B08_10 - CHOH 241450 Site Access Constraints Opt.pdf

Site Access Constraints for

CHOH 241450 – Improve Visitor Safety and Remediate Rock Fall

Hazards at Milepost 155.5 (Paw Paw Tunnel)

As Determined from Site Visit on: 4/2/2020

NPS staff reviewed the different access and spoil areas which would be used for the proposed rock scaling activities. This included the potential spoil area at the Paw Paw Campground, Spoiling material on Tunnel Hill Trail, and expanding the downstream spoil area near mile marker 153.3. The intent is to provide a working list of some of the existing known constraints along the routes, it is not to be considered to be an inclusive list since the contractor’s means and methods will drive requirements for access (ex. Width, height, weights, etc.). This may result in additional constraints such as widening, limbing, tree removal etc. that would have to be coordinated with NPS after award of the Design Build Contract. This document is being provided as an aid and convenience to the contractor – it does not relieve them of the responsibility to confirm existing conditions and identify any constraints prior to bidding. A combination of routes may be used during construction given proper mitigation techniques are executed. A pre-bid site visit will also be scheduled.

1.0 Disposal Site Along Tunnel Hill Trail/Road Constraints

This alternative assumes that the existing tunnel hill trail would be used for the transport of scaled material from paw paw hollow to be either crushed and placed as a wearing course on the existing trail or be used solely as a haul road with the material stockpiled elsewhere.

The team walked the entire length of the trail from the NPS gate at the “loop” on the top of the mountain, over 4,200-feet downstream to the towpath. The origination of the stationing used to describe features and log observations is the gate at the top of the mountain. Width measurements were collected every 100’. Generally, the trail varied from a minimum width of 7’ to 14’. In many areas the trail could be widened easily if necessary. Of note is that many of the surfaces of the trail have existing shale spoils on them. The following constraints were noted:

• Due to the width of the trail, hauling traffic would need to be one way to prevent conflicts in traffic patterns. This could be mitigated by using convoys of trucks (similar to how trucking has been done elsewhere on the towpath).

There were not any noted areas where passing areas or turnarounds could be installed easily. There are a few segments of constricted widths of the trail including Station 2100 where the overly steepened slope adjacent to the creek would need to be stabilized and the trail widened.

• There were at least four turns in the road which may prove to be constraints for large vehicles. They are located near the following locations: Station 600, 3585, and 3885. The most severely restricting change in horizontal alignment of the trail is located at 3885 which is the final switchback above the towpath. At this location there is little room to expand the existing turning area. The trail down slope of this turn has a minimum width of 7’, with some segments of the trail showing signs of being undermined and being held up by tree roots.

• Two stream crossings near Station 1465 and 1610 are conveyed under the existing tunnel hill trail by using two sections of 2’ diameter HDPE pipes with a length perpendicular to the road of approximately 20-linear feet. Of note is that there is minimal cover of road material. ADS Technical Note TN 2.02 indicates that Minimum Burial Depth for Corrugated HDPE Pipes is 1’ for pipe diameters of 4 – 48 inches. However, this also assumes that the pipes are properly bedded and installed with proper backfill. For bidding purposes, it should be assumed that a temporary structure such as timber mats would be used to carry any heavy hauling traffic over these structures.

• Cultural resources observed along the trail were noted mostly from Station 2600 to the intersection of the trail with the towpath. Near Station 2700 the spoils piles from previous canal construction operations were found. Specifically, remnants of a dry laid stone wall supporting the roadway were observed. The dry laid stone wall would need to be protected by the contractor for any construction operations in the direct vicinity.

• Directly adjacent to the tailings placed during the canal’s construction era are the ruins of the Sulphur Springs Schoolhouse which was surrounded by dwellings during the canal’s construction era. Any ground disturbance in this area would be strictly prohibited. The use of crane mats to prevent surcharging and damage to any ruins may also be considered necessary by NPS.

• Downslope of the canal era tailings pile, a series of cutbacks is present with what appears to be a series of different construction eras of spoilings from various scaling efforts. Additionally, a remnant of another hauling road with a series of cutbacks extends from the top of the canal era tailings pile to the towpath which has been overgrown with trees and has a portion of it being used as a social trail that leads up to the top of the North Portal of the Paw Paw Tunnel. Any ground disturbance into the legacy tailings should be minimized and avoided if possible.

• Near the bottom of slope of the canal construction era spoil pile, there are remnants of dry-laid stone springhouses.

These appear to have been outlets for any water that seeps through the embankments. Of note is that the stream upstream of the spoil was observed to flow into the spoil pile and likely moves through the shale mass and uses these outlets at the spring houses. These structures are located outside of the footprint of Tunnel Hill Trail but are directly adjacent – they would need to be protected during any hauling activities during the proposed construction project.

• Tunnel Hill Trail is within the boundary of the NPS property between approximately Station 2600 to the towpath and from station 0 to approximately station 200. From approximately Station 200 to 2600 the property is owned by the State of Maryland and is part of Greenridge State Forest. Approximately 2200 linear feet of Tunnel Hill Road (Station - 2200 to 0) between the public roads and the NPS gate appear to be within NPS lands. Any work outside of NPS boundaries would need to be coordinated and approved by State of Maryland.

• Any resurfacing of the road would need to be coordinated with the Maryland Historical Trust (MHT) and Maryland Department of Natural Resources (MD-DNR) as appropriate. Resurfacing would need to mobilize a crusher.

• Photos of the access route are included below in Figures 1 - 13. Additional mitigations are included in the final Environmental Assessment.

Figure 1, NPS Access Gate at "Loop" on top of Mountain (Station 0).

Figure 2,Turn in Tunnel Hill Road near Station 600.

Figure 3, Typical Trail condition near Station 1000.

Figure 4, 2’ Diameter HDPE Drainage Pipe near Station 1465.

Figure 5, 2’ Diameter HDPE Drainage Pipe near Station 1610.

Figure 6, Approximately 9’ wide existing trail with slope instability on creek bank near Station 2100.

Figure 7, Drylaid stone retaining wall retaining tunnel hill trail near Station 2700.

Figure 8, Drylaid stone retaining wall retaining tunnel hill trail near Station 2700.

Figure 9, Canal Construction Era Spoil Pile near Station 2700.

Figure 10, Alignment Change on Tunnel Hill Trail at upper Switchback near Station 3585.

Figure 11, Alignment Change on Tunnel Hill Trail at upper Switchback near Station 3885.

Figure 12, Typical Trail Width at Lower Limb of Tunnel Hill Trail Switchback.

Figure 13, Signs of Undermining and Slope Instability along the Downslope shoulder of the Lower Limb of Tunnel Hill Trail Switchback.

2.0 Disposal Site at Previously Used Twigg Hollow Area near Mile Marker 153.3 Spoils in many various events have been placed along the berm side of the canal, near mile marker 153.3. Crossing from the towpath to the spoil area has been made in the past through the use of a causeway – of which the remnant can still be seen today. Access to Outdoor Club Road would be possible via an improved crossing (to be constructed if necessary by design build contractor) over the stream (referred to as Twigg Hollow) and NPS gate. Alternatively, while access at Bond’s Landing is also theoretically possible via NPS gate and towpath – there are additional historic structures along this route that would need to be protected from damage (wasteweir, lock, and culvert) and local NPS maintenance staff indicated the towpath was in very poor condition with the presence of many “soft spots”. These concerns along the Bond’s Landing access route make the Outdoor Club Road route preferable. Table 1 provides a list of noted features on the access route between the spoil area and the existing ramp into the canal near miler marker 154.71. The concept placement areas are shown in Figure 14. Figure 15 provides a historic sketch showing the location of the locks, culvert, and Twigg/Gross Hollow.

Figure 14, Concept for Placement at Downstream Spoil Area.

Figure 15, Location Map from Composite Lock HSR.

Mile Marker Feature Remarks Potential Action to Mitigate Damage

153.3 Culvert 210

12' wide span and 6' tall rise, spandrels were comprised of red sandstone rubble and some gray sandstone. Riverside arch has been failing since as early as 1971. Currently the headwall has failed and the wingwalls are beginning to unravel. Barrel is bricklined.

Contractor to protect and monitor during construction to prevent damage. Signage to alert construction traffic of feature.

154 Sorrel Ridge HBO Sorrel Ridge Hiker Biker Campsite

May need to be closed during hauling operations or media used to provide alerts to campers.

154 Lock 62

Historic Composite Lift Lock - Constructed 1838

- 1839 and 1848 - 1849. Bolts and some timber remain in the walls with recesses faced with concrete in 1910. Lock house ruins remain as water well. Water well is only 20' offset from back of coping stone. Masonry retaining wall on downstream end supports the towpath.

Contractor to protect and monitor during construction to prevent damage. Signage to alert construction traffic of feature.

154.12 Waste Weir

Original overflow was about 100' long and 16' wide and constructed in 1849 - 1850. Concrete frame was placed in the overflow about 1913.

Two stone overflows on the side have been filled in. Deck appears to have been replaced in the modern era. Current deck spans about 20' and has a width between curbs of approximately 9.3'. Masonry retaining wall on downstream end supports the towpath.

Contractor to protect and monitor during construction to prevent damage. Temporary bridging or shoring would be necessary. Signage to alert construction traffic of feature.

154.34 Lock 63 1/3

Historic Composite Lift Lock - Constructed 1838

- 1839 and 1848 - 1849. Bolts and some timber remain in the walls with recesses faced with concrete in 1910. Bulge in berm side of canal wall directly underneath the pedestrian bridge and downstream of the lower lock pocket observed. Bulge extends from below the coping stone to approximate depth of 12'. There appears to be a flanking wall comprised of masonry that extends through the towpath.

Masonry retaining wall on downstream end supports the towpath. Greater than 20' available behind back of coping stone to the edge of slope. Upper towpath return wall on lock appeared to be failing. Composite Lock HSR indicates foundation likely on bedrock.

Depressions behind lock are likely attributable to snubbing posts and/or sinkholes.

Contractor to protect and monitor during construction to prevent damage. Temporary bridging over the flanking wall or shoring the lock would be necessary. Consideration of filling of lock to top of upper sill bottom could be undertaken to minimize stability related issues from developing. Larger stone would be placed at downstream end to dissipate energy and act as a grade control with smaller crushed stone placed between the upper lock gate and lower limit of fill. Existing ashlar stone pile on shoulder of towpath should be left in place since it likely dates to concrete repair era. Avoid voids behind the wall. Signage to alert construction traffic of feature.

154.45 Lock 64 2/3

Historic Composite Lift Lock - Constructed 1838

- 1839 and 1848 - 1849. Bolts and some timber remain in the walls. Masonry retaining wall on downstream end supports the towpath.

Greater than 20' available between edge of daylight on rubble stone return wall at upstream end of lock and edge of slope. Upper towpath return wall on lock appeared to be failing. Remains of lock house foundation on the South side of the towpath limits ability to offset. Depressions behind lock are likely attributable to snubbing posts and/or sinkholes. Modern concrete repair at downstream berm wall on lock. Composite Lock HSR indicates foundation likely on bedrock.

Contractor to protect and monitor during construction to prevent damage. Temporary shoring the lock may be necessary. Consideration of filling of lock to top of upper sill bottom could be undertaken to minimize stability related issues from developing. Larger stone would be placed at downstream end to dissipate energy and act as a grade control with smaller crushed stone placed between the upper lock gate and lower limit of fill. Timber mats may be necessary to limit point loads on archeological remains. Avoid voids behind the wall. Signage to alert construction traffic of feature.

154.52 Lock 66

Historic Composite Lift Lock - Constructed 1838

- 1839 and 1848 - 1849. Bolts and some timber remain in the walls with recesses faced with concrete in 1910. Masonry retaining wall on downstream end supports the towpath.

Greater than 13' available between edge of daylight on rubble stone return wall at upstream end of lock and edge of slope. Upper towpath return wall on lock appeared to be failing. Depressions behind lock are likely attributable to snubbing posts and/or sinkholes. Composite Lock HSR indicates foundation likely on bedrock.

Contractor to protect and monitor during construction to prevent damage. Shoring the lock may be necessary. Consideration of filling of lock to top of upper sill bottom could be undertaken to minimize stability related issues from developing.

Larger stone would be placed at downstream end to dissipate energy and act as a grade control with smaller crushed stone placed between the upper lock gate and lower limit of fill. Avoid voids behind the wall. Signage to alert construction traffic of feature.

154.71 Tunnel Hill

Trail

Spring Houses near confluence at base of spoil pile placed across the old ravine. Access ramp into the canal is existing via earthen ramp.

Contractor to protect and monitor during construction to prevent damage. Signage to alert construction traffic of feature.

Table 1, Constraints between Worksite and Twigg Hollow Spoil Area.

In addition to the items listed in Table 1, The following constraints were also noted:

• A portion of the areas directly adjacent to the existing spoils (from about elevation 501’ NAVD88 and below) are mapped as within the 100-year floodplain by the effective Flood Insurance Rate Map (FIRM). Any fill in this area would need to be accounted for by showing that it causes a no-rise in the base flood elevations (BFE) for the 100-year event.

See Figure 16 for the current FIRM. Hydraulic modeling would likely be necessary to showing engineering determination of the effect of proposed fill within the floodplain.

• Any fill within the canal, for example, filling of locks to increase their stability would need to be done as a permitted action since the canal is still regulated under Section 10 of the Rivers and Harbors Act by U.S. Army Corps of Engineers.

Any fill within the canal may be considered to be in a wetland depending on hydrologic conditions and presence of wetland species.

• A stabilized stream crossing would be necessary to be constructed over the stream adjacent to camp site #65 to gain access from Outdoor Club Road to the NPS Access Gate. The stream crossing should be left in place upon completion of the project for future NPS use.

• The causeway across the canal would need to be reconstructed, with proper drainage culverts provided through it to allow for water to flow through the canal.

• Tree clearing within the footprint of the proposed spoil areas would need to be completed outside of the typical window for bats.

• Access for vehicles through Tunnel Hill Road, Outdoor Club Road, and/or Bonds Landing would need to be coordinated with Maryland Department of Natural Resources (MD-DNR) & Alleghany County Since they are under their jurisdiction within Green Ridge State Forest. A portion of the concept placement area may be on MD-DNR property during the more detailed design stage the property boundary should be delineated and limits of fill adjusted accordingly.

• Outdoor Club Road Access may need to have drainage culverts reinforced or bridged with temporary structures.

Impacts to adjacent recreation campsites may also need to be coordinated to minimize disruption – multiple campsites located directly adjacent to the worksite and haul road include #65 &66. Preliminary conversations with MD-DNR have indicated that they are willing to close the campsites during construction.

• Limited hauling of equipment for slope stabilization (not hauling) through Paw Paw Tunnel may be acceptable to the government with vibration limiting measures and monitoring in place. This would be expected to be infrequent.

• Access through the canal between the immediate work area and the ramp to the towpath near mile marker 155 would need to be done in a manner to limit wave wash and erosion. Wetland and waterway impacts would need to be quantified.

• Protect the existing historic concrete blocks on the downstream berm side of the current spoil limits.

• Permitting would need to be done for authorizing work in the floodplain and in proximity to the canal/wetlands.

• Consideration should be given to restoring the historic drainage pattern that connects Twigg Hollow to Gross Hollow.

• Photos of the access route are included below in Figures 17 - 33. Additional mitigations are included in the final

Figure 16, FIRMette for Downstream Spoil Area.

Figure 17, Typical Condition of Upper Segment of Outdoor Club Road.

Figure 18, Typical Condition of Corrugated Metal Pipe along Upper Segment of Outdoor Club Road.

Figure 19, Typical Condition of Corrugated Metal Pipe along Upper Segment of Outdoor Club Road.

Figure 20, Typical Condition of Lower Segment of Outdoor Club Road.

Figure 21, Area of Potential Temporary Stream Crossing of Twigg Hollow.

Figure 22, Existing Spoil Pile Along Left Bank of Twigg Hollow.

Figure 23, Proposed Spoil Pile Upstream of Existing Large Placement Area.

Figure 24, Proposed Spoil Pile Downstream of Existing Large Placement Area.

Figure 25, Existing Causeway crossed the canal.

Figure 26, Failing Headwall at Outlet of Culvert 210.

Figure 27, Lock House, Well, and Lock 62 Constraints at Towpath.

Figure 28, Wasteweir near Mile Marker 154.

Figure 29, Bulge in Berm side of Lock 63 1/3.

Figure 30, Typical Retaining Wall Downstream of Lock 63 1/3.

Figure 31, Tieback wall through towpath at Lock 63 1/3.

Figure 32, Typical Failing return Wall at Upstream end of Lock 63 1/3.

Figure 33, Existing Ramp from Canal near Intersection of Tunnel Hill Trail and Towpath near Mile Marker 155.

3.0 Disposal Site at Paw Paw Campground

The existing entrance road into the campground is approximately 20’ wide at the NPS gate near the intersection of MD Route

51. The roadway narrows down from this width as the path of travel goes away from MD 51 towards the Paw Paw Campground. The existing width of the entrance road makes two way traffic problematic and thus a candidate for enlargement of the crest of the embankment. The concept placement area is shown in Figure 34. As seen in Figure 35, the conceptual placement areas are both within the mapped 100-year floodplain.

For this disposal site to be the most cost effective, access would be accomplished through the paw paw tunnel. However, due to vibration concerns on the aging masonry – heavy hauling through the tunnel is not anticipated to be feasible.

The following constraints were noted:

• Access through Paw Paw Tunnel – Vibration concerns for historic masonry exist, especially given current condition of the mortar joints and displacement of previously repaired sections that are separating from the underlaying courses of brick. Limited access for mobilization of equipment may be acceptable to the government if precautions are taken to limit and monitor vibrations. Air quality concerns through the tunnel with the use of heavy machinery would also need to be monitored and mitigated to avoid the accumulation of noxious gases. Monitoring of existing structure using methods similar to those identified in paragraph 15.3 of the Technical Manual for Design and Construction of Road Tunnels – Civil Elements (FHWA-NHI-10-034) or an equivalent industry standard would also be required, specifically on any existing structural defects. Important to note is that any drilling for instrumentation should be done in the mortar joints and NOT in the masonry. Vibration monitoring should be done in accordance with paragraph 15.5 of the Technical Manual for Design and Construction of Road Tunnels – Civil Elements (FHWA-NHI-10-034) or an equivalent industry standard. Regardless of level of access usage, vibration and structural monitoring must be accomplished to determine the effect of any construction activities adjacent to the historic tunnel (anticipated activities of concern include but not limited to blasting, trucking, earthmoving, scaling, etc.). It will be required that the contractor develop an instrumentation plan that will be submitted to the government for approval. The plan should address the items in paragraph 15.7 of the Technical Manual for Design and Construction of Road Tunnels – Civil Elements (FHWA-NHI-10-

034) or an equivalent industry standard. Structural monitoring devices should have the option of being left in place for long-term monitoring of the existing impairments by NPS.

• The footprint of the proposed ramp are currently mapped as within the 100-year floodplain by the effective Flood Insurance Rate Map (FIRM). Any fill in this area would need to be accounted for by showing that it causes a no-rise in the base flood elevations (BFE) for the 100-year event. See Figure 35 for the current FIRM. Hydraulic modeling would likely be necessary to showing engineering determination of the effect of proposed fill within the floodplain.

• To provide a competent material for construction of the ramp enlargement, crushing of the scaled material would be necessary to minimize voids and provide the necessary engineering characteristics. A crusher would need to be mobilized to the site and used.

• The existing drainage pipe underneath MD51 would need to be lengthened and a new headwall installed to allow for conveyance of the existing drainage patterns. Existing guard rail and NPS gate would need to be modified. In addition, the widening of the access roadway into MD51 would need to be coordinated with MD-SHA to ensure that all applicable codes and regulations are implemented into the intersection design. A permit may be necessary to be obtained from MD-SHA for the proposed improvements.

• Photos of the access route are included below in Figures 36 - 38. Additional mitigations are included in the final

Figure 34, Conceptual Spoil Area near Paw Paw Campground.

Figure 35, FIRMette for Access Road Enlargement Area.

Figure 36, Existing Drainage Pipe at MD51.

Figure 37, Existing Intersection with Access Road & MD51.

Figure 38, Existing Access Road from MD51.

Submitted by:

Joe Reed, P.E., CFM – Park Civil Engineer

Chesapeake & Ohio Canal National Historical Park

National Park Service