Bottom Sediment Sampling

Samples of Ohio River and tributary bottom sediments were collected during continuous low flows in August and September of 2001 on the upper 317 miles of the Ohio River and each major tributary. Samples were collected every five miles on the mainstem of the Ohio River, at twenty-six targeted sites, and in each major tributary of the study area. Ninety-two bottom sediment samples were collected, nine of those duplicates, at a total of eighty-three sites.  Dioxin, PCB’s, and Chlordane were tested for.

In 2002, 180 more sediment samples were collected in a similar screening of the middle and lower Ohio River. This survey was conducted the same way as the 2001 upper river survey. Sediment samples were collected every five miles on the mainstem of the Ohio River, at forty-eight targeted sites, and in each major tributary of the Ohio River from mile 317 to mile 981 at Cairo, Illinois.

Method
Ohio River and tributary sediments were collected using the ORSANCO Standard Operating Procedure for Collection of Bottom Sediments. Samples were collected from a boat using a Petite Ponar®clamshell-style dredge. Sediment samples were sieved in the field to remove particles larger than 2mm.

Mainstem sample locations other than targeted sites were pre-selected to a general mile point only.  Locations were chosen from navigation charts to provide even coverage at a five-mile resolution and allow for sample collection at the inside of bends and other natural sediment traps.

Site Selections
Twenty-six targeted sites were selected based on their proximity to sites listed on the final National Priorities List (NPL), Toxic Release Inventory (TRI), or state agency records of contaminated sites. These samples were taken below outfalls of industrial sites or at the mouth of creeks draining properties of interest.

Exact sample locations were determined by on-site investigation of bottom composition using physical means and observation of sediment-trapping structure and hydrologic features. The primary means of investigating bottom sediment composition was tapping the river bottom with a twenty-foot “habitat pole”. This simple bottom investigation was done to avoid grabs with high gravel content.

Equipment
Samples were collected using stainless steel Petite Ponar^® dredges built by Wildlife Supply Company (Wildco). All equipment used for sample processing in the field was stainless steel, Teflon^®, nalgene^®, or glass.

Sediment brought from the bottom was homogenized using a stainless steel bowl and spoon. Sieving was done with a stainless steel sieve and bucket. A Teflon^® policeman and nalgene^® wash bottle aided transfer of the samples to final containers. Sample containers were clear glass with Teflon^® lid liners.

Collection Method
Three grab samples from each site were collected and homogenized. Care was taken to lower and retrieve the sample dredge slowly to avoid the loss of fine sediment due to “blow-out” when the dredge strikes the bottom and “wash-out” during dredge retrieval. Each grab of the sample dredge was checked for completeness of dredge closure, percentage, and level filling of dredge capacity. The dredge was deployed until three grabs passing the above criteria were obtained.

Sieving
A 2mm (U.S. standard #10) sieve was used to remove gravel, shells and other materials from the sample. Depending on water content in the homogenized sample, from nine to twenty-seven spoonfuls of the sediment were sieved by agitation in a bucket with 2 liters of site native water. Quantitative transfer of the sieved sediment to the glass sample containers was achieved using a stainless steel funnel and nalgene^® wash bottle of water native to each sample location.

Post-collection processing, Containers, and Conditions
Four one-liter, clear, wide-mouth glass jars with Teflon^â-lined lids were used to contain samples. Sample jars were capped, wrapped in foam liners, and placed on ice immediately after collection. The samples were held at 4^°C until sufficient settling had occurred for consolidation of the sediment to one or two jars for shipment to the laboratory.

Decontamination Procedures
Sample containers were certified pre-cleaned by the supplier. All equipment used in sample collection was scrubbed with an alconox^â solution and rinsed with tap water, distilled water, methanol, and native (collected on site) water prior to use at each sample location. In-house sample consolidation techniques utilized the same wash procedure without the methanol rinse. Decanted sample water was used for in-house native water rinses.