Risk Assessment, Part One

This is a follow-up post to The Numbers where we provided laboratory analysis results for a sample of pit waste at a natural gas well site. Risk assessment is a huge topic so we’ll be splitting the post into two parts. In this part we’ll discuss some features of the site that have to be taken into consideration and use information on a table we’ve created with various screening levels and other information for the chemicals analyzed by the laboratory in the sample.

We’re not doing a full assessment of the site; what we’re doing is trying to find is out if a full assessment toward remediation is necessary.

The state’s DEP Office of Environmental Remediation has several publications that have been helpful to us. These are all associated with their program of voluntary remediation. A Plain Language Guide to Human Health Risk Assessment is a description of the process of analysis and decision-making. There is a helpful checklist at the end which is taken from Appendix A of West Virginia Voluntary Remediation and Redevelopment Act Guidance Manual which is a much more technical document written for remediation specialists. The third element in the publication mix is the De Minimis tables which are part of 60 Code of State Regulations 3. These tables provide screening levels for a large number of chemicals. (The state’s and EPA’s tables use exponents such as E-01 or E+02 with concentration, e.g., 3.89E-01. E-01 is equal to X 10^-1 and E+02 is equal to X 10². For the example 3.89E-01, the concentration is then 0.389. We find this method of presentation to be a pain and much prefer either a uniform parts per billion presentation or as we’ve presented the figures in our table. A scientific calculator will easily convert positive and negative exponents.)

When we had analysis done we just asked for metals, chloride and radium 226 and radium 228. Chloride doesn’t have a screening level, in spite of the fact that there is a secondary Maximum Contaminant Level for drinking water for chloride and in spite of the fact that chloride can be toxic to aquatic life, birds and mammals. Radiological screening levels are a whole other topic and since the radium in the sample was at an acceptable concentration we’ve put that aside.

Three of the metals that we had analyzed, even though they show high concentrations, are not considered important in an environmental assessment — calcium, magnesium and sodium. In the end, the assessment has to focus on arsenic, barium, chromium and lead (cadmium was not able to be detected by the laboratory), though we believe the high chloride is an important factor.

The site is a gas well drilled in 2005 to the Marcellus formation but two other shales were also fractured. Copies of the well completion report and plat are available for download. The well has a pad of about 100 by 200 feet with a drop off to the north where there’s a steep slope into a hollow. On a flat below the well is a spring-fed cistern (about 326 feet from the well according to our GPS). The pit is between the wellhead and the drop off and is partially in fill soil.

This is on the same ridge (but a mile north of us) that we live on and we have seasonally high groundwater in winter and spring with two ephemeral springs close to the house. It’s possible that the site we’re examining also has a perched aquifer with groundwater close to the surface. Some our neighbors, until this year when city water came to the ridge, depended on spring-fed cisterns (like the one below the well site), all at about the same elevation but in different areas, and it’s believed they all are fed by the same aquifer. I don’t know if everyone has city water now or if some still depend on spring-fed cisterns. The family with the cistern below the well site intended to use that cistern for a vegetable garden — their drinking water comes from a shallow well fed by a deeper aquifer. It’s possible that these aquifers are connected.

The photographs in The Numbers post give an idea of what we saw. The area bare of vegetation — the hot spot — is also the lowest spot on the site and has ponding water.

The well pad is next to a state road with a house opposite. That house is about 200 feet from the well and pit area and has a vegetable garden alongside the road. Since there is a residence so close to the site and since we believe that it’s possible that the pad area might be used as a building lot once the well structures are gone, we’ve considered this a residential site.

We’re also concerned about the ecological effects that the metals and chloride would have on vegetation and wildlife. We’ve seen plenty of deer tracks in the hot spot on the surface and assume that deer are attracted to the salts and minerals. In our assessment, since deer are hunted and eaten in this area, we have a possible crossover with not just ecological assessment concerns but also human risk concerns.

We’ll be doing a soil assessment and the factors we’ll be considering include what the sample metals concentrations are, what the typical background soil concentrations are in this state and then the various screening levels. That will be discussed in the second part. Here’s that link again to the risk assessment table we’ve created for this site.

October 3, 2009