2008-09-11_HYDROLOGY - M2004078 - Laserfiche WebLink

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CIVIL RES,7URCES,LLC ENGINEERS & PLANNERS September 8, 2008 ?4 . .: eH r Mr. Eric Scott SEP 1200$ Division of Reclamation Mining and Safety 1313 Sherman Street, Room 215 ®)b?S1Oi1 Ut kt-sainaation, Denver, Colorado 80203 Mining and Satoty RE: April 2008 Groundwater Quality Monitoring Results, Lupton Lakes Gravel Mine Permit No. M-2004-078 Dear Mr. Scott: The following letter report describes the results from the April 2008 Sampling Event. This report is being submitted in general compliance with approved Groundwater Sampling and Analysis Plan (GWSAP) included in Technical Revision 2 (TR2) to the Lupton Lakes Gravel Permit issued by the State of Colorado Division of Reclamation Mining and Safety. Dewatering began in the area of the south sediment pond near Weld County Road 6 in June 2007 and stopped in May of 2008. Dewatering began in the area of the north sediment pond in April 2008. The dewatering water was placed into an infiltration basin located near the northeast corner of the project until a sixteen (16) inch High Density Polyethylene Pipe (HDPE) pipe was installed. The sediment in the water was allowed to settle out then it was discharged through the HDPE pipe into the South Platte River. Discharge into the South Platte River began in May 2008. Groundwater Monitoring Results The April 2008 Sampling Event includes monitoring wells CRMW01, CRMW04, CRMW06, CRMW09, CRMW16, and CRMW41. CRMW02 was not sampled because a conveyor belt was placed over the well and there is no access. The well is still intact. The April monitoring event also included sampling at the three recharge areas denoted as the South, North and Far North Recharge samples, respectively. The dewatering volume being pumped from the south sediment pond area was recharged back to the natural alluvium aquifer instead of direct discharge to the river. The dewatering volume being pumped from the north sediment area was recharged back to the natural alluvium aquifer instead of direct discharge to the river. Refer to the attached figure for approximate locations of the recharge areas. Following is a listing of the major results and conclusions: • Arsenic, Fecal Coliform, Fluoride, Mercury, Chloride, Iron, and pH did not exceed the Primary Drinking Water Standards (PDWS) or Secondary Drinking Water Standards (SDWS). Nitrate (as N) exceeded PDWS in seven of the nine samples with nitrate concentration levels ranging from 1.54 mg/L up to 20.04 mg/L in CRMW41. The PDWS for nitrate is 10 mg/L. The currently proposed site wide baseline level for nitrate is 29.9 mg/L. The baseline level for well CRMW41 is 29.9 mg/L. Nitrate levels in all of the wells were below either the proposed site wide or individual well baseline levels. The recharge areas that have been sampled in previous events had concentrations of 17.82 mg/L and 15.11 mg/L. The nitrate concentrations for these two recharge areas have decreased in concentration levels but are similar to the January 2008 sampling event. This is the first sampling event of the far north recharge area with a concentration of 18.58 mg/L. Nitrate concentrations have consistently exceeded the PDWS before and during mining operations. 323 FIF-rH STREET 0 P.O. Box 6BO 0 FREDERICK, CO 80530 0 PHONE (303) 833-1 41 6 0 FAx (303) B33-2B50