Benthic Macroalgal Blooms as Indicators of Nutrient Loading from Aquifer-Injected Sewage Effluent in Environmentally Sensitive Near-Shore Waters Associated with the South Florida Keys

Abstract

Domestic wastewater is injected into Florida's permeable aquifer system via Class I and Class V wells theoretically to avoid nutrient loading and other contamination that occurs when domestic wastewater is discharged directly to surface waters, resulting in nutrient loading and harmful algal blooms (HABs). The majority of Class I aquifer-injection wells are used to inject secondary-treated effluent from domestic wastewater treatment plants. Class V aquifer-injection wells also include injection of domestic wastewater. As of July 28, 2014, 257 Class I aquifer-injection wells and 14,466 Class V aquifer-injection wells had been permitted in Florida by the Florida Department of Environmental Protection (FDEP), with 34 Class I wells and 10,671 Class V wells located in the Florida Keys, Monroe County and Miami-Dade County, in southeast Florida. The presumption is that the injected wastewater will be contained within the aquifer zone where the injection is permitted and not move into overlying aquifer zones or surface waters. No large-scale monitoring in surface waters is conducted to confirm that the predominantly non-saline domestic wastewater injected into aquifer zones of higher salinities is not discharging to surface waters, such as the near-shore coastal waters in southeast Florida that provide habitat for coral reefs and federally threatened and endangered species, such as sea turtles and manatees. As an example of how such monitoring could be conducted, a case study was initiated in the coastal waters of the Florida Keys to evaluate the hypothesis that: 1) deep-aquifer (Floridan) discharges occur in localized areas of environmental decline and 2) dense benthic macroalgae associated with submarine groundwater discharges (SGD) in those localized areas, exhibit stable nitrogen isotope ratios (δ 15 Ν) indicative of sewage effluent. Sites were selected in near-shore (continental shelf) surface waters in Biscayne Bay (vicinity of Black Point deep-aquifer sewage-effluent injection facility); Card Sound/Barnes Sound; Florida Bay (Everglades National Park); and Florida Keys ocean side (vicinity of >1000 primarily shallow-aquifer Class V injection wells). Dissolved helium (He) anomalies in surface waters were used as tracers of groundwater origin. Excesses of 4 He indicate deep-aquifer discharges. Greatest 4 He excesses were in the Marquesas Keys, where localized coral decline and dense benthic macroalgae occurred, and north Florida Bay, where seagrass dieoff occurred in 1987. Benthic macroalgal samples from sites with dense macroalgal growth and localized coral decline had δ 15 Ν ratios indicative of sewage: 1) where sewage effluent disposal was concentrated in aquifer-injection wells, and 2) in the Marquesas Keys, ~40 km from the nearest shallow-aquifer injection wells, septic tanks, and cess pits. Surfacewater signatures indicative of aquifer-injection zones reconfirm breached (leaky) aquifer confinement and ocean-side Floridan-aquifer discharges for the Keys. Remote sites with deep-aquifer signatures, ext...

Analysis and Extent of Santa Fe River Flooding in North Florida Attributed to Rainfall and Wind Damage Associated with Hurricane Irma

“…These are not the only CUP wells that may occur or have occurred during that mining operation. The acquisition and methods for the FDOT (1973) and Vernon (1951) mapped lineaments indicative of fractures in Florida were described in Bacchus et al (2014), Bernardes et al (2014), and Lines et al (2012). The Digital Elevation Models (DEMs) used to illustrate the lateral extent and relative depths of flooding associated with Hurricane Irma in the lower SFR vicinity of O'Leno State Park and Buzzards Roost Prairie, were obtained from the SRWMD.…”

Management Implications of Aquifer Fractures on Ecosystem and Habitat Suitability for Panthers in Southern Florida

“…Locations [33] lineaments in Florida were described in Bacchus et al [29] and Lines et al [24]. This is the most extensive fracture network mapped in …”

“…Bacchus et al [29] presented evidence of the distance from the source that adverse impacts to habitat can occur as the result of preferential flow through fractures. The results of that study suggested that preferential flow occurred through the areas of the panther habitat studies described above.…”

Mapped Fractures and Sinkholes in the Coastal Plain of Florida and Georgia to Infer Environmental Impacts from Aquifer Storage and Recovery (ASR) and Supply Wells in the Regional Karst Floridan Aquifer System

“…The reported "recovery" in the US Geological Survey (USGS) review of ASR wells and well data in Florida (Reese, 2002, Table 5) was based on the chloride concentration established under the SDWA for potable water (250 mg/L), rather than the much lower chloride concentration of the water injected into those ASR wells. Actual "recovery" was determined by adjusting the results of cycle testing conducted in ASR test wells constructed in south Florida to compensate for differences between chloride concentration of water injected into ASR wells and water withdrawn from those wells (i.e., reported chloride concentration/(recovered/injected concentration)), as summarized by Bacchus et al (2014;2015a;2015b). Actual "recovery," based solely on chloride content of the withdrawn water adjusted to match the chloride content of the injected water ranged from 0% to 16.8% for "storage" periods of 15 and 8 days, respectively for those ASR wells (Table 3 of Bacchus et al, 2015a).…”

“…Evidence that these injected wastes rapidly flow through preferential pathways in the karst aquifer system, then discharge into nearshore coastal water, was summarized by Bacchus et al (2014). Bacchus et al (2015a) illustrated the proximity and frequencies of permitted ASR wells, other injection and withdrawal wells, to reported modern sinkholes, mapped fractures and fracture intersections in Florida.…”