Written by Matt Williams Monday, 28 January 2013 05:30
By Matt Williams
Bob Dunning in his Sunday column spent a whole lot of words to ask a simple question, "Why is summer peak consumption used in the CBFR calculation?" Bob is smiling right now because his column constructed a very creative scenario using five "stars" of water use, Joe, Dan, Brett, Lucas and Rochelle.
I was somewhat surprised that Bob didn't refer to them as the Fab Five. The example Bob provides, is a mathematically well-crafted hypothetical with consumption amounts for each of the five "stars," but everyone in Davis knows that the water system in Davis isn't built to reliably deliver water to just 5 customers, but rather to over 16,000 customers. So lets put Bob's five "stars" into the context of the whole Davis "universe."
Bottom-line, Bob's examples, as fun as they are to contemplate, represent less than two one-thousandths of one percent (0.002%) of the Davis water consumption.
How do engineers design the right level of system capacity for a reliable water system? They start by adding up all the usage during the period when the aggregate demand on the water system is highest, and then they design a system that will A) reliably deliver that highest amount of water, and B) incur a specific amount of capital construction costs to build.
So, using Bob’s example numbers, when the engineers finish the adding up process for the peak month, Joe contributes 5 ccf of capacity and 5 units of capital construction cost, Dan contributes 10 ccf of capacity and 10 units of capital construction cost, Brett contributes 15 ccf of capacity and 15 units of capital construction cost, Lucas contributes 20 ccf of capacity and 20 units of capital construction cost, and Rochelle contributes 25 ccf of capacity and 25 units of capital construction cost.
All the other 15,995 accounts in Davis contribute 599,925 ccf of capacity and 599,925 units of capital construction cost. If the engineers built more than 5 ccf for Joe, then they would be incurring capital construction costs that would never be used and would also be wasting the ratepayers' money.
Similarly, if the engineers built less than 25 ccf for Rochelle, then they would be undersizing the system, and be putting us all at risk of standing in the shower early in the morning with no water coming out of the shower head.
What about Joe's 25 ccf per month in winter? Well, if you add those 25 ccf to the 200,000 ccf consumed in winter by the other 15,999 customers, you still have the 400,000 ccf of unused capacity surplus, so incurring any additional capital costs to deliver winter water to Joe is absolutely unnecessary.
There is more than enough excess winter capacity to handle Joe's winter water demand 16,000 times over. If we built specific extra capacity into the system in order to address Joe's winter demand, that would be system capacity that no one would ever use.
Over the past 12 months the WAC has worked very hard to be sure we are not incurring capital construction costs for system capacity that we will never use, and after all that hard work there wasn't a single WAC member who has any worries about whether the water system will run short of water while they are standing in the shower on a summer morning . . . because the water system is well engineered, right-sized, and reliable.
Despite Bob’s concerns, neither the WAC members, nor the rate consultant Bartle Wells, nor the City's attorneys, nor the design engineers, nor Frank Loge, nor I, nor Stevie Wonder will be breaking a sweat to explain how the rates are both fair and proportional. All the supporting data is there at their fingertips.
So, Bob's example is a fun read, but it is only a very carefully selected small sliver of the whole picture. We all need to look at Bob's "stars" in the context of the whole universe. Bob knows that, but it wouldn't make for anywhere near as entertaining an article . . . and after all Bob is an entertainer.