TRANSMITTAL LETTER FOR BOARD MEETING OF MAY 15, 2012
COMMITTEE ON MAINTENANCE AND OPERATIONS
Mr. David St. Pierre, Executive Director
Title
Final report on emergency Contract 11-700-05, Repair of the Collapsed Upper Des Plaines 11D Ext F Interceptor Sewer and Hicks Road Repair and Restoration, to Sheridan Plumbing & Sewer, Inc., Purchase Order 5001264, Account 901-30000-667220
Body
Dear Sir:
On the morning of July 23, 2011, following a major rain event during which an excess of 5.5" of rainfall hit the area, a major sinkhole developed on the District's Upper Des Plaines 11 D Ext. F Intercepting Sewer on the northwest corner of Hicks Road and Dundee Road in Palatine, Illinois. The failure of the interceptor was attributed to a combination of factors including deterioration due to Hydrogen Sulfide (H2S) gas, poor subsurface soil material and changes in groundwater flows due to the heavy rainfalls. The original 72" diameter sewer at the point of collapse deteriorated from an original wall thickness of 6" to approximately 3/8" to 1" at the crown of the interceptor. A hole developed allowing fine sand surrounding the pipe to quickly erode away, helped by pressure from a local groundwater stream.
An emergency repair contract was initiated with Sheridan Plumbing and Sewer, Inc., to do the repair of the interceptor. Prior to the repair, District plant forces performed Close Caption Television (CCTV) inspection on the damaged interceptor. CCTV of the interceptor revealed that approximately 110' of the interceptor showed signs of heavy deterioration due to H2S. Although it was originally anticipated that a spot repair would be sufficient, it was decided that it would be more cost effective to rehabilitate the entire portion of the sewer showing deterioration in lieu of a spot repair. A centrifugally cast fiberglass reinforced polymer mortar pipe, made by Hobas, was chosen as it would allow a repair without installing an additional bypass of the interceptor line.
The final cost of the emergency was $782,745.23. This was attributed to the extensive shoring that was required due to the unstable soil conditions and the 30-foot depth of the pipe, the cleaning of 110' of interceptor, the installation of 110' of Hobas pipe, the type of backfill required by the Illinois Department of Transportation and the restoration of the section of Hicks Road that was undermined by the sewer collapse.
Final completion of all emergency repairs was achieved on October 15, 2011.
Purchase order 5001264 was initially valued at $50,000.00, increased to $500,000.00 by the Board of Commissioners on August 11, 2011, and increased a second time by the Board to $825,000.00 on September 15, 2011.
At the Board meeting of February 2, 2012, the Board then approved a decrease of Contract 11-700-05 in the total amount of $42,254.77.
Respectfully submitted, Manju Prakash Sharma, Director of Maintenance and Operations, SES:SO’C:MAG:LSC