GROUND WATER/SURFACE WATER INTERACTIONS 1-3 AWRA SUMMER SPECIALTP CONFERENCE USING GIs TO MAP THE DEPTH TO SEDIMENT IN A POND

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1 JULY.. GROUND WATER/SURFACE WATER INTERACTIONS 1-3 AWRA SUMMER SPECIALTP CONFERENCE 2002 USING GIs TO MAP THE DEPTH TO SEDIMENT IN A POND Frank P. Beck, Jr.', Patrick J. Clark2, Robert Ford' and Victor Murray3 ABSTRACT Researchers at the National Risk Management Research Laboratory, USEPA, have been characterizing the source, form and extent of subsurface contamination of arsenic in an industrialized watershed for the past two years. A suhtask of that effort has focused on a particular pond, which acts as a major sink for arsenic contributed by the source area. Detailed investigations of the pond have included numerous samples and analysis of arsenic and other geochemical parameters. It has been important to precisely identify the locations of all sampling points in three dimensions, both in the water column and in the sediments beneath the pond. Bathymetric surveys have been very helpful in conjunction with GPS measurements to precisely locate all sampling points. Using these data together with aerial photos have enabled us to present all the data in a more accurate format for ease of interpretation. Of particular interest have been the conductivity data together with arsenic data which have allowed us to project where arsenic discharges into the pond from upgradient contaminated groundwater KEY TERMS: groundwater infiltration; sediment characterization, bathymetric survey. INTRODUCTION A watershed in the Boston area has been contaminated with arsenic due to the presence of the arsenic, the State of Massachusets has declared parts of the watershed (including groundwater sources) currently unusable for drinking purposes. The contamination is a result of historical waste disposal practices in an industrial area located within the headwaters of the watershed. This site was used by several companies starting in the middle 1800's and continued into the early 1900's. The location of waste disposal areas is unknown, due to site redevelopment during the period of operation, but a majority of potential disposal areas are currently covered with stmctures or paved parking areas. The goal of this research project objective was to locate the source and extent of the arsenic contamination and determine its fate during discharge of contaminated groundwater into the headwaters of the watershed. This information will be used in an effort to define the long-term risk derived from elevated levels of arsenic within the watershed and to evaluate alternatives to mitigate the transport of arsenic from the former industrial site. 3 O O l l F 'United States Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Subsurface Protection and Remediation Division, 919 Kerr Research Drive, Ada, OK 74820, *USEPA/ORD/NRMRUTechnology Transfer and Support Division, 26 West Martin Luther King Drive, Cincinnati, OH 45268, 3MANTECH Environmental, P. 0. Box 1198, Ada, OK

2 The Halls Brook Holding Area (HBHA) Pond is located within the upper portion of the watershed area and is generally the first location where arsenic is found in the surface water. There are several sources of water moving into the HBHA Pond including surface water and groundwater. Arsenic contamination appears to emanate from groundwater entering the north end of the pond. It was determined that characterization of the bottom sediment was important to differentiate between arsenic derived from groundwater source(s) versus re-dissolution from contaminated sediments. METHODS AND MATERIALS A Speedtech Instruments 400 khz. depth meter and a model TDC-1 Trimble GPS system were used to collect georeferenced depths from water surface to sediment in the HBHA Pond. This was done using a specialized barge that allowed us to measure the GPS and the depth from the same point on the barge. The depth meter is a hand held sonic meter where the working end has to be immersed at the water line to collect correct measurements. The depth meter collects the measurements in meters to the nearest tenth of a meter. The Trimble GPS system uses an interactive subscription system to correct the GPS readings to within 10 cm. The GPS readings were recorded in latitude and longitude. The shoreline of the pond was also mapped by performing a perimeter survey with the Trimble GPS system. The results of this survey were referenced to a USGS aerial photograph for the HBHA Pond. Figure 1 depicts the aerial photograph of the HBLA Pond with all of the sampling points within and along the pond perimeter. Collection of depths to sediment was initiated along the Eastem shore and terminated at the point where water depth was too shallow to allow barge movement (note that the depth survey terminate prior to reaching the Western shore). Thus, depth contouring for the entire pond was performed assuming a constant water depth from the Westem shore to the termination point of the depth survey transects. Once assembled, the data were used by our GIs study group to perform the following operations: 1) convert latitude & longitude coordinates to Massachusetts Main Land State Plane Coordinates Feet (MAMLSPF) using US Army Corps of Engineers (USACE) software Corpscon 2) edit, revise, & create ASCII text coordinate file with MicroSoft (MS) Excel 3) import coordinate file as points into Environmental Systems Research Institute (ESRI) Arcview (AV) software 4) import 1995 georeferenced aerial photo into (AV) 5) overlay coordinate points on air photo (AV) 6) create new point file defining holding pond's perimeter (AV) 7) create new point file to define gaps in field sampled coordinates by interpolating approximate pond depths based on known points (AV) 8) assign MAMLSPCF coordinates to all new files (AV) 9) merge field data coordinates with office created coordinates to create a final file (AV) 100

3 10) export final coordinates to an ASCII text file (AV) 11) import final coordinate file into Golden Software s Surfer (GSS) 12) generate isometric lines of pond depth (GSS) 13) export isometric lines of pond depth as an AutoDesk Data exchange Format (AD 4x0 14) import, generalize, and edit isometric lines to form smooth contours (bathymetry) with AutoDesk AutoCad Map (ACADM) 15) export smooth bathymetry from ACADM to ArcView (AV) line shape file (shp) 16) import bathymetry into AV (note: each bathametric line has depth associated in data file) 17) define & ramp colors of bathymetry (AV) 18) overlay bathymetry on 1995 air photo (AV) and 19) print and create images of combined bathymetry and air photo. RESULTS AND DISCUSSION Figure 1 is used to illustrate the number and location of data points used to generate the other figures. Using these data, the original contour line graph (Figure 2) was created. The contour lines ( Figure 2 and 3) are based on a 0.25 meter depth increment. This line graph was then added to the USGS aerial photograph to create the final product (Figure 3). A careful examination of the contour graph shows a series of deep holes at the north end of the lake. As part of our site characterization of the pond with a conductivity probe, one of these deep areas showed elevated conductivity readings. Due to this anomaly, we installed a cluster well at the site to allow us to examine the water found in the deep hole. The test results have indicated the intrusion of groundwater contaminated with high levels of salt contamination. We have also found high levels of arsenic in this infiltration area. The entire lake is eventually contaminated with arsenic, but the source appears to be the infiltration areas at the north end of the pond. Wells placed beneath the sediment surface into the sand beneath the lake show little or no contamination. The upgradient groundwater appears to be the major source of arsenic into the pond water and sediments. The georeferenced bathymetric survey allowed integration of site data to guide monitoring and assessment. This information hadwill be used to achieve the following research tasks: 1) guide placement of ground water-surface water monitoring network, 2) spatially integrate water and sediment chemical data within the HBHA Pond and adjacent upgradient ground-water wells, 3) calculate chemical budgets within the water column of the HBHA Pond, and 4) calculate contaminant fluxes from ground water and sediments based on time-series measurements of water chemistry. DISCLAIMER The U. S. Environmental Protection (Agency) through its Office of Research and Development funded and managed the research described here. It has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency. No official endorsement should be inferred. The mention of trade names or commercial products does not constitute endorsement or recommendation for use 101

4 Figure 1. Aerial photograph of the Hall's Brook Holding Area Pond showing the sampling points within and along the perimeter of the pond. 102

5 Figure 2. Calculated sediment depth contour lines and pond perimeter based on data points shown in Figure 103

6 Figure 3. Georeferenced bathymetric survey for the Hall's Brook Holding Area Pond. The deepest portions of the pond are located in the North and South ends. 104