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Plan of Study for City of North Olmsted Phase I by Floyd Browne Group January 4, 2006 FINDINGS & CONCLUSIONS Storm water contributions into the sanitary sewers from yard and roof areas are significant from home sites although connections may be indirect. Although a palpable pattern of sanitary/downspout tie-ins are not typically found, roof water and yard runoff during storm events find channels into the foundation drains. Sump pumps are often part of the network but final connection points are often obscure for sight. 2. The storm drain system is potentially undersized and bottlenecked in certain locations according to hydraulic calculations. Theoretically, this would suggest that accumulating surface water during sizeable precipitation events would place hydrostatic pressure on the sanitary sewers via groundwater saturation. However, City maintenance workers report that often the storm drain network is not surcharged or even flowing full even in severe weather. In fact, during the benchmark August 20th storm episode, the critically located 4' x 12' culvert bisecting under Clague Road had about a foot of freeboard at the upper end or perhaps'/4 of its capacity remained. At the same time, basement and sanitary sewer bypassing were underway. Similar reports were noted around town on a smaller scale. This indicates that water is not reaching the storm drain network, including runoff from home sites. A strong case cannot be made that reinforcements to the storm drain system would improve the performance of the sanitary system and either basement flooding or bypassing. 3. The mini-storm conveyance connections around each home site vary in design and capacity and no attempt was made to characterize these systems in-terms of adequacy. Accumulatively, they are the dominate storm drain attribute in the impact areas. Typically, land use in residential neighborhoods is composed of about 80% roof areas, lawn, driveway & sidewalks (house attributes) compared to about 20% street, curb & gutter and utility easement areas. Thus, storm water run-off flow is primarily from residential settings and storm capacity issues are due to the 80% portion of the land use. Since it is somewhat questionable that peak residential storm flows reach the public storm system with full intensity, the conclusion is that an unacceptable fraction of the water is finding its way into basements or lower home levels and/or the sanitary system. 4. The capacity of the storm drain system is also called into question. Indications are that it is handling the fraction of water that is directed to it but a much greater volume could potentially come its way from the acres and acres of residential sources. A moderate storm event would inundate the storm drain network based on hydraulic calculations (10 to 25-year). A severe storm event (50-100-year) would cause widespread basement flooding and sanitary sewer system impacts. This would be due to the flat topography of the community. Overland sheet flow, ditch flow, and pipe flow simply cannot reach velocities that would rapidly transport storm water away from the basements and sanitary sewers (it should be pointed out that this topographic factor also has the upside in not encouraging damage caused by rapidly moving water noted in hilly regions). 5. Both the LeBern and Dover pumping stations are operating at close to peak efficiencies. Significantly higher gpm rates can be achieved only with extensive physical modifications. The so-called "vortexing" phenomena could probably be greatly reduced or even eliminated by wet well modifications but a general increase in pumping capacity would not result. A second pumping factor is the downstream force main velocity and 27