EFFECTS OF WATER POLLUTION FROM ROADS

Robert J. Hares, Neil I. Ward* (ICP-MS Facility, Department of Chemistry, School of Physics and Chemistry, University of Surrey, Guildford, Surrey, GU2 7XH, UK.)

n.ward@surrey.ac.uk

 

ABSTRACT

 

Two biofiltration balancing pond facilities along the newly opened A34 Newbury Bypass have been investigated in terms of their capacity to remove heavy metals from highway stormwater. A study was also undertaken on a dry detention pond and a biofiltration pond along the London Orbital M25 motorway. Motorway-derived contaminants including Cr, Ni, Cu, Zn, Cd and Pb were measured in unfiltered stormwater samples using inductively coupled plasma mass spectrometry (ICP-MS). The study has shown a ‘well established’ reed bed and a long residence time may be the most effective in terms of heavy metal removal from stormwater.

 

INTRODUCTION

 

There are many chemical pollutants that originate from transportational activities. Exhaust emissions often contain CO, NOx, hydrocarbons (PAH’s and TPH’s; Cole et al., 1984) and heavy metal compounds (Dannecker and Stechmann, 1990). The wear of motor vehicle components can introduce many heavy metals into the adjacent environment, especially from the abrasion of tyres (Zn, Cd), brake linings (Cu, Ni, Cr, Mn) and engine components (Al, Cu, Ni, Cr, V, Sb). In addition there are many other chemicals associated with fuels, lubricating oils, brake fluids, anti-freeze compounds, transmission box oils, engine oils and greases (Blumberg and Bell, 1984). During periods of heavy precipitation these chemicals are transported via stormwater drainage systems into local receiving watercourses. Only in recent years has there been the introduction of specific devices to remove these chemicals from stormwater, including oil separators, silt traps and reed-bed biofiltration ponds. An investigation was undertaken to assess the heavy metal removal (Cr, Ni, Cu, Zn, Cd and Pb) capability through biofiltration balancing ponds along the newly opened A34 Newbury Bypass. In comparison, data concerning similar ‘well established’ facilities along the London Orbital M25 motorway will be discussed.

 

 

MATERIALS AND METHODS

 

Study sites: two balancing pond facilities, namely ponds J and K are responsible for controlling discharge into the river Lambourn (SSSI). Each balancing pond facility has a similar design incorporating an oil interceptor, silt trap and biofiltration reed bed system; and will be discussed together. Stormwater generated from the road surface (3.40 and 1.58 ha for pond J and K, respectively) infiltrates porous asphalt and is collected via a perforated inlet pipe. It then passes through an underground oil interceptor prior to discharge into a silt trap. Discharge from the silt trap (water depth of 1.1 m) involves laminar flow across the front edge and subsequent percolation over a grass filter or verge into the wet biofiltration pond areas. The holding volumes for ponds J and K are 1650 and 888 m3, respectively. Reed species present within these ponds includes B. erecta, C. riparia, G. maxima and C. stagnalis.

Sample collection, and instrumentation: samples of stormwater were taken at both facilities during dry weather and storm events throughout the period November 1998 to June 1999. A total of 520 mm of rainfall was recorded during the study period. Nine samples were taken during each sample collection visit at locations that included the silt trap, grass verge, pond area and flow controlling interceptor (see Figures 1 and 2). Samples were collected in pre-washed (1 % HNO3 - Aristar ®) polypropylene containers. Sample preparation involved direct analysis with no prior filtration. Sample analysis involved the use of a Finnigan MAT SOLA ICP-MS for the determination of the following isotopes: 52Cr+, 60Ni+, 65Cu+, 66Zn+, 112Cd+ and 208Pb+. All samples were analysed by conventional sample nebulisation (V-groove), with on-line internal standardisation using 115In+. Typical detection limits for the elements studied were between 0.1-0.2 mg/l. Validation of the results involved the use of a water certified reference material namely, NIST 1643d Trace Elements in Water and a river water material NRCC SLRS-3.

 

 

RESULTS AND DISCUSSION

 

Table 1 summarises the mean (over six storm events) stormwater heavy metal concentrations from the inlet and the outlet of each pond facility. Also reported are the percentage removal efficiencies during the initial stages of the storm events calculated from a ratio between the relative inlet and outlet heavy metal concentrations (Stotz, 1990). In general, the stormwater heavy metals levels found on the bypass are lower than from previous studies along the London Orbital M25 motorway (refer to Table 2). Differences in heavy metal stormwater levels may be a reflection of a higher daily traffic density along the London Orbital M25 motorway (>120,000 M25 compared with 20,000 along the Newbury bypass).

 

 

Table 1     Heavy metal levels of stormwater from balancing pond facilities K and J

                 (µg/l): Newbury Bypass.

 

                                    BALANCING POND K                           BALANCING POND J                

Element      Inflow     Outflow     Removal eff (%)*                 Inflow               Outflow    Removal eff (%)

Cr                 9.3            1.1                         99                                    20.8                   3.8                87

Ni                 0.88          0.28          93                                     1.98               0.48              91

Cu                33.8            3.8                          98                                   73.8                 13.5                87

Zn                30.5            15.8        97                                     73.6               27.5                86

Cd                2.09           0.15        96                                     4.61               0.66                87

Pb                8.32            0.48        97                                     18.00             2.70                86

* Comparison between the concentrations in and out during the initial stages of storm events.

 

The study of facilities along the London Orbital M25 motorway has revealed a biofiltration pond at Leatherhead is more effective than the dry detention pond at Oxted (refer to Table 2). The result was surprising due to the lack of specific pollutant removal devices at Leatherhead (such as the oil interceptors and grit traps that are present at Oxted). The data supported the use of biofiltration reed beds for long term pollutant removal, due primarily to increased residence time (Hares and Ward, 1999).

 

Table 2     Heavy metal levels of stormwater from balancing pond facilities along

                 the London Orbital M25 motorway (µg/l)

 

                                       OXTED                                                             LEATHERHEAD

Element     Inflow     Outflow     Removal eff (%)*                 Inflow                Outflow    Removal eff (%)

Cr                 86.0        14.1                       84                                          105.0          12.0                 91

Ni                 76.00        8.00       90                                        93.00            8.00               91

Cu              248.0          34.4                       88                                    274.1              24.0                   93

Zn              188.1          34.0                       84                                    208.2              28.1                   87

Cd                11.92        0.80       95                                      14.10              1.52                 90

Pb                70.30        8.10                 89                                             81.00           10.14                 89

* Comparison between the in and out facility concentrations during the initial stages of storm events

(Hares and Ward, 1999).

 

 

The treatment facilities along the Newbury bypass have been developed to incorporate both specific pollutant devices and biofiltration reed bed systems. A review of Table 1 reveals pond K is more effective in terms of pollutant removal capacity than pond J. The removal efficiencies of the pond facilities may depend on the presence of a ‘well established’ reed bed system. The presence of a well established reed bed with a high biomass within pond K acts to increase residence time of stormwater in the pond and thus increases the time for sedimentation, filtration and bioaccumulation processes. Furthermore, the broad shallow design of the reed bed system in pond K is in agreement with the optimum criteria established by Martin (1988) for the removal of contaminants in stormwater.

 

 

S = Silt trap           V = Verge

P = Pond                O = Outlet

 

Figure 1      Relative percentage lead removal in stormwater through ponds J and K

 

S = Silt trap           V = Verge

P = Pond                O = Outlet

 

Figure 2      Relative percentage cadmium removal in stormwater through ponds J and K (Newbury Bypass)

 

In contrast, a deficiency in the reed bed biomass within pond J allows hydraulic flow to be maintained at a greater distance from the silt trap thus reducing the residence time of stormwater within the pond. The high hydraulic flow and short residence time present within this pond facility may limit sedimentation and filtration processes (Nix et al., 1988). The data is consistent with a previous study relating pond efficiency and stormwater flow velocity (Oberts and Osgood, 1991). Figures 1 and 2 illustrate the relative lead and cadmium removal in stormwater (taking the difference between the inlet and outlet sites as 100 %) through each pond facility. The figures show a well established reed bed and long residence time within pond K aids in the effective removal of heavy metals from stormwater. In contrast, a poorly established reed bed system within pond J has resulted in lower heavy metal removal efficiencies. The development of balancing pond technology is a continues process and benefits from studies evaluating existing systems. Incorporation of a dilution pond either before or after the biofiltration area may further increase the effectiveness of these facilities.

 

REFERENCES

 

Cole RH, Frederick RE, Healy RP, and Rolan RG (1984), Journal of Water Pollution Control Federation, 56(7): 898-924.

Blumberg MS, and Bell JM (1984), NTIS PB84-207380, USEPA.

Dannecker W, Au M, and Stechmann H (1990), Sci Tot Environ, 93: 385-392.

Hares RJ, and Ward NI (1999), Sci Tot Environ, 235: 169-178.

Martin EH (1988), Journal of Environmental Engineering, 114(4): 810-827.

Nix SJ, Heaney JP, and Huber W C (1988), Journal of Environmental Engineering, 114(6): 1331-1343.

Oberts GL, and Osgood RA (1991), Environmental Management, 15(1): 131-138.

Stotz G (1990), Sci Tot Environ, 93: 507-514.