Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) sampling in 2001 and (2) IDNR/UHL water quality monitoring in 2001 and 2004 in support of TMDL development.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses were assessed (monitored) as "not supported" based on results of chemical/physical water quality monitoring in 2001 and 2004 and on results of biological monitoring in 2001. The sources of data for this assessment include results of (1) biological monitoring conducted by IDNR/UHL in September 2001 for the stream biocriteria project and (2) monthly chemical/physical water quality monitoring conducted by IDNR/UHL at one location (station 49; STORET station 11300002) from March to November 2001 and from May to October 2004 as part of monitoring in support of TMDL development. Both the chemical and biological monitoring were conducted in the lower reach of Milford Creek approximately 1 mile SW of Milford.
EXPLANATION: The current assessment was based on (1) data collected in 2001 as part of the IDNR/UHL stream biocriteria project and (2) results of IDNR/UHL TMDL-related water quality monitoring in 2004. Results of biological monitoring in 2001 suggest that the Class B(LR) uses are only “partially supported”. 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 FIBI scores were 38 (fair) and 50 (fair); the BMIBI scores were 14 (poor) and 44 (fair). The BMIBI average was 29. The aquatic life use support was assessed as partially supported (=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 1994-2004. The riffle site FIBI BIC for this ecoregion is 53, non-riffle FIBI BIC is 32 and the BMIBI BIC for this ecoregion is 62.
Results of chemical monitoring conducted in this stream segment as part of TMDL-related monitoring during the period from May to October 2004 suggest relatively poor water quality in this stream reach and “nonsupport” of the Class B(LR) aquatic life uses. Two of 10 samples collected in 2004 violated the Class B(LR) chronic criteria for ammonia; these samples were collected on July 6 (4.5 mg/l) and July 12 (0.74 mg/l). According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), more than one violation of a water quality criterion for a toxic contaminant in an abundant dataset (more than 10 values over a three-year period) within a three-year period indicates that the aquatic life uses are not fully supported (i.e., impaired). In addition, two of 16 samples violated the Class B(LR) criterion for dissolved oxygen of 5 mg/l; these samples were collected on August 4 (3.9 mg/l) and August 10 (4.2 mg/l). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of between 10 and 25% for conventional parameters such as dissolved oxygen suggests "partial support" of aquatic life uses. Based on IDNR’s assessment methodology, however, these results do not suggest that the violation frequency for dissolved oxygen is significantly greater than 10% and thus do not suggest impairment of Class B(LR) uses of this segment of Milford Creek. Nonetheless, the violations of the Class B(LR) dissolved oxygen criteria, especially in the context of high levels of ammonia, suggest impairment of the aquatic life uses of this stream segment. These results suggest a deterioration of chemical water quality since the previous (2004) assessment cycle when TMDL-related monitoring in 2001 at Milford Creek site 49 showed no violations of Class B(LR) criteria for either ammonia or dissolved oxygen in the 9 samples collected. The TMDL-related monitoring in 2004 did not include analysis for either pesticides or toxic metals.
This stream segment continues to show elevated levels of total phosphorus. The mean, median, and maximum total phosphorus levels for the nine samples collected in 2001 at TMDL monitoring station 49 in lower Milford Creek 1.0, 0.7, and 2.2 mg/l, respectively. These values for the 20 samples collected at station 49 in 2004 are 1.7, 1.8, and 3.4 mg/l, respectively. These summary statistics for the years 2001 and 2004 suggest atypically high levels of total phosphorus in lower Milford Creek that are trending upward.
