EFFECTIVE POROSITY OF UNCONSOLIDATED SAND - ESTIMATION AND IMPACT ON CAPTURE ZONE GEOMETRY

Effective and total porosity were measured for three sand samples, and a computer model was used to evaluate the impact of effective porosit y (n(e)) on the geometry of a groundwater capture zone. Estimates of e ffective porosity ranged from 90 to 94 percent of values obtained for total porosity. While the magnitude of effective porosity is inversely proportional to capture zone area, the upgradient radius of capture i s most sensitive to changes in the magnitude of n(e). Incremental chan ges in the magnitude of n(e) have the greatest impact on capture zone radii for low values of n(e). The results of this study suggest that: (1) a simple permeameter and vacuum pump apparatus can facilitate the estimation of effective porosity for unconsolidated sands, (2) the mag nitude of effective porosity is close to that of total porosity for un consolidated sand, and (3) accurate estimates of effective porosity ar e important for modeling the remediation of contaminated groundwater w ith capture zones.