UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

999 ISm STREET

- SUITE 300

DENVER. CO 80202-2466

J. David Holm, Director Water Quality Control Division Colorado Department of Public Health and ~ n & n n 4300 Cherry Creek Dr. S. Denver, Colorado 80246-1 53 0

Re:

L Approvals Straight Creek (xedimenf ) hnos4uito Creek (metals) $an Miguel River (sedimnf )

V

I

Dear Mr. Holm:

We have completed our review of the total m&um daily loads (TMDLs) as submitted by y w office for the waterbodies listed in the eaclo& to this letter. In accordance with the Clean Water Act (33 U.S.C. 1251 e t seq.), we approvk all aspects of the TMDLs as developed for the water quality limited waterbodies as described Section 303(d)(l). Based on our review, we fee1 the separate TMl?L elements listed in the enclosed review table adequately address the pollutants of concern, takhg into consideration seasonal variation and a margin of safety. Please find enclosed a detail& review of these TMDLs.

Thank you for your submittal. If you have an4 questions concerning this approval, feel free to contact Kathryn Hernandez of my M a t 303012-6101.

Assistant ~ e ~ i o nAdministrator al Office of Emsyhms Protection and Remediation

Enclosure

Total Maximum Daily Load Assessment Straight Creek Summit County, Colorado June, 2000 TMDL Summary Waterbody Name / WBID

Pollutant / Condition Addressed Relevant Portion of Segment (as applicable) Use Classifications / Designation Permittee(s) Names / CDPS Numbers Water Supplies / Type of Supply

All tributaries to the Blue River, including all wetlands, lakes, and reservoirs, from the outlet of Dillon Reservoir Dam to the outlet of Green Mountain Reservoir. / COUCBL18 Sediment The mainstem of Straight Creek below Interstate I-70 Aquatic Life Cold 1, Water Supply, Recreation 1, Agriculture / Reviewable Town of Dillon Water Treatment Plant / COG-640006 Town of Dillon / Public Dillon Metropolitan District / Public Colorado Department of Transportation / Tunnel Maintenance Facility Water Minimum substrate D50 of 60 mm Maximum stream pool V* of 0.15 Stable Stream Morphology Five Age Classes of Brook Trout Attainment of the Narrative Sediment Standard

Water Quality Targets

TMDL Goal Executive Summary

Section 303(d) of the federal Clean Water Act requires states to identify water bodies or stream segments which are water quality limited. Those water quality limited segments currently identified in Colorado are listed in the 1998 303(d) List (WQCC 1998a). Water quality limited segments are those water bodies or stream segments which, for one or more assigned use classifications or standards, the classification or standard is not fully achieved. Once listed, the State is required to quantify the amount of a specific pollutant that a listed water body can assimilate without violating the applicable water quality standards, and to apportion that allowable quantity among the different pollutant sources. This maximum allowable pollutant quantity is referred to as the Total Maximum Daily Load (TMDL). The TMDL is comprised of the Load Allocation (LA) which is that portion of the pollutant load attributed to natural background or the nonpoint sources, the Waste Load Allocation (WLA) which is that portion of the pollutant load associated with point source discharges, and a Margin of Safety (MOS). The TMDL may also include an allocation reserved to accommodate future growth. The TMDL may be expressed as the sum of the LA, WLA and MOS. The Straight Creek watershed is a small watershed in the Rocky Mountains west of Denver, Colorado. The mainstem of Straight Creek is listed on the Colorado 1998 303(d) List

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for impairment by sediment. Accelerated sediment loading into Straight Creek has occurred from the historical construction and maintenance of the Interstate I-70 (I-70) western approach to the Eisenhower Memorial Tunnel (Tunnel). This accelerated sediment loading has impaired the aquatic life use of the stream. The two main sources of sediment are the wash-off of applied traction sand, and erosion of the cut and fill slopes of the I-70 approach to the Tunnel. Relatively small contributions of sediment come from ambient loading of the surrounding watershed. This accelerated anthropogenic sediment loading into Straight Creek will be mitigated with proper controls. The control of sedimentation from the cut and fill slopes of I-70 will be accomplished by revegetation. Properly maintained sedimentation basins, and use of appropriate procedures and BMP’s in the application and removal of traction sand will control this sediment contribution. Controlling these sources of sedimentation into Straight Creek should let the stream achieve an unimpaired aquatic life use.

I. Introduction The Straight Creek watershed is a small (20 mi.2) watershed of alpine and subalpine streams located approximately 50 miles west of Denver, Colorado in Summit County in the Central Colorado Rocky Mountains (Map 1). The Straight Creek watershed lies in the United States Geologic Service (USGS) hydrologic unit code 14010002. The mainstem and tributary waters of Straight Creek are included in the Segment 18 of the Blue River Basin (COUCCL18). Straight Creek is appropriately named because of the natural linear morphology of the stream. Elevations in the watershed vary from 8800 feet at the lowest point to over 13,000 feet at the highest, with approximately one third of the watershed above timberline. Interstate I-70 enters the watershed from the west portal of the Eisenhower Memorial Tunnel at an elevation of 11,200 feet. I70 then roughly parallels Straight Creek, while both the stream and I-70 drop almost 3000 feet in elevation to the point where I-70 crosses the Blue River below Dillon Reservoir (Map 2). The I-70 bridge over the Blue River is just several hundred feet below the confluence of Straight Creek and the Blue River, which is immediately below Dillon Reservoir Dam. The Colorado Division of Wildlife (CDOW) has designated the Blue River below Dillon Reservoir Dam as a Gold Medal trout stream of Colorado. The impacted portion of the watershed is the mainstem of Straight Creek, which runs in the valley below the foot of the fill slope of the western approach of I-70 to the Tunnel (Map 3). This is 9 miles of the mainstem of Straight Creek, from the point where the stream crosses under I-70 at the west portal of the Tunnel, to the confluence with the Blue River. Straight Creek above I-70 has remained minimally altered by man so far. Monitoring of water chemistry of Straight Creek shows that other physical parameters (e.g. Temp., pH) and constituents (e.g. metals, dissolved oxygen) are well within numeric standards set by the State (Lewis 1998). The WQCD has determined that Straight Creek’s aquatic life use is impaired by sediment,

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and

the stream was listed on Colorado’s 1998 303(d) List for sediment impairment (WQCC 1998a). Extensive cutting and filling of the mountain side was required to create the roadbed for I-70. The sediment problems in Straight Creek started in the late 1960's and stem from construction and maintenance of I-70 along the length of the stream. I-70 and the Eisenhower Memorial Tunnel are operated and maintained by the Colorado Department of Transportation (CDOT). This TMDL addresses the sediment impairment of Straight Creek. Section I identifies the location and scale of the impaired waters. Section II discusses the water quality classifications and standards, and Section III describes the problem. Section IV identifies the goals to be attained by the TMDL. Section V discusses the source of sediment impairment. Section VI describes the analysis and methodology of source assessment, with Section VII discussing the TMDL allocation. Section VIII describes the public involvement and participation in the TMDL process.

II. Water Quality Classifications and Standards The waters of Straight Creek are classified by the Colorado Water Quality Control Commission (WQCC) as a Class 1 Cold Water Aquatic Life water that is currently capable of sustaining a wide variety of cold water biota, including sensitive species (WQCC 1999a). Straight Creek is classified for Domestic Water Supply with two public water systems (Dillon Valley, and the Town of Dillon) currently using the water, and a third (Denver Water Board) with rights to use the water when needed. The CDOT also diverts water from Straight Creek for drinking water purposes at the CDOT Tunnel facilities, but being above any anthropogenic disturbance protects this diversion. The waters of Straight Creek are also classified for Agriculture, and Class 1 Recreation (primary contact) uses. In Colorado there are currently no numeric standards for sediment, but narrative standards do apply and require (WQCC 1999b): Astate surface waters shall be free from substances attributable to human-caused point source or nonpoint source discharge in amounts, concentrations or combinations which: Acan settle to form bottom deposits detrimental to the beneficial uses. Depositions are stream bottom buildup of materials which include but are not limited to anaerobic sludges, mine slurry or tailings, silt, or mud;@ (Regulation No.31, 31.11(1)(a)(I))

The State does have “Provisional Implementation Guidance for Determining Sediment Deposition Impacts to Aquatic Life in Streams and Rivers@ (WQCC 1998b). This guidance requires that both habitat and aquatic life must be demonstrated to be impaired before a stream is considered to be impaired by sediment. The WQCD has documented impairments to both habitat and aquatic life of Straight Creek and therefore it is considered to be impaired by sediment deposition. This is why the affected portion of Straight Creek was placed on the 1998 303(d) List for sediment impairment and sediment TMDL development (WQCC 1998a).

III. Problem Identification CDPH&E, WQCD

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Excess sediment in Straight Creek impairs the Class 1 Cold Water Aquatic Life use, increases the maintenance necessary at the drinking water system=s intakes and plants, and has potential to impact the Gold Medal fishery of the Blue River. Studies by the Colorado Division of Wildlife (CDOW), and a Summit Water Quality Committee (SWQC) contractor, Resource Consultants & Engineers, Inc. (RCE), showed the streams aquatic life use impaired by sediment. The CDOW and RCE fish studies indicated severe habitat impairment such as infilling of pools, covering of natural stream substrate and reduction of fish populations (CDOW 1991, RCE 1993). The SWQC has monitored and maintains ten monumented stream sites along the affected portion of Straight Creek (Map 3). The CDOT has conducted sediment control studies in the watershed, which showed excessive sedimentation into Straight Creek (CDOT 1996a, CDOT 1996b). On-going studies of the stream=s aquatic life, substrate, and morphology by the SWQC, CDOW, and WQCD show these poor aquatic life conditions still exist today but are improving. Studies of the Straight Creek watershed and the impacts of I-70 construction and maintenance were first conducted in the 1970’s, and then in the 1980's and 1990’s. For a list of the studies in the Straight Creek watershed see the list of References at the end of this document. Habitat monitoring has been and is currently under way by volunteers and professionals under the guidance of the SWQC, and the United State Forest Service (USFS) at ten monumented stream sites (Map 3). These sites are numbered by elevation, and at each site are three monumented stream cross-sections. The CDOW and WQCD have conducted aquatic life studies on the fish and macro invertebrates of Straight Creek. The SWQC, Dillon Valley District, Town of Dillon, and the Denver Water Board all monitor water chemistry in Straight Creek. A USGS flow monitoring gage #09051050 currently monitors discharge in Straight Creek just below the drinking water diversions on the stream.

IV. Water Quality Goal The water quality goal for Straight Creek is attainment of the sediment standard, specifically, so that sediment shall not be deposited to the degree that it is detrimental to the aquatic life use. Meeting this goal will protect and enhance aquatic life in Straight Creek, improve the drinking water intake water quality conditions for the Town of Dillon and Dillon Valley, and protect the Gold Medal trout fishery of the Blue River below Dillon Reservoir Dam. Since the WQCC currently has no numeric standard for sediment, other surrogate measures, or water quality targets will be used to indicate narrative standard compliance. The WQCC AProvisional Implementation Guidance for Determining Sediment Deposition Impacts to Aquatic Life in Streams and Rivers@ describes methods that can be used to determine whether the sediment standard is being exceeded. These methods of determining sediment impact will be employed in determining whether the stream is attaining the narrative sediment standard. The water quality targets that have been established for Straight Creek are mostly quantitative measures that will indicate that the sediment standard is being attained. Conditions in Straight Creek will be compared against these water quality targets to determine the status of restoration. Four water quality targets have been chosen to show that Straight Creek is complying with the narrative sediment standard achieving the Class 1 Cold Water Aquatic Life use.

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The first water quality target chosen is to show an increase in the median (D50) particle substrate size. The size of the stream substrate affects macro invertebrate habitat, the ability of brook trout to spawn viably, and reduces cover (protection) for fry and small trout (USFWS 1995). The small particle size of the sand applied to the highway, and eroded cut and fill material settles between larger substrate particles and impairs the riffle/run habitat of the stream. The current D50 of the stream is less than 25 mm, varying over the last six years from 8 mm to 23 mm. A target D50 level of 60 mm was chosen to show an increase of stream substrate size through a reduction in delivery of fine sediment. The D50 will be determined by using Wolman pebble counts, or modified Wolman pebble counts from the stream cross-sections already monumented along the stream (USDA 1995). The sediment data will be collected during fall season low flow conditions if possible. Statistical analysis on aggregated sediment data from at least 25 of the cross-sections will be done at least once every two years. The sediment data will be collected by the WQCD, SWQC, USFS, and volunteers. Substrate particle size is a measure that encompasses seasonal variations within a stream system. The second water quality target chosen is to show a decrease in the instream pool volume filled with fine sediment. The quality of stream pool shape and depth is an important aspect of the cover (protection) for young and older fish provided by deeper pools (USFWS 1995). The pool sediment measure called V* (V star), is the percentage of a pool filled with fine sediment (Fig. 1). Fine sediment from the applied sand, and cut and fill slope erosion has filled the pools of Straight Creek with much more fine sediment than would be seen in a healthier system. The average V* of the stream is currently greater than 0.40. The water quality target is to decrease V* to less than or equal to 0.15, through the reduction of fine sediment available to fill pools. The average V* will be determined by using methods published by Hilton and Lisle, at pools located at some of the ten stream sites already monumented along the stream (USDS 1993). The average V* will consist of the average of data collected from at least three pool sites distributed evenly along the length of the stream. The WQCD, SWQC, USFS, and volunteers will collect this data. This measure, like substrate size, accounts for seasonal variations within the stream system. The third water quality target is to protect the morphology of the stream, insuring that negative trends are not occurring. A stream’s morphology suitable for aquatic life becomes negatively altered with excessive sediment loading. Streams with too large a sediment load tend to become wider and shallower, flattening the stream cross-section profile. This decreases the amount of instream cover (protection) that fish have, and potentially raises the stream temperature, negatively impacting populations of aquatic life. There are numerical measures for characteristics of morphology, but stream morphology is dynamic not lending itself well to finite numerical limits. Natural channel changes because of fallen trees, or beaver dams are not readily accounted for by a strict numeric system. It is more appropriate to examine a history of the shape of a stream’s profile, which involves an intensive amount of data collection. Fortunately that data exists for Straight Creek. There are surveying records of at least three separate stream cross-sections at each of the ten monumented sites along the stream. A thorough analysis of the stream=s morphology has been conducted annually for the last 8 years at 30 monumented cross-sections along the most affected portion of the stream. This gives the Straight Creek Clean Up Committee, which includes the WQCD, SWQC, CDOW, USFS, and CDOT the adequate information to annually review the stream morphology, and insure the sediment control measures are effectively protecting the stream morphology. Evidence of increasing width to depth ratios, ubiquitous stream channel braiding and lateral movement would be an indication to the Straight Creek Clean Up Committee to possibly alter CDPH&E, WQCD

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sediment reduction practices. Morphological stream characteristics as described by Rosgen will be used as a guide to determine the morphological health of the stream (Rosgen 1996). This measure will not be strictly numeric, and will depend on the best professional judgement of water quality professionals from the WQCD, USFS, CDOW, and SWQC in an annual review of the stream morphology. This measure like the other sediment measures accounts for seasonal variation, and shows whether the stream is attaining expected stream morphology. The fourth water quality target chosen is to show an improvement of the Brook Trout (Salvelinus fontinalis) population. Brook trout comprise the vast majority of the fish population in Straight Creek, and should normally do well in such a stream. Currently, at some of the CDOW fish collection sites only four or fewer age classes of Brook Trout are present, indicating fewer age classes than would normally live in an undisturbed mountain stream (CDOW 1991). Even though the presence of four age classes shows a reproducing fish population, a goal of five or more age classes at all of the CDOW fish collection sites will indicate a healthier, more stable population. Future fish studies by the CDOW are planned in Straight Creek, and these will document the brook trout population structure. The CDOW, WQCD, SWQC, and volunteers will collect fish population data every two years. Fish studies provide the proof of whether or not a water body is supporting its aquatic life use, indicating the year round aquatic life health of a stream since fish integrate all seasonal variations of water quality.

V. Source Analysis Straight Creek is impacted primarily by accelerated sediment loading from the construction and maintenance operations of the I-70 approach to the west portal of the Tunnel. Work on the Tunnel began in 1968, this included Tunnel boring and I-70 approach construction. The first bore opened to two-way traffic in 1973, with the second bore opening for full four-lane traffic in 1979. During and after the construction of the I-70 approach to Tunnel both the cut and fill slopes created large, easily erodible surfaces which greatly increased sediment loading to the mainstem of Straight Creek (Map 3). The mainstem of Straight Creek receives more sediment loading from the extensive application of traction sand to the I-70 roadway. The roadway and Tunnel are very high in elevation, and carry close to 10,000,000 cars/year (Fig. 2). On peak travel days more than 45,000 cars/day will pass through the Tunnel. The I-70 corridor through the Rocky Mountains must be kept open during winter months, and this requires extensive snow removal, sanding, and application of deicers by the CDOT (Fig. 3). The section of roadway on either side of the Tunnel is the part of the I-70 corridor that is most difficult to maintain because of high elevations and extreme weather conditions. More traction sand per mile is applied at these higher elevations than anywhere else in the I-70 corridor through the State. This is especially true for the section of I-70 roadway above what is known as the Box Culvert (Map 3). Deicers do not work as well at the persistently cold temperature of these high elevations, so the majority of sand applied to the western approach to the Tunnel is applied between the Box Culvert (I-70 mile point 211) and the mouth of the Tunnel.

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Annual Vehicles through Tunnel

Millions of Vehicles

12 10

Annual Vehicles

8

Winter Vehicles (Nov.-Apr.)

6 4 2 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Year

Figure 2

Traction Sand Usage Averages 10,000 Tons/Year-Straight Creek 16000 14000

Traction Sand 12000 Usage 10000 (tons) 8000 6000 4000 2000 0

1990-91

1991-92

1992-93

1993-94

1994-95

1995-96

1996-97

1997-98

1998-99

Winter Season

Figure 3

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Accelerated sediment loading into Straight Creek has occurred over the past 30 years. Erosion and sediment control practices have already been implemented to reduce sediment delivery to the stream. The Straight Creek Erosion Control Project completed in 1994 by the CDOT implemented many sediment control measures in the Straight Creek watershed (CDOT 1996b). A total of twelve large sediment collection basins have been constructed, and are currently operated by the CDOT (Fig. 4). Ten sediment collection basins between the foot of the I-70 fill slope and the stream, one basin in the upper mainstem of Straight Creek, and one basin near the Tunnel maintenance facilities to control sediment loading into Straight Creek from the I-70 roadway and sand storage (Map 3). The sedimentation basins are numbered by relative I-70 mile point, and were placed below the upper most section of the roadway mainly between the Box Culvert and Tunnel mouth. The majority of traction sanding occurs between the Box Culvert and the Tunnel mouth. The necessary maintenance frequency however was underestimated and sediment has historically filled and by-passed some of the sediment control structures. A twelfth sedimentation basin was constructed in 1999 near the mouth of the west portal to the Tunnel to improve the collection of stored and applied traction sand near the Tunnel maintenance facilities. The Best Management Practices (BMP=s) that the CDOT has used in sanding and maintenance of the road surface have been varied in their effectiveness at reducing the sediment contribution to Straight Creek. The CDOT also needs to continue to improve revegetation of the cut and fill slopes of the I-70 approach to the Tunnel to prevent extensive erosion of these areas. The natural background sources of sediment provide only small loads of sediment to the system. Development in the Straight Creek Watershed is confined to the I-70 construction, and the very bottom of the watershed where the Towns of Dillon and Silverthorne have developed some of the private land. The vast majority (90+%) of the land in the watershed is public White River National Forest land. Only two roads enter the public portion of the watershed, I-70 and a restricted-access maintenance road. Except for some timber harvesting in the middle 1900’s the majority of the land is minimally disturbed alpine, subalpine and forest land.

VI. Technical Analysis Hydrology The Straight Creek watershed is comprised of small first, second and third order streams. The hydrology of the majority of the watershed is similar to that of natural high mountain stream systems. The exceptions are below the drinking water intake diversion structure where the stream is affected by withdrawals at low flow periods, and some urban development runoff impacts at the bottom of the watershed, which also affects the stream hydrology at that point. The Rosgen stream morphology classification for Straight Creek in the upper part of the watershed varies from an A2a+ to an A3a+, because of sedimentation impacts (Rosgen 1996). Lower down in the watershed the stream gradient flattens to become a B4 to B5 morphological type of stream at the confluence with the Blue River. The steep gradients of the mainstem and surrounding watershed respond quickly to rainfall producing short flashy flows. The majority of precipitation in the watershed occurs as snowfall during the late fall, winter, and early spring. 300 to 400 inches of snow will fall annually on the peaks surrounding the Straight Creek watershed. Dangerous snow avalanches occur frequently in the winter. It can, and does snow CDPH&E, WQCD

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at any time of the year at these high elevations. The winter snows are stored in the watershed until the warmer temperatures of summer melt them creating the type of hydrograph shown at the USGS Gage #09051050 (Fig. 5). There are no trans-basin diversions above the drinking water intake points (Map 3). High spring runoff dominates the yearly flow hydrograph from May to July with long periods of low base flow through the late fall, winter, and early spring (Fig. 5). The characteristic diurnal flow pattern of high mountain streams in the summer, is also present. The sediment carrying capacity of this type of high mountain stream is very high, and most streams in similar settings are sediment Apoor@, easily transporting the natural load of sediment (Rosgen 1996).

Straight Creek Annual Hydrograph USGS Sta. 09051050 (P.O.R. 1986-1998)

Average Daily Flow (cfs)

90 80 70 60 50 40 30 20 10

1-Dec

1-Nov

1-Oct

1-Sep

1-Aug

1-Jul

1-Jun

1-May

1-Apr

1-Mar

1-Feb

1-Jan

0

Day of the Year

Figure 5 Source Assessment Methodology The major sources of sediment loading to the Straight Creek system are anthropogenic and come from three areas. The bare cut slopes, bare fill slopes, and the application of traction sand to the I-70 road surface. The excessive sedimentation into Straight Creek began with the construction of the I-70 approach to the west portal of the Tunnel. The cut and fill slopes of the roadway construction were the major initial source of sedimentation into the watershed, and continue to be a major source of sediment to the Straight Creek system. After completion of the roadway in 1972, there was a total of 358 acres of disturbed area in the cut and fill slopes above and below the roadway (Map 3). 192 acres of cut slopes and 166 acres of fill slope. These areas have been measured using as-built construction drawings and aerial photography. Sections of these slopes are currently, and will be in the future revegetated to an appropriate percentage of cover to minimize sediment loads from these areas (Table 1). CDPH&E, WQCD

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Table 1 Revegetation Status of the Cut/Fill Slopes Along the Western Approach to the Tunnel Cut Slope

Totals

Disturbed Area

Natural Cover

Revegetated Area *

Needing Revegetation

I-70 Mile Point

(ac)

(ac)

(ac)

(ac)

205.4-205.8

3.24

3.24

0.00

0.00

205.8-206.3

8.18

8.18

0.00

0.00

206.3-206.8

4.79

3.38

0.00

1.41

206.8-207.3

7.33

4.94

0.00

2.40

207.3-207.9

4.09

3.38

0.00

0.71

207.9-208.3

6.06

2.12

0.00

3.95

208.3-208.8

9.17

4.09

3.67

1.41

208.8-209.4

2.40

1.41

0.00

0.99

209.4-209.9

9.87

7.61

0.00

2.26

209.9-210.4

8.60

8.60

0.00

0.00

210.4-210.9

35.39

34.26

0.00

1.13

210.9-211.2

26.65

13.25

0.00

13.40

211.2-211.7

22.28

6.20

4.09

11.99

211.7-212.2

26.23

16.64

0.00

9.59

212.2-212.7

5.22

0.56

0.00

4.65

212.7-213.2

8.04

0.00

4.23

3.81

213.2-213.6

4.65

0.00

4.65

0.00

192.18

117.87 (61%)

16.63 (9%)

57.66 (30%)

205.4-205.8

3.10

3.10

0.00

0.00

205.8-206.3

3.81

3.81

0.00

0.00

206.3-206.8

6.91

6.91

0.00

0.00

206.8-207.3

7.90

7.90

0.00

0.00

207.3-207.9

9.02

9.02

0.00

0.00

207.9-208.3

11.42

0.00

0.00

11.42

208.3-208.8

4.79

0.00

0.00

4.79

208.8-209.4

3.10

0.00

0.00

3.10

209.4-209.9

3.38

0.00

0.00

3.38

209.9-210.4

3.95

0.00

0.00

3.95

210.4-210.9

23.97

0.00

18.33

5.64

210.9-211.2

16.07

0.00

16.07

0.00

211.2-211.7

11.28

0.00

11.28

0.00

211.7-212.2

12.69

0.00

12.69

0.00

212.2-212.7

14.38

0.00

14.38

0.00

212.7-213.2

12.97

0.00

12.97

0.00

213.2-213.6

17.48

10.43

7.05

0.00

205.4-213.6

166.24

41.17 (25%)

92.77 (56%)

32.28 (19%)

358.422

158.04 (44%)

109.4 (31%)

89.94 (25%)

205.4-213.6

Fill Slope

Totals

Location

Totals for Cut and Fill Slopes

* - Revegetation has been started. Whether or not appropriate percent cover is present still needs to be determined. When the road was complete, the second major source of sedimentation became the wash off CDPH&E, WQCD

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of the traction sand applied to the surface of the roadway. Over the last 8 years an average of 10,244 tons of sand/year were applied to the Straight Creek corridor between mile marker 205.0 and 213.3. The majority of this traction sand is applied to the very highest portions of roadway, which lie above the Box Culvert at mile marker 211. However, the CDOT records of the exact locations and actual amounts applied to the roadway have been incomplete. The amount of sand applied to the roadway is very weather dependent, and varied from a minimum of 6085 tons in 1997-1998 winter season to 14,075 tons in the 1990-1991 winter season (Fig. 3). Traction sand can be needed at any time of the year at the high altitudes of this roadway, but only very minimal amounts are occasionally applied during the summer seasons. There is some anthropogenic sediment loading that occurs from other comparatively minor disturbances such as the little used access road, and the urban development in the lowest parts of the watershed. These two smaller sediment sources have such a small contribution to the total sediment load that they figure little in the restoration of Straight Creek (Lewis 1998). Fortunately these small sediment sources are also mitigated through other means such as road maintenance, and Summit County erosion control and stormwater planning (Summit County 1988). Minimal non-anthropogenic sediment loading also comes from the surrounding watershed. Analysis of maps and on-site inspection shows over 90% of the watershed is completely forested or alpine tundra with only two roads, I-70 and a locked access road. High mountain watersheds in granitic rock such as Straight Creek are sediment poor, usually generating low quantities of fine sediment. Under natural conditions, A2a+ streams like Straight Creek in high mountain watersheds can easily transport the sediment loads they receive (Rosgen 1996). Individual Sources Contribution Since the accelerated sediment loading to Straight Creek comes from anthropogenic sources, control of these sources should move the stream toward achieving the water quality goal described. Accurate estimates of the historical sediment loading from the cut and fill slopes is not possible because of the historical and ongoing sediment control and revegetation of these areas, and incomplete sand application and sediment removal records. New complete records of sand application and sediment removal amounts will provide further sediment loading assessment data. As more slope area is protected from erosion and properly revegetated, the sediment loading decreases from these areas. The amounts of bare area and revegetated area are shown in Table 1. Identification of the sediment loading from traction sand applied to the I-70 roadway should be a relatively easy calculation, but historical CDOT sanding records for this part of the I-70 corridor are incomplete. Maintenance records from now into the future will be required to be much more thorough to accurately monitor sand and deicer application amounts. There is also a lack of accurate records of sand removal, both from the road surface and sedimentation basins. Some reconstruction of the more recent (1994 to 1998) records was possible and these numbers are shown in Table 2. It is important to note that some of these ponds were filled for periods of time with sediment, or worked improperly and by-passed sediment into Straight Creek. All twelve ponds have been recently cleaned and are currently operating properly.

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Table 2 Location

Estimated Sediment Removal from Straight Creek Watershed 1995-1996

207.9 Basin 210.9 Basin 211 Basin 211.7 Basin 211.8 Basin 212 Basin 212.1 Basin 212.5 Basin 212.7 Basin 213 Basin 213.1 Basin 213.2 Basin 213.3 Basin Culverts Road Cleaning Total (yds3) Total (tons)

1996-1997

1997-1998

1999-1999 120

190 160

225 208

686 846 1184

230

312

435 2961 3851 5391

270 374 1146 1604

243 144 268 146

1129 1581

Total Removed (yds3) 120 190 160 0 0 225 208 0 243 686 268 146 0 1391 3335 6972 NA

Total Removed (tons) 168 266 224 0 0 315 291 0 340 960 375 204 0 1947 4669 9761 9761

VII. TMDL Allocation

Waste Load Allocation The one listed permit for the Town of Dillon Water Treatment Plant (COG-640006) does not need a sediment load allocated to it. This is a permit to back flush the raw water filters at the water treatment plant. All of the sediment that could be released back into Straight Creek is a sediment load already in the stream, and would not increase the net sediment loading into the system. Permit effluent limit levels for suspended solids will also control the amount of sediment loading back into Straight Creek. The water treatment plant actually removes a load of sediment from Straight Creek. This sediment is removed at the diversion point, and is settled out in an off stream pond or passed through the system.

Load Allocations The load allocations of the Straight Creek sediment TMDL lie in the sediment control practices, and the sanding and storage BMP=s that the CDOT will follow for the life of the roadway. The three major sources of sediment loading to Straight Creek will be reduced by the CDOT sediment control practices and BMP=s. There are three sediment control practices to be done by CDOT: 1) The revegetation of at least 70% of the cut and fill slopes. CDPH&E, WQCD

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2) The cleaning and maintenance of the twelve sedimentation basins, holding pond above the Dillon drinking water diversion, and sediment control structures on the I-70 roadway. 3) The removal at least 25% of the traction sand applied yearly to the I-70 roadway between the Blue River and the west portal of the Tunnel. To control the sediment loading from the cut and fill slopes of the roadway, the CDOT has agreed to revegetate and maintain at least 70% of the area disturbed by the construction of the west approach of I-70 to the Eisenhower Memorial Tunnel to 70 % of potential cover. This revegetation is already underway, with the majority of the fill slopes already having been revegetated to some extent. Whether or not the appropriate percent cover has been attained on these slopes still needs to be ascertained. The CDOT has also already started revegetating the cut slopes, but the progress here is much more limited than that on the fill slopes with less than 20% being revegetated to some extent. Some of the disturbed areas such as cliff faces and talus slopes are not capable of supporting any vegetative cover, so these areas are not included in the area to be revegetated. These areas of bare rock and talus supply little sediment loading to the Straight Creek system. To control excessive erosion at the foot of the cut slope, the extended roadway paving of the shoulders and lower portion of the cut slope will be maintained, and lengthened where practicable. The current twelve large sediment retention basins have been constructed to retain sediment coming from some of the cut slopes, and from the roadway traction sanding. Historically not enough emphasis has been placed on the cleaning and maintenance of the sediment basins to the appropriate level to maximize their efficiency, especially the sediment traps highest on the mainstem of Straight Creek. Timely cleaning of the basins was difficult because of limited access, weather conditions, and improper machinery for cleaning the basins. New machinery, a better access road, and greater CDOT awareness will change this in the future. The sediment retention basins will require cleaning at differing times, so this means that the CDOT will have to monitor the condition of all sediment retention basins and clean them before they fail. All twelve of these basins will be inspected at the very least annually, to assure they are correctly operating. All twelve will be cleaned before they fill, and repaired before they fail to remove sediment as designed (where practicable). If the present number of sedimentation basins proves inadequate to achieve the water quality targets, more basins will be constructed. Along with the twelve large sediment basins at the foot of the fill slope and near the Tunnel maintenance facilities, the CDOT has also agreed to maintain and clean the small sediment basins already constructed by CDOT on the I-70 roadway. Sediment accumulating behind the Dillon diversion structure will also be removed by CDOT. The CDOT has agreed to annually remove at least 25 %, by weight, of the total traction sand applied annually between the Blue River and the west portal of the Tunnel. The number of 25 % was decided upon based on the limited historical sand application and removal data the CDOT was able to supply. It is not known how much of the sand that is applied to the surface of the road is actually plowed off or pushed away from sediment catchment areas. It is possible that more than 50% of the sand applied to the roadway (east bound lanes) is plowed away from catchment areas. This 25% by weight will include sediment cleaned from the roadway, sedimentation basins, and from the Dillon diversion structure. More accurate future records will greatly increase the confidence in these sediment removal numbers. If this removal level is too low to attain the four surrogate measures the level can be raised to an appropriate level. The CDOT has agreed to optimize their use of traction sanding BMP=s along the I-70 CDPH&E, WQCD

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approach to the west portal of the Tunnel. Several of the most important BMP=s that will be employed are the use of environmentally safe deicers, maximizing traction sanding application efficiencies, proper storage of new sand at the west portal, and proper removal of waste sand and snow. The CDOT has already spent much time and effort to reduce the sediment loading into the Straight Creek watershed. The current CDOT sediment reduction practices have already reduced the sediment loading to Straight Creek, because some sand and sediment is removed from the sediment traps and roadway surface. However, the mainstem of Straight Creek is still receiving too large a load of sediment from the I-70 western approach to the Tunnel. The CDOT=s current sediment reduction practices have been well intentioned, but have not been carefully monitored and implemented well enough to show the needed results. Historical records of sanding practices, application rates, and amounts of sediment removed are incomplete. The CDOT has instituted a new record keeping program to more accurately record sand application amounts, sediment removal amounts, revegetated area with percent cover, and the areas still needing complete revegetation. Margin of Safety Since no specific numeric criteria are being given for an appropriate sediment load to Straight Creek, the Margin of Safety in this TMDL is implicit and lies in diverse multiple surrogate measures, continued monitoring, and adaptive management of the CDOT sediment loading reduction practices. The Straight Creek Clean Up Committee will meet at least once annually to review attainment of these surrogate measures. These measures are as follows; I. Four surrogate measures chosen to show attainment; 1) The minimum D50 substrate size of 60 mm indicates the optimum substrate conditions in the riffle run habitat of the stream. 2) The maximum V* of 0.15 in pools shows optimum conditions in the pool habitat of the stream. 3) Annual review of the overall stream morphology, to insure the development of positive trends in the stream profile and channel shape. 4) At least five age classes present at all CDOW fish monitoring sites shows improved health of the fish population. II. Continued monitoring of all of the four measures over a long period will insure the attainment of these measures. III. Adaptive management of the required CDOT revegetation, cleaning of sediment traps, and application of appropriate sanding practice BMPs. If any of the surrogate measures shows non-attainment then appropriate changes will be made in the sediment loading reduction practices.

VIII. Public Involvement CDPH&E, WQCD

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In 1963 the USFS granted the CDOT a special use permit for the construction of I-70, and then in 1971 a Memorandum of Understanding (MOU) about the construction of I-70 was reached between the USFS and the CDOT. Both of these agreements were reached before the Clean Water Act and the National Environmental Policy Act were instituted. Because construction on the first bore began before Environmental Impact Statements were required, the first EIS for the Tunnel was not completed until 1974 for the second bore of the Tunnel. There is a 25-year involvement in the cleanup efforts in the Straight Creek watershed. The CDOT, SWQC, USFS, WQCD, CDOW and EPA involvement in projects and monitoring efforts in the watershed have continued over a twenty year period. The Straight Creek Clean Up Committee was started in 1991. Eight meetings were held by the Clean Up Committee between 1998-2000, to satisfy issues on the TMDL goal, targets, and implementation. The CDOT, Summit County, WQCD, USFS, EPA Region VIII and other entities listed below have been involved in rectifying problems in the Straight Creek watershed. All public entities with explicit interest in the improvement in the stream conditions in Straight Creek were brought together to discuss and decide on ways to correct sediment problems in the mainstem of Straight Creek. There will continue to be at least one meeting of the Straight Creek Clean Up Committee every year. Public meetings about TMDL’s in the State of Colorado have been held in Denver, at the CDPH&E, WQCD. Thoroughly noticed public meetings about the Straight Creek sediment TMDL were held in Summit County in April and May of 2000. No public comments were received by the WQCD for the Straight Creek sediment TMDL. List of Participants in the Straight Creek Cleanup Committee

CDOT; Terri Tiehen, Kandace Claybrook, Cecelia Joy RMR Consulting; Art Hirsch WQCD; Eric Oppelt, Bill McKee, Lori Martin EPA Region VIII; Bruce Zander USFS; Kathleen Phelps, Greg Kuyumjian CDOW; John Woodling, Tom Kroening Northwest Colorado Council of Governments; Robert Ray Summit County Water Quality Committee; Lane Wyatt, Brian Lorch Summit County; Ric Pocius, Dave Beard Denver Water Board; Steve Lohman, Linda Rosales Town of Dillon; Eric Holgerson Dillon Valley Water District; Francis Winston, Rich Carter Colorado Water Resources Division, District #36; Scott Hummer IX. References

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CDOT 1996a: Colorado Department of Transportation, Section 319 Grant Project Final Report, Straight Creek, May, 1996. CDOT 1996b: Colorado Department of Transportation, CDOT-DTD-SDHYD-R-96-2, Efficiency of Sediment Basin, Analysis of the Sediment Basin Constructed as Part of the Straight Creek Erosion Control Project, January, 1996. CDOW 1991: Woodling, Straight Creek Summit County, Colorado Division of Wildlife, June, 1991. Lewis 1998: Lewis, Saunders, Effects of Urbanization on Water Quality n the Vicinity of Silverthorne, Summit County, Colorado, April, 1998. RCE 1993: Resource Consultants & Engineers, Inc., Aquatic Associates, RCE Ref. No. 93-108, Straight Creek Sedimentation Investigation, December, 1993. Rosgen 1996: Rosgen, Wildland Hydrology, Applied River Morphology, 1996. Summit County 1988, Summit County, Summit County Land Use and Development Code, Resolution #88-52, September 1988. USDA 1993: Hilton, Lisle, U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, Research Note PSW-RN-414, Measuring the Fraction of Pool Volume Filled with Fine Sediment, July, 1993. USDA 1995: Bevenger, King, U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Research Paper RM-RP-319, A Pebble Count Procedure for Assessing Watershed Cumulative Effects, May, 1995 USFWS 1982: Raleigh, U.S. Fish and Wildlife Service, Habitat Evaluation Procedures Group, FWS/OBS82/10.24, Habitat Suitability Index Models: Brook Trout, September, 1982. WQCC 1999a: Colorado Department of Public Health and Environment, Water Quality Control Commission, Classifications and Numeric Standards for Upper Colorado River Basin and North Platte River (Planning Region 12), Regulation No. 33, Amended November 30, 1999. WQCC 1999b: Colorado Department of Public Health and Environment, Water Quality Control Commission, The Basic Standards and Methodologies for Surface Water, Regulation No. 31, 5 CCR 1002-31, Amended March 3, 1999. WQCC 1998a: Colorado Department of Public Health and Environment, Water Quality Control Commission, 1998 303(d) List of Impaired Waters, 1998. WQCC 1998b: Colorado Department of Public Health and Environment, Water Quality Control Commission, Provisional Implementation Guidance for Determining Sediment Deposition Impacts CDPH&E, WQCD

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to Aquatic Life in Streams and Rivers, Policy98-1, June, 1998.

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