SPDSS_Task39_Phase4_FinalWaterLevelMeasurement

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which probably represent the periodic pumping cycles of a nearby well or wells. There is a recovery of the water level in the well after the growing season, which is probably the result of both t11e cessation of irrigation-based pumping and the lagged return flow from any upgradient irrigated areas. Wells following the Category 3 and 4 patterns are distributed throughout the study area. The hydrograph patterns of wells in Category 3 are affected by stream stage, with groundwater levels tracking closely to changes in stream water levels. Figure 7 presents a representative 1ydrograph for an alluvial observation well (DSS22KRY) grouped in Category 3. DSS22KRY is located immediately adjacent to the South Platte River near t11e Kersey Gage. Figure 6 plots bot11 t11e hydrograph for DSS22KRY and the stream stage elevation recorded at the Kersey Gage. T11e trends shown on this figure indicate that groundwater levels at well DSS22KRY closely follow the stage in the Soutll Platte River. This indicates the aquifer and stream are u1 close hydraulic connection. The groundwater level elevation is generally higher than the river stage, indicating a gaining river (groundwater discharges to the river) in this area. Wells in Category 4 have water levels that show no discernable seasonal trend. Some of these wells show relatively constant water levels, possibly due to remoteness from t11e operation of irrigation ditches and pumping. Possible influences on the water levels that are not relatively constant include aggregate effects of pumping, recharge, stream stage, and/ or b oundwater evapotranspiration by nearby vegetation. Figure 8 presents a hydrograph for an alluvial observation well (DSSI5DIA) grouped i11 Category 4. The DSSI5DIA hydrograph shows very little season water level fluctuation and a slightly declining water level trend overall. The nearly constant groundwater levels are likely due to no nearby irrigation pumping or recharge. In the three and a half years of data gathered at well DSSI5DIA, t11e water level has declined approximately 0.5 feet, averaging 0.14 feet per year. For all categories, the seasonal oscillations in the alluvial aquifer water level patterns similar to those noted i11 Figures 5, 6, 7 and 8 can be observed on other hydrographs presented in Appendix E. Tl1e detailed hydrograplls provide useful information on the localized effects of irrigation activity, pumping, and stream stage changes. However, without a more detailed understanding of individual well pumping and irrigation activity near each observation well it is not possible to quantify the effect of individual irrigation practice on groundwater levels at a specific well. Hydrograplls of different categories may occur i11 t11e same area because the factors that influence the patterns of shallow groundwater levels may occur in close proxinuty to each other. Additionally, some wells have hydrographs that show stronger patterns for a certaiiz category than others, so the category assignments should be treated as general guidelines. Changes in nearby irrigation practice, continued conversion of agricultural water rights to urban uses may impact the patterns (or lack of pattern) in these wells. 2.2.2 Evaluation of Bedrock Water Level Trends There are five bedrock wells equipped with continuous data loggers. The water level measured in t11e bedrock wells represents the average piezometric head over t11e screened zone of t11e well u1 t11e aquifer at the location of the well. Under confined conditions, the water level in the well will rise above the top of the aquifer. Bedrock well DSSBR01 was completed in the Upper Arapahoe Aquifer near Berulett, and a data logger was installed in late 2003. Tl1e 1ydrograph for this well is presented in Appendix E, page E-38. Due to a data logger malfunction, there is a SPDSS Phase 4 Task 39 Technical Memorandum-Final 15 O~i20%2008