River Boyne Water Quality Management Plan - EPA

River Boyne Water Quality Managemm1 PlanThe impact of waste discharge on river water quality is a function of the waste volume andcharacteristics and the flow in the river (dilution). A further factor is the recovery rate of the riverassociated with the nature of the flow, extent of re-aeration, etc.The minimum standards for compliance with current regulations appropriate to rivers supportingabstraction for potable water use, bathing and water contact recreational activity and designated as asalmonid fishery are identified in this section. These standards have obvious implications for theamount of organic waste which can be accommodated in a river at any section, sometimes referred toas the assimilative capacity. Notwithstanding the over-riding requirement to minimise wastedischarges, the approach does permit an objective evaluation of whether a particular effluent can beaccommodated or whether a higher standard of treatment is essential. In this regard, the followingapproach-can be adopted:-Bioclremicnl Oqgen Demand (BOD 5) ; given the require~i~en~ for a rnaxinlurn level of 5mgnas 02 at 95% low jlow, there niwt be reasonable assurance that this lin~it will not bebreached. The EEC Directive 017 salnionid waters (78/659/EEC) sets a guideline value of the3mg/l as 02, Therefore, this value niight be regarded as an objective value in a salnioitidriver where possiblee Plrospknfes nrg/l P ; the Sal~no~tidli~nits for phosphates. In thecase of lakes, it p~oviaks a relationship for deterqfi,za$>li of like!y crifical loading expressedns nrg P per m2 of lake surface per year depe$& oil the ri:ea11 deprh of lhe lake rn7d thetheoreliczl retention time, expressed in other ca.ves, it states that the litnit valzre of0.2mg/l expressed as PO4 lnry be regar@&'indicative in order to reduce ezrtrophication.Q .Xii jigroc of doirble this value is su@f,&for cypri~iid waters. For sal~~ionid waters, fheequivalent vnlue e.rpressed as ntg/lG+@:p% approxittiate!~ 0.07 tng/l4.7 Existing Municipal Discliarge&Qc@-\a-E'Directive does not \&';.~For inspection purposes only.Consent of copyright owner required for any other use.Table 4.9 is a schedule of existing municipal wastewater treatment plants in the catchment,indicating the existing treatment process type, capacity, existing loading and typical effluent loadcharacteristics in terms of BOD5 (kgld) and orthophosphate as mgll P.Effluent quality dara is listed in Appendix 5 and it also includes key operating parameters of someplai~ts, including MLSS (aeration tank suspended solids) and SVI (sludge volume index). It isapparent that upgrading of existing plants is required in the major towns of Navan and Trim togetherwith smaller plants at Rhode, Moynalty and at Collon, where the results of effluent sampling appearto be unsatisfactory. In general, a minimum standard of 20mgll of BODj and 30mgllofS.S. is takenas standard for municipal discharges to inland waters.The effluent data for municipal wastewater treatment plants in Appendix 5 shows the following:-* Atlzboy S.T. K; this plant discharging to the Athboy River, is within capacity and occasional poorefluent results appear to be associated i18ith excessive sliidge acc~rmulation indicated by highiCfUS and elevated SVI valuesEPA Export 26-07-2013:17:27:00