Tolent Construction Ltd. Derwent House Lakeside Court Fifth Avenue Business Park Team Valley Gateshead Tyne & Wear NE11 0NL

Transcription

1 Tolent Construction Ltd. Derwent House Lakeside Court Fifth Avenue Business Park Team Valley Gateshead Tyne & Wear NE11 0NL Our Ref: _TC_Gas Risk Assessment 22 September 2017 Dear Sirs/Madam, RE: GAS RISK ASSESSMENT TEMPLE MEMORIAL PARK Please find enclosed the data from the recently completed gas monitoring for the above site. Comments on the data are presented below. It is understood that the site will be levelled and a new rugby/cricket clubhouse constructed with associated areas of soft landscaping and car parking. James Christopher Consulting (JCC) carried out a geoenvironmental and geotechnical investigation of the site and the findings are contained in the following report, issued in September 2017; Temple Memorial Park, South Shields Phase II Ground Investigation Report, Ref: (E)- 02. Date: September Reference should be made to the above report for details of the ground conditions, geotechnical and geochemical analysis. Contamination testing was scheduled and the soil samples were screened using a generic contamination suite including metals, TPH (banded) and PAH (speciated). The results of the laboratory chemical screening identified no elevations in the contaminants tested for when trigger-values for S4UL s relating to commercial end-use were utilised. This gas risk assessment has been carried out in accordance with the following publications: CIRIA report C665 Assessing risks posed by hazardous ground gases to buildings, 2007 BS8485:2007 Code of Practice for the characterisation and remediation from ground gas in affected developments NHBC Guidance on evaluation of development proposals on sites where methane and carbon dioxide are present, 2007 A number of factors have been considered in order to assess the potential risks associated with the ground gas on this site including potential gas sources, gas pathways, gas monitoring and the site gas regime. Potential methane and carbon dioxide gas sources were identified from the Phase 1 desk study carried out by James Christopher Consulting in August Although the site has remained undeveloped it has had many different land uses including landfills until approximately 1994 when the site returned to recreational land. The site is generally surrounded by roads, residential properties and the remaining sections of Temple Memorial Park. Therefore a risk rating of moderate was deemed appropriate in regards to ground gas. Taking the recommendations from the Phase 1 desk study into account; four gas monitoring wells were installed into boreholes WS01, WS02, WS04 and WS05. Please refer to the Phase 2 Site Investigation (reference: -(E)-02) for more details. The most recent guidance on gas risk assessment (CIRIA C665) includes recommendations for periods and frequencies for monitoring visits. These recommendations take into account the nature of the proposed development. The proposed development comprises a clubhouse for commercial use. Commercial properties 4 McMillan Close, Saltwell Business Park, Gateshead, NE9 5BF Tel: enquiries@jc-consulting.net website: James Christopher Consulting Limited, Registered in England No VAT registration No

2 fall into low sensitivity developments therefore gas monitoring at the site was carried out on five occasions over a total period of one month; between 23 rd August 2017 and the 20 th September Gas monitoring was carried out in accordance with current guidance and the results are attached. A summary of the monitoring results is shown below. Monitoring Point Range of gas concentrations (% v/v) Methane Carbon Dioxide Flow rates (l/hr) WS WS02 ND WS04 ND WS05 ND ND None Detected Gas screening values (GSV) for methane and carbon dioxide have been calculated based on the maximum steady state readings obtained from the boreholes and the maximum steady state flow rates. The GSV s are shown in the table below. The GSV s shown above would place the site in Characteristic Situation (CS) 1 as defined within Table 8.5 in Ciria C665. Therefore no gas protection measures will be required within the proposed development. Whilst gas monitoring was carried out, water levels were also recorded within the boreholes. A summary of results are indicated below. Monitoring Point Monitoring Point WS WS WS WS Maximum GSV s (l/hr) Methane WS WS WS WS Carbon Dioxide Range of Water Levels (metres below ground level) I trust that the enclosed are sufficient for your present needs, however, please do not hesitate to get in touch should you require further information. Yours sincerely, on behalf of James Christopher Consulting, Victoria Braniff Associate Geotechnical Engineer PhD, MSc, BSc (Hons), FGS

3 Date: 23/08/2017 Time (start & finish): Visit No. 1 of 5 Raining/overcast Ground Conditions: Wet Atmospheric Pressure: 992mb WS ND ND 2.15 WS ND WS ND WS ND ND 1.81

4 Date: 30/08/2017 Time (start & finish): Visit No. 2 of 5 Raining/overcast Ground Conditions: Wet Atmospheric Pressure: 994mb WS ND WS ND WS ND ND 1.90 WS ND

5 Date: 06/09/2017 Time (start & finish): Visit No. 3 of 5 Dry Ground Conditions: Damp Atmospheric Pressure: 1005mb WS ND ND 2.15 WS ND WS ND ND 1.95 WS ND

6 Date: 14/09/2017 Time (start & finish): Visit No. 4 of 5 Overcast, dry, windy Ground Conditions: Damp Atmospheric Pressure: 1004mb WS ND ND 2.01 WS ND WS ND ND 1.99 WS ND

7 Date: 20/09/2017 Time (start & finish): Visit No. 5 of 5 Dry/sunny Ground Conditions: Damp Atmospheric Pressure: 1013mb WS ND ND 2.24 WS ND ND ND WS ND ND ND WS ND ND ND ND 1.89