 ACCEPTANCE AND RECOMMISSIONING OF GSTs
PURPOSE
The purpose of the Ground Storage Tank (GST) acceptance Code of Practice is to establish a standardized method
and means by which the operations and engineering teams will disinfect and test a GST to be placed back into
service after construction, maintenance or repair.
STATEMENT
These directions apply specifically to the disinfection of GST’s following their construction, maintenance or repair
in order to destroy any bacteriological contamination incidental to such work. It is extremely important to assure
that no bacteriological contamination exists during this process in order to assure there is no introduction of
contamination into the distribution system.
PROCEDURE
After a new construction, maintenance or repair of a GST, the contractor shall follow the necessary steps before the
tank is introduced into the system:
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After completion of work in the tank, the contractor shall assure the walls and bottoms of the structure
are thoroughly cleansed to remove all dirt and loose material. A visual inspection by Global staff is
required on completion of this cleaning activity.
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The disinfection method is obtained from ADEQ Engineering Bulletin #8 for Disinfection of Water
Systems. This method consists of direct application of a strong chlorine solution to the inner surfaces
of the structures. The strong chlorine solution may be prepared by dissolving one ounce of chlorinated
lime (25% available chlorine) to each ten gallons of water or one ounce of Calcium Hypochlorite (70%
available chlorine) to each twenty-six gallons of water. The powder should be made into a paste and
then added to the water. If liquid bleach or sodium hypochlorite is used, solutions of 200mg/L
available chlorine are required. This strong solution is sprayed over the inner surfaces of the empty
structure by using a fruit-tree spraying type of equipment or the solution may be applied with
whitewash brushes. The surface should remain in contact with the strong solution no less than thirty
minutes before the structure is filled with water.
NOTE
The disinfectant procedure shall be accomplished in the presence of a
Global Water employee. If liquid chlorine is the choice of disinfectant, the
liquid shall be NSF certified. |
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Prior to filling the GST with water, the chlorine injection shall be adjusted to achieve a 3 ppm Cl2
concentration in the fill water. This concentration level will further assure the destruction of any
possible bacteriological pollution while allowing a buffer of 1ppm so as not to exceed the maximum
Code of Practice: GWR-CP-EX-016
Revision: GWR-CP-EX-016 (001) Responsible Agent: Operations & Compliance
Confirm Revision Prior to Release Page 2 of 3
chlorine concentration allowable (4 ppm). The GST shall be filled to the top of the structure until an
overflow condition is achieved.align="center"
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The tank shall stand filled with chlorinated water for 24 hours. After the 24 hour period, the first set of
two samples shall be pulled. Dependant on sample tap availability, the sample may be pulled at either
a sample tap, at the opening of the hatch by dipping the sample container or at the overflow assuring
the sample is a clean catch and ensuring there are no rust or other particles visible in the water. The
water in the tank shall be checked for Free and Total Chlorine during sampling and noted on the
laboratory chain of custody.
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48 hours after the tank has been filled and 24 hours after the first samples have been pulled, another set
of samples should be pulled for bacteriological analysis and chlorine testing.
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If both sets of bacteriological samples test negative, the tank can be introduced into the system for
service.
NOTE
The contractor shall provide a certificate of the
disinfection procedure for record. |
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If any of the bacteriological samples test positive, a determination will be made as to whether or not
the tank will need to be drained and inspected for probable causes of contamination. If the tank is
drained for further maintenance, the procedure must be repeated.
|
FINAL ACCEPTANCE
All data must be reviewed by the Compliance Department prior to final acceptance that all procedures were
REVISIONS
| Date |
Revision Number |
Revisions |
OPI |
| 30-Mar-06 |
ORIGINAL (000) |
|
SA |
| 15-Nov-06 |
001 |
General review and re-number |
GSS |
|
