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Ken Nelson <br />December 20, 2011 <br />Page 6 <br />overgrown vegetation effectively reduces the ditch flow capacity, causing water levels to rise to the <br />extent of breaching the canal bank and eroding the access road used for maintenance. <br />The Marshall Road bridge may also have limited remaining service life.. Structural steel niembers, <br />beams and colunins sho\,\r signs of rust, and are visible through spalling edges of the concrete deck. <br />In addition, the bridge is just wide enough for safe passage of a maintenance vehicle provided the <br />driver is paying close attentiori. The culvert at Longs Road and bridge crossing at 2100 Road have <br />no known structural or flow conveyance capacity issues, and are wide enough for vehicular traffic. <br />The NDIC is also concerned that ditch flow play contribute to increased salinity and/or selenium <br />loadings on the Gunnison River, `These are naturally Occurring elements in soil, that are readily <br />dissolved and transported by water. Earthen lined ditches that coi.ivey water, and surface flow <br />across a4jacent land (irrigation tailwater, snow melt and runoff from rainstorms) are primary <br />potential sources. Increased saiiiiity loading is not regulated' in irrigation systems, yet it is a primary <br />reason for major capital improvement projects along irrigation ditches in areas of shale formations. <br />However, there is a threshold limit assigned to domestic wastewater systems to the extent that total <br />dissolved solids (TDS, also referred to as salinity) of treated effluent that is discharged to rivers and <br />streams is no greater than the TDS of the raw water supply of the public drinking water system plus <br />500 mg/l, Open ditches of the entire canal system are very likely to increase TDS and/or selenium, <br />especially through the area beyond the study limits to the west to the Trap Club. Soils along an <br />approximate 3-mile reach of ditch between the Trap Club and the inverted siphon outlet primarily <br />consist of Persayo silty clay loarn. According to web soil survey of the Natural Resources <br />Conservation Services (MRCS), this soil type can have salinity levels upward of 8 Mmhos/cm. <br />Finally, natural water loss through evaporation and seepage were reviewed to provide estimated <br />theoretical losses in the open ditch system. Accordingly, it is estimated that peak seasonal, <br />evaporation. of 1/4" per day (NOAA Clinintography Data) may represent water loss of about I cfs per <br />mile of open ditch, Furthermore, NRCS general assessment of Persayo soil series permeability <br />ranges from 0.2 to 0.6 inches per hour (4,8 to 12 inches per day), which would equate to a <br />theoretical. seepage loss substantially greater than what has been observed. In the event design <br />criteria for needed capacity of canal system improvements would need to account for historic <br />(actual) water toss through the OPCIA ditch system, site specific permeability data should be <br />developed. Lambert and Associates Could collect samples for laboratory analysis of parameters <br />such as permeability, porosity and void ratio in this event. <br />Development and Assessment of Alternative Improvements <br />No A 4 �erred to as the "do nothing7 alternative and simply <br />sign This alternative is commonly ref <br />means that no actions are taken. Under existing conditions of the tunnel, combined with the <br />systern's age, deterioration, and maintenance required for vegetation control, the no action <br />alternative is contrary to the NDIC's dedication to responsible management of the irrigation system, <br />For reasons stated below, the no action alternative is not considered viable. <br />