FLOOD08209

• County: Adams
• County: Arapahoe
• County: Douglas, Jefferson
• Community: Denver Metroploitan Area
• Stream Name: South Platte River, Chatfield Dam to Baseline Road
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 8/1/1984
• Prepared For: Denver Metropolitan Area
• Prepared By: Wright Water Engineers, Inc.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

VI-2

Water Qual ity Parameters
Water quality between Chatfield Reservoir and Bowles Avenue is generally
~^~r;~ororl nnnrl Tn linht nf the relative cleanliness of this study segment
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discussion re9arding pollutant loads focuses on the reach from Bowles Avenue
to 104th Avenue. Some of the following discussion is adopted directly from
reports entitled: "Summary Report on the Water Qual ity Investigation of the
South Platte River, July 1, 1976 through June 29, 1977" (1), authored by
R. Dennis Anderson, Senior Public Health Engineer, Water Qual ity Control
Division, Colorado Department of Health, and "Urban kunoff Quality in the
Denver Region," by the Denver Regional Council of Governments (3). Another
study of South Platte water quality between Chatfield Reservoir and 50th
Avenue (2) is currently being conducted by the U.S. beologic Survey, and
sponsored by the Colorado Department of Health and the cities of Littleton
and Englewood. The final form of this study should be available in January
1985.

Dissolved Oxygen. Mean values for dissolved oxygen are normally above the
minimum standard for warm water aquatic life (5.0 mg/l) throuqhout the study
reach and only below 104th Avenue is the average less than the standard for
cold water aquatic life (6 mg/l). (Note the dissolved oxygen standards for
the three segments in Table VI-I.) Dissolved oxygen concentrations gradual-
ly decrease from Bowles Avenue to 104th Avenue. This reduction can be
attributed to the oxygen depleting characteristics of organic wastes enter-
ing the stream. Data substantiating dissolved oxygen below 104th Avenue was
not found in the various reports studied and firm conclusions cannot be made
regarding its levels.

Nitrogen Compounds. Nitrogen compounds constitute one of the major water
quality problems in the South Platte River. Although the 0.02 m9/1 standard
for unionized ammonia has not been exceeded, the 0.06 mg/l standard for Seg-
ments 14 and 15 is occasionally exceeded.

Fecal Coliform. Fecal coliform concentrations are used as an indicator of
the possible presence of pathogenic organisms. Fecal coliform counts of
under 20D are considered suitable for primary contact (swimming) and counts
under 2,000 are considered suitable for secondary contact (kayaking, wading,
etc.). The river at and above Bowles Avenue is the only portion of the
river that consistently meets the standards for both Class 1 (primary con-
tact) and Class 2 (secondary contact) criteria. Fecal coliform concentra-
tions increase significantly below Bowles Avenue, although mean counts do
not exceed 2,000 until after the confluence with Clear Creek.

Phosphorus. Mean orthophosphate levels have been found to range from less
than 0.05 mg/l at Bowles Avenue to 3.16 mg/l at 104th Avenue. Excessive
phosphorus availability could lead to significant plant growth on rivers
with velocities less than those associated with the South Platte. Note that
no formal stream standard exists for phosphorus.

Temperature. Temperature standards for COld water aquatic life require that
the maximum temperature not exceed 20.C, while for warm weather aquatic
life, the maximum is 30.C. Segment b meets the 20. standard most of the
time, and the 3D. criterion always. All of the river, in fact, meets the
30. standard throughout the full year in the stUdy area. Because Segment 6
tends to sustain colder flows than do Segments 14 and 15, Segment 6 is clas-
sified as COld water, Class 1 for aquatic life. The warming trend of the
river as it moves through Denver is reflected by the assigned aquatic life
classifications for Segments 14 and 15, as shown in Table VI-I.

Metals. Cadmium, chromium, copper, iron, lead, manganese, nickel and zinc
were analyzed in the Anderson study (1) and the DRCOG study (3). Levels of
cadmium in certain locations were found to exceed numeric standards (Table
VI-I) for all three segments by DRCOG. (Note, however, that DRCOG's analy-
sis of metals used "total analysis," which yields higher metal concentra-
tions than those which are reflected by standards, because standards are
based on the "acid soluble" method of analysis.) The copper standards for
aquatic life (.012 Segment 6 and .025 Segments 14 and 15) were violated the