Wells & Drinking Water Safety

Why Groundwater Protection Matters for Our Region

Groundwater is a critical resource in northwestern Comal County. While most Mystic Shores residents receive treated surface water from Texas Water Company (TWC), several nearby communities rely heavily on private wells and public‑supply wells drawing from the Middle Trinity Aquifer, particularly the Cow Creek Formation.

Several wells sit near the Canyon Ranchoutfall, along the flow path where infiltration may be rapid and unpredictable.

This page summarizes which wells are vulnerable, how wastewater can reach them, and why groundwater protection is a regional concern.

Communities That Rely on Groundwater

Mystic Shores

• Most residents receive treated surface water from Texas Water Company.

• A small minority of owners have private wells.

  • Some of the Mystic Shores wells are positioned adjacent to Devils Hollow or near the confluence with the Guadalupe River. These wells are not numerous, but they could be affected by infiltration moving through the dry channel or by subsurface flow entering the riverbed. 

  • Other wells are lateral to the flow path and may be less vulnerable than wells near Devils Hollow.

Cypress Cove (Highest Vulnerability)

Cypress Cove Water Supply Corporation operates multiple public‑supply wells, including:

• • • One well ~1.5 miles downstream of the outfall is quite vulnerable.

    • Two additional wells are near Devils Hollow, closer to the flow path.

These wells serve 731 households.

The well closest to the outfall (among Cypress Cove wells) has:

• • • cementing only from 0–42 ft,

    • an open borehole below that depth,

    • direct exposure to Cow Creek recharge pathways.

This well — and the other Cypress Cove wells downstream of Devils Hollow — are direct receptors of infiltration risk.

Cross Canyon Ranch

Cross Canyon Ranch is a large‑lot community consisting of approximately 65 properties, generally ranging from 12 to 25 acres. Development began in 2006, and the wells within a 3 mile radius of the Canyon Ranch outfall were drilled between 2016 and 2024, not older or shallow construction.

About half of the properties rely on private domestic wells, while the remainder use Texas Water Company. Many parcels maintain wildlife management or agriculture exemptions, so wells support not only household use but also livestock water and wildlife habitat.

These wells are located in the Trinity Aquifer contributing zone. While they sit on high ground, there is no confirmed fracture connectivity linking them to the Devils Hollow flow path. Their vulnerability is moderate because these wells are up‑gradient and in the contributing zone, and outside the Devils Hollow flow corridor .

Canyon Oaks Estates

Canyon Oaks Estates is a smaller-lot community, believed to rely entirely on private wells with no Texas Water Company service in the subdivision. 8 wells (190-400 feet deep) are located within a 3-mile radius of the Canyon Ranch outfall. The neighborhood sits west of the Devils Hollow flow path in the Trinity Aquifer contributing zone. Because of this positioning, their vulnerability is moderate, not high. They are part of the broader Trinity contributing zone, meaning they could be affected by long‑term regional aquifer impacts — but they are not among the wells most likely to receive early infiltration from the Canyon Ranch discharge. 

Future Domestic Wells in the Trinity Contributing Zone: Canyon Lake Ranches LLC (~709 acres)

Canyon Lake Ranches LLC is a planned 709‑acre development located west and north of the Canyon Ranch outfall, outside the Devils Hollow flow corridor and within the Trinity Aquifer contributing zone. 1–10 acre homesites are planned, making it an acreage‑style community. Dozens of new domestic wells may eventually be drilled.

Their vulnerability is low to moderate, and primarily regional, not direct.

Why Wells Are Vulnerable in This Region

1. Karst Terrain

Water moves rapidly through:

• conduits

• voids

• dissolution features

• unpredictable underground pathways

Karst bypasses natural filtration.

2. Exposed Cow Creek Formation

Inside the Nature Preserve, Cow Creek is at the surface, meaning:

• wastewater has direct contact with drinking‑water limestone,

• infiltration is fast,

• fractures provide direct pathways into the aquifer.

3. Trinity Aquifer Recharge Zone (Flow Path, Not Outfall)

The flow path downstream of the outfall enters the Trinity Aquifer Recharge Zone, where:

• Cow Creek actively recharges,

• faults and fractures accelerate infiltration,

• no special protections exist (unlike the Edwards Aquifer Recharge Zone).

4. Faults & Fractures

Ron’s field observations show:

• vertical fractures,

• dissolution‑enlarged cavities,

• caves forming along fracture planes,

• parallel fracture sets in the dry Guadalupe River bed.

These features allow wastewater to reach wells quickly.

5. Dry‑Creek Discharge

Devils Hollow is dry most of the year. Wastewater in a dry channel:

• spreads out,

• pools,

• infiltrates,

• finds fractures,

• moves underground.

6. Shallow Cementing in Some Public‑Supply Wells

The Cypress Cove well closest to the flow path has:

• shallow cementing,

• an open borehole below 42 ft,

• direct exposure to Cow Creek recharge pathways.

The Takeaway

Groundwater protection is not just a Mystic Shores issue — it is a regional drinking‑water issue affecting multiple communities.

Wastewater discharged into Devils Hollow may:

• infiltrate,

• move through fractures,

• reach Cow Creek,

• enter the Trinity recharge zone,

• threaten downstream wells, particularly in Cypress Cove and those Mystic Shores wells adjacent to the flow path,

• potentially migrate into the Edwards aquifer.

The permit does not account for this complexity.

Protecting wells means protecting the aquifer. Protecting the aquifer means protecting the region.