After the pump has been installed, all domestic wells shall be disinfected with a solution containing at least fifty (50) parts per million available chlorine, which shall remain in the well for a period of not less than twenty-four (24) hours or by an equivalent method of disinfection satisfactory to the building official, and such procedure shall be repeated on all public domestic wells as necessary to produce water which will yield negative results on two consecutive biological samples tested in the manner prescribed in Section 13.16.530. The gravel used in domestic gravel packed wells shall be disinfected by mixing one-half pound of tablets containing seventy (70) percent available chlorine with each tone of gravel introduced to the well. The chlorine tablets shall be evenly distributed throughout the volume of gravel used. (Prior code § 7809)