Serving the largest consumer population in the state of Florida, the Miami-Dade Water and
Sewer Department (MDWASD) produces over 340 million gallons a day (mgd) of potable
water to serve an estimated two million people in metropolitan Dade County. Dade County
relies on the local surficial Biscayne Aquifer for its potable supply. The productivity of this
aquifer is dependant on the recharge it receives during south Florida's rainy season (June
1- November 30). To maximize the use of this resource, the MDWASD has installed two
aquifer storage and recovery (ASR) well fields (West and Southwest) to store raw Biscayne
Aquifer water during the rainy season for use during the dry months. The ASR system
utilizes the Upper Floridan aquifer system for storage. As a result, this ASR system is an
inter-aquifer raw water transfer. Underground Injection Control (UIC) regulations
mandate that all injected waters must meet Primary Drinking Water Standards (PDWS)
including disinfection and disinfection byproducts (DBPs) regulatory requirements.
Currently, due to the infrequent presence of coliform bacteria in the raw water after heavy
rain events, the ASR system is required to shut down after rain events greater than 0.75-
inches until bacteriological clearance of the raw water can be demonstrated. Due to the
frequent heavy rain storms during the rainy season, the productivity of the ASR system is
limited.
The inability to infrequently recharge the ASR system during the rainy season caused
MDWASD to look for a method to disinfect the raw water prior to injection. By disinfecting
the raw water, MDWASD could assure the regulatory agencies that the injected ASR water
met PDWS at all times (including the rainy season). After an evaluation of disinfection
methods that included chlorination and ultraviolet (UV) light, MDWASD concluded that
UV disinfection would disinfect the ASR raw water prior to injection with the least amount
of effects to surrounding residents and avoid possible concerns regarding possible
introduction of DBPs, such as total trihalomethanes (TTHM) and haloacetic acids (HAA 5)
into the Floridan Aquifer. MDWASD is currently proceeding with the design of UV
disinfection systems at the West and Southwest ASR well fields that will disinfect raw water
to meet PDWS for coliform bacteria prior to injection into the Upper Floridan Aquifer. The
focus of this paper is on documenting the evaluation, permitting, design, and construction of
this project. Particular emphasis will be on the consideration of UV dosage requirements
for microbiological (e.g. coliform) inactivation. Includes tables.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 590 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 21 |
| Published : | 11/15/2004 |
