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PRS Erosion Matrix Score Assessment Date Structure Mesa Top Bench Canyon Floor Channel Topography Explanation Ground Explanation Slope Explanation Runoff Evidence Channelized Channel Description Runoff Wetland Runoff Other Terminus Explanation Runoff Explanation Structure Run-On Structure Explanation NPDES Run-On NPDES Explanation Natural Run-On Natural Run-On Explanation ESH-18 Representative BMP Prescription BMP Description Not BMPs Sediment Comments 55-009 10.6 3/3/1998 55-263 YES NO NO NO Inactive monitoring station/sump located in northern TA-55. Enclosed, asphalt surrounding. Flat. NO NO Covered pit with concrete curbing. Mortandad tributary is north of PRS YES Adjacent parking lots. NO NO S. Veenis Concrete curbing and metal covering NO 55-011(a) 46.3 9/17/1997 YES NO NO NO On edge of tributary to Mortandad Canyon, NW side of TA-55. Drainage outlet supplied by catch basins within the facility. Discharges to man-made channel cut into rock. Man-made channel cut into rock and natural channel with little to no vegetation. YES YES Flows from culvert into man-made channel and then into a natural channel. YES Buildings and parking areas on south and west side of TA-55. NO NO T. Lemke NO Discharge flows into established channels formed primarily from rock. 55-011(b) 56.6 9/17/1997 55-4 YES NO NO NO Catch basins and storm drains on NE side of TA-55-PF4. Discharge outlet is at edge of tributary to Mortandad Canyon. (b) and (e) discharge at the same outlet. Asphalt from discharge point to canyon edge. YES NO Run-off discharges onto asphalt apron. The asphalt apron has eroded and collapsed at the canyon edge. Pieces of asphalt scattered along canyon edge. YES Drainage from buildings and asphalt surfaces on northeast side of TA-55. NO NO T. Lemke Replace asphalt apron and patch crumbled asphalt. NO Asphalt has eroded away exposing bare soil. 55-011(c) 50.3 9/17/1997 55-6 YES NO NO NO Catch basin and storm drain on NE side of TA-55. Catch basin located SE of TA-55-6. Storm drain discharges at edge of tributary to Mortandad Canyon. Gravel, bare soil and some asphalt at point of discharge. Slope is flat at outfall but gradually increases below site as it nears Mortandad Canyon. YES YES Run-off flows from outfall to a natural channel that leads to a tributary to Mortandad Canyon. Discharges from outfall reach the canyon and are comprised of storm water and NPDES outfall 03A181. Erosion has not occurred at outfall, but the discharges from this outfall are responsible for the severe gully erosion immediately downstream. See PRS 42-004 for description of erosion. YES Drainage from buildings and asphalt areas on NE side of TA-55. YES NPDES outfall 03A181 discharges at this location. NO T. Lemke Diversion of run-on from the access road and re-directing of NPDES outfall discharges is needed to stop the severe gully erosion occurring down stream. NO See PRS 42-004 for related BMP and erosion descriptions. 55-011(d) 9/17/1997 55-41 YES NO NO NO Complete PRS cannot be located. See "Other internal notes" on page 4 of 4 for additional comments. NO NO NO NO NO T. Lemke NO This PRS was a catch basin and storm drain that discharged outside the security fence on the south side of TA-55. With the addition of TA-55-41 the discharge point has been recontoured, the topography of the general area changed, and the storm drain removed. The location of previous discharges can be neither identified nor evaluated. 55-011(e) 56.6 9/17/1997 55-4 YES NO NO NO Catch basins and storm drains on NE side of TA-55-PF4. Discharge outlet is at edge of tributary to Mortandad Canyon. (b) and (e) discharge at the same outlet. Asphalt from discharge point to canyon edge. YES NO Run-off discharges onto asphalt apron. The asphalt apron has eroded and collapsed at the canyon edge. Pieces of asphalt scattered along canyon edge. YES Drainage from buildings and asphalt surfaces on northeast side of TA-55. NO NO T. Lemke Replace asphalt apron and patch other asphalt areas as needed. NO Asphalt has eroded away exposing bare soil.