10200 19TH AVE SE COSTCO FUEL STATION 2016-01-01 MF Import

concentrations were not included in tlie report and therefore the report does no: substantiate its claims of sediment cuntamination. The aigae blooms that have been sEen in the area immediately downstream of thc sampling portal provide evidence that the high concentrations of phosphorus in tne portal samples were representative of the r�ncentrations t�iat were present. The water in the sampling portal may have reflected the qualiry of runoff/interflow in the immediate area. The northeast parking lot received significant quar,tities of fill a�d there is a significant amount of fill slope area that is expos2d to rair,fall. The scils that were brought in to fill the area for the northeast parking lot could tnemselves be a source of phosphorus — a scurce that was not included in the EIS analysis. (Note: The biofiltration swale and sand filter were reconstructed in 1999. Old c�ntainment soil and vegeta''on �vere removed at that time and replanted.) Stormwater facil�ties issues: To meet the original goals of the project, the amount of phosphorus leaving the site must be reduced. Reduction in phosphorus loading can be achieved by reducing the concentration of phosphorus entering the stormwater facilities ��d/or by increasing the phosphorus removal efficiencies af the stormwater facilities. There appears to be a source of phosphorus unanticipated by the EIS process. This source must be account�d for in the new loading analyses. The source should be found and mitigative actions shauld be taken to decrease the amount of phosphorus entering/leaving the stormwater facilities. Algae blooms are indicative of the presence of nuisance levels of phosphorus. �fhese levels must be reduced. As proposed, the parking lot modifications and gas station wiil increase the loading of phosphorus into the stormwater facilities. At the same time, the proposed modifications to the stormwater facilities will reduce their phosphorus removal efficiencies. The currently proposed plan is to construct new stormwater facilities that meet current City of Everett slormwater standards. This stormwater treatment strategy is not adequate. The original stormwater facilities were designed and constructed to exceed the stormwater standards of 1995, due to the sensitiv�;• of this drainage basin and concern= regarding the effects of the project. As noted above, these more stringent standards are required by specific provisions contained in the City's critical areas ordinance EMC 19.37.110.B.S.c. An EIS was required to address these concerns. The stormwater facilities on the site consist of two-celled wetponds and biofiltration swales. As in the wetlands, the primary characteristic that relates to phosphorus removal efficiencies in swales and wetponds is hydraulic residence time in vegeiated areas. The proposed modifications to the storm water facilities will reduce the amount 4