2.1
Urban Nonpoint Source Pollutants
This chapter develops a provisional list of significant urban diffuse pollutants which the GIS screening model should seek to address where possible. The characteristics, effects and urban sources of diffuse pollutants are described, and the most significant pollutants identified from a consideration of their prevalence, potential environmental impact (as potency/toxicity), relevance to water quality standards, and known failures in local water quality standards (Aire and Calder study site). Following consultation with UK urban stormwater quality practitioners at local and national level, a provisional list of pollutants to address in the screening model is identified. This provisional list is then subject to final revision (Chapter 5) according to modelling practicalities, particularly data describing stormwater concentrations.
2.1.1
Characteristics and Effects of Pollutants in Urban Runoff
Urban nonpoint sources have been identified as a major cause of pollution of surface water bodies. Among nonpoint sources urban runoff has been cited as the second most frequent cause of pollution after agriculture, and in urban river corridors is the most significant source
(Anonymous, 1986). Novotny and Olem (1994) note that over half of all failures to achieve water quality goals in the USA are attributed to diffuse pollution, where urban diffuse pollution is the fourth most important cause of river pollution of rivers, and the third most important source of lake pollution (US EPA 1990, quoted in Novotny and Olem, 1994:p439).
Table 2-1 shows that urban diffuse pollution is the third most significant cause of poor water quality in Scotland, accounting for 20% of all class 3 and 4 river stretches.
Table 2-1. Causes of Low River Quality (classes 3 and 4) in Scotland (SEPA, 1996)
Abandoned mines
Sewage from treatment works
Urban drainage
Sewage overflows
Industry
Agricultural point sources
Agricultural diffuse sources
Other
22%
21%
20%
12%
12%
4%
1%
8%
Urban diffuse pollution comprises a complex mixture of materials that originate from many sources and have numerous adverse effects (Table 2-2). Each pollutant can arise from multiple sources, and each source (area or activity) can give rise to multiple pollutants. The form that the pollutant occurs in, solution, solid particulates or salts, affects the pollutant load to receiving waters, particularly through the pollutants interaction with sediment which acts as a transport medium for a many contaminants including hydrocarbons, heavy metals, salts and nutrients. Sediment size is important in these transport processes, with particles of <63µ carrying most of the load. Collins and Ridgeway (1980) found that in urban storm events these small particles comprised 6% of the sediment load but transported 50% of the total pollutant load.
12

Table 2-2. Urban Runoff Pollutants Characteristics and Effects in Receiving Waters
P
Nutrients and Salts
Phosphorous,
Nitrogen compounds
Chlorides metals
OLLUTANT
Sediment
Sand, silt, clay in colloidal suspension.
Metals & Trace
Lead, Cadmium,
Copper, Zinc, Iron,
Manganese, Nickel, and Chromium.
Titanium, Vanadium,
Tin, Cobalt, Arsenic,
Tungsten, Antimony.
Oxygen Demanding
Organics
BOD, COD, TOC
C HARACTERISTICS AND EFFECTS IN RECEIVING WATERS
•
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 <63µ, circa 6% of the total sediment load.
•
Sediments can 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, and scouring causes destruction of bed and bank habitat.
•
Occur as soluble compounds. Nutrients are usually derived from organic matter decomposition, agricultural fertilisers and acidic rainfall.
Uptake ratio of 7.5N to 1P.
•
Nutrient enrichment of water bodies (esp. lakes and ponds) can result in algal growth causing excessive oxygen demand (through plant decomposition), reduction of light penetration and release of toxins on the death of blue-green algae.
•
90% of P and 85-90% of N loadings are removed with sediment, indicating problem can be addressed if sedimentation reduced.
•
Salts from road de-icer is known to give high salt loadings in highway runoff and has been banned in several areas of the USA for this reason.
High loadings have been observed from UK highways but no elevated chloride levels have been detected in groundwater’s.
•
Can occur in many forms: attached to inert sediment, in immiscible fluids, as particles, soluble salts or insoluble compounds. Not bioavailable when adsorbed to sediments but can be readily resuspended during high flows.
•
Chemically can occur as organic or inorganic, compounds or complexes, and ionic speciation depends primarily on redox and pH conditions (hence more mobile where runoff pH is low – e.g. where runoff naturally acidic and less mobile when well buffered through contact with alkaline building materials such as concrete).
•
Metals in highway runoff occur mostly in particulate phase, whilst bioavailability and mobility is greatest in soluble phase. Cu and Zn are the most water soluble of the metals.
•
Metals have varying toxicity’s: Cadmium is very toxic and bioaccumulates, although its use is in decline; similarly use of lead is declining through phasing out of leaded petrol, while its low solubility means that the eco-toxicological impacts are less significant; Zinc and copper are detrimental to fish at sub mg/l level; iron is not a major pollutant itself although it can cause water discoloration. Iron oxides
(rust) have a large surface area and can act to scavenge other metals.
•
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, levels of dissolved oxygen (DO) in receiving water can fall to levels at which aquatic life cannot be maintained. Technical measurement problems mean that tests for oxygen demand (COD/BOD) poorly correlate with DO.
13

P OLLUTANT
Pathogens
Bacteria, viruses, protozoa and helminths.
Hydrocarbons
Oil and its derivatives including petrol, diesel, lubricating oils, hydraulic fluids, tars, greases and solvents.
Persistent organics
Herbicides, pesticides and a wide range of synthetic chemicals.
C HARACTERISTICS AND EFFECTS IN RECEIVING WATERS
•
Microbial contaminants are associated with the particulate fraction of decaying organic matter. Faecal or total coliforms most commonly used as indicator of human pathogens.
•
Include infectious agents and disease producing organisms normally associated with human and animal wastes. Wind blown soil can also contain significant microbial populations.
•
Usually liquid, insoluble and lighter than water (largest hydrocarbons, such as bitumen and heavy fuel oil can become heavier than water when degraded by bacteria). Defined as soluble in trichlorotriflouroethane or not a specific compound
•
Circa 70% of hydrocarbons are attached to sediment, PAH’s have a higher affinity, while the Petrol additive MTBE is highly soluble in water.
•
Hydrocarbons are toxic in both sediment and water and can also give rise to problems of appearance, odour and taste making polluted waters unsuitable for potable water abstraction.
•
Hydrocarbons are degraded by microbial and oxidation processes, reducing toxic impacts but entailing an oxygen demand during breakdown.
•
These include a wide range of substances not readily classified in the above groups. They include herbicides and pesticides which are toxic to aquatic organisms in very low concentrations, and which resist rapid degradation. They may also be selectively adsorbed onto inorganic materials, or bio-accumulate within certain tissues of organisms.
•
Treatment is expensive as it requires the use of granular activated carbon filtration. UK in water standards are based on detection limits not eco-toxicological effects.
Source: Luker and Montague (1994); Nix (1994).
2.1.2
Sources of Pollutants in Urban Runoff
There are numerous sources of diffuse urban pollution, and Figure 2-1 illustrates some of the most important ones, along with pollutant pathways to receiving waters. Atmospheric deposition is a major source with total average combined wet and dry deposition ranging from about 1-50 tonnes per km
2
, with about 90% of the deposition on impervious surfaces eventually finding its way to receiving waters (Debo and Reese, 1995). The pollutants originate from industrial and vehicle emissions, smoke, wind erosion, domestic heating, natural forest emissions, and geological processes (e.g. volcanoes), and these sources may be local or remote. Wet deposition in urban areas has a COD of 15-70 mg/l, Ammonia-N 0.3-0.7
mg/l and Pb c. 0.03 mg/l (Debo and Reese op.cit
; Novotny and Chesters, 1981).
Vehicles and roads contribute pollutants through abrasion of road surfaces, corrosion of metal alloys and other vehicle parts (e.g. brake linings), application of road de-icing materials, and again, atmospheric emissions. Vehicles contribute a significant proportion of loads of metals and hydrocarbons, and can mobilise existing deposited pollutants through turbulence.
Sediment originates from natural weathering, surface erosion, and construction. Urban areas contribute several hundred kilograms of sediment per km
2/ yr, although construction sites generate several orders of magnitude more than this. Pollutants are also generated by many other activities related to urban land use. These include a variety of household, commercial
14

and industrial activities, fertiliser and pesticide applications in parks, gardens and roadside verges, pet excreta, leaf litter, rubbish and various waste disposal mechanisms. Details of predominant sources for selected pollutants are presented in Table 2-3, with a summary of pollutant sources in Table 2-4.
Table 2-3. Principal urban sources of selected diffuse pollutants
POLLUTANT
Sediment
Nutrients
Pathogens
Oxygen demanding substances
Copper
Zinc
Lead
PRINCIPAL URBAN SOURCES
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
10 arising from vehicle emissions. Other sources include particulates deposited from vehicles (e.g. rust, rubber), abrasion of road and building surfaces, application of de-icing salts, organic detritus, litter and a range of other wastes.
The principal sources of nutrients are atmospheric deposition, which account for c.
40% of the total nutrient load (Ellis, 1986). Acidic wet deposition and exhaust emissions are major sources of N. Other sources include weathering of soil
(especially for P), application of fertilisers, animal excrement and leaf fall degradation products which have much faster times of travel to receiving waters on impermeable urban surfaces than they would otherwise have. Disposal of organo-compounds, such as detergents and other industrial products also contribute.
The principal source of pathogens in urban stormwater is animal excrement, mostly bird droppings and pet excrement. Soil and wind blown soil also contain large quantities of micro-organisms that can include pathogens. Human waste is conveyed by foul sewers and hence is not usually considered in urban stormwater, although poorly maintained septic tanks can act as a source of pathogens.
All organic materials exert an oxygen demand upon oxidation, whether chemically or biologically mediated. In addition, eutrophication can occur following N and P runoff and nutrient enrichment (unless N limiting: >5N:1P, or P limiting >10N:1P), and the breakdown of the subsequent algal material exerts additional oxygen demand. The latter process occurs only in receiving water, particularly where they are still or slow moving.
Principle sources of copper in the urban environment include corrosion of copper plumbing and vehicle parts and industrial wastes, particularly those from electroplating works. It is also widely used in algaecides. 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 notable that c. 20-40% of total copper in urban runoff occurs in the soluble phase (Luker and Montague, 1994).
Predominant sources of Zinc are automobile tyres, and industrial works, especially electroplating and galvanising operations. Where galvanised roofs and guttering are commonplace, they can contribute 70-90% of the total load, and due to a short time to runoff, are the main source of peak concentrations in hydrographs (Ellis,
1986). Other sources include atmospheric deposition, road salt (6ug/g), mining operations, and in paint and stains, although as an additive Zn is being progressively eliminated. C. 30-50% of Zn in urban runoff is in the soluble phase.
Vehicle exhaust emissions are the principle source of Pb in urban stormwater, derived from atmospheric deposition. However, since the introduction of unleaded petrol in 1973, atmospheric concentrations of Pb have declined by c. 90%, and continue to fall. Other sources include lead pipes, and as an additive in paints and stains, although all these sources are being eliminated. 1-10% of Pb in urban runoff exists in the soluble phase.
15

POLLUTANT PRINCIPAL URBAN SOURCES
Arsenic
Cadmium
Other metals and inorganics
Hydrocarbons/
PAH’s
Pesticides and biocides
Persistent organics
The principal natural sources of arsenic are fossil fuel combustion products, atmospheric deposition form mining operations and insecticides.
The principle sources of cadmium are industrial wastes, especially 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 also used extensively in the manufacture of batteries, paints, and plastics.
Mercury is a widely used amalgam in scientific instruments, batteries, arc lamps, in extraction of gold and silver, and the electrolytic production of chlorine. Its salts are used as fumigants and insecticides. Nickel and Cobalt are used in electroplating, and galvanising. Selenium is occasionally used in electrical components, photoelectric cells and rectifiers. Silver is used in electroplating but waste recovery rates are high due to its value. Antimony, beryllium, mercury, selenium, silver, and thallium all occur naturally in rocks and soil. Cyanide occurs in petroleum, as an anti-caking ingredient in road salts (5.7ug/g), in plating operations and refinery and coal wastewater’s.
Principal sources of oil based hydrocarbons are vehicles (exhaust emissions, petrol, fuel oils, lubricating oils, hydraulic fluids), abrasion of asphalt/bitumen roads (e.g. containing Naphthalene). Phenanthrene, and Pyrene arise from the incomplete combustion of fossil fuels, especially wood and coal burned in domestic heating. Hydrocarbons readily attach to sediments, especially in concentrations of 2-20ug/l (Forrow et al ., 1993). Boxall et al ., (1993) demonstrated the toxicity of Gammarus pulex to the sediment bound PAH’s
Pyrene and Flouranthene.
Pesticides and biocides, including those identified by the NURP (
α
-Endosulfan,
α
-Hexachlorocyclohexane,
γ
-Hexachlorocyclohexane), are most widely used in the urban environment to control soil nematodes and pests in residential gardens, municipal parks and roadside verges (e.g. herbicides). They also find widespread application within some industries in order to control pests that attack materials and products in storage. Widespread in Humber river sediments (Long et al .,
1998).
These originate from many industrial sources. Pentachlorophenol is used to protect wood (e.g. telephone poles) from microbial and fungal decay, and occurs in paint and stains, Trichloromethane (chloroform) is a product of chemical interaction of road salt, petroleum and asphalt and also of chlorination of organic rich waters while the ester Bis (2-ethylhexyl) phthalate is widely used to make plastic flexible
(a plasticizer) and leaches from plastic products (garden hoses, floor tiles, packaging) and subsequently accumulates in sediments. The LOIS programme found many such persistent organics (many unidentified) and 25 pesticides in the sediments of the 6 Humber rivers (inc. Aire, Calder, Don), where they were missed by EA monitoring but could exert an eco-toxicological effect following resuspension (Long, et al ., 1998).
16

Table 2-4. Dominant Urban Sources of Selected Diffuse Pollutants
Atmospheric deposition
Fossil fuel emissions
Vehicle emissions
Vehicle wear m
Road abrasion
Road maintenance, inc. de-icing
† m
M M m M
M m m
M M
M m
M m M m m
M
M
M
M
Soil erosion
Construction sites
Industrial wastes
M m M m
M m m
M
M m m M M m M M
Roofs & other surface abrasion
Gardens, parks and trees m m M M m m m m M m
Animal wastes
Other wastes and spills
M M M m m m m
M = Major Source, m = minor source
†
De-icing salts applied only applied regularly to major roads and 10% of other roads (Luker and
Montague, 1994)
17

18

2.2
Selection of Pollutants for GIS-Modelling
Having identified that there are a great variety of pollutants in urban surface runoff which could usefully be addressed by modelling, it is appropriate to ask which of these should be addressed by the screening level model. The following criteria were used in the selection of a provisional list of pollutants to address:
•
Distribution and occurrence of pollutants with impact on receiving waters;
•
Potency/toxicity;
•
Potential for impairment of beneficial use of receiving waters; and
•
Existing failures in water quality standards for the study site.
2.2.1
Pollutant Distribution
The aim of the research is to develop a model that is applicable to urban diffuse water pollution management throughout the UK. Therefore, although the model is being developed for a specific catchment in West Yorkshire (Aire and Calder basin), it is important that a generic model is developed. Such a model requires that catchment characteristics can be described satisfactorily for most areas (i.e. widely available independent variable data), and that the load functions address pollutants of geographically widespread concern.
The literature indicates that all of the pollutants described in Table 2-2 are of concern, and that oxygen demanding materials, sediment, nutrients, and pathogens are appropriate subjects of storm water management. However, whilst these pollutants are routinely detected in the runoff of all urban areas, other pollutants are more sporadic in occurrence. Much less is known about the occurrence in urban stormwater of trace metals, PCB’s, PAH’s and other persistent organic chemicals, for example, and no comprehensive surveys of these pollutants has been conducted for UK or European urban runoff. However, the Priority Pollutant program of the US EPA National Urban Runoff Program (NURP) monitored the occurrence of 129 pollutants in nineteen cities throughout the continental USA was determined. The priority pollutants were all listed under the 1977 Clean Water Act, and comprised 10 classes
(pollutants per class in brackets):
•
•
•
•
•
•
•
•
•
•
Pesticides (21)
Metals and inorganics (15)
PCB’s and related compounds (8)
Halogenated aliphatics (26)
Ethers (7)
Monocyclic aromatics, excluding phenols, cresols, phthalates (12)
Phenols and cresols (11)
Phthalate esters (6)
Polycyclic aromatic hydrocarbons (16)
Nitrosamines and other nitrogen containing compounds (7)
The monitoring programme showed a widespread variation in the occurrence of these priority pollutants throughout US cities. Some pollutants are detected in most samples whilst others appear rarely, or were not detected at all. Table 2-5 presents the most frequently detected priority pollutants in the US NURP samples. Of the 129 priority pollutants listed in the US
Clean Water Act, 48 were not detected in any NURP samples, and only 24 occurred in
≥
10% of collected samples (a 10% cut off was selected to address the problem of few observations and to minimise the importance of unusual runoff conditions) (Cole et al ., 1984). Of these, inorganic materials occur most frequently, particularly metals, with copper, lead and zinc occurring in at least 95% of all samples, with at least half of all samples containing chromium and cadmium. Arsenic also occurred in more than half of all samples analysed.
19

Table 2-5. Most Frequently Detected Priority Pollutants in the US NURP Samples
Percent of NURP samples containing priority pollutants
≥
75%
50-74%
20-49%
10-19%
Inorganics Organics
Copper (96%)
Lead (96%)
Zinc (95%)
Arsenic (58%)
Chromium (57%)
Cadmium (55%)
Nickel (48%)
Selenium (19%)
Beryllium (17%)
Cyanides (16%)
Mercury (16%)
Antimony (14%)
Silver (12%)
Thallium (10%)
None
None
α
-Hexachlorocyclohexane (20%)
Pentachlorophenol (15%)
α
-Endosulfan (13%)
Bis(2-ethylhexyl) phthalate (13%)
Trichloromethane (chloroform) (12%)
Phenanthrene (12%)
γ
-Hexachlorocyclohexane (Lindane) (11%)
Napthalene (11%)
Pyrene (11%)
Fluoranthene (10%)
Source: Cole et al., (1984)
2.2.2
Potency
The potency (strength and toxicity) of pollutants is an important consideration in the selection of pollutants to address in stormwater hazard modelling. Materials that occur infrequently may be highly toxic, and merit inclusion in the modelling process, while conversely, materials that occur frequently in urban runoff, but which are largely benign may deserve exclusion, unless, as with sediments, they act as a compounding effect with materials of interest. Table
2-6 presents typical concentrations of common pollutants in stormwater and other waste waters. The data shows that stormwater is characterised by a very high suspended solid load, that BOD may be higher than raw sewage, and that nutrient levels although below that for sewage, are significant. Thus these determinants merit inclusion in the model.
Table 2-6. Characteristics of Urban Wastewater Streams (after Ellis, 1986).
Wastewater type
Stormwater
CSO’s
Untreated Sewage
WWTW discharge
BOD
(mg/l)
SS (mg/l) Total N
(mg/l)
10-250 3-11,000
60-200 100-1,000
160
20
235
20
3-10
3-24
35
30
Total P
(mg/l)
10
10
Lead
(mg/l)
0.2-1.7
0.03-3.1
1-11 0.4
-
-
Total Coliforms
(MPN/100 ml)
10
3
-10
8
10
5
-10
7
10
7
-10
9
10
4
-10
6
Single numbers are means, others represent a range.
20

All of the priority pollutants that exceeded the 10% frequency of detection limit in the NURP samples are potentially deleterious to health, being either toxic, as with most of the inorganic constituents, or mutagenic in the case of the organic constituents. The toxicity varies considerably between metals, and standards for both potable and surface water quality reflect their potency. As a general rule, the metals become increasingly toxic in the following sequence: Zn < Cu < Pb < Ni < Cd < Hg, although the realised toxicological effect varies for each metal dependent upon a variety of factors (e.g. speciation, ionic strength and organic content, ambient water pH, complexation with other elements, nature of exposed organism).
There are no lower limits for human carcinogens, and potency is expressed as a risk level. Of the priority pollutants detected in >10% of NURP samples, only antimony and 2 PAH’s occurred at concentrations not considered deleterious to human or freshwater aquatic health, as determined by standard US EPA tests. Table 2-7 details the failures in human health and freshwater ecosystem water quality standards for the remaining priority pollutants. Of these, the metals lead, copper, zinc and cadmium, and the inorganic element arsenic fail one or more of the standards in at least 50% of cases. No other priority pollutant fails any standard in more than 20% of samples.
Table 2-7. Summary of NURP Failures of US EPA Water Quality Standards
% of NURP samples failing US
EPA water quality standards
≥
50 %
11-49 %
≤
*
10 %
At 10
-7
risk level
•
•
Primary drinking water standards
Lead
(62%)
Selenium
(17%)
•
Arsenic
(2%)
•
Cadmium
(2%)
Standards for the ingestion of contaminated water and organisms (carcinogenic
* and non-carcinogenic)
•
Arsenic (58%)
24 hr freshwater toxicity standard (FC)
•
•
•
•
•
•
α
-Hexachloro, (20%)
Beryllium (17%)
Phenanthrene (12%)
Pyrene (11%)
γ
-Hexachloro, (11%)
Trichloromethane (10%)
•
Lead (96%)
•
Copper (87%)
•
Zinc (78%)
•
Cadmium (55%)
•
Mercury (16%)
•
Cyanides (14%)
• α
-Endosulfan (13%)
•
Bis(2-ethylhexyl) phthalate
(13%)
•
Silver (12%)
•
Beryllium (10%)
• γ
-Hexachloro, (10%)
•
Nickel (9%)
•
Pentachlorophenol (9%)
•
Selenium (8%)
Derived from Cole et al ., (1984)
Ellis (1986) notes that the NURP study did not consider the chronic toxicity of any of the priority pollutants, which varies dependent upon local circumstances. In addition, the accumulative and synergistic toxic effects, particularly of those accumulating in benthal sediments, where they would be available for extended periods of time, had not been considered. Thus the conclusions of the NURP study, that few priority pollutants associated with urban runoff pose any risk at the detected levels was considered questionable. This suggests that priority pollutants in Table 2-7 that exceeded water quality criteria in at least
10% of samples, and any others known to be accumulative in sediments, should also be considered.
21

2.2.3
Relevance to Water Quality Standards, Directives and Conventions
EC directives which contain mandatory water quality standards include the Surface Water
Abstraction Directive (75/440/EEC), the Bathing Water Directive (76/160/EEC), the
Dangerous substances directive (76/464/EEC), the Freshwater Fisheries Directive
(78/659/EEC), the Shellfish Directive (79/923/EEC), the Groundwater Directive (80/68/EEC) and the Urban Waste Water Treatment Directive (91/464/EEC). These directives are likely to be superseded by the Water Framework Directive (WFD) in 2001, but this was not available at the time of writing. However, it was assumed that pollutants addressed by current directives would remain significant in the WFD.
The EU directives all stipulate standards for relevant parameters which the directives seek to control. For example, copper and zinc both fail the Dangerous Substances Directive for several sites in the Aire catchment. In addition to these EC directives, the UK is a signatory to
OSPARCOM, the convention for the Prevention of Marine Pollution from Land-Based activities, which addresses a range of hazardous and other ‘red-list’ substances, and which commits the UK to a reduction in loads discharged to the North Sea. About 350 chemical inputs to the sea are monitored (see NRA, 1995) and particular efforts have been directed at the Aire catchment in recent years through the NERC sponsored Land Ocean Interaction
Study (LOIS). Table 2-8 details the substances detected in more than 10% of samples in the
NURP study (i.e. in urban runoff) and which are also addressed in EC water quality directives and OSPARCOM.
Within the UK, the Environment Agency’s General Quality Assessment (GQA) is the principal means of classifying surface water quality. The scheme will ultimately comprise assessments in broad areas, including biological and aesthetic, but to date only the chemical grading is used. The GQA will be used to assess surface water quality with respect to six beneficial use classes: fisheries ecosystem; abstraction for potable supply; abstraction for industrial and agricultural use; water sports; commercial harvesting for shellfish; and special ecosystems (NRA, 1992). Use classes will vary in terms of parameters included and the numerical values of those parameters, reflecting the beneficial use to which the river reach is put. Standards for water sports for example are likely to include indicators of microbiological quality, which may not be relevant to the fisheries ecosystem class. Similarly, where parameters are included in several use classes, the numerical standards for that parameter may vary according to use (cf. abstraction for industrial or potable use). Thus a river reach may fail one beneficial use standard while passing another.
The standards within each beneficial uses classes will be formally set as statutory water quality objectives (SWQO’s), providing the basis for all of the Agency’s discharge consenting and water quality planning activities. To date only the chemical assessment criteria of the
GQA has been set, and no standards underpinning the beneficial use classes have been set, thus the GQA, beneficial use classes and associated standards, are currently of limited use in prioritising parameter selection for the stormwater model. However, SWQO’s have been recommended for eight pilot catchments in the UK, including the study site (river Aire catchment). These recommended SWQO’s have been set for the River Ecosystem use only, based on the chemical assessment of the GQA. The SWQO’s recommended for the river Aire comprise a use class to be achieved, and compliance dates (2001 or 2006) by which the
SWQO should be met (EA, 1996). The standards addressed by the SWQO's are for DO,
BOD, total ammonia, unionised ammonia, pH, copper and zinc. Failures have been observed in SWQO's for all of these parameters in the Aire catchment (NRA, 1996), and additional failures against the more stringent 2006 standards are likely unless emissions are reduced.
22

Table 2-8 Priority Pollutants Found in the NURP and Addressed in OSPARCOM or
EC Water Quality Directives (and their amendments)
†
.
Percent of NURP samples containing priority pollutants
Priority pollutants detected in urban runoff
(US EPA NURP)
≥
75%
50-74%
20-49%
10-19%
Copper
Lead
Zinc
Arsenic
Chromium
Cadmium
Nickel
α
-Hexachlorocyclohexane
Selenium
Beryllium
Cyanides
Mercury
Antimony
Silver
Thallium
Pentachlorophenol
α
-Endosulfan
Trichloromethane
Phenanthrene
γ
-Hexachlorocyclohexane
Napthalene
Pyrene
Fluoranthene
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
†
No priority pollutants addressed by the Urban Waste Water Treatment (91/271/EEC)
‡
Annex, Section 17: “heavy metals such as:” – five listed, (i.e. not exhaustive list).
See Table 2-9 for non-priority pollutants addressed by EEC directives.
3
3
3
3
3
3
3
3
3
3
3
3
3
3 3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
23

2.3
Provisional List of Pollutants to Address in the GIS-Model
There are many substances capable of degrading the quality of surface waters, and many are found in urban stormwater. In developing a screening model to assist in stormwater management, it is appropriate to consider, initially, all of the pollutants that could give rise to concern. However, in order to develop a practical management tool it is necessary to focus attention on those pollutants of principle concern. Therefore, a priority pollutant list has been developed by considering, for as wide a range of pollutants as possible, the distribution
(occurrence in stormwater), and potency (physical, biological and chemical effects) of a pollutant, and also whether it is addressed in water quality legislation. Table 2-9 lists, by class of stormwater pollutant, the pollutant “performance” with respect to these selection criteria.
This table is then used to develop a prioritised list of pollutants to address in the stormwater screening model (Table 2-10).
Table 2-9. Criteria for Selection of Stormwater Pollutants for GIS modelling
Selection criteria
Pollutants
Sediment Ubiquitous
Nutrients and salts
Ubiquitous
Low, but acts as a carrier for other pollutants. V.high
concentration relative to other riverine inputs.
N/A
N c. 8-30%, and P c. 2-17% of untreated sewage value. N occurs as organic-N, and oxidises to ammonia (NH
3
), nitrites (N0
2
) and finally nitrates
(N0
3
). Ammonia-
N is toxic and its oxidation can give high COD.
All forms of N &
P add to eutrophication and oxygen depletion.
Failures in
Ammoniacal-N
TSS
(68/659/EEC),
(75/440/EEC),
(79/923/EEC),
(91/271/EEC), &
OSPARCOM
Nitrates,
Ammonia,
Phosphates & chlorides
(75/440/EEC);
Nitrates, K-N
Ammonia and
Phosphates
(76/160/EEC);
Organophosphates
(76/464/EEC),
(80/68/EEC);
Total P & Nitrites
(78/659/EEC);
Total P & N
(91/271/EEC);
Nitrate, Total N &
P,
Orthophosphates
(OSPARCOM)
24

Selection criteria
Pollutants
Pathogens
O
2 demanding organics
Ubiquitous
Ubiquitous
Can exceed lower untreated sewage values (TC’s)
Can be very high relative to untreated sewage
N/A
Multiple failures in BOD
& DO
TC’s, FC’s, FS &
Salmonella
(75/440/EEC); as above plus Entero viruses
(76/160/EEC);
FC’s and Saxitoxin
(79/923/EEC).
TOC, BOD, COD,
DO,
(75/440/EEC); DO
(76/160/EEC);
DO, BOD
(78/659/EEC); DO
(79/923/EEC);
BOD & COD
(91/271/EEC); DO
(OSPARCOM)
Metals and other inorganics
Cu, Zn, Pb in > 95% samples, As, Cd, Cr and Ni in c. 50% of samples. Seven other metals in at least of
10% NURP samples.
At least 50% of
NURP samples fail water quality standards for Pb,
Cu, Zn, As, and
Cd.
Petroleum & mineral oil hydrocarbons /
PAH’s
Persistent organics
PAH’s occur in 10-
19% of NURP samples.
3 pesticides (inc.
Lindane), cyanide, an ester, a phenol, and a halogenated aliphatic in at least 10% of
NURP samples
Varies subject to structure, can be very toxic. 10 &
12% of NURP samples with
PAH’s fail standards.
3 pesticides (inc.
Lindane), cyanide, an ester, a phenol, and a halogenated aliphatic fail US water quality standards in 9-
20% of NURP samples.
‡
See Table 2-7 for details of priority pollutants
Failure in Zn standard, & also
Cu with respect
(76/464/EEC)
N/A
N/A
Most directives and OSPARCOM
– see Table 2-8.
All directives and
OSPARCOM – see
Table 2-8.
Most directives and OSPARCOM
– see Table 2-8.
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Table 2-10. Prioritisation of Pollutants to Address in GIS-Model of Urban Runoff
POLLUTANTS TO ADDRESS (DESCENDING ORDER OF PRIORITY)
Copper and Zinc as Total Cu & Zn
Lead
Cadmium and Arsenic
Oxygen demanding substances as COD
Nutrients as Total-N, or TKN as Total soluble and
Particulate P
Sediment as TSS
•
83% of NURP samples failed US EPA standards for Cu
†
, and 74% for
Zn. Subject of 6 EC directives and recommended SWQO’s, of which it fails in several reaches of the study site.
•
92% of NURP samples failed US EPA standards for Pb, but emissions in decline due to unleaded petrol. Subject of 6 EC water quality directives. (NB. Fe indicative of all metals load)
•
34% of NURP samples failed US EPA standards for As, and 30% for
Cd. Subject of 6 EC directives.
•
O
2
demanding substances are a ubiquitous problem, addressed in 5 of the 7 EC directives listed in Table 2-8. and also in SWQO’s for the study site (not met in many reaches). Stormwater has demand similar to secondarily treated sewage, but no NURP site attributed low DO to urban runoff (but see note in Table 2-8).
•
Preferred measure of oxygen demand is COD (possibly TOC) as toxic materials in the sample can interfere with BOD.
•
N and P are always present in stormwater runoff and can be toxic (as ammonia), cause eutrophication and subsequent oxygen depletion in receiving waters. Widely addressed in EC directives (6 from 7), in
RQO’s and SWQO’s, of which it fails in several parts of the study site.
Little evidence of UK chloride problem.
•
All forms of N are important hence Total-N is the preferred measure, although organic-N (a measure of ammonia and its derivatives- few problems before these products formed) measured by Kjheldal-N relevant.
•
P is limiting for eutrophication, and as it occurs in many compounds of phosphate, is routinely measured as Total-P.
•
Ubiquitous and although exerts limited effects when inert, is efficient scavenger of priority pollutants. Removal of sediment from runoff removes majority of N, P and priority pollutants. Subject to 4 EC directives.
•
Ubiquitous, not accumulative pollutant, but health effects can be serious and more prolonged. Subject of 3 EC directives.
Pathogens
TC’s by MPN
Pesticides and biocides
Other metals and inorganics
Hydrocarbons/PAH’s
Persistent organics
•
NURP samples failing US EPA standards:
α
-Hexachlor,- 4%;
α
-
Endosulfan ,
γ
-Hexachloro,- (Lindane), 1%. 5 EC directives.
•
NURP samples failing US EPA standards: Ni 4%; Se, Hg and Be 3%;
Cyanides 2%; Ag 1%. There are no failures for Thallium, Chromium or
Antimony. 3-6 EC Directives.
•
NURP samples failing US EPA standards: Phenanthrene, Pyrene 1%.
No failures for Napthalene or Fluoranthene. Subject of all 7 EC directives listed.
•
NURP samples failing US EPA standards: phthalates esters 2%; pentachlorophenol 1%; Trichloromethane 1%. Subject of up to 6 EC directives.
†
Calculated from Cole et al ., 1984, but note no consideration of accumulative/chronic effects.
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2.4
Consultation Over Provisional Pollutant List
The pollutant selection process has drawn significantly on the results of the US NURP study.
Whilst this is the best urban runoff quality database available, several caveats are noted with respect to using the NURP results to prioritise pollutant selection. Firstly, in the NURP toxicity assessments no chronic or synergistic effects, or effects of pollutants accumulated in sediment were considered. This implies that pollutants low in the order of Table 2-10
(hydrocarbons, PAH’s, pesticides and other persistent organics) may merit greater consideration. Secondly, the NURP was a study of US urban stormwater, and results may not translate directly to Europe due to different polluting activity rates and pollution control mechanisms. Finally, priority pollutants not specified under US legislation, and hence not in the NURP, may be omitted, although this is not considered significant.
For these reasons, comments on the appropriateness of the provisional pollutant list were requested from the Environment Agency (local and national offices), Scottish Environmental
Protection Agency, the Water Research Centre, Yorkshire Water Services Ltd., and urban drainage practitioners in local authorities with the study site. The consultation exercise indicated that the provisional list was broadly acceptable, but that the following revisions were required:
•
•
•
Ammoniacal-N should be explicitly included as it can be significant in surface wash off
(i.e. is not limited to foul sewers);
Arsenic is not perceived as a problem in the UK and could be excluded;
Microbiological problems are associated with storm events and modelling process would need to address short temporal scale, not just annual loads (e.g. see Harremoes, 1988).
Local development plans were also consulted to assess whether there were any future urban developments in the study area likely to make add a pollutant or make others more significant
(e.g. by reference to knowledge expressed in Table 2-4). However, the provisional list is already extensive and planned urban developments in the study area were not thought to merit any revisions to the selection.
2.5
Selected Pollutants and the Water Framework Directive
The draft text of the EU Water Framework Directive (WFD) became available towards the end of the project. The WFD takes a combined approach to pollution control, seeking to limit pollution at source through emission limit values, and setting water quality objectives for water bodies. Annex II states that member states must estimate and identify significant point and diffuse pollution from urban, industrial, agricultural and other sources, while Annexes
VIII-X is intended to detail the pollutants of concern. The annexes were blank in the draft directive as the details were still under discussion.
Nevertheless, the draft WFD could still be used to assess the suitability of the project pollutant list. Firstly, the advice in WFD on key pollutants was that the commission would identify hazardous substances taking into account earlier directives and international agreements (Articles 16(2a)). This indicated that there were no major revisions forthcoming in the WFD and that the use of past water quality directives in the selection process was valid.
Secondly, the WFD states that water quality management must select pollutants to address on the basis of a risk assessment (Article 16). The risk assessment criteria, and the criteria used in the pollutant selection for this project are detailed in Table 2-11.
27

Table 2-11. Comparison of Selection Criteria for Hazardous Pollutants
Water Framework Directive Criteria for
Identifying Substances Hazardous to the
Aquatic Environment
Criteria for Selecting Pollutants
Appropriate to Urban Non Point Source
Assessment (This project)
Intrinsic hazard, in particular to aquatic and human toxicity.
Evidence of widespread contamination.
Urban stormwater samples which commonly fail aquatic (24-hr freshwater toxicity standard) and human health (drinking water, carcinogenicity) toxicity standards. (US
NURP stormwater data and EPA standards)
Literature assessment of prevalence of pollutants in urban stormwater. Physical parameters known to be widespread, priority pollutant distribution assessed using the
NURP priority pollutant study.
Other proven factors which indicate possibility of widespread contamination (e.g.
production and use patterns).
Failures of existing surface water quality standards (e.g. SWQO's) in the study area.
The pollutant selection process described above is entirely consistent with the simplified risk assessment procedure recommended in the WFD, hence the provisional list of pollutants selected here (Table 2-10, and considering reviewers comments in 2.4) is considered appropriate. The final list of pollutants addressed by the nonpoint source screening model will be determined by the modelling methodology selected, as described in the next chapter.
28