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<br />Storage routing was attempted for pond H. This method exemplifies the amount
<br />of conservatism in spillway designs. Anon-routed 25-year peak flow for pond
<br />H is 29.4 cfs, The flow routed by the applicant utilizing a triangular
<br />hydrograph approximation was 9 cfs through the spillway. And finally, by
<br />using a curvilinear hydrograph routing technique, the Division calculates only
<br />3.6 cfs will exit the spillway. From this, it becomes apparent that the
<br />spillways are conservatively designed for the 25-year, 24-hour event.
<br />During the course of the original review, another problem was identified with
<br />the sediment control system. This problem dealt with the method of dewatering
<br />pond H. Pond H was constructed to detain and trap sediment from a small
<br />portion of disturbed area and also store undisturbed drainage for augmentation
<br />purposes. In order to augment water when a "call" exists on Mann Draw, a
<br />large gated spillway was installed at the bottom of the pond. However, if
<br />this gate is opened, it will sluice sediment stored in the pond downstream and
<br />possibly violate effluent limitations. Since the area of disturbance is far
<br />from the spillway and the gradient between them is small, sediment should not
<br />accumulate at the spillway inlet if removed periodically. Therefore, if
<br />sediment removal is accomplished before it accumulates at the spillway,
<br />effluent limitations should be met. The applicant has committed to removal of
<br />sediment before accumulated sediment reaches the level of the gated spillway.
<br />Two additional requirements of Rule 4.05 have been addressed during the course
<br />of the permit review. The applicant has provided markers on sediment pond
<br />riser pipes which indicate the 60% sediment storage level. Additionally, the
<br />applicant has provided professional engineers certification that all ponds
<br />have been constructed in accordance with the plans contained in the
<br />application.
<br />The operation is in compliance with the requirements of this section,
<br />VI. Hydrologic Balance: Ground Water - Rules 2.04,5, 2.04,7
<br />Information on ground water can be found in Section I, Water Information;
<br />Appendices A and I; and Plate 1, Water Elevation Control Map in the
<br />application. A detailed description of the ground water resources and the
<br />impacts of mining on ground water can be found in Section IX of this document,
<br />ti tied "Probable Hydrologic Consequences of Mining and Cumulative Hydrologic
<br />Impacts Study".
<br />The Walden Coal Company has installed nine monitoring wells in the alluvium of
<br />Mann Draw. These wel]s are primarily used to measure fluctuation in alluvial
<br />water levels along three stream transects. These transects are located above,
<br />below and in the middle of the area which may be impacted by the Bourg Mine.
<br />One of the upstream wells, 33C, and one of the downstream wells, 30A, have
<br />been monitored for water quality. Since these monitoring wells are located
<br />downgradient of the bedrock strata and within the alluvium of Mann Draw, they
<br />provide adequate monitoring of the effects of mining on alluvial ground water
<br />for the following parameters: sulfate, total iron, total manganese, calcium,
<br />sodium, carbonate, bicarbonate, magnesium, potassium, aluminum, copper,
<br />selenium, fluoride, nitrate, orthophosphate, pH, conductivity, TDS, chlorine,
<br />boron, arsenic, barium, cadmium, chromium, lead, mercury, nickel, and zinc.
<br />The operation is in compliance with the requirements of this section.
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