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the storm water system. An outlet was installed around 1979 that enabled the basin to pass runoff from extreme events. Approximately 112 acres contribute runoff to Arona Pond. Over the years, the sandy bottom of this pond became sealed with sediment, eliminating the infiltration capacity of the basin. This resulted in localized flooding of the surrounding properties. As a part of the Applewood Pointe redevelopment project in 2003, the City reconstructed this pond. The reconstruction project nearly doubled the capacity of the basin. Years of sediment accumulation was excavated, restoring the infiltration capacity that had been sealed. In addition, a lift station was constructed to provide a secondary outlet for extreme events. The new pond serves as a regional storm water treatment facility for the subwatershed. 5.1.4 South Owasso Boulevard As a part of the 2006 South Owasso Boulevard Reconstruction project, the City constructed the improvements for the storm water runoff being discharged into Ladyslipper Park. Between Rice Street and Western Avenue, approximately 160 acres of single family residential property drain into Lake Owasso through a drainage ditch that cuts through Ladyslipper Park in a north south direction. This ditch was constructed in 1971 as a canoe access to Lake Owasso. In the 1991 Lake Owasso Survey report, it was determined that the removal efficiency of this system is very limited. Only 30 to 50% of suspended solids and 9% of the total phosphorus were removed before being discharged into Lake Owasso. In 2005, the City constructed a two cell pond system north of the road as well as three wetland/ biofiltration basins south of the road. These basins increased the TSS removal to 81% and Phosphorus removal to 52 %. This is a significant improvement to this subwatershed area. 5.2 Ongoing Issues While the previous section provided just a few of the many project examples and accomplishments the City has made in the 20 plus years since completing its first surface water management plan, there is also more work ahead. Many of the flooding issues of that past have been addressed, but some remain. New water quality issues and concerns are emerging each year, requiring varying levels of effort by the city to address. And, the ongoing maintenance and operation of the storm water system has grown much more complex over the years due to new regulations and a better understanding of what is necessary to keep the treatment ponds and filtration systems functioning properly. This section of the plan provides an overview of some of the more significant of these ongoing issues that will require substantial efforts and resource commitments. Location specific issues such as localized flooding issues and ongoing impairments are identified in Figure 19. 5.2.1 Localized Flooding Issues While many of the known flooding areas have been addressed by infrastructure improvements over the past 20 years, some remain and are identified in the implementation section of the plan. Unfortunately, the very nature of storm water management means that at some point new issues will likely present themselves due to the plugging of a storm system from debris, for example, or simply a larger or more intense rainfall event than the City has previously experienced. The flooding in Duluth, Minnesota in June 2012 is a notable example of how a storm larger than anticipated can create problems where none existed in the past and will require extensive repair and restoration work for months to years. Comprehensive Surface Water Management Plan ROSEV120222 City of Roseville Page 28