HB facilities plan
Introduction
Summary
1. Basis
2. In-water system
3. Technologies
4. Sites

5. Separation
6. Alternatives
7. Scenarios
8. Recommendation
9. Schedule
Appendices

Env Info Document

Harbor Brook CSO Abatement Project Facility Plan (Aug 2005)
by Brown and Caldwell
for Onondaga County Dept of Water Environment Protection

5. Sewer Separation

Quick reference
— 5.1 Introduction
— 5.2 Impacts
— 5.3 Cost

5.1 Introduction

The separation of combined sewers into sanitary and storm sewers is an effective method of eliminating CSO discharges. Separation normally requires the construction of a new sanitary sewer system parallel to the existing combined sewer system. The combined sewer system is then left in place to serve as a storm sewer, and all sanitary connections are redirected to the new sanitary sewer line. In some instances, new storm sewers are built and the combined sewers are left as the sanitary sewers. The ACJ required the County to perform:

A cost evaluation of sewer separation projects proposed by the City, or by any party to this agreement and order, shall be implemented by the County. When doing this evaluation, the cost of separation shall be compared with the savings realized from the sum total of: a.) reduced CSO abatement project costs; b.) reduced operating costs at the Metro Sewage Treatment Plant; and any other savings as applicable; and achieves comparable water quality benefits. The County is obligated to construct only those sewer separation projects for which the anticipated savings exceed expected costs.

5.2 Impacts

The advantages of sewer separation are that it prevents the discharge of untreated sewage to receiving waters and that it requires low operation and maintenance in comparison to other CSO abatement alternatives. As required by the ACJ, sewer separation was evaluated for applicability to Harbor Brook CSO abatement.

A significant disadvantage of performing sewer separation for this project is that the discharge of untreated stormwater to Harbor Brook can compromise the water quality of both the Brook and Onondaga Lake. Other disadvantages of sewer separation are the magnitude of the disruption that occurs during construction, the length of time it takes to complete sewer separation, the high capital cost and the pending future enforcement of current state regulations for storm water discharges. If the existing combined sewers were converted to storm sewers, another disadvantage is that sewer separation will not provide significant improvements to street or basement flooding conditions which may currently exist within the Harbor Brook Drainage Basin.

5.3 Cost

The following estimates have been developed for the cost of separating the combined sewers within each of the CSO drainage areas of the Harbor Brook drainage basin into independent sanitary and storm sewer systems. These estimates are based on the average costs per linear foot from recently completed sewer separation of CSO areas 053 and 054 in the Midland drainage basin.

The cost per linear foot for construction in residential and commercial areas is $691/lf and $655/lf (ENRCCI 6741), respectively. These costs include:

Mobilization
Plumbing permits
Replacement of lead water services
Renovation/stabilization of existing sewers where necessary
Milling and replacement of street surfaces
Plumbing modifications outside the public right-of-way.

These costs do not include contingencies, engineering, legal and administrative costs.

Also, it should be noted that these costs do not include the treatment of stormwater discharges under the proposed Federal Stormwater Policy that are anticipated to be enforced, the renovation-replacement of existing sewers or any other abatement requirements that may result from the Total Maximum Daily Load (TMDL) process.

The assessment of alternatives and the development of costs for any additional abatement requirements resulting from stormwater regulations are beyond the scope of this project.

The cost estimates contained herein are based upon a memo entitled “Review of Sewer Separation Costs” developed by Camp Dresser McKee-C&S Engineers, Inc. (CDM-C&S) summarizing the sewer separation costs encountered in recent projects undertaken by the County.
Click here for Appendix E. Review of sewer separation costs.

The total costs for sewer separation are detailed in Section 6 of this report.