The PHC process is discussed in the following sections:
The PHC process consists of the following steps, repeated as many times as necessary to mitigate adverse impacts-
The remaining unmitigated impacts must be documented in the PHC determination. This iterative PHC process is intended to reduce the predicted adverse impacts to the hydrologic balance to an acceptable level. An sample outline for the PHC determination is available for downloading.
The PHC process should consider:
The process suggests a sequential approach starting with the definition of information needs. The types of information needed, however, not only rely heavily on baseline conditions but also on postmining reclamation objectives to be achieved and characterization of the water resources that must be preserved to support those objectives. Therefore, the PHC process starts with a clear understanding of the intended postmining land uses. Hydrologic criteria necessary to support those water uses help define the information needs for the entire impact analysis.
Element (1) refers to defining information needs.
Element (2) refers to collecting baseline information which describes the hydrologic and geologic conditions that exist at the site to be mined. Emphasis should be placed on those characteristics defined in the first element that are critical to water uses.
Element (3) refers to the analysis of the baseline information collected to determine the nature and critical functions of the hydrologic system. The analysis helps to identify hydrologic units that may potentially be affected by the operation and to establish their pre-mining values. Both surface- and ground-water parameters should be considered and the level of analysis should be based on the complexity and variability of the hydrologic system on a seasonal basis, the importance of the water resource, and specific requirements of the RA.
Element (4) refers to planning the steps the applicant will take to minimize disturbance to the hydrologic balance within the permit area and prevent material damage outside the permit area. The Hydrologic Reclamation Plan should address impacts previously identified and should describe the measures planned to mitigate those impacts.
Element (5) defines the magnitude of impacts to be expected after the proposed preventive and remedial measures have been applied. This is considered to be the PHC determination which must make findings on:
Iterations of impact analysis and mitigation design continue until all impacts to the hydrologic balance within the permit and adjacent areas have been minimized and material damage outside the permit area has been prevented. If, during this process, analyses indicate adverse impacts from a surface mine on a water source being used for any legitimate purpose, then the applicant must provide information on alternate sources of water. These additional steps are represented by the Supplemental Information (4a) and Alternative Water Source Information (4b) elements.
Element (6) refers to development of ground- and surface-water monitoring plans to measure actual impacts to those resources resulting from the mining operation. These plans focus on parameters identified earlier as critical to maintaining water uses in support of reclamation objectives for postmining land uses.
Although the PHC determination is a projection of residual impacts after implementation of preventive and mitigative measures, the types of impacts anticipated to result from mining are identified in the initial iterations of the PHC process. These anticipated impacts are the focus of the detailed preventive and mitigative hydrologic planning described in the hydrologic reclamation plan.
The ground-water system comprises the water bearing strata and confining beds that lie beneath the Earth's surface. The system serves both as a water storage unit and as a conduit through which water is transmitted from recharge areas to discharge areas.
An understanding of the rate, direction, and overall pattern of ground-water movement in aquifer systems encountered in coal regions is essential for predicting impacts to ground-water quantity. Both surface and underground mining have the potential to disrupt and permanently alter the physical characteristics of aquifer systems through:
These alterations, in turn, may affect the hydraulic characteristics of aquifers, potentiometric heads, the rate of discharge from springs and wells, the direction of flow within and between aquifers, the types and rates of chemical reactions occurring within the ground-water system, and ultimately, the total quantity and chemical composition of the ground water moving through the permit area.
Seasonal variations in ground-water quantity in the permit and adjacent areas may be defined by measurements of water levels in observation wells, changes in spring discharges, and discharge of surface-water baseflow. These measurements, in addition to a water users inventory, are important components of the mine site investigation which the applicant should conduct in order to assess baseline conditions.
The hydrologic complexity of a site and the significance of the ground-water issues usually dictate an appropriate predictive method. The applicant should select a method that accurately reflects site conditions and that has been proven effective. It may be adequate to express ground-water quantity impacts qualitatively, alone or in combination with varying degrees of quantitative analyses.
Hydrologic models ranging from simple empirical equations to complex numerical computer solutions may be used for estimating ground-water impacts. Models must be calibrated with site-specific data or data representative of the site. Extrapolation of data from an adjacent or nearby area to a permit area is acceptable when the similarity of the areas is established and information is available to justify the correlations. Generally, ground-water quantity predictions are made with analytical or numerical flow models.
The composition and concentration of substances dissolved in ground water depends on the biologic and chemical reactions occurring on the land surface and in the soil zone, and the mineral composition of the aquifers and confining beds through which the water moves. Prior to mining, the relationships governing the movement of water through the permit area and those affecting the chemical composition of the water are likely to be in a state of relative equilibrium, reflected in the existing baseline water quantity and quality regimes.
With the onset of mining, the surface- and ground-water hydrology of the area will be altered disrupting the existing equilibrium. From a hydrogeologic standpoint, the most disruptive forces are the removal of the coal seam and the fragmentation and spoiling of the overburden material. These processes result in the exposure of mineral surfaces to air and water and alter the water holding and transmitting characteristics of the geologic materials. The rates at which ground waters move through a permit area and the chemical composition of that water are therefore, subject to significant change.
Ground-water quality impacts resulting from mining activities usually involve changes in the concentration of existing constituents dissolved in the water and/or the addition of new chemical constituents mobilized by oxidation/reduction reactions in the spoil material. Increased mineral concentrations result from:
When the spoil materials become re-saturated after mining and a hydraulic gradient is reestablished across the disturbed area, water will begin moving through the spoil towards discharge zones. This water has the potential of becoming highly mineralized due to the chemical reactions occurring in the spoil. Additionally, ground water may become mineralized and contaminated from poor quality surface water percolating through the spoil and recharging the water table aquifer. Potential sources of contaminated surface water include acid drainage, pit pumpage and waste-water from coal processing plants.
Contaminant transport models are available for use in analyzing the movement, mixing, and chemical reactions of contaminated water through an aquifer system. Because ground-water flow is a major factor affecting the movement of pollutants, contaminant transport models are extensions of ground-water flow models.
Streamflow at a particular site consists of ground water derived baseflow and surface runoff resulting from precipitation or snowmelt. Seasonal flow conditions refer to the fluctuation of flow over the course of a year. Peak discharges result from the addition to baseflow of surface runoff due to rainfall and snowmelt. Low flow refers to the minimum discharges during the year which are wholly composed of baseflow. For ephemeral streams, there is no baseflow component; their flows occur only in response to precipitation and snowmelt runoff.
Surface-water discharge parameters most often included in hydrologic analyses are peak and low-flow frequencies and mean flow values. Although seasonal flow conditions generally do not include values form instantaneous peak flows, the PHC determination should indicate the impact of the proposed operation on flooding or streamflow alteration. Therefore, some analysis of peak flows may be necessary. Generally, peak flows and flooding will be reduced during mining due to the increased infiltration capacity of the reclaimed area and the storage capacity of water-retention structures.
The following is a brief discussion of the various methods for analyzing surface flows. These methods may also be used for water-control structure designs.
Runoff volume is part of the information needed to characterize water resources. Runoff volume is calculated by subtracting losses (evapotranspiration and infiltration) from the amount of precipitation expected during a rainfall event. The amount of evapotranspiration is very small during a storm and can usually be neglected. Both empirical and physical methods are available for calculating infiltration. The most commonly used empirical methods are the Curve Number method, Index methods, and Horton's equation. These involve simplified representations of the physical system and may produce large errors at a specific site.
Of the empirical methods, the Curve Number method is the most widely used. The method lumps all water losses except evapotranspiration into a single initial abstraction. It correlates rainfall runoff to soil type, land use, and hydrologic condition. This method was developed for designing water-control structures on croplands and is suited for mining design. Because it is not easily calibrated to actual watershed responses, it is not well suited to prediction of streamflows. However, the method is popular because it is relatively easy to use under a variety of field conditions, especially for watersheds where site specific data is not available.
Storm peaks are normally estimated either by deriving hydrographs or by direct methods. A hydrograph illustrates the variation of discharge rate over time at a specified location in a watershed and, as such, provides a measure of the potential for flooding or streamflow alteration as a result of mining. The hydrograph shape determines the timing and magnitude of the peak discharge and is a function of how rapidly runoff volume forms (excess rainfall) and of the conditions along the flow path (time of concentration).
A common method of developing hydrographs is based on unit-hydrograph theory. The unit hydrograph is traditionally defined as a hydrograph produced by a storm of constant rainfall intensity and duration containing one unit of runoff volume. It is based on the assumptions of linearity and constant time increments governing equations, and that the same unit-hydrograph can be used throughout the storm's duration. The literature contains numerous unit hydrograph shapes that have been developed and applied. Those most commonly used are the triangular hydrograph, Haan's dimensionless hydrograph and the double-triangle hydrograph. The techniques for developing and using these and other unit hydrographs to develop a site-specific runoff hydrograph can be found in most standard hydrology texts. The baseflow hydrograph must be added to the runoff hydrograph to obtain the hydrograph of the total discharge.
Direct methods estimate peak discharges without computation of a runoff hydrograph. They are generally simpler to use than the hydrograph procedure and may be in the form of empirical procedures or regionalized regression equations. The rational method, Cook's method, Bureau of Public Roads methods, TPM method, and the SCS TR55 method are examples of empirical procedures. In general, use of these methods involves using coefficients selected from tables, graphs, or charts in an equation. Accuracy depends on how closely the method represents the hydrologic system and results are difficult to verify.
Regionalized methods are usually in the form of regression equations in which the dependent variable is a flow characteristic, and watershed and climatic characteristics are independent variables. Stream channel dimensions have also been used as independent variables. Such equations are most frequently developed to provide the peak discharges of a specified frequency, but they can also be developed to provide mean discharges, low-flow discharges, and runoff volumes. The process of developing regression equations also provides a statistical measure of the equation's accuracy (standard error of estimate). Regionalized regression equations have been developed to estimate peak discharges for all the coal-producing areas of the conterminous States.
A major shortcoming of direct methods of estimating discharges is that they usually represent relatively undisturbed watersheds. They are, however, useful for evaluating pre-mining streamflows and are, in many cases, preferable to the Curve Number method for this purpose.
The methods discussed above attempt to predict the hydrologic response of an area through empirical relationships or through greatly simplified expressions of hydrologic processes. Physical watershed models simulate watersheds mathematically by applying equations depicting several hydrologic processes over a geographical area. For surface runoff, a model might consider the effects of infiltration, evaporation, evapotranspiration, and interflow processes on the precipitation falling on a watershed. The stresses of mining can be incorporated into these models, and their effects can be evaluated at as many locations as desired. In theory, this approach should provide more accurate results than the empirical methods discussed above. Watershed models are not universally applicable and need to be tailored to the specific conditions of the area being analyzed.
Impacts to the quality of surface waters due to surface mining activities usually include changes in sediment loads, changes in Ph, and increases in trace metal and dissolved solids concentrations. The PHC determination therefore should include seasonal estimate of maximum and minimum concentrations and total loads of dissolved solids. In addition, predictions of seasonal concentrations of potentially deleterious trace metals, and sediment to be expected in runoff from disturbed areas should be provided as well as estimates of time necessary for these concentrations to reach equilibrium levels acceptable for the postmining land uses.
High concentrations of dissolved solids, suspended sediment, and metals can degrade the water quality potentially causing damage to the hydrologic balance and jeopardizing the approved postmining land uses. Irrigation water high in dissolved solids (salts) reduces crop yields and can corrode farm and industrial equipment. Waters high in trace elements such as boron, mercury, lead and selenium can be deleterious to plants and can also be toxic to livestock and wildlife. Waters having high trace metal concentrations have shown significant adverse health effects on humans, livestock, and wildlife. Furthermore, in some areas aquatic life may be adversely affected by increases in sediment and dissolved solids concentrations.
Acid mine drainage is a serious water quality problem especially in the Eastern and Mid-continental coal basins. Potentially harmful elements commonly associated with acid mine drainage include arsenic, boron, mercury, lead, zinc, cadmium, aluminum, copper, chromium, nickel, selenium and other trace elements.
Some methods for dealing with acid mine drainage problems are included later in this chapter and in the appendix on acid mine drainage. Although, acid mine drainage in the West is not as prevalent as in the East, pyritic conditions in western coals also produce environments of lowered Ph potentially resulting in increased mobilization of trace metals in the ground and surface waters.
During mining, and for some time following reclamation, many dissolved constituents can reach elevated levels from spoil due to the exposure of new mineral surfaces to air and water on an almost continual basis. Spoiling the overburden acts in two major ways to increase concentrations of dissolved solids and metals. First, overburden removal and spoiling increases the porosity of the material allowing more surface area of the materials to come into contact with air and water and increase the concentration of dissolved solids. Second, potential for oxidation of pyritic material and resultant acid mine drainage is increased. The rate at which this occurs is dependent on many physical factors. In the arid West, where precipitation is low and normally seasonal, this process could take hundreds of years. Therefore, predicting when all the pyritic material will be oxidized and the system will again approach equilibrium is problematic.
Once vegetation is established and disturbance of surface soil materials ends, the supply of minerals available at the land surface for solution and transport will normally decrease to premining levels. If erosion rates are higher than pre-mining levels, dissolved solids concentrations of surface runoff may remain at elevated levels for a longer period. If potentially toxic- or acid-forming materials are identified, the PHC should describe the steps to be taken during mining and reclamation to reduce exposure of this material to the atmosphere and contact with water in order to prevent development of acid mine drainage.
Methods are available for predicting concentrations of dissolved solids in surface runoff. These range from simple routing procedures to complex computer models which predict water, chemical, and sediment volumes and route them to various points in the stream system. A routing procedure is needed to combine the concentrations of surface- and ground-water components of flow in receiving streams.
Detailed, quantitative analyses in the PHC process are frequently unnecessary, especially for small sites in the East. However, for some of the large, western coal operations (permit areas of up to 100 square miles), numerical modeling for both quantity and quality is commonly utilized. The existing hydrologic data for a watershed may not be sufficient to calibrate a model or verify the credibility of the results. Depending on the complexity of the hydrologic system and the potential for adverse impacts to the hydrologic balance, additional baseline information may be required so that accurate PHC predictions can be made.
The disturbance of the land surface by mining and reclamation activities can significantly increase erosion and sediment yields. The PHC process should address impacts that the operation will have on sediment yield and on suspended solids concentrations of water draining from the permit area. Sediment yield is the volume of sediment that passes a designated point over a unit period of time, usually one year. The sediment yield at 2 watershed outfall is usually less than the hill-slope and channel erosion rates occurring within the watershed because some of the eroded material is redeposited before it reaches the measurement point.
The impacts of mining on sediment yield can be evaluated in two phases: (1) impacts on the erosional characteristics of hill-slopes, and (2) impacts on sediment transport characteristics, including channel erosion. Hill-slope erosion rates are a function of precipitation, surface soil characteristics, hill-slope gradient and configuration, and vegetation type and density. Sediment transport rates depend upon the sediment characteristics (particle size and density) and streamflow characteristics, which, in turn, are functions of stream channel shape and gradient. Simply stated, for a given particle-size distribution and density of sediment material, a larger water discharge can carry more sediment, if more is available to be transported.
Sediment yield can be addressed either qualitatively or quantitatively. A qualitative approach should describe design plans for sediment-control structures and measures to be employed during mining and reclamation to control sediment yields. Commonly used measures are discussed in the section on hydrologic reclamation plan mitigation measures.
Methods for estimating sediment yields quantitatively generally fall into two categories:
The Revised Universal Soil Loss Equation (RUSLE) is a computer program developed by the U.S. Agricultural Research Service that can be used to compute the soil loss from disturbed and undisturbed sites. The program calculates values for the six erosion factors that were developed for the USLE. These are multiplied to give an estimate of annual soil loss. RUSLE is more applicable to surface-mine conditions and provides more accurate estimates of soil loss over a wider range of site conditions than the USLE. The program has been used on surface-mines to evaluate the effectiveness of sediment control measures.
Regionalized multiple regression equations have been developed for predicting annual sediment yields. These equations relate sediment yield to easily measured watershed parameters, such as maximum annual peak discharge, cover density, and watershed area. These equations may not be directly applicable to predicting postmining sediment yields if parameter values are outside prescribed ranges.
The objective of these mitigative measures is to minimize disturbance to the hydrologic balance within the permit area and to prevent material damage to the hydrologic balance outside the permit area.
A surface coal mining operation may affect the hydrologic balance of the permit and adjacent areas in the following general ways: (1) by changing the quantity of surface runoff from the disturbed areas, (2) by exposing un-weathered mineral surfaces and potentially toxic/acid-forming materials to weathering processes, and (3) by intercepting and modifying existing ground-water flow patterns and rates. These impacts may result in changes in the volumes and flow rates of both surface-and ground-water discharges, and in changes to acid, salt and sediment content of those discharges. Mitigation measures should attempt to prevent large changes or to provide suitable treatment when such changes are unpreventable.
Mitigation measures applied to coal mining situations most commonly deal with water quality impacts and control of surface runoff. Some mitigative techniques address both situations. It is more difficult to mitigate changes in the ground-water system.
A variety of methods is available for mitigating potential adverse impacts to surface- and ground-water quality resulting from the presence of toxic- and acid-forming materials.
One method is to selectively handle materials so that oxidation and leaching do not occur or are minimized. Toxic- or acid-forming materials can be placed under an adequate layer of nontoxic soil or spoil or inundated in a permanent impoundment so that oxidation is prevented. Depending on the volume of suitable materials available and the volume of available burial space, special handling may be a feasible method for dealing with all of the toxic- or acid-forming materials.
In some instances, alkaline material may be used as a neutralizing agent for acid-forming materials, and a blending of the materials during back-filling may prevent the formation of an acid leachate. The chemical makeup of the material present will determine whether it is placed above or below the water table during special handling. In either case, the elevation of the postmining water table will have to be estimated. It should be noted that in cases where re-saturation occurs primarily from local surface sources, submerging may not preclude all oxidation because local infiltration may contain significant concentrations of dissolved oxygen.
Other methods of sealing toxic- and acid-forming materials are available, such as artificial barriers, and surface sealants like lime and gypsum. However, these methods are generally more expensive than special material handling techniques and require maintenance or reapplication. Clay, asphalt, or other inert barriers may be placed above the materials to prevent surface-water infiltration. Similar types of barriers may be placed around toxic materials to prevent infiltration by ground water. Unless the volume of material is relatively small, barriers are likely to be prohibitively expensive.
A different approach is treatment of unacceptable quality surface runoff through use of treatment ponds. Ponds for treating acid and toxic mine drainage should only be used during active mining as they require maintenance.
In cases where the mitigative measures will not result in surface or ground-water quality suitable for the postmining land use, the mining plan can still be designed to protect the hydrologic balance. Areas of toxic materials can be identified during pre- mining exploratory drilling and sampling programs. These areas can then be bypassed during mining.
Sediment production is a function of runoff rates and the erodibility of soil materials. The more runoff there is and the faster it moves over a site, the more soil erosion that is likely to occur. Therefore, control of sediment production involves control of both runoff and erosion. Erosion rates generally increase when protective vegetation is removed and the surface soil materials are stirred up to expose finer particles to rain splash and running water. The basic means of reducing erosion and transport of sediment are to reduce the quantity and velocity of water moving through the site and to protect erodible soil particles from the water's erosive forces.
There are several basic approaches to reduce erosion and sediment loads caused by mining.
Erosion impacts are minimal when detached soil is redeposited near its origin. Slowing runoff allows sediment to drop out of the flow. Designing reclamation to create slope gradients as flat as possible will assure low water velocities. Breaking long, steep slopes with benches or terraces, and contour furrowing are structural methods of reducing runoff velocities.
Runoff from undisturbed areas should be prevented from entering disturbed areas with properly designed up-gradient diversions. This minimizes the amount of water available to scour the erodible disturbed areas.
The prevention of off-site flooding and channel degradation is a consideration for most operations. A mitigation plan for these problems can be developed following a thorough initial evaluation of baseline hydrologic and geologic information for the mine site and adjacent areas. Predictive techniques can be used to evaluate the likely volumes of surface runoff which will occur during and following mining. Ponds, diversion ditches, check dams, and riprap can all be used to control the volume and velocity of runoff leaving the site. Impoundments may be left permanently on-site to continue runoff control following mining, if they are appropriate for the postmining land use and are structurally sound.
Problems with flooding can usually be solved with properly designed impoundments on the permit area, which usually also serve as sediment control structures. Stability of on-site reclamation channels is largely a function of the reconstructed topography. The mining and reclamation plan should be directed at reestablishing a postmining topography which will result in a stable drainage network. The most stable drainage configuration will most likely be very similar to the pre-mining drainage network. Off-site channel degradation is not usually a problem except when large amounts of excess water (pit de-watering) is continuously discharged to normally dry channels. Additional on-site impoundment storage volume would alleviate this problem, as would directing the excess discharge to more than one channel.
Verifying Mitigation
Ultimately, it is important to verify the effectiveness of mitigative measures in protecting the hydrologic resources. The objective is to verify or validate that mitigation measures are constructed and implemented as specified in the approved permit during both active mining and reclamation. Validation is generally straightforward for surface structures such as diversions and treatment facilities where installation and effectiveness can readily be observed during normal inspections.
Mitigative measures that utilize special overburden handling, blending or placement, and subsurface drains are not readily observable at all times during the operation. It becomes imperative that critical aspects of these measures be inspected at the time of emplacement. This may require that a condition be added to such permits requiring that the RA be notified when certain critical stages are imminent so that the inspector can arrange to be on-site when needed thus avoiding unnecessary work stoppages.
Measures requiring on-site inspection would include special handling techniques involving blending of potentially acid-forming material with alkaline material; isolation of toxic material by encapsulation within impermeable material such as natural clays, plastic film, or surface sealants; and the installation of an underdrain system designed to prevent buildup of saturation within the zone of emplacement. Thorough documentation during the inspection process is of utmost importance since there will be no further opportunity for inspection. Use of permanent documentation such as photographs or videotape recordings is encouraged for these processes. Also, during the inspection process, it is important that the inspector verify that all impermeable media are properly handled. Clays must be compacted according to approved permit specification. Membrane materials must be properly handled to prevent tearing, puncturing, or breaching; membrane joints must be properly sealed.
PROBABLE HYDROLOGIC CONSEQUENCES DETERMINATION
The PHC determination is a narrative summary of conclusions based on analyses and information developed and presented in other sections of the permit application package that show the impacts on the hydrologic balance that may occur as a result of the proposed operation. It should include a list of each potential problem identified during the initial evaluation of baseline hydrologic and geologic information and predict any residual impacts after application of proposed mitigation or preventative measures.
The following technical considerations should be considered in each PHC determination. Even if there is no impact with respect to a specific topic, the determination should still address that topic.
Purpose
The ultimate purpose of hydrologic monitoring is to measure on-the-ground success of mitigation. Ground- and surface-water monitoring plans should be designed to track impacts to the hydrologic balance, and evaluate changes in the physical and chemical parameters most likely to affect the suitability of the surface water and ground water for current and approved postmining land uses. The physical and chemical parameters that are chosen to reflect potential impacts to the hydrologic balance should be based on the data obtained from the baseline monitoring study and the results of the PHC determination.
Network Design
Ground Water
An operational ground-water monitoring plan should be designed to detect mining impacts to ground-water quantity and quality in the permit and adjacent areas by incorporating sites both up-gradient and down-gradient from mining. Network design should reflect possible alterations in ground-water flow direction. Monitoring sites may be existing water supply wells (if suitable), springs and seeps, wells that were drilled for collection of baseline information, and any additional wells deemed necessary to evaluate impacts of present and future mining activities. Inclusion of baseline data collection sites ensures the continuity of the data record from premining through the mining and reclamation phases of the operation.
At a minimum, Federal regulations require that the monitoring plan include analysis of total dissolved solids or specific conductance, Ph, total iron, total manganese, water levels, and any additional constituents identified in the overburden or baseline monitoring data as potentially deleterious to current and postmining water uses. Sampling frequency should be designed to reflect seasonal variations in water quantity and quality. It is advisable to consult the RA regarding selection of monitoring sites, sampling frequency, and the chemical constituents to be sampled.
Ground-water monitoring may be waived if the applicant can demonstrate that a potentially affected water-bearing stratum in the area does not serve as an aquifer that ensures the maintenance of the hydrologic balance within the CIA. Similarly, if the applicant can demonstrate that certain chemical parameters are no longer a concern to the ground-water quality in the region, then upon request, those parameters may be removed from the ground-water quality parameter list.
Surface Water
A surface-water monitoring plan should identify all surface-water bodies such as streams, lakes, and impoundments, and the location of any discharge into any surface-water body in the proposed permit or adjacent areas that may potentially be affected by mining operations. To determine and evaluate potential impacts, monitoring sites should be located upstream and downstream of the proposed operation. The plan should include discharge and, at a minimum, analysis of total dissolved solids or specific conductance, total suspended solids, Ph, total iron, total manganese, and any other constituents identified in the overburden or baseline monitoring data as potentially adverse to the current and postmining water uses. Sampling locations and frequency should be designed to detect seasonal variations in both water quantity and quality. It is advisable to consult the RA regarding sampling frequency, sampling site locations, and the chemical parameters to be monitored.
Surface-water monitoring must proceed through mining and continue during reclamation until bond release. The RA may modify the monitoring requirements if the applicant can demonstrate, using baseline and performance monitoring information, that continued monitoring of certain parameters or surface-water bodies are no longer necessary to protect the hydrologic balance. The RA may grant changes to the monitoring plan except for point-source monitoring required by the NPDES permitting authority. Point-source monitoring must be conducted as required by the NPDES permit.
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