According to best management practices (BMPs) being proposed by the TCEQ, pre-mining planning is one of the main ways to prevent sediment from leaving a mine.
So much sand piled up in the San Jacinto after Hurricane Harvey that it reduced the conveyance of the river, contributed to flooding, and cost hundreds of millions of dollars to remove.
I consider good sand mining operations so important to the reduction of future flooding that I am publishing a series of articles on these proposed BMPs. This is the fifth. The first provided an overview. Then, I discussed:
- Minimum setbacks from rivers and streams
- Vegetative controls for erosion
- Structural controls for erosion
This post will discuss BMPs for pre-mining and provide a list of suggestions for public comment at the end.
For brevity, I’ll summarize each of the pre-mining BMPs. To see exact text being proposed by the TCEQ, click here.
3.1 Site Evaluation
Miners must begin by evaluating a site for how mining will take place and what will happen to the mine when it closes. This is typically called a Mine Plan and includes:
- Location of processing plant, office, support facilities, roads, product staging areas, and overburden placement.
- An evaluation of the soil type(s) in the area planned for mining.
Susceptibility of these soils to erosion must be known when planning. Sands, silts and clays act differently when worked by earthmoving equipment.
3.2 Understanding Site Drainage
It is important to know pre-existing drainage patterns and where concentrated flows want to exit a site. This will determine the selection of structural control BMPs, such as culverts, to minimize adverse impacts.
3.2.1 Surface Water Flow
Identifying the receiving waters (i.e., Lake Houston, the San Jacinto, Spring Creek, Caney Creek, White Oak Creek) is vital before site preparation starts. Operators must determine all appropriate agencies with jurisdiction over the receiving waters. The TCEQ and USEPA Region 6 continuously develop Total Maximum Daily Loads (TMDLs) for water bodies not meeting their designated uses.
If the TMDL has already been developed, it may not allow additional inputs (discharges) to the receiving stream. Therefore, it is important to know which water bodies have had TMDLs developed for them or are scheduled for TMDLs. This information can also be found on the TCEQ’s Index of Water Quality Impairments.
Inspection during or after a rainfall event can provide a substantial amount of information regarding how surface water flows.
3.2.2 Ground Water Conditions
Understand that mining of a potable aquifer can negatively affect the yield of a potable well.
The following BMPs will help guide a ground water preservation effort:
- When a new sand and gravel operation is being considered, operators must first check the Texas Water Development Board water well reports data and the TCEQ water well report viewer to determine if registered public and private drinking water supply wells are located nearby.
- Perform a visual check for possible unregistered private wells or abandoned wells in the immediate vicinity of the new sand and gravel pit. If an unregistered private well or abandoned well is discovered, operators must refer to TCEQ’s Regulatory Guidance Landowner’s Guide to Plugging Abandoned Water Wells (RG-347) for more information on the necessary actions which must be taken.
3.3 Site Preparation
Only after surface water drainage and ground water conditions are thoroughly understood may site preparation be initiated.
Once initiated, operators must inspect disturbed areas (cleared, graded, or excavated) of the site at least once every seven (7) calendar days for signs of visible erosion.
3.3.1 Construction of Access and Haul Roads
Roads are a necessary component of any sand and gravel mining operation, especially on large pieces of property. Operators must take care to minimize impacts to the environment when constructing roads.
Roads must be designed to drain at all times by using crowning, graveling, compacting, ditching, and/or culverting
Proper construction and maintenance should minimize erosion by rainfall runoff, dust, and normal vehicle use. Where necessary, road surfaces must be graveled if the base does not already contain sufficient aggregate.
Crowning of Roads
Surfaces must be crowned to minimize erosion of the roadbed.
Graveling and Compacting
Graveling and compacting of road surfaces require less maintenance. It minimizes loose sediment runoff or tracking of sediment onto public roads.
Ditching and Culverting
Ditches and culverts carry runoff alongside or underneath a roadbed. They must be:
- Sized for anticipated rainfall events.
- Installed at the time of roadway construction
- Sloped to prevent silting and allow for maintenance (i.e., digging out sediment buildup).
- Kept free of debris and obstructions.
Typically, ditches can be used for routing surface water flow away from adjacent properties offsite.
Silt fencing can aid in soil erosion caused by surface runoff from roadways. The bottom must be secured beneath the ground surface to prevent under-washing.
3.3.2 Land Clearing and Grubbing Activities
Land clearing and grubbing involves removing all trees, stumps, roots and other debris from the site. It may also include removal and disposal of old, unwanted structures. Proper disposal will be discussed in a later post.
Disturb only those areas ready for immediate use. Install sediment holding basins before major site grading. They can catch and hold surface runoff before it leaves the site.
Divert upslope water around an area planned for disturbance.
Plan clearing and grubbing activities for a time of year that minimizes the impact of inclement weather on disturbed areas.
Temporarily stabilize or cover disturbed areas to minimize impacts on the environment.
Operators must only clear and grub acreage needed for activities occurring before the next anticipated storm event.
Clearing or grubbing too much land too early in construction dramatically increases the potential for surface water runoff and the costs to control it.
Operators must schedule grading to protect disturbed areas from stormwater runoff.
A minimum 100-foot buffer zone is required adjacent to perennial streams and water bodies in the State of Texas.
3.3.3 Stripping Activities
“Stripping” describes the removal of overburden on top of valuable sand reserves. Overburden is typically clay, silt, and fine sand. Operators may stockpile these materials for post-mining restoration. But the BMPs also allow disposal by placing them into a pit no longer being used.
Operators must control runoff from stockpiles.
Stockpiles should be located away from concentrated flows of storm water, drainage courses, and inlets, and protected with perimeter sediment barriers.
Operators should be able to effectively control runoff from any areas they disturb. So they should be careful not to strip too large of an area all at once. Stripping to large of an area contributes to excessive buildup of silt or clay in ditches.
Normally, operators will direct surface water to pits to keep the water table high in extended periods of dry weather.
Operators must leave enough undisturbed buffer at property boundaries to provide sufficient lateral support of property lines as determined by the licensed professional engineer or geoscientist certifying BMPs at the site.
While I applaud what the TCEQ is trying to do, I still have concerns with several BMPs listed above and plan to make public comments on them.
Section 3.1 – Site Evaluation
This section requires a mine plan, but not approval of the plan. The plan should be approved by the TCEQ.
Most of the mines are at least partially in FEMA defined floodways. But this section makes no mention of that. Hydrologic and hydraulic analyses should be performed by competent and reputable third-party engineers to show that no part of the mine will increase flood levels or erosion upstream, downstream, or to adjoining properties.
Section 3.2.1 – Surface Water Flow
Additional erosion controls or increased buffer widths may be needed where river erosion rates are high,
Also, the East Fork, West Fork, Caney Creek, White Oak Creek, Spring Creek and Lake Houston already are listed as impaired. Impairments have to do mostly with bacteria, PCB, and/or dioxin levels. All of the above already have Total Maximum Daily Loads or are scheduled to implement TMDLs soon.
I suspect the TCEQ permits some discharges from sand mines and postpones others to keep the streams under the TMDL limit. But I have also seen many TCEQ reports about un-permitted discharges. I have seen breaches in dikes remain open for months and years. I have seen rivers capture pits during storms.
The West Fork already has a bacteria problem from the Lake Conroe Dam to Lake Houston. Yet people still swim and fish in these waters. And more sand mines are expanding than closing.
I wish the TCEQ would step up inspections (especially after heavy rains) and increase fines for un-permitted discharges. Lake Houston, after all, is the source of water for more than 2 million people.
Section 3.2.2 – Ground Water Conditions
This section requires operators to study the impact on adjacent water wells, but specifies nothing to reduce the impact on them. Ooops. I suggest adding: “If present, waste management units must be located a minimum horizontal distance from adjacent water wells, in accordance with 16 Texas Administrative Code Chapter 76.”
Section 3.3.2 – Land Clearing and Grubbing Activities
Diverting upslope water around a planned area for disturbance is good; however, care must be taken to prevent diverted water from increasing downslope flooding.
When the TCEQ says operators should clear and grub an amount of acreage that they can finish “before the next anticipated storm event,” it gives them an opportunity to clear hundreds of acres at once. Who can anticipate the next large rainfall in Houston? No one. Ask the people of Elm Grove how devastating sheet flow from a large area can be when a large rain hits before additional protections (i.e., detention ponds and berms) are installed.
Section 3.3.3 – Stripping Activities
The stockpile protection measures listed are good. But I would add that stockpiles must be located outside of FEMA-defined floodways.
Buffer widths between mines and adjoining properties are good. But I would add that “Additional buffer width or structures may be required where pipeline or utility corridors are located.
To Submit Public Comments
Please submit your thoughts on pre-mining and other BMPs to the TCEQ. Email Macayla.Coleman@Tceq.Texas.gov with the subject line “BMPs Guidance Document” before August 19, 2021.
Posted by Bob Rehak on 8/14/2021
1446 Days since Hurricane Harvey
The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.