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CITY OF PLEASANTON I PEAS TREATMENT AND WELL REHABILITATION PROJECT I BASIS OF DESIGN REPORT EXECUTIVE SUMMARY ES.3 Recommended Project The following presents a summary of the BODR findings and recommendations. Figure 2 provides an overview of the recommended Project. Siting of PFAS Treatment Two alternatives were evaluated for siting PFAS treatment: 1. Dedicated treatment for Wells 5/6 at Amador Park and Well 8 at the Operations Service Center(OSC). 2. Centralized treatment for Wells 5, 6,and 8 at the OSC. Centralized treatment at the OSC is recommended because it has lower capital and operations costs,can be located outdoors near utility staff offices,has space for future expansion, eliminates the aesthetic and public impacts at Amador Park,and provides less schedule risk due to a simplified California Environmental Quality Act(CEQA)and City planning review process. The centralized treatment alternative also centralizes chemical treatment processes at the OSC and removes chemicals from the Well 5/6 area and the adjacent public facilities. The centralized treatment alternative requires pumping via a new 18-inch pipeline from Well 9 and Well 10(the proposed replacement wells for Well 5 and 6)to the OSC for treatment.The recommended alignment minimizes construction impacts and construction costs. Treated groundwater will be introduced to the distribution system near the OSC.To maximize the percentage of groundwater returned to the Black Avenue area(the current distribution system connection point for Well 5 and 6),it is recommended that an existing 14-inch watermain in Santa Rita Road between Valley Avenue and Black Avenue be upsized to 20-inch.This watermain has already been identified by the City for replacement due to age and condition. Centralized Treatment Facility The centralized treatment facility(CTF)at the OSC will provide PFAS treatment,chloramination, and fluoridation of groundwater from Wells 5,6,and 8.The recommended design capacity of the treatment system is 8,100 gallons per minute(gpm),which is the total capacity of all three wells (Well 5 and 6=2,300 gpm each;Well 8=3,500 gpm).The City typically operates up to two wells simultaneously to pump its annual allotment and meet maximum day demands.Operation of three wells simultaneously would be reflective of emergency conditions,such as reduced available water supply from Zone 7. The PFAS treatment system will be designed to meet the City's low treatment goal. However,it is recommended that the system be operated to the actual maximum contaminant levels(MCLs) that are adopted by the DDW in the future.The PFAS treatment system consists of pressure vessels equipped with media that removes PFAS as the groundwater is pumped through it.The vessels are in a lead-lag configuration to provide operational redundancy and flexibility. It is recommended that the system design allow the City to use either granular activated carbon (GAC)media or ion-exchange(IX)media due to the uncertainty of future regulations,volatility of media pricing,and a rapidly progressing field of research. For the initial vessel fill,GAC is recommended since it has lower life-cycle costs(as determined based on rapid small scale column testing),improved ability to keep all vessels on-line during low-flow well operation (reduced maintenance requirements),the potential to utilize reactivated media in the future,will result in the maximum number of vessels being installed during initial construction, and the single media type will simplify the vendor procurement process.The chemical treatment Car..Mi. 2 MAY 2021 DRAFT