Creating an aquifer model with only top depth values

[JoshM]

I am trying to use some water level data to build an aquifer model. Since it is considered an unconfined aquifer, I am using water levels taken from monitoring wells. However, I only have the depth values for the top of the surface and it appears that the aquifer model tool in Rockworks requires a bottom depth as well. I would like to make the aquifer extend down to the top of a surface that represents a confining unit. I have a grid for the confining unit surface, but I don't know how to make the aquifer unit extend to reach the confining surface. How do I go about doing this?

[Molly]

Hi Josh,

Can you look at the depth to the top of the confining surface as listed in your Stratigraphy table, and enter that as the base depth for the water level for each hole?

Molly Mayfield

RockWare Inc

[JoshM]

In this case I can't do that, because the confining surface picks come from CPT borehole data, and the water level data comes from monitoring wells.

[Molly]

Here is a thought: Assuming you have an RwGrd file in the project which represents the surface along the top of the confining unit, RockWorks can calculate "residuals" to that elevation from the top of each monitoring well:

1. In the Borehole Manager, disable all of the holes other than the monitoring wells.

2. Use the Borehole Manager's File | Transfer | Locations to Utilities Datasheet menu option to transfer the Enabled Only holes to the datasheet.

3. Select the Utilities | Grid | Statistics | Residuals menu option.

4. Set the Input Columns (along the left) to the Easting, Northing, and Elevation column. (Or choose Collar Elevation if that is where your water level tops were measured from.)

5. Set the Output Columns to any currently unused columns (e.g. "11" and "12").

6. For Grid Name, browse for the name of the RwGrd file which represents the top of the confining unit.

7. Click Process.

RockWorks will calculate the elevation where each borehole would intersect that confining surface and store that in the "Predicted Elevation" column. It will also calculate the difference between the surface elevation or collar elevation column (which you input in step 4 above) and that predicted elevation, giving you the depth from the top of the hole to that unit. If those numbers look right (e.g. the surface grid is good, the input columns were entered correctly, etc.) you can then enter those depths into the Water Levels table as the aquifer base for the monitoring wells.

You should probably use the Borehole Manager's File | Backup Database before making the changes to the Water Levels table, never hurts.

Molly Mayfield

RockWare Inc

[JoshM]

Using the "Utilities | Grid | Statistics | Residuals menu option" method works. I just added the depths to the depth2 column in my Aquifer table and re-imported the table into Rockworks.

Thanks so much for your help.