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January 4, 1999 <br />Mr. James C. Stevens <br />State of Colorado <br />Division of Minerals and Geology <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver. Colorado 80203 <br />~ 2~~ <br />~D~ <br />~~ ~ {`.F1vF[a <br />JAN U ti 1999 <br />pivision of Minerals a ..~ - <br />I.a. <br />RE: Costilla Landfill Pit, Costilla County, Colorado <br /> <br />Dear Mr. Stevens: <br />Greystone is submitting this letter on behalf of Costilla County to provide you with the data <br />collected during the quarterly groundwater monitoring and sampling site visit conducted on <br />December 9, 1998 at the above referenced site. <br />A regional site map is provided as Figure 1. A site map displaying the location of the monitor <br />wells is provided as Figure 2. A groundwater elevation map is included as Figure 3. <br />Groundwater elevations were calculated using the measured groundwater elevation data and the <br />surveyed well casing elevations. The survey data and groundwater level measurements are <br />included in Table 1. <br />The groundwater gradient observed on December 9, 1998 ranged from 0.02 to 0.03 feet per foot <br />(ft/ft) to the southwest. Depth to water ranged from 33.85 feet below grade in well MW 1 to 47.20 <br />feet below grade in well MW2. <br />A site map displaying the location of the monitor wells is included as Figure 2. Groundwater <br />samples were obtained and submitted for laboratory analysis from one monitor well (MWS). <br />Monitor wells MW1, MW2, MW3 and MW4 have been excluded from quarterly sampling and <br />were not sampled. However, samples are obtained from monitor well MW1 and placed on hold <br />in the event that the results of the samples obtained from monitor well MWS report results in <br />excess of permit requirements. <br />The sample was analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) using EPA <br />Method 602, and total dissolved solids (TDS) using EPA Method 160.1. Standards are presented <br />in Tables 4 and 5. The sample was also analyzed for Human Health Standards (total coliform, <br />barium, fluoride, lead, and nitrate+nitrite} and Secondary Drinking Water Standards (chloride, <br />5231 South Quebec Street • Greenwood Village, Colorado SO11I <br />Phone (303) 850-0930 • Fax (303) 721-9298 <br />Web Site: www.greystone-consultants.com • E-mail: greystoneC~greystone.consultants.com <br />Environmental Partners, Scientists, mtd Engineers <br />