Iowa DNR
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Water Quality Assessments

Impaired Waters List

South Skunk River IA 03-SSK-934

from the Ames Water Works dam in River Valley Park at Ames (S36 T84N R24W Story Co.) to the Co. Rd. at north line of S6 T85 R23W Story Co (approximately 1 mile NNE of Story City)

Assessment Cycle
2016
Release Status
Final
Cycle Period
2012 - 2014
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Unknown
Created
9/30/2016 8:23:51 AM
Updated
10/4/2016 11:26:14 AM
Assessment conducted in accordance with Iowa's 2016 IR methodology
Use Support
Class A1
Partially Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Partially Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2004
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class BWW1
Partially Supported
Biological: low fish & invert IBIs- cause unknown
Support Level
Partially Supported
Impairment Code
5b-v - Biological - verified
Cause Magnitude
Slight
Status
New
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2016
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
TMDL Priority
Tier IV
Fish Kill: Caused By Animal Waste
Support Level
Partially Supported
Impairment Code
4d - Pollutant-caused fish kill. No TMDL needed and administrative action taken against responsible party.
Cause Magnitude
High
Status
Continuing
Source
Agriculture: Confined Animal Feeding Operations
Source Confidence
N/A
Cycle Added
2014
Impairment Rationale
Pollutant-caused fish kill
Data Source
Fish kill investigation: Iowa DNR
Class HH
Fully Supported
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 uses are assessed (monitored) as “partially supported” (IR 5a) due to high levels of indicator bacteria that very slightly violate state water quality criteria. The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supporting" (IR 5b-v) based on the results of (1) IDNR/SHL biological sampling conducted in 2013 & 2014 and (2) an IDNR fish kill investigation in August 2011 (IR 4d). Ambient chemical/physical monitoring by IDNR/SHL from 2012-2014 suggest "full support" of the aquatic life uses. Fish consumption uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of fish contaminant monitoring in 2004. The sources of data for this assessment include (1) the results of monthly monitoring from January 2012 through September 2014 at the IDNR/SHL ambient city monitoring station located upstream from Ames at the Sleepy Hollow canoe access (station 10850003), (2) results of IDNR/SHL biological sampling in 2013 & 2014; (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004, and (4) results of an IDNR fish kill investigation in August 2011.

Assessment Explanation

The Class A1 uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E. coli) during recreational seasons of 2012 through 2014. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at IDNR station 10850003 upstream from Ames were as follows: the 2012 geometric mean was 46 orgs/100 ml, the 2013 geometric mean was 94 orgs/100 ml, and the 2014 geometric mean was 223 orgs/100 ml. Only the 2014 geometric means exceeded the Class A1 criterion of 126 orgs/100 ml; the 2012 and 2013 geometric means were well below the criterion. Seven of the 22 samples (32%) exceeded the 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "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 “impaired.”

The Class B(WW-1) (aquatic life) uses are assessed (monitored) as "partially supported" due to the occurrence of a fish kill near Story City in August 2011. The kill occurred on or before August 4, 2011. Approximately 27,400 fish were killed over five miles of stream. The value of the fish was reported as $38,056.16; the cost of the IDNR investigation was $1,928.83. The cause of the kill was identified as animal waste from a hog confinement.

According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody will be placed in IR Category 4d (impaired but TMDL not required). IDNR records show that the party responsible for the kill was identified, and IDNR sought and received restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. Thus, this assessment segment was placed in Category 4d of Iowa’s 2014 Integrated Report and remains there for the 2016 cycle.

Despite the indications of impairment suggested by the August 2011 fish kill, results of both chemical/physical water quality monitoring suggest relatively good quality conditions in this segment of the South Skunk River. Results of chemical/physical water quality monitoring during the 2010-12 period at the IDNR ambient station upstream from Ames showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, temperature, chloride, or sulfate in the 36 samples collected. These results suggest “full support” of the Class B(WW1) aquatic life uses.

In agreement with the fish kill assessment, the results of biological monitoring in 2013 and 2014 suggest “partial support” of the aquatic life uses of this river segment. A series of biological metrics which 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 fish species and benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate community index of biotic integrity (BMIBI). The indices rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2013 FIBI score was 13 (poor) and the BMIBI scores were 41 (fair) and 56, 63 (both good).  The 2014 BMIBI scores were 39, 53 (both fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment failed the FIBI BIC one time in 2013 and passed the BMIBI BIC 1/5 times in the last five years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.

This aquatic life assessment is now considered "monitored" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had multiple BMIBI samples collected in the previous five years.

Fish consumption remain assessed (evaluated) as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring conducted in 2004 near Story City. Because these data are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (lower confidence assessment.) The composite samples of fillets from common carp and smallmouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.069 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.031 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.109 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the fish tissue samples collected in 2004 do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.

Monitoring and Methods
Assessment Key Dates
8/4/2011 Fish Kill
7/18/2013 Biological Monitoring
8/14/2013 Biological Monitoring
9/4/2014 Biological Monitoring
1/10/2012 Fixed Monitoring Start Date
9/4/2014 Fixed Monitoring End Date
9/16/2004 Fish Tissue Monitoring
Methods
140 Incidence of spills and/or fish kills
150 Monitoring data more than 5 years old
230 Fixed station physical/chemical (conventional plus toxic pollutants)
260 Fish tissue analysis
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quan. measurements of instream parms-- channel morphology-- floodplain-- 1-2 seasons-- by prof
420 Water column surveys (e.g. fecal coliform)