Impacts of frozen soils on the performance of infiltration treatment facilities

Infiltration treatment best management practices (BMPs) mitigate stormwater runoff from impervious surfaces, taking advantage of water percolation through soil to remove pollutants and recharge groundwater. However, in cold regions, frozen soil moisture negatively impacts infiltration facility performance by reducing available pore spaces for infiltrating water, causing a significant increase in runoff volumes. To understand the impacts of frozen soils on infiltrability rates and to improve infiltration treatment BMP designs for cold climates, laboratory experiments examined two soil types (loam and sandy loam) from infiltration treatment facility sites located in the cities of Spokane and Richland, Washington. Soil infiltrability measurements for unfrozen and frozen soil columns were performed using a developed air permeameter flow test. The time allowed for soil-water redistribution prior to freezing was varied among the soil columns (t = 2. 4, 8, and 24 h) to determine reduction of soil infiltrability in frozen soils. Depending on the time allowed for soil-water redistribution prior to freezing, column-averaged infiltrability for the frozen loam samples increased from 5 % to 30 % of the unfrozen column infiltrability average. While for frozen sandy loam columns, soil infiltrability increased by about 4% of the unfrozen column infiltrability average. For both soils, the minimum reduction in soil infiltrability was observed when the soil columns were drained for a 24-hour prior to the onset of freezing. However, while a 24-hour draining period was sufficient for the soil infiltrability of the loam soil to return to the same order of magnitude before freezing (10(-3) cm/s), this draining period was insufficient for the frozen sandy loam soil to regain a soil infiltrability similar to the unfrozen soil. The results were used to derive two regression equations to provide soil infiltrability correction factors for loam and sandy loam soils to improve BMP design in cold regions. (C) 2009 Elsevier B.V. All rights reserved.