Cover Reservoir Doc Ragged Mountain Study Feb 2005

DATE: February 16, 2005 TO:

Project File

FROM: Aaron Keno RE:

Concept Development – Ragged Mountain Reservoir Expansion

PROJECT BACKGROUND The Rivanna Water and Sewer Authority (RWSA) is in the process of selecting a preferred alternative for expanding its water supply system. Gannett Fleming completed a Water Supply Alternatives Supplemental Evaluation in July 2004 supplemented by studies of Beaver Creek Reservoir in October 2004 and concluded that there are four primary water supply expansion concepts that have the potential to satisfy the raw water supply to the RWSA Urban System through 2055. These four concepts include: (1) an intake on the James River, (2) expanding the Ragged Mountain Reservoir, (3) expanding the South Fork Rivanna Reservoir (SFRR), and (4) dredging the SFRR. This technical memorandum discusses only the concept of expanding the Ragged Mountain Reservoir. This evaluation of the Ragged Mountain Reservoir expansion concept is intended to be used for comparison with the other water supply expansion concepts being evaluated. As part of the Urban Area System, RWSA owns and operates two dams in the Ragged Mountain region located immediately west of the City of Charlottesville. Upper Ragged Mountain Dam and Lower Ragged Mountain Dam form the Ragged Mountain Reservoir System. Currently, the two reservoirs are operated to store a combined total of 514 Million Gallons (MG) or 1,578 acre-feet of water. Of this volume, approximately 463 MG are considered to be usable storage and the remainder (51 MG) is considered to be dead storage. Upper Ragged Mountain Dam The Upper Ragged Mountain Dam (Upper Dam) impounds water from an unnamed tributary to Moores Creek. The drainage or watershed area for the dam was determined to be 1.26 square miles (mi2) with 0.81 mi2 (66%) located upstream of an Interstate 64 (I-64) embankment culvert. Located immediately downstream of the embankment toe of the Upper Dam, is the reservoir for the Lower Ragged Mountain Dam (Lower Dam). No record drawings of the Upper Dam are known to exist which could identify the Upper Dam’s as-built spillway crest elevation (normal pool level); however, 1960s drawings for the original construction of I-64 through the Upper Reservoir area identify the normal pool level as approximately Elevation 655.3 feet (GF local datum). The drawings also suggest that the highway alignment included a horizontal curve to avoid encroaching on the Upper Reservoir. As part of the federally sponsored National Dam Safety Program conducted in the late 1970s and early 1980s, both the Upper and Lower Dams were inspected to evaluate their design adequacy in terms of presenting any potential hazards to public safety associated with passing the Probable Maximum Flood (PMF) event. According to information provided in the 1978 Phase I Inspection Report, the Upper Dam was originally constructed around 1885. This earth embankment structure is 47 feet high and 470 feet long with a stone-masonry core wall. The embankment crest is approximately 12 feet wide and the upstream embankment slope is 3 horizontal to 1 vertical (3H:1V) and the downstream embankment slope is 2.5 horizontal to 1 vertical (2.5H:1V). The spillway for the structure is an open concrete-lined channel with an approximately 9-foot crest length located in the right (south) abutment area. A freestanding stone-masonry intake tower with a wood-frame gatehouse is located within the Upper Reservoir at about the midpoint of the embankment. A 10-inch outlet pipe and transmission line originates at the intake tower and passes through the embankment and follows the original streambed 1 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

downstream to the intake tower for the Lower Dam. Reportedly, a break exists along some point of the 10-inch transmission line that is located within the Lower Reservoir such that the pool levels for the Upper and Lower Reservoirs equalize during normal low base flow conditions. Lower Ragged Mountain Dam The Lower Dam and Reservoir are located immediately downstream of the Upper Dam on the same unnamed tributary to Moores Creek. The drainage or watershed area for this dam was reported to be 1.83 mi2 with 1.28 mi2 (70%) located upstream of the Upper Dam. The as-built (and current) spillway crest for the Lower Dam is at Elevation 641.0 feet (GF local datum). According to information provided in the 1978 Phase I Inspection Report, the Lower Dam was originally constructed in 1908. The Phase I report mistakenly identified the structure as an “earthfill dam with an upstream concrete gravity wall.” Based on a review of 1908 record drawings and original construction photographs, the structure is a 67-foot-high and 400-foot-long cyclopean concrete gravity dam founded on bedrock. The cyclopean masonry or concrete construction method represents a transition period (1870s-1920s) in dam building in the United States, between the earlier time when gravity dams were constructed of stone masonry and the later time when conventional mass concrete was used. Cyclopean concrete is formed by embedding large stones (up to 6 feet plus in diameter), commonly referred to as “plum” stones, into wet concrete mortar. Subsequently, the spaces between the plum stones were also filled with wet concrete mortar to form a continuous matrix of concrete and plum stones throughout the structure. Often times, these structures did not have horizontal lift joints or vertical contraction joints within the mass. Based on the construction photographs and record drawings, this also appears to be the case for the Lower Dam. The gravity section geometry consists of a vertical upstream face and a sloping downstream face with an 8-inch horizontal to 1-foot vertical (0.67H:1V) batter. The spillway for the structure is an open concrete and stone-masonry lined channel with an approximate 13-foot crest length located in the left abutment area. A concrete intake tower with a concrete gatehouse is adjoined to the upstream face of the gravity dam at about the midpoint of the dam crest length. According to information provided in the 1978 Phase I Inspection Report for the Upper Dam, an earthfill buttress was placed against the downstream face of the Lower Dam in the 1930s to reportedly “strengthen” the structure. Dam Safety Concerns In accordance with Virginia Department of Conservation and Recreation (VDCR), Division of Dam Safety Regulations the Upper Dam’s size classification is “Medium” since the embankment height is greater than 40 feet and the hazard potential classification is “I” meaning probable loss of life and excessive economic loss would occur as a result of dam failure. Therefore, the required spillway design flood (SDF) for the existing Upper Dam is the probable maximum flood (PMF). The 1978 Phase I Inspection report concluded, “…that the dam would be overtopped for all floods exceeding approximately 10 percent of the Probable Maximum Flood (PMF). The spillway is therefore adjudged seriously inadequate…Since the spillway capacity is unusually small and the consequences of dam overtopping and failure could cause a catastrophic event; the dam is classified as unsafe, emergency.” The Lower Dam’s current size classification is also “Medium” since the gravity dam height is greater than 40 feet and the maximum storage capacity is greater than 1,000 acre-feet. The hazard potential classification is “I” meaning probable loss of life and excessive economic loss would occur as a result of dam failure specifically since residences, businesses, Interstate 64, US Route 29, and the City of Charlottesville are located within a reasonable distance downstream. Therefore, the required SDF for the existing Lower Dam is also the PMF. The 1978 Phase I Inspection Report concluded, “…the dam would be overtopped for all storms exceeding approximately 25 percent of the Probable Maximum Flood. The spillway is, therefore, judged as seriously inadequate, and the dam is assessed as unsafe, non-emergency.”

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The inspection report also suggested that investigations into the effect of seepage on the stability of the steep earth buttress slope were warranted. Based on information provided by RWSA staff and associates, the spillway at the Upper Dam was modified sometime in the mid-1980s. Only limited information is available regarding this work; however, part of this improvement may have involved slightly lowering the spillway crest from the originally-constructed level to further improve overall spillway capacity. The Upper Dam’s current spillway crest elevation is Elevation 654.7 feet (or 0.6 feet lower than the as-built spillway crest elevation and 13.7 feet higher than the normal pool for the Lower Reservoir). The reservoir behind the Upper Dam is currently maintained at the same pool level as the reservoir behind the Lower Dower Dam (Elevation 641 feet, GF local datum). Based on information obtained from RWSA file documents, this operational mode began sometime in the mid-1980s as a concession with VDCR Dam Safety to address spillway capacity deficiencies at both the Upper and Lower Dams. The Upper Reservoir is maintained at a lower-than-normal level to provide flood storage to reduce the spillway discharge capacity requirement for both dams during a flood event. Since the issuance of the Phase I Inspection Reports, no dam modifications to either structure have been designed or constructed to fully address the dam safety deficiencies. The dams are currently being operated under “conditional” operation and maintenance certificates provided by VDCR Division of Dam Safety. The conditions stated for the operation and maintenance certificates for each dam are given below: 1. Resolve and/or rectify the existing inadequate spillway capacity of the Upper Ragged Mountain Dam and the Lower Ragged Mountain Dam 2. Resolve and/or rectify the stability analysis requirement identified in the Phase I Report for the Lower Ragged Mountain Dam Proposed Remediation Project In February 2003, Gannett Fleming, Inc. issued the results of a Feasibility Study in a report titled “Feasibility Study for Upgrading the Ragged Mountain Dams.” The purpose of the study was to reevaluate the design adequacy of the Lower Dam using state of the art engineering analysis methods developed since the 1978 Phase I inspections. The scope of this study also included the conceptual-level development of remedial or upgrade alternatives to address the design deficiencies. The February 2003 Feasibility Study confirmed the inadequacy of the spillway capacity at both the Upper and Lower Dams. The investigation also found that the static and dynamic (earthquake) stability of the embankment slope for the earthfill buttress for the Lower Dam is likely inadequate. The report recommended that if the upgrade alternative involves the continued use of the existing earthfill buttress, that the potential for liquefaction of the buttress soils be investigated. Each of the remedial upgrade alternatives developed as part of the study included partially breaching the Upper Dam embankment to remove it from service and raising the normal pool of the Lower Dam by 3.2 feet to regain reservoir storage capacity lost from the Upper Dam. None of the alternatives included upgrading the Upper Dam since the cost to increase spillway capacity at two dams would be greater than for one dam and any reservoir volume lost by removing the Upper Dam from service could be regained in raising the normal pool of the Lower Dam as part of its upgrade measure. The recommended remediation project consists of removing and replacing the existing earth buttress with a roller-compacted concrete (RCC) buttress.

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SAFE YIELD BENEFIT General Increasing the usable storage volume of the Ragged Mountain Reservoir System could be accomplished by raising the reservoir’s normal pool level either by raising the spillway crest of the existing Lower Dam or by constructing a new dam just downstream of the existing dam. Any such project would also include addressing the dam safety deficiencies at the Lower Ragged Mountain Dam and removing the Upper Ragged Mountain Dam from service. Due to the design and construction methods of the nearly 100-year-old existing Lower Dam, any proposed spillway raising greater than approximately 10-15 feet would best be accomplished by construction of a new dam immediately downstream. Construction of a new dam would have the benefit of allowing the existing dam and reservoir to remain in service during construction of the new dam. Mechums River Pumping Station Currently, the Ragged Mountain Reservoir is filled by runoff from its watershed and by transfer of water from Sugar Hollow Reservoir. As the volume of water able to be stored in the reservoir increases, the ability of the reservoir to be filled by runoff alone decreases. In order to reduce the time to refill the reservoir following an extended dry period, natural inflow could be supplemented by transfer of water from Sugar Hollow Reservoir and from a withdrawal pump station (PS) on the Mechums River. It may be necessary to increase the size of the existing pipeline from Sugar Hollow Reservoir to Ragged Mountain to better facilitate reservoir refill. Because additional raw water modeling is necessary to determine this, pipeline evaluations will be completed for the developed alternatives in the next phase of evaluation. The existing Mechums PS structure and dam are currently located on the eastern bank of the Mechums River near Lake Albemarle. The pump station and river intake were constructed in the 1950’s and have not been in operation since the mid-1960’s when the South Fork Rivanna Dam, Reservoir and Water Treatment Plant were constructed. When operational, water was withdrawn from Mechums River and discharged into the 18” pipeline connecting the Sugar Hollow Reservoir to the Ragged Mountain Reservoir. The pump station is in a state of disrepair and significant work is required to allow operation. The structure appears in fair condition; however, all mechanical equipment associated with the pump station has been removed or is in a condition requiring replacement. The existing influent channel is filled with silt, which must be removed prior to operation of the pump station. Electrical service for the pump station must also be reconnected from Tilman Road (Rt. 676) since the previous service has been removed. It is suggested that a detailed structural evaluation be performed on the pump station building prior to initiating any other modifications to ensure that the expected life of the structure is sufficient. The existing diversion dam (see Figure 1) at the pump station has a stoplog opening that can be used to regulate bypass flows. The original stoplogs are no longer available at the site and new stoplogs will be required.

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Figure 1: Mechums Pump Station Dam Structure The regulatory permits for operation of the Mechums River Pump Station stipulated that the RWSA could begin pumping 2.0 Million Gallons per Day (MGD) whenever the Mechums River flow is greater than 33 cubic feet per second (cfs). The permit allows pumpage of up to 4 MGD when the riverflow exceeds 66 cfs. To prevent the blockage of fish passage of resident species, the stoplogs at the pump station impoundment must be removed from February 14th to June 15th of each year; or, in consultation with the Virginia Department of Game and Inland Fisheries, the RWSA may construct acceptable fish passage at the impoundment prior to activating the pumps. A fish ladder will enhance passage of various fish species beyond the pump station intake structure. An investigation of historical flow data for the Mechums River indicates the flow rate in the river is often well above the 66 cfs threshold listed in the current permit. According to the data available, for approximately 4 months out of the year, the withdrawal rate from the Mechums River could be as much as 10 MGD while still maintaining a permitted flow-by of 66 cfs in the river. While this would result in a reduced refill time for the expanded Ragged Mountain Reservoir, it would require a larger diameter pipeline from the pump station to the Lower Reservoir and a new withdrawal permit to allow increased withdrawal rates under certain conditions. Reservoir Sizing For the purposes of this investigation, the Ragged Mountain Reservoir will be sized to satisfy the projected 2055 average daily water supply deficit of 9.9 MGD presented in the Water Supply Alternatives Supplemental Evaluation, dated July 2004. To limit the frequency and duration of severe drawdown, it is assumed that reservoir inflow is supplemented with raw water transfer from Sugar Hollow Reservoir and by pumpage from the Mechums River Pumping Station. The system is assumed to be operated according 5 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

to the other operational assumptions presented in the July 2004 Safe Yield Supplement No. 1. With these assumptions, the normal pool of Ragged Mountain Reservoir would be raised by approximately 45 feet to a pool elevation of 686 feet (GF local datum). The 45-foot raising of the normal pool elevation would provide an additional 1,862 MG of usable storage. Based on 5-foot-contour GIS Mapping, it is estimated that the new reservoir would have a total of 2,070 MG (7,930 acre-feet) of storage. With the assumptions stated, following an extreme drought, complete recharge time for the reservoir could reach three years. This duration may be reduced through appropriate selection of pump and pipeline sizes as well as operating procedures. Should an expanded Ragged Mountain Reservoir be selected as part of the preferred alternative, these matters will be investigated in detail. DAM DESIGN CRITERIA Classification For a 45-foot raising of the normal pool elevation, the proposed Ragged Mountain Dam would be at least 121 feet high. Based on the VDCR Dam Safety Regulations, the new dam with a normal pool at Elevation 686 feet (GF local datum) would be reclassified as “Large” size, since the gravity dam height would be greater than 100 feet. The hazard potential classification would remain as “I” meaning probable loss of life and excessive economic loss would occur as a result of dam failure specifically since residences, businesses, Interstate 64, US Route 29, and the City of Charlottesville are located within a reasonable distance downstream. Spillway Design Flood Based on the VDCR Dam Safety Regulations for a Hazard Class of “I” and a Size Class of “Large”, the SDF for the proposed structure is the PMF. The PMF is defined by VDCR as “the flood that might be expected from the most severe combination of critical meterologic and hydrologic conditions that are reasonably possible in the region. The PMF is derived from the current probable maximum precipitation (PMP) available from the National Weather Service, NOAA.” The probable maximum precipitation (PMP) depth for the Ragged Mountain Dam Watershed was determined for the 2003 Feasibility Study by use of Hydrometeorological Report (HMR) No. 51, as published by the National Weather Service. The temporal distribution of the PMP was estimated by application of the National Weather Service’s HMR No. 52 computer program. Temporal distribution of the PMP was assumed such that the storm was centered over the Ragged Mountain Dams watershed. The PMP was determined to be 42.8 inches in 72 hours. The PMF event was modeled using the U.S. Army Corps of Engineers’ HEC-1 computer program. Key hydrologic parameters were determined from previous reports using Geographical Information System (GIS) mapping. In order to size the spillway of the proposed structure, it was assumed that the entire watershed of the Lower Dam was unregulated. In other words, it was assumed that the Upper Dam and the culvert through the I-64 roadway embankment did not attenuate the flood peak. With these assumptions, the spillway will be conservatively large. Appropriate refinements of this analysis should be made during preliminary and final design if the expanded Ragged Mountain Reservoir is selected as part of the preferred alternative. The peak inflow to the reservoir for the SDF was determined to be 16,910 cfs. Conceptual-Level Design After the required reservoir surface elevation was determined, the size of the dam structure was estimated based on the assumption that foundation rock is approximately 20 feet below the ground surface. The depth to rock is based on subsurface exploration performed at the existing Lower Ragged Mountain Dam and engineering judgment. The dam crest elevation was selected (Elevation 693.5 feet) 6 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

based on hydrologic reservoir routing computations of the SDF using the U.S. Army Corps of Engineers’ HEC-1 computer program. A roller-compacted concrete gravity dam was selected as the preferred dam type over an embankment-type dam. This selection is primarily based on the assumption that the depth to suitable foundation rock is relatively shallow thus minimizing the structure’s size and construction cost. In general, if foundation rock is relatively shallow, gravity-type dams can be more economical to construct in comparison to equivalent height embankment dam types since the material volume needed for a gravity-type dam is significantly smaller than for an embankment-type dam. Furthermore, even though gravity-type dams tend to have a higher unit material cost, this is offset by the benefit of the ability to incorporate the spillway into the main body of the gravity structure. Conversely, and depending upon site hydrology and topography, embankment type dams require a separate spillway structure in an abutment area, increasing the cost of construction. Cost comparisons for different dam types are also highly dependent upon availability of suitable construction materials. Although beyond the scope of the present study, a cost analysis to determine if the proposed roller-compacted concrete gravity dam is more economical than equivalent height embankment dam types should be performed at the beginning of the preliminary design phase. The layout for the proposed roller-compacted concrete gravity dam was based on the use of 5-foot contour mapping of the proposed project site and the results of the engineering analyses performed during this study. Exhibit 1 (Appendix A) is a plan view showing the footprint of the new rollercompacted concrete gravity dam and Exhibit 2 (Appendix A) is a profile (looking downstream) of the valley. Exhibits 3 and 4 (Appendix A) provide typical sections for the non-overflow and overflow (spillway) portions of the proposed roller-compacted concrete gravity dam, respectively. These sections were applied to the topographic mapping to develop material quantity estimates for significant cost construction items. With regard to the non-overflow section (Exhibit 3, Appendix A), a 0.8 horizontal to 1 vertical slope (0.8H:1V) was selected as a reasonable downstream slope for feasibility level cost estimating purposes. During the preliminary design phase, more detailed geotechnical and structural analyses may incorporate a steeper downstream slope, reducing roller-compacted concrete material volume and overall cost. A variety of facing system options can be used on the upstream and downstream faces of a rollercompacted concrete gravity dam. Such facing systems are used to enhance the structure’s overall water tightness and durability. For the conceptual design, an economic 2-foot-wide band of conventional concrete placed integrally with the roller-compacted concrete was selected for both the upstream and downstream facings. Further optimization of the upstream and downstream facing systems will be performed during the preliminary and final design phases if the expanded Ragged Mountain Reservoir is selected as part of the preferred alternative. The spillway or overflow section (Exhibit 4, Appendix A) would be contained by conventional concrete spillway training walls. For conceptual design purposes, a standard United States Bureau of Reclamation (USBR) Type II Stilling Basin was selected for energy dissipation downstream of the spillway chute. A more detailed hydrologic and hydraulic analysis will be performed during the preliminary design phase to adequately define the Probable Maximum Flood event characteristics and to select and size final spillway structure features. RESERVOIR AND RESERVOIR RIM IMPACTS Interstate-64 As shown on the I-64 record drawings in Figure 2, the I-64 corridor passes through the Ragged Mountain area just upstream and south of the existing Upper Ragged Mountain Reservoir. Based on 5-foot contour mapping, and verified by field survey, it is known that a reservoir level increase of more than approximately 13 feet will submerge the engineered embankment slopes and the 8-foot by 8-foot 7 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

concrete box culvert that passes through the I-64 highway embankment. This box culvert carries perennial flows for an unnamed tributary to Moore’s Creek, which is also the main tributary for the Lower Ragged Mountain Dam. Currently, neither the highway embankment nor the box culvert is affected by the Lower Ragged Mountain Reservoir.

Figure 2: Portion of Record Drawings for Interstate 64 near the Upper Ragged Mountain Reservoir At the box culvert location, the I-64 highway embankment is approximately 140 feet in height. Initial hydrologic analyses indicate that for a 45-foot raise in reservoir level, the highway profile remains 8 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

more than 110 feet above the maximum reservoir level in the area upstream (worst case location) of the I64 embankment for the 100-year flood event. Exhibit 5 (Appendix A) delineates the proposed normal pool for a 45-foot raise (Elevation 686 feet) as well as the approximate 100-year maximum reservoir pool upstream of the I-64 culvert. In addition, initial analyses indicate that this is also true for the more extreme flood event used as the design criteria for the proposed dam, the Probable Maximum Flood (PMF). Therefore, a proposed increase in reservoir level by 45 feet would not pose a potential flooding hazard to the I-64 corridor, even for extreme flood events. Should the expanded Ragged Mountain Reservoir concept emerge as the preferred water supply expansion alternative, further detailed hydrologic and hydraulic analyses must be performed and provided to the Virginia Department of Transportation for review and concurrence. Another potential adverse impact to the I-64 embankment relates to the stability of the engineered highway embankment slopes both on the northern and southern sides. According to Special Report 247 “Landslides – Investigation and Mitigation” by the Transportation Research Board (TRB), water-level change adjacent to a slope is one of the most common causes for landslides or slope instability. Slope instability due to water-level change can be initiated because an increased water level does either or both of the following: (1) reduces the shear strength of the material, or (2) reduces the resisting or stabilizing forces within the slope due to the change to buoyant unit weights in the resisting portions of the slope. Slope instability can also be caused by the sudden lowering of the water level against a slope. Unless pore pressures within the slope can be dissipated quickly, the slope is subjected to higher shear stresses and potential instability. The existence or extent of the stability concern is dependent upon the characteristics of the embankment and foundation materials, level of submergence, and other factors. Since available record drawings of the I-64 highway embankment do not provide details regarding the types of materials encountered or used during construction, the precise nature of the embankment and foundation materials are unknown at this time. Regardless of the type of embankment material and whether or not the slope would be susceptible to failure in its present configuration, generally accepted methods have been successfully used to stabilize earthen or rock-fill embankment slopes either submerged or adjacent to a reservoir. At this point it is reasonable to assume that if the I-64 embankment is determined to be unstable under certain proposed loading conditions one of these accepted methods would satisfactorily remedy any deficiencies. The most likely remedy would involve placing a rockfill berm against the highway embankment to provide a freedraining buttress that would increase the resisting forces. Further detailed geotechnical investigations will be required if an expanded Ragged Mountain Reservoir is selected as part of the preferred alternative. It is recognized that this alternative will require extension of the concrete box culvert on both sides of the highway embankment. Initially the culvert could be modified such that the added length would allow the culvert to pass flood flows without endangering the highway embankment or highway itself. The preliminary and final design stages for this alternative will address the needed culvert modifications and its associated hydraulic capacity in conjunction with the design of necessary embankment stabilization measures. Recreational Use of Ragged Mountain Reservoir and Surrounding Lands The Ragged Mountain Natural Area surrounds the Upper and Lower Ragged Mountain Reservoirs. This Natural Area contains approximately 980 acres, most of which is forested, with approximately 7 miles of trails circling both reservoirs. A representative of the Ivy Creek Foundation, which manages the Ragged Mountain Natural Area, indicated that there is no swimming or motor boating activity allowed in the reservoirs; however, fishing and non-motorized boating activities are allowed. A permanent pool elevation change would likely have no detrimental impacts on the water related activities. Both the Upper and Lower Reservoirs have looped trails around them, with the existing dam between the two reservoirs serving as a land bridge and common stretch between the two trails. A raise of 45 feet would result in a pool elevation of 686 feet, which would inundate a large portion of the trails 9 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

currently located around the reservoirs. The upper Ragged Mountain Dam would be removed. At an elevation of 686 feet, the Ragged Mountain Reservoir would also back up against the steep embankment of I-64, thus eliminating the far side of the loop trail around the Upper Reservoir that is currently in use. All trails that are lost due to raising the pool elevation could be replaced in some form. It is possible that the Virginia Department of Transportation would allow a trail on their right-of-way so that a loop trail around the entire reservoir could be provided; however, a short trail, as currently exists across the Upper Ragged Mountain Dam Crest (“land bridge”), would require a new footbridge. The overall length of trails located within the Ragged Mountain Natural Area would likely be increased due to the increase in surface area of the reservoir. For the purposes of this investigation, one-half of the approximately 7 miles of existing trails are assumed to be impacted. This results in approximately 19,000 linear feet of new trail to be constructed. Utility Impacts Associated With Raising Ragged Mountain Reservoir Various utility providers were contacted in order to identify potential conflicts associated with the proposed 45-foot raise of the Ragged Mountain Reservoir. Charlottesville Gas indicated that there are no gas service lines in the proposed project area. Other utilities which were contacted and have not responded or returned information to date include: Columbia Gas of Virginia, Dominion Virginia Power, Verizon, Sprint, and Colonial Pipeline. Additional detail coordination with the utility providers will be necessary to further identify and resolve potential conflicts associated with this raw water concept. Based on the information available to date, it is believed that no utilities will be impacted by this project. ENVIRONMENTAL IMPACTS The upper reservoir was originally constructed to maintain a normal pool level of 654.7 feet (~655 feet). During the mid 1980’s, the water level was reduced to match the 641 foot elevation of the lower reservoir. This was done as a requirement by the Virginia Dam Safety Board when the upper dam was found to be unsafe and in need of repairs. The following discussion provides an inventory of the natural resources found between an elevation of 641 feet and the proposed elevation of 686 feet. Wetlands Methodology Biologists assessed the presence of wetland areas to the approximate elevation of 686 feet (the proposed normal pool level) utilizing the three parameter approach outlined in the 1987 Corps of Engineers Wetland Delineation Manual. Wetland boundaries were mapped in the field using a combination of 1994 color infrared aerial photographs at a 1 inch to 100 foot scale, topographic information, and GPS. Field investigations involved confirming the presence or absence of hydric soils, hydrophytic vegetation and wetland hydrology. Physical location data was collected with a hand-held GPS unit where needed. Widths and lengths of wetland areas were spot-checked in the field using a combination of tape measure and ocular estimation, then transposed to the maps for a higher degree of accuracy. Wetland habitat types (i.e., emergent, scrub-shrub, forested) were mapped during the field inspections using the aerial photographs and topographic maps in-hand. Project Area Wetland Inventory Wetlands primarily occur in the form of palustrine systems found just landward of the existing pool elevation of the upper and lower reservoirs. These systems occur as part of hydrologic inputs such as stream bottomlands and seeps in cove areas where they connect to the reservoirs. The largest system is associated with the main unnamed channel that approaches the upper reservoir from underneath Interstate 64. Between the reservoir pool and the interstate lies a series of interconnected forested and emergent 10 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

seeps, a portion of which are occupied and manipulated by beavers. The main channel contains three beaver dams within this reach, each dam occurring approximately 500 feet apart. The dam closest to the reservoir is the largest of the three observed, and currently floods an area approximately ¼ acre in size. The other two dams occur within the incised portion of the channel, and are not large enough to cause the water to overtop the channel banks. An assessment was performed to determine the acreage of palustrine vegetated wetlands that occur between the current reservoir elevation of 641 and the proposed elevation of 686. The results of the assessment are provided below. Forested Wetlands………………………3.3 acres Scrub-shrub Wetlands…………………. --- acres Emergent Wetlands…………………….. 0.7 acres Total…………………......4.0 acres Wetland Functional Values The U.S. Army Corps of Engineers and the Environmental Protection Agency have long held the policy that assessment of impacts and the determination of mitigation to achieve a no-net loss of wetlands should be based on the functions and values of the impacted wetlands (Memorandum of Agreement Between the Corps of Engineers and the Environmental Protection Agency, 1990). This long-standing policy was reinforced by headquarters of the Corps of Engineers in a Regulatory Guidance Letter dated December 24, 2002. The assessment of functional values as a requirement of the regulatory review process is founded on the understanding that certain wetlands are more valuable, offer more functions, and are of a higher quality than others. Wetlands with a higher standard of functional quality generally require a higher level of compensatory mitigation compared to impacts to a lower quality wetland with few functional values. The degree that wetlands differ in the level of value, however, can often be subjective. Biases due to personal preferences, perceptions, and individual experiences can also influence the comparisons between the values of different wetland types (emergent systems versus forested systems, for example). In an attempt to make fair, unbiased comparisons of value, wetland scientists over the years have developed assessment methodologies using a wide variety of techniques. Some techniques incorporate the extensive collection of data to be included in formulas and equations that ultimately employ a qualitative scoring method. Other techniques are based on the user’s best professional judgment and experience. VHB evaluated the functional values of the wetlands. The functional values were assessed solely on the basis of a wetland type offering that particular function (a “yes” or “no”) based on the professional opinion of the experienced scientist performing the assessment. No attempt was made to measure the degree, or level, of each function. Those functions analyzed included sedimentation/erosion control, water quality, flood-flow attenuation (storage), wildlife habitat, and recreation. A brief description of each function analyzed is provided below followed by a statement summarizing the functional abilities offered by the wetlands. Sedimentation/Erosion Control – This function is closely tied to the water quality function. The difference lies with the analysis of a wetland’s ability to retain sediments that are already present in the system, rather than the analysis of a wetland’s ability to filter sediments coming in from non-point sources. The presence of the sedimentation/erosion control function is largely based on the presence of vegetation, organic debris, and root matter that hold sediments in place. Water 11 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

velocity, topography, flood frequency, and energy dissipation are also contributing factors to sedimentation/erosion control. Wetlands were viewed to contain this function when the vegetative composition and structure were observed to be stable. Highly eroded wetlands or wetlands with exposed soils were viewed as lacking this function. All of the wetlands were observed to provide a high degree of sedimentation/erosion control because of the highly stable, densely vegetated conditions. In addition, fallen trees and logs from recent storm events also serve to hold sediments in place. Water Quality – This function relates to the wetland’s ability to maintain clean water by filtering/retaining nutrients, sediments, and toxicants from incoming runoff from the surrounding watershed before water moves through the system to downstream areas. The capture and filtering of nutrients, sediments, and other pollutants is dictated by such features as soil absorption, soil particle size, water retention, water velocity, and plant/root uptake. Connecting wetlands with stable, natural soils and vegetative cover are viewed as having this function. Wetlands associated with the beaver dam at the headwaters of the upper reservoir offer the greatest capacity to filter pollutants from incoming sources. These wetlands are the largest in the area, and occur on the flat terrace just before the water enters the reservoir pool. The presence of forested and emergent vegetation provides excellent filtration in this area. The other wetlands occur as small seeps at the confluence of stream channels with the reservoir. The forested condition of these systems provide some filtering of surface runoff, but the mere size of these systems render their ability to retain nutrients rather limited. Flood-Flow Attenuation – In addition to retaining and remediating sediments and other pollutants, wetlands also provide flood flow storage. The wetland’s ability to attenuate flood waters can serve to calm flood peaks and/or retain water over long periods of time, minimizing catastrophic flood events, and thereby allowing downstream areas to maintain their flow rates and stream geometry. This functional value also serves to protect ecological, social, and economic structures located downstream. Where surface water runoff flows from higher elevations down to the lower elevations, wetlands associated with overbank flooding from bankfull stream discharges, ponds, and depressions are viewed as having this function. The wetlands have no flood flow attenuation capacity. Wildlife Habitat – Wetlands provide food, cover, and reproductive habitat for numerous species of wildlife. This particular function is determined by the degree to which it serves various habitat needs for wetland dependent species only. Assessing this function can be complex due to the wide variety of wetlands (emergent, scrub/shrub, forested), each of which have their own habitat benefits. Wetlands with surface water, longer hydroperiods, and multiple vegetative layers, snags, and fallen debris (sticks, logs) tend to offer the greatest level of habitat diversity for a greater level of species richness and abundance. The larger wetland system at the headwaters of the upper reservoir provides the widest level of wildlife habitat. This system is manipulated by beavers, creating a series of forested and shrubby habitats intermixed with open emergent areas. Other animals benefiting from this wetland include woodpeckers, song birds, raccoons, mink, waterfowl, reptiles, and amphibians. Recreation – Wetlands, by their unique characteristics, can attract people as a setting for various outdoor recreational activities such as canoeing, kayaking, fishing, hunting, trapping, swimming, hiking, birding, etc. The recreation function is measured by the ability of a wetland to offer these types of active and passive recreational opportunities to the public. Qualities such as size, 12 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

aesthetics, access, value as wildlife/fisheries habitat, and uniqueness help to rate whether this function is available. The Ragged Mountain reservoirs are currently part of a natural preserve managed by The Ivy Creek Foundation and used by the public for recreation such as hiking, canoeing, fishing, and picnicking. A nature trail encircles the reservoirs, and brings visitors up close to the wetland habitats along the edges of the reservoirs. As such, these wetlands provide excellent recreational viewing of wildlife species for area birders and nature enthusiasts. Streams Biologists inspected each stream reach between the proposed 686-foot elevation and the existing pool elevations of 641. The assessment included a cursory inspection of each stream channel to qualitatively determine stream stability and character. An estimate was made of the point of existing back flooding caused by the normal pool elevation of the reservoir. From this location, an estimate was made to determine the limits of impact cause by the new pool level. This estimate was performed with the use of existing topographic mapping. A total of 15 streams occur in the study area, 14 of which are first order channels originating from the adjacent hillside seeps. The length of any one individual stream within the elevation boundaries defined above, typically ranges between 400 to 1,300 linear feet, with the lowest reach being 120 feet and the longest being over 2,500 feet. In total, approximately 11,382 linear feet of streams occur below the maximum study elevation of 686’.. Stream Assessment Methodology and Results The Norfolk District of the U.S. Army Corps of Engineers has developed a protocol for evaluating the quality of streams in the Piedmont physiographic region of Virginia (Stream Attributes Crediting Methodology: Impact and Compensation Reaches). The purpose of the protocol is to establish a reasonable approach to determining the mitigating needs for stream impacts, realizing that not all streams are the same. The protocol utilizes five variables determined to be reasonable indicators of the overall stream’s health and stability. These variables include channel incision, riparian condition, bank erosion, channelization, and instream habitat. Using an index ranging between 0 and 1.0, each of the five variables are assigned a score, with 1.0 being the highest possible score per variable. Variable scores are then added to determine the final index score (called the “Reach Condition Index”), with a 5.0 being the highest total score for any stream. The Reach Condition Index is then multiplied by the linear footage of stream impact for a particular stream. The product of the attributes score and the linear footage provides a “Total Reach Condition Units” that can then be compared to another stream targeted for mitigation. The Norfolk District’s stream mitigation policy is for applicants to achieve an equivalent “Total Reach Condition Units” score through stream restoration activities (i.e. the Total Reach Condition Units gained through mitigation equals the Total Reach Condition Units impacted). The Corps’s current stream attributes methodology was applied for each stream channel to an elevation of 686 feet. Overall, the health and stability of stream reaches adjacent to the reservoir are good, with an overall average Reach Condition Index being 3.93. The high score is mainly attributed to the lack of channelization, relatively low bank erosion, and the presence of forested riparian vegetation. The Reach Condition Indexes were used to calculate the Total Reach Condition Units for each stream. The Total Reach Condition Units were then added to determine an estimated total of approximately 43,705 units.

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Wetland and Stream Impacts As noted, the upper reservoir was originally constructed to maintain a normal pool elevation of 654.7 feet (~655’). However, in the mid 1980’s the water level was reduced to match the 641’ pool elevation of the lower reservoir in response to directives from the Virginia Dam Safety Board as a result of concerns over the condition of the dam. As a result, it is unclear at this time whether all of the environmental impacts that would be associated with construction of the Ragged Mountain Reservoir to a 686’ elevation (45’ raise) should be attributed to the water supply augmentation project or whether some portion of the impacts should be attributed to the repair/rehabilitation/replacement of the existing reservoir facilities. Impacts are summarized below in increments to identify the portion of impacts associated with each portion of the concept. Wetland and Stream Impacts Summarized for Three Increments, Ragged Mountain Reservoir

Impacts Wetlands (Acres)

Streams

Total Stream Total Permanent Reach Wetlands Lost Emergent Scrub/Shrub Forested Condition (l.f.) Units

Concept Ragged Increment Upper Mountain Reservoir 1 Increased Raised From By 45’ (Elev. 641’ to 686’) 655’ Increment Upper Reservoir 2 Raised from 655’ 686’

0.0

3.2

3.9

2,080

7,416

0.0

0.0

0.0

0.0

5,260

19,206

0.0

0.0

0.1

0.1

4,042

17,085

to

Increment Lower Reservoir 3 Raised from 641’ 686’

0.7

to

In the following discussion of the potential wetland and stream impacts and subsequent mitigation needs, the scenario where all impacts are attributed to the water supply project is quantified by summing Increments 1, 2 and 3. If those impacts that occur below the historic pool levels of each reservoir are attributed to a repair/rehabilitation/replacement project, then the impacts attributed to the 14 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

water supply project would be quantified by summing Increments 2 and 3 alone. Based on the forgoing, compensatory mitigation and cost opinions are outlined in the following paragraphs. Wetland/Stream Mitigation Wetland Mitigation : All impacts attributed to Water Supply Project The Norfolk District, U.S. Army Corps of Engineers (COE) and the Virginia Department of Environmental Quality (DEQ) rely on set mitigation ratios to serve in-lieu of various wetland functions offered by emergent, scrub-shrub, and forested systems. The in-lieu ratios include 1 to 1 mitigation for emergent systems, 1.5 to 1 for scrub-shrub wetlands, and 2 to 1 for forested wetlands. Using these ratios, the mitigation requirements for impacted wetlands at the Ragged Mountain Reservoir are as follows. Emergent: Scrub-Shrub: Forested:

0.7 acres of impact (1 to 1 ratio)……………….0.7 acres 0.0 acres of impact (1.5 to 1 ratio)……………. 0.0 acres 3.3 acres of impact (2 to 1 ratio)……………… 6.6 acres Total Mitigation Requirement……….. 7.3 acres

Stream Mitigation All impacts attributed to Water Supply Project: When applying the stream mitigation protocol, a stream being impacted loses all of the stream features calculated in terms of condition units when it is flooded. A stream targeted for mitigation, however, will exhibit some level of condition units before any work is done to improve the stream. The same protocol is applied to the mitigation stream reach to determine the condition units before and after mitigation is performed. The net gain in condition units obtained after mitigation is performed can then be used to offset the total condition units being impacted. In general, a stream with a Reach Condition Index of 4.0 will require twice as much of linear footage of stream mitigation when using a stream having an index of 2.0, provided the mitigation reach can obtain an index of 4.0 or higher when the mitigation is completed. As previously described, the COE’s Stream Attributes Crediting Methodology was applied for all streams, and an estimated total of 43,705 credit units would be required to offset all stream impacts assuming that all of the stream impacts were attributed to the water supply project and none to the repair of the existing facility. For calculation purposes, it is assumed that half of the credits could be obtained through full channel restoration. The other half could be acquired through buffer improvement. Assuming a stream targeted for full restoration receives an index score of 2.5 and it will be restored to an index score of 4.5 (2 credits per linear foot), and that buffered areas can be improved from a 0.25 to 1.00 (0.75 unit increase), approximately 40,063 linear feet of stream channel could be used to offset project impacts (10,926 lf of restoration and 29,137 lf of buffering). Mitigation Opportunities In assessing the potential cost for wetland and stream mitigation, it is important to consider the potential opportunities that may be available to compensate for unavoidable project impacts. These opportunities may occur on-site or next to the proposed reservoir, off-site within the watershed, or through a number of in-lieu fee options as outlined in the following paragraphs. On-Site Mitigation Opportunities Based on cursory review of adjacent topography, the formation of new wetlands adjacent to the new pool level appears to be limited to the somewhat flat area south of Interstate 64 where it is reasonable to expect approximately 1 acre of wetlands. Otherwise, the rest of the proposed shoreline will incur steep slopes that are not conducive to the formation of wetlands. 15 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

Assuming 1.0 acre of wetland creation could be accomplished at the headwaters of the reservoir, this would leave approximately 6.3 acres of mitigation remaining that would be obtained at off-site locations. Off-Site Mitigation Opportunities Due to the wetland and stream impacts associated with an increase of 45 feet in the Ragged Mountain Reservoir Dam, it is likely that the plan to mitigate adverse affects would include several components. Mitigation opportunities may include the following: ! ! ! ! !

Restoration of degraded or altered wetland and stream systems Creation of new wetlands in appropriate landscape positions Enhancement of existing, degraded wetland or stream systems Preservation of existing wetland and streams Contributions to banks or trust funds

To identify potential mitigation opportunities, the project team is coordinating with a number of knowledgeable local entities, including: ! ! ! ! !

Albemarle County The Natural Resources Conservation Service The Nature Conservancy Soil and Water Conservation District Local interest groups

Based on the discussions and reviews conducted to date, the following opportunities for compensatory mitigation can be considered. Restoration - Wetland restoration opportunities exist within the watershed in numerous floodplains along the tributaries to the Rivanna River, which have been altered through the installation of drain tiles and ditching for agricultural purposes. Similarly, several large tracts of land that have long-term agricultural histories have been identified as areas with floodplainwetland restoration potential. These lands are in private ownership and have not been specifically pursued at this point in the mitigation evaluation process. Stream restoration opportunities using natural channel design principles abound in Albemarle County where channels have been excavated and/or have become degraded due to agricultural and livestock activities. Such methods restore the sinuosity and profile of disturbed streams and re-establish naturally stable configurations that effectively transfer the flows generated by the contributing watersheds. Such mitigation has the duel benefit of compensating for stream impacts as well as reducing sediment loadings. Similar opportunities exist within the Mechums Creek watershed, which has been noted as the most highly disturbed watershed in the county. Creation - It appears the most efficient efforts to create wetlands would rely on other opportunities in nearby upland floodplains that have been historically used as agricultural or pasture land. In many circumstances, drainageways from sub-watersheds flow across these floodplain features, discharging to main stream channels. Often, these contributing flows can be distributed over the broad, flat pasture lands or fields to establish wetland hydrology with only minor grading requirements. Once the hydrology is established, the sites can be planted with tree species to create a forested wetland system.

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Enhancement- Opportunities to improve the character of existing wetland or stream systems, or to limit or halt degradation, occur in the form of construction of stormwater management facilities within the watershed, installation of cattle fencing to limit livestock usage within stream channels, or through the installation of woody plant materials along riparian areas that have been cut for pasture or agricultural purposes. Such options may also be considered as restoration, depending on specific site characteristics and history. Preservation - While preservation can be considered in compensatory mitigation options, it is usually included to supplement a base mitigation proposal involving creation or restoration. Such opportunities are limited within close proximity to the Ragged Mountain Reservoir since the adjacent lands are currently forested natural areas that already provide maximum buffering capacity. Bank or Trust Funds - Another potential alternative for mitigating unavoidable wetland impacts is a monetary contribution to the COE Aquatic Resource Trust Fund or purchase of wetland or stream credits from a private, COE/DEQ approved mitigation bank. However, prior to allowing the applicant to use the Trust Fund or private bank, the agencies require a rigorous analysis of opportunities for accomplishing the mitigation on-site, or in close proximity to the proposed impacts. It may be possible to use these options for a portion of the compensation requirements, specifically for stream impacts. The following private, approved mitigation banks and the associated credits are currently available for use in the South Fork Rivanna watershed: ! James River Mitigation Landbank – Goochland Co. 15.5 credits ! Byrd Creek Wetland Mitigation Bank – Goochland Co. 4.93 credits ! Willis River Mitigation bank – Buckingham Co., 4.4 credits, 685 l.f. stream Given consideration for the foregoing mitigation opportunities, the potential costs for wetland and stream mitigation are discussed with respect to two scenarios: 1) all impacts are attributed to the Water Supply Project, and 2) partial impacts are attributed to dam rehabilitation/repair or replacement. Wetland Mitigation Costs All impacts attributed to Water Supply Project Several reasonable assumptions allow for a variation in costs to offset the 4 acres of impact to wetland habitat if those impacts were deemed to result from augmentation of the Urban Service Area’s water supply and not the repair/rehabilitation/replacement of the existing Ragged Mountain facility. The principal assumptions include the following. 1. Of the 7.3 acres of mitigation required, one (1) acre of wetlands can be formed adjacent to the new pool elevation. 2. The remaining 6.3 acres of mitigation can be accomplished at a single, off-site floodplain location where surface water inputs from adjacent ridges (ditches, channelized streams, and seeps) may be redirected to restore/create wetlands with little earthworking and design efforts. The 1 acre of wetlands formed adjacent to the reservoir is not expected to require significant design and construction labor since the wetlands will function primarily as a result of the new pool level. Additionally, beavers will likely encroach into the area causing further backup of flows and flooding of land above the pool level. The cost of this scenario is estimated to be $17,000 per acre taking into consideration minor clearing and grubbing, grading, planting, maintenance monitoring and reporting.

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Similarly, it appears numerous opportunities exist to create or restore wetlands off-site. For offsite areas, the cost of creating wetlands from uplands can reach a cost as high as $100,000 per acre, depending on the amount of earthworking and the cost of the land. By comparison, the Virginia Aquatic Restoration Trust Fund costs for the area are in the $60,000 per acre range. We believe a more refined cost estimate for the Albemarle County area would be $50,000 per acre for new sites outside of the project limits. This would include site selection, land acquisition, design, construction, compliance monitoring, and reporting costs. This cost assumption is reasonable, and is consistent with the cost assumptions used for other concept plans. Again, VHB believes that approximately 1 acre of new wetlands can be created with minimal earthworking adjacent to the new pool level at Ragged Mountain at a cost of $17,000. The remaining 6.3 acres needed to offset the impacts would be located off-site at an estimated cost of $315,000 (assuming $50,000 per acre). Based on these assumptions, total wetland mitigation cost is estimated to be $332,000. Stream Mitigation Costs All impacts attributed to Water Supply Project At the high end of the range, stream mitigation costs would involve specific site selection, land or easement acquisition, legal services, survey, stream design, construction, and performance monitoring at an estimated cost of $300 per linear foot (lf). Conversely, simple planting of stream-side riparian corridors, which would also require similar tasks as the full restoration but with limited grading and monitoring work, has been estimated at approximately $100 per linear foot. Applying the COE Stream Attributes Crediting Methodology suggests that the project may require restoration of approximately 40,063 linear feet of stream channel to gain the necessary 43,705 credit units, assuming that all of the impacts were deemed to result from augmentation of the Urban Service Area’s water supply and not the repair/rehabilitation/replacement of the existing Ragged Mountain facility. To calculate the total mitigation costs for stream impacts, we applied the $300/lf value to half of the required credits (assuming a net improvement of 2 credit units per linear foot; yielding a need for 10,926 lf of stream) and the $100 value to the remaining half of the required credits (assuming a net increase of 0.75 credit units per linear foot; yielding a need for 29,137 lf of stream). Therefore, 10,926 lf of stream at $300/lf and 29,137 lf at $100/lf yields a total cost of $6,191,500. This estimate acknowledges a range of elements that are likely to be included in the mitigation package presented to the agencies. Wetland Mitigation and Rehabilitation/Repair/Replacement

Cost:

Partial

Impacts

Attributed

to

Dam

If we assume the flooding of the wetlands and streams located between elevation 641 feet and elevation 655 feet for the Upper Reservoir result from repair/rehabilitation/replacement of the exiting facility, then impacts attributable to the expansion of the water supply, impacts would be limited to the streams and wetlands between elevation 655 feet and elevation 686 feet for the upper reservoir and all impacts between elevation 641 feet and elevation 686 feet for the lower reservoir. Most all of the wetlands occur in the upper reservoir, with the exception of a 0.1 acre forested wetland in the lower reservoir. Therefore, only 0.1 acre of wetland impacts would be attributed to the water supply project under this scenario. Using a 2 to 1 mitigation ratio, the 0.1 acre forested wetland would require 0.2 acre of mitigation. We assumed that the 0.2 acre of wetlands can be achieved at the upper reaches of the new flood level with minimal earthworking and design. This acreage could be obtained adjacent to the new pool level at an estimated cost of $3,000 to $5,000.

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Stream Mitigation and Rehabilitation/Repair/Replacement

Cost:

Partial

Impacts

Attributed

to

Dam

If the 2,080 linear feet of channel in the upper reservoir between elevation 641 feet and elevation 655 feet were deemed to be affected by the repair/rehabilitation/replacement , that would leave 5,260 linear feet for the upper reservoir and 4,042 linear feet for the lower reservoir for a total of 9,302 linear feet of stream impacts that would be mitigated as part of the water supply augmentation project. The amount of reach condition units (RCU’s) for these streams was found to total 36,291 units. As previously described, the COE’s Stream Attributes Crediting Methodology was applied for all streams, and an estimated total of 36,291 credit units will be required to offset stream impacts. For calculation purposes, it is assumed that half of the needed credits can be obtained through full channel restoration. The other half may be acquired through buffer improvement. Assuming a stream targeted for full restoration receives an index score of 2.5 and it will be restored to an index score of 4.5 (2 credits per linear foot), and that buffered areas can be improved from a 0.25 to 1.00 (0.75 unit increase), approximately 33,261 linear feet of stream channel will be required to offset project impacts (9,071 lf of restoration and 24,190 lf of buffering). The cost would be approximately $5,140,900. Threatened and Endangered Species The only potential listed species affected by the project is the James spinymussel. A survey was performed by the Virginia Cooperative Fish and Wildlife Research Unit to determine the presence of this species within the stream channels proposed for flooding. The survey resulted in no James spinymussels being found. This information was presented to the U.S. Fish and Wildlife Service (USFWS) and Virginia Game and Inland Fisheries (VGIF), which have suggested that further surveys be performed downstream from the lower dam. However, no project impacts are projected to this downstream-area.. Cultural Resources Architectural Resources The following information represents likely architectural resources encountered within this concept and recommendations by the consultant concerning the extent to which such resources may be encountered during construction of the Ragged Mountain Concept. If this alternative is selected, consultation with the VDHR is recommended regarding the specific level of architectural work needed. There is one recorded architectural resource within the vicinity of the Ragged Mountain Reservoir System: the Jim Newell Farm, ca. 1770 (VDHR No. 002-1170); however, this resource is outside the anticipated project Area of Potential Effect (APE) and would not be directly or indirectly affected by the project. The field investigations identified two unrecorded early-twentieth century architectural resources within the APE of this alternative discovered during fieldwork, the former Gate House of the dam and the caretaker’s house. Both of these resources will be affected by the project and are old enough to be considered for eligibility to the National Register of Historic Places (NRHP). If the Ragged Mountain concept is chosen, these resources will need to be surveyed at the Phase I/reconnaissance level and their eligibility to the NRHP evaluated. The caretaker’s house is a relatively common resource type in the region that is typically not eligible for the NRHP for its architectural significance; however, such resources can be eligible to the NRHP if they are associated with important events or people of regional significance. The Gate House is a less common resource type and if it were found to be eligible to the NRHP, it would likely be due to its function. A detailed architectural survey at the Phase I/reconnaissance level will determine if these resources meet the criteria for eligibility to the NRHP. If these resources are determined eligible for the NRHP, then it is possible that the project may have an adverse effect on them and, if so, mitigation measures may be necessary. 19 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

Archaeological Resources There are no previously recorded archaeological resources within the project vicinity; however, there are two former house sites and one quarry within the anticipated APE of the Ragged Mountain Reservoir System. These potential resources are shown in Exhibit 6, Appendix A. The two house sites are represented by standing chimneys and archaeological sites surrounding them, and are either associated with a former caretaker’s residence or residences that were abandoned after the reservoir was created. These resources sit within a few feet of the existing pool elevation and will be affected by the project. The quarry is also within the anticipated APE of this concept. These resources should be surveyed and evaluated at the Phase I and/or Phase II level to determine their eligibility to the NRHP. If resources eligible for the NRHP are identified, and it is determined the project will have an adverse effect on them, mitigation measures may be necessary. Additionally, the field investigations identified three potential archaeological resource locations based on their topographic setting. These are relatively flat, preserved terraces less than 20 feet above the current reservoir pool. Prior to construction of the reservoir, they would have been first or second terraces above the stream and suitable locations for prehistoric or historic occupation. Each of these areas is less than 10 acres. These resources should be surveyed at the Phase I level to determine if archaeological resources are present. If archaeological resources are identified, then their eligibility to the NRHP will need to be evaluated either during the Phase I survey, or within a subsequent Phase II evaluation. If archaeological resources are identified which are eligible for the NRHP, and the project will likely have an adverse effect on them, mitigative measures may be necessary. Table 1 Cultural Resources and Locations Likely Affected by the Proposed Ragged Mountain Reservoir Expansion Concept RESOURCE NUMBER 002-1170 N/A

NAME

NRHP STATUS

Jim Newell Farm Caretaker’s House Gate House

Not Evaluated Not Evaluated

N/A

RESOURCE TYPE Farm Complex Caretaker’s House Gate House

N/A

House Site

N/A

Not Evaluated

N/A

House Site

N/A

Not Evaluated

Potential Archaeological Site Locations (n=4)

N/A

N/A

N/A

Not Evaluated

PROJECT EFFECT No Effect Affected (if NRHP eligible) Affected (if NRHP eligible) Affected (if NRHP eligible) Affected (if NRHP eligible) Affected (if NRHP eligible resources are identified)

PROJECT COSTS Assumptions and Derivation of Cost Estimates A project cost estimate included in the Water Supply Alternatives Supplemental Evaluation report (GF – July 2004) for the Raise Ragged Mountain With Pumped Storage alternative will be used here. In costs estimates prepared in the referenced report, the complete alternative including raw water supply, transmission, and treatment were included. For comparison purposes with other raw water concepts, only costs associated with raw water supply and transmission will be included in this analysis. 20 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

The project cost estimate has been modified to address only the raw water storage and conveyance requirements (eliminating any reference to water treatment) and to reflect additional findings presented in this technical memorandum. The following assumptions were made to compute the planning-level estimate of probable construction cost. 1. Based on existing permitting limitations, an assumed pumping rate of 4 MGD was applied at the Mechums Pump Station. 2. Costs for improvements to Mechums Pump Station for a 4 MGD pump station is $1,000,000. 3. As currently configured, Mechums Pump Station utilizes the 18-inch Sugar Hollow to Ragged Mountain pipeline for transfer of water. It was assumed that Mechums Pump Station will continue to utilize an 18-inch pipeline. Additional raw water modeling will be performed and this pipeline size may be increased. Normal water transfer and post-drought reservoir refill rates from Sugar Hollow Reservoir and Mechums Pump Station will be addressed. 4. It was assumed that the flows available for this raw water concept will be limited based on the current permitting allowances and existing pipeline sizes; however, should this raw water concept be developed further, a detailed hydraulic analysis should be conducted in order to determine appropriate capacities required for the Mechums River intake and pumps. Costs associated with the construction of a new fish ladder at the Mechums Pump Station and an uncomplicated electrical service extension to the pump station has been included in the cost estimate. 5. Assumed that the 133.5 acres to be inundated by the dam raise of 45 feet are forested and required tree clearing. 6. Assumed that 1 mile of roadway leading to the Pump Station would need to be replaced/repaired. 7. One-half of the approximately 7 miles of hiking trails in the Ragged Mountain Natural Area are assumed to be impacted resulting in approximately 19,000 linear feet of new trail replacement at a cost of $6 per linear foot. 8. Electrical costs were revised based on the pump horsepower required to handle the flow rate and head losses predicted over the pipeline. It is anticipated that the pump station would be required only to recharge the reservoir during drought conditions. Costs are based on the pumps operating 24 hours per day for 180 days per year during five years of the planning horizon. The cost of electricity is assumed to be $0.06 per kW-hr. 9. Dam construction material quantities were based on a typical roller-compacted concrete gravity dam located just downstream of the existing Lower Ragged Mountain Dam. Unit prices for the construction materials were based on bid prices for recent similar projects and recently published construction pricing information. 10. Cost to stabilize the I-64 embankment was based on engineering judgment and should be updated pending any detailed analysis performed during subsequent design phases. Costs provided are for the scenario considered “most probable.” 11. Cost to breach the existing Upper and Lower Ragged Mountain dam were based on excavation quantity estimates and unit prices based on bid prices for recent similar projects and recently published construction pricing information. This cost could be reduced if further analysis indicates that one or both existing dams can be partially breached as opposed to complete removal of the structure. Costs assume that beaching is completed coincidentally with dam construction, therefore providing cost savings for mobilization, demobilization, care and diversion of water, and erosion and sedimentation control as well as other items. 21 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

Projected Cost Estimates Table 2 summarizes the cost estimate for the expansion of the Ragged Mountain Reservoir to Elevation 686 feet. The costs are in 2004 dollars. Table 2 Ragged Mountain Reservoir Expansion Conceptual Cost Estimate Item

Cost

Construction of New Dam (Normal pool elevation = 686 feet)

$15,745,000

Breaching of Upper Ragged Mountain Dam

$360,000

Breaching of Lower Ragged Mountain Dam

$809,000

Clearing (133.5 acres @ $5,000/acre)

$668,000

Culvert Under I-64 (740 l.f. @ $931/l.f.)

$689,000

Embankment Stabilization (1,000 l.f. @ $521/l.f.)

$521,000

Rehabilitate Mechums Pump Station & Intake

$1,000,000

Construct Fish Ladder at Mechums Pump Station

$90,000

Road Reconstruction (5,280 l.f. @ $74.80/l.f.)

$395,000

Ivy Creek Trail Replacement (19,000 l.f. @ $6/l.f.)

$114,000

Electrical Extension to Mechums PS (3,750 l.f. @ $196/l.f.)

$735,000

18” Pipeline from Sugar Hollow to Ragged Mountain – Parallel to Existing Pipeline ($195/l.f. for 66,000 l.f.)

$12,870,000

Environmental Mitigation

$5,146,000 Subtotal

Engineering/Permitting and CM (20%)

$39,142,000 $7,828,000

Land Acquisition (133.5 acres @ $4,114/acre)

$549,000

Electrical Costs

$99,000 Subtotal

$47,618,000

Project Contingencies (25%)

$11,905,000

Total Project Cost

$59,524,000

Average Cost Per GPD of Safe Yield (provides 9.9 MGD)

$6.01/GPD

22 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

APPENDIX A EXHIBITS 1 - 6

23 Q:\43387 Rivanna Program Management\Phase III\Task 4 - Ragged Mountain\Tech Memo\Final Tech Memo - February 2005\2-16-2005\FINAL Technical Memorandum - Ragged Mountain 2-16-2005 ADK.doc

Exhibit 5 Inundation Area of theProposed Ragged Mountain Reservoir

29 Crozet

Charlottesville

64 Batesville

64

29

Covesville

Alberene Esmont Scottsville

Legend Normal Pool = 686 ft 100-YR WSEL Above I-64 Inundation areas were delineated using 10-ft topographic information. All elevations are referenced to NAVD 88 vertical datum.

I-64 Culvert Proposed Dam

64

0

500

1,000

2,000

3,000 Feet

Prepared By: 207 Senate Avenue, Camp Hill, PA 17011

September 2004

1UARRY3ITE !REAS7ITH !RCHAEOLOGICAL 0OTENTIAL

&ORMER (OUSE 3ITES

Exhibit 6

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