RTW Engineering - On-Site Filter Evaluation

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On-Site Filter Evaluation

Is Your Water Safe?
The Environmental Protection Agency's (EPA's) Interim Enhanced Surface Water Treatment Rule (IESWTR) and Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) create stringent requirements for water treatment utilities. According to these EPA rules, filtering systems using surface water or groundwater under the direct influence of surface water must meet a 2-log removal (99%) of Cryptosporidium. Most granular media filters are capable of providing at least 2-log removal, if operated and maintained correctly.

These EPA rules require that turbidity remain below 0.3 NTU at least 95 percent of the time, with no single measurement reading above 1.0 NTU. The EPA requires that an Exceptions Report be filed if the effluent is above 0.5 NTU for 2 consecutive 15-minute measurements after the first 4 hours of operation, or above 1.0 NTU for any 2 consecutive 15-minute measurements anytime during operation. If the effluent is above 1.0 NTU for 2 consecutive measurements at any time in 3 consecutive months, then the EPA requires an assessment, such as
Tetra Tech RTW's On-Site Filter Evaluation, be performed. Should your effluent ever be above 2.0 NTU for 2 consecutive 15-minute measurements at any time, the EPA then requires that a Comprehensive Performance Evaluation (CPE) be performed. To consistently meet these requirements, you need to keep your filters in top operating condition. If you have minor problems, you need to find and solve them before they become big problems.

Do You Filter Your Water Efficiently/Cost-Effectively?
Studies have shown ineffective backwash can lead to multiple performance issues including short-circuiting, poor turbidity removal, increased chemical usage, undue stresses on equipment in addition to increasing operation costs. Effective and efficient backwashing is essential to proper filter performance.

Do You Properly Maintain Your Filters?
The main goal of a water treatment utility is to provide drinking water meeting all EPA and State requirements at reasonable cost to the customer. Fulfilling this goalrequires an effective and efficient treatment process. Fortunately, these two concepts often go hand-in-hand in water treatment. When a treatment process is operating efficiently the water quality is high and the overall efficiency is optimal

Do You Have a Filter Problem?
Tetra Tech RTW offers a thorough on-site filter evaluation designed to help facilities maximize their efficiency and the quality of treatment from granular media filters, which is performed for a fixed low cost. The evaluation addresses all the questions raised here and additional issues unique to each facility. The evaluation consists of six steps, both on- and off-site.

Step #1: Preliminary Evaluation Prior to Site Visit
Review Filter Design Specifications
Review Water Quality Data: 2 years preferred
Calculate Filter Indices
Use Tetra Tech RTW Corrosion Model to determine precipitation potential

Step #2: Physical Observations
Carefully observe a backwash
Drain water from filter and observe
media for problems
Perform physical measurements in
the filter compartment

Step #3: Media Analysis
Granular Media Profile
Mudball Sieve Analysis

Step #4: Running Filters for Performance
Turbidity profile
Sludge retention profile before and
after a backwash

Step #5: Backwash Tests
Backwash flowrate profile
Bed Expansion Analysis
Backwash Turbidity Analysis

Step #6: Summary Report
Status of facility
Opinions and recommendations

Optional Services
Tetra Tech RTW can provide Microscopic ParticulateAnalysis (MPA) tests on the raw water and treated water, which is the only way to accurately determine the performance of a filter at removing dangerous pathogens such as Giardia and Cryptosporidium. The MPA testing and the filter evaluation will provide a comprehensive analysis to determine if you are meeting both the letter and the intent of the EPA requirements.

Other optional tests include a Calcium Carbonate Precipitation Test and a Media Sieve Analysis. In hard water, calcium carbonate can precipitate out of the water and collect on the filter media, causing an increase in the density of the media. This makes it difficult to fluidize the media bed during a backwash and can cause improper bed expansion. The Calcium Carbonate Precipitation Test calculates the relative mass and volume of calcium carbonate compared to the mass and volume of media. A Sieve Analysis can determine the uniformity coefficient of the media. If the uniformity coefficient calculated differs notably from the original media specification, it could indicate worn media or calcium carbonate build-up. A sieve analysis can also help determine if the filter should be capped with more media or skimmed to remove media fines.