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Have You Got Your Microbial Toolbox Ready?. Sarah Clark, P.E. HDR Denver Office. Effective. Proposed. Final. Drinking Water Regulatory Schedule. Financial. Operations. Schedule. FEASIBLE ALTERNATIVES. Regulatory. Water Quality. Why Utilities Should be Concerned:

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have you got your microbial toolbox ready

Have You Got Your Microbial Toolbox Ready?

Sarah Clark, P.E.

HDR Denver Office




Drinking Water Regulatory Schedule







Water Quality

Why Utilities Should be Concerned:

The Practical Effects of New Rules

Water utility flexibility is shrinking

Source: Balancing Multiple Water Quality Objectives, AWWARF, 1998

mean cryptosporidum concentration in source waters
% with no brackets indicate actual; in brackets is the expected assignment based on maximum RAA of 24 samples









Mean Cryptosporidum Concentration in Source Waters

Number of Source Waters





national microbial monitoring costs
National Microbial Monitoring Costs

Total National Cost = $39,250,700

finding your crypto bin
Measure 24 samples and calculate the highest running annual average

Measure 48 samples and calculate the simple mean

Finding Your Crypto Bin

Chose One:

“Binning” based on 48 samples is much more likely to put you in your “true” bin than “binning” based on 24 samples.
lt2 treatment requirements
LT2 Treatment Requirements

*Use any technology or combination from the Toolbox

**At least 1 log by ozone, chlorine dioxide, UV, membranes, bag/cartridge filters, or in-bank filtration.

what is the microbial toolbox
What is the Microbial Toolbox?
  • Tools for an individual plant to use in reducing risk of Crypto in finished water
  • Minimizes cost of treating for Crypto by reducing the number of plants shifting to advanced technologies
  • Tools provide some flexibility for treatment plants to meet multiple water quality objectives
key to table symbols
Key to Table Symbols
  • X indicates potential log credit based on proper design and implementation accordance with EPA guidance.
  • Arrow indicates estimation of potential log credit based on site specific or technology specific demonstration of performance
  • (1) Criteria to be specified in guidance to determine allowed credit
  • (2) Inactivation dependent on dose and source water characteristics
  • (3) Additional monitoring for Cryptosporidium after this action would determine new bin classification and whether additional treatment is required.
what tools are plants most likely to use
What Tools are Plants Most Likely to Use?
  • Least expensive
  • Most direct credit from States (without extra measurement and reporting)
  • Membranes
  • Disinfectants
expected lt2 direct credit for cryptosporidium removal
Expected LT2 Direct Credit for Cryptosporidium Removal
  • Off-stream storage
    • 0.5 log credit for 21-day storage
    • 1.0 log credit for 60-day storage
  • Pre-sedimentation with continuous coagulant addition – 0.5 log credit
  • Lime softening
    • 3-log credit for single-stage plants, as for conventional plants
    • Additional 0.5 log credit for two-stage softening
expected lt2 direct credit for cryptosporidium removal cont
Expected LT2 Direct Credit for Cryptosporidium Removal cont.
  • Improved filtration
    • 0.5 log credit where CFE turbidities are maintained below 0.15 NTU, 95% of time
  • Roughing filters – 0.5 log credit
  • Multiple filtration processes – 0.5 log credit
  • Slow sand filtration
    • 3.0 log credit as baseline
    • 2.5 log credit if added to a clarification/filtration system
  • Bank filtration – 0.5 or 1.0 log credit based on demonstration
guidance will also provide details for testing
Guidance Will Also Provide Details for Testing
  • EPA intends to provide draft guidance with the proposed rule, including
    • Requirements for completion of a Cryptosporidium challenge test on a full-scale membrane module
    • Requirements for UV reactor validation
    • Requirements for demonstrating credit above the minimum specified in the rule
what can utilities do now to prepare for lt2eswtr
What Can Utilities Do Now to Prepare for LT2ESWTR?
  • Consider beginning Cryptosporidium monitoring before the required date
  • Review Cryptosporidium data you already have to get an idea of your “bin” - but don’t be too optimistic about your bin if your data is slim
  • Review each plant with the microbial toolbox in mind to determine your options
  • Plan ahead for the expenses of monitoring and treatment changes
sources of information
Sources of Information
  • Proposed LT2 Rule expected in December 2002 or January 2003
  • Guidance manual expected for review along with the rule
  • AWWA Microbial Toolbox Report
  • Pre-proposal draft of the LT2 Rule
  • Call Sarah Clark – 303-764-1560 or [email protected]