R2004-54 ACCEPTING THE BID AND AUTHORIZING A CONTRACT

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City of Decatur, Illinois Ridgeway / Bay Shore Area Sanitary Sewer Study City Project 2002-26 EXECUTIVE SUMMARY Periodic sanitary sewer overflows (SSO's) and sewer backups into private residences have been occurring for several years in the Ridgeway Drive—Bay Shore Drive area, specifically along Ridgeway Drive in the South Shores 17'h Addition. The Illinois Environmental Protection Agency has notified the ! City of its concern regarding these overflows, and on September 20, 2002, the City authorized , Bainbridge, Gee, Milanski & Associates, Inc., to review the sewer system in that area in order to ��, provide the City with realistic options to correct those conditions contributing to the SSO's. I The SSO's and sewer backups into private residences in the Ridgeway Drive area appear to be the result of a lack of hydraulic capacity in downstream sewers that are subjected to periodic excessive flow during rainfall events. The short reaction time befinreen the onset of a significant rain event and the subsequent peak flows in the various sub-basins is generally indicative of structural failures in the various components of the sewer system: manhole joints and castings, sewer pipe joints, cracked pipe, and service lateral joints. The presence of illegal connections such as sump pumps should not be ruled out, but no specific likelihood of illegal connections can be determined due to the generally poor condition of the collection system. After considering several options for alleviating the SSO problems in the Ridgeway Drive area, we recommend that the following steps, listed in order of priority, be taken: 1. Repair all known defects in the sewers. Six point repairs on Ridgeway Drive have been identified. (Estimated cost=$30,000) 2. Increase the capacity of the sewers between MH 88-28 and MH 85-84 using a combination of pipe bursting and traditional excavation techniques, and rehabilitate the sewers from MH 88- 53 to MH 88-28 (Option No. 1). (Estimated cost=$330,000) 3. Perform televised inspections of all the sewers tributary to MH 85-84 from the south and repair any structural defects that are found. Current televised inspections suggest that there will be several. (Estimated cost=$90,000 for televising and repairs) 4. Perform smoke testing of the sewers televised in Recommendation No. 3 in order to help identify illegal connections, defective service laterals, and structural problems in the sewers and manholes. (Estimated cost=$10,000) 5. Using the results from Recommendations No. 3 and No. 4, prepare a comprehensive Rehabilitation Plan for the southern portion of the study area. (Estimated cost = $15,000 to $20,000) 6. Initiate the Rehabilitation Plan from Recommendation No. 5 in order to reduce I/I and to guard against the recurrence of those conditions that lead to SSO's and sewer backups. (Estimated cost=$300,000) 7. If sufficient reductions in I/I cannot be attained at a reasonable level of investment, the relief sewer(Option No. 4) should be constructed. (Estimated cost=$100,000) Recommendation No. 6 is tentatively estimated to cost $300,000, but this figure is highly dependent on the outcome of Recommendation No. 5 and can be phased in such a way as to minimize the costs of implementation. In addition to the above recommendations, we also urge the City to consider investigating that portion of the system tributary to Monitoring Site No. 2 at manhole 85-81 from the northwest. This area exhibited excessive flows during the primary storm event on May 10th and appears to be a prime candidate for rehabilitation.