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Home My WebLink About20053800.tiff � cki ® EarthTech 5575 DTC Parkway P 303.694.6660 Suite 200 F 303 694 4410 Englewood,CO 80111-3016 www.earthtech.com ATyco International Ltd Company October 14, 2005 Mr. Douglas Ikenberry, P.E. Weld Colorado Department of Public Health and Environment Cou1nty Ilan • Hazardous Materials and Waste Management Division CREELEy ingOpp �pa�me HMWMD-SWIM-B2 °CT CF nt 4300 Cherry Creek Drive South 1 8 200 Denver, Colorado 80246-1530 C eE Ms. Cindi Etcheverry Weld County Department of Public Health and Environment 1555 N. 17th Avenue Greeley, Colorado 80631 Re: Buffalo Ridge Landfill First Semi-Annual 2005 Groundwater Sampling Report Project No. 84158.0701 Dear Mr. Ikenberry and Ms. Etcheverry: Enclosed is the First Semi-Annual 2005 Groundwater Sampling Report for the Buffalo Ridge Landfill (BRLF). This report was prepared on behalf of Waste Management of Colorado, Inc. by Earth Tech,Inc.(Earth Tech). Severn Trent Laboratories,Inc.,Denver performed the analyses. Also enclosed is a 3.5-inch disk, which contains the analytical results for the first semi-annual 2005 sampling event as requested by the Colorado Department of Public Health and Environment (CDPHE). This report represents the seventh semi-annual monitoring event for the BRLF groundwater monitoring network since monitoring was temporarily suspended following the fourth quarter 1998 sampling event. This is also the sixth event since the commencement of landfilling operations,and the sixth event subject to statistical evaluation to satisfy detection monitoring requirements. The statistical evaluation was conducted as outlined in the Statistical Methods for Ground-Water Monitoring at Buffalo Ridge Landfill,prepared by Robert D.Gibbons,Ph.D.(March 2003). This is the second event since the submittal of the Alternative Source Demonstration (ASD) dated December 3, 2004 (Earth Tech 2004). Statistical analyses were performed using intra-well comparisons. Intra-well Combined Shewart- CUSUM Control Charts were prepared for wells MW01 through MW11, which monitor groundwater upgradient and downgradient of Phases 1 and 2 of the landfill. The enclosed results of the statistical analysis are displayed in tabular and graphical format. In accordance with the approved statistical methods and the ASD letter from CDPHE dated January 5,2005,the background period for most control charts has been updated on schedule to include data through June 2004. Cumulative Sum(CUSUM)is calculated starting at the end of the background period. In accordance with the ASD letter, this background update was applied to all wells and constituents with the exception of chloride in MW04 and sodium in MW06. The original background window remains in 2oo538cO EarthTech A two International Ltd.Company Mr. Douglas Ikenberry Ms. Cindi Etcheverry October 14, 2005 Page 2 place for these two constituents. Although there is no regulatory requirement to perform statistical analysis on upgradient wells,intra-well statistical comparisons have been performed for information purposes only. VERIFIED EXCEEDANCES FROM THE SECOND 2004 EVENT The constituents chloride in MW04 and sodium in MW06 had a continued CUSUM exceedance with detections below the control limits. These statistically significant increases(SSIs)for CUSUM first appeared with the second 2003 sampling event and were addressed in the December 3, 2004 ASD report. The constituent sulfate in MW06 had an initial detection and CUSUM exceedance during the second 2004 event that was verified during the first 2005 event. The following provides findings for these constituents. Chloride and Sodium During the first semi-annual 2005 groundwater sampling event,monitoring wells MW04 and MW06 continue to show a CUSUM SSI for chloride and sodium,respectively. However,the actual detected concentrations of chloride for MW04 and sodium for MW06 continue below the control limits(no detected concentration has ever exceeded the control limit). The following table summarizes the constituents, control limits, and detections for MW04 and MW06. Control Limit Detections Well Gradient Date Constituent (mg/L) (mg/L) MW04 Down 5/26/05 Chloride 229.10 200 11/04/04 200 7/7/04 210 12/31/03 200 MW06 Down 5/26/05 Sodium 167.33 150 11/04/04 160 7/7/04 150 12/31/03 140 mg/L-milligrams per liter BRLF submitted an ASD that showed that these two SSIs are the result of a source other than the landfill. In accordance with the ASD letter from CDPHE,the original background period continued to be applied to MW04 for chloride and MW06 for sodium during this event. It is anticipated that the CUSUM for chloride in MW04 and for sodium in MW06 will continue to exceed the control limits under the original background period since the original background does not include the recently observed variability. Since the detections for chloride in MW04 and sodium in MW06 have never exceeded the control limits and in accordance with the conclusions of the ASD, EarthTech A two International Ltd.Company Mr. Douglas Ikenberry Ms. Cindi Etcheverry October 14, 2005 Page 3 it is recommended that the statistical background window be updated for these two wells for the next semi-annual event to allow for the proper incorporation of recently observed variability. Sulfate During the second 2004 semi-annual detection monitoring event,sulfate was detected at 180 mg/L in MW06, relative to a control limit of 169.78 mg/L. This constituent was subject to verification sampling as part of the first 2005 sampling event. The following table summarizes initial statistical exceedances from the second 2004 event and the results of verification sampling performed during the first 2005 event. Initial Exceedances Exceedances Verified Second 2004 Event First 2005 Event Statistical Well Gradient CUSUM Detection CUSUM Detection Exceedance MW06 Down Sulfate Sulfate Yes Yes Yes During the first 2005 semi-annual detection monitoring event, sulfate was again detected above its control limit of 169.78 mg/L, at a concentration of 180 mg/L. It should be noted that sulfate has never been detected in any of the leachate samples from the BRLF. Leachate sampling and analytical testing have been performed five times since the site commenced accepting waste in 2002. As a result of the sulfate detection at MW06, and in accordance with Colorado Regulations Pertaining to Solid Waste Disposal Sites and Facilities, 6 CCR 1007-2(B4)(C)(1), Earth Tech Inc. (Earth Tech) on behalf of the Buffalo Ridge Landfill (BRLF), provided a 14-day notification of a confirmed statistically significant increase(SSI)over background for sulfate in down gradient well MW06. This was transmitted to CDPHE in a letter dated September 30, 2005 (Earth Tech 2005). Based on the geochemical history of groundwater at this site (parameter detections have shown relatively significant variability both upgradient and downgradient of the landfill, with upgradient wells showing greater variability in some cases), the results of leachate sampling (there has never been a detection of sulfate in any of the five leachate samples since the site commenced operations), and the spatial differences in sulfate concentrations (upgradient wells show sulfate concentrations more than ten times higher than this downgradient well). BRLF intends to proceed with an alternative source demonstration in accordance with 6 CCR 1007-2(B4)(C)(3). INITIAL EXCEEDANCE FROM THE FIRST 2005 EVENT The following table summarizes initial statistical exceedances and the status of required verification sampling as a result of the first 2005 monitoring event. EarthTech A two International Ltd Company Mr. Douglas Ikenberry Ms. Cindi Etcheverry October 14,2005 Page 4 Initial Exceedances Verified Sampling First 2005 Event Required Second 2005 Well Gradient CUSUM Detection Event MW02 Down TOC TOC Yes MW05 Down TOC TOC Yes MW06 Down Alkalinity Yes Chloride Chloride Yes Lead Yes TOC Yes TOC-total organic carbon These detections will be subject to verification sampling as part of the second 2005 semi-annual monitoring event. In accordance with 6 CCR 1007-2,Appendix B (84)(A)(1),BRLF is in the process of re-evaluating the current groundwater monitoring parameter list for purposes of potentially recommending a reduced list to CDPHE. Since the available groundwater quality data at BRLF demonstrates relatively significant temporal and spatial variability, reducing the parameter list should diminish statistical false positive detections and increase statistical power. A reduced parameter list was suggested by Dr. Gibbons in the initial statistical evaluations report (March 2003). Also enclosed with this report are the Monitoring Well Integrity Field Survey forms, completed during this event. There were no integrity issues noted which require immediate attention. Should you have any questions concerning this report,please call me at(303) 694-6660. Very truly yours, Earth Tech, Inc. /Randy Thompson, P.E. Environmental Engineer cc Alan Scheere, WM Bill Hedberg,NWLF Kim Ogle, WCDPS (w/o enclosures) Jack Epple, BRLF Lou Bull, WM Len Butler, WM work\84158\product\brftl st05gw.doc Hello