CCR Landfill Background
This 1.3-gigawatt, coal-fired power plant in Jefferson County, Indiana has been in operation for over 50 years. During the course of plant operations, Coal Combustion Residuals (CCRs) have been managed in two (2) CCR units – one (1) landfill and one (1) surface impoundment.
The landfill is unlined and constructed in an existing stream valley. The steep walls of the valley are underlain by impermeable limestone bedrock. A layer of fly ash is located at the base of the landfill. This fly ash layer is approximately 30 feet thick in the middle of the landfill and thins toward the edges of the landfill. The fly ash sits directly on top of an impermeable, 15-feet-thick layer of clay, which is underlain by limestone bedrock. Historic data indicates that none of the geologic units directly beneath the landfill meet the US EPA’s definition of an aquifer.
Alluvial deposits are present to the southwest and to the northeast of the landfill but are not present beneath the landfill. These alluvial deposits consist of approximately 15 feet of silty clay, overlying various depths of silty sand and gravel. These lower silty sand and gravel deposits are designated as the uppermost aquifer at the site.
One (1) surface impoundment is being monitored under the CCR program. This impoundment did not have an existing groundwater monitoring network in place. Several wells and piezometers had previously been installed around the impoundment and used to collect water levels but had never been sampled; and, most of these existing wells and piezometers were not installed in the uppermost aquifer.
CCR Groundwater Monitoring Project Work
The following tasks were completed by AGES to develop the CCR groundwater monitoring network for each CCR unit:
1. Data Review
AGES reviewed all available documents (reports, well and soil boring logs, historic water level data from existing wells and piezometers, etc.) for each CCR unit to evaluate the subsurface geology and determine which unit is the uppermost aquifer
2. Scope of Work
AGES developed a scope of work and timeline that included completing all tasks required for compliance with the CCR Rule before the October 2017 deadline.
3. Preliminary Groundwater Sampling
AGES collected preliminary groundwater samples from existing wells and piezometers using the same methodology to be used during the CCR program.
4. Evaluation of Existing Wells
AGES used data collected during preliminary sampling event to develop groundwater flow maps.
5. Subsurface Investigation
AGES conducted soil borings and collected soil samples around each CCR unit to determine the depth to, thickness of, and composition of the uppermost aquifer beneath each CCR unit. Samples of uppermost aquifer material were sent to a geotechnical laboratory for grain-size analysis.
6. Monitoring Well Design
AGES used grain-size analysis results to select the well pack and screen slot size for the new pre-packed, metal-free well screens to be used for the new monitoring wells. The wells were designed to allow for the collection of groundwater samples with very low turbidity (less than 5 NTUs) without field filtering, per the CCR rule.
7. Monitoring Well Installation and Development
AGES oversaw the installation of 40 new CCR wells around the surface impoundments and at the landfill. Following installation, AGES developed the new monitoring wells around the impoundments until turbidities in all wells were below 5 NTUs.
8. Aquifer Testing
AGES conducted rising and falling head aquifer tests to evaluate the hydrogeologic characteristics of the uppermost aquifer beneath each CCR unit.
9. Groundwater Sampling
AGES conducted low-flow sampling of all monitoring wells in accordance with US EPA’s guidelines. This included working with pump’s manufacturer to develop the best method to conduct low-flow sampling on wells more than 200 feet deep.
10. Data Analysis and Reporting
AGES will develop and maintain a database for all of the data collected under the CCR program. Appropriate statistical analyses will be conducted on all of the data and the results of the analytical and statistical analyses will be included in the required annual report to be published on the utility’s website.
