Table of Contents. Section 7 Alternatives for Conveyance and Treatment

Transcription

1 Table of Contents Conveyance / Location Alternatives Wastewater Facility Locations Alternatives Wastewater Treatment Method Alternatives Conveyance Alternatives List of Figures Figure 7-1 Plant Interconnect Routing Alternatives i

2 Section 7 Alternatives for Conveyance and Treatment 7.1 Conveyance / Location Alternatives The Regional Optimization Master Plan (ROMP) which was completed in November 2007 spells out many options that were considered and studied prior to the selection of a new Water Reclamation Campus (WRC) at Roger Road and expansion and upgrading the Ina Road Wastewater Reclamation Facility (WRF) Wastewater Facility Locations Alternatives Site of the two proposed treatment plants are based availability of land not only for expansion to 2030 projections, but also because of the space for further expansion and modification. Foremost the facilities locations are downstream of much of the development to allow for gravity flow to be used to transport a majority of the wastewater to the plants. Alternative locations would have affected the riparian habitat along the Santa Cruz River and would have interfered with Tucson Water s operations in conjunction with the plants Wastewater Treatment Method Alternatives Based on the projected flow for year 2030, several flow split options evaluated between the two major treatment facilities. The year 2030 wastewater flows for the combined service areas for the Roger Road WRF and the Ina Road WRF will have a total flow of approximately 82-mgd. The following options were selected for detailed evaluation of plant configurations, operations and economics. Option 1 Based on a flow split of 32-mgd and 50-mgd between Roger Road WRF and Ina Road WRF, respectively. Option 2 Based on some flow transfer from the Roger Road WRF to the Ina Road WRF to make a flow split of 20 mgd and 62 mgd, respectively. Option 3 Based on transferring all flow from the Roger Road WRF to the Ina Road WRF and therefore treatment of all 82 mgd at the Ina Road WRF. Wastewater characteristics were determined based on plant performance data, future loadings with a predication of water conservation, and mass balance with recycle flows from expected future biosolids operation. To meet the effluent goals and permit requirements, a review of various biological nutrient removal (BNR) processes was undertaken. Nine processes were screened based on economic and non-economic criteria. After the preliminary study was conducted, four were picked for further evaluation. The four included Bardenpho, Modified Ludzack-Ettinger (MLE), Integrated Fixed-film Activated Sludge, and Biotower/ Nitrifying Activated Sludge (BT/NAS). After these four were further evaluated, the Bardenpho process was determined to be the most reliable and cost effective for implementation at both the Ina Road WRF and the new WRC. 7-1

3 A No Action Alternative was not a viable alternative because it is PCRWRD s intent to improve the water quality of the treated effluent provided by the Ina Road WRF and Roger Road WRF and to provide the necessary capacity for the future. Following an evaluation of the current system provided in the ROMP, it was determined that there is insufficient capacity at the plants to handle the influx in population within the service areas. In addition, changes to current plant configurations are necessary to address the near future regulatory requirements of the Arizona Department of Environmental Quality (ADEQ) which requires a reduction in ammonia and nitrogen concentrations discharged into the Santa Cruz River. The option best suited for the community, most advantageous for the environment and most cost effective would be to expand and upgrade the Ina Road WRF and to create a New WRC at Roger Road. This option provides for new and/or expansion of water reuse facilities by Tucson Water, sustains eco-system and riparian habitats in the Santa Cruz River, provides space for future expansion beyond the year 2030 at both treatment plants and provides an opportunity for a new multi-faceted recreation, commercial and ecological development in the vicinity of the existing Roger Road WRF Conveyance Alternatives Conveyance needs for the Roger Road WRF and Ina Road WRF service areas over a 25-year plan planning period were evaluated. Goals were to evaluate how growth, regulatory requirements and system rehabilitation needs affected the system. A capital improvement plan (CIP) was then developed to plan for these needs. The population estimates were those provided by the Pima Association of Governments and 85 gpcd was used by both Tucson Water and PCRWRD for planning purposes. PCRWRD commissioned the development of a functional and highly calibrated, hydrology based hydraulic model. The advanced model has been integrated into the conveyance system Geographic Information System (GIS) platform and is an extension of previous PCRWRD models. This new hydraulic model provides the ability to identify current capacity issues, the ability to effectively plan for anticipated growth, and enables planning for inflow/infiltration improvements. After study of wet weather events, it was determined that changes are necessary as population increases. The alternative of No Action is not an option because of capacity needs within the conveyance system. While the Pima County conveyance system does experience an increase in flow in response to wet weather events, flow data indicate it has adequate excess capacity to convey these flows in accordance with Capacity, Management, Operation, and Maintenance (CMOM) criteria. But as the service area population grows, excess system capacity will be reduced and the ability for the system to reliably convey peak wet weather flows will be substantially reduced. Portions of the system will need to be augmented to maintain adequate excess capacity for wet weather flows. A major conveyance item studied was a plant-interconnect between the Ina Road WRF and the Roger Road WRF. Ability to transfer flow between the Roger Road service area and the Ina Road WRF is critical for the management of wastewater to accommodate growth. Based on current growth projections, it is anticipated that Roger Road WRF s capacity will be reached by the year 2011, or It was decided that the most cost effective flow split is 50-mgd treated at Ina Road WRF and 32-mgd treated at Roger Road WRF. This will require that approximately 28 mgd, on average, will flow through the pipeline. 7-2

4 There are various effluent demands. Two effluent demand includes Tucson Water s desire for 30 mgd at its Sweetwater facility for reclaimed water use and a minimum of 2 mgd to the Santa Cruz River for maintenance of riparian habitat. Four plant interconnect routing alternatives were evaluated. Alternative 1 Parallel existing sludge force main interconnect Alternative 2 Silverbell Road Alternative 3 Prince and Romero to El Camino Del Terra and De La Tierra Alternative 4 Alternative 3 Route to El Camino Del Cerro, under I-10, then Alternative 1 The four routing alternatives with respect to the treatment plants are shown in Figure 7-1. Under Alternative 3 transfer of the flow in the Santa Cruz interceptors is difficult and it is impossible to capture flows in the Northwest Outfall. Thus this alternative was eliminated from further consideration. The other three were examined in detail. Pipes were sized according to the capacity requirements. The recommended route for the plant interconnect pipeline is approximately 5 miles in length and varies in size from 54 inches to 66 inches in diameter. Routing Alternative 1 was the recommended choice and runs parallel to an existing 8-inch sludge transfer line from Roger Road WRF to Ina Rod WRF. 7-3

5 Figure 7-1 Plant Interconnect Routing Alternatives 7-4