• Mark L. Johnson

Know Your H2O-Part IX-Tucson Active Management Area (TAMA)

Updated: Jul 11

Part IX covers the Tucson Active Management Area (TAMA) including; (1) General Description, (2) Geohydrology (3) Supply & Demand, (4) Overdraft/Surplus & Safe-yield, (5) Water Conservation, (6) Renewable Water Sources, Underground Storage/Recharge & Assured Water Supply Program, (7) Groundwater Quality, (8) Water Budget and (9) TAMA Management Plan.

In Part VI-Groundwater Management Act, we learned about Active Management Areas (AMAs), groundwater rights and the Assured Water Supply (AWS) program. Here we will apply that background to TAMA.

Part IX is longer and more complex than usual because it presents physical information and data that integrates with the information provided in the earlier Parts.

Three maps are utilized. Each map is orientated with north at the top. An orange/red dot is shown on each map at the intersection of I-10 and Tangerine Road in Marana. This will help with reference and putting this all in perspective.

Many common water resource terms will be explained but you can go to the Water Lingo Tab for more details.

Much of the data, maps and information for Part IX comes from the TAMA Fourth Management Plan (5/13/16)[TAMA 4MP]. It is a very long and comprehensive document. The important information has been gleaned and is presented here. TAMA 4MP uses data through 2013 and is somewhat out of date. The Arizona Department of Water Resources (ADWR) AMA Data Website has more recent data that is also referenced in this blog.

Notes[1] containing other references and supplemental information are provided at the end of the blog.

Tucson Active Management Area (TAMA)

1. General Description

Figure 2-10 (TAMA-4MP) below shows the boundaries of TAMA. It is an expansive area and covers about 3,900 square miles. [1]

The average temperature is 52.6 F in January and 87.0 F in July. The annual average rainfall is 11.59". [2]

The orange/red dot is located at the intersection of I-10/Tangerine Road in Marana. This is also at the boundary (dashed maroon line) between the two TAMA sub-basins (aquifers). The Avra Valley Sub-basin is located to the left (west) and the Upper Santa Cruz Sub-basin is located to the right (east).

The goal of TAMA is to attempt to achieve long-term safe-yield by 2025. Safe-yield is achieved when there is a long-term balance between the amount of groundwater pumped and the amount of natural and artificial groundwater recharge.

The two primary management strategies to achieve this goal are; (1) water conservation and (2) replacement of groundwater use with renewable water supplies.

2. Geohydrology

The two sub-basins are separated by mountains and not hydraulically connected except the portion where the Santa Cruz River flows from the Upper Santa Cruz Sub-basin northwest into the Avra Valley Sub-basin through a gap in the mountains near the orange/red dot. The Google Earth Satellite Image (lead figure above) clearly shows the terrain.

Figure 2-10 also shows contours which represent the depth from ground surface to the groundwater surface (groundwater table) throughout each sub-basin. For example, the depth to groundwater at Marana is about 200'. This will be discussed further below.

The TAMA Regional Groundwater Flow Model Report (2013) was developed to provide a comprehensive, 3-dimensional computer groundwater model to simulate water inflow and outflow in order to better understand and manage TAMA groundwater. The groundwater model is calibrated with actual groundwater elevations, well pumping records and stream gauge data. Figure 4-Depth To Bedrock (below) is taken from that report.

Again, the orange/red dot is shown at the I-10/Tangerine Road intersection for reference. This figure dramatically shows the sub-basins (aquifers) tucked in between the mountains and the depth to bedrock in shades of tan/brown (depth contours). Bedrock is the bottom of the sub-basin (aquifer). Depth to bedrock gets shallower (tan) as you move toward the mountains. In fact, there is hardly any productive aquifer areas at the foothills of the mountains because bedrock is so close to the ground surface. That is why water must be imported to areas like Dove Mountain.

Figure-4 provides a better visualization of the sub-basins (aquifers). Pretend you are standing on the orange/red dot and imagine there are two huge swimming pools on each side of you---one to the west (Avra Valley) and one to the east (Upper Santa Cruz). The deepest section (dark brown) of each swimming pool is 9,600 feet and 11,200 feet deep, respectively. Then visualize these huge swimming pools being filled with sand and gravel all the way to today's ground surface. Then water is percolated down into the swimming pools from the surface, hits the bottom (bedrock) and fills the voids between the sand and gravel all the way up to today's groundwater table. Whamo, you have two large side-by side sub-basins (aquifers). Of course all this all happened over millions of years!

It is estimated that the Avra Valley Sub-basin and the Upper Santa Cruz Sub-basin, contain 16 million acre-feet (AF) and 33 million AF of groundwater in the area 1,000' below ground surface, respectively. However, not all of this goundwater is available for use due to groundwater quality and transmissivity issues in certain portions of each sub-basin (aquifer).

Any precipitation that falls within these subasins that does not evaporate or get used by vegetation will percolate directly down into the aquifer and/or flow overland as streams/rivers and eventually percolate down into the aquifer.

There is some groundwater movement between the AMAs but it is not significant. About 25,000 acre-feet per year (AFY) exits TAMA into the Pinal Active Management Area to the north but that is offset by about 21,000 AFY of groundwater entering TAMA from the Santa Cruz Active Management Area to the south. Therefore, TAMA is essentially a neutral and perhaps self-contained hydraulic system.

Even though the sub-basins are very deep in some locations, wells are typically only drilled down several hundred feet to a maximum of 2,500' below ground surface. For example, if the depth to groundwater is 200' from ground surface and the depth to bedrock at that location is 5,000' from ground surface, the well may only be drilled 500' to 1,000' below ground surface.

3.0 Supply & Demand

ADWR's AMA Data Website [3] is an excellent source for water supply, demand and overdraft (safe-yield) data and statistics.

The most recent data for water supply and demand is for 2018. In 2018, TAMA Total Demand was 316,476 AF. TAMA breaks out demand by Municipal, Agriculture, Industrial and Indian. The following chart shows how that demand was distributed across these categories:

ADWR AMA Data Website also has interactive graphs showing the water supply for each type of water user. See graph/table below for 2018. For example, Municipal used a total of 151,777 AF in 2018. Of that amount, 109,000 AF (72%) was Colorado River Water, 13,000 AF (9%) was Effluent (Recycled Wastewater) and 29,000 AF (19%) was Groundwater. The long-term graph is interesting as it shows how Groundwater pumping has been reduced and Colorado River Water supply has increased over time. This is a good thing.

4.0 Overdraft/Surplus & Safe-yield

TAMA keeps track of the amount of water inflow and water outflow. If there is more outflow than inflow, the difference is overdraft. If there is more inflow than outflow, the difference is surplus.

Safe-yield is a long-term balance between the annual amount of water withdrawn and the annual amount of natural and artificial recharge within an AMA. [1]

The various categories for inflow and outflow are shown below and are identified as to whether they are natural or artificial. Incidental recharge is water that is returned to the aquifer through artificial use, e.g. Agricultural Incidental Recharge is water not used by the plants that seeps down into the aquifer.

Inflow Categories:

  • Groundwater Inflow (Natural)

  • Streambed Recharge (Natural)

  • Mountain-front Recharge (Natural)

  • Agricultural Incidental Recharge (Artificial)

  • Municipal Incidental Recharge (Artificial)

  • Industrial Artificial Recharge (Artificial)

  • Canal Seepage (Artificial)

  • Cut to the Aquifer (Artificial)

  • CAGRD Replenishment (Artificial)

Outflow Categories:

  • Groundwater Outflow (Natural)

  • Riparian Demand (Natural)

  • Agricultural Demand (Artificial)

  • Municipal Demand (Artificial)

  • Industrial Demand (Artificial)

  • Indian Demand (Artificial)

The following figure shows the TAMA Overdraft/Surplus Dashboard taken from the ADWR-AMA website.

The data is only available through 2015. In 2015, TAMA inflows were 180,459 AF and outflows were 185,989 AF resulting in an overdraft of 5,530 AF. In the 30-years from 1985 to 2015, TAMA was in overdraft 26 years (87% of the time). Although, overdraft is lessening, sustainable long-term safe-yield has not been achieved.

It should be noted that safe-yield goal uses the words "attempts to achieve" and there is no definition of "long-term". The safe-yield goal needs be more definitive, e.g. safe-yield "will be achieved" and safe-yield is a surplus of the 20-year running balance of inflows and outflows.

TAMA goal should also include a provision to eliminate cumulative overdraft over a reasonable period of time.

5.0 Water Conservation

Water conservation is one of TAMA's key strategies to achieve safe-yield. TAMA-4MP includes a large amount of information on water conservation for each of the water sectors (Municipal, Agriculture, Industrial and Indian). The water conservation programs in place for each sector are very comprehensive. Water conservation targets are set and must be achieved.

Let's take a look at Municipal water conservation as it is the highest use sector and one that we are all familiar with. Large municipal water providers are subject to the Total Gallon Per Capita Day (GPCD) Program. This is how much water each person uses on average each day. Each large municipal water provider must meet a GPCD target based on a calculation in TAMA-4MP Appendix 5A. Table 5A (below) shows the Assigned Total GPCD Requirement for each of the TAMA large municipal providers. For example, Marana's target is 125 GPCD. We will see how Marana Water and Tucson Water are doing in a future blog.

It should be noted that these GPCD levels of use are remarkable. I previously worked at the Coachella Valley Water District (CVWD) in Southern California and the 2020 GPCD target in its state-mandated Urban Water Management Plan was 473 GPCD! And that was a desert environment with less annual precipitation (3") than Tucson.

6.0 Renewable Water Sources, Underground Storage/Recharge & Assured Water Supply Program

The other key strategy to achieve TAMA's goal of long-term safe-yield is to replace groundwater use with renewable water sources. The top two renewable resources are Colorado River water and recycled-wastewater (effluent). Integral with these renewable resources is underground storage and recharge.

Colorado River Water

In Part VII-Colorado River, we learned that Arizona's normal annual Colorado River allocation is 2.8 million acre-feet (MAF). In 2018, Arizona actually received 2.63 MAF and of that amount, 1.52 was delivered to the Central Arizona Project (CAP) and 1.11 MAF was delivered to 68 Arizona entities along the Colorado River. TAMA Municipal water utilities are contracted for 0.66 MAF.

In addition, Arizona's allocation is subject up to a 26% reduction due to its junior position and potential drought cut-backs.

It appears that additional Colorado River water within Arizona will be very difficult to obtain, especially considering the real potential for up to 26% drought cut-backs. Any Arizona entity with an existing Colorado River Water allocation would be nuts to give it up!

Recycled Wastewater (Effluent)

Pima County Wastewater Reclamation (PCWR) is the primary wastewater agency in the TAMA region. PCWR has 2 large wastewater reclamation facilities (WRFs) and 6 sub-regional WRFs with a total capacity of 95 million gallons per day (MGD). [4]

In 2018/19, these facilities treated 57 MGD of wastewater. 51 MGD (90%) of the incoming wastewater was treated to Class A+ standards and recycled. 36.5 MGD was discharged to the Santa Cruz River which ultimately recharges the Avra Valley Sub-basin and 14.4 MGD was distributed via Tucson Water's recycled water system to golf courses and other turf uses. A small portion 0.06 MGD was utilized to directly irrigate plants and trees.

Marana does have a wastewater reclamation facility that was once owned by PCWR but its capacity is only 0.5 MGD and its effluent goes to the Marana WRF Recharge Facility. In 2018, 215 AF of recycled wastewater was delivered and stored at this facility.

Recycled wastewater will not grow as a renewable source unless population increases. If additional water conservation takes place, that will negate a chunk of the additional wastewater from population growth.

Ironically, more population growth also means more groundwater pumping! Is recycled wastewater really a new water source?

It appears that additional recycled wastewater will be limited considering 90% of incoming wastewater is already recycled and additional volume from population growth will be partially offset with any additional water conservation.

Underground Storage & Recharge

In Part VI-Groundwater Management Act (GMA) we learned about GMA and the Groundwater Storage and Recharge Program in Arizona. Here we will apply this to TAMA.

TAMA 4MP Table 8-4 (below) show the permitted volume, source water and amount stored (2013) of the 23 TAMA water storage facilities. This includes both Groundwater Savings Facilities (GSFs) and Underground Storage Facilities (USFs).

Non-groundwater can be stored in GSFs and/or USFs and utilized in the same year or kept for future use via Long Term Storage Credits (LTSCs). The ADWR Website-Recharge contains a TAMA LTSC Balance Listing, which currently shows a total LTSC balance of 1.994 million AF. [5] The following chart summarizes the TAMA LTSC Listing.

Only 40% of the stored water is held by TAMA water agencies and tribes. The other 60% is held by other entities with future obligations for this stored water. The Arizona Water Banking Authority (AWBA) holds 814,005 AF (41%). The Central Arizona Groundwater Replenishment District holds 245,841 AF (12%).

In 2013, only 35% of the groundwater recovered occurred within the area of influence (1 mile) of the recharge facility. This indicates that sub-regional overdraft is not being addressed. Groundwater is being pumped in areas where recharge is non-existent or outside the area of influence.

Water stored for more than one year has a cut-to-the-aquifer requirement of 5%. As of 2103, the total cut-to-the-aquifer amount was only 200,000 AF. This is a minimal amount and TAMA should consider increasing the cut-to-the-aquifer percentage to a minimum of 10%.

Assured Water Supply Program

Part VI-Groundwater Management Act discussed the Assured Water Supply (AWS) Program. Water utilities become a Designated Water Provider (DWP) when they provide evidence that they meet current and future water demands for their service area for a period of 100 years. Developments not served by a municipal water utility must obtain a Certificate of Assured Water Supply under the same 100 year criteria.

When a water utility becomes a DWP, they receive an approved designated volume of groundwater that can be pumped. Any groundwater withdrawal beyond that amount must come from a renewable water supply (Colorado River Water or recycled wastewater). Table 12-1 shows the designated volumes for the TAMA water utilities.

7.0 Groundwater Quality

TAMA 4MP does include a section on groundwater quality. The various statutory and regulatory water quality requirements are discussed. TAMA pumped groundwater meets federal and state water quality requirements but there are 7-Water Quality Assurance Revolving Fund (WQARF) sites, 1-US EPA National Priorities List (NPL) site and 1-Department of Defense (DOD) site that have groundwater contamination and are in the process of being remediated. The sites are shown on Figure 7.1 below.

This does not include the PFAS/Dioxane pollution discovered and being remediated in the Marana Water system. This will be discussed in more detail in a future blog.

One issue that is not discussed is the potential for groundwater quality changes due to the introduction of Colorado River water into the aquifers. Colorado River water is quite different than the natural groundwater quality and the mixing of the two could result in possible long-term in situ groundwater quality concerns. I have seen this happen in other aquifers and sometimes the change from good to bad is sudden.

8.0 Water Budget