Pollution sources and importance

It may be a surprise to many, but in any large industrial estates usually only a handful of the industries have recognised, authorised process effluent discharges.

Most industrial units on an estate will be dry processes such as packaging, storage and distribution, machining and other engineering works, construction, logistics, metal finishing, assembly, and more. The absence of direct effluent discharges however, and a good safety record for pollution accidents, is not enough to prevent pollution from industry. Many industrial estates are very large, with numerous companies of all kinds spread over extensive areas. All have surface water drainage, and stormwater runoff is often contaminated by many diffuse sources. Pollution of the water environment from such extensive industrial and commercial zones is diffuse in nature, which is not to say that there are not hotspots where pollutants occur in greater quantities, and some activities present far more risk than others.

Some are ad hoc trade effluents, such as mobile steam cleaning units, which are very difficult to regulate. There is a complete spectrum of pollution incidents and accidents from the individually trivial but often regular (e.g., drips of oil, or chemicals gradually accumulating on roofs, the ground and in drains) to inadequate disposal of potentially polluting wastes, and large-scale irregular spills. That direct industrial/commercial activity overlies background contamination arising from combustion of fuel, power generation, heating/air conditioning, use of commercial vehicles and machinery, and includes roof runoff contaminated by extractor fans in machine workshops discharging very fine particulate pollutants onto roof areas.

Diffuse pollution hotspots occur when polluting activities result in significant contamination at particular premises or areas of ground or roofs, and pollutants are liable to be mobilised by rainfall and washed into drainage networks or otherwise into the aquatic environment. Industrial districts are often a worst case land-use for diffuse source pollution. Table 3.1 compares unit pollution loads for different land-uses and indicates that industrial and commercial areas can be important for several of the relatively small spectrum of contaminants measured in the studies cited.

In terms of characterising industrial estate pollution, it can be difficult to separate the effects of trade effluent discharges on an estate from diffuse pollution (rainfall mobilised wash off or seepage associated with chronic contamination or major accidents). Using water quality data (chemical and biological) interpreted by staff with expert local knowledge, the Scottish Environment Protection Agency

Industrial estates as sources of water pollution 39 (SEPA), assessed the impacts of industrial estates as causes of water pollution in 1999 and compared them as diffuse pollution sources with other urban and with trade effluent discharge impacts (Table 3.2). The pattern was similar to that which might be expected from the literature data in Tables 3.1(a) and (b).

Table 3.1(a) Single study of unit pollutant loads from homogeneous urban watersheds in Milwaukee, USA.

High density residential areas 133.42 0.31 0.25

Medium density residential areas 59.18 0.16 0.07

Low density residential areas 3.01 0.01 0.00

Parks 0.82 0.01 0.00

Source: Bannerman et al. (1983).

Table 3.1(b) Comparison of unit pollutant loads (literature 1983–2012).

References Land Kim et al. (2012) Industrial 143.86 52.45 6.65 1.75 0.10

MOE (1999) Urban 13.69 2.10

Bannerman et al. (1983) Industrial 262.19 0.41 0.74

Lee et al. (2008) Highway 399.50 356.30 12.29 2.46

Go et al. (2009) Road 580.13 331.17 14.68 1.43

NFWMD (1994) Industrial 213.73 3.05 1.46

Novotny et al. (1997) Industrial 262.25 0.41 0.74

Current water quality data for industrial estate surface water drainage discharges to watercourses is limited (the problem was well known and thought by many to be intractable), but spot samples were routinely collected in Scotland in the 1990s, as well as the biological data used in conjunction with that, to derive the impacts in Table 3.2. Table 3.3 is a summary of some of the industrial estate water quality evidence. It is almost certainly as relevant now as it was then, in many countries, wherever comparable industrial activities occur on industrial areas with hard standing and runoff. As well as showing the variable quality of industrial estate surface water drainage, Table 3.3 gives an idea of the number of industrial estates in the study river catchment (the River Forth in East Scotland); a widespread pollution source, wherever there are settlements.

Table 3.3 Quality of surface water drainage from industrial estates in the catchment of the River Forth, Scotland (mean and max data from spot samples, 22 locations, 1990–1993¹).

EQS, Environmental Quality Standard for a Scottish River²

25 mg/l

Eastfield 14 (54) 21 (230) 1.1 (10.6)

Bankhead 58 (169) 6 (15) 0.9 (2.5)

Nether Stenton 39 (279) 21 (180) 0.6 (2.4)

Southfield 11 (49) 4 (11) 0.2 (0.4)

Lower Bighty 13 (70) 6 (29) 0.2 (0.7)

Lyne Burn d/s Elgin St. 60 (650) 4 (23) 1.0 (9.4)

Lochlands Industrial estate 183 (1730) 29 (190) 0.7 (3.5)

Cowie Industrial estate 22 (199) 12 (152) 1.9 (7.5)

Cumbernauld No. 8A 80 (216) 28 (126) 0.2 (0.4)

Cumbernauld No. 8 56 (84) 14 (38) 3.4 (7.3)

Cumbernauld No. 1 27 (129) 31 (154) 0.2 (0.6)

Red Burn d/s Cumbernauld SWOS 15 (158) 3 (16) 0.1 (1.2)

Old Liston industrial estate 12 (29) 7 (20) 0.4 (1.6)

Gyle industrial estate 58 (183) 5 (14) 0.6 (0.8)

East Mains industrial estate 225 (3920) 9 (80) 0.5 (1.7)

Houston industrial estate 36 (252) 12 (47) 5.5 (32)

Houston industrial estate north 34 (125) 3 (9) 0.3 (1.8)

Deans industrial estate 23 (134) 6 (14) 0.1 (0.2)

Brucefield industrial estate 29 (122) 4 (15) 0.7 (2.7)

Kirkton Campus 27 (78) 17 (63) 1.9 (7.7)

South Deans industrial estate 7 (29) 7 (45) 2.1 (15.7)

1Table adapted from D’Arcy and Bayes (1995).

2EQS values from Appendices in D’Arcy et al. (2000).

Table 3.2 Importance of industrial estates as causes of pollution in Scotland.

Pollution Sources Rivers km

Downgraded

Comments

Urban (all categories, including industrial estates)

500 km Often impacts most evident in small watercourses

Industrial estates, including airports 168 + 47 km Included several of the poorest quality watercourses in Scotland

Trade effluents (for comparison) Including textiles, food & drink, paper, electronics and petrochemicals

66 km Waste minimisation including resource recovery, together with effective effluent treatment technology reduced detrimental impacts

Source: SEPA (1999).

Industrial estates as sources of water pollution 41 Table 3.3 also indicates the severity of contamination likely to occur, but cannot indicate whether this is as a result of an incident, or a storm event. The mean data from a set of spot samples is probably biased to dry weather sampling, but it does suggest evidence that an industrial estate is a pollution risk, especially on small watercourses with little catchment contribution from cleaner land-uses.