032819-TKWC+LBWC call notes_032219_STPUD Feasibility Study Alternatives TableSouth Tahoe PUD‐South Y Feasibility Study3/28/2019Alternatives OverviewN/A = Not detected during model simulation periodBeyond model= after end of model simulation period of 2068Ease of Construction Wells Piping Treatment InfrastructureFeedback from water companies ‐ what are the important issues?Infrastructure Elements (Existing and New)AssumptionsAlt No.Alt DescriptionModel Estimated PCE Removal EffectivenessYear to Achieve PCE < 4 ppb Drinking Water WellsPermitting RequirementsEnvironmental EffectsPreliminary Cost (Relative)Potential Funding SourcesOperations and MaintenanceDisposal/Reuse Options1No Action • 0.020‐0.476 kg/MG PCE removed over 20 years through biodegradation and water supply pumping• 121 kg PCE removed over 20 years by public supply wells in baseline modelLBWC 1: N/ALBWC 5: 7‐29 yearsTKWC 1: N/A ‐ beyond modelTKWC 2: 21 ‐ beyond modelTKWC 3: N/AEXISTING• Continue to operate LBWC 1, LBWC 5 with GAC, TKWC 1, TKWC 2 with GAC, TKWC 3, and STPUD wells to meet demand and maintain distribution system pressures.• Destroy LBWC Well 4 to remove potential conduit for vertical migration of PCE. • Continue to supplement LBWC supply with water purchased from STPUD to meet Demand, as needed• Sample/profile TKWC 2 for water quality by depth to investigate and determine if PCE is limited to a specific aquifer. Based on the results of the sampling and profiling, hydraulically manipulate TKWC 2 to isolate pumping to uncontaminated zone. • Potential destruction and replacement of TKWC 1 if PCE concentrations increaseNEW• Potential replacement of TKWC 1 if PCE concentrations increase, potentially more favorable on west side of PCE Plume• Continue to use existing distribution system piping• New piping to connect replacement well• Install grant‐funded GAC at LBWC 5 to intercept PCE plume, remove mass, and protect downgradient wells• Potential future increase in TKWC 2 GAC changeout if PCE concentrations increaseHigh ‐ minimal new infrastucture• Pumping and GAC changeout• Replacement well on west side, if needed, could pose operational challenges for water agenciesDISPOSAL• Potential for TKWC 2 and/or LBWC 5 to operate as PCE extraction system, discharge to sewer or Tahoe Keys lagoonREUSETKWC 2 and LBWC 5 with GAC planned for reuse• TKWC 1 assumption – PCE stays same or increases. Future replacement of TKWC 1 depending on rate of water quality degradation. Potential future need to add treatment to TKWC 1 if plume contaminates well. If GAC added to TKWC 1, potential future reduction in production capacity due to GAC contactors.• No new permitting unless PCE increases in existing wells• If LBWC 5 to continue operation as drinking water source, obtain 97‐005 permit to operate LBWC 5• If TKWC 2 and/or LBWC 5 to operate as PCE extraction system, new permitting/ infrastructure to discharge to sewer or Tahoe Keys lagoon• Same as existing unless TKWC 2 and/or LBWC 5 to operate as PCE extraction system only with discharge to sewer or Tahoe Keys lagoonLow at present PCE concentrations• New GAC at TKWC 1 = Prop 1• GAC O&M = SCAP and Prop 1• replacement well for TKWC 1 = DWSRF?• Private Well survey to identify potential conduits for vertical migration = Prop 1• TKWC 1 assumption – PCE stays same or increases. Future replacement of TKWC 1 depending on rate of water quality degradation. Potential future need to add treatment to TKWC 1 if plume contaminates well. If GAC added to TKWC 1, potential future reduction in production capacity due to GAC contactors.• Reach out to private well owners to determine well status and investigate other potential vertical migration conduitsTKWC:•Potential surface water discharge to Lake Tallac Lagoon or Upper Truckee River under NPDES permit (need additional piping to move discharge water that distance). Discharge to Tahoe Keys Lagoon is challenged by aquatic weed.•For pumping excess water to STPUD, need to evaluate intertie/piping capacity.•Question: How is the confining layer being accounted for in model Layer 3?LBWC:•LBWC 5 is being permitted by DDW for drinking water, GAC capacity up to 300 ppb 750 gpm max. GAC and well are taking up entire area, no additional space for future treatment•LBWC 1 could be pumped more but for the potential for drawing in more of the plume•Potential to use excess water for fire water storage in tank at Gardner Mountain ‐ potentially fundable by fire grant. Would require additional piping3 New Public Supply Wells for Alternative Water Supply• 0.033‐0.698 kg/MG PCE removed over 20 years• 88 kg of PCE removed by public water supply well pumping in baseline modelLBWC 1: N/ALBWC 5: 4‐27 yearsTKWC 1: N/A ‐ beyond modelTKWC 2: 20 ‐ beyond modelTKWC 3: N/AEXISTING• Continue to operate LBWC 1, LBWC 5 with GAC, TKWC 1, TKWC 2 with GAC, TKWC 3, and STPUD wells to meet demand and maintain distribution system pressures.• Destroy LBWC 4 to remove potential conduit for vertical migration of PCE.• Destroy TKWC 1 to remove potential conduit for vertical migration of plume• Adjust pumping at LBWC 5 and redistribute to replacement well• Sample/profile TKWC 2 for water quality by depth to investigate and determine if PCE is limited to a specific aquifer. Based on the results of the sampling and profiling, hydraulically manipulate TKWC 2 to isolate pumping to uncontaminated zone. NEW• Drill RW‐D to replace TKWC 1 capacity; Operate RW‐D at TKWC 1 pumping rate• Drill RW‐F (or RW‐E) to replace LBWC 5 capacity; Operate RW‐F (or RW‐E) to make up reduction in LBWC 5 pumping• New Piping to bring new well supplies to distribution system• Install grant‐funded GAC at LBWC 5 to intercept PCE plume, remove mass, and protect downgradient wells• No change unless PCE in wells increase in futureModerate for new wells and piping• Operate at new pumping scheme to meet demand and maintain distribution system pressuresDISPOSAL• If LBWC 5 to operate as PCE extraction system, discharge to sewer or Tahoe Keys lagoon• Potential disposal with NPDES permitting• Temporary impacts from construction• If discharge to Tahoe Keys Lagoon, need to evaluate impact on habitatModerate • New Well drilling = Prop 68• Private Well survey to identify potential conduits for vertical migration = Prop 1• Sample/profile TKWC 2 = SCAP and Prop 1• GAC O&M = SCAP and Prop 1TKWC:•Potential surface water discharge to Lake Tallac Lagoon or Upper Truckee River under NPDES permit (need additional piping to move discharge water that distance). Discharge to Tahoe Keys Lagoon is challenged by aquatic weed.•Question: How is the confining layer being accounted for in model Layer 3?•RW‐D site is potentially in floodplain, and is far from TKWC existing infrastructure and requires more coordination with STPUD than a site within TKWC boundary.LBWC:•LBWC 5 is being permitted by DDW for drinking water, GAC capacity up to 300 ppb 750 gpm max. GAC and well are taking up entire area, no additional space for future treatment.•LBWC 4 Site is 1 acre: plenty of room for new well + treatment train, and is <0.25 mile from LBWC 5. This is a preferred site for use. •RW‐F site new Council Rock is another preferred replacement well site, but only if there is a plume containment measure in place.•LBWC 1 could be pumped more but for the potential for drawing in more of the plume•Potential to use excess water for fire water storage in tank at Garner Mountain ‐ potentially fundable by fire grant. Would require additional piping\\Sac2\job\2017\1770027.00_South Tahoe PUD‐South Y Feasiblity Study\09‐Reports\9.09‐Reports\Task Q.1‐Q.2. Outreach (formerly Task F)\Water‐company\032819‐TKWC+LBWC call notes_032219_STPUD Feasibility Study Alternatives Table.xlsx
South Tahoe PUD‐South Y Feasibility Study3/28/2019Alternatives OverviewN/A = Not detected during model simulation periodBeyond model= after end of model simulation period of 2068Ease of Construction Wells Piping Treatment InfrastructureFeedback from water companies ‐ what are the important issues?Infrastructure Elements (Existing and New)AssumptionsAlt No.Alt DescriptionModel Estimated PCE Removal EffectivenessYear to Achieve PCE < 4 ppb Drinking Water WellsPermitting RequirementsEnvironmental EffectsPreliminary Cost (Relative)Potential Funding SourcesOperations and MaintenanceDisposal/Reuse Options• TKWC 1 assumption – PCE stays same or increases. Future replacement of TKWC 1 depending on rate of water quality degradation. Potential future need to add treatment to TKWC 1 if plume contaminates well. If GAC added to TKWC 1, potential future reduction in production capacity due to GAC contactors.• TKWC 1 assumption – PCE stays same or increases. Future replacement of TKWC 1 depending on rate of water quality degradation. Potential future need to add treatment to TKWC 1 if plume contaminates well. If GAC added to TKWC 1, potential future reduction in production capacity due to GAC contactors.• Additional TKWC 2 treatment could occur at Lagoon WTP site across from TKWC 2 site4a Use of Existing Public Supply Wells with Wellhead Treatment to Remove PCE ‐ 90% Treatment Capacity• 0.023‐0.333 kg/MG PCE removed over 20 years• 330 kg of PCE removed by public water supply wells in baseline modelLBWC 1: N/ALBWC 5: 10‐26 yearsTKWC 1: N/A ‐ 42 yearsTKWC 2: 17 ‐ 46 yearsTKWC 3: N/AEXISTING• Operate LBWC 1, TKWC 1, and TKWC 3, to meet demands and maintain system pressures.• Pump LBWC 5 and TKWC 2 at 90% of treatment capacity• Sample/profile TKWC 2 for water quality by depth to investigate and determine if PCE is limited to a specific aquifer. Based on the results of the sampling and profiling, hydraulically manipulate TKWC 2 to isolate pumping to uncontaminated zone. • Destroy LBWC 4 to remove potential conduit for vertical migration of PCE.NEW• New well pumping equipment to allow sufficient reduction in STPUD well pumping• If LBWC 5 and TKWC 2 operated as drinking water supply, upsize/new piping + new booster pump station to convey increased flows to STPUD potentially required• Install grant‐funded GAC at LBWC 5 to intercept PCE plume, remove mass, and protect downgradient wells• Increased GAC changeout frequency• If LBWC 5 and TKWC 2 operated as PCE extraction system, new treatment detention/ discharge infrastructureModerate for if upsizing of piping/interties is requiredDISPOSAL• If LBWC 5 and TKWC 2 operated PCE extraction system, discharge to sewer/ Tahoe KeysREUSE• If LBWC 5 and TKWC 2 operated as drinking water supply, sell excess water to STPUD. Reduce pumping at STPUD wells to accommodate increased supply from LBWC and TKWC• If TKWC 2 to operate as PCE extraction system, additional NPDES permitting to discharge to Tahoe keys• If LBWC 5 to continue operation as drinking water source, obtain 97‐005 permit to operate LBWC 5• If LBWC 5 to operate as PCE extraction system, new permitting/infrastructure to discharge to sewer or Tahoe Keys lagoon• Temporary impacts from construction• If discharge to Tahoe Keys Lagoon, need to evaluate impact on habitatModerate • GAC O&M = SCAP and Prop 1• Increased treatment = Prop 1• Infrastructure to discharge additional water = Prop 1• Private Well survey to identify potential conduits for vertical migration = Prop 1• Sample/profile TKWC 2 = SCAP and Prop 1TKWC:•Potential surface water discharge to Lake Tallac Lagoon or Upper Truckee River under NPDES permit (need additional piping to move discharge water that distance). Discharge to Tahoe Keys Lagoon is challenged by aquatic weed.•For pumping excess water to STPUD, need to evaluate intertie/piping capacity.•Question: How is the confining layer being accounted for in model Layer 3?•RW‐D site is potentially in floodplain, and is far from TKWC existing infrastructure.•A new well could be located upgradient from TKWC 2 at the Lagoon Recirculation facility site to intercept PCE.LBWC:•LBWC 5 is being permitted by DDW for drinking water, GAC capacity up to 300 ppb 750 gpm max. GAC and well are taking up entire area, no additional space for future treatment.•At 90% LBWC 5 pumping capacity, estimated GAC life is 39 days (GAC units in series)•LBWC 4 Site is 1 acre: plenty of room for new well + treatment train, and is <0.25 mile from LBWC 5 This is a preferred site for use. •RW‐F site new Council Rock is another preferred replacement well site, but only if there is a plume containment measure in place.•LBWC 1 could be pumped more but for the potential for drawing in more of the plume•Potential to use excess water for fire water storage in tank at Gardner Mountain ‐ potentially fundable by fire grant. Would require additional pipingTKWC:•Potential surface water discharge to Lake Tallac Lagoon or Upper Truckee River under NPDES permit (need additional piping to move discharge water that distance). Discharge to Tahoe Keys Lagoon is challenged by aquatic weed.•For pumping excess water to STPUD, need to evaluate intertie/piping capacity.•Question: How is the confining layer being accounted for in model Layer 3?•RW‐D site is potentially in floodplain, and is far from TKWC existing infrastructure.•A new well could be located upgradient from TKWC 2 at the Lagoon Recirculation facility site to intercept PCE.LBWC:•LBWC 5 is being permitted by DDW for drinking water, GAC capacity up to 300 ppb 750 gpm max. GAC and well are taking up entire area, no additional space for future treatment.•At 90% LBWC 5 pumping capacity, estimated GAC life is 39 days (GAC units in series)•LBWC 4 Site is 1 acre: plenty of room for new well + treatment train, and is <0.25 mile from LBWC 5 This is a preferred site for use. •RW‐F site new Council Rock is another preferred replacement well site, but only if there is a plume containment measure in place.•LBWC 1 could be pumped more but for the potential for drawing in more of the plume•Potential to use excess water for fire water storage in tank at Gardner Mountain ‐ potentially fundable by fire grant. Would require additional piping.Both LBWC and TKWC indicated that additional treatment needs for PCE clean up should not be the responsibility of their rate payers4b Use of Existing Public Supply Wells with Wellhead Treatment to Remove PCE ‐ 90% Pumping Capacity• 0.022‐0.245 kg/MG PCE removed over 20 years• 574 kg of PCE removed by public supply wells in baseline modelLBWC 1: N/ALBWC 5: 8‐19 yearsTKWC 1: N/A ‐ 14 yearsTKWC 2: 11‐24 yearsTKWC 3: N/AEXISTING• Continue to operate LBWC 1, LBWC 5 with GAC, TKWC 1, TKWC 2 with GAC, TKWC 3, and STPUD wells to meet demand and maintain distribution system pressures.• Pump LBWC 5 and TKWC 2 at 90% of pumping capacity• Sample/profile TKWC 2 for water quality by depth to investigate and determine if PCE is limited to a specific aquifer. Based on the results of the sampling and profiling, hydraulically manipulate TKWC 2 to isolate pumping to uncontaminated zone. • Destroy LBWC 4 to remove potential conduit for vertical migration of PCE.NEW• New well pumping equipment to allow sufficient reduction in STPUD well pumping• If LBWC 5 and TKWC 2 operated as drinking water supply, upsize/new piping + new booster pump station to convey increased flows to STPUD likely required• Install grant‐funded GAC at LBWC 5 to intercept PCE plume, remove mass, and protect downgradient wells• Reuse STPUD Hypox and/or air stripper at TKWC 2 for additional flow to intercept PCE plume, remove mass, and protect downgradient wells• Increased GAC changeout frequency• If LBWC 5 and TKWC 2 operated as PCE extraction system, new treatment detention/discharge infrastructureModerate if upsizing of piping/interties is requiredLow if additional treatment needed at TKWC 2Potentially more complex treatment trains to handle volume of waterDISPOSAL• If LBWC 5 and TKWC 2 operated PCE extraction system, discharge to sewer/ Tahoe KeysREUSE• If LBWC 5 and TKWC 2 operated as drinking water supply, sell excess water to STPUD. Reduce pumping at STPUD wells to accommodate increased supply from LBWC and TKWC• If TKWC 2 to operate as PCE extraction system, additional NPDES permitting to discharge to Tahoe keys• If LBWC 5 to continue operation as drinking water source, obtain 97‐005 permit to operate LBWC 5• If LBWC 5 to operate as PCE extraction system, new permitting/infrastructure to discharge to sewer or Tahoe Keys lagoon• Additional treatment technologies (eg Hypox) need to be approved by DDW for reuse• Temporary impacts from construction• If discharge to Tahoe Keys Lagoon, need to evaluate impact on habitat• Review environmental impacts from construction of additional treatment trainsModerate‐High for additional treatment • GAC O&M = SCAP and Prop 1• Increased treatment = Prop 1• Infrastructure to discharge additional water = Prop 1• Private Well survey to identify potential conduits for vertical migration = Prop 1• Sample/profile TKWC 2 = SCAP and Prop 1\\Sac2\job\2017\1770027.00_South Tahoe PUD‐South Y Feasiblity Study\09‐Reports\9.09‐Reports\Task Q.1‐Q.2. Outreach (formerly Task F)\Water‐company\032819‐TKWC+LBWC call notes_032219_STPUD Feasibility Study Alternatives Table.xlsx