10-21-2004 Council Work SessionA

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^ f ^ ' I 'r 4.0 Conclusions and Recommendations 4.1 Conclusions The results of the diagnostic study and this feasibility analysis support the following conclusions: • Based on the average total phosphorus concentration, Stubbs Bay water quality would only support restricted use, while the average chlorophyll-a concentration indicates that Stubbs Bay should be subject to nuisance algal blooms SO percent or more of the time. Based on the projected 2020 land uses, conversion of undeveloped and agricultural property will increase the residential land use percentage to approximately 80 percent of the upland area. Roadways will represent another ^ percent of the projected land use. Comparing the two land use coverages reveals that approximately 983 acres (56% of the watershed area) will be developed or redeveloped by 2020. Of this area, approximately 314 acres have soils that should be appropriate for infiltration practices. The updated average annual phosphorus load to Stubbs Bay for full development land use is estimated to be: .Stubbs Bay Hio.sphonis Load-Full Development Land U.se Average Load |kg]Peueutage Internal 567 48*W Atmospheric 61 5*0 External 565 47*--* Total 1193 100% The updated water quality modeling indicates that the predicted average annual total phosphorus concentration in Stubbs Bay will increase from 57 • g/L, under existing conditions, to 62 • g/L with fully developed land use conditions. Tlie primary drawback to killing algae with copper sulfate is that it is a short-term fix and not •/ long-term, sustainable solution. Also, the dead algae can release toxins to the w ater, toxic levels of copper can be deposited in the sediments and the composition of algae species can shift towards those that are more copper-resistant, but equally undesirable. rU3V:7\FI0\Duft Stubbs Bsy FcMibilily Study doc "i > ■ t n