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GENERAL33253
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Entry Properties
Last modified
8/24/2016 7:55:20 PM
Creation date
11/23/2007 7:35:22 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981039
IBM Index Class Name
General Documents
Doc Date
6/10/1998
Doc Name
INTEROFFICE MEMORANDUM GRASSY GAP RECLAMATION WORK
From
JANET BINNS
To
DAN HERNANCEZ
Permit Index Doc Type
RECLAMATION PROJECTS
Media Type
D
Archive
No
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<br />Interoffice 1`4emorandum <br />\\~alker to Bimts <br />luh ].1998 <br />Page 2 of 2 <br />older slide. At near the same elevation, the crest escarpments of the newer slide are shown in <br />Pictures 9 and 10. There is rill and gully erosion of reaches abo+e the escarpments (directly <br />below the hiuh-flow discharge from the pond priman spilh+~aY..4hhoueh this rill and gully <br />erosion is most pronounced above the southern slide, it extends for some distance to the north. <br />and for a short distance to the south across the slope. The Wrote extensive erosion features are <br />directly below the dischazge of the primary spilh+~ay barrel of the pond. There is a baffle plate. <br />half +vay up the barrel outlet. with a 6" dianteter pipe and plastic downspout sleeve from the <br />barrel down the slope. The sleeve discharges at the crest of the slide (you are standing at the <br />discharge outlet of the sleeve in Picture 10). The soils and talus debris appeaz to be permeable. <br />There was a sinl: hole approximatel}' 6 feet in front of you in Picture 9, near the center of the <br />escarpment in Picture 10. <br />There is a depression below the base of the priman~ spillway riser in the pond (Picture 8). The <br />riser is tilted slight]}• out of plumb. away from the embankment. A concrete`mushroom' at the <br />base indicated a spreading of concrete on an original surface during construction. This <br />depression could be the result of excavation afrer construction. subsidence, or loss of fines <br />(pumping) b}• seepage through the embankrrtent. Of these three. the last two are most like]}•. <br />There was no evidence of spoil material indicating excavation. During construction, the base of <br />the embankment was likely compacted. However, areas under the barrel may not have been <br />proper]}' compacted. There was no flo+v into or out of the depression below the riser at the time <br />of inspection (water level in the pond was at orjust below this elevation). I saw no indication of <br />seepage or loss of fines contiguous to the barrel, but my inspection was limited to the access <br />provided on the southern portion of the inlet side and heavil}• vegetated areas of the outslope. I <br />saw no indication of embankment failure. <br />The geology. topography, and mining history of the site suggest the area is predisposed to <br />sliding. Seepage through the pond embankment or bottom. and the primary riser discharges. <br />appear to have abetted the current slide. The potential for additional sliding is high. higher if the <br />pond is left in place. <br />.additional sliding. or failure of the pond, do not appear to presen[ a threat to life or pmpeny. <br />Continual sliding does impose a potential for temporary degradation of water qualm or mud- <br />flo++ dammin_ of the creek. 1`1ud flows hare. and would likeh continue to. reach the creek (see <br />Picture ~). Such damming is not lil:elv to endanger the road. The slide has scoured the slope to <br />bedmcl: (Picture 6). There just isn~t a lot of material [o font a substantial dam across the valle+. <br />Should the dart be retained. 1 suggest: grouting of the base of the priman riser to arrest loss of <br />materials under the riser and throu_~h the embanl:ntent, and to pre+ent failure of structu;~I <br />elements of the riser. lining the pond +vith hentonite; and replacement of the exit low-flo++ <br />dscharge plastic tuhe with -ttetal wipe. and the extension of the exit pipe to the base of the slope. <br />
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