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TO: HONORABLE MAYOR AND MEMBERS OF CITY COUNCIL FROM: DIRECTOR OF PUBLIC WORKS DATE: MAY 6, 2003 SUBJECT: PALOS VERDES DRIVE EAST and MUSTANG ROAD STORM DRAIN REPAIR PROJECT – REQUEST FOR FUNDING Staff Coordinator: Glen W.C. Kau, Sr. Engineer RECOMMENDATIONS:
BACKGROUND For some time now, staff has presented photographs of storm drains with eroded inverts, and discussed the associated risks due to our aging infrastructure system. On Tuesday, April 8, 2003, a small sinkhole appeared just outside the right of way, located at Palos Verdes Drive East at Mustang Drive (Fig. A). The sinkhole (Fig. B) appeared as a result of the heavy rains on Monday evening. DISCUSSION The subject 30"Ø Corrugated Metal Pipe (CMP) storm drain is in dire need of repair. As available information best indicates, the pipe is approximately 140’ long, and at least 40 years old. A field review discovered that the CMP has sustained severe damage from corrosion and age at the invert (bottom) portion of the pipe, exposing the support soil (Photo 1).
Fig. A
Fig. B
Photo 1 – CMP Inlet Even with the invert portion missing, the water continues to flow, following the natural drainage course, flow line (Fig. 3). The exposed support soil under the invert has been eroded away, carried along with the flow and re-deposited downstream at the outlet end of the pipe (Photo 2).
Photo 2 – CMP Outlet During rain events, the generated/collected flows that are conveyed by the CMP storm drain continue to flow and erode the support soil, eventually creating voids underneath the pipe. The start of the voids section was seen during a field review. It is estimated that the recent heavy rains have created large voids area (~2’-3’ deep x ~3’ wide) under the CMP storm drain, and is located primarily within the center section of the overall pipe length. The voids section length is estimated to be from 40’ to 80’ in length (See Fig. 1). To investigate/determine the actual voids situation, the storm drain’s inlet and outlet require clearing of debris and eroded soil to gain internal access to view the storm drain.
An initial field review was performed to determine the extent and rehabilitation methods with the City’s road maintenance contractor. Both staff and the contractor recommend that the first priority is to address structural integrity of the support soil around the CMP storm drain and to eliminate the void area, then determine if rehabilitation of the CMP storm drain is further needed. The first action is to clear all loose debris, soil, rocks, etc., within the pipe from the exposed flow line and voids area for the entire length of the pipe. Next, concrete slurry backfill (~100-E-100, minimum) will be placed/pumped into the voids area for the entire pipe length to a thickness of 6" just below the pipe invert elevation. The remaining 6" thickness voids area will be filled with f’c=3250psi (~565-C-3250P) concrete and hand formed to structurally restore the pipe and invert. The concrete will have a smooth finish to provide a flow line for drainage. It is suspected that the voids area most likely extends into the area near the center of the pipe (spring line, See Fig.2), and grout would be pressure injected into these areas behind the CMP to provide both pipe support an to eliminate the remaining voids. A debris basin, located upstream at the inlet and will require debris clearing and re-depositing of the soil that has been washed down towards the inlet. The soil will be re-deposited onto the slopes to fill in the depressed, eroded areas to minimize the amount of material haul-off.
CONCLUSION To alleviate future damage to the storm drain, and most importantly avert sustaining roadway surface damage, staff recommends that the storm drain repairs project be authorized and commenced as soon as possible. The rain season has "apparently" lessened, and has seemed to have almost disappeared. Adopting staff’s recommendations will provide the necessary funding for the storm drain repairs, construction management and inspection services to complete the Palos Verdes Drive East and Mustang Road Storm Drain repairs and associated debris clearing. FISCAL IMPACT It is estimated that the costs of repairs will be $30,000 and construction is expected to require approximately four weeks to complete. The estimated costs are as follows:
The work will be conducted on a time-and-material basis to account for the actual amount of materials and resources utilized for the repair work. The project was not anticipated in the FY 02-03 budget and to adequately fund the recommended repairs, staff is recommending a budget appropriation of $30,000 from the General Fund. The FY2002-2003 estimated General fund revenues in excess of adopted expenditures are only $827. Therefore, the additional appropriation for this project cannot be funded within this year’s anticipated revenues and will have to be drawn from the General fund reserve. The calculation of the projected General fund reserve available for appropriation, which is below the reserve policy level, is summarized below.
Respectfully Submitted, Reviewed, Attachments: Resolution 2003- RESOLUTION NO. 2003- A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF RANCHO PALOS VERDES, AMENDING RESOLUTION 2002-45, THE BUDGET APPROPRIATION FOR FISCAL YEAR 2002-03, FOR A BUDGET ADJUSTMENT TO THE CITY’S CAPITAL IMPROVEMENT PROGRAM FUND WHEREAS, Section 3.32 of the Rancho Palos Verdes Municipal Code provides that all expenditures in excess of budgeted allocations must be by supplemental appropriation of the City Council; and WHEREAS, on June 12, 2002, the City Council of the City of Rancho Palos Verdes adopted Resolution 2002-45, approving a spending plan and authorizing a budget appropriation for the 2002-03 fiscal year; and WHEREAS, it is necessary for the City to allocate additional funds for storm drain repair construction services; and WHEREAS, a budget increase in the CAPITAL IMPROVEMENT PROGRAM Fund is necessary to authorize the expenditure of additional funds for construction services. BE IT, THEREFORE, RESOLVED BY THE CITY COUNCIL OF THE CITY OF RANCHO PALOS VERDES: The following adjustment be made to the Capital Improvement Program Fund CIP Fund 330-930-82 Improvements $30,000 PASSED, APPROVED, AND ADOPTED THE 6th DAY OF May, 2003. ___________________________ MAYOR ATTEST: ______________________ CITY CLERK _____________________________ CITY CLERK CITY OF RANCHO PALOS VERDES | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
