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SPDSS Groundwater Technical Peer Review Committee Meeting Minutes <br />February 13, 2007 <br />Page 4 <br />i. Question: What is the extent of Plum Creek within the study area? <br />Response: The study area extends upstream several miles on Plum Creek above its <br />confluence with the South Platte River, to the extent of the available data. <br />3. Task 43 -Alluvial Aquifer Properties <br />a. Data sources and processing Transmissivity data ("I') _ (K data) * (SPDSS saturated thickness). <br />Specific capacity used to increase T dataset. Some data points excluded and some control points <br />added in boundaries and areas of low data density. K data kriged to generate initial model <br />inputs. <br />b. Specific capacity analysis: higher capacity wells (i.e. >50 gpm) were more representative than <br />smaller capacity wells (i.e. <= 50 gpm); plus pumping tests. <br />c. Aquifer property results: Median values: K = 425 ft/d; T = 16,400 ft2/d (where T = K <br />saturated thickness); T = 122,600 gpd/ft; S or Sy = 0.17. <br />d. Alluvial Aquifer Properties Conclusions: Specific capacity data from high capacity wells <br />(>=50gpm) are representative of bulk aquifer properties. Significant variability in observed K <br />values. <br />e. Alluvial Aquifer Properties Discussion <br />i. It was suggested by a PRC member that a confined aquifer storage coefficient value (S) of <br />10-a is too low for an alluvial aquifer. <br />ii. Question: How many Sy values were available from single well pumping tests vs. multi-well <br />tests? <br />Response: CDM will look into this and reply to the group via email. <br />iii. A suggestion was made to orient the K contours in the downstream direction, rather than <br />perpendicular to tributaries and channels as shown in the maps. <br />4. Task 39 and 44 -Aquifer Water Levels <br />a. Data sources -data obtained through a variety of sources, public and private. Key data obtained <br />from DWR and USGS. <br />b. Alluvial and bedrock monitoring wells <br />i. Hydrographs -show 10ft decline in Lower Dawson well, 30 ft decline in Arapahoe well. <br />ii. Decline in water level <br />1. Decline in water level observed during irrigation/pumping season. Waiting to see <br />during spring (non-irrigation/non-pumping season), should see some recovery from <br />drop in water level. <br />2. Observed fluctuation at a well -for example at the Upper Arapahoe well, only 2 ft <br />variability over 2 years, even though larger seasonal fluctuations exist. <br />