Jackson Creek IA 05-CHA-1332

The presumptive Class A1 (primary contact recreation) are assessed (evaluated) 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 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 DNR’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). In the 2014 assessment/listing cycle, the presumptive Class A1 uses should have been listed as (monitored)“partially supported" due to levels of indicator bacteria that exceeded state water quality criteria. Therefore, due to the lack of new data collected since, the Class A1 uses will remain be listed as "partially supported" for the current assessment/listing cycle.

The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supporting" based on biological data collected in 2011 by DNR/SHL for TMDL/SI sampling purposes. 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 2011 FIBI score was 31 (fair) and the BMIBI score was 40 (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 this ecoregion is 41. In 2011, this segment passed both the FIBI BIC (using the uncertainty adjustment value of 8 points applied to single sample assessments) and the BMIBI BIC (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 DNR assessment methodology. DNR 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 a single sample collected in 2011. According to DNR’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). DNR 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 Section 303(d) list of impaired waters.

Until this cycle, historic (2000-2002) DNR Fisheries Bureau fish sampling data were also used for the aquatic life assessment. Because the biological impairment of the Class B(WW2) uses is based on an “evaluated” (lower confidence) assessment, the DNR 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 DNR that biological impairments based on bioassessment data from the DNR Fisheries Bureau, even though DNR/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 chemical/physical water quality monitoring at Jackson Creek suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 30 Ammonia samples (maximum = 1.7 mg/L), 59 Temperature samples (maximum = 25.6° c) or 41 Chloride samples (maximum = 99 mg/L) occurred during monitoring from March 2012 to October 2014.Two of the 59 samples (3%) analyzed for Dissolved Oxygen (minimum = 4.6 mg/L) and one of the 59 samples (2%) analyzed for pH (range = 6.1 to 8) violated the Class B(WW2) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters is not greater than 10 percent, these results do not suggest impairment of the Class B(WW2) aquatic life uses.

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 18 samples collected during the 2012-14 period Station RA-39 (3.6 ug/l) is above the atrazine MCL of 3 ug/l, thus suggesting relatively low contributions of atrazine to Rathbun Reservoir. The maximum level of atrazine during the 2012-14 period was 21.0 ug/l.