Burrows of anecic earthworms that penetrate the infiltrative surface of soil-wastewater treatment system trenches may contribute to preferential flow through soil macropores in septic system filter fields. Adding a layer of sand on the bottom of the trench, however, may discourage earthworm burrowing. In this laboratory study, we investigated if the particle-size distribution and position of a sand layer would inhibit burrowing by the anecic earthworm Lumbricus terrestris L. Three earthworms were added to the top of soil columns containing a 3-cm-thick sand layer covered with 2 mm of loamy B-horizon material and underlain by 9 cm of the same material. We repeated this experiment with earthworms placed below the sand layer. In another experiment, the sand layer was covered by 11.3 cm of soil material to investigate whether worms added to the surface would avoid crossing a sand layer embedded within the columns. No treatments in the surface sand layer experiments prevented all worms from establishing burrows. The worms added to the surface, however, took an average of 1.7 to 5 times longer (P ≤ 0.05) to establish burrows, and earthworm mortality was greater in columns with a surface sand layer compared with the no-sand-layer controls. In the embedded-sand-layer experiment, no worms burrowed past the soil-sand interface, whereas all worms in the controls burrowed past the equivalent depth. Sand particle size distribution did not significantly affect earthworm burrowing. The results suggest that adding a layer of sand to the bottom of soil treatment system trenches may deter earthworms, but will not restrict burrowing.