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BASIS OF DESIGN REPORT EXECUTIVE SUMMARY I PFAS TREATMENT AND WELL REHABILITATION PROJECT I CITY OF PLEASANTON systems include bulk sodium hypochlorite and liquid ammonia sulfate for chloramination,and hydroflousilicic acid for fluoridation.The chemical facilities will be located under a canopy and include enhanced safety features. Figure 3 shows the CTF isometric and Figure 4 shows the CTF site plan. Well Facilities Well 8 is located at the OSC.The casing was constructed in 1992 and the casing is estimated to have a remaining useful life comparable to the new PFAS treatment system.Well 8 is currently operated at a reduced capacity because of increased turbidity at higher flow rates. It is recommended that field investigations be performed during final design to determine if Well 8 can be rehabilitated to restore its original pumping capacity.The Well 8 facility equipment is recommended for replacement because it has exceeded its useful life. Well 5 casing was constructed in 1962 and has exceeded the normal useful life for a well of this type.The existing well casing and pumping equipment is located in a below grade vault west of Alisal Elementary School(Alisal)with electrical power fed from the Well 6 building. It is recommended that the existing casing be abandoned,and a new casing be installed that is named Well 9. DDW requires a new well casing to extend aboveground, making the existing site not a feasible location.The preferred new location for Well 9 is within Amador Park between the pool and school facilities.Test drilling during final design will be required to confirm adequacy of the aquifer at this location.The new well casing and related pumping and electrical equipment will be in a new building.This location will have temporary impacts to the nearby facilities during test drilling and construction that will require coordination.The major benefit of this location is the property and facilities are owned by the City and carry less risk of implementation delays. Figure 5 shows the new Well 9 site plan. Well 6 casing was constructed in 1965 and has exceeded the normal useful life for a well of this type. It is recommended that the existing casing be abandoned,a new casing be installed in the east parking lot area of the site,and the well facility be renamed Well 10.The existing building would remain and be rehabilitated to house new mechanical and electrical equipment,due to condition and increased size requirements.Construction at this site will have temporary impacts to Alisal and the surrounding area that will require coordination.The major benefit is that the location keeps the well within the City's property and in a proven, high performing aquifer. The Alisal grass field can be carried forward to final design as an alternative location for Well 9 in the event test drilling at Amador Park determines the location is not feasible. Locating the facility at the Alisal requires discussions with Pleasanton Unified School District(PUSD)and subsequent test drilling.The major benefit of this location is the potential for simplified construction and reduced public impacts if the area can be temporarily designated for contractor use.The disadvantages associated with this location include a higher risk of implementation roadblocks,increased costs,and delays related to easement/land acquisition,storm drain improvements to support well blow-off operations,and electrical power feed. If it is determined the Well 9 facility should be located at Alisal,then it may be desirable to also locate Well 10 at Alisal.The benefit would be simplified construction implementation with a common site for both wells.The disadvantages are similar to Well 9, but would not significantly increase with one well compared to two wells located at the site.Test drilling would be required to determine if both wells could be located within the close vicinity without impacting performance during simultaneous operation. C CM/row/C.1, Mrow//^ DRAFT MAY 2021