2021-10-27 EMC Agenda item 5-b(i) Identifying wastewater management tradeoffs ... in Kona, Hawaii (RG)

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PLOS ONE Identifying wastewater management tradeoffs in Kona, Hawai'i i Cesspool Conversion WWTP Upgrade $500 $400 C 0 $300 $200 $100 $ 0 1MO R � MISHWitN�MI IPPPM EMOPHE IINMIID4WY \off �di Q Fig 8. Present value costs of cesspool and WWTP Piii:Apr;://rloil oiigl 10 37'1/lojirirura11.11oine,025�7i25:g O8 To aid in the simultaneous interpretation of the four metrics across the seven potential future scenarios, spider diagrams were generated using the ordinal rankings of scenarios within each metric category. The future permitted build out scenario ranked highest for the cost metric but lowest for all of the environmental metrics, and therefore generated the small- est area (equivalently, overall ranking) among the seven scenarios evaluated ffg 9(.3). At the other extreme, converting all cesspools to ATUs while simultaneously upgrading the WWTP was the most expensive but scored the highest for N reduction, P reduction, and marine habi- tat quality, resulting in the highest overall ranking (Fig 9A.). The remaining five scenarios fell somewhere in between (Fig 9P...9 F). Of note, the rankings were more sensitive to the WWTP upgrade than they were to the cesspool upgrade efficiency assumptions. In terms of cost - Table 4. Changes in N, P, marine habitat quality, and present value cost relative to the current scenario. L...... Scenario 4N 4P 4Habitat PV Cost Future per_ All ATU u] WWTP up Tar¢et low low efficiency+ WWTP 1 hieh efficiencv + WWTP M11:p! alal¢11i.eir,q/'10.137'1/,Gourroall, a) iine,0257125:13454 164 52 -319 0 92 -15 666 569 12 -3 10 160 134 51 339 267 111 46 403 267 42 -4 ..., 474 ............ .............. 427 ........... 66 -8 652 427 PLOS ONE I Ihii'tl ws://doaa .oirg/ n 0.1371/�OLuirirnalll,lpoi ne,025712 5 September 8, 2021 17 / 26