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Road Salt: USGS monitoring Shingle Creek
Source: University
of Minnesota Extension Service (January
11, 2005)
The USGS is doing real-time monitoring on Shingle
Creek, one of the three creeks in the metro area that
is developing a TMDL plan (water pollution reduction plan)
for chloride (salt = chloride). You can view this
monitoring data, plus other stream monitoring (new
window) that the USGS is doing in Minnesota. 
Of interest is that baseflow
(groundwater seepage) contains chloride concentrations
over the chronic criteria (see
below). It is thought that decades of deicing salt
use in this flat sandy watershed has resulted in the groundwater
becoming high in chloride.
When on the site, scroll down for Shingle Creek
(Mississippi River Basin), and when viewing Shingle Creek data, click
the Specific cond at 25C (what DuluthStreams calls EC25)
option on the Available Parameters selection box (it is
the last option) for specific conductance. As you will
remember from chemistry/physics class, dissolving salt
in water increases its electrical conductivity. Specific
conductance is measured in microsiemens per centimeter
(uS/cm) and then related to an associated chloride level.
When viewing the data, keep these state water quality
standards in mind:
Chronic criteria (harmful over long exposure) for trout
230 mg/L chloride, associated with a specific conductance
of about 1,400 uS/cm
Acute criteria (harmful over short exposure)
960 mg/L chloride, associated with a specific conductance
of about 4,000 uS/cm
Final acute value (harmful right now)
1,720 mg/L chloride, associated with a specific conductance
of about 6,200 uS/cm
Note: Relation between specific conductance and chloride
concentration has been studied, but results are not yet
published, so the relation between specific conductance
and chloride concentration given above is provisional.
Recent peaks in Shingle Creek specific conductivity that
are related to chloride concentrations that exceed the
chronic criteria and approach the acute criteria are:
uS/cm |
Date |
2,830 |
3/7/04 |
3,270 |
3/10/04 |
2,820 |
3/14/04 |
3,150 |
12/30/04 |
2,950 |
1/3/05 |
Data from 1996-97 show Nine Mile Creek ringing the bell
(near or over the Final Acute Value) with over 6,000 uS/cm
on 1/21/97 and 2/6/97, and 8,000 uS/cm on 1/31/97.
Thanks to James Fallon, Supervisory
Hydrologist, USGS, for this data and
analysis and Ron Struss, Extension Educator with the University
of
Minnesota Extension Service/Water Resources Center and
the Minnesota Board
of Water and Soil Resources (BWSR) for disseminating the
information.
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