Coal Brook Stream Restoration

Terence J. Ostrowski, P.E. Engineer – Stormwater Management and River/Stream Hydraulics Section Borton-Lawson Engineering

Abstract

The Coal Brook watershed has a history of uncoordinated and haphazard development. In the lower portions of the watershed, the stream channel has been significantly altered from its original course by prior coal mining activities and development. At a point approximately half way through the stream reach, the channel had been completely filled in by a 40- foot high embankment, thus preventing flows from the upper watershed from reaching the lower portions. During significant storm events, runoff from the upper watershed ponds behind the blockage and slowly percolates into the ground, contributing to the underground mine pools. A recent development boom has brought this problem to light since several businesses are interested in locating on lands upstream of this blockage. Due to the presence of numerous undersized culverts and bridges, removal of the blockage would threaten downstream areas with flooding. Several potential solutions to this problem were investigated. It was found that replacement of downstream culverts with adequately sized structures was improbable due to dense development in this area. Therefore, a solution to open the blockage and divert excess storm flows via underground conduit to an available constructed wetland area was investigated. This solution provides several benefits, which include not only the elimination of the ponding area, but also reduction of infiltration to the mine pools with a resultant decrease in Acid Mine Drainage (AMD) to the Susquehanna River, reduction of the flooding hazard to downstream areas, and enhancement of a hydrologically undercharged wetland area.

Existing Field Conditions

The Coal Brook watershed is typical of many watersheds in the coal mining regions of Luzerne County. The headwaters of the 2.6 square mile watershed begin as undisturbed forest lands in the Wilkes-Barre Mountains outside the limits of the coal measures. However, before the stream reaches developed areas on the northwest side of Interstate 81, the stream enters the coal measures and all base flow is lost due to infiltration into the deep mine pools. In this area, normal stream flow vanishes either through cracks in the streambed or subsidence created by weakening mine workings. From this point on, the channel flow is intermittent and limited to period of stormwater runoff from the developed areas downstream of Interstate 81. Along the lower Coal Brook reach, the channel

1

Figure 1 - Coal Brook Watershed Map has been severally impacted by prior strip mining and commercial development. Diverted long ago from its natural course, the channel has been enclosed it some parts by long reaches of culvert running under parking lots and buildings. In many cases, these culverts are significantly undersized, since water was rarely seen in the channel before the commercial development occurred.

2

Approximately 0.6 miles downstream of Interstate 81, more than half of the drainage area (1.5 sq. miles) is impounded behind a forty foot fill embankment, apparently created when a large debris pile was level in the early 1980s. Due to this blockage, all runoff from the upper watershed eventually infiltrates into the underground mine pools. The mine pools are connected by a series of underground mine tunnels which make up the major mine pool complexes of the Wyoming Valley. Prior studies have determined the water that infiltrates in this portion of the valley the Southeast Complex Lower Mine Pool.

Coal Brook d

Figure 2 - Wyoming Valley Mine Pool Complexes

Outflow from the lower mine pools are controlled primarily by a series of boreholes located in the adjacent Solomon Creek watershed. The boreholes were originally drilled into the deep mine workings as a way to control large fluctuations in mine pool levels. These fluctuations, due in part to an influx of surface water during storm events, create pressures in the underground mine workings that potentially lead to ground subsidence in the areas underlain by the workings. While the boreholes do their part in controlling mine pool fluctuations, the discharged mine water is highly acidic and contains large concentrations of metals, such as iron and manganese. This discharge is commonly referred to as Acid Mine Drainage (AMD). Solomon Creek, the receiving body of the borehole discharge, is encrusted with orange iron precipitate downstream of the outfall. Below this point, the water quality in the receiving stream is severely degraded.

3

Figure 3 - South Wilkes-Barre Borehole Figure 4 - Receiving Stream below Borehole

Below the fill embankment, the Coal Brook channel was diverted from it natural course to flow parallel Mundy Street. The channel slope is very steep in this section, ranging in slopes from 3 to 4 percent. Culm banks (refuse piles of unusable coal and rock), remnants from the old coal workings, extend from the channel overbank and reach heights of over 50 feet. Along this reach, the channel carries only local storm runoff from Mundy Street and the culm banks, until it combines with discharges from heavily developed commercial areas along the east side of Mundy Street. The confluence of the two sources occurs midway through an existing 72- inch corrugated metal pipe near the Kranson Men’s Clothing Store. Immediately below the outlet of this culvert, the stream crosses Mundy Street through an arch culvert that has been severely clogged by rock and debris from the upstream culm banks. Below this point, the channel is open for another 100 feet before it is enclosed in a 150 foot underground system beneath the existing Jiffy Lube parking lot. This system begins as an old stone arch culvert and transitions to a 60- inch corrugated metal pipe about midway through.

Figure 5 - Channel Along Mundy Street Figure 6 - Mundy Street Culvert (Culm banks on left)

4

At Spring Street, the channel enters a dense residential section of Wilkes-Barre City. The channel banks in this reach are steep, however the profile is very mild, which results in heavy deposition of silt and rock washed off from the upstream culm banks. Two bridges cross the channel at Spring and Scott Streets. Silt accumulation beneath the Spring Street Bridge has severely reduced the capacity of this structure. The Scott Street Bridge is currently being replaced by a structure sized to convey the 100- year flow. In the open channel between Spring and Scott Streets, a sanitary sewerline follows the channel with several manholes located at the bottom of the stream bed.

Below the Scott Street Bridge, the channel enters a 5ft by 5 ft box culvert which encloses the channel underground for a length of approximately 1000 feet. . The majority of this pipe lies underneath the parking lot of McCarthy Tire and it is presumed that a portion of the pipe runs beneath an existing garage. Part way through this system, the box section transitions to 60- inch corrugated metal pipe. The bottom of the corrugated pipe has been corroded significantly over the years, most notably near its outlet, where the pipe has partially collapsed.

Figure 7 - Channel Below Spring Street Figure 8 - Box Culvert Below Scott Street

After the channel exits the corrugated pipe, it is again diverted along the south side of Wilkes-Barre Boulevard. From this point on, the channel has adequate slope and capacity to convey storm flows within its banks until it joins the larger Laurel Run. Approximately 0.3 miles downstream of this point, Laurel Run joins the main stem of Mill Creek before draining into the Susquehanna River.

Approach to Alternatives

The pressure of impending development in the Coal Brook Watershed required a review of short- term solutions to the capacity problems of Coal Brook. In theory, the short-term alternatives, if cost effective and technically feasible, would allow development to proceed while funding for the longer- term solutions was obtained.

Any long-term alternatives presented would accommodate a 100-year flood for Coal Brook. These alternatives would ideally reduce the seepage of Coal Brook flows into underground voids and the mine pool. This will stabilize future groundwater conditions and reduce potential hazards such as

5

acid mine drainage and subsidence potential. Furthermore, the water presently ponding in the area of the fill embankment is immediately upstream of a newly built 8,500-seat arena complex. Ponding of water behind the embankment is actually higher than the Arena concourse and event floor and potentially threatens the stability of the structure.

Short Term Alternatives

Many short-term alternatives were considered. Three were developed for detailed evaluation. Basic engineering considerations that governed the evaluation of alternatives are as follows:

• Alternative 1 - Channel Diversion to the Highland Park Basin.

An overflow storm sewer would convey stormwater ponding above a specified elevation to a nearby stormwater basin near the newly built arena. When the capacity of the overflow sewer is reached, a secondary overflow pipe would convey the excess to the downstream Coal Brook channel. This overflow would only occur during very large storms. To relieve the excess volume in the receiving stormwater basin, a pump would be installed to convey the diverted flow back to the original channel, below the fill embankment. The pump discharge is limited due to capacity problems in the downstream reaches.

COST - $3,000,000

• Alternative 2 – Upgrading of Downstream Bridges and Culverts

This option replaces the most severe restrictions in Coal Brook, the Jiffy Lube culvert and the Kidder Street system to allow a 25 year storm event to pass. The fill embankment would be utilized as a detention basin where most storm flows would be stored. Larger storms would discharge overflow to a proposed overflow pipe through the embankment to the lower Coal Brook channel.

A special condition of this approach would be lining the slopes of the detention basin with clay to prevent horizontal migration of water downstream to the area of the Arena.

The advantage of this system is that the Jiffy Lube and Kidder Street culverts and the overflow pipe would be permanent improvements. The required size of detention area for this option is 6.3 acres.

COST - $2,500,000

6

• Alternative 3 – Combination of Alternatives

This option is similar to that of Alternatives 1 except that the impounding area would be eliminated and initial flows would be diverted to the large basin with excess flows directed to the partially upgraded Coal Brook channel of Alternative 2.

COST - $4,200,000

After evaluation of these alternatives, it was determined that the short-term options involved significant expenditures of money on temporary facilities upstream. Construction of a large sewer through the Arena parking lot is expensive and would be very deep in some areas. Major utilities would be crossed and the parking lot lighting would be interrupted by trenching. Options 1 & 2 required retaining a portion of the detention basin making it very difficult to develop a large commercial center. Option 3, which eliminates the basin, is very expensive and not justified from an economic standpoint.

Each short term alternative constrains immediate development opportunities by limiting the available acreage or by imposing high costs for the temporary systems.

None of these alternatives was considered feasible primarily due to the costs and uncertainties involved in the impacts of the infiltration of stream flows into the underground mine workings. Engineering uncertainties were too numerous and could not be addressed with an acceptable degree of confidence to ensure that the general safety of all structures is addressed over the life of the project.

Long Term Alternatives

Several solutions were investigated to correct the existing downstream capacity problems to abate flooding problems and allow future development to occur in the upstream areas. Three were fully developed to provide a basis for comparison of total construction costs.

For all long term alternatives, it was recommended that future development in the areas downstream of I-81 convey stormwater runoff directly to the Coal Brook channel, as opposed to detaining on site, as long as the runoff can be conveyed to the Coal Brook channel without exceeding existing channel or storm sewer system capacities. This is due to the overall timing of peaks in the Coal Brook watershed versus that of the Mill Creek watershed. Since flows from Coal Brook enter the main channel of Mill Creek prior to the peak flow from the remainder of the Mill Creek watershed, a delay in the Coal Brook peak, which may result from the standard detention of runoff, could adversely impact the overall peak on the main stem of Mill Creek. By delaying the peak on Coal Brook through detention, the peaks of Coal Brook and Mill Creek could be brought into alignment, producing an overall higher peak on the main stem of Mill Creek.

In general, two approaches were taken in this investigation. The first approach was to determine the feasibility of upgrading the existing channel and structures to allow conveyance of the anticipated

7

100-year storm flows with the channel blockage eliminated. This included upgrading the entire stream channel which does not have the capacity to pass the design storm. This approach is presented in Alternatives 1 & 2.

The second approach taken was to investigate the feasibility of diverting excess storm flows in a pressure conduit along Spring Street to a wetland near Exit 2 of the Cross Valley Expressway. This approach is Alternative 3.

The following discussion further details the alternatives.

• Alternative #1 – Reconstruction of Entire Length at Existing Location

With the stream capacity actually decreasing as one proceeds downstream along Coal Brook, total replacement of all channel features is required to accommodate future flows.

The lower portion of the new system would begin just above the Kranson Clothing Store on Mundy Street. A special inlet structure would be constructed to accommodate the existing 72” CMP culvert just above Kranson’s and a new deeper parallel 84” pipe culvert. These two culverts would be extended under Mundy Street to an area behind Jiffy Lube where a new 6’x12’ box culvert would begin and would run the remaining 2300 feet to the existing discharge point at Wilkes-Barre Boulevard. A special structure would reduce velocities and direct the flows to the existing Coal Brook channel along the Boulevard.

A realignment of the channel from Spring Street to Kidder Street was proposed where the existing sanitary sewer is located in the center of the existing stream. Right-of-way acquisition would be required for the new alignment.

Local drainage systems could be tied directly into the new culvert. If sections of the new culvert are designed as a pressure system for extreme events, flap gates would be provided on the outlets of the local systems. The new culvert would be buried below the surface and existing earth channel sections would be filled in resulting in a very big improvement in the appearance of the area.

Since this alternative generally follows the existing stream, permitting would face less obstacles. From Jiffy Lube to Kidder Street, the new alignment will need to address major conflicts with the existing sanitary sewer near Scott Street.

The upper reaches of the system would include upgrade of the swale along Mundy Street and new large diameter pipes through the existing fill embankment.

COST - $5,500,000

8

• Alternative #2 – Upgrade Downstream Structures and Channel

This alternative includes upgrading the downstream Coal Brook Channel to a 100- year storm capacity by replacing five structures from Mundy Street downstream to the existing McCarthy Tire site with a new 6’X 12’ box culvert and some upgraded open channel sections of Coal Brook.

Due to the low roadway profile in the area of the Spring Street bridge, and the low channel capacity above this bridge, it is recommended that the open channel between the outlet of the Jiffy Lube culvert and the Spring Street Bridge be eliminated to prevent flooding upstream of the bridge. This would consist of extending the replacement culvert at Jiffy Lube to downstream of Spring Street.

With the remaining existing culverts upgraded to meet design capacity, the Coal Brook open channel between Spring Street and Kidder Street would also require modifications to allow conveyance of the 100-year flows without flooding the overbank areas. These modifications would include regrading of the existing channel, lining the channel to reduce scour, and constructing approximately 500-feet of floodwalls above the Kidder Street culvert and Scott Street Bridge. It was also recommended that the existing sanitary sewer line in the bed of the channel from Spring Street to the Kidder Street culvert be partially relocated to prevent infiltration from the channel flows. Fencing of the entire 700-foot reach between Spring Street and Kidder Street was recommended for safety considerations.

The advantage of this alternative was a slightly lower cost, however, major infrastructure changes will have to occur for the channel to meet the required capacity. The most significant of these is in the improvement of conveyance under the existing McCarthy Tire site. The disadvantage of this alternative lies in the diversion of Coal Brook flows during construction. This portion alone could account for over $100,000 in project costs with a significant amount of properties requiring easements for the temporary diversion. Also, a sanitary sewer and its associated manholes follow the creek bed creating a difficult construction scenario. Improvements upstream of Kranson's Clothing would be the same as Alternative 1.

COST - $4,100,000

• Alternative #3 – Flow Diversion Above Significant Obstructions

In this alternative, a diversion of storm flows would be created above the significant obstructions. The preferred location for the diversion structure was located above the Kranson property on Mundy Street. The route of this diversion culvert would follow the existing stream channel from the south side of Mundy Street to behind the existing Jiffy Lube service station where it will turn and follow the right of way of Spring Street in a northeasterly direction, then turn through the old Battery Warehouse parcel crossing Kidder Street and discharge into an existing wetland mitigation site on lands owned by PennDOT.

9

At this point, the overflow would discharge directly into the lower section of Coal Brook upstream of the Exit 2 Interchange of the North Cross Valley Expressway.

The total length of the proposed diversion channel is approximately 2300-feet. Due to the lack of a significant drop in elevation between the inlet and outlet of the proposed culvert, the diversion structure will be required to build head above the culvert inlet to allow the design flow to pass through the culvert under pressure flow conditions.

Local storm sewers below the diversion would be conveyed to the downstream Coal Brook channel as they do under existing conditions. Total discharge from the lower portion can be safely conveyed through the existing channel and culverts.

In this alternative, the advantage lies in the fact that the construction difficulties of working in the Coal Brook channel are eliminated except for the repairs mentioned above. The majority of the construction will occur outside of the channel thus eliminating the need for a temporary stream diversion. This alternative also allows development to occur in the upstream areas without detention being required. The disadvantages lie in construction costs of working along Spring and Kidder Street and relocation of existing utilities along the route of the diversion culvert. Cost of the 2300-feet of required culvert contributes significantly to the overall cost of this alternative.

COST - $5,500,000

Conclusion

All three systems would convey the 100-year storm. Alternates 1 & 2 were less costly to construct and are gravity systems due to a more favorable slope along the existing channel. However, potential conflicts with the utilities especially the 24” sanitary sewer which runs along the center of the stream from Spring Street to Kidder Street may prove to be very costly to mitigate. Alternate 1 will reduce infiltration into the sanitary sewer between Spring and Kidder Streets, but future maintenance of the sanitary sewer will be very difficult and costly if spot replacements are necessary.

Alternate 2 was not recommended because open channel sections are less desirable for the relatively large flows of 1000 cfs in a residential neighborhood and they are more of a safety concern during high water events. The cost savings are not significant versus Alternate 1.

Alternative 3 was the final recommendation because it provides the best long-term solution with fewer impacts to existing utilities and properties. Since the majority of construction would occur in PennDOT right-of-way, with no encroachments or easements required from private property owners, a potential cause for delay in obtaining the easements would be avoided. This option also avoids the foreseen problems with the existing sanitary sewer along the original Coal Brook alignment. Additional benefits to this alternative included the improvement of a wetland mitigation area near the Cross Valley Expressway that has been failing due to inadequate hydrology. This alternative also provides a source of water necessary to establish and sustain the

10

wetland vegetation.

11