[Last post from the WateReuse conference....but posts on WEFTEC start Monday!]
Cortney Brand, from R.W. Beck, presented at the WateReuse conference about the costs of water development in Phoenix, and specifically the costs of using aquifers to store and recover reclaimed water. He compared three different engineering approaches (pictures here and here):
- ASR Wells (one well for both storage and recovery)
- Recharge into the vadose zone, and separate recovery wells
- Injection into the aquifer, and separate recovery wells.
I was mostly interested in his financial analysis, which took Net Present Values over 2009-2054, discounting at 5.5%. For me these were the key figures (and I thank him for e-mail clarifying them):
|NPV of costs in $/acre-ft||Capital Costs||O&M Costs||Total Costs|
|ASR: one well for both recharge and recovery||403.||68.||470.|
|Recharge in vadose zone + separate recovery wells||258.||168.||425.|
|Injection into aquifer + separate recovery wells||273.||83.||355.|
(These are from his p. 13; my numbers for “capital cost” are the ones that Brand gives as “capital cost of water resource”, divided by the 40 productive years. The total production is 0.55 milion acre-ft in all cases.)
I am always fond of good data on the price of water. This data is especially good because its separation of capital and O&M costs. As Brand pointed out, utilities often try to minimize capital costs, but this may not minimize overall costs. In this case, the vadose zone wells have the cheapest capital cost because they don’t go as deep, but the highest O&M cost because they’re most likely to clog. On a lifetime basis, this study found it most efficient to use the aquifer with separate injection and recovery wells.