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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 49-001(b) 34.6 2/26/1998 49-23 YES NO NO NO Mesa top area mostly covered with asphalt pad Covered with asphalt (surrounding area heavily vegetated). Relatively flat until surface water discharges into culvert below road onto PRS 49-001(g). YES YES Run-off to north is conveyed along roadway ditch into culvert. Run-off to east, infiltrates or ponds in southeast corner of site near road intersection and onto access road near gate. Culvert discharges into well defined drainage channel which is eventually reaches a tributary of Water Canyon. None observed, drainage swale from run-on, however. Sediment traps have formed in some locations. NO NO YES Sources from west of site are providing sheet flow run-on. S. Veenis Asphalt cover over PRSs. NO 49-001(c) 17.5 2/26/1998 49-23 YES NO NO NO Mesa top area west of asphalt pad (Area 2A). Area heavily vegetated slightly upslope from the asphalt pad. Relatively flat area just west of asphalt pad. YES NO Run-off to north is conveyed along roadway ditch into culvert. Run-off to east, infiltrates or ponds in southeast corner of site near road intersection (49-001(d)). swale If runoff reaches culvert, it discharges into well defined drainage channel which is designated as 49-001(g). None observed. NO NO YES Sources from west of site are providing sheet flow run-on. S. Veenis NO 49-001(d) 17.5 2/26/1998 49-23 YES NO NO NO Mesa top source, south of asphalt covered pad (Area 2B). Heavy vegetation, ground saturated from upslope sheet flow run-on. Gentle slope from west to east. YES NO Sheet flow to east to access road. Roadway ditch Sheet flow stops at roadway. Heavy vegetation throughout site. NO NO YES From the west. Sheet flow run-on. S. Veenis NO 49-001(g) 59.2 2/26/1998 49-23 NO YES YES NO Drainage swale and adjacent banks discharge directly towards tributary of Water Canyon. Mixed vegetation and exposed tuff within channel. Moderate to steep slope from south to north. YES YES Swale dissipates +/- 100 feet above canyon rim. Swale dissipates flow No evidence that flows reach canyon but slope indicates that heavy rains probably would sheet flow into canyon. Minor evidence of sediment transport (I.e., sediment traps) within drainage swale. No rill or gully erosion observed. YES Run-on from roadway plus PRS 49-001 (b & c). NO NO S. Veenis Flow dissipation and/or straw bale check dams would impede sediment migration potential. A BMP implementation plan was implemented as part of the MDA AB asphalt pad removal. Site inspection and maintenance program is ongoing. NO Flow dissipation and/or sediment/erosion controls needed. 49-003 36.8 8/3/1998 YES NO NO NO Inactive septic leach field, located on mesa top within a grassy meadow. Grasses and weeds with sparse pinon pine trees. Generally flat, gently sloping to the north. YES NO Sheet flow evidence, primarily on access road which is nearby. The leach field itself has minimal evidence of runoff. Channel drainage Sheet runoff from the vicinity enters into the run-on diversion channel installed 300-400 yards north of the site for PRS 49-001. The actual impact from 49-003 is suspect. Minimal sediment transport evidence found. Mostly near access road that is near site. The actual PRS boundary has little or no visible erosion. NO No structures are near site. NO YES Upslope vegetated meadow. S. Veenis NO Original assessment performed on 2/26/98 was performed outside the fenced area without knowledge of the actual PRS boundary. Upon further review, the PRS boundary was determined to be a small 30'x40' septic leach field located in the center of a heaviliy vegetated meadow. This updated score reflects the new information obtained from a field visit performed on 8/3/98. 49-005(b) 3.6 7/2/1999 YES NO NO NO Within fenced Area 5 at TA-49. A sump is located nearby (49-006). 49-005(b) is construction debris landfill. Heavy vegetation throughout site Flat lying area. NO NO Infiltrates NO No structures NO No operational impact NO No run-on Veenis, Steve NO 49-006 3.6 7/2/1999 YES NO NO NO Within fenced Area 5 at TA-49. A sump is located nearby (49-006), 49-005(b) is a debris construction landfill. Heavy vegetation throughout site. Flat lying area. NO NO Infiltrates None observed NO No structures NO No operational impact NO No run-on Veenis, Steve NO 49-008(d) 8.8 9/24/1998 49-23 YES NO NO NO NO NO NO NO NO S. Veenis NO