Water abstraction methods, routine well maintenance , use of chemicals in process, depth of drilling, pressure

Emily Mott made this Environmental Information Regulations request to Portsmouth Water Limited
You only have a right in law to access information about the environment from this authority


This request has been closed to new correspondence from the public body. Contact us if you think it ought be re-opened.

The request was successful.

Dear Portsmouth Water Limited,

With regard to drilling water abstraction wells in your catchment could you please further explain in detail, how you drill abstraction wells through the chalk and refurbish and maintain existing wells? I'm interested in wells in the Bedhampton /Havant Catchment area.

Please can you send details of the process including:
1. To what depth do you drill water abstraction wells?
2. Please specify type and quantity of drilling fluids used
3. What chemicals used to clean out the borehole and to maximise the flow of water?
4. Please list quantities and type of chemicals and acids used in the water abstraction process including volume . Please list volume percent Concentration of acid used ( for example is it HCl at 7% or 15%) Please list all chemicals used (corosion inhibitors, etc)
5. How do you put the treatment fluids into the ground and at what pressure?
6. Please list any biocides used in well maintenance and any other routine chemicals with volumes, concentrations and monitored annual usage.
7. Do you use a different drilling mud when drilling through chalk in Source Protection Zones
versus non protected zones?
8. Please can you send a list of all chemicals monitored/screened for ?
9. What dates were the abstraction wells used for the Bedhampton/Havant Catchment drilled?

Many thanks for your help answering these questions.

Emily Mott

H.Office@portsmouthwater.co.uk, Portsmouth Water Limited

--------------------------------

This is an automated response.

 

Thank you for contacting Portsmouth Water.  We
will endeavour to review and respond to your contact as soon as possible, and
undertake to action your e-mail within 5 working days if a query, or 10 working
days if a complaint that requires investigation.

If your contact is in respect of an emergency, due to a
problem with your water supply, water quality or a burst main, please contact
our 24 hour emergency line on 023 92 477999.  General queries can normally
be responded to immediately within office hours, 8-30am to 4-30pm Monday to
Friday, by calling 023 92 499888.

Head Office, Portsmouth Water Limited

1 Attachment

Dear Ms Mott,

Further to your request, please see the answers following each question.

With regard to drilling water abstraction wells in your catchment could you please further explain in detail, how you drill abstraction wells through the chalk and refurbish and maintain existing wells? I'm interested in wells in the Bedhampton /Havant Catchment area.

"The springs at Bedhampton (BED) and Havant (HAV) are artesian and other than collection chambers I am not aware of any wells or construction when first developed.

There are two boreholes at Lovedean WTW (LOV) that are within the catchment area for BED and HAV."

Please can you send details of the process including:

1. To what depth do you drill water abstraction wells?

"There are no wells or boreholes at BED and HAV.
The boreholes at LOV are at a depth of 138 metres."

2. Please specify type and quantity of drilling fluids used.

"There are no wells or boreholes at BED and HAV.
Standard practice for abstraction boreholes is to use a bentonite slurry as drilling fluid and the volume and viscosity will depend on site specifics, diameter, depth, ground conditions, etc."

3. What chemicals used to clean out the borehole and to maximise the flow of water?

"There are no wells or boreholes at BED and HAV.
Standard practice for abstraction boreholes is to use a 34% food grade Hydrochloric acid."

4. Please list quantities and type of chemicals and acids used in the water abstraction process including volume . Please list volume percent Concentration of acid used ( for example is it HCl at 7% or 15%) Please list all chemicals used (corosion inhibitors, etc)

"There are no wells or boreholes at BED and HAV.
The volume of 34% food grade Hydrochloric acid will depend on site specifics.
No other chemicals are used.
Before acidizing the borehole is air lifted to bring the chalk residue to the surface. "

5. How do you put the treatment fluids into the ground and at what pressure?

"There are no wells or boreholes at BED and HAV.
The 34% food grade Hydrochloric acid is pushed at low pressure from a tanker to the new borehole at the surface.
The top of the borehole is typically lined with a steel sleeve or a casing that is capped.
The 34% food grade Hydrochloric acid is not pumped in under pressure, the chemical reaction with the chalk causes the capped casing to pressurise.
The formation of CO2 forces the acid into the chalk fissures.
The pressure is managed by venting the system at the capped casing at the surface. "

6. Please list any biocides used in well maintenance and any other routine chemicals with volumes, concentrations and monitored annual usage.

"There are no wells or boreholes at BED and HAV.
No biocides or chemicals are used at our wells or boreholes at other sites."

7. Do you use a different drilling mud when drilling through chalk in Source Protection Zones versus non protected zones?

"No. We have not installed any boreholes inside a Source Protection Zones (SPZ) since their inception."

8. Please can you send a list of all chemicals monitored/screened for?

"The attached PDF details the standard monitoring in place for all abstraction sites."

9. What dates were the abstraction wells used for the Bedhampton/Havant Catchment drilled?

"There are no wells or boreholes at BED and HAV.
The springs at BED and HAV were first developed in 1859 for the public water supply.
The boreholes at LOV were constructed in 1964."

We hope the information provided is of assistance.

Many thanks,

Portsmouth Water