WEBVTT Kind: captions Language: en 00:00:02.275 --> 00:00:05.275 (soft guitar music) 00:00:08.192 --> 00:00:10.691 - This video demonstrates techniques to measure the total 00:00:10.691 --> 00:00:13.250 depth of a well below land surface using a weighted 00:00:13.250 --> 00:00:15.338 graduated steel tape. 00:00:15.338 --> 00:00:18.215 A graduated steel tape is commonly accurate 00:00:18.215 --> 00:00:21.794 to 1/100th of a foot, but the accuracy of the well depth 00:00:21.794 --> 00:00:24.797 measurement decreases with increasing depth. 00:00:24.797 --> 00:00:26.259 Materials needed. 00:00:26.259 --> 00:00:29.926 The materials needed include keys, wrenches, 00:00:31.027 --> 00:00:34.589 or other tools to access the well, a steel tape 00:00:34.589 --> 00:00:37.669 with brass, stainless steel or iron weight 00:00:37.669 --> 00:00:39.881 that is heavy enough to amplify the weight transfer 00:00:39.881 --> 00:00:43.112 sensation when the bottom of the well is struck. 00:00:43.112 --> 00:00:44.865 The weight should be attached to a ring 00:00:44.865 --> 00:00:47.142 on the end of the tape with wire strong enough 00:00:47.142 --> 00:00:49.887 to hold the weight but not as strong as the tape 00:00:49.887 --> 00:00:52.301 so that if the weight becomes lodged in the well, 00:00:52.301 --> 00:00:54.309 the tape can be pulled free. 00:00:54.309 --> 00:00:58.995 Engineer's ruler, clean towels or cloths, soap and water 00:00:58.995 --> 00:01:03.342 for cleaning the steel tape and weight, a field notebook, 00:01:03.342 --> 00:01:07.507 Groundwater Site Inventory System Groundwater Site Schedule 00:01:07.507 --> 00:01:10.362 form, and a writing implement. 00:01:10.362 --> 00:01:12.892 Step one: Determine you are at the correct well 00:01:12.892 --> 00:01:15.059 from the well description. 00:01:16.693 --> 00:01:19.803 Step two: Open the well and locate the documented 00:01:19.803 --> 00:01:23.803 measuring point from the well, photo or diagram. 00:01:29.903 --> 00:01:33.092 Step three: Measure from the zero point on the tape 00:01:33.092 --> 00:01:36.179 to the bottom of the weight. 00:01:36.179 --> 00:01:38.852 Record this number in the field notebook as the length 00:01:38.852 --> 00:01:40.769 of the weight interval. 00:01:42.390 --> 00:01:45.249 Locate the measuring point correction from a document 00:01:45.249 --> 00:01:49.106 such as the well station description, and record this number 00:01:49.106 --> 00:01:52.398 in the field notebook as MP correction. 00:01:52.398 --> 00:01:54.689 The MP correction is negative if the MP 00:01:54.689 --> 00:01:57.351 is above land surface, and positive if the MP 00:01:57.351 --> 00:01:59.160 is below land surface. 00:01:59.160 --> 00:02:01.396 Also record the serial number of the steel tape 00:02:01.396 --> 00:02:05.386 you will be using to make the depth measurement. 00:02:05.386 --> 00:02:09.553 Step four: Lower the weight and tape slowly into the well, 00:02:20.357 --> 00:02:22.409 until the weight reaches the bottom of the well 00:02:22.409 --> 00:02:24.242 and the tape slackens. 00:02:27.230 --> 00:02:30.684 Step five: Partially withdraw the tape from the well 00:02:30.684 --> 00:02:33.069 until the weight stands in a vertical position 00:02:33.069 --> 00:02:36.486 but still touches the bottom of the well. 00:02:37.706 --> 00:02:39.732 Pinch your thumb and index finger together 00:02:39.732 --> 00:02:43.498 on the steel tape at the measuring point. 00:02:43.498 --> 00:02:46.550 Note the depth below measuring point on the steel tape. 00:02:46.550 --> 00:02:49.242 Repeat the process of lowering and withdrawing the tape 00:02:49.242 --> 00:02:53.409 several times until a consistent measurement is obtained. 00:03:06.657 --> 00:03:09.427 Step six: Record the measurement in the field notebook 00:03:09.427 --> 00:03:12.344 as the tape reading held at the MP. 00:03:18.495 --> 00:03:22.583 Step seven: Withdraw the steel tape from the well 00:03:22.583 --> 00:03:25.709 one to two feet, so that the weight hangs freely 00:03:25.709 --> 00:03:28.126 above the bottom of the well. 00:03:29.117 --> 00:03:31.727 Repeat steps four, five, and six until two 00:03:31.727 --> 00:03:35.310 consistent depth measurements are obtained. 00:04:00.970 --> 00:04:03.780 Step eight: Calculate the total well depth below land 00:04:03.780 --> 00:04:07.137 surface datum by adding the value of the tape reading 00:04:07.137 --> 00:04:10.298 held at the MP and the length of the weight interval 00:04:10.298 --> 00:04:13.837 to get the total well depth below MP. 00:04:13.837 --> 00:04:16.096 The total well depth below land surface datum 00:04:16.096 --> 00:04:18.730 is calculated by subtracting the MP correction 00:04:18.730 --> 00:04:21.801 from the total well depth below the MP 00:04:21.801 --> 00:04:25.376 if the MP is above ground, or by adding the MP correction 00:04:25.376 --> 00:04:27.423 to the total well depth below MP 00:04:27.423 --> 00:04:29.590 if the MP is below ground. 00:04:32.591 --> 00:04:35.019 Transfer the calculated total well depth below land 00:04:35.019 --> 00:04:37.964 surface datum to the groundwater general site data 00:04:37.964 --> 00:04:42.105 section of the GWSI Groundwater Site Schedule 00:04:42.105 --> 00:04:43.188 in field C28. 00:04:44.934 --> 00:04:46.722 The recommended precision of the measurement 00:04:46.722 --> 00:04:48.875 is depth-dependent. 00:04:48.875 --> 00:04:51.568 Step nine: Withdraw the tape. 00:04:51.568 --> 00:04:53.985 Close and re-secure the well. 00:05:18.596 --> 00:05:22.463 Step ten: After completing the measurements, 00:05:22.463 --> 00:05:24.731 disinfect and rinse the part of the steel tape 00:05:24.731 --> 00:05:27.039 that was submerged below water surface, 00:05:27.039 --> 00:05:29.521 as described in the National Field Manual, 00:05:29.521 --> 00:05:31.871 in order to reduce the possibility of contaminating 00:05:31.871 --> 00:05:34.538 other wells with the steel tape. 00:05:36.760 --> 00:05:40.288 Keep in mind the following limitations of this method. 00:05:40.288 --> 00:05:42.650 Corrections to the measurements are necessary 00:05:42.650 --> 00:05:46.155 if the well casing is angled, and when measuring the well 00:05:46.155 --> 00:05:50.322 in deep wells because of tape expansion and stretch. 00:05:51.318 --> 00:05:53.521 This approach has several advantages. 00:05:53.521 --> 00:05:55.543 The weighted graduated steel tape is considered 00:05:55.543 --> 00:05:59.362 to be the most accurate method of measuring well depth. 00:05:59.362 --> 00:06:01.624 It is also easy to use. 00:06:01.624 --> 00:06:03.532 This method is not recommended for measuring the depth 00:06:03.532 --> 00:06:06.115 of wells that are being pumped.