AWWA WQTC60625

Serving the largest consumer population in the state of Florida, the Miami-Dade Water andSewer Department (MDWASD) produces over 340 million gallons a day (mgd) of potablewater to serve an estimated two million people in metropolitan Dade County. Dade Countyrelies on the local surficial Biscayne Aquifer for its potable supply. The productivity of thisaquifer is dependant on the recharge it receives during south Florida's rainy season (June1- November 30). To maximize the use of this resource, the MDWASD has installed twoaquifer storage and recovery (ASR) well fields (West and Southwest) to store raw BiscayneAquifer water during the rainy season for use during the dry months. The ASR systemutilizes the Upper Floridan aquifer system for storage. As a result, this ASR system is aninter-aquifer raw water transfer. Underground Injection Control (UIC) regulationsmandate 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 heavyrain 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 thefrequent heavy rain storms during the rainy season, the productivity of the ASR system islimited.The inability to infrequently recharge the ASR system during the rainy season causedMDWASD to look for a method to disinfect the raw water prior to injection. By disinfectingthe raw water, MDWASD could assure the regulatory agencies that the injected ASR watermet PDWS at all times (including the rainy season). After an evaluation of disinfectionmethods that included chlorination and ultraviolet (UV) light, MDWASD concluded thatUV disinfection would disinfect the ASR raw water prior to injection with the least amountof effects to surrounding residents and avoid possible concerns regarding possibleintroduction of DBPs, such as total trihalomethanes (TTHM) and haloacetic acids (HAA 5)into the Floridan Aquifer. MDWASD is currently proceeding with the design of UVdisinfection systems at the West and Southwest ASR well fields that will disinfect raw waterto meet PDWS for coliform bacteria prior to injection into the Upper Floridan Aquifer. Thefocus of this paper is on documenting the evaluation, permitting, design, and construction ofthis project. Particular emphasis will be on the consideration of UV dosage requirementsfor microbiological (e.g. coliform) inactivation. Includes tables.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

21

File Size:

1 file , 590 KB