10.—(1) In cases where the requirements of paragraphs 6 to 9 are met but an odour nuisance exists, an investigation shall be undertaken to identify and evaluate the sources and causes of the odour.
(2) Based upon the results of this investigation a detailed review shall be undertaken of the available options to control the odour release in order to avoid odour nuisance and to define the measures that represent the best practicable means for control of odour at the particular WWTW.
(3) The review carried out under sub paragraph (2) shall include (but is not limited to) the requirements set out in paragraph 11 and shall include consideration of financial implications as detailed in sub paragraph (7) and the environmental impact.
(4) Details of the investigation carried out under sub paragraph (1) and of the review carried out in accordance with sub paragraphs (2) and (3) shall be documented in an OIP.
(5) The OIP shall identify a phased investigation programme including defined dates for delivery of reports and other outputs, and may be prepared in a number of phases.
(6) The first phase of the OIP should contain–
(a)a preliminary plan which identifies and evaluates the likely sources and causes of odour nuisance following an investigation carried out under sub paragraph (1); and
(b)a timetable for the submission of plans for subsequent phases,
and shall be approved by the relevant local authority.
(7) The compliance timescales and the extent of the measures to be implemented in subsequent phases of the OIP shall take account of the phased approach of the OIP and the analysis of costs (including avoided costs) and benefits set out in sub paragraph (9) and shall be approved by the relevant local authority.
(8) The approach to odour control taken in the OIP shall be based upon a phased implementation of additional measures according to the following hierarchy:–
(a)the instigation of operational and/or waste water treatment process changes to prevent, where practicable, and, in any case, to minimise, the conditions that result in odour release;
(b)where operational changes are not appropriate the odour sources shall be reviewed to identify possible measures to contain emissions within the process equipment; and
(c)where emission reduction by operational change or containment is not sufficient to prevent odour nuisance, methods for enclosure of odour sources linked to the use of extract ventilation to control the emissions in accordance with paragraph 12 and, where necessary, the provision of end-of-pipe treatment of the exhausted air in accordance with paragraph 13, shall be reviewed.
(9) The control measures identified shall be subject to an assessment based upon costs (including avoided costs) and benefits to ensure that the selected measures are proportionate and represent the best practicable means.
(10) Where an odour nuisance existed immediately before and continues on 22nd April 2006, an investigation shall be undertaken to identify and evaluate the sources and causes of the nuisance (notwithstanding that the requirements of paragraphs 6 to 9 are not yet being met) and the first phase of the OIP as described in sub paragraph (6) shall be prepared and submitted to the relevant local authority for approval.