EXECUTIVE SUMMARY Urban stormwater runoff's impact on Flat Creek has been a concern since an initial investigation on the waterbody in 1982. Beginning in 1994 the Teton Conservation District, in cooperation with the Town of Jackson, began a thorough investigation of the non-point source pollutants affecting the creek and established permanent monitoring stations in key areas. During the course of the study it became apparent that the impact of runoff from the snow storage area at the rodeo grounds demanded immediate attention. Initially a proposal was developed that included the installation of commercially available stormwater filtration systems on the storage site. However, after analysis of runoff from the area it was determined that the commercially available units would require almost daily maintenance to handle the sediment load. It was decided to design an alternative custom three phase filtration system that included a detention basin, washed rock/filter fabric, and a sediment trap. This system was installed in the Fall of 1998 and was fully tested by the above average 98' - 99' snow year. Results of an evaluation of the system both during runoff and in early summer indicated that the system was effective in removing sand, silt, and clay from runoff. The filter system will function for one more year without modification for evaluation purposes. After which filter fabric of a smaller sieve size may be installed in place of the existing fabric.