I am assuming the gas drop is running perpendicular , i.e. , from the main ( along the street ) to the house , and your bore is crossing at about a 90 degree angle to the gas service . If you get a locator that displays depth , or enables you to approxiamate through triangulation , you will only have found the depth of the tracer wire / tracer tape ( the plastic roll tape that has some type of foil included with it ) . The actual service pipe , which maybe either metal or plastic , could vary in depth below the depth you have arrived at by mechanical locating . If you can pothole the gas service at another close point , ( between the curb and sidewalk , or , after it leaves out from under the driveway , you can make a determination of the actual distance between the locating wire or tape , and the actual pipe , and assume within some +/- factor the approximate depth under the driveway . If you are crossing a large diameter main , almost always , the gas company will insist on visual locating , regardless of the hard surface involved . Normally , you can get reimbursed for this expense , but , not always . If you are buring to the house where this gas service is , consider making the bore closer to the house , where the gas line may be out of play . Of course , you will have to talk to the homeowner , and possibly your supervisor about this action . Another possibility , if allowed by the service provider , may be to wrap the house , avoiding the driveway alltogether . Another scearario , may be to rote the drop through a crawl space under the house , or , as a last recourse , have the ground block relocated , providing their is an approved bonding point at the new location . Bottom line is , to safely cross the gas service , you must either visually pothole @ the point of crossing , or , do a little digging somewhere to gather some information you can use to make a determination of the approximate depth , and then proceed with a safe clearance depth allowing for minimum required seperation plus half the diameter of the bore hole ( the area made by the bore head and pipe ) . If you are back-reaming , to enlarge the hole for duct placement , use the diameter of the largest hole you will make . Some people forget that . The head makes it through safely , but , the backreamer does the damage , because the enlargement was not taken into consideration , which decreased the planned clearance .
In regards to some other points raised throughout this discussion , I would like to add : An induction clamp works well on CATV ( should be after the tap , or , before the ground block ) ELEC ( on the riser , before the meter ) if you have 60cycle on the locator , can locate by adjusting gain , but , be advised , TEL carries 60cycle bleed . For TEL , it is best to disconnect the drop from bond at ped , or NID , and take your 2 lead clips , placing one on the drop bond , and , the other to a good ground source ( rod , long steel screwdriver , etc. ) WATER in plastic pipe , can be divined within a foot of accurracy . ( If you wish to find out how , please ask via PM , or , contact @240-674-9890 . SEWER . can be located ( normally runs in straight lines ) by finding the cleanout , and knowing where the main runs , It should be a gravity flow , with a drop of 1-1.5 inches per 10 feet . Measure to the bottom of the clean-out . The clean-out should be the same diameter of the service run . If you here any pulsating noises while locating ELEC , there is a good chance you have crossed an electric dog fence , or , sometype of security wire . Lamp posts and landscape lighting may have buried lines ( they could be 110V , or 12 V ) . WELLS , will have electric lines and water pipes running to them . Out buildings , sheds may have power feeds to them . ALSO , please watch for privately owned communications towers ( CB&Ham ) . I knew one guy that buried a drop between a tower and a house one time , and , it cost him over $3000.00 to repair the damages .
One other alternitive I failed to mention , to locate that damm gas service , is to post hole or dig in from the grasss edge of the driveway towards where you think the service might be , and , probe with a metal tipped fiberglass probe rod/stick , and find the service that way .
Now , as to the Main Lines , well , thats the next level class .
Hope I have been a little bit more helpfull then my initial responce . I followed this discussion for awhile , to see where it was going . I swear by my SUBSITE . I'm called on to break-it-out all the time , and have amazed many a Boss-man , and , have stunned or corrected many a " Professional " locator ( the one's the utility companies pay to locate thier stuff ) .
