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<br />operation in full compliance with the evaluation criteria specified on page A-7 of the oversight <br />Agreement, which defines the limit of the OSM oversight rcview, <br />Although there were no indications of impending massive failure of either fill structure at the time <br />of the field review, several concerns were identified regarding long-teim stability. (See the <br />Findings section.) <br />Maintenance could improve the stability of RDA runoff control system. <br />Several topics for future oversight reviews are recommended. (See report recommendations.) <br />Recommendations <br />Present Fill Structure: <br />Because of the wording in the oversight Agreement, OSM cannot justify requiring DMG to _ <br />address the long-term-stability concerns of this report. However, it is believed that the following `` <br />actions would improve the stability of the RDA: <br />• The structure should be graded to allow drainage away from the fill slopes and to the side <br />drains, without any low spots so as to eliminate small depressions. <br />• The downdrains should be evaluated by a registered professional engineer to determine <br />the measures that are necessary to ensure long-term stability. <br />• On sloping areas where vegetation has nut been reestablished because topsoil is moving <br />down slope, measures should be taken to prevent slippage. <br />• The most important remedial measure that should be addressed at this site is the need to <br />minimize the surface runoff that is flowing down the GIl structure. Undisturbed runoff <br />above the RDA should be routed into drainage ways outside the valley fill. The top the <br />present fill stnicture should he graded to prevent runoff erosion. <br />• In general, vallty fill structures should be designed by a registered professional engineer. <br />Because of its size, it is especially important to have the RDA designed by a qualified <br />registered professional engineer. An engineered design would consider all natural and ~~ <br />man-made hazards (e.g., potential subsidence effects) that could affect long-term stability, <br />specify inspections and testing requirements needed during construction, and explain what <br />monitoring is necessary to detect problems. <br />Future OSM fh+ersi~t Reviews: <br />OSM should consider evaluating the following topics in future oversight evaluations: <br />Certified Eng?neercd Designs <br />S iE ttt90IA7.F.'A6 -w c n wtnn~tt• is-a~-~ •ia n~c <br />