Horizontal Roughing Filtration (HRF) is a pretreatment method used to remove excess turbidity and suspended solids of surface water fed into Slow Sand Filtration units, as these can only operate satisfactorily when the concentration suspended solids is below 25 mg/1 . A critical review and discussion of current pretreatment methods, HRF research and important filtration variables are presented together with a review of mathematical models of sand and roughing filters based on clarification and trajectory theories. A detailed historical review of head—loss theories, their development and adoption in multimedia filtration is given. I. Preliminary results from studies on a small scale HRF model suggested that: - A laboratory scale model must be over 1.2 m in length: 1.6 _in turned out to be acceptable. - An outlet chamber should be provided. — Sampling must be carried out in a two dimensional field. — Intermittent sampling is adequate. One of the main objectives of this research was to identify the Important variables affecting HRF, among velocity, temperature, particle size, particles density, arrangement of the gravel bed 'Coarse—Medium—Fine (LGF),Coarse/Fine—Fine—Coarse (SGF)§, and the bed depth. II. Experiments were conducted on a 1.6m filter scale model, using Fractional Factorial Design to identify the main variables. These were found to be particles size, velocity, and temperature. III. Further runs, using a suspension of kaolin, produced results which, upon analysis for suspended solids, turbidity, particles count, revealed that the efficiency decreases with increasing temperature and velocity and increases with increasing particles size. IV. Concentration curves along the bed enabled: — The development of the removal rate equation, — Defining the operating parts of the filter at various stages of the filtration, ' — The presence of density currents. V. Efficiency variations with the amounts of accumulated solids were monitored and revealed three main trends: a) Constant efficiency; b) Gradually decreasing efficiency; c) Increasing and then decreasing efficiency. - VI. Tracer tests showed the presence of dead zones, and - short—circuiting with either increased deposits or temperature. VII. Particles size analysis revealed that: a. The effect of velocity or temperature on the grade efficiency affects mainly suspended particles in water smaller than 10 pm and 7 pm for LGF and SGF respectively. For particles of larger diameters, an unknown repulsion phenomenon increasing with temperature rise was observed. b. The main mechanisms responsible for particles removal are sedimentation and hydrodynamic forces.

A critical review of the mechanisms of present water treatment systems including, chlorination, coagulation, filtration, granular and powdered activated carbon adsorption, ozonation and ultraviolet radiation for the removal of herbicides is presented. Rapid selective and sensitive HPLC methods were developed and rigorously validated for the analysis of the selected herbicides. Analysis of atrazine was made using Cl8 cartridges. For raw water containing interferences, extraction of the compound was made on SCX cartridges, followed by solvent exchange on C18 cartridges. A quantitative recovery of virtually 100% of the compound was achieved using C18. While the double cartridge extraction of the compound gave a recovery of about 89%. Previously developed methods for 2,4-D and MCPA were rigorously validated for the extraction and analysis of 2,4-D and MCPA. A quantitative recovery of usually greater than 90% was achieved for both compounds using Cl8 cartridges. For the extraction of paraquat different extraction systems including, reversed phase on C8 and C18, ion-paired reversed phase on C18, and cation exchange on SCX, CBA, and CN were investigated. A quantitative recovery, usually greater than 90%, of the compound was obtained using CN and CBA cartridges. The methods were then successfully used for the evaluation of the removal efficiency and establishment of mechanisms of removal of herbicides by biological filters at bench and pilot scale. Four herbicides belonging to three broad chemical categories were studied. The data presented in this study demonstrated that biological filters are very efficient in removing certain classes of herbicides. 2,4-D and MCPA were consistently removed to below a detection limit of 0.1 mug/1 for an influent concentration of 3-11 mug/1. Process variables such as flow rate, bed depth and contact time were investigated for the efficient removal of these herbicides. Seasonal variations in performance were observed and possible explanations proposed. A series of experiments was undertaken to establish .mechanisms of removal. Quantitative recovery of the herbicides from the river water proved that the processes in the filter bed as opposed to the processes in the water were responsible for removal of the herbicides. It was clear from the investigation of the adsorption of the herbicides both on the sand and organic and inorganic dirt that adsorption on these surfaces was not the main reason for removal. Filter maturation experiment showed that the presence of microorganisms in the bed is a precondition for the removal of herbicides. A depth experiment for the removal of 2,4-D showed that superficial efficient zone of removal imitates the distribution of microbial density. This evidence confirms the significance of microorganisms for the removal of herbicides by the filter bed. The ultimate proof of the biodegradation of 2,4-D by microorganisms in the filter bed was the identification of the biodegradation product 2-chlorophenol as predicted by the metabolic pathways of the compound. Filter design modifications using activated carbon were made to accommodate the removal of 'non-biodegradable' herbicides. A sandwich sand / GAC / sand filter was investigated. Filter efficiency for this arrangement was determined and short-comings were identified and a possible solution in the form of a double GAC sandwich is suggested.

6 pp. / 1. Drinking Water Wells; 2. Private Water Well Components; 3. Do Deeper Wells Mean Better Water; 4. Maintaining Your Private Well Water System; 5. Private Well Protection; 6. Well Water Testing and Understanding the Results; 7. Obtaining a Water Sample for Bacterial Analysis; 8. Microorganisms in Private Water Wells; 9. Lead in Private Water Wells; 10. Nitrate in Private Water Wells; 11.Arsenic in Private Water Wells; 12. Matching Drinking Water Quality Problems to Treatment Methods; 13. Commonly Available Home Water Treatment Systems; 14. Hard Water: To Soften or Not to Soften; 15. Shock Chlorination of Private Water Wells / This fact sheet is one in a series of fifteen for private water well owners. The one- to four-page fact sheets will be assembled into a two-pocket folder entitled Private Well Owners Guide. The titles will also be a part of the Changing Rural Landscapes project whose goal is to educate exurban, small acreage residents. The authors have made every effort to align the fact sheets with the proposed Arizona Cooperative Extension booklet An Arizona Well Owners Guide to Water Sources, Quality, Testing, Treatment, and Well Maintenance by Artiola and Uhlman. The private well owner project was funded by both the University of Arizonas Water Sustainability Program-Technology and Research Initiative Fund and the USDA-CSREES Region 9 Water Quality Program.