Assessment Comments
Assessment based on: (1) results of water quality monitoring conducted from 2010 through 2012 on Jackson Creek near Bridgeport (station RA-39) by Iowa State University under contract with the U.S. Army Corps of Engineers as part of the Rathbun Water Quality Project, (2) IDNR/SHl biological sampling conducted in 2011 and (3) results of biological sampling (fish surveys) conducted by the IDNR Fisheries Bureau from 1999-2002.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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), this segment is now designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported” (IR 5b-t) based on (1) results of biological sampling by the IDNR Fisheries Bureau and IDNR/SHL and (2) information in U.S. EPA's May 23, 2006 letter transmitting Iowa's final 2004 Section 303(d) list. This sources of data for this assessment include (1) results of water quality monitoring conducted from 2010 through 2012 on Jackson Creek near Bridgeport (station RA-39) by Iowa State University under contract with the U.S. Army Corps of Engineers as part of the Rathbun Water Quality Project, (2) IDNR/SHl biological sampling conducted in 2011 and (3) results of biological sampling (fish surveys) conducted by the IDNR Fisheries Bureau from 1999-2002.
EXPLANATION: The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 18 samples collected during the recreational seasons of 2010 through 2012 at Jackson Creek were as follows: the 2010 geometric mean was 836 orgs/100 ml, the 2011 geometric mean was 248 orgs/100 ml, and the 2012 geometric mean was 934 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 18 samples (72%) 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 "not supported" (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(WW2) aquatic life uses remain assessed (evaluated) as "partially supporting" based on biological data collected in 1999-2002 as part of an IDNR Fisheries stream sampling project: Chariton research station and on data collected in 2011 by IDNR/SHL for TMDL/SI sampling purposes. Despite results of chemical water quality monitoring that show “full support” of the Class B(WW2) uses, results of biological monitoring suggest only “partial support” of these uses. 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 benthic macroinvertebrate taxa and fish species 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 index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999-2002 Fisheries FIBI scores were 16, 20, 21, 22 (all poor), 29, 37 (fair) and 53 (good). The 2011 FIBI score was 31 (fair) and the BMIBI score was 41 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for thsi ecoregion is 41. This segment passed the FIBI BIC 2/8 times in the last 14 years. This segment passed the BMIBI BIC in 2011 (using the uncertainty adjustment value of 8 points applied to single sample assessments).
This aquatic life assessment is now considered "evaluated" 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 in a recent five year period to be considered “monitored”. This segment had multiple samples collected in the previous 14 years (fish); however, the multiple samples were not collected during a recent five year period. 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). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s 2010 Section 303(d) list of impaired waters.
Because the biological impairment of the Class B(WW2) uses is based on an “evaluated” (lower confidence) assessment, the IDNR assessment/listing methodology indicates that this assessment segment should be placed into IR Category 3b (potentially impaired; in need of further investigation). In their May 23, 2006 transmittal letter for Iowa’s 2004 Section 303(d) list, however, U.S. EPA Region 7 informed IDNR that biological impairments based on bioassessment data from the IDNR Fisheries Bureau, even though IDNR/SHL bioassessment protocols were not strictly followed, should nonetheless be placed into IR Category 5. Thus, this waterbody was placed into Category 5b of Iowa’s 2006 Integrated Report and will remain on Iowa’s future Section 303(d) lists.
Results of ambient chemical/physical water quality monitoring conducted from 2010-2012 do not suggest impairments of the Class B(WW2) aquatic life uses of this stream segment. None of 36 samples collected at station RA-39 from 2010-2012 violated the Class B(WW2) criterion for pH (range = 6.8-8.0), temperature (maximum = 27.6C), or ammonia (maximum = 0.7 mg/L). Three of the 36 samples (8%) collected during the 2010-12 period violated the Class B(WW2) criterion for dissolved oxygen (minimum value = 4.3 mg/l). According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station RA-39, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for dissolved oxygen. Thus, these results suggest that the Class B(WW2) uses should be assessed (monitored) as “fully supported.”
Although this stream is not designated for Class C drinking water uses, Jackson Creek does flow into Rathbun Reservoir which is designated for Class C uses. Thus, the seasonal elevation of pesticide levels in this stream and other tributaries of Rathbun Reservoir presents a continuing threat to full support of the Class C (drinking water) uses designated for Rathbun Reservoir. In contrast to mean levels of atrazine above the MCL in other tributaries of Rathbun Reservoir, the mean level of atrazine in the 12 samples collected during the 2010-12 period Station RA-39 (1.7 ug/l) was below the atrazine MCL of 3 ug/l. The maximum level of atrazine during the 2010-12 period was 7.5 ug/l.
