Desalination Hopscotch Enables Adaptation to More Frequent and Longer Droughts by Team_ISI

Here is our response to the judges’ comments. We have also edited the proposal to reflect the judges’ suggestions.

 

1. What if there are no rainy seasons to pump between aquifers?

That is a good question that is relevant to the content of an agreement that would be negotiated by parties who participate in Desalination Hopscotch If complete and lasting drought in Texas were to happen in areas seaward from San Antonio, Desalination Hopscotch would be needed more than ever. It would provide water for users who now depend on drawing groundwater directly from the Gulf Coast Aquifer. It would be a matter of negotiation about what amount of water from the Gulf Coast Aquifer would still be allowed to users in an Antonio. Agreement on that contingency should be part of the original agreement rather than done later on an ad hoc basis. Because of San Antonio's investment in the Desalination Hopscotch system, it would be in a strong position to negotiate a fair agreement for sharing of water during an unending drought.

 

2. What is the embedded energy in both the desalination and the pumping, transport and insertion?

The energy required for water desalination will vary greatly based, for example, in salinity of the water used and the desalination process used. Desalination typically requires 7-30 kWh of energy, obtained through burning of fossil fuels, with the consequent CO2 emissions, to produce 1000 gallons of desalinated water. On our proposal, we specified the use of renewable energies at every step possible, with zero CO2 emissions.

Regarding the energy needed for pumping, and referencing the values on our proposal:

“Assuming 100% efficiency, a pump can lift 319.5 gallons of water 1 foot with 1 watthour of energy. Water pump efficiency runs 40-70%. We choose the middle of this range: 55%. This means 175.7 gallons of water can be lifted 1 foot with 1 watthour of energy”.

Transport of water should be minimal, as the transportation will occur mostly through the aquifers. Final energy values for transportation and insertion, as well as energy requirements for desalination and pumping, will be determined once the sites have been selected.

 

3. You do speak of carbon GHG in your proposal - can you make some estimates?

So far, we have not estimated a specific amount of greenhouse gases that will be produced by Desalination Hopscotch. However, we have asserted that it will be minimal because renewable energy sources will be tapped whenever and wherever possible. In Texas, we have access to copious supplies of green energy from solar and wind farms.

In our proposal, we have estimated some lowered emissions of GHG over business-as-usual plans to tap water resources from aquifers, as shown in the paragraph copied and pasted below. We will return to this topic with more complete estimates after the fact-finding trip to the San Antonio area that we have planned to take place in February 2018.

Getting 151.1 GWh of energy from coal (anthracite) will yield 53,461 tonnes (117,860,354 lbs.) of CO2, or 27,362 tonnes (60,322,228 lbs.) of CO2 if natural gas is used instead. Most likely, a mix will be used resulting in between 27,362 and 53,461 tonnes of CO2 being emitted into the atmosphere every year. That’s how much CO2 emissions the environment will be spared when the Desalination Hopscotch Project is implemented using 100% zero-emissions renewable energy.

 

4. How many aquifers are there, that are close to sea water and overlap (no overland transfer required?) in the world? What is the potential for scaling out?

There are 22 aquifer systems around the world close to sea water (https://www.jpl.nasa.gov/news/news.php?feature=4626), see list below.  As mentioned on our proposal the Atlantic and Gulf Coastal Plains Aquifer in North America and the Nubian Aquifer System in Africa, are good candidates for the hopscotch water transportation.

Potentially, all the aquifers mentioned here could be good candidates for hopscotch water transportation, and determining which ones could be used would require deep analysis of the hydrogeology of each aquifer system (i.e. flow rate between aquifers, determined by nature of the substrate). As an example, the Guarani Aquifer in South America, the third largest groundwater reservoir in the world, is a very extensive and transboundary system across many countries (i.e. Brazil, Argentina, Paraguay and Uruguay). In Argentina, it connects three aquifer systems; the Puelches, Pampeano and Independence Aquifers.  Another example is the connection between the Senegalese and Mauritanian aquifers that are part of the Senegalo-Mauritanian Basin, in Africa (http://publication.lecames.org/index.php/ing/article/view/359/241). In Asia, the Indus Basin and the Ganges-Brahmaputra Basin are both connected and also connect with other aquifers inland, as the NW Frontier Aquifer and the Indian Cratonic Aquifer (http://www.sciencedirect.com/science/article/pii/S2214581815000233).

Atlantic and Gulf Coastal Plains Aquifer (North America, Gulf Coast Atlantic Ocean)

Californian Central Valley Aquifer System (North America, Pacific Ocean)

Amazon Basin (South America, Atlantic Ocean)

Maranhao Basin (South America, Atlantic Ocean)

Guarani Aquifer System (South America, Atlantic Ocean)

Nubian Aquifer System (Africa, Mediterranean Sea)

Northwestern Sahara Aquifer System (Africa, Mediterranean Sea)

Senegalo-Mauritanian Basin (Africa, Atlantic Ocean)

Ogaden-Juba Basin (Africa, Indian Ocean)

Karoo Basin (Africa, Indian Ocean)

Paris Basin (Europe, North Sea, Atlantic Ocean)

Russian Platform Basins (Europe, Artic Ocean)

Pechora Basin (Asia, Artic Ocean)

Arabian Aquifer System (Asia, Indian Ocean)

West Siberian Basin (Asia, Artic Ocean)

Tunguss Basin (Asia, Artic Ocean)

Indus Basin (Asia, Indian Ocean)

Ganges-Brahmaputra Basin (Asia, Indian Ocean)

North China Aquifer System (Asia, Pacific Ocean)

Song-Liao Basin (Asia, Pacific Ocean)

Great Artesian Basin (Australia, Pacific Ocean)

Canning Basin (Australia, Indian Ocean

 

5. The Desal itself is paid for by only those who get their water from Aquifer B? Shouldn’t water rates rise for both Aquifer A and B, since both see an improvement in water quality and water security? Saying more about the rate structure would be great.

Your question is well taken and thought-provoking. We agree that users of both Aquifer A and users of Aquifer B will benefit from Desalination Hopscotch. Given that reality, representatives for users of Aquifer A water should be willing to cover part of the costs for Desalination Hopscotch operations. We do not have enough information at this time to speculate on what a fair rate structure might be arrived at during negotiations. As stated in "1," above, "Because of San Antonio's investment in the Desalination Hopscotch system, it would be in a strong position to negotiate a fair agreement for sharing of water during an unending drought."

 

6. Is the volume of water available in an aquifer visible through earth observations and/or some other open source method?

The answer is no, there is not a direct method to measure the volume of water available from an aquifer. However, the Texas Water Development Board (TWDB) provides an accessible Groundwater Database (GWDB) with records for approximately 140,000 water wells across the state (http://www.twdb.texas.gov/groundwater/data/index.asp). The information include, among other values, the water level and quality. Water levels are measured every year in approximately 8,600 wells in Texas (http://www.twdb.texas.gov/groundwater/docs/studies/TexasAquifersStudy_2016.pdf).  The groundwater level gives us an estimate for changes in the groundwater storage, which can change due to various factors (natural recharge, over-pumping of the aquifer, etc.) over the years.  Knowing the changes of the water level gives us an idea of the “health” of the aquifer. In Addition, the quantity of groundwater is the amount of groundwater physically present in the aquifers; but not all the water is recoverable. Thus, water availability is the estimated amount of water that can be withdrawn from the aquifer (http://www.twdb.texas.gov/groundwater/docs/studies/TexasAquifersStudy_2016.pdf).  Texas aquifers have an estimate of 16.8 billion acre-feet of water, and between 25-75 % of this amount is probably recoverable. Numerical modeling is used to estimate groundwater availability per unit of time, and models are designed for specific aquifers, under defined conditions (http://www.twdb.texas.gov/groundwater/models/gam/czwx_c/czwx_c_full_report.pdf).

 

7. Discuss where there are sociopolitical and geopolitical issues raised by sharing water in the way you describe, even if it is at heart a business deal.

Because water is substance crucial to maintaining life, the decision for water to be shared goes beyond being a business deal. Nations will threaten to war to secure access to water (e.g., Egypt vs Ethiopia), and poor people will suffer if socioeconomic forces work to deny them clean water. (Sometimes this is the case in areas where people are poor and have little political power).

Desalination Hopscotch will not solve all the problems of the geopolitics and sociopolitics of water, but it will make those problems easier to solve. If the pie that represents water resources is made larger, slicing the pie so that everyone gets a slice is made easier.

The thinking behind Desalination Hopscotch is "outside the box." Similar kinds of thinking could help to solve other "wicked" problems of geopolitics and sociopolitics. It is clear that innovative thinking should be applied to those kinds of problems. New thinking is required if the human race is not to threaten its own destruction and that of all other species by continuing to degrade the natural environment on Planet Earth.

"A new type of thinking is essential if mankind is to survive and move toward higher levels.“

-- Albert Einstein

8. What is the feasibility is of 'injecting' water to the quantities needed to replace the amount of water abstracted?

Compared to other projects involving the injection of water, the amount needed to replace the amount of water subtracted is feasible. Injecting 50,000 acre-feet of water for Desalination Hopscotch per year can be compared to the injection rate that has been achieved in an aquifer replenishment program in The Orange County Water District of California. That project involves injecting up to 300,000 acre-feet per year of purified water to recharge underground storage. (See https://www.ocwd.com/media/3622/groundwatermanagementplan2015update_20150624.pdf.)

The overall feasibility of plans for injecting water in Texas is enhanced by the option of choosing from among many possible sites for injection along the Gulf Coast of Texas. Those many sites are located near the coastline where the Gulf Coast Aquifer stretches for over 300 miles in close proximity to seawaters of the Gulf of Mexico.

 

9. Ground water recharge is not always easy or possible, are the authors meaning injection wells direct to the aquifer?

Yes, injection will be directly into the aquifers. Injection is a well-understood technology, as discussed in "10," below.

 

10. How feasible will it be to pump water from one aquifer to another? How much geological resistance will there be, what will be the efficiency of attempting to direct water in this way?

The technology for pumping, transporting, and injecting fluids is well known. Resistance to injection is a potential problem at any specific location. Fortunately, Texas is a large state and with extensive aquifers; and, therefore, specific sites for injection can be selected from among sites where resistance to injection is not a problem that cannot be overcome. By comparison, the injection wells that are used successfully in Orange County, California, (described in "8," above) inhabit a much more restricted area for selecting among well sites than is the area contemplated for selecting injection sites in Texas. The Texas Board of Water Development is conversant with the topic of injecting water into aquifers for storage, as can be seen from the following quote: "In order to achieve cost-effective, sustainable and reliable water supplies sufficient to meet projected future demands for Texas, large volumes of water storage will be required. Storage above ground in surface water reservoirs is often problematic due to adverse environmental impacts; land requirements; high costs; and water losses due to evaporation, transpiration and siltation. ASR [Aquifer Storage and Retrieval] can provide a significant portion of the storage needed to meet that future demand. The existing ASR systems in Texas have shown that the technology is feasible using different water supply sources as well as in different types of aquifers and that the technical aspects of ASR are not the major factors inhibiting its implementation." (http://www.twdb.texas.gov/publications/reports/contracted_reports/doc/0904830940_AquiferStorage.pdf). The cost-efficiency of ASR in Texas can be expected to be no less than the cost-efficiency of the successful Orange County, California, project, given that costs in Texas are much less than in California for land, labor, and energy.

 

11. What will the pumping costs be? A related point is their cost estimates for water supply in this manner - what assumptions are underlying these cost estimates?

The cost of an ac-ft of water produced through the Desalination Hopscotch Plan was determined using standard industry estimates from the handbook “Desalination of Seawater” by the American Water Works Association [5] and the book “Groundwater Economics” [6]. We use the same assumption of water supply as the Vista Ridge Project: 50,000 ac-ft / year for 30 years.

Desalination water cost – $0.90 / m3 (264 gal) ($1,110 / ac-ft). The cost of desalinated water continues to go down. It has been reported that this cost could be as low as $0.50 / m3 ($617 / ac-ft).

Treatment costs – ($370,500,000) $0.10 /m3 at each of two locations ($247 / ac-ft). These costs are estimated for treating 50,000 ac-ft / year for 30 years at two locations: between aquifer A and B, and between aquifer B and C. This treatment might not be necessary depending on water quality of the two aquifers at the point of pumping/injecting from one aquifer to another in close proximity.

O&M costs – These are administrative costs ($175 / ac-ft), as stated in the Vista Ridge Project, and are assumed to be the same for both plans.

Pumping and injection costs – ($105,421,500) $0.0095 / m3 at each of six locations ($70 / ac-ft). These costs are estimated for pumping 50,000 ac-ft / year for 30 years. Average well depth is assumed to be 100 m (328 ft). In the three-aquifer example, we have one injection point and one pumping point per aquifer for a total of six pumping/injection locations.

Hopscotch pipeline costs – ($21,000,000) ($14 / ac-ft). Pipeline cost estimated at $175,000 / inch-mile; diameter in inches and length in miles. These costs are estimated for transporting 50,000 ac-ft / year for 30 years. We estimate a total of 10 miles of a 12-inch pipeline needed to implement the Desalination Hopscotch Plan for San Antonio.

 

12. Discuss the issue of the quality of the water and how it would be used. Desalinated water is not of drinking water standard, but ground water frequently is. (so replacing groundwater of a drinking water standard with desalinated water that can be used for a restricted range of uses will probably meet much resistance because like is not being replaced by like.)

We do mention on our proposal, that the water injected into the aquifers will be desalinated and treated to the same better quality than waters in the aquifers:

“Known methods of desalination, drilling, pumping, treatment, transport, and injection are used in a number of "hopscotch" steps that bring clean water from one aquifer to the next. Water quantity and quality are maintained or improved in each aquifer that is involved in the operation… The quality of the water injected [from Aquifer A] into Aquifer B is equal to or better than the quality level agreed upon by the interested parties.”

The process to make drinking water from desalination of water includes three steps (http://www.who.int/water_sanitation_health/publications/2011/desalination_guidance_en.pdf):

1) Pretreatment: coagulation and filtration are used to remove the organic matter and particulate.

2) Desalination: in the past the common method used was Flash distillation but new technology allows the use of Reverse Osmosis methods to remove dissolved solids.

3) Post treatment: desalinated water is disinfected and conditioned (i.e. blended and minerals added).

We also have contacted Dr. Wes Tunnel, a marine scientist at Corpus Crist campus of Texas A&M University who has dedicated more than 50 years to do research along the coast of South Texas. Dr. Tunnel responded that the desalinated water produced from water taken from the open ocean is safe to drink. However, there are some bay areas along the gulf where contamination could be an issue. Once the potential sites for the development of hopscotch are determined, evaluation of water quality will be made for each particular site.