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HomeMy WebLinkAbout; ECR - Ductile Iron Pipe Water Transmission Main; Soils Report; 1988-06-24DUCTILE IRON PIPE RESEARCHASSOCIM’ION ( 1% 245RiverchaseParkway,East Suite0 BirminghaqAL35244 (205)988-9870 June 24, 1988 Mr. Robert A. Johnston COSTA REAL MUNICIPAL WATER DISTRICT 5950 El Camino Real Carlsbad, California 92008 ~~Yovr~Yto MichaelS.Tucker,P.E. Regional Engineer 11161 Magnolia street GardenGrove, California92641 (714) 53043% Re: Soil Investigation Report El Camino Real 36" Ductile Iron Pipe Water Transmission main Carlsbad, California Dear Bob: Enclosed is a copy of the soil survey report concerning the soil analysis and potential stray current situation on the reference project. Potentially corrosive soil was found on the project as well as possible stray current interference in several locations. Details of the findings are included in the context of the report. Polyethylene encasement is recommended for the entire project due to low soil resistivity and potential stray current interference. It was a pleasure to be of assistance to you on this project, and I look forward to working with you in the future. If you have any questions about the report or findings, please call me. Sincerely, Regional Engineer MST:sh Enclosures ,- SOIL INVESTIGATION REPORT EL CAMINO REAL 36" DUCTILE IRON PIPE WATER TRANSMISSION MAIN CARLSBAD, CALIFORNIA JUNE 15-16, 1988 Reported by: Michael S. Tucker, P.E. Regional Engineer &fames Vogel, P.E. Director of Regional Engineers DUCTILE IRON PIPE RESEARCH ASSOCIATION 245 RIVERCHASE PARKWAY EAST SUITE 0 BIRMINGHAM, ALABAMA 35244 (205) 988-9870 SS88-104 r INDEX 3y Procedures 1 Test Results 2 Observations 2 Conclusions 2 Recommendations 3 BXFiIBITS Project Map ANsI/AWWA C105/A21.5 - American National Standard for Polyethylene Encasement for Ductile Iron Piping for Water and Other Liquids Test Results I II III This proposed water transmission line project involves approximately 12,000' of piping sizes 12" through 36" diameter. It is recommended that polyethylene encasement be installed on the entire project due to low soil resistivity and stray current interference. INTR0DlJCT10y Requested by: Robert A. Johnston Costa Real Municipal Water Dist. 5950 El Camino Real Carlsbad, California 92008 (619) 438-3367 The survey was conducted in a spirit of service and cooperation for the purpose of identifying potentially corrosive conditions relative to ductile iron piping systems. PROJECT Location: Carlsbad, California /- Pipe Quantities: ml- LensthIfeeti 12" 20' 14" 360' 20" 1,904' 24" 938 ' 36" 8.772' TOTAL 11,994' Date of Survey: June 15-16, 1988 Conducted by: Michael S. Tucker, P.E., Regional Engineer with DIPRA and Deon T. Fowles, P.E., Senior Regional Engineer with DIPRA, with preliminary information and mapping available through the engineering office of Costa Real Municipal Water District. Representative test locations were selected along the route of proposed pipe installation. Each was assigned a number which corresponds to a number appearing in the soil analysis listing and on r the project map, Exhibit I. Page 2 A small diameter boring to approximate proposed pipe depth at each location facilitated field testing and removal of soil specimens for laboratory analysis. All field and laboratory procedures were completed in accordance with Appendix A of ANSI/AWWA C105/A21.5 Standard, see w. TEST RESULTS Specific soil analysis results are listed in Exhibit III of this report. OSSERVATIONS At four (4) locations along the project, the proposed transmission main will cross or closely parallel a cathodically F~ protected gasline. Potential profile electrical measurements were conducted at these locations to assist in evaluating this possible interference situation. CONCUJSIONS Stray direct current resulting from cathodic protection systems can theoretically cause corrosion damage to other metallic structures in the vicinity of the protected pipeline. Actual field experience and theoretical consideration of the fact that ductile iron pipelines are not electrically continuous indicate that stray current corrosion on ductile iron pipe is a infrequent occurrence. The difficulty in predicting stray current corrosion on ductile iron pipe prior to installation, however, leads to recommendations which experience has shown to greatly minimize the risk of stray current r- corrosion on ductile iron pipe. rC Page 3 f- Polyethylene encasement is recommended for the entire project due to low soil resistivity and potential stray current interference. Total footage is 11,994'. The installation procedures and material specifications for polyethylene encasement are outlined in ANSI/AWWA C105/A21.5 Standard, (See Exhibit 111. The foregoing report and recommendations are based upon examinations and tests which were made in accordance with generally accepted professional engineering standards and considered necessary in the circumstances. By: Regional Engineer . , . . ., .: .iml w. . II I : ti !i ” . .I \I\ Xl’ I *. f I \\\ 1 .,\\Q.?q ; .e OJ f7 ’ . . .i I :.& 1L - I _- I u -m . . 1. I& a .e s ‘. . w 1 ::. ,, . ,o :-a?~ .:. .~ ,’ .a “. u.f-:I’ 2 D. ‘Q,. . . . z .I . 2: . .~, ;.~‘a _’ s .‘- a .- :z-. k ~0 )I) . . . 43 , : ’ -I ‘., is 0: .. ts ’ 5 ,a 0 6 qp&&J = ., & - I . /IIF -- . . . . + s, + +r % ./.. - . - ? .\ q, ‘- / / ANSIJAWWA C105/A21.5-82 [Revision of ANSI/AWWA C105-72 (R77)] B for POLYETHYLENE ENCASEMENT FOR DUCTILE-IRON PIPIl$iF&X3sWATER AND OTHER ADMINISTRATIVE SECRETARIAT AMERICAN WATER WORKS ASSOCIATION CO-SECRETARIATS AMERICAN GAS ASSOCIATION NEW ENGLAND WATER WORKS ASSOCIATLON First edition appraved by American National Skmdards lnstiture. Inc., Dec. 27. 1972. Revisededirion approvedby American Narionol Smndards Instirute. Inc.. May26 1982. Published by AMERICAN WATER WORKS ASSOCIATION 6666 West Quincy Avenue, Denver, Colorado 80235 I American National Standard An American National Standard implies a consensus of those substantially concerned with its scope and provisions..An American National Standard is intended as aguide to aid the manufacturer, the Consumer, and the general public. The existence of an American National Standard does not in any respect preclude anyone, whether he has approved the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standard. American National Standards are subject to periodic review, and users are cautioned to obtain the latest editions. Producers of goods made in conformity with an American National Standard are encouraged to state on their own responsibility in advertising and promotion material or on tags or labels that the goods are produced in conformity with particular American National Standards. CAUTION NOTICE. Thii American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard no later than five (5) years from the date of publication. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute, 1430 Broadway, New York, N.Y. 10018, (212) 354-3300. I Copyright e 1982 by Am&an Water Works Association Printed in USA ii Committee Personnel Subcommittee 4, Cast-Iron Pipe and Fittings, which reviewed this standard, had the following personnel at that time: TROY F. STROUD, Chairman KENNETH W. HENDERSON, Vice-Chairman User Members Producer Members S. C. BAKER A. M. HORTON B. W. FRANKLIN J. P. JOHNSON K. W. HENDERSON HAROLD KENNEDY JR. R. C. HOLMAN J. H. MILLER M. G. HOOVER J. H. SALE D. A. LINCOLN T. F. STROUD W. H. SMITH T. B. WRIGHT Standards Committee A21, Cast-Iron Pipe and Fittings, which reviewed and approved this standard, had the following personnel at the time of approval: ARNOLD M. TINKEY, Chairman THOMAS D. HOLMES, Vice-Chairman JOHN I. CAPITO, Secretary Organizotion Represented American Gas Association American Society for Testing and Materials American Water Works Association Name of Representative H. J. FORR GEORGE LUCIW* G. S. ALLEN R. A. ARTHUR D. R. BOYD J. I. CAPITO* K. W. HENDERSON a *Nonvoting liaison 111 Committee Personnel (continued) American Water Works Association Canadian Standards Association Ductile Iron Pipe Research Association Manufacturers’ Standardization Society of the Valve and Fittings Industry Naval Facilities Engineering Command New England Water Works Association Underwriters’ Laboratories, Inc. M. G. HOOVER R. J. Kocot. G. M. KRALIK D. M. KUKUK R. L. LEE J. H. MILLER W. H. SMITH A. M. TINKEY D. L. TIPPIN THURMAN UPCHURCH L. W. WELLER w. F. SEMENCHUK* T. D. HOLMES HAROLD KENNEDY JR. P. I. MCGRATH JR. L. L. NEEPER T. F. STROUD T. C. JESTER s. C. BAKER ALBERT HELT w. CAREYt L. J. DOSEDLO *Nonvoting liaison tAkemate iv Table of Contents SEC. Fanward 1. History of Standard . . Il. History of Polyethylene Encasement. III. Research . IV. Useful Life of Polyethylene V. Exposure to Sunlight . VI. Options . , . VII. Major Revisions . standaml 5-1 scope.......................... 5-2 Definition. . . . 5-3 Materials . . . . PAGE VI VI vii vii vii vii vii SEC. 5-4 Installation. . . . T..M9 5.1 TubeandSheetSizes . . . . . . . . . fwm 5.1 Method A . . . . . . . . . . . . . . . . . . . 5.2 Method B . . 5.3 Method C . . AppemUxA . . . . . . . . . . . . . . . . . . . . Appendfx Table A. I Soil-Test Evaluation PAGE 2 2 3 . 3 3 5 7 Foreword lkis foreword is for information only and is not a part of ANSI/A WWA Cl05 I. History of Standard In 1926, ASA (now ANSI) Committee A21, Cast-Iron Pipe and Fittings, was organized under the sponsorship of AGA, ASTM, AWWA, and NEWWA. The current sponsors are AGA, AWWA, and NEWWA, and the present scope of Committee A21 activity is standardiza- tion of specifications for cast-iron and ductile-iron pressure pipe for gas, water, and other liquids, and fittings for use with such pipe. These specifications are to include design, dimensions, materials, coatings, linings, joints, accessories, and methods of inspection and test. In 1958, Committee A21 was reorgan- ized. Subcommittees were established to study each group of standards in accor- dance with the review and revision policy of ASA (now ANSI). The present’scope of Subcommittee 4, Coatings and Lin- ings, is to review the matter of interior and exterior corrosion of gray and ductileiron pipe and fittings and to draft standards for the interior and exterior protection of gray and ductile-iron pipe and fittings. In accordance with this scope, Sub- committee 4 was charged with the respon- sibility for: 1. Development of standards on polyethylene encasement materials and their installation as corrosion protection, when required, for gray and ductile cast- iron pipe and fittings. 2. Development of procedures for the investigation of soil to determine when polyethylene protection is indi- cated. In response to these assignments, Sub- committee 4 has: Developed ANSI A21.5-1972 (Ak’WA ClOS-72), Standard for Poly- ethylene Encasement for Gray,and Duc- tile Cast-Iron Piping for Water and Other Liquids. 2. Developed Appendix A outlining soil-investigation procedures. In 1976, Subcommittee 4 reviewed the 1972 edition and submitted a recommen- dation to Committee A21 that the stand- ard be reaffirmed without change from the 1972 edition, except for the updating of this foreword. In 1981, Subcommittee 4 again reviewed the standard. The major revi- sions incorporated into the current edi- tion as a result of that review are listed in Sec. VII of this foreword. II. History of Polyethylene Encase- ment Loose polyethylene encasement was first used experimentally in the United States for protection of cast-iron pipe in corrosive environments in 1951. The first vi POLYETHYLENE ENCASEMENT FOR DUCTILE-IRON PIPING vii field installation of polyethylene wrap on cast-iron pipe in an operating water sys- tem was in 1958 and consisted of about 600 ft (180 m) of 12-in. pipe installed in a waste-dump fill area. Since that time, hundreds of installations have been made in severely corrosive soils throughout the United States in pipe sires ranging from 454 in. in diameter. Polyethylene encase- ment has been used as a soil-corrosion preventative in Canada, England, France, Germany, and several other countries since development of the procedure in the United States. III. Research Research by the Cast Iron Pipe Research Association (CIPRA)* on sev- eral severely corrosive test sites has indi- cated that polyethylene encasement provides a high degree of protection and results in minimal and generally insignifi- cant exterior surface corrosion of gray and ductile cast-iron pipe thus protected. Investigations of many field installa- tions in which loose polyethylene encase- ment has been used as protection for gray and ductile cast-iron pipe against soil cor- rosion have confirmed CIPRA’s findings with the experimental specimens. These field installations have further indicated that the dielectric capability of polyethyl- ene provides shielding for gray and duc- tile cast-iron pipe against stray direct current at most levels encountered in the field. IV. Useful Life of Polyethylene Tests on polyethylene used in the pro- tection of gray and ductile cast-iron pipe have shown that after 20 years of expo- sure to severely corrosive soils, strength loss and elongation reduction are insignif- icant. Studies by the Bureau of Reclama- *CIPRA became the Ductile Iron Pipe Research Association in 1979. tion of the US Department of the Interiort on polyethylene film used underground showed that tensile strength was nearly constant in a 7-yr test period and that elongation was only slightly affected. The Bureau’s accelerated soil- burial testing (acceleration estimated to be live to ten times that of field condi- tions) showed polyethylene to be highly resistant to bacteriological deterioration. V. Exposure to Sunlight Prolonged exposure to sunlight will eventually deteriorate polyethylene film. Therefore, such exposure prior to back- tilling the wrapped pipe should be kept to a minimum. If several weeks of exposure prior to backfilling are anticipated, Class C material should be used (see Sec. 5- 3.1.1). VI. options This standard includes certain options, which, if desired, must be specified. These options are: 1. Color of polyethylene material (Sec. 5-3). 2. Installation method-A, B, or C (Sec. 54)-if there is a preference. VII. Major Revisions The major revisions in this edition con- sist of the following: 1. Reference to gray cast-iron pipe in the title and throughout the standard was deleted because gray iron pipe is no longer produced in the United States. 2. Metric conversions of all dimen- sions are included in this standard. Metric dimensions are direct conversions of cus- tomary US inch-pound units and are not those specified in International Organiza- tion for Standardization (ISO) standards. tlaboratory and Field Investigations of Plastic Films, US Dept. of the Interior. Bureau of Reclama- tion, Rept. No. ChE-82 (Sept. 1968). ANSVAWWA ClO5/A21.5-82 [Revision of ANSI/AWWA ClO5-72 (R77)] Amerfcen NaUonel Standard for Polyethylene Encasement for Ductile-Iron Piping for Water and Other Liquids sec. 5-1 Scope This standard covers materials and installation procedures for polyethylene encasement to be applied to underground installations of ductile-iron pipe. This standard also may be used for polyethyl- ene encasement of fittings, valves, and other appurtenances to ductile-iron pipe systems. Sec. 5-2 Deflnltkm 5-2.1 Polyethylene encasement: The encasement of piping with polyethyl- ene film in tube or sheet form. Sec. 5-3 Materlals 5-3.1 Polyethylene. Polyethylene film shall be manufactured of virgin polyethylene material conforming to the following requirements of ASTM Stand- ard Specification D-1248-78-Polyethyl- ene Plastics Molding and Extrusion Materials: I 5-3.1.1 Raw material used to manic facture polyethylene film. Type: I Class: A (natural color) or C (black) Grade: E-l Flow rate (formerly melt index):’ 0.4 maximum Dielectric strength: Volume resistivity, minimum ohm-cm-’ = 10’5 5-3.1.2 Polyethylene film. Tensile strength: 1200 psi (8.3 MPa) minimum Elongation: 300 percent minimum Dielectric strength: 800 V/mil (31.5 V/pm) thickness minimum 5-3.2 Thickness. Polyethylene film shall have a minimum thickness of 0.008 in. (8 mil, or 200 wm). The minus toler- ance on thickness shall not exceed 10 per- cent of the nominal thickness. 5-3.3 Tube size or sheet width. Tube size or sheet width for each pipe diameter shall be as listed in Table 5.1. 2 ANSI/AWWA CIOS/A21.5-82 TABLE 5.1 Tube and Sheet Sizes Nominal Pipe Diameter in. Minimum Polyethylene Width In. (cm) Flat Tuk Sheet 3 14 (35) 28 (70) 4 16 (41) 32 (82) 6 20 (51) ‘lo (102) 8 24 (61) 48 (122) 10 27 (69) 54 (137) 12 30 (76) 60 (152) 14 34 (86) 68 (172) 16 37 (94) 74 (188) 18 41 (104) 82 (208) 20 45 (114) 90 (229) 24 54 (137) 108 (274) 30 67 (170) 134 (340) 36 81 (206) 162 (41 I) 42 95 (241) 190 (483) 48 108 (274) 216 (549) 54 I21 (307) 242 (615) Sec. 5-4 InNatlatkm fashion lengthwise until it clears the pipe ends. 5-4.1 General. The polyethylene encasement shall prevent contact between the pipe and the surrounding backfill and bedding material but is not intended to be a completely airtight and watertight enclosure. Overlaps shall be secured by the use of adhesive tape, plastic string, or any other material capable of holding the polyethylene encasement in place until backfilling operations are completed. 54.2 Pip. This standard includes three different methods of installation of polyethylene encasement on pipe. Meth- ods A and B are for use with polyethylene tubes and method C is for use with polyethylene sheets. 542.1 Method A. (Refer to Figure 5.1.) Cut polyethylene tube to a length approximately 2 ft (0.6 m) longer than that of the pipe section. Slip the tube around the pipe, centering it to provide a I-ft (0.3-m) overlap on each adjacent pipe section, and bunching it accordion- 0 11, Lower the pipe into the trench and make up the pipe joint with the preceding section of pipe. A shallow bell hole must be made at joints to facilitate installation of the polyethylene tube. After assembling the pipe joint, make the overlap of the polyethylene tube. Pull the bunched polyethylene from the preceding length of pipe, slip it over the end of the new length of pipe, and secure it in place. Then slip the end of the polyethylene from the new pipe section over the end of the first wrap until it overlaps the joint at theend of the preced- ing length of pipe. Secure the overlap in place. Take up the slack width to make a snug, but not tight, fit along the barrel of the pipe, securing the fold at quarter points. Repair any rips, punctures, or other damage to the polyethylene withadhesive tape or with a short length of polyethyl- 0 POLYETHYLENE ENCASEMENT FOR DUCTILE-IRON PIPING 3 ene tube cut open, wrapped around the pipe, and secured in place. Proceed with installation of the next section of pipe in the same manner. 542.2 Method B. (Refer to Figure 5.2.) Cut polyethylene tube to a length approximately 1 ft (0.3 m) shorter than that of the pipe section. Slip the tube around the pipe, centering it to provide 6 in. (I5 cm) of bare pipeateachend. Make polyethylene snug, but not tight; secure ends as described in Sec. 542.1. Before making up a joint, slip a 3-ft (0.9-m) length of polyethylene tube over the end of the preceding pipe section, bunching it accordion-fashion length- wise. After completing the joint, pull the 3-ft (0.9-m) length of polyethylene over the joint, overlapping the polyethylene previously installed on each adjacent sec- tion of pipe by at least 1 ft (0.3 m); make snug and secure each end as described in Sec. 542.1. Repair any rips, punctures, or other damage to the polyethylene as described in Sec. 542.1. Proceed with installation of the next section of pipe in the same manner. 542.3 M&rod C. (Refer to Figure 5.3.) Cut polyethylene sheet to a length approximately 2 ft (0.6 m) longer than that of the pipe section. Center the cut length to provide a I-ft (0.3-m) overlap on each adjacent pipe section, bunching it Figure 5.1. Method A: One length of polyethylene tube for each length of pipe, overlapped at joint. Flgure 5.2 Method B: Separate pieces of polyethylene tube for barrel of pipe and for joints. Tube over joints overlaps tube encasing barrel. Flgure 5.2 Method C: Plpellne completely wrapped with flat polyethylene 8heet. 4 ANSI/AWWA C105/AZl.S-82 until it clears the pipe ends. Wrap the polyethylene around the pipe so that it circumferentially overlaps the top quad- rant of the pipe. Secure the cut edge of polyethylene sheet at intervals of approxi- mately 3 ft (0.9 m). Lower the wrapped pipe into the trench and make up the pipe joint with the preceding section of pipe. A shallow bell hole must be made at joints to facilitate installation of the polyethylene. After completing the joint, make the overlap as described in Sec. 542.1. Repair any rips, punctures, or other damage to the polyethylene as described in Sec. 54.2.1. Proceed with installation of the next section of pipe in the same manner. 5-4.3 Pipe-shaped appurtenances. Cover bends, reducers, offsets, and other pipe-shaped appurtenances with polyethylene in the same manner as the pipe. 5-4.4 Odd-shaped appurtenances. When valves, tees, crosses, and other odd-shaped pieces cannot be wrapped practically in a tube, wrap with a tlat sheet or split length of polyethylene tube by passing the sheet under the appurtenance and bringing it up around the body. Make seams by bringing the edges together, folding over twice, and taping down. Handle width and overlaps at joints as described in Sec. 542.1. Tape polyethylene securely in place at valve- stem and other penetrations. 54.5 Openings in encasement. Pro- vide openings for branches, service taps, blow-offs, air valves, and similar appurte- nances by making an X-shaped cut in the polyethylene and temporarily folding back the film. After the appurtenance is installed, tape the slack securely to the appurtenance and repair the cut, as well as any other damaged areas in the polyethylene, with tape. 54.6 Junctions between wrapped and unwrappedpipe. Where polyethyl- ene-wrapped pipe joins an adjacent pipe that is not wrapped, extend the polyethyl- ene wrap to cover the adjacent pipe for a distance of at least 2 ft (0.6 m). Secure the end with circumferential turns of tape. 54.7 Backfillforpolyethylene- wrapped pipe. Use the same backtill material-as that specified for pipe without polyethylene wrapping, exercising care to prevent damage to the polyethylene wrap- ping when placing backfill. Backfill mate- rial shall be free from cinders, refuse, boulders, rocks, stones, or other material that could damage polyethylene. In gen- eral, backfilling practice should be in accordance with the latest revision of AWWA C600, Standard for Installation of Ductile-Iron Water Mains and Their Appurtenances. 6’, 0 1’ I Appendix A Notes on Procedures for Soil Survey Tests and Obsewations and Their Interpretation to Determine Whether Polyethylene Encasement Should Be Used This appendix is for information only and is not a part of ANSI/A WWA CIOS. In the appraisal of soil and othercondi- tions that affect the corrosion rate of gray and ductile cast-iron pipe, a minimum number of factors must be considered. They are outlined here. A method of eval- uating and interpreting each factor and a method of weighing each factor to deter- mine whether polyethylene encasement should be used are subsequently de- scribed. Soil Survey Tests and Observations 1. Earth Resistivity (a) Four-pin (b) Single-probe (c) Saturated-sample 2. pH 3. Oxidation-reduction (redox) po- tential 4. Sulfides (a) Azide (qualitative) 5. Moisture content (relative) (a) Prevalence 6. Soil description (a) Particle size (b) Uniformity (4 Type (d) Color 7. Potential stray direct current (a) Nearby cathodic protection utilizing rectifiers (b) Railroads (electric) (c) Industrial equipment, includ- ing welding equipment. (d) Mine transportation equip- ment 8. Experience with existing installa- tions in the area I. Earth resisfivity. There ate three methods for determining earth resistivity: four-pin, single-probe, and soil-box. In the field, a four-pin determination should be made with pins spaced at approximate pipe depth. This method yields an aver- age of resistivity from the surface to a depth equal to pin spacing. However, results am sometimes difficult to interpret where dry topsoil is underlain with wetter soils and where soil types vary with depth. The Wenner configuration is used in con- 5 4 ANSI/AWWA CtOS/AZl.S-82 nection with a soil resistivity meter, which is available with varying ranges of resist- ance. For all-around use, a unit with a capacity of up to lo4 ohms is suggested because of its versatility in permitting both field and laboratory testing in most soils. Because of the aforementioned diff- culty in interpretation, the same unit may be used with a single-probe that yields resistivity at the point of the probe. A boring is made into the subsoil so that the probe may be pushed into the soil at the desired depth. Inasmuch as the soil may not be typi- cally wet, a sample should be removed for resistivity determination, which may be accomplished with any one of several laboratory units that permit the introduc- tion of water to saturation, thus simulat- ing saturated field conditions. Each of these units is used in conjunction with a soil resistivity meter. Interpretation of resistivity results is extremely important. To base an opinion on a four-pin reading with dry topsoil averaged with wetter subsoil would prob- ably result in an inaccurate premise. Only by reading the resistivity in soil at pipe depth can an accurate interpretation be made. Also, every effort should be made to determine the local situation concern- ing groundwater table, presence of shal- low groundwater, and approximate percentage of time the soil is likely to be water saturated. With gray and ductile cast-iron pipe, resistance to corrosion through products of corrosion is enhanced if there are dry periods during each year. Such periods seem to permit hardening or toughening of the corrosion scale or products, which then become impervious and serve as bet- ter insulators. In making field determinations of resis- tivity, temperature is important. The result obtained increases as temperature decreases. As the water in the soil approaches freezing, resistivity increases greatly, and, therefore, is not reliable. Field determinations under frozen soil conditions should be avoided. Reliable results under such conditions can be obtained only by collection of suitable subsoil samples for analysis under labora- tory conditions at a suitable temperature. Interpretation of resisiivity. Because of the wide variance in results obtained under the methods described, it is difficult specifically to interpret any single reading without knowing which method was used. It is proposed that interpretation be based on the lowest reading obtained, with consideration being given to other conditions, such as normal moisture con- tent of the soil in question. Because of the lack of exact correlation between expe- riences and resistivity, it is necessary to assign ranges of resistivity rather than specific numbers. In Table A. 1, points are assigned to various ranges of resistivity. These points, when considered along with points assigned to other soil characteris- tics, are meaningful. 2. PH. In the pH range ofO.0 to4.0, the soil serves well as an electrolyte, and total acidity is important. In the pH range of 6.5 to 7.5, soil conditions are optimum for sulfate reduction. In the pH range of 8.5 to 14.0, soils are generally quite high in dissolved salts, yielding a low soil resistivity. In testing pH, glass and reference elec- trodes are pushed into the soil sample and a direct reading is made, following suit- able temperature setting on the instru- ment. Normal procedures are followed for standardization. 3. Oxidation-reduction (redox) po- tenfial. The oxidation-reduction (re- dox) potential of a soil is significant because the most common sulfate- reducing bacteria can live only under an- aerobic conditions. A redox potential POLYETHYLENE ENCASEMENT FOR DUCTILE-IRON PIPING 7 0 0 greater than +I00 mV shows the soil to be sufficiently aerated so that it will not sup- port sulfate reducers. Potentials of 0 to +lOO mV may or may not indicate anae- robic conditions; however, a negative redox potential definitely indicates anae- robic conditions under which sulfate reducers thrive. This test also is accom- plished using a pH meter, with platinum and reference electrodes inserted into the TABLE A. 1 Soil- Test Evaluation* Soil Charactcristicr Points Resistivity-ohm-cm (based on single-probe at pipe depth or water-saturated soil box): <700,, ....................... 10 700-1000 ......................... 8 1000-1200 ......................... 5 12w1500 ......................... 2 15004000 ......................... I >Moo.. ....................... 0 pH: o-2 ............................... 5 2-4. .............................. 3 4-6.5 ............................. 0 6.5-7.5.. .......................... Ot 7.5-8.5.. .......................... 0 >8.5 ............................. 3 Redox potential: >+lOOmV .................. 0 +50to+l00mV .................. 3.5 oto+50mv.. ................ .4 Negative .................. 5 Sulfides: Positive ........................... 3.5 Trace. ............................ 2 Negative ........................... 0 Moisture: Poor drainage, continuously wet ..... 2 Fair drainage, generally moist ....... I Good drainage, generally dry ........ 0 *Ten points-corrosive to gray or ductile caet- iron pipe: protection is indicated. tlf sulfides are present and low or negative redox-potential results are obtained, three points shall be given for this range. soil sample, which permits a reading of potential between the two electrodes. It should be noted that soil samples removed from a boring or excavation can undergo a change in redox potential on exposure to air. Such samples should be tested immediately on removal from the excavation. Experience has shown that heavy clays, muck, and organic soils are often anaerobic, and these soils should be regarded as potentially corrosive. 4. Sulfdes. The sulfide determina- tion is recommended because of its field expediency. A positive sulfide reaction reveals a potential problem due to sulfate- reducing bacteria. The sodium azide- iodine qualitative test is used. In this determination, a solution of 3 percent sodium azide in a 0.1 N iodine solution is introduced into a test tube containing a sample of the soil in question. Sulfides catalyze the reaction between sodium azide and iodine, with the resulting evolu- tion of nitrogen. If strong bubbling or foaming results, sulfides are present, and the presence of sulfate-reducing bacteria is indicated. If very slight bubbling is noted, sulfides are probably present in small concentration, and the result is noted as a trace. 5. Moisture content. Since prevail- ing moisture content is extremely impor- tant to all soil corrosion, every effort must be made to determine this condition. It is not proposed, however, to determine spe- cific moisture content of a soil sample, because of the probability that content varies throughout the year, but to ques- tion local authorities who are able to observe the conditions many timesduring the year. (Although mentioned under item 1, Earth Resistivity, this variability factor is being reiterated to emphasize the importance of notation.) 6. Soil description. In each investi- gation, soil types should be completely described. The description should include 8 ANSI/AWWA ClOS/A21.5-82 color and physical characteristics, such as particle sire, plasticity, friability, and uni- formity. Observation and testing will reveal whether the soil is high in organic content; this should be noted. Experience has shown that in a given area, corrosivity may often be reflected in certain types and colors of soil. This information is valua- ble for future investigations or for deter- mining the most likely soils to suspect. Soil uniformity is important because of the possible development of local corro- sion cells due to the difference in potential between unlike soil types, both of which are in contact with the pipe. The same is true for uniformity of aeration. If one segment of soil contains more oxygen than a neighboring segment, a corrosion cell can develop from the difference in potential. This cell is known as a differen- tial aeration cell. There are several basic types of soils that should be noted: sand, loam, silt, clay, muck. Unusual soils, such as peat or soils high in foreign material, also should be noted and described. 7. Potential stray direct current. Any soil survey should includeconsidera- tion of possible stray direct current with which the gray or ductile cast-iron pipe installation might interfere. The wides- pread use of rectifiers and ground beds for cathodic protection of underground structures has resulted in a considerable threat from this source. Proximity of such cathodic protection systems should be noted. Among other potential sources of stray direct current are electric railways, industrial equipment (including welding equipment), and mine-transportation equipment. 8. Experience with existing installa- tions. The best information on corrosiv- ity of soil with respect to gray and ductile cast-iron pipe is the result of experience with these materials in the area in ques- tion. Every effort should be made to acquire such data by questioning local officials and, if possible, by actually observing existing installations. Soil-lest Evaluation When the soil-test procedures de- scribed herein are employed, the follow- ing tests are considered in evaluating corrosivity of the soil: resistivity, pH, rcdox potential, sultides, and moisture. For each of these tests, results are catego- tired according to their contribution to corrosivity. Points are assigned based on experience with gray and ductilecast-iron pipe. When results of these five test- observations are available, the assigned points are totaled. If the sum is equal to ten or more, the soil is corrosive to gray or ductile cast-iron pipe, and protection against exterior corrosion should be pro- vided. This system is limited to soil corro- sion and does not include consideration of stray direct current. Table A.1 lists points assigned to the various test results. General. These notes deal only with gray and ductile cast-iron pipe, the soil environment in which they will serve, and methods of determining a need for polyethylene encasement. F rest Results Station/ a Location 1 Sta. 491 - El Camino Real. 2 Sta. 470 - El Camino Real. 3 Sta. 447 - El Camino Real. 4 Sta. 420 - El Camino Real. 5 Sta. 404 - El Camino Real. 6 Sta. 372 - El Camino Real. EXHIBIT III Resistivity Redox ohm-cm. mv. m 1,040 +220 7.0 440 +215 6.6 480 +228 6.9 560 +244 6.4 +242 6.6 1,080 +239 6.8 Soil sulfides DescriDtion Negative Brown silty clay, 8’, moist. Negative Brown clay, 5', moist. Negative Brown clay, 5', moist, Negative Brown clay, 5', moist. Negative Brown clay, 5', moist. Negative Brown silty clay, 5', moist. DIPRA SURFACE POTENTIAL GRADIENT SURVEY PORU SC-87 pate 6-16-88 Conducted by Michael S. Tucker, P.E. L Deon Fowles, P.E_. droject Name El Camino Real 36" DIP Transmis~sion P/S of gasline Survey Location Carlsbad, California Rectifier Output Dist. between anode bed h DI pipeline Soil Resistivity in area 700 Gas pipeline owner Phone number Remarks Anode bed is remote - one north of project and one south Survey Length Proposed Existing Pipe age Pipe sizes Joint type Pipe type sta. 441 North 25' - 16.1 North 50' - 32.1 -6.3 Sta. 485’50 Sta. 485’50 Station 6 + Or Field Direction - Reading North 50' - 11.0 North 75' + 21.0 NorthlOO' + 5.1 S/W 25' + 27.0 S/W 50' - 7.1 s/w 75' + 2.5 DIPRA SURFACE POTENTIAL GRADIENT SURVEY FORM SC-87 y?ate - - Conducted by -1 S. Tucker. & new Project Name El Camino Real 36" DIP Transmission P/S of gasline Survey Location Carlsbad, California Rectifier Output Dist. between anode bed 6 DI pipeline Soil Resistivity in area 700 Gas pipeline owner Phone number Remarks Anode bed is r~~,n+n - - north of Droiect and uuth Survey Length Proposed Existing Pipe age Pipe sizes Joint type Pipe type Sta. 373 1 Station &It or/ Field Direction - Reading (mv) South 25' + 9.9 /-.South 50' t 13.8 ,- South 75' + 13.5 South 100' + 17.5 South 125' + 17.7 North 25' + 14.5 North 50' + 22.G Ncrth 75' + 20.5 North 100' + 21.4 Sta. 401 IStation &I+ or! Field 1 Station & + or Field Direction - ReadinS