7 Del. Admin. Code § 7301-7.0

Current through Reigster Vol. 28, No. 6, December 1, 2024

Section 7301-7.0 - Well Disinfection

7.1 General Requirements

7.1.1 Disinfection of all newly constructed or repaired wells, in accordance with subsection 7.2 is required, except as noted in subsection 7.1 .6 and 7.1.7.

7.1.1.1 After disinfection of each new, modified, or reconditioned public well, one or more water samples shall be submitted to a certified laboratory for microbiological analysis with satisfactory results reported to the Division of Public Health prior to placing the well into service.

7.1.2 After any repair or maintenance to the well, pumping equipment or piping, or other system components, those components shall be disinfected. For domestic wells, the entire plumbing system shall be disinfected.

7.1.3 Bacteriological sampling and testing after the repair or maintenance of potable wells is required. Disinfection shall be repeated until bacteriological results meet applicable standards.

7.1.4 Calcium hypochlorite (National Sanitation Foundation/American National Standards Institute (NSF/ANSI) Standard 60 Drinking Water grade or equivalent) shall be used for disinfection unless otherwise approved by the Department.

7.1.5 Continuous disinfection directly into a well while in service is prohibited.

7.1.6 Monitor wells shall not be disinfected without prior written approval of the Department except for monitor wells used for bacterial sampling.

7.1.7 Dewatering wells shall not be disinfected unless specifically required as a condition of the well permit.

7.1.8 The Department may require specific disinfection procedures for deep wells with a higher pH, turbidity, lower temperatures, iron, organic matter, ammonia, or other chemical constituents that interfere with disinfection.

7.1.9 New public wells shall not be put into service until they are tested and approved for use by the Division of Public Health.

7.2 Disinfection Procedures

7.2.1 The following procedures shall be followed when disinfecting wells, unless otherwise approved by the Department.

7.2.2 Calcium hypochlorite (NSF/ANSI Standard 60 Drinking Water grade or equivalent) sufficient for a dosage of at least 100 milligrams per liter (mg/L) free available chlorine shall be emplaced into the well screen.

7.2.3 After the pump has been installed, the chlorine solution shall be fed through the entire supply line to waste until chlorine is detected. If the concentration is less than 100 milligrams per liter (mg/L), more calcium hypochlorite (NSF/ANSI Standard 60 Drinking Water grade) shall be added to the well until such concentration is reached.

7.2.4 The inside of the well above the static water level shall be disinfected with the chlorine solution for 30 minutes. If granular disinfectant is used, the interior metal surfaces of the well casing above the static water level shall be inspected, and any granules shall be rinsed prior to closing the well.

7.2.5 If the well is connected to a public distribution system, the chlorinated water shall be pumped to the permanent disinfection unit, if present, or to the end of the water main where it is isolated from the remainder of the distribution system and can be blown off. The well contractor shall coordinate public distribution system disinfection with the Division of Public Health.

7.2.6 If the well is connected to a residential system, the chlorinated water shall be pumped until chlorine is detected at each tap, unless otherwise approved by the Department.

7.2.7 Disinfectant shall be in contact with the well components and any distribution system components, pursuant to subsections 7.2 .5 and 7.2.6, a minimum of 24 hours, and not to exceed 48 hours.

7.2.8 If the free chlorine residual is less than 5 milligrams per liter (mg/L) after 24 hours, the procedure pursuant to subsection 7.2 .7 shall be repeated. When the free chlorine residual is at least five milligrams per liter (mg/L) after 24 hours, the well and distribution system shall be pumped to waste.

7.2.9 Total chlorine must be absent from the system before collecting the bacteria sample.

7.2.10 Should the well fail to be disinfected as determined by the Department; the Department may require other measures such as re-disinfection, repair, or sealing.

7.2.11 The amount of calcium hypochlorite needed to produce a dosage of 100 milligrams per liter (mg/L) free available chlorine per 100 feet of water column is given in the following table:

Calcium Hypochlorite Needed to Dose 100 Feet of Casing Water at 100 mg/L

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*65 percent available chlorine. The higher the pH, the higher the dosing must be to achieve disinfection.

7.2.12 Notes

7.2.12.1 Read the calcium hypochlorite label carefully and follow all safety and storage instructions. Calcium hypochlorite should always be added to water. Never add water to calcium hypochlorite.

7.2.12.2 The use of calcium hypochlorite warrants strict adherence to all applicable safety measures and utilization of proper protective equipment. The Department assumes no liability attendant to the handling, use and storage of calcium hypochlorite.

7 Del. Admin. Code § 7301-7.0

20 DE Reg. 180 (9/1/2016)<linebreak/> 20 DE Reg. 374 (11/1/2016) (Final)