The county board of health of any such county may promulgate specifications, rules and regulations governing septic tanks and their installation which shall accord with approved engineering standards in general and shall contain the following standards and requirements in particular:

(1) No septic tank shall be installed which has a net liquid capacity of less than five hundred gallons;

(2) The length of each tank shall be at least two but not more than three times the width;

(3) The uniform liquid depth of each tank shall be not less than two feet six inches; and

(4) The theoretical detention period of each tank shall be not less than twenty-four hours based upon the average daily flow.