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February 1998 H~G Coa! 1997 Annua! Rerlamatron ReOort • RaQe 11 <br />• 6.0 SEDIMENT PONDS <br />6.1 NPDES QUARTERLY REPORTS <br />HGCC applied for and received a NPDES permit renewal during 1997. As previously <br />indicated, Pond 003 was observed discharging by HGCC personnel in the months April <br />through December. Pond HG-8 was observed discharging by HGCC personnel during every <br />month of 1997 with the exception of March. All sediment pond discharges were sampled and <br />monitoring data was reported to the appropriate State agency. Copies of the quarterly <br />monitoring reports are found in Exhibit 6, Sediment Ponds -NPDES Discharge Monitoring <br />Reports. <br />6.2 QUARTERLY INSPECTIONS <br />The quarterly inspection reports are found in Exhibit 7, Sediment Ponds -Quarterly <br />Inspections. All inspection reports indicated there were no problems with any pond. <br />6.3 SEDIMENT SURVEY <br />In 1991, TR-60 (to Modify Sediment Control Structures) was approved by the DMG. <br />SEDCAD+ modeling was used to calculate runoff volumes and sediment delivery to the <br />Shop/Office Pond, outfall 003. Results of the modeling indicate that both the design storm <br />event runoff volume and sediment delivery to the pond is zero. <br />Sediment surveys were performed for Pond 003 and Pond HG-8 during August 1997. A <br />certified copy of the sediment pond surveys are included in Exhibit 8, 1997 Sediment Pond <br />Storage Surveys. <br />Pond 003 was originally designed with a three year sediment storage volume of 0.25 acre-feet <br />and a total storage capacity of 1.73 acre-k. As part of TR-60, H-G Coal Company submitted <br />new pond certifications and as-built maps to DMG in February 1993. The 1992 as-built survey <br />of Pond 003 indicates that the total storage capacity is 1.6 acre-k. The 1997 sediment survey <br />indicates that Pond 003 has storage sediment capacity of 1.1 acre-k. The 1997 sediment survey <br />confirms the SEDCAD+ modeling results, which were presented in TR-66, that the sediment <br />delivery [o Pond 003 is zero. The data indicate that Pond 003 has adequate storage capacity to <br />treat the expected 10-year, 24-hour storm event runoff and sediment volumes. <br />Due to excellent revegetation success on the reclaimed mine site, sediment delivery to Pond <br />HG-8 appears to be insignificant. HGCC demonstrated in TR-66, that with the addition of the <br />new trickle tube decant, Pond HG-8 has approximately 6.5 acre-feet of sediment storage <br />capacity. The 1997 sediment survey indicates that Pond HG-8 has a total storage capacity of <br />17.5 acre-k. <br />Results of the 1997 sediment survey for storage volumes in each pond is shown in Table 1, 1997 <br />Sediment Volumes. <br />• <br />Montgomery ll'/atson Americas, lnc. (dba TerraMatrixJ <br />!'O. Bax 774078 Steamboat Springs, CO 80~t77 "(970J 879-6260 <br />v. ~9JlUnnrl R0, \YY An•~u(Rq <br />:/1:/Y! p <br />