SPDSS_Task39_Phase4_FinalWaterLevelMeasurement

Home Browse Search

gap in tlne data collection in 2005. Water levels in this well have remained relatively constant until a sharp drawdo~nnn of approximately 10 feet in the w>lnter of 2006/2007. This trend is probably due to the influence of nearby pump>ing and continued monitoring will provide insight into long-term water level trends. In May of 2005, four additional bedrock wells were installed near Castle Rock with one well lln each of the four major Denver Basin bedrock aquifers. The site was selected due to the proximity to several large water providers who rely to a large extent on groundwater. During site selection, sites where there were no imnninent plans to install large production wells iln the vicinity were chosen so water levels would be more representative of regional trends than localized pumping. The four bedrock wells located iln the Castle Oaks area, wells C03LTDW (Appendix E page E-39), C03TKD (Appendix E page E-40), C03KLF (Appendix E page E-42), and C06KA (Appendix E page E-41), have not been monitored long enough to thoroughly assess seasonal trends; however, sharp changes in water levels are likely due to localized pumping. The annual change in water levels observed at alluvial wells ranges up to approximately 13 feet and at bedrock wells up to approximately 100 feet. Larger fluctuations are normal and expected in confined bedrock wells as compared to unconfined alluvial wells. Water levels in both the Dawson and Arapahoe aquifers monitored at these wells appear to follow a seasonal trend where water levels decrease in the spring and summertime, and increase during the winter. This may be due to higher usage from these two aquifers by municipal providers since water quality is generally better in these aquifers. The trends seen in these wells emulate municipal demands (increased suirunertime demand for lawn irrigation). The Denver aquifer shows an overall increase in water levels, but achieves approximately half this gain in large jumps followed by slower and steadier decline. This pattern is indicative of nearby pumping. However, water levels steadily >lncrease over the w>lnter of 2006. Water levels in tlne Laramie-Fox Hills aquifer decline steadily over the year of data presented. Cont>lnued collection of data from these bedrock wells will be critical in determining both seasonal patterns iln the bedrock aquifers as well as assessing regional groundwater trends. 2.2.3 Comparison of Continuous and Bi-Annual Measurements The hydrograplns in Appendices D and E show the variability in water levels during the year, sometimes with large changes over short time periods. The full extent of these fluctuations would not necessarily be apparent from bi-arunual (spring and fall) water level measurements. Additionally, bi-annual measurements might be heavily >lnfluenced by nearby well pumping. The insight gained from continuous (daily) water level measurements can be used to help develop a bi-annual measurement program that considers seasonal water level patterns and allows the program to better meet its objectives. Figure 9 presents fine continuous series of water level data for alluvial well DSS05WLD, and hypothetical bi-annual measurements if they had been collected on March 15 and November 15 for each year as part of tlne existing bi-annual measurement program. This figure reveals the bi-annual measurements, in this case, do not capture the nninimum and maximum water levels observed each year. The minimum water level observed in a given year from the continuous hydrograph is approximately 8 feet lower than the bi-annual measurement and the maximum water levels are about a foot higher. In this example, the bi-annual measurements record neither the high nor the low water levels from this well. A similar situation is expected to occur for all wells that show seasonal fluctuations in water levels, regardless of when the nlunimum and maximum water levels occur. SPDSS Phase 4 Task 39 Technical Memorandum-Final 16 O~i20%2008