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WATER SUPPLY
PLANNING COMMITTEE |
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ITEM: |
DISCUSSION ITEM |
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4. |
LONG-TERM EXPECTATIONS FOR AQUIFER STORAGE AND RECOVERY OUTPUT |
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Meeting Date: |
April 5, 2021 |
Budgeted: |
N/A |
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From: |
David J. Stoldt |
Program/ |
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General Manager |
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Prepared By: |
David Stoldt |
Cost Estimate: |
N/A |
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General Counsel Review: N/A |
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Committee
Recommendation: N/A |
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CEQA
Compliance: This action does not constitute a project as
defined by the California Environmental Quality Act Guidelines section 15378. |
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SUMMARY: There have been recent suggestions at the March 2021 Watermaster Technical Advisory Committee that the annual average ASR volume used in the Pure Water Monterey SEIR is too high because the operational history of the ASR project is lower than 1,300 acre feet per year. However, using the historical average of the project is not a good estimation of how the project will perform in the future.
The ASR project has been built out over the last 15 years and has transitioned from a pilot testing program into a fully functioning project. All 4 ASR wells have only been operational since 2017 and the Monterey Pipeline was not operational until 2018, which was identified by Cal-Am in the previous General Rate Case as having a positive effect on daily ASR injection volumes. Therefore it is a better forecast to use daily operational averages and an analysis of Carmel River flow related to ASR water rights to calculate the number of operational days in a normal water year. Daily injection volumes depend on the balance between sources and daily system demand. In the winter injection months demand is low, injection volumes are higher and as people begin to use more water in the spring, the daily ASR volumes drop. Daily injection values also depend on the condition of the Carmel Valley well field, therefore choosing to use the daily average of the last 4 years will take into account the effects of well outages and changing demand over the operational year. For water years 2017, 2018, 1019, and 2020, the average injection was 12.5 acre feet per day. For the 50% percentile of operational days over the last 60 water years is 98 days with 62 operational days at the bottom of the normal classification and 151 at the top.
Therefore the 50%, middle of Normal Classification, yearly predicts an ASR injection volume of 1,225 acre feet with Cal-Am System in its current state. In the most recent General Rate Case, Cal-Am has asked for funding to drill another Lower Valley well and to undertake a frequent treatment process of the Carmel Valley Wellfield to improve the production. An average daily rate of 13.2 Acre feet per day will provide the average 1,300 Acre feet per year for the 50% water year. The additional 0.7 acre feet per day improvement to go from 1,225 to 1,300 acre feet per year is an improvement in the Carmel Valley Wellfield of 160 gpm. The well identified in the General Rate Case should produce 1,200 to 1,500 gpm, which is a 5.3 to 6.63 acre feet per day increase over the current capacity of the Cal-Am system. The estimate of 1,300 acre feet per day is conservative because with the planned well installed, the estimate is using wellfield firm capacity to calculate the annual average injection total.
It should also be noted that the District and Cal-Am recently filed a Petition for Extension of Time related to the ASR Water Rights. The combined maximum daily ASR volume is 29 acre feet per day and the maximum daily operational volume has been 21 acre feet. In the Petition, the District and Cal-Am laid out a longer-term plan install more wells to raise the firm system capacity to 29 acre feet per day before licensing the Water Rights. The injection total for the 50% water year at 29 acre feet per day is 2,842 acre feet per year. There is more reason to expect higher daily ASR injection totals in the future than there is to expect lower daily totals.
Further, based on the Benito/Williams technical memorandum modeling assumptions contained in the Pure Water Monterey SEIR appendices, it can be concluded that build-up of ASR storage would be sufficient to meet a 5-year drought as well as yield at least 1,300 AF annually. The build-up occurs based on historical data including wet, normal, and dry years. If the data is randomized, the same results will occur – ASR acts like a lake behind a dam, building up supplies for use later during a drought. To remove ASR from the resource planning mix in a dry year is inappropriate and would be inconsistent with industry practice for estimating water supply availability. Even AWWA recognizes ASR in its reliability assessment: “ASR wells can improve water basin management by storing water underground from periods of excess supply…, and later allowing a portion of the stored water to be extracted during periods of demand or short supply”[1]
The manner in which ASR is expected to operate after the Cease and Desist Order is lifted is shown in the graphic below:
The
scenario shown actually starts at a higher demand assumption than current year
demand, but the annual growth in demand is similar to the AMBAG 2022 Growth
Forecast rate. However, actual results
will depend on the achieved diversion rates to ASR and other supplies available
to Cal-Am.
EXHIBITS
None
U:\staff\Board_Committees\WSP\2021\20210405\04\Item-4.docx