<p>In large intracontinental basins where the main rock formations are exposed in adjoining highlands and rare deeply buried within the basin itself.  The Madison Limestone is an example.</p>

<p>The Madison and its equivalent strata extend from the Black Hills of western South Dakota to western Montana and eastern Idaho, and from the Canada–United States border to western Colorado and the Grand Canyon of Arizona.</p>

<p>From <a href="https://en.wikipedia.org/wiki/Madison_Group" rel="nofollow noreferrer">Wikipedia</a>.</p>

<p>Ground-water ages vary from virtually modern to
about 23,000 yr. The 14C ages indicate flow velocities of
between 7 to 87 ft/yr. Hydraulic conductivities based on
average carbon-14 flow velocities are similar to those
based on digital simulation of the flow system (Downey,
1984).</p>

<p>From: <a href="https://pubs.usgs.gov/pp/1273f/report.pdf" rel="nofollow noreferrer">Geochemical Evolution of Water in the
Madison Aquifer in Parts of Montana,
South Dakota, and Wyoming
By JOHN F. BUSBY, L. NIEL PLUMMER, ROGER W. LEE, andEWJCE B. HANSHAW</a></p>

CC BY-SA 3.0
2017-10-26T14:16:16.280Z
Could you elaborate more about the reason for the existence of old gw in large intracontinential basins?
A Slow Learner
CC BY-SA 3.0
2017-10-26T13:05:33.323Z
2017-10-26T13:05:33.323Z
Earth Science Expatriate
<p>Virtually every oil / gas well contains old water. However , surface water , mixed with produced water, is injected in some to facilitate production .Last number I saw was that onshore wells in the US averaged 90 % water in the liquid phases.</p>

CC BY-SA 3.0
2017-10-26T17:12:24.633Z
2017-10-26T17:12:24.633Z
blacksmith37
<p>Where on Earth do we expect to find very old groundwater (infiltrated thousands of years ago)?</p>

CC BY-SA 3.0
2017-10-26T08:24:20.050Z
Welcome to EarthScience.SE! Are you looking for a specific geographic location or for a specific geological formation? Are you actually looking for groundwater or just for water, which has not been in contact with the atmosphere for thousands of years?
daniel.heydebreck
CC BY-SA 3.0
2017-10-26T12:49:46.890Z
I am looking for a geographical location. Thank you!
A Slow Learner
<groundwater><hydrogeology>
Where on Earth does paleo-groundwater exist?
A Slow Learner
# Where on Earth does paleo-groundwater exist?

(Asked by: username_0 on 2017-10-26)

Where on username_2 do we expect to find very old groundwater (infiltrated thousands of years ago)?

**Tags:** groundwater, hydrogeology

> **Comments:**
> **username_1**: Welcome to EarthScience.SE! Are you looking for a specific geographic location or for a specific geological formation? Are you actually looking for groundwater or just for water, which has not been in contact with the atmosphere for thousands of years?  
> **username_0**: I am looking for a geographical location. Thank you!  

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## 2 answers

### Answer by username_2 on 2017-10-26. Score: 1 | Accepted answer

In large intracontinental basins where the main rock formations are exposed in adjoining highlands and rare deeply buried within the basin itself. The Madison Limestone is an example.

The Madison and its equivalent strata extend from the Black Hills of western South Dakota to western Montana and eastern Idaho, and from the Canada–United States border to western Colorado and the Grand Canyon of Arizona.

From [Wikipedia](https://en.wikipedia.org/wiki/Madison_Group).

Ground-water ages vary from virtually modern to
about 23,000 yr. The 14C ages indicate flow velocities of
between 7 to 87 ft/yr. Hydraulic conductivities based on
average carbon-14 flow velocities are similar to those
based on digital simulation of the flow system (Downey,
1984).

From: [Geochemical Evolution of Water in the
Madison Aquifer in Parts of Montana,
South Dakota, and Wyoming
By JOHN F. BUSBY, L. NIEL PLUMMER, ROGER W. LEE, andEWJCE B. HANSHAW](https://pubs.usgs.gov/pp/1273f/report.pdf)

> **Comments:**
> **username_0**: Could you elaborate more about the reason for the existence of old gw in large intracontinential basins?  

---

### Answer by username_3 on 2017-10-26. Score: 1

Virtually every oil / gas well contains old water. However , surface water , mixed with produced water, is injected in some to facilitate production .Last number I saw was that onshore wells in the US averaged 90 % water in the liquid phases.


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