Clinton CSO Abatement: Environmental Information Document (Nov 2005)
Clinton Street CSO Abatement Project (Nov 2005)
Prepared by SGD Environmental Services for Environmental Engineering Associates, LLP
LEAD AGENCY: Onondaga Co. Dept of Water Environment Protection
650 Hiawatha Blvd., W., Syracuse, NY 13204
Contact: Randy R. Ott, PE, Commissioner, 315-435-2260

4. Impact evaluation and mitigation measures—natural resources

The following section describes the potential natural resource impacts associated with the implementation of the Clinton Street CSO Abatement Project. Natural resources consist of geological, air, water, ecological, and agricultural resources.

Identified impacts are potential and result when mitigation measures are not implemented. As such, following the identification of potential impacts, mitigation measures to minimize the identified impacts are discussed. Mitigation measures are primarily based on industry-specific standards and practices, County-accepted mitigation techniques, and/or mitigation measures reached through consensus during County-sponsored community meetings. (Section 9 provides information regarding public meetings and Clinton Mitigation Advisory Committee meetings). Resultant mitigation measures will be incorporated into the construction and/or design stages associated with the Clinton Street CSO Abatement Project.

In addition to the mitigation measures identified herein, the County will establish a complaint response program during the construction phase of the project. The program will be a systematic approach to receiving, processing, and addressing complaints regarding the construction of the Clinton Street CSO Abatement Project. As such, problematic areas identified during construction will be further minimized during actual project implementation.

4.1 Geology

Bedrock will not be encountered and, therefore, impacts to this geologic resource are not expected. In addition, no environmental impacts to the geologic setting are anticipated from the normal operation and/or maintenance of the Clinton Street CSO Abatement facilities. During construction, disruption of area soils and limited alterations to topography will occur from clearing, excavating, grading, and backfilling activities.

Potential erosion and/or sedimentation issues.
As a result of excavation activities associated with the RTF, disruption to area soils to depths from 10 to 50 feet (influent sump/wet well) will occur. Soil erosion and sedimentation of exposed soils (such as trenching and stockpiling activities) associated with pipe installations listed below also represent potential impacts:

• West Jefferson Street conveyance extending from the RTF site north/northeast to the back of the MOST:
  - Pipe diameter: 84 inch
     - Estimated average depth of excavation: 30 feet
     - Approximate length: 635 feet (assumed to include the 84-inch pipe in the West Jefferson CSO transmission pipeline)
• West Jefferson Street north of Walton Street to Fayette Street:
     - Pipe diameter: 42 inch
     - Estimated average depth of excavation: 25 feet
     - Approximate length: 280 feet (assumed to include the 42-inch pipe in the West Jefferson CSO transmission pipeline)
• West Street conveyance west of the Creek to Walton Street:
     - Pipe diameter: 30-36 inch
     - Estimated average depth of excavation: 20 feet
     - Approximate length: 1,240 feet (assumed to include all of the West Street CSO transmission pipeline from the west bank of the Creek to Walton Street)
• A small portion of the force main:
     - Pipe diameter: two 16-inch each
     - Estimated average depth of excavation: 15 feet
     - Approximate length: 140 feet (assumed to include the force main along Dickerson Street)
• Unmitigated, settlement may occur along the elevated railroad embankment as a result of excavation wall movements and/or consolidation settlement:
     - Pipe diameter: 84 inch
     - Estimated average depth of excavation: 30 feet
     - Approximate length: 330 feet (assumed to include the 84-inch pipe adjacent to railroad embankment)

In addition, clearing, excavation, and grading activities at the RTF site will result in localized soil disturbances and minimal alterations of site topography (less than two acres).

Without the implementation of erosion and sedimentation controls described below, exposed soils could result in siltation impacts to Onondaga Creek (water quality issues) and/or air quality issues (dust).

Erosion and sedimentation controls.
The County will comply with applicable soil and erosion control requirements and follow guidelines for urban and sediment control issues by the state. This will include the development of an erosion and sediment control plan designed to maximize erosion control and minimize nutrient and sediment runoff. Since the construction phase of the project will involve the disturbance of more than one acre, coordination with the NYSDEC will be required to obtain a SPDES permit for construction activities. Permit conditions will require the development and adherence to a site-specific storm water pollution prevention plan (SWPPP).

The above plans will be utilized by the contractor during the construction phase of the Clinton Street CSO Abatement Project. In summary, the plans will include the following industry-specific and accepted standards and practices:

• Identification of construction limits (minimal area required to complete construction activities).
• Inspection of construction activities to assess and correct areas of erosion and/or sedimentation (as necessary, corrective measures will be implemented).
• Inspection of areas of erosion and/or sedimentation and implementation of corrective measures, as necessary.
• Utilization of silt fencing, hay bales, stone check dams, and/or sediment traps on areas of potential erosion and/or sedimentation concern (including diversion swales to capture sediment-laden runoff, where necessary).
• Covering stockpiled soils with mulch or netting when not in use.
• Identification of storm water management technique(s) as outlined in the site-specific SWPPP (including, as needed, the installation of temporary sediment basins to minimize erosion and sedimentation caused by storm water runoff).
• Implementation of dust control measures (see Section 4.2.1).

Following construction, restoration activities will commence within the project area:

• Erosion control devices will be removed and the areas will be stabilized.
• Grading operations will return contours to their approximate original configuration (subsoil will be scarified prior to placement of topsoil).
• Disturbed soils outside the creek bank will be seeded and mulched consistent with flood control measures as soon as practicable after disturbance .
• Paved areas, curbs, sidewalks, etc., will be returned to their original condition.

(In the area of the proposed Onondaga Creekwalk, the County is working jointly with the City of Syracuse to define a mutually acceptable level of restoration that will minimize area impacts.)

In summary, as noted above, temporary impacts to the geological setting (i.e., upper 50 feet of soil or less) of the project area will occur as a result of construction activities. However, the above-described mitigation measures (including the complaint response program) will minimize these short-term impacts to minor disruptions and, therefore, no long-term permanent impacts to the geologic setting are expected.

Potential settlement impacts.
Based on the preliminary study prepared by Haley & Aldrich (2003), construction of the RTF building at Clinton Station appears feasible from a geotechnical standpoint. The existence of fill deposits is not considered to significantly impact construction of such a building at the site. Haley & Aldrich state that temporary construction dewatering requirements may represent a construction issue at the Clinton Station parking lot.

Directional boring to cross the railroad tracks is anticipated at the West Jefferson Street tunnel entrance to Clinton Station:

• Pipe diameter: 84 inch
• Anticipated boring pit depth of excavation: 25
feet deep (500 ft² excavation)
• Anticipated receiving area depth of excavation:
25 feet deep (400 ft² excavation)

In addition, the 84-inch West Jefferson Street conveyance will parallel approximately 300 feet of the elevated rail. Unmitigated, settlement could occur along the elevated railroad embankment as a result of excavation wall movements and/or consolidation settlement.

Measures to mitigate settlement.
The following measures will be undertaken by the County prior to construction activities to minimize the potential for settlement:

• Detailed geotechnical study to develop appropriate construction plans will be prepared.
• The County will work closely with Onondaga County Industrial Development Agency (owner of the railway) to obtain the necessary permits and easements for work in proximity to the railroad tracks including boring under the tracks.
• Tight sheeting to prevent settlement during excavation activities will occur.
• Ground improvements such as compaction and grouting will take place.
• Appropriate alteration of excavation and support sequence to minimize ground movement will take place.

In summary, the existence of fill deposits is not considered a significant impact to constructing a building such as the RTF at the site and settlement of the tracks is not anticipated.

4.2 Air resources

As expressed during public meetings, sewage-type odors emanating from Onondaga Creek in the project area have been identified by local residents. Given that project implementation will abate CSO entering the Creek, sewage-type odors from the Creek will be substantially reduced and/or eliminated. No impacts to area climate (including precipitation) will occur as a result of project implementation. It is recognized, however, that short-term air resource impacts (primarily dust) from construction activities will occur. The following subsections provide a discussion of anticipated construction-related emissions and dust as well as a discussion of the odor control features to be associated with the operational RTF.

4.2.1 Air quality (emissions and dust)

Construction-related potential impacts - vehicular emissions.
Minor air quality impacts will be caused by emissions from construction vehicles, equipment and personnel automobiles, and emissions from delayed traffic. Air pollutants typically emitted from vehicles include ozone, carbon monoxide, nitrogen dioxide, and particulates (NYSDEC 2000b). It is estimated that 8300 truck trips will be required during the construction period (3 - 3.5 years) for removal of spoil material and delivery of select backfill, concrete and other equipment and materials. The daily rate is estimated to range between 0 and 75 per day during periods when RTF and conveyance construction are being performed simultaneously. The peak rate is projected to occur only intermittently during excavation of the disinfection tank and other underground structures of the RTF (Albright 2004).

Truck trips associated with construction of the conveyances and force main are estimated to be 4000 trips over the course of construction and will range from 0 to 20 trips per day depending upon the sections of sewer being constructed. Approximately 4300 truck trips are projected for the RTF during the construction period with a range of 0 to 60 trips per day. The peak will occur during removal of excavated spoils associated with the RTF construction (Albright 2004).

Mitigation measures - vehicular emissions.
Although construction vehicle emissions will be offset given that up to 400 cars will no longer access Clinton Station on a daily basis during the construction of the RTF, industry-specific and accepted standards and practices will be required of the contractors and will include the following:

• The contractor will be responsible for maintaining properly functioning construction equipment to minimize exhaust.
• Construction equipment and vehicles will be turned off when not used for extended periods of time.
• To the extent possible, deliveries of construction material will be scheduled during off-peak hours.
• Unnecessary idling of construction vehicles will be prohibited.
• Effective traffic detour routes will be identified and maintained to avoid significant delays in and around the project area.

In summary, construction-related traffic is not anticipated to cause a contravention of federal air quality standards based on the above mitigation measures and based on comparisons to similar construction projects (i.e., Metro upgrades) (EEA 2000). Over the 3 - 3.5 year construction period, construction vehicle-related emissions will not constitute a significant increase in overall emissions and no significant impacts to local air quality are expected.

Construction-related potential impacts - dust.
Excavation activities associated with the construction of the RTF and pipe trenching and backfilling activities will generate dust from the movement of soils during construction activities. Given such activities, localized dust-related impacts are expected. The mitigation measures described below are expected to reduce dust-related impacts.

Mitigation measures - dust.
The County will continue to work closely with representatives from the community to identify areas of concern and to mitigate dust-related impacts effectively (e.g., through direct meetings, utilization of construction management and inspection program, and/or through the complaint response program). To date, to minimize issues related to the generation of dust during the construction phase of the project, the following measures have been identified:

• Identification of construction limits (minimal area required to complete construction activities).
• When practical, excavated spoils will be removed as the contractor proceeds along the length of the pipe.
• When necessary, stockpiling of backfill material will be covered or staged offsite location with backfill material being delivered as needed during the course of construction.
• Excessive soil on paved areas will be sprayed (wet) and/or swept and unpaved areas will be sprayed and/or mulched. (Given that pharmaceutical products are produced at Hanford, County representatives will work closely with Hanford to reduce potential dust emission impacts that may impair the quality of the product produced.) The use of petroleum products or similar products for such activities will be strictly prohibited.
• Contractors will be required to cover stockpiled soils and trucks hauling soil, sand, and other loose materials (or require trucks to maintain at least two feet of freeboard).
• Appropriate detours for effective traffic flow will be defined (see Section 5.1).

Based on the above-defined mitigation measures, as well as utilization of a complaint response program proposed by the County, air quality impacts from the generation of dust during construction will not exist or will be minor in nature.

Potential operational impacts - volatile emissions.
Vehicular traffic during operation of the RTF has been estimated at four trucks per event. Such figures represent a minor increase in vehicular emissions. Minor releases of VOCs may also occur during operation of the RTF due to the storage of CSO. It is anticipated that operational emissions will fall significantly below regulated thresholds based on similar construction projects (e.g., Metro upgrades, EEA 2000). As such, emissions from the implementation of the Clinton Street CSO Abatement Project are considered minor in nature.

Mitigation measures - volatile emissions.
As described in greater detail below, control equipment installed to reduce odors will minimize the release of VOCs associated with stored CSO. In addition, the County will comply and operate the facilities in accordance with applicable state air resource regulations (6 NYCRR 200-240).

4.2.2 Odor

Potential impacts.
It is anticipated that implementation of the Clinton Street CSO Abatement Project will significantly reduce odors currently observed in the Creek and the immediate area surrounding the Creek. As previously noted, current estimates indicate that 74% of the CSO generated within the service area is sent to Metro. The installation of the RTF will increase the capture volume to 86%. As such, the RTF will function to remove solids and floatables that currently contribute to Creek odors (EEA 2002).

The County has committed to incorporate odor control facilities with redundant features to maximize the capture of odors before air is exhausted from the RTF. Left unmitigated, odors could be released from RTF operations as a result of CSO storage. Organic constituents contained in the stored combined sewage undergo biodegradation depleting available oxygen and generating methane and hydrogen sulfide gases. Once the supply of oxygen has been depleted in the wastewater, odors can be produced. These odors are generally caused by the production of hydrogen sulfide gas by microbial activity. Typically, hydrogen sulfide is present in wastewater at a concentration up to 20 parts per million (ppm) (EEA 2002). The probability of odor development is increased with the length of time the material is stored, higher temperatures, higher solids concentrations, and increased number of access points. No odor-related impacts from construction vehicles are anticipated.

Mitigation measures.
The facility's exhaust system will be equipped with an advanced, state-of-the-art activated carbon odor control system. Exhaust will be discharged (after treatment) through an estimated 10-foot stack located on the roof of the RTF (i.e., total height above grade: approximately 35 feet) (EEA 2003a). Table 4-1 summarizes the design features, technologies, and/or activities that will be implemented by the County at the Clinton Street RTF.
 
Table 4-1 Summary of Odor Control Measures
 

Source: EEA 2002
Based on the above-described mitigation measures, normal operation and maintenance activities at the RTF will not result in odor impacts to area receptors. To the contrary, the operation of the RTF will substantially reduce and/or eliminate sewage-type odors currently observed in the Creek and surrounding the Creek.

4.3. Water resources

The following section focuses on potential impacts and mitigation measures associated with the water quality of Onondaga Creek and floodplains. Given that federal NWI wetlands and NYSDEC wetlands have not been mapped within the project area, impacts to wetlands will not occur.

4.3.1 Water quality

Implementation of the Clinton Street CSO Abatement Project will result in a substantial reduction in solids, floatables, and bacteria currently entering the Creek in connection with untreated CSO that enter the Creek. As such, project implementation will result in an overall improvement to the water quality of Onondaga Creek and, therefore Onondaga Lake. Short-term minor impacts in water quality, however, will occur as a result of construction activities; no significant negative impacts are anticipated.

Potential impacts.
The following construction activities in and around Onondaga Creek are anticipated:

• Installation of the West Onondaga Street and the West Street conveyance pipes across Onondaga Creek (see Figure 1-7) if an open trench methodology is employed:
  • West Onondaga Street creek crossing conveyance:
    
      - Pipe diameter: 72 inch
      - Anticipated average depth of excavation: 84 inch
      - Approximate crossing length: 60 feet (bank to bank)
  • West Onondaga Street conveyance parallel to creek:
    
      - Pipe diameter: 27 - 108 inch
      - Anticipated average depth of excavation: 25 feet (maximum)
      - Estimated length: 2,240 feet
  • West Street Creek creek crossing conveyance:
    
      - Pipe diameter: 36 inch
      - Anticipated average depth of excavation: 42 inch
      - Approximate crossing length: 60 feet (bank to bank)

• Construction of the disinfection tank outfall (120-inch diameter) (emergency controlled diversion spillway not designed at this time).
• Reconstruction activities at the Fabius Street bridge.
• Construction of bulkheads (CSOs 028 and 029)
• Installation of diversion structures at CSOs 027 and 030 through 036 (see Figure 1-2).

Unmitigated, potential impacts from the above activities could include siltation, flow disruptions, damage to the flood control channel, and creek bed contour changes. Furthermore, without mitigation measures employed, the direct discharge of ground water/storm water from excavated trenches and excavation areas at the RTF site could impair the water quality of the Creek. Lastly, from an operational standpoint, impacts to the water quality could be expected if the RTF treated effluent was not dechlorinated prior to discharge to the Creek.

Conveyances/force main - mitigation measures.
As described in Table 1-4 Anticipated approvals/permits, the County will be required to obtain state and federal permits to work within (or under) and adjacent to Onondaga Creek. As such, in order to comply with permit requirements, construction activities will be based on state and federally-accepted and approved technologies and monitored throughout the construction period. Typical mitigation measures associated with crossing the Creek utilizing an open cut methodology will include the following:

• Minimize the time required for trenching, pipe laying, and backfilling.
• Clear vegetation along creek banks only to the extent necessary for construction purposes.
• Utilize rights-of-way to access both sides of the Creek (to avoid vehicular crossings of the Creek itself).
• Place silt fencing and/or hay bales along the creek bank approaches to minimize siltation of the Creek, and bank approaches to minimize siltation along the Creek.
• Store petroleum products 100 feet or more beyond the Creek.
• If open trenching is utilized, backfill excavated trenches and restore the channel lining so that there is no change in the contour of the channel.
• If open trenching is utilized, utilize temporary creek diversions and turbidity barriers.
• Avoid non-construction areas during construction activities (as well as during routine maintenance of the RTF outfall).
• Inspect creek bank after restoration activities have been completed to assess whether additional restoration activities are warranted.

(Possible use of directional boring exists [as an option to open trenching method] to cross the Creek.)

Construction techniques to minimize potential adverse impacts from installation of the conveyances in proximity of the Creek include the following:

• Install tight sheeting in the trenches.
• Utilize techniques described in the project-specific erosion and sediment control plan and storm water management plan.
• Maintain haul roads and street routes.
• Restore disturbed banks consistent with those required to maintain the flood control channel; areas beyond the flood control portion of the channel will be restored to original or better condition through seeding the banks and placing erosion control matting on the vegetated banks.
• Match the existing grade and condition of creek bank. Coordination with the City and upon State concurrence may warrant modification of the existing grade to accommodate the Creekwalk if to be extended south behind Clinton Station.

Trench depths along the conveyance and force main pipes will range from 15-40 feet below grade. Ground water will likely be encountered along these installations based on preliminary geotechnical evaluations that estimate ground water depths at 6-20 feet. Dewatering of trench excavations from the infiltration of ground water, as well as storm water, will be required. During design, analysis of ground water and pump tests will be performed to assess ground water quality and to define the pumping rate and expected volume of water and to establish appropriate disposal procedures (e.g., filtration or settling basins followed by discharge to Onondaga Creek or sanitary sewer); silt-laden water will not be discharged directly into the Creek.

In summary, no or only minor temporary water quality impacts and impacts to localized ecosystems will occur during the construction of bulkheads, diversion structures, trenching, installation of conveyances and outfalls, and restoration activities. No permanent negative impacts, however, are anticipated from these activities.

RTF construction - mitigation measures.
Due to the presence of fill material at Clinton Station, it is estimated that 10 feet of fill material will require excavation to reach an adequate bearing layer. Underground facilities associated with the RTF are estimated to be approximately 50 feet below grade (maximum). Given this excavation depth, ground water will likely be encountered during excavation. In addition, storm water will enter the excavation during storm events. As such, dewatering of the excavation will be required. During design, analysis of ground water and pump tests will be performed to assess ground water quality and to define the pumping rate and expected volume of water and to establish appropriate disposal procedures (e.g., filtration or settling basins followed by discharge to Onondaga Creek or sanitary sewer); silt-laden water will not be discharged directly into the Creek. Furthermore, the use of sheet piling around deep excavations will reduce the amount of ground water entering the excavation.

Based upon significant ground water analytical studies performed by the United States Geological Survey (USGS) along the Onondaga Creek corridor,and the recent dewatering conditions encountered at the County's upstream Midland Avenue CSO RTF site, it is known that at deeper ground water depths the chloride concentration within the ground water along the Onondaga Creek corridor increases and ultimately approximates saline conditions (Kapel and Miller 2005). As discussed above, during design, ground water samples will be collected at depths up to 100 feet and analyzed for chloride and salinity characteristics. As currently being conducted in conjunction with the County's ongoing Midland Avenue CSO project, the results of the ground water analytical tests and the project site pup tests will be reviewed with the NYSDEC to establish the most appropriate saline management and ground water discharge requirements during construction of the project. The USGS will also be provided with the ground water analytical and pump test results obtained as part of the project implementation.

To mitigate potential issues from utilizing Clinton Station for staging, the following mitigation measures will be employed:

• Fuels and lubricants staged onsite will be kept in locked, well-maintained storage areas accessible to only authorized personnel. Storage of such products will not occur within 100 feet of the Creek.
• Work area and equipment will be secured at the end of the day.
• As needed, excessive dust/soil on paved areas will be sprayed (wet) and/or swept and unpaved areas will be sprayed and/or mulched. The use of petroleum products or similar products for such use will be prohibited to avoid storm water-related impacts.
• Contractors will be required to cover stockpiled soils and trucks hauling soil, sand, and other loose materials.

In conclusion, no significant impacts to the water quality of the Creek are anticipated from the construction of the RTF.

Operational mitigation measures.
As previously noted, the existing system currently stores approximately 74% of the total average annual wet weather flow. The Clinton CSO Abatement Project will store an additional 12% of the total average annual wet weather flow for treatment at Metro with remaining peak wet weather flows representing 14% being treated (removal of solids, disinfection, dechlorination) onsite and discharged to Onondaga Creek (18 times on an average annual basis). This represents approximately 118 MG of treated CSO being discharged to Onondaga Creek.

At this time it is anticipated that the County will utilize liquid sodium hypochlorite to treat (disinfect) the CSO discharge. Liquid sodium metabisulfite will be used to dechlorinate the treated CSO discharge. This dechlorinating agent reacts with the chlorine to convert it to a non-toxic liquid byproduct (EEA 2002). The CSO discharges will be dechlorinated to achieve compliance with NYSDEC requirements of not more than 0.1 milligrams per liter (mg/L) of free chlorine residual. This compares to New York State regulations for public water supply systems that require, for systems using chlorine, the free chlorine disinfection concentration in the water entering the distribution system cannot be less than 0.2 mg/L for more than four hours (EEA 2003a). The following summarizes information presented at a CSO Disinfection Workshop that supports that disinfection/dechlorination does not represent a significant water quality impact to the receiving waterway (OCDWEP 2002b).

• Chlorination/dechlorination has been accepted by the state for the ACJ and is recognized by the USEPA as the best alternative for CSO treatment at this time.
• NYSDEC's position on chlorination/dechlorination is that it is a safe practice for human contact recreation and sensitive aquatic organisms.
• It is not likely that chlorination/dechlorination by-products in receiving waters will result in adverse impacts to aquatic ecosystems or to human health.
• Use of chlorination/dechlorination has proven to be more commercially advanced, more reliable, and more cost effective than alternatives such as treatment with chlorine dioxide, ozone or ultraviolet light.
• Based on Water Environment Research Foundation (WERF)-sponsored chemical risk assessment, chlorination/dechlorination by-products have a very low tendency to bioconcentrate in aquatic organisms.
• The effective life of chlorine compounds in the environment is short.

Liquid sodium hypochlorite at a 12-15% concentration is currently proposed for use in the Clinton Street CSO Abatement Project. For comparison purposes, household bleach commonly contains liquid sodium hypochlorite at a concentration ranging from 6-8% (OCDWEP 2002b).

In summary, significant impacts to the water quality and aquatic ecology of Onondaga Creek are not anticipated from the operation of the RTF and discharge of treated effluent. The chlorination/dechlorination process is approved by the USEPA and NYSDEC for sewage-related uses and does not pose a significant risk to aquatic animals or to humans. In addition, the RTF will discharge in accordance with permit requirements imposed by the NYSDEC under the SPDES program. The completed project will result in improved water quality in Onondaga Creek and Onondaga Lake and an improved ecosystem in the Creek. No environmental impacts are anticipated from the normal operation of the Clinton Street CSO Abatement facilities.

Maintenance mitigation measures.
Mechanical system maintenance and repair and post event washdown will be required. Mitigation measures include an automated maintenance scheduling system, established operating procedures for personnel dispatch for maintenance and washdown operations, scheduled deliveries of liquid sodium hypochlorite and liquid sodium metabisulfite, and adherence to NYSDEC and Public Employee Occupational Safety and Health Act (PESHA) regulations for the storage and handling of chemicals. Based on the above factors, no environmental impacts are anticipated from the normal operation of the Clinton Street CSO Abatement facilities.

4.3.2 Flood prone areas

Potential impacts.
Flood hazard maps by Federal Emergency Management Agency indicate that flood prone areas exist within the project area (see Figure 2-1) (FEMA 1986). Permanent aboveground structures to be constructed within the 100-year flood plain, however, are limited to the RTF outfall and emergency controlled diversion spillway. Given the approximate size of the outfall (120-inch diameter), impacts to flood prone areas are not expected. The sizing of the emergency controlled diversion spillway has not been determined at this time but is not expected to result in significant long-term impacts to the flood plain.

Mitigation measures.
The Clinton Street CSO Abatement Project will reduce the potential for flooding given that restoration activities of the creek channel will improve current conditions (see Section 4.3). In addition, adherence to approved erosion and sediment control plans (including storm water pollution prevention) and the mitigation measures identified with regard to Creek disturbances will minimize and/or eliminate potential flood prone impacts during construction. Additionally, adherence to appropriate flood zone regulations will be required. In summary, as presented above, impacts to areas prone to flooding are not expected from the implementation of the Clinton Street CSO Abatement Project.

4.4 Ecological resources/setting

4.4.1 Terrestrial ecology

Potential impacts.
The majority of the project area is devoid of vegetation (e.g., areas of parking lots, vacant lots, and roadway rights-of-way). No species of significance (RTE and species of special concern) or habitats of significance (federal critical habitats and state CEAs) are known to exist within the Clinton Street CSO Abatement Project area. Disruptions will primarily be limited to the existing urban terrestrial setting in the vicinity of Onondaga Creek where the conveyances will be installed. Construction-related impacts will consist of the removal of a limited amount of vegetative cover (an estimated 700 ft² of grasses, shrubs, and saplings along the Creek) and the temporary displacement of natural habitats. A limited number of ornamental trees within Clinton Station will also likely be removed during construction activities.

Mitigation measures.
Previously noted construction-related mitigation measures (see 4.1 - Geology and 4.3 - Water resources) will mitigate unnecessary impacts to the terrestrial community within the project area. These measures include activities such as:

• Adhering to an approved sediment and erosion control plan
• Minimizing the time required for construction activities
• Minimizing the clearing of vegetation
• Backfilling excavated trenches to preconstruction contours
• Avoiding non-construction areas during construction activities
• Coordinating to the greatest extent possible, work with other planned projects to reduce construction-related impacts
• Conducting restoration and/or landscaping activities.

It should be noted that prior to work commencing on the conveyances, the OCDOH will inspect the area for rodent activity and bait the sewers as part of the Rodent Control Program (Letteney 2002).

In summary, the temporary loss of vegetation (habitat) at the RTF site and along the conveyances does not represent a major impact on terrestrial ecology. Restoration and landscaping activities will provide new habitats that are common throughout the downtown area.

4.4.2 Aquatic ecology

Potential impacts.
As identified throughout this document, the implementation of the Clinton Street CSO Abatement Project will result in beneficial improvements to the water quality of Onondaga Creek to support a more diverse species of plants and animals (i.e., a positive impact). The potential for short-term negative impacts are limited to conveyance installation activities along/beneath Onondaga Creek as well as installation of the RTF outfall piping. Unmitigated, siltation of the Creek could damage existing habitats and eliminate food resources. In addition, left unmitigated, impacts to the aquatic ecology of Onondaga Creek could be expected if the treated effluent was not required to be dechlorinated prior to discharge to the Creek.

Mitigation measures.
Approved site-specific construction-related mitigation measures will reduce siltation impacts to the aquatic ecology of Onondaga Creek. Sections 4.1 - Geology and 4.3 - Water resources specify the typical mitigation measures to be employed during the construction of the project. In addition, the complaint response program will be operative during the construction of the project. As such, implementation of the above identified measures will reduce potentially adverse impacts to short-term disruptions.

Negative impacts to the aquatic ecology of Onondaga Creek are not expected as the treated effluent will be dechlorinated prior to discharge to the Creek. The dechlorinating agent (sodium metabisulfate) will react with the chlorine to convert it to a non-toxic liquid byproduct (EEA 2002). These types of chemicals are used extensively for disinfection of CSOs throughout the United States. A CSO demonstration study conducted by the USEPA in 2001 reported that disinfection using doses 43% higher than what is proposed by the County would not provide an aquatic ecology concern (when followed by dechlorination prior to discharge from the RTF) (EEA 2002). Given these findings, as well as those presented in Section 4.3.1 - Water quality, impacts to the aquatic community with regard to the discharge of treated effluent are not expected. Overall improvement of water quality will stimulate growth and diversification of the aquatic ecology (Creek and Lake).

4.5 Agricultural

There are no agricultural uses within the project area, as such, there will be no impacts to agricultural.

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Susan Miller, Project Deputy Director
Phone 315-435-2260   Fax 315-435-5023
 Onondaga County Dept of Water Environment Protection