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Attachment 2 i UNRRA Forum Questions and Answers klnrba j Question 1 - What is the basis of North Carolina's chlorophyll-a standard,and how does it compare I to other States? • Falls Lake water quality impairment decisions and the Falls Lake rules are based on the non- attainment of the chlorophyll-a standard. NC first adopted a chlorophyll water quality standard in 1979 (-40 years ago). NC and SC both have a 40 pg/L chlorophyll-a standard. However, NC considers waters impaired if the chlorophyll-a standard is exceeded in more than 10% of the samples. South Carolina considers waters impaired when the chlorophyll-a standard is exceeded in more than 25%of samples. This is a significant difference. • Most states have a narrative standard for eutrophication concerns. Narrative standards evaluate impairment based on observable, negative impacts to the designated uses of a lake such as aquatic life, swimming, water supply, and recreation. Question 2 - How is NC's standard different than other States that have a numeric criterion? • Other states that have numeric standards for chlorophyll-a typically have specific applications such as growing season averages that are evaluated at specific locations within the lake. For example, locations identified near a dam, at a water supply intake, or at a certain bridge crossing are typical. Most other states with a chlorophyll-a water quality standard incorporate a duration, frequency, central tendency of magnitude, or specific conditions that provide for an allowable exceedance of the standard under certain circumstances. Question 3 - How is chlorophyll-a related to the designated uses of Falls Lake - swimming,drinking water, aquatic life, and recreation? • Quantifiable linkages between chlorophyll and designated uses are very difficult to define. Chlorophyll is an indicator of fertility and not necessarily a reliable indicator of problems. For example,you can have drinking water taste and odor problems even when chlorophyll-a levels are well below 40 pg/L. Alternatively, you may not have any taste and odor problems when chlorophyll-a is well above 40 pg/L. The same example may apply to toxic algae episodes, and not all algae are toxic. It is not the chlorophyll levels that are associated with toxicity but rather particular species of algae that may be triggered under certain conditions to produce toxins. I Question 4 - Did the UNC Collaboratory Report on Jordan Lake suggest that NC should reevaluate the chlorophyll-a standard with an emphasis on the standards being site-specific and seasonal? • The Jordan Lake UNC Collaboratory Report did suggest the need for NC to re-evaluate its water quality standard for chlorophyll-a as follows: UNC Collaboratory Jordan Lake Final Report December 2019 "The state's longstanding broad nutrient sensitive waters criterion (an instantaneous chlorophyll-a standard of 40 pg/I applied everywhere) should be reevaluated. For the past few years scientists have been reviewing this issue as part of the work of the Nutrient Criteria Development Plan Science Advisory Council. The Department of Environmental Quality should continue to engage in and encourage discussions related to development of new standards with an emphasis on the standards being site-specific and seasonal." 1