Item 19 - Agreements for On-Call Engineering Services

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PROPOSAL FOR On -Call Engineering Design Services PFAS Treatment Systems ■ Layout for each site is extremely important. Design needs to accommodate large tanker trucks to deliver the GAC or IX media. These trucks need room to access the site, unload spent media, and install new replacement media. ■ We highly recommend the use of 5 micron filters as a pre-treatment step prior to IX media. This prevents fine sediments that may come from the wells or pipelines from potentially clogging the filters and/or damaging the media. ■ On large systems where there is available space it is good to have a waste backwash tank. This tank stores the waste backwash during change outs, and allows suspended particles to settle and then be pumped back to the front of the plant. Due to the "forever nature" of PFAS, it is not a good idea to send waste into either sewer or storm drain systems. ■ Installation of a drainage system on the tank slab will allow drainage water from rainfall to be collected and disposed of. It can also be used to collect, store, and alarm the operators when a leak has occurred. Since the sites are in highly urban areas, it is best to prevent any leakage from discharging off the site. ■ Consider replacing rupture disks with pressure relief valves that contain limit switches that can signal an over pressurization and alarm the wells to shut down. Rupture disk needs to be replaced after every over pressurization. All of our designs on this project will be performed using 31) CADD Revit design drawings. As each site is completed, we will provide the City with a visualization of the proposed site. Below is an example of one of our sites currently in final design. Preferred layout for a leadllag configuration with pretreatment filters and backwash tank. Current code provisions for the anchorage of tanks and vessel contain specific requirements for the strength of the anchor bolts. These requirements can be found in Chapter 15 of the ASCE 7-16 and Chapter 17 of the ACI 318. The intent of these provisions is to avoid catastrophic, brittle failures of the concrete at anchor bolts by ensuring that the concrete at an anchor bolt group has significantly more strength than the anchors themselves. The anchor design provisions effectively prevent the use of post -installed anchors because of their limited bond strength. Cast -in -place anchors must be used for tanks and vessels, but cast -in -place anchor bolts are difficult to locate accurately. The use of cast -in -place anchors requires additional time and TETRA TECH Page 18