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City of Orono Page 2 <br /> - SWMP ReNsions Date <br /> is the specific subwatershed that is showing a shortfall and contains the bays of Maxwel% North <br /> Arm, North Lower,Jennings Bay,South Lower, Spring Park, Stubbs, and West Arm. <br /> The subwatersheds for which the P/an indicates excess phosphorus remova/are Painters Creek <br /> and Long Lake Creek. All these subwatersheds ultimately flow into Lake Minnetonka; therefore, <br /> the City proposes that this excess from the Painters Creek and Long Lake Creek subwatersheds <br /> count towards meeting the overall required reduction. <br /> This should be viewed as a trading of phosphorus removal reduction requirements between <br /> subwatersheds that all ultimately flow into the same basin, Lake Minnetonka. This will allow the <br /> City of Orono to meet its pollutant reduction requirements in the most cost-e�cient manner as <br /> fundrng becomes available. Table 9.2 demonstrates the City already faces a budget shortfall and <br /> will have to rely on other funding sources to meet the phosphorus reduction requirements; <br /> therefore, being able to rely on this trading strategy is a key e%ment in meeting the reduction <br /> goa/s. <br /> Comment 2a: The following discussion has been added to Section 9.4: Another method being <br /> used to reduce the phosphorus loading is implementation of ravine stabilizarion projects. These <br /> ravines have likely been showing mino�signs of erosion for hundreds of years; however, <br /> deve%pment of the areas without appropriate stormwater controls has led to an increase in <br /> erosion and ultimately the need for ravine restoration/stabilization projects. We are basing our <br /> phosphorous reduction estimate on when erosion began to increase or worsen and is the <br /> justificairon for the timeframes se%ted. The values provided should a/so be viewed as a <br /> planning leve/estimate and a detailed analysis will be provided once the projects are completed. <br /> The results will be provided in the annual report to the MCWD. <br /> In addition to this discussion revisions were made to the discussions regarding CIP-Ci, QP-1, <br /> and CIP-7. The underlined and struck out text represents those revisions. <br /> QP-C1: The "Offerman Ditch"Ravine Stabilization project(CIP-Ci)entailed the repair of <br /> approximately 700'of an eroding swale. The volume voided is based on the cross section <br /> �rovided in Apt�ndix F. This swale is assumed to have been eroding since deve%pment occurred <br /> in the 1970`s, which altered the drainage patterns and did not provide any on-site storage. The <br /> calculated phosphorus reduction for this activity is presented in Appendix F and totals 26.3/b/yr. <br /> CIP-1: The Stubbs Bay ravine stabilization(QP-1)calculation is presented in Appendix F. There <br /> are actually two calculations:one for restoradon of a catastrophic failure immediately east of <br /> Tonkawa Road and another for vegetation management(se%t tree cutting and planbng of <br /> grasses and forbs)to the west of Tonkawa Road. The primary failure is 200 feet long, 10 feet in <br /> depth, and I S feet in width. We estimate that the failure has been in rhe orocess since this area <br /> da�P/ �in(-ha latp 1g80's and have used 20 years for our phosvhorus reduction estimate �We <br /> The estimated phosphorus load reduction that can be achieved as a result of <br /> this project is 30.2/b/yr. <br /> QP-7: The Long Lake ravine stabilization(CIP-7)calculation is presented in Appendix F. Here <br /> ravine erosion occurs a/ong the entire 250-foot length with an approximately 8-foot wide by 3- <br /> foot deep failure zone. This area was deve%aed without any stormwater manaaement controls in <br /> p/ace and it is estimated that the erosion has been occurrina for approximate/y 30 vears. �We <br />