3 DESCRIPTIVE STATISTICS

Transcription

1 DESCRIPTIVE STATISTICS For each pollutant a brief description of the principal source in urban catchments is given, together with an indication of the effects in receiving water, and the range of observed instantaneous urban stormwater quality concentration (for comparison with flow weighted concentrations). Observed acute and chronic toxicological effect concentrations and European water quality standards are given. Descriptive statistics from an analysis of the database are then presented, divided according to the land classification described above, and three geographical regions: the UK, Northern Europe and "Global" (i.e. all data). The European data group contains all the UK data, and the Global region contains all the European and UK data. The Global region is included for comparative purposes, and has been used to provide an indicative EMC value where the sample size in the European data group is considered too small. The descriptive statistics include the maximum and minimum observed site EMC by geographical region, and a table of the following parameters: sample size, site mean EMC and standard error, inter-quartile values (all calculated from log values), and three other measures of central tendency, the median, and the arithmetic and geometric means. Alternative percentile values can be calculated using the data presented in these tables using equation. Appendix C presents further parameters descriptive of the EMC data distribution, including the standard deviation, skewness and kurtosis. The log-normality of the distribution is also assessed using the Shapiro-Wilk test (high values indicate log-normality) a powerful overall test for normality, and one recommended for sample sizes up to 5, for which the mean or variance of the hypothesised distribution are not specified in advance (Royston, 99). The Shapiro-Wilk test was not conducted for sample sizes <, as the power of the test was too low (i.e. possibility of rejecting the null hypothesis when it should be accepted). The significance level p of the Shapiro-Wilk statistic is also presented. The smaller the value of p, the more untenable the null hypothesis that there is no log-normality, that is, small values of p indicate that the data is not log-normally distributed. The Shapiro-Wilk test may indicate that a distribution is not normal, when examination of the frequency distribution and log-normality graphical plots strongly suggests normality. This is because the Shapiro-Wilk test is very strongly influenced by outliers. Removal of one or two outliers from a sample size of several hundred is sufficient to indicate normality by the Shapiro-Wilk test. Outliers in the site EMC data were examined using box plots (not shown), but only a few values were excluded. These were values that were considered to be a recording or typographic error, and several which were not considered to belong to the population (e.g. EMC values affected by a volcanic eruption in Washington). The normal probability (Q-Q) plot is considered the single most valuable aid to diagnosis of normality (BBN, 996), and was used as the final arbiter of log-normality. T-tests for differences in mean site EMC by land use were conducted, and a commentary on the results is presented in section for each pollutant. Final recommended values are given in section 4, where EMC values are presented for () each of three land use classes (Open, Developed Urban, Roads) which are a priori commonly considered to be significantly different to each other, an assumption supported by data from the US (Athahyde, 98; Strecker et al., 987), and () for each land use category (see Figure -) with a significantly different mean site EMC, as identified from the analysis presented here.

2 . Total Suspended Solids Sediments are an important mechanism for the transport of other pollutants which may cause problems related to toxicity, eutrophication, and suitability for recreational or potable use. Particle size is important as half the pollutant load may be transported bound to particles of <6µm, circa 6% of the total sediment load. Sediments can also be detrimental to water quality even when chemically inert. They cause turbidity, inhibit visual feeders, blanket fish spawning sites and feeding areas, eliminate prey organisms, reduce light penetration and photosynthesis of aquatic plants, cause gill abrasion and fin rot in fish, while scouring causes destruction of bed and bank habitat. The major sources of sediment in the urban environment are atmospheric deposition, natural weathering, and construction sites. Atmospheric deposits range from large colloids such as wind blown sand, to small particulates such as PM arising from vehicle emissions. Other sources include particulates deposited from vehicles (e.g. rust, rubber), abrasion of pervious road and building surfaces, application of de-icing salts, organic detritus, litter and a range of other wastes. Altogether 57 records were obtained, of which related to Northern Europe and 59 to the UK. This data was well distributed by land use group. The values ranged from.5mg/l for a low residential density development in Florida (Holler, 989), to 4 mg/l for a general urban site in Canberra, Australia (Sharpin, 99). The European values ranged from 5 mg/l at Edinburgh airport (Bayes et al., 994) to 7 mg/l for an A-road in Norway (Gjessing et al., 984). The highest TSS EMC in the UK was recorded by Hedley and Lockley (975) for the A8 urban motorway in Birmingham. Makepeace et al., (995) note that instantaneous (nonflow weighted) concentrations range from to 6, mg/l. The EC standard for TSS, for both fisheries and abstraction to a simple water treatment works is 5 mg/l. One observation, from a street in Leningrad had a very high value (4,54 mg/l) and was a clear far outlier, defined as more than three times the inter-quartile distance from the mean. The observation was derived from a secondary source (Duncan, 999) and could not be further verified, hence was dropped from the analysis. The remaining TSS concentrations from all land uses closely follows a log-normal distribution, as indicated by the frequency distribution and probability plots (Figure -). Appendix C presents normality statistics of skewness, kurtosis and the Shapiro-Wilk test. Figure -. Normality plots for Total Suspended Solids (a) distribution (Global data) (b) Log-normality plot (Global data) Log TSS (mg/l)

3 (c) Log-normality plot (N. Europe data) (d) Log-normality plot (UK data) Log TSS (mg/l) Log TSS (mg/l) Measures of centrality (arithmetic mean, geometric mean, median) are presented in Appendix D, along with quartile values. Additional percentile values can be calculated using the equation specified in section, and the additional descriptive statistic data in Appendix C T-tests for differences in mean site EMC were performed between land uses at both group and sub-group level, and for all three geographical regions (UK, Northern Europe, and the Global data set). A summary of land use differences is shown below, followed by recommendations for the most resolved land use classification for TSS EMC application in the UK and Europe. Industrial & Commercial No differences are found between industrial and commercial values. When treated as a single group, significant differences are found (up to p > 99.9%) with residential and highway land uses, for all three geographical regions, indicating that it is appropriate to treat this as a separate land use class for EMC purposes at the group level. Residential No clear pattern of differences in EMC is discernible between residential density groups. Highly significant differences are found with the Ind./Comm. group in the All data (p > 99%), and with the industrial group in the European data. Further differences are found between different residential groups and the industrial and commercial groups for all geographical regions. Significant differences are found with both A roads and motorways in all geographical areas, including the UK (p > 95%) and Europe (p > 99%). It is concluded it is appropriate to treat residential land use as a distinct land use class at the group level. Highways There are no significant differences between motorways and A-roads. Motorways have significantly higher EMC values than most other land uses, including the ind./comm. and residential groups, for all geographical regions, but this pattern is not generally repeated with the A-roads. It is considered appropriate to treat motorways as a distinct land use re EMC. Selected land-use categories Open (Global value) Residential, Industrial/Commercial Motorways, A-roads

4 The sample size is large for TSS, particularly for the European and Global regions, hence there is confidence that the detected differences in EMC by land use are real. Values could be drawn from either the UK or European data sets. However, for applications where multiple pollutants are of interest, geographical consistency is important. For most other pollutants it is not possible to recommend UK specific values due to limited sample sizes. Therefore, to maximise consistency it is recommended that values be selected wherever possible from the European region. Recommended values are presented in section 4.. Biochemical Oxygen Demand Biodegradable organic materials, whether natural or synthetic can enter water in solution or suspended in runoff. Sources include decaying plant and animal matter, animal excreta, litter, food wastes and hydrocarbons. In the process of decomposition (oxidation), organic materials exert an oxygen demand, either chemically or biologically mediated, which can cause dissolved oxygen (DO) in receiving water to fall to levels at which aquatic life cannot be maintained. The biochemical oxygen demand (BOD) is the amount of oxygen used in the metabolism of biodegradable organics, and usually determined using a standard five day test (BOD 5 ) involving the use of micro-organisms. Altogether 48 BOD 5 records were obtained, of which 8 were for Northern Europe and 4 for the UK. A reasonable spread of values is found amongst land use classes at the group level by geographical region, although BOD 5 data for UK highways is limited to a single observation. The values range from mg/l for an urban open area in the USA (Athayde, 98) to 46 mg/l for a developed urban area in Detroit, Michigan (Palmer, 95). The European data has low value of mg/l for an industrial estate in Scotland (Bayes et al., 994) to 45 mg/l for a medium density residential district in Aix-en Provence, Paris (Deutsch and Hemain, 984). The UK maximum of 6 mg/l was from an Edinburgh airport outlet (Bayes et al., 994). Instantaneous concentrations of BOD 5 range from to 77 mg/l, and stormwater can approach the value of untreated domestic wastewater (Makepeace et al., 995). Figure -. Normality plots for Biological Oxygen Demand (a) distribution (Global data) (b) Log-normality plot (Global data) Log BOD (mg/l) 4

5 (c) Log-normality plot (N. Europe data) (d) Log-normality plot (UK data) Log BOD (mg/l) Log BOD (mg/l) The BOD 5 values from all regions adheres to a log-normal distribution, as indicated by the frequency distribution and probability plots (Figure -). Appendix C presents the normality statistics of skewness, kurtosis and the robust Shapiro-Wilk statistic. The latter indicates that the assumption of normality is not significant (p < 95%), but tests on the stratified data indicates that the assumption of normality is acceptable. Measures of centrality (arithmetic mean, geometric mean, median) are presented in Appendix D, along with quartile values. Alternative percentile values can be calculated using the log-transformed data given in Appendix C, and equation in section. T-tests for differences in mean site EMC were performed between land uses at both group and sub-group level, and for all three geographical regions (UK, Northern Europe, and the Global data set). A summary of land use differences is shown below, including recommendations for the most resolved land use classification for BOD EMC application in the UK and Europe. Industrial & Commercial No differences are found between industrial and commercial EMC values. At the group level, significant differences are found with residential use (UK data, p > 95%) and with all categories of highway (p > 99% for European data), hence it is concluded that it is appropriate to treat this as a separate land use at the group level for EMC purposes. Residential No difference in EMC is discernible between residential density groups. Highly significant differences are found with the Ind./Comm. group in the UK data (p > 95%), with further differences between different residential groups and the industrial and commercial groups in the Global data. Significant differences are found with highways at the group and subgroup levels and also motorways in all geographical areas, and particularly in the UK (p > 95%) and European (p > 99%) data. It is concluded that it is appropriate to treat residential land use as a distinct group at the aggregate level. 5

6 Highways There are no significant differences between motorways and A-roads. Highways have significantly (better than p > 95%) higher EMC values than most other land uses including ind./comm. and residential use for European data, but there is insufficient data to identify any UK differences. This pattern is repeated with the European A-roads. Selected land-use categories Open (Global) Residential, Industrial/Commercial Main roads Recommended values for the selected land-uses are presented in section 4. Note that the European values are slightly higher than that for the UK, probably attributable to the larger sample size rather than any real effect. It is also noted that both the UK and European EMC values are consistent with the BOD 5 values recommended by Morris and Crabtree () for use in the preliminary planning procedures (e.g. SIMPOL model) of the UK Urban Pollution Management Manual (FWR, 994).. Chemical Oxygen Demand Like BOD, Chemical oxygen demand (COD) is a measure of the oxygen demanded by decomposing substances, and is a measure of the organic content of the water. Unlike the BOD test, which uses micro-organisms, COD is determined chemically, using a strong oxidising agent (potassium dichromate) with the process assisted by a silver sulphate catalyst. The COD test is rapid, about hours, but cannot be used to compare biologically oxidizable from inert organic matter. A total of 6 COD EMC records were obtained, of which 49 were from Northern Europe, but only 4 from the UK. A good spread of values by land use class is found in the European and Global data sets. The global range is from 5 mg/l for an urban district of Zhuhai, China (Zhen-Ren et al., 99) to mg/l for a commercial district of Burnaby, Canada (Hall and Anderson, 988). The European values range from a low of mg/l for a residential area of Leystad, Netherlands (Unnk and Van de Ven, 987) to 5 mg/l for an A-road in the Lake Padderunduann area of Norway (Gjessing et al., 984). Figure -. Normality plots for Chemical Oxygen Demand (a) distribution (Global data) (b) Log-normality plot (Global data) Log COD (mgl) 6

7 (c) distribution plot (N. Europe) (d) Log-normality plot (N. Europe) Log COD (mg/l) COD adheres very well to a log-normal distribution, as indicated by the frequency distribution and probability plots (Figure -). Appendix C presents the normality statistics of skewness and kurtosis and the Shapiro-Wilk test results, which indicate that the assumption of log-normality cannot be accepted (p < 95%) for the all urban data, but that the assumption is valid for the stratified and European data. Measures of centrality are presented in Appendix D along with quartile values. Alternative percentile values can be calculated using the descriptive log-transformed data in Appendix C and equation from section. Industrial & Commercial No UK data and limited European data limit the analysis. No differences were found between industrial and commercial values. When treated as a single (aggregate) group, significant differences are found with residential use (Europe, p > 95%). Differences are also found between the industrial and commercial groups and some residential and highway categories. It is concluded that it is appropriate to treat this as a distinct land use for EMC purposes at the group level. Residential No differences in EMC are discernible between residential density groups. Residential EMC is significantly lower than the Ind./Comm. group in the European data (p > 95%), with additional similar differences at the subgroup level The residential EMC is significantly lower than that of highways in the European group (p >99%). It is concluded that it is appropriate to treat residential land use as a distinct use at the group level. Highways Motorways have a significantly higher EMC than that for A-roads in the Global region (p >95%), but not the other regions (where N is small). A-road values are consistently and significantly lower (p > 95%) than most other land uses, including motorways in the All group, but not in the other regional groups, presumably due to a small sample size. It is concluded that it is appropriate to treat A roads distinctly from motorways if using the larger All data set, but that this distinction cannot be made for the other regions where N is too small. 7

8 Selected land use categories Open (from Global data set) Residential, Industrial/Commercial Highways (if Europe) else Motorways and A-roads (if Global data set). Results for differences in mean site EMC values by land use are summarised below, with recommendations for the most resolved land use classification for COD EMC application in the UK and Europe. Recommended COD EMC values are presented in section 4..4 Cadmium The principal sources of cadmium are combustion, including that of lubricating oil, wear of tyres and brake pads, and industrial emissions, especially from electroplating works. It is used to cover iron products (sheet iron, nuts and bolts) to prevent corrosion, although these do eventually corrode and release cadmium. Cadmium is used extensively in the manufacture of batteries, paints, and plastics, and is found in agricultural use of sludge, fertilisers and pesticides (Makepeace et al., 995). Cadmium is highly toxic, and standards are set for fisheries protection and drinking water. Its toxicity is affected by hardness, ph, water temperature and the presence of organic compounds. In stormwater, Cd is largely associated with dissolved solids (Makepeace et al., 995). A total of 4 Cd EMC records were obtained, of which 9 were from Northern Europe, but only 5 from the UK. A good spread of values by land use class is found in the Global data sets, but there is only one observation from an industrial/commercial site for Europe. The Global values range from. ug/l for a developed urban site in Sacremento, California (Bumgardner, 994) to 6 ug/l for a parking lot in Syracuse, New York (Owe et al., 98). The European range is from a low of.5 ug/l for a developed urban area in Viborg, Denmark (Arnberg-Nielsen et al., 987) to 9 ug/l for a developed urban area in Strassenabflusse, in the German Rhine valley (Muschack, 989). Figure -4 Normality plots for Cadmium (a) distribution (Global data) 4 5 (b) Log-normality plot (Global data) Log Cd (ug/l) 8

9 (c) distribution plot (N. Europe) 4 (d) Log-normality plot (N. Europe) Log COD (mg/l) Cadmium adheres well to a log-normal distribution, as indicated by the frequency distribution and probability plots (Figure -4). Appendix C presents the normality statistics of skewness and kurtosis and the Shapiro-Wilk test results, which indicate that the assumption of lognormality cannot be accepted (p < 95%) for the all urban data, but that the assumption is valid for the stratified and European data. Measures of centrality (arithmetic mean, geometric mean, median) are presented in Appendix D, along with quartile values. Additional percentile values can be calculated using descriptive (log-transformed) data given in Appendix C, and using equation from section. Results of t-tests for differences in mean site EMC values by land use are summarised below, including recommendations for the most resolved land use classification for Cd EMC application in the UK and Europe. Industrial & Commercial No differences were found between industrial and commercial values. Significant differences are found with residential land use, but these differences are not consistent between regions, suggesting that the differences are due to the small sample size. It is concluded that industrial and commercial land use cannot be treated as a distinct group. Residential No differences in EMC are discernible between residential density groups. Only one significant difference occurs between a residential land use and another land use (low density residential > A-roads in the Global region), but this is based on a sample size of N=. Residential land use cannot be treated as a distinct group. Highways Motorways have a consistently higher EMC than for A roads in all regions, but these differences are not significant, except in the European data, and only then when applying a one tailed t-test (p >9%). It is concluded that highways cannot be treated as a distinct group. Selected land-use categories All Urban 9

10 Few differences in Cadmium EMC between land uses were found, although it is likely that major roads are significant sources. The small sample size hampers a more definitive analysis. Significant differences are found between several land uses and the urban open category, but it is noted that the open EMC value appears much higher than might a priori be expected given the known sources of CD in the urban environment. The mean EMC value is based on only two observations both non-european and both drawn from a secondary source, with the original unpublished sources unavailable. It is therefore considered more appropriate to treat the Open EMC as a missing value. It is concluded that there are no significant land use differences, and that the EMC value should be drawn from the European "All Urban" group, where the sample size is considered adequate (N=8). Recommended Cd EMC values are presented in section 4..5 Chromium The main sources of Cr are corrosion of welded plating metal, wear of bearings and bushes in engines, dyes, paints, ceramics, paper, heating and cooling coils, fire sprinkler systems, pesticides and fertilisers. In its hexavalent form Cr 6+ is soluble, mobile and can be stable for long periods in water of low organic content. Its trivalent form CR + has a tendency to form stable complexes, notably with chromium hydroxide. Acute toxicity ranges from ug/l for algae, where it bio-accumulates readily, to 65ug/l for rainbow trout fry, whilst chronic toxicity ranges from ug/l for invertebrates to 7 ug/l for trout fry (Makepeace et al., 995). In stormwater it is predominately associated with suspended sediments, and is more toxic in soft water. A total of Cr EMC records were obtained, of which 9 were from Northern Europe, and just 4 from the UK. A good spread of values by land use class is found in the Global data sets, but the small sample size for the other regions limits the analysis. The Global values ranged from.5 ug/l for an urban open area in Burnaby, Canada (Hall and Anderson, 988) to 58 ug/l for an industrial area in Sydney, Australia (GH and D et al., 989). The European data has a similar minimum value, and a maximum 4ug/l from the A8 urban motorway in Birmingham, UK (Hedley and Lockley, 975). Figure -5. Normality plots for Chromium (a) distribution (Global data) (b) Log-normality plot (Global data) Log Cr (ug/l)

11 (c) distribution plot (N. Europe) (d) Log-normality plot (N. Europe) Log Cr (ug/l) Total chromium adheres well to a log-normal distribution, particularly at the land use level in the global data set where the sample size permits stratification for application of the Shapiro- Wilk test. distribution and probability plots are shown in Figure -5, whilst Appendix C presents the normality statistics, and Shapiro-Wilk test result. Measures of centrality (arithmetic mean, geometric mean, median) are presented in Appendix D, along with quartile values. Additional percentile values can be calculated using the descriptive logtransformed, data given in Appendix C, using the equation from section. Results of t-tests for differences in mean EMC values by land use are summarised below, including recommendations for the most resolved land use classification for total Cr EMC application in the UK and Europe. Recommended Cd EMC values are presented in section 4. Industrial & Commercial No differences were found between industrial and commercial values. At the group level ind./comm. is significantly lower than both residential and highway groups in the European data. However, N is very small, and this pattern is not repeated in the larger Global group. It is concluded that differences may occur, but that the sample size precludes a more powerful analysis, hence industrial and commercial land use cannot be treated as a distinct group. Residential No significant consistent differences in EMC are discernible between residential density groups, although it is notable that EMC values are inversely related to residential density in both European and All groups. Residential land has a significantly lower (p > 95%) EMC value than Roads in the European data, but there are no differences in the Global data. It is concluded that residential land use cannot be treated as a distinct group. Highways No difference in EMC by road type is found in the Global data. There is no A-road data for the other regions. Roads have a significantly (p >95%) higher value than residential use, and also the general Developed Urban category for the European data. This pattern is not repeated in the Global data, and is attributed to one exceptionally high value from the A8 urban motorway in the UK.

12 Selected land use categories It is concluded that there is insufficient data to support the treatment of highways as a distinct group. All Urban No consistently significant differences in total chromium EMC between land uses were found. The open EMC value is based on only two observations, both non-european and drawn from a secondary source, with the original unpublished sources unavailable. It is therefore considered more appropriate to treat the open EMC as a missing value. It is concluded that there are no significant differences in EMC by land use, and that the EMC value should be drawn from the "All Urban" category. The European EMC value for All Urban category is approximately half that of the All data set, but the sample size of 9 is considered sufficient to select the European value for European applications..6 Total Copper The principle sources of copper in the urban environment include wear of vehicle parts (bushes, tyres, brake linings), combustion of lubricating oils, corrosion of building materials (roofs, pipes) and industrial wastes, particularly those from electroplating works. It is also widely used in algaecides, fungicides and pesticides. As with all metals, the environmental mobility and bio-availability is dependent upon its concentration in solution. As most studies report total metal concentration (i.e. in solution + particulate phase), it is worth noting that c. -4% of total copper in urban runoff occurs in the soluble phase (Luker and Montague, 994). Instantaneous stormwater concentrations range from.6 to 4 ug/l. Copper is the major aquatic toxic metal in storm water, and its toxicity, which varies with hardness, begins at 7ug/l for invertebrates (D. magna) (Makepeace et al., 995). Toxicity varies with hardness. The EC standard for fisheries is 4 ug/l and 5ug/l for abstraction for a normal water treatment works, guidelines which are often exceeded. A total of 7 Cu EMC records were obtained, of which 65 were from Northern Europe, and from the UK. A good spread of values by land use class is found in the Global and European data sets, but the small sample size for the UK limits the land use analysis for that region. The values ranged from ug/l for a residential site in Scotland (Heal, 999) to 7 ug/l for an urban area of New Jersey (Wilber et al., 98). The maximum European value of 865 ug/l was recorded for an urban district of Stockholm (Palmgren and Bennerstedt, 984). One observation for Cu had a particularly high value of 7ug/l. This value was derived from Duncan (999), and is for an A-road in Washington, USA. Duncan notes that the observation is affected by aerial deposition from the Mt. St. Helens eruption, hence this value is considered as exceptional and dropped from the analysis, along with all the other Mt. St. Helens affected observations. The remaining observations adhere very well to a log-normal distribution for all geographical regions, as indicated by the frequency distribution and probability plots (Figure -6). These observations are confirmed by the normality statistics in Appendix C, showing strong log-normality by land use category. Measures of centrality are presented in Appendix D, along with quartile values. Alternative percentile values can be calculated using the mean, count and standard deviation values (logtransformed) given in Appendix C using equation from section.

13 Figure -6. Normality plots for Copper (a) distribution (Global data) (b) Log-normality plot (Global data) Log Cu (ug/l) (c) Log-normality plot (N. Europe) (d) Log-normality plot (UK) Log Cu (ug/l) Log Cu (ug/l) Results of t-tests for differences in Cu EMC values by land use are summarised below, with recommendations for the most resolved land use classification for Cu EMC application in the UK and Europe. Recommended Cu EMC values are presented in section 4. Industrial & Commercial A significant difference is found between commercial and industrial land uses in the European data (but only 5 df), but not in the UK (no data) or Global data sets. At the group level, the EMC is significantly lower than that of highways in the UK group (df=4), but not for the other regions.

14 There are numerous significant differences between industrial and commercial land uses and other land use categories in the European data, and to a lesser extent in the UK data, but none in the Global data. The observed differences are attributed to small sample sizes in the industrial (N=) and commercial (N=5) categories. It is concluded that ind./comm. cannot be treated as a distinct group. Residential No differences in EMC are discernible between residential density groups. No differences with other land uses are observed for UK data (N=4), but both the European and Global data display significantly lower EMC than that for highways. It is concluded that it is inappropriate to treat residential land use as a distinct group. Highways There are no significant differences between motorways and A-roads. Highways have significantly (better than p > 95%) higher EMC values than most other land uses including ind./comm. and residential use for European and to a lesser extent the UK and Global data. It is concluded that highways should be treated as a separate category. Selected LU categories Open (Global data). Developed Urban Main Roads No significant differences were observed with the urban open data, but the power of the test is low due to a small sample size (N=6 for the Global Region). The NURP study (Athayde et al., 98) did find a consistent and significant difference between Cu EMC values for open and urban land use, hence it is considered appropriate to recommend that open land is treated as a distinct category. Values for developed urban and highways should be drawn from the European region, where differences are more significant, but where values are broadly consistent with the Global data region. Recommended values are presented in section 4..7 Iron Sources of iron include corrosion from vehicles and other steel, combustion of coal and coke, iron and steel industry emissions and landfill leachate. Makepeace et al., (995) report that the acute toxicity of Fe is in the range. mg/l for mayfly to 6 mg/l for other invertebrates and fish, but that the addition of Fe to lead, copper and zinc reduces the overall toxicity of stormwater. Instantaneous stormwater concentrations range from.8 to 44mg/l, and drinking water standards from.5 to. mg/l. Iron in water is generally in the trivalent (ferric) state, rather than the divalent (ferrous state), and is associated mainly with suspended solids, where sediment concentrations range from.4 to 8 mg/g. A total of 77 Fe EMC records were obtained, of which only 7 were from Northern Europe, and just one from the UK. A good spread of values by land use class is found in the Global data set at the land use group level, but the small sample size limits the analysis for other regions. Global values ranged from. mg/l for a residential district of Singapore (Chiu, 99), to a value of 66.7 mg/l for the A8 Aston expressway, an urban motorway in Birmingham, UK. Although this value was a far outlier, a check of the source (Hedley and Lockley, 975), indicated that there was no reason to exclude it from the analysis. The minimum European value was.76 mg/l for a mixed development in Lelystad, Netherlands (Van den Berg, 977). 4

15 Figure -7. Normality plots for Iron (a) distribution (Global data) (b) Log-normality plot (Global data) Log Fe (mg/l) (c) distribution plot (N. Europe) (d) Log-normality plot (N. Europe) Log Fe (mg/l) The Fe observations adhere reasonably well to a log-normal distribution, as indicated by the frequency distribution and probability plots (Figure -7), and the tests for normality in Appendix C. Measures of centrality are presented in Appendix D, along with quartile values. Alternative percentile values can be calculated using the descriptive log-transformed data given in Appendix C, using equation from section. Results of t-tests for differences in Fe EMC values by land use are summarised below, including recommendations for the most resolved land use classification for Fe EMC application in the UK and Europe. Industrial & Commercial No significant differences occur between industrial and commercial land or between these uses and any other. N is very small in both UK and European data. Ind./Comm. cannot be treated as a distinct group. 5

16 Residential No significant differences occur between residential density groups, or between these uses and any other. N is very small in both UK and European data. Residential use cannot be treated as a distinct group. Roads Most of the high observations observed for Iron are associated with highways. However, there are no significant differences between motorways and A-roads, or between highways and other land uses. It is concluded that highways cannot be treated as a separate category. Selected land-use categories All Urban Whilst there are significant differences between the Open category and several others (inc. Ind./Comm., Residential) the power of the tests of difference is low as there are only two observations for the Open category. EMC values cannot clearly be identified for any distinct urban land use, hence the All Urban value is recommended. As the sample size for the European data is very small (N=7), the Global data set value is recommended. Recommended Fe EMC values are presented in section 4..8 Total Lead Vehicle exhaust emissions are the principle source of Pb in urban stormwater, derived from atmospheric deposition. Tyre abrasion is also a significant vehicular source. Other sources include lead pipes, plastic guttering, lead roofs and flashing, and as an additive in paints and stains, although these are being eliminated. Approximately -% of Pb in urban runoff exists in the soluble phase, and the remainder is associated with suspended sediment. Lead bioaccumulates in aquatic organisms, benthic bacteria, plants, invertebrates and fish, and exerts acute and chronic toxic effects. Acute toxicity of Pb report 96-h LC 5 values of.7 to.47 mg/l, depending on water hardness and ph. Synergistic effects are increased in the presence of Cu or Zn, but reduced by Fe. The chronic toxicity no effect level for rainbow trout ranges between.7 and.6 mg/l (Makepeace et al., 995). The EC guidelines for potable water abstraction is.5mg/l, with lower values for aquatic guidelines (e.g.. mg/l in Canada). Instantaneous stormwater concentrations range from.57 to 6 mg/l. A total of 4 Pb EMC records were obtained, of which 8 were from Northern Europe, and from the UK. A good spread of values by land use class is found. The Global values ranged from ug/l for a motorway in Austin, Texas (Barret and Malina, 998), to 468 ug/l for a site addressed by the US EPA NURP (Mustard et al., 987). The European values ranged from ug/l for a highway in Floda, Sweden (Malmqvist and Hard, 98) to 4 ug/l for the A8 motorway in Birmingham, UK (Hedley and Lockley, 975). The UK minimum was 9 ug/l for an industrial estate on the Forth river, Scotland (Bayes et al., 994). Several very low values were excluded from the analysis, including those of: Soderlund and Lehtinen (97) for a Swedish highway (probable printing error in units); Baird et al., (996) for a residential and commercial runoff in Texas (dissolved Pb, not total Pb); and Heal (999) influent to a BMP from a residential site (based on only samples hence probably not flow weighted). The Pb observations adhere well to a log-normal distribution (Figure -8), however, note the Shapiro-Wilk statistics (Appendix C) which illustrate how the assumption of log-normality becomes progressively stronger as the data is stratified by geographical region, and by land use class. 6

17 Figure -8. Normality plots for Lead (a) distribution (All Global data) (b) Log-normality plot (Global) Log Pb (ug/l) (c) Log-normality plot (N. Europe).. (d) Log-normality plot (UK) Log Pb (ug/l) Log Pb (ug/l) Measures of centrality are presented in Appendix D, along with quartile values. Additional percentile values can be calculated using the mean, count and standard deviation values (logtransformed) given in Appendix C, using the equation from section. Results of t-tests for differences in Pb EMC values by land use are summarised below, with recommendations for the most resolved land use classification for Fe EMC application in the UK and Europe. Industrial & Commercial There is no UK data, but the commercial land use has a higher EMC in both the European (P > 99.9%, 9 df) and Global (not significant) regions. The group EMC is significantly lower than that for most land uses (inc. residential and highways) for all geographical regions. It is concluded that it is appropriate to treat this as distinct land use at both the group and sub-group level. 7

18 Residential No differences in EMC are discernible between residential density groups. The residential EMC is significantly higher than Ind./Comm. land use and significantly lower than that for highways, as judged by both group and sub groups in the European and Global regions (insufficient UK data). It is concluded it is appropriate to treat residential land use as a distinct group at the aggregate level. Roads Motorways have a significantly higher EMC than A- roads in both the UK (p > 9%) and Global (p > 99%) regions. Highways have significantly (better than p > 95%) higher EMC values than most other land uses including ind./comm. and residential use. This is apparent for all three geographical regions. It is concluded that it is appropriate to treat roads as a distinct group at the sub-group level. Selected LU categories Open (from Global), Residential, Industrial/Commercial Motorways, A-roads The variation in lead EMC between land use categories is assumed to be a function of vehicle density, with motorways experiencing more traffic than A-roads, and commercial areas more traffic than industrial areas. It is noted however, that since the introduction of unleaded petrol in 97 lead emissions have declined significantly. Figure -9 illustrates this decline for both roads and developed urban land. For the period 995-9, the EMC is 7% of the long term average (97-99) for highways, and % for developed urban land. It is assumed that that the lower quartile EMC values are therefore the best estimate of current EMC values. The recommended lower quartile Pb EMC values are presented in section 4. Figure -9. Long term change in Pb site mean EMC (a) Developed urban land (N=4) (b) Highways (N=87) Pb EMC (ug/l)

19 .9 Total Mercury Sources of mercury include coal combustion, paint, dental amalgam and the chlor-alkali industry. Mercury is toxic at very low concentrations (e.g..4ug/l chronic toxicity to D. pulex, and.5 ug/l for chronic toxicity to trout, both as methyl mercury). Methyl mercury is the most toxic form, and bio-accumulates more readily than inorganic mercury. In urban stormwater, instantaneous concentrations range from. ug/l to.4 ug/l, levels which exceed drinking water and aquatic guidelines (Makepeace et al., 995). A total of 5 Hg EMC records were obtained, of which 8 were from Northern Europe and none from the UK. In the Global data set, only half of the given values could be allocated to a land use other than the most general built category of developed urban. Minimum values were. ug/l in the Global set, a composite EMC from twelve towns in the Canadian Great Lakes (Marsalek and Schroeter, 988) and. ug/l in Europe, for a mixed developed area in Goteburg, Sweden (Horkeby and Malmquist, 977). The highest value of 5.7 ug/l was recorded for a residential district in Aix-en-Provence, France (Deutsch and Hemain, 984). The Hg observations adhere well to a log-normal distribution (Figure -), although this is only apparent in the Global data set as the sample size is too small for the other regions. Appendix C presents the normality statistics, and measures of centrality are presented in Appendix D along with quartile values. Alternative percentile values can be calculated using the descriptive data in Appendix C, using equation from section. Figure -. Normality plots for Mercury (a) distribution plot (Global data) (b) Log-normality plot (Global data) Log Hg (ug/l) Results of t-tests for differences in Hg EMC values by land use are summarised below, including recommendations for the most resolved land use classification for Fe EMC application in the UK and Europe. Industrial & Commercial No significant differences occur between industrial and commercial land or between these uses and any other. There is no UK data and little European data, hence Ind./Comm. cannot be treated as a distinct group. Residential No significant differences occur between residential density groups, or between these uses and any other. There is no UK data and little European data and the residential use cannot be treated as a distinct group. 9

20 Highways There are no differences between motorways and A-roads, or between highways and any other land use, hence a separate category is not tenable. Selected land use categories All Urban. There is only observation of a Hg EMC for Open urban land use (non-european) and this is considered inadequate to define a separate category, given that the principal source of Hg is likely to be atmospheric deposition. As EMC values cannot clearly be identified for any distinct urban land use, the "All Urban" value is recommended. As the sample size for the European data is small, and dominated by two very high values from a Paris residential district (>5 ug/l), the Global data set value is recommended (see section 4).. Total Nickel Sources of Nickel in stormwater include corrosion of welded metal plating, wear of bearings and bushings and other moving engine parts, electroplating and alloy manufacture and food production. Although an essential element, Nickel is toxic to aquatic life at levels found in urban stormwater, and its toxicity increases when water is soft. Chronic toxicity ranges from 4.8 ug/l for D. magna, to 5 ug/l for fathead minnows in hard water. Nickel in stormwater is generally associated with suspended sediments and organic matter. Instantaneous stormwater concentrations range from. to 49 mg/l, whilst environmental and health guidelines range from.8 to mg/l (Makepeace et al., 995). A total of 8 Ni EMC records were obtained, of which 6 were from Northern Europe and only four from the UK. In the largest (Global) data set, only half of the given values could be allocated to a land use other than the most general built category of developed urban. The Global minimum is ug/l for a commercial areas in Fort Worth, Texas (Baird et al., 996), and a European minimum of.97 ug/l for Maurepas, a high density residential area in Paris (Deutsch and Hemain, 984). The highest value was recorded from an industrial estate on the Forth river in Scotland (Bayes et al., 994). Figure -. Normality plots for Nickel (a) distribution plot (Global data).. 5 (b) Log-normality plot (Global data) Log Ni (ug/l) 4

21 The Ni observations adhere very well to a log-normal distribution (Figure -), including for the small European data set. Appendix C presents the normality statistics, whilst measures of centrality are presented in Appendix D, along with quartile values. Alternative percentile values can be calculated using the log-transformed descriptive statistics given in Appendix C, using equation from section. Results of t-tests for differences in Ni EMC values by land use are summarised below, including recommendations for the most resolved land use classification for Ni EMC application in the UK and Europe. Industrial & Commercial No significant differences occur between industrial and commercial land use. The EMC for commercial land use is significantly higher than that for residential land in the European set (N=), but not in the Global set. The ind./comm. group cannot be treated as a distinct group. Residential The low residential density group (Global region) has a significantly higher EMC than the high residential group (P > 95%) but the sample size is small (N=). Residential use cannot be treated as a distinct group. Highways The highest observations for Ni are associated with highways, but the small sample size precludes identification of any statistically significant differences, hence highways cannot be treated as a distinct group. Selected land use categories Urban Open (Global) Developed Urban EMC values cannot clearly be identified for any distinct urban land use. The low mean value for the Open land use appears reasonable, considering the principal sources of nickel, but is based on only two observations hence caution is recommended. The sample size for the European Developed Urban group (N=), is considered sufficient to use the European value, particularly as it is broadly consistent with the Global region value. Recommended values are presented in section 4.. Total Zinc Sources of Zinc includes wear of tyres and brake pads, combustion of lubricating oil, corrosion of building materials and metal objects such as galvanised roof panels. Zinc is less toxic to aquatic life than copper or lead, but it bioaccumulates easily and is more toxic at high concentrations when in soft water. Chronic toxicity is affected by ph. Zinc is mostly associated with dissolved solids but will adsorb to suspended sediment and especially colloidal particles. Instantaneous concentrations in stormwater range from.7 to mg/l (Makepeace et al., 995). EC guidelines are. mg/l for salmonid river, mg/l for cyprinid rivers and -5 mg/l for potable water abstraction, depending on treatment works capability. A total of 44 Zn EMC records were obtained, of which 76 were from Northern Europe and 4 from the UK. The global values ranged from 5.9 ug/l for a commercial area in the US EPA NURP (Mustard et al., 987), to 58 ug/l for an industrial site in Melbourne, Australia (GH and D et al., 987). The European data ranged from 6.6 ug/l for a road in South Oxhey, Watford, UK (Hamilton et al., 987) to 55 ug/l for the A8 urban expressway in Birmingham, UK (Hedley and Lockley, 975). 4

22 The Zn observations adhere reasonably well to a log-normal distribution (Figure -), including for the small European data set. The Shapiro-Wilk statistics indicate that lognormality improves as the data is stratified. Appendix C presents the normality statistics, whilst measures of centrality are presented in Appendix D, along with quartile values. Alternative percentile values can be calculated using the log-transformed descriptive statistics given in Appendix C, using equation from section. Figure -. Normality plots for Zinc (a) distribution plot (Global data) (b) Log-normality plot (Global data) Log Zn (ug/l) (c) Log-normality plot (N. Europe) (d) Log-normality plot (UK) Log Zn (ug/l) Log Zn (ug/l) Results of t-tests for differences in Zn EMC values by land use are presented in Appendix E. A summary of land use differences is shown below, including recommendations for the most resolved land use classification for Zn EMC application in the UK and Europe. 4

23 Industrial & Commercial The European commercial EMC value is significantly higher than that for industrial land use (P > 99.9%, df), a pattern not repeated for the UK (no data) or Global regions. The group level EMC value is significantly less than that for residential and highways in all geographical regions. It is concluded that it is appropriate to treat this as distinct land use at the group level. Residential The high density residential land use group has a significantly higher EMC value in both the European and All regions (p > 95%), but not the UK (no data). There are significant differences in EMC value between residential and other land uses at the sub-group level, but not at the group level. It is concluded that it is appropriate to treat residential land use as a distinct group at the aggregate level, due to the observed sub-group differences, and because the very clear differences are observed for the non-residential developed urban values (i.e. the Comm./Ind. values). Highways Motorways have a significantly higher EMC than A-roads in the Global data set (p > 9%) and are consistently higher for the UK and European regions. Motorways have consistently and significantly higher EMC values across all land uses (except open where N is small) for all geographical regions. It is concluded that it is appropriate to treat motorways as a distinct group. Selected LU categories Open (Global), Residential, Industrial/Commercial Motorways, A-roads It is recommended that values from the European data set (N=76) are used in preference to the Global data set (N=44), for European applications. There is generally good agreement between these data sets, and to a lesser extent the smaller (N=4) UK data set. Recommended EMC values are given in section 4.. Total Phosphorous Total phosphorous is the sum of particulate phosphorous and dissolved or soluble phosphorous. Both of these fractions can be reactive, acid-hydrolysable or organically bound depending on chemical availability (Duncan, 999). The reactive phosphorous is readily available but powerful oxidising agents are required to release organic phosphorous. Sources of phosphorous include atmospheric deposition, leaf litter, fertilisers, industrial wastes (chemical, food and building materials) and detergents. Phosphorous is an essential nutrient, and where its supply is limiting it may restrict growth. If availability increases excessively plant and algae growth may proceed rapidly causing eutrophication and oxygen depletion. EC guide levels for phosphorous (P O 5 ) are.4 mg/l for fisheries and.4 to.7mg/l for water abstraction depending upon treatment capability. Makepeace et al., (995) report instantaneous concentration of. to 7. mg/l. A total of 4 P EMC records were obtained, of which 45 were from Northern Europe and just from the UK. The global values ranged from. mg/l for a developed urban area in Sydney (Sharpin 99) to 5.5 mg/l for an urban district in South Korea (Yu et al., 988). 4