Cumberland County Landfill Hopewell Expansion

Cumberland County, PA

Stream, Dam Removal and Wetland Mitigations

As part of the Hopewell Expansion of the Cumberland County Landfill and in fulfillment of federal and state permit compliance, ARM Group Inc. (ARM) completed a stream and wetland mitigation project in Hopewell and North Newton Townships, Cumberland County, Pennsylvania. ARM was responsible for the development of:

  • Approximately 1, 500 linear feet of perennial stream restoration and enhancements
  • Dam removal design to restore stream and wetland habitats
  • One acre of wetland mitigation, including creation and restoration/enhancements
  • A Stream and Wetland Mitigation Report, including final design plans
  • Stream and Wetland mitigation performance criteria for a five year monitoring program

The mitigation is required to offset the permanent loss of stream and wetland impacts within the Conodoguinet Creek watershed, resulting from the landfill expansion. The wetland and stream mitigation were developed using a watershed perspective and natural channel design methods were implemented for the stream design. State and federal regulatory agencies were consulted for comment in the development of the conceptual design and review of draft and final design plans in order to facilitate the compliance review process.

Stream Restoration and Enhancement

ARM scientists and engineers conducted longitudinal profiles, cross-sectional surveys, and pebble counts for the impaired on-site stream sections and surveyed reference reaches to establish baseline and proposed conditions. The stream restoration/enhancement activities consist of the following to improve stream conditions in the upper watershed area:

  • Establishment of dimension, pattern, and profile for the impaired stream channel based on reference conditions
  • Removal of an existing earthen dam (berm removal of a small impoundment)
  • Stabilization of the new stream banks through use of natural materials and bioengineering techniques
  • Placement of in-stream structures (log vanes and rock gradient controls) at selected points within the reach to maintain slope on the channel
  • Installation of log vanes at several locations to direct sediment deposition and thereby facilitate pool formation for an enhanced stream profile as well as to facilitate the potential for improved habitat diversity for aquatic benthos in the watershed

Enhancements also include stream debris (i.e., cars, tires, etc.) removal and the stabilization of channel embankments outside of the restoration/enhancement areas. Approved erosion and sediment pollution control measures will be implemented to maintain water quality of downstream wetlands and waters.

Wetland Mitigation

The wetland mitigation goal included development of a 1 acre system of on-site and in-kind replacement at a slightly greater than a 1:1 replacement ratio to ensure the replacement area is achieved and is designed to equal or exceed the functional value of the existing impacted wetlands.

The wetland replacement location was chosen based on detailed site selection criteria ensuring sufficient hydrology, soil suitability, and juxtaposition with existing wetlands, tree conservation, future land use plans, and the opportunity to provide functions. The mitigation focuses on the creation of an emergent and scrub-shrub habitat and is designed to improve surface water retention, hydroperiod and vegetation/water interspersion, improve stream flow stability and increase wetland vegetative diversity. Additionally, an upland buffer zone of native trees, shrubs and seed were specified to enhance the wetland mitigation and facilitate watershed improvements. Measures were prescribed to protect newly planted trees and shrubs from browse damage by the white-tailed deer population.