Clogging Mechanism of Stormwater Filter Media by NaCl as a Deicing Salt

Abstract

The effect of NaCl deicing salt on compost-included stormwater filtration media (SFM) has not been studied so far. This article presents results of an experimental and analytical study conducted to understand the mechanism of permeability reduction in two SFM caused by the application of a common deicing salt (NaCl). The two SFM used were made up of clayey silty sand with and without added compost (15% by mass). Constant-head flow experiments were conducted applying NaCl at two different concentrations. Permeability of SFM without compost reduced by an average of 19.1%, while the permeability of SFM with compost reduced by an average of 93.7%. Mercury intrusion porosimetry (MIP) tests and chemical analyses were conducted on representative samples of the media, both before and after salt application. MIP results showed that median pore sizes enlarged, while permeability reduced. This is counterintuitive, as we usually expect that permeability reduction would be caused by pore-size reduction. MIP results (enlarged pore sizes) suggest that deicing salts caused flocculation of aggregates. Based on analysis of our experimental results and comparison with similar results in the literature, we conclude that permeability reduction of SFM was due to blocking of pore throats by dispersed particles and biofilms. Permeability reduction of the SFM with compost was larger, because compost-salt interactions were comparatively greater than the soil-salt interactions. Results of this study suggest that saltladen snow should not be piled up near the bioretention facilities built with compost-included SFM.

Hydrologic conditions drive denitrification and greenhouse gas emissions in stormwater detention basins

“…Juncus sp., Typha sp.). Reasons for the change are uncertain, but may include reduced infiltration due to settling of fine particles (Paus et al, 2014), aggregate formation and pore clogging due to reactions with road salt (Kakuturu and Clark, 2015) or clogging of the underdrain. Soil and gas measurements were made at three locations within each basin and two reference locations directly outside of each basin (Figure 1b).…”

Stormwater subsurface gravel wetland hydraulics, phosphorus retention, and chloride dynamics in cold climates

“…Analysis of SGW soils in both years did not reveal obvious storage of chloride in the soil layer, although the observed increase in soil EC between years at both sites did indicate soil salinization is occurring over time (Table 2). Aside from negative impacts on vegetation, 25,26 this could also decrease the soil permeability, 23 which may be advantageous in SGWs where infiltration through the soil layer is not desirable, unlike in the context of bioretention. Some researchers have hypothesized that the increased ionic strength associated with salinization should weaken P sorption in freshwater soils and sediments (e.g., via Cl − competing with PO 4 3− for sorption sites), leading to P loss.…”

“…Emerging concerns about the impact of chloride (Cl − ) on natural waters and roadside soils in cold climates raises questions regarding the impact of road salt-laden runoff entering vegetated treatment practices such as SGWs. 23 In areas where salt application is significant, such as highways and state roadways, chloride loading to stormwater practices may change the hydraulic conductivity and/or vegetation health and survivalrendering practice performance different than what models predict. [24][25][26] Chloride concentrations in streams of Maryland, New York, and New Hampshire have reached as high as 5000 mg L −1 in winter and elevated chloride concentrations can persist into the summer.…”

Spatial and Temporal Analysis of Hydraulic Conductivity, Snow Depth, and Soil Properties of a Bioretention System

“…Physio-chemical processes are suspected to cause structural changes in the soil by causing flocculation of aggregates according to literature (Kakuturu & Clark, 2015). No chemical analysis has been carried out as part of this study, but salt concentrations are assumed to be higher in the central flow pathway.…”