analyzed, although some research has addressed the influence of subsurface heterogeneity in such systems [8,3,4]. A general analytic framework for analysis of either configuration is desirable, as it allows for rapid preliminary testing and sensitivity analysis.…”

Effect of Setback Distance on Ability of Gravel Trenches to Intercept Contaminated Groundwater

“…Previous investigators studied flow fields upgradient of interceptor trenches (gates) coupled with low-permeability walls (funnels), using groundwater flow models to identify travel pathways to these coupled configurations (Starr and Cherry, 1994;Sedivy et al, 1999;Bilbrey and Shafer, 2001). These studies considered advection, but not dispersion of contaminants in groundwater.…”