FLOOD10356

• County: Delta
• Title: North Fork Volunteer Water Quality Monitoring Project - April 2001-April 2002 Data Report
• Date: 9/30/2002
• Prepared For: North Fork River Improvement Association
• Prepared By: CSU Cooperative Extension and North Fork River Improvement Association
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

3.3 Bacteria

E.Coli

When the State evaluates compliance with surface water bacteria standards, they use a
geometric mean (the nth root of the product of n numbers). Therefore, the bacteria data
from this project are presented both as geometric means and as average values, for
comparison. Recall that different segments of the North Fork have different bacteria
standards, and in the case of Segment 3, these standards also vary seasonally. For a
discussion of the standards and river segmentation see Section 1.4, and Table 1.3. While
the North Fork volunteers are not collecting samples for compliance or regulatory
purposes, they are conducting a screening-level survey of the bacteria concentrations in
the river.

Segments 2 and 4

.In Segments 2 and 4 of the North Fork, which includes Muddy and Anthracite creeks as
well as the stretch of the North Fork below Paonia Reservoir, geometric mean
concentrations were well below the State standard of 126 colonies/lOa mL. However,
Muddy Creek did produce some surprisingly high bacteria concentrations, given the
relatively low level of development and disturbance in that area.

For example, when looking at daily averages the highest average E. Coli concentrations
in the whole watershed were recorded from the East Muddy, with an average value of
1,507 colonies/lOa mL on November 15, 2001. This was an average of three sequential
samples collected at 2 minute intervals on the same day. Potential causes may include
improperly functioning septic leach fields, wildlife inputs, or inputs from range cattle.

Segment 2, which includes the stretch of river around the town of Somerset showed
relatively low E. Coli concentrations. The highest value in this segment was an average
of 121 colonies/lOa mL recorded at NF-2, below Somerset, on January 9,2002.

Segment 3

Segment 3 of the North Fork encompasses the river from the Black Bridge near Paonia,
to its confluence with the Gunnison River. This segment has a bacteria standard that
varies seasonally. Sample results indicate that during the summer months, when the river
must meet a full-body contact recreation standard, this segment is generally under the
standard; however, bacteria concentrations may be somewhat more elevated around
Hotchkiss.

Our sample results indicate that station NF-4, Hotchkiss, had a geometric mean E. Coli
concentration from April to October 2001 of 172 colonies/lOa mL, exceeding the 126
colonies/lOa mL State standard. It should be noted that the NF-4 samples were collected
upstream from the Hotchkiss wastewater treatment plant. Station NF-5 is a better
reflection of the impacts of effluent discharges from this plant, and this station had a
geometric mean concentration of 112 colonies/lOO mL. The highest average
concentration recorded for Segment 3 was 1,297 colonies/lOa mL at NF-4 on August 26,

3-14