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Rockcastle Company, Grassy Creek Mine Adequacy Responeses • 2 D) Yegeta[ive cover values on newly reclaimed sites must be doctunented with field sampling when preparing hydraulics designs. ![ is unjustified to indicate that [Ire cortopy cover of the reclaim is 50% while Ure ground cover is 80% without empirical data. Response: Revege[ation monitoring for the Pit 4 reclaimed area would normally be completed per [he standard revege[a[ion monitoring schedule. Since monitoring would not normally occur for at leas[ two years following reseeding, Rockcastle based estimated canopy and ground cover values for hydrologic calculations on dtrec[ visual observation. Applicable regulations do not specify a required basis for hydrologic calculations so the concept of best engineering practice is appropriate. Given the stage of reclamation, [he time and expense of a separate vegetation survey to support hydrologic assumptions is not justifiable. While the estimated cover values utilized are not represented as being exac[,[hey are within a reasonable range of accuracy For the purpose for which [hey were used. REVISION ADEQUACY CONCERNS I) 17te inslopes of Pond No. 4 are er[raordinarily steep along [lre [op 9 feet of [he pond (44%50%). T7tis wilt be a problem if the pond is retained art a penrtanen[ basis, and contradicts [lte recorn»tertdation found in the October 1$ 1990ACZ submittal that the pond should have 3:1 slopes. The aforerrrerttioned submittal also recommended that Ditch 4-1 enter the pond ono 4:1 livestock ramp. While the Division understands that Rockcastle is withdrawing front their request to leave Pond 4 as pennmtent at this time, 16elieve [hat the company could accommodate reconfiguration cortcenu quite easily while regrading the overlying slope. Please modify the plan view, capacity table, a»d stage/storage curve on the Pond No. 4 Design Plate accordingly. Response: The Pond 4 Design Map, (Map R-3), submitted in November, 1991, graphically illustrates the proposed regraded configuration of Pond 4 following backsloping of the east slope. The regraded configuration includes relatively uniform 3H:1V slopes on the east side of [he pond, maximum 2H:1V interior basin slopes on [he south and west sides of [he pond and a uniform 4H:1V interior embankment slope on [he north end of the pond. All hydrologic calculations, including pond capacity and stage/storage relationships are based on [he illustrated configuration. The entire north end of Pond 4, which is approximately 40-50 fee[ wide, will be established at a 4H:1V slope providing effective access to impounded water for both livestock and wildlife. A copy of Map R-3 accompanies these responses for review and reference. 2) Rule 4.05.0(11)(() indicates [hat the combined upstream and downstream side slopes of the embanbnertt slmll be rto steeper [hmt 5: 1. 1 measured both [he inslope and outslope a[ 2: 1. Please modify the upslope portion of the embankment to accommodate [his reg[datory requirement. When modifying the design ensure that Rule 4.05.6(Il)(h), [he regulation on minimum top width, is in compliance. Response: As described in [he October S, 1990 ACZ submittal, Pond 4 is an incised pond created by partial backfdling against the final Pit 4 highwall. As an incised pond, under Rule 4.05.9(4), sideslopes are required to be ".., stable and shall not be steeper than O.Sh:ly.". The east inslope will be 3H:1V with no outslope. Similarly, [he north inslope will be 4H:1V with no outslope. The south inslope varies from 2H:1V [0 12H:1V with no outslope and the west inslope is approximately 2H:1V with a 2H:1V outslope. The west side of the pond appears to be the source of [his concern. For the west side inslope gradients are well within the regulatory limits for an incised pond. The existence of an outslope is a reflection of the natural terrain in this area which sloped away from the final pi[ highwall. Any attempt [o modify the outslope would result in unnecessary disturbance of the existing established vegetation. Modification of either the inslope or outslope would offer little or no potential benefit relative [o long-term pond stability. ACZ Inc. ' P.O. [3ox 774018 ` SteamDOar Springs, Colorado 80477 • (303)87&6260