Assessment Comments

Assessment is based on: (1) the results of monthly monitoring from January 2004 through December 2006 at the IDNR/UHL ambient monitoring station located at the Highway 63 bridge north of Oskaloosa (STORET station 10620001; formerly station 821035) and (2) the results of U.S. EPA/IDNR fish tissue (RAFT) monitoring near Oskaloosa in 2005 and 2006.

Basis for Assessment

[Note 1:  Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

[Note 2:  The assessments for segments IA 03-SSK-0010_2 and IA 03-SSK-0010_3 are the same except for the lack of the Class C (drinking water) assessment for the downstream segment (IA 03-SSK-0010_2).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2004 through 2006.   The Class C (drinking water) uses are assessed (monitored) as "not supported" due to violations of state water quality criteria for nitrate.   Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2005 and 2006.   The sources of data for this assessment include (1) the results of monthly monitoring from January 2004 through December 2006 at the IDNR/UHL ambient monitoring station located at the Highway 63 bridge north of Oskaloosa (STORET station 10620001; formerly station 821035) and (2) the results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring near Oskaloosa in 2005 and 2006.  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected (464 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Fifteen of the 24 samples (62%) exceed Iowa’s single-sample maximum value of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

The Class B(WW1) aquatic life uses are assessed as "fully supported" based on results of monitoring from the IDNR ambient station north of Oskaloosa from 2004 through 2006.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples analyzed.   Also, none of approximately 10 samples analyzed for toxic metals, and none of the approximately seven samples analyzed for pesticides, violated the respective Class B(WW1) criteria.   One of the 36 samples analyzed for pH, however, exceeded the Class B(WW1) criterion of 9.0 pH units (this sample contained a pH of 9.6 pH units).   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as pH nonetheless suggest "full support" of aquatic life uses.   Thus, the percentage of violations of the pH criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.  

The Class C (drinking water) uses are assessed (monitored) as "not supported" due to violations of state water quality criteria for nitrate.   Results of IDNR ambient monthly monitoring at the Oskaloosa station from 2004 through 2006 show 13 violations of the nitrate MCL (=state water quality standard) in the 36 samples collected (36% in violation).   According to IDNR's assessment guidelines, this dataset suggests that the Class C uses are "not supported."  That is, if more than 25% of the samples exceed the MCL for nitrate, the Class C uses are assessed as “not supported.”  None of 36 samples contained atrazine at a level above the MCL of 3.0 ug/l (maximum level was 2.6 ug/l).  

Fish consumption uses are assessed (monitored) as "fully supported" based on results of U.S.   EPA/IDNR fish tissue (RAFT) monitoring near Oskaloosa in 2005 and 2006.    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.    Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.    In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health (IDPH), in cooperation with Iowa DNR, developed a risk-based advisory protocol.    This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).    Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.  

Although this scenario does not apply to the fish contaminant data generated from the 2005 RAFT sampling conducted in this assessment segment, levels of contaminant were sufficiently high for concern and justified follow-up monitoring.    The 2005 composite sample of fillets from common carp had generally low levels of contaminants.    (Although sampled as a RAFT “status” site, a sufficient number of predator species was not available, and a predator sample was not submitted).    Levels of primary contaminants in the composite sample of the common carp fillets were as follows: mercury: 0.215 ppm; total PCBs: < 0.09 ppm; and technical chlordane: < 0.03 ppm.    Although assessed as “fully supported” for the 2006 reporting cycle, the level of at least one contaminant approached one or more advisory trigger levels:  the level of mercury in the sample of common carp fillets (0.215 ppm) slightly exceeded the interim IDNR/IDPH one meal per week trigger level of 0.20 ppm.    

According to the IDNR/IDPH advisory protocol, this single result from the 2005 sampling on the South Skunk River neither warranted issuance of an advisory nor indicated impairment of the fish consumption uses:  two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory.    But, this elevated level did indicate a concern and the need to conduct additional monitoring to better define contaminant levels in fish from this river segment.    Thus, follow-up monitoring was conducted in 2006 to better determine (1) levels of mercury in the edible portions (fillets) of fish in this river segment and (2) whether a one-meal-per-week consumption advisory needs to be issued.    The 2006 monitoring showed a lower level of mercury in the composite sample of common carp fillets (0.201 ppm), thus indicating that a consumption advisory is not justified for this river segment.    Also, the IDNR/IDPH trigger level for mercury for a one-meal/week consumption advisory was changed in 2007 to 0.3 ppm to be consistent with U.S.   EPA's recommendation for a tissue-based water quality criterion for mercury.