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City of Arden Hills March 2008 Figure 11 - Meter 054 flow chart shows an immediate sharp spike with the flow remaining elevated for more than a day following the peak event. This flow pattern suggests primarily longer acting sources such as sump pumps, direct footing drain tiles, or leaking sewer service pipes. Figure 13 - Meter 059 flow chart indicates a short duration quick spike in flow with the flow remaining elevated slightly for an extended period of time. This flow pattern suggests a possible mixture of some direct inflow sources, such as catch basins, area drains, low manholes, or roof drains, with some longer acting sources such as sump pump connections, direct footing drainage tile, or leaking service pipes. The flow spike is significantly higher than the normal flow during the same period which supports the relative severity of the inflow in this selVice area. Figure 15 - Meter Ml flow chart indicates a short duration quick spike in flow with the flow remaining elevated for an extended period of time. While the data are considered questionable, the flow pattern should reflect the flow response in the manhole location. This pattern suggests a possible mixture of some direct inflow sources, such as catch basins, area drains, low manholes, or roof drains, with some longer acting sources such as some sump pump connections, direct footing drainage tile, or leaking selVice pipes. VII. Preliminary Conclusions The peak flow analysis indicates that there is inflow in each of the four primary metersheds while the September 18, 2007 event resulted in a possible "flow exceedence" event at meters M054 and M059 only. The projected peak flow rate at M051 was very near the allowable peak rate, but did not exceed the rate. The work completed to date is the first step identifiying and removing the III in the collection system. Additional investigation will be necessary to further identify sources and complete rehabilitation to reduce the III flow rates. Based on the flow response, it is anticipated that private property type sources including sump pumps, direct foundation drains, and possibly deteriorated sewer selVice connections provide a portion of the inflow in each selVice area; however, in areas M 1 and MOS4 these connections may be the major contributors. In Area M2, the flow response is similar but the selVice area is primarily commercial I industrial so the number of foundation drain type connections is probably limited and this response may be due to a low manhole or area drain that drains slowly after a rainfall event. In areas MOS1, M3, M052, and MOS9, the flow response suggests that there are some direct type connections in addition to some private property sources. The current data are not sufficient to specifically identify sources for the inflow, however, they can be used to plan subsequent data collection and inflow investigation efforts. VIII. Recommendations for next steps The flow data collected during 2007 generally provided some background information and response data for a limited storm event following a very dry summer period. We would recommend conducting additional flow metering at each of the temporary meter sites to try and record the response to a larger (2") rainfall event during more normal groundwater conditions. In addition, all of the lift stations should be calibrated so the running time data can be used to subdivide the flows within the larger MCES meter areas. There are five lift stations in the MOS4 selVice area that may be able to further isolate the suspected private property type sources. Table 7 includes a summary of typical III sources, investigative procedures that are designed to identify these sources, and rehabilitation options typically associated with the particular source. This is not an exhaustive list but can be considered a guide for the next steps in the III identification and rehabilitation process. Page g of 12