Connoquenessing Creek Watershed Conservation Plan - Western ...

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Connoquenessing Creek Watershed Conservation PlanChapter 2. Land ResourcesLandslides cause damage to transportation routes, utilities, and buildings. They can create traveldelays and other side effects. The threat of landslides should always be assessed while planning anydevelopment project. Proactively avoiding a landslide is much cheaper in the long run than the clean upand repair that is required after a landslide. If development within a landslide-prone area is ultimatelychosen, additional precautionary measures during development, such as additional drainage features andproper site planning are essential to minimize the risk of a landslide (Delano and Wilshusen, 2001).Subsidence AreasSubsidence is the downward movement of surface material involving little or no horizontalmovement. Occurring naturally due to physical and chemical weathering of certain types of bedrock,subsidence usually occurs locally as a result of underground mining, excessive pumping of groundwater,or subsurface erosion due to the failure of existing utility lines (Kochanov, 1999). Subsidence usuallyoccurs slowly over a long period, but can happen rapidly. The development of a sinkhole, for example,occurs when the support of the land is gradually removed, causing the land surface to sag and finallycollapse, leaving a hole or cavity (Kochanov, 1999). Although subsidence is not common in thewatershed, the potential for it exists because of numerous abandoned coal mines located in the study area.SinkholesA sinkhole can be defined as a subsidence feature that can form rapidly. It is characterized by adistinct break in the land surface and the downward movement of the surface materials into the resultinghole or cavity. Sinkholes only occur in certain parts of Pennsylvania underlined by carbonate bedrock,typical in central and eastern parts of the Commonwealth. This region is generally not affected bysinkholes unless mine subsidence causes them.Mine SubsidenceMine subsidence is the movement of ground surfaces as a result of the collapse or failure ofunderground mine workings. In active underground mining operations using longwall mining or highextraction pillar recovery methods, subsidence usually occurs concurrently with the mining operation in apredictable manner.In abandoned mines where rooms and unmined coal pillars are often left in various sizes andpatterns, it may be impossible to predict if and when subsidence will occur. Mine subsidence resultingfrom abandoned room and pillar mines can generally be classified as either sinkhole subsidence or troughsubsidence.Sinkhole subsidence occurs in areas overlying shallow room-and-pillar underground mines. Themajority of sinkholes usually develop where the amount of cover is less than 50 feet. They are typicallyassociated with abandoned mines. DEP will no longer authorize underground mining beneath structureswhere the depth of overburden is less than 100 feet, unless the subsidence control plan demonstrates thatthe proposed mine working will be stable and that overlying structures will not suffer irreparable damage.This type of subsidence is fairly localized and is recognized by an abrupt depression evident at the groundsurface as overburden materials collapse into the mine void.Subsidence troughs over abandoned mines usually occur when the overburden sags downward due tothe failure of remnant mine pillars. The resultant surface effect is a large, shallow, yet broad, depressionin the ground, which is usually elliptical or circular in shape. The flow of streams may be altered ordisrupted and surface cracks may occur, particularly near the edges of the trough.Researching areas where mining occurred in the past to determine the risk of subsidence is needed.Homeowners should check with DEP to determine if their property is susceptible to mine subsidence andsecure insurance through the PA Mine Subsidence Insurance Fund, if necessary.2-14
Connoquenessing Creek Watershed Conservation PlanChapter 2. Land ResourcesErosion and SedimentationErosion is the transfer of soil particles through air or water. The relocation of these particles isknown as sedimentation. Erosion and sedimentation are natural earth-moving processes, but the extent ofthis movement can be greater than normal due to poor land-use practices. Erosion is common alongstreambanks, steep slopes, and ridgetops.DEP and Pennsylvania Code regulate the disturbance ofearth materials leading to erosion and sedimentation.Disturbances include any earth moving activities, such astimber harvesting, construction activities, agricultural plowingand tilling, etc. Disturbances less than 5,000 square feet arerequired to minimize the potential for accelerated erosion andsedimentation through the implementation and maintenance oferosion and sediment control BMPs. A written erosion andsediment control plan is required for any disturbance 5,000square feet or greater, if the disturbance has the potential todischarge to a high quality or exceptional value waterway, oris required under DEP regulations.Siltation fences, as depicted in thephoto, are a best management practiceused to contain loose soil atconstruction sitesAny disturbance of one acre or more, except foragricultural plowing or tilling, timber harvesting, or road maintenance activities, requires a general orindividual National Pollutant Discharge Elimination System (NPDES) permit. Timber harvesting or roadmaintenance activities involving 25 acres or more require an erosion and sedimentation control permit.To help combat erosion, there are seven erosion and control permits located within the project area.Erosion and sedimentation are discussed in greater detail in the Water Resources chapter.Groundwater Recharge AreasWater that comes from surface water or precipitation, such as rain or snowmelt that is storedunderground is groundwater. Within the U.S., groundwater supplies approximately one-third of publicwater supplies and 95 percent of rural domestic water supplies. Groundwater is pumped to the surfacewhere it is brought into homes through public water providers or private wells (Robson).Replacing the water depends on the grounds ability to absorb water from precipitation or surfacewaters, such as lakes and streams is a natural hydrologic process called recharging. The rate of rechargecan be influenced by different factors, such as soil, plant cover, water content of surface materials, andrainfall intensity. Groundwater recharge may also occur from surface water bodies in arid areas. Moreinformation about groundwater and groundwater recharge is available in the Water Resources chapter(Robson).Natural Resource ExtractionThe process of removing minerals, such as coal, oil, and gas is done through natural resourceextraction. Oil and gas are removed through the drilling of wells as discussed earlier in this chapter. Coal,limestone, and other industrial minerals are extracted by mining. The natural resources that underlie theregion are dictated by the geological formations present in the region, which was also discussed earlier inthis chapter.Fish and Wildlife HabitatHabitats are the natural environments in which animals and plants reside. Healthy habitats areimportant to maintaining a diversity of biological resources. Interferences and changes to habitat affect2-15
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