Assessment Comments
Assessment based on 2008-2010 IDNR/SHL biological sampling data: FIBI = 25 (poor), 26, 29, 31 (fair), 54 (good); BMIBI = 40, 54 (fair), 57, 62, 63 (good). FIBI BIC = 36, BMIBI BIC = 51. Assessment also based on results of bacterial monitoring in 2010 and 2011 as part of a Section 319 water quality project.
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, this segment is now presumptively 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 (E. coli) that exceed state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supported” (IR 5b-v) based on results of biological sampling from 2008-2010. The sources of data for this assessment include (1) results of IDNR/SHL biological sampling from 2008-2010 and (2) the results of monitoring as part of the Bear Creek Section 319 Watershed Monitoring Project during the 2010-2012 period at three stations: (moving from downstream to upstream): (1) WLNT-1 near Hartwick (STORET ID 13790008), (2) Site 2m at 328th Avenue (STORET ID 13790002) and (3) Site 4m near 150th Street (STORET ID 13790004). Note: Limited amounts of data are available for other stations monitored in this assessment segment during the 2010-2012 assessment period: Site WLNT2 (STORET station 11790009) and Walnut Creek at Holiday Lake (STORET station 12790002); too few data were collected at these stations (from one to two samples over the three-year period) to be useful for developing Section 305(b) water quality assessments. None of the samples collected at these stations, however, violated Class B(WW) water quality criteria.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of bacteria monitoring from March 2010 to September 2011. A total of 25 samples were collected at each of the three monitoring stations: 15 samples were collected during the recreation season of 2010, and 10 samples were collected during the recreation season of 2011. The geometric mean levels of indicator bacteria (E. coli) at all three stations exceed the Class A1 geometric mean criterion of 126 orgs/100 ml. The geometric means at Site WLNT-1 were 750 orgs/100 ml in 2010 and 1,105 orgs/100 ml in 2011 with 22 of the 25 samples (88%) exceeding the single-sample maximum criterion of 235 orgs/100 ml. The geometric means at Site 2m were 727 orgs/100 ml in 2010 and 977 orgs/100 ml in 2011 with nine of the 21 samples (84%) exceeding the single-sample maximum criterion of 235 orgs/100 ml. The geometric means at Site 4m were 541 orgs/100 ml in 2010 and 917 orgs/100 ml in 2011 with 21 of the 25 samples (84%) exceeding the single-sample maximum criterion 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, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The assessment of the Class B(WW2) aquatic life uses was based on data collected in 2008-2010 as part of the IDNR/SHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species 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 index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2008 FIBI score was 31 (fair) and the BMIBI score was 40 (fair). The 2009 FIBI scores were 26, 29 (fair) and 54 (good) and the 2009 BMIBI scores were 57, 62, 63 (good). The 2010 FIBI score was 25 (poor) and the BMIBI score was 54 (fair). The aquatic life use support was assessed (evaluated) 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 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 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 1/5 times and passed the BMIBI BIC 4/5 times in the past five years. 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 between 2008 and 2012 to be considered “monitored”.
Results of chemical/physical water quality monitoring conducted during the 2010-2012 period suggest good water quality conditions in this assessment segment. None of the combined 17 samples collected in 2010 and 2011 at the three monitoring stations (WLNT1, 2m, and 4m) violated the Class B(WW2) criteria for dissolved oxygen, ammonia-nitrogen, pH, or temperature.
