Sewer Main Line Extension Agreement - St Joseph County

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Ms. Jessica Clark DRAFT SJEC Cost Opinion & Sewer Analysis Page 5 1 September 21, 2015 provided at the crossing if additional development activity outside the SJCEDD2 boundaries is directed to this sewer, or higher flows from areas on the south side of the tracks are allowed in time. It should also be noted that a 24-inch sewer will require a slightly larger (36-inch or 42-inch) steel casing pipe under the railroad, depending on the carrier pipe material. Discussion During this review, several items were noted that warrant mention for a full understanding of the conditions surrounding the recommended sewer sizing. First, the area currently located outside SJCEDD2 boundaries west of Walnut Road, up to Wintergreen Road (1/2 mile west of the SJCEDD2 boundary) and north of Edison Road may eventually be included within the SJCEDD2 service area due to the topography of the area. This area slopes generally northeasterly from elevation 790 to 750 at the SJCEDD2 boundary along Niespodziany Ditch. This inclusion would add 320 acres to the drainage basin, and would have to be evaluated carefully to determine how much available capacity remained in the downstream sewer along US 20. It appears the available capacity of the 30-inch sewer on US 20 would be the potential constraint limiting such a connection. Evaluation of the actual flows at the time of development would be needed to determine if actual flows were less than planned. Steeper slopes for additional capacity along US 20 was considered and rejected due to only minimal cover in the upper reaches of the sewersystem. Undeveloped areas north of SJCEDD2's boundaries north of US 20 could also eventually flow into the district, but were not included in this analysis. Similar to the areas west of Walnut Road, no other likely connection points for this area exists. There are no economic forces to draw development activity to those areas currently, but as available land within SJCEDD2 is developed there may eventually be demand for these areas to connect. Evaluation of the actual flows at the time of development would be needed to determine if actual flows were less than planned in the critical sewer link on US 20 west of Smilax Road. During this analysis it was noted that although adequate sewer capacity can be developed with the proposed sewers to serve all the designated areas within the District, there is a high probability that additional lift stations or potentially low pressure sewers may be needed to connect all areas. This is due to the relatively shallow connection point at US 20 and Smilax, which has an invert elevation only about 10 feet below grade. Using minimum grades and only negligible (0.05 feet) fall through manholes, the invert connection at the SJEC is only about 5.5 feet below grade, and gravity flow from Area P along Niespodziany Ditch is unlikely. Similarly, the northern edge of the District (Areas B, C, D, E, F, G and H) has low elevations, and the Taylor Ditch crossing will not permit gravity flow to the interceptor on US 20. Alternative sewer alignments/configurations north of US 20 may be considered to minimize pumping, but would likely be difficult to sequence construction. Due to the relatively shallow sewer depths, it is probable that even developments immediately adjacent to US 20 or Walnut Road may be required to pump into the sewer system via lift stations and force mains due to their site -specific design requirements.