Lake Tahoe Boulevard Enhancement Project...10065 WQ5 Runoff Water 10065 WQ2-A Pelagic Lake Tahoe...

Lake Tahoe Boulevard Enhancement Project

(JN 95186)

Draft Project Alternatives Evaluation Report

March 2011

Draft Project Alternatives Evaluation Report - 1 - Lake Tahoe Boulevard Enhancement Project March 2011

Table of Contents: 1.0 Introduction..................................................................................................................3

1.1 Project Background .................................................................................................3 Figure A. Project Area....................................................................................................4

1.2 Project Goals...........................................................................................................5 1.3 Project Objectives ...................................................................................................6 1.4 Review of Existing Conditions .................................................................................6 Table 1. Key Site Conditions for the LTB Enhancement Project Area ...............................7 1.5 Project area Hydrologic and Water Quality Problems .............................................7 Table 2. Peak Flow Results ...............................................................................................8 Table 3. Typical Drainage, Erosion and Water Quality Issues within the Project Area.......8 1.6 Transportation and Traffic Conditions .....................................................................9 Table 4. Lake Tahoe Boulevard Accident Site Analysis Summary .....................................9

2.0 Design Criteria...........................................................................................................10 2.1 Bike Path ...............................................................................................................10 2.2 Erosion Control......................................................................................................10

2.2.1 Source Control...............................................................................................10 2.2.2 Hydraulic Design ...........................................................................................10 2.2.3 Treatment ......................................................................................................10

3.0 Project Alternatives ...................................................................................................11 3.1 Alternatives Summary ...........................................................................................12

3.1.1 Alternative 1...................................................................................................13 3.1.2 Alternative 2...................................................................................................15 3.1.3 Alternative 3...................................................................................................16 3.1.4 Alternative 4...................................................................................................18 3.1.5 Alternative 5...................................................................................................20

4.0 Sub Watershed Existing Conditions & Treatment .....................................................22 4.1 Sub watershed LTB-1............................................................................................22 4.2 Sub watershed LTB-2............................................................................................22 4.3 Sub watershed LTB-3............................................................................................23 4.4 Sub watershed LTB-4............................................................................................23 4.5 Sub watershed LTB-5............................................................................................24 4.6 Sub watershed LTB-6............................................................................................24 4.7 Sub watershed LTB-7............................................................................................25 4.8 Sub watershed LTB-8............................................................................................25

5.0 Alternatives Evaluation..............................................................................................26 5.1 Enhance Recreational Opportunities.....................................................................26 5.2 Provide a Bike Path Link to Local Businesses, Schools & Employment ..............26 5.3 Treatment of Fine Sediment..................................................................................26 5.4 Treatment of Course Sediment .............................................................................27 5.5 Reduction in Runoff Volume..................................................................................27 5.6 Reduction in Peak Flow.........................................................................................27 5.7 Capital Cost...........................................................................................................27 Table 5. Alternative ROM Construction Cost Estimate ....................................................28 5.8 Design/Planning Costs ..........................................................................................28 5.9 Operations and Maintenance Costs ......................................................................28 5.10 Design Life ............................................................................................................29 5.11 ROW Acquisition ...................................................................................................29 5.12 Impacts to Existing Utilities....................................................................................29 5.13 Disturbance ...........................................................................................................29


5.14 Aesthetics..............................................................................................................29 5.15 Constructability......................................................................................................29 5.16 Flooding.................................................................................................................30 5.17 Groundwater Impacts ............................................................................................30 5.18 Impervious Surfaces..............................................................................................30 5.19 Road Sand/Cinders ...............................................................................................30 5.20 Manmade Nutrient Sources...................................................................................31 5.21 Public Safety .........................................................................................................31 5.22 Wildlife Habitat ......................................................................................................31 5.23 Vegetation .............................................................................................................31 5.24 Cultural Resources................................................................................................31 5.25 Vector Control .......................................................................................................32 5.26 Permitability...........................................................................................................32 5.27 Fundability .............................................................................................................32 5.28 Forest Health.........................................................................................................32

6.0 Alternatives Evaluation Summary .............................................................................32 Table 6. Alternative Evaluation Summary ........................................................................33

7.0 Water Quality Conditions and Sediment Treatment ..................................................33 7.1 Precipitation.......................................................................................................34 7.2 Existing Precipitation Record.............................................................................34 Figure 2 – 15-Minute Angora Gage Rain Intensities .....................................................35 Figure 3 – 30-Minute Angora Gage Rain Intensities .....................................................36 Figure 4 – 60-Minute Angora Gage Rain Intensities .....................................................36

Table 7. PLR Precipitation Values ...................................................................................36 7.4 Pollutant Load Reduction (PLR) Analysis..........................................................37

Table 8. PLR Summary, Average Annual Sediment Load, Entire Watershed .................37 Table 9. PLR Summary, Average Annual Sediment Load, Right-of-way.........................37

7.5 Treatment ..........................................................................................................37 Table 10. PLR Summary Estimated Annual Sediment Removal, Right-of-way ...............38

8.0 Conclusion.................................................................................................................39 References: ...................................................................................................................39

Appendix A CTC Preferred Design Approach Appendix B Project Alternatives Evaluation Project Plans Appendix C BMP Toolbox Appendix D Bike Path Details Appendix E Watershed Figure and Rational Peak Flow Results Appendix F Road Intersection Alternatives Appendix G Photos Appendix H PLR Modeling Results Appendix I PDT / Public Comments


1.0 Introduction

1.1 Project Background The Lake Tahoe Boulevard Enhancement Project (Project) is intended to provide a critical link in the Regional bicycle path network and to stabilize soil, restore stream environment zones (SEZ) and improve storm water quality within the Project area. The Project supports the Tahoe Regional Planning Agency’s (TRPA) and the Tahoe Metropolitan Planning Organization’s (TMPO) “Bicycle and Pedestrian Master Plan” by installing a Class I and/or Class II bicycle facility along Lake Tahoe Boulevard (LTB) between Clear View Drive (CVD) and Viking Way (VW). The purpose of TRPA’s Bicycle Transportation Plan is to provide access to local businesses, schools, and offices for bicyclists and pedestrians, to reduce vehicular transportation, and to enhance recreational opportunities within the Lake Tahoe Basin (Basin). The Project also supports TRPA’s Environmental Improvement Program (EIP) and the California Tahoe Conservancy’s (CTC) March 1987 Report on Soil Erosion Control Needs and Projects in the Basin by installing low impact Best Management Practices (BMPs).

The Project is located in eastern El Dorado County, in the Lake Tahoe Basin, along LTB. The Project involves the installation of a Class I or Class II bicycle facility along LTB between CVD and VW and implementation of erosion control and water quality improvement measures along LTB. The Project is also intended to reduce nutrient and sediment loading to nearby waterways and treat storm run-off from the existing roadway infrastructure by installing appropriate BMPs. Design alternatives will incorporate popular recreational use for the area, such as Sawmill Pond, with opportunities to mitigate erosion along LTB.


Figure A. Project Area

In order to satisfy the recreational, water quality and erosion control objectives of the Project, various alternatives have been formulated to meet the goals and objectives of the Project. The Project alternatives were developed based on several factors, including but not limited to: topography, land ownership, connectivity to existing and future bike paths, public safety, American Disabilities Act (ADA) laws, cost, erosion source control, hydraulic design, and treatment of runoff.

The resource areas being addressed as part of the Project are listed on TRPA’s EIP project list as the following project numbers:


#10065 – Water Quality

#991 – Soil Conservation/SEZ Threshold

#10036 - Air Quality/Transportation, Recreation

The Project will affect the following threshold indicators as defined in the EIP:

EIP Project Numbers

Project Threshold Index Threshold Indicator

991 R1-A Multi-Use Trails

991 SC1-B Hard Coverage

991 SC2 Naturally-Functioning SEZ

10036 SC2 Naturally-Functioning SEZ

10036 AQ7 Vehicle Miles Traveled

10065 WQ5 Runoff Water

10065 WQ2-A Pelagic Lake Tahoe Winter Water Clarity

10065 WQ6 Groundwater

1.2 Project Goals The following Project goals were recommended by the Project Development Team (PDT) to guide the Project and decisions regarding design, formulating alternatives, and planning of improvements:

1. Implementation of the Lake Tahoe Boulevard (LTB) Enhancement Project shall be consistent with General Plans, Master Plans, Community Plans, and other applicable elements of the TRPA Regional Plan. The LTB Enhancement Project should be consistent with the programmatic goals for recreation access of the California Tahoe Conservancy (CTC) and the US Forest Service (USFS).

2. Implementation of the LTB Enhancement Project should collaborate with adjoining property owners, as well as neighborhoods served by the Project, to find mutual benefit and meet Project objectives.

3. El Dorado County must meet its commitment to achieve Basin objectives through the LTB Enhancement Project in carrying out the County’s environmental stewardship obligation under Basin restoration efforts.

4. Improvements/modifications to LTB should be implemented to reduce speeds in the corridor and accidents associated with speed and improve overall safety.

5. Traffic calming measures shall be considered at the LTB and Sawmill Road (SR) intersection to facilitate safe bicycle and pedestrian crossing from the future Sawmill 2 Bike Trail to the LTB bicycle facility, National Forest lands, and associated trails, as well as create an accommodating environment in and around the Sawmill Pond area which is a popular destination for families. The LTB and SR intersection exhibits dangerous roadway characteristics and driver behavior. A particular area of concern is the curve


in LTB west of SR. Other traffic calming measures for consideration are: 1) a radar speed limit sign showing the speed limit on a fixed sign, and the speed limit of the approaching motorist as a variable message; 2) providing an illuminated crosswalk to expand the motorist’s view of pedestrians, especially at night, 3) providing a warning sign with a flashing beacon advising motorists of the upcoming curve, and 4) physical hardscape traffic calming measures such pedestrian refuge islands.

6. The roadway shall include wide paved shoulders such that automobiles may pull off onto them to allow emergency vehicles to bypass in the through travel lanes. This is especially helpful in light of the Angora fire.

1.3 Project Objectives The LTB Enhancement Project objectives represent physical conditions that can be measured to assess the success of the Project in achieving the outlined goals. The LTB Enhancement Project will conform to the Preferred Design Approach as detailed in the Storm Water Quality Improvement Committee (SWQIC) process.

The objective of the LTB Enhancement Project is to improve recreational opportunities, safety, scenic resources, and air and water quality by:

1. Providing a bike trail link that is part of TMPO’s and TRPA’s “Bicycle and Pedestrian Master Plan”.

2. Providing access to local businesses, schools, and the South “Y” Transit Center.

3. Reducing Vehicle Miles Traveled (VMT).

4. Improving safety of the Lake Tahoe Boulevard corridor.

5. Improving aesthetics along Lake Tahoe Boulevard via landscaping.

6. Enhancing recreational opportunities within the Tahoe Basin.

7. Restoring SEZ.

8. Reducing peak runoff rate.

9. Reducing stormwater runoff volume.

10. Treating runoff before it reaches the Upper Truckee River and other nearby waterways.

11. Stabilizing eroding cut slopes.

12. Stabilizing roadside ditches.

13. Capturing road sand/cinders to prevent discharge.

14. Providing for a more accommodating environment through reductions in speeds and vehicle conflicts.

1.4 Review of Existing Conditions In July 2008, the County of El Dorado (County) utilized the expertise of Stantec, Inc. to prepare a Draft Existing Conditions and Feasibility Report for the Project. Following a review of the document by the County, Project TAC, and the Public, Stantec, Inc. incorporated comments and produced a Final Feasibility Report (Report) which was delivered to the PDT in December 2008. The Report is incorporated by reference into this document. The Report details the baseline conditions in the Project area and identifies both problem areas and potential resources that could be affected by the Project. Table 1


summarizes key site conditions within the Project area and their importance to formulating and evaluating the alternatives for Project design.

Table 1. Key Site Conditions for the LTB Enhancement Project Area Site Condition Importance to Design of Alternatives

Vegetation Resource for wildlife habitat, scenic quality, source control and slope stability, pollutant removal and infiltration, soil building.

SEZ Resource for water quality treatment and wildlife habitat. May have bearing on new coverage/disturbance, thus affecting design of bike path.

Soils Varying types of soils affect revegetation potential and infiltration rates. Erosion hazards are predominantly slight to moderate.

Cultural Two known cultural sites exist within the Project area, which may dictate the alignment of the bike path.

Topography Varying topography within Project area helps drive bike path alignment and BMP installation locations. Slopes along LTB contribute sediment and seasonal storm water flows.

Angora Creek Project area contributes flows to meadow area adjacent to Angora Creek.

Groundwater Limited areas of perennial flow within Project area. In some locations, abundant water sources exist for vegetation. Many arid and upland areas exist.

Land Ownership California State Parks and U.S. Forest Service owned parcels in the Project area provide open space and pervious surfaces that are a potential resource for bike path alignment and BMP installation.

Constructed Conveyance

Constructed roadside ditch along LTB is poorly designed, maintenance intensive and carries large volumes of sediment. Constructed channels are poorly designed; some deliver runoff to meadow areas above Angora Creek without treatment.

Hydrology Inadequate conveyance at most culverts under LTB. Seasonal and storm driven “natural” drainages carry flows and sediment into the Project area.

1.5 Project area Hydrologic and Water Quality Problems Hydrologic and water quality issues in the Project area were identified through site visits and discussions with agencies and local residents. Those issues were summarized by location within the Feasibility Report (Stantec, 2008). The Feasibility Report also included a hydrologic analysis of the Project area, however upon further review by County staff; the hydrologic analysis was not used for this report. In addition, the condition of each culvert was described and photographed in October 2005. See Table 2 below for existing sub-watershed size, existing culvert diameters and existing estimated peak flows.

See Appendix E for updated watershed figure and rational method peak flow results.


Table 2. Peak Flow Results

Table 2. Offsite Peak Flow Results Peak Flow Offsite Sub-

Culvert Diameter Area 10-year 25-year 100-year

Watershed ID (in) (acres) (cfs) (cfs) (cfs)

LTB-1 18 15.18 4.16 4.88 7.36

LTB-1&2 24 154.88 42.45 49.85 75.15

LTB-3 24 68.18 19.93 23.41 35.28

LTB-3&4 18 224.02 54.87 64.44 97.14

LTB-5 18 114.61 26.63 31.28 47.15

LTB-6 Watershed outfalls into existing CSLT culvert and basin

LTB-7 18 48.83 14.49 17.01 25.65

LTB-8 18 49.86 12.37 14.53 21.90

Typical drainage and erosion and water quality issues identified within the Project area fall into several general categories (Table 3).

Table 3. Typical Drainage, Erosion and Water Quality Issues within the Project Area

Problem Type1 Description Sediment production from soil instability SC Soil erodes from sparsely vegetated road

cuts and sloped areas.

Sediment production from exposed road shoulder

SC Soil erodes from compacted road shoulders and roadside parking.

Sediment production from USFS property SC Soil erodes from dirt roads and channels.

Sediment production from road sanding operations

SC Cinders wash off road surface with high concentrations at intersections and corners.

Inadequate treatment of storm water flows T Storm water flows lack treatment prior to discharging toward Angora Creek.

Inadequate conveyance under road HD Culverts are undersized and damaged.

Inadequate conveyance along road HD Undersized or nonexistent roadside ditch; inadequate placement of culverts.

Inadequate conveyance in drainage ditches HD Insufficient slope, channel or conveyance path for storm water flows exiting culverts.

Compacted turn-out areas SC Vehicle turnout areas produce sediment.

1 – Type of Problem SC – Source control

HD – Hydrologic Design T – Treatment


1.6 Transportation and Traffic Conditions D Street to Industrial Ave (0.32 miles) is currently a four-lane undivided arterial with unpaved shoulder on both sides. On-street parking is restricted. No pedestrian facilities exist on either side of the street. The posted speed limit is 55 miles per hour (mph) in both directions, with a reduction to 35 miles per hour approaching D Street.

Industrial Avenue to Sawmill Road (1.27 miles) is currently a four-lane arterial with unpaved shoulders on both sides. A 12-foot median starts approximately 2,000 feet west of Industrial Road. On-street parking is restricted. No pedestrian facilities exist on either side of the street. The posted speed limit is 55 mph in both directions.

Sawmill Road to Tahoe Mountain Road (0.30 miles) is currently a four-lane road with a 12-foot median in the middle and unpaved shoulders on both sides. The median contains a guardrail barrier. On-street parking is restricted. No pedestrian facilities exist on either side of the street. The posted speed limit is 45 mph in both directions with a reduction to 35 miles per hour approaching Tahoe Mountain Road.

The Project area contains three intersections. These include D Street-Viking Way, Sawmill Road, and Tahoe Mountain Road. Intersection characteristics are as follows.

Lake Tahoe Boulevard/D Street-Viking Way is a four-way stop controlled intersection with red flashing warning signals on all approaches. No exclusive left-turn or right-turn lanes exist. Both the westbound and southbound approaches contain marked crosswalks.

Lake Tahoe Boulevard/Sawmill Road is an un-signalized “T” intersection. A stop sign controls the Sawmill Road approach. Lake Tahoe Boulevard does not contain a left turn lane in this location. However, the 12-foot median provides a 200-foot opening at this intersection. Motorists may use this opening as a refuge to turn left onto Sawmill Road. No marked crosswalks currently exist to accommodate pedestrians crossing Lake Tahoe Boulevard or Sawmill Road. Posted speed limits are 55 mph on the southbound approach (Lake Tahoe Boulevard) and 45 mph on the northbound (Lake Tahoe Boulevard) and westbound (Sawmill Road) approaches.

Lake Tahoe Boulevard/Tahoe Mountain Road is an un-signalized “T” intersection. A stop sign controls the Tahoe Mountain Road approach. The northbound Lake Tahoe Boulevard approach contains a 50-foot exclusive left turn lane. A merge lane, approximately 120 feet long, facilitates the four-lane to two-lane transition for southbound Lake Tahoe Boulevard motorists crossing Tahoe Mountain Road. This intersection also represents the southwest terminus of the 12-foot-wide Lake Tahoe Boulevard median. No marked crosswalks currently exist to accommodate pedestrians crossing Lake Tahoe Boulevard, Sawmill Road or Tahoe Mountain Road.

The table 4 shows the accident site analysis summary for Lake Tahoe Boulevard for the period beginning January 1, 2007 and ending December 31, 2009.

Table 4. Lake Tahoe Boulevard Accident Site Analysis Summary

Year Accidents Injuries Fatalities

2007 1 0 0

2008 6 9 0

2009 5 3 0


2.0 Design Criteria

2.1 Bike Path The bike path will be designed to comply with American Association of State Highway and Transportation Officials (AASHTO) and Caltrans minimum requirements for Class I and Class II bike path facilities (AASHTO, 1999; Caltrans, 2006). The design will also utilize guidance outlined in the Federal Highway Administration Manual on Uniform Traffic Control Devices (MUTCD) for standards regarding signage and striping along with other applicable standards (FHWA, December 2007). The bike path will be designed to align with the Project goals and objectives. Furthermore, the bike path design will focus on balancing cut and fill quantities to minimize on and off hauling of material, and will focus on minimizing tree removal and disturbance. Other design considerations include: material life cycle costs, pavement material options, recreational experience, alignment, easements, vegetation, scenic resources, wildlife, cultural resources, land capability, and how the bike path works in unison with erosion control and storm water management techniques. Other amenities will be explored such as benches, fences, signs, lighting, waste receptacles and flexible bollards.

2.2 Erosion Control Initial field assessments have determined that erosion is not a significant problem along the entirety of Lake Tahoe Boulevard. The existing erosion problems include eroding ditches and slopes adjacent to the roadway. In addition, there are areas where there are exposed road shoulders.

See Appendix A for guidance on the CTC Preferred Design Approach and see Appendix C (BMP Toolbox) for a detailed discussion of County approved BMPs for source control, hydraulic design and treatment.

2.2.1 Source Control The stabilization of eroding slopes and channels is considered to be the most effective means of reducing the concentration of sediment in runoff from the Project area. In regions where treatment of sediment from the road surfaces is not feasible due to site constraints, additional sweeping frequency by County maintenance personnel is proposed and considered as a source control of sediment.

2.2.2 Hydraulic Design The hydraulic design Project alternatives were developed and evaluated for feasibility based on the techniques and requirements as outlined in the El Dorado County Drainage Manual (Ford, 1995). The hydraulic design component for this Project is intended to mitigate development, specifically with respect to the erosion of sediment which results from concentrated runoff from impervious surfaces within the Project area. Also, the majority of the culverts within the Project area are undersized or failing and will need to be replaced.

2.2.3 Treatment The treatment effectiveness of the double barrel sediment trap for the removal of tss (200 microns and less) has been demonstrated by the California Department of Transportation to be approximately 45% (Caltrans, 2003). The highest percentage of sediment recovered in terms of mass for the double barrel configuration was between 10 microns and 200 microns. The sediment captured in the up-gradient barrel had a coarser size distribution than the sediment collected in either the down-gradient barrel or the effluent. The effluent had a finer


grain size distribution than sediment collected from either the up-gradient or down-gradient barrels. The sediment trap was effective in reducing the mean influent turbidity from 424 NTU to 392 NTU, or approximately 8% (Caltrans, 2003).

Based on these conclusions, relative ease of maintenance, and the successful application of the sediment trap on similar County erosion control projects, a single, or double barrel sediment trap for more volume retention, will be used for this Project to treat a portion of the fine and coarse sediment (particles greater than 20 microns) throughout the entire runoff hydrograph. In addition, the sediment trap will allow for infiltration of a small volume of runoff through the open sediment trap bottom thereby treating a portion of the very fine sediment (less than 20 micron). For additional treatment of runoff after the sediment trap, alternative treatment methods will include check dams, underground infiltration, or unlined sedimentation/infiltration basin BMPs. These treatment BMPs will be configured to capture and retain the first flush of runoff and once the BMP has reached capacity, the remaining runoff will bypass the treatment BMP. . These BMPs will reduce the runoff volume by infiltration as well as treat the suspended fine and very fine sediment by sedimentation and infiltration. Since these BMP’s will be sized to accommodate 33% of the 1-inch, 1-hour storm where feasible, the infiltration or unlined sedimentation/infiltration basin BMP operated in first flush will not significantly reduce the peak runoff because at the time of peak runoff, the treatment BMP will have reached its storage capacity. However, these BMPs will reduce the volume and peak flow for the more common less intense or shorter duration rain events.

The treatment BMP Project alternatives were developed to meet the Project goals to the greatest extent feasible and were evaluated for feasibility based on a variety of codes, plans, and guidelines. The FHWA Urban Drainage Design Manual states that infiltration trenches are only feasible if the seasonal groundwater table is below the bottom of the trench (FHWA, 2001). Infiltrating BMPs must be designed and constructed such that the bottom of the infiltration trench or dry well is a minimum of one foot above the seasonal high water table (TRPA, 2002). The Tahoe Basin Interagency Roadway Maintenance and Operations Committee (TBIRMOC) requires a minimum of four feet separation from the invert of the infiltration structure to the seasonal high groundwater (TBIRMOC, 2001). In order to meet the effluent limits for storm water discharges to surface waters, the Water Quality Control Plan for the Lahontan Region may require five feet of separation between the highest anticipated groundwater level and the bottom of the infiltration system (Lahontan, 1994). Due to vector-borne disease concerns, runoff may be retained in the urban BMP for up to 96 hours between April 15th and October 1st, and as long as necessary between October 1st and April 15th (CDPH, 2007).

An additional treatment component aimed at improving the water quality of runoff from the Project area is street sweeping. Sweeping frequency in the Project area is currently dependent on the conditions of the road and the work load of El Dorado County maintenance crews. However, the typical timing of street sweeping within the Project area is twice per year; once in the spring, and once in the summer. Sweeping is a proven economically efficient means of capturing sediment from impervious surfaces and will continue within the Project area regardless of the selected alternative. However, if achieving the sediment reduction goal is not feasible in a particular sub-watershed, than the sweeping frequency could be increased for the segments of road within that sub-watershed.

3.0 Project Alternatives This Project Alternatives Evaluation Report will focus on both the water quality and erosion control aspects of the Project and the bike path design alternatives along the bike path alignments. These two major pieces of the Project will work in conjunction with each other


and in many cases will dictate decisions that are made as we move further through the design process.

The bike path alignments, source control, hydraulic design, and treatment alternatives are discussed below.

Once the Project Alternatives have been presented in this Report, the PDT and the public will help select the Preferred Alternative, which will be designed and studied in more detail to ready it for construction.

3.1 Alternatives Summary In order to meet the recreational and erosion control portions of the Project goals and objectives, the do nothing alternative will not be considered. This is because the bike path must be constructed for the entire length of Lake Tahoe Boulevard between D Street/Viking Way and Clear View Drive for the Project goals and objectives to be met. Also, because each aspect of the erosion control mitigation process addresses different objectives, without implementation of each aspect, the benefits of one measure could be negated. If designed, constructed, and properly maintained, each alternative will meet the goals and objectives of the Project.

Each alternative assumes that permitting agencies will permit the bike path with appropriate mitigation measures to span sensitive lands (land capability Class 1b) and that the environmental process properly surveys the Project area (vegetation, wildlife, and cultural) and allows for avoidance and/or appropriate mitigation measures to avoid or minimize environmental harm resulting from Project construction and use to a less than significant level.

A Cultural Resources Inventory Report was completed in March 2006 to document and evaluate the cultural resources present in the project area. This investigation resulted in the identification of two previously recorded archeological sites located within the Project area that may have an effect on the alignment of the proposed Class I bike path.

Alternatives for the existing center median are not included in the following alternative descriptions, but will be discussed here briefly. The existing median north of Sawmill Road is a paved shallow swale leading to drainage inlets at the existing culvert crossings. The portion of the median between Sawmill Road and Tahoe Mountain Road is not paved, with sparse vegetation to the west and more abundant vegetation near the meadow area. Two alternatives for the median area are proposed; maintain the existing median conditions to allowing sweeping of the paved median or remove the paved median and restore the median with vegetation. A vegetated median will help to infiltrate runoff but will be more difficult to maintain. A paved median will not infiltrate runoff but will be easier to maintain. Infiltration in the median may also have an effect on the adjacent roadway pavement. Either of these two alternatives can be worked into the preferred alternative that is selected.

For supporting information and Figures, Details and Photographs for the various elements proposed in the Alternatives see the following:

o Section 4.0 - Sub Watershed Existing Conditions & Treatment for sub watershed descriptions and water quality treatment options.

o Appendix B - Figures 1-13 for details of the key design features of the proposed Alternatives.

o Appendix F - Figures of the key features of the proposed road intersection Alternatives.


o Appendix G - Annotated photographs of key features of the proposed Alternatives.

Alternatives 1, 2, 3, 4 and 5 are presented below. The combinations of various alternatives for bike path design, bike path alignment, source control, hydraulic design and treatment are all based on economically achieving the Project goals and objectives.

3.1.1 Alternative 1 Alternative 1 is shown in Appendix B, Exhibit 1 and Figures 1A, 1B, and 1C, and consists of the following components:

Install Class II bike lanes along Lake Tahoe Boulevard (LTB) from Clear View Drive (CVD) to Tahoe Mountain Road (TMR).

Install Class II bike lanes within the existing outside lanes of LTB from TMR to Sawmill Road (SR).

Install Class I bike path on the north side of LTB along the existing dirt path on USFS property from SR to Viking Way (VW).

The proposed western portion of the Class II bike lanes will connect to the existing Class II bike lanes along LTB that end at CVD. Class II bike lanes are proposed on both sides of the existing two lanes of LTB from CVD to TMR. Additional minor pavement width will be required in this section to include the bike lanes.

Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from TMR to the intersection of SR, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 45 mph to 35 mph. The proposed bike lanes in this section will include a five foot separation from the inside travel lanes for pedestrian safety. The future Sawmill 2 Bike Path is proposed to end at the intersection of LTB and SR where the LTB bike lanes will link with the proposed Sawmill 2 Bike Path. A crosswalk and pedestrian warning light is proposed at this location to provide a safe crossing for pedestrians. This LTB crossing at SR will also link the Sawmill 2 Bike Path to the Class II bike lanes along LTB to the west and the proposed Class I bike path along the existing dirt path to the east.

The eastern section of the proposed Class I bike path begins on the north side of LTB at the intersection of SR. This section of the Class I bike path will generally follow the existing dirt path on the north side of LTB to the intersection of LTB and Viking Way. This portion of the bike path will require the installation of approximately six culvert crossings to convey runoff from the uphill watersheds beneath the bike path. The Class I bike path will consist of an 8’ wide paved path with a 2’ wood chip shoulder (clear-zone) on both sides of the bike path. The bike path is proposed to span stream environment zone (SEZ) areas with new culverts and improved upstream and downstream channels. These areas slated for improvement are at existing drainages along the existing dirt path. This section of the proposed bike path will link to the existing Class II bike lanes along LTB ending at the intersection of VW and LTB.

This alternative requires that a Special Use Permit be obtained from public property owners along the north side of LTB (USFS and CSLT).


Erosion Control Component

Revegetate eroding slopes and bare areas to provide source control.

Armor eroding conveyance channels to provide source control.

The primary focus for erosion control will be to provide source control on eroding roadside slopes and on bare road shoulders. Revegetation techniques will be used on eroding slopes and other bare eroding areas. Source control will also be achieved by armoring or vegetation lining portions of the bare soil conveyance ditches along LTB.

Hydraulic Conveyance Component

Replace failing or undersized culverts to prevent road damage and flooding.

Modify channels to correctly size conveyance upstream and downstream of culverts.

Install one drainage inlet to collect road runoff into the existing storm drain system at the intersection of LTB and BMR.

Install new culverts beneath the newly proposed bike path.

Hydraulic conveyance will primarily be enhanced by upgrading failing or undersized culverts that exist along LTB. Also, as mentioned above, new culverts will be installed to properly convey upland runoff beneath the newly proposed bike path. Channel armoring upstream and downstream of culverts will enhance conveyance to minimize road and bike path damage and flooding.

Water Quality Component

Install sediment traps, one sediment/infiltration basin and rock bowls to trap sediment and infiltrate runoff.

Water quality treatment options for storm water include sediment traps, rock bowls, and sediment basins.

SEZ Enhancement Component

SEZ enhancement will be achieved via installation of an additional culvert or bottom-less arch crossing LTB at a different location to increase hydraulic connectivity by routing previously diverted flows to additional parts of the SEZ to increase the stream zone treatment area.

Safety Component

Safety improvements/traffic calming will be accomplished via reduction of LTB from 4 lanes to 2 lanes with an accompanying speed limit reduction from 45 mph to 35 mph from TMR to SR.

Safety improvements will be installed including a pedestrian crosswalk and flashing beacon for crossing LTB at the intersection of SR.

A separation of 5 feet is designed between the bike lane and the traffic lane.



Bike Path and Bike Lane Component

Install Class II bike lanes along Lake Tahoe Boulevard (LTB) from Clear View Drive (CVD) to Tahoe Mountain Road (TMR).

Install Class II bike lanes within the existing outside lanes of LTB from TMR to 400 feet southwest of the intersection of Industrial Ave.

Install Class II bike lanes along LTB from approximately 400 feet southwest of the intersection of Industrial Ave on both sides of the existing 4 lane road. An additional 4 feet of pavement width will be required on both sides of LTB to accommodate the bike lanes.


Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from TMR to the intersection of SR, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 45 mph to 35 mph. The proposed bike lanes in this section will include a 5 foot separation from the existing inside travel lanes for pedestrian safety. The future Sawmill 2 Bike Path is proposed to end at the intersection of LTB and SR where the proposed LTB bike lanes will link with the proposed Sawmill 2 Bike Path. A crosswalk and pedestrian warning light is proposed at this location to provide a safe crossing for pedestrians.

Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from SR to approximately 400 feet southwest of the intersection of Industrial Ave, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 55 mph to 45 mph. The proposed bike lanes in this section will include a 5 foot separation from the inside travel lanes.

Continuing east, Class II bike lanes are proposed along LTB from approximately 400 feet southwest of the intersection of Industrial Ave on both sides of the existing four lane road. This portion of the roadway is proposed to remain a four lane road due to the high volume of truck traffic in this location. This section of the proposed bike lanes will link to the existing Class II bike lanes along LTB ending at the intersection of VW and LTB. An additional 4 feet of pavement width will be required on both sides of LTB to accommodate the bike lanes.









Install drainage inlets to collect road runoff into storm drain system.

Hydraulic conveyance will primarily be enhanced by upgrading failing or undersized culverts that exist along LTB. Channel armoring upstream and downstream of culverts will enhance conveyance to minimize road and bike path damage and flooding.


Install sediment traps and rock bowls to trap sediment.




Safety Component

Safety improvements/traffic calming will be accomplished via reduction of Lake Tahoe Boulevard from 4 lanes to 2 lanes with an accompanying speed limit reduction from 45 mph to 35 mph from TMR to SR, and 55 mph to 45 mph from SR to Industrial Ave.


A separation of 5 feet is designed between the bike lane and the traffic lane.



Install Class II bike lanes along Lake Tahoe Blvd. (LTB) from Clear View Drive (CVD) to Tahoe Mountain Road (TMR).

Install Class I bike path on the north side of LTB along the existing dirt path on USFS property from TMR to the intersection of Sawmill Road (SR).

Install Class I bike path on the north side of LTB along the existing dirt path on USFS property from the intersection of SR to Viking Way (VW).



Continuing east, the proposed Class I bike path begins on the north side of LTB at the intersection of TMR. Two crosswalks and pedestrian warning lights are proposed at this location to provide a safe crossing to link the Class II bike lanes along LTB and the proposed Class I bike path to the east. This section of the Class I bike path generally follows the existing dirt path on the north side of LTB to the intersection of LTB and SR. This portion of the bike path will require the installation of approximately 120’ of elevated bike path to span a section of meadow and stream zone. This portion of the Class I bike path will consist of an 8’ wide paved path with a 2’ wood chip shoulder (clear-zone) on both sides of the path. The future Sawmill 2 Bike Path is proposed to end at the intersection of LTB and SR where the LTB bike lanes will link with the proposed Sawmill 2 Bike Path. A crosswalk and pedestrian warning light is proposed at this location to provide a safe crossing for pedestrians. This LTB crossing at SR will link the Sawmill Bike Path to the proposed Class I bike path to the east and west.

Continuing east, the proposed Class I bike path begins on the north side of LTB at the intersection of SR. This section of the Class I bike path generally follows the existing dirt path on the north side of LTB to the intersection of LTB and D Street/Viking Way. This portion of the bike path will require the installation of approximately six culvert crossings to convey runoff from the uphill watersheds beneath the bike path. This portion of the Class I bike path will consist of an 8’ wide paved path with a 2’ wood chip shoulder (clear-zone) on both sides of the path. The bike path is proposed to span stream environment zone (SEZ) areas with new culverts and improved upstream and downstream channels. These areas slated for improvement are at existing drainages along the existing dirt path. This section of the proposed bike path will link to the existing Class II bike lanes along LTB ending at the intersection of VW and LTB.

This alternative requires that a Special Use Permit can be obtained from public property owners along the north side of LTB (USFS and CSLT).











Hydraulic conveyance will primarily be enhanced by upgrading failing or undersized culverts that exist along LTB. Also, as mentioned above, new culverts will be installed to properly convey upland runoff beneath the newly proposed bike path. Channel armoring upstream and downstream of culverts will enhance conveyance to minimize road and bike path damage and flooding.


Install sediment traps, one sediment basin, and rock bowls to trap sediment and infiltrate runoff.




Safety Component

Safety improvements will be installed including a pedestrian crosswalk and flashing beacon for crossing LTB at the intersections of SR and TMR.

A greater percentage of the bike path is located away from the roadway which increases pedestrian safety.

3.1.4 Alternative 4 Alternative 4 is graphically the same as what is shown in Appendix B, Exhibit 4 and Figures 1A, 1B, and 1C, and consists of the following components:



Install Class II bike lanes within the existing outside lanes of LTB from TMR to Sawmill Road (SR). Remove and restore approximately 6 feet of pavement on both sides of LTB.

Install Class I bike path on the north side of LTB along the existing dirt path on USFS property from SR to VW.

The proposed western portion of the Class II bike lanes will connect to the existing Class II bike lanes along LTB that end at CVD. Class II bike lanes are proposed on both sides of the existing two lanes of LTB from CVD to Tahoe Mountain Road. Additional minor pavement width will be required in this section to include the bike lanes.

Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from TMR to the intersection of SR, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 45 mph to 35 mph. The proposed four foot bike lanes in this section will be next to 14 foot wide inside travel


lanes. Approximately six feet of pavement is proposed to be removed and restored on both sides of LTB. The future Sawmill 2 Bike Path is proposed to end at the intersection of LTB and SR where the LTB bike lanes will link with the proposed Sawmill 2 Bike Path. A crosswalk and pedestrian warning light is proposed at this location to provide a safe crossing for pedestrians. This LTB crossing at SR will link the Sawmill Bike Path to the Class II bike lanes along LTB and the proposed Class I bike path to the east.

The eastern section of the proposed Class I bike path begins on the north side of LTB at the intersection of SR. This section of the Class I bike path generally follows the existing dirt path on the north side of LTB to the intersection of LTB and VW. This portion of the bike path will require the installation of approximately six culvert crossings to convey runoff from the uphill watersheds beneath the bike path. This portion of the Class I bike path will consist of an 8’ wide paved path with a 2’ wood chip shoulder (clear-zone) on both sides of the path. The bike path is proposed to span stream environment zone (SEZ) areas with new culverts and improved upstream and downstream channels. These areas slated for improvement are at existing drainages along the existing dirt path. This section of the proposed bike path will link to the existing Class II bike lanes along LTB ending at the intersection of VW and LTB.

This alternative requires that a Special Use Permit be obtained from public property owners along the north side of LTB (USFS and City of South Lake Tahoe).










Hydraulic conveyance will primarily be enhanced by upgrading failing or undersized culverts that exist along LTB Also, as mentioned above; new culverts will be installed to properly convey upland runoff beneath the newly proposed bike path. Channel armoring upstream and downstream of culverts will enhance conveyance to minimize road and bike path damage and flooding.


Install sediment traps, one sediment basin, rock bowls, and flow spreaders, to trap sediment and infiltrate runoff.





Pavement removal and revegetation from TMR to SR.

Safety Component

Safety improvements/traffic calming will be accomplished via reduction of LTB from 4 lanes to 2 lanes with an accompanying speed limit reduction from 45 mph to 35 mph from TMR to SR.


3.1.5 Alternative 5 Alternative 5 is graphically the same as what is shown in Appendix B, Exhibit 5 and Figures 2A, 2B, and 2C, and consists of the following components:



Install Class II bike lanes within the existing outside lanes of LTB from TMR to Viking Way (VW). Remove and restore approximately 6 feet of pavement on both sides of LTB.

The proposed western portion of the Class II bike lanes will connect to the existing Class II bike lanes along LTB that end at CVD. Class II bike lanes are proposed on both sides of the existing two lanes of LTB from CVD to TMR. Additional minor pavement width will be required in this section to include 4 foot bike lanes.

Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from TMR to the intersection of SR, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 45 mph to 35 mph. The proposed four foot bike lanes in this section will be next to 14 foot wide inside travel lanes. Approximately six feet of pavement is proposed to be removed and restored on both sides of LTB. The future Sawmill 2 Bike Path is proposed to end at the intersection of LTB and SR where the LTB bike lanes will link with the proposed Sawmill 2 Bike Path. A crosswalk and pedestrian warning light is proposed at this location to provide a safe crossing. This LTB crossing at SR also will link the Sawmill 2 Bike Path to the Class II bike lanes along LTB and the proposed Class I bike path to the east.

Continuing east, Class II bike lanes are proposed along LTB within the two existing outside travel lanes from SR to approximately 400 feet southwest of the intersection of Industrial Ave, reducing this section of LTB from four lanes to two lanes. This section also includes a speed limit reduction from 55 mph to 45 mph. The proposed four foot bike lanes in this section will be next to 14 foot wide inside travel lanes. Approximately six feet of pavement is proposed to be removed and restored on both sides of LTB.


Continuing east, Class II bike lanes are proposed along LTB from approximately 400 feet southwest of the intersection of Industrial Ave to VW on both sides of the existing four lane road. This portion of the roadway is proposed to remain a four lane road due to the high volume of truck traffic in this location. This section of the proposed bike lanes will link to the existing Class II bike lanes along LTB ending at the intersection of VW and LTB. Additional pavement four feet wide will be required on both sides of LTB to accommodate the bike lanes.









Hydraulic conveyance will primarily be enhanced by upgrading failing or undersized culverts that exist along LTB. Channel armoring upstream and downstream of culverts will enhance conveyance to minimize road and bike path damage and flooding.


Install sediment traps and rock bowls to trap sediment.




Pavement removal and revegetation from TMR to SR.

Safety Component

Safety improvements/traffic calming will be accomplished via reduction of LTB from 4 lanes to 2 lanes with an accompanying speed limit reduction from 45 mph to 35 mph from TMR to SR, and 55 mph to 45 mph from SR to Industrial Ave.



4.0 Sub Watershed Existing Conditions & Treatment See Appendix E Figure WS, for watershed boundaries and culvert identifications. The following treatment options apply to all alternatives unless otherwise stated.

See Appendix B Figures 1-13 for details of the key design features of the proposed Alternatives.

4.1 Sub watershed LTB-1 Existing Conditions

Sub-watershed LTB-1 consists of approximately 15.2 acres, of which approximately 5.5% is impervious roadways. The smallest watershed in the Project area extends generally to the north of Lake Tahoe Boulevard (LTB), in the vicinity of Tahoe Mountain Road (TMR) and Boulder Mountain Road (BMR). The County right-of-way portion of the watershed is approximately 1.7 acres. Watershed LTB-1 includes a small number of houses along BMR with additional impervious surfaces. The highest point in the watershed is at approximately the 6443’ elevation, with the outfall point at approximately the 6365’ elevation.

Runoff from the lower portion of BMR currently collects at the intersection of LTB and BMR and then flows along the north side of LTB in a roadside channel and a section of eroding channel to the inlet of culvert LTB1. Another section of eroding channel on the west side of TMR also leads to the inlet of culvert LTB1. The existing 18 inch outfall culvert LTB1 is located at the intersection of LTB and TMR and conveys runoff beneath TMR. This culvert discharges into a section of eroding channel followed by open meadow before reaching the watershed LTB-2 outfall culvert LTB2.

Treatment

Water quality treatment options for storm water include the installation of a sediment trap at the intersection of LTB and BMR, and a culvert to connect to the existing storm drain beneath LTB at BMR. The installation of armored channels in both eroding channels leading to the inlet of culvert LTB1. Two sediment traps are proposed at the culvert inlet. Replacement of the existing culvert is proposed, including a flared end section at the outlet. The culvert outlet channel is also proposed to be armored to a point where the existing channel is less steep and stable. Runoff from watershed LTB-1 discharges into watershed LTB-2 and the open meadow between TMR and SR, a natural resource for water quality treatment.


Sub-watershed LTB-2 consists of approximately 139.7 acres, of which approximately 2.3% is impervious roadways. The third largest watershed in the Project area extends generally to the north of LTB, between TMR and SR. The County right-of-way portion of the watershed is approximately 10.3 acres. Watershed LTB-2 includes a large number of houses along the upper part of BMR and Iron Mountain Circle with additional impervious surfaces. The highest point in the watershed is at approximately the 7000’ elevation, with the outfall point at approximately the 6320’ elevation.

The existing 24 inch outfall culvert LTB2 is located at the low point of a large area of open meadow bisected by LTB. Runoff from watershed LTB-1 also reaches this point after


flowing across the open meadow. Culvert LTB2 conveys runoff beneath LTB into the lower part of the open meadow and eventually Angora Creek.

Treatment

Water quality treatment options for storm water include replacement of the existing 24 inch culvert LTB2, including flared end sections and rock dissipaters at the inlet and outlet. Also the installation of three sediment traps connected to culvert LTB2 in the road median area is proposed. Also proposed is the installation of a new 24 inch culvert beneath LTB approximately 300 feet to the east, including installation of three sediment traps connected to the new culvert in the road median area, and flared end sections and rock dissipaters at the inlet and outlet. This new culvert is proposed to alleviate chronic flooding of the roadway and split a portion of the meadow runoff to other parts of the downstream meadow. This new culvert also includes the installation of three sediment traps connected to the new culvert in the road median area. Runoff from watersheds LTB-1&2 ultimately reaches the lower portion of the open meadow between TMR and SR, a natural resource for water quality treatment.


Sub-watershed LTB-3 consists of approximately 68.2 acres, of which approximately 3.1% is impervious roadways. The fifth largest watershed in the Project area is located generally to the north of LTB, including the middle portion of TMR and Forest Mountain Drive (FMD). The County right-of-way portion of the watershed is approximately 4.3 acres. Watershed LTB-3 includes a small number of houses along BMR and FMD with additional impervious surfaces. The highest point in the watershed is at approximately the 6950’ elevation, with the outfall point at approximately the 6357’ elevation.

The existing 24 inch outfall culvert LTB3 is located on USFS property approximately 600 feet north of the intersection of SR. This culvert conveys runoff beneath the existing dirt trail into a section of eroding channel on USFS property then into the outfall culvert LTB4 of watershed LTB-4.

Treatment

The following proposed treatment option only applies to Alternatives 1, 3, and 4.

Water quality treatment options for storm water include the construction of a sediment basin near the outlet of culvert LTB3. The proposed sediment basin will be located within a disturbed area just south and east of culvert LTB3. Armored channel is proposed from the outlet of culvert LTB3 to the proposed basin and out of the basin back to the existing downstream channel.


Sub-watershed LTB-4 consists of approximately 155.8 acres, of which approximately 3.6% is impervious roadways. The second largest watershed in the Project area is located generally to the north of LTB, in the vicinity of the upper part of TMR including a large portion of the Angora Highlands subdivision. The County right-of-way portion of the watershed is approximately 11.3 acres. Watershed LTB-4 also includes a large number of


houses along BMR and the Angora Highlands subdivision with additional impervious surfaces. The highest point in the watershed is at approximately the 7125’ elevation, with the outfall point at approximately the 6337’ elevation.

The existing 18 inch outfall culvert LTB4 is located just east of the intersection of SR and conveys runoff from watersheds LTB-3&4 beneath LTB to the south into the outlet channel of Sawmill Pond.

Treatment

Water quality treatment options for storm water include the installation of three sediment traps at the inlet of culvert LTB4. Replacement of the existing culvert LTB4 is proposed, including a flared end section and rock dissipater at the outlet. The installation of armored channel leading to the proposed sediment traps at the inlet of the culvert is also proposed. Also the installation of three sediment traps connected to culvert LTB4 in the road median area will occur. Runoff from watersheds LTB-3&4 ultimately reaches the Sawmill Pond outlet channel leading to the open meadow between TMR and SR, a natural resource for water quality treatment.


Sub-watershed LTB-5 consists of approximately 114.6 acres, of which approximately 1.3% is impervious roadways. The fourth largest watershed in the Project area is located generally to the north of LTB, and east of SR. The County right-of-way portion of the watershed is approximately 1.8 acres. Watershed LTB-5 does not include any additional impervious surfaces. The highest point in the watershed is at approximately the 7125’ elevation, with the outfall point at approximately the 6350’ elevation.

The existing 18 inch outfall culvert LTB5 is located just east of the intersection of SR and conveys runoff beneath LTB into the east end of Sawmill Pond.

Treatment

Water quality treatment options for storm water include the installation of two sediment traps at the inlet of culvert LTB5. Replacement of the existing culvert LTB5 is proposed, including a flared end section rock dissipater at the outlet. The installation of armored channel leading to the proposed sediment traps at the inlet of the culvert, along with the installation of two sediment traps connected to culvert LTB5 in the road median area are also proposed. Runoff from watershed LTB-5 discharges into Sawmill Pond.


Sub-watershed LTB-6 consists of approximately 304.6 acres, of which approximately 0.01% is impervious roadways. The largest watershed in the Project area is located generally to the north of LTB, on the eastern end of the Project area to Viking Way. The County right-of-way portion of the watershed is approximately 5.8 acres. Watershed LTB-6 does not include any additional impervious surfaces. The highest point in the watershed is at approximately the 7125’ elevation, with the outfall point at approximately the 6287’ elevation.


The runoff from watershed LTB-6 eventually reaches the existing large sediment basin on City of South Lake Tahoe (CSLT) property installed after the Angora Fire, prior to discharging into the 30 inch outfall culvert crossing LTB at D Street.

Treatment

Water quality treatment options for storm water include the diversion of the western most portion of the LTB roadside channel. The channel diversion is proposed to direct the flows into a large, well vegetated natural channel treatment area on the north side of LTB. This channel then reenters the roadside channel just downstream of culvert LTB7, eventually reaching the existing large sediment basin at LTB and Viking Way.


Sub-watershed LTB-7 consists of approximately 48.8 acres, of which approximately 0.3% is impervious roadways. The seventh largest watershed in the Project area is located generally to the south of LTB, on the eastern end near Industrial Ave. The County right-of-way portion of the watershed is approximately 0.5 acres. Watershed LTB-7 does not include any additional impervious surfaces. The highest point in the watershed is at approximately the 7008’ elevation, with the outfall point at approximately the 6320’ elevation.

The existing 18 inch outfall culvert LTB7 is located just west of the intersection of Industrial Ave. and conveys runoff beneath LTB to the north into watershed LTB-6.

Treatment

Water quality treatment options for storm water include the installation of two sediment traps at the inlet of culvert LTB7. Replacement of the existing culvert LTB7 is proposed, including a flared end section and armored channel at the outlet. Runoff from watershed LTB-7 discharges into the roadside channel on the north side of LTB, eventually reaching the existing large sediment basin at LTB and Viking Way.


Sub-watershed LTB-8 consists of approximately 49.9 acres, of which approximately 4.6% is impervious roadways. The sixth largest watershed in the Project area is located generally to the south of LTB, on the eastern end of the Project. The County right-of-way portion of the watershed is approximately 2.9 acres. Watershed LTB-8 does not include any additional impervious surfaces. The highest point in the watershed is at approximately the 6467’ elevation, with the outfall point at approximately the 6353’ elevation.

The existing 18 inch outfall culvert LTB-8 is located west of the intersection of Industrial Ave. and conveys runoff beneath LTB to the north into watershed LTB-6.

Treatment

Water quality treatment options for storm water include the installation of two sediment traps at the inlet of culvert LTB8. Replacement of the existing culvert LTB8 is proposed, including flared end sections and rock dissipaters at the inlet and outlet. Also the installation of three sediment traps connected to culvert LTB8 in the road median area is proposed. Watershed LTB-8 treatment area is the same as watershed LTB-6. Proposed improvements include


diverting the runoff into the existing large well vegetated natural channel treatment area on the north side of LTB. This channel then reenters the LTB roadside channel, just downstream of culvert LTB7, eventually reaching the existing large sediment basin at LTB and Viking Way.

5.0 Alternatives Evaluation The alternative evaluation matrix was developed for the five alternatives and the evaluation for each matrix ranged from 1 (poor effectiveness), 2 (fair effectiveness), and 3 (good effectiveness). If an Alternative did nothing to achieve the goals then the effectiveness of the alternative was 0 (ineffective). The matrix also includes an importance weighting for the following criteria for the evaluation of each alternative. See Table 5 Alternative Evaluation Summary.

5.1 Enhance Recreational Opportunities Each alternative was developed in order to satisfy ‘the enhance recreational opportunities’ objective. In general, Class I bike paths offer a greater range of opportunities (transportation, recreation, scenic and wildlife viewing, education/interpretation, etc.) to the broadest user group (families, children, inexperienced riders, persons with disabilities, and other types of wheeled transportation users) as opposed to Class II bike lanes. And, within the larger context of filling network gaps, the majority of the LTB bike path is anticipated to be a Class 1 facility; thus a Class I facility along Lake Tahoe Boulevard (LTB) is most desired. The relative weight of ‘the enhance recreational opportunities’ evaluation portion of this alternative evaluation analysis is 4.

5.2 Provide a Bike Path Link to Local Businesses, Schools & Employment Each alternative was developed in order to satisfy the ‘provide a bike path link to local businesses, schools & employment’ objective. Since each alternative has the bike path beginning and ending in the same location, the effectiveness of each alternative for the ‘provide a bike path link to local businesses, schools & employment’ objective is somewhat equal. However, if a Class 1 bike path serves a broader spectrum of users, then a Class 1 alignment will meet this objective better than a Class 2 facility as more people may be willing to access these amenities via a Class 1 bike path due to increased safety and more enjoyable recreation experience. The relative weight of the ‘provide a bike path link to local businesses, schools & employment’ portion of this alternative evaluation analysis is 3.

5.3 Treatment of Fine Sediment Each alternative for all sub-watersheds was developed in order to satisfy the goal of treating very fine and fine sediment to the maximum extent practical. The effectiveness of each alternative for treating very fine and fine sediment was evaluated for the proposed treatment BMPs relative to all sub-watersheds for treatment of the first flush of runoff. For this analysis sand traps followed by sediment basins and infiltration was determined to have good effectiveness. The effectiveness of a sand trap followed by flow spreading was determined to have moderate effectiveness and the effectiveness of sand traps alone was determined to be poor. The overall effectiveness of the alternatives was based on the treatment of very fine and fine sediment as presented in Section 5. Therefore, Alternative 1 was determined to have the best opportunities for treating fine sediment and Alternatives 2 and 3 were equal


for having less opportunity for treating fine sediment. The relative weight for this alternative evaluation analysis is 4.

5.4 Treatment of Course Sediment Each alternative was developed and the effectiveness was evaluated in order to satisfy the goal of treatment of coarse sediment. Without the treatment of coarse sediment, the treatment effectiveness of each BMP for very fine and fine sediments will be compromised. Each alternative included the treatment of coarse sediment with sand traps and the effectiveness of sand traps was determined to be good. The relative weight of the treatment of coarse sediment evaluation portion of this alternative evaluation analysis is 2.

5.5 Reduction in Runoff Volume Each alternative was developed in order to satisfy the goal of reduction in runoff volume. The effectiveness of each alternative for reducing runoff volume was evaluated specifically for each sub-watershed as outlined in Section 5. For the reduction of runoff volume the effectiveness of sediment basins and infiltration was good, flow spreading was considered fair, and sediment traps was considered poor. Therefore, Alternative 1 was considered good, and Alternatives 2 and 3 were considered fair. The relative weight of the reduction in runoff volume evaluation portion of this alternative evaluation analysis is 2.

5.6 Reduction in Peak Flow Each alternative was developed in order to attempt to satisfy the goal of reduction in peak flow. Each of the proposed treatment BMPs provides some peak attenuation for small rain events, but since the reduction in runoff volume will likely be less than 33% of the 1-inch 1-hour storm, the reduction in peak flow is considered to be poor for all Alternatives. The relative weight of the reduction in peak flow evaluation portion of this alternative evaluation analysis is 2.

5.7 Capital Cost A Rough Order of Magnitude (ROM) cost estimate was prepared for each of the Project alternatives. The quantities for each alternative were tabulated based on proposed improvements as identified on Figures 1A-1C, 2A-2C, and 3A-3C. The unit costs for each improvement was estimated based on the El Dorado County Department of Transportation (EDOT) Engineers Estimate database using bid summaries between 2002 and 2009 for all bids. Table 5 presents the ROM construction cost estimate for each of the alternatives.


Table 5. Alternative ROM Construction Cost Estimate

Of the five alternatives evaluated for this Project Alternative 3 is more costly than the other alternatives. The primary reason for this cost difference is the greater length of the Class I bike path including the cost of the elevated bike path. Alternative 2 is least costly of all the Alternatives. The primary reason for this cost difference is the simplicity of the Alternative utilizing the existing roadway for the majority of the bike trail. Alternatives 1 and 4 are the second and third most costly mainly due to the cost of the Class I bike path and associated culvert crossings. Alternative 5 is the second least costly also due to the simplicity of the Alternative utilizing the existing roadway for the majority of the bike trail. The relative weight of the capital cost evaluation portion of this alternative evaluation analysis is 1.

5.8 Design/Planning Costs The level of detail and effort necessary for the design and planning for all Alternatives is not believed to be similar. Alternatives 1, 3, and 4 involve additional planning and design for a Class 1 bike path, which is more intensive than for the Class II bike trail along the existing roadway. The relative weight of the design and planning cost evaluation portion of this alternative evaluation analysis is 1.

5.9 Operations and Maintenance Costs The operation and maintenance costs for Alternatives 1, 3 and 4 will be roughly equal. The operation and maintenance costs for Alternatives 2 and 5 will be roughly equal. Operation and maintenance costs for Alternatives 2 and 5 are anticipated to be less due to the ease of access and location next to the traveled way, not in a heavily forested setting. BMP maintenance requirements for Alternatives 1, 3, and 5 are anticipated to be greater due to the increased number of proposed culverts associated with the Class I bike path, and the bike path location in a heavily forested setting. The relative weight of the operations and maintenance cost evaluation portion of this alternative evaluation analysis is 2.


5.10 Design Life The design life for most components of each of the five Alternatives is similar due to the design and proposed materials involved with each Alternative. Design life varies between BMPs, amount of vehicular and bicycle use and weather. If designed and installed properly, BMPs should last for 20 to 50 years. Revegetation, if properly designed, can last forever. The relative weight of the design life evaluation portion of this alternative evaluation analysis is 1.

5.11 ROW Acquisition Right-of-way (ROW) acquisitions are most intensive for Alternative 1, 3, and 4 due to the Class I bike path alignment crossing US Forest Service property. The County is currently investigating the exact requirements for ROW acquisition that will require Special Use Permits from the US Forest Service and possibly an easement from California State Parks. Alternatives 2 and 5 are designed to minimize the amount of ROW acquisition needed for construction. The relative weight of the ROW acquisition evaluation portion of this alternative evaluation analysis is 2.

5.12 Impacts to Existing Utilities The impacts to existing utilities are anticipated to be similar for all Alternatives since the proposed BMPs such as road culverts and sediment traps are essentially the same for all alternatives. The relative weight of the impacts to existing utilities evaluation portion of this alternative evaluation analysis is 1.

5.13 Disturbance The least amount of disturbance that is necessary to construct the Project is assumed to occur. Disturbance is assumed to be similar for Alternatives 2 and 5, due to the Class II bike lane alignment only affecting existing paved areas or road shoulder areas. The greatest amount of disturbance is assumed to occur in Alternatives 1, 3, and 4 due to the Class I bike path alignment which is proposed to be constructed generally within existing disturbed trails. The relative weight of the disturbance evaluation portion of this alternative evaluation analysis is 2.

5.14 Aesthetics Alternative 3 is assumed to have the best aesthetic appeal due to most of the Class I bike path being offset from LTB, and riders will experience the surrounding forest on the bike path. Alternatives 1 and 4 are assumed to have the second best aesthetic appeal because the majority of the path follows a Class I bike path being offset from LTB, and riders will experience the surrounding forest on the bike path. Alternatives 2 and 5 are assumed to have the lowest ranking aesthetic appeal due to the bike lanes being on the roadway. The relative weight of the aesthetics evaluation portion of this alternative evaluation analysis is 1.

5.15 Constructability Alternatives 1, 3, and 4 involve constructing a bike path over disturbed ground. Alternative 2 includes very little construction, mainly bike path striping and minimal paving. Alternative 5 also includes very little construction, mainly bike path striping, pavement removal, and paving. Constructability concerns are not similar between all Alternatives. The relative weight of the constructability evaluation portion of this alternative evaluation analysis is 1.


5.16 Flooding Each of the five Alternatives will be designed to help address the reported flooding concerns within the Project area by improving drainage infrastructure such as pipes and channels. Alternative 2 bike path alignment proposes adding four feet of pavement in one section on each side of LTB, causing greater chance of right-of-way flooding is created with the additional impervious surface. Alternative 4 bike path alignment proposes removing 6 feet of pavement along a small portion of both sides of LTB, and adding four feet of pavement in one section on each side of LTB, causing less of a chance of right-of-way flooding due to less impervious surface. Alternative 5 bike path alignment also proposes removing 6 feet of pavement along both sides of the majority of LTB, and adding 4 feet of pavement in one section on each side of LTB, causing less chance of right-of-way flooding due to less impervious surface. Alternatives 1, 3, and 4 include a separated bike path that is not anticipated to increase flooding potential due to being designed to sheet flow into the surrounding soils. The relative weight of the flooding evaluation portion of this alternative evaluation analysis is 1.

5.17 Groundwater Impacts All Project Alternatives have been designed to attempt to minimize impacts to groundwater. The Alternatives rely on either infiltration in drier areas or shallow detention or flow spreading in wetter areas. Therefore, the impacts to groundwater quality will be the same for all Project Alternatives. The relative weight of the groundwater impacts evaluation portion of this alternative evaluation analysis is 1.

5.18 Impervious Surfaces Alternative 1 will increase the impermeable area by approximately 71,352 ft2, Alternative 2 will increase the impermeable area by approximately 16,584 ft2 and Alternative 3 will increase the impermeable area by approximately 86,264 ft2. Alternative 2 is considered to have the greatest impact because the bike path alignment essentially widens the road by 8’, 4’ on each side, thus increasing peak flows from the largest impervious surface within the Project area. Alternatives 1, 2, and 3, while also increasing impervious area, are easier to mitigate because the new impervious surface is separated from the road and can be easily designed to sheet flow to natural areas for infiltration. Alternatives 4 and 5 are considered to have the least impact because the bike path alignment essentially narrows a portion of LTB by 12’; 6’ on each side, in effect decreasing peak flows. The relative weight of the impervious surfaces evaluation portion of this alternative evaluation analysis is 2.

5.19 Road Sand/Cinders The EDOT Maintenance Department does routinely apply road sands/cinders for safety within the Project area. Alternatives 1, 2, and 3 are considered to have the same effectiveness at recovering road sand and cinders due to no changes to the roadway area. Each Alternative proposes sediment traps in areas where heavy road sanding takes place. Alternatives 4 and 5 pavement removal does provide a smaller impervious surface where road sands could be applied. Each Alternative also proposes maintenance crew training to help increase the sweeping frequency of LTB. The relative weight of the road sand/cinders evaluation portion of this alternative evaluation analysis is 2.


5.20 Manmade Nutrient Sources The collection, conveyance, and treatment of manmade nutrients are not goals and objectives for this Project. For this reason the alternatives were not formulated specifically to address manmade nutrients. However, through the stabilization and collection of sediment the Project is anticipated to reduce phosphorus loading. The Project does not propose to add large sources of nitrogen. The relative weight of the manmade nutrient source evaluation portion of this alternative evaluation analysis is 1.

5.21 Public Safety Alternatives 1, 3, and 4 are assumed to be the best alignment for public safety due to a portion of the Class I bike path being separated from the road, thus reducing the chance for an accident between a bicyclist and an automobile. Alternative 2 is assumed to be the next safest alignment due to it being a Class II bike lane alignment with a 5 foot separation between the traffic lanes. Alternatives 4 and 5 are considered to be the most dangerous alignment due to the bike lanes not having a 5 foot separation from the traffic lanes. The relative weight of the public safety evaluation portion of this alternative evaluation analysis is 2.

5.22 Wildlife Habitat There remains a possibility that the bike path alignments proposed for Alternatives 1, 3 and 4 could have an affect on wildlife habitat due to the new disturbance being created by the bike path and the alignment location in the forest. Surveys conducted as part of the environmental process for this Project will determine what wildlife habitat is present and what affects the proposed Project may have. It is doubtful that Alternatives 2 and 5 would have any additional adverse affects on wildlife due to the proposed bike lanes location along the existing road. The relative weight of the wildlife habitat evaluation portion of this alternative evaluation analysis is 1.

5.23 Vegetation There remains a possibility that the bike path alignments proposed for Alternatives 1, 3 and 4 could have an affect on vegetation due to the new disturbance being created by the Class I bike path. Surveys conducted as part of the environmental process for this Project will determine what vegetation is present and what affects the proposed Project may have. The Class I bike path alignments will provide an opportunity to enhance forest health by removing over crowded stands of trees or downed vegetative material. It is doubtful that Alternatives 2 and 5 would have any adverse affects on vegetation due to the proposed bike lanes location along the existing road. The relative weight of the vegetation evaluation portion of this alternative evaluation analysis is 1.

5.24 Cultural Resources Alternatives 1, 3, and 4, as proposed, may interfere with known cultural sites within the Project area. Surveys conducted as part of the environmental process for this Project will determine what cultural resources are present and what affects the proposed Project may have on them. The County will work with the USFS Archeologists to ensure that proper mitigation and avoidance measures are taken during design and construction of the Project. It is doubtful that Alternatives 2 and 5 would have any adverse affects on cultural resources due to the bike lanes location along the existing road. The relative weight of the cultural resources evaluation portion of this alternative evaluation analysis is 2.


5.25 Vector Control Each of the five Alternatives will be designed and constructed in a way that standing water will be present for less than 96 hours. The relative weight of the vector control evaluation portion of this alternative evaluation analysis is 1.

5.26 Permitability The permit process for the Alternatives 1, 3, and 4 will likely be similar and more complicated due to the Class II bike path alignment crossing national forest. Each Alternative will construct a bike trail and water quality improvements aimed at helping to attain environmental thresholds established for the Tahoe Basin. Each Alternative will require a permit from Lahontan, TRPA, and the US Army Corps of Engineers, due to jurisdiction over hydrologically connected wetlands and waters of the United States to navigable waterways. However, permitability relates heavily to disturbance and Project effects on wildlife, vegetation, cultural resources, sensitive lands, wetlands and right-of-way. Alternatives 1, 3, and 4 propose creating new coverage for the Class I bike path, which potentially could affect sensitive lands and species. Therefore, the length of time for permitting each of the five Alternatives will likely not be similar considering that each alternative will require a different level of effort. The relative weight of the permitability evaluation portion of this alternative evaluation analysis is 1.

5.27 Fundability The construction costs of each of the five Alternatives are not similar; therefore the number of funding sources may need to be increased. The goals and objectives of each of the Alternatives are the same, so the County should qualify for the same funding sources regardless of which Alternative is constructed. The relative weight of the fundability evaluation portion of this alternative evaluation analysis is 1.

5.28 Forest Health Alternatives 1, 3, and 4 are assumed to be the best alignment for improving forest health due to the Class 1 bike path location in overly dense forested areas. Alternatives 2 and 5 are assumed to have the least impact on forest health due to the bike lanes location along the existing road. The relative weight of the forest heath evaluation portion of this alternative evaluation analysis is 1.

6.0 Alternatives Evaluation Summary Table 6 presents a tabulation of the evaluation of the alternatives based on the criteria and weights as summarized above.


Table 6. Alternative Evaluation Summary

Based on this comparison, Alternatives 1 and 4 most effectively satisfy the goals and objectives established for this Project.

7.0 Water Quality Conditions and Sediment Treatment A small portion of the Project area is rural residential with impervious surfaces associated with roads, dirt turnouts, private driveways, and homes. The majority of the Project area outside of the roadways consists of forested lands and a large meadow.

Two water features are located at the southern end of the LTB Enhancement Project corridor with Sawmill Pond located at the southeast corner of the Sawmill Road and Lake Tahoe Boulevard intersection and a small, unnamed pond just north of the intersection.


Both of these water features should contribute to improved water quality due to retention and particle settling.

At the southern end of the corridor is a large meadow area known as Washoe Meadows. The southwestern half of the corridor drains into the Washoe Meadows and then south into Angora Creek.

The northeastern portion of the corridor drains along Lake Tahoe Boulevard toward the City of South Lake Tahoe into the CSLT’s new water quality basin. The basin is located south of Viking Way and west of Lake Tahoe Boulevard. The basin was designed to treat runoff from the upper watershed area, which includes the northern watersheds for this Project. It is our understanding that the water quality basin was sized to treat runoff from the upper watershed, which includes the Lake Tahoe Boulevard watershed.

Preliminary research regarding the number of wetlands was performed using the National Wetlands Inventory Maps provided by the Fish and Wildlife Service. Based on the required wetland parameters, approximately seven potential wetland areas were identified within the Project area. In addition to wetlands, there are potential Waters of the US and Waters of the State in the Project area. Both Waters of the US and Waters of the State will be further investigated during the alternatives evaluation phase of the project. All of the potential Waters of the US eventually drain to Lake Tahoe via the Upper Truckee River. The delineation and mapping of wetlands and Waters of the US identified the existence of approximately 4.06 acres of potential jurisdictional wetlands.

7.1 Precipitation For this report we looked at three different approaches in determining the precipitation to estimate the runoff volume: the Mean Annual Precipitation (MAP) as defined in the EDCDM (Ford, 1995); using the reduced amount of MAP based on the amount of runoff due to rainfall and not snow melt; and using precipitation gage data from the Angora site.

7.2 Existing Precipitation Record The existing precipitation record near the Project area was analyzed in order to estimate the average annual sediment load from the Project area and evaluate the treatment effectiveness of the proposed BMPs. The existing precipitation record from the Angora weather station between July 22, 1997 and April 21, 2008 represents 10 years and 9 months of available discontinuous meteorological data and includes rain and snow. If the air temperature at the time of the precipitation measurement was greater than 32º F, the precipitation measurement was accepted to represent rain. The time interval for the precipitation record varies between 5 minute and 30 minute intervals and contains 9,829 independent rain measurements.

The depth of rain for this time duration was equal to 190.83 inches which represented an average of 17.75 inches of rain per year with the remainder of precipitation being in the form of snow. Peak rain intensities of 0.73 inches in 15 minutes (2.92 inches per hour) and 0.55 inches in 15 minutes (2.2 inches per hour) were measured on January 31, 2002 and August 3, 2000 respectively, representing 15 minute rain intensity return periods of approximately 100-years (Ford, 1995). This rain event also represented peak rain intensities of 1.07 inches in 60 minutes and represented a 60 minute duration return period of approximately 10-years (Ford, 1995). The return period for the peak measured rain intensity for each year was calculated using the Weibull plotting equation.

In order to evaluate the El Dorado County Drainage Manual rain intensity frequency curves, a limited statistical analysis was undertaken on the 10.75 years of measured peak annual


15, 30, and 60 minute rain intensities at the Angora gage. The goal of the statistical analysis was to extend the measured record by a factor of approximately 3 to include the 25-year return period. The 25-year log-pearson type III estimated peak rain intensities are 2.9, 1.9, and 1.1 inches per hour for the 15, 30, and 60 minute rain intensities respectively. Figures 2, 3, and 4 present the 15, 30, and 60 minute peak annual rain intensities measured at the Angora gage, El Dorado County Drainage Manual rain intensity frequency curve values based on a 36 inch mean annual precipitation, and the extended Angora peak rain intensities.

Based on this limited statistical review of the Angora gage, the El Dorado County Drainage Manual rain intensity curves generally under estimates the mean annual peak rain intensities and under estimates the 10-year and 25-year return period rain events for the 15, 30, and 60 minute durations. The snow fraction of the precipitation record was not included in this analysis since the snow accumulation onto impervious areas is generally moved to pervious regions and for the purposes of this calculation, the runoff from snow melt is assumed to infiltrate into the soil. The runoff from the fraction of snowmelt within the impervious regions of the Project area is assumed to melt at a rate which is similar to the runoff generated from rain. Rain on the pervious surfaces was determined to infiltrate into the ground since the initial abstraction for the Project area ranged from 2.8 to 4.7 inches (Stantec, 2007).

Figure 2 – 15-Minute Angora Gage Rain Intensities

Angora 15 Minute Rain Intensity Return Periods

y = 1.0972Ln(x) + 0.1753

y = 0.3528Ln(x) + 1.08870.0

1.0

2.0

3.0

4.0

1 10 100

Return Period

Rai

n In

tens

ity (i

n/ho

ur)

Gauge EDOT 40" MAPLog. (Gauge) Log. (EDOT 40" MAP)




y = 0.7222Ln(x) + 0.3171

y = 0.2525Ln(x) + 0.77820.0

1.0

2.0

3.0

4.0

1 10 100

Return Period

Rai

n In

tens

ity (i

n/ho

ur)




y = 0.363Ln(x) + 0.3175

y = 0.1807Ln(x) + 0.55660.0

0.5

1.0

1.5

2.0

1 10 100

Return Period

Rain

Inte

nsity

(in/

hour

)


The PLR precipitation values shown below in Table 7 were developed using the previously described methods.

Table 7. PLR Precipitation Values Method Precipitation

MAP – Total1 36” MAP –Rainfall Only (40% of MAP)2 14.4”

Gage Data3 17.75” 1. Ford, 1995 2. NHC, 2004 3. Angora Gage; 1997 – 2009.


7.4 Pollutant Load Reduction (PLR) Analysis The Pollutant Load Reduction Analysis used the Lake Tahoe TMDL Land Use GIS layer created by Tetra Tech for use in TMDL modeling efforts along with corresponding EMC data per watershed based on land use. The County went through an extensive conversion effort to utilize the land use data to determine pollutant loading by land use per sub-watershed within the Project area. The TMDL Technical Report (dated June 2010) indicated the fine sediment distributions for <20 µm averaged 63% of the total runoff fines. See Appendix H for the entire PLR modeling results.

Table 8. PLR Summary, Average Annual Sediment Load, Entire Watershed

Table 9. PLR Summary, Average Annual Sediment Load, Right-of-way

7.5 Treatment

As described in section 2.3.3 the treatment BMP Project alternatives were developed to meet the Project goals to the greatest extent feasible and were evaluated for feasibility based on a variety of codes, plans, and guidelines. The FHWA Urban Drainage Design Manual states that infiltration trenches are only feasible if the seasonal groundwater table is below the bottom of the trench (FHWA, 2001). Infiltrating BMPs must be designed and constructed such that the bottom of the infiltration trench or dry well is a minimum of one foot above the seasonal high water table (TRPA, 2002). The Tahoe Basin Interagency Roadway Maintenance and Operations Committee (TBIRMOC) require a minimum of four feet separation from the invert of the infiltration structure to the seasonal high groundwater (TBIRMOC, 2001). In order to meet the effluent limits for storm water discharges to surface waters, the Water Quality Control Plan for the Lahontan Region may require five feet of separation between the highest anticipated groundwater level and the bottom of the infiltration system (Lahontan, 1994).


Results from a geotechnical investigation by (Stantec December 2008) indicated seasonal high groundwater within 5 feet of the surface at each of the boring locations near the proposed sediment trap locations. Due to the results of this investigation the proposed sediment traps have been designed to not include the infiltration component.

As described in section 2.3.3 the treatment effectiveness of the double barrel sediment trap for the removal of tss (200 microns and less) has been demonstrated by the California Department of Transportation to be approximately 45%.

An additional treatment component with respect to the water quality of runoff from the Project area is street sweeping. Sweeping frequency in the Project area is currently dependent on the conditions of the road and the work load of El Dorado County maintenance crews.

In general the bike path will be constructed approximately 6 inches above existing grade so that the storm water runoff from the bike path will be conveyed across the trail and into adjacent vegetation rather than longitudinally along the trail. This will allow for the constant diffusion of storm water runoff. Runoff from the land adjacent to the bike path will be conveyed along the toe of the bike path and will cross under the bike path in cross culverts at low points in the alignment. The slopes on either side of the trail will be revegetated with grasses and/or shrubs, and there will be 2 feet of clearance from the edge of pavement to any shrubs. Therefore, the storm water runoff will receive treatment by being filtered through vegetated strips.

Additional treatment will be achieved via installation of an additional culvert or bottom-less arch culvert crossing LTB where the meadow intersects the road. The new culvert is proposed at a different location in the meadow area to increase hydraulic connectivity by routing previously diverted flows to additional parts of the SEZ to increase the treatment area.

A large portion of watershed LTB-6 and all of watershed LTB-8 proposed improvements include diverting the runoff into the existing large well vegetated natural channel treatment area on the north side of LTB. This channel then reenters the LTB roadside channel, just downstream of culvert LTB7, eventually reaching the existing large sediment basin at LTB and Viking Way.

Table 10 shows a summary of the PLR estimated annual sediment and sediment removal with properly maintained sediment traps, for the entire Project right-of-way, with a treatment effectiveness of 45%. The TMDL Technical Report (dated June 2010) indicated the fine sediment distributions for <20 µm averaged 63% of the total runoff fines.

Table 10. PLR Summary Estimated Annual Sediment Removal, Right-of-way


8.0 Conclusion Comments from the public following the October 1, 2008 Lake Tahoe Boulevard (LTB) Enhancement Project (Project) public meeting indicated that about half of the comments received were not in favor of the lane reduction alternative, citing concerns about inadequate snow removal and emergency vehicle access while showing support for a bike path separated from LTB. The other half of the comments generally supported the Project but cited concerns about safety and traffic speed.

Four of the five proposed alternatives include a lane reduction in each direction for a portion of or all of LTB. Two of the five alternatives propose a lane reduction for only the portion of LTB between Sawmill Road (SR) and Boulder Mountain Road (BMR), where the wet meadow area exists adjacent to the roadway. In this location, LTB has a proven accident history along the sharp curve south of SR and enhancements are proposed in these alternatives to make this area safer, while also building the bike path. Even with the lane reduction in this area the existing pavement will remain in its present condition to be utilized in case of an emergency situation. Alternative three proposes no lane reduction, requiring the bike path to cross the upper part of the wet meadow area with an elevated bike path, which poses many challenges and a high cost to construct a Class 1 bike path.

It can be assumed that once a safe and convenient bicycle facility is constructed that certain vehicle trips will convert to non-motorized trips. Based on County records (for the years 2007-2009) the Average Daily Traffic (ADT) volume was 5,269 vehicle trips on LTB just north of SR. The mode shift percentages identified in the Lake Tahoe Regional Bicycle and Pedestrian Master Plan indicates that construction of this trail could result in approximately 10% to 20% of the ADT, or 527 to 1,054 daily bicycle trips during the summer months. While this estimation may or may not be exact, this assumption is further supported by a recent survey conducted by the Tahoe Regional Planning Agency and the Tahoe Coalition of Recreation Providers (TCORP) titled the Lake Tahoe Basin Bike Trail Survey, May 2009, which asks survey respondents if they would walk or bike more of a Class I/Multi Use Path were present. In the survey, 93% of the respondents indicated they would. It is also important to acknowledge that the bicycle/pedestrian trail portion of the Project is part of the TRPA Bicycle and Pedestrian Master Plan, which, upon completion, will connect the Mountain View Estates and Angora Highlands neighborhoods with the City of South Lake Tahoe, the South Y Transit Center, and the South Tahoe High School as well as residential areas along North Upper Truckee which is presently served by an existing Class II bicycle facility. Additionally, this portion of trail is being planned in conjunction with facilities under construction or planning that will connect Meyers with the City of South Lake Tahoe via Highway 50 and Sawmill Road.

References: American Association of State Highway and Transportation Officials (AASHTO). (March 1999). Guide for the Development of Bicycle Facilities.

California Department of Public Health (CDPH). (July 2007). Statewide Relaxation of 72-Hour Water Detention Policy for Mosquito Prevention in Structural Best Management Practices (BMPs).

California Department of Transportation (Caltrans). (September 2006). Highway Design Manual.


California Department of Transportation (Caltrans). (June 2003). Caltrans Tahoe Highway Runoff Characterization and Sand Trap Effectiveness Studies.

California Regional Water Quality Control Board Lahontan Region. (October 1994). Water Quality Control Plan for the Lahontan Region North and South Basins.

California Storm Water Quality Association (CASQA). (January 2003). California Storm Water BMP Handbook.

Ford, T. D. and others. (March 1995). El Dorado County Drainage Manual.

Federal Highway Administration (FHWA). (August 2001). Urban Drainage Design Manual.

Federal Highway Administration (FHWA). (December 2007). Manual on Uniform Traffic Control Devices.

Kayhanian, M. and Stenstrom, M. (2008). “First-Flush Characterization for Storm Water Runoff Treatment.” Stormwater, March/April, 32-45.

Northwest Hydraulic Consultants (NHC). (July 2004). Formulating and Evaluating Alternatives for Water Quality Improvement Projects.

Stantec Consulting Inc. (December 2008). Lake Tahoe Boulevard. Enhancement Project Feasibility Report.

Tahoe Basin Interagency Roadway Maintenance and Operations Committee (TBIRMOC). (November 2001). Planning Guidance for Implementing Permanent Storm Water Best Management Practices in the Lake Tahoe Basin.

Tahoe Resource Conservation District (TRCD). (October 2007). Soil Characteristics Survey.

Tahoe Regional Planning Agency (TRPA). (December 2002). Code of Ordinances.

Tahoe Regional Planning Agency (TRPA). (2010). Lake Tahoe Region Bicycle and Pedestrian Plan.

California Regional Water Quality Control Board Lahontan Region. Nevada Division of Environmental Protection. (June 2010) Lake Tahoe Total Maximum Daily Load Technical Report

Appendix A

CTC PREFERRED DESIGN APPROACH

Excerpt from California Tahoe Conservancy Soil Erosion Control Grants Program – Program Announcement and Guidelines, July 2002 D. Preferred Design Approach This section presents an overall strategy to consider when designing projects. It is intended to apply not only to grant application preparation, but also to the more detailed design work that occurs after a grant is awarded. The Preferred Design Approach is a refinement of previous erosion control program guidelines, and reflects the current assessment of state-of-the-art technology and experience in implementing erosion control projects at Lake Tahoe. The Preferred Design Approach emphasizes project elements that prevent the mobilization of fine sediment and nutrients by erosion (source control), and that reduce the volume of runoff reaching natural surface waters (hydrologic design considerations). Source control measures and hydrologic design considerations, primarily infiltration, are the most cost-effective and efficient means to improve water quality. Water quality treatment measures to remove pollutants from runoff are to be considered after application of the other two groups of design considerations (source control and hydrologic design). In cases where applicants find it difficult to apply a specific portion of the Preferred Design Approach to a project or element of a project, the applicant should consult with Conservancy staff on specific barriers to implementation of the Preferred Design Approach before submitting site improvement applications. If project designs are not based on this approach, grantees will be required to explain the specific barriers to the application of the Preferred Design Approach and provide documentation to support how the proposed alternative approach meets program objectives (e.g., maximizes water quality benefit). The Conservancy recognizes that this approach must be applied within the context of professional engineering practices to avoid impacts on public health and safety and damage to public and private property. It also recognizes that there are legal and regulatory limitations to the application of these principles, such as applicable drainage law. Specific elements of the Preferred Design Approach are: Source Control

1. Place higher priority on source controls than on treatment. Source controls are measures that prevent erosion. Treatment facilities remove pollutants from runoff.

2. Emphasize reduction in bare, erodible surfaces (e.g., steep cut slopes, dirt roads) and impervious area.

3. Emphasize stabilization of gullies, unstable channels, and other sources that contribute especially high sediment loads.

4. Maximize self-sustaining source control methods, such as revegetation with native plants, pine needle mulching, and adding soil amendments such as mycorrhizal inoculum to soils when appropriate.

Hydrologic Design

5. Maintain or create distributed flow patterns (e.g., flows which discharge from the right-of-way frequently, or from shoulders by unconcentrated "sheet flow") and avoid concentration of flows where feasible.

6. Maximize infiltration of runoff from impervious surfaces. In some cases this can be accomplished by techniques described in number 5 above or also by the construction of leach fields, dry wells, or detention basins, for example.

7. Keep runoff from non-urban areas separate from urban runoff until urban runoff is treated. Treatment efficiency is much greater when flow volumes are smaller.

8. Keep treated urban runoff separate from untreated urban runoff to avoid resuspension of sediments and decreased treatment efficiency in downstream facilities.

9. Apply geomorphologic principles to natural channel design and mimic natural processes when stabilizing, restoring, or recreating natural drainage channels. For example, channels with floodplains tend to be more stable than those without. Channels with steps and pools are a frequent natural stream form and have better habitat values than those with continuous slopes. Avoid adding to or decreasing natural stream flows or changing watershed boundaries.

Treatment

10. Emphasize removal of fine sediments and phosphorous. For the purposes of the program guidelines, fine sediment is considered to be those particles that pass the number 200 sieve (less than 75 microns). Examples of improvements that are likely to achieve this objective are properly-sized, flat or gently-sloping, well-vegetated, detention areas (meadow-like areas).

11. Use natural treatment systems, such as meadows, where feasible. Because of the critical importance of wetland plants in removing pollutants from runoff, projects located in Stream Environment Zones (SEZ) should generally preserve the existing vegetation and function of the SEZs to the maximum extent practicable.

These guidelines continue to place a priority on SEZ restoration work. Such restoration work is cost-effective and beneficial for removing nutrients and fine sediment from runoff. The Environmental Improvement Program (EIP) calls for 40 acres of SEZ restoration over the 10-year EIP period in each of the primary grantee jurisdictions. In addition, the 208 Plan calls for the restoration of 1,100 acres of disturbed SEZs in the Basin. As in past years' programs, preference will be given to qualified projects that provide for infiltration of runoff and absorption of nutrients by plants and soil. This concept will continue to be promoted in the plan review process.

Appendix B

PROJECT ALTERNATIVES EVALUATION REPORT PLANS

ALTERNATIVE 1

LTB3204.6

LEGEND

EXISTING ERODING CHANNELEXISTING SEDIMENT ACCUMULATIONEXISTING DISTURBED AREAEXISTING CULVERT & FLOW DIRECTIONPROJECT BOUNDARYEXISTING CONTOUREXISTING PROPERTY LINEEXISTING STORM DRAIN MANHOLEEXISTING EDGE OF PAVEMENTEXISTING DRAIN INLET OR SEDIMENT TRAPEXISTING PIPE ID/SIZE/PEAK Q 10-YEAREXISTING WATERSHED BOUNDARYEXISTING DIRT TRAIL

WATERSHED IDENTIFICATIONWATERSHED ACRES

ALTERNATIVE 1- EXISTING CONDITIONSPROPOSED CLASS I BIKE PATHPROPOSED CLASS II BIKE PATHPROPOSED SEDIMENT TRAPPROPOSED ROCK DISSIPATORPROPOSED CULVERT REPLACEMENT & FLOW DIRECTIONPROPOSED FLARED END SECTIONPROPOSED NEW CULVERTPROPOSED REVEGETATIONPROPOSED ARMORED CHANNELPROPOSED FENCEPROPOSED CROSSWALK WARNING LIGHTPROPOSED CROSSWALKPROPOSED BASIN

PROPOSED ALTERNATIVESLEGEND

BCNR, MD RP?LQNMPR?RGML

CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

1B

FIG 1A

PROJECT BOUNDARY

INDEX MAP & WATERSHEDS

FIG 1B

FIG 1C

PROJECT BOUNDARY

PROPOSED SAWMILL 2BIKE PATH

PROPOSED CROSSWALKAND WARNING LIGHT

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

PROPOSED SAWMILL 2BIKE PATH CROSSWALK

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

1C

PROJECT BOUNDARY

MATC

H LI

NE ~

SEE

FIG

URE

1A

FIG 1A


FIG 1B FIG 1C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

PROJECT BOUNDARY

FIG 1A


FIG 1B

FIG 1C

PROJECT BOUNDARY

MATCH LINE ~ SEE FIGURE 1B

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

ALTERNATIVE 2

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

2B

FIG 2A

PROJECT BOUNDARY


FIG 2B FIG 2C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET




LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

2C

PROJECT BOUNDARY

MATC

H LI

NE ~

SEE

FIG

URE

2A

FIG 2A


FIG 2B

FIG 2C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW


PROJECT BOUNDARY

FIG 2A


FIG 2B

FIG 2C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

ALTERNATIVE 3

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

3B

FIG 3A

PROJECT BOUNDARY


FIG 3B

FIG 3C

PROJECT BOUNDARY

PROPOSEDCROSSWALK ANDWARNING LIGHTS

ELEVATED BIKE PATH REQUIREDCROSSING STREAM ZONE AREA

LAKE TA

HOE BLVD

SAWMILL RD

D STREET




LTB3204.6

LEGEND






CJ BMP?BM AMSLRW

MATC

H LI

NE ~

SEE

FIG

URE

3C

PROJECT BOUNDARY

MATC

H LI

NE ~

SEE

FIG

URE

3A

FIG 3A


FIG 3B FIG 3C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

LTB3204.6

LEGEND






CJ BMP?BM AMSLRW


PROJECT BOUNDARY

FIG 3A


FIG 3B

FIG 3C

PROJECT BOUNDARY

LAKE TA

HOE BLVD

SAWMILL RD

D STREET

TAlexander

FreeText

ALTERNATIVE 4 IS SHOWN ESSENTIALLY THE SAME AS ALTERNATIVE 1 FIGURES

TAlexander

FreeText

ALTERNATIVE 5 IS SHOWN ESSENTIALLY THE SAME AS ALTERNATIVE 2 FIGURES

Appendix C

BMP TOOLBOX

APPENDIX C - BMP TOOLBOX Numerous Best Management Practices (BMPs) have been used in the Lake Tahoe Basin to control and treat runoff. Additional BMPs, available from communities outside the Basin, could also be used in the Project Area. A BMP list was compiled for the Project Alternatives Evaluation Report to assist in identifying BMPs that could be utilized in the alternatives.

1.1 Source Control The source control aspects within the Project Area are generally limited to eroding road shoulders, eroding roadside ditches and eroding slopes. The source control alternatives have been segregated between stabilization of the roadside and stabilization of the slopes. While there are more potential alternatives to mitigate these source control deficiencies, the alternatives discussed and recommendations for implementation in this section are based on which source control alternatives are expected to be most cost effective and maintenance free for this Project Area.

1.1.1 Revegetation In order for revegetation to be successful as a soil stabilization alternative within the Project Area, the plant selection, soil amendment and application methods must be tailored to the specific characteristics of the Lake Tahoe Boulevard Enhancement Project Area. These characteristics include the soil types, topography, aspect, land use and available water of the Project Area.

Keys to outlining a good revegetation strategy involves soil testing, the selection of appropriate soil restoration activities and materials, the selection of appropriate vegetation types to optimize success, the selection of the appropriate soil stabilization materials and developing an appropriate plan for the growth and maintenance of the vegetation. Upon preliminary review of the soil types within the project area, revegetation could be difficult on the road cuts along the north side of Lake Tahoe Blvd. This is primarily due to the dryness and granular characteristics of the soil and the depth to groundwater. However, revegetation remains a viable alternative for all sub-watersheds within the Project Area if the soils are properly amended and the correct vegetation types are selected.

1.1.2 Rock Cobble with Vegetation The rock cobble alternative is the placement of small rounded rock which ranges in diameter between 4 and 8 inches along bare soil, eroding road side ditches, eroding channels or eroding slopes and also includes the option of allowing vegetation to grow within the voids between the rocks. This technique can be economical and can mimic the look and conditions of natural channels. The advantages of rock cobble for this Project Area include the economic stabilization of bare soil while maintaining the infiltration of the existing soil and the nutrient uptake of native vegetation. The limitations include limited hydraulic conveyance within steep channels, the inability to be placed on slopes steeper than 3:1, and an inability to withstand snow plowing activity adjacent to the paved road. The use of rock cobble with vegetation in channels is a good alternative for this Project Area due to the relatively flat slopes of the conveyance channels.

1.1.3 Pavement Pavement is a proven technique for stabilizing bare soil and has successfully been implemented on past erosion control projects. Pavement can be installed as either

BMP Toolbox Lake Tahoe Boulevard Enhancement Project January 2011

permeable or impermeable. Permeable pavement can be effective in reducing the runoff peak flows and volumes, while impermeable pavement increases the runoff peak flows and volumes. Pavement as a source control alternative is best suited to address eroding bare soil caused by roadside parking or vehicular disturbance of the soil. Pavement is considered a good option to stabilize the road surface, concentrate flows for appropriate treatment and allow a stable surface for snow plowing. Additionally, bare road shoulders do exist, especially along Lake Tahoe Blvd, which can be stabilized with pavement.

1.1.4 Woodchip/Native Pine Needle Mulch Woodchip/Native Pine Needle Mulch (mulch) is an economical technique to provide source control for gently sloping or flat areas with bare soil. These areas could be adjacent to the paved road or eroding slopes where soils do not permit acceptable vegetative growth potential. The mulch layer, typically 2” thick, provides protective cover from rain drop impact and wind erosion to help stabilize the surface. Mulch layers also allow infiltration, retain soil moisture, moderate soil temperature, add organic material and enhance vegetative success. Mulch is a very economical way to protect surfaces that cannot be paved, but which are used for parking. In addition to placing mulch on the soil surface, mulch can be mixed into the soil profile to a depth of roughly 6” to reduce compaction and add structure and porosity to soil. Mulch is not very resistant to concentrated flow or to snow removal activities. Because of the infiltration capacity of the existing soil beneath the mulch, this alternative provides a reduction in runoff volume and peak flow as well as treatment of fine sediments by means of source control. For these reasons, mulch is proposed as a source control alternative for gently sloping bare road shoulders and eroding slopes where soils do not permit acceptable vegetative growth potential.

1.1.5 Rock Slope Protection In prior erosion control projects in the Tahoe Basin, rock slope protection has successfully been used to stabilize a wide range of eroding slopes; however this source control alternative has generally been applied to large or very steep eroding slopes. In the Project Area there are many varying types of eroding slopes; ranging from long, gently sloping hill sides to rather steep short cut slopes. It is impractical to place rock slope protection the length of Lake Tahoe Blvd where many eroding slopes exist, mostly due to cost and aesthetics, so slopes where rock slope protection will be considered will be within the County ROW in close proximity to the road and will be actively eroding. Rock slope protection must allow adequate setbacks from the road to accommodate snow removal. Rock slope protection is a long term means to stabilizing actively eroding cut slopes.

1.1.6 Contour Log Contour logs can be an economical alternative to stabilize steep slope segments to prevent soil erosion and provide benched areas to encourage seed germination and vegetative growth. Another benefit to using contour logs is that trees that must be removed to install the bike path or other erosion control improvements can remain onsite, instead of being off hauled, and be used as contour roughness logs. Contour logs are typically keyed into the soil by burying roughly a third of the log level on the contour of the slope. To add roughness, some limbs can remain on the log. Contour logs should be considered a source control option for this Project Area for slopes where erosion is occurring or where flow concentrates.


1.1.7 No Source Control There currently are limited erosion source control measures within the Project Area and without improvements there will be no reduction in the fine and course sediment suspended in storm water runoff. Source control is generally the most effective, and cost effective, means of reducing sediment in runoff and without source control the goals & objectives of the project cannot be satisfied.

1.2 Hydraulic Design The hydraulic design aspects within the Project Area include the evaluation of the hydraulic capacity of the channels conveying runoff, the hydraulic review of existing and proposed pipes, and the analysis of the conveyance of flow from the Project Area toward Angora Creek. Due to the size of the project area, the amount of sub-watersheds and the amount of publicly owned parcels, there are many hydraulic design alternatives available.

1.2.1 Channels The primary channel conveying flows from the upland portion of the project area runs parallel along Lake Tahoe Blvd. The channel conveys flows both from the road and from the natural drainages flowing down the hillside above the channel. The Lake Tahoe Blvd channels are relatively flat and are continually filled with eroded decomposed granite from the hillside and natural conveyance channels above. It is difficult to tell if the channel is actively eroding, or just carrying sediment from the hillside above. Due to the channel’s length, roughly 1.5 miles, a cost effective, maintenance non-intensive solution is needed. It is also impractical, due to the size, length and recreational use, that the entire hillside above the channel will be stabilized adequately to prevent sediment accumulation in the channel. Therefore appropriate capture devices, which are easily maintained, are necessary.

There are many perpendicular channels carrying flow from the hillside on the north side of Lake Tahoe Blvd, which carry seasonal or storm event flows through culverts under Lake Tahoe Blvd and out into the forest or meadow areas below. Many of the natural channels above the road are bare and erode during large storm events or spring runoff.

Many options exist to stabilize the main channel along Lake Tahoe Blvd. Options include: curb and gutter, rock lined channel, cobble and vegetation channel, intermittent rock lined channel, native seed and erosion control blanket, or do nothing.

Concrete curb and gutter is resilient to snow plows and effective in containing flow within the paved road surface. For this reason, concrete curb and gutter is a possible alternative to mitigate erosion and convey runoff along the channel adjacent to the Lake Tahoe Blvd. In addition, curb and permeable gutter is also worthy of consideration based on past performance on similar erosion control projects in the Tahoe Basin. However, concrete curb and gutter is relatively expensive and does add connectivity.

Armored channels, rock lined or articulated block, are a proven alternative for stabilizing channels and for treating runoff. Coarse suspended sediments in runoff settle into the voids, and portions of the fine suspended sediments are treated as runoff is infiltrated into the existing soils beneath the armored channel. Armored channels have been constructed on numerous erosion control projects. For the Project Area, armored channels are proposed as an alternative as a means of stabilizing channels, reducing erosion, and providing some treatment of suspended sediment in runoff. Armored channels can be combined with native vegetation where smaller cobbles are used and


are spaced to allow seed to germinate. This technique could be an option due to the flatness of the topography. Large angular rocks are most likely are not hydraulically necessary for channels within the Project Area. Another possible alternative is to build armored channels in key areas along the Lake Tahoe Blvd ditch adjacent to culvert crossings and in actively eroding ditch areas; the remaining portions of the channel could then be seeded or cleaned out and left in a native state.

Grass lined channels are considered as an alternative for hydraulic design for the entire Project Area, however in portions of the Project Area the roadside conditions are not conducive to the propagation of grasses primarily due to the absence of base flow or soil moisture and due to snow removal activities. However, in some watersheds which are closer to the meadow areas, where groundwater is closer to the surface, the soils are moister and the organic soil composition are more conducive to the propagation of grasses, it may be possible to sustain and maintain grass lined channels. For this reason the grass lined channel alternative is included as an alternative for hydraulic design.

Native seed and erosion control blanketed channels are considered an alternative for hydraulic conveyance in the Project Area and are appropriate due to the relatively flat nature of the lower Project Area. Native channel designs are an economical option to stabilize conveyance channels, support native vegetation and convey storm water flows. Native channels provide source control and treatment through infiltration and polishing through removal of nutrients and sediment by the native vegetation.

1.2.2 Pipes Eight culverts exist which convey flows next to or beneath Lake Tahoe Blvd (LTB1 – LTB8). The existing culverts are in varying states of disrepair. Many are clogged or failing and most are undersized. For these reasons and in order to adequately convey larger flows, it is proposed to replace or abandon and move or consolidate many of the culverts. Culverts will also need to convey storm water flows beneath the bike path in several areas.

1.2.3 Conveyance Toward Angora Creek Few options exist for conveying flows toward Angora Creek from culverts flowing beneath Lake Tahoe Blvd. In many instances alternatives for different types of BMPs will be evaluated to attenuate flows and spread them toward forested and meadow areas above Angora Creek. Options range from armored channels, to grass lined swales, to seeded channels with erosion control blanket to native existing swales.

1.2.4 No Hydraulic Design There currently are limited hydraulic design aspects for runoff within the Project Area, mostly undersized culverts, and without improvements to the hydraulic conveyance of runoff there will be no reduction in the suspended fine sediment in the runoff. For this reason, with the no hydraulic design alternative, the objectives of the project cannot be satisfied.

1.3 Treatment The eight sub-watersheds within the Project Area were evaluated for treatment potential for storm water and sediment. There remains a possibility that treatment is not necessary in each of the eight sub-watersheds due to the fact that flows from certain sub-watersheds can be combined and therefore treatment locations can be strategically located. It also may be possible that some smaller watersheds will not require


considerable treatment other than an updated culvert and a rock energy dissipater. By slowing and spreading flows, it is possible that adequate treatment can be achieved by spreading flows across forested or meadow areas.

Due to the publicly owned parcels on the north side of the Project Area, it is possible that different arrays of treatment types can be explored. If treatment options are to be limited to the County ROW due to easement issues or other issues, space will be constrained and treatment may be limited, especially for fine sediment. The alternatives that were selected for treatment were based on the Project objectives for treatment which primarily are to reduce the volume of runoff, reduce the peak flow, and to capture coarse and fine sediment.

The effectiveness of each treatment alternative is directly related to the dimensions of the treatment alternative, the peak flow and volume of the runoff, the sediment load characteristics and the design and operational considerations of the alternative. The reduction in runoff volume includes the volume of storage within the alternative plus the volume of runoff which will be treated or infiltrated during the design storm. The reduction in peak flow is dependent on the type of treatment alternative.

Locating any treatment alternative within the EDOT ROW may be a challenge due to the width constraints, topographic limitations, and the presence of physical features such as trees, boulders, utilities, driveways and other structures. Larger, more successful treatment options may be installed within adjacent publicly or privately owned parcels. Construction and maintenance costs are a key factor to consider and economic consideration must be given to the quantifiable treatment effectiveness of each alternative. The extent and frequency of inspection and removal of sediment and debris from the treatment system is dependent on the design of the system and the characteristics of the runoff.

An important consideration in the selection and design of the treatment alternatives is whether the alternative is operated in order to capture and treat the first flush, with a high flow bypass, or operated as a flow through process, particularly with respect to the treatment of fine sediment. With the first flush process, the treatment alternative is allowed to capture, retain and treat the first flush of runoff, which monitoring data has show often has the highest concentration of pollutants, and once the treatment alternative has reached volumetric capacity, the remaining runoff bypasses the treatment alternative. The flow through process is such that all runoff passes through the treatment alternative regardless of the treatment effectiveness of the alternative for a variety of volumes or flow rates. Generally, the reductions in runoff volume and peak flow will be similar whether the treatment alternative is designed for first flush or flow through operation. However, assuming that fine sediment concentrations are greatest in the first flush of runoff and assuming that each alternative is incapable of treating fine sediment in a flow through configuration, it is generally accepted that storm water treatment alternatives are more effective when operated in a first flush configuration.

Considering the project objectives as well as the design and operational factors for this project, the treatment alternatives identified include detention basins, grass lined swales, rock bowls, sediment traps, regional and source infiltration, and no treatment. In order to determine the effectiveness of any treatment alternative, flow measurements and water quality monitoring should take place after construction. For detention basins, and infiltration treatment alternatives operated in a first flush configuration, groundwater monitoring should be considered in order to determine the treatment effectiveness of the removal of fine sediment from the groundwater. For detention basins operated in flow


through configuration, surface water monitoring should be considered in order to determine the treatment effectiveness of the removal of fine sediment from the surface water runoff.

1.3.1 Detention Basin A detention basin is a storm water treatment alternative which reduces runoff volume and treats fine sediment by detention of runoff in a depression or bermed basin. The amount of potential space that is available for the construction of detention basins within the Project Area make the treatment of runoff with a detention basin a good option. If land is available, the detention basin is likely the most cost effective treatment alternative per unit volume of runoff treated. The reduction in peak flow likely includes the infiltration rate of the detention basin bottom but also is dependent on the runoff volume and the volume of infiltration storage.

For the treatment of suspended fine sediment in runoff, the detention basin relies on gravitational settling of particles that are denser than water. For fine particles suspended in runoff the settling time is such that treatment by a detention basin is impractical for a flow through configuration. Therefore the detention basin should be designed and operated in a first flush configuration in order to capture and treat the fine sediment. Ideally, a detention basin will be designed with a low flow meandering channel and will be vegetated with native species. Also, a detention basin should be designed for easy maintenance.

1.3.2 Grass Lined Channel (Bio-Swale) with Flow Spreading A grass lined channel is a storm water conveyance and treatment alternative which can reduce runoff volume and treat fine sediment by allowing some infiltration and by polishing storm water and intercepting particles as runoff flows down the channel. Ideally, grass lined channels are constructed with native species and have side slope angles of 3:1 minimum. Rock dissipaters are typically installed at the inflow of a grass lined channel to dissipate runoff energy. A good option is to have grass lined channels flowing into rock bowls, flared end sections or rock level spreaders to distribute flow slowly and evenly over an area for additional treatment and infiltration.

The amount of potential space that is available for the construction of grass lined swales within the Project Area make the treatment of runoff with a grass lined channel a potential option. The obstacle to potentially using grass lined channels in a majority the Project Area is the lack of base flow and the difficulty of supporting sod through the dry months of summer. However, with native species, it is possible to establish bio-swales with native seed and erosion control blankets. In moister areas, closer to Angora Creek, grass lined channels may be a good BMP, especially with native species. 1.3.3 Source Infiltration Source infiltration is a storm water treatment alternative which reduces runoff volume and treats fine sediment by infiltration of runoff throughout the sub-watershed near the source of the runoff. Source infiltration can include directing surface runoff at the source to perforated sediment traps, rock bowls, drainage inlets, permeable pavement, or rock lined channels. The depth to groundwater and the relatively high rate of infiltration of the soils within the Project Area are such that treatment of runoff by source infiltration is a feasible alternative. Treatment within EDOT ROW within the Project Area could include source infiltration adjacent to the paved road surface at the locations of source control. The reduction in peak flow likely includes the infiltration rate of the system but also is dependent on the runoff volume and the volume of infiltration storage.


For the treatment of suspended fine sediment in runoff, the source infiltration alternative relies on filtration and removal of particles from the runoff by the soils beneath the infiltration system. The source infiltration system should be designed and operated in a first flush configuration since a flow through configuration would not provide treatment of fine sediments. In contrast to the other treatment alternatives, the source infiltration alternative requires maintenance of multiple infiltration locations rather than maintaining a single central treatment system.

1.3.6 No Treatment There currently is limited treatment of runoff within the Project Area and without treatment there will be no reduction in the volume of runoff or the peak flow. In addition, without treatment of runoff there will be no reduction in the fine and course sediment suspended in the runoff. For these reasons, with the no treatment alternative, the objectives of the project can not be satisfied. Furthermore, it is possible that by providing source control and hydraulic design alone within the Project Area without including treatment, the volume of runoff and the peak flow could be increased. An increase in runoff would potentially make flooding problems worse for the residents, and increase the suspended sediment in the runoff leaving the Project Area.


Appendix D

BIKE PATH DETAILS

Appendix E

WATERSHED FIGURE AND RATIONAL PEAK FLOW RESULTS

LTB-1JN 95186

Rational Method

1/27/2011

NOTES 3.000 = P2 (2 yr, 24 hr rainfall depth based on 33 inches mean annual precip)10.0 = Initial Time of Concentration for all areas0.9 = C (Improved)0.2 = C (Unimproved)

Time of Concentration based on El Dorado County Hydrology Manual (Chapter 2)Time of Concentration determined using Longest Travel Path in WatershedC value a composite of pervious and impervious areas (determined from CN for pervious areas and value of 0.9 for impervious areas)

**100 Year Storm Assumes 25% increase in CDATA RUN = Computed Automatically

= Slope DependentLTB-1

NO

DE

Con

veya

nce

Flow Length (ft)

High Elev (ft) Low Elev (ft) Slope (%) n

Overland Travel Time

(min)

Velo

city

(ft/s

)

Area (acres) % Imp Tc (min)

Com

posi

te C

Rainfall Intensity (in/hr)

Peak Runoff (cfs) Flow Area Flow

Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 15.18 5.48% 10.00 0.24

overland 300 6443.00 6425.00 6.00% 0.40 34.42 0.15 661244 36263 34.42

shallow (unpave) 842 6425.00 6365.00 7.13% 4.31 3.26

0.00% 0.00

0.00% 0.00

0.00% 0.00

curb 0.00% Initial Vel 9.0 47.68 1.15 4.16 #DIV/0! #DIV/0!

2 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

47.68 0.24 1.15 4.16 6 0.75491.35 4.88 #DIV/0! #DIV/0!

#DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

47.68 0.24 1.35 4.88 1 0.33201.63 7.36 #DIV/0! #DIV/0!


47.68 0.30 1.63 7.36 24 2.7327

channel

10 Year

25 Year

100 Year

LTB-1-2JN 95186

Rational Method

1/27/2011




= Slope DependentLTB-1&2

NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 154.88 3.39% 10.00 0.22

overland 300 7000.00 6920.00 26.67% 0.40 18.95 0.26 6746486 228655 18.95

shallow (unpave) 4517 6920.00 6320.00 13.28% 5.88 12.80

0.00% 0.00

0.00% 0.00

0.00% 0.00



41.75 0.22 1.23 42.45 6 7.22861.44 49.85 #DIV/0! #DIV/0!


41.75 0.22 1.44 49.85 1 3.17911.74 75.15 #DIV/0! #DIV/0!


41.75 0.28 1.74 75.15 24 26.1661

channel

10 Year

25 Year

100 Year

LTB-3JN 95186

Rational Method

1/27/2011





NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 68.18 3.05% 10.00 0.22

overland 300 6950.00 6850.00 33.33% 0.40 17.33 0.29 2969962 90497 17.33

shallow (unpave) 3195 6850.00 6357.00 15.43% 6.34 8.40

0.00% 0.00

0.00% 0.00

0.00% 0.00



35.74 0.22 1.32 19.93 6 3.14811.55 23.41 #DIV/0! #DIV/0!


35.74 0.22 1.55 23.41 1 1.38461.87 35.28 #DIV/0! #DIV/0!


35.74 0.28 1.87 35.28 24 11.3956

channel

10 Year

25 Year

100 Year

LTB-3-4JN 95186

Rational Method

1/27/2011




= Slope DependentLTB-3&4

NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 224.02 3.45% 10.00 0.22

overland 300 7125.00 7085.00 13.33% 0.40 25.01 0.20 9758299 336768 25.01

shallow (unpave) 6078 7085.00 6337.00 12.31% 5.66 17.90

0.00% 0.00

0.00% 0.00

0.00% 0.00



52.90 0.22 1.09 54.87 6 10.47591.28 64.44 #DIV/0! #DIV/0!


52.90 0.22 1.28 64.44 1 4.60731.55 97.14 #DIV/0! #DIV/0!


52.90 0.28 1.55 97.14 24 37.9205

channel

10 Year

25 Year

100 Year

LTB-5JN 95186

Rational Method

1/27/2011





NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 114.61 1.27% 10.00 0.21

overland 300 7125.00 7087.00 12.67% 0.40 25.53 0.20 4992413 63469 25.53

shallow (unpave) 5485 7087.00 6350.00 13.44% 5.91 15.46

0.00% 0.00

0.00% 0.00

0.00% 0.00



50.98 0.21 1.11 26.63 6 4.99471.31 31.28 #DIV/0! #DIV/0!


50.98 0.21 1.31 31.28 1 2.19671.58 47.15 #DIV/0! #DIV/0!


50.98 0.26 1.58 47.15 24 18.0798

channel

10 Year

25 Year

100 Year

LTB-7JN 95186

Rational Method

1/27/2011





NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 48.83 0.31% 10.00 0.20

overland 300 7008.00 6858.00 50.00% 0.40 14.74 0.34 2127100 6562 14.74

shallow (unpave) 2002 6858.00 6320.00 26.87% 8.36 3.99

0.00% 0.00

0.00% 0.00

0.00% 0.00



28.73 0.20 1.47 14.49 6 2.05941.72 17.01 #DIV/0! #DIV/0!


28.73 0.20 1.72 17.01 1 0.90572.08 25.65 #DIV/0! #DIV/0!


28.73 0.25 2.08 25.65 24 7.4547

channel

10 Year

25 Year

100 Year

LTB-8JN 95186

Rational Method

1/27/2011





NO

DE

Con

veya

nce

Flow Length (ft)



(min)

Velo

city

(ft/s

)


Com

posi

te C



Velocity Final Tc

Dur

atio

n (h

ours

)

Volu

me

(acr

e-ft)

1 49.86 4.59% 10.00 0.23

overland 300 6467.00 6438.00 9.67% 0.40 28.44 0.18 2171877 99659 28.44

shallow (unpave) 2839 6438.00 6353.00 2.99% 2.79 16.95

0.00% 0.00

0.00% 0.00

0.00% 0.00



55.39 0.23 1.07 12.37 6 2.41441.26 14.53 #DIV/0! #DIV/0!


55.39 0.23 1.26 14.53 1 1.06191.51 21.90 #DIV/0! #DIV/0!


55.39 0.29 1.51 21.90 24 8.7397

channel

10 Year

25 Year

100 Year

Appendix F

ROAD INTERSECTIONS ALTERNATIVES

TAHOE ENGINEERING DIVISION









Appendix G

PHOTOS


CJ BMP?BM AMSLRW



CJ BMP?BM AMSLRW



CJ BMP?BM AMSLRW



CJ BMP?BM AMSLRW



CJ BMP?BM AMSLRW



CJ BMP?BM AMSLRW


Appendix H

POLLUTANT LOAD REDUCTION MODELING RESULTS

LegendCounty Roads

Grid Code1

2

11

14

500

501

502

503

504

1001

1002

1013¹

0 1,000 2,000 3,000 4,000500Feet

Lake Tahoe Blvd ECP - Land Use

Total WS Project Summary - EDC Precip

EMC Totals

GRIDCODE: Area (sf) Area (Ac)LUName:

PROJECT ID: 95186

1048051.37 24.06Residential_SFP1317.31 0.01Residential_MFP2

17000.71 0.39Water_Body11116541.31 2.68Roads_Unpaved14

4645.36 0.11Veg_Unimpacted500395860.02 9.09Veg_EP1501

24802923.68 569.40Veg_EP250211032527.26 253.27Veg_EP3503147516.78 3.39Veg_EP4504252597.65 5.80Residential_SFI1001

17.78 0.00Residential_MFI10021184415.10 27.19Roads_Secondary1013

TOTAL 39002414.33 895.37

Grid Code

LU Name 'c' MAP (in)

Rain (in)

Precip Vol (cf) TN Mass DN Mass TP Mass DP Mass TSS Mass(lb) (lb) (lb) (lb) (lb)

PROJECT ID: 95186

Area (ac)

1 Residential_SFP 0.2 36 14.4 251529 33 3 9 3 107624.06

2 Residential_MFP 0.2 36 14.4 76 0 0 0 0 10.01

14 Roads_Unpaved 0.2 36 14.4 27743 5 0 3 1 21372.68

500 Veg_Unimpacted 0.2 36 14.4 1114 0 0 0 0 10.11

501 Veg_EP1 0.2 36 14.4 95007 1 0 0 0 1019.09

502 Veg_EP2 0.2 36 14.4 5952665 74 5 15 13 16982569.40

503 Veg_EP3 0.2 36 14.4 2647791 33 2 7 6 20270253.27

504 Veg_EP4 0.2 36 14.4 35404 0 0 0 0 7273.39

1001 Residential_SFI 0.9 36 14.4 272752 36 3 10 3 11675.80

1002 Residential_MFI 0.9 36 14.4 19 0 0 0 0 00.00

1013 Roads_Secondary 0.9 36 14.4 1279143 276 41 57 14 1455827.19

TOTAL Area (acres): 894.98 TOTAL TSS (lb): 5702010563244

Notes:1) Rain values assumed to be 40% of Mean Annual Precipitation (MAP) value2) 'c" values: 0.2 for pervious and 0.9 for impervious3)Event Mean Concentraion (EMC) based on TMDL Event Mean Values as published in the Lake Tahoe TMDL Pollutant Reduction Opportunity Report, September 2007

Page 1 of 4r_TotalReport

Individual Watershed SummaryWS: LTB-1

TEMP ID GRIDCODE Area (sf)Sub WS Area (Ac)Land Use Name TSS Mass (lb)

MEAN ANNUAL RAIN (in/yr) : 14.4

Volume (cf):1

0 1 47630 1.09Residential_SFP 4911431

0 502 266655 6.12Veg_EP2 18363997

0 503 275515 6.32Veg_EP3 50666121

0 1001 20603 0.47Residential_SFI 9522247

0 1013 50867 1.17Roads_Secondary 62554930

661270 15.18 1458218725

TOTAL 661270 15.18WS: LTB-1 1458218725

WS: LTB-2



Volume (cf):2

0 1 330356 7.58Residential_SFP 33979284

0 14 12921 0.30Roads_Unpaved 2393101

0 502 2901169 66.60Veg_EP2 1986696278

0 503 2496203 57.30Veg_EP3 4586599087

0 504 7409 0.17Veg_EP4 371777

0 1001 59818 1.37Residential_SFI 27664588

0 1013 292983 6.73Roads_Secondary 3601316409

6100858 140.06 110651760524

TOTAL 6100858 140.06WS: LTB-2 110651760524

WS: LTB-3



Volume (cf):3

0 1 175260 4.02Residential_SFP 18042062

0 14 461 0.01Roads_Unpaved 9111

0 502 1753130 40.25Veg_EP2 1200420753

0 503 772079 17.72Veg_EP3 1419185298

0 504 100628 2.31Veg_EP4 49624151

0 1001 30427 0.70Residential_SFI 14132856

0 1013 122333 2.81Roads_Secondary 1504132121

2954318 67.82 4948837351

TOTAL 2954318 67.82WS: LTB-3 4948837351


WS: LTB-4



Volume (cf):4

0 1 494805 11.36Residential_SFP 508118752

0 14 8371 0.19Roads_Unpaved 1552009

0 500 4645 0.11Veg_Unimpacted 11114

0 502 4096930 94.05Veg_EP2 2805983229

0 503 1732389 39.77Veg_EP3 3183415763

0 504 92 0.00Veg_EP4 022

0 1001 141750 3.25Residential_SFI 655153060

0 1013 294075 6.75Roads_Secondary 3614317595

6773057 155.48 109221991544

TOTAL 6773057 155.48WS: LTB-4 109221991544

WS: LTB-5



Volume (cf):5

0 14 12167 0.28Roads_Unpaved 2252920

0 502 4033809 92.60Veg_EP2 2762968114

0 503 875939 20.11Veg_EP3 1609210225

0 504 472 0.01Veg_EP4 2113

0 1013 68306 1.57Roads_Secondary 84073771

4990693 114.57 54381255143

TOTAL 4990693 114.57WS: LTB-5 54381255143

WS: LTB-6



Volume (cf):6

0 2 317 0.01Residential_MFP 176

0 14 67329 1.54Roads_Unpaved 124416149

0 501 5742 0.13Veg_EP1 11378

0 502 8846085 203.08Veg_EP2 60572123061

0 503 4035824 92.65Veg_EP3 7415968597

0 504 38917 0.89Veg_EP4 1929341

0 1002 18 0.00Residential_MFI 019

0 1013 211772 4.86Roads_Secondary 2603228713

13206003 303.17 175133347334

TOTAL 13206003 303.17WS: LTB-6 175133347334


WS: LTB-7



Volume (cf):7

0 14 9220 0.20Roads_Unpaved 1652140

0 501 389523 8.94Veg_EP1 9993486

0 502 1443084 33.13Veg_EP2 988346340

0 503 260077 5.97Veg_EP3 47862419

0 1013 25193 0.58Roads_Secondary 31027206

2127097 48.82 2040531591

TOTAL 2127097 48.82WS: LTB-7 2040531591

WS: LTB-8



Volume (cf):8

0 14 6072 0.13Roads_Unpaved 1011313

0 501 595 0.01Veg_EP1 0143

0 502 1462061 33.56Veg_EP2 1001350895

0 503 584502 13.42Veg_EP3 1074140280

0 1013 118887 2.73Roads_Secondary 1461128399

2172118 49.85 3638621031

TOTAL 2172118 49.85WS: LTB-8 3638621031

TOTAL 38985414 894.9595186 5702010563244


ROW Only - Project Summary - EDC Precip

EMC Totals

GRIDCODE: Area (sf) Area (Ac)LUName:

PROJECT ID: 95186

4734.73 0.11Residential_SFP19122.76 0.21Roads_Unpaved14

315090.69 7.23Veg_EP2502224414.97 5.15Veg_EP35036245.61 0.14Veg_EP45042554.02 0.06Residential_SFI1001

1125184.52 25.83Roads_Secondary1013

TOTAL 1687347.30 38.74

Grid Code

LU Name 'c' MAP (in)

Rain (in)

Precip Vol (cf) TN Mass DN Mass TP Mass DP Mass TSS Mass(lb) (lb) (lb) (lb) (lb)

PROJECT ID: 95186

Area (ac)

1 Residential_SFP 0.2 36 14.4 1132 0 0 0 0 50.11

14 Roads_Unpaved 0.2 36 14.4 2189 0 0 0 0 1690.21

502 Veg_EP2 0.2 36 14.4 75604 1 0 0 0 2167.23

503 Veg_EP3 0.2 36 14.4 53854 1 0 0 0 4125.15

504 Veg_EP4 0.2 36 14.4 1500 0 0 0 0 310.14

1001 Residential_SFI 0.9 36 14.4 2743 0 0 0 0 120.06

1013 Roads_Secondary 0.9 36 14.4 1215195 262 39 54 13 1383025.83

TOTAL Area (acres): 38.74 TOTAL TSS (lb): 146741352218

Notes:1) Rain values assumed to be 40% of Mean Annual Precipitation (MAP) value2) 'c" values: 0.2 for pervious and 0.9 for impervious3)Event Mean Concentraion (EMC) based on TMDL Event Mean Values as published in the Lake Tahoe TMDL Pollutant Reduction Opportunity Report, September 2007


Individual Watershed SummaryWS: LTB-1



Volume (cf):1

0 1 1596 0.04Residential_SFP 2383

0 502 10892 0.25Veg_EP2 72615

0 503 10835 0.25Veg_EP3 202599

0 1001 1715 0.04Residential_SFI 81854

0 1013 48711 1.12Roads_Secondary 59952605

73749 1.69 63660055

TOTAL 73749 1.69WS: LTB-1 63660055

WS: LTB-2



Volume (cf):2


0 14 7925 0.18Roads_Unpaved 1461902

0 502 105711 2.43Veg_EP2 7225371

0 503 62856 1.44Veg_EP3 11515084

0 504 1013 0.02Veg_EP4 5244

0 1001 313 0.01Residential_SFI 1329

0 1013 270890 6.22Roads_Secondary 3330292562

449663 10.32 3671335719

TOTAL 449663 10.32WS: LTB-2 3671335719

WS: LTB-3



Volume (cf):3


0 14 0 0.00Roads_Unpaved 00

0 502 60047 1.38Veg_EP2 4114409

0 503 22999 0.53Veg_EP3 425519


0 1013 106742 2.45Roads_Secondary 1312115283

190109 4.36 1396135353

TOTAL 190109 4.36WS: LTB-3 1396135353


WS: LTB-4



Volume (cf):4


0 502 138441 3.18Veg_EP2 9533209

0 503 63144 1.45Veg_EP3 11615153


0 1013 289087 6.64Roads_Secondary 3553312213

493060 11.32 3768361515

TOTAL 493060 11.32WS: LTB-4 3768361515

WS: LTB-5



Volume (cf):5

0 503 9748 0.22Veg_EP3 182340

0 1013 68188 1.57Roads_Secondary 83873644

77936 1.79 85675984

TOTAL 77936 1.79WS: LTB-5 85675984

WS: LTB-6



Volume (cf):6

0 14 1092 0.03Roads_Unpaved 20262

0 503 45453 1.04Veg_EP3 8410908

0 504 5233 0.12Veg_EP4 261257

0 1013 203208 4.67Roads_Secondary 2498219464

254985 5.85 2627231891

TOTAL 254985 5.85WS: LTB-6 2627231891

WS: LTB-7



Volume (cf):7

0 14 106 0.00Roads_Unpaved 225

0 503 369 0.01Veg_EP3 189

0 1013 19718 0.45Roads_Secondary 24221292

20194 0.46 24521406

TOTAL 20194 0.46WS: LTB-7 24521406

WS: LTB-8



Volume (cf):8

0 503 9012 0.21Veg_EP3 172163

0 1013 118640 2.72Roads_Secondary 1458128131

127652 2.93 1475130294

TOTAL 127652 2.93WS: LTB-8 1475130294

TOTAL 1687347 38.7395186 146741352218


Appendix I

PDT / PUBLIC COMMENTS

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