Florida Water Daily on Flowpaths for ASR

Fractures as Preferential Flowpaths for Aquifer Storage and Recovery (ASR) Injections and Withdrawals

In theory, "aquifer storage and recovery" (ASR) is a form of artificial aquifer recharge consisting of three components:

(1) aquifer injections of fluids;

(2) withdrawals of the injected fluids; and

(3) a period of time between the injections and withdrawals that is considered to be aquifer "storage" of the injected fluids.

The injected fluids may be:

(1) treated sewage effluent (also known as reclaimed, reuse, or bright water);

(2) stormwater runoff pumped out of canals, mine pits or other areas;

(3) surface waters from natural lakes and streams; or

(4) ground water from different aquifer zones.

An evaluation of existing data from more than 80 injection/withdrawal cycle tests at 18 ASR sites in 9 counties throughout southern Florida, in the regional karst Floridan aquifer system of the United States (US) revealed that less than 25% actual "recovery" was achieved from ASR wells where water from various sources was injected into the regional karst aquifer system.

Determination of actual "recovery" was based on the reported chloride content of injected and recovered water and was more suggestive of fluid disposal than aquifer "recharge."Actual "recovery" for those ASR tests,adjusted to the chloride concentrations of injected fluids, ranged from 0-17% for "storage" periods that ranged from 0-181 days. Although results of actual "recovery" provide little support for the concept of "stored" water, in reality those results also over-estimate the volume of injected water that is stored because it assumes that water recovered at the same chloride concentration is the same water that was injected.

There is no evidence in the ASR data to support that assumption. The low actual "recovery" rates occurred despite the fact that 28 of the cycle tests had a "storage" period

Despite those results, the agency's Final Technical Data Report (TDR) and groundwater model released in 2014 concluded that:

(1) "recovery" from those wells would range from 70-100% and

(2) 232 ASR wells (94 in the upper Floridan aquifer, 37 in the Avon Park Permeable Zone of the middle Florida aquifer and 101 in the Boulder Zone) could be completed in Florida's Greater Everglades Basin (basin) as restoration.

That Final TDR did not consider differences in chloride content between water that was injected into and withdrawn from theASR cycle tests and that groundwater model for the basin did not include the anisotropy option or preferential flow through karst conduits such as fractures. Preferential flow of water injected and withdrawn could result in both low ASR "recovery" rates and environmental harm, such as submarine groundwater discharge (SGD)contaminated with pollutants, including nutrients that result in harmful algal blooms (HABs).

That TDR and groundwater model for southern Florida also did not evaluate the direct, indirect or cumulative adverse impacts of preferential flow from ASR injections and withdrawals (e.g., through fractures) on federally threatened and endangered species, environmentally sensitive areas or on sinkhole formation.

Our evaluation of the basin vicinity also included analyses of fracture frequency, length and proximity to ASR wells, other injection and withdrawal wells and modern sinkholes, based on georeferenced and transformed lineaments from three independent sources: the US Army Corps of Engineers (ACOE, 2004c), Florida Department of Transportation(FDOT, 1973), and Vernon (1951). Based on the three lineament data sets included in our study, including 118 fractures that extend for considerable distances through environmentally sensitive areas in the basin such as the Big Cypress National Preserve, Biscayne National Park, Estero Bay, Everglades National Park, Florida Keys National Marine Sanctuary, Indian River Lagoon and Marquesas Keys Wildlife Management Area. Some of these fractures also extend beyond the boundaries of the basin.

Source: Floriday Water Daily

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Taxonomy

• Aquifer
• Hydrology
• Aquifer Treatment