Animal Waste, Water Quality and Human Health

Economic evaluation 449Three potential sources identified with the help of the GIS model (discharges fromfood processing industries, slaughterhouses and non-functioning sanitary facilities atrecreational bathing locations) could not be identified at any location. Illegaldischarges of animal waste were also suspected but difficult to prove and thereforenot mentioned by any of the water managers. They may nevertheless play animportant role explaining why sites are contaminated, but the extent to which illegaldischarges play a role is unknown.In order to get an indication of the relative weighted contribution of the differentsources to the overall recreational bathing water quality problem the identifiedsources of pollution were linked to the recreational bathing sites’ percentile valueswith which they exceed the new BWQ standard. A source which contributes tenpercent to a 95 th percentile value twenty times higher than the standard is, forinstance, considered relatively more important than a source which contributes 100per cent to a 95 th percentile value twice as a high as the standard. The weightedcontribution of the various sources is presented in Figure 12.1.25%20%15%10%5%0%Untreated sewerageCSO without measuresCSO with measuresWWTPManure from farmManure from landManure from cattle drinkingMarinasRecreational boatsCommercial shipsPets on siteBathersBird coloniesInternational riversNot identifiedFigure 12.1 Estimated relative contribution of pollution sources to the overall problem ofbacteriological bathing water contamination.Source: Brouwer & Bronda (2005).Important observations from Figure 12.1 are, first of all, the high percentage (22%)of non-identified sources of pollution. These include a mix of different pollutionsources at or near large flowing surface waters, the exact origin of which is difficultor impossible to determine. Secondly, the large contribution of diffuse sources isremarkable, that is, wastewater discharge from recreational boats (13%), bathers