Rule 62-303.450. Assessments of Numeric Interpretation of Narrative Nutrient Criterion

(1) A stream or estuary without applicable numeric criteria in subsection 62-302.531(2), F.A.C., shall be placed on the Verified List for impairment due to nutrients if it exceeds the chlorophyll a thresholds in subsection 62-303.351(4), F.A.C., or subsection 62-303.353(2), F.A.C., more than once in any consecutive three year period, and there are sufficient data from the last 7.5 years to meet the data sufficiency requirements of subsections 62-303.350(2), (3), and (6), F.A.C. If there are insufficient data, additional data shall be collected as needed to meet the requirements. Once these additional data are collected, the Department shall determine if there is sufficient information to develop a site-specific chlorophyll a threshold that better reflects conditions beyond which an imbalance in flora or fauna occurs in the water segment. If there is sufficient information, the Department shall re-evaluate the data using the site-specific thresholds. If there is insufficient information, the Department shall re-evaluate the data using the thresholds provided in subsections 62-303.351(4) and 62-303.353(2), F.A.C., for streams and estuaries and verify impairment if there is more than one exceedance in any consecutive three year period. In any case, the Department shall limit its analysis to the use of data collected during the last 7.5 years. If alternative thresholds are used for the analysis, the Department shall provide the thresholds for the record and document how the alternative threshold better represents conditions beyond which an imbalance in flora or fauna is expected to occur.

(2) If the waterbody was listed on either the Planning or Study List for nutrient enrichment based on other information indicating an imbalance in flora or fauna, as provided in paragraphs or subsection 62-303.350(1), 62-303.351(3), 62-303.352(1)(b) or 62-303.353(3), F.A.C., the Department shall verify the imbalance before placing the water on the Verified List for impairment due to nutrients and shall provide documentation supporting the imbalance in flora or fauna.

(3) If the waterbody was listed on the Planning List based on paragraphs or subsections 62-303.351(1), 62-303.352(1)(a), 62-303.353(1) and (5), or 62-303.354(1), F.A.C., the Department shall place the waterbody on the Verified List for exceedances of the narrative nutrient criteria in paragraph 62-302.530(48)(b), F.A.C., if the applicable numeric interpretation of the narrative nutrient criterion is exceeded based on the last 7.5 years of data.

(4) If a lake was listed on the Planning List based on paragraph 62-303.352(1)(d), F.A.C., and there are still insufficient data to determine the long-term geometric mean color or alkalinity, the Department shall place the lake on the Verified List for exceedances of the narrative nutrient criterion in paragraph 62-302.530(48)(b), F.A.C., if the annual geometric mean chlorophyll a exceeds20ug/L more than once in a three year period in the last 7.5 years.

(5) If the waterbody was listed on the Planning List for an adverse trend in nutrients or response variables pursuant to paragraph 62-303.352(1)(c), F.A.C.; or, subsection 62-303.351(5), 62-303.353(4), or 62-303.354(3), F.A.C., the Department shall place the waterbody on the Verified List if there is statistically significant increasing trend at the 95 percent confidence level for a given nutrient or nutrient response variable using the Mann-Kendall Trend Test; and either:

(a) There is a reasonable expectation that the water will become impaired within 4 years, taking into consideration the Sen-Theil fitted line based on the annual geometric means in the assessment period and the magnitude of the applicable criterion, or

(b) The contiguous downstream waterbody segment is impaired and either is included on the Verified List or has a total maximum daily load for a given nutrient, nutrient trend, or nutrient response variable. In cases where there is no contiguous downstream waterbody segment, the department will evaluate this subparagraph for the receiving waterbody.

(6) The thresholds for impairment due to nutrients in paragraph 62-302.531(2)(c) and subsections 62-303.351(4) and 62-303.353(2), F.A.C., are not required to be used during development of wasteload allocations or TMDLs where a site-specific interpretation of the narrative nutrient criterion in paragraph 62-302.530(48)(b), F.A.C., is established.

(7) When assessing waters for nutrient impairment, the Department shall evaluate whether the data were collected under extreme climatic conditions, such as floods, droughts, and hurricanes. If the needed supporting information is provided to the Department, the Department shall also evaluate whether the data were collected under conditions that are representative of the type of waterbody used to derive the applicable criteria, and whether the samples are biased towards specific non-representative flow conditions. When assessing estuary specific numeric interpretations of the narrative nutrient criterion in rule 62-302.532, F.A.C., the Department shall also evaluate whether the current ambient monitoring network is representative of the network that was the basis for the numeric interpretation of the narrative nutrient criterion in Rule 62-302.532, F.A.C. The Department will consider this information when developing the final Verified List and shall not list waters as impaired based solely on extreme climatic conditions, non-representative data, or changes in the monitoring network. Rulemaking Authority 403.061, 403.067 FS. Law Implemented 403.062, 403.067 FS. History–New 6-10-02, Amended 12-11-06, 7-2-12, 8-1-13, 2-17-16, 11-25-25.