Land application of waste water presents potential for ground water pollution if not properly managed. In situ breakthrough tests were conducted using potato (Solanum tuberosum L.)-processing waste-water and a Br tracer to characterize P leaching in seasonally frozen sandy outwash soils. In the first test, P and Br breakthrough were measured in a 7-m deep well following wastewater [2.94 mg L-1 total P (TP); 280 mg L-1 Br] application at the site that had 13.1 mg water-extractable P (WEP) kg -1 and 94.4 mg Bray-1 P kg-1. Bromide was detected in the well after -0.4 pore volumes, but there was no P breakthrough after 7 pore volumes. In the second breakthrough test, waste-water containing 3.6 mg L -1 TP and 259 mg L-1 Br was applied on 1.5-m deep lysimeters at low (0.8 mg WEP kg-1; 12.1 mg Bray-1 P kg-1) and high soil test P sites (104 mg WEP kg-1; 585 mg Bray-1 P kg -1). Leachate TP concentration during the test remained constant (0.04 mg L-1) at the low P sites but increased from -3.5 to 5.6 mg L-1 at the high P sites. These results indicate no P leaching in low P soils, but leaching in high P soils, thus suggesting that most of the P leached at the high P sites was mainly due to desorption and dissolution of weakly adsorbed P from prior P applications. This was consistent with P transport simulations using the convective-dispersive equation. We conclude that P concentration in land-applied waste-water should be regulated based on soil test-P level plus wastewater P loading.