The Wastewater Tsunami is Coming

Transcription

1 The Wastewater Tsunami is Coming How do we stop it? Trooper Smith, PE, Freese and Nichols, Inc. Jennifer Baldwin, Ph.D., PE, Jacobs

2 Outline Project Background Central Basin Rilling Road Storage 30% Design

3 SAWS by the Numbers 7 th largest city in the nation 1.8 million customers Sustainable Affordable Water Services 1,700 employees

4 Project Background SAWS entered into Consent Decree with USEPA Negotiations July 23, 2013 Lodged October 15, 2013 Entered Year Duration 8 Major Components Capacity, Management, Operation & Maintenance (CMOM) Early Action Program Condition Assessment and Remedial Measures Capacity Assessment and Remedial Measures Lift Stations Force Mains Water Quality Program Reporting Central Basin Freese and Nichols (FNI) and CH2M, now Jacobs

5 Central Basin Basin drains heavily residential and commercial portions of San Antonio, including downtown Main stem sewer for Central Basin conveys flow along creeks and drainage ways Parallel sewers in many points Sewer in waterway at various points Sewers come together at Rilling Road location (former WWTP) and convey flow in 90-inch sewer to Dos Rios Water Reclamation Center (WRC)

6 Central BPC Plan - Methodology 10% Design Develop and finalize alternatives Assessment & design Recommendation to move forward to the 30% 30% Design Perform field verifications/evaluations Develop cost data Allows rapid progress in final Design & Construction

7 Central BPC Plan Methodology (Cont d) Evaluated alternatives for the BPC with SAWS s InfoWorks model 5-year, 6-hour assessment storm 2014 condition Central Basin assumes no appreciable growth for 2040 condition Utilized assumption of 30% I/I reduction throughout the basin Assumed early action projects were constructed and operational Approximately 80 MGD Reduction in Peak Flow with 15 MG Rilling Rd Offline Storage Facility

8 Central BPC Rilling Road Storage Alternatives Evaluated Evaluated five alternatives A. Upstream offline storage at two locations B. Conveyance improvements in upstream system & offline storage at Rilling Road location C. Deep tunnel parallel to main stem D. Combination of upstream offline storage at two locations and offline storage at Rilling Road location E. Combination of upstream offline storage at two locations and offline storage at Rilling Road location with less flow diverted into storage and additional surcharging in main stem sewers SAWS chose to move forward with Alternative B Table 1. Alternatives Analysis Wet Weather Peak Flow to Dos Rios WRF from Central Basin Alternative A B C D E Wet Weather Peak Flow (mgd)

9 Alternative B Chosen Because Condition constraints are eliminated in areas where new main stem sewer will be constructed Rilling Road location is a key hydraulic point in the system Storage at this location will provide flexibility to SAWS for wet weather operation in both collection and treatment at Dos Rios WRF SAWS owns the property Avoids construction of parallel sewer to Dos Rios WRC

10 Alternative B - Selection

11 Alternative B - Selection

12 Rilling Road Storage Determined optimal volume based on I/I removal sensitivity analysis Volume chosen was 15 MG, expandable to 30 MG

13 Rilling Road Storage 30% Design Type of Storage Method of filling and draining storage Evaluated Fill rate and drain rate for storage Diversion method Return method Covering of basin/tank Site layout

14 Type of Storage & Method for Filling and Draining Evaluated several options for storage Earthen basin, gravity fill, pumped drain Earthen basin, pumped fill, gravity drain Earthen basin, hybrid gravity/pumped fill, pumped drain Below grade tank, gravity fill, pumped drain Below grade tank, pumped fill, gravity drain Below grade tank, hybrid gravity/pumped fill, pumped drain Above grade tank, pumped fill, gravity drain For 30% design, narrowed down to two options Earthen basin, gravity fill, pumped drain Below grade tank, gravity fill, pumped drain

15 Type of Storage & Method for Filling and Draining Conducted Site Visits July 2017

16 Filling and Draining Rates Based upon the duration of the storm event hydrograph, filling rate was set at 6 hours Draining rate was set at 12 hours in order to have storage available to SAWS for multiple wet weather storm events Return pump station will be designed to allow slower drain rate that will be controlled by Dos Rios WRF operators

17 Diversion Method Side discharge weir: 1) Complicates flow measurement into storage 2) Calculations based on May, et al, 2003 & confirmed with InfoWorks mdoeling Diversion structure to be constructed on existing 90-inch sewer Used 3-10 ft weir gates to give SAWS flexibility for diversion rate & amount of surcharging allowed in upstream sewers

18 Return Method Basins/tank will have a drain gate Gate will be opened remotely by Dos Rios WRF operators Return flow is conveyed to return pump station Pump station has capacity of 30 mgd, to allow draining of 15 MG of storage in 12 hours VFDs will allow turn down of pumps to allow flexibility in drain rate

19 Covering of Basin/Tank Basin option only considers uncovered basin cells Covering of basin cells would add cost due to foundation considerations Tank option considers: Uncovered tank Uncovered tank that will be covered in the future Covered tank Covered tank that is buried with at least 3 feet of soil

20 Site Layout Earthen Basin Option

21 Site Layout Tank Option

22 Rilling Road Storage Summary Rilling Road Storage Facility will allow SAWS flexibility to convey and treat wet weather flows into the future Designed with flexibility for expansion from 15 MG to 30MG Rilling Road location is hydraulically important Prevents need to increase capacity of 90- inch sewer to Dos Rios WRC with a parallel sewer

23 SAWS Consent Decree Updated Timeline