TECHNICAL NOTE

POLLUTANT BUILD UP & RUN OFF ON HIGHWAYS; EXPANDING THE CURRENT

METHODOLOGY FOR ADDITIONAL DETERMINANDS

Junaid Patel* and Olivier Drieu**

ABSTRACT Pollutants build up on highways and are washed off during a rainfall event; and are usually discharged via an outfall to a watercourse. ClRlA report 142 (1994) guidance for evaluating water quality downstream of a highway outtall considers only copper and zinc in the water quallty assessment of highway outfalls; determinands thought to occur in significant concentrations in highway runoff. This guidance has since been adopted in the Design Manual for Roads and Bridges environmental assessment. However, recent investigations suggest that other determinands may occur in unacceptabiy high concentrations. This paper demonstrates that additional determinands should be considered in the water quality assessment downstreum of a highway outfall.

Key words: AADC DMRB; Em; hlghway Ouffcrl; hlghway NnoK

*Graduate Engineer MSc, Atkins Water, Wanington.

"Senior Engineer MSC. Atkins Water, Warrington.

INTRODUCTION It has been recognised that runoff from roads can have an adverse impact on the environment. The Highways Agency has a right to discharge runoff from roads to watercourses (I),

but does not have the right to pollute them; whilst the Environment Agency has a statutory duty to protect and monitor water quality m. The current state of knowledge in predicting the polluting potential of highway runoff in the UK is summarised in ClRlA report 142 (') (1994). This has been reproduced in the Design Manual for Roads and Bridges (4 (DMRB 11.3.10. 1993) which recommends a three stage approach for the environmental assessment. The intermediate stage of the assessment involves calculating spillage risk and evaluating the water quality downstream of the discharge outfall for copper and zinc; determinands considered ecologically significant at the range of concentration present in highway runoff. The methodology centres on the loading rates of copper and zinc on roads, which are derived from studies performed in the 70s and 80s. ClRlA report 142 identifies traffic flow as the major factor in

Figure 1: A Highway Ouifall

pollutant loading build up, by directly relating traffic flow to pollutant build up rates, the effect of which is capped for a traffic flow greater than 30.000 vehicles per day (annual average daily traffic, AADT). In order to calculate the concentration of copper and zinc downstream of a highway outfall (Figure l), a mass balance calculation is performed, assuming that the determinand builds up during a dry period and is then washed off completely during a single rainfall event.

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Current research suggests that pollutants other than copper and zinc may occur in slgnificantly high concentrations in highway runoff. This paper considers the pollutant build up rates for additional determinands in order to Identify determinands which m y occur in excessive concentrations In highway runoff, applying the ClRlA 142 methodology.

0.60

0.50

f 0.40

9 0.30 z

g 0.20

v

U

4

0.1 0

0.00

METHODS Building the Database A database was developed from recent studies (post ClRlA report 142, 1994) in order to derive relationships between traffic flow (AADT) and pollutant loading rate (kg/ha/yr) for the following determinands:

Lead (Pb) Chromium (Cr) Nickel (Ni) Cadmium (Cd) Total Suspended Solids (rSS)

Biochemical Oxygen Demand (BOD) Ammoniacal Nitrogen (NH4-N)

A

/

A

I I I I I

Studies were initially screened for their relevance to the UK in terms of hydrology. surrounding land use and type of highway. all of which have been shown to have an influence on pollutant loading c5)ca)c"? studies were accepted or rejected into the database based on these criteria. The availability of studies which met the specific criteria of this review was limited further because use of the 'event mean

concentration' (EMC) value has superseded the use of loading rates (kg/ha/yr) for many environmental practitioners.

Table 1: Pronles of studies lncludlng In the database.

Auihar (s)

Barretet a1 (5)

(1

Wu et a1 (6)

(1996) Shinya el ai (7)

(1997) Drappr et a1 (8)

Sludy Pmnle Results from a 2 year study of 3 sites in Austin,

Texas (Mo Pac Express Way), USA

Determinands included same heavy metals and organics.

Water quality monitoring (1 year) from 3 sites in North Carolina. USA.

A 1 year study in Japan of a single site including

metals and cfaanics.

A 1.5 year study in Queensland Australia of 3

sites in urban, and residential seftings.

A 1 year study (1 995-1 99s) of a single motaway site in Northem France. Determinands included

heavy metals and organics

A Long Term water quality monitoring study of 6

sites in the UK, an exhaustive list of metals,

hhicides, hydrocarbons and organics was investigated.

The key studies included in the database are given in Table 1. it should be noted that each study contained a number of study sites, and that not every study investigated all determinands listed above. The data pool was strongly weighted in favour of UK sites as the WRc report represented 6 of the 16 sites studied. Furthermore, the magnitude of loading rates for ail determinands were comparable to those found In the UK. A typical plot of loading rate and AADT can be seen in Figure 2 for lead.

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Table 2: Pollufanf loading rates defermlned for the addMona1 determlnands included In this study

Determinand

Lead (Pb)

Chromium (Cr)

Nickel (Ni)

Cadmium (Cd)

Total Suspended Solids

BOD

Pollutant Load (kgha/yr)

(vehiclWdav)

5000- 15,000-

<5000 15.000 30,000 >30,000 0.15 0.20 0.30 0.45

0.07 0.08 0.09 0.15

0.07 0.08 0.08 0.08 0.005 0.01 0.01 0.01 5

600 700 850 1250

30 40 55 85

Cadmium (CU) TSS

BOD

NHd-N 1 4 1 9 1 20

Dangerous Substances Directive (I1)

Freshwater Fish Directive (Guideline only) (I2)

RE Classification Reoulations (Is1

The relationship between traffic flow and loading rate was assumed to be linear as indicated in ClRlA report 142. It can be seen from Figure 2 that the magnitude of loading rate values are comparable and that the correiatlon coefficient (r?) is reasonably high, slmiiar flndings were observed for the other determinands. The derlved loading rates for ail the above determinands are given in Table 2.

Environmental Quality Standards In order to compare the downstream concentratlon of a specific determinand, corresponding envlronmental quality standards (EQSs) were obtained from current legislation set for flsheries protection. The sources of these EQSs for comparison with determinand concentration downstream of a highway outfall are given in Table 3. In this study. results of downstream concentration are presented as a ratio of the corresponding EQS for a speciflc determinand. a value greater than unity therefore represents exceedance of the EQS.

RESULTS AND DISCUSSION Concentration of Determinands in Highway Runoff The determinand concentration In highway runoff. which is independent of catchment size. Is required in order to categorise which pollutants occur in excessive concentrations. Pollutants which exceed EQSs In highway runoff have the potential to exceed EQSs downstream of an ouffoll. The CiRlA report 142 guidance was implemented In order to obtain the concentration of determinands in highway runoff. The foilowlng (CIRIA) assumptions were considered in order to calculate the concentration of determinands in highway runoff:

(I) A flve day pollutant build up (antecedent dry period) (ii) Highway runoff coefficient of 0.5 (ill) Total pollutant wash off (iv) A 1 Omm rainfall event (1 year- 24hr)

The concentration of a specific determlnand can therefore be expressed as:

(p/365y.,A c, =I000 (7) = 1000 ( DAR ) Where:

C, = concentration of determinand (mg/i) M, = absolute mass of determinand @g) V = volume of runoff (m7 b = Lwdlng rate of determinand @g/m2/yr, see Table 2) D = depth of rainfall (m) A = Rwd Catchment Area (m?) R = Runoff Coefficient p = antecedent dry perlod. pollutant build up period (days)

It can be Seen that the concentration (CJ is catchment area independent, the area term (A) has been given for completeness. Table 4 and Table 5 below provide the concentrations of the determinonds in highway runoff. These values give an indication of the polluting potential of highway runoff for the seven determinands considered in this review. Failures are observed for ail determinands except nickel and cadmium. Clearly, varying the rainfall depth has a major impact on the concentration of determinands. ClRlA report 142 indicates the use of the Wallingford Procedure (I6 which considers the one year 24hr storm in order to determine the site speclflc rainfall.This method provides a rainfall range of 8 - lbmm for the UK. In this study lOmm has been used, however,

Table 3: Sources of €nvlronmental Qualify Standards (EQS)

Determlnand I source al €as Lead (Pb) I Dongerous Substances Directive ( " I

Chromium (Cr) I Dongerous Substances Directive (I1)

Nickel (Ni) I Donaems Substances Directive (I1)

NH4-N I RE Classilcation Regulahons ('''

Table 4: Concentrations of specllic determlnands In highway runoff (expressed as a ratio of correspondlng EQS) for a lOmm ralnfall evenf (AADT>3o.ooO). Shadlng Indicates Ibllure. Failure is deflned as exceedance of the corresponding EQS.

I Rlver Ecosvstem ciassmcotion

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Table 5: Concentrations of hardness related determinands in highway runoff (expressed as a rafio of corresponding EQS) for a lOmm rainfall evenf (AADb30,oOO). Shading indicafes faiiure. failure is dehed as exceedance of the Corresponding €0.5.

I I IDeterminand I

RE 1

&

RE2

I Pb I Cr I NI River

Class

<50 30.8 8.22 0 44

50-100 12.3 4.11 0 22

100-150 12.3 2.06 0 15

150-200 6.16 2.05 0 15

200-250 6.16 082 011

RE3

I >250 I 6.16 I 0.82 I 0.11

.~ 1 -

100-150 I 099 I 021 I 0 15

I <50 I 6.16 I 027 I 044

RE4 200-250 I 0.49 I 0.16 I 0.1 1 >250 I 0.49 I 0.16 I 0.1 1

& I 150-200 I 0.49 I 0.21 I 0.15

River Class

I

DMRB Examples Addfflonal Examples

1 1 2 1 3 A l B l C RE2 I RE2 I RE1 RE2 I RE4 1 RE2

pSs low flow (m3/s)

Hardness (mg/l)

Rainfall (mm)

Table 6: Key inputs required for implemenfafion of ClRlA methodology for all example snes. AADT values for examples A€ were measured in 2W 1.

0.016 0.01 1 0.063 0.735 0.03 0.006

610 97 65 150 198 150

1 1 13 1 1 12 9 5.75

€h low flow (mY sl 10.016 10.01 1 10.063 10.735 I 0.03 IO.006 "" . I

Hardness (mg/l) I I I I I

I 610 I 97 I 65 I 150 I 198 I 150

Rainfall (mm) I 1 1 I 13 I 1 1 I 12 I 9 15.75

Table 7: Summary table indicating EBS failure for a number of examples. Shading indlcafes fallure. hilure is defined as exceedance of me corresponding EQS.

I DMRB ExamDles I Addfflonai ExamDles

Motorway Catchment Area (ha) Annual Average Dally TraMc (AADT, 000s)

6.45 11.25 30.0 10.6 18.1 8.44

18 120 40 42 109 71

Determinand

Lead

Chromium

BOD Il.Oe12.2311.421051 107311.66

NHa-N I 1.15' 13.34 12.03 I 0 50 I 0 39 I 2.5

1 2 3 A B C

1.15 4.41 2.82 054 047 3.32 048 1.88 1.10 050 036 068

If 8mm had been implemented, cadmium would also exceed Its EQS. However, if 16mm had been implemented. the above Initial result (i.e. number of failures) would remain unchanged.

I Slmliarly, for the hardness related pollutants lead and

ClRlA report 142 recognised the need to model the worse case scenario for water quality assessment. However, the values of rainfall obtained from the Wallingford Procedure are relatively large in comparison to the minimum rainfall required for pollutant wash-off and may not represent the worse case (least dilution) scenario. For a simple assessment, the use of a single value of minimum rainfall required for pollutant wash-off may be advantageous in order to develop the worse case scenario. Such a value would represent the depth which exceeds the road infiltration capacity to produce runoff and wash-off the pollutants.This value has been shown to be in the range of 0.1- 2.2 mm ('5)(16)(111. Values of infiltration capacity do suggest that much smaller values of ralnfall than those provided by the Wallingford procedure could be implemented to represent the worse case (least dilution) scenario. The subject of reviewing current ClRlA 142 model has been discussed elsewhere (I8),

Nickel 042 036 038 050

Cadmium 050 056 0.49 050

TSS 2 12 4.86 2.88 0 54

DMRB Examples In order to understand the significance of the above results, the water quality assessment has been performed for the three example sites (1-3) given in the DMRB (1 1.3.10, annexe Ill). In addition to the DMRB examples. three more example sites (A-C) have been included. based on specific watercourses and motorway catchments in England. The key inputs required for implementation of the ClRlA methodology are given in Table 6.

035 020

041 030

2,22 3.67

The results of implementing the ClRlA methodology for the additional determinands are given in Table 7. In summary. watercourses which are at risk of exceeding EQSs set for fisheries protection are characterised by the following:

(i) Good quality rivers (RE 2 target and above) (ii) Low hardness values (<100mg/l). for determinands with

hardness related EQSs (iii) Low Qg5 values (<0.1 m3/s) (iv) Low rainfall (i.e. low dilution) (v) Large highway catchment size (vi) High traffic fiow (AADT>30.000 vehicles/day)

CONCLUSIONS In this study the following determinands have been identified as pollutants which occur in highway runoff in concentrations which consistently exceed thresholds set for fisheries protection (EQSs). In descending order of priority:

(1) Total Suspended Solids (TS) (ii) Ammoniacal Nitrogen (NH,-N) (ill) Blochemical Oxygen Demand (BOD)

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chromium have been found to occur in excessive concentrations. Nickel and cadmium have been shown to occur in concentrations which do not exceed corresponding EQSs.

These preliminary findings indicate that the CiRlA 142 water quality assessment should be expanded to accommodate the additional determinands cited in this review.

Highway discharges are intermittent discharges which can have a disproportionate impact on the water environment. The isue of pollutant loading (and runoft) on roads is increasingly becoming an important isue since the adoption of the Water Framework Directive. which aims to achieve 'good ecological status for a11 surface waters.'

Currently average daily traffic Rows exceed 70.003 vehicles/day on UK highways with flows greater than 100,003 the norm for major motorwoys.The effect of such high traffic fiow on pollutant loading is un-quantified. Given that there are thought to be more than 12,000 outfalls on the highway network, a need therefore clearly exists to re-evaluate pollutant loading and its effects in the UK.

ACKNOWLEDGEMENTS The authors would like to thank Dr. Jason Kirby for his enthusiastic supervision, good will and patience throughout this study. in addition, many thanks go to Dr J.R. West, Dr A. Shamseldin, Dr. R.J. Martin, Dr. L.E. Coates and Prof. D.W. Knight.

REFERENCES (1) HMSO (1980) Highways Act (Section 100) (2) HMSO (1 991) Water Resources Act (Section 85 & 89) (3) ClRlA Report 142 (1994). Control offollution from Highway

Drainage Discharges. (4) DEPARTMENT OF TRANSPORT (1 993. Amended 1998) Design

Manual for Roads and Bridges, 11.3.10: "Water Qualityand Drainage". Highways Agency.

(5) BARRET M.E. IRISH JR. B.L.. MALiNA JR. J.F.. CHARBENEAU R.J.(1998): Characferisation of highway runoff in Austin Texas area. Journal of Environmental Engineering. 124 (2)

(6) WU J.S.. ALLEN C.J.. SAUNDERS W.L., EVEll J.B., (1998): Characferlsatlon and pollutant loading estimation for highway runoff. Journal of Environmental Engineering, 124

(7) SHINYA M., TSURUHO K., KONlSHl T., ISHIKAWA M., (2003): Evaludon of Factors influencing dimsion of poliutant loads in urban highway runoff. Water Science & Technology, 47 (7-8). 227-232.

131-137.

(7) 584-592.

(8) DRAPPER D, TOMLINSON R., WlLLiAMS I?, (2KQ): Pollutant Concentratlons In road runoff: Southeast Queensland case study. Journal of Envlronmenfal Engineering. 126 (4)

(9) LEGRET M., PAGOTTO C., (1999): Evaluation of pollutants loadings in the runoff waters from a major rural highway. h e Science of fhe Total Environment. 235,143-1 50.

(10) WRC, WATER RESEARCH CENTRE (2002): Long term monitoring of pollution for highway runoff: final report, Wrc RefUC 6037.

(1 1) EC (1976): Dangerous Substances Directive (76/464/EEC). (12) EC (1978): EC Freshwater Fish Directive (78/659/EEC). (13) HMSO (1994): The Surface Waters (River Ecosystem)

(Classification) Regulations 1994 Statutory Instrument 1994 No. 1057

(14) DOE (1981) Wallingford Procedure for design and analysis of Urban Storm Drainage, National Water Council, Standing Technical Committee Reports.

Fractionation of heavy metals In pavement runoff. h e Science of fhe Total Environment, 189/190 pp 331-378.

(16)ELLIS J B, HARROP D 0 AND REVIll D M (1986). Hydrological Controls of Pollutant Removal from Highway Surfaces. Water Research, Volume 20, No 5.

(17) HARRISON R M AND WILSON S J (1985). The Chemical Composition of Highway Drainage Water. The Science of the Total Environment. 43.63-77.

(18) PATEL J A (2005). Review of ClRlA Report 142 on Highway Pollutants. Proceedings ol fhe lnsf/fuffon of Civil Engineers. Transport 158 (lR3) 137-1 38 August.

31 3-320.

(15) SANSALONE JJ, BUCHBERGER S G, AL-ABED S R (1996).

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