Iowa DNR
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Water Quality Assessments

Impaired Waters List

East Nishnabotna River IA 05-NSH-1415

from confluence with Fisher Cr. (S27, T69N, R40W, Fremont Co.) to Page/Montgomery county line

Assessment Cycle
2016
Release Status
Final
Result Period
2012 - 2014
Created
10/3/2016 10:21:00 AM
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Stable
Last Updated
10/5/2016 3:48:30 PM
Use Support
Class A1
Recreation
Primary contact

Partially Supporting - Bacteria: Indicator Bacteria, E. coli

Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Moderate
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2008
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class B(WW-1)
Aquatic Life
Warm Water Type 1

Partially Supporting - Biological: low aquatic macroinvertebrate IBI

Impairment Code
3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2004
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
Class HH
Human Health

Not Assessed

General Use
General Use water

Not Assessed

Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria. Although results of ambient water quality monitoring suggest “full support,” the Class B(WW1) aquatic life uses for this assessment segment are assessed (evaluated) as "partially supported" (IR 3b-u) based on results of IDNR/SHL biological monitoring in 2012 and 2013. Fish consumption uses remain “not assessed” (IR 3a) due to the lack of fish contaminant monitoring in this river segment. This assessment is based on (1) results of IDNR/SHL monthly ambient monitoring conducted during the 2012-2014 assessment period near Shenandoah (STORET station 10360001 (at Hwy 59 bridge; formerly station 821008)) and (2) results of IDNR/SHL biological sampling conducted in 2012 and 2013 as part of the large river sampling projects.

Assessment Explanation

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at the East Nishnabotna River near Shenadoah were as follows: the 2012 geometric mean was 366 orgs/100 ml, the 2013 geometric mean was 261 orgs/100 ml, and the 2014 geometric mean was 991 orgs/100 ml.  All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Eleven of the combined 24 samples (46%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

The Class B(WW1) aquatic life uses for this assessment segment are assessed (evaluated) as "partially supported" (IR 3b-u) based on results of IDNR/SHL biological sampling in 2012 and 2013.  A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 and 2013 BMIBI scores were 22 (poor) and 53 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 54. This segment passed the BMIBI BIC 0/2 times in the last five years. This assessment is considered evaluated because the drainage area (1022 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.  Even though this segment failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

In contrast to results of biological sampling, results of chemical/physical water quality monitoring at the East Nishnabotna River near Shenadoah continue to suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.6 mg/L), 36 Dissolved Oxygen samples (minimum = 6.4 mg/L), 35 pH samples (range = 7.2 to 8.8), 36 Temperature samples (maximum = 28.5° c), 36 Chloride samples (maximum = 26 mg/L), or 36 Sulfate samples (maximum = 41 mg/L) occurred during monitoring from January 2012 to December 2014. According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

One of the three samples analyzed for toxic metals violated the Class B(WW1) chronic criterion for chromium: the sample collected on July 9, 2008, contained 50 ug/l of total chromium, thus violating both the Class B(WW1) chronic (11 ug/l) and acute (16 ug/l) criteria for chromium VI. This sample was the only one with a detectable level of chromium in the 25 samples from this station analyzed for chromium since 1998. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, impairment due to toxics in indicated when more than one violation of an acute criterion occurs within a three-year period. Because the violation of the acute criterion that occurred on July 9, 2008 was the only chromium violation during the 2008-10 period, this violation does not indicate impairment of the Class B(WW1) aquatic life uses.

In addition, one of the three samples analyzed for toxic metals violated the Class B(WW1) chronic and acute criteria for zinc (both = 120 ug/l based on an assumed hardness of 100 mg/l). This sample was also collected on July 9, 2008, and contained 210 ug/l of total zinc. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, impairment due to toxics in indicated when more than one violation of an acute criterion occurs within a three-year period. Because the violation of the acute criterion that occurred on July 9, 2008 was the only zinc violation during the 2008-10 period—and is the only violation, acute or chronic, in the 20 samples collected at this station between 2002 and 2008—this violation does not indicate impairment of the Class B(WW1) aquatic life uses. A relatively high level of total suspended solids in the July 9, 2008 sample (3,100 mg/l) may have influenced the level of metals in this sample, thus contributing to the violations of the Class B(WW1) metals criteria. These results suggest that the Class B(WW1) aquatic life uses should be assessed as “fully supported.”

In addition, one of the three samples analyzed for toxic metals violated the Class B(WW1) chronic criteria for cadmium (0.4 ug/L). This sample was also collected on July 9, 2008, and contained 2 ug/l of total cadmium. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, impairment due to toxics in indicated when more than one violation of an acute criterion occurs within a three-year period. Because this sample did not violate the acute criterion, this violation does not indicate impairment of the Class B(WW1) aquatic life uses. These results suggest that the Class B(WW1) aquatic life uses should be assessed as “fully supported.”

In addition, one of the three samples analyzed for toxic metals violated the Class B(WW1) chronic and acute criteria for copper (chronic = 14.68 ug/L, acute = 23.08 ug/L). This sample was also collected on July 9, 2008, and contained 60 ug/l of total copper. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, impairment due to toxics in indicated when more than one violation of an acute criterion occurs within a three-year period. Because the violation of the acute criterion that occurred on July 9, 2008 was the only cadmium violation during the 2008-10 period—and is the only violation, acute or chronic, in the 20 samples collected at this station between 2002 and 2008—this violation does not indicate impairment of the Class B(WW1) aquatic life uses. These results suggest that the Class B(WW1) aquatic life uses should be assessed as “fully supported.”

In addition, one of the three samples analyzed for toxic metals violated the Class B(WW1) chronic criteria for lead (6.26 ug/L). This sample was also collected on July 9, 2008, and contained 40 ug/l of total lead. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, impairment due to toxics in indicated when more than one violation of an acute criterion occurs within a three-year period. Because this sample did not violate the acute criterion, this violation does not indicate impairment of the Class B(WW1) aquatic life uses. These results suggest that the Class B(WW1) aquatic life uses should be assessed as “fully supported.”

Fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river segment.

Monitoring and Methods
Assessment Key Dates
7/16/2012 Biological Monitoring
8/5/2013 Biological Monitoring
Methods
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
420 Water column surveys (e.g. fecal coliform)