Mark L. Johnson
Marana Water DAWS Modification Part II-Analysis
The 6-Step Procedure for developing the Designated Assured Water Supply (DAWS) was described in Part I. In Part II, we go through Steps 1-4 to methodically analyze the Marana Water (MW) DAWS Modification Application and offer some Conclusions.
Steps 5 & 6 will be covered when the Arizona Department of Water Resources (ADWR) issues the draft decision which could occur anytime in the next 45 days.
As noted in Part I, ADWR issued a Notice of Deficiency Letter (10/17/22) in regards to the original DAWS Modification Application (5/18/22) and MW responded to the Deficiency Letter on 1/12/23. This analysis includes the updated information provided in MW's Deficiency Response and will be denoted with [DR].
If you want to skip the details, go directly to the Conclusions.
MW DAWS Modification Analysis
Step 1-Water Demands
MW selected a Designation Period of 20 years (2021-2041).
Residential Water Demands
The residential portion of the Application Water Demands were developed by multiplying projected housing units (equivalent dwelling unit or EDU) by 0.30 acre-feet (AF)/EDU. The EDUs were developed from planned subdivisions in the three Marana planning areas-Northwest, Northeast and South.
The 0.3 AF/EDU factor is based on MW historical water use. It does not incorporate any potential future water conservation savings or the impacts of climate change.
Non-Residential Water Demands
The non-residential portion of the Application Water Demands were developed by multiplying projected commercial area acreage by 4 EDU/acre to get the number of non-residential EDU. The non-residential EDU was multiplied by 0.30 acre-feet/EDU to get the non-residential water demand. The non-residential areas were developed from planned subdivisions in the three Marana planning areas-Northwest, Northeast and South.
Total Application Water Demands
The resulting Application Water Demand formula is:
Water Demand=[(EDU x 0.3 AF/EDU)+(Commercial Acres x 4 EDU/acre x 0.3 AF/EDU)]
The map below shows the projected number of total dwelling units with the associated water demand (residential only) in acre-feet/year (AFY) and the corresponding population in 2041 for the MW service area (excludes TW service area in Marana). The population for the MW service area is calculated by multiplying residential EDU by 2.7 persons/EDU, which is utilized by Marana for its planning purposes. Clearly, the Northwest sector is projected with the largest growth and water demand.
The 2041 non-residential water demand is estimated at 2,178 AFY. Additionally, MW does have an obligation to serve 520 dwelling units outside of its service area with a demand of 157 AFY. Therefore, the projected Total Application Water Demand (residential, non-residential & outside) in 2041 is 15,660 AFY serving a population of 121,330 as shown in the Table below.
Total Town of Marana Population & Water Demands
To get the overall picture for the entire Town of Marana, the data for the TW service area in Marana has been added to the Table. It was obtained from TW and was utilized in their One Water 2100 Water Plan for Housing (EDU), Employment and Population projections from 2018 to 2045. For ease of analysis, this data is added to the MW projections (2021 & 2045) to get the following total Town of Marana projections for 2041:
Housing-57,177 EDU (5.29% annual growth rate)
Water Use-20,030 AFY (5.69% annual growth rate)
Population-151,440 (5.42% annual growth rate)
Note that the 2041 MW service area population in the Northeast sector is only 8,195 or 6.8% of the total (121,330). Also, annual growth rates in the TW sectors in Marana are only about 1%. This confirms that the Northeast sector is not planned for extensive growth like the Northwest and South sectors.
[DR]-MW supplied some additional information regarding the preparation of the water demand projections but they remained unchanged.
Step-2 Groundwater Model
MW engaged Montgomery & Associates (M&A) to prepare a report entitled the Demonstration of Physical Availability of Groundwater for the Town of Marana, May 18, 2022. Montgomery utilized the latest version of the Tuscon Active Management Area (TAMA) groundwater model. This model has the latest Existing Water Demands and Issued Demands incorporated into the model. Montgomery then added the 15,660 AFY Total Application Water Demands to simulate growth from 2021 to 2041. The model assumed the 15,660 AFY water demands continued each year from 2041 to 2121 (end of the 100-year period).
The model includes water recharged and stored by other entities outside the impact area but does not include water recharged and stored by MW within the impact area. This is an odd feature of the groundwater modeling/analysis requirements which is discussed in more detail below.
[DR]-ADWR wisely questioned how the DAWS Modification incorporates the fact that MW has 7 separate water systems that are not interconnected. MW responded with a plan to interconnect the systems over time and provided supply/demand information with the assumption that there will be three separate systems. Water demands were allocated to the wells serving the three separate systems. This makes sense from a groundwater modeling standpoint but how the portions of the aquifer(s) serving the three separate systems will be replenished needs to be addressed and perhaps should be considered as three separate DAWS applications.
Step-3 Groundwater Level In 100 Years
[DR] ADWR requested 6 groundwater model deficiencies to be addressed. M&A responded to these 6 items and made some technical corrections to the model. The results/figures presented below come from the updated groundwater model.
The groundwater modeling results shows that groundwater levels will drop to a maximum level of about 800' below land surface (bls) in 100-years. See Figure 3. This level does not exceed the 1,000' bls requirement but is a significant drop. This criteria has been criticized by many water supply professionals, including the Kyle Center for Water Policy at Arizona State University.
This also equates to a maximum groundwater level drop of 120' (12-story building) over the 100-year period. See Figure 5.
As mentioned above, this groundwater modeling effort did not include replenishment of the MW's renewable water supplies in the impact area. The DAWS application/requirements simply assume that the volume of water consumed by demand over the 100-year period is replaced by the proposed sources of supply (see Step 4). Perhaps a better requirement would be to model replenishment in the impact area over the 100-year period to determine the exact quantity of renewable water resources (replenishment volume) required to achieve safe yield throughout the 100-year period.
Step 4-Source of Supply
The DAWS Application includes two scenarios (DAWS A & DAWS B) for the sources of supply to service the 15,660 AFY Application Water Demand. The graph below shows the existing DAWS and associated sources of supply compared to the two proposed scenarios in the DAWS application. Minor amounts of Long-Term Storage Credits are not included.
First, you will note that the MW DAWS Modification adds 8,080 AFY of demand beyond the existing DAWS of 7,580 AFY. We had previously reported that there were 17,228 building lots approved (6,227 AFY) at the end of 2021 without an approved DAWS. This indicates that there are plans to add another 1,853 AFY of residential and commercial demand beyond that which is already approved by the Marana Planning Commission and Town Council.
DAWS A assumes that MW will not be adding any additional renewable sources of water to its portfolio and 11,644 AFY (74%) will come from groundwater.
DAWS B assumes that MW will get credit for some additional recycled wastewater (effluent) (+1,896 AFY) and the Non-Indian Agricultural (NIA) Priority Central Arizona Project (CAP) water (+242 AFY) but 9,506 AFY (61%) will still come from groundwater.
In each case (DAWS A or B), the Application does not adjust the CAP allocation for the real potential for permanent Colorado River shortage cuts. TA has recently sent a letter to the United States Bureau of Reclamation (USBR) recommending a permanent 20% cut across the board of Colorado River water delivery contracts because the Colorado River is over-allocated and aridification of the southwest will mostly cause the Colorado River water supply to diminish in the future. For DAWS and other planning purposes, Marana Water's CAP allocation should be adjusted downward by 20%.
MW does have a contract with the CARGD to replenish any groundwater withdrawn from the aquifer in excess of MW's renewable supplies (CAP & Effluent) and the Groundwater Allowance (discussed below). However, the cost of CAGRD water is expensive ($785/AF-TAMA) compared to CAP water ($228/AF).
In addition, CAGRD's sources of supply are not permanent and are subject to the same Colorado River shortage cuts. In fact, less than 50% of CARGD's water supplies are permanent or 100-year supplies. See chart from CAGRD website below. Only guaranteed delivery of CAGRD permanent or 100-Year supplies should be considered for planning purposes.
If CAGRD adds New Water (e.g., desalinated sea water) to its water supply portfolio, the cost of CAGRD water could explode as desalinated sea water costs about $2,350/AF!
Only new users should pay the cost of New Water (e.g., CAGRD water). Existing MW customers should not be burdened with these potential huge water costs.
Step 5-Groundwater Allowance
Awaiting ADWR calculation.
Step 6-Draft DAWS & Comment Period
Awaiting ADWR submittal and public comment period.
MW's water planning periods are incongruent and should utilize the same planning period (2022-2100) as TW's comprehensive One Water 2100 water plan. For example, the DAWS Designation Period is 20 years (2021-2041), the DAWS analysis period is 100 years (2021-2121) and the Water Impact Fee Infrastructure Improvement Plan (IIP) is 10 years (2022-2032).
MW's demand projections should incorporate the potential for future water conservation savings and the impacts of climate change.
Population and resulting water demand growth in the Northwest and Southwest sectors is intensive.
Total Town of Marana population is projected to triple over the next 20 years and grow at a rate of 5.42%/year from 52,723 (2021) to 151,440 (2041).
Total Town of Marana water demands are projected to triple over the next 20 years and grow at a rate of 5.69%/year from 6,618 AFY (2021) to 20,030 AFY (2041).
MW Service Area population is projected to grow at a rate of 7.48%/year from 28,674 (2021) to 121,330 (2041).
MW Service Area demands are projected to grow at a rate of 8.76%/year from 2,920 AFY (2021) to 15,660 AFY (2041).
TW Service Area (Marana) population is projected to grow at a rate of 1.13%/year from 24,049 (2021) to 30,110 (2041).
TW Service Area(Marana) water demands are projected to grow at a rate of 0.84%/year from 3,698 AFY (2021) to 4,370 AFY (2041).
Population and resulting water demand growth in the Northeast sector is fortunately limited as the Tortolita Fan area (including the Tortolita Preserve) is not intended to be served by MW and cannot be served by TW.
Groundwater modeling (no impact area replenishment) indicates groundwater levels will drop to 800' below land surface (bls) at the end of the 100-year period (2121). This meets the statutory requirement to not exceed 1,000' bls. However, this criteria has been criticized by many water supply professionals, including the Kyle Center for Water Policy at Arizona State University.
Groundwater modeling (no impact area replenishment) indicates groundwater levels will drop a maximum of 120' (12 story building) at the end of the 100-year period (2121).
Groundwater modeling should include replenishment in the impact area over the 100-year period to determine the exact quantity of renewable water resources (Replenishment Volume) required to achieve safe yield throughout the 100-year period.
MW's non-integrated water system needs to be further analyzed.
MW currently has 7 separate water systems that are not interconnected.
MW plans to interconnect the systems over time and provided supply/demand information with the assumption that there will be three separate systems.
Groundwater modeling did allocate water demands to the wells serving the three separate systems.
Groundwater modeling including replenishment in the impact area should be conducted to demonstrate how the portions of the aquifer(s) serving the three separate systems are physically replenished.
In the alternative, an individual DAWS application for each system should be required.
MW sources of supply include two options:
DAWS A-CAP (15%), recycled water (effluent) (11%) and groundwater (74%)
DAWS B- CAP (15%), recycled water (effluent) (23%) and groundwater (61%)
MW's CAP allocation should be adjusted downward by 20% to account for inevitable Colorado River shortages.
Only guaranteed delivery of CAGRD permanent or 100-Year supplies should be considered for planning purposes and DAWS.
MW's water supply portfolio is highly reliant on groundwater (61%-74%) and must be replenished via CAGRD but less than 50% of CAGRD water supplies are permanent or 100-year supplies.
Groundwater replenishment by CAGRD is costly ($785/AF) and may increase dramatically if New Water sources (e.g., desalinated sea water-$2,350/AF) are required to provide a more permanent water supply portfolio.
Only new users should pay the cost of New Water (e.g., CAGRD water). Existing MW customers should not be burdened with these high water costs.
The DAWS groundwater modeling should be enhanced to include a water quality simulation/analysis to access ultimate water quality impacts on the groundwater source of supply.
Picture Rocks and Airline-Lambert systems have already been impacted by PFAS compound pollution. Both systems had to install water treatment plants to remove PFAS and 1,4 Dioxane.
There is evidence that these compounds exist in other portions of the aquifer(s).
In addition, USEPA recently lowered to health goal for these compounds to essentially zero.
The DAWS analysis does not take into consideration the 1.8 million acre-feet of cumulative TAMA aquifer overdraft that occurred from 1985 through 2020 (ADWR TAMA Webpage).
Part III will include Steps 5 & 6 and will be published when ADWR releases its draft DAWS decision. We will include TA's comment comment letter, which you can use as an example to submit your own comments.