Laserfiche WebLink
III. COMMENTS -COMPLIANCE <br />Below are comments on the inspection. The comments include discussion of observations made <br />during the inspection. Comments also describe any enforcement actions taken during the inspection <br />and the facts or evidence supporting the enforcement action. <br />There was minor downcutting between the 1~` and 2°' checks immediately below theriprap segment; riprap <br />may be warranted in this location. <br />• Along the lower portion of the ditch (Segment 6), rock check spacing vazied from 66' to 75'. The <br />ditch was "V" shaped along this segment, and three cross sections were measured. Upper section, <br />d=2', tw=8'; middle section d=18", tw=9'; lower section d=14", tw=8' (at lower rock check). <br />RP-513 Clean Water Diversion Ditch <br />This is the undisturbed diversion ditch located to the west of Refuse Area SA. Diversion design specified <br />in Permit Illustration 6A is a "V" ditch, with d=2.52' and tw=10.09' (cross-sectional azea approximately <br />12.5 sq.ft). No riprap or rock checks aze specified in the design, with the exception that original design <br />specified a short riprap segment where the lower end of the ditch entered the deeply incised undisturbed <br />drainage arroyo. <br />The ditch has functioned effectively and is stable, however along most of its length the ditch is trapemidal <br />rather than "V" shaped. At a typical location, measured cross-section was d=2',bw=5', tw=8' (cross- <br />sectional area approximately 13 sq.ft.). The upper section of the ditch is lined with small diameter river <br />cobble, while the lower section of the ditch has a stable grass lined channel, with small cobble checks at <br />regular intervals. Neither the cobble liner nor the cobble checks aze specified in the approved design. The <br />cobble checks do not appeaz to be necessary or effective. At some locations, flow has skirted azound the <br />checks, causing minor channel side-cutting. The cobble checks should be removed or modified to prevent <br />side-cutting, by ensuring that cobble extends to each edge of the channel, and that the checks aze not higher <br />at the center than on their edges. <br />The terminal end of the ditch at the riprap transition into the steep sided arroyo has been a recurring <br />maintenance problem. During the inspection, it was noted thatheadctitting was again initiating in the <br />vicinity, and a modification to the design was discussed. 7'he rriodification entails termination of the <br />diversion at a point 200' to 250' upgradient from the arroyo, with minor grading to direct ditch flow into a <br />low gradient natural drainage. This plan was subsequently submitted by the operator as Minor Revision <br />124, and approved by DMG on 4/10/02. The operator stated within the revision Urat "at the point where the <br />existing diversion empties into the lazger drainage the area ofdowncutting will be regraded to blend into <br />the adjacent azea. A slight berm will be placed azound this depressed azea to keep runoff from further <br />eroding this site. All portions of the diversion that will be eliminated will bereseeded." <br />Refuse Area RP-] <br />RP-1 perimeter containment ditch locations aze depicted on Map 77, and designs aze specified on Map 78 <br />and within Permit Illustration 4. There aze minor discrepancies among the different pemtit designs, and an <br />appazent discrepancy with respect to the location of the lower segment of the west perimeter ditch, between <br />Map 77 and the actual on-the-ground ditch. <br />West Perimeter Ditch <br />The upper, low gradient section of the west ditch is located at the immediate base of the refuse pile slope, <br />as depicted on map. The ditch is a stable vegetated channel, "V" shaped with d=2'; tw=9', which exceeds <br />