WSP10010

• File Number: 8449.700
• Description: Cherry Creek
• State: CO
• Basin: South Platte
• Date: 9/1/1995
• Author: Halepaska & Assoc.
• Title: Phase 1 Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin - Final Report
• Water Supply Pro - Doc Type: Publication

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either from the well being sampled or from a production well adjacent to the monitoring well
being sampled. The cross-sectional saturated area has been calculated based on the water level
measured at each monthly site visit and the estimated geometry of the alluvial materials at that
location. The hydraulic gradient has been calculated based on topographic gradients in the
vicinity of each cross-section where underflow is being measured. An example of how this
Darcy calculation is made is shown in Figure 8, and the input to the equation for each station
is presented in Table D-3 (Appendix D).

The range of underflows that have been observed at each of the monitoring well cross-section
locations is shown in Figure 5, and are summarized in Table 0-2 (Appendix D). As the range
of values shows, there is very little seasonal fluctuation in alluvial underflows by location, as
indicated by the small range from maximum to minimum values. Alluvial flows generally
increased from an upstream to a downstream location, although alluvial underflow was relatively
constant through Parker (MW-4 through MW-6)(Figure 9).

The water quality data from the ground water monitoring wells indicate similar quality to the
surface water stations, although there appears to be larger fluctuations spatially. Ammonia-
nitrogen concentrations are at, or below, the detection limit (0.2 mg/L) at all stations throughout
the year.

Concentration profiles through the study reach for the major constituents of concern (nitrate,
total dissolved phosphorus and soluble reactive phosphorus) are shown in Figure 9. Similar to
the surface water stations, the nitrate-nitrogen concentrations observed in the alluvial aquifer are
higher than those observed for total dissolved phosphorus or SRP. While there are several
changes in the l2-month average nitrate concentrations throughout the reach (as high as 3.5
mg/L) , the average nitrate concentration at MW-I was approximately 1.5 mg/L, while the
nitrate-nitrogen concentration going into Cherry Creek Reservoir was approximately 2.2 mg/L
(Figure 9). While the nitrate-nitrogen loading increased from approximately 20 Ibs/day at

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