IWRA Proceedings

Introduction Recent research conducted on runoff quality from the highways qualified the runoff as a potential source of hazard to water bodies (particularly following Water Framework Directive (WFD). For example, zinc can be found out in runoff from tyre wear and iron from vehicle corrosion. Clutch and brake use are thought to release nickel and copper (Hulscotte et al. 2007; Crabtree et al. 2008). Knowledge of concentrations of pollutants entering a water body provides only limited information on the impact on water quality (mass load), but information about the volume of the runoff is also important because the latter provides an idea of the mass of pollutant and an event mean concentration (EMC). Understanding the 'first flush' of pollutants is an important concept to the improvement of stormwater quality. Some authors, however, reported that there was no strong indication of a first flush effect for pollutants (Davis and McCuen 2005), whereas other publications (Mosley and Peake, 2001; Prestes et al. 2006) provided evidence from which a first flush of pollutants could be noted. In the majority of cases "first flush" has been linked to total suspended solids (TSS). Less information is available for metals or other pollutants, for example, organic matter.

Thus, the objectives of this research were: to evaluate the impact of pollutant mass loads linked to rainfall characteristics and ADWP on receiving water bodies and report on the performance of a typical treatment system.

Methods The location selected on the M1 was on the northbound carriageway (J 24A). This section of the M1 motorway is one of the busiest sections, linking as it does the major East Midlands cities, and it has one of the highest levels of traffic in the UK (peak traffic flows are 30,000 vehicles an hour). During rain the runoff flows along a ditch adjacent to the motorway which links up with the drainage from the A50 slipway and then into an interceptor before a SuDS lagoon.

Samples were collected by hand using pre-acid washed polyethylene bottles (10% nitric acid). Total (tot) and soluble (dis) metals were analysed (APHA). Metals were tested for using the ICP-OES. The paper gives further details concerning the sample preparation necessary to improve reproducibility.

To measure the discharge from the motorway catchment into the inlet a "STARFLOW" Ultrasonic Doppler Instrument was used.

Results and Discussion The first part of this section presents the data obtained from the M1 during 7 monitored rainfall events compared to a dry weather period in the same season. it describes metals concentrations and their behaviour. One of the important features of this data is that the values for some pollutants (TSS, Zntot) during storms are comparable with dry weather samples and in some cases are even higher than during rainfall (TSS, Fetot, TOC). It can be explained by combination of two factors: dilution effect during the rainfalls and the accumulation of pollutants in the inlet and drains. During dry weather, either because of evaporation or re-solubilisation from the sediment, TSS concentration increases as well as total metals. The paper analyses in detail wet and dry weather concentrations of pollutants from the inlet of the lagoon, before and after the interceptor, and compares with other studies (Hallberg et al. 2007 and Pezzaniti, et al. 2012).

Taking the mean values, for wet weather conditions, then Fe was always at the highest concentrations, it is the most ubiquitous element in the environment. The Fe solubility was the lowest of the metals 5.8%. Little information comparable is available in the literature because the toxicity is low and amounts negligible compared to the background and EQS (Fedis = 1 mg/l).

The solubility of Zn was shown to depend on the presence of de-icer salts and therefore temperature which releases it from sludge and silt (average solubility 25% in wet weather samples). The concentration of total Zn in the inlet and many of the outlet samples exceeded the EQS (EQS for Zntot is 0.075 mg/l for hardness value between 200 to 250 mg/l).

Cu concentrations in this study varied widely: from negligible amounts to values exceeded the EQS (Cudis is 0.01 mg/l for hardness 150 -- 200 mg/l).

The paper also gives rainfall characteristics for observed rainfall events, that is ADWP, amount of rainfall and its intensity, runoff duration and peak flow.

The second part of the paper deals with 'First Flush' behaviour for 2 events and the important features are as follows:

1. In both events the 'first flush' phenomenon was not apparent with the exception for TOC, where the concentration increased from 3.19 to 10.31 mg/l.

2. Drainage area conditions and consequently background concentration of pollutants is an important factor while observing the 'first flush'. For example, the Fetot concentration in the beginning of the rainfall was 3.76 mg/l and decreased sharply, which implied that the continuous wet weather diluted and improved the runoff quality.

3. ADWP plays an important role in accumulating pollutants on the roads and drainage systems. Another feature of the data described in the full paper is that the rainfall event (1) showed that the 'first flush' with more than 40% of Fetot, Zntot and TSS discharging within the first 30% of the runoff volume, whereas the rainfall event (2) created linear concentrations of pollutants vs flow with no indication of 'first flush'.

Conclusions

1. Substantial amounts of TSS and consequently affiliated metals can be removed through standard SuDS techniques such as interceptors. Additional treatment should be applied while dealing with dissolved metals and organic matter.

2. Prolonged rainfall dilutes the pollutants and rainfall intensity, magnitude and storm duration all affect pollutant concentrations.

3. ADWP and local conditions of the catchment will influence the first flush phenomenon and consequently the water quality response of a treatment process.

1. APHA. Standard methods for the examination of water and wastewater, 21st ed. Washington, DC: American Public Health Association; 2005.

2. Crabtree, B.; Dempsey, P.; Johnson, I.; Whitehead, M. (2008) The development of a risk-based approach to managing the ecological impact of pollutants in highway runoff. Water Sc. and Technology. J 57.10: 1595 -- 1600.

3. Davis A. and McCUEN R. (2005). Stormwater Management for Smart Growth. USA: Springer Science and Business Media Inc.

4. Hallberg, M.; Renman, G.; Lundbom, T.; 2007: Seasonal variations of ten metals in highway runoff and their partion between dissolved and particulate matter. Water Air Soil Pollut. 181: 183 -- 191.

5. Hulscotte, J.H.J.; Denier van der Gon, H.A.C.; Visschedijk, A.J.H.; Schaap, M.; 2007: Brake wear from vehicles as an important source of diffuse copper pollution. Environ. Sci. Technol J. 56: 223 -- 231.

6. Prestes, E.; Anjous, V.; Sobre, F.; Grassi, M.; 2006: Copper, lead and cadmium loads and behaviour in urban storm water runoff in Curitiba, Brazil. J. Braz.Chem.Soc,. 17: № 1, 53 -- 60.

7. Mosley, L. M.; Peake, B. M.; 2001: Partioning of metals (Fe, Pb, Cu, Zn) in urban run-off from the Kaikorai Valley, Dunedin, New Zealand N.Z. J Mar. and Fresh Water Res. 35: 615-624.

8. Pezzaniti, D.; Beecham, S.; Kandasamy, J. (2012) Stormwater detention basin for improving road-runoff quality. Proceedings of the Institution of Civil Engineers: Water Management 165(9): 461 - 471.