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(d) Landfill Closure Deadline—For landfill Units subject to the CIWMB-promulgated provisions of this <br /> division,any closure deadline extensions the discharger proposes to the EA(under 421110)shall be effective only <br /> after concurrence by the RWQCB. <br /> (e) Final Cover Surveys. <br /> This subsection[i.e.,through&(e)(3)]applies only to landfills,or portions thereof,that are final-closed after July <br /> 18, 1997. <br /> (1) Initial Survey and Map—For a closed landfill(including a surface impoundments or waste pile closed as <br /> a landfill),upon completion of all closure activities for the Unit[or portion thereof,pursuant to&(b)(1)(D)],the <br /> discharger shall conduct an aerial photographic survey[or alternative survey under&(e)(3)] of the closed portions of <br /> the Unit and of its immediate surrounding area,including at least the surveying monuments[of f20950(d)].The data <br /> so obtained shall be used to produce [or to augment,in the case of incremental closure under&(b)(1)(D)] a <br /> topographic map of the site at a scale and contour interval sufficient to depict the as-closed topography of each <br /> portion of the Unit,and to allow the early identification of any differential settlement,pursuant to&(e)(2).For <br /> landfills undergoing incremental closure[under&(b)(1)(D)],the survey for each closed portion of the landfill shall <br /> be carried out immediately following completion of closure activities for that portion of the landfill;such data shall <br /> be used to create or augment a map showing the closure date and as-closed topography of each portion of the Unit. <br /> The map produced pursuant to this paragraph shall act as a base-line against which to measure the total settlement, <br /> through time,of all portions of the final cover since the date when that landfill,or portion thereof,was closed.Upon <br /> completion of this topographic map(or,in the case of incremental closure,of each revision thereof),the discharger <br /> shall submit a copy to the RWQCB,the CIWMB,and the EA. <br /> (2) Five-Yearly Iso-Settlement Map—At least every five years after completing closure of the landfill[or of <br /> the last remaining portion,for landfills undergoing incremental closure under&(b)(1)(D)],the discharger shall <br /> produce and submit to the RWQCB an iso-settlement map accurately depicting the estimated total change in <br /> elevation of each portion of the final cover's low-hydraulic-conductivity layer.Therefore, for each portion of the <br /> landfill,this map shall show the total lowering of the surface elevation of the final cover,relative to the baseline <br /> topographic map [of&(e)(1)],and shall indicate all areas where visually noticeable differential settlement[noted <br /> under&(e)(4)]may have been obscured by grading operations.The map shall be drawn to the same scale and <br /> contour interval as the topographic map under&(e)(1),but showing the current topography of the final cover and <br /> featuring overprinted isopleths indicating the total settlement to-date.The RWQCB shall apply the requirements of <br /> this paragraph only to a closed landfill which the RWQCB finds is likely to undergo differential settlement of such <br /> magnitude as to impair either the Unit's containment features(e.g.,final cover)or the free drainage of surface flow. <br /> [Note: The RWQCB's choosing to forego requiring iso-settlement mapping for the purpose of water quality <br /> protection does not preclude the ClidWIEA from requiring such mapping for other purposes(e.g.,structural <br /> integrity considerations regarding a building sited on top of the closed landfill);see 121142(b).J <br /> (3) Alternative Surveying Techniques—The RWQCB can approve the use of any alternative technique(to an <br /> aerial survey)for producing the maps required by&(e)(1 &2),so long as the maps so produced meet the <br /> performance standards of&(e)(1 &2). <br /> (4) Tracking Differential Settlement—Prior to conducting periodic grading operations on the closed landfill <br /> [under&(b)(1)(A)],the discharger shall note on a map of the landfill the approximate location and outline of any <br /> areas where differential settlement is visually obvious.Each five-yearly iteration of the iso-settlement map[under <br /> &(e)(2)]shall show all areas where differential settlement has been noted(under this paragraph)since the previous <br /> map submittal,and shall highlight areas of repeated or severe differential settlement.Map notations and delineations <br /> made pursuant to this paragraph need not be surveyed,so long as all areas where differential settlement was visually <br /> identifiable prior to regrading can be relocated. Such notation and delineation shall be made by,or under the <br /> supervision of,a registered civil engineer or registered geologist. <br /> (f) Optional Clean-Closure—Notwithstanding any other SWRCB-promulgated closure or post-closure <br /> maintenance requirement in this subdivision,a discharger proposing to clean-close a landfill shall submit a clean- <br /> closure plan meeting the requirements of this subsection.[Note: see also CIWAM s additional landfill clean-closure <br /> requirements under 121810.] The purpose of clean-closure is to render the landfill(including all surrounding <br /> environs contaminated by waste released from the landfill)no longer capable of posing a threat to water quality.The <br /> purpose of a clean-closure plan is to propose a series of actions,including an accurate estimate of the cost of each <br />