Conceptual Framework for Evaluating the Impact of Inactive Wells on
Download
1 / 19

Conceptual Framework for Evaluating the Impact of Inactive Wells on - PowerPoint PPT Presentation


  • 107 Views
  • Uploaded on

Conceptual Framework for Evaluating the Impact of Inactive Wells on Public Water Supply (PWS) Wells. Rick Johnson Oregon Health & Science University. Inactive Well. PWS Well. Aquitard. Downward vertical gradients are often created near PWS wells in confined aquifers

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Conceptual Framework for Evaluating the Impact of Inactive Wells on ' - ashton-conway


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Conceptual Framework for Evaluating the Impact of Inactive Wells on

Public Water Supply (PWS) Wells

Rick Johnson

Oregon Health & Science University


Inactive Well Wells on

PWS Well

Aquitard

  • Downward vertical gradients are often created near PWS wells in confined aquifers

  • Many inactive (e.g., irrigation) wells are screened across aquitards

  • Under these conditions the inactive wells will leak water to the confined aquifer


Numerical Model of Inactive Well Impacts Wells on

Inactive Well

PWS Well

Unconfined Aquifer

100 m

Confined Aquifer

3000 m

8000 m

Aquitard=10 m thick


Key Definition: 10-Year Capture Zone Area (CZA) Wells on

PWS Well

3000 m

10-year capture zone

8000 m


) Wells on

16

2

14

12

10

High

10-Year Capture Zone Area (km

8

6

Medium

4

2

Low

0

0

1.5

3

4.5

Pumping Rate (mgd)


0.20 Wells on

Low

0.16

0.12

High

Fraction of PWS Well Flow

0.08

0.04

0.00

0

500

1000

1500

2000

Distance from PWS Well

Contribution of water to PWS from inactive well significant!


Why is the inactive well contribution “constant” for different pumping rates?

One reason is that vertical gradient increases as pumping increases

0.16

High

0.14

0.12

0.1

Vertical Hydraulic Gradient

0.08

0.06

0.04

Low

0.02

0

0

500

1000

1500

2000

Distance from PWS Well (m)


  • CONCLUSIONS FOR A SINGLE PWS WELL different pumping rates?

  • Flow through even a single inactive well can be a significant fraction of the total flow through a PWS well

  • The contribution of the inactive well to total flow is roughly constant

  • The contribution of the inactive well does not depend strongly on the location of the inactive well within the capture zone of the PWS well.



3000 m different pumping rates?

PWS Well

8000 m

To examine the effect of multiple wells, we can use the simplified case of a continuously-operating PWS well surrounded by 8 seasonally-inactive irrigation wells

  • PWS well flow = 1.5 mgd

  • Irrigation wells on a 1-km grid each pumping at 0.75 mgd for 6 months of each year


  • Assume wintertime recharge different pumping rates?

  • Assume summertime recharge from irrigation in 1 km2 area surrounding each well

10-year capture

zone area

3000 m

Summertime recharge due to irrigation

8000 m


As with the single well case, the inactive well has a significant impact on total PWS Well flow

0.2

0.15

Fraction of PWS Well Flow

0.1

0.05

0

0

500

1000

1500

2000

Distance from PWS Well (m)


1.00 significant impact on total PWS Well flow

0.80

0.60

in Confined Aquifer

Fraction of Leaked Mass Retained

0.40

0.20

0.00

0

500

1000

1500

2000

Distance from PWS Well (m)

How much water leaked into the confined aquifer is pumped out by irrigation wells? Almost None!


0.2 significant impact on total PWS Well flow

0.15

Coming from Confined Aquifer

0.1

Fraction of Irrigation Water

0.05

0

0

500

1000

1500

2000

Distance from PWS Well (m)

Why does so much mass remain in the confined aquifer?

Because most of the irrigation water comes from the unsaturated aquifer


10 significant impact on total PWS Well flow

8

6

Volume Leaked/ Volume Pumped

from Confined Aquifer

4

2

0

0

500

1000

1500

2000

Distance from PWS Well (m)

Another way of looking at this is that the volume of water leaked to the confined aquifer is 2-6 times greater than volume pumped from the confined aquifer.


  • CONCLUSIONS FOR A PWS WELL AND MULTIPLE SEASONALLY-INACTIVE IRRIGATION WELLS

  • The 10-year CZA is reduced somewhat by the irrigation wells

  • The fraction of the total PWS well flow coming from a single irrigation well is still significant.

  • The fraction does not vary much with distance from the CWS well

  • Nearly all of the water leaking into the confined aquifer during inactive periods remains in the confined aquifer.


  • Next Steps: IRRIGATION WELLS

  • To put the magnitude of the inactive well problem in perspective:

  • We need to better understand the density of inactive wells in the vicinity of PWS wells

    • The kind of detailed well-distribution data shown for the York case is being examined at other locations by NAWQA


  • Next Steps (cont): IRRIGATION WELLS

  • 2. We need to better understand the probability that inactive wells are delivering contaminants to the confined aquifer and the PWS well.

  • Water quality data at the PWS and from monitoring wells is helping to determine this

  • Environmental tracers from the PWS can be used to estimate the potential impact of inactive wells



ad