The Secondary Water Supply for Laredo? The Problem: • The Rio Grande is not infinite! • The City of Laredo has rights to about 40 mgd • ALSO CONSIDER DROUGHT - Falcon and Amistad as of late has recorded record low volumes of water So there is a clear need to develop a secondary water supply for the City of Laredo.

Some Geology: Since our water supply is surface-based, which is subject to our highly variable climate it makes sense to consider groundwater as a potential secondary water source. To understand groundwater one must know a little geology Relevant Terms: Superposition Regional Dip Recharge Area Porosity Permeability

Webb County Geology

The Possibilities: Edwards/Trinity Aquifers (Using the Rio to transport the water from Kinney County) Laredo/Carrizo Aquifers (Within 10 miles of the city) Carrizo Aquifer (Northwest Webb County) Carrizo Aquifer (Dimmit County) Major Difficulties: There are significant problems with all of these possibilities is that the cost is 3 to 6 times more than obtaining and treating water directly from the Rio Grande.

Edwards/Trinity Aquifers (Using the Rio to transport the water from Kinney County) Problem: Effectiveness depends on maintaining minimum flow within the Rio Grande Does not help during Drought situations

Webb County Geology

Laredo/Carrizo Aquifers (Within 10 miles of the city) Problem: High Total dissolved Solid (TDS) content. Can not drink this water! Need desalination plan

Laredo/Carrizo Aquifers (Within 10 miles of the city) Main Problem: For desalination to be cost effective need aquifers with very high permeabilities and hydraulic conductivities • NEED MINIMUM OF 5 MGD The Laredo/Carrizo aquifers in the Laredo area have relatively low hydraulic conductivities. • Can not pump water out of these aquifers at needed rates Other Issues: Pipeline Interstructure Brine Disposal Depletion of Aquifers - VERY LOW RECHARGE RATES < 1 in/yr

Carrizo Aquifer (Northwest Webb County) Transfer of water by: Rio Grande River (Note Previous Objections) Pipeline (Nearly doubles cost) Water quality not as good as Carrizo water from closer to the recharge zone in Dimmit County Carrizo Aquifer (Dimmit County) Political Cooperation with Dimmit County may be difficult

Webb County Geology

Thinking Outside the Box: Interbasinal Water Transfers • Perhaps from eastern Texas Q: What is the problem with this concept especially during a drought? Aquifer Storage and Recovery • Pump Rio Grande water into local aquifers (Laredo/ Carrizo) - Problems - Clogging of Wells SILT CALCITE ENCRUSTATION

Storage of Water in Lake Casa Blanca • Pump Water from Rio Grande into Lake Casa Blanca Good as only a short- term solution Also, excessive evaporation during severe drought conditions can rapidly deplete this resource

¿Aqua por colonias?