A Study of Soil Pollution by Road Runoff

Road runoff, a representative non-point source pollution, is known to seriously deteriorate the river water quality. In order to prevent river contamination due to road runoff, road runoff is infiltrated into the soil along the river. However, road runoff containing high concentrations of heavy metals and total petroleum hydrocarbons (TPH) can cause soil pollution. In this study, soil samples were collected at the point where road runoff flows, and the concentrations of heavy metals, such as cadmium, lead, and zinc, and TPH in them were compared with that in uncontaminated soil. Consequently, the concentration of heavy metals in the soil into which the road runoff flows was up to 21 times higher than that of the nearby uncontaminated soil. In conclusion, the discharge of road runoff into the soil seriously pollutes the soil. Therefore, direct discharge of road runoff to soil should be prevented to prevent soil pollution.

Review of tools for road runoff quality prediction and application to European roads

Pollutants discharged by roads may impact water bodies and soils. The best method to characterize road runoff is by monitoring, which is not always possible due to human or material constraints. Therefore, prediction tools can be a valuable method to manage road runoff discharges and protect the environment. The present work reviewed and evaluated international tools for road runoff quality prediction, in order to assess if an existing tool could be suitable for wide usage by stakeholders in Europe. Four tools from the USA and Europe were selected and tested at 22 road sites located in regions with annual precipitation values ranging from 500 to 1,000 mm, from 7 European countries. The results for the SMC of TSS, Zn, Cu, Pb and Cd showed coefficients of determination (R2) from 0.0,004 to 0.2890 for the different pollutants and tools. It was concluded that none of the tools could predict the road runoff pollutant concentrations, except for the country where it has been calibrated. The findings support practitioners and researchers all over the world, pointing out directions, and gaps to be filled, regarding the management of road runoff discharges and use of prediction tools.

Removal Effect of Basic Oxygen Furnace Slag Porous Asphalt Concrete on Copper and Zinc in Road Runoff

In order to improve the utilization efficiency of road runoff and the remove effects of heavy metals, porous asphalt pavements have been used as an effective measure to deal with heavy metals in road runoff. However, the removal effect on dissolved heavy metal is weak. In this paper, basic oxygen furnace (BOF) slag was used as aggregate in porous asphalt concrete to improve the removal capacity of heavy metal. Road runoff solution with a copper concentration of 0.533 mg/L and a zinc concentration of 0.865 mg/L was artificially synthesized. The removal effect of BOF slag porous asphalt concrete on cooper and zinc in runoff was evaluated by removal tests. The influence of rainfall intensity and time on the removal effect was discussed. The results obtained indicated that BOF slag porous asphalt concrete has a better removal effect on copper. The removal rate of copper is 57–79% at the rainfall intensity of 5–40 mm/h. The removal rate of zinc is more susceptible to the changes of rainfall intensity than copper. The removal rate of zinc in heavy rain conditions (40 mm/h) is only 25%. But in light rain conditions (5 mm/h), BOF slag porous asphalt concrete maintains favorable removal rates of both copper and zinc, which are more than 60%. The heavy metal content of runoff infiltrating through the BOF slag porous asphalt concrete meets the requirements for irrigation water and wastewater discharge. The results of this study provide evidence for the environmentally friendly reuse of BOF slag as a road material and the improvement of the removal of heavy metal by porous asphalt concrete.

Towards a model for road runoff infiltration management

In human society, there is a demand for sustainable solutions for water preservation and efficient treatment systems. An important water reservoir is road runoff defined as rainwater leaching from roads, loading micropollutants and infiltrating the soil. We aimed to study this poorly understood feature using large-scale metabolomic analysis coupled with analysis of soil physico-chemical properties and molecular chemical similarity enrichment. A total of 2406 micropollutants were assayed to understand their distribution and assess the trapping abilities of a road runoff infiltration system composed of a sedimentation pond and an infiltration pond. Here, we confirm the essential role of the infiltration pond in preventing environmental contamination and propose a model correlating micropollutant abundance and the soil physico-chemical properties. We demonstrate that sand in infiltration ponds is a key player, helping retain 86% of the micropollutant abundance and propose a model that could be easily applied for road runoff management.

Microbial retention and resistances in stormwater quality improvement devices treating road runoff

Current knowledge about the microbial communities that occur in in urban road runoff is scarce. Road runoff of trafficked roads can be heavily polluted and is treated by stormwater quality improvement devices (SQIDs). However, microbes may influence the treatment process of these devices or could lead to stress resistant opportunistic microbial strains. In this study, the microbial community in the influent, effluent and the filter materials for the removal of dissolved heavy metals of two different SQIDs were analyzed to determine the microbial load, retention, composition, and mobile resistance genes. Although the microbes were replaced by new taxa in the effluent, there was no major retention of microbial genera. Further, the bacterial abundance of the SQIDs effluent was relatively stable over time. The heavy metal content correlated with intl1 and with microbial genera. The filter media itself was enriched with Intl1 gene cassettes, carrying several heavy metal and multidrug resistance genes (e.g. czrA, czcA, silP, mexW and mexI), indicating that this is a hot spot for horizontal gene transfer. Overall, the results shed light on road runoff microbial communities, and pointed to distinct bacterial communities within the SQIDs, which subsequently influence the microbial community and the genes released with the treated water.

Using Multiple Isotopes to Identify Sources and Transports of Nitrate in Urban Residential Stormwater Runoff

Increased nitrogen (N) from urban stormwater runoff aggravates the deterioration of aquatic ecosystems as urbanisation develops. In this study, the sources and transport of nitrate (NO3−) in urban stormwater runoff were investigated by analysing different forms of N, water isotopes (δD-H2O and δ18O-H2O), and NO3− isotopes (δ15N-NO3− and δ18O-NO3−) in urban stormwater runoff in a residential area in Hangzhou, China. The results showed that the concentrations of total N and nitrate N in road runoff were higher than those in roof runoff. Moreover, high concentrations of dissolved organic N and particulate N in road runoff led to significantly different TN concentrations in road runoff (mean: 3.76 mg/L) and roof runoff (mean: 1.23 mg/L). The high δ18O-NO3− values (mean: 60 ± 13.1‰) indicated that atmospheric deposition was the predominant NO3− source in roof runoff, as confirmed by the Bayesian isotope mixing model (SIAR model), contributing 83.6–97.8% to NO3−. The SIAR model results demonstrated that atmospheric deposition (34.2–91.9%) and chemical fertilisers (6.27–54.3%) were the main NO3− sources for the road runoff. The proportional contributions from soil and organic N were smaller than other sources in both the road runoff and roof runoff. For the initial period, the NO3− contributions from atmospheric deposition and chemical fertilisers were higher and lower, respectively, than those in the middle and late periods in road runoff during storm events 3 and 4, while an opposite trend of road runoff in storm event 7 highlighted the influence of short antecedent dry weather period. It was suggested that reducing impervious areas and more effective management of fertiliser application in urban green land areas were essential to minimize the presence of N in urban aquatic ecosystems.

Performance Analysis for Road-Bioretention with Three Types of Curb Inlet Using Numerical Model

The FullSWOF-ZG (Full Shallow Water Overland Flow with infiltration determined by Zones and Grate-inlet submodules) program was used to simulate the road-bioretention (RB) stripe and evaluate the performance of the RB stripe with three types of curb inlet. The program was revised from the open-source FullSWOF-2D program and the validation results indicated FullSWOF-ZG predicts the RB stripe performance accurately. The model cases of 27 RB with different longitude slopes (S0), cross slopes (Sx), and curb inlet lengths (Lci) for the undepressed, composite depressed, and local depressed curb inlets were established in this study. Therefore, 81 cases in total were simulated to explore the curb inlet type and design parameter’s influence on the RB stripe performance. Overall, it was found that the bioretention control efficiency will increase with the S0 decrease, Sx increase, and Lci increase. The composite depressed curb inlet was the most efficient to intercept the road runoff into the bioretention strip, the next best is the local depressed curb inlet, and the undepressed curb inlet was the least efficient. The curb inlet and grate inlet combination in composite depressed curb inlet cases were able to deal with all the road surface runoff for the small longitudinal slope (S0 = 0.1% and 0.3%) to relieve the road local flood inundation.

Pollutant first flush identification and its implications for urban runoff pollution control: a roof and road runoff case study in Beijing, China

First flush is a common phenomenon in urban runoff pollution. Typical cement roof and asphalt road runoff in Beijing, China were monitored for 2 years. Based on the M(v) curve, the suspended solids (SS), chemical oxygen demand (COD), total phosphorus (TP) and particulate phosphorus in cement roof runoff presented a stronger first flush than those in asphalt road runoff. The first flush volume (VFF) of SS, COD, total nitrogen (TN) and TP in asphalt road runoff differed slightly from the cement roof. There were also differences in the first flush assessment depending on which method was used. We proposed a new method based on the runoff depth versus pollutant cumulative mass curve. According to the national standards in China (VFF = 3 mm), various masses of different pollutants, such as 91.42 ± 9.80% (cement roof) and 78.49 ± 19.41% (asphalt road) of SS and 86.85 ± 13.54% (cement roof) and 72.80 ± 25.79% (asphalt road) of COD, can be effectively controlled, but our mass control efficiencies were 55.91%–66.65% when VFF = 1 mm. The new method proposed in this study provides an alternative approach for assessing runoff pollution control efficiency of different VFF.

N, P, and COD conveyed by urban runoff: a comparative research between a city and a town in the Taihu Basin

Stormwater runoff containing various pollutants exerts adverse effects on receiving water bodies and deteriorates the urban aquatic environment. Although numerous studies have been conducted on runoff pollution, research comparing its characteristics in cities with those in towns is rare in the literature. To close this gap, the present study was conducted. The outflow concentration and peak value of N in the town were higher than those in the city in most conditions (at 75% and 67%, respectively). The second peak value of P in the town was higher and occurred earlier than the city. EMCs of TN and DTN in the town were 20%–60% (10%–50%) higher than those in the city. DTP accounted for 76.9%–83.3% of the total P (TP) in the town, which was generally higher than the city values of 50%–87.5%. According to our results, road runoff in the town contributed more to urban aquatic pollution, thus further research should concentrate on this particular type of runoff.